U.S. patent application number 16/086188 was filed with the patent office on 2020-09-24 for electrode for battery, battery having electrode and method for manufacturing electrode and battery having electrode.
This patent application is currently assigned to NEC Corporation. The applicant listed for this patent is NEC CORPORATION. Invention is credited to Makihiro OTOHATA, Shinya SUDO, Noboru YOSHIDA.
Application Number | 20200303743 16/086188 |
Document ID | / |
Family ID | 1000004902885 |
Filed Date | 2020-09-24 |
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United States Patent
Application |
20200303743 |
Kind Code |
A1 |
YOSHIDA; Noboru ; et
al. |
September 24, 2020 |
ELECTRODE FOR BATTERY, BATTERY HAVING ELECTRODE AND METHOD FOR
MANUFACTURING ELECTRODE AND BATTERY HAVING ELECTRODE
Abstract
Provided is an electrode for a battery which effectively
suppress a short circuit between a positive electrode and a
negative electrode at high temperature of the battery. The
electrode includes a current collector 110, an active material
layer 111 formed on at least one side of the current collector 110
and an insulating layer 112 formed on the surface of the active
material layer 111. The electrode was formed so that peeling occurs
between the current collector 110 and the active material layer 111
and the peeling strength was 10 mN/mm or more when a 90.degree.
peeling test was performed at a peeling rate of 100/min.
Inventors: |
YOSHIDA; Noboru; (US)
; OTOHATA; Makihiro; (Tokyo, JP) ; SUDO;
Shinya; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NEC CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
NEC Corporation
Tokyo
JP
|
Family ID: |
1000004902885 |
Appl. No.: |
16/086188 |
Filed: |
May 18, 2017 |
PCT Filed: |
May 18, 2017 |
PCT NO: |
PCT/JP2017/018650 |
371 Date: |
September 18, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/623 20130101;
H01M 2/1673 20130101; H01M 10/0525 20130101; H01M 2004/027
20130101; H01M 4/0433 20130101; H01M 2004/028 20130101; H01M 4/364
20130101; H01M 2004/021 20130101; H01M 4/366 20130101; H01M 4/661
20130101; H01M 10/0569 20130101 |
International
Class: |
H01M 4/66 20060101
H01M004/66; H01M 4/62 20060101 H01M004/62; H01M 4/04 20060101
H01M004/04; H01M 4/36 20060101 H01M004/36; H01M 10/0569 20060101
H01M010/0569; H01M 10/0525 20060101 H01M010/0525; H01M 2/16
20060101 H01M002/16 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2016 |
JP |
2016-104345 |
Claims
1. An electrode for a battery comprising: a current collector, an
active material layer formed on at least one surface of the current
collector, an insulating layer formed on a surface of the active
material layer, and wherein peeling occurs between the current
collector and the active material layer and a peeling strength
thereof is 10 mN/mm or more when a 90.degree. peeling test is
carried out at a peeling rate of 100 mm/min.
2. The electrode according to claim 1, wherein the current
collector and the active material layer are the current collector
for a positive electrode.
3. The electrode according to claim 2, wherein the active material
layer for the positive electrode includes polyvinylidene fluoride
as a binder.
4. The electrode according to claim 1, wherein the current
collector and the active material layer are the current collector
and the active material layer for a negative electrode.
5. The electrode according to claim 4, wherein the active material
layer for the negative electrode includes at least one of styrene
butadiene rubber, polyacrylic acid and polyvinylidene fluoride as a
binder.
6. The electrode according to claim 1, wherein the active material
layer includes N-methyl-2-pyrrolidone.
7. A battery comprising: at least one positive electrode, at least
one negative electrode disposed to face the positive electrode, and
wherein at least one of the positive electrode and the negative
electrode includes a current collector, an active material layer
formed on at least one surface of the current collector, and an
insulating layer formed on a surface of the active material layer,
and peeling occurs between the current collector and the active
material layer and a peeling strength thereof is 10 mN/mm or more
when a 90.degree. peeling test is carried out at a peeling rate of
100 mm/min.
8. The battery according to claim 7, wherein the positive electrode
and the negative electrode are disposed to face each other with the
insulating layer interposed therebetween.
9. The battery according to claim 7, further comprising a separator
disposed between the positive electrode and the negative
electrode.
10. The battery according to claim 7, wherein the active material
layer includes polyvinylidene fluoride as a binder.
11. The battery according to claim 7, wherein the active material
layer includes N-methyl-2-pyrrolidone.
12. A method for manufacturing an electrode for a battery, the
method comprising; forming an active material layer on at least one
surface of a current collector, forming an insulating layer such
that the insulating layer is finally laminated on a surface of the
active material layer, and wherein at least one of a material of
the active material layer, a formation condition of the active
material layer, a material of the insulating layer and a formation
condition of the insulating layer is determined such that peeling
occurs between the current collector and the active material layer
and a peeling strength thereof is 10 mN/mm or more when a
90.degree. peeling test is carried out at a peeling rate of 100
mm/min.
13. The method for manufacturing the electrode according to claim
12, wherein the step of forming the active material layer
comprises: applying a mixture for the active material layer in
which an active material and a binder are dispersed in a solvent,
drying the mixture for the active material layer after the mixture
is applied, and compression-molding the mixture for the active
material layer after the mixture is dried, and wherein the step of
forming the insulating layer comprises: applying a mixture for the
insulating layer in which an insulating material and a binder are
dispersed in a solvent, drying the mixture for the insulating layer
after the mixture is applied, and compression-molding the mixture
for the insulating layer after the mixture is dried.
14. The method for manufacturing the electrode according to claim
13, wherein the step of applying the mixture for the active
material layer, the step of drying the mixture for the active
material layer, the step of compression-molding the mixture for the
active material layer, the step of applying the mixture for the
insulating layer, the step of drying the mixture for the insulating
layer and the step of compression-molding the mixture for the
insulating layer are carried out in this order.
15. The method for manufacturing the electrode according to claim
13, wherein the step of applying the mixture for the active
material layer, the step of drying the mixture for the active
material layer, the step of applying the mixture for the insulating
layer and the step of drying the mixture for the insulating layer
are carried out in this order, and wherein the step of
compression-molding the mixture for the active material layer and
the step of compression-molding the mixture for the insulating
layer are carried out simultaneously after the step of drying the
mixture for the insulating layer.
16. The method for manufacturing the electrode according to claim
13, wherein the step of applying the mixture for the active
material layer and the step of applying the mixture for the
insulating layer are carried out in this order, the step of drying
the mixture for the active material layer and the step of drying
the mixture for the insulating layer are carried out simultaneously
after the step of applying the mixture for the insulating layer,
and the step of compression-molding the mixture for the active
material layer and the step of compression-molding the mixture for
the insulating layer are carried out simultaneously thereafter.
17. The method for manufacturing the electrode according to claim
13, wherein the mixture for the active material layer includes
polyvinylidene fluoride as the binder.
18. The method for manufacturing the electrode according to claim
13, wherein the mixture for the active material layer includes
N-methyl-2-pyrrolidone as the solvent.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electrode for a battery
and a method for manufacturing the electrode, and in particular, to
an electrode having an insulating layer on an active material layer
and the like.
BACKGROUND ART
[0002] Secondary batteries are widely used as power sources for
portable electronic devices such as smart phones, tablet computers,
notebook computers, digital cameras, and the like. In addition,
secondary batteries have been expanding their application as power
sources for electric vehicles and household power supplies. Among
them, since lithium ion secondary batteries are high in energy
density and light in weight, they are indispensable energy storage
devices for current life.
