U.S. patent application number 13/993403 was filed with the patent office on 2013-10-03 for electrode material and method for producing the same.
This patent application is currently assigned to SUMITOMO OSAKA CEMENT CO., LTD.. The applicant listed for this patent is Takao Kitagawa, Masaru Uehara, Hirofumi Yasumiishi. Invention is credited to Takao Kitagawa, Masaru Uehara, Hirofumi Yasumiishi.
Application Number | 20130260245 13/993403 |
Document ID | / |
Family ID | 46244494 |
Filed Date | 2013-10-03 |
United States Patent
Application |
20130260245 |
Kind Code |
A1 |
Kitagawa; Takao ; et
al. |
October 3, 2013 |
ELECTRODE MATERIAL AND METHOD FOR PRODUCING THE SAME
Abstract
The present invention provides an electrode material in which
unevenness in a supporting amount of a carbonaceous film is less
when using an electrode-active material having a carbonaceous film
on a surface thereof as the electrode material, and which is
capable of improving conductivity, and a method for producing the
electrode material. The electrode material includes an aggregate
formed by aggregating an electrode-active material in which a
carbonaceous film is formed on a surface. In the electrode
material, an average particle size of the aggregate is 0.5 to 100
.mu.m, a volume density of the aggregate is 50 to 80 vol % of a
volume density in a case in which the aggregate is a solid, and 80%
or more of the surface of the electrode-active material is covered
with the carbonaceous film. Alternatively, the electrode material
includes an aggregate formed by aggregating electrode-active
material particles in which a carbonaceous film is formed on a
surface. In the electrode material, an average particle size of the
aggregate is 0.5 to 100 .mu.m, a pore size (D50) when an
accumulated volume percentage of a pore size distribution of the
aggregate is 50% is 0.1 to 0.2 .mu.m, and porosity of the aggregate
is 15 to 50 vol % with respect to a volume in a case in which the
aggregate is a solid.
Inventors: |
Kitagawa; Takao; (Tokyo,
JP) ; Yasumiishi; Hirofumi; (Tokyo, JP) ;
Uehara; Masaru; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kitagawa; Takao
Yasumiishi; Hirofumi
Uehara; Masaru |
Tokyo
Tokyo
Tokyo |
|
JP
JP
JP |
|
|
Assignee: |
SUMITOMO OSAKA CEMENT CO.,
LTD.
Chiyoda-ku, Tokyo
JP
|
Family ID: |
46244494 |
Appl. No.: |
13/993403 |
Filed: |
November 28, 2011 |
PCT Filed: |
November 28, 2011 |
PCT NO: |
PCT/JP2011/077394 |
371 Date: |
June 12, 2013 |
Current U.S.
Class: |
429/220 ;
252/182.1; 429/221; 429/223; 429/224; 429/231; 429/231.1;
429/231.3; 429/231.8 |
Current CPC
Class: |
H01M 2004/021 20130101;
H01M 4/5825 20130101; Y02E 60/10 20130101; H01M 4/366 20130101;
H01M 4/505 20130101; H01M 4/525 20130101; Y02P 70/50 20151101; C01B
32/05 20170801; H01M 4/625 20130101; H01M 4/485 20130101; H01M
4/131 20130101 |
Class at
Publication: |
429/220 ;
429/231.8; 429/231.3; 429/223; 429/231.1; 429/224; 429/221;
429/231; 252/182.1 |
International
Class: |
H01M 4/133 20060101
H01M004/133 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 17, 2010 |
JP |
2010282353 |
Sep 22, 2011 |
JP |
2011207833 |
Claims
1. An electrode material, comprising: an aggregate formed by
aggregating electrode-active material particles having a
carbonaceous film formed on a surface, wherein an average particle
size of the aggregate is 0.5 to 100 .mu.m, and a volume density of
the aggregate is 50 to 80 vol % of the volume density in a case in
which the aggregate is a solid.
2. The electrode material according to claim 1, wherein 80% or more
of the surface of the electrode-active material is covered with the
carbonaceous film.
3. The electrode material according to claim 1, wherein the
aggregate is a shell-like aggregate having a void at the inside,
and a ratio of an average film thickness of the carbonaceous film
in an outer peripheral portion and an inner peripheral portion of
an outer shell of the shell-like aggregate (a thickness of the
carbonaceous film in the inner peripheral portion/a thickness of
the carbonaceous film in the outer peripheral portion) is 0.7 to
1.3.
4. The electrode material according to claim 1, wherein an amount
of carbon in the carbonaceous film is 0.6 to 10 parts by mass on
the basis of 100 parts by mass of the electrode-active
material.
5. The electrode material according to claim 1, wherein a tap
density of the aggregate is 1.0 to 1.5 g/cm.sup.3.
6. The electrode material according to claim 1, wherein the
electrode-active material contains one kind selected from the group
consisting of lithium cobaltate, lithium nickelate, lithium
manganate, lithium titanate, and Li.sub.xA.sub.yD.sub.zPO.sub.4
(provided that, A is one or more kinds selected from the group
consisting from Co, Mn, Ni, Fe, Cu, and Cr, D is one or more kinds
selected from the group consisting of Mg, Ca, S, Sr, Ba, Ti, Zn, B,
Al, Ga, In, Si, Ge, Sc, Y, and rare-earth elements, 0<x<2,
0<y<1.5, and 0.ltoreq.z<1.5) as a main component.
7. A method for producing an electrode material, comprising: drying
slurry which contains an electrode-active material or a precursor
of the electrode-active material, and an organic compound, and in
which a ratio (D90/D10) of D90 to D10 of a particle size
distribution of the electrode-active material or the precursor of
the electrode-active material is 5 to 30; and baking the resultant
dried product that is obtained at 500.degree. C. to 1,000.degree.
C. in a non-oxidizing atmosphere.
8. An electrode material, comprising: an aggregate formed by
aggregating electrode-active material particles having a
carbonaceous film formed on a surface, wherein an average particle
size of the aggregate is 0.5 to 100 .mu.m, a pore size (D50) when
an accumulated volume percentage of a pore size distribution of the
aggregate is 50% is 0.1 to 0.2 .mu.m, and porosity of the aggregate
is 15 to 50 vol % with respect to a volume in a case in which the
aggregate is a solid.
9. The electrode material according to claim 8, wherein 80% or more
of the surface of the electrode-active material is covered with the
carbonaceous film.
10. The electrode material according to claim 8, wherein the
aggregate is a shell-like aggregate having a void at the inside,
and a ratio of an average film thickness of the carbonaceous film
in an outer peripheral portion and an inner peripheral portion of
an outer shell of the shell-like aggregate (a thickness of the
carbonaceous film in the inner peripheral portion/a thickness of
the carbonaceous film in the outer peripheral portion) is 0.7 to
1.3.
11. The electrode material according to claim 8, wherein an amount
of carbon in the carbonaceous film is 0.6 to 10 parts by mass on
the basis of 100 parts by mass of the electrode-active
material.
12. The electrode material according to claim 8, wherein a tap
density of the aggregate is 1.0 to 1.5 g/cm.sup.3.
13. The electrode material according to claim 8, wherein the
electrode-active material contains one kind selected from the group
consisting of lithium cobaltate, lithium nickelate, lithium
manganate, lithium titanate, and Li.sub.xA.sub.yD.sub.zPO.sub.4
(provided that, A is one or more kinds selected from the group
consisting from Co, Mn, Ni, Fe, Cu, and Cr, D is one or more kinds
selected from the group consisting of Mg, Ca, S, Sr, Ba, Ti, Zn, B,
Al, Ga, In, Si, Ge, Sc, Y, and rare-earth elements, 0<x<2,
0<y<1.5, and 0.ltoreq.z<1.5) as a main component.
14. A method for producing an electrode material, comprising:
drying slurry which contains an electrode-active material or a
precursor of the electrode-active material, and an organic
compound, and in which a ratio (D90/D10) of a particle size (D90)
when an accumulated volume percentage of a particle size
distribution of the electrode-active material or the precursor of
the electrode-active material is 90% to a particle size (D10) when
the accumulated volume percentage is 10% is 5 to 30; and baking the
resultant dried product that is obtained at 500.degree. C. to
1,000.degree. C. in a non-oxidizing atmosphere.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electrode material and a
method for producing the same, and more particularly, to an
electrode material suitable for use in a positive electrode
material for a battery, in particular, a positive electrode
material for a lithium ion battery, and to a method for producing
the electrode material.
[0002] Priority is claimed on Japanese Patent Application No.
2010-282353, filed Dec. 17, 2010, and Japanese Patent Application
No. 2011-207833, filed Sep. 22, 2011, the contents of which are
incorporated herein by reference.
[0003] (Incorporation)
BACKGROUND ART
[0004] In recent years, as a battery that meets the expectations
for miniaturization, lightness, and high capacity, a non-aqueous
electrolyte-based secondary battery such as a lithium ion battery
has been suggested, and has been put into practical use.
[0005] The lithium ion battery includes positive electrode and
negative electrode that have properties capable of reversibly
intercalating and deintercalating lithium ions, and a non-aqueous
electrolyte.
[0006] With regard to a negative electrode material of the lithium
ion battery, as a negative electrode-active material, Li-containing
metal oxides such as a carbon-based material and lithium titanate
(Li.sub.4Ti.sub.5O.sub.12) that have properties capable of
reversibly intercalating and deintercalating lithium ions have been
used.
[0007] On the other hand, as a positive electrode material of the
lithium ion battery, an electrode material mixture, which contains
a Li-containing metal oxide such as iron lithium phosphate
(LiFePO.sub.4) having properties capable of reversibly
intercalating and deintercalating lithium ions as a positive
electrode-active material, a binder, and the like, has been used.
