U.S. patent application number 17/565879 was filed with the patent office on 2022-04-21 for carbon material, method for producing carbon material, and non-aqueous secondary battery using carbon material.
This patent application is currently assigned to MITSUBISHI CHEMICAL CORPORATION. The applicant listed for this patent is MITSUBISHI CHEMICAL CORPORATION. Invention is credited to Satoshi AKASAKA, Tooru FUSE, Hiromitsu IKEDA, Nobuyuki ISHIWATARI, Takashi KAMEDA, Shingo MOROKUMA, Daigo NAGAYAMA, Koichi NISHIO, Iwao SOGA, Hideaki TANAKA, Shunsuke YAMADA.
Application Number | 20220123308 17/565879 |
Document ID | / |
Family ID | 1000006066117 |
Filed Date | 2022-04-21 |
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United States Patent
Application |
20220123308 |
Kind Code |
A1 |
YAMADA; Shunsuke ; et
al. |
April 21, 2022 |
CARBON MATERIAL, METHOD FOR PRODUCING CARBON MATERIAL, AND
NON-AQUEOUS SECONDARY BATTERY USING CARBON MATERIAL
Abstract
A carbon material may satisfying inequality (1K): 10.914 > 5
.times. x k - y k - 0.0087 .times. a , ( 1 .times. K ) ##EQU00001##
wherein a is a volume-based average particle diameter in um of the
carbon material, x.sub.k is a true density in g/cm.sup.3 of the
carbon material, and y.sub.k is a value determined by equation
(2K): y k = D 100 - D T , ( 2 .times. K ) ##EQU00002## wherein
D.sub.100 is density in g/cm.sup.3 of carbon material under
uniaxial load of 100 kgf/3.14 cm.sup.2, and D.sub.T is tap density
of carbon material in g/cm.sup.3. Such carbon materials may be used
in electrodes and batteries.
Inventors: |
YAMADA; Shunsuke;
(Inashiki-gun, JP) ; ISHIWATARI; Nobuyuki;
(Inashiki-gun, JP) ; AKASAKA; Satoshi;
(Inashiki-gun, JP) ; NAGAYAMA; Daigo;
(Inashiki-gun, JP) ; MOROKUMA; Shingo;
(Inashiki-gun, JP) ; NISHIO; Koichi;
(Inashiki-gun, JP) ; SOGA; Iwao; (Inashiki-gun,
JP) ; TANAKA; Hideaki; (Inashiki-gun, JP) ;
KAMEDA; Takashi; (Sakaide-shi, JP) ; FUSE; Tooru;
(Sakaide-shi, JP) ; IKEDA; Hiromitsu;
(Sakaide-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI CHEMICAL CORPORATION |
Chiyoda-ku |
|
JP |
|
|
Assignee: |
MITSUBISHI CHEMICAL
CORPORATION
Chiyoda-ku
JP
|
Family ID: |
1000006066117 |
Appl. No.: |
17/565879 |
Filed: |
December 30, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15399423 |
Jan 5, 2017 |
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17565879 |
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PCT/JP2015/069574 |
Jul 7, 2015 |
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15399423 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/625 20130101;
C01P 2004/32 20130101; H01M 4/587 20130101; H01M 10/0525 20130101;
C01B 32/21 20170801; H01M 2004/021 20130101; H01M 4/583 20130101;
C01P 2006/14 20130101; C01P 2006/16 20130101 |
International
Class: |
H01M 4/587 20060101
H01M004/587; H01M 10/0525 20060101 H01M010/0525; H01M 4/62 20060101
H01M004/62; H01M 4/583 20060101 H01M004/583; C01B 32/21 20060101
C01B032/21 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 7, 2014 |
JP |
2014-139782 |
Nov 19, 2014 |
JP |
2014-234606 |
Dec 8, 2014 |
JP |
2014-248251 |
Mar 26, 2015 |
JP |
2015-064897 |
Mar 27, 2015 |
JP |
2015-067180 |
Mar 27, 2015 |
JP |
2015-067184 |
Mar 27, 2015 |
JP |
2015-067194 |
Mar 27, 2015 |
JP |
2015-067201 |
Jun 17, 2015 |
JP |
2015-122197 |
Jun 17, 2015 |
JP |
2015-122198 |
Claims
1. A carbon material, satisfying inequality (1K): 10.914 > 5
.times. x k - y k - 0.0087 .times. a , ( 1 .times. K ) ##EQU00068##
wherein a is a volume-based average particle diameter in .mu.m of
the carbon material, x.sub.k is a true density in g/cm.sup.3 of the
carbon material, and y.sub.k is a value determined by equation
(2K): y k = D 100 - D T , ( 2 .times. K ) ##EQU00069## wherein
D.sub.100 is density in g/cm.sup.3 of carbon material under
uniaxial load of 100 kgf/3.14 cm.sup.2, and D.sub.T is tap density
of carbon material in g/cm.sup.3.
2. A carbon material, satisfying inequality (3K): 10.990 > 5
.times. x k - y k , ( 3 .times. K ) ##EQU00070## wherein x.sub.k is
a true density in g/cm.sup.3 of the carbon material, and y.sub.k is
a value determined by equation (2K) y k = D 100 - D T , ( 2 .times.
K ) ##EQU00071## wherein D.sub.100 is density in g/cm.sup.3 of
carbon material under uniaxial load of 100 kgf/3.14 cm.sup.2, and
D.sub.T is tap density of carbon material in g/cm.sup.3.
3. The carbon material of claim 1, having a true density of 2.20
g/cm.sup.3 or more.
4. The carbon material of claim 1, having a true density of less
than 2.262 g/cm.sup.3.
5. The carbon material of claim 1, having a tap density of 0.85
g/cm.sup.3 or more.
6. The carbon material of claim 1, wherein at least part of the
surface of the carbon material is coated with an amorphous
carbon.
7. The carbon material of claim 1, which is a spheroidal graphite
particle.
8. The carbon material of claim 2, having a true density of 2.20
g/cm.sup.3 or more.
9. The carbon material of claim 2, having a true density of less
than 2.262 g/cm.sup.3.
10. The carbon material of claim 2, having a tap density of 0.85
g/cm.sup.3 or more.
11. The carbon material of claim 2, wherein at least part of the
surface of the carbon material is coated with an amorphous
carbon.
12. The carbon material of claim 2, wherein the carbon material is
a spheroidal graphite particle.
13. A method for producing the carbon material of claim 1, the
method comprising: granulating flake graphite, crystalline
graphite, and vein graphite to form the carbon material as a
spheroidal graphite particle.
14. The method of claim 13, wherein the granulating comprises
applying at least one selected from the group consisting of impact,
compression, friction, and shear force.
15. The method of claim 13, wherein the granulating comprises
placing the graphite in an apparatus comprising (i) a rotatable
member that rotates at a high speed in a casing and (ii) a rotor
equipped with a plurality of blades in the casing, and applying any
one of impact, compression, friction, and shear force to the
graphite placed in the apparatus by rotating the rotor at a high
speed.
16. A negative electrode, comprising: the carbon material of claim
1.
17. A secondary battery, comprising: the carbon material of claim
1.
18. A method for making a negative electrode, the method
comprising: forming the negative electrode employing the carbon
material of claim 1.
19. A method for making a secondary battery, the method comprising:
including the carbon material of claim 1 in a component of the
secondary battery.
20. A method for producing a secondary battery comprising a
positive electrode, a negative electrode, and an electrolyte, the
method comprising: producing the negative electrode by forming a
negative electrode active material layer comprising the carbon
material of claim 1 on a current collector.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a continuation of U.S. Ser. No. 15/399,423, filed
Jan. 5, 2017, and published as US 2017/0187041 A1, which was a
bypass continuation of PCT/JP2015/069574, filed on Jul. 7, 2015,
designated the United States, and claiming priority to JP
2014-139782, filed on Jul. 7, 2014, JP 2014-234606, filed on Nov.
19, 2014, JP 2014-248251, filed on Dec. 8, 2014, JP 2015-064897,
filed on Mar. 26, 2015, JP 2015-067180, filed on Mar. 27, 2015, JP
2015-067184, filed on Mar. 27, 2015, JP 2015-067194, filed on Mar.
27, 2015. JP 2015-067201, filed on Mar. 27, 2015, JP 2015-122197,
filed on Jun. 17, 2015, and JP 2015-122198, filed on Jun. 17, 2015,
the entire contents of each of which are incorporated by reference
herein.
TECHNICAL FIELD
[0002] The present invention relates to a carbon material, a method
for producing a carbon material, and a non-aqueous secondary
battery including a carbon material.
BACKGROUND ART
[0003] In recent years there has been an increasing demand for
higher-performance non-aqueous secondary batteries having high
energy densities and excellent high-current charge-discharge
characteristics, and there has been a need to achieve further
increases in capacity, input and output, and service life.
[0004] It is known that in non-aqueous secondary batteries,
carbon-based materials, such as graphite, are used as carbon
materials that serve as negative electrode materials (negative
electrode active materials). Graphite, which has a high degree of
graphitization, can provide a capacity near 372 mAh/g, which is a
theoretical capacity of lithium occlusion, and is low cost and
durable, and thus is suitable as a carbon material for non-aqueous
secondary batteries, particularly, lithium ion secondary
batteries.
[0005] Patent Document 1 has disclosed a technique for improving
filling properties and fast charge-discharge characteristics by
treating a flake natural graphite with mechanical energy to prepare
a spheroidized natural graphite and coating the surface of the
spheroidized natural graphite, a core graphite, with amorphous
carbon.
[0006] Patent Document 2 has disclosed a technique for reducing the
expansion during charging and discharging by spheroidizing a
spheroidal graphite to inhibit the costal orientation of graphite
particles. Patent Document 3 has disclosed a technique for
improving fast charge-discharge characteristics and cycle
characteristics by isotropically pressurizing a spheroidized
graphite obtained by spheroidizing a flake graphite to produce a
highly isotropic graphite having a high density with no
intra-particle voids.
[0007] Patent Document 4 has disclosed a method for producing a
powdered carbon material by mixing a flake natural graphite, a
meltable organic substance, and a pitch having a softening point of
70.degree. C. under heating, applying a mechanical impact with a
hybridizer, adding carbon black, applying another mechanical impact
to prepare a spheroidized powder, and burning the powder. Patent
Document 5 has disclosed a method for producing a spheroidized
graphite particle having a smooth surface by adding a resin binder
to raw carbon material (raw graphite) particles and spheroidizing
the mixture. Patent Document 6 has disclosed a method of rapidly
stirring coal-derived calcined coke and paraffin wax under heating
to produce spheroidal particles.
[0008] Patent Document 7 has disclosed a carbon material produced
by burning a spheroidized natural graphite in an air atmosphere at
650.degree. C. using a muffle furnace and removing fine powder on
the particle surface.
[0009] Patent Document 8 has disclosed a carbon material having an
increased amount of micropore produced by irradiating a
spheroidized natural graphite with ultrasonic waves in a
circulating ultrasonic homogenizer.
[0010] Patent Document 2 has disclosed a carbon material having a
frequency of particles with a diameter of 5 .mu.m or less, as
measured after ultrasonic waves have been applied for 10 minutes,
of 40% to 55%.
[0011] Patent Document 9 has disclosed a technique for improving
filling properties and input-output characteristics by treating a
flake natural graphite with mechanical energy to prepare a
spheroidized natural graphite and coating the surface of the
spheroidized natural graphite, a core graphite, with amorphous
carbon.
[0012] Patent Document 10 has disclosed a technique for improving
input-output characteristics at low temperatures by loading carbon
black particles and amorphous carbon onto the surface of a
spheroidized graphite obtained by spheroidizing a flake graphite to
form a fine structure on the particle surface.
[0013] Patent Document 11 has disclosed a multi-layered carbon
material comprising a carbide of an organic substance deposited on
the surface of a graphitic carbonaceous material; by controlling
the residual amount of the carbide of an organic substance to be 12
parts by mass to 0.1 part by mass based on 100 parts by mass of the
graphitic carbonaceous material, a non-aqueous solvent secondary
battery can be produced having a high discharge capacity, a low
charge-discharge irreversible capacity in an initial cycle, and a
high level of safety against electrolyte solution.
[0014] Patent Document 12 has disclosed a composite carbon material
made of high-crystallinity carbonaceous particles and a
low-crystallinity carbon material on the particle surface; by
controlling a tap density to be 0.43 to 0.69 g/cm.sup.3 and the
percentage of carbon materials having a microscopic Raman R value
of 0.2 or larger to be at least 20%, a non-aqueous solvent
secondary battery having excellent low-temperature characteristics
can be produced.
[0015] Patent Document 10 has disclosed composite particles of
graphite particles and carbon fine particles having a primary
particle diameter of 3 nm to 500 nm; by controlling an
R.sub.(90/10) value, a ratio of a microscopic Raman R value at 90%
from the smallest value to an R value at 10%, to be 1 to 4.3, a
non-aqueous solvent secondary battery having excellent input-output
characteristics at low temperatures can be produced.
[0016] Patent Document 14 has disclosed a technique for controlling
a pore volume by selecting conditions of curing and carbonizing a
phenolic resin or other resins. Patent Document 15 has disclosed a
technique for controlling a tap density, a specific surface area,
and a pore volume by coating agglomerated particles obtained by
isotropically pressurizing flake graphite particles and
spheroidized graphite particles each with low-crystallinity carbon
and blending the coated particles.
[0017] Patent Document 16 has disclosed a technique for controlling
the excess reactivity with an electrolyte solution and improving
fast charge-discharge characteristics by heat-treating a
spheroidized natural graphite in a nitrogen atmosphere at
500.degree. C. to 1,250.degree. C.
PRIOR ART DOCUMENTS
Patent Documents
[0018] Patent Document 1: JP 2000-340232 A
[0019] Patent Document 2: JP 2011-086617 A
[0020] Patent Document 3: JP 2005-50807 A
[0021] Patent Document 4: JP 2008-305722 A
[0022] Patent Document 5: JP 2014-114197 A
[0023] Patent Document 6: WO 2014/141372
[0024] Patent Document 7: JP 2010-251126 A
[0025] Patent Document 8: JP 2012-84520 A
[0026] Patent Document 9: JP 2012-074297 A
[0027] Patent Document 10: JP 2014-060148 A
[0028] Patent Document 11: JP 09-213328 A
[0029] Patent Document 12: WO 11/145178
[0030] Patent Document 14: JP 2003-297352 A
[0031] Patent Document 15: JP 2013-8526 A
[0032] Patent Document 16: JP 2010-135314 A
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0033] However, the investigation by the present inventors has
shown that although the spheroidized natural graphites disclosed in
Patent Document 1 and Patent Document 2 provide a high capacity and
good fast charge-discharge characteristics as compared with the
flake graphite used as a raw material, these characteristics are
still insufficient. This is because the spheroidized natural
graphites have coarse intra-particle voids and structures lacking
fineness, and thus electrolyte solution cannot be smoothly and
efficiently distributed into the intra-particle voids, and Li-ion
insertion/extraction sites in the particles cannot be effectively
used.
[0034] The isotropically pressurized spheroidized natural graphite
disclosed in Patent Document 3, although providing a certain
improvement in fast charge-discharge characteristics, which is due
to the smooth movement of electrolyte solution between electrodes
resulting from filling properties improved by the increased density
of the particles, provides insufficient low-temperature output
characteristics. This is because electrolyte solution cannot
penetrate into the particles as a result of the elimination of
intra-particle voids, and Li-ion insertion/extraction sites in the
particles cannot be efficiently used.
[0035] The spheroidized natural graphite disclosed in Patent
Document 1, although providing a high capacity and good fast
charge-discharge characteristics as compared with the flake
graphite used as a raw material, unfortunately provides low battery
characteristics and productivity because the particles poorly
adhere to each other to cause residual flake graphite and generate
fine powder during the spheroidization.
[0036] The powdered carbon material disclosed in Patent Document 4
provides an insufficient improvement in battery characteristics
because the meltable organic substance and the pitch contained
during the spheroidization of the graphite contain softened solids,
and thus the raw carbon materials poorly adhere to each other, and
residual flake graphite and the generation of fine powder during
the spheroidization cannot be reduced.
[0037] The method for producing a spheroidized graphite disclosed
in Patent Document 5 also provides an insufficient improvement in
battery characteristics because the addition of a resin binder
hardly improves the adhesion between the graphite particles, and
the generation of fine powder cannot be reduced. Although a method
of spheroidization including the addition of a solution of the
resin binder in toluene has also been disclosed, the method
requires further improvement because the temperature during the
spheroidization may exceed the low flash point of the solvent,
which involves the risk of explosion or fire during the
production.
[0038] Patent Document 6 has not disclosed a method of granulating
a graphite into spheroidal particles, and, in addition, the method
disclosed provides an insufficient reduction in generation of fine
powder during the spheroidization and an insufficient improvement
in battery characteristics because paraffin wax is solid.
[0039] The carbon materials disclosed in Patent Documents 7 and 8
still contain fine powder generated through the fracture of a raw
flake graphite during the spheroidization, and the fine powder has
a low binding capacity to parent particles. Thus, when a negative
electrode is produced using these carbon materials, a great amount
of fine powder may occur, for example, upon physical impact, and
non-aqueous secondary batteries including these carbon materials
may fail to provide a sufficient input and output in initial and
subsequent cycles.
[0040] Specifically, for the carbon material described in Patent
Document 7, only the fine powder on the surface of a spheroidized
natural graphite contactable with the air is removed, and fine
powder that generates upon physical impact is difficult to remove.
The treatment performed on the carbon material described in Patent
Document 8 can remove only the fine powder that increases the
amount of micropore and can hardly remove fine powder that
generates upon physical impact.
[0041] The carbon material described in Patent Document 2, which
has a frequency of particles with a diameter of 5 .mu.m or less, as
measured after ultrasonic waves have been applied for 10 minutes,
of 40% to 85%, can be considered to be a carbon material that
generates a great amount of fine powder upon physical impact.
[0042] The investigation by the present inventors has shown that
the spheroidized natural graphites disclosed in Patent Document 1
and Patent Document 9 have a structure lacking particle fineness, a
poor balance between a specific surface area and a tap density
(also referred to as tapping density), a small number of Li-ion
insertion/extraction sites on particles, and insufficient filling
properties of negative electrode, and thus there is room for
improvement in input-output characteristics and increase in
capacity of batteries.
[0043] The spheroidized natural graphite with carbon black
deposited thereon disclosed in Patent Document 10, although
providing a certain improvement in input-output characteristics,
which is due to the smooth movement of electrolyte solution
resulting from the fine structure formed on the particle surface,
still has a poor balance between a specific surface area and a tap
density; there is room for improvement in input-output
characteristics and increase in capacity of batteries.
[0044] The above-described improvement in input-output
characteristics can be achieved, for example, by increasing the
specific surface area of the carbon material to improve the
reactivity with an electrolyte solution. The increase in density of
an active material layer for the increase in capacity can be
achieved, for example, by increasing the tap density of the carbon
material. The investigation by the present inventors has revealed
that in the case of graphite particles having substantially the
same true density and average particle diameter, the tap density
increases as the shape comes closer to spheroidal and the particle
surface becomes flat. In other words, to increase the tap density,
it is important that the particle shape be rounded and closer to
spheroidal, and the particle surface be made free from frays and
chips and kept flat. A particle shape closer to spheroidal and a
flat particle surface significantly improves powder filling
properties. However, there is usually a trade-off between the
specific surface area and the tap density, and, unfortunately,
increasing the specific surface area decreases the tap density.
[0045] The investigation by the present inventors has shown that
the spheroidized natural graphites disclosed in Patent Document 1
and Patent Document 9 have a structure lacking particle fineness,
and coating the particle surface with amorphous carbon results in a
reduced specific surface area and a small number of Li-ion
insertion extraction sites on particles; there is room for
improvement in input-output characteristics of batteries.
[0046] It is generally known that graphite particles having a large
specific surface area have a large number of Li-ion
insertion/extraction sites and thus provide a battery with improved
input-output characteristics.
[0047] Meanwhile, a carbonaceous material coating on graphite
particles has shown to have a structure that has lower
crystallinity than graphite and facilitates Li-ion
insertion/extraction and thus provide a battery with improved
input-output characteristics. That is to say, a large specific
surface area and graphite particles with reduced crystallinity can
enhance input-output characteristics. However, the carbonaceous
material coating on graphite particles for increasing the
low-crystallinity region that facilitates Li-ion
insertion/extraction covers the fine structure of the particle
surface; there is a trade-off between the increase in specific
surface area and the increase in low-crystallinity region through
the carbonaceous material coating.
[0048] The investigation by the present inventors has shown that
although the composite graphites disclosed in Patent Documents 1
and 11, which are made of a graphite and an amorphous carbon
coating on the graphite surface, can provide a high capacity and
good fast charge-discharge characteristics as compared with the
flake graphite or the spheroidized graphite particles used as a raw
material, these characteristics are still insufficient because the
coating uniformity of the amorphous carbon is not taken into
account. For the composite carbon material disclosed in Patent
Document 12, although exposed portions of high-crystallinity
carbonaceous particles having a microscopic Raman R value of 0.2 or
less are reduced by controlling the percentage of carbon materials
having a microscopic Raman R value of 0.2 or larger to be at least
20%, the distribution and variation of microscopic Raman values,
particularly, the distribution and variation of microscopic Raman
values of particles having a large microscopic Raman R value, that
is, the degree of maldistribution of portions coated with
low-crystallinity carbon material is not taken into account, and
the characteristics are still insufficient. For the composite
particles disclosed in Patent Document 10, although particles
having extremely large microscopic Raman R values and particles
having extremely small values are not contained, the distribution
and variation of microscopic Raman R values are not taken into
account, similarly to Patent Document 12, and the characteristics
are still insufficient.
[0049] The investigation by the present inventors has shown that
the technique disclosed in Patent Document 14 provides an
improvement in charge-discharge efficiency through the use of an
amorphous carbon having a controlled volume of pores of 0.33 n/m to
0.40 nm but has a drawback in that the amorphous carbon is hard to
densify for its small true density and poor pressability.
[0050] The investigation by the present inventors has shown that
the technique disclosed in Patent Document 15 using an
isotropically pressurized spheroidized natural graphite, although
providing a certain improvement in fast charge-discharge
characteristics, which is due to the smooth movement of electrolyte
solution between the particles resulting from filling properties
improved by the increased density of the particles, provides
insufficient low-temperature output characteristics. This is
because electrolyte solution cannot penetrate into the particles as
a result of the elimination of intra-particle voids, and Li-ion
insertion/extraction sites in the particles cannot be efficiently
used.
[0051] The investigation by the present inventors has shown that
although the spheroidized natural graphite disclosed in Patent
Document 16, which is heat treated in a nitrogen atmosphere at
500.degree. C. to 1,250.degree. C., has low-temperature charge
characteristics improved by the disorder of surface crystal
structure, the characteristics are still insufficient. This is
because the number of Li-ion insertion/extraction sites is still
insufficient, and the increase of labile carbon layers resulting
from the elimination of oxygen functional groups during the heat
treatment impedes the smooth movement of Li ions.
[0052] The investigation by the present inventors has shown that
although the granulated natural graphites disclosed in Patent
Document 1 and Patent Document 2 provide a high capacity and good
fast charge-discharge characteristics as compared with the flake
graphite used as a raw material, these characteristics are still
insufficient because the number of Li-ion insertion/extraction
sites inside the graphites is small. Furthermore, side reactions
with an electrolyte solution frequently occur due to the large
amount of oxygen functional group, which disadvantageously results
in the increase in irreversible capacity and gas generation.
[0053] Although the granulated natural graphite disclosed in Patent
Document 16, which is heat treated in a nitrogen atmosphere at
500.degree. C. to 1,250.degree. C., can reduce side reactions with
an electrolyte solution due to the reduction in oxygen functional
group and has low-temperature charge characteristics improved by
the moderately disordered surface crystal structure, the number of
Li-ion insertion/extraction sites inside the graphite is
insufficient, and the characteristics are insufficient.
[0054] The technique in Patent Document 6, in which coal-derived
calcined coke is used as a raw material and granulated into
spheroidal particles, provides a low discharge capacity, which is
insufficient.
[0055] The investigation by the present inventors has shown that
the spheroidized natural graphite disclosed in Patent Document 1,
although providing a high capacity and good fast charge-discharge
characteristics as compared with the flake graphite used as a raw
material, unfortunately provides low battery characteristics and
productivity because the particles poorly adhere to each other to
cause residual flake graphite and generate fine powder during the
spheroidization.
[0056] The powdered negative electrode material disclosed in Patent
Document 4 provides an insufficient improvement in battery
characteristics because the meltable organic substance and the
pitch contained during the spheroidization of the graphite contain
softened solids, and thus the raw carbon materials poorly adhere to
each other, and residual flake graphite and the generation of fine
powder during the spheroidization cannot be reduced. Furthermore,
since the affinity with the pitch is not taken into account, the
meltable organic substance contained during the spheroidization of
the graphite cannot uniformly cover the carbonaceous material and
provides an insufficient improvement in battery characteristics
also when used as a raw material of composite particles containing
the resulting spheroidized graphite particles and a carbonaceous
material.
[0057] The method for producing a spheroidized graphite disclosed
in Patent Document 5 also provides an insufficient improvement in
battery characteristics because the addition of a resin binder
hardly improves the adhesion between the graphite particles, and
the generation of fine powder cannot be reduced. Although a method
of spheroidization including the addition of a solution of the
resin hinder in toluene has also been disclosed, the method
requires further improvement because the temperature during the
spheroidization may exceed the low flash point of the solvent,
which involves the risk of explosion or fire during the production.
Furthermore, since the affinity with an organic substance, serving
as a precursor of the carbonaceous material, is not taken into
account, the resin binder described cannot uniformly cover the
carbonaceous material and provides an insufficient improvement in
battery characteristics also when used as a raw material of
composite particles containing the resulting spheroidized graphite
particles and a carbonaceous material.
[0058] Patent Document 6 has not disclosed a method of granulating
a graphite into spheroidal particles, and, in addition, the method
disclosed provides an insufficient reduction in generation of fine
powder during the spheroidization and an insufficient improvement
in battery characteristics because paraffin wax is solid.
Furthermore, since the affinity with an organic substance, serving
as a precursor of the carbonaceous material, is not taken into
account, the paraffin wax cannot uniformly cover the carbonaceous
material and provides an insufficient improvement in battery
characteristics also when used as a raw material of composite
particles containing the resulting granulated particles and a
carbonaceous material.
[0059] Although the composite graphites disclosed in Patent
Documents 1 and 11 to 12, which are made of a graphite and an
amorphous carbon coating on the graphite surface, can provide a
high capacity and good fast charge-discharge characteristics as
compared with the flake graphite or the spheroidized graphite
particles used as a raw material, these characteristics are still
insufficient because the relationship between the tap density, the
true density, and the density under a load of the graphite is not
taken into account.
[0060] The present invention has been made in view of the above
circumstances, and an object (object A) of the present invention is
to provide a carbon material that can provide a non-aqueous
secondary battery having a high capacity of 355 mAh/g or more, for
example, and excellent input-output characteristics
(low-temperature output characteristics) and, as a result, provide
a high-performance non-aqueous secondary battery.
[0061] Another object (object B) of the present invention is to
provide a method for producing a carbon material for a non-aqueous
secondary battery, comprising the step of granulating a raw carbon
material. The method can produce carbon materials for non-aqueous
secondary batteries having various types of particle structures and
can stably produce carbon materials that can be processed in bulk,
have a high degree of spheroidization, good filling properties, and
low anisotropy, and generate little amount of fine powder. A still
another object is to provide a carbon material that can provide a
non-aqueous secondary battery having a high capacity of 355 mAh/g
or more, for example, and excellent input-output characteristics
(low-temperature output characteristics) by this method and, as a
result, provide a high-performance non-aqueous secondary
battery.
Means for Solving the Problems
[0062] The inventors have intensively studied to achieve the object
A to discover that a carbon material for a non-aqueous secondary
battery, comprising a graphite capable of occluding and releasing
lithium ions, the carbon material having a cumulative pore volume
at pore diameters in a range of 0.01 .mu.m to 1 .mu.m of 0.08 mL/g
or more, a roundness, as determined by flow-type particle image
analysis, of 0.88 or greater, and a ratio (PD/d50 (%)) of mode pore
diameter (PD) in a pore diameter range of 0.01 .mu.m to 1 .mu.m in
a pore distribution determined by mercury intrusion to volume-based
average particle diameter (d50) of 1.8 or less can provide a
non-aqueous secondary battery negative electrode material having a
high capacity and excellent low-temperature output characteristics
and cycle characteristics, thereby completing Invention A.
More Specific Aspects of Invention A are as Follows:
[0063] (A1) A carbon material for a non-aqueous secondary battery,
comprising a graphite capable of occluding and releasing lithium
ions, the carbon material having a cumulative pore volume at pore
diameters in a range of 0.01 .mu.m to 1 .mu.m of 0.08 mL/g or more,
a roundness, as determined by flow-type particle image analysis, of
0.88 or greater, and a pore diameter to particle diameter ratio
(PD/d50 (%)) of 1.8 or less, the ratio being given by equation
(1A):
PD .times. / .times. d .times. .times. 50 .times. .times. ( % ) =
mode .times. .times. pore .times. .times. diameter .times. .times.
( PD ) .times. .times. in .times. .times. a .times. .times. pore
.times. .times. diameter .times. .times. range .times. .times. of
.times. .times. 0.01 .times. .times. .mu.m .times. .times. to
.times. .times. 1 .times. .times. .mu.m .times. .times. in .times.
.times. a .times. .times. pore .times. .times. distribution .times.
.times. determined .times. .times. by .times. .times. mercury
.times. .times. intrusion .times. / .times. volume .times. -
.times. based .times. .times. average .times. .times. particle
.times. .times. diameter .times. .times. ( d .times. .times. 50 )
.times. 100. ( 1 .times. A ) ##EQU00003##
[0064] (A2) A carbon material for a non-aqueous secondary battery
capable of occluding and releasing lithium ions, the carbon
material being formed from a plurality of graphite particles
without being pressed and having a pore diameter to particle
diameter ratio (PD/d50 (%)) of 1.8 or less, the ratio being given
by equation (1A):
PD .times. / .times. d .times. .times. 50 .times. .times. ( % ) =
mode .times. .times. pore .times. .times. diameter .times. .times.
( PD ) .times. .times. in .times. .times. a .times. .times. range
.times. .times. of .times. .times. 0.01 .times. .times. .mu.m
.times. .times. to .times. .times. 1 .times. .times. .mu.m .times.
.times. in .times. .times. a .times. .times. pore .times. .times.
distribution .times. .times. determined .times. .times. by .times.
.times. mercury .times. .times. intrusion .times. / .times. volume
.times. - .times. based .times. .times. average .times. .times.
particle .times. .times. diameter .times. .times. ( d .times.
.times. 50 ) .times. 100. ( 1 .times. A ) ##EQU00004##
[0065] (A3) The carbon material for a non-aqueous secondary battery
according to (A1) or (A2), wherein the carbon material is a
spheroidized graphite made of flake graphite, crystalline graphite,
and vein graphite and has a half width at half maximum of pore
distribution (log (nm)) of 0.45 or greater, the half width at half
maximum of pore distribution (log (nm)) referring to a half width
at half maximum at a micropore side of a peak in a pore diameter
range of 0.01 .mu.m to 1 .mu.m in a pore distribution (nm), as
determined by mercury intrusion (mercury porosimetry), of the
carbon material for a non-aqueous secondary battery, with a
horizontal axis expressed in common logarithm (log (nm)).
[0066] (A4) The carbon material for a non-aqueous secondary battery
according to (A1) or (A2), wherein the carbon material is a
composite carbon material comprising a spheroidized graphite made
of flake graphite, crystalline graphite, and vein graphite and a
carbonaceous material and has a half width at half maximum of pore
distribution (log (nm)) of 0.3 or greater, the half width at half
maximum of pore distribution (log (nm)) referring to a half width
at half maximum at a micropore side of a peak in a pore diameter
range of 0.01 .mu.m to 1 .mu.m in a pore distribution (nm), as
determined by mercury intrusion (mercury porosimetry), of the
carbon material for a non-aqueous secondary battery, with a
horizontal axis expressed in common logarithm (log (nm)).
[0067] (A5) The carbon material for a non-aqueous secondary battery
according to any one of (A1) to (A4), wherein the carbon material
is a spheroidized graphite made of flake graphite.
[0068] (A6) The carbon material for a non-aqueous secondary battery
according to any one of (A1) to (A5), wherein the carbon material
has a frequency of particles with a particle diameter of 3 .mu.m or
less of 1% to 60%, the particle diameter and the frequency of
particles being measured using a flow-type particle image analyzer
after the carbon material has been irradiated with ultrasonic waves
of 28 kHz at a power of 60 W for 5 minutes.
[0069] (A7) A non-aqueous secondary battery comprising: a positive
electrode and a negative electrode, each being capable of occluding
and releasing lithium ions; and an electrolyte, the negative
electrode comprising a current collector and a negative electrode
active material layer on the current collector, the negative
electrode active material layer comprising the carbon material
according to any one of (A1) to (A6).
[0070] The inventors have intensively studied to achieve the object
B to find a method for producing a carbon material for a
non-aqueous secondary battery, comprising: a granulation step of
granulating a raw carbon material by applying at least one type of
mechanical energy selected from impact, compression, friction, and
shear force, the step of granulating a raw carbon material being
carried out in the presence of a granulating agent that satisfies
conditions 1) and 2):
[0071] 1) being liquid during the step of granulating the raw
carbon material; and
[0072] 2) in the granulating agent, no organic solvent is
contained, or if contained, at least one of the organic solvents
has no flash point or a flash point of 5.degree. C. or higher.
More Specific Aspects of Invention B are as Follows:
[0073] (B1) A method for producing a carbon material for a
non-aqueous secondary battery, comprising
[0074] a granulation step of granulating a raw carbon material by
applying at least one type of mechanical energy selected from
impact, compression, friction, and shear force, the granulation
step being carried out in the presence of a granulating agent that
satisfies conditions 1) and 2):
[0075] 1) being liquid during the step of granulating the raw
carbon material; and
[0076] 2) in the granulating agent, no organic solvent is
contained, or if contained, at least one of the organic solvents
has no flash point or a flash point of 5.degree. C. or higher.
[0077] (B2) The production method according to (B1), wherein the
granulating agent has a contact angle .theta. with a graphite of
less than 90.degree., the contact angle being measured by the
following method:
Method for Measuring Contact Angle .theta. with Graphite
[0078] Onto a surface of HOPG, 1.2 .mu.L of a granulating agent is
added dropwise, and when wetting and spreading has settled down and
a rate of change in contact angle .theta. of the granulating agent
added dropwise in one second has reached 3% or lower, the contact
angle is measured using a contact angle meter (DM-501 automatic
contact angle meter available from Kyowa. Interface Science Co.,
Ltd). When a granulating agent having a viscosity at 25.degree. C.
of 500 cP or lower is used, a value at 25.degree. C. is employed as
a measurement of the contact angle .theta., and when a granulating
agent having a viscosity at 25.degree. C. of higher than 500 cP is
used, a value at an increased temperature where the viscosity is
not higher than 500 cP is employed.
[0079] (B3) The production method according to (B1) or (B2),
wherein the granulating agent has a viscosity of 1 cP or more
during the granulation step.
[0080] (B4) The production method according to any one of (B1) to
(B3), wherein the granulating agent has a viscosity at 25.degree.
C. of 1 cP to 100,000 cP.
[0081] (B5) The production method according to any one of (B1) to
(B4), wherein the raw carbon material comprises at least one
selected from the group consisting of flake, crystalline, and vein
natural graphites.
[0082] (B6) The production method according to any one of (B1) to
(B5), wherein the raw carbon material has a d.sub.002 of 0.34 nm or
less.
[0083] (B7) The production method according to any one of (B1) to
(B6), wherein the granulation step comprises granulating the raw
carbon material in the presence of at least one selected from the
group consisting of metals capable of forming alloys with Li,
oxides thereof, amorphous carbon, and green coke.
[0084] (B8) The production method according to any one of (B1) to
(B7), wherein the granulation step is carried out in an atmosphere
at 0.degree. C. to 250.degree. C.
[0085] (B9) The production method according to any one of (B1) to
(B8), wherein the granulation step comprises placing the graphite
in an apparatus comprising a rotatable member that rotates at a
high speed in a casing and having a rotor equipped with a plurality
of blades in the casing, and applying any one of impact,
compression, friction, and shear force to the graphite placed in
the apparatus by rotating the rotor at a high speed.
[0086] (B10) The production method according to any one of (B1) to
(B9), further comprising the step of depositing a carbonaceous
material having lower crystallinity than the raw carbon material on
the granulated carbon material obtained in the granulation
step.
[0087] The inventors have intensively studied to achieve the object
A to find another object, that is, to achieve a carbon material for
a non-aqueous secondary battery having so high particle strength as
to generate little amount of fine powder even upon physical impact,
and discovered that using a carbon material for a non-aqueous
secondary battery capable of occluding and releasing lithium ions
and formed from a plurality of graphite particles as a negative
electrode active material, the carbon material satisfying
inequality (1C):
Q 5 .times. .times. min .times. .times. ( % ) .times. / .times. D
.times. .times. 50 .times. .times. ( .mu.m ) .ltoreq. 3.5 ( 1
.times. C ) ##EQU00005##
where Q.sub.5min (%) is a frequency (%) of particles with a
diameter of 5 .mu.m or less measured using a flow-type particle
image analyzer after the carbon material has been irradiated with
ultrasonic waves of 28 kHz at a power of 60 W for 5 minutes;
and
[0088] D50 (.mu.m) is a volume-based median diameter determined by
laser diffraction/scattering after the carbon material has been
irradiated with ultrasonic waves of 28 kHz at a power of 60 W for 1
minute, can provide a non-aqueous secondary battery having
excellent input-output characteristics and excellent cycle
characteristics, thereby completing Invention C.
[0089] More specific aspects of Invention C are as follows:
[0090] (C1) A carbon material for a non-aqueous secondary battery
capable of occluding and releasing lithium ions and formed from a
plurality of graphite particles, the carbon material satisfying
inequality (1C):
Q 5 .times. .times. min .times. .times. ( % ) .times. / .times. D
.times. .times. 50 .times. .times. ( .mu.m ) .ltoreq. 3.5 ( 1
.times. C ) ##EQU00006##
where Q.sub.5min (%) is a frequency (%) of particles with a
diameter of 5 .mu.m or less measured using a flow-type particle
image analyzer after the carbon material has been irradiated with
ultrasonic waves of 28 kHz at a power of 60 W for 5 minutes; and
[0091] D50 (.mu.m) is a volume-based median diameter determined by
laser diffraction/scattering after the carbon material has been
irradiated with ultrasonic waves of 28 kHz at a power of 60 W for 1
minute.
[0092] (C2) The carbon material for a non-aqueous secondary battery
according to (C1), wherein the carbon material has a Q.sub.5min (%)
of 40% or less.
[0093] (C3) The carbon material for a non-aqueous secondary battery
according to (C1) or (C2), wherein the total amount of eliminated
CO and eliminated CO.sub.2, as measured using a pyrolysis mass
spectrometer (TPD-MS) by heating the carbon material from room
temperature to 1,000.degree. C., is 125 .mu.mol/g or less.
[0094] (C4) The carbon material for a non-aqueous secondary battery
according to any one of (C1) to (C3), wherein the amount of
eliminated CO, as measured using a pyrolysis mass spectrometer
(TPD-MS) by heating the carbon material from room temperature to
1,000.degree. C., is 100 .mu.mol/g or less.
[0095] (C5) The carbon material for a non-aqueous secondary battery
according to any one of (C1) to (C4), wherein the amount of
eliminated CO.sub.2 as measured using a pyrolysis mass spectrometer
(TPD-MS) by heating the carbon material from room temperature to
1,000.degree. C., is 25 .mu.mol/g or less.
[0096] (C6) The carbon material for a non-aqueous secondary battery
according to any one of (C1) to (C5), wherein the carbon material
has a tap density of 0.7 g/cm.sup.3 to 1.3 g/cm.sup.3.
[0097] (C7) The carbon material for a non-aqueous secondary battery
according to any one of (C1) to (C6), wherein the carbon material
has a roundness of 0.86 or greater.
[0098] (C8) The carbon material for a non-aqueous secondary battery
according to any one of (C1) to (C7), wherein the carbon material
has a BET specific surface area of 2 m.sup.2/g to 30 m.sup.2/g.
[0099] (C9) The carbon material for a non-aqueous secondary battery
according to any one of (C1) to (C8), wherein the carbon material
has a volume-based median diameter (D50) of 1 .mu.m to 50
.mu.m.
[0100] (C10) The carbon material for a non-aqueous secondary
battery according to any one of (C1) to (C9), wherein the carbon
material has an Lc of 90 nm or more and a d.sub.002 of 0.337 nm or
less, the values being determined by wide-angle X-ray
diffractometry.
[0101] (C11) The carbon material for a non-aqueous secondary
battery according to any one of (C1) to (C10), wherein the graphite
particles contain a natural graphite.
[0102] (C12) A composite carbon material for a non-aqueous
secondary battery, comprising the carbon material according to any
one of (C1) to (C11); and a carbonaceous material combined with the
carbon material.
[0103] (C13) A non-aqueous lithium ion secondary battery
comprising: a positive electrode and a negative electrode, each
being capable of occluding and releasing lithium ions, and an
electrolyte, the negative electrode comprising the carbon material
for a non-aqueous secondary battery according to any one of (C1) to
(C11) or the composite carbon material for a non-aqueous secondary
battery according to (C12).
[0104] The inventors have intensively studied to achieve the object
A to discover that a carbon material for a non-aqueous secondary
battery capable of occluding and releasing lithium ions, the carbon
material comprising a carbonaceous material on a particle surface
and having a tap density and a specific surface area (SA)
determined by BET method satisfying a specific relationship, can
provide a non-aqueous secondary battery negative electrode material
having a high capacity and excellent input-output characteristics
and cycle characteristics, thereby completing Invention D.
More Specific Aspects of Invention D are as Follows:
[0105] (D1) A carbon material for a non-aqueous secondary battery
capable of occluding and releasing lithium ions, the carbon
material comprising a carbonaceous material on a particle surface
and satisfying the relationship of inequality (1D):
10 .times. Y d + 0.26 .times. X d .gtoreq. .alpha. ( 1 .times. D )
##EQU00007##
(Y.sub.d=tap density (g/cm.sup.3), X.sub.d=specific surface area
(SA) (m.sup.2/g) of carbon material determined by BET method,
.alpha.=12.60).
[0106] (D2) The carbon material for a non-aqueous secondary battery
according to (D1), wherein the specific surface area (SA)
(m.sup.2/g) of the carbon material determined by BET method is 2 or
greater.
[0107] (D3) The carbon material for a non-aqueous secondary battery
according to (D1) or (D2), wherein the carbon material comprises a
plurality of graphites selected from the group consisting of at
least one of flake graphite, crystalline graphite, and vein
graphite.
[0108] (D4) The carbon material for a non-aqueous secondary battery
according to any one of (D1) to (D3), wherein the carbon material
has a 1st discharge capacity of 300 mAh/g or more.
[0109] (D5) A non-aqueous secondary battery comprising: a positive
electrode and a negative electrode, each being capable of occluding
and releasing lithium ions; and an electrolyte, the negative
electrode comprising a current collector and a negative electrode
active material layer on the current collector, the negative
electrode active material layer comprising the carbon material
according to any one of (D1) to (D4).
[0110] The inventors have intensively studied to achieve the object
A to find another object, that is, to provide a carbon material for
a non-aqueous secondary battery overcoming the traditional
trade-off between specific surface area and low-crystallinity
region and having excellent input-output characteristics, and
discovered that a carbon material for a non-aqueous secondary
battery capable of occluding and releasing lithium ions, the carbon
material comprising a carbonaceous material on a particle surface
and having a true density and a specific surface area (SA)
determined by BET method satisfying a specific relationship, can
provide a carbon material for a non-aqueous secondary battery
having excellent input-output characteristics, thereby completing
Invention E. The true density is a physical property that indicates
the crystallinity of graphite particles.
More Specific Aspects of Invention E are as Follows:
[0111] (E1) A carbon material for a non-aqueous secondary battery
capable of occluding and releasing lithium ions, the carbon
material comprising a carbonaceous material on a particle surface
and satisfying the relationship of inequality (1E):
Y e - 0.01 .times. X e .ltoreq. .alpha. ( 1 .times. E )
##EQU00008##
(Y.sub.e=true density (g/cm.sup.3), X.sub.e=specific surface area
(SA) m.sup.2/g) of carbon material determined by BET method,
.alpha.=2.20).
[0112] (E2) The carbon material for a non-aqueous secondary battery
according to (E1), wherein the specific surface area (SA)
(m.sup.2/g) of the carbon material determined by BET method is 2 or
greater.
[0113] (E3) The carbon material for a non-aqueous secondary battery
according to (E1) or (E2), wherein the carbon material comprises a
plurality of graphites selected from the group consisting of at
least one of flake graphite, crystalline graphite, and vein
graphite.
[0114] (E4) The carbon material for a non-aqueous secondary battery
according to any one of (E1) to (E3), wherein the carbon material
has a 1st discharge capacity of 300 mAh/g or more.
[0115] (E5) The carbon material for a non-aqueous secondary battery
according to any one of (E1) to (E4), wherein the carbon material
has a 90% particle diameter (d90) to 10% particle diameter (d10)
ratio (d90/d10) in a volume-based particle size distribution of 2.6
or greater.
[0116] (E6) A non-aqueous secondary battery comprising: a positive
electrode and a negative electrode, each being capable of occluding
and releasing lithium ions; and an electrolyte, the negative
electrode comprising a current collector and a negative electrode
active material layer on the current collector, the negative
electrode active material layer comprising the carbon material
according to any one of (E1) to (E5).
[0117] The inventors have intensively studied to achieve the object
A to discover that a composite carbon material comprising a carbon
material (A) capable of occluding and releasing lithium ions
(hereinafter also referred to as "the carbon material (A)") and a
carbonaceous material (B) on the surface of the carbon material (A)
(hereinafter also referred to as "the composite carbon material"),
wherein the average value of microscopic Raman R values of 30
randomly selected composite carbon materials is 0.1 to 0.85, and
the standard deviation (.sigma..sub.R) is 0.1 or less, can provide
a non-aqueous secondary battery negative electrode material having
a high capacity and excellent low-temperature output
characteristics and cycle characteristics, thereby completing
Invention F.
More Specific Aspects of Invention F are as Follows:
[0118] (F1) A composite carbon material comprising: a carbon
material (A) capable of occluding and releasing lithium ions: and a
carbonaceous material (B) on the surface of the carbon material
(A), wherein the average value of microscopic Raman R values of 30
randomly selected composite carbon materials is 0.1 to 0.85, and
the standard deviation (.sigma..sub.R) is 0.1 or less.
[0119] (F2) The composite carbon material for a non-aqueous
secondary battery according to (F1), wherein the composite carbon
material has a microscopic Raman R.sub.15 value of 12% or less, the
value being given by equation (1F):
Microscopic .times. .times. Raman .times. .times. R ( 15 ) .times.
.times. value .times. .times. ( % ) = the .times. .times. number
.times. .times. of .times. .times. composite .times. .times. carbon
.times. .times. materials .times. .times. having .times. .times. a
.times. .times. microscopic .times. .times. Raman .times. .times. R
.times. .times. value .times. .times. of .times. .times. 0.15
.times. .times. or .times. .times. less .times. .times. among
.times. .times. 30 .times. .times. randomly .times. .times.
selected .times. .times. composite .times. .times. carbon .times.
.times. materials .times. / .times. 30 .times. 100. ( 1 .times. F )
##EQU00009##
[0120] (F3) The composite carbon material for a non-aqueous
secondary battery according to (F1) or (F2), wherein the composite
carbon material has a tap density of 0.6 g/cm.sup.3 to 1.20
g/cm.sup.3.
[0121] (F4) The composite carbon material for a non-aqueous
secondary battery according to any one of (F1) to (F3), wherein the
composite carbon material has a specific surface area (SA) of 1
m.sup.2/g to 30 m.sup.2/g.
[0122] (F5) The composite carbon material for a non-aqueous
secondary battery according to any one of (F1) to (F4), wherein the
carbon material is a spheroidized graphite made of at least one
carbon material selected from the group consisting of flake natural
graphite, crystalline natural graphite, and vein natural
graphite.
[0123] (F6) A method for producing a composite carbon material for
a non-aqueous secondary battery, comprising: mixing a carbon
material having a cumulative pore volume in a range of 0.01 .mu.m
to 1 .mu.m of 0.07 mL/g or more and a pore diameter to particle
diameter ratio (PD/d50 (%)), as given by equation (2F), of 1.8 or
less with a carbonaceous material precursor at a temperature equal
to or higher than a softening point of the carbonaceous material
precursor; and then carbonizing the carbonaceous material precursor
by heat treatment.
PD .times. / .times. d .times. .times. 50 .times. .times. ( % ) =
mode .times. .times. pore .times. .times. diameter .times. .times.
( PD ) .times. .times. in .times. .times. a .times. .times. range
.times. .times. of .times. .times. 0.01 .times. .times. .mu.m
.times. .times. to .times. .times. 1 .times. .times. .mu.m .times.
.times. in .times. .times. a .times. .times. pore .times. .times.
distribution .times. .times. determined .times. .times. by .times.
.times. mercury .times. .times. intrusion .times. / .times. volume
.times. - .times. based .times. .times. average .times. .times.
particle .times. .times. diameter .times. .times. ( d .times.
.times. 50 ) .times. 100. ( 2 .times. F ) ##EQU00010##
[0124] (F7) The method for producing a composite carbon material
for a non-aqueous secondary battery according to (F6), wherein the
carbon material is a spheroidized graphite made of at least one
carbon material selected from the group consisting of flake natural
graphite, crystalline natural graphite, and vein natural
graphite.
[0125] (F8) The method for producing a composite carbon material
for a non-aqueous secondary battery according to (F6) or (F7),
wherein the carbonaceous material precursor has a softening point
of 400.degree. C. or lower.
[0126] (F9) A composite carbon material for a non-aqueous secondary
battery produced by the method for producing a composite carbon
material for a non-aqueous secondary battery according to any one
of (F6) to (F8).
[0127] (F10) A non-aqueous secondary battery comprising: a positive
electrode and a negative electrode, each being capable of occluding
and releasing lithium ions; and an electrolyte, the negative
electrode comprising a current collector and a negative electrode
active material layer on the current collector, the negative
electrode active material layer comprising the composite carbon
material according to any one of (F1) to (F5) and (F9).
[0128] The inventors have intensively studied to achieve the object
A to discover that a carbon material having specific values of a
cumulative pore volume at pore diameters in a range of 2 to 4 mm
and a tap density improves low-temperature output characteristics,
thereby completing Invention G.
More Specific Aspects of Invention G are as Follows:
[0129] (G1) A carbon material for a non-aqueous secondary battery
capable of occluding and releasing lithium ions, the carbon
material having a cumulative pore volume at pore diameters in a
range of 2 to 4 nm, as determined by nitrogen gas adsorption, of
0.0022 cm.sup.3/g or more and a tap density of 0.83 g/cm.sup.3 or
more.
[0130] (G2) The carbon material for a non-aqueous secondary battery
according to (G1), wherein the carbon material has a maximum dV/d
log (D) (V: cumulative pore volume, D: pore diameter) at pore
diameters in a range of 2 to 4 nm, as determined by nitrogen gas
adsorption, of 0.0090 cm.sup.3/g or more.
[0131] (G3) The carbon material for a non-aqueous secondary battery
according to (G1) or (G2), wherein the carbon material has a
cumulative pore volume at pore diameters in a range of 2 to 100 nm
of 0.025 cm .sup.3/g or more.
[0132] (G4) The carbon material for a non-aqueous secondary battery
according to any one of (G1) to (G3), wherein the carbon material
comprises a plurality of graphites selected from the group
consisting of at least one of flake graphite, crystalline graphite,
and vein graphite.
[0133] (G5) A non-aqueous secondary battery comprising: a positive
electrode and a negative electrode, each being capable of occluding
and releasing lithium ions; and an electrolyte, the negative
electrode comprising a current collector and a negative electrode
active material layer on the current collector, the negative
electrode active material layer comprising the carbon material
according to any one of (G1) to (G5).
[0134] The inventors have intensively studied to achieve the object
A to discover that a carbon material for a non-aqueous secondary
battery capable of occluding and releasing lithium ions, the carbon
material having a Raman R value given by the following equation 1H
and a thermal weight loss ratio per unit area (.DELTA.TG/SA) in
specific ranges, can provide a non-aqueous secondary battery
negative electrode material having a high capacity and excellent
low-temperature output characteristics and cycle characteristics,
thereby completing Invention H.
More Specific Aspects of Invention H are as Follows:
[0135] (H1) A carbon material for a non-aqueous secondary battery
capable of occluding and releasing lithium ions, the carbon
material having a Raman R value, as given by equation (1H), of 0.31
or greater and a thermal weight loss ratio per unit area
(.DELTA.TG/SA), as given by equation (2H), of 0.05 to 0.45.
Raman .times. .times. value .times. .times. R = intensity .times.
.times. I B .times. .times. of .times. .times. peak .times. .times.
P B .times. .times. near .times. .times. 1 .times. , .times. 360
.times. .times. cm - 1 .times. / .times. intensity .times. .times.
I A .times. .times. of .times. .times. peak .times. .times. P A
.times. .times. near .times. .times. 1 .times. , .times. 580
.times. .times. cm - 1 .times. .times. by .times. .times. Raman
.times. .times. spectrum .times. .times. analysis Equation .times.
.times. ( 1 .times. H ) ( .DELTA. .times. .times. TG .times. /
.times. SA ) = ( thermal .times. .times. weight .times. .times.
loss .times. .times. ( .DELTA. .times. .times. TG ) .times. .times.
( % ) .times. .times. on .times. .times. heating .times. .times.
from .times. .times. 400 .times. .degree. .times. .times. C .
.times. to .times. .times. 600 .times. .degree. .times. .times. C .
.times. at .times. .times. 2 .times. .degree. .times. .times. C . /
.times. min .times. .times. in .times. .times. air .times. .times.
atmosphere , measured .times. .times. with .times. .times.
differential .times. .times. thermal .times. .times. balance )
.times. / .times. ( specific .times. .times. surface .times.
.times. area .times. .times. ( SA ) .times. .times. ( m 2 .times. /
.times. g ) .times. .times. of .times. .times. carbon .times.
.times. material .times. .times. determined .times. .times. by
.times. .times. BET .times. .times. method ) Equation .times.
.times. ( 2 .times. H ) ##EQU00011##
[0136] (H2) The carbon material for a non-aqueous secondary battery
according to (H1), wherein the carbon material is a spheroidized
graphite made of flake graphite, crystalline graphite, and vein
graphite.
[0137] (H3) The carbon material for a non-aqueous secondary battery
according to (H1) or (H2), wherein the carbon material has a
roundness, as determined by flow-type particle image analysis, of
0.88 or greater.
[0138] (H4) A non-aqueous secondary battery comprising: a positive
electrode and a negative electrode, each being capable of occluding
and releasing lithium ions; and an electrolyte, the negative
electrode comprising a current collector and a negative electrode
active material layer on the current collector, the negative
electrode active material layer comprising the carbon material
according to any one of (H1) to (H3).
[0139] The inventors have intensively studied to achieve the object
A to discover that a carbon material for a non-aqueous secondary
battery capable of occluding and releasing lithium ions, the carbon
material being graphite particles satisfying the relationship of
inequality (1I), can provide a non-aqueous secondary battery
negative electrode material having a high capacity and excellent
low-temperature output characteristics and cycle characteristics,
thereby completing Invention I.
100 .times. Y i + 0.26 .times. X i > .alpha. Inequality .times.
.times. ( 1 .times. I ) ##EQU00012##
[0140] (In inequality (1I), Y.sub.i is an oxygen functional group
dispersity given by equation (2I); X.sub.i is a volume-based
average particle diameter (d50) (.mu.m); and .alpha.=9.4)
Oxygen .times. .times. functional .times. .times. group .times.
.times. dispersity .times. .times. ( Y i ) = total .times. .times.
oxygen .times. .times. content .times. .times. ( mol .times.
.times. % ) .times. .times. determined .times. .times. by .times.
.times. elemental .times. .times. analysis .times. / .times.
surface .times. .times. oxygen .times. .times. content .times.
.times. ( O .times. / .times. C ) .times. .times. ( mol .times.
.times. % ) .times. .times. determined .times. .times. by .times.
.times. X .times. - .times. ray .times. .times. photoelectron
.times. .times. spectroscopy Equation .times. .times. ( 2 .times. I
) ##EQU00013##
More Specific Aspects of invention I are as Follows:
[0141] (I1) A carbon material for a non-aqueous secondary battery
capable of occluding and releasing lithium ions, the carbon
material being graphite particles satisfying the relationship of
inequality (1I).
100 .times. Y i + 0.26 .times. X i > .alpha. Inequality .times.
.times. ( 1 .times. I ) ##EQU00014##
[0142] (In inequality (1), Y.sub.i is an oxygen functional group
dispersity given by equation (2I); X.sub.i is a volume-based
average particle diameter (d50) (.mu.m); and .alpha.=9.4)
Oxygen .times. .times. functional .times. .times. group .times.
.times. dispersity .times. .times. ( Y i ) = total .times. .times.
oxygen .times. .times. content .times. .times. ( mol .times.
.times. % ) .times. .times. determined .times. .times. by .times.
.times. elemental .times. .times. analysis .times. / .times.
surface .times. .times. oxygen .times. .times. content .times.
.times. ( O .times. / .times. C ) .times. .times. ( mol .times.
.times. % ) .times. .times. determined .times. .times. by .times.
.times. X .times. - .times. ray .times. .times. photoelectron
.times. .times. spectroscopy Equation .times. .times. ( 2 .times. I
) ##EQU00015##
[0143] (I2) The carbon material for a non-aqueous secondary battery
according to (I1), wherein the surface oxygen content (O/C)
determined by X-ray photoelectron spectroscopy is 2 mol % or
less.
[0144] (I3) The carbon material for a non-aqueous secondary battery
according to any one of (I1) or (I2), wherein the carbon material
has a Tap density of 0.7 g/cm.sup.3 or more.
[0145] (I4) The carbon material for a non-aqueous secondary battery
according to any one of (I1) to (I3), wherein the carbon material
has a roundness, as determined by flow-type particle image
analysis, of 0.88 or greater.
[0146] (I5) The carbon material for a non-aqueous secondary battery
according to any one of (I1) to (I4), wherein the graphite
particles are spheroidal graphite particles formed by granulation
of flake graphite, crystalline graphite, and vein graphite.
[0147] (I6) The carbon material for a non-aqueous secondary battery
according to any one of (I1) to (I5), wherein the granulation is
carried out by applying at least one type of mechanical energy
selected from impact, compression, friction, and shear force.
[0148] (I7) The carbon material for a non-aqueous secondary battery
according to any one of (I1) to (I6), wherein the granulation is
carried out by placing the graphite in an apparatus comprising a
rotatable member that rotates at a high speed in a casing and
having a rotor equipped with a plurality of blades in the casing,
and applying any one of impact, compression, friction, and shear
force to the graphite placed in the apparatus by rotating the rotor
at a high speed.
[0149] (I8) A non-aqueous secondary battery comprising: a positive
electrode and a negative electrode, each being capable of occluding
and releasing lithium ions; and an electrolyte, the negative
electrode comprising a current collector and a negative electrode
active material layer on the current collector, the negative
electrode active material layer comprising the carbon material
according to any one of (I1) to (I7).
[0150] The inventors have intensively studied to achieve the object
B to find another object, that is, to provide a method for
producing composite particles for a non-aqueous secondary battery,
comprising spheroidally granulated graphite particles having a
structure in which fine powder having a great number of Li-ion
insertion/extraction sites exists on and in the particles, the
graphite particles being uniformly coated with a carbonaceous
material, and discovered that a production method comprising: 1)
applying at least one type of mechanical energy selected from
impact, compression, friction, and shear force in the presence of a
granulating agent having an aniline point of 80.degree. C. or lower
or no aniline point to granulate a raw carbon material; and 2)
mixing the granulated carbon material particles obtained in 1) with
an organic compound, serving as a carbonaceous material precursor,
and heat-treating the mixture, thereby completing Invention J.
More Specific Aspects of Invention J are as Follows:
[0151] (J1) A method for producing composite particles for a
non-aqueous secondary battery comprising a granulated carbon
material and a carbonaceous material having lower crystallinity
than the granulated carbon material, the method comprising the
steps of 1) and 2): 1) applying at least one type of mechanical
energy selected from impact, compression, friction, and shear force
in the presence of a granulating agent having an aniline point of
80.degree. C. or lower or no aniline point to granulate a raw
carbon material; and 2) mixing the granulated carbon material
obtained in 1) with an organic compound, serving as a carbonaceous
material precursor, and heat-treating the mixture.
[0152] (J2) The method for producing composite particles for a
non-aqueous secondary battery according to (J1), wherein the
granulating agent is an organic compound having an aromatic ring
and is liquid at 25.degree. C.
[0153] (J3) The method for producing composite particles for a
non-aqueous secondary battery according to (J1) or (J2), wherein
the organic compound, serving as a carbonaceous material precursor,
comprises an organic compound having an aromatic ring.
[0154] (J4) The method for producing composite particles for a
non-aqueous secondary battery according to any one of (J1) to (J3),
wherein the organic compound, serving as a carbonaceous material
precursor, is a coal-derived raw oil.
[0155] (J5) The method for producing composite particles for a
non-aqueous secondary battery according to any one of (J1) to (J4),
wherein the raw carbon material particles comprise at least one
selected from the group consisting of flake, crystalline, and vein
natural graphites.
[0156] (J6) The method for producing composite particles for a
non-aqueous secondary battery according to any one of (J1) to (J5),
wherein the raw carbon material has a d.sub.002 of 0.34 nm or
less.
[0157] (J7) The method for producing composite particles for a
non-aqueous secondary battery according to any one of (J1) to (J6),
wherein the granulation step is carried out in an atmosphere at
0.degree. C. to 250.degree. C.
[0158] (J8) The method for producing composite particles for a
non-aqueous secondary battery according to any one of (J1) to (J7),
wherein the granulation step comprises placing the graphite in an
apparatus comprising a rotatable member that rotates at a high
speed in a casing and having a rotor equipped with a plurality of
blades in the casing, and applying any one of impact, compression,
friction, and shear force to the graphite placed in the apparatus
by rotating the rotor at a high speed.
[0159] (J9) Composite particles for a non-aqueous secondary battery
produced by the production method according to any one of (J1) to
(J8).
[0160] (J10) A non-aqueous secondary battery comprising: a positive
electrode and a negative electrode, each being capable of occluding
and releasing lithium ions; and an electrolyte, the negative
electrode comprising a current collector and a negative electrode
active material layer on the current collector, the negative
electrode active material layer comprising the composite particles
for a non-aqueous secondary battery according to (J9).
[0161] The inventors have intensively studied to achieve the object
A to discover that while the reasons are not fully understood, a
carbon material having a true density that satisfies a specific
relationship with a density under a specific load minus a tap
density can provide a carbon material for a non-aqueous secondary
battery negative electrode having a high capacity and excellent
low-temperature output characteristics, thereby completing
invention K.
[0162] More specific aspects of Invention K are as follows:
[0163] (K1) A carbon material for a non-aqueous secondary battery,
satisfying inequality (1K).
10.914 > 5 .times. x k - y k - 0.0087 .times. a Inequality
.times. .times. ( 1 .times. K ) ##EQU00016##
[0164] (In inequality (1K), x.sub.L is a true density [g/cm.sup.3]
of the carbon material; y.sub.k is a value determined by equation
(2K); and a is a volume-based average particle diameter [.mu.m] of
the carbon material.)
y k = ( density .times. [ g .times. / .times. cm 3 ] .times.
.times. of .times. .times. carbon .times. .times. material .times.
.times. under .times. .times. uniaxial .times. .times. load .times.
.times. of .times. .times. 100 .times. .times. kgf .times. /
.times. 3.14 .times. .times. cm 2 ) - ( tap .times. .times. density
.times. .times. of .times. .times. carbon .times. .times. material
.times. [ g .times. / .times. cm 3 ] ) Equation .times. .times. ( 2
.times. K ) ##EQU00017##
[0165] (K2) A carbon material for a non-aqueous secondary battery,
satisfying inequality (3K).
10.990 > 5 .times. x k - y k Inequality .times. .times. ( 3
.times. K ) ##EQU00018##
[0166] (In inequality (3K), x.sub.k is a true density [g/cm.sup.3]
of the carbon material, and y.sub.k is a value determined by
equation (2K).)
y k = ( density .times. [ g .times. / .times. cm 3 ] .times.
.times. of .times. .times. powder .times. .times. carbon .times.
.times. material .times. .times. under .times. .times. uniaxial
.times. .times. load .times. .times. of .times. .times. 100 .times.
.times. kgf .times. / .times. 3.14 .times. .times. cm 2 ) - ( tap
.times. .times. density .times. .times. of .times. .times. carbon
.times. .times. material .times. [ g .times. / .times. cm 3 ] )
Equation .times. .times. ( 2 .times. K ) ##EQU00019##
[0167] (K3) The carbon material for a non-aqueous secondary battery
according to (K1) or (K2), wherein the carbon material has a true
density of 2.20 g/cm.sup.3 to 2.262 g/cm.sup.3.
[0168] (K4) The carbon material for a non-aqueous secondary battery
according to any one of (K1) to (K3), wherein the carbon material
has a tap density of 0.85 g/cm.sup.3 or more.
[0169] (K5) The carbon material for a non-aqueous secondary battery
according to any one of (K1) to (K4), wherein at least part of the
surface of the carbon material is coated with an amorphous
carbon.
[0170] (K6) The carbon material for a non-aqueous secondary battery
according to any one of (K1) to (K4), wherein the carbon material
comprises spheroidal graphite particles formed by granulation of
flake graphite, crystalline graphite, and vein graphite.
[0171] (K7) The carbon material for a non-aqueous secondary battery
according to (K6), wherein the granulation is carried out by
applying at least one type of mechanical energy selected from
impact, compression, friction, and shear force.
[0172] (K8) The carbon material for a non-aqueous secondary battery
according to (K6) or (K7), wherein the granulation is carried out
by placing the graphite in an apparatus comprising a rotatable
member that rotates at a high speed in a casing and having a rotor
equipped with a plurality of blades in the casing, and applying any
one of impact, compression, friction, and shear force to the
graphite placed in the apparatus by rotating the rotor at a high
speed.
[0173] (K9) A non-aqueous secondary battery comprising: a positive
electrode and a negative electrode, each being capable of occluding
and releasing lithium ions; and an electrolyte, the negative
electrode comprising a current collector and a negative electrode
active material layer on the current collector, the negative
electrode active material layer comprising the carbon material
according to any one of (K1) to (K8).
[0174] The inventors have intensively studied to achieve the object
A to discover that fining intra-particle pores (L'), uniformly
dispersing intra-particle pores (L.sup.2), or controlling the
orientation of and the interval between intra-particle voids
(L.sup.3) can provide a non-aqueous secondary battery negative
electrode material having a high capacity and excellent
low-temperature output characteristics and cycle characteristics,
thereby completing Inventions L (L.sup.1 to L.sup.3).
More Specifically, Aspects of Invention L.sup.1 are as Follows:
[0175] (L.sup.11) A carbon material for a non-aqueous secondary
battery, comprising granulated particles satisfying (1L) and (2L):
the carbon material for a non-aqueous secondary battery having an
average box-counting dimension relative to void regions of 30
particles of 1.55 or greater, as calculated from images obtained by
randomly selecting 30 granulated particles from a cross-sectional
SEM image of the carbon material for a non-aqueous secondary
battery, dividing the cross-sectional SEM image of each granulated
particle into void regions and non-void regions, and binarizing the
image.
[0176] (1L) The granulated particles are made of a carbonaceous
material; and (2L) The granulated particles satisfy the
relationship |X.sub.1-X|/X.sub.1.ltoreq.0.2, where X is a
volume-based average particle diameter determined by laser
diffraction, and X.sub.1 is an equivalent circular diameter as
determined from a cross-sectional SEM image, provided that the
cross-sectional SEM image is a reflected electron image acquired at
an acceleration voltage of 10 kV.
[0177] (L.sup.12) The carbon material for a non-aqueous secondary
battery according to (L.sup.11), wherein the granulated particles
satisfy the relationship |R-R.sub.1|.ltoreq.0.1, where R is a
roundness determined with a flow-type particle image analyzer, and
R.sub.1 is a roundness determined from a cross-sectional SEM
image.
[0178] (L.sup.13) The carbon material for a non-aqueous secondary
battery according to (L.sup.11) or (L.sup.12), wherein the carbon
material has a tap density of 0.7 g/cm.sup.3 or more.
[0179] (L.sup.14) The carbon material for a non-aqueous secondary
battery according to any one of (L.sup.11) to (L.sup.13), wherein
the carbon material has a roundness, as determined by flow-type
particle image analysis, of 0.88 or greater.
[0180] (L.sup.15) The carbon material for a non-aqueous secondary
battery according to any one of (L.sup.11) to (L.sup.14), wherein
the graphite particles are spheroidal graphite particles formed by
granulation of flake graphite, crystalline graphite, and vein
graphite.
[0181] (L.sup.16) The carbon material for a non-aqueous secondary
battery according to any one of (L.sup.11) to (L.sup.15), wherein
the granulation is carried out by applying at least one type of
mechanical energy selected from impact, compression, friction, and
shear force.
[0182] (L.sup.17) The carbon material for a non-aqueous secondary
battery according to any one of (L.sup.11) to (L.sup.16), wherein
the granulation is carried out by placing the graphite in an
apparatus comprising a rotatable member that rotates at a high
speed in a casing and having a rotor equipped with a plurality of
blades in the casing, and applying any one of impact, compression,
friction, and shear force to the graphite placed in the apparatus
by rotating the rotor at a high speed.
[0183] (L.sup.18) A non-aqueous secondary battery comprising: a
positive electrode and a negative electrode, each being capable of
occluding and releasing lithium ions; and an electrolyte, the
negative electrode comprising a current collector and a negative
electrode active material layer on the current collector, the
negative electrode active material layer comprising the carbon
material according to any one of (L.sup.11) to (L.sup.17).
Aspects of Invention L.sup.2 are as Follows:
[0184] (L.sup.21) A carbon material for a non-aqueous secondary
battery, comprising granulated particles satisfying (1L) and (2L),
the carbon material for a non-aqueous secondary battery having an
average dispersity D of 30 granulated particles, as determined by
the following measurement method, of 60% or more, the 30 particles
being randomly selected from a cross-sectional SEM image of the
carbon material for a non-aqueous secondary battery.
[0185] (1L) Being made of a carbonaceous material.
[0186] (2L) Satisfying the relationship
|X.sub.1-X|X.sub.1.ltoreq.0.2, where X is a volume-based average
particle diameter determined by laser diffraction, and X.sub.1 is
an equivalent circular diameter determined from a cross-sectional
SEM image.
Measurement Method
[0187] Using a cross-sectional SEM image, grid lines are drawn to
split the minor axis and the major axis of a target granulated
particle each into 20 parts. Using cells in the grid, the
granulated particle is compartmentalized as defined below. The
expectation E of void area of each compartment is calculated using
equation (A) below, and the dispersity D of the granulated particle
is calculated using equation (B) below.
[0188] The cross-sectional SEM image is a reflected electron image
acquired at an acceleration voltage of 10 kV.
Definition of Compartment of Granulated Particle
[0189] The compartment is defined as a granulated particle portion
and/or a region where a void is present in the granulated particle
in each cell of the above-described grid. The outside of the
boundary of the granulated particle is excluded from the
compartment.
Expectation .times. .times. E .times. [ .mu.m 2 ] .times. .times.
of .times. .times. void .times. .times. area .times. .times. in
.times. .times. target .times. .times. compartment = ( gross
.times. .times. area .times. [ .mu.m 2 ] .times. .times. of .times.
.times. internal .times. .times. voids .times. .times. of .times.
.times. one .times. .times. target .times. .times. granulated
.times. .times. particle ) .times. / .times. { ( cross .times. -
.times. sectional .times. .times. area .times. [ .mu.m 2 ] .times.
.times. of .times. .times. one .times. .times. target .times.
.times. granulated .times. .times. particle ) .times. ( area
.times. [ .mu.m 2 ] .times. .times. of .times. .times. target
.times. .times. compartment ) } Equation .times. .times. ( A )
Dispersity .times. .times. D .times. .times. ( % ) = ( sum .times.
.times. total .times. [ .mu.m 2 ] .times. .times. of .times.
.times. areas .times. .times. of .times. .times. compartments
.times. .times. that .times. .times. satisfy .times. .times. (
gross .times. .times. area .times. [ .mu.m 2 ] .times. .times. of
.times. .times. voids .times. .times. in .times. .times. target
.times. .times. compartment ) .times. / .times. ( expectation
.times. .times. E .times. [ .mu.m 2 ] .times. .times. of .times.