[0003] A conventional battery including a secondary battery has a
structure in which a positive electrode and a negative electrode,
which are electrodes, are opposed to each other with a separator
interposed therebetween. The positive electrode and the negative
electrode each have a sheet-like current collector and active
material layers formed on both sides of the current collector. The
separator serves to prevent a short circuit between the positive
electrode and the negative electrode and to effectively move ions
between the positive electrode and the negative electrode.
Conventionally, a polyolefin system microporous separator made of
polypropylene or polyethylene material is mainly used as the
separator. However, the melting points of polypropylene and
polyethylene materials are generally 110.degree. C. to 160.degree.
C. Therefore, when a polyolefin system separator is used for a
battery with a high energy density, the separator melts at a high
temperature of the battery, and a short circuit may occur between
the electrodes in a large area.
[0004] Therefore, in order to improve the safety of the battery, it
has been proposed to form an insulating layer which is a substitute
for a separator in at least one of the positive electrode and the
negative electrode. For example, Patent Literature 1 (Japanese
Patent Laid-Open No. 2009-43641) discloses a negative electrode for
a battery in which a negative electrode active material layer is
formed on a surface of a negative electrode current collector, and
a porous layer is formed on the surface of the negative electrode
active material layer. Similarly, Patent Literature 2 (Japanese
Patent Laid-Open No. 2009-301765) discloses an electrode in which a
porous protective film is provided on a surface of an active
material layer formed on a current collector. Patent Literature 3
(Japanese Patent No. 5454295) discloses a method in which two or
more paste layers are overlaid on a core material (current
collector) of a positive electrode or a negative electrode, and
then the paste layer is dried to form a positive electrode plate or
a negative electrode.
[0005] Generally, the active material layer is formed on the
current collector as follows. First, a long current collector foil
wound on a roll is prepared as a current collector and a slurry for
forming an active material layer is prepared. The slurry for
forming the active material layer is a slurry obtained by
dispersing fine particles of an active material and a binder in a
solvent. Then, while feeding the current collector foil from the
roll, the slurry for forming the active material layer is applied
to the surface of the current collector foil by means of a die
coater or the like. After applying the slurry for forming active
material layer, the slurry for forming active material layer is
dried and compression-molded, whereby the active material layer is
formed on the surface of the current collector.
[0006] The insulating layer on the surface of the active material
layer can be formed in the same manner as the formation of the
active material layer. That is, a slurry for forming an insulating
layer in which fine particles of an insulating material and a
binder are dispersed in a solvent is applied to the surface of the
active material layer, and then the slurry is dried and
compression-molded. Thereby, the insulating layer is formed on the
surface of the active material layer.
CITATION LIST
Patent Literature
Patent Literature 1: Japanese Patent Laid-Open No. 2009-43641
Patent Literature 2: Japanese Patent Laid-Open No. 2009-301765
Patent Literature 3: Japanese Patent No. 5454295
SUMMARY OF INVENTION
Technical Problem
[0007] However, in the above-described conventional electrode, when
the temperature of the battery becomes high and the separator
shrinks in the in-plane direction, there was a possibility that the
insulating layer was dragged by the separator and peeled off from
the active material layer to expose the active material layer. When
the active material layer is exposed, it causes a short circuit
between the positive electrode and the negative electrode. In
addition, at high temperature, shrinkage force in the in-plane
direction also acts on the active material layer itself and the
insulating layer itself. Therefore, when the adhesion between the
current collector and the active material layer is weak, the active
material layer separates from the surface of the current collector
and shrinks, and a part of the surface of the current collector is
exposed. Alternatively, when the adhesion between the active
material layer and the insulating layer is weaker than the adhesion
between the active material layer and the current collector,
although the adhesion between the active material layer and the
current collector is maintained and shrinkage of the active
material layer does not occur, there is a possibility that the
insulating layer separates from the surface of the active material
layer and shrinks, and a part of the active material layer is
exposed.
[0008] An object of the present invention is to provide an
electrode having an active material layer and an insulating layer
on a current collector and a method for manufacturing the electrode
in which the electrode is capable of suppressing the occurrence of
a short circuit even when the electrode is assembled as a battery
and used to reach a high temperature.
Solution to Problem
[0009] According to one aspect of the present invention,
an electrode for a battery comprising:
[0010] a current collector,
[0011] an active material layer formed on at least one surface of
the current collector,
[0012] an insulating layer formed on a surface of the active
material layer, and
wherein peeling occurs between the current collector and the active
material layer and a peeling strength thereof is 10 mN/mm or more
when a 90.degree. peeling test is carried out at a peeling rate of
100 mm/min is provided.
[0013] According to the other aspect of the present invention,
[0014] a battery comprising:
[0015] at least one positive electrode,
[0016] at least one negative electrode disposed to face the
positive electrode, and
[0017] wherein at least one of the positive electrode and the
negative electrode includes a current collector, an active material
layer formed on at least one surface of the current collector, and
an insulating layer formed on a surface of the active material
layer, and peeling occurs between the current collector and the
active material layer and a peeling strength thereof is 10 mN/mm or
more when a 90.degree. peeling test is carried out at a peeling
rate of 100 mm/min is provided.
[0018] The present invention further provides a method for
manufacturing an electrode for a battery, the method
comprising;
[0019] forming an active material layer on at least one surface of
a current collector,
[0020] forming an insulating layer such that the insulating layer
is finally laminated on a surface of the active material layer,
and
[0021] wherein at least one of a material of the active material
layer, a formation condition of the active material layer, a
material of the insulating layer and a formation condition of the
insulating layer is determined such that peeling occurs between the
current collector and the active material layer and a peeling
strength thereof is 10 mN/mm or more when a 90.degree. peeling test
is carried out at a peeling rate of 100 mm/min.
Definition of Terms Used in the Present Invention
[0022] "90.degree. peeling test" refers to a test of obtaining
peeling strength from the maximum load applied to a sample before
the sample peels off when the sample prepared from an electrode
having an active material layer and an insulating layer formed on
the surface of a current collector was fixed on the surface of a
sample table, and the sample was peeled from the sample table at a
peeling rate of 100 mm/min while holding one end portion of the
fixed sample and keeping the peel angle at 90.degree.. In the
present invention, the "90.degree. peeling test" is carried out
under an ambient temperature environment (15.degree. C. to
25.degree. C.). As the sample, an electrode cut into a width of 20
mm and a length of 100 mm is used. For fixing the sample to the
sample table, the surface on which the active material layer and
the insulating layer are formed is fixed to the sample table. At
this time, only the portion of the sample from the one end to 80 mm
in the longitudinal direction is fixed, and a portion of the sample
not fixed is set as a grip margin by a chuck or the like at the
time of peeling the sample. The method of fixing the sample to the
sample table is not particularly limited as long as the sample can
be fixed so that the insulation layer does not peel from the sample
table when the sample is peeled off. For fixing the sample, for
example, double-sided tape can be used.
[0023] "Peeling strength" is expressed as a value obtained by
dividing the maximum load measured in the "90.degree. peeling test"
by the width of the sample of 20 mm and converting it into force
per 1 mm of the sample width.
Advantageous Effects of Invention
[0024] According to the present invention, a short circuit between
the positive electrode and the negative electrode at high
temperature can be effectively suppressed.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIG. 1 is an exploded perspective view of a battery
according to one embodiment of the present invention.
[0026] FIG. 2 is a schematic cross-sectional view of an electrode
assembly shown in FIG. 1.
[0027] FIG. 3 is a schematic cross-sectional view for explaining
the structures of the positive electrode and the negative electrode
shown in FIG. 2.
[0028] FIG. 4A is a cross-sectional view showing an example of
arrangement of the positive electrode and the negative electrode in
the electrode assembly.
[0029] FIG. 4B is a cross-sectional view showing another example of
arrangement of the positive electrode and the negative electrode in
the electrode assembly.