In addition, this electrode material mixture is applied on a
surface of metal foil called a current collector to form a positive
electrode of the lithium ion battery.
[0008] Since the lithium ion battery is light in weight and small
in size, and has high energy compared to a secondary battery such
as a lead battery, a nickel-cadmium battery, a nickel-hydrogen
battery, and the like in the related art, the lithium ion battery
has been used as a power supply of portable electronic apparatuses
such as a cellular phone and a note-type personal computer. In
addition, in recent years, the lithium ion battery has been
reviewed as a high-output power supply of an electric vehicle, a
hybrid vehicle, an electromotive tool, and the like, and high-speed
charge and discharge characteristics have been required for the
battery that is used as the high-output power supply.
[0009] However, the electrode material, which contains an
electrode-active material, for example, the Li-containing metal
oxide having properties capable of reversibly intercalating and
deintercalating lithium ions, has a problem in that conductivity is
low. Therefore, there is suggested an electrode material in which a
particle surface of the electrode-active material is covered with
an organic component that is a carbon source, the organic component
are carbonized to form a carbonaceous film on a surface of the
electrode-active material, and carbon of the carbonaceous film is
interposed as an electronic conductive material to increase the
conductivity of the electrode material (refer to PTL 1).
CITATION LIST
Patent Literature
[0010] [PTL 1] Japanese Laid-Open Patent Publication No.
2001-15111
SUMMARY OF INVENTION
Technical Problem
[0011] However, when using the electrode-active material as a
battery material of a lithium ion battery, the conductivity is
requisite, and it is preferable that the conductivity of the
electrode-active material be as high as possible.
[0012] However, in an electrode material that is formed by baking
an electrode-active material supporting an organic compound or a
precursor of the electrode-active material in a non-oxidizing
atmosphere, an aromatic carbon compound generated due to thermal
decomposition of the organic compound during the baking condenses,
and thus a carbonaceous film is formed on a surface of the
electrode-active material. On the other hand, the aromatic carbon
compound is volatile at a high temperature. Particularly, at a
baking temperature of 500.degree. C. to 1,000.degree. C., the
higher the concentration of a vaporized material of the aromatic
carbon compound is, the more supporting amount of the carbonaceous
film is, and the larger thickness of the film is. However, the
lower the concentration of the vaporized material is, the less the
supporting amount of the carbonaceous film is, and the lower the
thickness of the film is.
[0013] Therefore, with regard to an assembly of primary particles
of the electrode-active material, in a case where the
electrode-active material is not aggregated, and even though the
electrode-active material is aggregated, in a case where the
resultant aggregate has a number of voids, when being baked in a
non-oxidizing atmosphere, the concentration of the vaporized
material of the aromatic carbon compound decreases, and the
supporting amount of the carbonaceous film decreases as a whole or
partially. Therefore, the thickness of the carbonaceous film
decreases, and thus the coverage rate of the carbonaceous film
decreases.
[0014] The invention has been made to solve the above-described
problems, and an object thereof is to provide an electrode material
in which unevenness in a supporting amount of the carbonaceous film
is less when using an electrode-active material having a
carbonaceous film formed on a surface thereof as the electrode
material and which is capable of improving conductivity and a
method for producing the electrode material.
Solution to Problem
[0015] The present inventors made a thorough investigation to solve
the above-described problems. As a result, they found that with
regard to a particle size distribution of an electrode-active
material or a precursor of the electrode-active material in slurry
containing the electrode-active material or the precursor of the
electrode-active material, and an organic compound, when a ratio
(D90/D10) of D90 to D10 of the particle size distribution is set to
5 to 30 during production of the electrode material, a volume
density of an aggregate that is obtained may be set to 50 to 80 vol
% of the volume density in a case in which the aggregate is a
solid, and accordingly, a concentration of a vaporized material of
an aromatic carbonaceous compound inside the aggregate may be
raised, and as a result, a carbonaceous film in which unevenness is
less may be supported on a surface of the electrode-active material
inside the aggregate, and the present inventors accomplished the
invention.
[0016] That is, according to an embodiment of the invention, an
electrode material is provided including an aggregate formed by
aggregating electrode-active material particles having a
carbonaceous film formed on a surface. An average particle size of
the aggregate is 0.5 to 100 .mu.m. A volume density of the
aggregate is 50 to 80 vol % of the volume density in a case in
which the aggregate is a solid.
[0017] In the electrode material of the invention, it is preferable
that 80% or more of the surface of the electrode-active material be
covered with the carbonaceous film.
[0018] The aggregate may be a shell-like aggregate having a void at
the inside thereof, and it is preferable that a ratio of an average
film thickness of the carbonaceous film in an outer peripheral
portion and an inner peripheral portion of an outer shell of the
shell-like aggregate (a thickness of the carbonaceous film in the
inner peripheral portion/a thickness of the carbonaceous film in
the outer peripheral portion) be 0.7 to 1.3.
[0019] It is preferable that an amount of carbon in the
carbonaceous film be 0.6 to 10 parts by mass on the basis of 100
parts by mass of the electrode-active material. It is preferable
that a tap density of the aggregate be 1.0 to 1.5 g/cm.sup.3.
[0020] It is preferable that the electrode-active material contain
one kind selected from the group consisting of lithium cobaltate,
lithium nickelate, lithium manganate, lithium titanate, and
Li.sub.xA.sub.yD.sub.zPO.sub.4 (provided that, A is one or more
kinds selected from the group consisting from Co, Mn, Ni, Fe, Cu,
and Cr, D is one or more kinds selected from the group consisting
of Mg, Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and
rare-earth elements, 0<x<2, 0<y<1.5, and
0.ltoreq.z<1.5) as a main component.
[0021] According to another embodiment of the invention, a method
for producing an electrode material is provided. The method
include: drying slurry which contains an electrode-active material
or a precursor of the electrode-active material, and an organic
compound, and in which a ratio (D90/D10) of D90 to D10 of a
particle size distribution of the electrode-active material or the
precursor of the electrode-active material is 5 to 30; and baking
the resultant dried product that is obtained at 500.degree. C. to
1,000.degree. C. in a non-oxidizing atmosphere.
[0022] In addition, the present inventors made a thorough
investigation to solve the above-described problems. As a result,
they found that in slurry containing an electrode-active material
or a precursor of the electrode-active material, and an organic
compound, when a ratio (D90/D10) of a particle size (D90) when an
accumulated volume percentage of a particle size distribution of
the electrode-active material or the precursor of the
electrode-active material is 90% to a particle size (D10) when the
accumulated volume percentage is 10% is 5 to 30 during production
of the electrode material, a pore size (D50) when the accumulated
volume percentage of the pore size distribution of the aggregate
that is obtained is 50% may be set to 0.1 to 0.2 .mu.m, porosity of
the aggregate may be set to 15 to 50 vol % with respect to a volume
in a case in which the aggregate is a solid, and accordingly, a
concentration of a vaporized material of an aromatic carbonaceous
compound inside the aggregate may be raised, and as a result, a
carbonaceous film in which unevenness is less may be supported on a
surface of the electrode-active material inside the aggregate, and
the present inventors accomplished the invention.
[0023] That is, according to still another embodiment of the
invention, an electrode material is provided including an aggregate
formed by aggregating electrode-active material particles having a
carbonaceous film formed on a surface. An average particle size of
the aggregate is 0.5 to 100 .mu.m. A pore size (D50) when an
accumulated volume percentage of a pore size distribution of the
aggregate is 50% is 0.1 to 0.2 .mu.m. Porosity of the aggregate is
15 to 50 vol % with respect to a volume in a case in which the
aggregate is a solid.
[0024] In the electrode material of the invention, it is preferable
that 80% or more of the surface of the electrode-active material be
covered with the carbonaceous film.
[0025] The aggregate may be a shell-like aggregate having a void at
the inside thereof, and it is preferable that a ratio of an average
film thickness of the carbonaceous film in an outer peripheral
portion and an inner peripheral portion of an outer shell of the
shell-like aggregate (a thickness of the carbonaceous film in the
inner peripheral portion/a thickness of the carbonaceous film in
the outer peripheral portion) be 0.7 to 1.3.
[0026] It is preferable that an amount of carbon in the
carbonaceous film be 0.6 to 10 parts by mass on the basis of 100
parts by mass of the electrode-active material.
[0027] It is preferable that a tap density of the aggregate be 1.0
to 1.5 g/cm.sup.3.
[0028] It is preferable that the electrode-active material contains
one kind selected from the group consisting of lithium cobaltate,
lithium nickelate, lithium manganate, lithium titanate, and
Li.sub.xA.sub.yD.sub.zPO.sub.4 (provided that, A is one or more
kinds selected from the group consisting from Co, Mn, Ni, Fe, Cu,
and Cr, D is one or more kinds selected from the group consisting
of Mg, Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and
rare-earth elements, 0<x<2, 0<y<1.5, and
0.ltoreq.z<1.5) as a main component.
[0029] According to still another embodiment of the invention, a
method for producing an electrode material is provided. The method
includes: drying slurry which contains an electrode-active material
or a precursor of the electrode-active material, and an organic
compound, and in which a ratio (D90/D10) of a particle size (D90)
when an accumulated volume percentage of a particle size
distribution of the electrode-active material or the precursor of
the electrode-active material is 90% to a particle size (D10) when
the accumulated volume percentage is 10% is 5 to 30; and baking the
resultant dried product that is obtained at 500.degree. C. to 1,
000.degree. C. in a non-oxidizing atmosphere.
