U.S. patent application number 12/254987 was filed with the patent office on 2009-05-14 for non-aqueous electrolyte battery.
This patent application is currently assigned to Sony Corporation. Invention is credited to Hiroyuki Chigiri.
Application Number | 20090123832 12/254987 |
Document ID | / |
Family ID | 40624023 |
Filed Date | 2009-05-14 |
United States Patent
Application |
20090123832 |
Kind Code |
A1 |
Chigiri; Hiroyuki |
May 14, 2009 |
NON-AQUEOUS ELECTROLYTE BATTERY
Abstract
A non-aqueous electrolyte battery is disclosed. The non-aqueous
electrolyte battery include a positive electrode, a negative
electrode, and a separator disposed between the positive electrode
and the negative electrode. The negative electrode includes an
anode mixture layer having a volume density of 1.70 to 1.90
g/cm.sup.3 prior to being subjected to charge and discharge
processes. The anode mixture layer includes mixed particles
composed of spherical graphite having an average particle size of
25 to 35 .mu.m and non-spherical graphite having an average
particle size of 8 to 22 .mu.m.
Inventors: |
Chigiri; Hiroyuki;
(Fukushima, JP) |
Correspondence
Address: |
K&L Gates LLP
P. O. BOX 1135
CHICAGO
IL
60690
US
|
Assignee: |
Sony Corporation
Tokyo
JP
|
Family ID: |
40624023 |
Appl. No.: |
12/254987 |
Filed: |
October 21, 2008 |
Current U.S.
Class: |
429/163 ;
429/199; 429/231.8 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 4/133 20130101; H01M 2004/021 20130101; H01M 10/0525 20130101;
H01M 4/02 20130101; H01M 4/364 20130101; H01M 50/103 20210101; H01M
50/10 20210101; H01M 50/411 20210101; H01M 50/46 20210101; H01M
10/0587 20130101; H01M 4/587 20130101; H01M 50/116 20210101 |
Class at
Publication: |
429/163 ;
429/231.8; 429/199 |
International
Class: |
H01M 4/02 20060101
H01M004/02; H01M 2/02 20060101 H01M002/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 14, 2007 |
JP |
2007-296069 |
May 30, 2008 |
JP |
2008-142154 |
Claims
1. A non-aqueous electrolyte battery comprising: a positive
electrode; a negative electrode; and a separator disposed between
the positive electrode and the negative electrode, wherein the
negative electrode includes an anode mixture layer having a volume
density of 1.70 to 1.90 g/cm.sup.3 prior to being subjected to
charge and discharge processes, and wherein the anode mixture layer
includes mixed particles composed of spherical graphite having an
average particle size of 25 to 35 .mu.m and non-spherical graphite
having an average particle size of 8 to 22 .mu.m.
2. The non-aqueous electrolyte battery according to claim 1,
wherein polymer compound layers are disposed between the negative
electrode and the separator, and between the positive electrode and
the separator.
3. The non-aqueous electrolyte battery according to claim 2,
wherein the polymer compound layer is composed of a porous polymer
compound retaining an electrolytic solution therein.
4. The non-aqueous electrolyte battery according to claim 3,
wherein the polymer compound layer has a uniform thickness.
5. The non-aqueous electrolyte battery according to claim 1,
wherein the mixed particles have particle size distributions such
that D10 is 5 to 11 .mu.m, D50 is 13 to 25 .mu.m, and D90 is 27 to
45 .mu.m.
6. The non-aqueous electrolyte battery according to claim 1,
wherein: the spherical graphite is mesocarbon microbeads; and the
non-spherical graphite is a powder obtained by pulverizing
mesocarbon microbeads.
7. The non-aqueous electrolyte battery according to claim 2,
wherein the polymer compound layer contains a polymer compound
including repeating units derived from vinylidene fluoride.
8. The non-aqueous electrolyte battery according to claim 2,
wherein the polymer compound layer contains a copolymer including
at least repeating units derived from vinylidene fluoride and
repeating units derived from hexafluoropropylene.
9. The non-aqueous electrolyte battery according to claim 2,
wherein the polymer compound layer has a bonding strength of 5
mN/mm or more with the electrode and the separator.
10. The non-aqueous electrolyte battery according to claim 2,
wherein: the positive electrode, the negative electrode, the
separator, and the polymer compound layer are spirally wound
together to form a battery element; and the battery has a flattened
shape.
11. The non-aqueous electrolyte battery according to claim 10,
further comprising a casing member for containing the battery
element therein, the casing member being composed of a
moisture-proof laminate film including a polymer film and a
metallic foil.
12. The non-aqueous electrolyte battery according to claim 1,
wherein the anode mixture layer has a volume density of 1.50 to
1.90 g/cm.sup.3 with respect to a cell ready for shipping, the cell
being subjected to 0.2 C constant-current discharging until
becoming a cut-off voltage of 3.0 V.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims benefit of priority of
Japanese patent Applications No. 2007-296069 filed in the Japanese
Patent Office on Nov. 14, 2007, and No. 2008-142154 filed in the
Japanese Patent Office on May 30, 2008, the entire disclosures of
which are incorporated herein by reference.
BACKGROUND
[0002] The present application relates to a non-aqueous electrolyte
battery. More particularly, the present application relates to a
non-aqueous electrolyte battery including a positive electrode and
a negative electrode which are opposed to each other through a
separator.
[0003] In recent years, various types of portable electronic
devices, such as camera-integrated videotape recorders (VTRs),
cellular phones, and laptop computers, have come on the market, and
those having smaller size and weight are being developed. As the
portable electronic devices are miniaturized, batteries,
particularly secondary batteries as a power source of them, are
vigorously developed.