[0030] FIG. 4C is a cross-sectional view showing still another
example of arrangement of the positive electrode and the negative
electrode in the electrode assembly.
[0031] FIG. 5 is an exploded perspective view of a battery
according to another embodiment of the present invention.
[0032] FIG. 6 is a schematic view of one embodiment of an electrode
manufacturing apparatus according to the present invention.
[0033] FIG. 6A is a plan view of a current collector at the stage
of intermittently applying an active material layer on the current
collector for explaining a manufacturing process of an electrode
according to one embodiment of the present invention.
[0034] FIG. 6B is a plan view of a current collector at the stage
of further applying an insulating layer on the active material
layer on the current collector for explaining a manufacturing
process of an electrode according to one embodiment of the present
invention.
[0035] FIG. 6C is a plan view illustrating a cutting shape in a
stage of cutting a current collector applied the active material
layer and the insulating layer into a desired shape for explaining
a manufacturing process of an electrode according to one embodiment
of the present invention.
[0036] FIG. 7 is a schematic view of another embodiment of the
electrode manufacturing apparatus according to the present
invention.
[0037] FIG. 8 is a schematic view showing an embodiment of an
electric vehicle equipped with a battery.
[0038] FIG. 9 is a schematic diagram showing an example of a power
storage device equipped with a battery.
DESCRIPTION OF EMBODIMENTS
[0039] Referring to FIG. 1, an exploded perspective view of a
battery 1 according to one embodiment of the present invention is
shown, which comprises an electrode assembly 10 and a casing
enclosing the electrode assembly 10 together with an electrolyte.
The casing has casing members 21, 22 that enclose the electrode
assembly 10 from both sides in the thickness direction thereof and
seal outer circumferential portions thereof to thereby seal the
electrode assembly 10. A positive electrode terminal 31 and a
negative electrode terminal 32 are respectively connected to the
electrode assembly 10 with protruding part of them from the
casing.
[0040] As shown in FIG. 2, the electrode assembly 10 has a
configuration in which a plurality of positive electrodes 11 and a
plurality of negative electrodes 12 are disposed so as to be
alternately positioned. Between the positive electrode 11 and the
negative electrode 12, a separator 13 for preventing
short-circuiting between the positive electrode 11 and the negative
electrode 12 while securing ionic conduction between the positive
electrode 11 and the negative electrode 12 is arranged as necessary
according to the structure of the positive electrode 11 and the
negative electrode 12 described below.
[0041] Structures of the positive electrode 11 and the negative
electrode 12 will be described with further reference to FIG. 3. In
the structure shown in FIG. 3, the positive electrode 11 and the
negative electrode 12 are not particularly distinguished, but the
structure is applicable to both the positive electrode 11 and the
negative electrode 12. The positive electrode 11 and the negative
electrode 12 (collectively referred to as "electrode" in a case
where these are not distinguished) include a current collector 110
which can be formed of a metal foil, an active material layer 111
formed on one or both surfaces of the current collector 110. The
active material layer 111 is preferably formed in a rectangular
shape in plan view, and the current collector 110 has a shape
having an extended portion 110a extending from a region where the
active material layer 111 is formed.
[0042] The extended portion 110a of the positive electrode 11 and
the extended portion 110a of the negative electrode 12 are formed
at positions not overlapping each other in a state where the
positive electrode 11 and the negative electrode 12 are laminated.
However, the extension portions 110a of the positive electrodes 11
are positioned to overlap with each other, and the extension
portions 110a of the negative electrodes 12 are also similar to
each other. With such arrangement of the extended portions 110a, in
each of the plurality of positive electrodes 11, the respective
extended portions 110a are collected and welded together to form a
positive electrode tab 10a. Likewise, in the plurality of negative
electrodes 12, the respective extended portions 110a are collected
and welded together to form a negative electrode tab 10b. A
positive electrode terminal 31 is electrically connected to the
positive electrode tab 10a and a negative electrode terminal 32 is
electrically connected to the negative electrode tab 10b.
[0043] At least one of the positive electrode 11 and the negative
electrode 12 further includes an insulating layer 112 formed on the
active material layer 111. The insulating layer 112 is formed in a
region where the active material layer 111 is not exposed in plan
view. In the case where the active material layer 111 is formed on
both surfaces of the current collector 110, the insulating layer
112 may be formed on both of the active materials 111, or may be
formed only on one of the active materials 111.
[0044] What is important here is that when a 90.degree. peeling
test is carried out with a sample cut out with an electrode having
the active material layer 111 and the insulating layer 112 on the
current collector 110 with a width of 20 mm at a peeling rate of
100 mm/min, peeling occurs between the current collector 110 and
the active material layer 111, and its peeling strength is 10 mN/mm
or more. Peeling between the current collector 110 and the active
material layer 111 during the 90.degree. peeling test means that
the peeling strength between the active material layer 111 and the
insulating layer 112 is higher than the peeling strength between
the current collector 110 and the active material layer 111. By
specifying the peeling strength between the current collector 110,
the active material layer 111 and the insulating layer 112 in this
manner, even when the battery becomes high in temperature when used
as a battery, the positive electrode and the negative electrode can
be effectively suppressed.
[0045] Some examples of the arrangement of the positive electrode
11 and the negative electrode 12 having such a structure are shown
in FIGS. 4A to 4C. In the arrangement shown in FIG. 4A, the
positive electrode 11 having the insulating layer 112 on both sides
and the negative electrode 12 not having the insulating layer are
alternately laminated. In the arrangement shown in FIG. 4B, the
positive electrode 11 and the negative electrode 12 having the
insulating layer 112 on only one side are alternately laminated in
such a manner that the respective insulating layers 112 do not face
each other. In the structures shown in FIGS. 4A and 4B, since the
insulating layer 112 exists between the positive electrode 11 and
the negative electrode 12, the separator 13 (see FIG. 2) can be
omitted.
[0046] On the other hand, in the arrangement shown in FIG. 4C, the
positive electrode 11 having the insulating layer 112 on only one
side and the negative electrode 12 not having the insulating layer
are alternately laminated. In this case, the separator 13 is
required between the positive electrode 11 and the negative
electrode 12 opposed to the surface not having the insulating layer
112. However, since the separator 13 can be omitted between the
positive electrode 11 and the negative electrode 12 opposed to the
surface having the insulating layer 112, the number of the
separators 13 can be reduced.
[0047] The structure and arrangement of the positive electrode 11
and the negative electrode 12 are not limited to the above examples
and various modifications are possible as long as the insulating
layer 112 is provided on at least one surface of at least one of
the positive electrode 11 and the negative electrode 12. For
example, in the structures shown in FIGS. 4A to 4C, the
relationship between the positive electrode 11 and the negative
electrode 12 can be reversed.
[0048] Since the electrode assembly 10 having a planar laminated
structure as illustrated has no portion having a small radius of
curvature (a region close to a winding core of a winding
structure), the electrode assembly 10 has an advantage that it is
less susceptible to the volume change of the electrode due to
charging and discharging as compared with the electrode assembly
having a wound structure. That is, the electrode assembly having a
planar laminated structure is effective for an electrode assembly
using an active material that is liable to cause volume
expansion.
[0049] In the embodiment shown in FIGS. 1 and 2, the positive
electrode terminal 31 and the negative electrode terminal 32 are
drawn out in opposite directions, but the directions in which the
positive electrode terminal 31 and the negative electrode terminal
32 are drawn out may be arbitrary. For example, as shown in FIG. 5,
the positive electrode terminal 31 and the negative electrode
terminal 32 may be drawn out from the same side of the electrode
assembly 10. Although not shown, the positive electrode terminal 31
and the negative electrode terminal 32 may also be drawn out from
two adjacent sides of the electrode assembly 10. In both of the
above case, the positive electrode tab 10a and the negative
electrode tab 10b can be formed at positions corresponding to the
direction in which the positive electrode terminal 31 and the
negative electrode terminal 32 are drawn out.