Advantageous Effects of Invention
[0030] According to the electrode material of the invention, the
average particle size of the aggregate formed by aggregating
electrode-active material particles having a carbonaceous film
formed on a surface thereof is set to 0.5 to 100 .mu.m, and a
volume density of the aggregate is set to 50 to 80 vol % of the
volume density in a case in which the aggregate is a solid, and
thus unevenness in a supporting amount of the carbonaceous film
formed on the surface of the electrode-active material particles
may be reduced, and as a result, unevenness in conductivity of the
electrode-active material may be reduced. Accordingly, when the
electrode-active material is used as an electrode material of a
lithium ion battery, internal resistance may be reduced.
[0031] When the electrode-active material in which the unevenness
in conductivity is reduced is used as the electrode material of the
lithium ion battery, a reaction related to intercalation and
deintercalation of lithium ions may be uniformly carried out in the
entirety of the surface of the electrode-active material, and thus
the internal resistance may be reduced.
[0032] In addition, the internal resistance mentioned here
represents internal resistance at a site at which reaction
resistance related to intercalation and deintercalation of lithium
ions is high in a particle, which does not have the carbonaceous
film formed on a surface thereof or in which the thickness of the
carbonaceous film is small, of the electrode-active material.
Specifically, when the electrode-active material is used as an
electrode-active material of the lithium ion battery, the internal
resistance is shown as a magnitude of voltage drop at the final
stage of discharge. That is, in an electrode-active material in
which the intercalation and deintercalation reaction of lithium
ions is uniformly carried out over the entirety of the surface of
the electrode-active material, the voltage drop at the final stage
of discharge is small. Conversely, in an electrode-active material
in which the intercalation and deintercalation reaction resistance
of lithium ions is high at a part of the surface of the
electrode-active material, the voltage drop at the final stage of
discharge becomes significant.
[0033] According to the method for producing an electrode material
of the invention, slurry, which contains an electrode-active
material or a precursor of the electrode-active material, and an
organic compound, and in which a ratio (D90/D10) of D90 to D10 of a
particle size distribution of the electrode-active material or the
precursor of the electrode-active material is 5 to 30, is dried,
and the resultant dried product that is obtained is baked at
500.degree. C. to 1,000.degree. C. in a non-oxidizing atmosphere.
Accordingly, unevenness in a supporting amount of the carbonaceous
film formed on a surface of the electrode-active material may be
reduced. As a result, an electrode material capable of reducing
unevenness in conductivity of the electrode-active material may be
easily produced.
[0034] According to another electrode material of the invention, an
average particle size of the aggregate formed by aggregating
electrode-active material particles having a carbonaceous film
formed on a surface is set to 0.5 to 100 .mu.m, and a pore size
(D50) when an accumulated volume percentage of a pore size
distribution of the aggregate is 50% is set to 0.1 to 0.2 .mu.m,
and the porosity of the aggregate is set to 15 to 50 vol % with
respect to a volume in a case in which the aggregate is a solid.
Accordingly, unevenness in a supporting amount of the carbonaceous
film formed on the surface of the electrode-active material
particles may be made small, and thus unevenness in conductivity of
the electrode-active material may be reduced. As a result, when the
electrode-active material is used as the electrode material of the
lithium ion battery, the internal resistance may be reduced.
[0035] In addition, when the electrode-active material in which the
unevenness in conductivity is reduced is used as the electrode
material of the lithium ion battery, a reaction related to
intercalation and deintercalation of lithium ions may be uniformly
carried out in the entirety of the surface of the electrode-active
material, and thus the internal resistance may be reduced.
[0036] According to another method for producing an electrode
material of the invention, slurry, which contains an
electrode-active material or a precursor of the electrode-active
material, and an organic compound, and in which a ratio (D90/D10)
of D90 to D10 of a particle size distribution of the
electrode-active material or the precursor of the electrode-active
material is 5 to 30, is dried, and the resultant dried product that
is obtained is baked at 500.degree. C. to 1,000.degree. C. in a
non-oxidizing atmosphere. Accordingly, unevenness in a supporting
amount of the carbonaceous film formed on the surface of the
electrode-active material may be reduced. As a result, an electrode
material capable of reducing unevenness in conductivity of the
electrode-active material may be easily produced.
BRIEF DESCRIPTION OF DRAWINGS
[0037] FIG. 1 is a diagram illustrating charge and discharge
characteristics of Example 1 and Comparative Example 1 of the
invention at room temperature, respectively.
[0038] FIG. 2 is a diagram illustrating charge and discharge
characteristics of Example 5 and Comparative Example 4 of the
invention at room temperature, respectively.
DESCRIPTION OF EMBODIMENTS
First Embodiment
[0039] An embodiment (first embodiment) of an electrode material
and a method for producing the same of the invention will be
described.
[0040] In addition, this embodiment makes a description in detail
for easy comprehension of the gist of the invention, and does not
limit the invention unless otherwise stated.
[0041] [Electrode Material]
[0042] An electrode material of this embodiment includes an
aggregate formed by aggregating electrode-active material particles
having a carbonaceous film formed on a surface, an average particle
size of the aggregate is 0.5 to 100 .mu.m, and a volume density of
the aggregate is 50 to 80 vol % of the volume density in a case in
which the aggregate is a solid.
[0043] Here, it is assumed that a solid aggregate is an aggregate
in which a void is not present at all, and a density of an actual
aggregate is the same as a theoretical density of an
electrode-active material.
[0044] Here, the aggregate that is formed by aggregating each
electrode-active material having the carbonaceous film formed on a
surface thereof represents an aggregate in which the
electrode-active materials having the carbonaceous film formed on a
surface thereof are aggregated in a point contact state, and thus a
contact portion of the electrode-active materials becomes a neck
shape having a small cross-sectional area, whereby the
electrode-active materials are strongly connected to each other. In
this manner, the contact portion between the electrode-active
materials has a neck shape having a small cross-sectional area, and
thus channel-shaped (network-shaped) voids inside the aggregate
have a three-dimensionally expanded structure.
[0045] In addition, when the volume density of the aggregate is 50
vol % or more, the aggregate becomes dense, and the strength of the
aggregate increases. Accordingly, for example, when the
electrode-active material is mixed with a binder, a conductive
auxiliary agent, and a solvent to prepare electrode slurry, the
aggregate is not likely to collapse. As a result, an increase in
viscosity of the electrode slurry is suppressed, and flowability is
maintained. Accordingly, coating properties are improved, and
filling properties of the electrode-active material in a coated
film of the electrode slurry are also improved. In a case where the
aggregate collapses during preparation of the electrode slurry,
since a necessary amount of the binder that binds the
electrode-active materials increases, the viscosity of the
electrode slurry increases, and a concentration of a solid content
of the electrode slurry decreases. As a result, a percentage of the
electrode-active material in the weight of a positive electrode
film decreases, and thus this case is not preferable.
[0046] It is preferable that the electrode-active material contain
one kind selected from the group consisting of lithium cobaltate,
lithium nickelate, lithium manganate, lithium titanate, and
Li.sub.xA.sub.yD.sub.zPO.sub.4 (provided that, A is one or more
kinds selected from the group consisting from Co, Mn, Ni, Fe, Cu,
and Cr, D is one or more kinds selected from the group consisting
of Mg, Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and
rare-earth elements, 0<x<2, 0<y<1.5, and
0.ltoreq.z<1.5) as a main component.
[0047] Here, with regard to A, Co, Mn, Ni, and Fe are preferable,
and with regard to D, Mg, Ca, Sr, Ba, Ti, Zn, and Al are preferable
from the viewpoints of a high discharge potential, abundant
resources, stability, and the like.
[0048] Here, the rare-earth elements represent 15 elements of La,
Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu that
belong to lanthanide series.
[0049] In the electrode-active material, 80% or more of a surface
thereof is covered with a carbonaceous film, and preferably 90% or
more in order for a reaction related to intercalation and
deintercalation of lithium ions to be uniformly carried out over
the entirety of the surface of the electrode-active material during
use as an electrode material of a lithium ion battery.
[0050] A coverage rate of the carbonaceous film may be measured
using a transmission electron microscope (TEM), and an energy
dispersive X-ray spectrometer (EDX). Here, when the coverage rate
of the carbonaceous film is less than 80%, a covering effect of the
carbonaceous film becomes insufficient, and thus when the
intercalation and deintercalation reaction of lithium ions is
carried out on a surface of the electrode-active material, reaction
resistance related to the intercalation and deintercalation of
lithium ions at a site at which the carbonaceous film is not formed
increases, and thus voltage drop at a final stage of discharge
becomes significant. Therefore, this range is not preferable.
[0051] It is preferable that an amount of carbon in the
carbonaceous film be 0.6 to 10 parts by mass on the basis of 100
parts by mass of the electrode-active material, and more preferably
0.8 to 2.5 parts by mass.
[0052] Here, the reason why the amount of carbon in the
carbonaceous film is limited to the above-described range is as
follows. When the amount of carbon is less than 0.6 parts by mass,
the coverage rate of the carbonaceous film becomes less than 80%.
Therefore, when a battery is formed, a discharge capacity at a
high-speed charge and discharge rate decreases.
[0053] As a result, it is difficult to realize a sufficient charge
and discharge rate performance. On the other hand, when the amount
of carbon exceeds 10 parts by mass, the amount of carbonaceous film
relative to the electrode-active material increases. Therefore,
carbon is contained in an amount larger than an amount necessary to
obtain conductivity, and thus in a state of the aggregate, the mass
and volume density of carbon decrease. As a result, an electrode
density decreases, and thus a battery capacity of the lithium ion
battery per unit volume decreases.