.times. void .times. .times. area .times. .times. in .times.
.times. target .times. .times. compartment ) = 0.5 .times. .times.
or .times. .times. greater ) .times. / .times. ( sum .times.
.times. total .times. [ .mu.m 2 ] .times. .times. of .times.
.times. areas .times. .times. of .times. .times. all .times.
.times. the .times. .times. compartments .times. .times. of .times.
.times. one .times. .times. target .times. .times. granulated
.times. .times. particle ) .times. 100 Equation .times. .times. ( B
) ##EQU00020##
[0190] (L.sup.22) The carbon material for a non-aqueous secondary
battery according to (L.sup.21), wherein the granulated particles
satisfy the relationship |R-R.sub.1|.ltoreq.0.1, where R is a
roundness determined with a flow-type particle image analyzer, and
R.sub.1 is a roundness determined from a cross-sectional SEM
image.
[0191] (L.sup.23) The carbon material for a non-aqueous secondary
battery according to (L.sup.21) or (L.sup.22), wherein the carbon
material has a tap density of 0.7 g/cm.sup.3 or more.
[0192] (L.sup.24) The carbon material for a non-aqueous secondary
battery according to any one of (L.sup.21) to (L.sup.23), wherein
the carbon material has a roundness, as determined by flow-type
particle image analysis, of 0.88 or greater.
[0193] (L.sup.25) The carbon material for a non-aqueous secondary
battery according to any one of (L.sup.21) to (L.sup.24), wherein
the graphite particles are spheroidal graphite particles formed by
granulation of flake graphite, crystalline graphite, and vein
graphite.
[0194] (L.sup.26) The carbon material for a non-aqueous secondary
battery according to any one of (L.sup.21) to (L.sup.25), wherein
the granulation is carried out by applying at least one type of
mechanical energy selected from impact, compression, friction, and
shear force.
[0195] (L.sup.27) The carbon material for a non-aqueous secondary
battery according to any one of (L.sup.21) to (L.sup.26), wherein
the granulation is carried out by placing the graphite in an
apparatus comprising a rotatable member that rotates at a high
speed in a casing and having a rotor equipped with a plurality of
blades in the casing, and applying any one of impact, compression,
friction, and shear force to the graphite placed in the apparatus
by rotating the rotor at a high speed.
[0196] (L.sup.28) A non-aqueous secondary battery comprising: a
positive electrode and a negative electrode, each being capable of
occluding and releasing lithium ions; and an electrolyte, the
negative electrode comprising a current collector and a negative
electrode active material layer on the current collector, the
negative electrode active material layer comprising the carbon
material according to any one of (L.sup.21) to (L.sup.27),
Aspects of Invention L.sup.3 are as Follows:
[0197] (L.sup.31) A carbon material for a non-aqueous secondary
battery, comprising granulated particles satisfying (1L) and (2L),
the carbon material for a non-aqueous secondary battery having an
average inter-void distance Z (Zave) of 30 granulated particles
defined below and a volume-based average particle diameter X
determined by laser diffraction in a ratio (Zave/X) of 0.060 or
less, the 30 particles being randomly selected from a
cross-sectional SEM image of the carbon material for a non-aqueous
secondary battery.
[0198] (1L) Being made of a carbonaceous material.
[0199] (2L) Satisfying the relationship
|X.sub.1-X|/X.sub.1.ltoreq.0.2, where X is a volume-based average
particle diameter determined by laser diffraction, and X.sub.1 is
an equivalent circular diameter determined from a cross-sectional
SEM image.
Definition of Average Inter-Void Distance Z (Zave) of 30
Particles
[0200] Three lines are drawn that are parallel to the minor axis of
the granulated particle and split the major axis of the granulated
particle into four parts, and inter-void distances Z (.mu.m) of the
granulated particle on each line are each measured. The average of
30 particles in total is calculated. This is defined as the average
Z (Zave) of 30 particles.
[0201] The cross-sectional SEM image is a reflected electron image
acquired at 10 kV.
[0202] (L.sup.32) The carbon material for a non-aqueous secondary
battery according to (L.sup.31), wherein the carbon material has a
standard deviation (W) of void sizes Y of 30 granulated particles
defined below and a volume-based average particle diameter X
determined by laser diffraction in a ratio (W/X) of 0.018 or less,
the 30 particles being randomly selected from a cross-sectional SEM
image of the carbon material for a non-aqueous secondary
battery,
Definition of Standard Deviation (W) of Void Sizes V of 30
Particles
[0203] Three lines are drawn that are parallel to the minor axis of
the granulated particle and split the major axis of the granulated
particle into four parts, and void sizes Y (.mu.m) of the
granulated particle on each line are each measured. The standard
deviation of 30 particles in total is calculated. This is defined
as the standard deviation (W) of void sizes Y of 30 particles.
[0204] (L.sup.33) The carbon material for a non-aqueous secondary
battery according to (L.sup.31) or (L.sup.32), wherein 70% or more
of 30 granulated particles randomly selected from a cross-sectional
SEM image of the carbon material for a non-aqueous secondary
battery have slit-like voids, and the slit-like voids are arranged
mainly in layers.
[0205] (L.sup.34) The carbon material for a non-aqueous secondary
battery according to any one of (L.sup.31) to (L.sup.33), wherein
the carbon material has a tap density of 0.7 g/cm.sup.3 or
more.
[0206] (L.sup.35) The carbon material for a non-aqueous secondary
battery according to any one of (L.sup.31) to (L.sup.34), wherein
the carbon material has a roundness, as determined by flow-type
particle image analysis, of 0.88 or greater.
[0207] (L.sup.36) The carbon material for a non-aqueous secondary
battery according to any one of (L.sup.31) to (L.sup.35), wherein
the graphite particles are spheroidal graphite particles formed by
granulation of flake graphite, crystalline graphite, and vein
graphite.
[0208] (L.sup.37) The carbon material for a non-aqueous secondary
battery according to any one of (L.sup.31) to (L.sup.36), wherein
the granulation is carried out by applying at least one type of
mechanical energy selected from impact, compression, friction, and
shear force.
[0209] (L.sup.38) The carbon material for a non-aqueous secondary
battery according to any one of (L.sup.31) to (L.sup.37), wherein
the granulation is carried out by placing the graphite in an
apparatus comprising a rotatable member that rotates at a high
speed in a casing and having a rotor equipped with a plurality of
blades in the casing, and applying any one of impact, compression,
friction, and shear force to the graphite placed in the apparatus
by rotating the rotor at a high speed.
[0210] (L.sup.39) A non-aqueous secondary battery comprising: a
positive electrode and a negative electrode, each being capable of
occluding and releasing lithium ions; and an electrolyte, the
negative electrode comprising a current collector and a negative
electrode active material layer on the current collector, the
negative electrode active material layer comprising the carbon
material according to any one of (L.sup.31) to (L.sup.38).
Effects of the Invention
[0211] The carbon material of Invention A, when used as a negative
electrode active material for a non-aqueous secondary battery, can
provide a non-aqueous secondary battery having a high capacity and
good low-temperature output characteristics and cycle
characteristics.
[0212] The inventors believe that the above effect of the carbon
material according to Invention A is due to the following
reason.
[0213] Specifically, the intra-particle pores of the carbon
material formed to have a moderately fine intra-particle void
structure such that the cumulative pore volume at pore diameters in
a range of 0.01 .mu.m to 1 .mu.m is 0.08 mL/g or more, and the
ratio of the mode pore diameter (PD) in a pore diameter range of
0.01 .mu.m to 1 .mu.m in a pore distribution determined by mercury
intrusion to the volume-based average particle diameter (d50)
(PD/d50 (%)) is 1.8 or less allow an electrolyte solution to be
smoothly and efficiently distributed into the particles. This
enables effective and efficient use of Li-ion insertion extraction
sites in the particles as well as on the periphery of the particles
during charging and discharging, thus providing a high capacity and
good low-temperature output characteristics.
[0214] The production method of Invention B, that is, the method
for producing a carbon material for a non-aqueous secondary
battery, comprising the step of granulating a raw carbon material,
can produce carbon materials for non-aqueous secondary batteries
having various types of particle structures and stably produce
spheroidized graphite particles that can be processed in bulk, have
a moderately increased particle diameter (particle size), a high
degree of spheroidization, good filling properties, and low
anisotropy, and generate little amount of fine powder.
[0215] The inventors believe that the above effect is produced due
to the following reason.
[0216] As a result of the addition of a granulating agent, the
liquid adheres between particles to form liquid bridges (a
phenomenon where bridges are built between the particles by the
liquid). An attractive force caused by the capillary negative
pressure in the liquid bridges and the surface tension of the
liquid acts as a liquid cross-linking adhesive force between the
particles to increase the liquid cross-linking adhesion between the
raw carbon materials, allowing the raw carbon materials to adhere
more firmly to each other. In addition, the granulating agent acts
as a lubricant to reduce the generation of fine powder from the raw
carbon materials. Furthermore, most of the fine powder generated
during the granulation step adhere to the raw carbon materials due
to the increased liquid cross-linking adhesive force, which leads
to reduced independent fine powder particles. These effects enable
the production of spheroidized graphite particles that include raw
carbon materials adhering more firmly to each other, have a
moderately increased particle diameter and a high degree of
spheroidization, and generate little amount of fine powder.
[0217] When the granulating agent contains an organic solvent, the
organic solvent has no flash point or a flash point of 5.degree. C.
or higher. This can avoid the risk of ignition of the granulating
agent induced by impact or heat during the granulation step, fire,
and explosion, and thus spheroidized graphite particles can be
produced stably and efficiently.
[0218] The carbon material produced by the method of the present
invention has a structure in which fine powder having a great
number of Li-ion insertion/extraction sites exists on and in the
particles. Furthermore, the structure formed by the granulation of
a plurality of raw carbon materials enables effective and efficient
use of the Li-ion insertion/extraction sites in the particles as
well as on the periphery of the particles. As a result, the use of
the carbon material obtained by the present invention in a
non-aqueous secondary battery provides excellent input-output
characteristics.
[0219] The carbon material for a non-aqueous secondary battery of
Invention C has so high particle strength as to generate little
amount of fine powder even upon physical impact and, when used as a
negative electrode active material, can provide a non-aqueous
secondary battery, particularly, a lithium secondary battery,
having a capacity as high as 355 mAh/g or more and excellent
input-output characteristics and excellent cycle
characteristics.
[0220] The reason why using the carbon material of Invention C as a
negative electrode active material can provide a non-aqueous
secondary battery, particularly, a lithium ion secondary battery,
having excellent input-output characteristics and excellent cycle
characteristics is probably as follows: When an electrode plate is
formed using a carbon material as a negative electrode active
material, step (A) of preparing a slurry by kneading the carbon
material with a binder and other materials and step (B) of
increasing the density by applying the slurry to a current
collector, drying the slurry, and further applying a pressure, for
example, with a roll press are typically employed. In step (A) of
preparing a slurry, it is necessary to sufficiently knead the
carbon material with a binder and other materials in order to bond
the binder to the particle surface of the carbon material. During
the kneading, the carbon material experiences a mechanical stress.
Also in step (B) of increasing the density, the carbon material
experiences a mechanical stress. These stresses can cause the
carbon material, for example, to fracture to generate fine powder.
Even if the fine powder is apparently in contact with parent
particles of the carbon material after the formation of an
electrode plate, when the electrode plate is used as a negative
electrode of a non-aqueous secondary battery, the fine powder
readily separates from the parent particles of the carbon material
during charging and discharging in initial conditioning. This leads
to (i) an increase in resistance between the particles due to a
conductive path break (reduction in electrical conductivity) or
(ii) an increase in resistance due to increased side reactions
(film formation) by an increased contact area with an electrolyte
solution, which presumably causes degradation of input-output
characteristics.
[0221] When a non-aqueous secondary battery is charged, ions such
as lithium ions are inserted into carbon material particles, a
negative electrode active material, to swell the particles, and
when the non-aqueous secondary battery is discharged, the ions are
extracted from the carbon material particles to shrink the carbon
material particles. Non-aqueous secondary batteries are
rechargeable batteries, and carbon material particles repeatedly
swell and shrink upon repeated charging and discharging. In this
swelling and shrinking of the carbon material particles, fine
powder is separated and isolated from parent particles of the
carbon material and stops contributing to charging and discharging,
which presumably causes a reduction in battery capacity. This
separated and isolated fine powder tends to increase as charging
and discharging is repeated, which presumably results in
degradation in cycle characteristics.
[0222] The carbon material for a non-aqueous secondary battery of
Invention C satisfies inequality (IC): Q.sub.5min (%)/D50
(.mu.m).ltoreq.3.5, where Q.sub.5min (%) is a frequency (%) of
particles with a diameter of 5 .mu.m or less measured using a
flow-type particle image analyzer after the carbon material has
been irradiated with ultrasonic waves of 28 kHz at a power of 60 W
for 5 minutes, and D50 (.mu.m) is a volume-based median diameter
determined by laser diffraction/scattering after the carbon
material has been irradiated with ultrasonic waves of 28 kHz at a
power of 60 W for 1 minute. This means that the carbon material has
a high particle strength and generates little amount of fine powder
when a mechanical stress, such as a physical impact, is applied.
That is to say, little amount of fine powder is generated in the
above step (A) of preparing a slurry and step (B) of increasing the
density. Thus, using the carbon material of the present invention
as a negative electrode active material provides a non-aqueous
secondary battery (particularly, a lithium ion secondary battery)
that experiences less reduction in electrical conductivity and less
increase in side reaction and has excellent input-output
characteristics. Furthermore, the carbon material of the present
invention, for its high particle strength, generates little amount
of separated and isolated fine powder upon repeated charging and
discharging and, in turn, is unlikely to experience a reduction in
electrical conductivity, thus providing a non-aqueous secondary
battery (lithium ion secondary battery) having excellent cycle
characteristics.
[0223] The carbon material of Invention D, when used as a negative
electrode active material for a non-aqueous secondary battery, can
provide a non-aqueous secondary battery having a high capacity and
good low-temperature output characteristics and cycle
characteristics.
[0224] The inventors believe that the above effect of the carbon
material according to Invention D is due to the following
reason.
[0225] Specifically, the carbon material according to Invention D,
as compared with traditional carbon materials containing
carbonaceous materials on particle surfaces, has a high tap density
despite its large specific surface area (SA) (m.sup.2/g), as
determined by BET method. Thus, the carbon material according to
Invention D allows Li-ion insertion/extraction sites to be used
over an extensive area and is excellent in filling properties of a
negative electrode, thus providing a carbon material for a battery
having good low-temperature output characteristics and a high
capacity.
[0226] The carbon material of Invention E, when used as a negative
electrode active material for a non-aqueous secondary battery, can
provide a non-aqueous secondary battery having a high capacity and
good low-temperature output characteristics and cycle
characteristics.
[0227] The inventors believe that the above effect of the carbon
material according to Invention E is due to the following
reason.
[0228] The carbon material according to Invention E, as compared
with traditional carbon materials containing carbonaceous materials
on particle surfaces, has a large specific surface area (SA), as
determined by BET method, and thus allows Li-ion
insertion/extraction sites to be used over an extensive area.
Despite the large specific surface area (SA), as determined by BET
method, the carbon material according to Invention E has a low true
density (i.e., contains a high proportion of low-crystallinity
carbonaceous material components), and thus provides good
insertion/extraction of Li ions. That is to say, a carbon material
for a non-aqueous secondary battery that combines an improvement in
input-output characteristics due to its specific surface area and
an improvement in input-output characteristics due to its
low-crystallinity carbonaceous material can be provided.
[0229] The composite carbon material of Invention F, when used as a
negative electrode active material for a non-aqueous secondary
battery, can provide a non-aqueous secondary battery having a high
capacity and good low-temperature output characteristics and cycle
characteristics.
[0230] The inventors believe that the above effect of the composite
carbon material according to Invention F is due to the following
reason.
[0231] Specifically, the average value of microscopic Raman R
values of 30 randomly selected composite carbon materials of 0.1 to
0.85 and the standard deviation (.sigma..sub.R) of 0.1 or less
means that the composite carbon material uniformly contains, on the
surface of the carbon material (A), a low-crystallinity
carbonaceous material into and from which Li ions are readily
inserted and extracted. This inhibits a concentrated excessive
current flow into a specific site on the carbon material (A) into
and from which Li ions are readily inserted and extracted and
enables uniform and smooth insertion/extraction of Li ions even at
low temperatures and during high-current charging and discharging,
thus providing a high capacity and excellent low-temperature output
characteristics and cycle characteristics.
[0232] The carbon material of Invention G, when used as a negative
electrode active material for a non-aqueous secondary battery, can
provide a non-aqueous secondary battery having a capacity as high
as 355 mAh/g or more and excellent low-temperature output
characteristics.
[0233] The inventors believe that the above effect of the carbon
material according to Invention G is due to the following
reason.
[0234] The investigation by the present inventors has shown that
the cumulative pore volume at pore diameters in a range of 2 to 4
nm larger than a specific value increases the number of lithium-ion
insertion/extraction sites on the carbon material, which promotes
the lithium insertion/extraction reaction on the carbon material
surface during charging and discharging to improve low-temperature
output characteristics. In addition, the tap density of 0.83
g/cm.sup.3 or more smoothens the movement of electrolyte solution
between particles to improve input-output characteristics.
[0235] The carbon material of Invention H, when used as a negative
electrode active material for a non-aqueous secondary battery, can
provide a non-aqueous secondary battery having a high capacity and
good low-temperature output characteristics and cycle
characteristics.
[0236] The inventors believe that the above effect of the carbon
material according to Invention H is due to the following
reason.
[0237] Specifically, having a Raman R value in the above range
means that the carbon material has a moderately disordered surface
crystal structure and a sufficient number of Li-ion
insertion/extraction sites. Having a thermal weight loss ratio per
unit area (.DELTA.TG/SA) in the above range means that the number
of labile carbons, which are carbons prone to thermal oxidation, is
moderately small. This enables Li ions to smoothly move without
being impeded during charging and discharging. Thus, despite the
moderately disordered surface crystal structure, the moderately
small number of labile carbons, which are carbons prone to thermal
oxidation, enables Li ions to smoothly move without being impeded
during charging and discharging despite the sufficient number of
Li-ion insertion/extraction sites, thus providing a high capacity
and good low-temperature output characteristics.
[0238] The carbon material of Invention I, when used as a negative
electrode active material for a non-aqueous secondary battery, can
provide a non-aqueous secondary battery having a high capacity and
good low-temperature output characteristics and cycle
characteristics.
[0239] The inventors believe that the above effect of the carbon
material according to Invention I is due to the following
reason.
[0240] Specifically, having Y.sub.i (oxygen functional group
dispersity given by the above equation (2I)) and X.sub.i
(volume-based average particle diameter (d50) (.mu.m)) in the above
ranges means that oxygen functional groups are not maldistributed
on the particle surface and dispersed also in the particles. The
presence of oxygen functional groups at graphite crystal edge
portions that functions as Li-ion insertion/extraction sites
suggests that the carbon material of Invention I has a moderate
number of Li-ion insertion/extraction sites not only on but also in
the particles. This enables efficient Li-ion insertion/extraction
also in the particles, thus providing a high capacity and good
low-temperature output characteristics.
[0241] The production method of Invention J can provide composite
particles for a non-aqueous secondary battery, comprising
spheroidally granulated graphite particles having a structure in
which fine powder having a great number of Li-ion
insertion/extraction sites exists on and in the particles, the
graphite particles being uniformly coated with a carbonaceous
material. The composite particles, when used as a negative
electrode active material for a non-aqueous secondary battery, can
provide a non-aqueous secondary battery having a high capacity and
excellent low-temperature output characteristics and
high-temperature storage characteristics.
[0242] The inventors believe that the above effect of the
production method according to Invention J is due to the following
reason.
[0243] As a result of the addition of a granulating agent, the
liquid adheres between particles to form liquid bridges (a
phenomenon where bridges are built between the particles by the
liquid). An attractive force caused by the capillary negative
pressure in the liquid bridges and the surface tension of the
liquid acts as a liquid cross-linking adhesive force between the
particles to increase the liquid cross-linking adhesion between the
raw carbon materials (hereinafter also referred to as raw
graphites), allowing the raw graphites to adhere more firmly to
each other. In addition, the granulating agent acts as a lubricant
to reduce the generation of fine powder from the raw graphites.
Furthermore, most of the fine powder generated during the
granulation step adhere to the raw graphites due to the increased
liquid cross-linking adhesive force, which leads to reduced
independent fine powder particles. These effects enable the
production of spheroidized graphite particles that include raw
graphite adhering more firmly to each other, have a moderately
increased particle diameter and a high degree of spheroidization,
and generate little amount of fine powder.
[0244] The composite particles produced by the method of invention
J has a structure in which fine powder having a great number of
Li-ion insertion/extraction sites exists on and in the particles.
Furthermore, the structure formed by the granulation of a plurality
of raw graphites enables effective and efficient use of the Li-ion
insertion/extraction sites in the particles as well as on the
periphery of the particles.
[0245] Furthermore, in mixing the resulting granulated graphite
particles with an organic compound, serving as a carbonaceous
material precursor, and heat-treating the resulting mixture to
obtain composite particles containing graphite particles and a
carbonaceous material, selecting an organic compound, serving as a
carbonaceous material precursor, and a granulating agent having a
good affinity with each other allows the organic compound, serving
as a carbonaceous material precursor, to be uniformly deposited on
the surface of the granulated graphite. This enables the
carbonaceous material suitable for Li-ion insertion/extraction to
uniformly cover the composite particle surface to prevent the
exposure of the granulated graphite surface.
[0246] As a result, the composite particles obtained by Invention
J, when used for a non-aqueous secondary battery, can provide a
high capacity and excellent input-output characteristics and
high-temperature storage characteristics.
[0247] The carbon material of invention K, when used as a negative
electrode active material for a non-aqueous secondary battery, can
provide a non-aqueous secondary battery having a high capacity and
good low-temperature output characteristics and cycle
characteristics.
[0248] The inventors believe that the above effect of the carbon
material according to Invention K is presumably due to the
following reason.
[0249] True density is an indicator of crystallinity of carbon
materials. As the true density of a carbon material decreases and
gets away from its theoretical value, the crystallinity lowers, and
thus the particles of the carbon material will probably get harder,
resulting in low filling properties under a specific load.
[0250] The density under a specific load minus a tap density will
probably be an indicator that reflects the surface slidability and
the particle strength of a carbon material under a specific
load.
[0251] Specifically, having a true density and a density under a
specific load minus a tap density in a specific relationship means
that the carbon material of Invention K, as compared with
traditional carbon materials having comparable crystallinities,
undergoes less particle fracture and is easier to fill, leading to
reduced particle fracture in pressing an electrode. This reduces
the separation of amorphous carbon covering at least part of the
carbon material during the pressing and enables filling to a
predetermined density while maintaining lithium
insertion/extraction sites derived from amorphous carbon and the
particle shape, thus providing a high capacity and good
low-temperature output characteristics.
[0252] The carbon material of inventions L, when used as a negative
electrode active material for a non-aqueous secondary battery, can
provide a non-aqueous secondary battery having a high capacity and
good low-temperature output characteristics and cycle
characteristics.
[0253] The inventors believe that the above effects of the carbon
materials according to Inventions L (L.sup.1 to L.sup.3) are
presumably due to the following reason.
[0254] Specifically, fining intra-particle pores (L.sup.1),
uniformly dispersing intra-particle pores (L.sup.2), or controlling
the orientation of and the interval between intra-particle voids
(L.sup.3) allows an electrolyte solution to be smoothly and
efficiently distributed into the particles. This enables effective
and efficient use of Li-ion insertion/extraction sites in the
particles as well as on the periphery of the particles during
charging and discharging, thus providing a high capacity and good
low-temperature output characteristics.
BRIEF DESCRIPTION OF THE DRAWINGS
[0255] FIG. 1 is a graph showing the relationship between X.sub.d
and 10Y.sub.d of fourth Examples and Comparative Examples. Points
of (X.sub.d, 10Y.sub.d): Example D1, (7.38, 1.16); Example D2,
(5.79, 1.19); Example D3, (5.15, 1.18); Example D4, (4.30, 1.20);
Example D5, (2.88, 1.19); Comparative Example D1, (3.92, 1.08);
Comparative Example D2, (2.97, 1.11); Comparative Example D3,
(3.53, 1.11); Comparative Example D4, (2.51, 1.15); Comparative
Example D5, (4.48, 1.07); Comparative Example D6, (1.82, 1.21);
[0256] FIG. 2 is a graph showing the relationship between X.sub.e
and Y.sub.e of fifth Examples and Comparative Examples. Points of
(X.sub.e, Y.sub.e): Example E1, (7.38, 2.25); Example E2, (5.79,
2.24); Example E3, (5.15, 2.24); Example E4, (4.30, 2.23); Example
E5, (2.88, 2.22); Example E6, (8.69, 2.23); Example E7, (6.21,
2.22); Comparative Example E1, (3.92, 2.25); Comparative Example
E2, (2.97, 2.24); Comparative Example E3, (3.53, 2.25); Comparative
Example E4, (2.51, 2.24); Comparative Example E5, (4.48, 2.25);
Comparative Example E6, (1.82, 2.23);
[0257] FIG. 3 is a graph showing the relationship between X.sub.i
and Y.sub.i of ninth Examples and Comparative Examples. Points of
(X.sub.i, Y.sub.i): Example I1, (12.7, 0.108); Example I2, (12.9,
0.071); Example 13, (16.3, 0.063); Example 14, (19.4, 0.047);
Comparative Example I1 (10.9, 0.066); Comparative Example I2,
(11.3, 0.060), Comparative Example 13, (15.4, 0.053); Comparative
Example 14, (18.2, 0.047);
[0258] FIG. 4 is a graph showing the relationship between
high-temperature storage characteristics and lain-temperature
output characteristics of tenth Examples and Comparative Examples.
Points of (high-temperature storage characteristics,
low-temperature output characteristics): Example J1 (98.9, 109.9);
Example J2, (100.4, 104.8); Example J3, (101.1, 103.1); Reference
Example J1, (98.6, 94.4); Reference Example J2, (100.0, 100.0);
Reference Example J3, (100.4, 91.2); Comparative Example J1,
(104.4, 68.1);
[0259] FIG. 5 is a graph showing the relationship between
inequality (1K) and true density of eleventh Examples and
Comparative Examples. The results of Example K1 to 6 and
Comparative Example K1 to K8 are shown with the right side of
inequality (1K) plotted on the vertical axis and the true density
of a carbon material on the horizontal axis;
[0260] FIG. 6 is a graph showing the relationship between
inequality (3K) and true density of eleventh Examples and
Comparative Examples. The results of Example K1 to 6 and
Comparative Example K1 to K8 are shown with the right side of
inequality (3K) plotted on the vertical axis and the true density
of a carbon material on the horizontal axis;
[0261] FIG. 7 shows binarized images (photographs substituted for
drawings) of one granulated particle in the carbon material of
Example L1 and a logarithmic graph, as determined by the
box-counting method, with box size plotted on the horizontal axis
and the number of boxes counted on the vertical axis:
[0262] FIG. 8 shows binarized images (photographs substituted for
drawings) of one granulated particle in the carbon material of
Comparative Example L1 and a logarithmic graph, as determined by
the box-counting method, with box size plotted on the horizontal
axis and the number of boxes counted on the vertical axis;
[0263] FIG. 9 shows a cross-sectional SEM image (a photograph
substituted for a drawing) and a binarized image of one granulated
particle in the carbon material of Example L1;
[0264] FIG. 10 shows exemplary images (photographs substituted for
drawings) unsuitable for analysis in SEM image binarization;
[0265] FIG. 11 shows a method of binarization, drawing of grid
lines, and compartmentalization of one granulated particle in the
carbon material of Example L1 (photographs substituted for
drawings);
[0266] FIG. 12 shows a compartment and a non-compartment in a cell
defined by grid lines (photographs substituted for drawings);
[0267] FIG. 13 shows a method for calculating the void distance and
the distance between voids of one granulated particle in the carbon
material of Example L1 (photographs substituted for drawings);
[0268] FIG. 14 is an SEM image of one granulated particle in the
carbon material of Example L1 (a photograph substituted for a
drawing); and
[0269] FIG. 15 is an SEM image of one granulated particle in the
carbon material of Comparative Example L1 (a photograph substituted
for a drawing).
MODE FOR CARRYING OUT THE INVENTION
[0270] The present invention will now be described in detail. It
should be appreciated that the following description of the
features of the invention is one aspect (a typical example) of the
present invention, and other variations may be applied without
departing from the spirit of the invention. One embodiment of the
carbon material for a non-aqueous secondary battery according to
the present invention is a carbon material for a non-aqueous
secondary battery, comprising a graphite capable of occluding and
releasing lithium ions, the carbon material having a cumulative
pore volume at pore diameters in a range of 0.01 .mu.m to 1 .mu.m
of 0.08 mL/g or more, a roundness, as determined by flow-type
particle image analysis, of 0.88 or greater, and a pore diameter to
particle diameter ratio (PD/d50 (N) of 1.8 or less, the ratio being
given by equation (1A):
PD .times. / .times. d .times. .times. 50 .times. .times. ( % ) =
mode .times. .times. pore .times. .times. diameter .times. .times.
( PD ) .times. .times. in .times. .times. a .times. .times. pore
.times. .times. diameter .times. .times. range .times. .times. of
.times. .times. 0.01 .times. .times. .mu.m .times. .times. to
.times. .times. 1 .times. .times. .mu.m .times. .times. in .times.
.times. a .times. .times. pore .times. .times. distribution .times.
.times. determined .times. .times. by .times. .times. mercury
.times. .times. intrusion .times. / .times. volume .times. -
.times. based .times. .times. average .times. .times. particle
.times. .times. diameter .times. .times. ( d .times. .times. 50 )
.times. 100. ( 1 .times. A ) ##EQU00021##
[0271] Another embodiment is a carbon material for a non-aqueous
secondary battery capable of occluding and releasing lithium ions,
the carbon material being formed from a plurality of graphite
particles without being pressed and having a pore diameter to
particle diameter ratio (PD/d50 (%)) of 1.8 or less, the ratio
being given by equation (1A):
[0272] PD/d50 (%)=mode pore diameter (PD) in a range of 0.01 .mu.m
to 1 .mu.m in a pore distribution determined by mercury
intrusion/volume-based average particle diameter
(d50).times.100(1A).
[0273] "Without being pressed" means not being pressed to the
extent that the density or the isotropy of the graphite particles
is increased. Specifically, for example, the pressure may be 50
kgf/cm.sup.2 or more, 100 kgf/cm.sup.2 or more, or 200 kgf/cm.sup.2
or more.
Types of Carbon Material for Non-Aqueous Secondary Battery
[0274] Examples of the carbon material for a non-aqueous secondary
battery capable of occluding and releasing lithium ions according
to the present invention include, but are not limited to,
graphites, amorphous carbons, and carbonaceous materials with low
degrees of graphitization. Of these, graphites are preferred
because it is commercially readily available, has, theoretically, a
charge-discharge capacity as high as 372 mAh/g, and, further, is
more effective in improving high-current-density charge-discharge
characteristics as compared with other negative electrode active
materials. Graphites having low impurity contents are preferred,
and, if necessary, various known purification treatments may be
carried out before use. Examples of graphites include natural
graphites and artificial graphites, and natural graphites, which
have high capacities and good high-current-density charge-discharge
characteristics, are more preferred.
[0275] These may be coated with a carbonaceous material, for
example, an amorphous carbon or a graphitized carbon. In the
present invention, these graphites may be used alone or in
combination.
[0276] Examples of amorphous carbons include particles obtained by
burning a bulk mesophase and particles obtained by infusibilizing
and burning a carbon precursor.
[0277] Examples of carbonaceous material particles with low degrees
of graphitization include those obtained by burning organic
substances typically at a temperature lower than 2,500.degree. C.
Examples of organic substances include coal-derived heavy oils,
such as coal-tar pitch and dry distillation/liquefaction oil;
straight-run heavy oils, such as atmospheric residues and vacuum
residues; petroleum-derived heavy oils such as heavy oils resulting
from cracking, such as ethylene tar produced as a by-product of
thermal cracking of crude oil, naphtha, or other oils; aromatic
hydrocarbons, such as acenaphthylene, decacyclene, and anthracene;
nitrogen-containing cyclic compounds, such as phenazine and
acridine; sulfur-containing cyclic compounds, such as thiophene;
aliphatic cyclic compounds, such as adamantane; and thermoplastic
polymers, including polyphenylenes, such as biphenyl and terphenyl,
polyvinyl esters, such as polyvinyl chloride, polyvinyl acetate,
and polyvinyl butyral, and polyvinyl alcohols.
[0278] Depending on the degree of graphitization of the
carbonaceous material particles, the burning temperature may be
600.degree. C. or higher, preferably 900.degree. C. or higher, more
preferably 950.degree. C. or higher, and may be typically in the
range of lower than 2,500.degree. C., preferably 2,000.degree. C.
or lower, more preferably 1,400.degree. C. or lower.
[0279] In burning, the organic substance may be mixed with acids,
such as phosphoric acid, boric acid, and hydrochloric acid, and
alkalis, such as sodium hydroxide.
[0280] Examples of artificial graphites include those obtained by
burning and graphitizing organic substances such as coal-tar pitch,
coal-derived heavy oils, atmospheric residues, petroleum-derived
heavy oils, aromatic hydrocarbons, nitrogen-containing cyclic
compounds, sulfur-containing cyclic compounds, polyphenylenes,
polyvinyl chlorides, polyvinyl alcohols, polyacrylonitriles,
polyvinyl butyrals, natural polymers, polyphenylene sulfides,
polyphenylene oxides, furfuryl alcohol resins, phenol-formaldehyde
resins, and imide resins.
[0281] The burning temperature may be in the range of 2,500.degree.
C. to 3,200.degree. C., and in burning, a silicon-containing
compound, a boron-containing compound, or other compounds may be
used as a graphitizing catalyst.
[0282] Natural graphites are classified into flake graphite,
crystalline graphite, vein graphite, and amorphous graphite
depending on their properties (see "Encyclopedia of powder process
industry and technology" (Industrial Technology Center, 1974),
Section "Graphite", and "HANDBOOK OF CARBON, GRAPHITE, DIAMOND AND
FULLERENES" (published by NoyesPubLications)). Crystalline graphite
and vein graphite have highest degrees of graphitization of 100%,
and flake graphite has a next highest degree of graphitization of
99.9%. Graphites having higher degrees of graphitization are more
suitable for the present invention. In particular, those having low
impurity contents are preferred, and, if necessary, various known
purification treatments may be carried out before use.
[0283] Natural graphites are produced in Madagascar, China, Brazil,
Ukraine, Canada, and other districts. Among natural graphites,
crystalline graphite is mainly produced in Sri Lanka, and amorphous
graphite is mainly produced in the Korean Peninsula, China, Mexico,
and other districts.
[0284] Among natural graphites, for example, crystalline, flake,
and vein natural graphites, highly purified flake graphite, and
natural graphite subjected to spheroidization described below
(hereinafter referred to as spheroidized natural graphite) are
preferred. Of these, in an embodiment of the present invention,
spheroidized natural graphite is most preferred because it can form
favorable fine pores in a carbon material to provide excellent
particle-filling properties and charge-discharge load
characteristics.
[0285] For carbon materials for non-aqueous secondary batteries,
use may also be made of natural graphite or artificial graphite
particles coated with an amorphous carbon and/or a graphite
material having a low degree of graphitization. In addition, oxides
and other metals may be contained. Examples of other metals include
metals capable of forming alloys with Li, such as Sn, Si, Al, and
Bi.
Method for Producing Carbon Material for Non-Aqueous Secondary
Battery
[0286] In one embodiment, the carbon material of the present
invention can be produced, for example, by spheroidizing a flake
natural graphite whose particle size has been adjusted to a d50 of
80 .mu.m or less while depositing and/or incorporating fine powder
generated during the spheroidization (granulation) on and/or into a
base material, the graphite that has been subjected to
spheroidization (hereinafter also referred to as spheroidized
graphite). Specifically, the carbon material is preferably produced
by a method for producing a carbon material for a non-aqueous
secondary battery, comprising a granulation step of granulating a
raw carbon material by applying at least one type of mechanical
energy selected from impact, compression, friction, and shear
force, the granulation step being carried out in the presence of a
granulating agent that satisfies conditions 1) and 2): 1) being
liquid during the step of granulating the raw carbon material; and
2) in the granulating agent, no organic solvent is contained, or if
contained, at least one of the organic solvents has no flash point
or a flash point of 5.degree. C. or higher.
[0287] In another embodiment, the carbon material of the present
invention can be produced by a method for producing composite
particles for a non-aqueous secondary battery comprising a
granulated carbon material and a carbonaceous material having lower
crystallinity than the granulated carbon material, the method
comprising the steps of 1) and 2): 1) applying at least one type of
mechanical energy selected from impact, compression, friction, and
shear force in the presence of a granulating agent having an
aniline point of 80.degree. C. or lower or no aniline point to
granulate a raw carbon material; and 2) mixing the granulated
carbon material obtained in 1) with an organic compound, serving as
a carbonaceous material precursor, and heat-treating the
mixture.
[0288] As long as the granulation step is included, the method may
optionally include other steps. The other steps may be carried out
individually or simultaneously. One embodiment includes the
following 1st step to 6th step.
[0289] 1st step: adjusting the particle size of a raw carbon
material
[0290] 2nd step: mixing the raw carbon material with a granulating
agent
[0291] 3rd step: granulating the raw carbon material
[0292] 4th step: removing the granulating agent
[0293] 5th step: increasing the purity of the granulated carbon
material
[0294] 5'th step: increasing the crystallinity of the granulated
carbon material
[0295] 6th step: depositing a carbonaceous material having lower
crystallinity than the raw carbon material on the granulated carbon
material
[0296] These steps will be described below.
1st Step: Adjusting Particle Size of Raw Carbon Material
[0297] In the present invention, any raw carbon material may be
used, and artificial graphites and natural graphites described
above can be used. In particular, natural graphites, which have
high crystallinity and high capacities, are suitable for use.
[0298] Examples of natural graphites include crystalline, flake,
vein, and plate-like natural graphites, among which flake graphite
is preferred.
[0299] The raw carbon material such as a flake graphite obtained
through the 1st step, which is used as a raw material of a
spheroidized graphite, has an average particle diameter
(volume-based median diameter: d50) of preferably 1 .mu.m or more,
more preferably 2 .mu.m or more, still more preferably 3 .mu.m or
more, preferably 80 .mu.m or less, more preferably 50 .mu.m or
less, still more preferably 35 .mu.m or less, very preferably 20
.mu.m or less, particularly preferably 10 .mu.m or less, most
preferably 8 .mu.m or less. The average particle diameter can be
determined by the method described below.
[0300] An average particle diameter in this range can prevent the
increase in irreversible capacity and the degradation of cycle
characteristics and strictly control the intra-particle void
structure of the spheroidized graphite. This allows an electrolyte
solution to be efficiently distributed into intra-particle voids
and enables the efficient use of Li-ion insertion/extraction sites
in the particles, as a result of which low-temperature output
characteristics and cycle characteristics tend to improve.
Furthermore, such an average particle diameter can adjust the
roundness of the spheroidized graphite to be high and thus allows
an electrolyte solution to smoothly move in intra-particle voids
with no increase in flection of Li-ion diffusivity, leading to
improved fast charge-discharge characteristics.
[0301] Furthermore, an average particle diameter in the above range
enables performing granulation while depositing or incorporating
the fine powder generated during the granulation step on or into a
base material, the granulated graphite (hereinafter referred to as
granulated carbon material), thus providing a granulated carbon
material that has a high degree of spheroidization and generates
little amount of fine powder.
[0302] The average particle diameter (d50) of the raw carbon
material can be adjusted to be in the above range, for example, by
crushing and/or classifying (natural) graphite particles.
[0303] Examples of apparatuses for use in crushing include, but are
not limited to, coarse crushers, such as shear mills, jaw crushers,
impact crushers, and cone crushers; intermediate crushers, such as
roll crushers and hammer mills; and fine crushers, such as
mechanical crushers, air-flow crushers, and swirl-flow crushers.
Specific examples include ball mills, vibration mills, pin mills,
agitation mills, jet mills, cyclone mills, and turbo mills. In
particular, when graphite particles of 10 .mu.m or less are
produced, air-flow crushers and swirl-flow crushers are suitable
for use.
[0304] In classification, any apparatuses can be used. In the case
of dry sieving, a rotary sieve, a shaking sieve, a gyratory sieve,
a vibratory sieve, or other sieves can be used. In the case of dry
air-flow classification, a gravity classifier, an inertia
classifier, or a centrifugal classifier (e.g., a classifier or a
cyclone) can be used. In the case of wet sieving, a mechanical wet
classifier, a hydraulic classifier, a sedimentation classifier, a
centrifugal wet classifier, or other classifiers can be used.
[0305] The raw carbon material obtained through the 1st step
preferably has physical properties as described below.
[0306] The ash content of the raw carbon material is preferably 1%
by mass or less, more preferably 0.5% by mass or less, still more
preferably 0.1% by mass or less, based on the total mass of the raw
carbon material. The ash content is preferably at least 1 ppm.
[0307] An ash content in this range can provide a non-aqueous
secondary battery that undergoes only negligible degradation of
battery performance due to the reaction between carbon material and
electrolyte solution during charging and discharging. In addition,
such an ash content does not require much time or energy to produce
a carbon material and eliminates the need for equipment for
preventing contamination, thus reducing the increase in cost.
[0308] The raw carbon material has an aspect ratio of preferably 3
or greater, more preferably 5 or greater, still more preferably 10
or greater, particularly preferably 15 or greater, and preferably
1,000 or less, more preferably 500 or less, still more preferably
100 or less, particularly preferably 50 or less. The aspect ratio
is determined by the method described below. An aspect ratio in
this range is less likely to yield large particles having a
particle diameter of approximately 100 .mu.m and, on the other
hand, more likely to yield a robust granulated carbon material
because a moderate contact area is provided when pressure is
applied from one direction. An excessively high aspect ratio tends
to yield large particles having a particle diameter of
approximately 100 .mu.m. Excessively small particles tend to fail
to form robust granulated particles because a small contact area is
provided when pressure is applied from one direction, and if the
particles are granulated, the granulated particles tend to have a
specific surface area of more than 30 m.sup.2/g reflecting the
small specific surface area of flake graphite.
[0309] For an interplanar spacing of the (002) plane (d.sub.002)
and a crystallite size (Lc), as determined by wide-angle X-ray
diffractometry, of the raw carbon material, typically, (d.sub.002)
is 3.37 angstroms or less, and (Lc) is 900 angstroms or more;
preferably, (d.sub.002) is 3.36 angstroms or less, and (Lc) is 950
angstroms or more. The interplanar spacing (d.sub.002) and the
crystallite size (Lc) are indicators of the crystallinity of a
carbon material bulk. As the interplanar spacing of the (002) plane
(d.sub.002) decreases and the crystallite size (Lc) increases, the
crystallinity of the carbon material increases, and the amount of
lithium that enters between graphite layers comes closer to the
theoretical value to increase the capacity. When the crystallinity
is low, excellent battery characteristics (a high capacity and a
low irreversible capacity) that are exhibited when a
high-crystallinity graphite is used as an electrode are not
exhibited. Particularly preferably, the interplanar spacing
(d.sub.002) and the crystallite size (Lc) are both in the above
ranges.
[0310] The X-ray diffraction is carried out as follows: using a
mixture of carbon powder and X-ray standard high-purity silicon
powder in an amount of about 15% by mass based on the total mass as
a sample and a CuK.alpha. radiation monochromatized with a graphite
monochromator as a radiation source, a wide-angle X-ray
diffractometry curve is obtained by reflection diffractometry.
After that, the method of the Japan Society for Promotion of
Scientific Research is used to determine an interplanar spacing
(d.sub.002) and a crystallite size (Lc).
[0311] The packed structure of the raw carbon material varies
depending on the size and shape of particles, the degree of
interactivity between particles, and other factors, and in this
specification, tap density can be used as an indicator for
quantitatively discussing the packed structure. The investigation
by the present inventors has revealed that in the case of lead
particles having substantially the same true density and average
particle diameter, the tap density increases as the shape comes
closer to spheroidal and the particle surface becomes flat. In
other words, to increase the tap density, it is important that the
particle shape be rounded and closer to spheroidal, and the
particle surface be made free from frays and chips and kept flat. A
particle shape closer to spheroidal and a flat particle surface
significantly improves powder filling properties. The tap density
of the raw carbon material is preferably 0.1 g/cm.sup.2 or more,
more preferably 0.15 g/cm.sup.3 or more, still more preferably 0.2
g/cm.sup.3 or more, particularly preferably 0.3 g/cm.sup.3 or more.
The tap density is determined by the method described below in
Examples.
[0312] The argon-ion laser Raman spectrum of the raw carbon
material is used as an indicator of conditions of a particle
surface. The Raman R value, a ratio of peak intensity near 1,360
cm.sup.-1 to peak intensity near 1,580 cm.sup.-1 in the argon-ion
laser Raman spectrum of the raw carbon material, is preferably 0.05
to 0.9, more preferably 0.05 to 0.7, still more preferably 0.05 to
0.5. The Raman R value is an indicator of the crystallinity near
the surface (from the particle surface to a depth of about 100
angstroms) of a carbon particle, and smaller Raman R values
indicate higher crystallinities or less disordered crystalline
states. The Raman spectrum is measured by the method described
below. Specifically, a sample is loaded by gravity-dropping target
particles into a measuring cell of a Raman spectroscope, and the
measuring cell is irradiated with an argon-ion laser beam while
being rotated in a plane perpendicular to the laser beam. The
wavelength of the argon-ion laser beam is 514.5 nm.
[0313] The wide-angle X-ray diffractometry of the raw carbon
material is used as an indicator of the crystallinity of the whole
particle. The 3R/2H ratio of intensity 3R (101) of the (101) plane
based on a rhombohedral crystal structure to intensity 2H (101) of
the (101) plane based on a hexagonal crystal structure, as
determined by wide-angle X-ray diffractometry, of the flake
graphite is preferably 0.1 or greater, more preferably 0.15 or
greater, still more preferably 0.2 or greater. The rhombohedral
crystal structure is a crystal form in which network structures of
a graphite are stacked on top of each other at every three layers.
The hexagonal crystal structure is a crystal form in which network
structures of a graphite are stacked on top of each other at every
two layers. A flake graphite having a crystal form containing a
high proportion of rhombohedral crystal structures 3R has high
Li-ion receiving properties as compared with a graphite containing
a low proportion of rhombohedral crystal structures 3R.
[0314] The raw carbon material has a specific surface area as
measured by BET method of preferably 0.3 m.sup.2/g or more, more
preferably 0.5 m.sup.2/g or more, still more preferably 1 m.sup.2/g
or more, particularly preferably 2 m.sup.2/g or more, most
preferably 5 m.sup.2/g or more, and preferably 30 m.sup.2/g or
less, more preferably 20 m.sup.2/g or less, still more preferably
15 m.sup.2/g or less. The specific surface area as measured by BET
method is determined by the method in Examples below. A specific
surface area of the raw carbon material in this range improves the
Li-ion receiving properties, which can prevent the decrease in
battery capacity due to the increase in irreversible capacity. An
excessively small specific surface area of the flake graphite
reduces the Li-ion receiving properties, and an excessively large
specific surface area tends to fail to prevent the decrease in
battery capacity due to the increase in irreversible capacity.
[0315] The water content of the raw carbon material (raw graphite)
of a granulated carbon material is preferably 1% by mass or less,
more preferably 0.5% by mass or less, still more preferably 0.1% by
mass or less, particularly preferably 0.05% by mass or less, most
preferably 0.01% by mass or less, based on the total mass of the
raw graphite. The water content, is preferably at least 1 ppm. The
water content can be determined, for example, by a method in
accordance with JIS M8811. A water content in this range
advantageously increases the interparticle electrostatic attraction
during spheroidization, leading to increased interparticle
adhesion, which facilitates the deposition of fine powder on a base
material and the incorporation of fine powder into spheroidized
particles. In addition, such a water content can prevent the
decrease in wettability when a hydrophobic granulating agent is
used.
[0316] To adjust the water content of the raw carbon material (raw
graphite) of a granulated carbon material to be in the above range,
a drying treatment may optionally be performed. The drying
treatment is carried out typically at 60.degree. C. or higher,
preferably 100.degree. C. or higher, more preferably 200.degree. C.
or higher, still more preferably 250.degree. C. or higher,
particularly preferably 300.degree. C. or higher, most preferably
350.degree. C. or higher, and typically 1,500.degree. C. or lower,
preferably 1,000.degree. C. or lower, more preferably 800.degree.
C. or lower, still more preferably 600.degree. C. or lower. An
excessively low temperature tends to fail to sufficiently reduce
the water content, and an excessively high temperature tends to
lead to reduced productivity and increased cost.
[0317] The drying treatment is carried out typically for 0.5 to 48
hours, preferably 1 to 40 hours, more preferably 2 to 30 hours,
still more preferably 3 to 24 hours. An excessively long time tends
to lead to reduced productivity, and an excessively short time
tends to fail to fully exert a heat treatment effect.
[0318] The atmosphere in the heat treatment may be an active
atmosphere, such as an air atmosphere, or an inert atmosphere, such
as a nitrogen atmosphere or an argon atmosphere. When the heat
treatment is carried out at 200.degree. C. to 300.degree. C., there
is no particular restriction, but when the heat treatment is
carried out at 300.degree. C. or higher, it is preferable to use an
inert atmosphere, such as a nitrogen atmosphere or an argon
atmosphere, to prevent the oxidation of the graphite surface.
[0319] The surface functional group amount O/C value (%), as
determined by XPS, of the flake graphite, a raw carbon material
which is used as a raw material of a spheroidized graphite, is
preferably 0.01 or greater, more preferably 0.1 or greater, still
more preferably 0.3 or greater, particularly preferably 0.5 or
greater, preferably 5 or less, more preferably 3 or less, still
more preferably 2.5 or less, particularly preferably 2 or less,
most preferably 1.5 or less. An O/C value in this range
advantageously reduces hygroscopicity, making it easy to keep the
particles dry, and increases the interparticle electrostatic
attraction during spheroidization, leading to increased
interparticle adhesion, which facilitates the deposition of fine
powder on a base material and the incorporation of fine powder into
spheroidized particles.
2nd Step: Mixing Raw Carbon Material with Granulating Agent
[0320] The granulating agent for use in one embodiment of the
present invention satisfies conditions 1) being liquid during the
step of granulating the raw carbon material, and 2) in the
granulating agent, no organic solvent is contained, or if
contained, at least one of the organic solvents has no flash point
or a flash point of 5.degree. C. or higher.
[0321] In the subsequent 3rd step of granulating the raw carbon
material, the granulating agent satisfying these conditions forms
liquid bridges between the raw carbon materials, whereby an
attractive force caused by the capillary negative pressure in the
liquid bridges and the surface tension of the liquid acts as a
liquid cross-linking adhesive force between the particles to
increase the liquid cross-linking adhesion between the raw carbon
materials, allowing the raw carbon materials to adhere more firmly
to each other.
[0322] In one embodiment of the present invention, the strength of
the liquid cross-linking adhesive force between the raw carbon
materials produced by the liquid bridges of the granulating agent
between the raw carbon materials is proportional to .gamma. cos
.theta. value (where .gamma. is a surface tension of a liquid, and
.theta. is a contact angle between the liquid and a particle). That
is to say, in granulating the raw carbon material, the granulating
agent preferably has higher wettability to the raw carbon material.
Specifically, it is preferable to select a granulating agent that
satisfies cos .theta.>0 so that .gamma. cos .theta.>0 is
satisfied, and the granulating agent preferably has a contact angle
.theta. with a graphite, as measured by the following method, of
less than 90.degree..
Method for Measuring Contact Angle .theta. with Graphite
[0323] Onto a surface of HOPG, 1.2 .mu.L of a granulating agent is
added dropwise, and when wetting and spreading has settled down and
a rate of change in contact angle .theta. in one second has reached
3% or lower (also referred to as a steady state), the contact angle
is measured using a contact angle meter (e.g., DM-501 automatic
contact angle meter available from Kyowa Interface Science Co.,
Ltd). When a granulating agent having a viscosity at 25.degree. C.
of 500 cP or lower is used, a value at 25.degree. C. is employed as
a measurement of the contact angle .theta., and when a granulating
agent having a viscosity at 25.degree. C. of higher than 500 cP is
used, a value at an increased temperature where the viscosity is
not higher than 500 cP is employed.
[0324] Furthermore, as the contact angle .theta. between the raw
carbon material and the granulating agent comes closer to
0.degree., the .gamma. cos .theta. value increases to increase the
liquid cross-linking adhesion between the graphite particles,
allowing the graphite particles to adhere more firmly to each
other. Thus, the contact angle .theta. between the granulating
agent and the graphite is more preferably 85.degree. or less, still
more preferably 80.degree. or less, even more preferably 50.degree.
or less, particularly preferably 30.degree. or less, most
preferably 20.degree. or less.
[0325] Also by using a granulating agent having a high surface
tension .gamma., the .gamma. cos .theta. value is increased to
improve the adhesion between the graphite particles, and thus
.gamma. is preferably 0 or greater, more preferably 15 or greater,
still more preferably 30 or greater.
[0326] The surface tension .gamma. of the granulating agent for use
in the present invention is measured by the Wilhelmy method using a
surface tensiometer (e.g., DCA-700 available from Kyowa Interface
Science Co., Ltd).
[0327] A viscous force acts as a resistant to the extension of
liquid bridges associated with the movement of particles, and the
strength of the viscous force is proportional to viscosity. Thus,
the viscosity of the granulating agent, although not limited to any
particular value as long as the granulating agent is liquid during
the granulation step of granulating the raw carbon material, is
preferably 1 cP or more during the granulation step.
[0328] In addition, the granulating agent has a viscosity at
2.5.degree. C. of preferably 1 cP to 100,000 cP, more preferably 5
cP to 10,000 cP, still more preferably 10 cP to 8,000 cP,
particularly preferably 50 cP to 6,000 cP. A viscosity in this
range can prevent deposited particles from being detached by impact
force, such as a collision with a rotor or a casing, in granulating
the raw carbon material.
[0329] The viscosity of the granulating agent for use in the
present invention is measured using a rheometer (e.g., ARES
available from Rheometric Scientific) by placing an appropriate
amount of a target (in this case, the granulating agent) into a cup
and adjusting the temperature to a predetermined temperature. In
this specification, the viscosity is defined as a measurement at a
shear rate 100 s.sup.-1, in the case where the shear stress at a
shear rate 100 s.sup.-1 is not less than 0.1 Pa; a measurement at
1,000 s.sup.-1, in the case where the shear stress at a shear rate
100 s.sup.-1 is less than 0.1 Pa; and a measurement at a shear rate
at which the shear stress is not less than 0.1 Pa, in the case
where the shear stress at a shear rate 1,000 s.sup.-1 is less than
0.1 Pa. The shear stress can be not less than 0.1 Pa also by using
a spindle having a shape suitable for low-viscosity fluids.
[0330] Furthermore, in the granulating agent for use in one
embodiment of the present invention, no organic solvent is
contained, or if contained, at least one of the organic solvents
has no flash point or a flash point of 5.degree. C. or higher. This
can avoid the risk of ignition of the organic compound induced by
impact or heat, fire, and explosion in the subsequent 3rd step of
granulating the raw carbon material, thus achieving stable and
efficient production.
[0331] In one aspect of another embodiment of the present invention
(e.g., but not limited to, Invention J), the granulating agent for
use in this step is preferably a granulating agent having an
aniline point of 80.degree. C. or lower or no aniline point.
Granulating Agent Having Aniline Point of 80.degree. C. or Lower or
No Aniline Point
[0332] Since the solvency for organic compounds increases with
decreasing aniline point, the use of a granulating agent satisfying
the above requirement improves the affinity for an organic
compound, serving as a carbonaceous material precursor, and allows
the organic compound, serving as a carbonaceous material precursor,
when mixed with granulated graphite particles obtained through this
step, to be uniformly deposited on the surface and in the internal
voids of the granulated graphite. In particular, the granulating
agent for use in the present invention, having an aniline point of
80.degree. C. or lower or no aniline point, has high affinity and
compatibility also with an organic compound containing an aromatic
compound, for which a granulating agent having a high aniline point
has low affinity and poor solvency. Thus, even when such an organic
compound containing an aromatic compound is used as a carbonaceous
material precursor, the organic compound, serving as a carbonaceous
material precursor, when mixed with granulated graphite particles
obtained through this step, can be uniformly deposited on the
surface and in the internal voids of the granulated graphite.
[0333] For example, the aniline point and the mixed aniline point
of hydrocarbon compounds tend to decrease in order of paraffinic
hydrocarbons, naphthenic hydrocarbons, and aromatic hydrocarbons,
and the aniline point and the mixed aniline point tend to decrease
with decreasing molecular weight.
[0334] The aniline point of the granulating agent is typically
80.degree. C. or lower, preferably 50.degree. C. or lower, more
preferably 30.degree. C. or lower, still more preferably 10.degree.
C. or lower, particularly preferably 0.degree. C. or lower. For the
lower limit, some granulating agents have aniline points lower than
their freezing points, that is, have no aniline point. The
properties of such granulating agents having no aniline point can
be evaluated by their mixed aniline points, and the mixed aniline
point is preferably 50.degree. C. or lower, more preferably
30.degree. C. or lower, still more preferably 20.degree. C. or
lower, particularly preferably 0.degree. C. or lower.
[0335] The aniline point and the mixed aniline point are determined
in accordance with JIS K2256. The aniline point is defined as a
minimum temperature at which a mixed solution of aniline and a
measurement sample (granulating agent) (volume ratio, 1:1) can be
in the form of a homogeneous solution (a temperature at which
aniline and the measurement sample (granulating agent) completely
mixed with each other begin to separate and cause turbidity with
decreasing temperature). The mixed aniline point is defined as a
minimum temperature at which a mixed solution of aniline, a
measurement sample (granulating agent), and heptane (volume ratio,
2:1:1) can be in the form of a homogeneous solution (a temperature
at which aniline, the measurement sample (granulating agent), and
heptane completely mixed with each other begin to separate and
cause turbidity with decreasing temperature).
[0336] Examples of granulating agents include coal tar;
petroleum-derived heavy oils; synthetic oils, such as paraffinic
oils, including liquid paraffin, olefinic oils, naphthenic oils,
and aromatic oils; natural oils, such as vegetable oils and fats,
animal fats, esters, and higher alcohols; organic compounds such as
solutions of resin binders in organic solvents having flash points
of 5.degree. C. or higher, preferably 21.degree. C. or higher;
aqueous solvents, such as water; and mixtures thereof. Examples of
organic solvents having flash points of 5.degree. C. or higher
include aromatic hydrocarbons, such as alkylbenzenes, including
xylene, isopropylbenzene, ethylbenzene, and propylbenzene,
alkylnaphthalenes, including methylnaphthalene, ethylnaphthalene,
and propylnaphthalene, alkylbenzenes, including styrene, and
alkylnaphthalenes; aliphatic hydrocarbons, such as octane, nonane,
and decane; ketones, such as methyl isobutyl ketone, diisobutyl
ketone, and cyclohexanone; esters, such as propyl acetate, butyl
acetate, isobutyl acetate, and amyl acetate; alcohols, such as
methanol, ethanol, propanol, butanol, isopropyl alcohol, isobutyl
alcohol, ethylene glycol, propylene glycol diethylene glycol,
triethylene glycol, tetraethylene glycol, and glycerol; glycol
derivatives, such as ethylene glycol monomethyl ether, ethylene
glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene
glycol monobutyl ether, triethylene glycol monobutyl ether,
tetraethylene glycol monobutyl ether, methoxy propanol, methoxy
propyl-2-acetate, methoxymethyl butanol, methoxybutyl acetate,
diethylene glycol dimethyl ether, dipropylene glycol dimethyl
ether, diethylene glycol ethyl methyl ether, triethylene glycol
dimethyl ether, tripropylene glycol dimethyl ether, tetraethylene
glycol dimethyl ether, and ethylene glycol monophenyl ether;
ethers, such as 1,4-dioxane; nitrogen-containing compounds, such as
dimethylformamide, pyridine, 2-pyrrolidone, and
N-methyl-2-pyrrolidone; sulfur-containing compounds, such as
dimethyl sulfoxide; halogen-containing compounds, such as
dichloromethane, chloroform, carbon tetrachloride, dichloroethane,
trichloroethane, and chlorobenzene; and mixtures thereof, and
exclude compounds having low flash points, such as toluene. These
organic solvents can be used alone as a granulating agent. In this
specification, the flash point can be determined by any known
method.
[0337] The resin binder may be any known resin binder. For example,
use may be made of cellulose resin binders, such as ethylcellulose,
methylcellulose, and salts thereof; acrylic resin binders, such as
polymethyl acrylate, polyethyl acrylate, polybutyl acrylate,
polyacrylic acid, and salts thereof; methacryl resin binders, such
as polymethyl methacrylate, polyethyl methacrylate, and polybutyl
methacrylate; and phenolic resin binders. Among the granulating
agents listed above, coal tar, petroleum-derived heavy oils,
paraffinic oils, including liquid paraffin, and aromatic oils are
preferred because they have high degrees of spheroidization
(roundness) and can provide carbon materials that generate little
amount of fine powder.
[0338] The granulating agent having an aniline point of 80.degree.
C. or lower or no aniline point, for its tendency to have a low
aniline point, preferably contains an organic compound having an
aromatic and has an average molecular weight of preferably 5,000 or
less, more preferably 1,000 or less, still more preferably 700 or
less, particularly preferably 500 or less. The aniline point can be
adjusted also by introducing a functional group having a hetero
element such as oxygen or nitrogen.
[0339] More preferably, the granulating agent contains an organic
compound having a polycyclic aromatic, such as naphthalene,
acenaphthylene, acenaphthene, fluorene, anthracene, phenanthrene,
and pyrene, because these compounds are highly interactive with the
basal surface of graphite and allow an organic compound, serving as
a carbonaceous material precursor, when mixed with granulated
graphite particles obtained through this step, to be more uniformly
deposited on the surface and in the internal voids of the
granulated graphite.
[0340] Specific examples include synthetic oils, such as olefinic
oils, naphthenic oils, and aromatic oils; natural oils, such as
vegetable oils and fats, animal fats, esters, and higher alcohols;
coal-derived light oil fractions produced through the distillation
of coal tar, such as light oil, carbolic oil, creosote oil,
naphthalene oil, and anthracene oil; and mixtures thereof.
[0341] Use may also be made of solutions adjusted to have an
aniline point of 80.degree. C. or lower by diluting a coal-derived
raw oil or a petroleum-derived heavy oil, such as coal tar or
pitch, with an organic solvent having a flash point of 5.degree. C.
or higher, preferably 21.degree. C. or higher. Examples of the
organic solvent having a flash point of 5.degree. C. or higher
include the organic solvents listed above, and of these organic
solvents, those having an aniline point of 80.degree. C. or lower
can be used alone as a granulating agent.
[0342] Among the granulating agents having an aniline point of
80.degree. C. or lower or no aniline point listed above, aromatic
oils are more preferred because they can provide granulated
graphite particles having a high degree of spheroidization and
generating little amount of fine powder, have a good affinity for
an organic compound, serving as a carbonaceous material precursor,
and allow the organic compound, serving as a carbonaceous material
precursor, when mixed with granulated graphite particles obtained
through this step, to be uniformly deposited on the surface and in
the internal voids of the granulated graphite.
[0343] The granulating agent preferably has properties that enable
efficient removal in the step of removing the granulating agent
described below (4th step) and have no adverse effect on battery
characteristics such as capacity, input-output characteristics, and
storage/cycle characteristics. Specifically, those which undergo a
weight loss of typically 50% or more, preferably 80% or more, more
preferably 95% or more, still more preferably 99% or more,
particularly preferably 99.9% or more, when heated to 700.degree.
C. in an inert atmosphere, can be selected as appropriate.
[0344] Examples of the method of mixing the raw carbon material and
the granulating agent include mixing the raw carbon material with
the granulating agent using a mixer or a kneader; mixing the raw
carbon material with the granulating agent in the form of a
solution of an organic compound in a low-viscosity diluted solvent
(organic solvent), and then removing the diluted solvent (organic
solvent); and mixing the raw carbon material and the granulating
agent placed in a granulator while performing granulation in the
subsequent 3rd step of granulating the raw carbon material.
[0345] The amount of granulating agent added is preferably 0.1 part
by mass or more, more preferably 1 part by mass or more, still more
preferably 3 parts by mass or more, even more preferably 6 parts by
mass or more, still even more preferably 10 parts by mass or more,
particularly preferably 12 parts by mass or more, most preferably
15 parts by mass or more, and preferably 1,000 parts by mass or
less, more preferably 100 parts by mass or less, still more
preferably 80 parts by mass or less, particularly preferably 50
parts by mass or less, most preferably 20 parts by mass or less,
based on 100 parts by mass of the raw carbon material. Within this
range, problems are less likely to occur, such as decreases in
degree of spheroidization due to decreases in interparticle
adhesion and decreases in productivity due to the adhesion of the
raw carbon material to apparatuses.
3rd Step: Granulating Raw Carbon Material (Subjecting Raw Carbon
Material to Spheroidization)
[0346] The carbon material is preferably prepared by subjecting a
raw carbon material to spheroidization (hereinafter also referred
to as granulation) by applying a mechanical action(s) such as
impact compression, friction, and/or shear force to the raw carbon
material. The spheroidized graphite is preferably made of a
plurality of flake graphites or crystalline graphites and ground
graphite fine powder, particularly preferably made of a plurality
of flake graphites.
[0347] One embodiment of the present invention (e.g., but not
limited to, inventions B and J) includes the granulation step of
granulating a raw carbon material by applying at least one type of
mechanical energy selected from impact, compression, friction, and
shear force.
[0348] For this step, for example, apparatuses can be used that
repeatedly apply a mechanical action(s), mainly impact force such
as compression, friction, and/or shear force, including the
interaction of the raw carbon material.
[0349] Specifically, those apparatuses are preferred which have a
rotor equipped with numbers of blades in a casing, the rotor being
configured to rotate at a high speed to apply a mechanical
action(s) such as impact, compression, friction, and/or shear force
to a raw carbon material placed in the apparatus, thereby surface
treating the raw carbon material. Furthermore, those apparatuses
are preferred which have a mechanism by which a mechanical
action(s) is repeatedly applied by circulating the raw carbon
material.
[0350] Examples of such apparatuses include Hybridization System
(Nara Machinery Co., Ltd.), Kryptron and Kryptron Orb
(Earthtechnica Co., Ltd.), CF Mill (Ube Industries, Ltd.),
Mechanofusion System, Nobilta, and Faculty (Hosokawa Micron
Corporation), Theta Composer (Tokuju Co., Ltd.), and COMPOSI
(Nippon Coke & Engineering. Co., Ltd). Of these, Hybridization
System available from Nara Machinery Co., Ltd. is preferred.
[0351] When the treatment is carried out using any of these
apparatuses, for example, the peripheral speed of the rotor is
preferably 30 m/sec or more, more preferably 50 m/sec or more,
still more preferably 60 m/sec or more, particularly preferably 70
m/sec or more, most preferably 80 m/sec or more, and preferably 100
m/sec or less. A peripheral speed in this range advantageously
enables more efficient spheroidization and, at the same time, the
deposition and the incorporation of fine powder on and into a base
material.
[0352] Although the mechanical action(s) can be applied to the raw
carbon material simply by passing the raw carbon material through
the apparatus, preferably, the raw carbon material is circulated
through or retained in the apparatus for 30 seconds or more, more
preferably 1 minute or more, still more preferably 3 minutes or
more, particularly preferably 5 minutes or more.
[0353] In the step of granulating the raw carbon material, the raw
carbon material may be granulated in the presence of any other
substances. Examples of the other substances include metals capable
of forming alloys with lithium and oxides thereof, flake graphite,
crystalline graphite, ground graphite fine powder, amorphous
carbon, and green coke. Granulation in combination with substances
other than the raw carbon material can produce carbon materials for
non-aqueous secondary batteries having various types of particle
structures.
[0354] The raw carbon material, the granulating agent, and the
other substances each may be loaded into the above-described
apparatus all at one time, sequentially in several times, or
continuously. The raw carbon material, the granulating agent, and
the other substances may be loaded into the apparatus
simultaneously, as a mixture, or individually. The raw carbon
material, the granulating agent, and the other substances may be
mixed at one time; the other substances may be added to a mixture
of the raw carbon material and the granulating agent; or the raw
carbon material may be added to a mixture of the other substances
and the granulating agent. Depending on the particle design, they
can be added/mixed at any other appropriate timing.
[0355] In spheroidizing the carbon material, it is more preferable
to carry out the spheroidization while depositing and/or
incorporating fine powder generated during the spheroidization on a
base material and/or into spheroidized particles. Carrying out the
spheroidization while depositing and/or incorporating fine powder
generated during the spheroidization on a base material and/or into
spheroidized particles can form a finer intra-particle void
structure. As a result, an electrolyte solution tends to be
effectively and efficiently distributed into the intra-particle
voids, and Li-ion insertion/extraction sites in the particles
cannot be efficiently used, thus providing good low-temperature
output characteristics and cycle characteristics. The fine powder
to be deposited on a base material may be generated during the
spheroidization, may be generated in adjusting the flake graphite
particle size, or may be added/mixed at any other appropriate
timing.
[0356] To deposit and incorporate the fine powder on a base
material and into spheroidized particles, it is preferable to
enhance flake graphite particle-flake graphite particle, flake
graphite particle-fine powder particle, and fine powder
particle-fine powder particle adhesive forces. Specific examples of
adhesive forces between particles include van der Waals force and
electrostatic attraction, which involve no interparticle mediator,
and physical and/or chemical cross-linking forces, which involve
interparticle mediators.
[0357] For Van der Waals force, the relation of
"self-weight<adhesion" becomes distinct as the average particle
diameter (d50) decreases from 100 .mu.m. Thus, as the average
particle diameter (d50) of the flake graphite, a raw material of a
spheroidized graphite (raw carbon material), decreases, the
interparticle adhesion increases, which advantageously facilitates
the deposition and the incorporation of fine powder on a base
material and into spheroidized particles. The average particle
diameter (d50) of the flake graphite is preferably 1 .mu.m or more,
more preferably 2 .mu.m or more, still more preferably 3 .mu.m or
more, preferably 80 .mu.m or less, more preferably 50 .mu.m or
less, still more preferably 35 .mu.m or less, very preferably 20
.mu.m or less, particularly preferably 10 .mu.m or less, most
preferably 8 .mu.m or less.
[0358] Electrostatic attraction is derived from electrification
resulting, for example, from particle friction, and drier particles
tend to be more easily electrified and have stronger interparticle
adhesion. Thus, the interparticle adhesion can be enhanced, for
example, by reducing the water content of a graphite before being
spheroidized.
[0359] The spheroidization is preferably carried out in a
low-humidity atmosphere to keep the flake graphite under treatment
from absorbing moisture. Furthermore, to prevent the surface of the
flake graphite from being oxidized by the energy of a machine
process and receiving acidic functional groups during the
treatment, the spheroidization is preferably carried out in an
inert atmosphere.
[0360] Examples of physical and/or chemical cross-linking forces,
which involve interparticle mediators, include physical and/or
chemical cross-linking forces that involve liquid mediators and
solid mediators. Examples of the chemical cross-linking forces
include cross-linking forces of covalent bonds, ionic bonds,
hydrogen bonds, and other bonds formed between particles and
interparticle mediators, for example, by chemical reactions,
sintering, and mechanochemical effects.
[0361] In one embodiment of the present invention, the spheroidized
graphite is prepared by carrying out spheroidization while
depositing and/or incorporating fine powder generated by the
fracture of a flake graphite during the spheroidization on and/or
into a parent particle, whereby the particle strength can be
increased to reduce the generation of fine powder upon physical
impact. To deposit and/or incorporate the fine powder generated
during the spheroidization on and/or into a parent particle, it is
preferable to enhance parent particle-parent particle, parent
particle-fine powder, and fine powder-fine powder binding
capacities. For example, when a flake graphite is spheroidized by
repeatedly applying a mechanical action(s), mainly impact force
such as compression, friction, and/or shear force, including the
interaction of the target particles, the graphite reacts with
oxygen in the atmosphere to generate CO.sub.2 and CO. The inventors
intensively studied to discover that the parent particle-parent
particle, parent particle-fine powder, and fine powder-fine powder
binding capacities can be enhanced by carrying out spheroidization
under conditions where the amount of CO.sub.2 and CO generated is
in a specific range, thereby achieving a carbon material that can
provide a high capacity and low-temperature output characteristics
when used in a non-aqueous secondary battery.