[0004] Among the secondary batteries, a lithium-ion secondary
battery which possibly achieves high energy density has attracted
attention. With respect to the lithium-ion secondary battery, by
using a laminate film or the like as a casing member instead of a
battery can made of a metal, such as aluminum or iron, the battery
is being further reduced in size, weight, and thickness. The
lithium-ion secondary battery is used in a wide variety of
applications, so that a higher energy density in the battery has
been demanded.
[0005] For achieving a lithium-ion secondary battery having a
higher energy, an attempt is made to increase the volume density of
the electrode mixture. For example, Japanese Unexamined Patent
Application Publication No. 2003-323895 discloses a technique in
which different spherical carbonaceous materials are used in the
electrode mixture to improve the energy density.
SUMMARY
[0006] However, the lithium-ion secondary battery which has a
electrode mixture having a high volume density suffers marked
deformation when the electrode expands and shrinks repeatedly
during the charge and discharge operations. Consequently, when the
laminate film is used as a casing member for the lithium-ion
secondary battery, the rigidity of the laminate film is poor as
compared to a casing made of a metal, whereby it is difficult to
prevent the battery from suffering deformation due to a change of
the pressure in the battery.
[0007] Once the electrode deforms, a gap between the electrode and
the separator widens, thereby increasing the cell thickness.
Further, when the electrode deforms, a gap between the electrode
and the separator widens, so that the battery capacity considerably
deteriorates with an increase in the number of repetition of charge
and discharge cycles.
[0008] Accordingly, it is desirable to provide a non-aqueous
electrolyte battery which is advantageous in that the electrode
mixture layer has a high volume density and the battery can be
prevented from suffering deformation even when using a laminate
film as a casing member, thus achieving excellent battery
properties.
[0009] In accordance with an embodiment, there is provided a
non-aqueous electrolyte battery which includes a positive
electrode, a negative electrode, and a separator disposed between
the positive electrode and the negative electrode. The negative
electrode includes an anode mixture layer having a volume density
of 1.70 to 1.90 g/cm.sup.3 prior to being subjected to charge and
discharge processes. The anode mixture layer includes mixed
particle composed of spherical graphite having an average particle
size of 25 to 35 .mu.m and non-spherical graphite having an average
particle size of 8 to 22 .mu.m, thus achieving excellent battery
properties.
[0010] According to an embodiment, the negative electrode has an
anode mixture layer having a volume density of 1.70 to 1.90
g/cm.sup.3 prior to being subjected to charge and discharge
processes, whereby the negative electrode having such a high volume
density contains mixed particles of spherical graphite having an
average particle size of 25 to 35 .mu.m and non-spherical graphite
having an average particle size of 8 to 22 .mu.m, thus achieving
excellent battery properties.
[0011] Additional features and advantages are described herein, and
will be apparent from the following Detailed Description and the
figures.
BRIEF DESCRIPTION OF THE FIGURES
[0012] FIG. 1 is an exploded perspective view showing the
construction of a non-aqueous electrolyte battery according to an
embodiment of the present application.
[0013] FIG. 2 is a cross-sectional view of the spirally-wound
electrode structure shown in FIG. 1, taken along the line
II-II.
DETAILED DESCRIPTION
[0014] Hereinbelow, embodiments of the present application will be
described with reference to accompanying drawings. An example of
the construction of a non-aqueous electrolyte battery according to
an embodiment of the present application is first described with
reference to FIGS. 1 and 2.
[0015] FIG. 1 is a perspective view showing an example of the
construction of a non-aqueous electrolyte battery according to an
embodiment of the present application. This non-aqueous electrolyte
battery is, for example, a non-aqueous electrolyte secondary
battery. This non-aqueous electrolyte battery includes a
spirally-wound electrode structure 10 having fitted thereto a
positive electrode lead 11 and a negative electrode lead 12 and
being contained in a casing member 1 in a film form, and the
battery has a flattened shape.
[0016] The positive electrode lead 11 and negative electrode lead
12 individually have, for example, a strip shape, and are
electrically extended from the inside of the casing member 1 to the
outside, for example, in the same direction. The positive electrode
lead 11 is composed of, e.g., a metal material, such as aluminum
(Al), and the negative electrode lead 12 is composed of, e.g., a
metal material, such as nickel (Ni).
[0017] The casing member 1 is a laminate film having a structure
including, for example, an insulating layer, a metal layer, and the
outermost layer which are stacked in this order and bonded together
by lamination or the like. The casing member 1 is disposed so that,
for example, the insulating layer constitutes the inner side, and
has the respective outer edge portions sealed by heat sealing or by
using an adhesive.
[0018] The insulating layer is composed of a polyolefin resin, such
as polyethylene, polypropylene, modified polyethylene, modified
polypropylene, or a copolymer thereof. The use of these materials
provides the reduction in moisture permeability of the casing
member, thereby achieving excellent airtightness. The metal layer
is made of aluminum, stainless steel, nickel, iron, or the like in
the form of foil or plate. The outermost layer may be composed of,
for example, the same resin as that used for the insulating layer,
or nylon or the like. In this case, the casing member can be
improved in resistance to breakage, nail penetration, or the like.
The casing member 1 may have any layer other than the insulating
layer, metal layer, and outermost layer.
[0019] A bonding film 2 is inserted to portions between the casing
member 1 and the positive electrode lead 11, and between the casing
member 1 and the negative electrode lead 12. The bonding film 2
improves the adhesion of the positive electrode lead 11 and
negative electrode lead 12 to the inner side of the casing member 1
to prevent external air from going into the battery. The bonding
film 2 is composed of a material having bonding properties with the
positive electrode lead 11 and negative electrode lead 12, and, for
example, when the positive electrode lead 11 and negative electrode
lead 12 are individually composed of the above-mentioned metal
material, it is preferred that the bonding film 2 is made of a
polyolefin resin, such as polyethylene, polypropylene, modified
polyethylene, or modified polypropylene.