[0054] It is preferable that an average particle size of the
aggregate be 0.5 to 100 .mu.m, and more preferably 1 to 20
.mu.m.
[0055] Here, the reason why the average particle size of the
aggregate is limited to the above-described range is as follows.
When the average particle size is less than 0.5 .mu.m, the
aggregate is too fine, and thus there is a tendency for the
aggregate to fly. Therefore, it is difficult to handle the
aggregate during manufacturing of paste for electrode coating. On
the other hand, when the average particle size exceeds 100 .mu.m,
when an electrode for a battery is manufactured, a possibility that
an aggregate having a size larger than the film thickness of the
electrode after being dried is present increases. Accordingly, it
is difficult to maintain uniformity of the film thickness of the
electrode.
[0056] The volume density of the aggregate may be measured using a
mercury porosimeter, and it is preferable that the volume density
be 50 to 80 vol % of the volume density in a case in which the
aggregate is a solid, and more preferably, 55 to 75 vol %.
[0057] Here, when the volume density of the aggregate is less than
50 vol % of the volume density in the case in which the aggregate
is a solid, a vapor concentration of an aromatic carbon compound in
the void inside the aggregate of the electrode-active material
becomes too low, and thus the film thickness of the carbonaceous
film in the inner peripheral portion of the outer shell of the
aggregate becomes small. Therefore, the internal resistance of the
electrode-active material increases, and thus this range is not
preferable. On the other hand, when the volume density of the
aggregate exceeds 80 vol % of the volume density in the case in
which the aggregate is a solid, the density inside the aggregate
becomes too high, and thus a channel-shaped (network-shaped) void
inside the aggregate decreases. As a result, a tarry material,
which is generated during carbonization of the organic compound, is
trapped inside the aggregate, and thus this range is not
preferable.
[0058] It is preferable that a tap density of the aggregate be 1.0
to 1.5 g/cm.sup.3.
[0059] Here, when the tap density of the aggregate is less than 1.0
g/cm.sup.3, an amount of a solvent that is maintained in the void
inside the aggregate and an aggregate gap increases during
preparation of the electrode slurry, and thus a concentration of a
solid content of the electrode slurry decreases. Therefore, the
time necessary to dry a coated film formed by application of the
electrode slurry becomes long, and thus this range is not
preferable. On the other hand, when the tap density of the
aggregate exceeds 1.5 g/cm.sup.3, filling properties of the
aggregate in the coated film obtained by the application of the
electrode slurry increases too much. As a result, a solvent is not
likely to vaporize at the time of drying the coated film, and thus
this range is not preferable.
[0060] When this aggregate is made into a shell-like aggregate, it
is preferable that the size of the void that is formed inside the
aggregate be 80% or less of a diameter of aggregate particles, and
more preferably 70% or less.
[0061] Here, when the size of the void exceeds 80%, it is difficult
to maintain a shell shape of the aggregate, and thus the
concentration of the vapor of the aromatic carbon compound inside
the void becomes too low. As a result, the film thickness of the
carbonaceous film in the inner peripheral portion of the outer
shell of the aggregate becomes small, and the internal resistance
of the electrode-active material increases, and thus this range is
not preferable.
[0062] It is preferable that a ratio of average film thickness of
the carbonaceous film in the outer peripheral portion and the inner
peripheral portion of the outer shell of the shell-like aggregate
(the thickness of the carbonaceous film in the inner peripheral
portion/the thickness of the carbonaceous film in the outer
peripheral portion) be 0.7 to 1.3.
[0063] Here, when the ratio of average film thickness of the
carbonaceous film in the outer peripheral portion and the inner
peripheral portion of the outer shell (the thickness of the
carbonaceous film in the inner peripheral portion/the thickness of
the carbonaceous film in the outer peripheral portion) is out of
the above-described range, the thickness of the carbonaceous film
in the outer peripheral portion or the inner peripheral portion of
the outer shell of the aggregate becomes small. Therefore, the
internal resistance of the electrode-active material increases, and
thus this range is not preferable.
[0064] [Method for Producing Electrode Material]
[0065] A method for producing an electrode material of this
embodiment includes drying slurry which contains an
electrode-active material or a precursor of the electrode-active
material, and an organic compound, and in which with regard to a
particle size distribution of the electrode-active material or the
precursor of the electrode-active material, a ratio (D90/D10) of
D90 to D10 of the particle size distribution is 5 to 30, and baking
the resultant dried product that is obtained at 500.degree. C. to
1,000.degree. C. in a non-oxidizing atmosphere.
[0066] Here, D90 represents a particle size when an accumulated vol
% in the particle size distribution is 90%, and D10 represents a
particle size when the accumulated vol % in the particle size
distribution is 10%.
[0067] As described in the electrode material, it is preferable
that the electrode-active material contain one kind selected from
the group consisting of lithium cobaltate, lithium nickelate,
lithium manganate, lithium titanate, and
Li.sub.xA.sub.yD.sub.zPO.sub.4 (provided that, A is one or more
kinds selected from the group consisting from Co, Mn, Ni, Fe, Cu,
and Cr, D is one or more kinds selected from the group consisting
of Mg, Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and
rare-earth elements, 0<x<2, 0<y<1.5, and
0.ltoreq.z<1.5) as a main component.
[0068] Here, with regard to A, Co, Mn, Ni, and Fe are preferable,
and with regard to D, Mg, Ca, Sr, Ba, Ti, Zn, and Al are preferable
from the viewpoints of a high discharge potential, abundant
resources, stability, and the like.
[0069] Here, the rare-earth elements represent 15 elements of La,
Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu that
belong to lanthanide series.
[0070] As a compound (Li.sub.xA.sub.yD.sub.zPO.sub.4 powder)
expressed by Li.sub.xA.sub.yD.sub.zPO.sub.4, a compound, which is
produced by a solid phase method, a liquid phase method, and a
vapor phase method, or the like in the related art, may be
used.
[0071] As the compound (Li.sub.xA.sub.yD.sub.zPO.sub.4powder), for
example, a compound (Li.sub.xA.sub.yD.sub.zPO.sub.4 powder) that is
obtained by the following method may be appropriately used. The
method includes: hydrothermally synthesizing a slurry mixture,
which is obtained by mixing a Li source selected from the group
consisting of lithium salts such as lithium acetate (LiCH.sub.3COO)
and lithium chloride (LiCl) or lithium hydroxide (LiOH), bivalent
iron salts such as iron (II) chloride (FeCl.sub.2), iron (II)
acetate (Fe(CH.sub.3COO).sub.2), and iron (II) sulfate
(FeSO.sub.4), phosphate compounds such as phosphoric acid
(H.sub.3PO.sub.4), ammonium dihydrogen phosphate
(NH.sub.4H.sub.2PO.sub.4), diammonium hydrogen phosphate
((NH.sub.4).sub.2HPO.sub.4), and water, using a pressure-resistant
airtight container; washing a precipitate that is obtained with
water to generate a cake-shaped precursor material; and baking the
cake-shaped precursor material.
[0072] The Li.sub.xA.sub.yD.sub.zPO.sub.4 powder may be a
crystalline particle, an amorphous particle, or a mixed crystal
particle in which a crystalline particle and an amorphous particle
coexist. Here, the reason why the Li.sub.xA.sub.yD.sub.zPO.sub.4
powder may be an amorphous particle is that when being thermally
treated in a non-oxidizing atmosphere at 500.degree. C. to
1,000.degree. C., the amorphous Li.sub.xA.sub.yD.sub.zPO.sub.4
powder is crystalized.
[0073] The size of the electrode-active material is not
particularly limited, but it is preferable that an average particle
size of primary particles be 0.01 to 20 .mu.m, and more preferably
0.02 to 5 .mu.m.
[0074] Here, the reason why the average particle size of the
primary particles of the electrode-active material is limited to
the above-described range is as follows. When the average particle
size of the primary particles is less than 0.01 .mu.m, it is
difficult to sufficiently cover the surface of each of the primary
particles with a thin film-shaped carbon, and thus a discharge
capacity at a high-speed charge and discharge rate becomes low. As
a result, it is difficult to realize a sufficient charge and
discharge rate performance, and thus this range is not preferable.
On the other hand, when the average particle size of the primary
particles exceeds 20 .mu.m, the internal resistance of the primary
particles increases. Therefore, the discharge capacity at a
high-speed charge and discharge rate becomes insufficient, and thus
this range is not preferable.
[0075] The shape of the electrode-active material is not
particularly limited. However, from the viewpoints that an
electrode material constituted by secondary particles having a
spherical shape, particularly, a real spherical shape may be easily
generated, it is preferable that the shape of the electrode-active
material be a spherical shape, particularly a real spherical
shape.
[0076] Here, the reason why it is preferable that the shape of the
electrode-active material be a spherical shape is as follows. When
preparing a paste for a positive electrode by mixing an
electrode-active material, a binder resin (binding agent), and a
solvent, an amount of solvent may be reduced, and the paste for the
positive electrode may be easily plated on a current collector.
[0077] In addition, when the shape of the electrode-active material
is a spherical shape, a surface area of the electrode-active
material becomes the minimum, and thus a mixing amount of the
binder resin (binding agent) that is added to an electrode material
mixture may be the minimum. Accordingly, the internal resistance of
the positive electrode that is obtained may be made small, and thus
this shape is preferable.
[0078] Furthermore, there is a tendency for the electrode-active
material to be closely packed, and thus a filled amount of the
positive material per unit volume increases. Accordingly, an
electrode density may be increased. As a result, high-capacity of
the lithium ion battery may be realized, and thus this shape is
preferable.