[0362] Specifically, the spheroidization is preferably carried out
under conditions where the amount of CO that generates from 1 kg of
a flake graphite is 5 mmol or less, more preferably 4 mmol or less,
still more preferably 3 mmol or less. The lower limit of the amount
of CO that generates from 1 kg of a flake graphite can be, for
example, but not limited to, 0.05 mmol or more. The spheroidization
is preferably carried out under conditions where the amount of
CO.sub.2 that generates from 1 kg of a flake graphite is 9 mmol or
less, more preferably 8 mmol or less, still more preferably 7 mmol
or less. The lower limit of the amount of CO.sub.2 that generates
from 1 kg of a flake graphite can be, for example, but not limited
to, 0.1 mmol or more. The spheroidization is preferably carried out
under conditions where the total amount of CO and CO.sub.2 that
generate from 1 kg of a flake graphite is 14 mmol or less, more
preferably 12 mmol or less, still more preferably 10 mmol or less.
The lower limit the total amount of CO and CO.sub.2 that generate
from 1 kg of a flake graphite can be, for example by but not
limited to, 0.15 mmol or more. Carrying out the spheroidization
under conditions within these ranges reduces the amount of graphite
functional group of flake graphite particles, such as hydroxy
(--OH), carboxyl (--C.dbd.O(--OH)), carbonyl (C.dbd.O), and
quinone, which can reduce the obstruction of parent particle-parent
particle, parent particle-fine powder, and fine powder-fine powder
bindings, thus providing a carbon material having high particle
strength. As a result, the carbon material used as a negative
electrode material for a non-aqueous secondary battery generates a
reduced amount of fine powder even when a physical impact is
applied.
[0363] The amount of CO.sub.2 and CO that generate in the
spheroidization can be controlled to be in the above ranges, for
example, by reducing the oxygen concentration in an apparatus for
applying a mechanical action(s) by purging with an inert gas
atmosphere, such as nitrogen, or reducing the pressure; treating
the flake graphite without being exposed to oxygen; adding an
auxiliary that is more reactive with oxygen than the flake graphite
to preferentially react the auxiliary with oxygen, thereby
inhibiting the reaction between the flake graphite and oxygen; or
if a raw natural graphite is exposed to oxygen, deoxidizing the
graphite by burning before use. These methods may be combined as
appropriate. Alternatively, the spheroidization can be carried out
by repeatedly applying a mechanical action(s), mainly impact force
such as compression, friction, and/or shear force, including the
interaction of the target particles, to the flake graphite to
enhance the parent particle-parent particle, parent particle-fine
powder, and fine powder-fine powder binding capacities, thus
reducing the amount of graphite functional group.
4th Step: Removing Granulating Agent
[0364] One embodiment of the present invention may include the step
of removing the granulating agent. The granulating agent can be
removed, for example, by washing with a solvent or
volatilizing/decomposing the granulating agent by heat
treatment.
[0365] The heat treatment is carried out preferably at 60.degree.
C. or higher, more preferably 100.degree. C. or higher, still more
preferably 200.degree. C. or higher, even more preferably
300.degree. C. or higher, particularly preferably 400.degree. C. or
higher, most preferably 500.degree. C. or higher, preferably
1,500.degree. C. or lower, more preferably 1,000.degree. C. or
lower, still more preferably 800.degree. C., or lower. A heat
treatment temperature in this range can sufficiently
volatilize/decompose the granulating agent away, leading to
improved productivity.
[0366] The heat treatment is carried out preferably for 0.5 to 48
hours, more preferably 1 to 40 hours, still more preferably 2 to 30
hours, particularly preferably 3 to 24 hours. A heat treatment time
in this range can sufficiently volatilize/decompose the granulating
agent away, leading to improved productivity.
[0367] The atmosphere in the heat treatment may be an active
atmosphere, such as an air atmosphere, or an inert atmosphere, such
as a nitrogen atmosphere or an argon atmosphere. When the heat
treatment is carried out at 200.degree. C. to 300.degree. C. there
is no particular restriction, but when the heat treatment is
carried out at 300.degree. C. or higher, it is preferable to use an
inert atmosphere, such as a nitrogen atmosphere or an argon
atmosphere, to prevent the oxidation of the graphite surface.
5th Step: Increasing Purity of Granulated Carbon Material
[0368] One embodiment of the present invention may include the step
of increasing the purity of the granulated carbon material. The
purity of the granulated carbon material can be increased, for
example, by treating with acids including nitric acid and
hydrochloric acid. This method can advantageously remove impurities
in the graphite, such as metals, metal compounds, and inorganic
compounds, without introducing sulfates, which can be highly active
sulfur sources, into the system.
[0369] For the acid treatment, acids including nitric acid and
hydrochloric acid may be used, and use may also be made of other
acids, for example, acids made by appropriately mixing inorganic
acids, such as bromic acid, hydrofluoric acid, boric acid, and
iodine acid, or organic acids, such as citric acid, formic acid,
acetic acid, oxalic acid, trichloroacetic acid, and trifluoroacetic
acid. Preferred are concentrated hydrofluoric acid, concentrated
nitric acid, and concentrated hydrochloric acid, and more preferred
are concentrated nitric acid and concentrated hydrochloric acid. In
the present invention, the graphite may be treated with sulfuric
acid, provided that sulfuric acid is used in such an amount and at
such a concentration that have no adverse effect on the effects and
the physical properties of the present invention.
[0370] When different acids are used, for example, the combination
of hydrofluoric acid, nitric acid, and hydrochloric acid is
preferred because it can efficiently remove the above-described
impurities. For the mixing ratio of a mixed acid made by combining
types of acids as described above, the amount of the fewest
component is typically 10% by mass or more, preferably 20% by mass
or more, more preferably 25% by mass or more. The upper limit is a
value of acids mixed in equal amounts (expressed as 100% by
mass/types of acids).
[0371] The mixing ratio (by mass) of graphite to acids in the acid
treatment is typically 100:10 or greater, preferably 100:20 or
greater, more preferably 100:30 or greater, still more preferably
100:40 or greater, and 100:1,000 or less, preferably 100:500 or
less, more preferably 100:300 or less. An excessively small ratio
tends to fail to efficiently remove the above-described impurities.
An excessively large ratio disadvantageously reduces the amount of
graphite that can be washed at one time, leading to reduced
productivity and increased cost.
[0372] The acid treatment is carried out by immersing the graphite
into an acidic solution as described above. The immersion is
carried out typically for 0.5 to 48 hours, preferably 1 to 40
hours, more preferably 2 to 30 hours, still more preferably 3 to 24
hours. An excessively long immersion tends to lead to reduced
productivity and increased cost, and an excessively short immersion
tends to fail to sufficiently remove the above-described
impurities.
[0373] The immersion is carried out typically at 25.degree. C. or
higher, preferably 40.degree. C. or higher, more preferably
50.degree. C. or higher, still more preferably 60.degree. C. or
higher. When an aqueous acid is used, the theoretical upper limit
is 100.degree. C., which is the boiling point of water. An
excessively low temperature tends to fail to sufficiently remove
the above-described impurities.
[0374] To remove a residual acid content after the acid washing to
increase the pH from weak acid to neutral, it is preferable to
further perform washing with water. For example, when the pH of the
graphite washed with acids (the treated graphite) is typically 3 or
greater, preferably 3.5 or greater, more preferably 4 or greater,
still more preferably 4.5 or greater, washing with water can be
omitted, and when the pH is not in this range, it is preferable to
wash the treated graphite with water as required. The water used
for washing is preferably ion-exchanged water or distilled water to
improve washing efficiency and prevent contamination. A specific
resistance, an indicator of ion content of the water, is typically
0.1 M.OMEGA.cm or more, preferably 1 M.OMEGA.#cm or more, still
more preferably 10 M.OMEGA.cm or more. The theoretical upper limit
at 25.degree. C. is 18.24 M.OMEGA.cm. A small specific resistance
means a high ion content of the water and tends to lead to
contamination and reduced washing efficiency.
[0375] The time for washing with water, that is, stirring the
treated graphite and water is typically 0.5 to 48 hours, preferably
1 to 40 hours, more preferably 2 to 30 hours, still more preferably
3 to 24 hours. An excessively long stirring tends to reduce
production efficiency, and an excessively short stirring tends to
increase residual impurities/acid content.
[0376] The mixing ratio of the treated graphite to water is
typically 100:10 or greater, preferably 100:30 or greater, more
preferably 100:50 or greater, still more preferably 100:100 or
greater, and 100:1,000 or less, preferably 100:700 or less, more
preferably 100:500 or less, still more preferably 100:400 or less.
An excessively high ratio tends to reduce production efficiency,
and an excessively low ratio tends to increase residual
impurities/acid content.
[0377] The stirring is carried out typically at 25.degree. C. or
higher, preferably 40.degree. C. or higher, more preferably
50.degree. C. or higher, still more preferably 60.degree. C. or
higher. The upper limit is 100.degree. C., which is the boiling
point of water. An excessively low temperature tends to increase
residual impurities/acid content.
[0378] When the washing with water is carried out batchwise, the
process of stirring in pure water and filtration is preferably
repeated several times to remove impurities/acid content. This
process may be carried out repeatedly until the pH of the
above-described treated graphite is in the above range, typically
once or more, preferably twice or more, more preferably three times
or more.
[0379] As a result of the above-described treatment, the
hydrogen-ion concentration of waste water of the resulting graphite
is typically 200 ppm or less, preferably 100 ppm or less, more
preferably 50 ppm or less, still more preferably 30 ppm or less,
and typically 1 ppm or more, preferably 2 ppm or more, more
preferably 3 ppm or more, still more preferably 4 ppm or more. An
excessively high hydrogen-ion concentration tends to result in a
residual acid content to decrease the pH, and an excessively low
hydrogen-ion concentration tends to result in a prolonged treating
time to lead to reduced productivity.
5'th Step: Heat Treating Granulated Carbon Material
[0380] The present invention may include the step of heat-treating
the granulated carbon material to adjust its labile carbon content
and crystallinity. Although the labile carbon content on the
surface of the carbon material particles may excessively increase
in the granulation described above, the heat treatment can decrease
the labile carbon content to a moderate level.
[0381] The temperature condition in the heat treatment is not
limited and typically in the range of 300.degree. C. or higher,
preferably 500.degree. C., more preferably 700.degree. C.,
particularly preferably 800.degree. C. or higher, and typically
2,000.degree. C. or lower, preferably 1,500.degree. C. or lower,
particularly preferably 1,200.degree. C. or lower, depending on the
desired degree of crystallinity. Such temperature conditions can
moderately increase the crystallinity of the surface of the carbon
material particles.
[0382] When the granulated carbon material contains a
low-crystallinity carbon material, the low-crystallinity carbon
material can be graphitized to increase its crystallinity in this
step for the purpose of increasing discharge capacity. The
temperature condition in the heat treatment is not limited and
typically in the range of 600.degree. C. or higher, preferably
900.degree. C. or higher, more preferably 1,600.degree. C. or
higher, particularly preferably 2,500.degree. C. or higher, and
typically 3,200.degree. C. or lower, preferably 3,100.degree. C. or
lower, depending on the desired degree of crystallinity. Such
temperature conditions can increase the crystallinity of the
surface of the carbon material particles.
[0383] Crystals on the surface of the carbon material particles may
be disordered, and the disorder is particularly pronounced when the
above-described granulation is performed. The heat treatment can
repair the disordered crystals on the surface of the carbon
material particles.
[0384] In the heat treatment, the retention time during which the
temperature is held in the above range is not limited and typically
longer than 10 seconds and up to 72 hours.
[0385] The heat treatment is carried out in an inert gas
atmosphere, such as nitrogen gas, or in a non-oxidizing atmosphere
created by the gas generated from raw graphite. Examples of
apparatuses that can be used for the heat treatment include, but
are not limited to, shuttle furnaces, tunnel furnaces, electric
furnaces, lead hammer furnaces, rotary kilns, direct energization
furnaces, Acheson furnaces, resistance heating furnaces, and
induction heating furnaces.
6th Step: Depositing Carbonaceous Material Having Lower
Crystallinity than Raw Carbon Material on Granulated Carbon
Material
[0386] One embodiment of the present invention may include the step
of depositing a carbonaceous material (B) having lower
crystallinity than the raw carbon material on the granulated carbon
material. In other words, the above-described carbon material and
the carbonaceous material (B) can be combined to form a composite
carbon material for the purpose of inhibiting side reactions with
an electrolyte solution and improving fast charge-discharge
characteristics. This step can provide a carbon material that can
inhibit side reactions with an electrolyte solution and improve
fast charge-discharge characteristics.
[0387] The composite graphite obtained by depositing the
carbonaceous material having lower crystallinity than the raw
carbon material on the granulated carbon material is also referred
to as a "composite carbon material with a carbonaceous material
(composite graphite with a carbonaceous material)"or a "composite
carbon material".
Carbonaceous Material (B) Content of Composite Carbon Material
[0388] The carbonaceous material (B) content of the composite
carbon material is typically 0.01% by mass or more, preferably 0.1%
by mass or more, more preferably 0.5% or more, still more
preferably 1% by mass or more, particularly preferably 2% by mass
or more, most preferably 3% by mass or more, based on the carbon
material (A) content. The carbonaceous material (B) content is
typically 30% by mass or less, preferably 20% by mass or less, more
preferably 15% by mass or less, still more preferably 10% by mass
or less, particularly preferably 7% by mass or less, most
preferably 5% by mass or less.
[0389] An excessively high carbonaceous material (B) content of the
composite carbon material tends to cause damage to the carbon
material (A) to cause material fracture when the composite carbon
material is rolled under a sufficient pressure in order to achieve
a non-aqueous secondary battery having a high capacity, leading to
an increased charge-discharge irreversible capacity in an initial
cycle and reduced initial efficiency. An excessively low content
tends to be less likely to produce an effect of the coating.
[0390] The carbonaceous material (B) content of the composite
carbon material can be calculated from sample masses before and
after the material is burnt using the equation below. The
calculation is made on the assumption that the mass of the carbon
material (A) shows no change before and after burning.
Carbonaceous .times. .times. material .times. .times. ( B ) .times.
.times. content .times. .times. ( % .times. .times. by .times.
.times. mass ) = [ ( w .times. .times. 2 - w .times. .times. 1 )
.times. / .times. w .times. .times. 1 ] .times. 100
##EQU00022##
(where w1 is a mass (kg) of the carbon material (A), and w2 is a
mass (kg) of the composite carbon material)
[0391] When the carbonaceous material (B) is combined by a mixing
method, the amount of the carbonaceous material (B) in the
composite carbon material can be controlled, for example, by the
amount of a carbonaceous material (B) precursor added when the
carbon material (A) and the carbonaceous material (B) precursor are
combined or the residual carbon ratio of the carbonaceous material
(B) precursor. For example, when the residual carbon ratio of the
carbonaceous material (B) precursor, as determined by a method
described in JIS K2270, is p %, the carbonaceous material (B)
precursor is added in an amount 100/p times the desired amount of
the carbonaceous material (B). When the carbonaceous material (B)
is combined by a gas phase method, the amount of the carbonaceous
material (B) can be controlled by conditions of the distribution of
the carbonaceous material (B) precursor, such as temperature,
pressure, and time.
X-Ray Parameter of Carbonaceous Material (B)
[0392] The carbonaceous material (B) has a d-value (interplanar
spacing) of lattice planes ((002) planes), as determined by X-ray
diffractometry in accordance with the method of the Japan Society
for Promotion of Scientific Research, of typically 0.3445 nm or
less, preferably 0.335 nm to less than 0.340 nm. The d-value is
more preferably 0.339 nm or less, still more preferably 0.337 nm or
less. A d.sub.002-value in this range increases the amount of
lithium that enters between graphite layers, thus providing a high
charge-discharge capacity.
[0393] The carbonaceous material (B) has a crystallite size (Lc),
as determined by X-ray diffractometry in accordance with the method
of the Japan Society for Promotion of Scientific Research, in the
range of preferably 1.5 nm or more, more preferably 3.0 nm or more.
A crystallite size in this range increases the amount of lithium
that enters between graphite layers, thus providing a high
charge-discharge capacity. The lower limit of Lc is a theoretical
value of graphite.
[0394] The X-ray parameter of the carbonaceous material (B) can be
analyzed, for example, by heating and burning the carbonaceous
material (B) precursor alone to yield the carbonaceous material
(B).
Combination with Carbon Material (A)
[0395] To load the carbonaceous material (B) onto the surface of
the carbon material (A), for example, a precursor of the
carbonaceous material (B) is mixed with the carbon material (A), or
the carbonaceous material (B) is vapor deposited on the carbon
material (A). Particularly preferred methods include (e.g., but not
limited to, Invention F) mixing the carbon material (A) with an
organic compound, serving as a carbonaceous material (B) precursor,
so as to be uniformly coated, and heating the mixture in a
non-oxidizing atmosphere (which is referred to as a mixing method
in the present invention), and uniformly vapor-depositing a
material compound for gas phase coating, serving as a carbonaceous
material (B) precursor, on the carbon material (A) in an inert gas
atmosphere (which is referred to as a gas phase method in the
present invention). The mixing method and the gas phase method will
be described below.
Mixing Method
[0396] In the mixing method, the carbon material (A) is mixed with
an organic compound, serving as a carbonaceous material (B)
precursor, so as to be uniformly coated, and the mixture is heated
in a non-oxidizing atmosphere.
Types of Organic Compound Serving as Carbonaceous Material (B)
Precursor
[0397] As an organic compound, serving as a carbonaceous material
(B) precursor, use can be made of various types of compounds
including coal-derived heavy oils, such as soft to hard various
coal-tar pitches, coal tars, and coal liquefaction oils;
petroleum-derived heavy oils, such as residual oils from
atmospheric or vacuum distillation of crude oil; and heavy oils
resulting from cracking, such as by-products of ethylene production
by naphtha cracking.
[0398] In one embodiment of the present invention,
petroleum-derived raw oils and coal-derived raw oils, which have a
good affinity for granulating agents having aniline points of
80.degree. C. or lower and allow the organic compound, serving as a
carbonaceous material precursor, to be uniformly deposited on the
surface of a granulated graphite, are suitable for use, and
coal-derived raw oils are particularly suitable for use.
[0399] Examples of resin-derived organic compounds include
thermosetting resins, such as phenolic resins, polyacrylonitriles,
and polyimides; thermoplastic resins, such as polyvinyl chlorides,
polyvinylidene chlorides, and polyvinyl alcohols, and natural
polymers, such as celluloses, starch, and polysaccharides.
[0400] Examples of coal-derived raw oils that can be used include
coal-derived heavy oils produced from coal, such as coal-tar
pitches, impregnating pitches, molded pitches, and coal liquids;
and refined coal-tar pitches produced by removing insolubles in
coal-tar pitches. Coal-derived raw oils contain large amounts of
flat aromatic hydrocarbons formed of numbers of benzene rings
bonded to each other, such as dibenzocoronene and pentacene. When
aromatic hydrocarbons having flat structures are heated in the
burning step to be more flowable, planes of the aromatic
hydrocarbons having flat structures tend to be superposed on each
other, and a thermal polycondensation reaction proceeds with the
flat structures superposed on each other. As a result, the van der
Waals force between the planes of the hydrocarbons polymerized by
the polycondensation tends to be enhanced to reduce the
plane-to-plane distance between the polymerized hydrocarbons,
resulting in a higher degree of crystallinity.
[0401] Examples of petroleum-derived raw oils include residual oils
from a distillation of heavy oils, residual oils from naphtha
cracking, and catalytically cracked heavy oils. Other examples
include heat-treated pitches obtained by heat treating heavy oils
resulting from cracking, such as ethylene tar pitch, FCC decant
oil, and Ashland pitch. It is known that petroleum-derived raw
oils, although containing flat aromatic hydrocarbons formed of
numbers of benzene rings bonded to each other, contain large
amounts of linear paraffinic hydrocarbons; moreover, the flat
aromatic hydrocarbons formed of numbers of benzene rings bonded to
each other often have pendant methyl or other groups, and some of
the benzene rings are often substituted with cyclohexane rings.
Thus, when aromatic hydrocarbons having flat structures are heated
in the burning step to be more flowable and planes of the aromatic
hydrocarbons having flat structures are superposing on each other,
the large amounts of linear paraffins on the planes tend to
obstruct the superposition. The flat aromatic hydrocarbons having
pendant methyl or other groups tend to hinder the superposition of
the flat aromatic hydrocarbons. The cyclohexane rings also tend to
obstruct the superposition of the aromatic hydrocarbons, and the
cyclohexane rings tend to be pyrolyzed to be pendant methyl or
other groups, further obstructing the superposition. These facts
suggest that coal-derived raw oils, as compared with
petroleum-derived raw oils, tend to crystallize to a higher decree
and thus are suitable for use as the organic compound, serving as a
carbonaceous material precursor, for use in the present
invention.
[0402] Specifically, preferred are petroleum-derived heavy oils
produced in oil refining and coal-derived raw oils produced using
coal tar, which is produced when coke for ironmaking is produced,
as a starting material, and more preferred are pitches called a
soft pitch or a middle pitch having a softening point of 0.degree.
C. or higher, preferably 30.degree. C. to 100.degree. C., which are
recovered from a column bottom during the distillation of coal tar.
The organic compound, serving as a carbonaceous material precursor,
of the present invention may be a mixture of these coal-derived raw
oils and petroleum-derived raw oils, resin-derived organic
compounds, and other solvents.
[0403] These coal-derived raw oils, which typically contain a light
oil fraction, are preferably refined by distillation to extract
useful fractions and improve productivity.
Physical Properties of Organic Compound, Serving as Carbonaceous
Material (B) Precursor
[0404] The organic compound, serving as a carbonaceous material (B)
precursor, may be any compound as long as a carbonaceous powder
obtained by burning and crushing the organic compound, serving as a
carbonaceous material (B) precursor, in an inert atmosphere at
1,300.degree. C. has an interplanar spacing of the crystallite
(002) plane (d.sub.002), as determined by wide-angle X-ray
diffractometry in accordance with the method of the Japan Society
for Promotion of Scientific Research, of 0.3445 nm or less. A
description will be given below of physical properties and a
production method of a coal-derived raw oil, a preferred organic
compound, by way of illustration and not by way of limitation.
Quinoline Insoluble (Hereinafter Referred to as Qi) Content and
.beta.-Resin Content
[0405] The Qi content of the organic compound, serving as a
carbonaceous material (B) precursor, is typically 0% by mass or
more, and typically 30% by mass or less, preferably 20% by mass or
less, more preferably 15% by mass or less, still more preferably
10% by mass or less, particularly preferably 5% by mass or less,
most preferably 1% by mass or less. The .beta.-resin content of the
organic compound, serving as a carbonaceous material precursor, is
typically 1% by mass or more, preferably 2% by mass or more, more
preferably 3% by mass or more, and typically 80% by mass or less,
preferably 70% by mass or less, more preferably 60% by mass or
less, still more preferably 50% by mass or less, particularly
preferably 30% by mass or less, most preferably 15% by mass or
less.
[0406] Within the above ranges, composite particles for a
non-aqueous secondary battery can be obtained which has a
good-quality carbon structure due to good crystal growth during the
carbonization by burning and has a structure in which graphite
particles are uniformly coated with a carbonaceous material due to
the high affinity for the above-described granulating agent, and
thus excellent low-temperature output characteristics and
high-temperature storage characteristics tend to be exhibited.
[0407] The Qi content and the .beta.-resin content can be
determined by the method described below.
[0408] If the organic compound, serving as a carbonaceous material
(B) precursor, contains a large amount of Qi, crystals will grow
insufficiently during the process of carbonization by burning,
resulting in poor-quality carbon. Thus, it is preferable to remove
Qi from the organic compound, serving as a carbonaceous material
(B) precursor, before carbonization in advance.
[0409] Qi can be removed by any known method such as
centrifugation, mass sedimentation, or filtration. To reduce
residual Qi, Qi is preferably removed by filtration or mass
sedimentation. In this case, an appropriate solvent may optionally
be used to facilitate operations. When Qi is removed by filtration,
it is carried out under the conditions of a pressure of typically
0.05 to 1.0 MPa, preferably 0.1 to 0.5 MPa, and a temperature of
20.degree. C. to 200.degree. C., preferably 50.degree. C. to
150.degree. C. The opening size of a filter used for the filtration
is preferably 3 microns or less.
[0410] When Qi is removed by mass sedimentation, it is carried out
under the conditions of a temperature of typically 20.degree. C. to
350.degree. C. and a standing time of typically 10 minutes to 10
hours.
[0411] After the Qi removal treatment has been performed as
described above, the Qi content of the organic compound, serving as
a carbonaceous material precursor, is typically 0.1% by mass or
less, preferably 0.01% by mass or less. After the Qi removal
operation, the .beta.-resin content of the organic compound,
serving as a carbonaceous material precursor, is typically 1.0 to
15.0% by mass, preferably 4.0 to 10.0% by mass.
[0412] Qi Content, .beta.-Resin Content, and Measuring Method
[0413] Quinoline (purity: 95.0% or more, available from Wako Pure
Chemical Industries, Ltd.) and toluene (purity: 99.5% or more,
available from Wako Pure Chemical Industries, Ltd.) were provided
as solvents, and insolubles of the organic compound, serving as a
carbonaceous material precursor, in each solvent are measured by
the following procedures (1) to (6). [0414] (1) Take 2.0 g of a
sample (e.g., coal tar or coal-tar pitch) into a flask and
precisely weigh it (W1). [0415] (2) Pour 100 mL of the
above-described measurement solvent (e.g., quinoline) into the
flask containing the sample, attach a condenser, and put the flask
into an oil bath at 110.degree. C. (130.degree. C. in the case of
toluene). Heat the solution with stirring for 30 minutes to
dissolve the sample in the solvent. [0416] (3) Attach filter paper
(W2) precisely weighed in advance to a filter. Pour the solution
obtained in (2) into the filter and perform suction filtration.
Pour 100 mL of the measurement solvent heated at 60.degree. C. onto
the filtration residue to dissolve and wash it. Repeat this
operation four times. [0417] (4) Dry the filtration residue on the
filter paper in a dryer at 110.degree. C. for 60 minutes. [0418]
(5) Remove the filtration residue on the filter paper from the
dryer, allow it to cool in a desiccator for 30 minutes, and then
precisely weigh its weight (W3). [0419] (6) Calculate the solvent
insoluble by the following equation.
[0419] Solvent .times. .times. insoluble .times. .times. ( %
.times. .times. by .times. .times. mass ) = ( residue .times.
.times. weight .times. .times. after .times. .times. dissolution
.times. / .times. sample .times. .times. weight ) .times. 100 = ( (
W .times. .times. 3 - W .times. .times. 2 ) .times. / .times. W
.times. .times. 1 ) .times. 100 ##EQU00023##
[0420] The measurements were made according to the above procedure
(1) to (6) using various measurement solvents: acetone, quinoline,
nitrobenzene, morpholine, and toluene. Insolubles (% by mass) in
these solvents are respectively referred to as acetone insoluble,
quinoline insoluble, nitrobenzene insoluble, morpholine insoluble,
and toluene insoluble.
[0421] Based on the insoluble measured for each solvent, .beta.,
.alpha., and .beta.1 can be obtained as follows:
.beta. (toluene insoluble that is soluble in quinoline)=(toluene
insoluble)-(quinoline insoluble)
.alpha. (acetone insoluble that is soluble in toluene)=(acetone
insoluble)-(toluene insoluble)
[0422] .beta.1 (morpholine insoluble that is soluble in
nitrobenzene)=(morpholine insoluble)-(nitrobenzene insoluble)
[0423] In the present invention, a soluble in each solvent is a
value obtained by subtracting the insoluble (% by mass) measured by
the above method from 100 (% by mass).
Specific Gravity
[0424] The lower limit of the specific gravity of the organic
compound, serving as a carbonaceous material (B) precursor, is
typically 1.1 or greater, preferably 1.14 or greater, more
preferably 1.17 or greater, still more preferably 1.2 or greater.
The upper limit is typically 1.5 or less, preferably 1.45 or less,
more preferably 1.4 or less, still more preferably 1.35 or less. An
excessively small specific gravity tends to increase the amount of
linear paraffinic hydrocarbon in the organic compound, leading to
low crystallinity in the carbonization by burning. An organic
compound having an excessively large specific gravity tends to have
a high molecular weight and a high melting point. An organic
compound having an excessively high melting point, when mixed with
graphite particles to deposit the organic compound on the graphite
particles in the 6th step of the method for producing a carbon
material for a non-aqueous secondary battery, the step of
depositing a carbonaceous material having lower crystallinity than
a raw carbon material on a granulated carbon material, tends to mix
with the graphite particles ununiformly. The specific gravity is a
value at 15.degree. C.
Softening Point
[0425] The upper limit of the softening point of the organic
compound, serving as a carbonaceous material (B) precursor, is
typically 400.degree. C. or lower, preferably 200.degree. C. or
lower, more preferably 150.degree. C. or lower, still more
preferably 100.degree. C. or lower. The lower limit of the
softening point of the organic compound is typically 0.degree. C.
or higher, preferably 25.degree. C. or higher, more preferably
30.degree. C. or higher, still more preferably 40.degree. C. or
higher. A softening point over the upper limit can make it
difficult to uniformly mix with graphite particles, thus
necessitating mixing at a higher temperature and leading to low
productivity. An organic compound having a softening point below
the lower limit tends to contain flat aromatic hydrocarbons in a
small amount and linear paraffinic hydrocarbons in a relatively
large amount and tends to provide a carbonaceous material coating,
obtained by carbonization by burning, with low crystallinity and a
carbon material for an non-aqueous secondary battery with a high
specific surface area.
[0426] The organic compound, serving as a carbonaceous material (B)
precursor, has a residual carbon ratio of typically 1% or more,
preferably 10% or more, more preferably 20% or more, still more
preferably 30% or more, particularly preferably 45% or more, and
typically 99% or less, preferably 90% or less, more preferably 70%
or less, still more preferably 60% or less. The residual carbon
ratio can be measured by a method in accordance with JIS 2270, for
example. A residual carbon ratio in this range tends to enable
uniform diffusion and permeation on the surface and into micropores
of the carbon material (A) and enable the surface and the
micropores of the carbon material (A) to be more uniformly coated
with the carbonaceous material (B), thus making it possible to
control the average value and the standard deviation
(.sigma..sub.R) of microscopic Raman R values to be in the
preferred ranges of the present invention, leading to improved
input-output characteristics.
[0427] The addition amount of the carbonaceous material (B)
precursor by volume (=mass/density) is typically at least 0.1 time
the cumulative pore volume at pore diameters in a range of 0.01
.mu.m to 1 .mu.m of the carbon material (A), preferably at least
0.5 time, more preferably at least 0.7 time, still more preferably
at least 0.8 time, particularly preferably at least 0.9 time, most
preferably at least 0.95 time, and typically up to 10 times,
preferably up to 5 times, more preferably up to 3 times, still more
preferably up to 2 times, particularly preferably up to 1.4 times,
most preferably up to 1.2 times. An addition amount in this range
tends to enable sufficient permeation into pores of the carbon
material (A) having a diameter in the range of 0.01 .mu.m to 1
.mu.m and prevent the excess carbonaceous material (B) precursor
from overflowing the pores to be maldistributed on the surface of
the carbon material (A), thus enabling the carbonaceous material
(B) precursor to more uniformly diffuse and permeate on the surface
and into the micropores of the carbon material (A), which allows
the average value and the standard deviation (.sigma..sub.R) of
microscopic Raman R values of 30 randomly selected composite carbon
materials to be controlled within the preferred ranges of the
embodiment of the present invention.
[0428] Furthermore, the carbonaceous material (B) precursor can be
diluted by adding a solvent or the like as required. Adding a
solvent or the like tends to reduce the viscosity of the
carbonaceous material (B) precursor, thereby improving the
permeability into the pores of the carbon material (A) having a
diameter in the range of 0.01 .mu.m to 1 .mu.m, as a result of
which the carbonaceous material (B) precursor more uniformly
diffuses and permeates on the surface and into the micropores of
the carbon material (A).
[0429] The organic compound, serving as a carbonaceous material (B)
precursor, can be mixed with the granulated carbon material by any
method, for example, by mixing the granulated carbon material and
the organic compound, serving as a carbonaceous material (B)
precursor, using a commercially available mixer, kneader, or the
like to obtain a mixture in which the organic compound is deposited
on the granulated carbon material.
[0430] The granulated carbon material, the organic compound,
serving as a carbonaceous material (B) precursor, and other raw
materials such as solvents optionally added are mixed under heating
as required. As a result, the organic compound, serving as a
carbonaceous material (B) precursor, in liquid form is deposited on
the granulated carbon material. The mixing may be carried out in
such a manner that all of the raw materials are charged into a
mixer, and mixing and heating are performed at the same time, or
that components other than the organic compound, serving as a
carbonaceous material (B) precursor, are charged into a mixer and
preheated with stirring, and after the temperature has increased to
a mixing temperature, the organic compound, serving as a
carbonaceous material precursor, at normal temperature or preheated
to be molten is added. To prevent the organic compound, serving as
a carbonaceous material (B) precursor, when brought into contact
with the granulated graphite particles, from being cooled to have
an increased viscosity and form an multiform coating, the mixing is
preferably carried out in such a manner that components other than
the organic compound, serving as a carbonaceous material (B)
precursor, are charged into a mixer and preheated with stirring,
and after the temperature has increased to a mixing temperature,
the organic compound, serving as a carbonaceous material (B)
precursor, preheated to a mixing temperature to be molten is
added.
[0431] The heating is carried out typically at a temperature equal
to or higher than the softening point of the organic compound,
serving as a carbonaceous material (B) precursor, preferably a
temperature higher than the softening point by 10.degree. C. or
more, more preferably a temperature higher than the softening point
by 20.degree. C. or more, still more preferably by 30.degree. C. or
more, particularly preferably by 50.degree. C. or more, and
typically 450.degree. C. or lower, preferably 250.degree. C. or
lower. An excessively low heating temperature may increase the
viscosity of the organic compound, serving as a carbonaceous
material (B) precursor, to make it difficult to perform mixing,
resulting in an ununiform coating. An excessively high heating
temperature may cause the organic compound, serving as a
carbonaceous material (B) precursor, to be volatilized and
polycondensed, which increases the viscosity of the mixing system
to make it difficult to perform mixing, resulting in an ununiform
coating.
[0432] The mixer is preferably of a type having a stirring blade,
and for example, use can be made of commercially available products
such as ribbon mixers, MC processors, plowshare mixers, and KRC
kneaders. The mixing is carried out typically for 1 minute or more,
preferably 2 minutes or more, more preferably 5 minutes or more,
and typically 300 minutes or less, preferably 120 minutes or less,
more preferably 80 minutes or less. An excessively short mixing may
form an ununiform coating, and an excessively long mixing tends to
cause reduced productivity and increased cost.
[0433] Although the heating temperature (burning temperature)
varies depending on the carbonaceous material (B) precursor used to
prepare the mixture, the heating is typically carried out at
800.degree. C. or higher, preferably 900.degree. C. or higher, more
preferably 950.degree. C. or higher, to achieve sufficient
amorphous carbonization or graphitization. The upper limit of the
heating temperature is a temperature at which a carbide of the
carbonaceous material (B) precursor does not form a crystal
structure equivalent to the crystal structure of a flake graphite,
which is the carbon material (A) in the mixture, and typically up
to 3,500.degree. C. The upper limit of the heating temperature is
3,000.degree. C., preferably 2,000.degree. C., more preferably
1,500.degree. C.
[0434] To prevent oxidation, the heat treatment is performed under
a stream of an inert gas, such as nitrogen or argon, or in a
non-oxidizing atmosphere in which gaps are filled with a granular
carbon material, such as breeze or packing coke. The equipment used
for the heat treatment may be any equipment that suits the above
purpose, including reaction vessels such as shuttle furnaces,
tunnel furnaces, lead hammer furnaces, rotary kilns, and
autoclaves, cokers (heat treatment vessels for coke production),
electric furnaces, gas furnaces, and Acheson furnaces for electrode
materials. The heating rate, the cooling rate, the heat treatment
time, and other conditions can be freely selected within the
allowable range of the equipment used.
Gas Phase Method
[0435] Examples of gas phase methods include processes such as
chemical vapor deposition (CVD) in which a material compound for
gas phase coating, serving as a carbonaceous material (B)
precursor, is uniformly vapor deposited on the surface of the
carbon material (A) in an inert gas atmosphere.
[0436] A specific example of the material compound for gas phase
coating, serving as a carbonaceous material (B) precursor, that can
be used is a gaseous compound capable of being decomposed by heat,
plasma, or the like to form the carbonaceous material (B) coating
on the surface of the carbon material (A). Examples of the gaseous
compound include unsaturated aliphatic hydrocarbons, such as
ethylene, acetylene, and propylene; saturated aliphatic
hydrocarbons, such as methane, ethane, and propane; and aromatic
hydrocarbons, such as benzene, toluene, and naphthalene. These
compounds may be used alone or as a mixture of two or more gases.
The temperature, pressure, time, and other conditions in the CVD
process can be appropriately selected depending on the type of
coating material used and the desired amount of the carbonaceous
material (B) coating.
[0437] When the carbon material (A) is combined with the
carbonaceous material (B) by the gas phase method, adjusting the
cumulative pore volume and the pore diameter (e.g., cumulative pore
volume at pore diameters in a range of 0.01 .mu.m to 1 .mu.m of the
carbon material (A), 0.07 mL/g or more; PD/d50 (%), 1.8 or less)
enables diffusion via the pores to contact portions between the
carbon material (A) particles and into the particles where the
material compound for gas phase coating can hardly reach, thus
enabling the surface and the micropores of the carbon material (A)
to be more uniformly coated with the carbonaceous material (B),
which allows the average value and the standard deviation
(.sigma..sub.R) of microscopic Raman R values of 30 randomly
selected composite carbon materials to be easily controlled within
the preferred ranges of the present invention.
Other Steps
[0438] After the mixing method or the gas phase method described
above is performed, processes such as disintegration and/or
crushing and classification can be optionally performed to provide
a composite carbon material of the present invention.
[0439] The composite carbon material may be of any shape and
typically has an average particle diameter of 2 to 50 .mu.m,
preferably 5 to 35 .mu.m, particularly preferably 8 to 30 .mu.m. To
achieve the particle diameter in this range, disintegration and/or
crushing and/or classification are performed as required.
[0440] As long as the effect of the embodiment is not adversely
affected, other additional steps may be performed, or control
conditions not described above may be added.
[0441] According to the production method according to one
embodiment of the present invention, carbon materials having
various types of particle structures can be stably produced.
Typical particle structures include carbon materials produced by
folding a flake graphite, a raw carbon material, having a large or
medium average particle diameter, carbon materials produced by
granulating (folding) a flake graphite having a small average
particle diameter, and carbon materials produced by depositing an
artificial graphite on a natural graphite.
[0442] As an indicator of stable production of such carbon
materials having various types of particle structures, the yield
expressed as a carbon material weight to total solid material
weight ratio (carbon material weight/total solid material weight)
is typically 60% or more, preferably 80% or more, more preferably
95% or more.
Mixing with Other Carbon Materials
[0443] To improve the orientation of electrode plates, the
permeability of electrolyte solution, the conductive path, and
other properties to improve cycle characteristics, electrode plate
expansion, and other characteristics, a carbon material different
from the above-described granulated carbon material or the
above-described composite carbon material can be mixed (hereinafter
the carbon material different from the granulated carbon material
or the composite carbon material is also referred to as an
"additional carbon material", and a carbon material obtained by
mixing the granulated carbon material or the composite carbon
material with the carbon material different from the granulated
carbon material or the composite carbon material is also referred
to as a "mixed carbon material").
[0444] As the additional carbon material, use can be made of a
material selected from natural graphites, artificial graphites,
coated graphites made of carbon materials and carbonaceous material
coatings thereon, amorphous carbons, and carbon materials
containing metal particles or metal compounds. The carbon material
(A) may be mixed. These materials may be used alone or in any
combination and composition of two or more materials.
[0445] Examples of natural graphites that can be used include
highly purified carbon materials and spheroidized natural
graphites. The high purification typically means an operation of
dissolving away ash, metals, and other impurities in a low-purity
natural graphite by treating in an acid, such as hydrochloric acid,
sulfuric acid, nitric acid, or hydrofluoric acid, or performing
different acid treatments in combination. Typically, water washing
or any other treatment is performed following the acid treatment to
remove the acids used in the high purification process. In place of
the acid treatment, a high-temperature treatment at 2,000.degree.
C. or higher may be performed to evaporate off ash, metals, and
other impurities. The high-temperature heat treatment may be
performed in a halogen gas atmosphere, such as chlorine gas, to
remove ash, metals, and other impurities. Furthermore, these
techniques may be used in any combination.
[0446] The volume-based average particle diameter (also referred to
as the average particle diameter for short) of such a natural
graphite is typically in the range of 5 .mu.m or more, preferably 8
.mu.m or more, more preferably 10 .mu.m or more, particularly
preferably 12 .mu.m or more, and typically 60 .mu.m or less,
preferably 40 .mu.m or less, particularly preferably 30 .mu.m or
less. An average particle diameter in this range advantageously
improves fast charge-discharge characteristics and
productivity.
[0447] The BET specific surface area of the natural graphite is
typically in the range of 1 m.sup.2/g or more, preferably 2
m.sup.2/g or more, and typically 30 m.sup.2/g or less, preferably
15 m.sup.2/g or less. A specific surface area in this range
advantageously improves fast charge-discharge characteristics and
productivity.
[0448] The tap density of the natural graphite is typically in the
range of 0.6 g/cm.sup.3 or more, preferably 0.7 g/cm.sup.3 or more,
more preferably 0.8 g/cm.sup.3 or more, still more preferably 0.85
g/cm.sup.3 or more, and typically 1.3 g/cm.sup.3 or less,
preferably 1.2 g/cm.sup.3 or less, more preferably 1.1 g/cm.sup.3
or less, A tap density in this range advantageously improves fast
charge-discharge characteristics and productivity.
[0449] Examples of artificial graphites include particles obtained
by graphitizing a carbon material, and, for example, use can be
made of particles obtained by burning and graphitizing a single
graphite precursor particle in powder form and granulated particles
obtained by forming, burning, graphitizing, and disintegrating a
plurality of graphite precursor particles.
[0450] The volume-based average particle diameter of such an
artificial graphite is typically in the range of 5 .mu.m or more,
preferably 10 .mu.m or more, and typically 60 .mu.m or less,
preferably 40 .mu.m or more, more preferably 30 .mu.m or less. An
average particle diameter in this range advantageously reduces the
expansion of electrode plates and improves productivity.
[0451] The BET specific surface area of the artificial graphite is
typically in the range of 0.5 m.sup.2/g or more, preferably 1.0
m.sup.2/g or more, and typically 8 m.sup.2/g or less, preferably 6
m.sup.2/g or less, more preferably 4 m.sup.2/g or less. A BET
specific surface area in this range advantageously reduces the
expansion of electrode plates and improves productivity.
[0452] The tap density of the artificial graphite is typically in
the range of 0.6 g/cm.sup.3 or more, preferably 0.7 g/cm.sup.3 or
more, more preferably 0.8 g/cm.sup.3 or more, still more preferably
0.85 g/cm.sup.3 or more, and typically 1.5 g/cm.sup.3 or less,
preferably 1.4 g/cm.sup.3 or less, more preferably 1.3 g/cm.sup.3
or less. A tap density in this range advantageously reduces the
expansion of electrode plates and improves productivity,
[0453] Examples of coated graphites made of carbon materials and
carbonaceous material coatings thereon that can be used include
particles obtained by coating a natural graphite or an artificial
graphite with the above-described organic compound, serving as a
carbonaceous material precursor, and burning and/or graphitizing
the coated material and particles obtained by coating a natural
graphite or an artificial graphite with a carbonaceous material by
CVD.
[0454] The volume-based average particle diameter of such a coated
graphite is typically in the range of 5 .mu.m or more, preferably 8
.mu.m or more, more preferably 10 .mu.m or more, particularly
preferably 12 .mu.m or more, and typically 60 .mu.m or less,
preferably 40 .mu.m or less, particularly preferably 30 .mu.m or
less. An average particle diameter in this range advantageously
improves fast charge-discharge characteristics and
productivity.
[0455] The BET specific surface area of the coated graphite is
typically in the range of 1 m.sup.2/g or more, preferably 2
m.sup.2/g or more, more preferably 2.5 m.sup.2/g, or more, and
typically 20 m.sup.2/g or less, preferably 10 m.sup.2/g or less,
more preferably 8 m.sup.2/g or less, particularly preferably 5
m.sup.2/g or less. A specific surface area in this range
advantageously improves fast charge-discharge characteristics and
productivity.
[0456] The tap density of the coated graphite is typically 0.6
g/cm.sup.3 or more, preferably 0.7 g/cm.sup.3 or more, still more
preferably 0.8 g/cm.sup.3 or more, even more preferably 0.85
g/cm.sup.3 or more, and typically 1.3 g/cm.sup.3 or less,
preferably 1.2 g/cm.sup.3 or less, more preferably 1.1 g/cm.sup.3
or less. A tap density in this range advantageously improves fast
charge-discharge characteristics and productivity.
[0457] Examples of amorphous carbons that can be used include
particles obtained by burning a bulk mesophase and particles
obtained by infusibilizing and burning a readily graphitizable
organic compound.
[0458] The volume-based average particle diameter of such an
amorphous carbon is typically in the range of 5 .mu.m or more,
preferably 12 .mu.m or more, and typically 60 .mu.m or less,
preferably 40 .mu.m or less. An average particle diameter in this
range advantageously improves fast charge-discharge characteristics
and productivity.
[0459] The BET specific surface area of the amorphous carbon is
typically in the range of 1 m.sup.2/g or more, preferably 2
m.sup.2/g or more, more preferably 2.5 m.sup.2/g or more, and
typically 8 m.sup.2/g or less, preferably 6 m.sup.2/g or less, more
preferably 4 m.sup.2/g or less. A specific surface area in this
range advantageously improves fast charge-discharge characteristics
and productivity.
[0460] The tap density of the amorphous carbon is typically 0.6
g/cm.sup.3 or more, preferably 0.7 g/cm.sup.3 or more, more
preferably 0.8 g/cm.sup.3 or more, still more preferably 0.85
g/cm.sup.3 or more, and typically 1.3 g/cm.sup.3 or less,
preferably 1.2 g/cm.sup.3 or less, more preferably 1.1 g/cm.sup.3
or less. A tap density in this range advantageously improves fast
charge-discharge characteristics and productivity.
[0461] Examples of carbon materials containing metal particles or
metal compounds include composite materials of a graphite and a
metal selected from the group consisting of Fe, Co, Sb, Bi, Pb, Ni,
Ag, Si, Sn, Al, Zr, Cr, P, S, V, Mn, Nb, Mo, Cu, Zn, Ge, In, and Ti
or a compound thereof. The metal or compound thereof may be an
alloy of two or more metals, and the metal particles may be alloy
particles formed of two or more metal elements. Of these, metals
selected from the group consisting of Si, Sn, As, Sb, Al, Zn, and W
and compounds thereof are preferred, and Si and SiOx are
particularly preferred. The general formula SiOx is made from Si
dioxide (SiO.sub.2) and metal Si (Si), and the value of x is
typically 0<x<2, preferably 0.2 to 1.8, more preferably 0.4
to 1.6, still more preferably 0.6 to 1.4. A value of x in this
range can provide a high capacity and also reduce the irreversible
capacity due to the bond of Li and oxygen.
[0462] From the viewpoint of cycle life, the volume-based average
particle diameter of such metal particles is typically 0.005 .mu.m
or more, preferably 0.01 .mu.m or more, more preferably 0.02 .mu.m
or more, still more preferably 0.03 .mu.m or more, and typically 10
.mu.m or less, preferably 9 .mu.m or less, more preferably 8 .mu.m
or less. An average particle diameter in this range reduces the
volume expansion that accompanies charging and discharging, thus
providing good cycle characteristics while maintaining
charge-discharge capacity.
[0463] The BET specific surface area of the metal particles is
typically 0.5 m.sup.2/g to 120 m.sup.2/g, preferably 1 m.sup.2/g to
100 m.sup.2/g. A specific surface area in this range advantageously
provides a battery with high charge-discharge efficiency, a high
discharge capacity, quick insertion and extraction of lithium in
fast charging and discharging, and excellent rate
characteristics.
[0464] Examples of apparatuses used to mix the above-described
granulated carbon material or the above-described composite carbon
material with the additional carbon material include, but are not
limited to, rotary mixers, such as cylindrical mixers,
twin-cylindrical mixers, double-cone mixers, regular cubic mixers,
and hoe mixers; and fixed mixers, such as spiral mixers, ribbon
mixers, Muller mixers, Helical Flight mixers, Pugmill mixers, and
fluidizing mixers.
Physical Properties of Carbon Material for Non-Aqueous Secondary
Battery
[0465] A description will be given below of preferred physical
properties of the carbon material according to an embodiment of the
present invention.
Volume-Based Average Particle Diameter (Average Particle Diameter
d50)
[0466] The volume-based average particle diameter (also referred to
as "average particle diameter d50" or "median diameter") of the
carbon material is preferably 1 .mu.m or more, more preferably 3
.mu.m or more, still more preferably 5 .mu.m or more, even more
preferably 8 .mu.m or more, particularly preferably 10 .mu.m or
more, most preferably 12 .mu.m or more. The average particle
diameter d50 is typically 80 .mu.m or less, preferably 50 .mu.m or
less, more preferably 40 .mu.m or less, still more preferably 35
.mu.m or less, even more preferably 31 .mu.m or less, particularly
preferably 30 .mu.m or less, most preferably 25 .mu.m or less. An
average particle diameter in this range tends to prevent the
increase in irreversible capacity and prevent streaks that can
occur during a slurry application, thus leading to no reduction in
productivity.
[0467] An excessively small average particle diameter d50 tends to
cause an increase in irreversible capacity and a loss in initial
battery capacity of a non-aqueous secondary battery comprising the
carbon material. An excessively large average particle diameter d50
can cause process defects such as streaks that occur in a slurry
application, degraded high-current-density charge-discharge
characteristics, and degraded low-temperature output
characteristics.
[0468] The average particle diameter d50 is defined as a
volume-based median diameter determined by suspending 0.01 g of a
carbon material in 10 mL of a 0.2% by mass aqueous solution of a
polyoxyethylene sorbitan monolaurate surfactant (e.g., Tween 20
(registered trademark)), placing the suspension (a measurement
sample) in a commercially available laser diffraction/scattering
particle size distribution analyzer (e.g., LA-920 available from
HORIBA), irradiating the measurement sample with ultrasonic waves
of 28 kHz at a power of 60 W for 1 minute, and then performing a
measurement with the analyzer.
Tap Density
[0469] The tap density of the carbon material is typically 0.7
g/cm.sup.3 or more, preferably 0.75 g/cm.sup.3 or more, more
preferably 0.8 g/cm.sup.3 or more, still more preferably 0.83
g/cm.sup.3 or more, even more preferably 0.85 g/cm.sup.3 or more,
very preferably 0.88 g/cm.sup.3 or more, particularly preferably
0.9 g/cm.sup.3 or more, most preferably 0.95 g/cm.sup.3 or more,
and preferably 1.3 g/cm.sup.3 or less, more preferably 1.2
g/cm.sup.3 or less, still more preferably 1.1 g/cm.sup.3 or
less.
[0470] A tap density in this range prevents streaks that can occur
during the formation of an electrode plate, thus leading to
improved productivity and excellent fast charge-discharge
characteristics. In addition, such a tap density tends to inhibit
the increase in intraparticle carbon density, thus providing good
rolling properties and making it easy to form a high-density
negative electrode sheet.
[0471] The tap density is defined as a density calculated from a
volume and a mass of a sample (carbon material). The volume is
determined as follows: using a powder density meter, the carbon
material of the present invention is dropped through a sieve with
openings of 300 .mu.m into a cylindrical tap cell with a diameter
of 1.6 cm and a volume capacity of 20 cm.sup.3 to fill up the cell;
a tap with a stroke length of 10 mm is given 1,000 times; and the
volume at this time is measured.
[0472] Mode Pore Diameter (PD) in Pore Diameter Range of 0.01 .mu.m
to 1 .mu.m
[0473] The mode pore diameter (PD) in a pore diameter range of 0.01
.mu.m to 1 .mu.m of the carbon material is a value determined by
mercury intrusion (mercury porosimetry) and typically 0.01 .mu.m or
more, preferably 0.03 .mu.m or more, more preferably 0.05 .mu.m or
more, still more preferably 0.06 .mu.m or more, particularly
preferably 0.07 .mu.m or more, and typically 1 .mu.m or less,
preferably 0.65 .mu.m or less, more preferably 0.5 .mu.m or less,
still more preferably 0.4 .mu.m or less, even more preferably 0.3
.mu.m or less, particularly preferably 0.2 .mu.m or less, most
preferably 0.1 .mu.m or less.
[0474] A mode pore diameter (PD) in the range of 0.01 .mu.m to 1
.mu.m outside this range tends to prevent an electrolyte solution
from being efficiently distributed into intra-particle voids and
prevent. the efficient use of Li-ion insertion/extraction sites in
the particles, thus resulting in degraded low-temperature output
characteristics and cycle characteristics.
[0475] Furthermore, when a composite carbon material is formed,
such a mode pore diameter (PD) tends to prevent the carbonaceous
material (B) precursor from uniformly diffusing and permeating to
the surface and into the micropores of the carbon material (A),
thus resulting in reduced coating uniformity of the carbonaceous
material (B). This makes it difficult to control the average value
and the standard deviation (.sigma..sub.R) of microscopic Raman R
values of the composite carbon material and results in degraded
low-temperature output characteristics and cycle
characteristics.
Cumulative Pore Volume at Pore Diameters in Range of 0.01 .mu.m to
1 .mu.m
[0476] The cumulative pore volume at pore diameters in a range of
0.01 .mu.m to 1 .mu.m of the carbon material is a value determined
by mercury intrusion (mercury porosimetry) and, even when pressure
is applied, typically 0.07 mL/g or more, preferably 0.08 mL/g or
more, more preferably 0.09 mL/g or more, most preferably 0.10 mL/g
or more, and preferably 0.3 mL/g or less, more preferably 0.25 mL/g
or less, still more preferably 0.2 mL/g or less, particularly
preferably 0.18 mL/g or less.
[0477] An excessively small cumulative pore volume at pore
diameters in a range of 0.01 .mu.m to 1 .mu.m tends to prevent an
electrolyte solution from permeating into the particles and prevent
the efficient use of Li-ion insertion/extraction sites in the
particles. This impedes smooth insertion/extraction of lithium ions
in fast charging and discharging and results in degraded
low-temperature output characteristics. A cumulative pore volume
within the above range tends to allow an electrolyte solution to be
smoothly and efficiently distributed into the particles, thus
enabling the effective and efficient use of Li-ion
insertion/extraction sites in the particles as well as on the
periphery of the particles during charging and discharging and
providing good low-temperature output characteristics.
Half Width at Half Maximum of Pore Distribution (log (nm))
[0478] The half width at half maximum of pore distribution (log
(nm)) of the carbon material refers to a half width at half maximum
at a micropore side of a peak in a pore diameter range of 0.01
.mu.m to 1 .mu.m in a pore distribution (nm), as determined by
mercury intrusion (mercury porosimetry), with a horizontal axis
expressed in common logarithm (log (nm)).
[0479] (In the case where the carbon material has a d50 of 13 .mu.m
or more)
[0480] When the carbon material having a d50 of 13 .mu.m or more is
a spheroidized carbon material made of flake graphite, crystalline
graphite, and vein graphite, its half width at half maximum of pore
distribution (log (nm)) is preferably 0.45 or greater, more
preferably 0.5 or greater, still more preferably 0.6 or greater,
particularly preferably 0.65 or greater, most preferably 0.7 or
greater, and preferably 10 or less, more preferably 5 or less,
still more preferably 3 or less, particularly preferably 1 or
less.
[0481] (In the case where the carbon material has a d50 of less
than 13 .mu.m)
[0482] When the d50 of the carbon material is less than 13 .mu.m,
its half width at half maximum of pore distribution (log (nm)) is
preferably 0.01 or greater, more preferably 0.05 or greater, still
more preferably 0.1 or greater, and preferably 0.33 or less, more
preferably 0.3 or less, still more preferably 0.25 or less,
particularly preferably 0.23 or less.
[0483] When the half width at half maximum of pore distribution
(log (nm)) is in this range, intra-particle voids in a pore
diameter range of 0.01 .mu.m to 1 .mu.m tend to be formed to have a
finer structure and thus allow an electrolyte solution to be
smoothly and efficiently distributed into the particles. This
enables the effective and efficient use of Li-ion
insertion/extraction sites in the particles as well as on the
periphery of the particles during charging and discharging, thus
providing good low-temperature output characteristics and cycle
characteristics.
Total Pore Volume
[0484] The total pore volume of the carbon material is a value
determined by mercury intrusion (mercury porosimetry) and
preferably 0.1 mL/g or more, more preferably 0.3 mL/g or more,
still more preferably 0.5 mL/g or more, particularly preferably 0.6
mL/g or more, most preferably 0.7 mL/g or more. The total pore
volume of the carbon material is preferably 10 mL/g or less, more
preferably 5 mL/g or less, still more preferably 2 mL/g or less,
particularly preferably 1 mL/g or less.
[0485] A total pore volume in this range eliminates the need for
using an excess amount of binder in forming an electrode plate and
facilitates the diffusion of a thickener and a binder in forming an
electrode plate.
[0486] As an apparatus for the mercury porosimetry, a mercury
porosimeter (Autopore 9520 available from Micromeritics Corp.) can
be used. A sample (carbon material) is weighed to around 0.2 g and
placed in a powder cell. The cell is sealed, and a pretreatment is
carried out by degassing the cell at room temperature under vacuum
(50 .mu.mHg or lower) for 10 minutes.
[0487] Subsequently, mercury is introduced into the cell under a
reduced pressure of 4 psia (approximately 28 kPa). The pressure is
increased stepwise from 4 psia (approximately 28 kPa) to 40,000
psia (approximately 280 MPa) and then reduced to 25 psia
(approximately 170 kPa).
[0488] The number of steps in the pressure increase is at least 80.
In each step, the amount of mercury intrusion is measured after an
equilibration time of 10 seconds. From the mercury intrusion curve
thus obtained, a pore distribution is calculated using the Washburn
equation.
[0489] The calculation is made assuming that the surface tension
(.gamma.) of mercury is 485 dyne/cm, and the contact angle (.psi.)
is 140.degree.. The average pore diameter is defined as a pore
diameter at a cumulative pore volume of 50%.
Ratio (PD/d50 (%)) of Mode Pore Diameter (PD) in Pore Diameter
Range of 0.01 .mu.m to 1 .mu.m to Volume-Based Average Particle
Diameter (d50)
[0490] The ratio (PD/d50) of mode pore diameter (PD) in a pore
diameter range of 0.01 .mu.m to 1 .mu.m to volume-based average
particle diameter (d50) of the carbon material is expressed by
equation (1A) and typically 1.8 or less, preferably 1.80 or less,
more preferably 1.00 or less, still more preferably 0.90 or less,
particularly preferably 0.80 or less, most preferably 0.70 or less,
and typically 0.01 or greater, preferably 0.10 or greater, more
preferably 0.20 or greater.
PD .times. / .times. d .times. .times. 50 .times. .times. ( % ) =
mode .times. .times. pore .times. .times. diameter .times. .times.
( PD ) .times. .times. in .times. .times. a .times. .times. pore
.times. .times. diameter .times. .times. range .times. .times. of
.times. .times. 0.01 .times. .times. .mu.m .times. .times. to
.times. .times. 1 .times. .times. .mu.m .times. .times. in .times.
.times. a .times. .times. pore .times. .times. distribution .times.
.times. determined .times. .times. by .times. .times. mercury
.times. .times. intrusion .times. / .times. volume .times. -
.times. based .times. .times. average .times. .times. particle
.times. .times. diameter .times. .times. ( d .times. .times. 50 )
.times. 100 Equation .times. .times. ( 1 .times. A )
##EQU00024##
[0491] A mode pore diameter (PD) in a pore diameter range of 0.01
.mu.m to 1 .mu.m outside this range tends to prevent an electrolyte
solution from being efficiently distributed into intra-particle
voids and prevent the efficient use of Li-ion insertion/extraction
sites in the particles, thus resulting in degraded low-temperature
output characteristics and cycle characteristics.
[0492] Furthermore, when the carbon material is formed into a
composite carbon material, such a mode pore diameter (PD) tends to
prevent the carbonaceous material (B) precursor from more uniformly
diffusing and permeating to the surface and into the micropores of
the carbon material (A). This makes it difficult to control the
average value and the standard deviation (.sigma..sub.R) of
microscopic Raman R values of the composite carbon material and
results in degraded low-temperature output characteristics and
cycle characteristics.
Frequency of Particles of 3 .mu.m or Less
[0493] The frequency of particles with a particle diameter of 3
.mu.m or less of the carbon material after ultrasonic waves of 28
kHz have been applied at a power of 60 W for 5 minutes is
preferably 1% or more, more preferably 10% or more, and preferably
60% or less, more preferably 55% or less, still more preferably 50%
or less, particularly preferably 40% or less, most preferably 30%
or less.
[0494] A frequency of particles in this range tends to cause less
particle decay and fine powder separation during, for example,
kneading for preparing a slurry, rolling an electrode, and charging
and discharging, thus providing good low-temperature output
characteristics and cycle characteristics.
[0495] The frequency of particles with a particle diameter of 3
.mu.m or less after ultrasonic waves of 28 kHz have been applied at
a power of 60 W for 5 minutes is a value determined by mixing 50 mL
of a 0.2% by volume aqueous solution of a polyoxyethylene sorbitan
monolaurate surfactant (e.g., Tween 20 (registered trademark)) with
0.2 g of a carbon material, applying ultrasonic waves of 28 kHz at
a power of 60 W for a predetermined time using a flow-type particle
image analyzer "FPIA-2000 available from Sysmex Industrial Corp.",
and then counting the number of particles with a detection range
set to 0.6 to 400 .mu.m.
Roundness
[0496] The roundness of the carbon material according to this
embodiment is typically 0.88 or greater, preferably 0.90 or
greater, more preferably 0.91 or greater, still more preferably
0.92 or greater. The roundness is preferably 1 or less, more
preferably 0.98 or less, still more preferably 0.97 or less.
[0497] A roundness in this range tends to inhibit the degradation
of high-current-density charge-discharge characteristics of
non-aqueous secondary batteries. The roundness is defined by the
following equation, and a theoretically perfect sphere has a
roundness of 1.
[0498] A roundness in the above range tends to decrease the degree
of flection of Li-ion diffusivity to smoothen the movement of
electrolyte solution in intra-particle voids and enable moderate
contact between the carbon materials, thus providing good fast
charge-discharge characteristics and cycle characteristics.
[0499] Roundness=(perimeter of equivalent circle having the same
area as projected particle shape)/(actual perimeter of projected
particle shape)
[0500] As the value of the roundness is used a value determined,
for example, using a flow-type particle image analyzer (e.g., FPIA
available from Sysmex Industrial Corp.) by dispersing about 0.2 g
of a sample (carbon material) in a 0.2% by mass aqueous solution
(approximately 50 mL) of a polyoxyethylene (20) sorbitan
monolaurate surfactant, irradiating the dispersion with ultrasonic
waves of 28 kHz at a power of 60 W for 1 minute, and then measuring
the roundness of particles with a diameter in the range of 1.5 to
40 .mu.m with a detection range set to 0.6 to 400 .mu.m. The ratio
of the perimeter of a circle (equivalent circle) having the same
area as the projected particle shape measured, as the numerator, to
the perimeter of the projected particle shape measured, as the
denominator, is calculated, and the average is calculated to
determine the roundness.
[0501] X-Ray Parameter
[0502] The d-value (interplanar spacing) of lattice planes ((002)
planes) of the carbon material, as determined by X-ray
diffractometry in accordance with the method of the Japan Society
for Promotion of Scientific Research, is preferably 0.335 nm to
less than 0.340 nm. The d-value is more preferably 0.339 nm or
less, still more preferably 0.337 nm or less, particularly
preferably 0.336 nm or less. A d.sub.002-value in this range tends
to increase the crystallinity of the graphite, thus inhibiting the
increase in initial irreversible capacity. The theoretical value of
graphite is 0.335 nm.
[0503] The crystallite site (Lc) of the carbon material, as
determined by X-ray diffractometry in accordance with the method of
the Japan Society for Promotion of Scientific Research, is
preferably in the range of 30 nm or more, more preferably 50 nm or
more, still more preferably 90 nm or more, particularly preferably
100 nm or more. A crystallite size in this range provides particles
having not too low crystallinity, thus providing a non-aqueous
secondary battery the reversible capacity of which is less likely
to decrease.
Ash Content
[0504] The ash content of the carbon material is preferably 1% by
mass or less, more preferably 0.5% by mass or less, still more
preferably 0.1% by mass or less, based on the total mass of the
carbon material. The ash content is preferably at least 1 ppm.
[0505] An ash content in this range can provide a non-aqueous
secondary battery that undergoes only negligible degradation of
battery performance due to the reaction between carbon material and
electrolyte solution during charging and discharging. In addition,
such an ash content does not require much time or energy to produce
a carbon material and eliminates the need for equipment for
preventing contamination, thus reducing the increase in cost.
[0506] Furthermore, such an ash content can inhibit the increase in
the reactivity of a negative electrode formed using the carbon
material with an electrolyte solution to reduce gas generation,
thus providing a preferred non-aqueous secondary battery.
BET Specific Surface Area (SA)
[0507] The specific surface area (SA) of the carbon material, as
determined by BET method, is preferably 1 m.sup.2/g or more, more
preferably 2 m.sup.2/g or more, still more preferably 3 m.sup.2/g
or more, particularly preferably 4 m.sup.2/g or more. The specific
surface area (SA) is preferably 30 m.sup.2/g or less, more
preferably 25 m.sup.2/g or less, still more preferably 20 m.sup.2/g
or less, even more preferably 18 m.sup.2/g or less, particularly
preferably 17 m.sup.2/g or less, most preferably 15 m.sup.2/g or
less.
[0508] A specific surface area in this range tends to sufficiently
secure sites where Li enters and exits, thus providing excellent
fast charge-discharge characteristics and output characteristics,
and tends to moderately control the activity of an active material
against electrolyte solution, thus inhibiting the increase in
initial irreversible capacity, as a result of which a high-capacity
battery can be produced.
[0509] Furthermore, such a specific surface area can inhibit the
increase in the reactivity of a negative electrode formed using the
carbon material with an electrolyte solution to reduce gas
generation, thus providing a preferred non-aqueous secondary
battery.
[0510] The BET specific surface area is defined as a value
determined as follows: using a surface area meter (e.g., a Gemini
2360 specific surface area analyzer available from Shimadzu
Corporation), a carbon material sample is preliminarily vacuum
dried under a nitrogen stream at 100.degree. C. for 3 hours and
then cooled to liquid nitrogen temperature, and using a
nitrogen-helium mixed gas precisely regulated so as to have a
nitrogen pressure of 0.3 relative to atmospheric pressure, a BET
specific surface area is measured by a nitrogen adsorption BET
multipoint method according to a flowing gas method.
True Density
[0511] The true density of the carbon material is preferably 1.9
g/cm.sup.3 or more, more preferably 2 g/cm.sup.3 or more, still
more preferably 2.1 g/cm.sup.3 or more, even more preferably 2.2
g/cm.sup.3 or more, and up to 2.26 g/cm.sup.3. The upper limit is
the theoretical value of graphite. A true density in this range
tends to avoid too low carbon crystallinity, thus inhibiting the
increase in initial irreversible capacity of non-aqueous secondary
batteries.
Aspect Ratio
[0512] The aspect ratio of the carbon material in powder form is
theoretically 1 or greater, preferably 1.1 or greater, more
preferably 1.2 or greater. The aspect ratio is preferably 10 or
less, more preferably 8 or less, still more preferably 5 or
less.
[0513] An aspect ratio in this range tends to prevent streaks of a
slurry (a material for forming a negative electrode) containing the
carbon material from occurring during the formation of an electrode
plate so as to provide a uniform coated surface, thus avoiding
degraded high-current-density charge-discharge characteristics of
non-aqueous secondary batteries.
[0514] The aspect ratio is expressed as A/B, where A is the longest
diameter of a carbon material particle observed in a
three-dimensional manner, and B is the shortest diameter among the
diameters orthogonal to the longest diameter. The observation of
the carbon material particle is carried out under a scanning
electron microscope capable of magnifying observation. Fifty carbon
material particles immobilized on the surface of a metal having a
thickness of 50 microns or less are randomly selected. For each of
the particles, A and B are determined while a stage on which the
samples are immobilized is rotated and tilted, and the average
value of A/B is calculated.
Maximum Particle Diameter dmax
[0515] The maximum particle diameter dmax of the carbon material is
preferably 200 .mu.m or less, more preferably 150 .mu.m or less,
still more preferably 120 .mu.m or less, particularly preferably
100 .mu.m or less, most preferably 80 .mu.m or less. A dmax in this
range tends to inhibit the occurrence of process defects such as
streaks.
[0516] The maximum particle diameter is defined as a value of the
largest particle diameter in a particle size distribution obtained
in the measurement of average particle diameter d50.
Raman R Value
[0517] The Raman R value of the carbon material is preferably, but
not necessarily, 0.01 or greater, more preferably 0.05 or greater,
still more preferably 0.1 or greater, particularly preferably 0.15
or greater, most preferably 0.2 or greater. The Raman R value is
typically 1 or less, preferably 0.8 or less, more preferably 0.7 or
less, still more preferably 0.6 or less, particularly preferably
0.5 or less, most preferably 0.4 or less.
[0518] The Raman R value is defined as an intensity ratio
(I.sub.B/I.sub.A) in a Raman spectrum obtained by Raman
spectroscopy, where I.sub.A is an intensity of peak P.sub.A near
1,580 cm.sup.-1, and I.sub.B is an intensity of peak P.sub.B near
1,360 cm.sup.-1.
[0519] As used herein, "near 1,580 cm.sup.-1" refers to a range of
1,580 to 1,620 cm.sup.-1, and "near 1,360 cm.sup.-1" a range of
1,350 to 1,370 cm.sup.-1.
[0520] The Raman R value is an indicator of the crystallinity near
the surface (from the particle surface to a depth of about 100
angstroms) of a carbon particle, and smaller Raman R values
indicate higher crystallinities or less disordered crystalline
states. A Raman R value in this range tends to reduce the
possibility that the crystallinity of the surface of the carbon
material particles increases and that crystals, when the density is
increased, are oriented in the direction parallel to a negative
electrode plate, thus avoiding degraded load characteristics.
Furthermore, such a Raman R value tends to reduce the possibility
that crystals on the particle surface are disordered and inhibit
the increase in the reactivity of a negative electrode with an
electrolyte solution, thus avoiding reduced charge-discharge
efficiency and increased gas generation of non-aqueous secondary
batteries.
[0521] The Raman spectrum described above can be measured using a
Raman spectroscope. Specifically, a sample is loaded by
gravity-dropping target particles into a measuring cell, and the
measuring cell is irradiated with an argon-ion laser beam while
being rotated in a plane perpendicular to the laser beam. The
measurement conditions are as follows:
[0522] Wavelength of argon-ion laser beam: 514.5 nm
[0523] Laser power on sample: 25 mW
[0524] Resolution: 4 cm.sup.-1
[0525] Measurement range: 1,100 cm.sup.-1 to 1,730 cm.sup.-1
[0526] Measurement of peak intensity, measurement of peak
half-width: background processing, smoothing processing
(convolution by simple average, 5 points)
DBP Absorption
[0527] The dibutyl phthalate (DBP) absorption of the carbon
material is preferably 85 mL/100 g or less, more preferably 70
mL/100 g or less, still more preferably 65 mL/100 g or less,
particularly preferably 60 mL/100 g or less. The DBP absorption is
preferably 30 mL/100 g or more, more preferably 40 mL/100 g or
more.
[0528] A DBP absorption in this range, which means that the carbon
material is spheroidized to a sufficient degree, tends to reduce
the risk of causing defects such as streaks when a slurry
containing the carbon material is applied. Also, such a DBP
absorption tends to avoid the decrease in reactivity because of the
presence of pore structures in the particles.
[0529] The DBP absorption is defined as a value obtained by making
a measurement in accordance with JIS K6217 using 40 g of a target
material (carbon material) under the conditions of a drip rate of 4
mL/min, a rotation speed of 125 rpm, and a torque of 500 Nm. For
the measurement, use can be made of a Brabender Model E
absorptometer, for example.
Average Particle Diameter d10
[0530] The particle diameter corresponding to a cumulative total of
10% from the smallest particle (d10) of the carbon material, as
measured on a volume basis, is preferably 30 .mu.m or less, more
preferably 20 .mu.m or less, still more preferably 17 .mu.m or
less, and preferably 1 .mu.m or more, more preferably 3 .mu.m or
more, still more preferably 5 .mu.m or more.
[0531] A d10 in this range does not lead to too strong an
aggregation tendency of the particles, thus avoiding process
defects, such as increases in slurry viscosity, and reduced
electrode strength and reduced initial charge-discharge efficiency
of non-aqueous secondary batteries. Furthermore, such a d10 tends
to avoid degraded high-current-density charge-discharge
characteristics and degraded low-temperature output
characteristics.