[0020] FIG. 2 is a cross-sectional view of the spirally-wound
electrode structure 10 shown in FIG. 1, taken along the line II-II.
The spirally-wound electrode structure 10 includes a positive
electrode 13, a negative electrode 14, a separator 15, and polymer
compound layers 16 formed on both sides of the separator 15,
wherein the separator 15 and polymer compound layers 16 are
disposed between the positive electrode 13 and the negative
electrode 14. The outermost winding layer is preferably protected
by a protective tape 17, but there can be used no protective
tape.
[0021] The positive electrode 13 includes, for example, a positive
electrode current collector 13A and cathode mixture layers 13B
formed on both sides of the positive electrode current collector
13A. The positive electrode current collector 13A is composed of,
for example, a metallic foil, such as an aluminum foil.
[0022] The cathode mixture layer 13B includes, for example, as a
cathode active material, at least one positive electrode material
capable of occluding and releasing lithium (Li) which is an
electrode reactive substance, and optionally a conductor, such as a
carbon material, and a binder, such as polyvinylidene fluoride.
[0023] With respect to the positive electrode (cathode) material
capable of occluding and releasing lithium, a lithium composite
oxide having lithium and a transition metal, a lithium metal
phosphate compound having an olivine structure, or the like can be
used. Specifically, for example, LiCoO.sub.2, LiNiO.sub.2,
LiMn.sub.2O.sub.4, LiCo.sub.0.33Ni.sub.0.33Mn.sub.0.33O.sub.2, or
LiFePO.sub.4 can be used.
[0024] As with the positive electrode 13, the negative electrode 14
includes, for example, a negative electrode current collector 14A
and anode mixture layers 14B formed on both sides of the negative
electrode current collector 14A. The negative electrode current
collector 14A is composed of, for example, a metallic foil, such as
a copper foil.
[0025] The anode mixture layer 14B includes, for example, at least
one negative electrode (anode) material capable of occluding and
releasing lithium, and optionally a conductor and a binder.
[0026] With respect to the negative electrode (anode) material, a
mixture of spherical graphite and non-spherical graphite is used.
The term "spherical graphite" used herein means a carbon material,
such as artificial graphite, natural graphite, easily graphitizable
carbon, or hardly graphitizable carbon, which has a shape of sphere
or substantial sphere. The term "non-spherical graphite" used
herein means a carbon material, such as artificial graphite,
natural graphite, easily graphitizable carbon, or hardly
graphitizable carbon, which has a shape of flake, fiber, or bulk.
More specifically, examples of spherical graphite include
mesocarbon microbeads (MCMB) which are artificial graphite, and
examples of non-spherical graphite include powder obtained by
pulverizing MCMB.
[0027] The negative electrode material includes mixed particles of
spherical graphite having an average particle size of 25 to 35
.mu.m and non-spherical graphite having an average particle size of
8 to 22 .mu.m, and the mixed particles preferably have particle
size distribution such that D10 is 5 to 11 .mu.m, D50 is 13 to 25
.mu.m, and D90 is 27 to 45 .mu.m. When using the above negative
electrode material, excellent properties can be obtained.
[0028] In the measurement of particle size distribution, a laser
diffraction-type particle size distribution measuring machine
(manufactured and sold by SEISHIN ENTERPRISE CO., LTD.; trade name:
LMS-30) or the like can be used. A particle size distribution is
represented by a particle size distribution in terms of a volume.
For example, D10 of 5 to 11 .mu.m indicates that a particle size
such that the cumulative value of particle size distribution is 10%
is 5 to 11 .mu.m. An average particle size is a value of D50
obtained when particle size distribution is measured similarly
using a laser diffraction-type particle size distribution measuring
machine (manufactured and sold by SEISHIN ENTERPRISE CO., LTD.;
trade name: LMS-30) or the like.
[0029] With respect to the mixed particles, there are preferably
used mixed particles of MCMB as spherical graphite and an MCMB
pulverized product as non-spherical graphite, which is obtained by
pulverizing MCMB and non-crystallizing the pulverized plane of
MCMB. Measurement of X-ray diffraction (XRD) (manufactured and sold
by Rigaku Corporation; trade name: RINT) with respect to the mixed
particles identifies that the mixed particles are composed solely
of MCMB. Examination under a scanning electron microscope (SEM)
(manufactured and sold by JEOL LTD.; trade name: JSM-5600LV)
ascertains that the mixed particles include spherical particles and
pulverized particles.
[0030] With respect to the negative electrode 14, a negative
electrode having an anode mixture layer 14B having a volume density
controlled to fall within the range of from 1.70 to 1.90 g/cm.sup.3
prior to being subjected to charge and discharge processes, i.e., a
so-called high volume-density negative electrode is used. In cell
ready for shipping, the anode mixture layer 14B in the completely
discharged state preferably has a volume density in the range of
from 1.50 to 1.90 g/cm.sup.3. The completely discharged state means
a state in which the battery has been discharged at a
constant-current of 0.2 C until the voltage becomes 3.0 V. Cells
ready for shipping include, for example, a cell which has been once
charged to a predetermined voltage, a cell which has been charged
once and discharged to a voltage suitable for shipping, and a cell
which has not yet been charged and discharged and which is put on
the market as a product.
[0031] The separator 15 is composed of, for example, a porous film
made of a polyolefin resin material, such as polypropylene or
polyethylene, or a porous film made of an inorganic material, such
as ceramic nonwoven fabric, and a separator composed of two or more
porous films stacked into a laminated structure may be used.
[0032] The polymer compound layer 16 has a uniform thickness, and
includes an electrolytic solution and a polymer compound retaining
the electrolytic solution, and it is in a so-called gel form. The
electrolytic solution includes an electrolyte salt and a solvent
dissolving the electrolyte salt. Examples of electrolyte salts
include lithium salts, such as LiPF.sub.6, LiClO.sub.4, LiBF.sub.4,
LiN(CF.sub.3SO.sub.2).sub.2, LiN(C.sub.2F.sub.5SO.sub.2).sub.2, and
LiAsF.sub.6. The electrolyte salts may be used individually or in
combination.