[0079] In addition, examples of the organic compound include
polyvinyl alcohol, polyvinyl pyrrolidone, cellulose, starch,
gelatin, carboxymethyl cellulose, methyl cellulose, hydroxymethyl
cellulose, hydroxyethyl cellulose, polyacrylic acid, polystyrene
sulfonate, polyacrylamide, polyvinyl acetate, glucose, fructose,
galactose, mannose, maltose, sucrose, lactose, glycogen, pectin,
alginic acid, glucomannan, chitin, hyaluronic acid, chondroitin,
agarose, polyether, and polyvalent alcohols.
[0080] When the total amount of the organic compound is converted
to an amount of carbon, it is preferable that a mixing ratio of the
electrode-active material and the organic compound be 0.6 to 10
parts by mass on the basis of 100 parts by mass of the
electrode-active material, and more preferably 0.8 to 2.5 parts by
mass.
[0081] Here, when the mixing ratio of the organic compound in terms
of the amount of carbon is less than 0.6 parts by mass, the
coverage rate of the carbonaceous film is less than 80%. Therefore,
when a battery is formed, a discharge capacity at a high-speed
charge and discharge rate decreases. As a result, it is difficult
to realize a sufficient charge and discharge rate performance. On
the other hand, when the mixing ratio of the organic compound in
terms of the amount of carbon exceeds 10 parts by mass, the mixing
ratio of the electrode-active material relatively decreases.
Therefore, when a battery is formed, a battery capacity decreases,
and the volume of the electrode-active material increases due to
excessive supporting of the carbonaceous film. As a result, an
electrode density decreases, and thus the battery capacity of the
lithium ion battery per unit volume considerably decreases.
[0082] The electrode-active material and the organic compound may
be dissolved or dispersed in water to prepare uniform slurry.
During the dissolution or dispersion, a dispersant may be
added.
[0083] A method of dissolving or dispersing the electrode-active
material or the organic compound in water is not particularly
limited as long as the electrode-active material may be dispersed,
and the organic compound may be dissolved or dispersed. However,
for example, a medium stirring type dispersing apparatus such as a
planetary ball mill, a vibration ball mill, a bead mill, a painter
shaker, and an attritor that stirs medium particles at a high speed
is preferably used.
[0084] During the dissolution or dispersion, it is preferable to
perform the stirring in such a manner that the electrode-active
material is dispersed as a primary particle, and then the organic
compound is dissolved. In this manner, a surface of the primary
particle of the electrode-active material is covered with the
organic compound. As a result, carbon originating from the organic
compound is uniformly interposed between primary particles of the
electrode-active material.
[0085] In addition, it is preferable to appropriately adjust
dispersion conditions of the slurry such as a concentration of the
electrode-active material or the organic compound in the slurry, a
stirring time, and the like so that with regard to the particle
size distribution of the electrode-active material or the precursor
of the electrode-active material in the slurry, a ratio (D90/D10)
of D90 to D10 of the particle size distribution becomes 5 to 30.
According to this, a tap density of the aggregate that is obtained
by spraying and drying the slurry becomes 1.0 g/cm.sup.3.
[0086] Then, the slurry is sprayed and dried in the air and in a
high-temperature atmosphere, for example, 70.degree. C. to
250.degree. C.
[0087] It is preferable that an average diameter of liquid droplets
during the spraying be 0.05 to 100 .mu.m, and more preferably 1 to
20 .mu.m.
[0088] When the average diameter of the liquid droplets during the
spraying is set within the above-described range, a dried product
having an average particle size of 0.5 to 100 .mu.m, and preferably
1 to 20 .mu.m may be obtained.
[0089] Then, the dried product is baked in a non-oxidizing
atmosphere at a temperature within a range of 500.degree. C. to
1,000.degree. C., and preferably 600.degree. C. to 900.degree. C.
for 0.1 hours to 40 hours.
[0090] As the non-oxidizing atmosphere, an inert atmosphere of
nitrogen (N.sub.2), argon (Ar), or the like is preferable. In a
case where it is desired to further suppress oxidization, a
reducing atmosphere containing a reducing gas such as hydrogen
(H.sub.2) is preferable. In addition, a burnable or combustible gas
such as oxygen (O.sub.2) may be introduced to the inert atmosphere
to remove an organic component that is vaporized in the
non-oxidizing atmosphere during the baking.
[0091] In addition, the reason why the baking temperature is set to
500.degree. C. to 1,000.degree. C. is as follows. When the baking
temperature is lower than 500.degree. C., the decomposition
reaction of an organic compound contained in the dried product does
not progress sufficiently, and thus carbonization of the organic
compound becomes insufficient. As a result, a highly resistive
decomposed product of the organic material is generated in the
aggregate that is obtained. On the other hand, when the baking
temperature is higher than 1,000.degree. C., Li in the
electrode-active material is evaporated, and a compositional
deviation occurs in the electrode-active material, and grain growth
of the electrode-active material is promoted. As a result, the
discharge capacity in the high charge and discharge rate decreases,
and thus it is difficult to realize a sufficient charge and
discharge rate performance.
[0092] Here, the particle size distribution of the aggregate that
is obtained may be controlled by appropriately adjusting conditions
during the baking of the dried product, for example, a temperature
rising rate, the maximum holding temperature, a holding time, and
the like.
[0093] As described above, the surface of the primary particles of
the electrode-active material is covered with carbon that is
generated by the thermal decomposition of the organic compound in
the dried product, and thus aggregate including secondary particles
in which carbon is interposed between the primary particles of the
electrode-active material may be obtained.
[0094] This aggregate is used as the electrode material of this
embodiment.
[0095] According to the electrode material of this embodiment, the
average particle size of the aggregate formed by aggregating
electrode-active material particles having a carbonaceous film
formed on a surface thereof is set to 0.5 to 100 .mu.m, and a
volume density of the aggregate is set to 50 to 80 vol % of the
volume density in a case in which the aggregate is a solid, and
thus unevenness in a supporting amount of the carbonaceous film
formed on a surface of the electrode-active material may be
reduced, and thus unevenness in conductivity of the
electrode-active material may be reduced. Accordingly, when the
electrode-active material is used as an electrode material of a
lithium ion battery, the internal resistance may be reduced.
[0096] According to the method for producing an electrode material
of this embodiment, slurry, which contains an electrode-active
material or a precursor of the electrode-active material, and an
organic compound, and in which with regard to the particle size
distribution of the electrode-active material or the precursor of
the electrode-active material, a ratio (D90/D10) of D90 to D10 of
the particle size distribution is 5 to 30, is dried, and the
resultant dried product that is obtained is baked at 500.degree. C.
to 1,000.degree. C. in a non-oxidizing atmosphere. Accordingly,
unevenness in a supporting amount of the carbonaceous film formed
on the surface of the electrode-active material may be reduced. As
a result, an electrode material capable of reducing unevenness in
conductivity of the electrode-active material may be easily
produced.
EXAMPLES
[0097] Hereinafter, the first embodiment of the invention will be
described in detail referring to Examples 1 to 4, and Comparative
Examples 1 to 3, but the invention is not limited by the
examples.
[0098] In the examples, metal Li is used for a negative electrode
to reflect the behavior of the electrode material itself on data,
but, a negative electrode material such as a carbon material, a Li
alloy, and Li.sub.4Ti.sub.5O.sub.12 may be used. In addition, a
solid electrolyte may be used instead of an electrolyte and a
separator.
Example 1
[0099] (Preparation of Electrode Material)
[0100] 4 mol lithium acetate (LiCH.sub.3COO), 2 mol iron (II)
sulfate (FeSO.sub.4), and 2 mol phosphoric acid (H.sub.3PO.sub.4)
were mixed to 2 L (liters) of water so that the entire amount
became 4 L, whereby a uniform slurry mixture was prepared.
[0101] Then, this mixture was accommodated in an 8-L
pressure-resistant airtight container, and hydrothermal synthesis
was performed at 120.degree. C. for one hour.
[0102] Then, a precipitate that was obtained was washed with water,
whereby a cake-shaped precursor of the electrode-active material
was obtained.
[0103] Then, 150 g (in terms of a solid content) of the precursor
of the electrode-active material, an aqueous polyvinyl alcohol
solution, which was obtained dissolving 20 g of polyvinyl alcohol
in 200 g of water, as the organic compound, and 500 g of zirconia
balls having a diameter of 5 mm as a medium particle were put into
a ball mill, and a dispersion treatment was carried out after
adjusting a stirring time of the ball mill so that D90/D10 of the
particle size distribution of the precursor particle of the
electrode-active material in the slurry became 7.
[0104] Then, the slurry that was obtained was sprayed in the air
atmosphere at 180.degree. C. and was dried to obtain a dried
product having an average particle size of 6 .mu.m.
[0105] Then, the dried product that was obtained was baked in a
nitrogen atmosphere at 700.degree. C. for one hour to obtain an
aggregate having an average particle size of 6 .mu.m, and this
aggregate was set as an electrode material of Example 1.
[0106] (Evaluation of Electrode Material)
[0107] A volume density of the aggregate of the electrode material,
a maximum void inside the aggregate, a ratio of an average film
thickness of a carbonaceous film (a thickness of the carbonaceous
film in an inner peripheral portion/a thickness of the carbonaceous
film in an outer peripheral portion), a tap density, and a coverage
rate of the carbonaceous film were evaluated, respectively.
[0108] Evaluation method is as follows.
[0109] (1) Volume Density of Aggregate
[0110] The volume density of the aggregate was measured using a
mercury porosimeter.