[0532] The d10 is defined as a value at which the particle
frequency % is accumulated to 10% from the smallest particle
diameter in a particle size distribution obtained in the
measurement of average particle diameter d50.
Average Particle Diameter d90
[0533] The particle diameter corresponding to a cumulative total of
90% from the smallest particle (d90) of the carbon material, as
measured on a volume basis, is preferably 100 .mu.m or less, more
preferably 70 .mu.m or less, still more preferably 60 .mu.m or
less, even more preferably 50 .mu.m or less, particularly
preferably 45 .mu.m or less, most preferably 42 .mu.m or less, and
preferably 20 .mu.m or more, more preferably 26 .mu.m or more,
still more preferably 30 .mu.m or more, particularly preferably 34
.mu.m or more.
[0534] A d90 in this range tends to avoid reduced electrode
strength and reduced initial charge-discharge efficiency of
non-aqueous secondary batteries and also avoid process defects,
such as streaks during the application of a slurry, degraded
high-current-density charge-discharge characteristics, and degraded
low-temperature output characteristics.
[0535] The d90 is defined as a value at which the particle
frequency % is accumulated to 90% from the smallest particle
diameter in a particle size distribution obtained in the
measurement of average particle diameter d50.
[0536] The silicon content of the carbon material, as determined by
X-ray fluorescence analysis (XRF), is typically 5 ppm or more,
preferably 10 ppm or more, more preferably 15 ppm or more, still
more preferably 20 ppm or more, and typically 500 ppm or less,
preferably 300 ppm or less, more preferably 200 ppm or less, still
more preferably 170 ppm or less, particularly preferably 150 ppm or
less, most preferably 100 ppm or less.
[0537] A silicon content in this range tends to avoid reduced
electrode strength and reduced initial charge-discharge efficiency
of non-aqueous secondary batteries.
Frequency (%) of Particles with Diameter of 5 .mu.m or Less
[0538] In one embodiment of the present invention (e.g., but not
limited to, Invention C), Q.sub.5min (%), the frequency of
particles with a diameter of 5 .mu.m or less of the carbon material
after ultrasonic waves of 28 kHz have been applied at a power of 60
W for 5 minutes, is preferably 40% or less, more preferably 35% or
less, still more preferably 30% or less.
[0539] Q.sub.1min (%), the frequency of particles with a diameter
of 5 .mu.m or less of the carbon material after ultrasonic waves of
28 kHz have been applied at a power of 60 W for 1 minute, is
preferably 30% or less, more preferably 27% or less, still more
preferably 23% or less.
[0540] Furthermore, Q.sub.10min (%), the frequency of particles
with a diameter of 5 .mu.m or less of the carbon material after
ultrasonic waves of 28 kHz have been applied at a power of 60 W for
10 minutes, is preferably 60% or less, more preferably 50% or less,
still more preferably 45% or less, most preferably 40% or less.
[0541] Frequencies of particles in these ranges tend to cause less
carbon material decay and fine powder separation during, for
example, kneading for preparing a slurry, rolling an electrode, and
charging and discharging, thus providing good low-temperature
output characteristics and cycle characteristics.
[0542] In one embodiment of the present invention (e.g., but not
limited to, Invention C), the carbon material for a non-aqueous
secondary battery is preferably a carbon material for a non-aqueous
secondary battery capable of occluding and releasing lithium ions
and formed from a plurality of graphite particles, the carbon
material satisfying inequality (1C):
Q 5 .times. .times. min .times. .times. ( % ) .times. / .times. D
.times. .times. 50 .times. .times. ( .mu.m ) .ltoreq. 3.5 ( 1
.times. C ) ##EQU00025##
where Q.sub.5min (%) is a frequency (%) of particles with a
diameter of 5 .mu.m or less determined with a flow-type particle
image analyzer after the carbon material has been irradiated with
ultrasonic waves of 28 kHz at a power of 60 W for 5 minutes, and
D50 (.mu.m) is a volume-based median diameter determined by laser
diffraction/scattering after the carbon material has been
irradiated with ultrasonic waves of 28 kHz at a power of 60 W for 1
minute.
[0543] The ratio of Q.sub.5min (%), a frequency of particles with a
diameter of 5 .mu.m or less after ultrasonic irradiation for 5
minutes, to D50 (.mu.m), a volume-based median diameter, falling
within the range defined by inequality (1C) indicates that the
carbon material has so high particle strength as to generate little
amount of fine powder even upon physical impact. Thus, the carbon
material generates little amount of fine powder when used as a
negative electrode active material to form an electrode plate, for
example, and generates little amount of separated and isolated fine
powder upon repeated charging and discharging of a battery, thus
providing a non-aqueous secondary battery, particularly, a lithium
ion secondary battery, having excellent input-output
characteristics and excellent cycle characteristics.
[0544] The frequency (%) of particles with a diameter of 5 .mu.m or
less after ultrasonic irradiation and the volume-based median
diameter in this specification are determined as described
below.
Frequency (%) of Particles with Diameter of 5 .mu.m or Less After
Ultrasonic Irradiation
[0545] The frequency (%) of particles with a diameter of 5 .mu.m or
less after ultrasonic irradiation is a percentage of the number of
particles with a diameter of 5 .mu.m or less in the total, as
determined by mixing 50 mL of a dispersion medium with 0.2 g of a
sample, placing the mixture in a flow-type particle image analyzer
(e.g., FPIA-2000 available from Sysmex Industrial Corp.), applying
ultrasonic waves of 28 kHz at a power of 60 W for a predetermined
time, and then counting the number of particles with a detection
range set to 0.6 to 400 .mu.m. In this specification, the frequency
(%) of particles with a diameter of 5 .mu.m or less is expressed as
Q.sub.5min (%), Q.sub.1min (%), and Q.sub.10min (%) when the
ultrasonic irradiation time is 5 minutes, 1 minute, and 10 minutes,
respectively.
[0546] The dispersion medium may be any medium capable of
homogeneously dispersing the sample in the liquid, and, for
example, alcohols, such as ethanol and butanol, and water can be
used. Dispersant solutions containing dispersants can also be used,
and examples include 0.2% by volume aqueous solutions of
polyoxyethylene sorbitan monolaurate surfactants (e.g., Tween 20,
registered trademark).
Ratio of Frequency of Particles with Diameter of 5 .mu.m or Less
(%) Volume-Based Median Diameter D50 (.mu.m)
[0547] In one embodiment of the present invention (e.g., but not
limited to, Invention C), the ratio of Q.sub.5min (%), a frequency
(%) of particles with a diameter of 5 .mu.m or less after applying
ultrasonic waves of 28 kHz to the carbon material at a power of 60
W for 5 minutes, to D50 (.mu.m), a volume-based median diameter,
(Q.sub.5min/D50) is 3.5 or less, preferably 3.0 or less, more
preferably 2.5 or less. Although the lower limit is not limited to
a particular value, it can be at least 0.1.
[0548] A Q.sub.5min/D50 ratio in this range can further reduce the
generation of fine powder during the formation of an electrode
plate and reduces the risk of causing a conductive path break and a
side reaction with an electrolyte solution to increase resistance,
thus providing a non-aqueous secondary battery, particularly, a
lithium ion secondary battery, having excellent input-output
characteristics. In addition, such a ratio reduces the risk of
causing separation and isolation of fine powder to cause a
conductive path break when the carbon material particles swell and
shrink upon repeated charging and discharging, thus providing a
non-aqueous secondary battery, particularly, a lithium ion
secondary battery, having excellent cycle characteristics.
[0549] The ratio of Q.sub.1min (%), a frequency (%) of particles
with a diameter of 5 .mu.m or less after applying ultrasonic waves
of 28 kHz at a power of 60 W for 1 minute, to D50 (.mu.m)
(Q.sub.1min/D50) is preferably, but not necessarily, 2.4 or less,
more preferably 2.0 or less, still more preferably 1.8 or less,
particularly preferably 1.5 or less. Although the lower limit is
not limited to a particular value, it can be at least 0.1.
[0550] A Q.sub.1min/D50 ratio in this range can readily provide a
non-aqueous secondary battery, particularly, a lithium ion
secondary battery, comprising a negative electrode active material
made of the carbon material, the battery being less likely to
undergo separation and isolation of fine powder during charging and
discharging to experience a conductive path break and having
excellent cycle characteristics.
[0551] Furthermore, the ratio of Q.sub.10min, a frequency (%) of
particles with a diameter of 5 .mu.m or less after applying
ultrasonic waves of 28 kHz at a power of 60 W for 10 minutes. to
D50 (.mu.m) (Q.sub.10min/D50) is preferably, but not necessarily,
4.0 or less, more preferably 3.5 or less, still more preferably 3.3
or less, particularly preferably 3.0 or less. Although the lower
limit is not limited to a particular value, it can be at least
0.1.
[0552] A Q.sub.10min/D50 ratio in this range can readily provide a
non-aqueous secondary battery, particularly, a lithium ion
secondary battery, comprising a negative electrode active material
made of the carbon material, the battery being less likely to
undergo separation and isolation of fine powder, for example,
during charging and discharging to experience a conductive path
break and having excellent cycle characteristics.
Total Amount of Eliminated CO and Eliminated C.sub.O2 During
Temperature Rise from Room Temperature to 1,000.degree. C. Using
Pyrolysis Mass Spectrometer (TPD-MS)
[0553] In one embodiment of the present invention (e.g., but not
limited to, Invention C), the total amount of eliminated CO and
eliminated CO.sub.2 measured using a pyrolysis mass spectrometer
(TPD-MS) by heating the carbon material from room temperature to
1,000.degree. C. is preferably 125 .mu.mol/g or less, more
preferably 100 .mu.mol/g or less, still more preferably 75
.mu.mol/g or less. Although the lower limit is not limited to a
particular value, it can be at least 1 .mu.mol/g. As used herein,
"room temperature" means 20.degree. C. to 25.degree. C.
[0554] Amount of Eliminated CO during Temperature Rise from Room
Temperature to 1,000.degree. C., Using Pyrolysis Mass Spectrometer
(TPD-MS)
[0555] The amount of eliminated CO measured using a pyrolysis mass
spectrometer (TPD-MS) by heating the carbon material according to
this embodiment from room temperature to 1,000.degree. C. is
preferably 100 .mu.mol/g or less, more preferably 80 .mu.mol/g or
less, still more preferably 60 .mu.mol/g or less. Although the
lower limit is not limited to a particular value, it can be at
least 1 .mu.mol/g.
[0556] Amount of Eliminated CO.sub.2 during Temperature Rise from
Room Temperature to 1,000.degree. C. Using Pyrolysis Mass
Spectrometer (TPD-MS)
[0557] The amount of eliminated CO.sub.2 measured using a pyrolysis
mass spectrometer (TPD-MS) by heating the carbon material according
to this embodiment from room temperature to 1,000.degree. C. is
preferably 25 .mu.mol/g or less, more preferably 20 .mu.mol/g or
less, still more preferably 15 .mu.mol/g or less. Although the
lower limit is not limited to a particular value, it can be at
least 1 .mu.mol/g.
[0558] Within the above ranges, the amount of graphite functional
group, such as hydroxy (--OH), carboxyl (--C.dbd.O(--OH)), carbonyl
(C.dbd.O), and quinone, of graphite particles of the carbon
material is small, which reduces the obstruction of parent
particle-parent particle, parent particle-fine powder, and fine
powder-fine powder bindings that might otherwise be caused by these
functional groups, thus providing a carbon material having high
particle strength. As a result, the carbon material generates a
reduced amount of fine powder even when a physical impact is
applied. In addition, when the carbon material is used as a
negative electrode of a battery, the small amount of functional
group reduces the risk of side reactions with an electrolyte
solution, which can reduce the amount of gas generated in the
battery.
[0559] In one aspect of the carbon material according to an
embodiment of the present invention, preferred is a carbon material
for a non-aqueous secondary battery capable of occluding and
releasing lithium ions, the carbon material having a cumulative
pore volume at pore diameters in a range of 2 to 4 nm, as
determined by nitrogen gas adsorption, of 0.0022 cm.sup.3/g or more
and a tap density of 0.83 g/cm.sup.3 or more.
[0560] In this embodiment (e.g., but not limited to, Invention G),
a carbon material or a mixed carbon material is preferred.
Cumulative Pore Volume at Pore Diameters in Range of 2 to 4 nm
Determined by Nitrogen Gas Adsorption
[0561] In this embodiment (e.g., but not limited to, Invention G),
the carbon material has a cumulative pore volume at pore diameters
in a range of 2 to 4 am, as determined by nitrogen gas adsorption,
of 0.0022 cm.sup.3/g or more, preferably 0.0025 cm.sup.3/g or more,
more preferably 0.0028 cm.sup.3/g or more, still more preferably
0.0032 cm.sup.3/g or more, particularly preferably 0.0035
cm.sup.3/g or more, and typically 1.0 cm.sup.3/g or less,
preferably 0.10 cm.sup.3/g or less, more preferably 0.050
cm.sup.3/g or less, still more preferably 0.010 cm.sup.3/g or less,
particularly preferably 0.0050 cm.sup.3/g or less.
[0562] A cumulative pore volume at pore diameters in a range of 2
to 4 nm of the carbon material smaller than 0.0022 cm.sup.3/g
results in insufficient lithium insertion/extraction sites, thus
leading to a low-temperature output. An excessively large
cumulative pore volume tends to increase side reactions with an
electrolyte solution, thus reducing storage characteristics and
charge-discharge efficiency.
[0563] The cumulative pore volume can be determined by nitrogen gas
adsorption. As an apparatus for the measurement, an Autoforb
(Quantachrome) can be used. A sample is placed in a powder cell,
and the cell is sealed and pre-treated at 350.degree. C. under
vacuum (1.3 Pa or lower) for 2 hours, after which an adsorption
isotherm (adsorption gas: nitrogen) is measured at liquid nitrogen
temperature.
[0564] Using the adsorption isotherm obtained, a BJH analysis was
performed to determine a micropore distribution, from which the
cumulative pore volume at pore diameters in a range of 2 nm to 100
nm is calculated.
Maximum dV/d log (D) (V: Cumulative Pore Volume, D: Pore Diameter)
at Pore Diameters in Range of 2 to 4 nm Determined by Nitrogen Gas
Adsorption
[0565] In one embodiment of the present invention (e.g., but not
limited to, Invention G), the maximum dV/d log (D) (V: cumulative
pore volume, D: pore diameter) at pore diameters in a range of 2 to
4 nm of the carbon material, as determined by nitrogen gas
adsorption, is typically 0.0090 cm.sup.3/g or more, preferably
0.011 cm.sup.3/g or more, more preferably 0.013 cm.sup.3/g or more,
and typically 0.50 cm.sup.3/g or less, preferably 0.10 cm.sup.3/g
or less, more preferably 0.050 cm.sup.3/g or less, still more
preferably 0.020 cm.sup.3/g or less.
[0566] A maximum dV/d log in this range tends to ensure sufficient
lithium-ion insertion/extraction sites, thus effectively improving
low-temperature output.
[0567] The dV/d log (D) is a quotient of a differential cumulative
pore volume dV divided by the logarithmic differential value d (log
D) of a pore diameter and is calculated by measuring the above
cumulative pore volume at pore diameters in a range of 2 to 4 nm,
as determined by nitrogen gas adsorption, such that the interval of
log (D) is 0.010 to 0.050.
Cumulative Pore Volume at Pore Diameters in Range of 2 to 100 nm
Determined by Nitrogen Gas Adsorption
[0568] In this embodiment (e.g., but not limited to, Invention G),
the cumulative pore volume at pore diameters in a range of 2 to 100
nm of the carbon material, as determined by nitrogen gas
adsorption, is typically 0.025 cm.sup.3/g or more, preferably 0.030
cm.sup.3/g or more, more preferably 0.035 cm.sup.3/g or more, still
more preferably 0.040 cm.sup.3/g or more, and typically 5.0
cm.sup.3/g or less, preferably 2.0 cm.sup.3/g or less, more
preferably 1.0 cm.sup.3/g or less, still more preferably 0.50
cm.sup.3/g or less, particularly preferably 0.10 cm.sup.3/g or
less.
[0569] A cumulative pore volume at pore diameters in a range of 2
to 100 nm of the carbon material in this range smoothens the
movement of electrolyte solution between particles, thus improving
input-output characteristics.
[0570] The cumulative pore volume at pore diameters in a range of 2
to 100 nm determined by nitrogen gas adsorption is calculated by
the same measurement method as for the above cumulative pore volume
at pore diameters in a range of 2 to 4 nm.
[0571] In one aspect of one embodiment of the present invention,
preferred is a carbon material for a non-aqueous secondary battery
capable of occluding and releasing lithium ions, the carbon
material having a Raman R value, as given by equation (1H), of 0.31
or greater and a thermal weight loss ratio per unit area
(.DELTA.TG/SA), as given by equation (2H), of 0.05 to 0.45.
[0572] In other words, the carbon material according to an
embodiment of the present invention (e.g., but not limited to,
Invention H) is preferably a carbon material for a non-aqueous
secondary battery capable of occluding and releasing lithium ions,
the carbon material having a Raman R value, as given by equation
(1H), of 0.31 or greater and a thermal weight loss ratio per unit
area (.DELTA.TG/SA), as given by equation (2H), of 0.05 to
0.45.
Raman .times. .times. value .times. .times. R = intensity .times.
.times. I B .times. .times. of .times. .times. peak .times. .times.
P B .times. .times. near .times. .times. 1 .times. , .times. 360
.times. .times. cm - 1 .times. / .times. intensity .times. .times.
I A .times. .times. of .times. .times. peak .times. .times. P A
.times. .times. near .times. .times. 1 .times. , .times. 580
.times. .times. cm - 1 .times. .times. by .times. .times. Raman
.times. .times. spectrum .times. .times. analysis Equation .times.
.times. ( 1 .times. H ) ( .DELTA. .times. .times. TG .times. /
.times. SA ) = ( thermal .times. .times. weight .times. .times.
loss .times. .times. ( .DELTA. .times. .times. TG ) .times. .times.
( % ) .times. .times. on .times. .times. heating .times. .times.
from .times. .times. 400 .times. .degree. .times. .times. C .
.times. to .times. .times. 600 .times. .degree. .times. .times. C .
.times. at .times. .times. 2 .times. .degree. .times. .times. C . /
.times. min .times. .times. in .times. .times. air .times. .times.
atmosphere , measured .times. .times. with .times. .times.
differential .times. .times. thermal .times. .times. balance )
.times. / .times. ( specific .times. .times. surface .times.
.times. area .times. .times. ( SA ) .times. .times. ( m 2 .times. /
.times. g ) .times. .times. of .times. .times. carbon .times.
.times. material .times. .times. determined .times. .times. by
.times. .times. BET .times. .times. method ) Equation .times.
.times. ( 2 .times. H ) ##EQU00026##
Raman R Value
[0573] The Raman R value of the carbon material according to this
embodiment (e.g., but not limited to, Invention H), as given by
equation (1H), is 0.31 or greater, preferably 0.32 or greater, more
preferably 0.33 or greater, still more preferably 0.35 or greater,
particularly preferably 0.36 or greater, most preferably 0.37 or
greater. The upper limit of the Raman R value is typically, but not
necessarily, 1 or less, preferably 0.7 or less, more preferably 0.6
or less, still more preferably 0.5 or less.
Raman .times. .times. value .times. .times. R = intensity .times.
.times. I B .times. .times. of .times. .times. peak .times. .times.
P B .times. .times. near .times. .times. 1 .times. , .times. 360
.times. .times. cm - 1 .times. / .times. intensity .times. .times.
I A .times. .times. of .times. .times. peak .times. .times. P A
.times. .times. near .times. .times. 1 .times. , .times. 580
.times. .times. cm - 1 .times. .times. by .times. .times. Raman
.times. .times. spectrum .times. .times. analysis Equation .times.
.times. ( 1 .times. H ) ##EQU00027##
[0574] As used herein, "near 1,580 cm.sup.-1" refers to a range of
1,580 to 1,620 cm.sup.-1, and "near 1,360 cm.sup.-1" a range of
1,350 to 1,370 cm.sup.-1.
[0575] A Raman R value of less than 0.31 tends to increase the
crystallinity of the surface of the carbon material particles to
reduce Li-ion insertion/extraction sites, thus resulting in
degraded low-temperature output characteristics. An excessively
large Raman R value tends to reduce graphite crystallinity, thus
resulting in a low discharge capacity.
[0576] The Raman spectrum described above can be measured using a
Raman spectroscope. Specifically, a sample is loaded by
gravity-dropping target particles into a measuring cell, and the
measuring cell is irradiated with an argon-ion laser beam while
being rotated in a plane perpendicular to the laser beam. The
measurement conditions are as follows: Wavelength of argon-ion
laser beam: 514.5 nm
[0577] Laser power on sample: 25 mW
[0578] Resolution: 4 cm.sup.-1
[0579] Measurement range: 1,100 cm.sup.-1 to 1,730 cm.sup.-1
[0580] Measurement of peak intensity, measurement of peak
half-width: background processing, smoothing processing
(convolution by simple average, 5 points)
Thermal Weight Loss Ratio per Unit Area (.DELTA.TG/SA)
[0581] The thermal weight loss (.DELTA.TG) (%) of the carbon
material according to this embodiment (e.g., but not limited to,
Invention H) is determined as follows: into a platinum pan, 5 mg of
a carbon material is weighed, and the pan is placed in a
differential thermal balance (TG8120 available from Rigaku
Corporation); under an air stream of 100 mL/min, the temperature is
raised from room temperature to 400.degree. C., at a rate of
20.degree. C./min and then from 400.degree. C. to 600.degree. C. at
a rate of 2.degree. C./min, and the amount of thermal weight loss
is measured. The calculated value of thermal weight loss between
400.degree. C. and 600.degree. C. in this measurement is defined as
a thermal weight loss (.DELTA.TG) (%) in the present invention. The
thermal weight loss ratio per unit area (.DELTA.TG/SA) is
calculated by equation (2H),
[0582] The .DELTA.TG/SA is typically 0.05 or greater, preferably
0.08 or greater, more preferably 0.10 or greater, still more
preferably 0.13 or greater, particularly preferably 0.15 or
greater, most preferably 0.17 or greater, and typically 0.45 or
less, preferably 0.43 or less, more preferably 0.40 or less, still
more preferably 0.35 or less, particularly preferably 0.30 or less,
most preferably 0.25 or less.
( .DELTA. .times. .times. TG .times. / .times. SA ) = ( thermal
.times. .times. weight .times. .times. loss .times. .times. (
.DELTA. .times. .times. TG ) .times. .times. ( % ) .times. .times.
on .times. .times. heating .times. .times. from .times. .times. 400
.times. .degree. .times. .times. C . .times. to .times. .times. 600
.times. .degree. .times. .times. C . .times. at .times. .times. 2
.times. .degree. .times. .times. C . / .times. min .times. .times.
in .times. .times. air .times. .times. atmosphere , measured
.times. .times. with .times. .times. differential .times. .times.
thermal .times. .times. balance ) .times. / .times. ( specific
.times. .times. surface .times. .times. area .times. .times. ( SA )
.times. .times. ( m 2 .times. / .times. g ) .times. .times. of
.times. .times. carbon .times. .times. material .times. .times.
determined .times. .times. by .times. .times. BET .times. .times.
method ) Equation .times. .times. ( 2 .times. H ) ##EQU00028##
[0583] A .DELTA.TG/SA of greater than 0.45 reduces graphite
crystallinity, thus resulting in a low discharge capacity, and
further impedes the smooth movement of Li ions, thus resulting in
degraded low-temperature output characteristics. A .DELTA.TG/SA of
less than 0.05 reduces the number of Li-ion insertion/extraction
sites, thus resulting in degraded low-temperature output
characteristics.
[0584] In this embodiment (e.g., but not limited to, Invention H),
a carbon material or a mixed carbon material is preferred.
[0585] In one aspect of one embodiment of the present invention,
the carbon material is preferably a carbon material for a
non-aqueous secondary battery capable of occluding and releasing
lithium ions, the carbon material being graphite particles
satisfying the relationship of inequality (1I).
100 .times. Y i + 0.26 .times. X i > .alpha. Inequality .times.
.times. ( 1 .times. I ) ##EQU00029##
[0586] (In the inequality, Y.sub.i is an oxygen functional group
dispersity given by equation (2I); X.sub.i is a volume-based
average particle diameter (d50) (.mu.m); and .alpha.=9.4)
Oxygen .times. .times. functional .times. .times. group .times.
.times. dispersity .times. .times. ( Y i ) = total .times. .times.
oxygen .times. .times. content .times. .times. ( mol .times.
.times. % ) .times. .times. determined .times. .times. by .times.
.times. elemental .times. .times. analysis .times. / .times.
surface .times. .times. oxygen .times. .times. content .times.
.times. ( O .times. / .times. C ) .times. .times. ( mol .times.
.times. % ) .times. .times. determined .times. .times. by .times.
.times. X .times. - .times. ray .times. .times. photoelectron
.times. .times. spectroscopy Equation .times. .times. ( 2 .times. I
) ##EQU00030##
[0587] Specifically, the carbon material for a non-aqueous
secondary battery according to one embodiment of the present
invention (e.g., but, not limited to, Invention I) preferably
satisfies the relationship of inequality (1I), which is a
relationship between oxygen functional group dispersity and
volume-based average particle diameter (d50)
100 .times. Y i + 0.26 .times. X i > .alpha. Inequality .times.
.times. ( 1 .times. I ) ##EQU00031##
[0588] (In the inequality, Y.sub.i is an oxygen functional group
dispersity given by equation (2I); X.sub.i is a volume-based
average particle diameter (d50) (.mu.m); and .alpha.=9.4)
Oxygen .times. .times. functional .times. .times. group .times.
.times. dispersity .times. .times. ( Y i ) = total .times. .times.
oxygen .times. .times. content .times. .times. ( mol .times.
.times. % ) .times. .times. determined .times. .times. by .times.
.times. elemental .times. .times. analysis .times. / .times.
surface .times. .times. oxygen .times. .times. content .times.
.times. ( O .times. / .times. C ) .times. .times. ( mol .times.
.times. % ) .times. .times. determined .times. .times. by .times.
.times. X .times. - .times. ray .times. .times. photoelectron
.times. .times. spectroscopy Equation .times. .times. ( 2 .times. I
) ##EQU00032##
[0589] The value .alpha. given by inequality (1I) of the carbon
material according to this embodiment (e.g., but not limited to,
Invention I) is 9.4, preferably 9.5, more preferably 9.6, still
more preferably 9.7, particularly preferably 9.8, most preferably
10.0. When the relationship represented by inequality (1I) is
unsatisfied, efficient Li-ion insertion/extraction cannot be
effected in the particles, which tends to result in degraded
low-temperature output characteristics and a reduced capacity.
Surface Functional Group Amount O/C Value (mol %)
[0590] For X-ray photoelectron spectroscopy (XPS), an X-ray
photoelectron spectroscope (e.g., ESCA, available from Ulvac-Phi,
Incorporated) is used. A measuring object (in this case, a graphite
material, i.e., the carbon material) is mounted on a sample stage
such that the surface of the object is fiat, and a multiplex
measurement is performed using a K.alpha. radiation of aluminum as
an X-ray source to measure spectra of C1s (280 to 300 eV) and O1s
(525 to 545 eV). Charge correction is performed with the C1s peak
top obtained set to 284.3 eV. Peak areas of the spectra of C1s and
O1s are determined and then multiplied by an apparatus sensitivity
to determine the surface atom concentrations of C and O. The O/C
ratio of the atom concentrations of O and C obtained (O atom
concentration/C atom concentration).times.100 is defined as the
surface functional group amount O/C value of the carbon
material.
[0591] The O/C value determined by XPS is preferably 0.01 or
greater, more preferably 0.1 or greater, still more preferably 0.3
or greater, particularly preferably 0.5 or greater, most preferably
0.7 or greater, and preferably 2 or less, more preferably 1.5 or
less, still more preferably 1.2 or less, particularly preferably 1
or less, most preferably 0.8 or less. A surface functional group
amount O/C value in this range tends to enhance the desolvation
reactivity of Li ions with an electrolyte solution solvent on the
surface of a negative electrode active material, thus leading to
improved fast charge-discharge characteristics, and reduce the
reactivity with an electrolyte solution, thus leading to improved
charge-discharge efficiency.
Total Oxygen Content (mol %)
[0592] For measuring oxygen/nitrogen/hydrogen contents, an
oxygen/nitrogen/hydrogen analyzer (TCH600 ONH determinator
available from LECO) is used. In an inert gas atmosphere impulse
furnace, 50 mg of the carbon material is melted and decomposed, and
the amounts of carbon monoxide and carbon dioxide in a discharged
carrier gas are measured using an infrared detector to determine
the total oxygen content (mol %) of the carbon material.
[0593] The total oxygen content (mol %), as determined by the
measurement of oxygen/nitrogen/hydrogen contents, is preferably
0.001 mol % or more, more preferably 0.01 mol % or more, still more
preferably 0.02 mol % or more, particularly preferably 0.03 mol %
or more, most preferably 0.04 mol % or more, and preferably 0.5 mol
% or less, more preferably 0.2 mol % or less, still more preferably
0.15 mol % or less, particularly preferably 0.1 mol % or less, most
preferably 0.08 mol % or less. A total oxygen content (mol %) in
this range tends to promote the desolvation reaction of Li ions
with an electrolyte solution solvent on the surface of a negative
electrode active material, thus leading to improved fast
charge-discharge characteristics, and reduce the reactivity with an
electrolyte solution, thus leading to improved charge-discharge
efficiency.
Y.sub.i: Oxygen Functional Group Dispersity
[0594] The oxygen functional group dispersity of the carbon
material is typically 0.01 or greater, preferably 0.04 or greater,
more preferably 0.06 or greater, still more preferably 0.07 or
greater, and typically 1 or less, preferably 0.5 or less, more
preferably 0.3 or less, still more preferably 0.2 or less.
[0595] An oxygen functional group dispersity in this range means
that oxygen functional groups are not maldistributed on the
particle surface and dispersed also in the particles. The presence
of oxygen functional groups at graphite crystal edge portions that
functions as Li-ion insertion/extraction sites suggests that the
carbon material having an oxygen functional group dispersity in
this range has a moderate number of Li-ion insertion/extraction
sites not only on but also in the particles. Thus, an oxygen
functional group dispersity in this range enables efficient Li-ion
insertion/extraction also in the particles and tends to provide a
high capacity and good low-temperature output characteristics.
[0596] In this embodiment (e.g., but not limited to, Invention I),
a carbon material or a mixed carbon material is preferred.
[0597] In one aspect of one embodiment of the present invention,
the carbon material for a non-aqueous secondary battery is a carbon
material for a non-aqueous secondary battery characterized in that
a large number of voids having fine structures are present in the
particles.
[0598] Specifically, the carbon material for a non-aqueous
secondary battery according to an embodiment of the present
invention (e.g., but not limited to, Inventions L.sup.1 to L.sup.3)
preferably comprises a carbon material made of granulated particles
satisfying (1L) and (2L) and further has a characteristic particle
cross section such that a box-counting dimension is determined from
an image of the particle cross section.
Carbon Material (Granulated Particles) Satisfying (1L) and (2L) in
Carbon Material for Non-Aqueous Secondary Battery
[0599] The granulated particles in the carbon material for a
non-aqueous secondary battery satisfies the following:
[0600] (1) Being made of a carbonaceous material; and
[0601] (2) Satisfying the relationship
|X.sub.1-X|X.sub.1.ltoreq.0.2, preferably .ltoreq.0.15, more
preferably .ltoreq.0.1, where X is a volume-based average particle
diameter determined by laser diffraction, and X.sub.1 is an
equivalent circular diameter determined from a cross-sectional SEA!
image.
[0602] If |X.sub.1-X|/X.sub.1 is too large, typical particles
cannot be selected, which may result in failure to express the
overall tendency.
[0603] The volume-based average particle diameter X is defined as a
volume-based median diameter determined by suspending 0.01 g of a
carbon material in 10 mL of a 0.2% by mass aqueous solution of a
polyoxyethylene sorbitan monolaurate surfactant (e.g., Tween 20
(registered trademark)), placing the suspension (a measurement
sample) in a commercially available laser diffraction/scattering
particle size distribution analyzer (e.g., LA-920 available from
HORIBA), irradiating the measurement sample with ultrasonic waves
of 28 kHz at a power of 60 W for 1 minute, and then performing a
measurement with the analyzer.
[0604] The equivalent circular diameter X.sub.1 determined from a
cross-sectional SEM image is expressed by the following formula
using a particle circumference L [.mu.m].
X 1 = L 2 .times. .pi. [ Mathematical .times. .times. 1 ]
##EQU00033##
[0605] The granulated particles in the carbon material for a
non-aqueous secondary battery satisfies the relationship
|R-R.sub.1|.ltoreq.0.1, preferably .ltoreq.0.08, more preferably
.ltoreq.0.06, where R is a roundness determined with a flow-type
particle image analyzer, and R.sub.1 is a roundness determined from
a cross-sectional SEM image.
[0606] If |R-R.sub.1| is too large, a particle boundary is not
defined correctly but overestimated, which may result in incorrect
analysis.
[0607] As the value of the roundness R determined with a flow-type
particle image analyzer is used a value determined, for example,
using a flow-type particle image analyzer (e.g., FPIA available
from Sysmex Industrial Corp.) by dispersing about 0.2 g of a sample
(carbon material for a non-aqueous secondary battery) in a 0.2% by
mass aqueous solution (approximately 50 mL) of a polyoxyethylene
(20) sorbitan monolaurate surfactant, irradiating the dispersion
with ultrasonic waves of 28 kHz at a power of 60 W for 1 minute,
and then measuring the roundness of particles with a diameter in
the range of 1.5 to 40 .mu.m with a detection range set to 0.6 to
400 .mu.m.
[0608] The roundness R.sub.1 determined from a cross-sectional SEM
image is calculated by the following formula using a particle area
S [.mu.m.sup.2] determined from a cross-sectional SEM image and a
circumference L [.mu.m].
R 1 = 4 .times. .pi. .times. .times. S ( L ) 2 [ Mathematical
.times. .times. 2 ] ##EQU00034##
[0609] The particle boundary may be defined by any method, and it
may be defined automatically or manually using commercially
available analysis software. It is preferable to approximate a
particle by a polygon, and in this case, an approximation by a
polygon with 15 or more sides is more preferred. This is because if
a polygon with less than 15 sides is used, a background portion may
be determined to be a part of the particle in approximating a
curve.
Acquisition of Particle Cross-Sectional Image
[0610] For the image of a particle cross section is used a
reflected electron image acquired at an acceleration voltage of 10
kV using a scanning electron microscope (SEM). An SEM observation
sample for acquiring a particle cross-sectional image may be
prepared by any method, and a particle cross-sectional image is
acquired using an SEM after a sample is prepared by cutting an
electrode plate containing the carbon material for a non-aqueous
secondary battery, a film coated with the carbon material for a
non-aqueous secondary battery, with a focused ion beam (FIB) or ion
milling to obtain a particle cross section.
[0611] The acceleration voltage in observing the cross section of
the carbon material for a non-aqueous secondary battery with a
scanning electron microscope (SEM) is 10 kV.
[0612] This acceleration voltage makes a difference between a
reflected electron SEM image and a secondary electron SEM image to
allow void regions and other regions of the carbon material for a
non-aqueous secondary battery to be easily distinguished. The
imaging magnification is typically 500.times. or more, more
preferably 1,000.times. or more, still more preferably 2,000.times.
or more, and typically 10,000 or less. An imaging magnification in
this range enables the acquisition of an entire image of one
particle of the carbon material for a non-aqueous secondary
battery. The resolution is 200 dpi (ppi) or more, preferably 256
dpi (ppi) or more. The number of picture elements suitable for
evaluation is at least 800 pixels.
[0613] Average Box-Counting Dimension Relative to Void Regions in
Cross-Sectional SEM Image
[0614] The carbon material for a non-aqueous secondary battery has
an average box-counting dimension relative to void regions of 1.55
or greater, preferably 1.60 or greater, more preferably 1.62 or
greater, and typically 1.80 or less, preferably 1.75 or less, more
preferably 1.70 or less, as calculated from images obtained by
randomly selecting 30 granulated particles satisfying (1L) and (2L)
above from a cross-sectional SEM image, dividing the
cross-sectional SEM image of each granulated particle into void
regions and non-void regions, and binarizing the image.
[0615] An excessively small average box-counting dimension relative
to void regions means that the amount of finer structure is small,
in which case excellent output characteristics, one of the effects
of the present invention, cannot be provided. An excessively large
average box-counting dimension increases the specific surface area
of the particles, leading to low initial efficiency.
[0616] The box-counting dimensions of the particles of the carbon
material for a non-aqueous secondary battery are determined taking
the following (a) to (d) into account.
[0617] (a) Definition and Calculation Method of Box-Counting
Dimension
[0618] Box-counting dimension is a method for estimating a fractal
dimension by observing a certain area split into certain sizes (box
sizes) to examine how much fractal patterns are contained (see, for
example, JP 2013-77702 A). Box-counting dimension is an indicator
of shape complexity, the degree of surface irregularity, and
others, and larger fractal dimensions indicate more complex
irregularities. The Box-counting dimension is defined below. The
fractal dimension is defined by the following formula, where
N.delta. (F) is the number of square boxes of side .delta.
necessary for covering a pattern F.
D = lim .delta. .fwdarw. 0 .times. N .delta. .function. ( F ) log
.times. .times. .delta. [ Mathematical .times. .times. 3 ]
##EQU00035##
[0619] In this embodiment (e.g., but not limited to, Invention
L.sup.1), a cross-sectional SEM image of a particle composed of
voids and carbon is split into grid areas (boxes) at regular
intervals .delta. (split into square subareas of side .delta.), and
the number of boxes containing voids is counted with varying values
of .delta.. Next, a double logarithmic graph is created with the
number of boxes counted plotted on the vertical axis and .delta. on
the horizontal axis, and a fractal dimension is determined from the
slope of the graph.
[0620] Specifically, in a cross-sectional SEM image of a particle
composed of voids and carbon, voids and other regions of the
particle are binarized. The binarization is performed in units of
pixels of the image. Analysis objects are portions representing
pixels of voids among the binarized regions. The region outside the
particle (outside the outline of the particle) requires value
conversion so as not to be regarded as a void. The image is split
into grid areas (boxes) having a specific pixel size. Although the
boxes may be arranged in any manner, they are preferably arranged
parallel to the major axis (the longest diameter passing through
the barycenter) of the particle. In the arrangement, the image is
split into boxes as shown in FIGS. 7 and 8. The number of split
boxes including at least one pixel representing a void is counted.
The same procedure is repeated with varying box sizes, and a double
logarithmic graph is created with the number of boxes counted
plotted on the vertical axis and the box size .delta. on the
horizontal axis. A linear approximation of this plot is performed,
and the slope of the line is multiplied by -1. The product obtained
is the fractal dimension according to the box-counting method. The
slope may be calculated by the least-squares method.
[0621] The fractal dimension is an indicator of the degree of
self-similarity, and in expressing a binarized image, it serves as
an indicator of the complexity and the fineness of a structure.
This means that in a binarized image having a more complicated
partial structure, the proportion of fine structure in a box tends
to increase, that is, the slope tends to be steeper with decreasing
box size, and the fineness of the partial structure and the amount
of such structure are expressed. In other words, the box-counting
dimension in the present invention is an indicator of the
complexity of a fine structure of voids and the amount of such
structure.
[0622] (b) Definition of Box Size
[0623] The image may be split into any box size, but based on the
maximum pixel of the image, it is preferably split into 10 parts or
more, more preferably 15 parts or more, particularly preferably 20
parts or more, and typically 50 parts or less, preferably 40 parts
or less, more preferably 30 parts or less, on a logarithmic graph.
A box size in this range reduces the possibility that differences
between picture elements occur and eliminates the need for a
high-resolution image.
[0624] (c) Method of Binarization
[0625] The binarization may be carried out by any method by which
intra-particle voids and carbon portions are clearly distinguished
from each other, as shown in FIG. 9. The binarization, when
performed on an 8-bit gray-scale image, such as an SEM image,
refers to dividing luminances into two and representing the two
divided images in two values (e.g., 0 and 255, in the case of
8-bit). The binarization may be carried out using any desired image
processing software. The division by setting a threshold can be
carried out using any algorithm, such as the mode method and the
Iterative Self-Organizing Data (ISOData) method, by which void
portions and carbon portions can be clearly distinguished from each
other.
[0626] The target image needs to be a binarizable image. The
binarizable image, in this case, refers to an image in which the
luminance of void portions and the luminance of carbon portions are
clearly distinguished from each other by a certain threshold. In
some images, the surface may be rough due to low processing
accuracy; the cross section may be facing, obliquely; or the
luminances of void portions and carbon portions may be close to
each other depending on the settings such as contrast and
brightness. Such images may show incorrect void distributions when
binarized and thus are preferably excluded from analysis objects.
For example, FIG. 10 is an image in which the surface of a graphite
portion in the middle has a rough pattern and a low luminance, and
fine voids have high luminances. When such an image is binarized
picking up fine parts, carbon portions are also expressed as voids;
by contrast, if a luminance at a carbon portion with no void is
used as a threshold, fine voids, which are actually voids, cannot
be displayed. Although such particles are preferably not selected,
the cross section of such particles may be typical, and thus it is
necessary not to analyze such an SEM image unsuitable for
binarization but to retake an image and adjust the brightness and
the contrast.
[0627] (d) Definition of Particle Boundary
[0628] The particle boundary may be established by any method by
which the boundary is clearly defined. For example, it may be
established by freehand or the approximation by a polygon. In
defining the boundary, it is necessary to establish the boundary
between the particle and other regions such that the region of
interest (ROI) representing the shape of the particle is completely
included. When the boundary is not a simple oval but has a
complicated shape, for example, the boundary may be divided into
any desired number of equally spaced sections to approximate the
particle region by a polygon. The boundary, however, is established
so as not to deviate from a roundness R determined with a flow-type
particle image analyzer. As used herein, "not deviate" means that a
degree of spheroidization R determined by a flow-type particle
image analyzer and a degree of spheroidization R.sub.1 determined
from a cross-sectional SEM image satisfy the relationship
|R-R.sub.1|.ltoreq.0.1. When an electrode coated with a binder
having poor conductivity is used, the boundary may be difficult to
determine under the measurement conditions in this embodiment. This
is probably a phenomenon that occurs due to the poor conductivity
of the binder when the side of the particle is visible in depth of
the cross section of the particle. In such a case, it is necessary
to take an image with a clear boundary at a lower acceleration
voltage to determine a boundary.
[0629] In one aspect of one embodiment of the present invention,
the carbon material for a non-aqueous secondary battery is a carbon
material for a non-aqueous secondary battery comprising uniformly
dispersed intra-particle pores.
[0630] Specifically, the carbon material for a non-aqueous
secondary battery according to an embodiment of the present
invention (e.g., but not limited to, Invention L.sup.2) comprises a
carbon material made of granulated particles satisfying (1L) and
(2L) above and further has a characteristic particle cross section
such that the void dispersity D of the present invention is
determined from an image of the particle cross section.
[0631] Void Dispersity D in Cross-Sectional SEM Image
[0632] The carbon material for a non-aqueous secondary battery
typically has an average dispersity D of 30 particles, as
determined by the following measurement method using 30 granulated
particles satisfying (1L) and (2L) above randomly selected from a
cross-sectional SEM image, of 60% or more, preferably 61% or more,
more preferably 62% or more, and typically 90% or less, preferably
85% or less, more preferably 80% or less.
[0633] Measurement Method
[0634] Using a cross-sectional SEM image, grid lines are drawn to
split the minor axis and the major axis of a target granulated
particle each into 20 parts. Using cells in the grid, the
granulated particle is compartmentalized as defined below. The
expectation E of void area of each compartment is calculated using
equation (A) below, and the dispersity D of the granulated particle
is calculated using equation (B) below.
[0635] The cross-sectional SEM image is a reflected electron image
acquired at an acceleration voltage of 10 kV.
[0636] How to Create Grid
[0637] Using a cross-sectional SEM image, grid lines are drawn to
split the minor axis and the major axis of a target granulated
particle each into 20 parts, as shown in FIG. 11. This image needs
to be parallel to the particle major axis and the image.
[0638] Definition of Compartment
[0639] The compartment is defined as a granulated particle portion
and/or a region where a void is present in the granulated particle
in each cell of the grid. The outside of the boundary of the
granulated particle is excluded from the compartment. For grid
cells that are divided by the particle boundary into two, as shown
in FIG. 12, the region including the particle is defined as a
compartment.
[0640] Definition of Expectation
[0641] For compartments defined by grid lines and the particle
boundary, the expectation E of a void area corresponding to each
compartment area is determined from equation (A).
Expectation .times. .times. E .times. [ .mu.m 2 ] .times. .times.
of .times. .times. void .times. .times. area .times. .times. in
.times. .times. target .times. .times. compartment = ( gross
.times. .times. area .times. [ .mu.m 2 ] .times. .times. of .times.
.times. internal .times. .times. voids .times. .times. of .times.
.times. one .times. .times. target .times. .times. granulated
.times. .times. particle ) .times. / .times. ( cross .times. -
.times. sectional .times. .times. area .times. [ .mu.m 2 ] .times.
.times. of .times. .times. one .times. .times. target .times.
.times. granulated .times. .times. particle ) .times. ( area
.times. [ .mu.m 2 ] .times. .times. of .times. .times. target
.times. .times. compartment ) Equation .times. .times. ( A )
##EQU00036##
[0642] The expectation E of a compartment defined by the particle
boundary is calculated to be smaller than the expectation E of a
grid cell according to the area of the compartment.
Definition of Dispersity D
[0643] The dispersity D, an indicator of the void dispersity in a
particle, is calculated by equation (B).
Dispersity .times. .times. D .times. .times. ( % ) = ( sum .times.
.times. total .times. [ .mu.m 2 ] .times. .times. of .times.
.times. areas .times. .times. of .times. .times. compartments
.times. .times. that .times. .times. satisfy .times. .times. (
gross .times. .times. area .times. [ .mu.m 2 ] .times. .times. of
.times. .times. voids .times. .times. in .times. .times. target
.times. .times. compartment ) .times. / .times. ( expectation
.times. .times. E .times. [ .mu.m 2 ] .times. .times. of .times.
.times. void .times. .times. area .times. .times. in .times.
.times. target .times. .times. compartment ) = 0.5 .times. .times.
or .times. .times. greater ) .times. / .times. ( sum .times.
.times. total .times. [ .mu.m 2 ] .times. .times. of .times.
.times. areas .times. .times. of .times. .times. all .times.
.times. the .times. .times. compartments .times. .times. of .times.
.times. one .times. .times. target .times. .times. granulated
.times. .times. particle ) .times. 100 Equation .times. .times. ( B
) ##EQU00037##
[0644] The dispersity D indicates how voids are dispersed
throughout the inside of a particle, excluding compartments having
only a small void area.
[0645] The equation (A) and the equation (B) of the carbon material
for a non-aqueous secondary battery are calculated taking the
following (a) to (d) into account.
[0646] (a) Method of Selecting Granulated Particles and Definition
of Major Axis and Minor Axis
[0647] The particle boundary may be established by any method by
which the boundary is clearly defined. For example, it nay be
established by freehand or the approximation by a polygon. In
defining the boundary, it is necessary to establish the boundary
between the particle and other regions such that the region of
interest (ROI) representing the shape of the particle is completely
included. When the boundary is not a simple oval but has a
complicated shape, for example, the boundary may be divided into
any desired number of equally spaced sections to approximate the
particle region by a polygon. The boundary, however, is established
so as not to deviate from a roundness R determined with a flow-type
particle image analyzer. As used herein, "not deviate" means that a
degree of spheroidization R determined by a flow-type particle
image analyzer and a degree of spheroidization R.sub.1 determined
from a cross-sectional SEM image satisfy the relationship
|R-R.sub.1|.ltoreq.0.1. When an electrode coated with a binder
having poor conductivity is used, the boundary may be difficult to
determine under the measurement conditions in this embodiment. This
is probably a phenomenon that occurs due to the poor conductivity
of the binder when the side of the particle is visible in depth of
the cross section of the particle. In such a case, it is necessary
to retake an image with a clear boundary at a lower acceleration
voltage to determine a boundary.
[0648] For one randomly selected granulated particle, the
barycenter (centroid) is defined. First, the particle defined by
the boundary is approximated by square cells. The size of each cell
is preferably, but not necessarily, 5 nm or less in actual size.
Two-dimensional coordinates are determined in the image. The
coordinates of the barycenter of each cell are defined. Assuming
that the weights of the cells are the same, the cells are numbered
from 1 to N. The following formula is used to determine the
coordinates of the barycenter of the granulated particle.
r G .fwdarw. = .SIGMA. 1 N .times. r i .fwdarw. N [ Mathematical
.times. .times. 4 ] ##EQU00038##
[0649] In the formula, r.sub.i represents the coordinates of an
i-th cell, and r.sub.G represents the coordinates of the
barycenter. The barycenter may be determined by operating any
desired image software, or by the following formula if the
barycenter of each divided mesh can be defined by any given
figure.
r G .fwdarw. = .SIGMA. 1 N .times. A i .times. r i .fwdarw. .SIGMA.
1 N .times. A i [ Mathematical .times. .times. 5 ] ##EQU00039##
[0650] In the formula, A.sub.i is the area of an i-th figure, and
r.sub.i is the barycentric (centroid) coordinates of the i-th
figure.
[0651] Next, the longest line segment among line segments passing
through the barycenter obtained. and bounded by the boundary fixed
as described above is defined as a major axis. The line segment
orthogonal to the major axis among line segments passing through
the barycenter and bounded by the boundary fixed as described above
is defined as a minor axis.
[0652] (b) Definition of Void Region and Non-Void Region and Method
of Calculating their Areas
[0653] The binarization may be carried out by any method by which
intra-particle voids and carbon portions are clearly distinguished
from each other, as shown in FIG. 9, and is preferably carried out
such that void regions and other carbon particle regions are
clearly distinguished from each other. The binarization, when
performed on an 8-bit gray-scale image, such as an SEM image,
refers to dividing luminances into two and representing the two
divided images in two values (e.g., 0 and 255, in the case of
8-bit). The binarization may be carried out using any desired image
processing software. The division by setting a threshold can be
carried out using any algorithm, such as the mode method and the
ISOData method, by which void portions and carbon portions can be
clearly distinguished from each other. The target image needs to be
a binarizable image. The binarizable image refers to an image in
which the luminance of void portions and the luminance of carbon
portions are clearly distinguished from each other by a certain
threshold. In some images, the surface may be rough due to low
processing accuracy; the cross section may be facing obliquely; or
the luminances of void portions and carbon portions may be close to
each other depending on the settings such as contrast and
brightness. Such images may show incorrect void distributions when
binarized and thus are preferably excluded from analysis objects.
For example, FIG. 10 is an image in which the surface of a graphite
portion in the middle has a rough pattern and a low luminance, and
fine voids have high luminances. When such an image is binarized
picking up fine parts, carbon portions are also expressed as voids;
by contrast, if a luminance at a carbon portion with no void is
used as a threshold, fine voids, which are actually voids, cannot
be displayed. Although such particles are preferably not selected,
the cross section of such particles may be typical, and thus it is
necessary not to analyze such an SEM image unsuitable for
binarization but to retake an image and adjust the brightness and
the contrast.
[0654] The areas of the void region and the non-void region in the
particle thus calculated are each calculated as an approximation in
a pixel unit and converted into an actual unit.
[0655] (c) Creation of Grid
[0656] In the binarized image is created cells that split the minor
axis and the major axis of the granulated particle each into 20
parts. As for the cell arrangement, the cells may be arranged such
that they are parallel to the major axis and the minor axis of the
granulated particle.
[0657] (d) Calculation of Expectation E and Dispersity D of Target
Compartment
[0658] For each of the 400 cells created by splitting the minor
axis and the major axis of the granulated particle each into 20
parts, the expectation E is calculated by equation (A) above. The
sum total of areas of compartments having an expectation E of 0.5
or greater is calculated, and the dispersity D is calculated by
equation (B) above.
[0659] For each of the 30 granulated particles selected, the
dispersity D is calculated, and the average dispersity D of the 30
particles is calculated.
[0660] In one aspect of one embodiment of the present invention,
the carbon material for a non-aqueous secondary battery is
preferably a carbon material for a non-aqueous secondary battery
comprising intra-particle voids the orientation of which and the
interval between which are controlled.
[0661] Specifically, the carbon material for a non-aqueous
secondary battery according to an embodiment of the present
invention (e.g., but not limited to, Invention L.sup.3) comprises a
carbon material made of granulated particles satisfying the
following (1L) and (2L) and further has a characteristic particle
cross section such that the ratio (Zave/X) of average inter-void
distance Z (Zave) of 30 particles to volume-based average particle
diameter X determined by laser diffraction of the present invention
is determined from an image of the particle cross section.
Zave/X
[0662] The carbon material for a non-aqueous secondary battery
according to this embodiment (e.g., but not limited to, Invention
L.sup.3) comprises granulated particles satisfying (1L) and (2L)
above and has an average inter-void distance Z (Zave) of 30
particles as defined below and a volume-based average particle
diameter X determined by laser diffraction in a ratio (Zave/X) of
typically 0.060 or less, preferably 0.055 or less, more preferably
0.050 or less, still more preferably 0.045 or less, and typically
0.001 or greater, preferably 0.010 or greater, more preferably
0.020 or greater, the 30 granulated particles satisfying (1L) and
(2L) above and being randomly selected from a cross-sectional SEM
image.
[0663] An excessively large Zave/X means that the distance between
the carbon material and voids constituting the granulated particle
is wide, which results in a low liquid retention in the
particle.
[0664] Definition of Average Inter-Void Distance Z (Zave) of 30
Particles
[0665] As shown in the left figure of FIG. 13, three lines are
drawn that are parallel to the minor axis of a target granulated
particle and split the major axis of the granulated particle into
four parts, and inter-void distances Z (.mu.m) of the granulated
particle on each line (see the right figure of FIG. 13) are each
measured. The average of 30 particles in total is calculated. This
is defined as the average inter-void distance Z (Zave) of 30
particles.
W/X
[0666] In this embodiment (e.g., but not limited to, invention
L.sup.3), the carbon material for a non-aqueous secondary battery
comprises granulated particles satisfying (1L) and (2L) above and
has a standard deviation (W) of void sizes Y of 30 particles as
defined below and a volume-based average particle diameter X
determined by laser diffraction in a ratio (W/X) of preferably
0.018 or less, more preferably 0.016 or less, still more preferably
0.014 or less, and typically 0.001 or greater, preferably 0.005 or
greater, more preferably 0.008 or greater, the 30 granulated
particles satisfying (1L) and (2L) above and being randomly
selected from a cross-sectional SEM image.
[0667] W/X is a quotient of a standard deviation of void sizes
divided by a particle size, and a larger value of W/X means that a
higher proportion of relatively large voids.
[0668] A W/X in the above range means relatively uniform void sizes
or a low proportion of large voids, meaning that the carbon
material has a fine void structure that allows an electrolyte
solution to uniformly permeate into the particles.
[0669] Definition of Standard Deviation (W) of Void Sizes Y (.mu.m)
of 30 Particles
[0670] As shown in the left figure of FIG. 13, three lines are
drawn that are parallel to the minor axis of a target granulated
particle and split the major axis of the granulated particle into
four parts, and void sizes Y (.mu.m) of the granulated particle on
each line (see the right figure of FIG. 13) are each measured. The
standard deviation of 30 particles in total is calculated. This is
defined as the standard deviation (W) of void sizes Y of 30
particles.
[0671] The standard deviation is determined by the following
formula, where Yave is the average of Y, and Ny is the number of
Y.
W = ( .SIGMA. .function. ( Y - Y ave ) 2 Ny ) 1 .times. / .times. 2
[ Mathematical .times. .times. 6 ] ##EQU00040##
[0672] Condition of Voids
[0673] Preferably, the granulated particles in the carbon material
for a non-aqueous secondary battery according to this embodiment
(e.g., but not limited to, Invention L.sup.3) have slit-like voids,
and the slit-like voids are arranged mainly in layers.
[0674] More specifically, among 30 granulated particles satisfying
(1L) and (2L) above randomly selected from a cross-sectional SEM
image, the proportion (by number) of particles having slit-like
voids arranged mainly in layers is more preferably 70% or more,
particularly preferably 80% or more, most preferably 90% or more.
Within this range, it can be said that most of all the particles
have voids having a slit-like and layered structure.
[0675] "Slit-like void" refers to a long and narrow void (with a
high aspect ratio) like a gap. The aspect ratio of the void is
preferably 10 or greater, more preferably 15 or greater. The aspect
ratio is a value obtained by dividing the major axis of the void by
the minor axis, that is, (major axis of void)/(minor axis of void).
The major axis and the minor axis of the void can be calculated by
the same method as in Selection of Granulated Particles and
Definition of Minor Axis described below.
[0676] "Voids in layers" means that major axes of voids in a
particle are arranged in parallel. If the angle between the major
axes of two voids is within .+-.30.degree., the two voids are
regarded as being in parallel.
[0677] The proportion of the area of voids in layers (the area of
voids in layers/the gross area of voids) in a granulated particle
is preferably 40% or more, more preferably 50% or more, still more
preferably 60% or more, and typically 100% or less, preferably 90%
or less. The proportion of the number of slit-like voids (the
number of slit-like voids/the total number of voids) is preferably
70% or more, more preferably 80% or more, still more preferably 90%
or more, and typically 100% or less, preferably 90% or less. If the
number and the area of slit-like voids are in these ranges, it can
be said that the particle has so many fine slit-like structures
that provide more reaction initiation surfaces of Li and sufficient
permeability of electrolyte solution.
[0678] The above-described Zave/X and W/X of the carbon material
for a non-aqueous secondary battery are calculated taking the
following (a) to (d) into account.
[0679] (a) Selection of Granulated Particles and Definition of
Minor Axis
[0680] In an SEM image acquired, 30 granulated particles satisfying
the above conditions (1L) and (2L) are randomly selected. In the
selection, particle boundaries are established along the outlines
of the granulated particles. The particle boundary may be
established by any method by which the boundary is clearly defined,
that is, the boundary between the particle and other regions is
established such that the region of interest (ROI) representing the
shape of the particle is completely included. For example, it may
be established by freehand or the approximation by a polygon. When
the boundary is not linear-like but has a complicated shape, for
example, the boundary may be divided into any desired number of
equally spaced sections to approximate the particle region by a
polygon. The boundary is established so as not to deviate from a
roundness R determined with a flow-type particle image analyzer. As
used herein, "not deviate" means that a degree of spheroidization R
determined by a flow-type particle image analyzer and a degree of
spheroidization R.sub.1 determined from a cross-sectional SEM image
satisfy the relationship |R-R.sub.1|.ltoreq.0.1.
[0681] For one randomly selected granulated particle, the
barycenter (centroid) is defined. First, the particle defined by
the boundary is approximated by square cells. The size of each cell
is preferably, but not necessarily, 5 nm or less in actual size.
Two-dimensional coordinates are determined in the image. The
coordinates of the barycenter of each cell are defined. Assuming
that the weights of the cells are the same, the cells are numbered
from 1 to N. The following formula is used to determine the
coordinates of the barycenter of the granulated particle.
r G .fwdarw. = .SIGMA. 1 N .times. r i .fwdarw. N [ Mathematical
.times. .times. 7 ] ##EQU00041##
[0682] In the formula, r.sub.i represents the coordinates of an
i-th cell, and r.sub.G represents the coordinates of the
barycenter. The barycenter may be determined by operating any
desired image software, or by the following formula if the
barycenter of each divided mesh can be defined by any given
figure.
r G .fwdarw. = .SIGMA. 1 N .times. A i .times. r i .fwdarw. .SIGMA.
1 N .times. A i [ Mathematical .times. .times. 8 ] ##EQU00042##
[0683] In the formula, A.sub.i is the area of an i-th figure, and
r.sub.i is the barycentric (centroid) coordinates of the i-th
figure.
[0684] Next, the longest line segment among line segments passing
through the barycenter obtained and bounded by the boundary fixed
as described above is defined as a major axis. The line segment
orthogonal to the major axis among line segments passing through
the barycenter and bounded by the boundary fixed as described above
is defined as a minor axis.
[0685] (b) Definition and Calculation Method of Intra-Particle
Voids
[0686] If necessary, binarization may be performed such that void
regions and other carbon particle regions are clearly distinguished
from each other. As shown in FIG. 9, the binarization may be
carried out by any method by which intra-particle voids and carbon
portions are clearly distinguished from each other. It is supposed
that the image to be processed is an 8-bit gray-scale image, the
luminance of one picture element (1 Pixel) of which is expressed by
a natural number from 0 to 255. The binarization refers dividing
luminances into two and representing the two divided images in two
values (e.g., 0 and 255 in this case). The binarization may be
carried out using any desired image processing software. The
division by setting a threshold can be carried out using any
algorithm, such as the mode method and the ISOData method, by which
void portions and carbon portions can be clearly distinguished from
each other. The target image needs to be a binarizable image. The
binarizable image, in this case, refers to an image in which the
luminance of void portions and the luminance of carbon portions are
clearly distinguished from each other by a certain threshold. In
some images, the surface may be rough due to low processing
accuracy the cross section may be facing obliquely; or the
luminances of void portions and carbon portions may be close to
each other depending on the settings such as contrast and
brightness. Such images may show incorrect void distributions when
binarized and thus are preferably excluded from analysis objects.
For example, FIG. 10 is an image in which the surface of a graphite
portion in the middle has a rough pattern and a low luminance, and
fine voids have high luminances. When such an image is binarized
picking up fine parts, carbon portions are also expressed as voids;
by contrast, if a luminance at a carbon portion with no void is
used as a threshold, fine voids, which are actually voids, cannot
be displayed. Although such particles are preferably not selected,
the cross section of such particles may be typical, and thus it is
necessary not to analyze such an SEM image unsuitable for
binarization but to retake an image and adjust the brightness and
the contrast.
[0687] (c) Voids on Line of Granulated Particle
[0688] "Voids in a granulated particle intersecting the minor axis
of the granulated particle" refers to voids on three lines that are
parallel to the minor axis of the granulated particle and split the
major axis of the granulated particle into four parts (see FIG.
13). Picture elements intersecting lines translated from the three
lines parallel to the minor axis of the granulated particle in the
major axis direction by .+-.0.5 pixel are regarded as voids on the
minor axis.
[0689] (d) Average Interval (Zave) Between Voids and Standard
Deviation (W) of Void Sizes
[0690] The interval between voids (the distance between a void and
a void) in one randomly selected granulated particle is determined
on the above-described three lines parallel to the minor axis of
the granulated particle (see FIG. 13). In one granulated particle,
distances Z between voids on the three lines parallel to the minor
axis are each measured. This measurement is made on 30 particles.
Its average value is defined as the average inter-void distance Z
(Zave) of 30 particles.
[0691] Furthermore, sizes Y of voids on the three lines (see FIG.
13) are each measured. This measurement is made on 30 particles.
Its standard deviation is defined as the standard deviation (W) of
void sizes Y of 30 particles.
[0692] In this embodiment (e.g., but not limited to, Invention
L.sup.3), voids in the granulated particle are preferably arranged,
mainly, relatively parallel to the major axis of the granulated
particle.
Physical Properties of Composite Carbon Material for Non-Aqueous
Secondary Battery
[0693] A description will be given below of preferred physical
properties of the composite carbon material. Physical properties
not described in this section are preferably within the ranges of
the physical properties of the carbon material for a non-aqueous
secondary battery described above.
Volume-Based Average Particle Diameter (Average Particle Diameter
d50)
[0694] The volume-based average particle diameter (also referred to
as "average particle diameter d50") of the composite carbon
material is preferably 1 .mu.m or more, more preferably 5 .mu.m or
more, still more preferably 8 .mu.m or more, particularly
preferably 10 .mu.m or more, most preferably 11 .mu.m or more. The
average particle diameter d50 is preferably 50 .mu.m or less, more
preferably 40 .mu.m or less, still more preferably 35 .mu.m or
less, even more preferably 31 .mu.m or less, particularly
preferably 30 .mu.m or less, most preferably 25 .mu.m or less. An
average particle diameter in this range tends to prevent the
increase in irreversible capacity and prevent streaks that can
occur during a slurry application, thus leading to no reduction in
productivity. In other words, an excessively small average particle
diameter d50 tends to cause an increase in irreversible capacity
and a loss in initial battery capacity of a non-aqueous secondary
battery comprising the composite carbon material, and an
excessively large average particle diameter d50 can cause process
defects such as streaks that occur in a slurry application,
degraded high-current-density charge-discharge characteristics, and
degraded low-temperature output characteristics.
[0695] The average particle diameter d50 is defined as a
volume-based median diameter determined by suspending 0.01 g of a
composite carbon material in 10 mL of a 0.2% by mass aqueous
solution of a polyoxyethylene sorbitan monolaurate surfactant
(e.g., Tween 20 (registered trademark)), placing the suspension (a
measurement sample) in a commercially available laser
diffraction/scattering particle size distribution analyzer (e.g.,
LA-920 available from HORIBA), irradiating the measurement sample
with ultrasonic waves of 28 kHz at a power of 60 W for 1 minute,
and then performing a measurement with the analyzer.
Tap Density
[0696] The tap density of the composite carbon material is
typically in the range of 0.6 g/cm.sup.3 or more, preferably 0.70
g/cm.sup.3 or more, more preferably 0.75 g/cm.sup.3 or more, still
more preferably 0.8 g/cm.sup.3 or more, even more preferably 0.85
g/cm.sup.3 or more, particularly preferably 0.88 g/cm.sup.3 or
more, more particularly preferably 0.9 g/cm.sup.3 or more, most
preferably 0.93 g/cm.sup.3 or more, and typically 1.5 g/cm.sup.3 or
less, preferably 1.3 g/cm.sup.3 or less, more preferably 1.2
g/cm.sup.3 or less, still more preferably 1.1 g/cm.sup.3 or
less.
[0697] A tap density in this range prevents streaks that can occur
during the formation of an electrode plate, thus leading to
improved productivity and excellent fast charge-discharge
characteristics. In addition, such a tap density tends to inhibit
the increase in intraparticle carbon density, thus providing good
rolling properties and making it easy to form a high-density
negative electrode sheet.
[0698] The tap density is defined as a density calculated from a
volume and a mass of a sample. The volume is determined as follows:
using a powder density meter, the composite carbon material
particles are dropped through a sieve with openings of 300 .mu.m
into a cylindrical tap cell with a diameter of 1.6 cm and a volume
capacity of 20 cm.sup.3 to fill up the cell; a tap with a stroke
length of 10 mm is given 1,000 times; and the volume at this time
is measured.
Roundness
[0699] The roundness of the composite carbon material is 0.88 or
greater, preferably 0.90 or greater, more preferably 0.91 or
greater. The roundness is preferably 1 or less, more preferably
0.98 or less, still more preferably 0.97 or less. A roundness in
this range tends to inhibit the degradation of high-current-density
charge-discharge characteristics of non-aqueous secondary
batteries. The roundness is defined by the following equation, and
a theoretically perfect sphere has a roundness of 1.
[0700] A roundness in the above range tends to decrease the degree
of flection of Li-ion diffusivity to smoothen the movement of
electrolyte solution in intra-particle voids and enable moderate
contact between the composite particles, thus providing good fast
charge-discharge characteristics and cycle characteristics.
Roundness = ( perimeter .times. .times. of .times. .times.
equivalent .times. .times. circle .times. .times. having .times.
.times. the .times. .times. same .times. .times. area .times.
.times. as .times. .times. projected .times. .times. particle
.times. .times. shape ) .times. / .times. ( actual .times. .times.
perimeter .times. .times. of .times. .times. projected .times.
.times. particle .times. .times. shape ) ##EQU00043##
[0701] As the value of the roundness is used a value determined,
for example, using a flow-type particle image analyzer (e.g., FPIA
available from Sysmex Industrial Corp.) by dispersing about 0.2 g
of a sample (composite particles) in a 0.2% by mass aqueous
solution (approximately 50 mL) of a polyoxyethylene (20) sorbitan
monolaurate surfactant, irradiating the dispersion with ultrasonic
waves of 28 kHz at a power of 60 W for 1 minute, and then measuring
the roundness of particles with a diameter in the range of 1.5 to
40 .mu.m with a detection range set to 0.6 to 400 .mu.m.
X-Ray Parameter
[0702] The d-value (interplanar spacing) of lattice planes ((002)
planes) of the composite carbon material, as determined by X-ray
diffractometry in accordance with the method of the Japan Society
for Promotion of Scientific Research, is preferably 0.335 nm to
less than 0.340 nm. The d-value is more preferably 0.339 nm or
less, still more preferably 0.337 nm or less. A d.sub.002-value in
this range tends to increase the crystallinity of the graphite,
thus inhibiting the increase in initial irreversible capacity. The
theoretical value of graphite is 0.335 nm.
[0703] The crystallite size (Lc) of the composite particles, as
determined by X-ray diffractometry in accordance with the method of
the Japan Society for Promotion of Scientific Research, is
preferably in the range of 90 nm or more, more preferably 100 nm or
more. A crystallite size in this range provides particles having
not too low crystallinity, thus providing a non-aqueous secondary
battery the reversible capacity of which is less likely to
decrease.
Ash Content
[0704] The ash content of the composite carbon material is
preferably 1% by mass or less, more preferably 0.5% by mass or
less, still more preferably 0.1% by mass or less, based on the
total mass of the composite carbon material. The ash content is
preferably at least 1 ppm.
[0705] An ash content in this range can provide a non-aqueous
secondary battery that undergoes only negligible degradation of
battery performance due to the reaction between composite particles
and electrolyte solution during charging and discharging. In
addition, such an ash content does not require much time or energy
to produce a carbon material and eliminates the need for equipment
for preventing contamination, thus reducing the increase in
cost.
BET Specific Surface Area (SA)
[0706] The specific surface area (SA) of the composite carbon
material, as determined by BET method, is preferably 1 m.sup.2/g or
more, more preferably 2 m.sup.2/g or more, still more preferably 3
m.sup.2/g or more, particularly preferably 4 m.sup.2/g or more, and
preferably 30 m.sup.2/g or less, more preferably 20 m.sup.2/g or
less, still more preferably 17 m.sup.2/g or less, particularly
preferably 15 m.sup.2/g or less, most preferably 12 m.sup.2/g or
less.
[0707] A specific surface area in this range tends to sufficiently
secure sites where Li enters and exits, thus providing excellent
fast charge-discharge characteristics and output characteristics,
and tends to moderately control the activity of the composite
carbon material, an active material, against electrolyte solution,
thus inhibiting the increase in initial irreversible capacity, as a
result of which a high-capacity battery can be produced.
[0708] Furthermore, such a specific surface area can inhibit the
increase in the reactivity of a negative electrode formed using the
composite carbon material with an electrolyte solution to reduce
gas generation, thus providing a preferred non-aqueous secondary
battery.
[0709] The BET specific surface area is defined as a value
determined as follows: using a surface area meter (e.g., a Gemini
2360 specific surface area analyzer available from Shimadzu
Corporation), a composite particle sample is preliminarily vacuum
dried under a nitrogen stream at 100.degree. C. for 3 hours and
then cooled to liquid nitrogen temperature, and using a
nitrogen-helium mixed gas precisely regulated so as to have a
nitrogen pressure of 0.3 relative to atmospheric pressure, a BET
specific surface area is measured by a nitrogen adsorption BET
multipoint method according to a flowing gas method.
True Density
[0710] The true density of the composite carbon material is
preferably 1.9 g/cm.sup.3 or more, more preferably 2 g/cm.sup.3 or
more, still more preferably 2.1 g/cm.sup.3 or more, particularly
preferably 2.2 g/cm.sup.3 or more, and up to 2.26 g/cm.sup.3. The
upper limit is the theoretical value of graphite. A true density in
this range tends to avoid too low carbon crystallinity, thus
inhibiting the increase in initial irreversible capacity of
non-aqueous secondary batteries.
Aspect Ratio
[0711] The aspect ratio of the composite carbon material in powder
form is theoretically 1 or greater, preferably 1.1 or greater, more
preferably 1.2 or greater. The aspect ratio is preferably 10 or
less, more preferably 8 or less, still more preferably 5 or
less.
[0712] An aspect ratio in this range tends to prevent streaks of a
slurry (a material for forming a negative electrode) containing the
composite particles from occurring during the formation of an
electrode plate so as to provide a uniform coated surface, thus
avoiding degraded high-current-density charge-discharge
characteristics of non-aqueous secondary batteries.
[0713] The aspect ratio is expressed as A/B, where A is the longest
diameter of a composite particle observed in a three-dimensional
manner, and B is the shortest diameter among the diameters
orthogonal to the longest diameter. The observation of the
composite particle is carried out under a scanning electron
microscope capable of magnifying observation. Fifty composite
particles immobilized on the surface of a metal having a thickness
of 50 microns or less are randomly selected. For each of the
particles, A and B are determined while a stage on which the
samples are immobilized is rotated and tilted, and the average
value of A/B is calculated.