[0050] Furthermore, in the illustrated embodiment, the electrode
assembly 10 having a laminated structure having a plurality of
positive electrodes 11 and a plurality of negative electrodes 12 is
shown. However, the electrode assembly having the winding structure
may have one positive electrode 11 and one negative electrode
12.
[0051] Hereinafter, elements constituting the electrode assembly 10
and the electrolytic solution will be described in detail. In the
following description, although not particularly limited, elements
in the lithium ion secondary battery will be described.
[1] Negative Electrode
[0052] The negative electrode has a structure in which, for
example, a negative electrode active material is adhered to a
negative electrode current collector by a negative electrode
binder, and the negative electrode active material is laminated on
the negative electrode current collector as a negative electrode
active material layer. Any material capable of absorbing and
desorbing lithium ions with charge and discharge can be used as the
negative electrode active material in the present embodiment as
long as the effect of the present invention is not significantly
impaired. Normally, as in the case of the positive electrode, the
negative electrode is also configured by providing the negative
electrode active material layer on the current collector. Similarly
to the positive electrode, the negative electrode may also have
other layers as appropriate.
[0053] The negative electrode active material is not particularly
limited as long as it is a material capable of absorbing and
desorbing lithium ions, and a known negative electrode active
material can be arbitrarily used. For example, it is preferable to
use carbonaceous materials such as coke, acetylene black, mesophase
microbead, graphite and the like; lithium metal; lithium alloy such
as lithium-silicon, lithium-tin; lithium titanate and the like as
the negative electrode active material. Among these, carbonaceous
materials are most preferably used from the viewpoint of good cycle
characteristics and safety and further excellent continuous charge
characteristics. One negative electrode active material may be used
alone, or two or more negative electrode active materials may be
used in combination in any combination and ratio.
[0054] Furthermore, the particle diameter of the negative electrode
active material is arbitrary as long as the effect of the present
invention is not significantly impaired. However, in terms of
excellent battery characteristics such as initial efficiency, rate
characteristics, cycle characteristics, etc., the particle diameter
is usually 1 .mu.m or more, preferably 15 .mu.m or more, and
usually about 50 .mu.m or less, preferably about 30 .mu.m or less.
Furthermore, for example, it can be also used as the carbonaceous
material such as a material obtained by coating the carbonaceous
material with an organic substance such as pitch or the like and
then calcining the carbonaceous material, or a material obtained by
forming amorphous carbon on the surface using the CVD method or the
like. Examples of the organic substances used for coating include
coal tar pitch from soft pitch to hard pitch; coal heavy oil such
as dry distilled liquefied oil; straight run heavy oil such as
atmospheric residual oil and vacuum residual oil, crude oil;
petroleum heavy oil such as decomposed heavy oil (for example,
ethylene heavy end) produced as a by-product upon thermal
decomposition of crude oil, naphtha and the like. A residue
obtained by distilling these heavy oil at 200 to 400.degree. C. and
then pulverized to a size of 1 to 100 .mu.m can also be used as the
organic substance. In addition, vinyl chloride resin, phenol resin,
imide resin and the like can also be used as the organic
substance.
[0055] In one embodiment of the present invention, the negative
electrode includes a metal and/or a metal oxide and carbon as the
negative electrode active material. Examples of the metal include
Li, Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, and
alloys of two or more of these. These metals or alloys may be used
as a mixture of two or more. In addition, these metals or alloys
may contain one or more non-metal elements.
[0056] Examples of the metal oxide include silicon oxide, aluminum
oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, and
composites of these. In the present embodiment, tin oxide or
silicon oxide is preferably contained as the negative electrode
active material, and silicon oxide is more preferably contained.
This is because silicon oxide is relatively stable and hardly
causes reaction with other compounds. Also, for example, 0.1 to 5
mass % of one or more elements selected from nitrogen, boron and
sulfur can be added to the metal oxide. In this way, the electrical
conductivity of the metal oxide can be improved. Also, the
electrical conductivity can be similarly improved by coating the
metal or the metal oxide with an electroconductive material such as
carbon by vapor deposition or the like.
[0057] Examples of the carbon include graphite, amorphous carbon,
diamond-like carbon, carbon nanotube, and composites of these.
Highly crystalline graphite has high electrical conductivity and is
excellent in adhesiveness with respect to a negative electrode
current collector made of a metal such as copper and voltage
flatness. On the other hand, since amorphous carbon having a low
crystallinity has a relatively small volume expansion, it has a
high effect of alleviating the volume expansion of the entire
negative electrode, and deterioration due to nonuniformity such as
crystal grain boundaries and defects hardly occurs.
[0058] The metal and the metal oxide have the feature that the
capacity of accepting lithium is much larger than that of carbon.
Therefore, the energy density of the battery can be improved by
using a large amount of the metal and the metal oxide as the
negative electrode active material. In order to achieve high energy
density, it is preferable that the content ratio of the metal
and/or the metal oxide in the negative electrode active material is
high. A larger amount of the metal and/or the metal oxide is
preferable, since it increases the capacity of the negative
electrode as a whole. The metal and/or the metal oxide is
preferably contained in the negative electrode in an amount of
0.01% by mass or more of the negative electrode active material,
more preferably 0.1% by mass or more, and further preferably 1% by
mass or more. However, the metal and/or the metal oxide has large
volume change upon absorbing and desorbing of lithium as compared
with carbon, and electrical junction may be lost. Therefore, the
amount of the metal and/or the metal oxide in the negative active
material is 99% by mass or less, preferably 90% or less, more
preferably 80 mass % or less. As described above, the negative
electrode active material is a material capable of reversibly
absorbing and desorbing lithium ions with charge and discharge in
the negative electrode, and does not include other binder and the
like.
[0059] For example, the negative electrode active material layer
may be formed into a sheet electrode by roll-forming the
above-described negative electrode active material, or may be
formed into a pellet electrode by compression molding. However,
usually, as in the case of the positive electrode active material
layer, the negative electrode active material layer can be formed
by applying and drying an application liquid on a current
collector, where the application liquid may be obtained by
slurrying the above-described negative electrode active material, a
binder, and various auxiliaries contained as necessary with a
solvent.
[0060] The negative electrode binder is not particularly limited,
and examples thereof include polyvinylidene fluoride, vinylidene
fluoride-hexafluoropropylene copolymer, vinylidene
fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer
rubber, polytetrafluoroethylene, polypropylene, polyethylene,
acrylic, polyimide, polyamide imide and the like. In addition to
the above, styrene butadiene rubber (SBR) and the like can be
included. When an aqueous binder such as an SBR emulsion is used, a
thickener such as carboxymethyl cellulose (CMC) can also be used.
The amount of the negative electrode binder to be used is
preferably 0.5 to 20 parts by mass relative to 100 parts by mass of
the negative electrode active material from the viewpoint of a
trade-off between "sufficient binding strength" and "high energy".
The negative electrode binders may be mixed and used.
[0061] As the material of the negative electrode current collector,
a known material can be arbitrarily used, and for example, a metal
material such as copper, nickel, stainless steel, aluminum,
chromium, silver and an alloy thereof is preferably used from the
viewpoint of electrochemical stability. Among them, copper is
particularly preferable from the viewpoint of ease of processing
and cost. It is also preferable that the negative electrode current
collector is also subjected to surface roughening treatment in
advance. Further, the shape of the current collector is also
arbitrary, and examples thereof include a foil shape, a flat plate
shape and a mesh shape. A perforated type current collector such as
an expanded metal or a punching metal can also be used.