[0111] (2) Maximum Void Inside Aggregate
[0112] A cross-section of the aggregate was observed using a
scanning electron microscope (SEM) to measure a maximum value of
the void inside the aggregate.
[0113] (3) Ratio of Average Film Thickness of Carbonaceous Film
[0114] The carbonaceous film of the aggregate was observed using a
transmission electron microscope (TEM) to measure the thickness of
the carbonaceous film in the inner peripheral portion of the
aggregate and the thickness of the carbonaceous film in the outer
peripheral portion thereof, and the ratio of the average film
thickness of the carbonaceous film (the thickness of the
carbonaceous film in the inner peripheral portion/the thickness of
the carbonaceous film in the outer peripheral portion) was
calculated.
[0115] (4) Tap Density
[0116] The tap density was measured according to Japanese
Industrial Standard JIS R 1628 "Test method for bulk density of
fine ceramic powder."
[0117] (5) Coverage Rate of Carbonaceous Film
[0118] The carbonaceous film of the aggregate was observed using
the transmission electron microscope (TEM) and an energy dispersive
X-ray spectrometer (EDX) to calculate a ratio of a portion covered
with the carbonaceous film on the surface of the aggregate, and
this ratio was set to the coverage rate.
[0119] Evaluation results are shown in Table 1.
[0120] (Preparation of Lithium Ion Battery)
[0121] The electrode material, polyvinylidene fluoride (PVdF) as a
binder, and acetylene black (AB) as a conductive auxiliary agent
were mixed in a mass ratio of 90:5:5, and N-methyl-2-pyrrolidone
(NMP) as a solvent was further added to the resultant mixture to
give flowability, whereby slurry was prepared.
[0122] Then, the slurry was applied onto aluminum (Al) foil having
a thickness of 15 .mu.m, and was dried. Then, the aluminum foil was
compressed at a pressure of 600 kgf/cm.sup.2, whereby a positive
electrode of a lithium ion battery of Example 1 was prepared.
[0123] A lithium metal as a negative electrode was disposed with
respect to the positive electrode of the lithium ion battery, a
separator formed from porous polypropylene was disposed between the
positive electrode and the negative electrode, and the resultant
member was set as a member for a battery.
[0124] On the other hand, ethylene carbonate and diethyl carbonate
were mixed in a ratio of 1:1 (mass ratio), and 1 M LiPF.sub.6
solution was further added to the resultant mixture, whereby an
electrolyte having lithium ion conductivity was prepared.
[0125] Then, the member for a battery was immersed in the
electrolyte, whereby a lithium ion battery of Example 1 was
prepared.
[0126] (Evaluation of Lithium Ion Battery)
[0127] Internal resistance, and charge and discharge
characteristics of the lithium ion battery were evaluated,
respectively.
[0128] An evaluation method is as follows.
[0129] (1) Charge and Discharge Characteristics
[0130] A charge and discharge test of the above-described lithium
ion battery was carried out under conditions of room temperature
(25.degree. C.), a cut-off voltage of 2 to 4.5 V, and a constant
current at a charge and discharge rate of 1 C (discharge for one
hour after charge of one hour).
[0131] The charge and discharge characteristics are shown in FIG.
1.
[0132] (2) Internal Resistance
[0133] In a discharge curve shown in FIG. 1, voltage drop
recognized at a final stage of discharge represents presence of the
electrode-active material not covered with the carbonaceous film.
Accordingly, a sample in which the voltage drop was significantly
recognized was determined as a sample with high internal
resistance.
[0134] Here, a sample in which the voltage drop was not recognized
or the voltage drop was small was evaluated as "O", and a sample in
which the voltage drop was significantly recognized was evaluated
as "X".
Example 2
[0135] An electrode material, and a positive electrode of the
lithium ion battery were prepared in the same manner as Example 1
except that the stirring time of the ball mill was adjusted so that
D90/D10 of the particle size distribution of the precursor particle
of the electrode-active material in the slurry became 10. Then,
evaluation was performed. Evaluation results are shown in Table
1.
[0136] In addition, in Example 2, the same voltage drop at the
final stage of discharge as Example 1 was also recognized.
Example 3
[0137] An electrode material, and a positive electrode of the
lithium ion battery were prepared in the same manner as Example 1
except that the stirring time of the ball mill was adjusted so that
D90/D10 of the particle size distribution of the precursor particle
of the electrode-active material in the slurry became 20. Then,
evaluation was performed. Evaluation results are shown in Table
1.
[0138] In addition, in Example 3, the same voltage drop at the
final stage of discharge as Example 1 was also recognized.
Example 4
[0139] An electrode material, and a positive electrode of the
lithium ion battery were prepared in the same manner as Example 1
except that the stirring time of the ball mill was adjusted so that
D90/D10 of the particle size distribution of the precursor particle
of the electrode-active material in the slurry became 25. Then,
evaluation was performed. Evaluation results are shown in Table
1.
[0140] In addition, in Example 4, the same voltage drop at the
final stage of discharge as Example 1 was also recognized.
Comparative Example 1
[0141] An electrode material, and a positive electrode of the
lithium ion battery were prepared in the same manner as Example 1
except that the stirring time of the ball mill was adjusted so that
D90/D10 of the particle size distribution of the precursor particle
of the electrode-active material in the slurry became 1.5. Then,
evaluation was performed. Evaluation results are shown in Table 1,
and the charge and discharge characteristics are shown in FIG. 1,
respectively.
Comparative Example 2
[0142] An electrode material, and a positive electrode of the
lithium ion battery were prepared in the same manner as Example 1
except that the stirring time of the ball mill was adjusted so that
D90/D10 of the particle size distribution of the precursor particle
of the electrode-active material in the slurry became 3. Then,
evaluation was performed. Evaluation results are shown in Table
1.
Comparative Example 3
[0143] An electrode material, and a positive electrode of the
lithium ion battery were prepared in the same manner as Example 1
except that the stirring time of the ball mill was adjusted so that
D90/D10 of the particle size distribution of the precursor particle
of the electrode-active material in the slurry became 40. Then,
evaluation was performed. Evaluation results are shown in Table
1.
TABLE-US-00001 TABLE 1 Ratio of Average average Amount particle
Volume Maximum film of Coverage size density void thickness carbon
rate of of of of of Tab (parts carbonaceous aggregate aggregate
aggregate carbonaceous density Internal by film D90/D10 (.mu.m)
(vol %) (%) film (g/cm.sup.3) resistance mass) (%) Example 1 7 6 61
80 0.7 1.1 .smallcircle. 1 93 Example 2 10 4 68 78 0.8 1.3
.smallcircle. 1.1 99 Example 3 20 2 75 73 2.0 1.2 .smallcircle. 1.8
100 Example 4 25 1 78 65 3.0 1.4 .smallcircle. 2.2 100 Comparative
1.5 21 42 82 0.1 0.9 x 0.3 65 Example 1 Comparative 3 24 48 84 0.1
0.9 x 0.5 78 Example 2 Comparative 40 0.4 85 52 7.0 0.8 x 12 100
Example 3
[0144] According to the results described above, it can be seen
that in the electrode materials of Examples 1 to 4, the ratio of
the average film thickness of the carbonaceous film was within a
range of 0.7 to 1.3, the tap density and the coverage rate of the
carbonaceous film was high compared to the electrode materials of
Comparative Examples 1 to 3, and unevenness in the supporting
amount of the carbonaceous film formed on the surface of the
electrode-active material was small. In addition, in the electrode
materials of Examples 1 to 4, it can be seen that the internal
resistance was low compared to the electrode materials of the
Comparative Examples 1 to 3, and when being used as the electrode
material of the lithium ion battery, the internal resistance may be
reduced.
[0145] In addition, according to FIG. 1, in the electrode material
of Example 1, the discharge capacity was large and discharge
characteristics were excellent compared to the electrode material
of Comparative Example 1.
Second Embodiment
[0146] An embodiment (second embodiment) of the electrode material
and the method for producing the same of the invention will be
described.
[0147] In addition, this embodiment makes a description in detail
for easy comprehension of the gist of the invention, and does not
limit the invention unless otherwise stated.
[0148] In addition, with respect to the redundant contents as that
of the first embodiment, the description thereof may be
omitted.
[0149] [Electrode Material]
[0150] The electrode material of this embodiment includes an
aggregate formed by aggregating electrode-active material particles
having a carbonaceous film formed on a surface, an average particle
size of the aggregate is 0.5 to 100 .mu.m, a pore size (D50) when
an accumulated volume percentage of a pore size distribution of the
aggregate is 50% is 0.1 to 0.2 .mu.m, and porosity of the aggregate
is 15 to 50 vol % with respect to a volume in a case in which the
aggregate is a solid.
[0151] Here, it is assumed that a solid aggregate is an aggregate
in which a void is not present at all, and a density of the solid
aggregate is the same as a theoretical density of an
electrode-active material.
[0152] The pore size distribution of the aggregate may be measured
using a mercury porosimeter.
[0153] The pore size (D50) when the accumulated volume percentage
of the pore size distribution of the aggregate is 50% is preferably
0.1 to 0.2 .mu.m.
[0154] Here, the reason why D50 of the pore size distribution of
the aggregate is limited is as follows. When D50 is less than 0.1
.mu.m, the density inside the aggregate becomes too high, and thus
a channel-shaped (network-shaped) void inside the aggregate
decreases. As a result, a tarry material, which is generated during
carbonization of the organic compound, is trapped inside the
aggregate, and thus this range is not preferable. On the other
hand, when D50 exceeds 0.2 .mu.m, a vapor concentration of an
aromatic carbon compound in the void inside the aggregate of the
electrode-active material becomes too low, and thus the film
thickness of the carbonaceous film in the inner peripheral portion
of the outer shell of the aggregate becomes small. Therefore, the
internal resistance of the electrode-active material increases, and
thus this range is not preferable.