Raman R Value
[0714] The Raman R value of the composite carbon material is
preferably 0.01 or greater, more preferably 0.1 or greater, still
more preferably 0.15 or greater, particularly preferably 0.2 or
greater. The Raman R value is typically 1 or less, preferably 0.6
or less, more preferably 0.5 or less, still more preferably 0.4 or
less.
[0715] The Raman R value is defined as an intensity ratio
(I.sub.B/I.sub.A) in a Raman spectrum obtained by Raman
spectroscopy, where I.sub.A is an intensity of peak P.sub.A near
1,580 cm.sup.-1, and I.sub.B is an intensity of peak P.sub.B near
1,360 cm.sup.-1.
[0716] As used herein, "near 1,580 cm.sup.-1" refers to a range of
1,580 to 1,620 cm.sup.-1, and "near 1,360 cm.sup.-1" a range of
1,350 to 1,370 cm.sup.-1.
[0717] A Raman R value in this range tends to reduce the
possibility that the crystallinity of the surface of the composite
carbon material increases and that crystals, when the density is
increased, are oriented in the direction parallel to a negative
electrode plate, thus avoiding degraded load characteristics.
Furthermore, such a Raman R value tends to reduce the possibility
that crystals on the particle surface of the composite carbon
material are disordered and inhibit the increase in the reactivity
of a negative electrode with an electrolyte solution, thus avoiding
reduced charge-discharge efficiency and increased gas generation of
non-aqueous secondary batteries.
[0718] The Raman spectrum described above can be measured using a
Raman spectroscope. Specifically, a sample is loaded by
gravity-dropping target particles into a measuring cell, and the
measuring cell is irradiated with an argon-ion laser beam while
being rotated in a plane perpendicular to the laser beam. The
measurement conditions are as follows:
[0719] Wavelength of argon-ion laser beam: 514.5 nm
[0720] Laser power on sample: 25 mW
[0721] Resolution: 4 cm.sup.-1
[0722] Measurement range: 1,100 cm.sup.-1 to 1,730 cm.sup.-1
[0723] Measurement of peak intensity, measurement of peak
half-width: background processing, smoothing processing
(convolution by simple average, 5 points)
Mode Pore Diameter (PD) in Pore Diameter Range of 0.01 .mu.m to 1
.mu.m
[0724] The mode pore diameter (PD) in a pore diameter range of 0.01
.mu.m to 1 .mu.m of the composite carbon material is a value
determined by mercury intrusion (mercury porosimetry) and typically
0.01 .mu.m or more, preferably 0.03 .mu.m or more, more preferably
0.05 .mu.m or more, still more preferably 0.06 .mu.m or more,
particularly preferably 0.07 .mu.m or more, and typically 1 .mu.m
or less, preferably 0.65 .mu.m or less, more preferably 0.5 .mu.m
or less, still more preferably 0.4 .mu.m or less, even more
preferably 0.3 .mu.m or less, particularly preferably 0.2 .mu.m or
less, most preferably 0.1 .mu.m or less.
[0725] A mode pore diameter (PD) in a pore diameter range of 0.01
.mu.m to 1 .mu.m outside this range tends to prevent an electrolyte
solution from being efficiently distributed into intra-particle
voids and prevent the efficient use of Li-ion insertion/extraction
sites in the particles, thus resulting in degraded low-temperature
output characteristics and cycle characteristics.
Cumulative Pore Volume at Pore Diameters in Range of 0.01 .mu.m to
1 .mu.m
[0726] The cumulative pore volume at pore diameters in a range of
0.01 .mu.m to 1 .mu.m of the composite carbon material is a value
determined by mercury intrusion (mercury porosimetry) and, even
when pressure is applied, typically 0.07 mL/g or more, preferably
0.08 mL/g or more, more preferably 0.09 mL/g or more, most
preferably 0.10 mL/g or more, and preferably 0.3 mL/g or less, more
preferably 0.25 mL/g or less, still more preferably 0.2 mL/g or
less, particularly preferably 0.18 mL/g or less.
[0727] An excessively small cumulative pore volume at pore
diameters in a range of 0.01 .mu.m to 1 .mu.m tends to prevent an
electrolyte solution from permeating into the particles and prevent
the efficient use of Li-ion insertion/extraction sites in the
particles. This impedes smooth insertion/extraction of lithium ions
in fast charging and discharging and results in degraded
low-temperature output characteristics. A cumulative pore volume
within the above range tends to allow an electrolyte solution to be
smoothly and efficiently distributed into the particles, thus
enabling the effective and efficient use of Li-ion
insertion/extraction sites in the particles as well as on the
periphery of the particles during charging and discharging and
providing good low-temperature output characteristics.
[0728] Half Width at Half Maximum of Pore Distribution (log
(nm))
[0729] The half width at half maximum of pore distribution (log
(nm)) of the composite carbon material refers to a half width at
half maximum at a micropore side of a peak in a pore diameter range
of 0.01 .mu.m to 1 .mu.m in a pore distribution (nm), as determined
by mercury intrusion (mercury porosimetry), with a horizontal axis
expressed in common logarithm (log (nm)).
[0730] (In the case where the composite carbon material has a d50
of 13 .mu.m or more)
[0731] The half width at half maximum of pore distribution (log
(nm)) of the composite carbon material having a d50 of 13 .mu.m or
more is preferably 0.3 or greater, more preferably 0.35 or greater,
still more preferably 0.4 or greater, particularly preferably 0.45
or greater, preferably 10 or less, more preferably 5 or less, still
more preferably 3 or less, particularly preferably 1 or less.
[0732] (In the case where the composite carbon material has a d50
of less than 13 .mu.m)
[0733] When the d50 of the composite carbon material is less than
13 .mu.m, its half width at half maximum of pore distribution (log
(nm)) is preferably 0.01 or greater, more preferably 0.05 or
greater, still more preferably 0.1 or greater, and preferably 0.33
or less, more preferably 0.3 or less, still more preferably 0.25 or
less, particularly preferably 0.23 or less.
[0734] When the half width at half maximum of pore distribution
(log (nm)) is in this range, intra-particle voids in a pore
diameter range of 0.01 .mu.m to 1 .mu.m tend to be formed to have a
finer structure and thus allow an electrolyte solution to be
smoothly and efficiently distributed into the particles. This
enables the effective and efficient use of Li-ion
insertion/extraction sites in the particles as well as on the
periphery of the particles during charging and discharging, thus
providing good low-temperature output characteristics and cycle
characteristics.
Total Pore Volume
[0735] The total pore volume of the composite carbon material is a
value determined by mercury intrusion (mercury porosimetry) and
preferably 0.1 mL/g or more, more preferably 0.3 mL/g or more,
still more preferably 0.5 mL/g or more, particularly preferably 0.6
mL/g or more, most preferably 0.7 mL/g or more, and preferably 10
mL/g or less, more preferably 5 mL/g or less, still more preferably
2 mL/g or less, particularly preferably 1 mL/g or less.
[0736] A total pore volume in this range eliminates the need for
using an excess amount of binder in forming an electrode plate and
facilitates the diffusion of a thickener and a binder in forming an
electrode plate.
[0737] As an apparatus for the mercury porosimetry, a mercury
porosimeter (Autopore 9520 available from Micromeritics Corp.) can
be used. A sample (carbon material) is weighed to around 0.2 g and
placed in a powder cell. The cell is sealed, and a pretreatment is
carried out by degassing the cell at room temperature under vacuum
(50 .mu.mHg or lower) for 10 minutes.
[0738] Subsequently, mercury is introduced into the cell under a
reduced pressure of 4 psia (approximately 28 kPa). The pressure is
increased stepwise from 4 psia (approximately 28 kPa) to 40,000
psia (approximately 280 MPa) and then reduced to 25 psia
(approximately 170 kPa).
[0739] The number of steps in the pressure increase is at least 80.
In each step, the amount of mercury intrusion is measured after an
equilibration time of 10 seconds. From the mercury intrusion curve
thus obtained, a pore distribution is calculated using the Washburn
equation.
[0740] The calculation is made assuming that the surface tension
(.gamma.) of mercury is 485 dyne/cm, and the contact angle (.psi.)
is 140.degree.. The average pore diameter is defined as a pore
diameter at a cumulative pore volume of 50%.
Ratio (PD/d50 (%)) of Mode Pore Diameter (PD) in Pore Diameter
Range of 0.01 .mu.m to 1 .mu.m to Volume-Based Average Particle
Diameter (d50)
[0741] The ratio (PD/d50) of mode pore diameter (PD) in a pore
diameter range of 0.01 .mu.m to 1 .mu.m to volume-based average
particle diameter (d50) of the composite carbon material is
expressed by equation (1A) and typically 1.8 or less, preferably
1.80 or less, more preferably 1.00 or less, still more preferably
0.90 or less, particularly preferably 0.80 or less, most preferably
0.70 or less, and typically 0.01 or greater, preferably 0.10 or
greater, more preferably 0.20 or greater.
PD .times. / .times. d .times. .times. 50 .times. .times. ( % ) =
mode .times. .times. pore .times. .times. diameter .times. .times.
( PD ) .times. .times. in .times. .times. a .times. .times. pore
.times. .times. diameter .times. .times. range .times. .times. of
.times. .times. 0.01 .times. .times. .mu.m .times. .times. to
.times. .times. 1 .times. .times. .mu.m .times. .times. in .times.
.times. a .times. .times. pore .times. .times. distribution .times.
.times. determined .times. .times. by .times. .times. mercury
.times. .times. intrusion .times. / .times. volume .times. -
.times. based .times. .times. average .times. .times. particle
.times. .times. diameter .times. .times. ( d .times. .times. 50 )
.times. 100 Equation .times. .times. ( 1 .times. A )
##EQU00044##
[0742] A mode pore diameter (PD) in a pore diameter range of 0.01
.mu.m to 1 .mu.m outside this range tends to prevent an electrolyte
solution from being efficiently distributed into intra-particle
voids and prevent the efficient use of Li-ion insertion/extraction
sites in the particles, thus resulting in degraded low-temperature
output characteristics and cycle characteristics.
[0743] In one aspect of the composite carbon material according to
one embodiment of the present invention, the relationship of
inequality (1D) is satisfied.
Inequality .times. .times. ( 1 .times. D ) .times. ##EQU00045## 10
.times. Y d + 0.26 .times. X d .gtoreq. .alpha. ( 1 .times. D )
##EQU00045.2##
[0744] (Y.sub.d=tap density (g/cm.sup.3), X.sub.d=specific surface
area (SA) (m.sup.2/g) of carbon material determined by BET method,
.alpha.=12.60)
[0745] In the composite carbon material according to this
embodiment (e.g., but not limited to, Invention D), a given by
inequality (1D) is 12.60 or greater, preferably 12.65, more
preferably 12.70, more preferably 12.80, particularly preferably
13.00.
[0746] If the relationship represented by inequality (1D) is not
satisfied, the balance between usable regions in Li-ion
insertion/extraction sites in the particles and particle-filling
properties tends to be poor, thus resulting in degraded
low-temperature output characteristics and a reduced capacity.
[0747] The tap density of the composite carbon material according
to this embodiment is preferably 1.00 g/cm.sup.3 or more, more
preferably 1.05 g/cm.sup.3 or more, still more preferably 1.10
g/cm.sup.3 or more, particularly preferably 1.12 g/cm.sup.3 or
more, most preferably 1.14 g/cm.sup.3 or more, and preferably 1.40
g/cm.sup.3 or less, more preferably 1.35 g/cm.sup.3 or less, still
more preferably 1.30 g/cm.sup.3 or less, particularly preferably
1.25 g/cm.sup.3 or less.
[0748] A tap density in this range provides sufficient filling
properties, thus increasing capacity. In addition, such a tap
density tends to inhibit the increase in intraparticle carbon
density, thus providing good rolling properties and making it easy
to form a high-density negative electrode sheet.
Specific Surface Area (SA) Determined by BET Method
[0749] The specific surface area (SA) of the carbon material
according to this embodiment (e.g., but not limited to, Invention
D), as determined by BET method, is preferably 2 m.sup.2/g or more,
more preferably 2.5 m.sup.2/g or more, still more preferably 3
m.sup.2/g or more, particularly preferably 4 m.sup.2/g or more, and
preferably 30 m.sup.2/g or less, more preferably 20 m.sup.2/g or
less, still more preferably 17 m.sup.2/g or less, particularly
preferably 15 m.sup.2/g or less.
[0750] A specific surface area in this range tends to sufficiently
secure sites where Li enters and exits, thus providing excellent
input-output characteristics, and tends to moderately control the
activity of an active material against electrolyte solution, thus
inhibiting the increase in initial irreversible capacity, as a
result of which a high-capacity battery can be produced.
[0751] In this embodiment, the composite carbon material is
produced by coating irregularities of the surface of the carbon
material to have reduced dibutyl phthalate (DBP) absorption and
thus, when processed into a coating material in forming an
electrode, can have a low viscosity, leading to improved coating
properties.
[0752] "Coated" in this embodiment refers to a state in which at
least part or all of the surface of the carbon material is coated
or deposited with a carbonaceous material.
[0753] In this embodiment (e.g., but not limited to, Invention D),
the crystallite size (Lc) of the carbon material, as determined by
X-ray diffractometry in accordance with the method of the Japan
Society for Promotion of Scientific Research, is typically in the
range of 30 nm or more, preferably 50 nm or more, more preferably
100 nm or more, still more preferably 500 nm or more, particularly
preferably 1,000 nm or more. A crystallite size in this range
provides particles having not too low crystallinity, thus providing
a non-aqueous secondary battery the reversible capacity of which is
less likely to decrease. The lower limit of Lc is the theoretical
value of graphite.
[0754] In one aspect of the composite carbon material according to
one embodiment of the present invention, the true density and the
specific surface area (SA) determined by BET method preferably
satisfy a particular relationship.
[0755] Specifically, the composite carbon material according to an
embodiment of the present invention (e.g., but not limited to,
Invention E) preferably satisfies the relationship of inequality
(1E).
Inequality .times. .times. ( 1 .times. E ) .times. ##EQU00046## Y e
- 0.01 .times. X e .ltoreq. .alpha. ( 1 .times. E )
##EQU00046.2##
[0756] (Y.sub.e=true density (g/cm.sup.3), X.sub.e=specific surface
area (SA) (m.sup.2/g) of carbon material determined by BET method,
.alpha.=2.20)
[0757] In the carbon material, .alpha. given by inequality (1E) is
2.20, preferably 2.195, more preferably 2.19, still more preferably
2.16.
[0758] If the relationship represented by inequality (1E) is not
satisfied, the balance between usable regions in Li-ion
insertion/extraction sites in the particles and a carbonaceous
material having such crystallinity that facilitates Li-ion
insertion/extraction tends to be poor, thus resulting in degraded
low-temperature output characteristics.
[0759] In this embodiment (e.g., but not limited to, Invention E),
the true density of the composite carbon material is preferably
2.15 g/cm.sup.3 or more, more preferably 2.16 g/cm.sup.3 or more,
still more preferably 2.17 g/cm.sup.3 or more, particularly
preferably 2.18 g/cm.sup.3 or more, most preferably 2.19 g/cm.sup.3
or more, and preferably 2.26 g/cm.sup.3 or less, more preferably
2.25 g/cm.sup.3 or less.
[0760] A true density in this range provides a moderate amount of
low-crystallinity structure, which facilitates Li-ion
insertion/extraction, thus providing good input-output
characteristics.
Specific Surface Area (SA) Determined by BET Method
[0761] The specific surface area (SA) of the composite carbon
material according to this embodiment (e.g., but not limited to,
Invention E), as determined by BET method, is preferably 2
m.sup.2/g or more, more preferably 2.5 m.sup.2/g or more, still
more preferably 3 m.sup.2/g or more, particularly preferably 4
m.sup.2/g or more, and preferably 30 m.sup.2/g or less, more
preferably 20 m.sup.2/g or less, still more preferably 17 m.sup.2/g
or less, particularly preferably 15 m.sup.2/g or less. A specific
surface area in this range tends to sufficiently secure sites where
Li enters and exits, thus providing excellent input-output
characteristics, and tends to moderately control the activity of an
active material against electrolyte solution, thus inhibiting the
increase in initial irreversible capacity, as a result of which a
high-capacity battery can be produced.
90% Particle Diameter (d90) to 10% Particle Diameter (d10) Ratio
(d90/d10) in Volume-Based Particle Size Distribution
[0762] The 90% particle diameter (d90) to 10% particle diameter
(d10) ratio (d90/d10) in a volume-based particle size distribution
of the composite carbon material according to this embodiment
(e.g., but not limited to, Invention E) is typically 2.0 or
greater, preferably 2.2 or greater, more preferably 2.4 or greater,
still more preferably 2.5 or greater, even more preferably 2.6 or
greater, particularly preferably 2.7 or greater, and typically 5.0
or less, preferably 4.5 or less, more preferably 4.0 or less, still
more preferably 3.8 or less, particularly preferably 3.5 or
less.
Average Value and Standard Deviation (.sub..sigma.R) of Microscopic
Raman R Values
[0763] In one aspect of one embodiment of the present invention,
the composite carbon material preferably comprises the carbon
material (A) capable of occluding and releasing lithium ions and
the carbonaceous material (B) on the surface of the carbon material
(A), wherein the average value of microscopic Raman R values of 30
randomly selected composite carbon materials is 0.1 to 0.85, and
the standard deviation (.sigma..sub.R) is 0.1 or less.
[0764] The average value of microscopic Raman R values of the
composite carbon material according to this embodiment (e.g., but
not limited to, invention F) is 0.1 to 0.85, preferably 0.15 or
greater, more preferably 0.2 or greater, still more preferably 0.23
or greater, particularly preferably 0.25 or greater, and preferably
0.8 or less, more preferably 0.65 or less, still more preferably
0.5 or less, particularly preferably 0.4 or less.
[0765] The standard deviation is 0.1 or less, preferably 0.085 or
less, more preferably 0.08 or less, still more preferably 0.07 or
less, particularly preferably 0.06 or less, and typically 0.001 or
greater, preferably 0.01 or greater, more preferably 0.02 or
greater.
[0766] The average value and the standard deviation (.sigma..sub.R)
of microscopic Raman R values described above are determined from
30 randomly selected composite carbon materials according to an
embodiment of the present invention using measurement methods
described below.
[0767] An average value and a standard deviation (.sigma..sub.R) of
microscopic Raman R values outside the above ranges mean that the
surface of the carbon material (A) is not uniformly coated with a
carbonaceous material into and from which Li ions are readily
inserted and extracted. This tends to cause, for example, a
concentrated excessive current flow into a specific site where the
carbonaceous material is sufficiently deposited and Li ions are
readily inserted and extracted, particularly at low temperatures
and during fast charging and discharging, so as to cause
electrodeposition, which impedes uniform and smooth
insertion/extraction of Li ions, resulting in degraded
low-temperature output characteristics and cycle
characteristics.
[0768] The Raman R values are determined by Raman microspectroscopy
using a Raman spectroscope (e.g., Nicolet Almega XR available from
Thermo Fisher Scientific) under the following conditions.
[0769] Target particles are gravity-dropped onto a sample stage,
and Raman microspectroscopy is performed with the surface of the
target flat.
[0770] Excitation wavelength: 532 nm
[0771] Laser power on sample: 1 mW or less
[0772] Resolution: 10 cm.sup.-1
[0773] Irradiation area: 1 .mu.m .PHI.
[0774] Measurement range: 400 cm.sup.-1 to 4,000 cm.sup.-1
[0775] Measurement of peak intensity: straight baseline subtraction
in the range of about 1,100 cm.sup.-1 to 1,750 cm.sup.-1
[0776] Method for calculating Raman R value: In a spectrum after
straight baseline subtraction, a peak intensity I.sub.A at the peak
top of a peak P.sub.A near 1,580 cm.sup.-1 and a peak intensity
I.sub.B at the peak top of a peak P.sub.B near 1,360 cm.sup.-1 are
read to calculate an R value (I.sub.B/I.sub.A). The average value
and the standard deviation (.sigma..sub.R) of 30 randomly selected
target particles are calculated.
[0777] Microscopic Raman .sub.R15 Value
[0778] The microscopic Raman R.sub.15 value given by equation (1F)
of the composite carbon material according to an embodiment of the
present invention (e.g., but not limited to, Invention E) is
typically 25% or less, preferably 15% or less, more preferably 12%
or less, still more preferably 9% or less, particularly preferably
5% or less, and typically more than 0%. A microscopic Raman
R.sub.15 value in this range indicates that the surface of the
carbon material (A) is uniformly coated with the carbonaceous
material (B) and the surface of the carbon material (A) is less
exposed. This enables uniform and smooth insertion/extraction of Li
ions, thus providing a composite carbon material with excellent
low-temperature output characteristics and cycle
characteristics.
Microscopic .times. .times. Raman .times. .times. R ( 15 ) .times.
.times. value .times. .times. ( % ) = the .times. .times. number
.times. .times. of .times. .times. composite .times. .times. carbon
.times. .times. materials .times. .times. having .times. .times. a
.times. .times. microscopic .times. .times. Raman .times. .times. R
.times. .times. value .times. .times. of .times. .times. 0.15
.times. .times. or .times. .times. less .times. .times. among
.times. .times. 30 .times. .times. randomly .times. .times.
selected .times. .times. composite .times. .times. carbon .times.
.times. materials .times. / .times. 30 .times. 100 ( 1 .times. F )
##EQU00047##
[0779] In one aspect of one embodiment of the present invention,
the composite carbon material preferably satisfies the relationship
of inequality (1K). In inequality (1K), "carbon material" means
"composite carbon material".
10.914 > 5 .times. x k - y k - 0.0087 .times. a Inequality
.times. .times. ( 1 .times. K ) ##EQU00048##
[0780] In inequality (1K), x.sub.k is a true density [g/cm.sup.3]
of the carbon material; y.sub.k is a value determined by equation
(2K); and a is a volume-based average particle diameter [.mu.m] of
the carbon material.
y k = ( density .times. [ g .times. / .times. cm 3 ] .times.
.times. of .times. .times. carbon .times. .times. material .times.
.times. under .times. .times. uniaxial .times. .times. load .times.
.times. of .times. .times. 100 .times. .times. kgf .times. /
.times. 3.14 .times. .times. cm 2 ) - ( tap .times. .times. density
.times. .times. of .times. .times. carbon .times. .times. material
.times. [ g .times. / .times. cm 3 ] ) Equation .times. .times. ( 2
.times. K ) ##EQU00049##
[0781] In one aspect of the present invention, the carbon material
according to another embodiment of the present invention preferably
satisfies the relationship of inequality (3K). In other words, the
carbon material according to an embodiment of the present invention
(e.g., but not limited to, Invention K) preferably satisfies
inequality (1K) or (3K).
10.990 > 5 .times. x k - y k Inequality .times. .times. ( 3
.times. K ) ##EQU00050##
[0782] (In inequality (3K), x.sub.k is a true density [g/cm.sup.3]
of the carbon material, and y.sub.k is a value determined by
equation (2K).)
y k = ( density .times. [ g .times. / .times. cm 3 ] .times.
.times. of .times. .times. carbon .times. .times. material .times.
.times. under .times. .times. uniaxial .times. .times. load .times.
.times. of .times. .times. 100 .times. .times. kgf .times. /
.times. 3.14 .times. .times. cm 2 ) - ( tap .times. .times. density
.times. .times. of .times. .times. carbon .times. .times. material
.times. [ g .times. / .times. cm 3 ] ) Equation .times. .times. ( 2
.times. K ) ##EQU00051##
[0783] When the relationship represented by inequality (1K) or (3K)
is not satisfied, the particles tend to fracture in pressing an
electrode in battery production so as to cause flattening of the
particles or separation of the amorphous carbon, thus resulting in
degraded low-temperature output characteristics and a reduced
capacity. Methods for measuring physical properties used to
calculate inequality (1K) or (3K) will be described below.
[0784] Particle Density under Uniaxial Load of 100 kgf/3.14
c.sup.m2
[0785] The density under a uniaxial load of 100 kgf/3.14 cm.sup.2
of the carbon material according to this embodiment (e.g., but not
limited to, Invention K) is preferably 0.7 g/cm.sup.3 or more, more
preferably 0.9 g/cm.sup.3 or more, still more preferably 1.2
g/cm.sup.3 or more, particularly preferably 1.24 g/cm.sup.3 or
more, and preferably 1.8 g/cm.sup.3 or less, more preferably 1.7
g/cm.sup.3 or less, still more preferably 1.6 g/cm.sup.3 or
less.
[0786] A density in this range can prevent particle fracture under
a given load, thus leading to excellent input-output
characteristics.
[0787] The density under a uniaxial load of 100 kgf/3.14 cm.sup.2
can be measured using an apparatus capable of measuring a load and
a thickness under any given uniaxial pressure. For example, the
measurement is made using an MCP-PD51 powder resistivity
measurement system available from Mitsubishi Chemical Analytech
Co., Ltd. First, values of the apparatus are corrected. For a load
correction, the load measured when the bottom of a cylindrical
container for accommodating the carbon material and a push rod to
be inserted into the container from above to apply pressure to the
carbon material are not in contact is confirmed to be 0 kgf/3.14
cm.sup.2. Next, a thickness gauge is corrected. While the
cylindrical container and the push rod are brought close using a
hydraulic pump, a zero-point correction is carried out such that
the thickness gauge indicates 0.00 mm when the load reaches 2.0
kgf/3.14 cm.sup.2. After the corrections are carried out, 3.0 g of
the carbon material is placed in the cylindrical container with a
diameter of 2 cm, and the height of the carbon material is adjusted
so as to receive a load evenly. A seat is lifted using the
hydraulic pump, and the push rod is inserted into the cylindrical
container. After the thickness gauge has indicated 15.0 mm, loads
are measured at thicknesses at 0.5-mm intervals until the load
exceeds 1,000 kgf/3.14 cm.sup.2. From the thicknesses obtained, the
densities of the powder are calculated, and using Microsoft Excel,
a graph is created with powder density plotted on the horizontal
axis and load on the vertical axis. A cubic spline curve of the
graph is created, and the formula obtained is used to calculate a
carbon material density under a load of 100 kgf/3.14 cm.sup.3. To
reduce variation in measurements, the measurement is made at least
twice. When variation occurs, the measurement is made three times,
and the average of two closest values is used.
[0788] y.sub.k: (density [g/cm.sup.3] of carbon material under
uniaxial load of 100 kgf/3.14 cm.sup.2)-(tap density of carbon
material [g/cm.sup.3])
[0789] The value of y in this embodiment (e.g., but not limited to,
invention K) is typically 0.10 or greater, more preferably 0.12 or
greater, still more preferably 0.18 or greater, particularly
preferably 0.19 or greater, and preferably 1 or less, more
preferably 0.9 or less, still more preferably 0.5 or less.
[0790] A value of y in this range causes less particle fracture
under a given load to reduce amorphous separation and particle
deformation, thus providing excellent input-output
characteristics.
[0791] In one aspect of one embodiment of the present invention,
the composite carbon material has a large number of voids having
fine structures in the particles.
[0792] Specifically, the carbon material for a non-aqueous
secondary battery according to an embodiment of the present
invention (e.g., but not limited to, Inventions L.sup.1 to L.sup.3)
comprises a composite carbon material made of granulated particles
satisfying (1L) and (2L) and further has a characteristic particle
cross section such that a box-counting dimension is determined from
an image of the particle cross section.
Carbon Material (Granulated Particles) Satisfying (1L) and (2L) in
Carbon Material for Non-Aqueous Secondary Battery
[0793] The granulated particles in the carbon material for a
non-aqueous secondary battery satisfies the following: (1) Being
made of a carbonaceous material; and (2) Satisfying the
relationship |X.sub.1-X|/X.sub.1.ltoreq.0.2, preferably
.ltoreq.0.15, more preferably .ltoreq.0.1, where X is a
volume-based average particle diameter determined by laser
diffraction, and X.sub.1 is an equivalent circular diameter
determined from a cross-sectional SEM image.
[0794] If |X.sub.1-X|/X.sub.1 is too large, typical particles
cannot be selected, which results in failure to express the overall
tendency.
[0795] The volume-based average particle diameter X is defined as a
volume-based median diameter determined by suspending 0.01 g of a
carbon material in 10 L of a 0.2% by mass aqueous solution of a
polyoxyethylene sorbitan monolaurate surfactant (e.g., Tween 20
(registered trademark)), placing the suspension (a measurement
sample) in a commercially available laser diffraction/scattering
particle size distribution analyzer (e.g., LA-920 available from
HORIBA), irradiating the measurement sample with ultrasonic waves
of 28 kHz at a power of 60 W for 1 minute, and then performing a
measurement with the analyzer.
[0796] The equivalent circular diameter X.sub.1 determined from a
cross-sectional SEM image is expressed by the following formula
using a particle circumference L [.mu.m].
X 1 = L 2 .times. .pi. [ Mathematical .times. .times. 9 ]
##EQU00052##
[0797] The granulated particles in the carbon material for a
non-aqueous secondary battery satisfies the relationship
|R-R.sub.1.ltoreq.0.1, preferably .ltoreq.0.08, more preferably
.ltoreq.0.06, where R is a roundness determined with a flow-type
particle image analyzer, and R.sub.1 is a roundness determined from
a cross-sectional SEM image.
[0798] If |R-R.sub.1| is too large, a particle boundary is not
defined correctly but overestimated, which may result in incorrect
analysis.
[0799] As the value of the roundness R determined with a flow-type
particle image analyzer is used a value determined, for example,
using a flow-type particle image analyzer (e.g., FPIA available
from Sysmex Industrial Corp.) by dispersing about 0.2 g of a sample
(the carbon material for a non-aqueous secondary battery according
to the present invention) in a 0.2% by mass aqueous solution
(approximately 50 mL) of a polyoxyethylene (20) sorbitan
monolaurate surfactant, irradiating the dispersion with ultrasonic
waves of 28 kHz at a power of 60 W for 1 minute, and then measuring
the roundness of particles with a diameter in the range of 1.5 to
40 .mu.m with a detection range set to 0.6 to 400 .mu.m.
[0800] The roundness R.sub.1 determined from a cross-sectional SEM
image is calculated by the following formula using a particle area
S [.mu.m.sup.2] determined from a cross-sectional SEM image and a
circumference L [.mu.m].
R 1 = 4 .times. .pi. .times. .times. S ( L ) 2 [ Mathematical
.times. .times. 10 ] ##EQU00053##
[0801] The particle boundary may be defined by any method, and it
may be defined automatically or manually using commercially
available analysis software. It is preferable to approximate a
particle by a polygon, and in this case, an approximation by a
polygon with 15 or more sides is more preferred. This is because if
a polygon with less than 15 sides is used, a background portion may
be determined to be a part of the particle in approximating a
curve.
Acquisition of Particle Cross-Sectional Image
[0802] For the image of a particle cross section is used a
reflected electron image acquired at an acceleration voltage of 10
kV using a scanning electron microscope (SEM). An SEM observation
sample for acquiring a particle cross-sectional image may be
prepared by any method, and a particle cross-sectional image is
acquired using an SEM after a sample is prepared by cutting an
electrode plate containing the carbon material for a non-aqueous
secondary battery, a film coated with the carbon material for a
non-aqueous secondary battery, with a focused ion beam (FIB) or ion
milling to obtain a particle cross section.
[0803] The acceleration voltage in observing the cross section of
the carbon material for a non-aqueous secondary battery with a
scanning electron microscope (SEM) is 10 kV.
[0804] This acceleration voltage makes a difference between a
reflected electron SEM image and a secondary electron SEM image to
allow void regions and other regions of the carbon material for a
non-aqueous secondary battery to be easily distinguished. The
imaging magnification is typically 500.times. or more, more
preferably 1,000.times. or more, still more preferably 2,000.times.
or more, and typically 10,000 or less. An imaging magnification in
this range enables the acquisition of an entire image of one
particle of the carbon material for a non-aqueous secondary
battery. The resolution is 200 dpi (ppi) or more, preferably 256
dpi (ppi) or more. The number of picture elements suitable for
evaluation is at least 800 pixels.
[0805] Average Box-Counting Dimension Relative to Void Regions in
Cross-Sectional SEM Image
[0806] The carbon material for a non-aqueous secondary battery has
an average box-counting dimension relative to void regions of 1.55
or greater, preferably 1.60 or greater, more preferably 1.62 or
greater, and typically 1.80 or less, preferably 1.75 or less, more
preferably 1.70 or less, as calculated from images obtained by
randomly selecting 30 granulated particles satisfying (1L) and (2L)
above from a cross-sectional SEM image, dividing the
cross-sectional SEM image of each granulated particle into void
regions and non-void regions, and binarizing the image.
[0807] An excessively small average box-counting dimension relative
to void regions means that the amount of finer structure is small,
in which case excellent output characteristics, one of the effects
of the present invention, cannot be provided. An excessively large
average box-counting dimension increases the specific surface area
of the particles, leading to low initial efficiency.
[0808] The box-counting dimensions of the particles of the carbon
material for a non-aqueous secondary battery are determined taking
the following (a) to (d) into account.
[0809] (a) Definition and Calculation Method of Box-Counting
Dimension
[0810] Box-counting dimension is a method for estimating a fractal
dimension by observing a certain area split into certain sizes (box
sizes) to examine how much fractal patterns are contained (see JP
2013-77702 A). Box-counting dimension is an indicator of shape
complexity, the degree of surface irregularity, and others, and
larger fractal dimensions indicate more complex irregularities. The
fractal dimension is defined by the following formula, where
N.delta. (F) is the number of square boxes of side .delta.
necessary for covering a pattern F.
D = lim .delta. .fwdarw. 0 .times. N .delta. .function. ( F ) log
.times. .times. .delta. [ Mathematical .times. .times. 11 ]
##EQU00054##
[0811] In this embodiment (e.g., but not limited to, Invention
L.sup.1), a cross-sectional SEM image of a particle composed of
voids and carbon is split into grid areas (boxes) at regular
intervals .delta. (split into square subareas of side .delta.), and
the number of boxes containing voids is counted with varying values
of .delta.. Next, a double logarithmic graph is created with the
number of boxes counted plotted on the vertical axis and .delta. on
the horizontal axis, and a fractal dimension is determined from the
slope of the graph.
[0812] Specifically, in a cross-sectional SEM image of a particle
composed of voids and carbon, voids and other regions of the
particle are binarized. The binarization is performed in units of
pixels of the image. Analysis objects are portions representing
pixels of voids among the binarized regions. The region outside the
particle (outside the outline of the particle) requires value
conversion so as not to be regarded as a void. The image is split
into grid areas (boxes) having a specific pixel size. Although the
boxes may be arranged in any manner, they are preferably arranged
parallel to the major axis (the longest diameter passing through
the barycenter) of the particle. In the arrangement, the image is
split into boxes as shown in FIGS. 7 and 8. The number of split
boxes including at least one pixel representing a void is counted.
The same procedure is repeated with varying box sizes, and a double
logarithmic graph is created with the number of boxes counted
plotted on the vertical axis and the box size .delta. on the
horizontal axis. A linear approximation of this plot is performed,
and the slope of the line is multiplied by -1. The product obtained
is the fractal dimension according to the box-counting method. The
slope may be calculated by the least-squares method.
[0813] The fractal dimension is an indicator of the degree of
self-similarity, and in expressing a binarized image, it serves as
an indicator of the complexity and the fineness of a structure.
This means that in a binarized image having a more complicated
partial structure, the proportion of fine structure in a box tends
to increase, that is, the slope tends to be steeper with decreasing
box size, and the fineness of the partial structure and the amount
of such structure are expressed. In other words, the box-counting
dimension in the present invention is an indicator of the
complexity of a fine structure of voids and the amount of such
structure.
[0814] (b) Definition of Box Size
[0815] The image may be split into any box size, but based on the
maximum pixel of the image, it is preferably split into 10 parts or
more, more preferably 15 parts or more, particularly preferably 20
parts or more, and typically 50 parts or less, preferably 40 parts
or less, more preferably 30 parts or less, on a logarithmic graph.
A box size in this range reduces the possibility that differences
between picture elements occur and eliminates the need for a
high-resolution image.
[0816] (c) Method of Binarization
[0817] The binarization may be carried out by any method by which
intra-particle voids and carbon portions are clearly distinguished
from each other, as shown in FIG. 9. The binarization, when
performed on an 8-bit gray-scale image, such as an SEM image,
refers to dividing luminances into two and representing the two
divided images in two values (e.g., 0 and 255, in the case of
8-bit). The binarization may be carried out using any desired image
processing software. The division by setting a threshold can be
carried out using any algorithm, such as the mode method and the
ISOData method, by which void portions and carbon portions can be
clearly distinguished from each other. The target image needs to be
a binarizable image. The binarizable image, in this case, refers to
an image in which the luminance of void portions and the luminance
of carbon portions are clearly distinguished from each other by a
certain threshold. In some images, the surface may be rough due to
low processing accuracy the cross section may be facing obliquely;
or the luminances of void portions and carbon portions may be close
to each other depending on the settings such as contrast and
brightness. Such images may show incorrect void distributions when
binarized and thus are preferably excluded from analysis objects.
For example, FIG. 10 is an image in which the surface of a graphite
portion in the middle has a rough pattern and a low luminance, and
fine voids have high luminances. When such an image is binarized
picking up fine parts, carbon portions are also expressed as voids;
by contrast, if a luminance at a carbon portion with no void is
used as a threshold, fine voids, which are actually voids, cannot
be displayed. Although such particles are preferably not selected,
the cross section of such particles may be typical, and thus it is
necessary not to analyze such an SEM image unsuitable for
binarization but to retake an image and adjust the brightness and
the contrast.
[0818] (d) Definition of Particle Boundary
[0819] The particle boundary may be established by any method, for
example, by freehand or the approximation by a polygon, provided
that the boundary needs to be clearly defined. Although there is no
limitation, it is necessary to establish the boundary between the
particle and other regions such that the region of interest (ROI)
representing the shape of the particle is completely included. When
the boundary is not a simple oval but has a complicated shape, for
example, the boundary may be divided into any desired number of
equally spaced sections to approximate the particle region by a
polygon. The boundary, however, is established so as not to deviate
from a roundness R determined with a flow-type particle image
analyzer. As used herein, "not deviate" means that a degree of
spheroidization R determined by a flow-type particle image analyzer
and a degree of spheroidization R.sub.1 determined from a
cross-sectional SEM image satisfy the relationship
|R-R.sub.1|.ltoreq.0.1. When an electrode coated with a binder
having poor conductivity is used, the boundary may be difficult to
determine under the measurement conditions of the present
invention. This is a phenomenon that occurs due to the poor
conductivity of the binder when the side of the particle is visible
in depth of the cross section of the particle. In such a case, it
is necessary to take another image with a clear boundary at a lower
acceleration voltage to determine a boundary.
[0820] In one aspect of one embodiment of the present invention,
the carbon material for a non-aqueous secondary battery comprises
uniformly dispersed intra-particle pores.
[0821] Specifically, the carbon material for a non-aqueous
secondary battery according to an embodiment of the present
invention (e.g., but not limited to, Invention L.sup.2) comprises a
composite carbon material made of granulated particles satisfying
(1L) and (2L) above and further has a characteristic particle cross
section such that the void dispersity D of the present invention is
determined from an image of the particle cross section.
[0822] Void Dispersity D in Cross-Sectional SEM Image
[0823] The carbon material for a non-aqueous secondary battery
typically has an average dispersity D of 30 particles, as
determined by the following measurement method using 30 granulated
particles satisfying (1L) and (2L) above randomly selected from a
cross-sectional SEM image, of 60% or more, preferably 61% or more,
more preferably 62% or more, and typically 90% or less, preferably
85% or less, more preferably 80% or less.
[0824] Measurement Method
[0825] Using a cross-sectional SEM image, grid lines are drawn to
split the minor axis and the major axis of a target granulated
particle each into 20 parts. Using cells in the grid, the
granulated particle is compartmentalized as defined below. The
expectation E of void area of each compartment is calculated using
equation (A) below, and the dispersity D of the granulated particle
is calculated using equation (B) below.
[0826] The cross-sectional SEM image is a reflected electron image
acquired at an acceleration voltage of 10 kV.
[0827] How to Create Grid
[0828] Using a cross-sectional SEM image, grid lines are drawn to
split the minor axis and the major axis of a target granulated
particle each into 20 parts, as shown in FIG. 11. This image needs
to be parallel to the particle major axis and the image.
[0829] Definition of Compartment
[0830] The compartment is defined as a granulated particle portion
and/or a region where a void is present in the granulated particle
in each cell of the grid. The outside of the boundary of the
granulated particle is excluded from the compartment. For grid
cells that are divided by the particle boundary into two, as shown
in FIG. 12, the region including the particle is defined as a
compartment.
[0831] Definition of Expectation
[0832] For compartments defined by grid lines and the particle
boundary, the expectation E of a void area corresponding to each
compartment area is determined from equation (A).
Expectation .times. .times. E .times. [ .mu.m 2 ] .times. .times.
of .times. .times. void .times. .times. area .times. .times. in
.times. .times. target .times. .times. compartment = ( gross
.times. .times. area .times. [ .mu.m 2 ] .times. .times. of .times.
.times. internal .times. .times. voids .times. .times. of .times.
.times. one .times. .times. target .times. .times. granulated
.times. .times. particle ) .times. / .times. ( cross .times. -
.times. sectional .times. .times. area .times. [ .mu.m 2 ] .times.
.times. of .times. .times. one .times. .times. target .times.
.times. granulated .times. .times. particle ) .times. ( area
.times. [ .mu.m 2 ] .times. .times. of .times. .times. target
.times. .times. compartment ) Equation .times. .times. ( A )
##EQU00055##
[0833] The expectation E of a compartment defined by the particle
boundary is calculated to be smaller than the expectation E of a
grid cell according to the area of the compartment.
[0834] Definition of Dispersity D
[0835] The dispersity D, an indicator of the void dispersity in a
particle, is calculated by equation (B).
Dispersity .times. .times. D .times. .times. ( % ) = ( sum .times.
.times. total .times. [ .mu.m 2 ] .times. .times. of .times.
.times. areas .times. .times. of .times. .times. compartments
.times. .times. that .times. .times. satisfy .times. .times. (
gross .times. .times. area .times. [ .mu.m 2 ] .times. .times. of
.times. .times. voids .times. .times. in .times. .times. target
.times. .times. compartment ) .times. / .times. ( expectation
.times. .times. E .times. [ .mu.m 2 ] .times. .times. of .times.
.times. void .times. .times. area .times. .times. in .times.
.times. target .times. .times. compartment ) = 0.5 .times. .times.
or .times. .times. greater ) .times. / .times. ( sum .times.
.times. total .times. [ .mu.m 2 ] .times. .times. of .times.
.times. areas .times. .times. of .times. .times. all .times.
.times. the .times. .times. compartments .times. .times. of .times.
.times. one .times. .times. target .times. .times. granulated
.times. .times. particle ) .times. 100 Equation .times. .times. ( B
) ##EQU00056##
[0836] The dispersity D indicates how voids are dispersed
throughout the inside of a particle, excluding compartments having
only a small void area.
[0837] The equation (A) and the equation (B) of the carbon material
for a non-aqueous secondary battery are calculated taking the
following (a) to (d) into account.
[0838] (a) Method of Selecting Granulated Particles and Definition
of Major Axis and Minor Axis
[0839] The particle boundary may be established by any method by
which the boundary is clearly defined, provided that the boundary
between the particle and other regions needs to be established such
that the region of interest (ROI) representing the shape of the
particle is completely included. For example, it may be established
by freehand or the approximation by a polygon. When the boundary is
not a simple oval but has a complicated shape, for example, the
boundary may be divided into any desired number of equally spaced
sections to approximate the particle region by a polygon. The
boundary, however, is established so as not to deviate from a
roundness R determined with a flow-type particle image analyzer. As
used herein, "not deviate" means that a degree of spheroidization R
determined by a flow-type particle image analyzer and a degree of
spheroidization R.sub.1 determined from a cross-sectional SEM image
satisfy the relationship |R-R.sub.1|.ltoreq.0.1. When an electrode
coated with a binder having poor conductivity is used, the boundary
may be difficult to determine under the measurement conditions of
the present invention. This is a phenomenon that occurs due to the
poor conductivity of the binder when the side of the particle is
visible in the cross section of the particle. In such a case, it is
necessary to take another image with a clear boundary at a lower
acceleration voltage to determine a boundary.
[0840] For one randomly selected granulated particle, the
barycenter (centroid) is defined. First, the particle defined by
the boundary is approximated by square cells. The size of each cell
is preferably, but not necessarily, 5 nm or less in actual size.
Two-dimensional coordinates are determined in the image. The
coordinates of the barycenter of each cell are defined. Assuming
that the weights of the cells are the same, the cells are numbered
from 1 to N. The following formula is used to determine the
coordinates of the barycenter of the granulated particle.
r G .fwdarw. = .SIGMA. 1 N .times. r i .fwdarw. N [ Mathematical
.times. .times. 12 ] ##EQU00057##
[0841] In the formula, r.sub.i represents the coordinates of an
i-th cell, and r.sub.G represents the coordinates of the
barycenter. The barycenter may be determined by operating any
desired image software, or by the following formula if the
barycenter of each divided mesh can be defined by any given
figure.
r G .fwdarw. = .SIGMA. 1 N .times. A i .times. r i .fwdarw. .SIGMA.
1 N .times. A i [ Mathematical .times. .times. 13 ]
##EQU00058##
[0842] In the formula, A.sub.i is the area of an i-th figure, and
r.sub.i is the bar centric (centroid) coordinates of the i-th
figure.
[0843] Next, the longest line segment among line segments passing
through the barycenter obtained and bounded by the boundary fixed
as described above is defined as a major axis. The line segment
orthogonal to the major axis among line segments passing through
the barycenter and bounded by the boundary fixed as described above
is defined as a minor axis.
[0844] (b) Definition of Void Region and Non-Void Region and Method
of Calculating their Areas
[0845] The binarization may be carried out by any method by which
intra-particle voids and carbon portions are clearly distinguished
from each other, as shown in FIG. 9, and is preferably carried out
such that void regions and other carbon particle regions are
clearly distinguished from each other. The binarization, when
performed on an 8-bit gray-scale image, such as an SEM image,
refers to dividing luminances into two and representing the two
divided images in two values (e.g., 0 and 255, in the case of
8-bit). The binarization is not particularly limited to, and may be
carried out using any desired image processing software. The
division by setting a threshold can be carried out using any
algorithm, such as the mode method and the ISOData method, by which
void portions and carbon portions can be clearly distinguished from
each other. The image needs to be a binarizable image. The
binarizable image, in this case, refers to an image in which the
luminance of void portions and the luminance of carbon portions are
clearly distinguished from each other by a certain threshold. In
some images, the surface may be rough due to low processing
accuracy; the cross section may be facing obliquely; or the
luminances of void portions and carbon portions may be close to
each other depending on the settings such as contrast and
brightness. Such images may show incorrect void distributions when
binarized and thus are preferably excluded from analysis objects.
For example, FIG. 10 is an image in which the surface of a graphite
portion in the middle has a rough pattern and a low luminance, and
fine voids have high luminances. When such an image is binarized
picking up fine parts, carbon portions are also expressed as voids;
by contrast, if a luminance at a carbon portion with no void is
used as a threshold, fine voids, which are actually voids, cannot
be displayed. Although such particles are preferably not selected,
the cross section of such particles may be typical, and thus it is
necessary not to analyze such an SEM image unsuitable for
binarization but to retake an image and adjust the brightness and
the contrast.
[0846] The areas of the void region and the non-void region in the
particle thus calculated are each calculated as an approximation in
a pixel unit and converted into an actual unit.
[0847] (c) Creation of Grid
[0848] In the binarized image is created cells that split the minor
axis and the major axis of the granulated particle each into 20
parts. The cells may be arranged such that they are parallel to the
major axis and the minor axis of the granulated particle.
[0849] (d) Calculation of Expectation E and Dispersity D of Target
Compartment
[0850] For each of the 400 cells created by splitting the minor
axis and the major axis of the granulated particle each into 20
parts, the expectation E is calculated by equation (A) above. The
sum total of areas of compartments having an expectation E of 0.5
or greater is calculated, and the dispersity D is calculated by
equation (B) above.
[0851] For each of the 30 granulated particles selected, the
dispersity D is calculated, and the average dispersity D of the 30
particles is calculated.
[0852] In one aspect of the present invention, the carbon material
for a non-aqueous secondary battery comprises intra-particle voids
the orientation of which and the interval between which are
controlled.
[0853] Specifically, the carbon material for a non-aqueous
secondary battery according to an embodiment of the present
invention (e.g., but not limited to, Invention L.sup.3) comprises a
composite carbon material made of granulated particles satisfying
the following (1L) and (2L) and further has a characteristic
particle cross section such that the ratio (Zave/X) of average
inter-void distance Z (Zave) of 30 particles to volume-based
average particle diameter X determined by laser diffraction of the
present invention is determined from an image of the particle cross
section.
Zave/X
[0854] The carbon material for a non-aqueous secondary battery
according to this embodiment (e.g., but not limited to, Invention
L.sup.3) comprises granulated particles satisfying (1L) and (2L)
above and has an average inter-void distance Z (Zave) of 30
particles as defined below and a volume-based average particle
diameter X determined by laser diffraction in a ratio (Zave/X) of
typically 0.060 or less, preferably 0.055 or less, more preferably
0.050 or less, still more preferably 0.045 or less, and typically
0.001 or greater, preferably 0.010 or greater, more preferably
0.020 or greater, the 30 granulated particles satisfying (1L) and
(2L) and being randomly selected from a cross-sectional SEM
image.
[0855] An excessively large Zave/X means that the distance between
the carbon material and voids constituting the granulated particle
is wide, which disadvantageously results in a low liquid retention
in the particle.
[0856] Definition of Average Inter-Void Distance Z (Zave) of 30
Particles
[0857] As shown in the left figure of FIG. 13, three lines are
drawn that are parallel to the minor axis of a target granulated
particle and split the major axis of the granulated particle into
four parts, and inter-void distances Z (.mu.m) of the granulated
particle on each line (see the right figure of FIG. 13) are each
measured. The average of 30 particles in total is calculated. This
is defined as the average inter-void distance Z (Zave) of 30
particles.
W/X
[0858] In this embodiment (e.g., but not limited to, Invention
L.sup.3), the carbon material for a non-aqueous secondary battery
comprises granulated particles satisfying (1L) and (2L) above and
has a standard deviation (W) of void sizes Y of 30 particles as
defined below and a volume-based average particle diameter X
determined by laser diffraction in a ratio (W/X) of preferably
0.018 or less, more preferably 0.016 or less, still more preferably
0.014 or less, and typically 0.001 or greater, preferably 0.005 or
greater, more preferably 0.008 or greater, the 30 granulated
particles satisfying (1L) and (2L) above and being randomly
selected from a cross-sectional SEM image.
[0859] W/X is a quotient of a standard deviation of void sizes
divided by a particle size, and a larger value of W/X means that a
higher proportion of relatively large voids.
[0860] A W/X in the above range means relatively uniform void sizes
or a low proportion of large voids, i.e., a fine void structure
that allows an electrolyte solution to uniformly permeate into the
particles.
Definition of Standard Deviation (W) of Void Sizes Y (.mu.m) of 30
Particles
[0861] As shown in the left figure of FIG. 13, three lines are
drawn that are parallel to the minor axis of a target granulated
particle and split the major axis of the granulated particle into
four parts, and void sizes Y (.mu.m) of the granulated particle on
each line (see the right figure of FIG. 13) are each measured. The
standard deviation of 30 particles in total is calculated. This is
defined as the standard deviation (W) of void sizes Y of 30
particles.
[0862] The standard deviation is determined by the following
formula, where Yave is the average of Y, and Ny is the number of
Y.
W = ( .SIGMA. .function. ( Y - Y ave ) 2 Ny ) 1 .times. / .times. 2
[ Mathematical .times. .times. 14 ] ##EQU00059##
[0863] Condition of Voids
[0864] Preferably, the granulated particles in the carbon material
for a non-aqueous secondary battery according to the present
invention have slit-like voids, and the slit-like voids are
arranged mainly in layers.
[0865] More specifically, among 30 granulated particles satisfying
(1L) and (2L) above randomly selected from a cross-sectional SEM
image, the proportion (by number) of particles having slit-like
voids arranged mainly in layers is more preferably 70% or more,
particularly preferably 80% or more, most preferably 90% or more.
Within this range, it can be said that most of the particles have a
slit-like and layered structure.
[0866] "Slit-like void" refers to a long and narrow void (with a
high aspect ratio) like a gap. The aspect ratio of the void is
preferably 10 or greater, more preferably 15 or greater. The aspect
ratio is a value obtained by dividing the major axis of the void by
the minor axis, that is, (major axis of void)/(minor axis of void).
The major axis and the minor axis of the void can be calculated by
the same method as in Selection of Granulated Particles and
Definition of Minor Axis described below.
[0867] In the present invention, "voids in layers" means that major
axes of voids in a particle are arranged in parallel. For example,
if the angle between the major axes of two voids is within
.+-.30.degree., the two voids are regarded as being in
parallel.
[0868] The proportion of the area of voids in layers the area of
voids in layers/the gross area of voids) in a granulated particle
is preferably 40% or more, more preferably 50% or more, still more
preferably 60% or more, and typically 100% or less, preferably 90%
or less. The proportion of the number of slit-like voids (the
number of slit-like voids/the total number of voids) is preferably
70% or more, more preferably 80% or more, still more preferably 90%
or more, and typically 100% or less, preferably 90% or less. If the
number and the area of slit-like voids are in these ranges, it can
be said that the particle has so many fine slit-like structures
that provide more reaction initiation surfaces of Li and sufficient
permeability of electrolyte solution.
[0869] The above-described Zave/X and W/X of the carbon material
for a non-aqueous secondary battery are calculated taking the
following (a) to (d) into account.
[0870] (a) Selection of Granulated Particles and Definition of
Minor Axis
[0871] In an SEM image acquired, 30 granulated particles satisfying
the above conditions (1L) and (2L) are randomly selected. In the
selection, particle boundaries are established along the outlines
of the granulated particles. The particle boundary may be
established by any method by which the boundary is clearly defined.
For example, it may be established by freehand or the approximation
by a polygon. It is necessary to establish the boundary between the
particle and other regions such that the region of interest (ROI)
representing the shape of the particle is completely included. When
the boundary is not linear-like but has a complicated shape, for
example, the boundary may be divided into any desired number of
equally spaced sections to approximate the particle region by a
polygon. The boundary is established so as not to deviate from a
roundness R determined with a flow-type particle image analyzer. As
used herein, "not deviate" means that a degree of spheroidization R
determined by a flow-type particle image analyzer and a degree of
spheroidization R.sub.1 determined from a cross-sectional SEM image
satisfy the relationship |R-R.sub.1|.ltoreq.0.1.
[0872] For one randomly selected granulated particle, the
barycenter (centroid) is defined. First, the particle defined by
the boundary is approximated by square cells. The size of each cell
is preferably, but not necessarily, 5 nm or less in actual size.
Two-dimensional coordinates are determined in the image. The
coordinates of the barycenter of each cell are defined. Assuming
that the weights of the cells are the same, the cells are numbered
from 1 to N. The following formula is used to determine the
coordinates of the barycenter of the granulated particle.
r G .fwdarw. = .SIGMA. 1 N .times. r i .fwdarw. N [ Mathematical
.times. .times. 15 ] ##EQU00060##
[0873] In the formula, r.sub.i represents the coordinates of an
i-th cell, and r.sub.G represents the coordinates of the
barycenter. The barycenter may be determined by operating any
desired image software, or by the following formula if the
barycenter of each divided mesh can be defined by any given
figure.
r G .fwdarw. = .SIGMA. 1 N .times. A i .times. r i .fwdarw. .SIGMA.
1 N .times. A i [ Mathematical .times. .times. 16 ]
##EQU00061##
[0874] In the formula, A.sub.i is the area of an i-th figure, and
r.sub.i is the barycentric (centroid) coordinates of the i-th
figure.
[0875] Next, the longest line segment among line segments passing
through the barycenter obtained and bounded by the boundary fixed
as described above is defined as a major axis. The line segment
orthogonal to the major axis among line segments passing through
the barycenter and bounded by the boundary fixed as described above
is defined as a minor axis.
[0876] (b) Definition and Calculation Method of Intra-Particle
Voids
[0877] The binarization may be carried out by any method by which
intra-particle voids and carbon portions are clearly distinguished
from each other, as shown in FIG. 9. It is supposed that the image
to be processed is an 8-bit gray-scale image, the luminance of one
picture element (1 Pixel) of which is expressed by a natural number
from 0 to 255. The binarization refers dividing luminances into two
and representing the two divided images in two values (e.g., 0 and
255 in this case). The binarization may be carried out using any
desired image processing software. The division by setting a
threshold can be carried out using any algorithm, such as the mode
method and the ISOData method, by which void portions and carbon
portions can be clearly distinguished from each other. The target
image needs to be a binarizable image. The binarizable image, in
this case, refers to an image in which the luminance of void
portions and the luminance of carbon portions are clearly
distinguished from each other by a certain threshold. In some
images, the surface may be rough due to low processing accuracy;
the cross section may be facing obliquely; or the luminances of
void portions and carbon portions may be close to each other
depending on the settings such as contrast and brightness. Such
images may show incorrect void distributions when binarized and
thus are preferably excluded from analysis objects. For example,
FIG. 10 is an image in which the surface of a graphite portion in
the middle has a rough pattern and a low luminance, and fine voids
have high luminances. When such an image is binarized picking up
fine parts, carbon portions are also expressed as voids; by
contrast, if a luminance at a carbon portion with no void is used
as a threshold, fine voids, which are actually voids, cannot be
displayed. Although such particles are preferably not selected, the
cross section of such particles may be typical, and thus it is
necessary not to analyze such an SEM image unsuitable for
binarization but to retake an image and adjust the brightness and
the contrast.
[0878] (c) Voids on Line Segment of Granulated Particle
[0879] "Voids in a granulated particle intersecting the minor axis
of the granulated particle" refers to voids on three line segments
that are parallel to the minor axis of the granulated particle and
split the major axis of the granulated particle into four parts
(see FIG. 13). Picture elements intersecting line segments
translated from the three line segments parallel to the minor axis
of the granulated particle in the major axis direction by .+-.0.5
pixel are regarded as voids on the minor axis.
[0880] (d) Average Interval (Zave) Between Voids and Standard
Deviation (W) of Void Sizes
[0881] The interval between voids (the distance between a void and
a void) in one randomly selected granulated particle is determined
on the above-described three line segments parallel to the minor
axis of the granulated particle (see FIG. 13). In one granulated
particle, distances Z between voids on the three line segments
parallel to the minor axis are each measured. This measurement is
made on 30 particles. Its average value is defined as the average
inter-void distance Z (Zave) of 30 particles.
[0882] Furthermore, sizes Y of voids on the three line segments
(see FIG. 13) are each measured. This measurement is made on 30
particles. Its standard deviation is defined as the standard
deviation (W) of void sizes Y of 30 particles.
[0883] In this embodiment (e.g., but not limited to, Invention
L.sup.3), voids in the granulated particle are preferably arranged,
mainly, relatively parallel to the major axis of the granulated
particle.
Negative Electrode for Non-Aqueous Secondary Battery
[0884] The present invention also relates to a negative electrode
comprising the carbon material of the present invention described
above. There is no limitation on the basic configuration and the
production method of the negative electrode of the present
invention. Hereinafter, the carbon material includes a composite
carbon material and a mixed carbon material unless otherwise
specified, The negative electrode (hereinafter also referred to as
"electrode sheet" as appropriate) for a non-aqueous secondary
battery comprising the carbon material of the present invention or
a carbon material produced by the method of the present invention
comprises a current collector and a negative electrode active
material layer on the current collector, the active material layer
comprising the carbon material of the present invention or a carbon
material produced by the method of the present invention. More
preferably, the active material layer comprises a binder.
[0885] Any binders may be used, but those having olefinic
unsaturated bonds in their molecules are preferred. Specific
examples include, but are not limited to, styrene-butadiene
rubbers, styrene-isoprene-styrene rubbers, acrylonitrile-butadiene
rubbers, butadiene rubbers, and ethylene-propylene-diene
copolymers. These binders, having olefinic unsaturated bonds, can
inhibit the active material layer from being swollen by an
electrolyte solution. In particular, styrene-butadiene rubbers are
preferred from the viewpoint of availability.
[0886] Combining the carbon material, an active material, of the
present invention with such a binder having an olefinic unsaturated
bond can increase the strength of a negative electrode plate. A
negative electrode with increased strength is less prone to
degradation by charging and discharging, leading to a prolonged
cycle life. Furthermore, in the negative electrode according to the
present invention, the adhesive strength between the active
material layer and the current collector is high. Thus, even if the
amount of binder in the active material layer is small, the active
material layer will not probably be peeled off the current
collector when the negative electrode is wound to produce a
battery.
[0887] Preferred binders having olefinic unsaturated bonds in their
molecules are those having high molecular weights and/or those
having high proportions of unsaturated bonds. Specifically, in the
case of binders having high molecular weights, preferred are those
having weight average molecular weights preferably in the range of
10,000 or greater, more preferably 50,000 or greater, and
preferably 1,000,000 or less, more preferably 300,000 or less. In
the case of binders having high proportions of unsaturated bonds,
preferred are those having olefinic unsaturated bonds in a molar
amount preferably in the range of 2.5.times.10.sup.-7 mol or more,
more preferably 8.times.10.sup.-7 mol or more, and preferably
1.times.10.sup.-6 mol or less, more preferably 5.times.10.sup.-6
mol or less, per gram of the binders. Although the binder is only
required to satisfy one of the regulation of molecular weight and
the regulation of proportion of unsaturated bonds, those satisfying
both the regulations are more preferred. A molecular weight of a
binder having an olefinic unsaturated bond in this range provides
high mechanical strength and flexibility.
[0888] The binder having an olefinic unsaturated bond preferably
has a degree of unsaturation of 15% or more, more preferably 20% or
more, still more preferably 40% or more, and preferably 90% or
less, more preferably 80% or less. The degree of unsaturation is a
proportion (%) of double bonds relative to repeating units of a
polymer.
[0889] In the present invention, a binder having no olefinic
unsaturated bond can be used in combination with the
above-described binder having an olefinic unsaturated bond to the
extent that the effects of the present invention are eliminated.
The binder having no olefinic unsaturated bond is added in an
amount preferably in the range of 150% by mass or less, more
preferably 120% by mass or less, relative to the binder having an
olefinic unsaturated bond.
[0890] Combined use of a binder having no olefinic unsaturated bond
can improve coating properties, but an excessive amount of binder
reduces the strength of the active material layer.
[0891] Examples of binders having no olefinic unsaturated bond
include polysaccharide thickeners, such as methylcellulose,
carboxymethylcellulose, starch, carrageenan, pullulan, guar gum,
and xanthan gum (xanthane gum); polyethers, such as polyethylene
oxide and polypropylene oxide; vinyl alcohols, such as polyvinyl
alcohol and polyvinyl butyral; polyacids, such as polyacrylic acid
and polymethacrylic acid; metal salts of these polymers;
fluorine-containing polymers, such as polyvinylidene fluoride;
alkane polymers, such as polyethylene and polypropylene; and
copolymers thereof.
[0892] When the carbon material according to the present invention
is used in combination with the above-described binder having an
olefinic unsaturated bond, the ratio of the binder in the active
material layer can be smaller than before. Specifically, the mass
ratio of the carbon material according to the present invention to
a binder (which may optionally be a mixture of a binder having an
unsaturated bond and a binder having no unsaturated bond as
described above) is preferably in the range of 90/10 or greater,
more preferably 95/5 or greater, and preferably 99.9/0.1 or less,
more preferably 99.5/0.5 or less, on a dry mass basis. A binder in
a ratio in this range can prevent or reduce the decrease in
capacity and the increase in resistance, and further provides an
electrode plate with high strength.
[0893] The negative electrode is formed by dispersing the carbon
material and the binder described above in a dispersion medium to
prepare a slurry and applying the slurry to a current collector.
Examples of dispersion media that can be used include organic
solvents, such as alcohols, and water. To the slurry, a conductive
agent (conductive auxiliary) may optionally be added. Examples of
conductive agents include carbon blacks, such as acetylene black,
Ketjen black, and furnace black, and fine powders of Cu, Ni, and
alloys thereof with an average particle diameter of 1 .mu.m or
less. The amount of conductive agent is preferably about 10% by
mass or less relative to the carbon material of the present
invention.
[0894] The current collector to which the slurry is applied may be
those known in the art. Specific examples include thin metal films
such as rolled copper foil, electrolytic copper foil, and stainless
foil. The thickness of the current collector is preferably 4 .mu.m
or more, more preferably 6 .mu.m or more, and preferably 30 .mu.m
or less, more preferably 20 .mu.m or less.
[0895] The slurry, after being applied to the current collector, is
dried in dry air or an inert atmosphere at a temperature of
preferably 60.degree. C. or higher, more preferably 80.degree. C.
or higher, and preferably 200.degree. C. or lower, more preferably
195.degree. C. or lower, to form an active material layer.
[0896] The active material layer obtained by applying and drying
the slurry preferably has a thickness of 5 .mu.m or more, more
preferably 20 .mu.m or more, still more preferably 30 .mu.m or
more, and preferably 200 .mu.m or less, more preferably 100 .mu.m
or less, still more preferably 75 .mu.m or less. The thickness of
the active material layer in this range is well-balanced with the
particle diameter of the active material to provide a highly
practical negative electrode that sufficiently occludes and
releases Li at a high-density current.
[0897] The thickness of the active material layer may be adjusted
to be a thickness in the above range by pressing the slurry that
has been applied and dried.
[0898] In applications where capacity is important, the density of
the carbon material in the active material layer is preferably 1.55
g/cm.sup.3 or more, more preferably 1.6 g/cm.sup.3 or more, still
more preferably 1.65 g/cm.sup.3 or more, particularly preferably
1.7 g/cm.sup.3 or more, and preferably 1.9 g/cm.sup.3 or less,
although the density varies depending on the application. A density
in this range can ensure a sufficient battery capacity per unit
volume and reduces the possibility of degradation of rate
characteristics.
[0899] For example, in applications where input-output
characteristics are important, such as automotive applications and
power tool applications, the density is typically 1.1 g/cm.sup.3 to
1.65 g/cm.sup.3. A density in this range can avoid increases in
contact resistance between particles, which might occur at an
excessively low density, and, on the other hand, can prevent or
reduce the degradation of rate characteristics, which might occur
at an excessively high density. In these applications, the density
is preferably 1.2 g/cm.sup.3 or more, more preferably 1.25
g/cm.sup.3 or more.
[0900] In applications where capacity is important, including
mobile device applications such as cellular phones and personal
computers, the density can be typically 1.45 g/cm.sup.3 or more,
and typically 1.9 g/cm.sup.3 or less. A density in this range can
avoid decreases in battery capacity per unit volume, which might
occur at an excessively low density, and, on the other hand, can
prevent or reduce the degradation of rate characteristics, which
might occur at an excessively high density. In these applications,
the density is preferably 1.55 g/cm.sup.3 or more, more preferably
1.65 g/cm.sup.3 or more, particularly preferably 1.7 g/cm.sup.3 or
more.
[0901] When a negative electrode for a non-aqueous secondary
battery is produced using the carbon material described above,
there is no limitation on the method and the selection of other
materials. Furthermore, when a lithium ion secondary battery is
produced using this negative electrode, there is no limitation on
the selection of members that constitute the lithium ion secondary
battery and are essential for a battery configuration, such as a
positive electrode and an electrolyte solution. Hereinafter, a
detailed description will be given of a negative electrode for a
lithium ion secondary battery comprising the carbon material of the
present invention and a lithium ion secondary battery comprising
the carbon material of the present invention, but the following
specific examples of usable materials, production methods, and
others should not be construed as limiting.
Non-Aqueous Secondary Battery
[0902] The non-aqueous secondary battery, particularly, the lithium
ion secondary battery, the basic configuration of which is the same
as those of lithium ion secondary batteries known in the art,
typically comprises a positive electrode and a negative electrode,
each being capable of occluding and releasing lithium ions, and an
electrolyte. The negative electrode comprises the above-described
carbon material according to one embodiment of the present
invention or a carbon material produced by the method according to
one embodiment of the present invention.
[0903] The positive electrode comprises a current collector and a
positive electrode active material layer on the current collector,
the positive electrode active material layer comprising a positive
electrode active material and a binder.
[0904] Examples of positive electrode active materials include
metal chalcogenides, which are capable of occluding and releasing
alkali metal cations, such as lithium ions, during charging and
discharging. Examples of metal chalcogenides include transition
metal oxides, such as oxides of vanadium, oxides of molybdenum,
oxides of manganese, oxides of chromium, oxides of titanium, and
oxides of tungsten; transition metal sulfides, such as sulfides of
vanadium, sulfides of molybdenum, sulfides of titanium, and CuS;
phosphorus-sulfur compounds of transition metals, such as
NiPS.sub.3 and FePS.sub.2; selenium compounds of transition metals,
such as VSe.sub.2 and NbSe.sub.3; composite oxides of transition
metals, such as Fe.sub.0.25V.sub.0.75S.sub.2 and
Na.sub.0.1CrS.sub.2; and composite sulfides of transition metals,
such as LiCoS.sub.2 and LiNiS.sub.2.
[0905] Of these, from the viewpoint of occlusion and release of
lithium ions, preferred are, for example, V.sub.2O.sub.5,
V.sub.5O.sub.13, VO.sub.2, Cr.sub.2O.sub.5, MnO.sub.2, TiO.sub.2,
MoV.sub.2O.sub.8, LiCoO.sub.2, LiNiO.sub.2, LiMn.sub.2O.sub.4,
TiS.sub.2, V.sub.2S.sub.5, Cr.sub.0.25V.sub.0.75S.sub.2, and
Cr.sub.0.5V.sub.0.5S.sub.2, and particularly preferred are
LiCoO.sub.2, LiNiO.sub.2, LiMn.sub.2O.sub.4, and lithium-transition
metal composite oxides in which these transition metals are
partially substituted with other metals. These positive electrode
active materials may be used alone or in combination.
[0906] For binding the positive electrode active material, any
known binder can be selected for use. Examples include inorganic
compounds, such as silicates and water glass, and resins having no
unsaturated bond, such as Teflon (registered trademark) and
polyvinylidene fluoride. Of these, resins having no unsaturated
bond are preferred because they are less likely to decompose during
oxidation reactions. Resins having an unsaturated bond, when used
as resins for binding the positive electrode active material, may
decompose during oxidation reactions. The weight average molecular
weights of these resins are typically in the range of 10,000 or
greater, preferably 100,000 or greater, and typically 3,000,000 or
less, preferably 1,000,000 or less.
[0907] To the positive electrode active material layer, a
conductive agent (conductive auxiliary) may be added to improve the
conductivity of the electrode. The conductive agent may be any
conductive agent capable of imparting conductivity when added in an
appropriate amount to the active material, and typical examples
include carbon powders, such as acetylene black, carbon black, and
graphite powder, metal fibers, metal powders, and metal foils.
[0908] A positive plate is formed using a method similar to that
for producing a negative electrode described above by slurrying the
positive electrode active material and the binder with a solvent
and applying the slurry to a current collector, followed by drying.
Examples of raw materials of the current collector of the positive
electrode include, but are not limited to, aluminum, nickel, and
stainless steel (SUS).
[0909] The electrolyte (also referred to as "electrolyte solution")
for use is, for example, a non-aqueous electrolyte solution of a
lithium salt in a non-aqueous solvent, or a variant of the
non-aqueous electrolyte solution formed into a gel, a rubber, or a
solid sheet by adding a macromolecular organic compound or other
compounds.
[0910] The non-aqueous solvent for use in the non-aqueous
electrolyte solution is not limited to a particular solvent, and it
can be appropriately selected from known non-aqueous solvents that
have been conventionally used as solvents for non-aqueous
electrolyte solutions. Examples include linear carbonates, such as
diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate;
cyclic carbonates, such as ethylene carbonate, propylene carbonate,
and butylene carbonate; linear ethers, such as 1,2-dimethoxyethane;
cyclic ethers, such as tetrahydrofuran, 2-methyltetrahydrofuran,
sulfolane, and 1,3-dioxolane; linear esters, such as methyl
formate, methyl acetate, and methyl propionate; and cyclic esters,
such as .gamma.-butylrolactone and .gamma.-valerolactone.
[0911] Any one of these non-aqueous solvents may be used alone, or
two or more of these may be used in combination. In the case of a
mixed solvent, preferred is a mixed solvent containing a cyclic
carbonate and a linear carbonate, and particularly preferred is a
mixed solvent containing ethylene carbonate and propylene carbonate
as cyclic carbonates because such a mixed solvent can provide high
ion conductivity even at low temperatures to improve
low-temperature charge load characteristics. In particular, the
amount of propylene carbonate is preferably in the range of 2% by
mass to 80% by mass, more preferably in the range of 5% by mass to
70% by mass, still more preferably in the range of 10% by mass to
60% by mass, based on the total amount of non-aqueous solvent.