[0033] Examples of solvents include non-aqueous solvents, e.g.,
carbonic ester solvents, such as ethylene carbonate, propylene
carbonate, vinylene carbonate, dimethyl carbonate, ethylmethyl
carbonate, and diethyl carbonate; ether solvents, such as
1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,2-diethoxyethane,
tetrahydrofuran, and 2-methyltetrahydrofuran; lactone solvents,
such as .gamma.-butyrolactone, .gamma.-valerolactone,
.delta.-valerolactone, and .epsilon.-caprolactone; nitrile
solvents, such as acetonitrile; sulfolane solvents; phosphoric
acid; phosphate solvents; and pyrrolidone. The solvents may be used
individually or in combination.
[0034] For improving the properties, an additive, e.g., a cyclic
carbonic ester derivative, such as 4-fluoro-1,3-dioxolan-2-one or
4,5-difluoro-1,3-dioxolan-2-one, may be added to the solvent.
[0035] With respect to the polymer compound, a fluorine polymer
compound is used. An example of the fluorine polymer compound
include a polymer compound including repeating units derived from
vinylidene fluoride. Specific examples include polyvinylidene
fluoride and a copolymer of vinylidene fluoride and
hexafluoropropylene. Other fluorine polymer compounds may be used.
More specifically, for example, polytetrafluoroethylene and
derivatives thereof can be used individually or in combination.
Polychlorotrifluoroethylene (PCTFE), polyvinyl fluoride (PVF), a
perfluoroalkoxy fluororesin (PFA), a
tetrafluoroethylene-hexafluoropropylene copolymer (FEP), an
ethylene-tetrafluoroethylene copolymer (ETFE), an
ethylene-chlorotrifluoroethylene copolymer (ECTFE), and the like
may be used individually or in combination.
[0036] A polymer compound having bonding force other than the
fluorine polymer compound may be used. Specifically, for example,
polyacrylonitrile, polyethylene oxide, polymethyl methacrylate,
polyvinyl chloride, a styrene-butadiene rubber, and derivatives
thereof may be used individually or in combination.
[0037] The polymer compound layer 16 is formed by, for example,
forming a porous fluorine polymer compound on the separator 15 and
then allowing the porous fluorine polymer to retain an electrolytic
solution. The porous fluorine polymer compound may be formed by
applying a solution obtained by dissolving a fluorine polymer
compound in a solvent, such as N-methyl-2-pyrrolidone (NMP), to
both sides of the separator 15 and drying the solution applied.
[0038] It is preferred that the polymer compound layer 16 has a
peel strength of 5 mN/mm or more with the electrode and the
separator. A peel strength can be measured by, for example, pulling
at a rate of 100 mm/min the negative electrode and separator bonded
with each other so that the separator peels off the negative
electrode and determining this peel strength by means of a digital
force gauge (manufactured and sold by IMADA CO., LTD.).
[0039] Also when the polymer compound layer 16 contains as filler a
compound having a high heat resistance, such as Al.sub.2O.sub.3,
SiO.sub.2, TiO.sub.2, or BN (boron nitride), the polymer compound
layer maintains its bonding properties and hence achieves the
similar effect.
[0040] Next, an example of the method for producing a non-aqueous
electrolyte battery according to an embodiment of the present
application is described.
[0041] A cathode mixture layer 13B is formed on a positive
electrode current collector 13A to prepare a positive electrode 13.
The cathode mixture layer 13B is formed by, for example, mixing
together a cathode active material, a conductor, and a binder and
dispersing the resultant mixture in a solvent, such as
N-methyl-2-pyrrolidone (NMP), to form a paste, and then applying
the paste to the positive electrode current collector 13A and
drying the paste and subjecting it to compression molding.
[0042] An anode mixture layer 14B is formed on a negative electrode
current collector 14A to prepare a negative electrode 14. The anode
mixture layer 14B is formed by, for example, mixing together an
anode active material and a binder and dispersing the resultant
mixture in a solvent, such as N-methyl-2-pyrrolidone (NMP), to form
a paste, and then applying the paste to the negative electrode
current collector 14A and drying the paste and subjecting it to
compression molding. Then, a positive electrode lead 11 is fitted
to the positive electrode current collector 13A, and a negative
electrode lead 12 is fitted to the negative electrode current
collector 14A.
[0043] A solution obtained by dissolving a fluorine polymer
compound in a solvent, such as N-methyl-2-pyrrolidone (NMP), is
applied to both sides of a separator 15, and the resultant
separator is immersed into a poor solvent, such as water, and then
dried using hot air or the like to form a porous fluorine polymer
compound layer on both sides of the separator 15.
[0044] The positive electrode 13, separator 15, negative electrode
14, and separator 15 are stacked on one another and spirally wound
together, and a protective tape 17 is bonded with the outermost
winding layer to form a spirally-wound electrode structure 10, and
then the electrode structure is disposed between a folded casing
member 1, and three sides of the outer edge portion of the casing
member 1 are heat-sealed under a reduced pressure. In this
instance, a bonding film 2 is inserted into portions between the
positive electrode lead 11 and the casing member 1 and between the
negative electrode lead 12 and the casing member 1.
[0045] Then, an electrolytic solution is injected into the
resultant casing member, and the remaining one side of the outer
edge portion is heat-sealed under a reduced pressure to
hermetically seal the casing member. The casing member is finally
hot-pressed to obtain a non-aqueous electrolyte battery according
to an embodiment. Upon heating for the hot pressing, part of or
whole of the porous fluorine polymer compound becomes in a gel
form, thus forming a polymer compound layer 16.