[0155] Similarly to the pore size distribution, the porosity of the
aggregate may be measured using the mercury porosimeter.
[0156] It is preferable that the porosity of the aggregate be 15 to
50 vol % with respect to a volume in a case in which the aggregate
is a solid, and more preferably 20 to 45 vol %.
[0157] Here, when the porosity of the aggregate is less than 15 vol
% with respect to the volume in a case in which the aggregate is a
solid, the density inside the aggregate becomes too high, and thus
a channel-shaped (network-shaped) void inside the aggregate
decreases. As a result, a tarry material, which is generated during
carbonization of the organic compound, is trapped inside the
aggregate, and thus this range is not preferable. On the other
hand, when the porosity exceeds 50 vol % with respect to the volume
in a case in which the aggregate is a solid, a vapor concentration
of an aromatic carbon compound in the void inside the aggregate of
the electrode-active material becomes too low, and thus the film
thickness of the carbonaceous film in the inner peripheral portion
of the outer shell of the aggregate becomes small. Therefore, the
internal resistance of the electrode-active material increases, and
thus this range is not preferable.
[0158] In addition, when the porosity of the aggregate is 50 vol %
or less, the aggregate becomes dense, and the strength of the
aggregate increases. Accordingly, for example, when the
electrode-active material is mixed with the binder, the conductive
auxiliary agent, and the solvent to prepare electrode slurry, the
aggregate is not likely to collapse. As a result, an increase in
viscosity of the electrode slurry is suppressed, and flowability is
maintained. Accordingly, coating properties are improved, and
filling properties of the electrode-active material in a coated
film of the electrode slurry are also improved. In a case where the
aggregate collapses during preparation of the electrode slurry,
since a necessary amount of the binder that binds the
electrode-active materials increases, the viscosity of the
electrode slurry increases, and a concentration of a solid content
of the electrode slurry decreases. As a result, a percentage of the
electrode-active material in the weight of a positive electrode
film decreases, and thus this case is not preferable.
[0159] When this aggregate is made into a shell-like aggregate
having a void at the inside thereof, it is preferable that the size
of the void that is formed inside the aggregate be 80% or less of a
diameter of aggregate particles, and more preferably 70% or
less.
[0160] Here, when the size (diameter) of the void exceeds 80% of
the diameter of the aggregate particles, it is difficult to
maintain a shell shape of the aggregate, and thus the concentration
of the vapor of the aromatic carbon compound inside the void
becomes too low. As a result, the film thickness of the
carbonaceous film in the inner peripheral portion of the outer
shell of the aggregate becomes small, and the internal resistance
of the electrode-active material increases, and thus this range is
not preferable.
[0161] In the electrode material of this embodiment, since the
porosity of the aggregate is set to 15 to 50 vol % with respect to
a volume in a case in which the aggregate is a solid, unevenness in
a supporting amount of the carbonaceous film formed on the surface
of the electrode-active material particles may be made small, and
thus unevenness in conductivity of the electrode-active material
may be reduced. In addition, when the electrode-active material in
which the unevenness in conductivity is reduced is used as the
electrode material of the lithium ion battery, a reaction related
to intercalation and deintercalation of lithium ions may be
uniformly carried out in the entirety of the surface of the
electrode-active material, and thus the internal resistance may be
reduced.
[0162] Here, the "internal resistance" described above represents
internal resistance at a site at which reaction resistance related
to intercalation and deintercalation of lithium ions is high in a
particle, which does not have the carbonaceous film formed on a
surface thereof or in which the thickness of the carbonaceous film
is small, of the electrode-active material. Specifically, when the
electrode-active material is used as the electrode-active material
of the lithium ion battery, the internal resistance is shown as a
magnitude of voltage drop at the final stage of discharge. That is,
in an electrode-active material in which the intercalation and
deintercalation reaction of lithium ions is uniformly carried out
over the entirety of the surface of the electrode-active material,
the voltage drop at the final stage of discharge is small. On the
other hand, in an electrode-active material in which the
intercalation and deintercalation reaction resistance of lithium
ions is high at a part of the surface of the electrode-active
material, the voltage drop at the final stage of discharge becomes
significant.
[0163] According to the electrode material of this embodiment, the
average particle size of the aggregate formed by aggregating
electrode-active material particles having the carbonaceous film
formed on a surface is set to 0.5 to 100 .mu.m, and the pore size
(D50) when the accumulated volume percentage of the pore size
distribution of the aggregate is 50% is set to 0.1 to 0.2 .mu.m,
and the porosity of the aggregate is set to 15 to 50 vol % with
respect to a volume in a case in which the aggregate is a solid.
Accordingly, unevenness in a supporting amount of the carbonaceous
film formed on the surface of the electrode-active material may be
made small, and thus unevenness in conductivity of the
electrode-active material may be reduced. As a result, when the
electrode-active material is used as the electrode material of the
lithium ion battery, the internal resistance may be reduced.
[0164] According to the method for producing an electrode material
of this embodiment, the slurry, which contains the electrode-active
material or the precursor of the electrode-active material, and the
organic compound, and in which the ratio (D90/D10) of the particle
size (D90) when the accumulated volume percentage of the particle
size distribution of the electrode-active material or the precursor
of the electrode-active material is 90% to the particle size (D10)
when the accumulated volume percentage is 10% is 5 to 30, is dried;
and the resultant dried product that is obtained is baked at
500.degree. C. to 1,000.degree. C. in a non-oxidizing atmosphere.
Accordingly, unevenness in the supporting amount of the
carbonaceous film formed on the surface of the electrode-active
material may be reduced. As a result, an electrode material capable
of reducing unevenness in conductivity of the electrode-active
material may be easily produced.
[0165] Hereinafter, the second embodiment of the invention will be
described in detail referring to Examples 5 to 9, and Comparative
Examples 4 to 6, but the invention is not limited to these
examples.
Example 5
[0166] (Preparation of Electrode Material)
[0167] 4 mol lithium acetate (LiCH.sub.3COO), 2 mol iron (II)
sulfate (FeSO.sub.4), and 2 mol phosphoric acid (H.sub.3PO.sub.4)
were mixed to 2 L (liters) of water so that the entire amount
became 4 L, whereby a uniform slurry mixture was prepared.
[0168] Then, this mixture was accommodated in an 8-L
pressure-resistant airtight container, and hydrothermal synthesis
was performed at 120.degree. C. for one hour.
[0169] Then, a precipitate that was obtained was washed with water,
whereby a cake-shaped precursor of the electrode-active material
was obtained.
[0170] Then, 150 g (in terms of a solid content) of the precursor
of the electrode-active material, an aqueous polyvinyl alcohol
solution, which was obtained dissolving 20 g of polyvinyl alcohol
in 200 g of water, as the organic compound, and 500 g of zirconia
balls having a diameter of 5 mm as a medium particle were put into
a ball mill, and a dispersion treatment was carried out after
adjusting a stirring time of the ball mill so that D90/D10 of the
particle size distribution of the precursor particle of the
electrode-active material in the slurry became 7.
[0171] Then, the slurry that was obtained was sprayed in the air
atmosphere at 180.degree. C., and was dried to obtain a dried
product having an average particle size of 6 .mu.m.
[0172] Then, the dried product that was obtained was baked in a
nitrogen atmosphere at 700.degree. C. for one hour to obtain an
aggregate having an average particle size of 6 .mu.m, and this
aggregate was set as an electrode material of Example 5.
[0173] (Evaluation of Electrode Material)
[0174] The pore size distribution (D50) of the aggregate of the
electrode material, the porosity of the aggregate, the ratio of the
average film thickness of the carbonaceous film (the thickness of
the carbonaceous film in the inner peripheral portion/the thickness
of the carbonaceous film in the outer peripheral portion), the tap
density, and the coverage rate of the carbonaceous film were
evaluated, respectively.
[0175] Evaluation method is as follows.
[0176] (1) Pore Size Distribution (D50) of Aggregate
[0177] The pore size distribution (D50) was measured using the
mercury porosimeter.
[0178] (2) Porosity of Aggregate
[0179] The porosity of the aggregate was measured using the mercury
porosimeter.
[0180] (3) Ratio of Average Film Thickness of Carbonaceous Film
[0181] The carbonaceous film of the aggregate was observed using a
transmission electron microscope (TEM) to measure the thickness of
the carbonaceous film in the inner peripheral portion of the
aggregate and the thickness of the carbonaceous film in the outer
peripheral portion thereof, and the ratio of the average film
thickness of the carbonaceous film (the thickness of the
carbonaceous film in the inner peripheral portion/the thickness of
the carbonaceous film in the outer peripheral portion) was
calculated.
[0182] (4) Tap Density
[0183] The tap density was measured according to Japanese
Industrial Standard JIS R 1628 "Test method for bulk density of
fine ceramic powder."
[0184] (5) Coverage Rate of Carbonaceous Film
[0185] The carbonaceous film of the aggregate was observed using
the transmission electron microscope (TEM) and an energy dispersive
X-ray spectrometer (EDX) to calculate a ratio of a portion covered
with the carbonaceous film on the surface of the aggregate, and
this ratio was set to the coverage rate. Evaluation results are
shown in Table 2.
[0186] (Preparation of Lithium Ion Battery)
[0187] The electrode material, polyvinylidene fluoride (PVdF) as a
binder, and acetylene black (AB) as a conductive auxiliary agent
were mixed in a mass ratio of 90:5:5, and N-methyl-2-pyrrolidone
(NMP) as a solvent was further added to the resultant mixture to
give flowability, whereby slurry was prepared.