Propylene carbonate in an amount below this range reduces ion
conductivity at low temperatures. Propylene carbonate in an amount
above this range, when a graphite electrode is used, is solvated in
lithium ions to penetrate between graphite phases, thereby causing
the graphite negative electrode active material to delaminate and
degrade, which disadvantageously results in an insufficient
capacity.
[0912] The lithium salt for use in the non-aqueous electrolyte
solution is also not limited to a particularly salt, and it can be
appropriately selected from known lithium salts known to be usable
in this application. Examples include inorganic lithium salts, such
as halides including LiCl and LiBr, perhalogen acid salts including
LiClO.sub.4, LiBrO.sub.4, and LiClO.sub.4, and inorganic fluoride
salts including LiPF.sub.6, LiBF.sub.4, and LiAsF.sub.6; and
fluorine-containing organic lithium salts, such as
perfluoroalkanesulfonic acid salts including LiCF.sub.3SO.sub.3 and
LiC.sub.4F.sub.9SO.sub.3, and perfluoroalkanesulfonic imide salts
including Li trifluoromethanesulfonyl imide
((CF.sub.3SO.sub.2).sub.2NLi). Of these, LiClO.sub.4, LiPF.sub.6,
and LiBF.sub.4 are preferred.
[0913] These lithium salts may be used alone or in a combination of
two or more. The concentration of lithium salts in the non-aqueous
electrolyte solution is typically in the range of 0.5 mol/L to 2.0
mol/L.
[0914] When the non-aqueous electrolyte solution is used in the
form of a gel, a rubber, or a solid sheet by incorporating a
macromolecular organic compound, specific examples of
macromolecular organic compounds include macromolecular polyether
compounds, such as polyethylene oxide and polypropylene oxide;
cross-linked polymers of macromolecular polyether compounds;
macromolecular vinyl alcohol compounds, such as polyvinyl alcohol
and polyvinyl butyral, insolubilized macromolecular vinyl alcohol
compounds; polyepichlorohydrin; polyphosphazene; polysiloxane,
macromolecular vinyl compounds, such as polyvinylpyrrolidone,
polyvinylidene carbonate, and polyacrylonitrile; and polymer
copolymers, such as poly(-methoxyoligooxyethylene methacrylate),
poly(-methoxyoligooxyethylene methacrylate-co-methyl methacrylate),
and poly(hexafluoropropylene-vinylidene fluoride).
[0915] The non-aqueous electrolyte solution may further contain a
film-forming agent. Specific examples of film-forming agents
include carbonate compounds, such as vinylene carbonate, vinyl
ethyl carbonate, and methylphenyl carbonate; alkene sulfides, such
as ethylene sulfide and propylene sulfide; sultone compounds, such
as 1,3-propane sultone and 1,4-butane sultone; and acid anhydrides,
such as maleic anhydride and succinic anhydride. Furthermore, an
overcharge inhibitor such as diphenyl ether or cyclohexyl benzene
may be added.
[0916] When these additives are used, the amount thereof is
typically in the range of 10% by mass or less, preferably 8% by
mass or less, more preferably 5% by mass or less, particularly
preferably 2% by mass or less, based on the total mass of the
non-aqueous electrolyte solution. An excessive amount of these
additives may have adverse effects on battery characteristics, such
as increases in initial irreversible capacity, degradation of
low-temperature characteristics and rate characteristics, and other
effects.
[0917] The electrolyte may also be a polymer solid electrolyte,
which conducts alkali metal cations, such as lithium ions. Examples
of polymer solid electrolytes include solutions of lithium salts in
the above-described macromolecular polyether compounds and
polyether derivatives terminated with alkoxides in place of
hydroxyl groups.
[0918] Typically, the positive electrode and the negative electrode
are intervened by a porous separator, such as a porous membrane or
a nonwoven fabric, to prevent a short circuit between the
electrodes. In this case, the porous separator is impregnated with
the non-aqueous electrolyte solution. Examples of raw materials of
the separator include polyolefins, such as polyethylene and
polypropylene, and polyethersulfone, and polyolefins are
preferred.
[0919] The non-aqueous secondary battery may be of any type.
Examples include cylindrical batteries including spirally-disposed
sheet electrodes and a separator, cylindrical batteries having an
inside-out structure combining pellet electrodes and a separator,
and coin batteries in which pellet electrodes and a separator are
laminated. The batteries of these types can be put in any desired
outer case of any desired shape, such as coins, cylinders, and
prisms, and any desired size.
[0920] The non-aqueous secondary battery may be assembled in any
appropriate procedure depending on the battery structure. For
example, a negative electrode is placed on an outer case; an
electrolyte solution and a separator are placed thereon; a positive
electrode is placed oppositely to the negative electrode; and these
are caulked with a gasket and a sealing plate to form a
battery.
[0921] The carbon material for a non-aqueous secondary battery
negative electrode of the present invention can provide a
non-aqueous secondary battery having high stability, a high output,
a high capacity, a low irreversible capacity, and a high cycle
retention.
EXAMPLES
[0922] Specific embodiments of the present invention will now be
described in more detail with reference to examples, but these
examples are not intended to limit the present invention.
[0923] The viscosity, contact angle, surface tension, and r cos
.theta. of granulating agents were each measured by the methods
described in the specification.
[0924] First examples (Examples A) of the present invention will
now be described.
[0925] In Examples A, physical properties of carbon materials
produced were measured by the following methods.
Preparation of Electrode Sheet
[0926] An electrode plate having an active material layer with an
active material layer density of 1.60.+-.0.03 g/cm.sup.3 was
prepared using graphite particles of Examples or Comparative
Examples. Specifically, 50.00.+-.0.02 g of a carbon material,
50.00.+-.0.02 g (0.500 g on a solids basis) of a 1% by mass aqueous
carboxymethylcellulose sodium salt solution, and 1.00.+-.0.05 g
(0.5 g on a solids basis) of an aqueous dispersion of a
styrene-butadiene rubber having a weight average molecular weight
of 270,000 were stirred with a Keyence hybrid mixer for 5 minutes,
and the mixture was defoamed for 30 seconds to give a slurry.
[0927] The slurry was applied to a 10-.mu.m-thick copper foil,
serving as a current collector, to a width of 10 cm using a small
die coater available from Itochu Machining Co., Ltd. such that the
carbon material adhered in an amount of 12.00.+-.0.3 mg/cm.sup.2.
The coated foil was roll-pressed using a roller having a diameter
of 20 cm to adjust the density of the active material layer to be
1.60.+-.0.03 g/cm.sup.3, thereby preparing an electrode sheet.
Production of Non-Aqueous Secondary Battery (2016 Coin Battery)
[0928] The electrode sheet prepared by the above-described method
was cut into a disk having a diameter of 12.5 mm, and lithium metal
foil was cut into a disk having a diameter of 14 mm to prepare a
counter electrode. A separator (made of a porous polyethylene film)
was placed between the two electrodes, the separator being
impregnated with an electrolyte solution of 1 mol/L of LiPF.sub.6
in a mixed solvent of ethylene carbonate and ethyl methyl carbonate
(volume ratio=3:7). In this manner, 2016 coin batteries were
produced.
Method of Producing Non-Aqueous Secondary Battery (Laminate
Battery)
[0929] The electrode sheet prepared by the above-described method
was cut to 4 cm.times.3 cm to prepare a negative electrode, and a
positive electrode made of NMC was cut to the same area. The
negative electrode and the positive electrode were combined with a
separator (made of a porous polyethylene film) placed therebetween.
An electrolyte solution of 1.2 mol/L of LiPF.sub.6 in a mixed
solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl
carbonate (volume ratio=3:3:4) was injected in an amount of 250
.mu.L to produce a laminate battery.
Method for Measuring Discharge Capacity
[0930] Using the non-aqueous secondary battery (2016 coin battery)
produced by the above-described method, the capacity of the battery
during charging and discharging was measured by the following
method.
[0931] The lithium counter electrode was charged to 5 mV at a
current density of 0.05 C and further charged at a constant voltage
of 5 mV to a current density of 0.005 C. The negative electrode was
doped with lithium, and then the lithium counter electrode was
discharged to 1.5 V at a current density of 0.1 C. Subsequently, a
second charging and discharging was performed at the same current
density. The discharge capacity at the second cycle was defined as
a discharge capacity of this battery.
Low-Temperature Output Characteristics
[0932] Using the laminate non-aqueous electrolyte secondary battery
produced by the method for producing a non-aqueous electrolyte
secondary battery described above, low-temperature output
characteristics were measured by the following method.
[0933] A non-aqueous electrolyte secondary battery that had yet to
go through a charge and discharge cycle was subjected to an initial
charge and discharge that involves three cycles in a voltage range
of 4.1 V to 3.0 V at 25.degree. C. and a current of 0.2 C (1 C is a
current at which a rated capacity at a 1-hour rate discharge
capacity is discharged in 1 hour, and so on) and two cycles in a
voltage range of 4.2 V to 3.0 V at a current of 0.2 C (in charging,
a constant-voltage charge at 4.2 V was further performed for 2.5
hours).
[0934] Furthermore, charging was performed at a current of 0.2 C to
an SOC of 50%, and then constant-current discharging was performed
in a low-temperature environment at -30.degree. C., for 2 seconds
at varying currents of 1/8 C, 1/4 C, 1/2 C, 1.5 C, and 2 C. The
battery voltage drop at 2 seconds after discharging under each
condition was measured. From each measurement, a current I that
could be passed in 2 seconds when the upper limit charge voltage
was 3 V was calculated, and a value calculated from the formula:
3.times.I (W) was defined as the low-temperature output
characteristics of each battery.
d50
[0935] The d50 was determined as a volume-based median diameter by
suspending 0.01 g of a carbon material in 10 mL of a 0.2% by mass
aqueous solution of a polyoxyethylene sorbitan monolaurate
surfactant (Tween 20 (registered trademark)), placing the
suspension (a measurement sample) in a commercially available laser
diffraction/scattering, particle size distribution analyzer (e.g.,
LA-920 available from HORIBA, Ltd.), irradiating the measurement
sample with ultrasonic waves of 28 kHz at a power of 60 W for 1
minute, and then perforating a measurement with the analyzer.
Mode Pore Diameter (PD) in Pore Diameter Range of 0.01 .mu.m to 1
.mu.m, Half Width at Half Maximum of Pore Distribution (log (nm)),
Cumulative Pore Volume at Pore Diameters in Range of 0.01 .mu.m to
1 .mu.m, and Total Pore Volume
[0936] The measurement by mercury intrusion was carried out using a
mercury porosimeter (Autopore 9520 available from Micromeritics
Corp). Around 0.2 g of a sample (carbon material) was weighed into
a powder cell, and the cell was sealed. The cell was subjected to a
degassing pretreatment at room temperature under vacuum (50 .mu.mHg
or lower) for 10 minutes, and then the pressure in the cell was
reduced stepwise to 4 psia. Mercury was introduced into the cell,
and the pressure was increased stepwise from 4 psia to 40,000 psia
and then reduced to 25 psia. From the mercury intrusion curve
obtained, a pore distribution was calculated using the Washburn
equation. The calculation was made assuming that the surface
tension of mercury was 485 dyne/cm, and the contact angle of
mercury was 140.degree..
[0937] From the pore distribution obtained, a mode pore diameter
(PD) in a pore diameter range of 0.01 .mu.m to 1 .mu.m, a
cumulative pore volume at pore diameters in a range of 0.01 .mu.m
to 1 .mu.m, and a total pore volume were calculated. The half width
at half maximum of pore distribution (log (nm)) is defined as a
half width at half maximum at a micropore side of a peak in a pore
diameter range of 0.01 .mu.m to 1 .mu.m in the pore distribution
(nm) with the horizontal axis expressed in common logarithm (log
(nm)).
Roundness (Average Roundness)
[0938] Using a flow-type particle image analyzer (FPIA-2000
available from Sysmex Corporation), a particle size distribution
based on equivalent circle diameter was measured, and a roundness
was determined. Ion-exchanged water was used as a dispersion
medium, and polyoxyethylene (20) monolaurate was used as a
surfactant. The equivalent circle diameter is a diameter of a
circle (equivalent circle) having the same projected area as that
of a captured particle image, and the roundness is a ratio of the
perimeter of the equivalent circle, as the numerator, to the
perimeter of the captured particle projection image, as the
denominator. Roundnesses of particles having an equivalent diameter
in the range of 1.5 to 40 .mu.m were averaged to determine the
roundness.
Frequency of Particles of 3 .mu.m or Less
[0939] The frequency of particles with a particle diameter of 3
.mu.m or less was determined by mixing 50 mL of a 0.2% by volume
aqueous solution of a polyoxyethylene sorbitan monolaurate
surfactant (Tween 20 (registered trademark)) with 0.2 g of a carbon
material, applying ultrasonic waves of 28 kHz at, a power of 60 W
for 5 minutes using a flow-type particle image analyzer "FPIA-2000
available from Sysmex Industrial Corp.", and then counting the
number of particles with a detection range set to 0.6 to 400
.mu.m.
Tap Density
[0940] Using a powder density meter, the carbon material of the
present invention was dropped through a sieve with openings of 300
.mu.m into a cylindrical tap cell with a diameter of 1.6 cm and a
volume capacity of 20 cm.sup.3 to fill up the cell, and then a tap
with a stroke length of 10 mm was given 1,000 times. The density
calculated from the volume at this time and the mass of the sample
was defined as the tap density.
Specific Surface Area (SA)
[0941] The BET specific surface area was defined as a value
determined as follows: using a surface area meter (e.g., a Gemini
2360 specific surface area analyzer available from Shimadzu
Corporation a carbon material sample was preliminarily vacuum dried
under a nitrogen stream at 100.degree. C. for 3 hours and then
cooled to liquid nitrogen temperature, and using a nitrogen-helium
mixed gas precisely regulated so as to have a nitrogen pressure of
0.3 relative to atmospheric pressure, a BET specific surface area
was measured by a nitrogen adsorption BET multipoint method
according to a flowing gas method.
Example A1
[0942] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a mechanical crusher having a crushing rotor and a
liner to give a flake natural graphite having a d50 of 30 .mu.m and
a water content of 003% by mass. To 100 g of the resulting flake
natural graphite, 6 g of a granulating agent of a paraffinic oil
(liquid paraffin available from Wako Pure Chemical Industries,
Ltd., first grade, physical properties at 25.degree. C.:
viscosity=95 cP, contact angle=13.2.degree., surface tension=31.7
mN/m, r cos .theta.=30.9) was added and mixed with stirring. The
sample obtained was disintegrated and mixed using a hammer mill
(MF10 available from IKA) at a rotation speed of 3,000 rpm to give
a flake natural graphite to which the granulating agent uniformly
adhered. Using a Model NHS-1 hybridization system available from
Nara Machinery Co., Ltd., the flake natural graphite to which the
granulating agent uniformly adhered was mechanically spheroidized
at a rotor peripheral speed of 85 m/sec for 10 minutes while fine
powder generated during the spheroidization was deposited on the
base material and incorporated into the spheroidized particles, and
heat treated in an inert gas at 720.degree. C. to give a
spheroidized natural graphite having a d50 of 19.4 .mu.m. Using the
measurement methods described above, d50, Tap (tap density),
specific surface area, pore diameter, pore volume, roundness, pore
distribution, frequency of particles, discharge capacity, and
low-temperature output characteristics were measured. The results
are shown in Tables 1A and 2A.
Comparative Example A1
[0943] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 3 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite fine powder not
deposited on the base material or incorporated into the
spheroidized particles. This sample was classified to remove the
flake graphite fine powder, thereby providing a spheroidized
graphite having a d50 of 19.5 .mu.m. The results of the
measurements made in the same manner as in Example A1 are shown in
Tables 1A and 2A.
Comparative Example A2
[0944] The sample obtained in Comparative Example A1 was further
mechanically spheroidized at a rotor peripheral speed of 85 m/sec
for 3 minutes using a Model NHS-1 hybridization system available
from Nara Machinery Co., Ltd. In the sample obtained was confirmed
the presence of a large amount of flake graphite fine powder not
deposited on the base material or incorporated into the
spheroidized particles. This sample was classified to remove the
flake graphite fine powder, thereby providing a spheroidized
graphite having a d50 of 19.3 .mu.m. The results of the
measurements made in the same manner as in Example A1 are shown in
Tables 1A and 2A.
Example A2
[0945] The spheroidized natural graphite before heat treatment
obtained in Example A1 and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.03. The results of the
measurements made in the same manner as in Example A1 are shown in
Tables 1A and 2A.
Example A3
[0946] A multi-layered carbon material made of graphite particles
and an amorphous carbon combined with each other was obtained in
the same manner as in Example A2, except that the mass ratio of
spheroidized graphite particle to amorphous carbon (spheroidized
graphite particle/amorphous carbon) was 1:0.065. The results of the
measurements made in the same manner as in Example A1 are shown in
Tables 1A and 2A.
Comparative Example A3
[0947] The spheroidized natural graphite obtained in Comparative
Example A2 and a coal-tar pitch, serving as an amorphous carbon
precursor, were mixed and heat treated in an inert gas at
1,300.degree. C., and then the burned product was disintegrated and
classified to give a multi-layered carbon material made of graphite
particles and an amorphous carbon combined with each other. The
burning yield showed that the mass ratio of spheroidized graphite
particle to amorphous carbon (spheroidized graphite
particle/amorphous carbon) of the multi-layered carbon material was
1:0.03. The results of the measurements made in the same manner as
in Example A1 are shown in Tables 1A and 2A.
Example A4
[0948] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry air-flow crusher to give a flake natural
graphite having a d50 of 6 .mu.m, a Tap of 0.13 g/cm.sup.3, and a
water content of 0.08% by mass. To 100 g of the resulting flake
natural graphite, 12 g of a granulating agent of a paraffinic oil
(liquid paraffin available from Wako Pure Chemical Industries,
Ltd., first grade, physical properties at 25.degree. C.:
viscosity=95 cP, contact angle=13.2.degree., surface tension=31.7
mN/m, r cos .theta.=30.9) was added and mixed with stirring. The
sample obtained was disintegrated and mixed using a hammer mill
(MF10 available from IKA) at a rotation speed of 3,000 rpm to give
a flake natural graphite to which the granulating agent uniformly
adhered. Using a Model NHS-1 hybridization system available from
Nara Machinery Co., Ltd., the flake natural graphite to which the
granulating agent uniformly adhered was mechanically spheroidized
at a rotor peripheral speed of 85 m/sec for 10 minutes while fine
powder generated during the spheroidization was deposited on the
base material and incorporated into the spheroidized particles, and
heat treated in an inert gas at 720.degree. C. to give a
spheroidized graphite having a d50 of 9.2 .mu.m. The results of the
measurements made in the same manner as in Example A1 are shown in
Tables 1A and 2A.
Example A5
[0949] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry swirl-flow crusher to give a flake natural
graphite having a d50 of 6 .mu.m, a Tap of 0.38 g/cm.sup.3, and a
water content of 0.08% by mass. To 100 g of the resulting flake
natural graphite, 12 g of a granulating agent of a paraffinic oil
(liquid paraffin available from Wako Pure Chemical Industries,
Ltd., first grade, physical properties at 25.degree. C.:
viscosity=95 cP, contact angle=13.2.degree., surface tension=31.7
mN/m, r cos .theta.=30.9) was added and mixed with stirring. The
sample obtained was disintegrated and mixed using a hammer mill
(MF10 available from IKA) at a rotation speed of 3,000 rpm to give
a flake natural graphite to which the granulating agent uniformly
adhered. Using a Model NHS-I hybridization system available from
Nara Machinery Co., Ltd., the flake natural graphite to which the
granulating agent uniformly adhered was mechanically spheroidized
at a rotor peripheral speed of 85 m/sec for 10 minutes while fine
powder generated during the spheroidization was deposited on the
base material and incorporated into the spheroidized particles, and
heat treated in an inert gas at 720.degree. C. to give a
spheroidized graphite having a d50 of 9.9 .mu.m. The results of the
measurements made in the same manner as in Example A1 are shown in
Tables 1A and 2A.
Comparative Example A4
[0950] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 10 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite fine powder not
deposited on the base material or incorporated into the
spheroidized particles. This sample was classified to remove the
flake graphite fine powder, thereby providing a spheroidized
graphite having a d50 of 10.8 .mu.m. The results of the
measurements made in the same manner as in Example A1 are shown in
Tables 1A and 2A.
Comparative Example A5
[0951] A flake natural graphite having a d50 of 100 .mu.m was
spheroidized and then classified to remove the above-described
flake graphite fine powder. The spheroidized graphite obtained by
spheroidizing the flake graphite was isotropically pressurized to
give a spheroidized natural graphite having a cumulative pore
volume at pore diameters of 0.01 .mu.m to 1 .mu.m of 0.069. After
that, the spheroidized natural graphite and a coal-tar pitch,
serving as an amorphous carbon precursor, were mixed and heat
treated in an inert gas at 1,300.degree. C., and then the burned
product was disintegrated and classified to give a multi-layered
carbon material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.03. The results of the
measurements made in the same manner as in Example A1 are shown in
Tables 1A and 2A.
Example A6
[0952] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry swirl-flow crusher to give a flake natural
graphite having a d50 of 8.1 .mu.m, a Tap of 0.39 g/cm.sup.3, and a
water content of 0.08% by mass. To 100 g of the resulting flake
natural graphite, 12 g of a granulating agent of a paraffinic oil
(liquid paraffin available from Wako Pure Chemical Industries,
Ltd., first grade, physical properties at 25.degree. C.:
viscosity=95 cP, contact angle=13.2.degree., surface tension=31.7
mN/m, r cos .theta.=30.9) was added and mixed with stirring. The
sample obtained was disintegrated and mixed using a hammer mill
(MF10 available from IKA) at a rotation speed of 3,000 rpm to give
a flake natural graphite to which the granulating agent uniformly
adhered. Using a Model NHS-1 hybridization system available from
Nara Machinery Co., Ltd., the flake natural graphite to which the
granulating agent uniformly adhered was mechanically spheroidized
at a rotor peripheral speed of 85 m/sec for 10 minutes while fine
powder generated during the spheroidization was deposited on the
base material and incorporated into the spheroidized particles, and
heat treated in an inert gas at 720.degree. C. to give a
spheroidized graphite having a d50 of 12.9 .mu.m. The results of
the measurements made in the same manner as in Example A1 are shown
in Tables 1A and 2A.
Example A7
[0953] The spheroidized natural graphite before heat treatment
obtained in Example A6 and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.065. The results of the
measurements made in the same manner as in Example A1 are shown in
Tables 1A and 2A.
Example A8
[0954] The spheroidized natural graphite before heat treatment
obtained in Example A6 and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.08. The results of the
measurements made in the same manner as in Example A1 are shown in
Tables 1A and 2A.
Comparative Example A6
[0955] The spheroidized natural graphite obtained in Comparative
Example A4 and a coal-tar pitch, serving as an amorphous carbon
precursor, were mixed and heat treated in an inert gas at
1,300.degree. C., and then the burned product was disintegrated and
classified to give a multi-layered carbon material made of graphite
particles and an amorphous carbon combined with each other. The
burning yield showed that the mass ratio of spheroidized graphite
particle to amorphous carbon (spheroidized graphite
particle/amorphous carbon) of the multi-layered carbon material was
1:0.065. The results of the measurements made in the same manner as
in Example A1 are shown in Tables 1A and 2A.
TABLE-US-00001 TABLE 1A Freq. of Particles Intra- Having Cumulative
Particle Pore Pore Vol. Half Diam. at Pore Total Width of 3 .mu.m
Diam. of Pore d50, Tap, SA, PD, PD/d50, at Half or less, 0.01 .mu.m
to Vol., .mu.m g/cm.sup.3 Roundness m.sup.2/g .mu.m % Max. % 1
.mu.m, mL mL Example A1 19.4 1.06 0.93 13.4 0.22 1.11 0.71 51 0.11
0.76 Comp. Ex. A1 19.5 0.9 0.91 4.9 0.67 3.44 0.42 64 0.14 0.57
Comp. Ex. A2 19.3 1.08 0.94 6.3 0.43 2.24 0.41 66 0.12 0.56 Example
A2 18.4 1.19 0.93 5.6 0.22 1.19 0.46 -- 0.09 0.47 Example A3 20 1.2
0.93 4.1 0.22 1.09 0.38 -- 0.1 0.48 Comp. Ex. A3 19.2 1.19 0.94
2.79 0.44 2.29 0.26 -- 0.1 0.47 Example A4 9.2 0.77 0.92 15 0.09
0.99 0.24 20 0.19 0.88 Example A5 9.9 0.91 0.93 21.3 0.06 0.64 0.21
13 0.16 0.78 Comp. Ex. A4 10.8 0.93 0.93 8.8 0.22 2.03 0.35 44 0.13
0.65 Comp. Ex. A5 21.9 1.2 0.92 8.8 -- -- -- -- <0.069 <0.54
Example A6 12.9 0.88 0.93 15.3 0.11 0.84 0.28 16 0.13 0.67 Example
A7 12 1.05 0.93 7.9 0.11 0.91 0.25 -- 0.12 0.62 Example A8 11.8
1.02 0.93 7.1 0.11 0.92 0.26 -- 0.11 0.67 Comp. Ex. A6 11.4 1.04
0.92 3.1 0.54 4.77 0.33 -- 0.11 0.63
TABLE-US-00002 TABLE 2A Low-Temperature Output Characteristics,
Discharge (Comparative Capacity, Example A1 = mAh/g 100) Example A1
367 122 Comparative 368 100 Example A1 Comparative 368 104 Example
A2 Example A2 362 132 Example A3 363 126 Comparative 366 108
Example A3 Example A4 365 128 Example A5 362 172 Comparative 365
118 Example A4 Comparative 362 91 Example A5 Example A6 365 128
Example A7 362 142 Example A8 359 151 Comparative 362 103 Example
A6
[0956] In Examples A1 to A8, the flake natural graphite adjusted to
have a prescribed particle size was spheroidized while fine powder
generated during the spheroidization was deposited on the base
material and/or incorporated into the spheroidized particles,
whereby a PD/d50 (%) in the prescribed range was successfully
achieved to provide a high capacity and excellent low-temperature
output characteristics. By contrast, in Comparative Examples A1 to
A4 and A6, where the PD/d50 (%) was outside the prescribed range,
and Comparative Example A5, where the cumulative pore volume, in a
range of 0.01 .mu.m to 1 .mu.m was outside the prescribed range,
degraded low-temperature output characteristics were provided.
[0957] Second examples (Examples B) of the present invention will
now be described. In Examples B, physical properties of carbon
materials produced were measured by the following methods.
d50
[0958] The d50 was determined as a volume-based median diameter by
suspending 0.01 g of a carbon material in 10 mL of a 0.2% by mass
aqueous solution of a polyoxyethylene sorbitan monolaurate
surfactant (Tween 20 (registered trademark)), placing the
suspension (a measurement sample) in a commercially available laser
diffraction/scattering particle size distribution analyzer (e.g.,
LA-920 available from HORIBA, Ltd.), irradiating the measurement
sample with ultrasonic waves of 28 kHz at a power of 60 W for 1
minute, and then performing a measurement with the analyzer.
Tap Density
[0959] Using a powder density meter, the carbon material was
dropped through a sieve with openings of 300 .mu.m into a
cylindrical tap cell with a diameter of 1.6 cm and a volume
capacity of 20 cm.sup.3 to fill up the cell, and then a tap with a
stroke length of 10 mm was given 1,000 times. The density
calculated from the volume at this time and the mass of the sample
was defined as the tap density.
Specific Surface Area SA
[0960] The specific surface area SA was defined as a value
determined as follows: using a surface area meter (Gemini 2360
specific surface area analyzer available from Shimadzu
Corporation), a carbon material sample was preliminarily vacuum
dried under a nitrogen stream at 100.degree. C. for 3 hours and
then cooled to liquid nitrogen temperature, and using a
nitrogen-helium mixed gas precisely regulated so as to have a
nitrogen pressure of 0.3 relative to atmospheric pressure, a BET
specific surface area was measured by a nitrogen adsorption BET
multipoint method according to a flowing gas method.
Residual Carbon Ratio of Granulating Agent
[0961] Sample weights before and after heat treatment of a
granulating agent in an inert atmosphere at 700.degree. C. for 1
hour were measured, and the residual carbon ratio of the
granulating agent was calculated by the following formula.
Residual .times. .times. carbon .times. .times. ratio .times.
.times. ( % .times. .times. by .times. .times. mass ) .times.
.times. of .times. .times. granulating .times. .times. agent = [ w
.times. .times. 2 .times. / .times. w .times. .times. 1 ] .times.
100 ##EQU00062##
(w1 is a mass (g) of a granulating agent before heat treatment, and
w2 is a mass (g) of the granulating agent after heat treatment)
Example B1
[0962] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry swirl-flow crusher to give a flake natural
graphite having a d50 of 8.1 .mu.m, a Tap of 0.39 g/cm.sup.3, and a
water content of 0.08% by mass. To 100 g of the resulting flake
natural graphite, 9 g of a granulating agent of
N-methyl-2-pyrrolidone (NMP) (Wako Pure Chemical Industries, Ltd.,
special grade; flash point, 86.degree. C.) was added and mixed with
stirring. The sample obtained was disintegrated and mixed using a
hammer mill (MF10 available from IKA) at a rotation speed of 3,000
rpm to give a flake natural graphite to which the granulating agent
uniformly adhered. Using a Model NHS-I hybridization system
available from Nara Machinery Co., Ltd., the sample obtained was
mechanically spheroidized at a rotor peripheral speed of 85 m/sec
for 10 minutes. The sample obtained was heat treated in a nitrogen
atmosphere at 700.degree. C., to give a spheroidized graphite
sample from which the granulating agent was removed. Using the
measurement methods described above, the residual carbon ratio,
viscosity, contact angle with graphite, and surface tension of the
granulating agent were measured, and the d50, d10, d90, SA, and Tap
of the sample obtained were measured. The results are shown in
Table 1B.
Example B2
[0963] A sample was prepared in the same manner as in Example B1
except that 12 g of a granulating agent of NMP (Wako Pure Chemical
Industries, Ltd., special grade; flash point, 86.degree. C.) was
added. The results of the measurements made in the same manner as
in Example B1 are shown in Table 1B.
Example B3
[0964] A sample was prepared in the same manner as in Example B1
except that 15 g of a granulating agent of NMP (Wako Pure Chemical
industries, Ltd., special grade; flash point, 86.degree. C.) was
added. The results of the measurements made in the same manner as
in Example B1 are shown in Table 1B.
Example B4
[0965] A sample was prepared in the same manner as in Example B1
except that 12 g of a granulating agent of a solution of 3% by mass
methyl methacrylate polymer (PMMA) (Wako Pure Chemical industries,
Ltd.) in NMP (Wako Pure Chemical Industries, Ltd., special grade;
flash point, 86.degree. C.) was added. The results of the
measurements made in the same manner as in Example B1 are shown in
Table 1B.
Example B5
[0966] A sample was prepared in the same manner as in Example B1
except that 12 g of a granulating agent of a solution of 10% by
mass PMMA (Wako Pure Chemical Industries, Ltd.) in NMP (Wako Pure
Chemical industries, Ltd., special grade; flash point, 86.degree.
C.) was added. The results of the measurements made in the same
manner as in Example B1 are shown in Table 1B.
Example B6
[0967] A sample was prepared in the same manner as in Example B1
except that 12 g of a granulating agent of a solution of 15% by
mass PMMA (Wako Pure Chemical industries, Ltd.) in NMP (Wako Pure
Chemical Industries, Ltd., special grade; flash point, 86.degree.
C.) was added. The results of the measurements made in the same
manner as in Example B1 are shown in Table 1B.
Example B7
[0968] A sample was prepared in the same manner as in Example B1
except that 12 g of a granulating agent of pure water was added.
The results of the measurements made in the same manner as in
Example B1 are shown in Table 1B.
Example B8
[0969] A sample was prepared in the same manner as in Example B1
except that 12 g of a granulating agent of an aqueous solution of
10% by mass polyacrylic acid ammonium (PAANH.sub.3) (Wako Pure
Chemical industries, Ltd., first grade) was added. The results of
the measurements made in the same manner as in Example B1 are shown
in Table 1B.
Example B9
[0970] A sample was prepared in the same manner as in Example B1
except that 12 g of a granulating agent of an aqueous solution of
30% by mass polyacrylic acid ammonium (PAANH.sub.3) (Wako Pure
Chemical Industries, Ltd., first grade) was added. The results of
the measurements made in the same manner as in Example B1 are shown
in Table 1B.
Example B10
[0971] A sample was prepared in the same manner as in Example B1
except that 12 g of a granulating agent of an aqueous solution of
44% by mass PAANH.sub.3 (Wako Pure Chemical Industries, Ltd., first
grade) was added. The results of the measurements made in the same
manner as in Example B1 are shown in Table 1B.
Example B11
[0972] A sample was prepared in the same manner as in Example B1
except that 15 g of a granulating agent of coal tar (flash point,
70.degree. C.) was added. Since the viscosity of the coal tar was
500 cP or more at 25.degree. C., the contact angle was measured in
accordance with the measurement method described above after the
sample was heated to 60.degree. C. to decrease the viscosity to 500
cP or lower. The other properties were measured in the same manner
as in Example B1. The results are shown in Table 1B.
Example B12
[0973] A sample was prepared in the same manner as in Example B1
except that 9 g of a granulating agent of creosote oil (flash
point, 70.degree. C.) was added. The results of the measurements
made in the same manner as in Example B1 are shown in Table 1B.
Example B13
[0974] A sample was prepared in the same manner as in Example B1
except that 12 g of a granulating agent of creosote oil was added.
The results of the measurements made in the same manner as in
Example B1 are shown in Table 1B.
Example B14
[0975] A sample was prepared in the same manner as in Example B1
except that 15 g of a granulating agent of creosote oil was added.
The results of the measurements made in the same manner as in
Example B1 are shown in Table 1B.
Example B15
[0976] A sample was prepared in the same manner as in Example B1
except that 9 g of a granulating agent of a paraffinic oil (liquid
paraffin available from Wako Pure Chemical Industries, Ltd., first
grade; flash point, 238.degree. C.; aniline point, >100.degree.
C.) was added. The results of the measurements made in the same
manner as in Example B1 are shown in Table 1B.
Example B16
[0977] A sample was prepared in the same manner as in Example B1
except that 12 g of a granulating agent of a paraffinic oil (liquid
paraffin available from Wako Pure Chemical Industries, Ltd., first
grade; flash point, 238.degree. C.; aniline point, >100.degree.
C.) was added. The results of the measurements made in the same
manner as in Example B1 are shown in Table 1B.
Example B17
[0978] A sample was prepared in the same manner as in Example B1
except that 15 g of a granulating agent of a paraffinic oil (liquid
paraffin available from Wako Pure Chemical Industries, Ltd., first
grade; flash point, 238.degree. C.; aniline point, >100.degree.
C.) was added. The results of the measurements made in the same
manner as in Example B1 are shown in Table 1B.
Example B18
[0979] A sample was prepared in the same manner as in Example B1
except that 9 g of a granulating agent of an aromatic oil (1)
(flash point, 242.degree. C.; aniline point, 29.degree. C.;
containing a naphthalene ring structure in its molecule) was added.
The results of the measurements made in the same manner as in
Example B1 are shown in Table 1B.
Example B19
[0980] A sample was prepared in the same manner as in Example B1
except that 12 g of a granulating agent of the aromatic oil (1)
(flash point, 242.degree. C.; aniline point, 29.degree. C.;
containing a naphthalene ring structure in its molecule) was added.
The results of the measurements made in the same manner as in
Example B1 are shown in Table 1B.
Example B20
[0981] A sample was prepared in the same manner as in Example B1
except that 15 g of a granulating agent of the aromatic oil (1)
(flash point, 242.degree. C.; aniline point, 29.degree. C.;
containing a naphthalene ring structure in its molecule) was added.
The results of the measurements made in the same manner as in
Example B1 are shown in Table 1B.
Example B21
[0982] A sample was prepared in the same manner as in Example B1
except that 9 g of a granulating agent of an aromatic oil (2)
(flash point, 50.degree. C.; aniline point, none; mixed aniline
point, 15.degree. C.; containing a benzene ring structure in its
molecule) was added. The results of the measurements made in the
same manner as in Example B1 are shown in Table 1B.
Example B22
[0983] A sample was prepared in the same manner as in Example B1
except that 12 g of a granulating agent of the aromatic oil (2)
(flash point, 150.degree. C.; aniline point, none; mixed aniline
point, 15.degree. C.: containing a benzene ring structure in its
molecule) was added. The results of the measurements made in the
same manner as in Example B1 are shown in Table 1B.
Example B23
[0984] A sample was prepared in the same manner as in Example B1
except that 15 g of a granulating agent of the aromatic oil (2)
(flash point, 150.degree. C.; aniline point, none; mixed aniline
point, 15.degree. C.; containing a benzene ring structure in its
molecule) was added. The results of the measurements made in the
same manner as in Example B1 are shown in Table 1B.
Comparative Example B1
[0985] A sample was prepared in the same manner as in Example B1
except that no granulating agent was added. The results of the
measurements made in the same manner as in Example B1 are shown in
Table 1B.
Comparative Example B2
[0986] A sample was prepared in the same manner as in Example B1
except that 12 g of a granulating agent of coal-tar pitch
(softening point, 90.degree. C.; being solid during granulation)
was added. The results of the measurements made in the same manner
as in Example B1 are shown in Table 1B.
Comparative Example B3
[0987] A sample was prepared in the same manner as in Example B1
except that 12 g of an organic compound of PMMA (Wako Pure Chemical
Industries, Ltd.; melting point, 105.degree. C.; being solid during
granulation) was added. The results of the measurements made in the
same manner as in Example B1 are shown in Table 1B.
Comparative Example 134
[0988] The sample obtained in Comparative Example B1 was air
classified to remove the flake graphite fine powder that had not
been granulated to give a spheroidized graphite having a d50 of
10.9 .mu.m and a Tap density of 0.88 g/cm.sup.3. The results of the
measurements made in the same manner as in Example B1 are shown in
Table 1B.
TABLE-US-00003 TABLE 1B Surface Contact Tension Residual Viscosity,
Angle .gamma., Amount of Granulating Carbon cP .theta., .degree.
mN/m Granulating d10, d50, d90, Tap, SA, Agent Ratio, % (25.degree.
C.) (25.degree. C.) (25.degree. C.) .gamma.cos.theta. Agent, g
.mu.m .mu.m .mu.m g/cm.sup.3 m.sup.2/g Example B1 NMP 0 1.9 4.4
40.8 40.7 9 6.6 10.4 15.7 0.92 15.8 Example B2 12 7.5 11.3 17.1
0.91 16 Example B3 15 6.7 10.6 16 0.89 16.4 Example B4 3% PMMA 0
6.2 7.3 41 40.6 12 7.8 11.7 17.3 0.92 16.6 in NMP solution Example
B5 10% PMMA 0 43 9.7 41.3 40.7 12 8.1 12.1 17.9 0.92 16.6 in NMP
solution Example B6 15% PMMA 0 164 13.1 41.7 40.6 12 9 14.1 22.6
0.96 17.4 in NMP solution Example B7 Pure water 0 0.9 95.5 72.1
-6.9 12 2.9 6.9 12.6 0.76 11.2 Example B8 Aqueous 1.5 3.9 94.8 72.9
-6.1 12 3.9 8 13.3 0.87 10.3 solution of 10% PAANH3 Example B9
Aqueous 4.4 32 88.1 75.8 2.5 12 6.5 11.1 18.1 1 11.4 solution of
30% PAANH3 Example B10 Aqueous 6.5 169 83.8 78.6 8.5 12 5.5 10.8
20.4 1 13.2 solution of 44% PAANH3 Example B11 Coal tar 27 6030
20.8 (60.degree. C.) 37.6 35.1 15 7.8 12.9 22.1 0.93 11.9 Example
B12 Creosote 0.4 5 10.8 39.4 38.7 9 7 10.8 16.2 0.94 15.4 Example
B13 oil 12 8 11.9 17.7 0.94 15.3 Example B14 15 8.2 12.3 18.1 0.89
15.2 Example B15 Paraffinic 0 90 13.2 31.7 30.9 9 7.5 11.4 17 0.85
15.1 Example B16 oil 12 8.4 12.5 18.3 0.86 15.9 Example B17 15 9.5
14.7 24.1 0.88 18.5 Example B18 Aromatic 0 58 12.9 33.7 32.8 9 7.5
11.4 17 0.92 15.9 Example B19 oil (1) 12 8.2 12.4 18.6 0.92 16.3
Example B20 15 9.4 14.3 22.4 0.92 17.9 Example B21 Aromatic 0 8.4
11.4 36.4 35.7 9 7.1 10.8 15.9 0.92 15.5 Example B22 oil (2) 12 7.8
11.5 16.7 0.9 15.5 Example B23 15 7.7 12 18.3 0.81 15.1 Comparative
-- -- -- -- -- -- 0 2.7 6.5 12.1 0.79 12.7 Example B1 Comparative
Coal-tar 40 -- -- -- -- 12 4.8 9.7 17.2 0.71 7.4 Example B2 pitch
Comparative PMMA 0 -- -- -- -- 12 2.9 6.8 12.6 0.73 12.1 Example B3
Comparative -- -- -- -- -- -- 0 6.8 10.9 17.3 0.88 8.4 Example
B4
[0989] In Examples B1 to B23, the flake natural graphite adjusted
to have a suitable particle size was spheroidized with a
granulating agent having prescribed physical properties added, as a
result of which the granulation spheroidization was promoted to
reduce the amount of flake graphite fine powder generated, leading
to increases in d10 and d50. Furthermore, the spheroidization
improved particle-filling properties, leading to increases in Tap
density.
[0990] By contrast, in Comparative Examples B1 and B4, where the
flake natural graphite was spheroidized with no granulating agent
added, and Comparative Examples B2 and B3, where the
spheroidization was carried out with a granulating agent not
satisfying the requirements added, the flake natural graphites
poorly adhered to each other, and thus the granulation
spheroidization was not sufficiently promoted, leading to
insufficient, increases in d50 and Tap.
[0991] Batteries produced using the carbon materials of Example B16
and Comparative Example B4 were evaluated by the following method.
The results are shown in Table 2B.
Preparation of Electrode Sheet
[0992] An electrode plate having an active material layer with an
active material layer density of 1.60.+-.0.03 g/cm.sup.3 or
1.35.+-.0.03 g/cm.sup.3 was prepared using a carbon material of
Examples or Comparative Examples. Specifically, 50.00.+-.0.02 g of
a carbon material, 50.00.+-.0.02 g (0.500 g on a solids basis) of a
1% by mass carboxymethylcellulose sodium salt aqueous solution, and
1.00.+-.0.05 g (0.5 g on a solids basis) of an aqueous dispersion
of a styrene-butadiene rubber having a weight average molecular
weight of 270,000 were stirred with a Keyence hybrid mixer for 5
minutes, and the mixture was defoamed for 30 seconds to give a
slurry.
[0993] The slurry was applied to a 10-.mu.m-thick copper foil,
serving as a current collector, to a width of 10 cm using a small
die coater available from Itochu Machining Co., Ltd. such that the
carbon material adhered in an amount of 12.00.+-.0.3 mg/cm.sup.2 or
6.00.+-.0.3 mg/cm.sup.2. The coated foil was roll-pressed using a
roller having a diameter of 20 cm to adjust the density of the
active material layer to be 1.60.+-.0.03 g/cm.sup.3 or 1.35.+-.0.03
g/cm.sup.3, thereby preparing an electrode sheet.
Production of Non-Aqueous Secondary Battery (2016 Coin Battery)
[0994] The electrode sheet prepared by the above-described method,
to which the carbon material adhered in an amount of 12.00.+-.0.3
mg/cm.sup.2 and in which the density of the active material layer
was adjusted to be 1.60.+-.0.03 g/cm.sup.3, was cut into a disk
having a diameter of 12.5 mm, and lithium metal foil was cut into a
disk having a diameter of 14 mm to prepare a counter electrode. A
separator (made of a porous polyethylene film) was placed between
the two electrodes, the separator being impregnated with an
electrolyte solution of 1 mol/L of LiPF.sub.6 in a mixed solvent of
ethylene carbonate and ethyl methyl carbonate (volume ratio=3:7).
In this manner, 2016 coin batteries were produced.
Method of Producing Non-Aqueous Secondary Battery (Laminate
Battery)
[0995] The electrode sheet prepared by the above-described method,
to which the carbon material adhered in an amount of 6.00.+-.0.3
mg/cm.sup.2 and in which the density of the active material layer
was adjusted to be 1.35.+-.0.03 g/cm.sup.3, was cut to 4 cm.times.3
cm to prepare a negative electrode, and a positive electrode made
of NMC was cut to the same area. The negative electrode and the
positive electrode were combined with a separator (made of a porous
polyethylene film) placed therebetween. An electrolyte solution of
1.2 mol/L of LiPF.sub.6 in a mixed solvent of ethylene carbonate,
ethyl methyl carbonate, and dimethyl carbonate (volume ratio=3:3:4)
was injected in an amount of 200 .mu.L to produce a laminate
battery.
Method for Measuring Discharge Capacity
[0996] Using the non-aqueous secondary battery (2016 coin battery)
produced by the above-described method, the capacity of the battery
during charging and discharging was measured by the following
method.
[0997] The lithium counter electrode was charged to 5 mV at a
current density of 0.05 C and further charged at a constant voltage
of 5 mV to a current density of 0.005 C. The negative electrode was
doped with lithium, and then the lithium counter electrode was
discharged to 1.5 V at a current density of 0.1 C. The discharge
capacity at this time was defined as a discharge capacity of this
battery.
[0998] Low-Temperature Output Characteristics
[0999] Using the laminate non-aqueous electrolyte secondary battery
produced by the method for producing a non-aqueous electrolyte
secondary battery described above, low-temperature output
characteristics were measured by the following method.
[1000] A non-aqueous electrolyte secondary battery that had yet to
go through a charge and discharge cycle was subjected to an initial
charge and discharge that involves three cycles in a voltage range
of 4.1 V to 3.0 V at 25.degree. C. and a current of 0.2 C (1 C is a
current at which a rated capacity at a 1-hour rate discharge
capacity is discharged in 1 hour, and so on) and two cycles in a
voltage range of 4.2 V to 3.0 V at a current of 0.2 C (in charging,
a constant-voltage charge at 4.2 V was further performed for 2.5
hours).
[1001] Furthermore, charging was performed at a current of 0.2 C to
an SOC of 50%, and then constant-current discharging was performed
in a low-temperature environment at -30.degree. C. for 2 seconds at
varying currents of 1/8 C, 1/4 C, 1/2 C, 1.5 C, and 2 C. The
battery voltage drop at 2 seconds after discharging under each
condition was measured. From each measurement, a current I that
could be passed in 2 seconds when the upper limit charge voltage
was 3 V was calculated, and a value calculated from the formula:
3.times.I (W) was defined as the low-temperature output
characteristics of each battery.
TABLE-US-00004 TABLE 2B Low-Temperature Output Characteristics,
Discharge (Comparative Capacity, Example B4 = mAh/g 100) Example
B16 367 131 Comparative 365 100 Example B4
[1002] The carbon material produced in Example B16 had a discharge
capacity and low-temperature output characteristics sufficiently
superior to those of the carbon material produced in Comparative
Example B4.
[1003] A carbonaceous material having lower crystallinity than the
raw carbon material was deposited on the carbon material obtained
by the present invention to produce a carbon material, and
batteries produced using this carbon material were evaluated. The
production of this carbon material (Examples B24 and B25) and
Comparative Example B5 will be described below, and the evaluation
results of the batteries are shown in Table 3B.
Example B24
[1004] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry swirl-flow crusher to give a flake natural
graphite having a d50 of 8.1 .mu.m, a Tap of 0.39 g/cm.sup.3, and a
water content of 0.08% by mass. To 100 g of the resulting flake
natural graphite, 12 g of a granulating agent of a liquid paraffin
(Wako Pure Chemical Industries, Ltd., first grade, physical
properties at 25.degree. C.: viscosity=95 cP, contact
angle=13.2.degree., surface tension=31.7 mN/m, r cos .theta.=30.9)
was added and mixed with stirring. The sample obtained was
disintegrated and mixed using a hammer mill (MF10 available from
IKA) at a rotation speed of 3,000 rpm to give a flake natural
graphite to which the granulating agent uniformly adhered. Using a
Model NHS-1 hybridization system available from Nara Machinery Co.,
Ltd., the sample obtained was mechanically spheroidized at a rotor
peripheral speed of 85 m/sec for 10 minutes to give granulated
carbon material particles.
[1005] The granulated carbon material particles and a coal-tar
pitch, serving as a carbonaceous material precursor having lower
crystallinity than the raw carbon material, were mixed using a
mixer at 120.degree. C. for 20 minutes. The resulting mixture was
heat treated in an inert gas at 1,300.degree. C. for 1 hour, and
then the burned product was disintegrated and classified to give
multi-layered graphite particles made of the granulated carbon
material particles and the carbonaceous material having lower
crystallinity than the raw carbon material combined with each
other. The burning yield showed that the mass ratio of the
granulated carbon material particles to the carbonaceous material
having lower crystallinity than the raw carbon material (granulated
carbon material particle/amorphous carbon) of the multi-layered
graphite particles was 1:0.065. The d50, SA, Tap, discharge
capacity, and low-temperature output characteristics of the sample
obtained were measured. The results are shown in Table 3B.
Example B25
[1006] Multi-layered graphite particles were obtained in the same
manner as in Example B24 except that the mass ratio of the
granulated carbon material particles to the carbonaceous material
having lower crystallinity than the raw carbon material (granulated
carbon material particle/amorphous carbon) of the multi-layered
graphite particles was 1:0.08. The results of the measurements made
in the same manner as in Example B24 are shown in Table 3B.
Comparative Example B5
[1007] A multi-layered carbon material was obtained in the same
manner as in Example B24 except that the granulated carbon material
particles were replaced with the sample obtained in Comparative
Example 134. The results of the measurements made in the same
manner as in Example B24 are shown in Table 3B.
TABLE-US-00005 TABLE 3B Low-Temperature Output Characteristics,
Discharge (Comparative d50, Tap SA, Capacity, Example B5 = .mu.m
g/cm.sup.3 m.sup.2/g mAh/g 100) Example B24 12.0 1.05 7.9 362 139
Example B25 11.8 1.02 7.1 359 147 Comparative 11.4 1.04 3.1 362 100
Example B5
[1008] In Examples B24 and B25, the low-temperature output
characteristics was sufficiently superior to those of Comparative
Example B5.
Third Examples (Examples C) of the Present Invention will Now be
Described.
[1009] The properties of the carbon materials of Examples C or
Comparative Examples C were measured as described below.
Measurement of Volume-Based Median Diameter d50
[1010] A sample in an amount of 0.01 g was suspended in 10 mL of
ethanol. The suspension was placed in a laser
diffraction/scattering particle size distribution analyzer (LA-920
available from HORIBA, Ltd.) and irradiated with ultrasonic waves
of 28 kHz at a power of 60 W for 1 minute, and then a volume-based
median diameter d50 was measured (ultrasonic intensity, 4; relative
refractive index, 1.50). In Examples C3 and C4 and Comparative
Examples C3 and C4, 10 mL of a 0.2% by volume aqueous solution of
polyoxyethylene sorbitan monolaurate (registered trademark, Tween
20) was used as a dispersion medium in place of ethanol.
Frequency of Particles with Diameter of 5 .mu.m or Less
[1011] A sample in an amount of 0.2 g was suspended in 50 mL of
ethanol. The suspension was placed in a flow-type particle image
analyzer (ETTA-2000 available from Sysmex Industrial Corp.) and
irradiated with ultrasonic waves of 28 kHz at a power of 60 W for a
predetermined time, and then the number of particles was counted
with a detection range set to 0.6 to 400 .mu.m to determine the
percentage of the number of particles with a diameter of 5 .mu.m or
less in the total. In Examples C3 and C4 and Comparative Examples
C3 and C4, 50 mL of a 0.2% by volume aqueous solution of
polyoxyethylene sorbitan monolaurate (registered trademark, Tween
20) was used as a dispersion medium in place of ethanol.
Tap Density
[1012] The tap density was measured using a powder density meter
(Tap Denser available from Hosokawa Micron Corporation) as follows:
a sample was dropped through a sieve with openings of 300 .mu.m
into a cylindrical tap cell with a diameter of 1.6 cm and a volume
capacity of 20 cm.sup.3 to fill up the cell; a tap with a stroke
length of 10 mm was given 1,000 times; the volume at this time was
measured; and the density was calculated from the volume and the
mass of the sample.
Roundness
[1013] A sample in an amount of 0.2 g was suspended in 50 mL of a
0.2% by mass aqueous solution of polyoxyethylene sorbitan
monolaurate (registered trademark, Tween 20). The suspension was
placed in a flow-type particle image analyzer (FPIA available from
Sysmex Industrial Corp.) and irradiated with ultrasonic waves of 28
kHz at a power of 60 W for 1 minute, and then the roundness of
particles with a diameter in the range of 1.5 to 40 .mu.m was
measured with a detection range set to 0.6 to 400 .mu.m. The ratio
of the perimeter of a circle (equivalent circle) having the same
area as the projected particle shape measured, as the numerator, to
the perimeter of the projected particle shape measured, as the
denominator, was calculated, and the average was calculated to
determine the roundness.
BET Specific Surface Area
[1014] Using a surface area meter (Gemini 2360 specific surface
area analyzer available from Shimadzu Corporation), a sample was
preliminarily vacuum dried under a nitrogen stream at 100.degree.
C. for 3 hours and then cooled to liquid nitrogen temperature, and
using a nitrogen-helium mixed gas precisely regulated so as to have
a nitrogen pressure of 0.3 relative to atmospheric pressure, a BET
specific surface area was measured by a nitrogen adsorption BET
multipoint method according to a flowing gas method.
Lc and .sub.d002
[1015] X-ray standard high-purity silicon powder was added to a
sample to prepare a mixture containing 15% by mass of the sample.
Using a CuK.alpha. radiation monochromatized with a graphite
monochromator as a radiation source, a wide-angle. X-ray
diffractometry curve was obtained by reflection diffractometry. The
method of the Japan Society for Promotion of Scientific Research
was used to determine an interplanar spacing (d.sub.002) and a
crystallite size (Lc).
Amounts of Eliminated CO and C.sub.O2 During Temperature Rise from
Room Temperature to 1,000.degree. C. Using Pyrolysis Mass
Spectrometer (TPD-MS)
[1016] A sample was heat treated under a nitrogen stream at
200.degree. C. for 5 hours. After that, the temperature was raised
from room temperature to 1,000.degree. C. at a rate of 10.degree.
C./min under a stream of He gas at 50 mL/min. The amounts of CO and
CO.sub.2 generated during this process were quantitatively measured
using a pyrolysis mass spectrometer (TPD-MS) to measure the amount
of eliminated CO (.mu.mol/g) and the amount of eliminated CO.sub.2
(.mu.mol/g) per gram of the sample.
[1017] The production of electrode sheets and non-aqueous batteries
(laminate batteries) each including the carbon material of Examples
or Comparative Examples was carried out as described below.
Preparation of Electrode Sheet
[1018] An electrode plate having an active material layer with an
active material layer density of 1.60.+-.0.03 g/cm.sup.3 was
prepared using a carbon material of Examples or Comparative
Examples. Specifically, 50.00.+-.0.02 g of a carbon material,
50.00.+-.0.02 g (0.500 g on a solids basis) of a 1% by mass
carboxymethylcellulose sodium salt aqueous solution, and
1.00.+-.0.05 g (0.5 g on a solids basis) of an aqueous dispersion
of a styrene-butadiene rubber having a weight average molecular
weight of 270,000 were stirred with a Keyence hybrid mixer for 5
minutes, and the mixture was defoamed for 30 seconds to give a
slurry.
[1019] The slurry was applied to a 10-.mu.m-thick copper foil,
serving as a current collector, to a width of 10 cm using a small
die coater available from Itochu Machining Co., Ltd. such that the
carbon material adhered in an amount of 12.00.+-.0.3 mg/cm.sup.2.
The coated foil was roll-pressed using a roller having a diameter
of 20 cm to adjust the density of the active material layer to be
1.60.+-.0.03 g/cm.sup.3, thereby preparing an electrode sheet.
Method of Producing Non-Aqueous Secondary Battery (Laminate
Battery)
[1020] The electrode sheet was cut to 4 cm.times.3 cm to prepare a
negative electrode, and a positive electrode made of
LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.2 (NMC) was cut to the same
area. The negative electrode and the positive electrode were
combined with a separator (made of a porous polyethylene film)
placed therebetween. An electrolyte solution of 1.2 mol/L of
LiPF.sub.6 in a mixed solvent of ethylene carbonate, ethyl methyl
carbonate, and dimethyl carbonate (volume ratio=3:3:4) was injected
in an amount of 250 .mu.L to produce a laminate battery.
[1021] The characteristics of the laminate batteries produced were
measured as described below.
[1022] Initial Low-Temperature Output Characteristics The initial
low-temperature output characteristics of the laminate batteries
were measured by the following method.
[1023] A laminate battery that had yet to go through a charge and
discharge cycle was subjected to an initial charge and discharge
that involves three cycles in a voltage range of 4.1 V to 3.0 V at
25.degree. C. and a current of 0.2 C (1 C is a current at which a
rated capacity at a 1-hour rate discharge capacity is discharged in
1 hour, and so on) and two cycles in a voltage range of 4.2 V to
3.0 V at a current of 0.2 C (in charging, a constant-voltage charge
at 4.2 V was further performed for 2.5 hours).
[1024] For the battery that had been subjected to the initial
charge and discharge, charging was further performed at a current
of 0.2 C to a charging rate (SOC, State Of Charge) of 50%, and then
constant-current discharging was performed in a low-temperature
environment at -30.degree. C., for 2 seconds at varying currents of
1/8 C, 1/4 C, 1/2 C, 1.5 C, and 2 C. The battery voltage drop at 2
seconds after discharging under each condition was measured. From
each measurement, a current I that could be passed in 2 seconds
when the upper limit charge voltage was 3 V was calculated, and a
value calculated from the formula: 3.times.I (W) was defined as the
low-temperature output characteristics in initial 2 seconds of each
battery.
[1025] Likewise, a current I that could be passed in 10 seconds was
calculated, and the calculated value was defined as the
low-temperature output characteristics in initial 10 seconds.
Post-Cycle Low-Temperature Output Characteristics
[1026] The post-cycle low-temperature output characteristics of the
laminate batteries were measured by the following method.
[1027] A laminate battery that had yet to go through a charge and
discharge cycle was subjected to a charge and discharge that
involves 3 cycles in a voltage range of 4.1 V to 3.0 V at
25.degree. C. and a current of 0.2 C and 300 cycles in a voltage
range of 4.2 V to 3.0 V at a current of 0.2 C (in charging, a
constant-voltage charge at 4.2 V was further performed for 2.5
hours).
[1028] For the battery that had been subjected to the 300-cycle
charge and discharge, charging was performed at a current of 0.2 C
to a charging rate (SOC) of 50%, and then constant-current
discharging was performed in a low-temperature environment at
-30.degree. C. for 2 seconds at varying currents of 1/8 C, 1/4 C,
1/2 C, 1.5 C, and 2 C. The battery voltage drop at 2 seconds after
discharging under each condition was measured. From each
measurement, a current I that could be passed in 2 seconds when the
upper limit charge voltage was 3 V was calculated, and a value
calculated from the formula: 3.times.I (W) was defined as the
low-temperature output characteristics in post-cycle 2 seconds of
each battery.
[1029] Likewise, a current I that could be passed in 10 seconds was
calculated, and the calculated value was defined as the
low-temperature output characteristics in post-cycle 10
seconds.
Production of Non-Aqueous Secondary Battery (2016 Coin Battery)
[1030] The electrode sheet prepared by the above-described method
was cut into a disk having a diameter of 12.5 mm, and lithium metal
foil was cut into a disk having a diameter of 14 mm to prepare a
counter electrode. A separator (made of a porous polyethylene film)
was placed between the two electrodes, the separator being
impregnated with an electrolyte solution of 1 mol/L of LiPF.sub.6
in a mixed solvent of ethylene carbonate and ethyl methyl carbonate
(volume ratio=3:7). In this manner, 2016 coin batteries were
produced.
Method for Measuring Initial Discharge Capacity
[1031] Using the non-aqueous secondary battery (2016 coin battery)
produced by the above-described method, the capacity of the battery
during charging and discharging was measured by the following
method.
[1032] The lithium counter electrode was charged to 5 mV at a
current density of 0.05 C and further charged at a constant voltage
of 5 mV to a current density of 0.005 C. The negative electrode was
doped with lithium, and then the lithium counter electrode was
discharged to 1.5 V at a current density of 0.1 C. Subsequently, a
second charging and discharging was performed at the same current
density. The discharge capacity at the second cycle was defined as
an initial discharge capacity (1st discharge capacity) of this
battery.
Example C1
[1033] A flake natural graphite having a volume-based median
diameter d50 of 100 .mu.m was crushed with a mechanical crusher
(Turbo Mill available from Freund Corporation) having a crushing
rotor and a liner to give a flake natural graphite having a
volume-based median diameter d50 of 30 .mu.m. Using an NHS-1
hybridization system available from Nara Machinery Co., Ltd., 300 g
of the flake natural graphite was mechanically spheroidized at a
rotor peripheral speed of 88 m/sec for 1 minute while fine powder
generated during the spheroidization was deposited on the base
material and incorporated into the spheroidized particles. The
spheroidized graphite was further spheroidized for 2 minutes while
30 g of a liquid paraffin (Wako Pure Chemical Industries, Ltd.,
first grade; flash point, 238.degree. C.) was added to the
spheroidized graphite to reduce the amount of exposure of the
graphite to oxygen. The gas phase during the process was sampled
and analyzed by gas chromatography to show that the amount of CO
and the amount of CO.sub.2 generated from 1 kg of the flake natural
graphite were respectively 0.3 mmol and 0.9 mmol.
[1034] The carbon material obtained had a D50 (.mu.m), a
volume-based median diameter, of 15.0 .mu.m, a Q.sub.5min (%), a
frequency of particles with a diameter of 5 .mu.m or less (fine
powder content) after ultrasonic irradiation for 5 minutes, of 13%,
and a Q.sub.5min (%)/D50 (.mu.m) of 0.9.
[1035] The carbon material had a Q.sub.1min (%), a frequency of
particles with a diameter of 5 .mu.m or less (fine powder content)
after ultrasonic irradiation for 1 minute, of 5%, a Q.sub.10min
(%), a frequency of particles with a diameter of 5 .mu.m or less
(fine powder content) after ultrasonic irradiation for 10 minutes,
of 27%, a Q.sub.1min(%)/D50 (.mu.m) of 0.3, and a Q.sub.10min
(%)/D50 (.mu.m) of 1.8.
[1036] The carbon material had a roundness of 0.89, a tap density
of 0.79 g/cm.sup.3, and a BET specific surface area of 12.9
m.sup.2/g.
[1037] The carbon material was embedded in a resin to prepare a
sample for cross-sectional observation, and a cross section was
observed under a scanning electron microscope to show that the
carbon material was formed of different graphite particles.
[1038] The amount of eliminated CO and the amount of CO.sub.2 of
the carbon material during the temperature rise from room
temperature to 1,000.degree. C. using a pyrolysis mass spectrometer
(TPD-MS) were respectively 9 .mu.mol/g and 2 .mu.mol/g.
[1039] The carbon material had an Lc, as determined by wide-angle
X-ray diffractometry, of 100 nm or more and a d.sub.002 of 0.336
nm.
[1040] The physical properties of the carbon material are shown in
Tables 1C to 3C. Initial output characteristics and post-cycle
output characteristics of laminate batteries produced using the
carbon material and initial discharge capacities of coin batteries
produced using the carbon material are shown in Table 4C.
Example C2
[1041] The same procedure as in Example C1 was repeated except that
a flake natural graphite and a liquid paraffin were mixed before
spheroidization and then spheroidized for 3 minutes so that the
amount of CO and the amount of CO.sub.2 generated from 1 kg of the
flake natural graphite would be respectively 0.3 mmol and 1.0
mmol.
[1042] The carbon material obtained had a Q.sub.5min (%)/D50
(.mu.m) of 1.1.
[1043] The carbon material was embedded in a resin to prepare a
sample for cross-sectional observation, and a cross section was
observed under a scanning electron microscope to show that the
carbon material was formed of different graphite particles. The
physical properties of the carbon material are shown in Tables 1C
to 3C. The properties of laminate batteries and coin batteries
produced using the carbon material are shown in Table 4C.
Example C3
[1044] The same procedure as in Example C1 was repeated except that
the spheroidization was carried out using ethylene glycol (Wako
Pure Chemical Industries, Ltd., first grade; flash point,
110.degree. C.) in place of the liquid paraffin so that the amount
of CO and the amount of CO.sub.2 generated from 1 kg of the flake
natural graphite would be respectively 2.1 mmol and 4.0 mmol.
Furthermore, the carbon material obtained was dried in a nitrogen
atmosphere at 250.degree. C.
[1045] The carbon material obtained had a Q.sub.5min (%)/D50
(.mu.m) of 1.9.
[1046] The carbon material was embedded in a resin to prepare a
sample for cross-sectional observation, and a cross section was
observed under a scanning electron microscope to show that the
carbon material was formed of different graphite particles.
[1047] The physical properties of the carbon material are shown in
Tables 1C to 3C. The properties of laminate batteries and coin
batteries produced using the carbon material are shown in Table
4C.
Example C4
[1048] The same procedure as in Example C3 was repeated except that
a flake graphite and ethylene glycol were mixed before
spheroidization and spheroidized for 3 minutes in an apparatus for
applying a mechanical action(s) so that the amount of CO and the
amount of CO.sub.2 generated from 1 kg of the flake natural
graphite would be respectively 2.5 mmol and 5.0 mmol.
[1049] The carbon material obtained had a Q.sub.5min (%)/D50
(.mu.m) of 2.3.
[1050] The carbon material was embedded in a resin to prepare a
sample for cross-sectional observation, and a cross section was
observed under a scanning electron microscope to show that the
carbon material was formed of different graphite particles.
[1051] The physical properties of the carbon material are shown in
Tables 1C to 3C. The properties of laminate batteries and coin
batteries produced using the carbon material are shown in Table
4C.
Comparative Example C1
[1052] The same procedure as in Example C1 was repeated except that
the flake natural graphite having a volume-based median diameter
d50 of 30 .mu.m used in Example C1 was spheroidized in an air
atmosphere. The gas phase during the process was sampled and
analyzed by gas chromatography to show that the amount of CO and
the amount of CO.sub.2 generated from 1 kg of the flake natural
graphite were respectively 7.2 mmol and 11.2 mmol.
[1053] The carbon material obtained had a D50 (.mu.m), a
volume-based median diameter, of 14.4 .mu.m, a Q.sub.5min (%), a
frequency of particles with a diameter of 5 .mu.m or less (fine
powder content) after 5-minute ultrasonic, of 75%, and a Q.sub.5min
(%)/D50 (.mu.m) of 5.2.
[1054] The carbon material was embedded in a resin to prepare a
sample for cross-sectional observation, and a cross section was
observed under a scanning electron microscope to show that the
carbon material was formed of different graphite particles.
[1055] The physical properties of the carbon material are shown in
Tables 1C to 3C. The properties of laminate batteries and coin
batteries produced using the carbon material are shown in Table
4C.
Comparative Example C2
[1056] The carbon material of Comparative Example C1 obtained
through the spheroidization was dried in a nitrogen atmosphere in
the same manner as in Example C3 to prepare a carbon material of
Comparative Example C2.
[1057] The carbon material obtained had a Q.sub.5min (%)/D50
(.mu.m) of 5.3.
[1058] The carbon material was embedded in a resin to prepare a
sample for cross-sectional observation, and a cross section was
observed under a scanning electron microscope to show that the
carbon material was formed of different graphite particles.
[1059] The physical properties of the carbon material are shown in
Tables 1C to 3C. The properties of laminate batteries and coin
batteries produced using the carbon material are shown in Table
4C.
Comparative Example C3
[1060] A commercially available spheroidized natural graphite A had
a D50 (.mu.m) of 20.3 .mu.m, a Q.sub.5min (%) of 76%, and a
Q.sub.5min (%)/D50 (.mu.m) of 3.7, as measured in the same manner
as in Example C3.
[1061] The natural graphite A was embedded in a resin to prepare a
sample for cross-sectional observation, and a cross section was
observed under a scanning electron microscope to show that natural
graphite A was formed of different graphite particles.
[1062] The physical properties of the natural graphite A are shown
in Tables 1C and 3C. The properties of laminate batteries and coin
batteries produced using the natural graphite A are shown in Table
4C.
Comparative Example C4
[1063] A commercially available spheroidized natural graphite B had
a D50 (.mu.m) of 16.0 .mu.m, a Q.sub.5min (%) of 69%, and a
Q.sub.5min (%)/D50 (.mu.m) of 4.3, as measured in the same manner
as in Comparative Example C3.
[1064] The natural graphite B was embedded in a resin to prepare a
sample for cross-sectional observation, and a cross section was
observed under a scanning electron microscope to show that natural
graphite B was formed of different graphite particles.
[1065] The physical properties of the natural graphite B are shown
in Tables 1C and 3C. The properties of laminate batteries and coin
batteries produced using the natural graphite B are shown in Table
4C.
TABLE-US-00006 TABLE 1C Q.sub.5 min Q.sub.1 min Q.sub.10 min (%)/
(%)/ (%)/ D50 D50 D50 Q.sub.5 min Q.sub.1 min Q.sub.10 min (.mu.m)
(.mu.m) (.mu.m) (%) (%) (%) Example C1 0.9 0.3 1.8 13 5 27 Example
C2 1.1 0.5 1.8 16 7 26 Example C3 1.9 0.6 2.9 28 9 42 Example C4
2.3 0.6 2.8 33 9 40 Comparative 5.2 5.0 5.3 75 72 77 Example C1
Comparative 5.3 5.1 5.4 76 73 78 Example C2 Comparative 3.7 2.7 4.1
76 55 83 Example C3 Comparative 4.3 3.0 4.8 69 48 76 Example C4
TABLE-US-00007 TABLE 2C Amount of Amount of Amount of eliminated CO
+ CO.sub.2 eliminated CO eliminated CO.sub.2 (.mu.mol/g)
(.mu.mol/g) (.mu.mol/g) during during during temperature
temperature temperature rise from room rise from room rise from
room temperature to temperature to temperature to 1,000.degree. C.,
as 1,000.degree. C., as 1,000.degree. C., as determined by
determined by determined by TPD-MS TPD-MS TPD-MS Example C1 11 9 2
Example C2 11* 10 2 Example C3 51 40 11 Example C4 62 49 13
Comparative 163 130 33 Example C1 Comparative 155 127 28 Example C2
Comparative -- -- -- Example C3 Comparative -- -- -- Example C4 *11
(.mu.mol/g) is a value obtained by rounding off 11.3 (.mu.mol/g),
the total amount of the amount of eliminated CO 9.7 (.mu.mol/g) and
the amount of eliminated CO.sub.2 1.6 (.mu.mol/g), to the nearest
integer.
TABLE-US-00008 TABLE 3C BET Volume- Specific Based Tap Surface
Median Density Area Diameter Lc d.sub.002 (g/cm.sup.3) Roundness
(m.sup.2/g) (.mu.m) (nm) (nm) Example C1 0.79 0.89 12.9 15.0
>100 0.336 Example C2 0.85 0.89 13.5 14.7 >100 0.336 Example
C3 0.98 0.90 11.7 14.7 >100 0.336 Example C4 0.98 0.90 11.7 14.5
>100 0.336 Comparative 0.76 0.87 11.0 14.4 >100 0.336 Example
C1 Comparative 0.73 0.88 11.0 14.4 >100 0.336 Example C2
Comparative 0.92 0.89 5.1 20.3 >100 0.336 Example C3 Comparative
1.02 0.93 7.0 16.0 >100 0.336 Example C4
TABLE-US-00009 TABLE 4C Low- Low- Low- Low- Temperature Temperature
Temperature Temperature Output in Output in Output in Post- Output
in Post- Initial Initial 2 Initial 10 Cycle 2 Cycle 10 Discharge
Seconds Seconds Seconds Seconds Capacity (W) (W) (W) (W) (mAh/g)
Example C1 0.093 0.076 0.068 0.044 365 Example C2 0.098 0.080 0.068
0.043 365 Example C3 0.079 0.064 0.060 0.040 364 Example C4 0.083
0.068 0.062 0.041 362 Comparative 0.074 0.061 0.055 0.038 365
Example C1 Comparative 0.077 0.063 0.055 0.038 365 Example C2
Comparative 0.046 0.037 0.044 0.027 368 Example C3 Comparative
0.060 0.047 0.049 0.030 368 Example C4
[1066] The batteries produced using Examples C1 to C4, the carbon
materials of the present invention, have high and excellent initial
and post-cycle low-temperature output characteristics. By contrast,
the carbon materials used in Comparative Examples C1 to C4 have a
Q.sub.5min (%) to D50 (.mu.m) ratio outside the prescribed range,
where Q.sub.5min is a frequency of particles with a diameter of 5
.mu.m or less (fine powder content) after ultrasonic irradiation
for 5 minutes, and D50 is a volume-based median diameter, and thus
provide low initial and post-cycle low-temperature output
characteristics.