EXAMPLES
[0046] The present application will be described in more detail
with reference to the following Examples, which should not be
construed as limiting the scope of the present application.
[0047] Studies on optimum negative electrode
Sample 1
[0048] As a negative electrode material, mixed particles including
spherical graphite having an average particle size of 31.7 .mu.m
and non-spherical graphite having an average particle size of 7.2
.mu.m mixed in a 1:1 mass ratio, and having particle size
distribution such that D10 is 4.1 .mu.m, D50 is 10.5 .mu.m, D90 is
29.6 .mu.m were prepared. To the mixed particles was added PVdF as
a binder, and the resultant mixture was dispersed in NMP as a
solvent, and the dispersion was applied to a Cu foil and dried,
followed by pressing so that the volume density of the anode
mixture layer became 1.85 g/cm.sup.3. When the volume density did
not become 1.85 g/cm.sup.3, pressing was controlled so that the
volume density was close to that value. Pressing was conducted to
achieve a volume density of 1.82 g/cm.sup.3, thus preparing a
negative electrode of sample 1.
Sample 2
[0049] A negative electrode of sample 2 was prepared in the same
manner as in sample 1, except that, as a negative electrode
material, mixed particles including spherical graphite having an
average particle size of 31.7 .mu.m and non-spherical graphite
having an average particle size of 11.7 .mu.m mixed in a 1:1 mass
ratio, and having particle size distribution such that D10 is 5.5
.mu.m, D50 is 15.2 .mu.m, and D90 is 31.4 .mu.m were prepared, and
that the anode mixture layer had a volume density of 1.85
g/cm.sup.3.
Sample 3
[0050] A negative electrode of sample 3 was prepared in the same
manner as in sample 1, except that, as a negative electrode
material, mixed particles including spherical graphite having an
average particle size of 31.7 .mu.m and non-spherical graphite
having an average particle size of 14.1 .mu.m mixed in a 1:1 mass
ratio, and having particle size distribution such that D10 is 8.5
.mu.m, D50 is 21.9 .mu.m, and D90 is 37.8 .mu.m were prepared, and
that the anode mixture layer had a volume density of 1.85
g/cm.sup.3.
Sample 4
[0051] A negative electrode of sample 4 was prepared in the same
manner as in sample 1, except that, as a negative electrode
material, mixed particles including spherical graphite having an
average particle size of 31.7 .mu.m and non-spherical graphite
having an average particle size of 20.3 .mu.m mixed in a 1:1 mass
ratio, and having particle size distribution such that D10 is 9.7
.mu.m, D50 is 23.6 .mu.m, and D90 is 41.5 .mu.m were prepared, and
that the anode mixture layer had a volume density of 1.85
g/cm.sup.3.
Sample 5
[0052] A negative electrode of sample 5 was prepared in the same
manner as in sample 1, except that, as a negative electrode
material, mixed particles including spherical graphite having an
average particle size of 42.1 .mu.m and non-spherical graphite
having an average particle size of 7.2 .mu.m mixed in a 1:1 mass
ratio, and having particle size distribution such that D10 is 4.1
.mu.m, D50 is 11.6 .mu.m, and D90 is 48.6 .mu.m were prepared, and
that the anode mixture layer had a volume density of 1.79
g/cm.sup.3.
Sample 6
[0053] A negative electrode of sample 6 was prepared in the same
manner as in sample 1, except that, as a negative electrode
material, mixed particles including spherical graphite having an
average particle size of 42.1 .mu.m and non-spherical graphite
having an average particle size of 11.7 .mu.m mixed in a 1:1 mass
ratio, and having particle size distribution such that D10 is 5.7
.mu.m, D50 is 14.8 .mu.m, and D90 is 48.7 .mu.m were prepared.
Sample 7
[0054] A negative electrode of sample 7 was prepared in the same
manner as in sample 1, except that, as a negative electrode
material, mixed particles including spherical graphite having an
average particle size of 42.1 .mu.m and non-spherical graphite
having an average particle size of 14.1 .mu.m mixed in a 1:1 mass
ratio, and having particle size distribution such that D10 is 7.4
.mu.m, D50 is 21.7 .mu.m, and D90 is 48.8 .mu.m were prepared, and
that the anode mixture layer had a volume density of 1.82
g/cm.sup.3.
Sample 8
[0055] A negative electrode of sample 8 was prepared in the same
manner as in sample 1, except that, as a negative electrode
material, mixed particles including spherical graphite having an
average particle size of 42.1 .mu.m and non-spherical graphite
having an average particle size of 20.3 .mu.m mixed in a 1:1 mass
ratio, and having particle size distribution such that D10 is 9.8
.mu.m, D50 is 24.7 .mu.m, and D90 is 49.2 .mu.m were prepared, and
that the anode mixture layer had a volume density of 1.80
g/cm.sup.3.
Sample 9
[0056] A negative electrode of sample 9 was prepared in the same
manner as in sample 1, except that, as a negative electrode
material, mixed particles including spherical graphite having an
average particle size of 51.3 .mu.m and non-spherical graphite
having an average particle size of 11.7 .mu.m mixed in a 1:1 mass
ratio, and having particle size distribution such that D10 is 5.7
.mu.m, D50 is 15.7 .mu.m, and D90 is 57.7 .mu.m were prepared, and
that the anode mixture layer had a volume density of 1.75
g/cm.sup.3.
Sample 10
[0057] A negative electrode of sample 10 was prepared in the same
manner as in sample 1, except that, as a negative electrode
material, mixed particles including spherical graphite having an
average particle size of 51.3 .mu.m and non-spherical graphite
having an average particle size of 14.1 .mu.m mixed in a 1:1 mass
ratio, and having particle size distribution such that D10 is 7.5
.mu.m, D50 is 23.3 .mu.m, and D90 is 57.8 .mu.m were prepared, and
that the anode mixture layer had a volume density of 1.73
g/cm.sup.3.