[0062] The negative electrode can be produced, for example, by
forming a negative electrode active material layer containing a
negative electrode active material and a negative electrode binder
on a negative electrode current collector. Examples of a method for
forming the negative electrode active material layer include a
doctor blade method, a die coater method, a CVD method, a
sputtering method, and the like. After forming the negative
electrode active material layer in advance, a thin film of
aluminum, nickel or an alloy thereof may be formed by a method such
as vapor deposition, sputtering or the like to obtain a negative
electrode current collector.
[0063] An electroconductive auxiliary material may be added to a
coating layer containing the negative electrode active material for
the purpose of lowering the impedance. Examples of the
electroconductive auxiliary material include flaky, sooty, fibrous
carbonaceous microparticles and the like such as graphite, carbon
black, acetylene black, vapor grown carbon fiber (for example, VGCF
(registered trademark) manufactured by Showa Denko K.K.), and the
like.
[2] Positive Electrode
[0064] The positive electrode refers to an electrode on the high
potential side in a battery. As an example, the positive electrode
includes a positive electrode active material capable of reversibly
absorbing and desorbing lithium ions with charge and discharge, and
has a structure in which a positive electrode active material is
laminated on a current collector as a positive electrode active
material layer integrated with a positive electrode binder. In one
embodiment of the present invention, the positive electrode has a
charge capacity per unit area of 3 mAh/cm.sup.2 or more, preferably
0.3.5 mAh/cm.sup.2 or more. From the viewpoint of safety and the
like, the charge capacity per unit area of the positive electrode
is preferably 15 mAh/cm.sup.2 or less. Here, the charge capacity
per unit area is calculated from the theoretical capacity of the
active material. That is, the charge capacity of the positive
electrode per unit area is calculated by (theoretical capacity of
the positive electrode active material used for the positive
electrode)/(area of the positive electrode). Note that the area of
the positive electrode refers to the area of one surface, not both
surfaces of the positive electrode.
[0065] The positive electrode active material in the present
embodiment is not particularly limited as long as it is a material
capable of absorbing and desorbing lithium, and can be selected
from several viewpoints. A high-capacity compound is preferably
contained from the viewpoint of high energy density. Examples of
the high-capacity compound include nickel lithate (LiNiO.sub.2) and
a lithium nickel composite oxide obtained by partially replacing Ni
of nickel lithate with another metal element, and a layered lithium
nickel composite oxide represented by formula (A) below is
preferable.
Li.sub.yNi.sub.(1-x)M.sub.xO.sub.2 (A)
(provided that 0.ltoreq.x<1, 0<y.ltoreq.1.2, and M is at
least one element selected from the group consisting of Co, Al, Mn,
Fe, Ti, and B.)
[0066] From the viewpoint of high capacity, the Ni content is
preferably high, or that is to say, x is less than 0.5 in formula
(A), and more preferably 0.4 or less. Examples of such compounds
include
Li.sub..alpha.Ni.sub..beta.Co.sub..gamma.Mn.sub..delta.O.sub.2
(0<.alpha..ltoreq.1.2, preferably 1.ltoreq..alpha..ltoreq.1.2,
.beta.+.gamma.+.delta.=1, .beta..gtoreq.0.7, and
.gamma..ltoreq.0.2) and
Li.sub..alpha.Ni.sub..beta.Co.sub..gamma.Al.sub..delta.O.sub.2
(0<.alpha..ltoreq.1.2 preferably 1.ltoreq..alpha..ltoreq.1.2,
.beta.+.gamma.+.delta.=1, .beta..gtoreq.0.6 preferably
.beta..gtoreq.0.7, .gamma..ltoreq.0.2), and, in particular,
LiNi.sub..beta.Co.sub..gamma.Mn.sub..delta.O.sub.2
(0.75.ltoreq..beta..ltoreq.0.85, 0.05.ltoreq..gamma..ltoreq.0.15,
0.10.ltoreq..delta..ltoreq.0.20). More specifically, for example,
LiNi.sub.0.8Co.sub.0.05Mn.sub.0.15O.sub.2,
LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2,
LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2, and
LiNi.sub.0.8Co.sub.0.1Al.sub.0.1O.sub.2 can be preferably used.
[0067] From the viewpoint of heat stability, it is also preferable
that the Ni content does not exceed 0.5, or that is to say, x is
0.5 or more in formula (A). It is also preferable that a certain
transition metal does not account for more than half. Examples of
such compounds include
Li.sub..alpha.Ni.sub..beta.Co.sub..gamma.Mn.sub..delta.O.sub.2
(0<.alpha..ltoreq.1.2 preferably 1.ltoreq..alpha..ltoreq.1.2,
.beta.+.gamma.+.delta.=1, 0.2.ltoreq..beta..ltoreq.0.5,
0.1.ltoreq..gamma..ltoreq.0.4, 0.1.ltoreq..delta..ltoreq.0.4). More
specific examples include LiNi.sub.0.4Co.sub.0.3Mn.sub.0.3O.sub.2
(abbreviated as NCM433), LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2,
LiNi.sub.0.5Co.sub.0.2Mn.sub.0.3O.sub.2 (abbreviated as NCM523),
and LiNi.sub.0.5Co.sub.0.3Mn.sub.0.2O.sub.2 (abbreviated as NCM532)
(provided that these compounds include those in which the content
of each transition metal is varied by about 10%).
[0068] Also, two or more compounds represented by formula (A) may
be used as a mixture, and, for example, it is also preferable to
use NCM532 or NCM523 with NCM433 in a range of 9:1 to 1:9 (2:1 as a
typical example) as a mixture. Moreover, a battery having a high
capacity and a high heat stability can be formed by mixing a
material having a high Ni content (x is 0.4 or less) with a
material having a Ni content not exceeding 0.5 (x is 0.5 or more,
such as NCM433) in formula (A).
[0069] Other than the above positive electrode active materials,
examples include lithium manganates having a layered structure or a
spinel structure, such as LiMnO.sub.2, Li.sub.xMn.sub.2O.sub.4
(0<x<2), Li.sub.2MnO.sub.3, and
Li.sub.xMn.sub.1.5Ni.sub.0.5O.sub.4 (0<x<2); LiCoO.sub.2 and
those obtained by partially replacing these transition metals with
other metals; those having an excess of Li based on the
stoichiometric compositions of these lithium transition metal
oxides; and those having an olivine structure such as LiFePO.sub.4.
Moreover, materials obtained by partially replacing these metal
oxides with Al, Fe, P, Ti, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd,
Pt, Te, Zn, La, or the like can be used as well. One of the
positive electrode active materials described above may be used
singly, or two or more can be used in combination.
[0070] A positive electrode binder similar to the negative
electrode binder can be used. Among them, polyvinylidene fluoride
or polytetrafluoroethylene is preferable from the viewpoint of
versatility and low cost, and polyvinylidene fluoride is more
preferable. The amount of the positive electrode binder used is
preferably 2 to 15 parts by mass relative to 100 parts by mass of
the positive electrode active material from the viewpoint of a
trade-off between "sufficient binding strength" and "high
energy".
[0071] An electroconductive auxiliary material may be added to a
coating layer containing the positive electrode active material for
the purpose of lowering the impedance. Examples of the conductive
auxiliary material include flaky, sooty, fibrous carbonaceous
microparticles and the like such as graphite, carbon black,
acetylene black, vapor grown carbon fiber (for example, VGCF
manufactured by Showa Denko K.K.) and the like.
[0072] A positive electrode current collector similar to the
negative electrode current collector can be used. In particular, as
the positive electrode, a current collector using aluminum, an
aluminum alloy, iron, nickel, chromium, molybdenum type stainless
steel is preferable.
[0073] An electroconductive auxiliary material may be added to a
positive electrode active material layer containing the positive
electrode active material for the purpose of lowering the
impedance. Examples of the conductive auxiliary material include
carbonaceous microparticles such as graphite, carbon black and
acetylene black.