[0188] Then, the slurry was applied onto aluminum (Al) foil having
a thickness of 15 .mu.m, and was dried. Then, the aluminum foil was
compressed at a pressure of 600 kgf/cm.sup.2, whereby a positive
electrode of a lithium ion battery of Example 5 was prepared.
[0189] A lithium metal as a negative electrode was disposed with
respect to the positive electrode of the lithium ion battery, a
separator formed from porous polypropylene was disposed between the
positive electrode and the negative electrode, and the resultant
member was set as a member for a battery.
[0190] On the other hand, ethylene carbonate and diethyl carbonate
were mixed in a ratio of 1:1 (mass ratio), and 1 M LiPF.sub.6
solution was further added to the resultant mixture, whereby an
electrolyte having lithium ion conductivity was prepared.
[0191] Then, the member for a battery was immersed in the
electrolyte, whereby a lithium ion battery of Example 5 was
prepared.
[0192] (Evaluation of Lithium Ion Battery)
[0193] Internal resistance, and charge and discharge
characteristics of the lithium ion battery were evaluated,
respectively.
[0194] An evaluation method is as follows.
[0195] (1) Charge and Discharge Characteristics
[0196] A charge and discharge test of the above-described lithium
ion battery was carried out under conditions of room temperature
(25.degree. C.), a cut-off voltage of 2 to 4.5 V, and a constant
current at a charge and discharge rate of 1 C (discharge for one
hour after charge of one hour). An initial discharge capacity is
shown in Table 3, and the charge and discharge characteristics are
shown in FIG. 2, respectively.
[0197] (2) Internal Resistance
[0198] In a discharge curve shown in FIG. 2, voltage drop
recognized at a final stage of discharge represents presence of the
electrode-active material not covered with the carbonaceous film.
Accordingly, a sample in which the voltage drop was significantly
recognized was determined as a sample with high internal
resistance.
[0199] Here, a sample in which the voltage drop was not recognized
or the voltage drop was small was evaluated as "O", and a sample in
which the voltage drop was significantly recognized was evaluated
as "X".
[0200] Evaluation results are shown in Table 3.
Example 6
[0201] An electrode material, and a positive electrode of the
lithium ion battery were prepared in the same manner as Example 5
except that the stirring time of the ball mill was adjusted so that
D90/D10 of the particle size distribution of the precursor particle
of the electrode-active material in the slurry became 10. Then,
evaluation was performed. Evaluation results are shown in Tables 2
and 3.
[0202] In addition, in Example 6, the same voltage drop at the
final stage of discharge as Example 5 was also recognized.
Example 7
[0203] An electrode material, and a positive electrode of the
lithium ion battery were prepared in the same manner as Example 5
except that the stirring time of the ball mill was adjusted so that
D90/D10 of the particle size distribution of the precursor particle
of the electrode-active material in the slurry became 20. Then,
evaluation was performed. Evaluation results are shown in Tables 2
and 3.
[0204] In addition, in Example 7, the same voltage drop at the
final stage of discharge as Example 5 was also recognized.
Example 8
[0205] An electrode material, and a positive electrode of the
lithium ion battery were prepared in the same manner as Example 5
except that the stirring time of the ball mill was adjusted so that
D90/D10 of the particle size distribution of the precursor particle
of the electrode-active material in the slurry became 25. Then,
evaluation was performed. Evaluation results are shown in Tables 2
and 3.
[0206] In addition, in Example 8, the same voltage drop at the
final stage of discharge as Example 5 was also recognized.
Example 9
[0207] A precursor of an electrode-active material of Example 9 was
obtained in the same manner as Example 5 except that manganese
[0208] (II) sulfate (MnSO.sub.4) as a manganese source was used
instead of iron (II) sulfate (FeSO.sub.4) as the iron source.
[0209] An electrode material and a positive electrode of the
lithium ion battery of Example 9 were prepared in the same manner
as Example 5 except that a precursor of iron lithium phosphate as a
carbonization catalyst was added to the aqueous polyvinyl alcohol
solution in the same mass as that of a polyvinyl alcohol solid
content in the aqueous polyvinyl alcohol solution. Then, evaluation
was performed. Evaluation results are shown in Tables 2 and 3.
[0210] In addition, in Example 9, the same voltage drop at the
final stage of discharge as Example 5 was also recognized.
Comparative Example 4
[0211] An electrode material, and a positive electrode of the
lithium ion battery were prepared in the same manner as Example 5
except that the stirring time of the ball mill was adjusted so that
D90/D10 of the particle size distribution of the precursor particle
of the electrode-active material in the slurry became 1.5. Then,
evaluation was performed. Evaluation results are shown in Tables 2
and 3, and charge and discharge characteristics are shown in FIG.
2, respectively.
Comparative Example 5
[0212] An electrode material, and a positive electrode of the
lithium ion battery were prepared in the same manner as Example 5
except that the stirring time of the ball mill was adjusted so that
D90/D10 of the particle size distribution of the precursor particle
of the electrode-active material in the slurry became 3. Then,
evaluation was performed. Evaluation results are shown in Tables 2
and 3.
Comparative Example 6
[0213] An electrode material, and a positive electrode of the
lithium ion battery were prepared in the same manner as Example 5
except that the stirring time of the ball mill was adjusted so that
D90/D10 of the particle size distribution of the precursor particle
of the electrode-active material in the slurry became 40. Then,
evaluation was performed. Evaluation results are shown in Tables 2
and 3.
TABLE-US-00002 TABLE 2 Ratio of Average average Amount particle
film of Coverage size thickness carbon rate of of Pore size of Tab
(parts carbonaceous aggregate distribution Porosity carbonaceous
density by film D90/D10 (.mu.m) (D50) (%) film (g/cm.sup.3) mass)
(%) Example 5 7 6 0.19 39 0.7 1.1 1 93 Example 6 10 4 0.18 32 0.8
1.3 1.1 99 Example 7 20 2 0.16 25 2.0 1.2 1.8 100 Example 8 25 1
0.13 22 3.0 1.4 2.2 100 Example 9 7 4 0.15 43 1.2 1.1 2.4 93
Comparative 1.5 21 0.25 58 0.1 0.9 0.3 65 Example 4 Comparative 3
24 0.25 52 0.1 0.9 0.5 78 Example 5 Comparative 40 0.4 0.08 2 7.0
0.8 12 100 Example 6
TABLE-US-00003 TABLE 3 Initial discharge Internal capacity (mAh/g)
resistance Example 5 157 .largecircle. Example 6 158 .largecircle.
Example 7 159 .largecircle. Example 8 159 .largecircle. Example 9
150 .largecircle. Comparative Example 4 135 X Comparative Example 5
140 X Comparative Example 6 149 X
[0214] According to the results described above, in the electrode
materials of Examples 5 to 9, it can be seen that the ratio of the
average film thickness of the carbonaceous film was within a range
of 0.7 to 1.3, the tap density and the coverage rate of the
carbonaceous film was high compared to the electrode materials of
Comparative Examples 4 to 6, and unevenness in the supporting
amount of the carbonaceous film formed on the surface of the
electrode-active material was small. In addition, in the electrode
materials of Examples 5 to 9, it can be seen that the internal
resistance was low compared to the electrode materials of the
Comparative Examples 4 to 6, and when being used as the electrode
material of the lithium ion battery, the internal resistance may be
greatly reduced.
[0215] In addition, according to FIG. 2, in the electrode material
of Example 5, the discharge capacity was large and discharge
characteristics were excellent compared to the electrode material
of Comparative Example 4.
INDUSTRIAL APPLICABILITY
[0216] In the electrode material of the invention, the average
particle size of the aggregate formed by aggregating
electrode-active material having the carbonaceous film formed on a
surface thereof is set to 0.5 to 100 .mu.m, and the volume density
of the aggregate is set to 50 to 80 vol % of the volume density in
a case in which the aggregate is a solid. Accordingly, unevenness
in a supporting amount of the carbonaceous film formed on the
surface of the electrode-active material may be reduced. As a
result, unevenness in conductivity of the electrode-active material
may be reduced. In addition, when the electrode material is used as
the electrode material of the lithium ion battery, the internal
resistance may be reduced. Accordingly, a new improvement in the
discharge characteristics of the lithium ion battery may be made,
and the electrode material may be applied to a next-generation
secondary battery in which better miniaturization, lightness, and
high capacity are expected, and in the case of the next-generation
secondary battery, the effect will be significant.
[0217] In addition, in another electrode material of the invention,
the average particle size of the aggregate formed by aggregating
the electrode-active material particles having the carbonaceous
film formed on a surface thereof is set to 0.5 to 100 .mu.m, the
pore size (D50) when the accumulated volume percentage of the pore
size distribution of the aggregate is 50% is set to 0.1 to 0.2
.mu.m, and porosity of the aggregate is set to 15 to 50 vol % with
respect to the volume in a case in which the aggregate is a solid.
Accordingly, unevenness in a supporting amount of the carbonaceous
film formed on the surface of the electrode-active material
particles may be reduced. As a result, unevenness in conductivity
of the electrode-active material may be reduced. In addition, when
the electrode material is used as the electrode material of the
lithium ion battery, the internal resistance may be greatly
reduced. Accordingly, a new improvement in the discharge
characteristics of the lithium ion battery may be made, and the
electrode material may be applied to a next-generation secondary
battery in which further miniaturization, lightness, and high
capacity are expected, and in the case of the next-generation
secondary battery, the effect will be significant.
* * * * *