Evaluation of Capacity
[0058] Coin cells were individually prepared using the negative
electrodes of samples 1 to 10, and a capacity of each coin cell was
measured.
[0059] With respect to the positive electrode, there was used a
positive electrode obtained by mixing together lithium cobaltate,
ketjen black, and polyvinylidene fluoride (PVdF) in a 7:2:1 ratio,
and dispersing the resultant mixture in N-methyl-2-pyrrolidone
(NMP) and applying the dispersion to an Al foil and then drying the
dispersion applied. The coating weight was adjusted to 1.5 times
the coating weight in the negative electrode.
[0060] The positive electrode and negative electrode were
individually punched into discs, and the resultant positive
electrode and negative electrode and a separator composed of a
microporous polyethylene film were stacked on one another in the
order of the positive electrode, separator, and negative electrode,
and the resultant stacked structure was placed in a battery
can.
[0061] Then, an electrolytic solution, which was obtained by
dissolving LiPF.sub.6 in a mixed solvent including ethylene
carbonate and diethyl carbonate in a 3:7 mass ratio so that the
concentration became 1.0 mol/l, was injected into the battery can,
followed by caulking of the battery can through an insulating
gasket, thereby obtaining a coin cell.
[0062] With respect to the coin cell obtained, a constant-current
and constant-voltage charging at a charge current of 1 C was
conducted at an upper limit voltage of 4.2 V for 2 hours, and then
a 0.2 C constant-current discharging was conducted until the
voltage became a cut-off voltage of 3.0 V, and a discharge capacity
was measured, and the capacity was evaluated using a value
determined from the following formula.
[0063] Formula:
(Initial discharge capacity)/(Theoretical
capacity).times.100(%)
[0064] The results of measurement are shown in Table 1.
TABLE-US-00001 TABLE 1 Particle size distribution (Initial
discharge Spherical Non-spherical of mixed Volume
capacity)/(Theoretical Negative graphite graphite particles (.mu.m)
density capacity) electrode (.mu.m) (.mu.m) D10 D50 D90
(g/cm.sup.3) (%) Sample 1 31.7 7.2 4.1 10.5 29.6 1.82 92 Sample 2
31.7 11.7 5.5 15.2 31.4 1.85 92 Sample 3 31.7 14.1 8.5 21.9 37.8
1.85 93 Sample 4 31.7 20.3 9.7 23.6 41.5 1.85 92 Sample 5 42.1 7.2
4.1 11.6 48.6 1.79 88 Sample 6 42.1 11.7 5.7 14.8 48.7 1.85 88
Sample 7 42.1 14.1 7.4 21.7 48.8 1.82 87 Sample 8 42.1 20.3 9.8
24.7 49.2 1.80 87 Sample 9 51.3 11.7 5.7 15.7 57.7 1.75 84 Sample
10 51.3 14.1 7.5 23.3 57.8 1.73 84
[0065] As can be seen from Table 1, samples 2 to 4 achieve
excellent properties.
Studies on Effect of Polymer Compound Layer
[0066] Using the negative electrode of sample 3, a laminate cell
(A) and a laminate cell (B) were individually prepared as
follows.
Laminate cell (A)
[0067] With respect to the positive electrode, there was used a
positive electrode obtained by mixing together lithium cobaltate,
ketjen black, and PVdF in a 7:2:1 (mass ratio), and dispersing the
resultant mixture in NMP and applying the dispersion to both sides
of an Al foil and then drying the dispersion applied. The coating
amount was adjusted to 1.5 times the coating amount in the negative
electrode.
[0068] With respect to the negative electrode, as with the negative
electrode of sample 3, there was used a negative electrode obtained
by adding PVdF as a binder to the mixed particles prepared in the
same manner as in sample 3, and dispersing the resultant mixture in
NMP as a solvent and applying the dispersion to both sides of a Cu
foil and drying the dispersion applied, and then pressing the
resultant foil so that the volume density of the anode mixture
layer became 1.85 g/cm.sup.3.
[0069] With respect to the separator, a microporous polyethylene
film was used. A solution obtained by dissolving PVdF in NMP so
that the concentration became 15 wt % was applied to both sides of
the separator and dried to form porous polyvinylidene fluoride
having a thickness of 5 .mu.m on the both sides of the
separator.
[0070] A terminal was attached to each of the positive electrode
and negative electrode prepared as described above, and then the
positive electrode and negative electrode were put together through
the separator coated with a porous fluororesin, and they were
spirally wound together in the longitudinal direction to prepare a
battery element.
[0071] The prepared battery element was sandwiched with a casing
member composed of a laminate film, and three sides of the casing
member were heat-sealed. With respect to the casing member, there
was used a moisture-proof aluminum laminate film including a nylon
film having a thickness of b 25 .mu.m, an aluminum foil having a
thickness of 40 .mu.m, and a polypropylene film having a thickness
of 30 .mu.m, which were stacked on one another in this order from
the outermost layer.
[0072] Then, an electrolytic solution was injected into the
resultant casing member containing the battery element, and the
remaining one side was heat-sealed under a reduced pressure to
hermetically seal the casing member. With respect to the
electrolytic solution, there was used an electrolytic solution
obtained by dissolving LiPF.sub.6 in a mixed solvent comprising
ethylene carbonate and diethyl carbonate in a 3:7 mass ratio so
that the concentration became 1 mol/l. The casing member containing
the battery element was sandwiched between iron plates and heated
at 70.degree. C. for 3 minutes to bond together the positive
electrode, negative electrode, and separator through the porous
polyvinylidene fluoride, thereby preparing a laminate cell (A).
Laminate Cell (B)
[0073] A laminate cell (B) was prepared in the same manner as in
the laminate cell (A), except that no porous polyvinylidene
fluoride was formed on both sides of the separator.