Fourth Examples (Examples D) of the Present Invention will Now be
Described.
[1067] Preparation of Electrode Sheet An electrode plate having an
active material layer with an active material layer density of
1.50.+-.0.03 g/cm.sup.3 was prepared using graphite particles of
Examples or Comparative Examples. Specifically, 50.00.+-.0.02 g of
a negative electrode material (carbon material), 50.00.+-.0.02 g
(0.500 g on a solids basis) of a 1% by mass aqueous
carboxymethylcellulose sodium salt solution, and 1.00.+-.0.05 g
(0.5 g on a solids basis) of an aqueous dispersion of a
styrene-butadiene rubber having a weight average molecular weight
of 270,000 were stirred with a Keyence hybrid mixer for 5 minutes,
and the mixture was defoamed for 30 seconds to give a slurry.
[1068] The slurry was applied to a 1.0-.mu.m-thick copper foil,
serving as a current collector, to a width of 10 cm using a small
die coater available from Itochu Machining Co., Ltd. such that the
negative electrode material adhered in an amount of 6.00.+-.0.3
mg/cm.sup.2 or 12.00.+-.0.3 mg/cm.sup.2. The coated foil was
roll-pressed using a roller having a diameter of 20 cm to adjust
the density of the active material layer to be 1.50.+-.0.03
g/cm.sup.3, thereby preparing an electrode sheet.
Production of Non-Aqueous Secondary Battery (2016 Coin Battery)
[1069] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
12.00.+-.0.3 mg/cm.sup.2, was cut into a disk having a diameter of
12.5 mm, and lithium metal foil was cut into a disk having a
diameter of 14 mm to prepare a counter electrode. A separator (made
of a porous polyethylene film) was placed between the two
electrodes, the separator being impregnated with an electrolyte
solution of 1 mol/L of LiPF.sub.6 in a mixed solvent of ethylene
carbonate and ethyl methyl carbonate (volume ratio=3:7). In this
manner, 2016 coin batteries were produced.
Method of Producing Non-Aqueous Secondary Battery (Laminate
Battery)
[1070] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
6.00.+-.0.3 mg/cm.sup.2, was cut to 4 cm.times.3 cm to prepare a
negative electrode, and a positive electrode made of NMC was cut to
the same area. The negative electrode and the positive electrode
were combined with a separator (made of a porous polyethylene film)
placed therebetween. An electrolyte solution of 1.2 mol/L of
LiPF.sub.6 in a mixed solvent of ethylene carbonate, ethyl methyl
carbonate, and dimethyl carbonate (volume ratio=3:3:4) was injected
in an amount of 250 .mu.L to produce a laminate battery.
Method for Measuring 1st Discharge Capacity
[1071] Using the non-aqueous secondary battery (2016 coin battery)
produced by the above-described method, the capacity of the battery
during charging and discharging was measured by the following
method.
[1072] The lithium counter electrode was charged to 5 mV at a
current density of 0.04 C and further charged at a constant voltage
of 5 mV to a current density of 0.005 C. The negative electrode was
doped with lithium, and then the lithium counter electrode was
discharged to 1.5 V at a current density of 0.08 C. Subsequently, a
second charging and discharging was performed at the same current
density. The discharge capacity at the second cycle was defined as
a 1st discharge capacity of this battery.
Low-Temperature Output Characteristics
[1073] Using the laminate non-aqueous electrolyte secondary battery
produced by the method for producing a non-aqueous electrolyte
secondary battery described above, low-temperature output
characteristics were measured by the following method.
[1074] A non-aqueous electrolyte secondary battery that had yet to
go through a charge and discharge cycle was subjected to an initial
charge and discharge that involves three cycles in a voltage range
of 4.1 V to 3.0 V at 25.degree. C. and a current of 0.2 C (1 C is a
current at which a rated capacity at a 1-hour rate discharge
capacity is discharged in 1 hour, and so on) and two cycles in a
voltage range of 4.2 V to 3.0 V at a current of 0.2 C (in charging,
a constant-voltage charge at 4.2 V was further performed for 2.5
hours).
[1075] Furthermore, charging was performed at a current of 0.2 C to
an SOC of 50%, and then constant-current discharging was performed
in a low-temperature environment at -30.degree. C. for 2 seconds at
varying currents of 1/8 C, 1/4 C, 1/2 C, 1.5 C, and 2 C. The
battery voltage drop at 2 seconds after discharging under each
condition was measured. From each measurement, a current I that
could be passed in 2 seconds when the upper limit charge voltage
was 3 V was calculated, and a value calculated from the formula:
3.times.I (W) was defined as the low-temperature output
characteristics of each battery.
Average Particle Diameter d50; d50
[1076] The d50 was determined as a volume-based median diameter by
suspending 0.01 g of a carbon material in 10 mL of a 0.2% by mass
aqueous solution of a polyoxyethylene sorbitan monolaurate
surfactant (Tween 20 (registered trademark)), placing the
suspension (a measurement sample) in a commercially available laser
diffraction/scattering particle size distribution analyzer (e.g.,
LA-920 available from HORIBA, Ltd.), irradiating the measurement
sample with ultrasonic waves of 28 kHz at a power of 60 W for 1
minute, and then performing a measurement with the analyzer.
Tap Density; Tap (.sub.Yd)
[1077] Using a powder density meter, the carbon material of the
present invention was dropped through a sieve with openings of 300
.mu.m into a cylindrical tap cell with a diameter of 1.6 cm and a
volume capacity of 20 cm.sup.3 to fill up the cell, and then a tap
with a stroke length of 10 mm was given 1,000 times. The density
calculated from the volume at this time and the mass of the sample
was defined as the tap density.
Specific Surface Area Determined by BET Method; SA (.sub.Xd)
[1078] Using a surface area meter (fully automatic surface area
analyzer available from Ohkura Riken Co., Ltd.), a carbon material
sample was preliminarily dried under a nitrogen stream at
350.degree. C. for 15 minutes, and then using a nitrogen-helium
mixed gas precisely regulated so as to have a nitrogen pressure of
0.3 relative to atmospheric pressure, a BET specific surface area
was measured by a nitrogen adsorption BET multipoint method
according to a flowing gas method.
Example D1
[1079] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a mechanical crusher having a crushing rotor and a
liner to give a flake natural graphite having a d50 of 30 .mu.m and
a water content of 0.03% by mass. To 100 g of the resulting flake
natural graphite, 6 g of a granulating agent of a paraffinic oil
(liquid paraffin available from Wako Pure Chemical Industries,
Ltd., first grade, physical properties at 25.degree. C.;
viscosity=95 cP, contact angle=13.2.degree., surface tension=31.7
mN/m, r cos .theta.=30.9) was added and mixed with stirring. The
sample obtained was disintegrated and mixed using a hammer mill
(MF10 available from IKA) at a rotation speed of 3,000 rpm to give
a flake natural graphite to which the granulating agent uniformly
adhered. Using a Model NHS-1 hybridization system available from
Nara Machinery Co., Ltd., the flake natural graphite to which the
granulating agent uniformly adhered was mechanically spheroidized
at a rotor peripheral speed of 85 m/sec for 10 minutes while fine
powder generated during the spheroidization was deposited on the
base material and incorporated into the spheroidized particles,
thereby providing a spheroidized natural graphite having a d50 of
19.4 .mu.m. The spheroidized natural graphite and a coal-tar pitch,
serving as an amorphous carbon precursor, were mixed and heat
treated in an inert gas at 1,300.degree. C., and then the burned
product was disintegrated and classified to give a multi-layered
carbon material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.030. Using the measurement
methods described above, d50, SA, Tap, 1st discharge capacity, and
low-temperature output characteristics were measured. The results
are shown in Table 1D.
Example D2
[1080] The spheroidized natural graphite obtained in Example D1 and
a coal-tar pitch, serving as an amorphous carbon precursor, were
mixed and heat treated in an inert gas at 1,300.degree. C., and
then the burned product was disintegrated and classified to give a
multi-layered carbon material made of graphite particles and an
amorphous carbon combined with each other. The burning yield showed
that the mass ratio of spheroidized graphite particle to amorphous
carbon (spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.042. The results of the
measurements made in the same manner as in Example D1 are shown in
Table 1D.
Example D3
[1081] The spheroidized natural graphite obtained in Example D1 and
a coal-tar pitch, serving as an amorphous carbon precursor, were
mixed and heat treated in an inert gas at 1,300.degree. C., and
then the burned product was disintegrated and classified to give a
multi-layered carbon material made of graphite particles and an
amorphous carbon combined with each other. The burning yield showed
that the mass ratio of spheroidized graphite particle to amorphous
carbon (spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.050. The results of the
measurements made in the same manner as in Example D1 are shown in
Table 1D.
Example D4
[1082] The spheroidized natural graphite obtained in Example D1 and
a coal-tar pitch, serving as an amorphous carbon precursor, were
mixed and heat treated in an inert gas at 1,300.degree. C. and then
the burned product was disintegrated and classified to give a
multi-layered carbon material made of graphite particles and an
amorphous carbon combined with each other. The burning yield showed
that the mass ratio of spheroidized graphite particle to amorphous
carbon (spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.065. The results of the
measurements made in the same manner as in Example D1 are shown in
Table 1D.
Example D5
[1083] The spheroidized natural graphite obtained in Example D1 and
a coal-tar pitch, serving as an amorphous carbon precursor, were
mixed and heat treated in an inert gas at 1,300.degree. C., and
then the burned product was disintegrated and classified to give a
multi-layered carbon material made of graphite particles and an
amorphous carbon combined with each other. The burning yield showed
that the mass ratio of spheroidized graphite particle to amorphous
carbon (spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.100. The results of the
measurements made in the same manner as in Example D1 are shown in
Table 1D.
Comparative Example D1
[1084] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 10 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 10.8 .mu.m.
[1085] The spheroidized natural graphite and a coal-tar pitch,
serving as an amorphous carbon precursor, were mixed and heat
treated in an inert gas at 1,300.degree. C., and then the burned
product was disintegrated and classified to give a multi-layered
carbon material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.020. The results of the
measurements made in the same manner as in Example D1 are shown in
Table 1D.
Comparative Example D2
[1086] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 10 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 10.8 .mu.m. The
spheroidized natural graphite and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.040. The results of the
measurements made in the same manner as in Example D1 are shown in
Table 1D.
Comparative Example D3
[1087] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 3 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 15.7 .mu.m. The
spheroidized natural graphite and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.015. The results of the
measurements made in the same manner as in Example D 1 are shown in
Table 1D.
Comparative Example D4
[1088] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 3 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 15.7 .mu.m. The
spheroidized natural graphite and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.040. The results of the
measurements made in the same manner as in Example D1 are shown in
Table 1D.
Comparative Example D5
[1089] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 10 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 10.8 .mu.m. The
spheroidized natural graphite and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.013. The results of the
measurements made in the same manner as in Example D1 are shown in
Table 1D.
Comparative Example D6
[1090] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 3 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 19.5 .mu.m. The
spheroidized natural graphite and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.075. The results of the
measurements made in the same manner as in Example D1 are shown in
Table 1D.
[1091] Table 10
TABLE-US-00010 TABLE 1D 1st Discharge Low- d50 SA (X.sub.d) Tap
(Y.sub.d) 10Y.sub.d + Capacity Temperature (.mu.m) (m.sup.2/g)
(g/cm.sup.3) 0.26X.sub.d (mAh/g) Output (W) Example D1 17.9 7.38
1.16 13.51 366 0.094 Example D2 18.4 5.79 1.19 13.37 363 0.099
Example D3 19.4 5.15 1.18 13.15 363 0.099 Example D4 20.0 4.30 1.20
13.08 362 0.102 Example D5 22.4 2.88 1.19 12.64 358 0.090
Comparative 10.4 3.92 1.08 11.82 364 0.087 Example D1 Comparative
10.5 2.97 1.11 11.87 360 0.080 Example D2 Comparative 15.8 3.53
1.11 12.06 362 0.085 Example D3 Comparative 15.4 2.51 1.15 12.13
361 0.069 Example D4 Comparative 10.7 4.48 1.07 11.88 364 0.086
Example D5 Comparative 19.3 1.82 1.21 12.56 361 0.059 Example
D6
[1092] In Examples D1 to D5, the flake natural graphite adjusted to
have a prescribed particle size was spheroidized while fine powder
generated during the spheroidization was deposited on the base
material and/or incorporated into the spheroidized particles,
whereby the above inequality (1D) was successfully satisfied to
provide a high capacity and excellent low-temperature output
characteristics.
Fifth Examples (Examples E) of the Present Invention will Now be
Described.
Preparation of Electrode Sheet
[1093] An electrode plate having an active material layer with an
active material layer density of 1.50.+-.0.03 g/cm.sup.3 was
prepared using graphite particles of Examples or Comparative
Examples. Specifically, 50.00.+-.0.02 g of a negative electrode
material, 50.00.+-.0.02 g (0.500 g on a solids basis) of a 1% by
mass aqueous carboxymethylcellulose sodium salt solution, and
1.00.+-.0.05 g (0.5 g on a solids basis) of an aqueous dispersion
of a styrene-butadiene rubber having a weight average molecular
weight of 270,000 were stirred with a Keyence hybrid mixer for 5
minutes, and the mixture was defoamed for 30 seconds to give a
slurry.
[1094] The slurry was applied to a 10-.mu.m-thick copper foil,
serving as a current collector, to a width of 10 cm using a small
die coater available from Itochu Machining Co., Ltd. such that the
negative electrode material adhered in an amount of 6.00.+-.0.3
mg/cm.sup.2 or 12.00.+-.0.3 mg/cm.sup.2. The coated foil was
roll-pressed using a roller having a diameter of 20 cm to adjust
the density of the active material layer to be 1.50.+-.0.03
g/cm.sup.3, thereby preparing an electrode sheet.
Production of Non-Aqueous Secondary Battery (2016 Coin Battery)
[1095] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
12.00.+-.0.3 mg/cm.sup.2, was cut into a disk having a diameter of
12.5 mm, and lithium metal foil was cut into a disk having a
diameter of 14 cm to prepare a counter electrode. A separator (made
of a porous polyethylene film) was placed between the two
electrodes, the separator being impregnated with an electrolyte
solution of 1 mol/L, of LiPF.sub.6 in a mixed solvent of ethylene
carbonate and ethyl methyl carbonate (volume ratio=3:7). In this
manner, 2016 coin batteries were produced.
Method of Producing Non-Aqueous Secondary Battery (Laminate
Battery)
[1096] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
6.00.+-.0.3 mg/cm.sup.2, was cut to 4 cm.times.3 cm to prepare a
negative electrode, and a positive electrode made of NMC was cut to
the same area. The negative electrode and the positive electrode
were combined with a separator (made of a porous polyethylene film)
placed therebetween. An electrolyte solution of 1.2 mol/L of
LiPF.sub.6 in a mixed solvent of ethylene carbonate, ethyl methyl
carbonate, and dimethyl carbonate (volume ratio=3:3:4) was injected
in an amount of 250 .mu.l to produce a laminate battery.
Method for Measuring Initial Discharge Capacity
[1097] Using the non-aqueous secondary battery (2016 coin battery)
produced by the above-described method, the capacity of the battery
during charging and discharging was measured by the following
method.
[1098] The lithium counter electrode was charged to 5 mV at a
current density of 0.04 C and further charged at a constant voltage
of 5 mV to a current density of 0.005 C. The negative electrode was
doped with lithium, and then the lithium counter electrode was
discharged to 1.5 V at a current density of 0.08 C. Subsequently, a
second charging and discharging was performed at the same current
density. The discharge capacity at the second cycle was defined as
an initial discharge capacity (1st discharge capacity) of this
battery.
Low-Temperature Output Characteristics
[1099] Using the laminate non-aqueous electrolyte secondary battery
produced by the method for producing a non-aqueous electrolyte
secondary battery described above, low-temperature output
characteristics were measured by the following method.
[1100] A non-aqueous electrolyte secondary battery that had yet to
go through a charge and discharge cycle was subjected to an initial
charge and discharge that involves three cycles in a voltage range
of 4.1 V to 3.0 V at 25.degree. C. and a current of 0.2 C (1 C is a
current at which a rated capacity at a 1-hour rate discharge
capacity is discharged in 1 hour, and so on) and two cycles in a
voltage range of 4.2 V to 3.0 V at a current of 0.2 C (in charging,
a constant-voltage charge at 4.2 V was further performed for 2.5
hours).
[1101] Furthermore, charging was performed at a current of 0.2 C to
an SOC of 50%, and then constant-current discharging was performed
in a low-temperature environment at -30.degree. C. for 2 seconds at
varying currents of 1/8 C, 1/4 C, 1/2 C, 1.5 C, and 2 C. The
battery voltage drop at 2 seconds after discharging under each
condition was measured. From each measurement, a current I that
could be passed in 2 seconds when the upper limit charge voltage
was 3 V was calculated, and a value calculated from the formula:
3.times.I (W) was defined as the low-temperature output
characteristics of each battery.
Average Particle Diameter d50; d50
[1102] The d50 was determined as a volume-based median diameter by
suspending 0.01 g of a carbon material in 10 mL of a 0.2% by mass
aqueous solution of a polyoxyethylene sorbitan monolaurate
surfactant (Tween 20 (registered trademark)), placing the
suspension (a measurement sample) in a commercially available laser
diffraction/scattering particle size distribution analyzer (e.g.,
LA-920 available from HORIBA, Ltd.), irradiating the measurement
sample with ultrasonic waves of 28 kHz at a power of 60 W for 1
minute, and then performing a measurement with the analyzer.
Average Particle Diameter d90; d90
[1103] d90 is a particle diameter corresponding to a cumulative
total of 90% from the smallest particle, as measured on a volume
basis.
Average Particle Diameter d10; d10
[1104] d10 is a particle diameter corresponding to a cumulative
total of 10% from the smallest particle, as measured on a volume
basis.
Tap Density
[1105] Using a powder density meter, the carbon material of the
present invention was dropped through a sieve with openings of 300
.mu.m into a cylindrical tap cell with a diameter of 1.6 cm and a
volume capacity of 20 cm.sup.3 to fill up the cell, and then a tap
with a stroke length of 10 mm was given 1,000 times. The density
calculated from the volume at this time and the mass of the sample
was defined as the tap density.
Specific Surface Area Determined by BET Method; SA (X.sub.e)
[1106] Using a surface area meter (TriStar II3020 available from
Micromeritics Corp.), a carbon material sample was preliminarily
dried under a nitrogen stream at 350.degree. C. for 60 minutes, and
then using a nitrogen-helium mixed gas precisely regulated so as to
have a nitrogen pressure of 0.3 relative to atmospheric pressure, a
BET specific surface area was measured by a nitrogen adsorption BET
multipoint method according to a flowing gas method.
True Density: Y.sub.e
[1107] The true density of a carbon material sample was measured by
pycnometry using a true density meter (MAT-7000 Auto True Denser
available from Seishin Enterprise Co., Ltd).
Example E1
[1108] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a mechanical crusher having a crushing rotor and a
liner to give a flake natural graphite having a d50 of 30 .mu.m and
a water content of 0.03% by mass. To 100 g of the resulting flake
natural graphite, 6 g of a granulating agent of a paraffinic oil
(liquid paraffin available from Wako Pure Chemical Industries,
Ltd., first grade, physical properties at 25.degree. C.:
viscosity=95 cP, contact angle=13.2.degree., surface tension=31.7
mN/m, r cos .theta.=30.9) was added and mixed with stirring. The
sample obtained was disintegrated and mixed using a hammer mill
(MF10 available from IKA) at a rotation speed of 3,000 rpm to give
a flake natural graphite to which the granulating agent uniformly
adhered. Using a Model NHS-1 hybridization system available from
Nara Machinery Co., Ltd., the flake natural graphite to which the
granulating agent uniformly adhered was mechanically spheroidized
at a rotor peripheral speed of 85 m/sec for 10 minutes while fine
powder generated during the spheroidization was deposited on the
base material and incorporated into the spheroidized particles,
thereby providing a spheroidized natural graphite having a d50 of
19.4 .mu.m. The spheroidized natural graphite and a coal-tar pitch,
serving as an amorphous carbon precursor, were mixed and heat
treated in an inert gas at 1,300.degree. C., and then the burned
product was disintegrated and classified to give a multi-layered
carbon material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.03. Using the measurement
methods described above, d50, d90, d10, SA, Tap, true density,
initial discharge capacity, and low-temperature output
characteristics were measured. The results are shown in Table
1E.
Example E2
[1109] The spheroidized natural graphite obtained in Example E1 and
a coal-tar pitch, serving as an amorphous carbon precursor, were
mixed and heat treated in an inert gas at 1,300.degree. C., and
then the burned product was disintegrated and classified to give a
multi-layered carbon material made of graphite particles and an
amorphous carbon combined with each other. The burning yield showed
that the mass ratio of spheroidized graphite particle to amorphous
carbon (spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.042. The results of the
measurements made in the same manner as in Example E1 are shown in
Table 1E.
Example E3
[1110] The spheroidized natural graphite obtained in Example E1 and
a coal-tar pitch, serving as an amorphous carbon precursor, were
mixed and heat treated in an inert gas at 1,300.degree. C., and
then the burned product was disintegrated and classified to give a
multi-layered carbon material made of graphite particles and an
amorphous carbon combined with each other. The burning yield showed
that the mass ratio of spheroidized graphite particle to amorphous
carbon (spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.05. The results of the
measurements made in the same manner as in Example E1 are shown in
Table 1E.
Example E4
[1111] The spheroidized natural graphite obtained in Example E1 and
a coal-tar pitch, serving as an amorphous carbon precursor, were
mixed and heat treated in an inert gas at 1,300.degree. C., and
then the burned product was disintegrated and classified to give a
multi-layered carbon material made of graphite particles and an
amorphous carbon combined with each other. The burning yield showed
that the mass ratio of spheroidized graphite particle to amorphous
carbon (spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.065. The results of the
measurements made in the same manner as in Example E1 are shown in
Table 1E.
Example E5
[1112] The spheroidized natural graphite obtained in Example E1 and
a coal-tar pitch, serving as an amorphous carbon precursor, were
mixed and heat treated in an inert gas at 1,300.degree. C., and
then the burned product was disintegrated and classified to give a
multi-layered carbon material made of graphite particles and an
amorphous carbon combined with each other. The burning yield showed
that the mass ratio of spheroidized graphite particle to amorphous
carbon (spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.10. The results of the
measurements made in the same manner as in Example E1 are shown in
Table 1E.
Example E6
[1113] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a mechanical crusher having a crushing rotor and a
liner to give a flake natural graphite having a d50 of 6 .mu.m and
a water content of 0.08% by mass. To 100 g of the resulting flake
natural graphite, 12 g of a granulating agent of a paraffinic oil
(liquid paraffin available from Wako Pure Chemical Industries,
Ltd., first grade, physical properties at 25.degree. C.:
viscosity=95 cP, contact angle=13.2.degree., surface tension=31.7
mN/m, r cos .theta.=30.9) was added and mixed with stirring. The
sample obtained was disintegrated and mixed using a hammer mill
(MF10 available from IKA) at a rotation speed of 3,000 rpm to give
a flake natural graphite to which the granulating agent uniformly
adhered. Using a Model NHS-1 hybridization system available from
Nara Machinery Co., Ltd., the flake natural graphite to which the
granulating agent uniformly adhered was mechanically spheroidized
at a rotor peripheral speed of 85 m/sec for 10 minutes while fine
powder generated during the spheroidization was deposited on the
base material and incorporated into the spheroidized particles,
thereby providing a spheroidized natural graphite having a d50 of
9.2 .mu.m. The spheroidized natural graphite and a coal-tar pitch,
serving as an amorphous carbon precursor, were mixed and heat
treated in an inert gas at 1,300.degree. C., and then the burned
product was disintegrated and classified to give a multi-layered
carbon material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.065. The results of the
measurements made in the same manner as in Example E1 are shown in
Table 1E.
Example E7
[1114] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a mechanical crusher having a crushing rotor and a
liner to give a flake natural graphite having a d50 of 6 .mu.m and
a water content of 0.08% by mass. To 100 g of the resulting flake
natural graphite, 12 g of a granulating agent of a paraffinic oil
(liquid paraffin available from Wako Pure Chemical Industries,
Ltd., first grade, physical properties at 25.degree. C.:
viscosity=95 cP, contact, angle=13.2.degree., surface tension=31.7
mN/m, r cos .theta.=30.9) was added and mixed with stirring. The
sample obtained was disintegrated and mixed using a hammer mill
(MF10 available from IKA) at a rotation speed of 3,000 rpm to give
a flake natural graphite to which the granulating agent uniformly
adhered. Using a Model NHS-1 hybridization system available from
Nara Machinery Co., Ltd., the flake natural graphite to which the
granulating agent uniformly adhered was mechanically spheroidized
at a rotor peripheral speed of 85 m/sec for 10 minutes while fine
powder generated during the spheroidization was deposited on the
base material and incorporated into the spheroidized particles,
thereby providing a spheroidized natural graphite having a d50 of
9.2 .mu.m. The spheroidized natural graphite and a coal-tar pitch,
serving as an amorphous carbon precursor, were mixed and heat
treated in an inert gas at 1,300.degree. C., and then the burned
product was disintegrated and classified to give a multi-layered
carbon material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.1. The results of the
measurements made in the same manner as in Example E1 are shown in
Table 1E.
Comparative Example E1
[1115] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 10 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 10.8 .mu.m. The
spheroidized natural graphite and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.02. The results of the
measurements made in the same manner as in Example E1 are shown in
Table 1E.
Comparative Example E2
[1116] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 10 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 10.8 .mu.m. The
spheroidized natural graphite and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.04. The results of the
measurements made in the same manner as in Example E1 are shown in
Table 1E.
Comparative Example E3
[1117] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 3 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 15.7 .mu.m. The
spheroidized natural graphite and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.015. The results of the
measurements made in the same manner as in Example E1 are shown in
Table 1E.
Comparative Example E4
[1118] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 3 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 15.7 .mu.m. The
spheroidized natural graphite and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.04. The results of the
measurements made in the same manner as in Example E1 are shown in
Table 1E.
Comparative Example E5
[1119] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 10 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 10.8 .mu.m. The
spheroidized natural graphite and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.013. The results of the
measurements made in the same manner as in Example E1 are shown in
Table 1E.
Comparative Example E6
[1120] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 3 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 19.5 .mu.m. The
spheroidized natural graphite and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.075. The results of the
measurements made in the same manner as in Example E1 are shown in
Table 1E.
TABLE-US-00011 TABLE 1E Low- Y.sub.e: Initial Temperature X.sub.e:
Time Discharge Output SA Density Y.sub.e - d50 d90/ Tap Capacity
Characteristics (m.sup.2/g) (g/cm.sup.3) 0.01X.sub.e (.mu.m) d10
(g/cm.sup.3) (mAh/g) (W) Example E1 7.38 2.25 2.17 17.9 3.2 1.16
366 0.094 Example E2 5.79 2.24 2.18 18.4 3.1 1.19 363 0.098 Example
E3 5.15 2.24 2.19 19.4 3.0 1.18 363 0.099 Example E4 4.30 2.23 2.19
20.0 2.8 1.20 362 0.102 Example E5 2.88 2.22 2.19 22.4 3.1 1.19 358
0.090 Example E6 8.69 2.23 2.14 8.9 2.8 0.94 361 0.107 Example E7
6.21 2.22 2.15 10.2 3.1 0.80 356 0.106 Comparative 3.92 2.25 2.21
10.4 2.3 1.08 364 0.087 Example E1 Comparative 2.97 2.24 2.21 10.6
2.1 1.11 360 0.080 Example E2 Comparative 3.53 2.25 2.22 15.8 2.4
1.11 362 0.085 Example E3 Comparative 2.51 2.24 2.21 15.4 2.2 1.15
361 0.069 Example E4 Comparative 4.48 2.25 2.21 10.5 2.2 1.07 364
0.086 Example E5 Comparative 1.82 2.23 2.21 19.3 2.5 1.21 361 0.059
Example E6
[1121] In Examples E1 to E7, the flake natural graphite adjusted to
have a prescribed particle size was spheroidized while fine powder
generated during the spheroidization was deposited on the base
material and/or incorporated into the spheroidized particles,
whereby the above inequality (1E) was successfully satisfied to
provide a high capacity and excellent low-temperature output
characteristics.
Sixth Examples (Examples F) of the Present Invention will Now be
Described.
[1122] In Examples F, physical properties and characteristics of
carbon materials produced were measured by the following
methods.
Preparation of Electrode Sheet
[1123] An electrode plate having an active material layer with an
active material layer density of 1.35.+-.0.03 g/cm.sup.3 was
prepared using graphite particles of Examples or Comparative
Examples. Specifically, 50.00.+-.0.02 g of a negative electrode
material, 50.00.+-.0.02 g (0.500 g on a solids basis) of a 1% by
mass aqueous carboxymethylcellulose sodium salt solution, and
1.00.+-.0.05 g (0.5 g on a solids basis) of an aqueous dispersion
of a styrene-butadiene rubber having a weight average molecular
weight of 270,000 were stirred with a Keyence hybrid mixer for 5
minutes, and the mixture was defoamed for 30 seconds to give a
slurry.
[1124] The slurry was applied to a 10-.mu.m-thick copper foil,
serving as a current collector, to a width of 10 cm using a small
die coater available from Itochu Machining Co., Ltd. such that the
negative electrode material adhered in an amount of 6.00.+-.0.3
mg/cm.sup.2. The coated foil was roll-pressed using a roller having
a diameter of 20 cm to adjust the density of the active material
layer to be 1.35.+-.0.03 g/cm.sup.3, thereby preparing an electrode
sheet.
Production of Non-Aqueous Secondary Battery (2016 Coin Battery)
[1125] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
12.00.+-.0.3 mg/cm.sup.2, was cut into a disk having a diameter of
12.5 mm, and lithium metal foil was cut into a disk having a
diameter of 14 mm to prepare a counter electrode. A separator (made
of a porous polyethylene film) was placed between the two
electrodes, the separator being impregnated with an electrolyte
solution of 1 mol/L of LiPF.sub.6 in a mixed solvent of ethylene
carbonate and ethyl methyl carbonate (volume ratio=3:7). In this
manner, 2016 coin batteries were produced.
Method for Measuring Initial Discharge Capacity
[1126] Using the non-aqueous secondary battery (2016 coin battery)
produced by the above-described method, the capacity of the battery
during charging and discharging was measured by the following
method.
[1127] The lithium counter electrode was charged to 5 mV at a
current density of 0.04 C and further charged at a constant voltage
of 5 mV to a current density of 0.005 C. The negative electrode was
doped with lithium, and then the lithium counter electrode was
discharged to 1.5 V at a current density of 0.08 C. Subsequently, a
second charging and discharging was performed at the same current
density. The discharge capacity at the second cycle was defined as
an initial discharge capacity (1st discharge capacity) of this
battery.
Method of Producing Non-Aqueous Secondary Battery (Laminate
Battery)
[1128] The electrode sheet prepared by the above-described method
was cut to 4 cm.times.3 cm to prepare a negative electrode, and a
positive electrode made of NMC was cut to the same area. The
negative electrode and the positive electrode were combined with a
separator (made of a porous polyethylene film) placed therebetween.
An electrolyte solution of 1.2 mol/L of LiPF.sub.6 in a mixed
solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl
carbonate (volume ratio=3:3:4) was injected in an amount of 200
.mu.L to produce a laminate battery.
Low-Temperature Output Characteristics
[1129] Using the laminate non-aqueous electrolyte secondary battery
produced by the method for producing a non-aqueous electrolyte
secondary battery described above, low-temperature output
characteristics were measured by the following method.
[1130] A non-aqueous electrolyte secondary battery that had yet to
go through a charge and discharge cycle was subjected to an initial
charge and discharge that involves three cycles in a voltage range
of 4.1 V to 3.0 V at 25.degree. C. and a current of 0.2 C (1 C is a
current at which a rated capacity at a 1-hour rate discharge
capacity is discharged in 1 hour, and so on) and two cycles in a
voltage range of 4.2 V to 3.0 V at a current of 0.2 C (in charging,
a constant-voltage charge at 4.2 V was further performed for 2.5
hours).
[1131] Furthermore, charging was performed at a current of 0.2 C to
an SOC of 50%, and then constant-current discharging was performed
in a low-temperature environment at -30.degree. C. for 2 seconds at
varying currents of 1/8 C, 1/4 C, 1/2 C, 1.5 C, and 2 C. The
battery voltage drop at 2 seconds after discharging under each
condition was measured. From each measurement, a current I that
could be passed in 2 seconds when the upper limit charge voltage
was 3 V was calculated, and a value calculated from the formula:
3.times.I (W) was defined as the low-temperature output
characteristics of each battery.
Average Value, Standard Deviation (.sub..sigma.R), and Raman
.sub.R15 Value of Microscopic Raman R Values
[1132] Using a Raman spectroscope (Nicolet Almega SCR available
from Thermo Fisher Scientific K.K.), Raman microspectroscopy was
performed under the following conditions to determine the average
value and the standard deviation (.sigma..sub.R) of microscopic
Raman R values.
[1133] Target particles were gravity-dropped onto a sample stage,
and Raman microspectroscopy was performed with the surface of the
target flat.
[1134] Excitation wavelength: 532 nm
[1135] Laser power on sample: 1 mW or less
[1136] Resolution: 10 cm.sup.-1
[1137] Irradiation area: 1 .mu.m
[1138] Measurement range: 400 cm.sup.-1 to 4,000 cm.sup.-1
[1139] Measurement of peak intensity: straight baseline subtraction
in the range of about 1,100 cm .sup.-1 to 1,750 cm.sup.-1
[1140] Method for calculating Raman R value: In a spectrum after
straight baseline subtraction, a peak intensity I.sub.A at the peak
top of a peak P.sub.A near 1,580 cm.sup.-1 and a peak intensity
I.sub.B at the peak top of a peak P.sub.B near 1,360 cm.sup.-1 were
read to calculate an R value (I.sub.B/I.sub.A), and the average
value and the standard deviation (.sigma..sub.R) were
calculated.
[1141] Method of calculating Raman R.sub.(15) value (%): the number
of composite carbon materials having a microscopic Raman R value of
0.15 or less among 30 randomly selected composite carbon
materials/30.times.100
d50
[1142] The d50 was determined as a volume-based median diameter by
suspending 0.01 g of a carbon material in 10 mL of a 0.2% by mass
aqueous solution of a polyoxyethylene sorbitan monolaurate
surfactant (Tween 20 (registered trademark)), placing the
suspension (a measurement sample) in a commercially available laser
diffraction/scattering particle size distribution analyzer (e.g.,
LA-920 available from HORIBA, Ltd.), irradiating the measurement
sample with ultrasonic waves of 28 kHz at a power of 60 W for 1
minute, and then performing a measurement with the analyzer.
Mode Pore Diameter (PD) in Pore Diameter Range of 0.01 .mu.m to 1
.mu.m, Half Width at Half Maximum of Pore Distribution (log (nm)),
Cumulative Pore Volume at Pore Diameters in Range of 0.01 .mu.m to
1 .mu.m, and Total Pore Volume
[1143] The measurement by mercury intrusion was carried out using a
mercury porosimeter (Autopore 9520 available from Micromeritics
Corp). Around 0.2 g of a sample (negative electrode material) was
weighed into a powder cell, and the cell was sealed. The cell was
subjected to a degassing pretreatment at room temperature under
vacuum (50 .mu.mHg or lower) for 10 minutes, and then the pressure
in the cell was reduced stepwise to 4 psia. Mercury was introduced
into the cell, and the pressure was increased stepwise from 4 psia
to 40,000 psia and then reduced to 25 psia. From the mercury
intrusion curve obtained, a pore distribution was calculated using
the Washburn equation. The calculation was made assuming that the
surface tension of mercury was 485 dyne/cm, and the contact angle
was 140.degree..
[1144] From the pore distribution obtained, a mode pore diameter
(PD) in a pore diameter range of 0.01 .mu.m to 1 .mu.m, a
cumulative pore volume at pore diameters in a range of 0.01 .mu.m
to 1 .mu.m, and a total pore volume were calculated. The half width
at half maximum of pore distribution (log (nm)) is defined as a
half width at half maximum at a micropore side of a peak in a pore
diameter range of 0.01 .mu.m to 1 .mu.m in the pore distribution
(nm) with the horizontal axis expressed in common logarithm (log
(nm)).
BET Specific Surface Area (SA)
[1145] Using a surface area meter (Gemini 2360 specific surface
area analyzer available from Shimadzu Corporation), a carbon
material sample was preliminarily vacuum dried under a nitrogen
stream at 100.degree. C. for 3 hours and then cooled to liquid
nitrogen temperature, and using a nitrogen-helium mixed gas
precisely regulated so as to have a nitrogen pressure of 0.3
relative to atmospheric pressure, a BET specific surface area was
measured by a nitrogen adsorption BET multipoint method according
to a flowing gas method.
Tap Density (Tap)
[1146] Using a powder density meter, the carbon material of the
present invention was dropped through a sieve with openings of 300
.mu.m into a cylindrical tap cell with a diameter of 1.6 cm and a
volume capacity of 20 cm.sup.3 to fill up the cell, and then a tap
with a stroke length of 10 mm was given 1,000 times. The density
calculated from the volume at this time and the mass of the sample
was defined as the tap density.
Example F1
[1147] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry air-flow crusher to give a flake natural
graphite having a d50 of 6 .mu.m and a Tap of 0.13 g/cm.sup.3. To
100 g of the resulting flake natural graphite, 12 g of a
granulating agent of a paraffinic oil (liquid paraffin available
from Wako Pure Chemical Industries, Ltd., first grade, physical
properties at 25.degree. C.: viscosity=95 cP, contact
angle=13.2.degree., surface tension=31.7 mN/m, r cos .theta.=30.9)
was added and mixed with stirring. The sample obtained was
disintegrated and mixed using a hammer mill (MF10 available from
IKA) at a rotation speed of 3,000 rpm to give a flake natural
graphite to which the granulating agent uniformly adhered. Using a
Model NHS-1 hybridization system available from Nara Machinery Co.,
Ltd., the flake natural graphite to which the granulating agent
uniformly adhered was mechanically spheroidized at a rotor
peripheral speed of 85 m/sec for 10 minutes while the flake natural
graphites were made to adhere to each other and fine powder
generated during the spheroidization was deposited on the base
material and incorporated into the spheroidized particles, thereby
providing a spheroidized graphite having a d50 of 9.2 .mu.m, a Tap
density of 0.71 g/cm.sup.3, a PD of 0.09 .mu.m, a PD/d50 of 0.99,
and a cumulative pore volume at pore diameters in a range of 0.01
.mu.m to 1 .mu.m of 0.16 mL/g. The spheroidized graphite powder
obtained and a coal-tar pitch having a residual carbon ratio of 40%
and a density of 1.2 g/cm.sup.3, serving as an amorphous carbon
precursor, were mixed while being heated to a temperature equal to
or higher than the softening point of the coal-tar pitch, and heat
treated in an inert gas at 1,300.degree. C., after which the burned
product was disintegrated and classified to give a multi-layered
carbon material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.07. Using the measurement
methods described above, d50, SA, Tap density, average value of
microscopic Raman R values, .sigma..sub.R, Raman R.sub.15 value,
discharge capacity, and low-temperature output characteristics were
measured. The results are shown in Tables 1F and 2F.
Example F2
[1148] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry swirl-flow crusher to give a flake natural
graphite having a d50 of 9 .mu.m and a Tap of 0.42 g/cm.sup.3. To
100 g of the resulting flake natural graphite, 12 g of a
granulating agent of a paraffinic oil (liquid paraffin available
from Wako Pure Chemical Industries, Ltd., first grade, physical
properties at 25.degree. C.: viscosity=95 cP, contact
angle=13.2.degree., surface tension=31.7 mN/m, r cos .theta.=30.9)
was added and mixed with stirring. The sample obtained was
disintegrated and mixed using a hammer mill (MF10 available from
IKA) at a rotation speed of 3,000 rpm to give a flake natural
graphite to which the granulating agent uniformly adhered. Using a
Model NHS-1 hybridization system available from Nara Machinery Co.,
Ltd., the flake natural graphite to which the granulating agent
uniformly adhered was mechanically spheroidized at a rotor
peripheral speed of 85 m/sec for 10 minutes while the flake natural
graphites were made to adhere to each other and fine powder
generated during the spheroidization was deposited on the base
material and incorporated into the spheroidized particles, thereby
providing a spheroidized graphite having a d50 of 12.7 .mu.m, a Tap
density of 0.87 g/cm.sup.3, a PD of 0.09 .mu.m, a PD/d50 of 0.71,
and a cumulative pore volume at pore diameters in a range of 0.01
.mu.m to 1 .mu.m of 0.16 mL/g. The spheroidized graphite powder
obtained and a coal-tar pitch having a residual carbon ratio of 40%
and a density of 1.2 g/cm.sup.3, serving as an amorphous carbon
precursor, were mixed while being heated to a temperature equal to
or higher than the softening point of the coal-tar pitch, and heat
treated in an inert gas at 1,300.degree. C., after which the burned
product was disintegrated and classified to give a multi-layered
carbon material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.08. The results of the
measurements made in the same manner as in Example F1 are shown in
Table 1F.
Example F3
[1149] A multi-layered carbon material was obtained in the same
manner as in Example 2 except that a coal tar having a residual
carbon ratio of 28% and a density of 1.2 g/cm.sup.3 was used as an
amorphous carbon precursor. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.08. The results of the
measurements made in the same manner as in Example F1 are shown in
Table 1F.
Comparative Example F1
[1150] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 10 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 10.8 .mu.m, a Tap
density of 0.88 g/cm.sup.3, a PD of 0.36 .mu.m, a PD/d50 of 3.27,
and a cumulative pore volume at pore diameters in a range of 0.01
.mu.m to 1 .mu.m of 0.14 mL/g.
[1151] The spheroidized graphite powder obtained and a coal tar
having a residual carbon ratio of 28% and a density of 1.2
g/cm.sup.3, serving as an amorphous carbon precursor, were mixed
while being heated to a temperature equal to or higher than the
softening point of the coal-tar pitch, and heat treated in an inert
gas at 1,300.degree. C., after which the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.07. The results of the
measurements made in the same manner as in Example F1 are shown in
Table 1F.
Comparative Example F2
[1152] A multi-layered carbon material was obtained in the same
manner as in Comparative Example 1 except that a coal-tar pitch
having a residual carbon ratio of 40% and a density of 1.2
g/cm.sup.3 was used as an amorphous carbon precursor. The burning
yield showed that the mass ratio of spheroidized graphite particle
to amorphous carbon (spheroidized graphite particle/amorphous
carbon) of the multi-layered carbon material was 1:0.07. The
results of the measurements made in the same manner as in Example
F1 are shown in Table 1F.
Example F4
[1153] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a mechanical crusher having a crushing rotor and a
liner to give a flake natural graphite having a d50 of 30 .mu.m. To
100 g of the resulting flake natural graphite, 4 g of a granulating
agent of a paraffinic oil (liquid paraffin available from Wako Pure
Chemical industries, Ltd., first grade, physical properties at
25.degree. C.: viscosity=95 cP, contact angle=13.2.degree., surface
tension=31.7 mN/m, r cos .theta.=30.9) was added and mixed with
stirring. The sample obtained was disintegrated and mixed using a
hammer mill (MF10 available from IKA) at a rotation speed of 3,000
rpm to give a flake natural graphite to which the granulating agent
uniformly adhered. Using a Model NHS-1 hybridization system
available from Nara Machinery Co., Ltd., the flake natural graphite
to which the granulating agent uniformly adhered was mechanically
spheroidized at a rotor peripheral speed of 85 m/sec, for 10
minutes while fine powder generated during the spheroidization was
deposited on the base material and incorporated into the
spheroidized particles, thereby providing a spheroidized natural
graphite having a d50 of 16.3 .mu.m, a Tap density of 1.03
g/cm.sup.3, a PD of 0.22 .mu.m, a PD/d50 of 1.33, and a cumulative
pore volume at pore diameters in a range of 0.01 .mu.m to 1 .mu.m
of 0.10 mL/g. The spheroidized graphite powder and a coal-tar pitch
having a residual carbon ratio of 40% and a density of 1.2
g/cm.sup.3, serving as an amorphous carbon precursor, were mixed
while being heated to a temperature equal to or higher than the
softening point of the coal-tar pitch, and heat treated in an inert
gas at 1,300.degree. C., after which the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.04. The results of the
measurements made in the same manner as in Example F1 are shown in
Table 1F.
Example F5
[1154] A multi-layered carbon material was obtained in the same
manner as in Example 5 except that a coal tar having a residual
carbon ratio of 28% and a density of 1.2 g/cm.sup.3 was used as an
amorphous carbon precursor. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.04. The results of the
measurements made in the same manner as in Example F1 are shown in
Table 1F.
Comparative Example F3
[1155] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 3 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of15.7 .mu.m, a Tap
density of 1.02 g/cm.sup.3, a PD of 0.36 .mu.m, a PD/d50 of 2.31,
and a cumulative pore volume at pore diameters in a range of 0.01
.mu.m to 1 .mu.m of 0.13 mL/g. The spheroidized graphite powder
obtained and a petroleum-derived heavy oil having a residual carbon
ratio of 18% and a density of 1.1 g/cm.sup.3, serving as an
amorphous carbon precursor, were mixed while being heated to a
temperature equal to or higher than the softening point of the
coal-tar pitch, and heat treated in an inert gas at 1,300.degree.
C., after which the burned product was disintegrated and classified
to give a multi-layered carbon material made of graphite particles
and an amorphous carbon combined with each other. The burning yield
showed that the mass ratio of spheroidized graphite particle to
amorphous carbon (spheroidized graphite particle/amorphous carbon)
of the multi-layered carbon material was 1:0.04. The results of the
measurements made in the same manner as in Example F1 are shown in
Table 1F.
TABLE-US-00012 TABLE 1F Low-Temperature Output Characteristics
Initial Average Raman (Comparative Discharge d50 SA Tap Raman R
R.sub.15 value Example F1 = Capacity (.mu.m) (m.sup.2/g)
(g/cm.sup.3) value .sigma..sub.R (%) 100) (mAh/g) Example F1 9.4
8.7 0.94 0.28 0.077 3.3 139 362 Example F2 11.8 7.1 1.02 0.24 0.056
3.3 147 359 Example F3 12.2 7.6 0.78 0.28 0.088 10.0 126 359
Comparative 11.4 3.1 1.04 0.33 0.150 6.7 100 362 Example F1
Comparative 11.3 3.1 1.02 0.27 0.126 13.3 107 362 Example F2
Example F4 15.8 4.8 1.22 0.22 0.058 13.3 121 363 Example F5 15.6
5.2 1.16 0.23 0.084 20.0 122 363 Comparative 16.8 3.3 1.16 0.28
0.107 20.0 107 363 Example F3
[1156] In Examples F1 to F5, a carbon material having specific
intra-particle pores was mixed with an appropriate amount of a
specific carbonaceous material precursor, whereby the standard
deviation (.sigma..sub.R) of microscopic Raman R values was
controlled within the prescribed range to provide excellent
low-temperature output characteristics. In Examples F1 to F3, the
percentage of R values of 0.15 or less was in the preferred range,
thus leading to particularly excellent low-temperature output
characteristics. By contrast, in Comparative Examples F1 to F3,
where the .sigma..sub.R was outside the prescribed range, degraded
low-temperature output characteristics were provided.
Seventh Examples (Examples G) of the Present Invention will Now be
Described.
[1157] In Examples G, physical properties of negative electrode
materials produced were measured by the following methods.
Preparation of Electrode Sheet
[1158] An electrode plate having an active material layer with an
active material layer density of 1.50.+-.0.03 g/cm.sup.3 was
prepared using graphite particles of Examples or Comparative
Examples. Specifically, 50.00.+-.0.02 g of a negative electrode
material, 50.00.+-.0.02 g (0.500 g on a solids basis) of a 1% by
mass aqueous carboxymethylcellulose sodium salt solution, and
1.00.+-.0.05 g (0.5 g on a solids basis) of an aqueous dispersion
of a styrene-butadiene rubber having a weight average molecular
weight of 270,000 were stirred with a Keyence hybrid mixer for 5
minutes, and the mixture was defoamed for 30 seconds to give a
slurry.
[1159] The slurry was applied to a 10-.mu.m-thick copper foil,
serving as a current collector, to a width of 10 cm using a small
die coater available from Itochu Machining Co., Ltd. such that the
negative electrode material adhered in an amount of 6.00.+-.0.3
mg/cm.sup.2. The coated foil was roll-pressed using a roller having
a diameter of 20 cm to adjust the density of the active material
layer to be 1.35.+-.0.03 g/cm.sup.3, thereby preparing an electrode
sheet.
Production of Non-Aqueous Secondary Battery (2016 Coin Battery)
[1160] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
12.00.+-.0.3 mg/cm.sup.2, was cut into a disk having a diameter of
12.5 mm, and lithium metal foil was cut into a disk having a
diameter of 14 mm to prepare a counter electrode. A separator (made
of a porous polyethylene film) was placed between the two
electrodes, the separator being impregnated with an electrolyte
solution of 1 mol/L of LiPF.sub.6 in a mixed solvent of ethylene
carbonate and ethyl methyl carbonate (volume ratio=3:7). In this
manner, 2016 coin batteries were produced.
Method for Measuring Initial Discharge Capacity
[1161] Using the non-aqueous secondary battery (2016 coin battery)
produced by the above-described method, the capacity of the battery
during charging and discharging was measured by the following
method.
[1162] The lithium counter electrode was charged to 5 mV at a
current density of 0.04 C and further charged at a constant voltage
of 5 mV to a current density of 0.005 C. The negative electrode was
doped with lithium, and then the lithium counter electrode was
discharged to 1.5 V at a current density of 0.08 C. Subsequently, a
second charging and discharging was performed at the same current
density. The discharge capacity at the second cycle was defined as
an initial discharge capacity (1st discharge capacity) of this
battery.
Method of Producing Non-Aqueous Secondary Battery (Laminate
Battery)
[1163] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
6.00.+-.0.3 mg/cm.sup.2, was cut to 4 cm.times.3 cm to prepare a
negative electrode, and a positive electrode made of NMC was cut to
the same area. The negative electrode and the positive electrode
were combined with a separator (made of a porous polyethylene film)
placed therebetween. An electrolyte solution of 1.2 mol/L of
LiPF.sub.6 in a mixed solvent of ethylene carbonate, ethyl methyl
carbonate, and dimethyl carbonate (volume ratio=3:3:4) was injected
in an amount of 250 .mu.l to produce a laminate battery.
Low-Temperature Output Characteristics
[1164] Using the laminate non-aqueous electrolyte secondary battery
produced by the method for producing a non-aqueous electrolyte
secondary battery described above, low-temperature output
characteristics were measured by the following method.
[1165] A non-aqueous electrolyte secondary battery that had yet to
go through a charge and discharge cycle was subjected to an initial
charge and discharge that involves three cycles in a voltage range
of 4.1 V to 3.0 V at 25.degree. C. and a current of 0.2 C (1 C is a
current at which a rated capacity at a 1-hour rate discharge
capacity is discharged in 1 hour, and so on) and two cycles in a
voltage range of 4.2 V to 3.0 V at, a current of 0.2 C (in
charging, a constant-voltage charge at 4.2 V was further performed
for 2.5 hours).
[1166] Furthermore, charging was performed at a current of 0.2 C to
an SOC of 50%, and then constant-current discharging was performed
in a low-temperature environment at -30.degree. C. for 2 seconds at
varying currents of 1/8 C, 1/4 C, 1/2 C, 1.5 C, and 2 C. The
battery voltage drop at 2 seconds after discharging under each
condition was measured. From each measurement, a current I that
could be passed in 2 seconds when the upper limit charge voltage
was 3 V was calculated, and a value calculated from the formula:
3.times.I (W) was defined as the low-temperature output
characteristics of each battery.
Average Particle Diameter d50; d50
[1167] The d50 was determined as a volume-based median diameter by
suspending 0.01 g of a carbon material in 10 mL of a 0.2% by mass
aqueous solution of a polyoxyethylene sorbitan monolaurate
surfactant (Tween 20 (registered trademark)), placing the
suspension (a measurement sample) in a commercially available laser
diffraction/scattering particle size distribution analyzer (e.g.,
LA-920 available from HORIBA, Ltd.), irradiating the measurement
sample with ultrasonic waves of 28 kHz at a power of 60 W for 1
minute, and then performing a measurement with the analyzer.
Tap Density; Tap
[1168] Using a powder density meter, the carbon material of the
present invention was dropped through a sieve with openings of 300
.mu.m into a cylindrical tap cell with a diameter of 1.6 cm and a
volume capacity of 20 cm.sup.3 to fill up the cell, and then a tap
with a stroke length of 10 mm was given 1,000 times. The density
calculated from the volume at this time and the mass of the sample
was defined as the tap density.
Specific Surface Area Determined by BET Method; SA
[1169] Using a surface area meter (fully automatic surface area
analyzer available from Ohkura Riken. Co., Ltd.), a carbon material
sample was preliminarily dried under a nitrogen stream at,
350.degree. C. for 15 minutes, and then using a nitrogen-helium
mixed gas precisely regulated so as to have a nitrogen pressure of
0.3 relative to atmospheric pressure, a BET specific surface area
was measured by a nitrogen adsorption BET multipoint method
according to a flowing gas method.
Pore Volume
[1170] Using an Autoforb (Quantachrome Co.), a sample was placed in
a powder cell, and the cell was sealed and pre-treated at
350.degree. C. under vacuum (1.3 Pa or lower) for 2 hours, after
which an adsorption isotherm (adsorption gas: nitrogen) was
measured at liquid nitrogen temperature. Using the adsorption
isotherm obtained, a BJH analysis was performed to determine a
micropore distribution, from which the cumulative pore volume at
pore diameters in a range of 2 to 4 nm, the cumulative pore volume
at pore diameters in a range of 2 to 100 nm, and the maximum dV/d
log (D) (V: cumulative pore volume, D: pore diameter) at pore
diameters in a range of 2 to 4 nm were calculated. The dV/d log (D)
was measured such that the interval of log (D) was 0.010 to
0.050.
Example G1
[1171] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a mechanical crusher having a crushing rotor and a
liner to give a flake natural graphite having a d50 of 8.5 .mu.m.
To 100 g of the resulting flake natural graphite, 12 g of a
granulating agent of a paraffinic oil (liquid paraffin available
from Wako Pure Chemical Industries, Ltd., first grade, physical
properties at 25.degree. C.: viscosity=95 cP, contact
angle=13.2.degree., surface tension=31.7 mN/m, r cos .theta.=30.9)
was added and mixed with stirring. The sample obtained was
disintegrated and mixed using a hammer mill (MF10 available from
IKA) at a rotation speed of 3,000 rpm to give a flake natural
graphite to which the granulating agent uniformly adhered.
[1172] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., the flake natural graphite to which the
granulating agent uniformly adhered was mechanically spheroidized
at a rotor peripheral speed of 85 m/sec for 10 minutes while fine
powder generated during the spheroidization was deposited on the
base material and incorporated into the spheroidized particles, and
heat treated in an inert gas at 720.degree. C. to give a
spheroidized natural graphite having a d50 of 12.9 .mu.m. Using the
measurement methods described above, d50, SA, Tap, pore volume,
low-temperature output characteristics, and initial discharge
capacity were measured. The results are shown in Table 1G.
Example G2
[1173] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a mechanical crusher having a crushing rotor and a
liner to give a flake natural graphite having a d50 of 30 .mu.m. To
100 g of the resulting flake natural graphite, 4 g of a granulating
agent of a paraffinic oil (liquid paraffin available from Wako Pure
Chemical Industries, Ltd., first grade, physical properties at
25.degree. C.: viscosity=95 cP, contact angle=13.2.degree., surface
tension=31.7 mN/m, r cos .theta.=30.9) was added and mixed with
stirring. The sample obtained was disintegrated and mixed using a
hammer mill (MF10 available from IKA) at a rotation speed of 3,000
rpm to give a flake natural graphite to which the granulating agent
uniformly adhered. Using a Model NHS-1 hybridization system
available from Nara Machinery Co., Ltd., the flake natural graphite
to which the granulating agent uniformly adhered was mechanically
spheroidized at a rotor peripheral speed of 85 m/sec for 10 minutes
while fine powder generated during the spheroidization was
deposited on the base material and incorporated into the
spheroidized particles, and heat treated in an inert gas at
720.degree. C. to give a spheroidized natural graphite having a d50
of 16.3 .mu.m. The results of the measurements made in the same
manner as in Example G1 are shown in Table 1G.
Example G3
[1174] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a mechanical crusher having a crushing rotor and a
liner to give a flake natural graphite having a d50 of 30 .mu.m. To
100 g of the resulting flake natural graphite, 6 g of a granulating
agent of a paraffinic oil (liquid paraffin available from Wako Pure
Chemical Industries, Ltd., first grade, physical properties at
25.degree. C.: viscosity=95 cP, contact angle=13.2.degree., surface
tension=31.7 mN/m, r cos .theta.=30.9) was added and mixed with
stirring. The sample obtained was disintegrated and mixed using a
hammer mill (MF10 available from IKA) at a rotation speed of 3,000
rpm to give a flake natural graphite to which the granulating agent
uniformly adhered. Using a Model NHS-1 hybridization system
available from Nara Machinery Co., Ltd., the flake natural graphite
to which the granulating agent uniformly adhered was mechanically
spheroidized at a rotor peripheral speed of 85 m/sec for 10 minutes
while fine powder generated during the spheroidization was
deposited on the base material and incorporated into the
spheroidized particles, and heat treated in an inert gas at
720.degree. C. to give a spheroidized natural graphite having a d50
of 19.4 .mu.m. The results of the measurements made in the same
manner as in Example G1 are shown in Table 1G.
Comparative Example G1
[1175] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 10 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 10.9 .mu.m. The
results of the measurements made in the same manner as in Example
G1 are shown in Table 1G.
Comparative Example G2
[1176] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 5 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
heat treated in an inert gas at 720.degree. C. and classified to
remove the flake graphite fine powder, thereby providing a
spheroidized graphite having a d50 of 15.7 .mu.m. The results of
the measurements made in the same manner as in Example G1 are shown
in Table 1G.
Comparative Example G3
[1177] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a mechanical crusher having a crushing rotor and a
liner to give a flake natural graphite having a d50 of 9.8 .mu.m.
The results of the measurements made in the same manner as in
Example G1 are shown in Table 1G.
TABLE-US-00013 TABLE 1G Pore Pore Max. Vol. Vol. dV/dlog at at (D)
at Pore Pore Pore Low-Temp. Diam. Diam. Diam. Output Initial of 2
of 2 of 2 Characteristics, Discharge d.50 Tap SA to 4 nm to 100 nm
to 4 nm (Comp. Ex. G1 = Capacity (.mu.m) (g/cm.sup.3) (m.sup.2/g)
(cm.sup.3/g) (cm.sup.3/g) (cm.sup.3/g) 100) (mAh/g) Example G1 12.9
0.88 15.3 0.0037 0.056 0.0143 130 361 Example G2 16.3 1.03 13.8
0.0038 0.0405 0.0163 114 362 Example G3 19.4 1.06 13.4 0.0035
0.0487 0.0154 107 362 Comp. Ex. G1 10.9 0.88 8.4 0.002 0.0234
0.0087 100 369 Comp. Ex. G2 15.7 1.02 6.9 0.0018 0.0156 0.0079 89
368 Comp. Ex. G3 9.8 0.69 7.1 0.0023 0.0223 0.0103 100 369
[1178] The carbon materials of Examples G1 to G3 provided excellent
low-temperature output characteristics. This is probably because of
abundant lithium-ion insertion/extraction sites due to a large
cumulative pore volume at pore diameters in a range of 2 to 4 nm,
and the smooth movement of electrolyte solution between particles
due to a high tap density.
Eighth Examples (Examples H) of the Present Invention will Now be
Described.
[1179] In Examples H, physical properties of negative electrode
materials produced were measured by the following methods.
Preparation of Electrode Sheet
[1180] An electrode plate having an active material layer with an
active material layer density of 1.60.+-.0.03 g/cm.sup.3 was
prepared using graphite particles of Examples or Comparative
Examples. Specifically, 50.00.+-.0.02 g of a negative electrode
material, 50.00.+-.0.02 g (0.500 g on a solids basis) of a 1% by
mass aqueous carboxymethylcellulose sodium salt solution, and
1.00.+-.0.05 g (0.5 g on a solids basis) of an aqueous dispersion
of a styrene-butadiene rubber having a weight average molecular
weight of 270,000 were stirred with a Keyence hybrid mixer for 5
minutes, and the mixture was defoamed for 30 seconds to give a
slurry.
[1181] The slurry was applied to a 10-.mu.m-thick copper foil,
serving as a current collector, to a width of 10 cm using a small
die coater available from Itochu Machining Co., Ltd. such that the
negative electrode material adhered in an amount of 6.0.+-.0.3
mg/cm.sup.2 or 9.0.+-.0.3 mg/cm.sup.2. The coated foil was
roll-pressed using a roller having a diameter of 20 cm to adjust
the density of the active material layer to be 1.35.+-.0.03
g/cm.sup.3 or 1.60.+-.0.03 g/cm.sup.3, thereby preparing an
electrode sheet.
Production of Non-Aqueous Secondary Battery (2016 Coin Battery)
[1182] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
9.0.+-.0.3 mg/cm.sup.2 and in which the density of the active
material layer was 1.60.+-.0.03 g/cm.sup.3, was cut into a disk
having a diameter of 12.5 mm, and lithium metal foil was cut into a
disk having a diameter of 14 mm to prepare a counter electrode. A
separator (made of a porous polyethylene film) was placed between
the two electrodes, the separator being impregnated with an
electrolyte solution of 1 mol/L of LiPF.sub.6 in a mixed solvent of
ethylene carbonate and ethyl methyl carbonate (volume ratio=3:7).
In this manner, 2016 coin batteries were produced.
Method of Producing Non-Aqueous Secondary Battery (Laminate
Battery)
[1183] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
6.0.+-.0.3 mg/cm.sup.2 and in which the density of the active
material layer was 1.35.+-.0.03 g/cm.sup.3, was cut to 4 cm.times.3
cm to prepare a negative electrode, and a positive electrode made
of NMC was cut to the same area. The negative electrode and the
positive electrode were combined with a separator (made of a porous
polyethylene film) placed therebetween. An electrolyte solution of
1.2 mol/L of LiPF.sub.6 in a mixed solvent of ethylene carbonate,
ethyl methyl carbonate, and dimethyl carbonate (volume ratio=3:3:4)
was injected in an amount of 200 .mu.L to produce a laminate
battery.
Method for Measuring Discharge Capacity
[1184] Using the non-aqueous secondary battery (2016 coin battery)
produced by the above-described method, the capacity of the battery
during charging and discharging was measured by the following
method.
[1185] The lithium counter electrode was charged to 5 mV at a
current density of 0.05 C and further charged at a constant voltage
of 5 mV to a current density of 0.005 C. The negative electrode was
doped with lithium, and then the lithium counter electrode was
discharged to 1.5 V at a current density of 0.1 C. Subsequently, a
second charging and discharging was performed at the same current
density. The discharge capacity at the second cycle was defined as
a discharge capacity of this battery.
Low-Temperature Output Characteristics
[1186] Using the laminate non-aqueous electrolyte secondary battery
produced by the method for producing a non-aqueous electrolyte
secondary battery described above, low-temperature output
characteristics were measured by the following method.
[1187] A non-aqueous electrolyte secondary battery that had yet to
go through a charge and discharge cycle was subjected to an initial
charge and discharge that involves three cycles in a voltage range
of 4.1 V to 3.0 V at 25.degree. C. and a current of 0.2 C (1 C is a
current at which a rated capacity at a 1-hour rate discharge
capacity is discharged in 1 hour, and so on) and two cycles in a
voltage range of 4.2 V to 3.0 V at a current of 0.2 C (in charging,
a constant-voltage charge at 4.2 V was further performed for 2.5
hours).
[1188] Furthermore, charging was performed at a current of 0.2 C to
an SOC of 50%, and then constant-current discharging was performed
in a low-temperature environment at -30.degree. C. for 2 seconds at
varying currents of 1/8 C, 1/4 C, 1/2 C, 1.5 C, and 2 C. The
battery voltage drop at 2 seconds after discharging under each
condition was measured. From each measurement, a current I that
could be passed in 2 seconds when the upper limit charge voltage
was 3 V was calculated, and a value calculated from the formula:
3.times.I (W) was defined as the low-temperature output
characteristics of each battery.
Measurement of Thermal Weight Loss (.DELTA.TG) (%)
[1189] Into a platinum pan, 5 mg of a carbon material was weighed,
and the pan was placed in a differential thermal balance (TG8120
available from Rigaku Corporation). Under an air stream of 100
mL/min, the temperature was raised from room temperature to
400.degree. C. at a rate of 20.degree. C./min and then from
400.degree. C. to 600.degree. C. at a rate of 2.degree. C./min, and
the amount of thermal weight loss was measured. The thermal weight
loss between 400.degree. C. and 600.degree. C. in this measurement
was calculated and defined as a thermal weight loss (.DELTA.TG) (%)
in the present invention.
BET Specific Surface Area (SA)
[1190] Using a surface area meter (AMS8000 specific surface area
analyzer available from Ohkura Riken Co., Ltd.), 0.4 g of a carbon
material was loaded into a cell, and the carbon material sample was
preliminarily dried under a nitrogen stream at 350.degree. C. for
15 minutes, after which using a nitrogen-helium mixed gas precisely
regulated so as to have a nitrogen pressure of 0.3 relative to
atmospheric pressure, a BET specific surface area was measured by a
nitrogen adsorption BET method according to a flowing gas
method.
Raman R Value
[1191] The measurement was made as follows: using a Raman
spectroscope (Raman spectroscope available from JASCO Corporation),
a sample was loaded by gravity-dropping a carbon material into a
measuring cell, and the measuring cell was irradiated with an
argon-ion laser beam while being rotated in a plane perpendicular
to the laser beam.
[1192] Wavelength of argon-ion laser beam: 514.5 nm
[1193] Laser power on sample: 25 mW
[1194] Resolution: 4 cm.sup.-1
[1195] Measurement range: 1,100 cm.sup.-1 to 1,730 cm.sup.-1
[1196] Measurement of peak intensity, measurement of peak
half-width: background processing, smoothing processing
(convolution by simple average, 5 points)
d50
[1197] The d50 was determined as a volume-based median diameter by
suspending 0.01 g of a carbon material in 10 mL of a 0.2% by mass
aqueous solution of a polyoxyethylene sorbitan monolaurate
surfactant (Tween 20 (registered trademark)), placing the
suspension (a measurement sample) in a commercially available laser
diffraction/scattering particle size distribution analyzer (e.g.,
LA-920 available from HORIBA, Ltd.), irradiating the measurement
sample with ultrasonic waves of 28 kHz at a power of 60 W for 1
minute, and then performing a measurement with the analyzer.
Roundness
[1198] Using a flow-type particle image analyzer (FPIA-2000
available from Sysmex Corporation), a particle size distribution
based on equivalent circle diameter was measured, and a roundness
was determined. Ion-exchanged water was used as a dispersion
medium, and polyoxyethylene (20) monolaurate was used as a
surfactant. The equivalent circle diameter is a diameter of a
circle (equivalent circle) having the same projected area as that
of a captured particle image, and the roundness is a ratio of the
perimeter of the equivalent circle, as the numerator, to the
perimeter of the captured particle projection image, as the
denominator. Roundnesses of particles having an equivalent diameter
in the range of 1.5 to 40 .mu.m were averaged to determine the
roundness.
Tap Density
[1199] Using a powder density meter, the carbon material of the
present invention was dropped through a sieve with openings of 300
.mu.m into a cylindrical tap cell with a diameter of 1.6 cm and a
volume capacity of 20 cm.sup.3 to fill up the cell, and then a tap
with a stroke length of 10 mm was given 1,000 times. The density
calculated from the volume at this time and the mass of the sample
was defined as the tap density.
Example H1
[1200] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry swirl-flow crusher to give a flake natural
graphite having a d50 of 8.1 .mu.m and a Tap of 0.39 g/cm.sup.3. To
100 g of the resulting flake natural graphite, 12 g of a
granulating agent of a liquid paraffin (Wako Pure Chemical
Industries, Ltd., first grade, physical properties at 25.degree.
C.: viscosity=95 cP, contact angle=13.2.degree., surface
tension=31.7 mN/m, r cos .theta.=30.9) was added and mixed with
stirring. The sample obtained was disintegrated and mixed using a
hammer mill (MF10 available from IKA) at a rotation speed of 3,000
rpm to give a flake natural graphite to which the granulating agent
adhered. Using a Model NHS-1 hybridization system available from
Nara Machinery Co., Ltd., the sample obtained was mechanically
spheroidized at a rotor peripheral speed of 85 m/sec for 10
minutes. The sample obtained was heat treated in a nitrogen
atmosphere at 500.degree. C. to give a spheroidized graphite sample
from which the granulating agent was removed. Using the measurement
methods described above, d50, SA, Tap, roundness, TG (%)/SA
(m.sup.2/g), Raman R value, discharge capacity, and low-temperature
output characteristics were measured. The results are shown in
Tables 1H and 2H.
Example H2
[1201] A sample was prepared in the same manner as in Example H1
except that the heat-treatment temperature was 700.degree. C. The
results of the measurements made in the same manner as in Example
H1 are shown in Tables 1H and 2H.
Example H3
[1202] A sample was prepared in the same manner as in Example H1
except that the heat-treatment temperature was 850.degree. C. The
results of the measurements made in the same manner as in Example
H1 are shown in Tables 1H and 2H.
Example H4
[1203] A sample was prepared in the same manner as in Example H1
except that the heat-treatment temperature was 1,000.degree. C. The
results of the measurements made in the same manner as in Example
H1 are shown in Tables 1H and 2H.
Comparative Example H1
[1204] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 10 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite fine powder not
deposited on the base material or incorporated into the
spheroidized particles. This sample was classified to remove the
flake graphite fine powder, thereby providing a spheroidized
graphite having a d50 of 10.8 .mu.m. The results of the
measurements made in the same manner as in Example H1 are shown in
Tables 1H and 2H.
Comparative Example H2
[1205] A sample was prepared in the same manner as in Example H1
except that the spheroidized graphite of Comparative Example H1 was
heat treated in a nitrogen atmosphere at 700.degree. C. The results
of the measurements made in the same manner as in Example H1 are
shown in Tables 1H and 2H.
Comparative Example H3
[1206] A sample was prepared in the same manner as in Comparative
Example H2 except that the heat-treatment temperature was
850.degree. C. The results of the measurements made in the same
manner as in Example H1 are shown in Tables 1H and 2H.
Comparative Example H4
[1207] A sample was prepared in the same manner as in Comparative
Example H2 except that the heat-treatment temperature was
1,000.degree. C. The results of the measurements made in the same
manner as in Example H1 are shown in Tables 1H and 2H.
Comparative Example H5
[1208] A sample was prepared in the same manner as in Comparative
Example H2 except that the heat-treatment temperature was
1,300.degree. C. The results of the measurements made in the same
manner as in Example H1 are shown in Tables 1H and 2H.
Comparative Example H6
[1209] The spheroidized graphite of Comparative Example H1 and a
coal-tar pitch, serving as an amorphous carbon precursor, were
mixed and heat treated in an inert gas at 1,300.degree. C., and
then the burned product was disintegrated and classified to give a
multi-layered carbon material made of graphite particles and an
amorphous carbon combined with each other. The burning yield showed
that the mass ratio of spheroidized graphite particle to amorphous
carbon (spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.07. The results of the
measurements made in the same manner as in Example H1 are shown in
Tables 1H and 2H.
Comparative Example H7
[1210] A sample was prepared in the same manner as in Example H1
except that the heat-treatment temperature was 1,300.degree. C. The
results of the measurements made in the same manner as in Example
H1 are shown in Tables 1H and 2H.
Example H5
[1211] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a mechanical crusher having a crushing rotor and a
liner to give a flake natural graphite having a d50 of 30 .mu.m. To
100 g of the resulting flake natural graphite, 4 g of a granulating
agent of a liquid paraffin (Wako Pure Chemical Industries, Ltd.,
first grade, physical properties at 25.degree. C.: viscosity=95 cP,
contact angle=13.2.degree., surface tension=31.7 mN/m, r cos
.theta.=30.9) was added and mixed with stirring. The sample
obtained was disintegrated and mixed using a hammer mill (MF10
available from IKA) at a rotation speed of 3,000 rpm to give a
flake natural graphite to which the granulating agent adhered.
Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., the sample obtained was mechanically
spheroidized at a rotor peripheral speed of 85 m/sec for 10
minutes. The sample obtained was heat treated in a nitrogen
atmosphere at 700.degree. C. to give a spheroidized graphite sample
from which the granulating agent was removed. The results of the
measurements made in the same manner as in Example H1 are shown in
Tables 1H and 2H.
Comparative Example H8
[1212] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 10 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite fine powder not
deposited on the base material or incorporated into the
spheroidized particles. This sample was classified to remove the
flake graphite fine powder, thereby providing a spheroidized
graphite having a d50 of 15.4 .mu.m. The results of the
measurements made in the same manner as in Example H1 are shown in
Tables 1H and 2H.
Example H6
[1213] A sample was prepared in the same manner as in Example H4
except that 6 g of a granulating agent of a liquid paraffin (Wako
Pure Chemical Industries, Ltd., first grade) was added. The results
of the measurements made in the same manner as in Example H1 are
shown in Tables 1H and 2H.
Comparative Example H9
[1214] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
70 m/sec for 5 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite fine powder not
deposited on the base material or incorporated into the
spheroidized particles. This sample was classified to remove the
flake graphite fine powder, thereby providing a spheroidized
graphite having a d50 of 18.2 .mu.m. The results of the
measurements made in the same manner as in Example H1 are shown in
Tables 1H and 2H.
TABLE-US-00014 TABLE 1H d50 (X) SA, Tap, .DELTA.TG (%)/SA Raman
.mu.m m.sup.2/g g/cm.sup.3 Roundness (m.sup.2/g) R value Example H1
12.2 15.9 0.84 0.94 0.29 0.38 Example H2 12.9 15.3 0.88 0.94 0.20
0.38 Example H3 12.4 16.0 0.93 0.94 0.14 0.38 Example H4 12.3 15.9
0.94 0.94 0.12 0.37 Comparative 10.8 7.2 0.87 0.92 0.35 0.24
Example H1 Comparative 10.9 7.3 0.92 0.92 0.51 0.32 Example H2
Comparative 11.1 7.4 0.95 0.92 0.21 0.29 Example H3 Comparative
11.2 7.4 0.96 0.92 0.12 0.29 Example H4 Comparative 10.8 7.1 0.98
0.92 0.02 0.15 Example H5 Comparative 11.4 2.8 1.04 0.92 0.47 0.37
Example H6 Comparative 12.6 15.5 0.97 0.94 0.03 0.16 Example H7
Example H5 16.3 13.8 1.03 0.93 0.15 0.39 Comparative 15.4 5.9 1.01
0.93 0.35 0.24 Example H8 Example H6 19.4 13.4 1.06 0.93 0.14 0.35
Comparative 18.2 5.6 1.08 0.93 0.31 0.27 Example H9
TABLE-US-00015 TABLE 2H Low-Temperature Output Characteristics,
Discharge (Comparative Capacity, Example H1 = mAh/g 100) Example H1
365 122 Example H2 367 126 Example H3 364 118 Example H4 364 118
Comparative 365 100 Example H1 Comparative 363 86 Example H2
Comparative 366 88 Example H3 Comparative 366 94 Example H4
Comparative 366 89 Example H5 Comparative 358 103 Example H6
Comparative 365 114 Example H7 Example H5 368 116 Comparative 367
91 Example H8 Example H6 367 117 Comparative 367 89 Example H9
[1215] In Examples H1 to H6, the flake natural graphite adjusted to
have a prescribed particle size was granulated with a granulating
agent having prescribed physical properties added, whereby a Raman
R value and a TG/SA value in the prescribed ranges were
successfully achieved to provide a high capacity and excellent
low-temperature output characteristics. By contrast, in Comparative
Examples H1 to H9, where the Raman R value and/or the TG/SA value
were outside the prescribed ranges, degraded low-temperature output
characteristics were provided.
Ninth Examples (Examples I) of the Present Invention will Now be
Described.
[1216] In the Examples, physical properties of negative electrode
materials produced were measured by the following methods. The
viscosity, contact angle, surface tension, and r cos .theta. of
granulating agents were each measured by the methods described in
the specification.
Preparation of Electrode Sheet
[1217] An electrode plate having an active material layer with an
active material layer density of 1.35.+-.0.03 g/cm.sup.3 or
1.60.+-.0.03 g/cm.sup.3 was prepared using graphite particles of
Examples or Comparative Examples. Specifically, 50.00.+-.0.02 g of
a negative electrode material, 50.00.+-.0.02 g (0.500 g on a solids
basis) of a 1% by mass aqueous carboxymethylcellulose sodium salt
solution, and 1.00.+-.0.05 g (0.5 g on a solids basis) of an
aqueous dispersion of a styrene-butadiene rubber having a weight
average molecular weight of 270,000 were stirred with a Keyence
hybrid mixer for 5 minutes, and the mixture was defoamed for 30
seconds to give a slurry.
[1218] The slurry was applied to a 10-.mu.m-thick copper foil,
serving as a current collector, to a width of 10 cm using a small
die coater available from Itochu Machining Co., Ltd. such that the
negative electrode material adhered in an amount of 6.0.+-.0.3
mg/cm.sup.2 or 9.0.+-.0.3 mg/cm.sup.2. The coated foil was
roll-pressed using a roller having a diameter of 20 cm to adjust
the density of the active material layer to be 1.35.+-.0.03
g/cm.sup.3 or 1.60.+-.0.03 g/cm.sup.3, thereby preparing an
electrode sheet.
Production of Non-Aqueous Secondary Battery (2016 Coin Battery)
[1219] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
9.0.+-.0.3 mg/cm.sup.2 and in which the density of the active
material layer was 1.60.+-.0.03 g/cm.sup.3, was cut into a disk
having a diameter of 12.5 mm, and lithium metal foil was cut into a
disk having a diameter of 14 mm to prepare a counter electrode. A
separator (made of a porous polyethylene film) was placed between
the two electrodes, the separator being impregnated with an
electrolyte solution of 1 mol/L of LiPF.sub.6 in a mixed solvent of
ethylene carbonate and ethyl methyl carbonate (volume ratio=3:7),
In this manner, 2016 coin batteries were produced.
Method of Producing Non-Aqueous Secondary Battery (Laminate
Battery)
[1220] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
6.0.+-.0.3 mg/cm.sup.2 and in which the density of the active
material layer was 1.35.+-.0.03 g/cm.sup.3, was cut to 4 cm.times.3
cm to prepare a negative electrode, and a positive electrode made
of NMC was cut to the same area. The negative electrode and the
positive electrode were combined with a separator (made of a porous
polyethylene film) placed therebetween. An electrolyte solution of
1.2 mol/L of LiPF.sub.6 in a mixed solvent of ethylene carbonate,
ethyl methyl carbonate, and dimethyl carbonate (volume ratio=3:3:4)
was injected in an amount of 200 .mu.l to produce a laminate
battery.
Method for Measuring Discharge Capacity
[1221] Using the non-aqueous secondary battery (2016 coin battery)
produced by the above-described method, the capacity of the battery
during charging and discharging was measured by the following
method.
[1222] The lithium counter electrode was charged to 5 mV at a
current density of 0.05 C and further charged at a constant voltage
of 5 mV to a current density of 0.005 C. The negative electrode was
doped with lithium, and then the lithium counter electrode was
discharged to 1.5 V at a current density of 0.1 C. Subsequently, a
second charging and discharging was performed at the same current
density. The discharge capacity at the second cycle was defined as
a discharge capacity of this battery.
Low-Temperature Output Characteristics
[1223] Using the laminate non-aqueous electrolyte secondary battery
produced by the method for producing a non-aqueous electrolyte
secondary battery described above, low-temperature output
characteristics were measured by the following method.
[1224] A non-aqueous electrolyte secondary battery that had yet to
go through a charge and discharge cycle was subjected to an initial
charge and discharge that involves three cycles in a voltage range
of 4.1 V to 3.0 V at 25.degree. C. and a current of 0.2 C (1 C is a
current at which a rated capacity at a 1-hour rate discharge
capacity is discharged in 1 hour, and so on) and two cycles in a
voltage range of 4.2 V to 3.0 V at a current of 0.2 C (in charging,
a constant-voltage charge at 4.2 V was further performed for 2.5
hours).
[1225] Furthermore, charging was performed at a current of 0.2 C to
an SOC of 50%, and then constant-current discharging was performed
in a low-temperature environment at -30.degree. C. for 2 seconds at
varying currents of 1/8 C, 1/4 C, 1/2 C, 1.5 C, and 2 C. The
battery voltage drop at 2 seconds after discharging under each
condition was measured. From each measurement, a current I that
could be passed in 2 seconds when the upper limit charge voltage
was 3 V was calculated, and a value calculated from the formula:
3.times.I (W) was defined as the low-temperature output
characteristics of each battery.
Surface Oxygen Content (O/C)
[1226] For X-ray photoelectron spectroscopy, an X-ray photoelectron
spectroscope was used. A measuring object was mounted on a sample
stage such that the surface of the object was flat, and a multiplex
measurement was performed using a K.alpha. radiation of aluminum as
an X-ray source to measure spectra of C1s (280 to 300 eV) and O1s
(525 to 545 eV).
[1227] Charge correction was performed with the C1s peak top
obtained set to 284.3 eV. Peak areas of the spectra of C1s and O1s
were determined and then multiplied by an apparatus sensitivity to
determine the surface atom concentrations of C and O. The O/C ratio
of the atom concentrations of O and C obtained (O atom
concentration/C atom concentration).times.100 was defined as the
surface oxygen content O/C value of the carbon material.
Total Oxygen Content
[1228] An oxygen/nitrogen/hydrogen analyzer (TCH600 ONH
determinator available from LECO) was used. In an inert gas
atmosphere impulse furnace, 50 mg of the carbon material was melted
and decomposed, and the amounts of carbon monoxide and carbon
dioxide in a discharged carrier gas were measured using an infrared
detector to determine the total oxygen content (mold) of the carbon
material.
BET Specific Surface Area (SA)
[1229] Using a surface area meter (AMS8000 specific surface area
analyzer available from Ohkura Riken Co., Ltd.), 0.4 g of a carbon
material was loaded into a cell, and the carbon material sample was
preliminarily dried under a nitrogen stream at 350.degree. C. for
15 minutes, after which using a nitrogen-helium mixed gas precisely
regulated so as to have a nitrogen pressure of 0.3 relative to
atmospheric pressure, a BET specific surface area was measured by a
nitrogen adsorption BET method according to a flowing gas
method.
d50
[1230] The d50 was determined as a volume-based median diameter by
suspending 0.01 g of a carbon material in 10 mL of a 0.2% by mass
aqueous solution of a polyoxyethylene sorbitan monolaurate
surfactant (Tween 20 (registered trademark)), placing the
suspension (a measurement sample) in a commercially available laser
diffraction/scattering particle size distribution analyzer (e,g.,
LA-920 available from HORIBA, Ltd.), irradiating the measurement
sample with ultrasonic waves of 28 kHz at a power of 60 W for 1
minute, and then performing a measurement with the analyzer.
Roundness (Average Roundness)
[1231] Using a flow-type particle image analyzer (FPIA-2000
available from Sysmex Corporation), a particle size distribution
based on equivalent circle diameter was measured, and a roundness
was determined. Ion-exchanged water was used as a dispersion
medium, and polyoxyethylene (20) monolaurate was used as a
surfactant. The equivalent circle diameter is a diameter of a
circle (equivalent circle) having the same projected area as that
of a captured particle image, and the roundness is a ratio of the
perimeter of the equivalent circle, as the numerator, to the
perimeter of the captured particle projection image, as the
denominator. Roundnesses of particles having an equivalent diameter
in the range of 1.5 to 40 .mu.m were averaged to determine the
roundness.
Tap Density
[1232] Using a powder density meter, the carbon material of the
present invention was dropped through a sieve with openings of 300
.mu.m into a cylindrical tap cell with a diameter of 1.6 cm and a
volume capacity of 20 cm.sup.3 to fill up the cell, and then a tap
with a stroke length of 1.0 mm was given 1,000 times. The density
calculated from the volume at this time and the mass of the sample
was defined as the tap density.
Oxygen Functional Group Dispersity
[1233] The oxygen functional group dispersity was determined by the
following formula.
Oxygen .times. .times. functional .times. .times. group .times.
.times. dispersity .times. .times. ( Y i ) = total .times. .times.
oxygen .times. .times. content .times. .times. ( mol .times.
.times. % ) .times. .times. determined .times. .times. by .times.
.times. elemental .times. .times. analysis .times. / .times.
surface .times. .times. oxygen .times. .times. content .times.
.times. ( O .times. / .times. C ) .times. .times. ( mol .times.
.times. % ) .times. .times. determined .times. .times. by .times.
.times. X .times. - .times. ray .times. .times. photoelectron
.times. .times. spectroscopy ##EQU00063##
Example I1
[1234] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry swirl-flow crusher to give a flake natural
graphite having a d50 of 8.1 .mu.m, a Tap of 0.39 g/cm.sup.3, and a
water content of 0.08% by mass. To 100 g of the resulting flake
natural graphite, 12 g of a granulating agent of a liquid paraffin
(Wako Pure Chemical Industries, Ltd., first grade, physical
properties at 25.degree. C.: viscosity=95 cP, contact
angle=13.2.degree., surface tension=31.7 mN/m, r cos .theta.30.9)
was added and mixed with stirring. The sample obtained was
disintegrated and mixed using a hammer mill (MF10 available from
IKA) at a rotation speed of 3,000 rpm to give a flake natural
graphite to which the granulating agent adhered. Using a Model
NHS-1 hybridization system available from Nara Machinery Co., Ltd.,
the sample obtained was mechanically granulated at a rotor
peripheral speed of 85 m/sec for 10 minutes. The sample obtained
was heat treated in a nitrogen atmosphere at 500.degree. C. to give
a granulated carbon material from which the granulating agent was
removed. Using the measurement methods described above, d50, SA,
Tap, roundness, O/C, total oxygen content, oxygen functional group
dispersity, discharge capacity, and low-temperature output
characteristics were measured. The results are shown in Tables 1I
and 2I.
Example I2
[1235] A sample was prepared in the same manner as in Example I1
except that the heat-treatment temperature was 700.degree. C. The
results of the measurements made in the same manner as in Example
I1 are shown in Tables 1I and 2I.
Example I3
[1236] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a mechanical crusher having a crushing rotor and a
liner to give a flake natural graphite having a d50 of 30 .mu.m and
a water content of 0.03% by mass. To 100 g of the resulting flake
natural graphite, 4 g of a granulating agent of a liquid paraffin
(Wako Pure Chemical industries, Ltd., first grade, physical
properties at 25.degree. C.: viscosity=95 cP, contact
angle=13.2.degree., surface tension=31.7 mN/m, r cos .theta.=30.9)
was added and mixed with stirring. The sample obtained was
disintegrated and mixed using a hammer mill (MF10 available from
IKA) at a rotation speed of 3,000 rpm to give a flake natural
graphite to which the granulating agent adhered. Using a Model
NHS-1 hybridization system available from Nara Machinery Co., Ltd.,
the sample obtained was mechanically granulated at a rotor
peripheral speed of 85 m/sec for 10 minutes. The sample obtained
was heat treated in a nitrogen atmosphere at 700.degree. C. to give
a granulated carbon material from which the granulating agent was
removed. The results of the measurements made in the same manner as
in Example I1 are shown in Tables 1I and 2I.
Example I4
[1237] A sample was prepared in the same manner as in Example I3
except that 6 g of a granulating agent of a liquid paraffin (Wako
Pure Chemical Industries, Ltd., first grade) was added. The results
of the measurements made in the same manner as in Example I1 are
shown in Tables 1I and 2I.
Comparative Example I1
[1238] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically granulated at a rotor peripheral speed of 85
m/sec for 10 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite fine powder not
deposited on the base material or incorporated into the granulated
particles. This sample was classified to remove the flake graphite
fine powder, thereby providing a granulated carbon material having
a d50 of 10.9 .mu.m. The results of the measurements made in the
same manner as in Example I1 are shown in Tables 1I and 2I.
Comparative Example I2
[1239] A sample was prepared in the same manner as in Example 1
except that the granulated carbon material of Comparative Example
I1 was heat treated in a nitrogen atmosphere at 700.degree. C. The
results of the measurements made in the same manner as in Example
I1 are shown in Tables 1I and 2I.
Comparative Example I3
[1240] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically granulated at a rotor peripheral speed of
8.5 m/sec for 5 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite fine powder not
deposited on the base material or incorporated into the granulated
particles. This sample was classified to remove the flake graphite
fine powder, thereby providing a granulated carbon material having
a d50 of 15.4 .mu.m. The results of the measurements made in the
same manner as in Example I1 are shown in Tables 1I and 2I.
Comparative Example I4
[1241] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically granulated at a rotor peripheral speed of 70
m/sec for 3 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite fine powder not
deposited on the base material or incorporated into the granulated
particles. This sample was classified to remove the flake graphite
fine powder, thereby providing a granulated carbon material having
a d50 of 19.5 .mu.m. The granulated carbon material was further
mechanically granulated at a rotor peripheral speed of 70 m/sec for
3 minutes using a Model NHS-1 hybridization system available from
Nara Machinery Co., Ltd. and then classified to remove the flake
graphite fine powder not deposited on the base material or
incorporated into the granulated particles, thereby providing a
granulated carbon material having a d50 of 18.2 .mu.m. The results
of the measurements made in the same manner as in Example I1 are
shown in Tables 1I and 2I.
TABLE-US-00016 TABLE 1I Oxygen Total Functional d50 Oxygen Group
(X.sub.i), Tap, SA, O/C, Content, Dispersity 100Y.sub.i + .mu.m
g/cm.sup.3 m.sup.2/g mol % mol % (Y.sub.i) 0.26X.sub.i Roundness
Example I1 12.7 0.87 15.4 0.72 0.078 0.108 14.1 0.94 Example I2
12.9 0.88 15.3 0.78 0.055 0.071 10.4 0.94 Example I3 16.3 1.03 13.8
0.65 0.041 0.063 10.5 0.93 Example I4 19.4 1.06 13.4 0.72 0.034
0.047 9.7 0.93 Comp. Ex. I1 10.9 0.88 8.4 2.79 0.183 0.066 9.4 0.92
Comp. Ex. I2 11.3 0.89 8.4 0.83 0.05 0.06 9 0.92 Comp. Ex. I3 15.4
1.01 5.9 2.6 0.139 0.053 9.3 0.93 Comp. Ex. I4 18.2 1.08 5.6 2.31
0.109 0.047 9.4 0.93
TABLE-US-00017 TABLE 2I Low-Temperature Output Characteristics,
Discharge (Comparative Capacity, Example I1 = mAh/g 100) Example I1
365 122 Example I2 367 126 Example I3 368 116 Example I4 367 117
Comparative 365 100 Example I1 Comparative 363 86 Example I2
Comparative 367 91 Example I3 Comparative 367 89 Example I4
[1242] In Examples I1 to I4, the flake natural graphite adjusted to
have a prescribed particle size was granulated with a granulating
agent having prescribed physical properties added, whereby the
relationship between oxygen functional group dispersity and d50
(.mu.m) in the prescribed range was successfully achieved to
provide a high capacity and excellent low-temperature output
characteristics. By contrast, in Comparative Examples I1 to I4,
where the relationship between oxygen functional group dispersity
and d50 (.mu.m) was outside the prescribed range, degraded
low-temperature output characteristics were provided.
Tenth Examples (Examples J) of the Present Invention will Now be
Described.
[1243] In Examples J, physical properties and characteristics of
carbon materials produced were measured by the following
methods.
d50
[1244] The d50 was determined as a volume-based median diameter by
suspending 0.01 g of a negative electrode material in 10 mL of a
0.2% by mass aqueous solution of a polyoxyethylene sorbitan
monolaurate surfactant (Tween 20 (registered trademark)), placing
the suspension (a measurement sample) in a commercially available
laser diffraction/scattering particle size distribution analyzer
(e.g., LA-920 available from HORIBA, Ltd.), irradiating the
measurement sample with ultrasonic waves of 28 kHz at a power of 60
W for 1 minute, and then performing a measurement with the
analyzer.
Tap Density
[1245] Using a powder density meter, the negative electrode
material was dropped through a sieve with openings of 300 .mu.m
into a cylindrical tap cell with a diameter of 1.6 cm and a volume
capacity of 20 cm.sup.3 to fill up the cell, and then a tap with a
stroke length of 10 mm was given 1,000 times. The density
calculated from the volume at this time and the mass of the sample
was defined as the tap density.
Specific Surface Area SA
[1246] The specific surface area SA was defined as a value
determined as follows: using a surface area meter (Gemini 2360
specific surface area analyzer available from Shimadzu
Corporation), a negative electrode material sample was
preliminarily vacuum dried under a nitrogen stream at 100.degree.
C. for 3 hours and then cooled to liquid nitrogen temperature, and
using a nitrogen-helium mixed gas precisely regulated so as to have
a nitrogen pressure of 0.3 relative to atmospheric pressure, a BET
specific surface area was measured by a nitrogen adsorption BET
multipoint method according to a flowing gas method.
Preparation of Electrode Sheet
[1247] An electrode plate having an active material layer with an
active material layer density of 1.60.+-.0.03 g/cm.sup.3 or
1.35.+-.0.03 g/cm.sup.3 was prepared using a negative electrode
material of Examples or Comparative Examples. Specifically,
50.00.+-.0.02 g of a negative electrode material, 50.00.+-.0.02 g
(0.500 g on a solids basis) of a 1% by mass aqueous
carboxymethylcellulose sodium salt solution, and 1.00.+-.0.05 g
(0.5 g on a solids basis) of an aqueous dispersion of a
styrene-butadiene rubber having a weight average molecular weight
of 270,000 were stirred with a Keyence hybrid mixer for 5 minutes,
and the mixture was defoamed for 30 seconds to give a slurry.
[1248] The slurry was applied to a 10-.mu.m-thick copper foil,
serving as a current collector, to a width of 10 cm using a small
die coater available from Itochu Machining Co., Ltd. such that the
negative electrode material adhered in an amount of 12.00.+-.0.3
mg/cm.sup.2 or 6.00.+-.0.3 mg/cm.sup.2. The coated foil was
roll-pressed using a roller having a diameter of 20 cm to adjust
the density of the active material layer to be 1.60.+-.0.03
g/cm.sup.3 or 1.35.+-.0.03 g/cm.sup.3, thereby preparing an
electrode sheet.
Production of Non-Aqueous Secondary Battery (2016 Coin Battery)
[1249] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
12.00.+-.0.3 mg/cm.sup.2 and in which the density of the active
material layer was adjusted to be 1.60.+-.0.03 g/cm.sup.3, was cut
into a disk having a diameter of 12.5 mm, and lithium metal foil
was cut into a disk having a diameter of 14 mm to prepare a counter
electrode. A separator (made of a porous polyethylene film) was
placed between the two electrodes, the separator being impregnated
with an electrolyte solution of 1 mol/L of LiPF.sub.6 in a mixed
solvent of ethylene carbonate and ethyl methyl carbonate (volume
ratio=3:7). In this manner, 2016 coin batteries were produced.
Method of Producing Non-Aqueous Secondary Battery (Laminate
Battery)
[1250] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
6.00.+-.0.3 mg/cm.sup.2 and in which the density of the active
material layer was adjusted to be 1.35.+-.0.03 g/cm.sup.3, was cut
to 4 cm.times.3 cm to prepare a negative electrode, and a positive
electrode made of NMC was cut to the same area. The negative
electrode and the positive electrode were combined with a separator
(made of a porous polyethylene film) placed therebetween. An
electrolyte solution of 1.2 mol/L of LiPF.sub.6 in a mixed solvent
of ethylene carbonate, ethyl methyl carbonate, and dimethyl
carbonate (volume ratio=3:3:4) was injected in an amount of 200
.mu.L to produce a laminate battery.
Method for Measuring Discharge Capacity
[1251] Using the non-aqueous secondary battery (2016 coin battery)
produced by the above-described method, the capacity of the battery
during charging and discharging was measured by the following
method.
[1252] The lithium counter electrode was charged to 5 mV at a
current density of 0.05 C and further charged at a constant voltage
of 5 mV to a current density of 0.005 C. The negative electrode was
doped with lithium, and then the lithium counter electrode was
discharged to 1.5 V at a current density of 0.1 C. The discharge
capacity at this time was defined as a discharge capacity of this
battery.
Low-Temperature Output Characteristics
[1253] Using the laminate non-aqueous electrolyte secondary battery
produced by the method for producing a non-aqueous electrolyte
secondary battery described above, low-temperature output
characteristics were measured by the following method.
[1254] A non-aqueous electrolyte secondary battery that had yet to
go through a charge and discharge cycle was subjected to an initial
charge and discharge that involves three cycles in a voltage range
of 4.1 V to 3.0 V at 25.degree. C. and a current of 0.2 C (1 C is a
current at which a rated capacity at a 1-hour rate discharge
capacity is discharged in 1 hour, and so on) and two cycles in a
voltage range of 4.2 V to 3.0 V at a current of 0.2 C (in charging,
a constant-voltage charge at 4.2 V was further performed for 2.5
hours).
[1255] Furthermore, charging was performed at a current of 0.2 C to
an SOC of 50%, and then constant-current discharging was performed
in a low-temperature environment at -30.degree. C. for 2 seconds at
varying currents of 1/8 C, 1/4 C, 1/2 C, 1.5 C, and 2 C. The
battery voltage drop at 2 seconds after discharging under each
condition was measured. From each measurement, a current I that
could be passed in 2 seconds when the upper limit charge voltage
was 3 V was calculated, and a value calculated from the formula:
3.times.I (W) was defined as the low-temperature output
characteristics of each battery.
High-Temperature Storage Characteristics
[1256] High-temperature storage characteristics were measured by
the following measurement method using the laminate non-aqueous
electrolyte secondary battery produced by the method for producing
a non-aqueous electrolyte secondary battery described above.
[1257] A non-aqueous electrolyte secondary battery that has yet to
go through a charge and discharge cycle was subjected to an initial
charge and discharge that involves three cycles in a voltage range
of 4.1 V to 3.0 V at 25.degree. C. and a current of 0.2 C (1 C is a
current at which a rated capacity at a 1-hour rate discharge
capacity is discharged in 1 hour, and so on) and two cycles in a
voltage range of 4.2 V to 3.0 V at a current of 0.2 C (in charging,
a constant-voltage charge at 4.2 V was further performed for 2.5
hours).
[1258] The battery was further charged at a current of 0.2 C to an
SOC of 80% and then stored in a high-temperature environment at
60.degree. C. for 2 weeks. After that, the battery was discharged
at 25.degree. C. and 0.2 C to 3.0 V, charged at 0.2 C to 4.2 V, and
discharged at 0.2 C to 3.0 V. The discharge capacity at this time
was defined as a discharge capacity A (mAh). The ratio (%) of the
discharge capacity A to a discharge capacity B (mAh) at a fifth
initial charge and discharge cycle was used as high-temperature
storage characteristics. (High-temperature storage characteristics
(%)=A (mAh)/B (mAh).times.100)
Example J1
[1259] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry swirl-flow crusher to give a flake natural
graphite having a d50 of 8.1 .mu.m, a Tap of 0.39 g/cm.sup.3, and a
water content of 0.08% by mass. To 100 g of the resulting flake
natural graphite, 12 g of a granulating agent of an aromatic oil I
(aniline point, 29.degree. C.; containing a naphthalene ring
structure in its molecule) was added and mixed with stirring. The
sample obtained was disintegrated and mixed using a hammer mill
(MF10 available from IKA) at a rotation speed of 3,000 rpm to give
a flake natural graphite to which the granulating agent uniformly
adhered. Using a Model NHS-1 hybridization system available from
Nara Machinery Co., Ltd., the sample obtained was mechanically
spheroidized at a rotor peripheral speed of 85 m/sec for 10 minutes
to give granulated carbon material particles.
[1260] The granulated carbon material particles and a coal-tar
pitch, serving as a carbonaceous material precursor having lower
crystallinity than the raw carbon material, were mixed using a
mixer at 120.degree. C. for 20 minutes. The resulting mixture was
heat treated in an inert gas at 1,300.degree. C. for 1 hour, and
then the burned product was disintegrated and classified to give
multi-layered graphite particles made of the granulated carbon
material particles and the carbonaceous material having lower
crystallinity than the raw carbon material combined with each
other. The burning yield showed that the mass ratio of the
granulated carbon material particles to the carbonaceous material
having lower crystallinity than the raw carbon material (granulated
carbon material particle/amorphous carbon) of the multi-layered
graphite particles was 1:0.065. The d50, SA, Tap, discharge
capacity, low-temperature output characteristics, and
high-temperature storage characteristics of the sample obtained
were measured. The results are shown in Table 1J.
Example J2
[1261] Multi-layered graphite particles were obtained in the same
manner as in Example J1 except that the mass ratio of the
granulated carbon material particles to the carbonaceous material
having lower crystallinity than the raw carbon material (granulated
carbon material particle/amorphous carbon) was 1:008. The results
of the measurements made in the same manner as in Example J1 are
shown in Table 1J.
Example J3
[1262] Multi-layered graphite particles were obtained in the same
manner as in Example J2 except that an aromatic oil II (aniline
point, none; mixed aniline point, 15.degree. C.; containing a
benzene ring structure in its molecule) was used as a granulating
agent. The results of the measurements made in the same manner as
in Example J1 are shown in Table 1J.
Reference Example J1
[1263] Multi-layered graphite particles were obtained in the same
manner as in Example J1 except that a paraffinic oil (aniline
point, >100.degree. C.) was used as a granulating agent. The
results of the measurements made in the same manner as in Example
J1 are shown in Table 1J.
Reference Example J2
[1264] Multi-layered graphite particles were obtained in the same
manner as in Comparative Example 11 except that the mass ratio of
the granulated carbon material particles to the carbonaceous
material having lower crystallinity than the raw carbon material
(granulated carbon material particle/amorphous carbon) was 1:0.08.
The results of the measurements made in the same manner as in
Example J1 are shown in Table 1J.
Reference Example J3
[1265] Multi-layered graphite particles were obtained in the same
manner as in Comparative Example J1 except that the mass ratio of
the granulated carbon material particles to the carbonaceous
material having lower crystallinity than the raw carbon material
(granulated carbon material particle/amorphous carbon) was 1:0.1.
The results of the measurements made in the same manner as in
Example J1 are shown in Table 1J.
Comparative Example J1
[1266] A flake natural graphite having a d50 of 100 .mu.m was
mechanically spheroidized as it is at a rotor peripheral speed of
85 m/sec for 10 minutes using a Model NHS-1 hybridization system
available from Nara Machinery Co., Ltd. In the sample obtained was
confirmed the presence of a large amount of flake graphite fine
powder not deposited on the base material or incorporated into the
spheroidized particles. This sample was classified to remove the
flake graphite fine powder, thereby providing a spheroidized
graphite having a d50 of 10.8 .mu.m and a Tap density of 0.88
g/cm.sup.3. The spheroidized graphite and a coal-tar pitch, serving
as a carbonaceous material precursor having lower crystallinity
than the raw carbon material, were mixed using a mixer at
120.degree. C. for 20 minutes. The resulting mixture was heat
treated in an inert gas at 1,300.degree. C. for 1 hour, and then
the burned product was disintegrated and classified to give
multi-layered graphite particles made of the granulated carbon
material particles and the carbonaceous material having lower
crystallinity than the raw carbon material combined with each
other. The burning yield showed that the mass ratio of the
granulated carbon material particles to the carbonaceous material
having lower crystallinity than the raw carbon material (granulated
carbon material particle/amorphous carbon) of the multi-layered
graphite particles was 1:0.065. The d50, SA, Tap, discharge
capacity, low-temperature output characteristics, and
high-temperature storage characteristics of the sample obtained
were measured. The results are shown in Table 1J.
TABLE-US-00018 TABLE 1J Low-Temperature High-Temperature Output
Storage Characteristics, Characteristics, Discharge (Reference
(Reference d50, Tap, SA, Capacity, Example J2 = Example J2 = .mu.m
g/cm.sup.3 m.sup.2/g mAh/g 100) 100) Example J1 11.8 1.02 7.8 362
109.9 98.9 Example J2 12.0 0.92 6.1 359 104.8 100.4 Example J3 11.9
0.94 5.8 359 103.1 101.1 Reference 12.0 1.05 7.9 362 94.4 98.6
Example J1 Reference 11.8 1.02 7.1 359 100.0 100.0 Example J2
Reference 12.0 0.92 5.7 357 91.2 100.4 Example J3 Comparative 11.4
1.04 3.1 362 68.1 104.4 Example J1
[1267] In Examples J1 to J3, the low-temperature output
characteristics and the high-temperature storage characteristics
were sufficiently superior to those in Reference Examples J1 to J3
and Comparative Example J1.
Eleventh Examples (Examples K) of the Present Invention will Now be
Described.
Preparation of Electrode Sheet
[1268] An electrode plate having an active material layer with an
active material layer density of 1.35.+-.0.03 g/cm.sup.3 was
prepared using graphite particles of Examples or Comparative
Examples. Specifically, 50.00.+-.0.02 g of a negative electrode
material, 50.00.+-.0.02 g (0.500 g on a solids basis) of a 1% by
mass aqueous carboxymethylcellulose sodium salt solution, and 0.5 g
(on a solids basis) of an aqueous dispersion of a styrene-butadiene
rubber having a weight average molecular weight of 270,000 were
stirred with a Keyence hybrid mixer for 5 minutes, and the mixture
was defoamed for 30 seconds to give a slurry.
[1269] The slurry was applied to a 1.0-.mu.m-thick copper foil,
serving as a current collector, to a width of 10 cm using a small
die coater available from Itochu Machining Co., Ltd. such that the
negative electrode material adhered in an amount of 6.0.+-.0.3
mg/cm.sup.2 or 12.0.+-.0.3 mg/cm.sup.2. The coated foil was
roll-pressed using a roller having a diameter of 20 cm to adjust
the density of the active material layer to be 1.35.+-.0.03
g/cm.sup.3, thereby preparing an electrode sheet.
Production of Non-Aqueous Secondary Battery (2016 Coin Battery)
[1270] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
12.0.+-.0.3 mg/cm.sup.2 and in which the density of the active
material layer was 1.35.+-.0.03 g/cm.sup.3, was cut into a disk
having a diameter of 12.5 mm, and lithium metal foil was cut into a
disk having a diameter of 14 mm to prepare a counter electrode. A
separator (made of a porous polyethylene film) was placed between
the two electrodes, the separator being impregnated with an
electrolyte solution of 1 mol/L, of LiPF.sub.6 in a mixed solvent
of ethylene carbonate and ethyl methyl carbonate (volume
ratio=3:7). In this manner, 2016 coin batteries were produced.
Method of Producing Non-Aqueous Secondary Battery (Laminate
Battery)
[1271] The electrode sheet prepared by the above-described method,
to which the negative electrode material adhered in an amount of
6.0.+-.0.3 mg/cm.sup.2 and in which the density of the active
material layer was 1.35.+-.0.03 g/cm.sup.3, was cut to 4 cm.times.3
cm to prepare a negative electrode, and a positive electrode made
of NMC was cut to the same area. The negative electrode and the
positive electrode were combined with a separator (made of a porous
polyethylene film) placed therebetween. An electrolyte solution of
1.2 mol/L of LiPF.sub.6 in a mixed solvent of ethylene carbonate,
ethyl methyl carbonate, and dimethyl carbonate (volume ratio=3:3:4)
was injected in an amount of 200 .mu.L to produce a laminate
battery.
Method for Measuring Discharge Capacity
[1272] Using the non-aqueous secondary battery (2016 coin battery)
produced by the above-described method, the capacity of the battery
during charging and discharging was measured by the following
method.
[1273] The lithium counter electrode was charged to 5 mV at a
current density of 0.05 C and further charged at a constant voltage
of 5 mV to a current density of 0.005 C. The negative electrode was
doped with lithium, and then the lithium counter electrode was
discharged to 1.5 V at a current density of 0.1 C. Subsequently, a
second charging and discharging was performed at the same current
density. The discharge capacity at the second cycle was defined as
a discharge capacity of this battery.
Low-Temperature Output Characteristics
[1274] Using the laminate non-aqueous electrolyte secondary battery
produced by the method for producing a non-aqueous electrolyte
secondary battery described above, low-temperature output
characteristics were measured by the following method.
[1275] A non-aqueous electrolyte secondary battery that had yet to
go through a charge and discharge cycle was subjected to an initial
charge and discharge that involves three cycles in a voltage range
of 4.1 V to 3.0 V at 25.degree. C. and a current of 0.2 C (1 C is a
current at which a rated capacity at a 1-hour rate discharge
capacity is discharged in 1 hour, and so on) and two cycles in a
voltage range of 4.2 V to 3.0 V at a current of 0.2 C (in charging,
a constant-voltage charge at 4.2 V was further performed for 2.5
hours).
[1276] Furthermore, charging was performed at a current of 0.2 C to
an SOC of 50%, and then constant-current discharging was performed
in a low-temperature environment at -30.degree. C. for 2 seconds at
varying currents of 1/8 C, 1/4 C, 1/2 C, 1.5 C, and 2 C. The
battery voltage drop at 2 seconds after discharging under each
condition was measured. From each measurement, a current I that
could be passed in 2 seconds when the upper limit charge voltage
was 3 V was calculated, and a value calculated from the formula:
3.times.I (W) was defined as the low-temperature output
characteristics of each battery.
a: Volume-Based Average Particle Diameter (d50)
[1277] The d50 was determined as a volume-based median diameter by
suspending 0.01 g of a carbon material in 10 mL of a 0.2% by mass
aqueous solution of a polyoxyethylene sorbitan monolaurate
surfactant (Tween 20 (registered trademark)), placing the
suspension (a measurement sample) in a commercially available laser
diffraction scattering particle size distribution analyzer (e.g.,
LA-920 available from HORIBA, Ltd.), irradiating the measurement
sample with ultrasonic waves of 28 kHz at a power of 60 W for 1
minute, and then performing a measurement with the analyzer.
x.sub.k: True Density
[1278] The true density of a carbon material sample was measured by
pycnometry using a true density meter (MAT-7000 Auto True Denser
available from Seishin Enterprise Co., Ltd).
Density Under Uniaxial Load of 100 kgf/73.14 c.sup.m2
[1279] The density under a uniaxial load of 100 kgf/3.14 cm.sup.2
was measured using an MCP-PD51 powder resistivity measurement
system available from Mitsubishi Chemical Analytech Co., Ltd.
First, values of the apparatus were corrected. For a load
correction, the load measured when the bottom of a cylindrical
container for accommodating the carbon material and a push rod to
be inserted into the container from above to apply pressure to the
carbon material were separated from each other was confirmed to be
0 kgf/3.14 cm.sup.2. Next, a thickness gauge was corrected. While
the cylindrical container and the push rod were brought close using
a hydraulic pump, a zero-point correction was carried out such that
the thickness gauge indicated 0.00 mm when the load reached 20
kgf/3.14 cm.sup.2. After the corrections were carried out, 3.0 g of
the carbon material was placed in the cylindrical container with a
diameter of 2 cm, and the height of the carbon material was
adjusted so as to receive a load evenly. A seat was lifted using
the hydraulic pump, and the push rod was inserted into the
cylindrical container. After the thickness gauge had indicated 15.0
mm, loads were measured at thicknesses at 0.5-mm intervals until
the load exceeded 1,000 kgf/3.14 cm.sup.2. From the thicknesses
obtained, the densities of the powder were calculated, and using
Microsoft Excel, a graph was created with powder density plotted on
the horizontal axis and load on the vertical axis. A cubic spline
curve of the graph was created, and the formula obtained was used
to calculate a carbon material density under a load of 100 kgf/3.14
cm.sup.3. To reduce variation in measurements, the measurement was
made at least twice. When variation occurred, the measurement was
made three times, and the average of two closest values was
used.
Tap Density: Tap
[1280] Using a powder density meter, the carbon material of the
present invention was dropped through a sieve with openings of 300
.mu.m into a cylindrical tap cell with a diameter of 1.6 cm and a
volume capacity of 20 cm.sup.3 to fill up the cell, and then a tap
with a stroke length of 10 mm was given 1,000 times. The density
calculated from the volume at this time and the mass of the sample
was defined as the tap density.
[1281] y.sub.k: Density Under Uniaxial Load of 100 kgf/3.14
c.sup.m2--Tap Density
[1282] y.sub.k is a value obtained by subtracting a tap density
from a density under a uniaxial load of 100 kgf/3.14 cm.sup.2.
Example K1
[1283] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry swirl-flow crusher to give a flake natural
graphite having a d50 of 8.1 .mu.m, a tap density of 0.39
g/cm.sup.3, and a water content of 0.08% by mass. To 100 g of the
resulting flake natural graphite, 12 g of a granulating agent of a
paraffinic oil (liquid paraffin available from Wako Pure Chemical
Industries, Ltd., first grade, physical properties at 25.degree.
C.; viscosity=95 cP, contact angle=13.2.degree., surface
tension=31.7 mN/m, r cos .theta.=30.9) was added and mixed with
stirring. The sample obtained was disintegrated and mixed using a
hammer mill (MF10 available from IKA) at a rotation speed of 3,000
rpm to give a flake natural graphite to which the granulating agent
uniformly adhered. Using a Model NHS-1 hybridization system
available from Nara Machinery Co., Ltd., the flake natural graphite
to which the granulating agent uniformly adhered was mechanically
spheroidized at a rotor peripheral speed of 85 m/sec for 10 minutes
while fine powder generated during the spheroidization was
deposited on the base material and incorporated into the
spheroidized particles, and heat treated in an inert gas at
720.degree. C. to give a spheroidized graphite having a d50 of 13
.mu.m.
[1284] The spheroidized natural graphite and a coal-tar pitch,
serving as an amorphous carbon precursor, were mixed and heat
treated in an inert gas at 1,300.degree. C., and then the burned
product was disintegrated and classified to give a multi-layered
carbon material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of the granulated graphite particles to the carbonaceous
material having lower crystallinity than the raw graphite
(granulated graphite particle/amorphous carbon) of the
multi-layered graphite particles was 1:0.065. The true density,
d50, tap density, density under a uniaxial load of 100 kgf/3.14
cm.sup.2, discharge capacity, and low-temperature output
characteristics of the sample obtained were measured. The results
are shown in Table 1K.
Example K2
[1285] Multi-layered graphite particles were obtained in the same
manner as in Example K1 except that the mass ratio of the
granulated graphite particles to the carbonaceous material having
lower crystallinity than the raw graphite (granulated graphite
particle/amorphous carbon) of the multi-layered graphite particles
was 1:0.08. The results of the measurements made in the same manner
as in Example K1 are shown in Table 1K.
Comparative Example K1
[1286] A spheroidized natural graphite was prepared in the same
manner as in Example K1 except that no granulating agent was added,
and the spheroidized natural graphite was air classified to remove
the flake graphite fine powder that had not been granulated,
thereby providing a spheroidized natural graphite having a d50 of
10.9 .mu.m and a Tap density of 0.88 g/cm.sup.3. The spheroidized
natural graphite and a petroleum-derived heavy oil, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.02. The results of the
measurements made in the same manner as in Example K1 are shown in
Table 1K.
Comparative Example K2
[1287] A multi-layered carbon material was obtained in the same
manner except that the mixing ratio of the petroleum-derived heavy
oil was changed from that in Comparative Example K1. The burning
yield showed that the mass ratio of spheroidized graphite particle
to amorphous carbon (spheroidized graphite particle/amorphous
carbon) of the multi-layered carbon material was 1:0.04. The
results of the measurements made in the same manner as in Example
K1 are shown in Table 1K.
Comparative Example K3
[1288] A multi-layered carbon material was obtained in the same
manner except that the mixing ratio of the petroleum-derived heavy
oil was changed from that in Comparative Example K1. The burning
yield showed that the mass ratio of spheroidized graphite particle
to amorphous carbon (spheroidized graphite particle/amorphous
carbon) of the multi-layered carbon material was 1:0.05. The
results of the measurements made in the same manner as in Example
K1 are shown in Table 1K.
Comparative Example K4
[1289] A multi-layered carbon material was obtained in the same
manner as in Comparative Example K1 except that a coal-tar pitch
was used as an amorphous carbon precursor in place of the
petroleum-derived heavy oil, and its mixing ratio was changed. The
burning yield showed that the mass ratio of spheroidized graphite
particle to amorphous carbon (spheroidized graphite
particle/amorphous carbon) of the multi-layered carbon material was
1:0.07. The results of the measurements made in the same manner as
in Example K1 are shown in Table 1K.
Example K3
[1290] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a mechanical crusher having a crushing rotor and a
liner to give a flake natural graphite having a d50 of 30 .mu.m and
a water content of 0.03% by mass. To 100 g of the resulting flake
natural graphite, 6 g of a granulating agent of a paraffinic oil
(liquid paraffin available from Wako Pure Chemical Industries,
Ltd., first grade, physical properties at 25.degree. C.:
viscosity=95 cP, contact angle=13.2.degree., surface tension=31.7
mN/m, r cos .theta.=30.9) was added and mixed with stirring. The
sample obtained was disintegrated and mixed using a hammer mill
(MF10 available from IKA) at a rotation speed of 3,000 rpm to give
a flake natural graphite to which the granulating agent uniformly
adhered. Using a Model NHS-1 hybridization system available from
Nara Machinery Co., Ltd., the flake natural graphite to which the
granulating agent uniformly adhered was mechanically spheroidized
at a rotor peripheral speed of 85 m/sec for 10 minutes while fine
powder generated during the spheroidization was deposited on the
base material and incorporated into the spheroidized particles,
thereby providing a spheroidized natural graphite having a d50 of
19.4 .mu.m. The spheroidized natural graphite and a coal-tar pitch,
serving as an amorphous carbon precursor, were mixed and heat
treated in an inert gas at 1,300.degree. C., and then the burned
product was disintegrated and classified to give a multi-layered
carbon material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.03. The results of the
measurements made in the same manner as in Example K1 are shown in
Table 1K.
Example K4
[1291] The spheroidized natural graphite obtained in Example K3 and
a coal-tar pitch, serving as an amorphous carbon precursor, were
mixed and heat treated in an inert gas at 1,300.degree. C., and
then the burned product was disintegrated and classified to give a
multi-layered carbon material made of graphite particles and an
amorphous carbon combined with each other. The burning yield showed
that the mass ratio of spheroidized graphite particle to amorphous
carbon (spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.04. The results of the
measurements made in the same manner as in Example K1 are shown in
Table 1K.
Example K5
[1292] The spheroidized natural graphite obtained in Example K3 and
a coal-tar pitch, serving as an amorphous carbon precursor, were
mixed and heat treated in an inert gas at 1,300.degree. C., and
then the burned product was disintegrated and classified to give a
multi-layered carbon material made of graphite particles and an
amorphous carbon combined with each other. The burning yield showed
that the mass ratio of spheroidized graphite particle to amorphous
carbon (spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.05. The results of the
measurements made in the same manner as in Example K1 are shown in
Table 1K.
Example K6
[1293] The spheroidized natural graphite obtained in Example K1 and
a coal-tar pitch, serving as an amorphous carbon precursor, were
mixed and heat treated in an inert gas at 1,300.degree. C., and
then the burned product was disintegrated and classified to give a
multi-layered carbon material made of graphite particles and an
amorphous carbon combined with each other. The burning yield showed
that the mass ratio of spheroidized graphite particle to amorphous
carbon (spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.10. The results of the
measurements made in the same manner as in Example K1 are shown in
Table 1K.
Comparative Example K5
[1294] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 3 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite and flake graphite
fine powder generated during the spheroidization that were not
deposited on the base material or incorporated. This sample was
classified to remove the flake graphite fine powder, thereby
providing a spheroidized graphite having a d50 of 19 .mu.m. The
spheroidized natural graphite and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.01. The results of the
measurements made in the same manner as in Example K1 are shown in
Table 1K.
Comparative Example K6
[1295] A multi-layered carbon material was obtained in the same
manner except that the mixing ratio of the coal-tar pitch was
changed from that in Comparative Example K5. The burning yield
showed that the mass ratio of spheroidized graphite particle to
amorphous carbon (spheroidized graphite particle/amorphous carbon)
of the multi-layered carbon material was 1:0.03.
[1296] The results of the measurements made in the same manner as
in Example K1 are shown in Table 1K.
Comparative Example K7
[1297] A multi-layered carbon material was obtained in the same
manner except that the mixing ratio of the coal-tar pitch was
changed from that in Comparative Example K5. The burning yield
showed that the mass ratio of spheroidized graphite particle to
amorphous carbon (spheroidized graphite particle/amorphous carbon)
of the multi-layered carbon material was 1:0.06.
[1298] The results of the measurements made in the same manner as
in Example K1 are shown in Table 1K.
Comparative Example K8
[1299] A multi-layered carbon material was obtained in the same
manner except that the mixing ratio of the coal-tar pitch was
changed from that in Comparative Example K5. The burning yield
showed that the mass ratio of spheroidized graphite particle to
amorphous carbon (spheroidized graphite particle/amorphous carbon)
of the multi-layered carbon material was 1:0.08.
[1300] The results of the measurements made in the same manner as
in Example K1 are shown in Table 1K.
TABLE-US-00019 TABLE 1K Density under Low-Temp. X.sub.k 100 Right
Right Output True a kgf/3.14 Side of Side or Discharge
Characteristics Density d50 Tap cm.sup.2 y.sub.k Inequality
Inequality Capacity (Comp. Ex. K4 = (g/cm.sup.3) (.mu.m)
(g/cm.sup.3) (g/cm.sup.3) (g/cm.sup.3) (1K) (3K) (mAh/g) 100) (%)
Example K1 2.23 12 1.05 1.24 0.19 10.868 10.972 362 139 Example K2
2.23 12 1.02 1.25 0.24 10.817 10.92 359 147 Comp. Ex. K1 2.25 11
0.99 1.23 0.24 10.923 11.02 368 111 Comp. Ex. K2 2.24 11 1.03 1.21
0.18 10.931 11.029 365 103 Comp. Ex. K3 2.24 11 1.04 1.2 0.16
10.934 11.03.3 363 102 Comp. Ex. K4 2.23 11 1.04 1.18 0.14 10.927
11.026 361 100 Example K3 2.25 18 1.16 1.34 0.18 10.896 11.052 366
118 Example K4 2.24 18 1.19 1.34 0.15 10.896 11.056 363 124 Example
K5 2.24 19 1.18 1.35 0.16 10.864 11.033 363 124 Example K6 2.22 22
1.19 1.31 0.12 10.796 10.991 358 113 Comp. Ex. K5 2.25 18 1.14 1.31
0.18 10.935 11.095 367 91 Comp. Ex. K6 2.25 19 1.17 1.29 0.12
10.961 11.128 367 93 Comp. Ex. K7 2.24 19 1.19 1.28 0.09 10.96
11.127 364 79 Comp. Ex. K8 2.23 19 1.21 1.28 0.07 10.92 11.087 358
67
[1301] In Examples K1 to K6, values of the right side of inequality
(1K) are less than 10.914, showing that the capacity and the
low-temperature output characteristics were superior to those of
Comparative Examples K1 to K8, where values of the right side of
inequality (1K) are greater than 10.914. Furthermore, in Examples
K1 to K2, values of the right side of inequality (3K) are less than
10.990, showing that the capacity and the low-temperature output
are very excellent.
Twelfth Examples (Examples L) of the Present Invention will Now be
Described.
Preparation of Electrode Sheet
[1302] An electrode plate having an active material layer with an
active material layer density of 1.60.+-.0.03 g/cm.sup.3 was
prepared using graphite particles of Examples or Comparative
Examples. Specifically, 50.00.+-.0.02 g of a negative electrode
material, 50.00.+-.0.02 g (0.500 g on a solids basis) of a 1% by
mass aqueous carboxymethylcellulose sodium salt solution, and
1.00.+-.0.05 g (0.5 g on a solids basis) of an aqueous dispersion
of a styrene-butadiene rubber having a weight average molecular
weight of 270,000 were stirred with a Keyence hybrid mixer for 5
minutes, and the mixture was defoamed for 30 seconds to give a
slurry.
[1303] The slurry was applied to a 10-.mu.m-thick copper foil,
serving as a current collector, to a width of 10 cm using a small
die coater available from Itochu Machining Co., Ltd. such that the
negative electrode material adhered in an amount of 12.00.+-.0.3
mg/cm.sup.2. The coated foil was roll-pressed using a roller having
a diameter of 20 cm to adjust the density of the active material
layer to be 1.60.+-.0.03 g/cm.sup.3, thereby preparing an electrode
sheet.
Production of Non-Aqueous Secondary Battery (2016 Coin Battery)
[1304] The electrode sheet prepared by the above-described method
was cut into a disk having a diameter of 12.5 mm, and lithium metal
foil was cut into a disk having a diameter of 14 mm to prepare a
counter electrode. A separator (made of a porous polyethylene film)
was placed between the two electrodes, the separator being
impregnated with an electrolyte solution of 1 mol/L of LiPF.sub.6
in a mixed solvent of ethylene carbonate and ethyl methyl carbonate
(volume ratio=3:7). In this manner, 2016 coin batteries were
produced.
Method of Producing Non-Aqueous Secondary Battery (Laminate
Battery)
[1305] The electrode sheet prepared by the above-described method
was cut to 4 cm.times.3 cm to prepare a negative electrode, and a
positive electrode made of NMC was cut to the same area. The
negative electrode and the positive electrode were combined with a
separator (made of a porous polyethylene film) placed therebetween.
An electrolyte solution of 1.2 mol/L of LiPF.sub.6 in a mixed
solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl
carbonate (volume ratio=3:3:4) was injected in an amount of 250
.mu.l to produce a laminate battery.
Method for Measuring Discharge Capacity
[1306] Using the non-aqueous secondary battery (2016 coin battery)
produced by the above-described method, the capacity of the battery
during charging and discharging was measured by the following
method.
[1307] The lithium counter electrode was charged to 5 mV at a
current density of 0.05 C and further charged at a constant voltage
of 5 mV to a current density of 0.005 C. The negative electrode was
doped with lithium, and then the lithium counter electrode was
discharged to 1.5 V at a current density of 0.1 C. Subsequently, a
second charging and discharging was performed at the same current
density. The discharge capacity at the second cycle was defined as
a discharge capacity of this battery.
Low-Temperature Output Characteristics
[1308] Using the laminate non-aqueous electrolyte secondary battery
produced by the method for producing a non-aqueous electrolyte
secondary battery described above, low-temperature output
characteristics were measured by the following method.
[1309] A non-aqueous electrolyte secondary battery that had yet to
go through a charge and discharge cycle was subjected to an initial
charge and discharge that involves three cycles in a voltage range
of 4.1 V to 3.0 V at 25.degree. C. and a current of 0.2 C (1 C is a
current at which a rated capacity at a 1-hour rate discharge
capacity is discharged in 1 hour, and so on) and two cycles in a
voltage range of 4.2 V to 3.0 V at a current of 0.2 C (in charging,
a constant-voltage charge at 4.2 V was further performed for 2.5
hours).
[1310] Furthermore, charging was performed at a current of 0.2 C to
an SOC of 50%, and then constant-current discharging was performed
in a low-temperature environment at -30.degree. C. for 2 seconds at
varying currents of 1/8 C, 1/4 C, 1/2 C, 1.5 C, and 2 C. The
battery voltage drop at 2 seconds after discharging under each
condition was measured. From each measurement, a current I that
could be passed in 2 seconds when the upper limit charge voltage
was 3 V was calculated, and a value calculated from the formula:
3.times.I (W) was defined as the low-temperature output
characteristics of each battery.
Roundness R Determined with Flow-Type Particle Image Analyzer
[1311] Using a flow-type particle image analyzer (FPIA-2000
available from Sysmex Corporation), a particle size distribution
based on equivalent circle diameter was measured, and a roundness
was determined. Ion-exchanged water was used as a dispersion
medium, and polyoxyethylene (20) monolaurate was used as a
surfactant. The equivalent circle diameter is a diameter of a
circle (equivalent circle) having the same projected area as that
of a captured particle image, and the roundness is a ratio of the
perimeter of the equivalent circle, as the numerator, to the
perimeter of the captured particle projection image, as the
denominator. Roundnesses of particles having an equivalent diameter
in the range of 1.5 to 40 .mu.m were averaged to determine the
roundness R.
Volume-Based Average Particle Diameter X Determined by Laser
Diffraction: d50
[1312] The d50 was determined as a volume-based median diameter
(d50) by suspending 0.01 g of a carbon material in 10 mL of a 0.2%
by mass aqueous solution of a polyoxyethylene sorbitan monolaurate
surfactant (Tween 20 (registered trademark)), placing the
suspension (a measurement sample) in a commercially available laser
diffraction/scattering particle size distribution analyzer (e.g.,
LA-920 available from HORIBA, Ltd.), irradiating the measurement
sample with ultrasonic waves of 28 kHz at a power of 60 W for 1
minute, and then performing a measurement with the analyzer.
Tap Density
[1313] Using a powder density meter, the carbon material of the
present invention was dropped through a sieve with openings of 300
.mu.m into a cylindrical tap cell with a diameter of 1.6 cm and a
volume capacity of 20 cm.sup.3 to fill up the cell, and then a tap
with a stroke length of 10 mm was given 1,000 times. The density
calculated from the volume at this time and the mass of the sample
was defined as the tap density.
Acquisition of Cross-Sectional SEM Image
[1314] The cross-sectional SEM image of the carbon material was
measured as described below. As an electrode plate containing the
carbon material was used the same electrode plate as used to
produce the above-described battery for performance evaluation.
First, an electrode cross section was processed using a cross
section polisher (IB-09020CP available from JEOL Ltd). From the
processed electrode cross-section, a reflected electron image was
acquired with an SEM (SU-70 available from Hitachi
High-Technologies Corporation). The SEM observation was carried out
under the conditions of an acceleration voltage of 10 kV and a
magnification of 1,000.times. to obtain an image that enables the
acquisition of one particle at a resolution of 256 dpi. After that,
in accordance with the above-described method and conditions for
measuring dispersity, 30 or more particles satisfying
|X.sub.1-X|/X.sub.1.ltoreq.0.2 and |R-R.sub.1|.ltoreq.0.1 were
selected using two SEM images of 150 .mu.m.times.100 .mu.m.
Moreover, 30 particles each having graphite portions with an
average luminance of 80 or greater and void portions with an
average luminance of 65 or less were selected as binarizable
images.
Establishment of Particle Boundary
[1315] Using image processing software imageJ, a particle boundary
was established by an approximation by a polygon. The approximation
was made by a polygon with 15 or more sides to the particle shape.
The non-particle region was processed so as to have a luminance of
255 at every pixel.
Binarization of Cross-Sectional SEM Image (Division into Void
Regions and Non-Void Regions)
[1316] Void regions and non-void regions of the carbon material
observed in the cross-sectional SEM image were binarized using
image software imageJ with a threshold set to a luminance of 80 to
85.
Equivalent Circular Diameter .sub.X1 Determined from
Cross-Sectional SEM Image
[1317] The equivalent circular diameter X.sub.1 was calculated by
the following formula, where L is a particle circumference [.mu.m],
that is, the total length of line segments of a polygonal particle
boundary.
X 1 = L 2 .times. .pi. [ Mathematical .times. .times. 17 ]
##EQU00064##
Roundness R.sub.1 Determined from Cross-Sectional SEM Image
[1318] The roundness R.sub.1 was calculated by the following
formula using the particle circumference L obtained above, where S
is an area of the polygon defined by the particle boundary.
R 1 = 4 .times. .pi. .times. .times. S ( L ) 2 [ Mathematical
.times. .times. 18 ] ##EQU00065##
Box-Counting Dimension Relative to Void Regions
[1319] Since the maximum length of the image obtained was about 260
pixel, analyses were carried out at Box sizes of 2, 3, 4, 6, 8, 16,
32, and 64. For the 30 randomly selected particles satisfying
|X.sub.1-X|/X.sub.1.ltoreq.0.2 and |R-R.sub.1|.ltoreq.0.1 in the
cross-sectional SEM image, box-counting dimensions relative to void
regions were calculated and averaged to determine the average
box-counting dimension relative to void regions.
Average Dispersity D
[1320] In the cross-sectional SEM image, 30 granulated particles
satisfying |X.sub.1-X|/X.sub.1.ltoreq.0.2 and
|R-R.sub.1|.ltoreq.0.1 were randomly selected, and for each
particle, the dispersity D given by equation (B) was calculated.
The dispersities D of the 30 particles were averaged. The
expectation E of the void area in a target compartment is
calculated by equation (A).
Dispersity .times. .times. D .times. .times. ( % ) = ( sum .times.
.times. total .times. [ .mu.m 2 ] .times. .times. of .times.
.times. areas .times. .times. of .times. .times. compartments
.times. .times. that .times. .times. satisfy .times. .times. (
gross .times. .times. area .times. [ .mu.m 2 ] .times. .times. of
.times. .times. voids .times. .times. in .times. .times. target
.times. .times. compartment ) .times. / .times. ( expectation
.times. .times. E .times. [ .mu.m 2 ] .times. .times. of .times.
.times. void .times. .times. area .times. .times. in .times.
.times. target .times. .times. compartment ) = 0.5 .times. .times.
or .times. .times. greater ) .times. / .times. ( sum .times.
.times. total .times. [ .mu.m 2 ] .times. .times. of .times.
.times. areas .times. .times. of .times. .times. all .times.
.times. the .times. .times. compartments .times. .times. of .times.
.times. one .times. .times. target .times. .times. granulated
.times. .times. particle ) .times. 100 Equation .times. .times. ( B
) Expectation .times. .times. E .times. [ .mu.m 2 ] .times. .times.
of .times. .times. void .times. .times. area .times. .times. in
.times. .times. target .times. .times. compartment = ( gross
.times. .times. area .times. [ .mu.m 2 ] .times. .times. of .times.
.times. internal .times. .times. voids .times. .times. of .times.
.times. one .times. .times. target .times. .times. granulated
.times. .times. particle ) .times. / .times. ( cross .times. -
.times. sectional .times. .times. area .times. [ .mu.m 2 ] .times.
.times. of .times. .times. one .times. .times. target .times.
.times. granulated .times. .times. particle ) .times. ( area
.times. [ .mu.m 2 ] .times. .times. of .times. .times. target
.times. .times. compartment ) Equation .times. .times. ( A )
##EQU00066##
Zave/X
[1321] In the cross-sectional SEM image, 30 granulated particles
satisfying |X.sub.1-X|/X.sub.1.ltoreq.0.2 and
|R-R.sub.1|.ltoreq.0.1 were randomly selected, and for each
particle, the inter-void distance Z was calculated as described
below. The average (Zave) of the inter-void distances Z of the 30
particles was calculated, and the ratio of the average to the
volume-based average particle diameter X determined by laser
diffraction (Zave/X) was calculated.
Definition of Average Inter-Void Distance Z (Zave) of 30
Particles
[1322] Three lines were drawn that were parallel to the minor axis
of the granulated particle and split the major axis of the
granulated particle into four parts, and inter-void distances Z
(.mu.m) of the granulated particle on each line were each measured.
The average of 30 particles in total was calculated. This was
defined as the average inter-void distance Z (Zave) of 30
particles.
W/X
[1323] For each of the 30 particles selected in calculating Zave/X,
the void size Y was calculated as described below. The standard
deviation (W) of the void sizes Y of the 30 particles was
calculated, and the ratio of the standard deviation to the
volume-based average particle diameter X determined by laser
diffraction (W/X) was calculated.
Definition of Standard Deviation (W) of Void Sizes Y (.mu.m) of 30
Particles
[1324] Three lines were drawn that were parallel to the minor axis
of the granulated particle and split the major axis of the
granulated particle into four parts, and void sizes Y (.mu.m) of
the granulated particle on each line were each measured. The
standard deviation of 30 particles in total was calculated. This
was defined as the standard deviation (W) of void sizes Y of 30
particles.
[1325] The standard deviation was determined by the following
formula, where Y.sub.ave is the average of Y, and Ny is the number
of Y.
W = ( .SIGMA. .function. ( Y - Y ave ) 2 Ny ) 1 .times. / .times. 2
[ Mathematical .times. .times. 19 ] ##EQU00067##
The Number (Percentage) of Particles Having Voids Arranged in
Layers
[1326] Among the 30 particles selected in calculating Zave/X, the
number of particles was counted in which the proportion of the area
of slit-like voids in layers (the area of voids in layers/the gross
area of voids) was 50% or more, and the proportion of the number of
slit-like voids (the number of slit-like voids/the total number of
voids) was 70% or more, as observed in the cross-sectional SEM
image. The percentage in the 30 particles was calculated.
Example L1
[1327] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry swirl-flow crusher to give a flake natural
graphite having a d50 of 8.1 .mu.m, a Tap of 0.39 g/cm.sup.3, and a
water content of 0.08% by mass. To 100 g of the resulting flake
natural graphite, 12 g of a granulating agent of a liquid paraffin
(Wako Pure Chemical industries, Ltd., first grade, physical
properties at 25.degree. C.: viscosity=95 cP, contact
angle=13.2.degree., surface tension=31.7 mN/m, r cos .theta.=30.9)
was added and mixed with stirring. The sample obtained was
disintegrated and mixed using a hammer mill (MF10 available from
IKA) at a rotation speed of 3,000 rpm to give a flake natural
graphite to which the granulating agent adhered. Using a Model
NHS-1 hybridization system available from Nara Machinery Co., Ltd.,
the flake natural graphite to which the granulating agent uniformly
adhered was mechanically spheroidized at a rotor peripheral speed
of 85 m/sec for 10 minutes while fine powder generated during the
spheroidization was deposited on the base material and incorporated
into the spheroidized particles, and heat treated in an inert gas
at 720.degree. C. to give a spheroidized graphite having a d50 of
12.9 .mu.m. Using the measurement methods described above, d50,
Tap, roundness, average box-counting dimension, average dispersity
D, Zave/X, W/X, the number (percentage) of particles having voids
arranged in layers, discharge capacity, and low-temperature output
characteristics were measured. The results are shown in Tables 1L
and 2L.
Example L2
[1328] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry air-flow crusher to give a flake natural
graphite having a d50 of 6 .mu.m, a Tap of 0.13 g/cm.sup.3, and a
water content of 0.08% by mass. To 100 g of the resulting flake
natural graphite, 12 g of a granulating agent of a paraffinic oil
(liquid paraffin available from Wako Pure Chemical Industries,
Ltd., first grade, physical properties at 25.degree. C.:
viscosity=95 cP, contact angle=13.2.degree., surface tension=31.7
mN/m, r cos .theta.=30.9) was added and mixed with stirring. The
sample obtained was disintegrated and mixed using a hammer mill
(MF10 available from IKA) at a rotation speed of 3,000 rpm to give
a flake natural graphite to which the granulating agent uniformly
adhered. Using a Model NHS-1 hybridization system available from
Nara Machinery Co., Ltd., the flake natural graphite to which the
granulating agent uniformly adhered was mechanically spheroidized
at a rotor peripheral speed of 85 m/sec for 10 minutes while fine
powder generated during the spheroidization was deposited on the
base material and incorporated into the spheroidized particles, and
heat treated in an inert gas at 720.degree. C. to give a
spheroidized graphite having a d50 of 9.2 .mu.m. The results of the
measurements made in the same manner as in Example L1 are shown in
Tables 1L and 2L.
Example L3
[1329] A flake natural graphite having a d50 of 100 .mu.m was
crushed with a dry swirl-flow crusher to give a flake natural
graphite having a d50 of 6 .mu.m, a Tap of 0.38 g/cm.sup.3, and a
water content of 0.08% by mass. To 100 g of the resulting flake
natural graphite, 12 g of a granulating agent of a paraffinic oil
(liquid paraffin available from Wako Pure Chemical Industries,
Ltd., first grade, physical properties at 25.degree. C.:
viscosity=95 cP, contact angle=13.2.degree., surface tension=31.7
mN/m, r cos .theta.=30.9) was added and mixed with stirring, The
sample obtained was disintegrated and mixed using a hammer mill
(MF10 available from IKA) at a rotation speed of 3,000 rpm to give
a flake natural graphite to which the granulating agent uniformly
adhered. Using a Model NHS-1 hybridization system available from
Nara Machinery Co., Ltd., the flake natural graphite to which the
granulating agent uniformly adhered was mechanically spheroidized
at a rotor peripheral speed of 85 m/sec for 10 minutes while fine
powder generated during the spheroidization was deposited on the
base material and incorporated into the spheroidized particles, and
heat treated in an inert gas at 720.degree. C. to give a
spheroidized graphite having a d50 of 9.9 .mu.m. The results of the
measurements made in the same manner as in Example L1 are shown in
Tables 1L and 2L.
Comparative Example L1
[1330] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically spheroidized at a rotor peripheral speed of
85 m/sec for 10 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite fine powder not
deposited on the base material or incorporated into the
spheroidized particles. This sample was classified to remove the
flake graphite fine powder, thereby providing a spheroidized
graphite having a d50 of 10.8 .mu.m. The results of the
measurements made in the same manner as in Example L1 are shown in
Tables 1L and 2L.
Comparative Example L2
[1331] Using a Model NHS-1 hybridization system available from Nara
Machinery Co., Ltd., a flake natural graphite having a d50 of 100
.mu.m was mechanically granulated at a rotor peripheral speed of 85
m/sec for 5 minutes. In the sample obtained was confirmed the
presence of a large amount of flake graphite fine powder not
deposited on the base material or incorporated into the granulated
particles. This sample was classified to remove the flake graphite
fine powder, thereby providing a granulated carbon material having
a d50 of 15.4 .mu.m. The results of the measurements made in the
same manner as in Example L1 are shown in Tables 1L and 2L.
TABLE-US-00020 TABLE 1L Number (Percentage) of Particles Average
Having Box- Average Voids d50 Tap Counting Dispersity Arranged in
(.mu.m) (g/cm.sup.3) Roundness Dimension D (%) Zave/X W/X Layers
Example L1 12.9 0.88 0.94 1.65 70 0.03 0.012 28 (93%) Example L2
9.2 0.77 0.92 1.6 63 0.047 0.014 24 (80%) Example L3 9.9 0.91 0.93
1.63 64 0.043 0.013 25 (83%) Comp. Ex. L1 10.8 0.93 0.93 1.51 53
0.069 0.02 8 (27%) Comp. Ex. L2 15.4 1.01 0.93 1.52 56 0.063 0.02 9
(30%)
TABLE-US-00021 TABLE 2L Low-Temperature Output Characteristics,
Discharge (Comparative Capacity Example L1 = (mAh/g) 100) Example
L1 367 124 Example L2 365 126 Example L3 362 169 Comparative 365
100 Example L1 Comparative 367 90 Example L2
Example L4
[1332] The spheroidized natural graphite before heat treatment
obtained in Example L1 and a coal-tar pitch, serving as an
amorphous carbon precursor, were mixed and heat treated in an inert
gas at 1,300.degree. C., and then the burned product was
disintegrated and classified to give a multi-layered carbon
material made of graphite particles and an amorphous carbon
combined with each other. The burning yield showed that the mass
ratio of spheroidized graphite particle to amorphous carbon
(spheroidized graphite particle/amorphous carbon) of the
multi-layered carbon material was 1:0.08. The results of the
measurements made in the same manner as in Example L1 are shown in
Tables 3L and 4L.
Comparative Example L3
[1333] The spheroidized natural graphite obtained in Comparative
Example L1 and a coal-tar pitch, serving as an amorphous carbon
precursor, were mixed and heat treated in an inert gas at
1,300.degree. C., and then the burned product was disintegrated and
classified to give a multi-layered carbon material made of graphite
particles and an amorphous carbon combined with each other. The
burning yield showed that the mass ratio of spheroidized graphite
particle to amorphous carbon (spheroidized graphite
particle/amorphous carbon) of the multi-layered carbon material was
1:0.065. The results of the measurements made in the same manner as
in Example L1 are shown in Tables 3L and 4L.
TABLE-US-00022 TABLE 3L Number (Percentage) of Particles Average
Having Box- Average Voids d50 Tap Counting Dispersity Arranged in
(.mu.m) (g/cm.sup.3) Roundness Dimension D (%) Zave/X W/X Layers
Example L4 11.8 1.02 0.93 1.56 64 0.05 0.012 21 (70%) Comp. Ex. L3
11.4 1.04 0.92 1.46 49 0.075 0.02 5 (17%)
TABLE-US-00023 TABLE 4L Low-Temperature Output Characteristics,
Discharge (Comparative Capacity Example L3 = (mAh/g) 100) Example
L4 359 147 Comparative 362 100 Example L3
INDUSTRIAL APPLICABILITY
[1334] The carbon material of the present invention, when used as
an active material for a non-aqueous secondary battery negative
electrode, can provide a non-aqueous secondary battery having a
high capacity, excellent low-temperature output characteristics,
and other characteristics. According to the production method of
the present invention, which involves a small number of steps,
carbon materials can be stably, efficiently, and inexpensively
produced. Furthermore, carbon materials for non-aqueous secondary
batteries having various types of particle structures can be stably
produced.
CLAIM SCOPE AND INCORPORATED BY REFERENCE
[1335] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made therein without departing from the spirit and scope
thereof.
* * * * *