[3] Insulating Layer
(Material and Manufacturing Method Etc.)
[0074] The insulating layer can be formed by applying a slurry
composition for an insulating layer so as to cover a part of the
active material layer of the positive electrode or the negative
electrode and drying and removing a solvent. Although the
insulating layer may be formed on only one side of the active
material layer, there is an advantage that the warpage of the
electrode can be reduced by forming the insulating layer on both
side (in particular, as a symmetrical structure).
[0075] A slurry for the insulating layer is a slurry composition
for forming a porous insulating layer. Therefore, the "insulating
layer" can also be referred to as "porous insulating layer". The
slurry for the insulating layer comprises non-conductive particles
and a binder (or a binding agent) having a specific composition,
and the non-conductive particles, the binder and optional
components are uniformly dispersed as a solid content in a
solvent.
[0076] It is desirable that the non-conductive particles stably
exist in the use environment of the lithium ion secondary battery
and are electrochemically stable. As the non-conductive particles,
for example, various inorganic particles, organic particles and
other particles can be used. Among them, inorganic oxide particles
or organic particles are preferable, and in particular, from the
viewpoint of high thermal stability of the particles, it is more
preferable to use inorganic oxide particles. Metal ions in the
particles sometimes form salts near the electrode, which may cause
an increase in the internal resistance of the electrode and a
decrease in cycle characteristics of the secondary battery. The
other particles include particles to which conductivity is given by
surface treatment of the surface of fine powder with a
non-electrically conductive substance. The fine powder can be made
from a conductive metal, compound and oxide such as carbon black,
graphite, SnO.sub.2, ITO and metal powder. Two or more of the
above-mentioned particles may be used in combination as the
non-conductive particles.
[0077] Examples of the inorganic particles include inorganic oxide
particles such as aluminum oxide, silicon oxide, magnesium oxide,
titanium oxide, BaTiO.sub.2, ZrO, alumina-silica composite oxide;
inorganic nitride particles such as aluminum nitride and boron
nitride; covalent crystal particles such as silicone, diamond and
the like; sparingly soluble ionic crystal particles such as barium
sulfate, calcium fluoride, barium fluoride and the like; clay fine
particles such as talc and montmorillonite. These particles may be
subjected to element substitution, surface treatment, solid
solution treatment, etc., if necessary, and may be used singly or
in combination of two or more kinds. Among them, inorganic oxide
particles are preferable from the viewpoints of stability in the
electrolytic solution and potential stability.
[0078] The shape of the inorganic particles is not particularly
limited, and may be spherical, needle-like, rod-like,
spindle-shaped, plate-like, or the like. From the viewpoint of
effectively preventing penetration of the needle-shaped object, the
shape of the inorganic particle may be in the form of a plate.
[0079] By orienting the inorganic particles as described above, it
is conceivable that the inorganic particles are arranged so as to
overlap with each other on a part of the flat surface, and voids
(through holes) from one surface to the other surface of the porous
film are formed not in a straight but in a bent shape (that is, the
curvature ratio is increased). This is presumed to prevent the
lithium dendrite from penetrating the porous film and to better
suppress the occurrence of a short circuit.
[0080] Examples of the plate-like inorganic particles preferably
used include various commercially available products such as
"SUNLOVELY" (SiO.sub.2) manufactured by AGC Si-Tech Co., Ltd.,
pulverized product of "NST-B 1" (TiO.sub.2) manufactured by
Ishihara Sangyo Kaisha, Ltd., plate like barium sulfate "H series",
"HL series" manufactured by Sakai Chemical Industry Co., Ltd.,
"Micron White" (Talc) manufactured by Hayashi Kasei Co., Ltd.,
"Benger" (bentonite) manufactured by Hayashi Kasei Co., Ltd., "BMM"
and "BMT" (boehmite) manufactured by Kawaii Lime Industry Co.,
Ltd., "Serasur BMT-B" [alumina (Al.sub.2O.sub.3)] manufactured by
Kawaii Lime Industry Co., Ltd., "Serath" (alumina) manufactured by
Kinsei Matec Co., Ltd., "AKP series" (alumina) manufactured by
Sumitomo Chemical Co., Ltd., and "Hikawa Mica Z-20" (sericite)
manufactured by Hikawa Mining Co., Ltd. In addition, SiO.sub.2,
Al.sub.2O.sub.3, and ZrO can be produced by the method disclosed in
Japanese Patent Laid-Open No. 2003-206475.
[0081] The average particle diameter of the inorganic particles is
preferably in the range of 0.005 to 10 .mu.m, more preferably 0.1
to 5 .mu.m, particularly preferably 0.3 to 2 .mu.m. When the
average particle size of the inorganic particles is in the above
range, the dispersion state of the porous film slurry is easily
controlled, so that it is easy to manufacture a porous film having
a uniform and uniform thickness. In addition, such average particle
size provides the following advantages. The adhesion to the binder
is improved, and even when the porous film is wound, it is possible
to prevent the inorganic particles from peeling off, and as a
result, sufficient safety can be achieved even if the porous film
is thinned. Since it is possible to suppress an increase in the
particle packing ratio in the porous film, it is possible to
suppress a decrease in ion conductivity in the porous film.
Furthermore, the porous membrane can be made thin.
[0082] The average particle size of the inorganic particles can be
obtained by arbitrarily selecting 50 primary particles from an SEM
(scanning electron microscope) image in an arbitrary field of view,
carrying out image analysis, and obtaining the average value of
circle equivalent diameters of each particle.
[0083] The particle diameter distribution (CV value) of the
inorganic particles is preferably 0.5 to 40%, more preferably 0.5
to 30%, particularly preferably 0.5 to 20%. By setting the particle
size distribution of the inorganic particles within the above
range, a predetermined gap between the non-conductive particles is
maintained, so that it is possible to suppress an increase in
resistance due to the inhibition of movement of lithium. The
particle size distribution (CV value) of the inorganic particles
can be determined by observing the inorganic particles with an
electron microscope, measuring the particle diameter of 200 or more
particles, determining the average particle diameter and the
standard deviation of the particle diameter, and calculating
(Standard deviation of particle diameter)/(average particle
diameter). The larger the CV value means the larger variation in
particle diameter.
[0084] When the solvent contained in the slurry for insulating
layer is a non-aqueous solvent, a polymer dispersed or dissolved in
a non-aqueous solvent can be used as a binder. As the polymer
dispersed or dissolved in the non-aqueous solvent, polyvinylidene
fluoride (PVdF), polytetrafluoroethylene (PTFE),
polyhexafluoropropylene (PHFP), polytrifluoroethylene chloride
(PCTFE), polyperfluoroalkoxyfluoroethylene, polyimide,
polyamideimide, and the like can be used as a binder, and it is not
limited thereto.
[0085] In addition, a binder used for binding the active material
layer can also be used.
[0086] When the solvent contained in the slurry for insulating
layer is an aqueous solvent (a solution using water or a mixed
solvent containing water as a main component as a dispersion medium
of the binder), a polymer dispersed or dissolved in an aqueous
solvent can be used as a binder. A polymer dispersed or dissolved
in an aqueous solvent includes, for example, an acrylic resin. As
the acrylic resin, it is preferably to use homopolymers obtained by
polymerizing monomers such as acrylic acid, methacrylic acid,
acrylamide, methacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl
methacrylate, methyl methacrylate, ethylhexyl acrylate, butyl
acrylate. The acrylic resin may be a copolymer obtained by,
polymerizing two or more of the above monomers. Further, two or
more of the homopolymer and the copolymer may be mixed. In addition
to the above-mentioned acrylic resin, polyolefin resins such as
styrene butadiene rubber (SBR) and polyethylene (PE),
polytetrafluoroethylene (PTFE), and the like can be used. These
polymers can be used singly or in combination of two or more kinds.