[0074] With respect to each of the laminate cells (A) and (B), a
charging and discharging test was conducted, and a capacity
retention ratio and a thickness increase ratio were measured.
Measurement of Capacity Retention Ratio
[0075] A capacity retention ratio was measured by a method in which
one cycle of charge and discharge operation was conducted and then
300 cycles of charge and discharge operations were conducted, and a
discharge capacity in the 1st cycle and a discharge capacity in the
300th cycle were measured and a capacity retention ratio was
determined from the following formula.
[0076] Formula:
Capacity retention ratio (%)=(Discharge capacity in 300th
cycle)/(Discharge capacity in 1st cycle).times.100(%)
[0077] With respect to the charging, a constant-current and
constant-voltage charging at a charge current of 1.0 C was
conducted at an upper limit voltage of 4.2 V for 2 hours. With
respect to the discharging, a 1.0 C constant-current discharging
was conducted until the voltage became a cut-off voltage of 3.0
V
Measurement of Thickness Increase Ratio
[0078] Under the same conditions as those in the measurement of
capacity retention ratio, 300 cycles of charge and discharge
operations were conducted, and subsequently a thickness of the
battery in the charged state in the 1st cycle and a thickness of
the battery in the charged state in the 300th cycle were measured,
and a thickness increase ratio was determined from the following
formula.
[0079] Formula:
Thickness increase ratio (%)=((Thickness after discharging in 300th
cycle)-(Thickness after discharging in 1st cycle))/(Thickness after
discharging in 1st cycle).times.100(%)
[0080] A thickness of the battery was measured by means of
Digimatic Indicator (manufactured and sold by Mitutoyo Corporation)
in a state such that the battery was sandwiched between two
parallel plates so that a difference in thickness was not caused
between the measurement sites.
[0081] The results of measurements are shown in Table 2.
TABLE-US-00002 TABLE 2 Capacity Thickness increase Polyvinylidene
retention ratio ratio fluoride (%) (%) Laminate cell (A) Formed 83
3 Laminate cell (B) Not formed 58 11
[0082] As can be seen from Table 2, the laminate cell (A), in which
porous polyvinylidene fluoride was formed on both sides of the
separator, achieved more excellent capacity retention ratio and
thickness increase ratio than those of the laminate cell (B). The
similar results are probably obtained with respect to the laminate
cells prepared using the negative electrodes of samples 2 and
4.
[0083] Studies on effect according to composition of electrolytic
solution and the like
[0084] Experiments were made to check whether a similar effect was
obtained when the composition of the electrolytic solution was
changed or an additive was further added. Laminate cells (C) to (K)
shown below are the same as the laminate cell (A), except that the
composition of the electrolytic solution is changed or an additive
is further added, and, in these laminate cells, a bonding layer
composed of polyvinylidene fluoride (PVdF) is formed between the
electrode and the separator.
Laminate Cell (C)
[0085] A laminate cell (C) was prepared in the same manner as in
the laminate cell (A) except that an electrolytic solution obtained
by dissolving LiPF.sub.6 in a mixed solvent including ethylene
carbonate (EC) and ethylmethyl carbonate (EMC) in a 30:70 mass
ratio so that the concentration became 1 mol/l was used.
Laminate Cell (D)
[0086] A laminate cell (D) was prepared in the same manner as in
the laminate cell (A), except that an electrolytic solution
obtained by dissolving LiPF.sub.6 in a mixed solvent including
ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 30:70
mass ratio so that the concentration became 1 mol/l was used.
Laminate Cell (E)
[0087] A laminate cell (E) was prepared in the same manner as in
the laminate cell (A), except that an electrolytic solution
obtained by dissolving LiPF.sub.6 in a mixed solvent including
ethylene carbonate (EC), diethyl carbonate (DEC), and propylene
carbonate (PC) in a 25:70:5 mass ratio so that the concentration
became 1 mol/l was used.
Laminate Cell (F)
[0088] A laminate cell (F) was prepared in the same manner as in
the laminate cell (A), except that an electrolytic solution
obtained by dissolving LiPF.sub.6 in a mixed solvent including
ethylene carbonate (EC), ethylmethyl carbonate (EMC), and propylene
carbonate (PC) in a 25:70:5 mass ratio so that the concentration
became 1 mol/l was used.
Laminate Cell (G)
[0089] A laminate cell (G) was prepared in the same manner as in
the laminate cell (A), except that an electrolytic solution
obtained by adding 4-fluoro-1,3-dioxolan-2-one (FEC) in an amount
of 1.0 wt % to a mixed solvent including ethylene carbonate (EC)
and diethyl carbonate (DEC) in a 30:70 mass ratio and dissolving
LiPF.sub.6 in the resultant solvent so that the concentration
became 1 mol/l was used.
Laminate Cell (H)
[0090] A laminate cell (H) was prepared in the same manner as in
the laminate cell (A), except that an electrolytic solution
obtained by adding 4-fluoro-1,3-dioxolan-2-one (FEC) in an amount
of 1.0 wt % to a mixed solvent including ethylene carbonate (EC),
diethyl carbonate (DEC), and propylene carbonate (PC) in a 25:70:5
mass ratio and dissolving LiPF.sub.6 in the resultant solvent so
that the concentration became 1 mol/l was used.
Laminate Cell (I)
[0091] A laminate cell (I) was prepared in the same manner as in
the laminate cell (A), except that an electrolytic solution
obtained by adding 4-fluoro-1,3-dioxolan-2-one (FEC) in an amount
of 1.0 wt % to a mixed solvent including ethylene carbonate (EC),
ethylmethyl carbonate (EMC), and propylene carbonate (PC) in a
25:70:5 mass ratio and dissolving LiPF.sub.6 in the resultant
solvent so that the concentration became 1 mol/l was used.