Among them, it is preferable to use an acrylic resin. The form of
the binder is not particularly limited, and particles in the form
of particles (powder) may be used as they are, or those prepared in
a solution state or an emulsion state may be used. Two or more
kinds of binders may be used in different forms.
[0087] The insulating layer may contain a material other than the
above-described inorganic filler and binder, if necessary. Examples
of such material include various polymer materials that can
function as a thickener for a slurry for the insulating layer,
which will be described later. In particular, when an aqueous
solvent is used, it is preferable to contain a polymer functioning
as the thickener. As the polymer functioning as the thickener,
carboxymethyl cellulose (CMC) or methyl cellulose (MC) is
preferably used.
[0088] Although not particularly limited, the ratio of the
inorganic filler to the entire insulating layer is suitably about
70 mass % or more (for example, 70 mass % to 99 mass %), preferably
80 mass % or more (for example, 80 mass % to 99 mass %), and
particularly preferably about 90 mass % to 95 mass %.
[0089] The ratio of the binder in the insulating layer is suitably
about 1 to 30 mass % or less, preferably 5 to 20 mass % or less. In
the case of containing an insulating layer-forming component other
than the inorganic filler and the binder, for example, a thickener,
the content ratio of the thickener is preferably about 10 mass % or
less, more preferably about 7 mass % or less. If the ratio of the
binder is too small, strength (shape retentivity) of the insulating
layer itself and adhesion to the active material layer are lowered,
which may cause defects such as cracking and peeling. If the ratio
of the binder is too large, gaps between the particles of the
insulating layer become insufficient, and the ion permeability in
the insulating layer may decrease in some cases.
[0090] In order to maintain ion conductivity, The porosity (void
ratio) (the ratio of the pore volume to the apparent volume) of the
insulating layer is preferably 20% or more, more preferably 30% or
more. However, if the porosity is too high, falling off or cracking
of the insulating layer due to friction or impact applied to the
insulating layer occurs, the porosity is preferably 80% or less,
more preferably 70% or less.
[0091] The porosity can be calculated from the ratio of the
materials constituting the insulating layer, the true specific
gravity and the coating thickness.
(Forming of Insulating Layer)
[0092] A method of forming the insulating layer will be described.
As a material for forming the insulating layer, a paste type
material (including slurry form or ink form, the same applies
below) mixed and dispersed with an inorganic filler, a binder and a
solvent can be used.
[0093] A solvent used for the insulating layer slurry includes
water or a mixed solvent mainly containing water. As a solvent
other than water constituting such a mixed solvent, one or more
kinds of organic solvents (lower alcohols, lower ketones, etc.)
which can be uniformly mixed with water can be appropriately
selected and used. Alternatively, it may be an organic solvent such
as N-methylpyrrolidone (NMP), pyrrolidone, methyl ethyl ketone,
methyl isobutyl ketone, cyclohexanone, toluene, dimethylformamide,
dimethylacetamide, or a combination of two or more thereof. The
content of the solvent in the slurry for the insulating layer is
not particularly limited, and it is preferably 40 to 90 mass %,
particularly preferably about 50 to 70 mass %, of the entire
coating material.
[0094] The operation of mixing the inorganic filler and the binder
with the solvent can be carried out by using a suitable kneading
machine such as a ball mill, a homodisper, Diaper Mill (registered
trademark), Clearmix (registered trademark), Filmix (registered
trademark), an ultrasonic dispersing machine.
[0095] For the operation of applying the slurry for the insulating
layer, conventional general coating means can be used without
restricting. For example, a predetermined amount of the slurry for
the insulating layer can be applied by coating in a uniform
thickness by means of a suitable coating device (a gravure coater,
a slit coater, a die coater, a comma coater, a dip coater,
etc.).
[0096] Thereafter, the solvent in the slurry for the insulating
layer may be removed by drying the coating material by means of a
suitable drying means.
(Thickness)
[0097] The thickness of the insulating layer is preferably 1 .mu.m
or more and 30 .mu.m or less, and more preferably 2 .mu.m or more
and 15 .mu.m or less.
[4] Electrolyte
[0098] As the electrolytic solution, a non-aqueous electrolytic
solution that is stable at the operating potential of the battery
is preferable, but it is not particularly limited. Specific
examples of the non-aqueous electrolytic solution include an
aprotic organic solvent including cyclic carbonates such as
propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene
carbonate (FEC), t-difluoroethylene carbonate (t-DFEC), butylene
carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate
(VEC); chain carbonates such as allyl methyl carbonate (AMC),
dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl
carbonate (EMC), dipropyl carbonate (DPC); propylene carbonate
derivatives; aliphatic carboxylic acid esters such as methyl
formate, methyl acetate, ethyl propionate and the like; cyclic
esters such as .gamma.-butyrolactone (GBL). The non-aqueous
electrolytic solution may be used singly or in combination of two
or more. Sulfur-containing cyclic compounds such as sulfolane,
fluorinated sulfolane, propane sultone, propene sultone and the
like can be used as the non-aqueous electrolytic solution.
[0099] Specific examples of supporting salts contained in the
electrolytic solution include lithium salts such as LiPF.sub.6,
LiAsF.sub.6, LiAlCl.sub.4, LiClO.sub.4, LiBF.sub.4, LiSbF.sub.6,
LiCF.sub.8SO.sub.3, LiC.sub.4F.sub.9SO.sub.3,
Li(CF.sub.3SO.sub.2).sub.2, LiN(CF.sub.3SO.sub.2).sub.2 and the
like, but are not limited. As the supporting salt, one type may be
used alone, or two kinds or more may be used in combination.
[5] Separator
[0100] When the battery has a separator, the separator is not
particularly limited, and a porous film or a nonwoven fabric made
of polypropylene, polyethylene, fluororesin, polyamide, polyimide,
polyester, polyphenylene sulfide or the like can be used as the
separator. In addition, those including inorganic materials such as
silica, alumina, glass and the like adhered or joined to the porous
firm or the nonwoven fabric used as a base material and the
inorganic materials alone processed into a nonwoven fabric or a
cloth can also be used as the separator. Furthermore, a laminate of
the these can be used as the separator.
[0101] The present invention is not limited to the above described
lithium ion secondary battery and can be applied to any battery.
However, since the problem of heat often occurs in batteries with
high capacity in many cases, the present invention is preferably
applied to batteries with high capacity, particularly lithium ion
secondary batteries.
[0102] Next, embodiments of method for manufacturing the electrode
shown in FIG. 3 will be described. In the following description,
the positive electrode 11 and the negative electrode 12 will be
described as "electrodes" without particularly distinguishing from
each other, but the positive electrode 11 and the negative
electrode differ only in the materials, shapes, etc. to be used,
and the following explanation will be made on the positive
electrode 11 and the negative electrode 12.
[0103] The electrode has a structure in which the active material
layer 111 and the insulating layer 112 are laminated in this order
on the current collector 110 finally and the manufacturing method
is not particularly limited as long as peeling occurs between the
current collector 110 and the active material layer 111 and its
peeling strength is 10 mN/mm or more when a 90.degree. peeling test
is carried out at a peeling rate of 100 mm/min. At least one of the
materials of the active material layer 111, the formation condition
of the active material layer 111, the materials of the insulating
layer 112 and the formation condition of the insulating layer 112
can be determined so as to satisfy the above peeling
conditions.