Laminate Cell (J)
[0092] A laminate cell (J) was prepared in the same manner as in
the laminate cell (A), except that an electrolytic solution
obtained by dissolving LiPF.sub.6 in a mixed solvent including
ethylene carbonate (EC), diethyl carbonate (DEC), and ethylmethyl
carbonate (EMC) in a 30:35:35 mass ratio so that the concentration
became 1 mol/l was used.
Laminate Cell (K)
[0093] A laminate cell (K) was prepared in the same manner as in
the laminate cell (A), except that an electrolytic solution
obtained by adding 4-fluoro-1,3-dioxolan-2-one (FEC) in an amount
of 1.0 wt % to a mixed solvent including ethylene carbonate (EC),
diethyl carbonate (DEC), and ethylmethyl carbonate (EMC) in a
30:35:35 mass ratio and dissolving LiPF.sub.6 in the resultant
solvent so that the concentration became 1 mol/l was used.
[0094] With respect to each of the laminate cells (C) to (K)
prepared, a capacity retention ratio and a thickness increase ratio
after the 300 cycles were measured in the same manner as in the
laminate cell (A).
[0095] The results of measurements for the laminate cells (C) to
(K) and laminate cell (A) are shown in Table 3.
TABLE-US-00003 TABLE 3 Capacity Thickness Formulation of
electrolytic FEC retention increase solution (Mass ratio) (wt ratio
ratio EC DEC EMC DMC PC %) (%) (%) Laminate 30 70 0 0 0 0 83 3.0
cell (A) Laminate 30 0 70 0 0 0 80 4.2 cell (C) Laminate 30 0 0 70
0 0 79 4.6 cell (D) Laminate 25 70 0 0 5 0 81 4.1 cell (E) Laminate
25 0 70 0 5 0 78 4.9 cell (F) Laminate 30 70 0 0 0 1 86 2.2 cell
(G) Laminate 25 70 0 0 5 1 83 3.2 cell (H) Laminate 25 0 70 0 5 1
82 3.8 cell (I) Laminate 30 35 35 0 0 0 81 4.0 cell (J) Laminate 30
35 35 0 0 1 83 3.3 cell (K) EC: Ethylene carbonate DEC: Diethyl
carbonate EMC: Ethylmethyl carbonate DMC: Dimethyl carbonate PC:
Propylene carbonate FEC: 4-Fluoro-1,3-dioxolan-2-one
[0096] As can be seen from Table 3, the laminate cells having
various formulations of electrolytic solution achieved excellent
results. In addition, the above results have ascertained that the
use of an additive, such as 4-fluoro-1,3-dioxolan-2-one (FEC),
possibly further improves the properties. The reason that expansion
was suppressed when 4-fluoro-1,3-dioxolan-2-one (FEC) was added
resides in that a film is formed on the surface of the negative
electrode during the initial charging to suppress decomposition of
the electrolytic solution (gas generation) on the surface of the
charged negative electrode. When the thickness increase ratio is 9%
or less, a capacity retention ratio of 70% or more can be
expected.
[0097] Change of negative electrode volume density due to charge
and discharge operations
[0098] Test Example
[0099] With respect to the negative electrode, as with the negative
electrode of sample 3, there was used a negative electrode obtained
by adding PVdF as a binder to the mixed particles prepared in the
same manner as in sample 3, and dispersing the resultant mixture in
NMP as a solvent and applying the dispersion to both sides of a Cu
foil and drying the dispersion applied, and then pressing the
resultant foil so that the volume density of the anode mixture
layer became 1.80 g/cm.sup.3. Using this negative electrode, a
laminate cell was prepared in the same manner as in the laminate
cell (A).
[0100] With respect to the laminate cell prepared, one cycle of
charge and discharge operation at an upper limit voltage of 4.2 V,
4.3 V, or 4.4 V was conducted, and a volume density of the anode
mixture layer in the completely discharged state was measured. With
respect to the charging, a constant-current and constant-voltage
charging at a charge current of 1.0 C was conducted at a charge
voltage of 4.2 V, 4.3 V, or 4.4 V for 2 hours. With respect to the
discharging, a 0.2 C constant-current discharging was conducted
until the voltage became a cut-off voltage of 3.0 V.
[0101] The results of measurement are shown in Table 4.
TABLE-US-00004 TABLE 4 Volume density of anode mixture layer Volume
density of anode of electrode Charge mixture layer in completely
just prepared voltage discharged state (g/cm.sup.3) (V)
(g/cm.sup.3) Test example 1.80 4.2 1.64 4.3 1.61 4.4 1.59
[0102] As can be seen from Table 4, as the charge voltage increases
and the electrode more markedly expands, the electrode hardly
shrinks in the complete discharge until the voltage becomes 3 V, so
that the volume density tends to be smaller.
[0103] According to embodiments, the volume density of the
electrode mixture layer is high, and the battery can be prevented
from suffering deformation even when using a laminate film as a
casing member, thus achieving excellent battery properties.
Further, in the present application, the volume density of the
electrode mixture layer can be increased, making it possible to
produce a battery having high energy density.
[0104] The present application is not limited to the above
embodiment of the present application, and can be changed or
modified as long as the non-aqueous electrolyte battery of the
present application can be obtained. For example, in the
non-aqueous electrolyte battery according to an embodiment, with
respect to the shape of cylinder, rectangle, or the like, there is
no particular limitation, and the battery may be of various sizes,
such as a thin type or a large size. Furthermore, the non-aqueous
electrolyte battery is not limited to the secondary battery, and
can be applied to other batteries, such as a primary battery.
[0105] It should be understood that various changes and
modifications to the presently preferred embodiments described
herein will be apparent to those skilled in the art. Such changes
and modifications can be made without departing from the spirit and
scope of the present subject matter and without diminishing its
intended advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
* * * * *