[0104] The active material layer 111 can be formed by applying an
mixture for an active material layer prepared by dispersing an
active material and a binder in a solvent to form a slurry and
drying the applied mixture for the active material layer. After the
mixture for the active material layer is dried, the method may
further include the step of compression-molding the dried mixture
for the active material layer. The insulating layer 12 can also be
formed in the same process as the active material layer 111. That
is, the insulating layer 112 can be formed by applying an mixture
for an insulating layer prepared by dispersing an insulating
material and a binder in a solvent to form a slurry, and drying the
applied mixture for the insulating layer. After the mixture for the
insulating layer is dried, the method may further include the step
of compression molding the dried mixture for the insulating
layer.
[0105] The process for forming the active material layer 111 and
the process for forming the insulating layer 112 described above
may be carried out separately or in appropriate combination. In the
case where the process for forming the active material layer 111
and the process for forming the insulating layer 112 are separately
carried out, the manufacturing method for the electrode
includes
(1) applying a mixture for an active material on a current
collector 110, (2) drying the applied mixture for the active
material, (3) forming an active material layer 111 by
compression-molding the dried mixture for the active material
mixture, (4) applying a mixture for an insulating layer on the
formed active material layer 111, (5) drying the applied mixture
for the insulating layer, and (6) forming an insulating layer 112
by compression-molding the dried mixture for the insulating layer.
In this case, since the insulating layer 112 is formed after the
active material layer 111 is formed, it is possible to easily
manage the thickness of each layer and the like. The step of
compression-molding the mixture for the active material layer and
the step of compression molding the mixture for the insulating
layer can be omitted.
[0106] When combining the process of forming the active material
layer 111 and the process of forming the insulating layer 112,
there are several examples of the combination. Two examples among
them are described below.
Combination Example A
[0107] In Combination Example A, the process of manufacturing the
electrode includes
(A1) applying the mixture for the active material layer on the
current collector 110, (A2) drying the applied mixture for the
active material layer, (A3) applying a mixture for an insulating
layer on the dried mixture for the active material layer, (A4)
drying the applied mixture for the insulating layer, and (A5)
compression-molding the dried mixture for the active material layer
and the dried mixture for the insulating layer mixture
simultaneously. In this case, only one step of compression-molding
is required, and the manufacturing process is simplified
correspondingly. The above step of compression-molding can be
omitted.
Combination Example B
[0108] In the combination Example B, the process of manufacturing
the electrode includes
(B1) applying a mixture for an active material layer on the current
collector 110, (B2) applying an mixture for an insulating layer on
the applied mixture for the active material layer, (B3) drying the
whole of the applied mixture for the active material layer and the
applied mixture for the insulating layer simultaneously, and (B4)
compression-molding the whole of the dried mixture for the active
material layer and the mixture for the insulating layer
simultaneously. In this case, since only one step of drying and one
step of compression-molding are required, the manufacturing process
is further simplified. The above step of compression-molding can be
omitted.
[0109] For manufacturing the electrode, for example, the
manufacturing apparatus shown in FIG. 6 can be used. The
manufacturing apparatus shown in FIG. 6 includes a backup roller
201, a die coater 210 and a drying machine 203.
[0110] The backup roller 201 rotates in a state in which the long
current collector 110 is wound on the outer peripheral surface of
the backup roller 201 whereby the current collector 110 is fed in
the rotation direction of the backup roller 201 while the rear
surface of the current collector 110 is supported. The die coater
210 has a first die head 211 and a second die head 212 which are
spaced from each other in the radial direction and the
circumferential direction of the backup roller 201 with respect to
the outer circumferential surface of the backup roller 201.
[0111] The first die head 211 is for applying the active material
layer 111 on the surface of the current collector 110 and is
located on the upstream side of the second die head 212 with
respect to the feed direction of the current collector 110. A
discharge opening 211a having a width corresponding to the applying
width of the active material layer 111 is opened at the tip of the
first die head 211 facing the backup roller 201. The slurry for the
active material layer is discharged from the discharger opening
211a. The slurry for the active material layer is prepared by
dispersing particles of an active material and a binder (binding
agent) in a solvent, and is supplied to the first die head 211.
[0112] The second die head 212 is for applying the insulating layer
112 on the surface of the active material layer 111 and is located
on the downstream side of the first die head 211 with respect to
the feed direction of the current collector 110. A discharge
opening 212a having a width corresponding to the applying width of
the insulating layer 112 is opened at the tip of the second die
head 212 facing the backup roller 201. The slurry for the
insulating layer is discharged from the discharge opening 212a. The
slurry for the insulating layer is prepared by dispersing
insulating particles and a binder (binding agent) in a solvent, and
is supplied to the second die head 212.
[0113] A solvent is used for preparing the slurry for the active
material layer and the slurry for the insulating layer. When
N-methyl-2-pyrrolidone (NMP) is used as the solvent, peeling
strength of the layer obtained by evaporating the solvent can be
increased compared with the case of using an aqueous solvent. When
N-methyl-2-pyrrolidone was used as a solvent, the solvent did not
evaporate completely even if the solvent was evaporated in a
subsequent step, and the obtained layer contains a slight amount of
N-methyl-2-pyrrolidone.
[0114] The drying machine 203 is for evaporating the solvent from
the slurry for the active material layer and the slurry for the
insulating layer respectively discharged from the first die head
211 and the second die head 212. The slurries are dried by the
evaporation of the solvent, whereby the active material layer 111
and an insulating layer 112 are formed.
[0115] Next, a manufacturing process of the electrode by means of
the manufacturing apparatus shown in FIG. 6 will be described. For
convenience of explanation, the slurry for the active material
layer and the active material layer obtained therefrom are
described as "active material layer 111" without distinguishing
between them. Actually, the "active material layer 111" before
drying means the slurry for the active material layer. Similarly,
the "insulating layer 112" before drying means the slurry for the
insulating layer.
[0116] First, the active material layer 111 slurried with a solvent
is intermittently applied to the surface of the long current
collector 110 supported and fed on the backup roller 201 by using
the first die head 211. As a result, as shown in FIG. 6A, a slurry
of the active material layer 111 is applied to the current
collector 110 at intervals in the feeding direction A of the
current collector 110. By intermittently applying the active
material layer 111 with the first die head 211, the active material
layer 111 is applied in a rectangular shape having a longitudinal
length parallel to the feeding direction A of the current collector
110 and a lateral length along a direction orthogonal thereto.
[0117] Next, when the leading end of the applied active material
layer 111 in the feeding direction of the current collector 111 is
fed to a position facing the discharge opening 212a of the second
die head 212, the insulating layer 112 slurried with solvent is
intermittently applied to the active material layer 111 by using
the second die head 212. The insulating layer 112 is applied so
that a part thereof is exposed at the end portion of the active
material layer 111 when viewing the current collector 110 in its
thickness direction. The insulating layer 112 is applied before the
active material layer 111 is dried, that is, before the solvent of
the active material layer 111 is evaporated. By intermittently
applying the insulating layer 112 with the second die head 212, the
insulating layer 112 is applied in a rectangular shape having a
longitudinal length parallel to the feeding direction A of the
current collector 110 and a lateral length along a direction
perpendicular thereto.
[0118] In the present embodiment, the first die head 211 and the
second die head 212 have the same width (the dimension in the
direction orthogonal to the feeding direction A of the current
collector 110) of the projecting openings 211a and 212a, and the
active material layer 111 and the insulating layer 112 have the
same applying width.
[0119] After applying the active material layer 111 and the
insulating layer 112, the current collector 110 is fed to the
drying machine 203, the solvents of the slurry for the active
material layer and the slurry for the insulating layer slurry are
evaporated in the drying machine 203. After evaporation of the
solvent, the current collector 110 is fed to a roll press where the
active material layer 111 and the insulating layer 112 are
compression-molded. Thus, the active material layer 111 is formed
simultaneously with the formation of the insulating layer 112.
[0120] Finally, the current collector 110 is cut into a desired
shape, as indicated by a broken line in FIG. 6C, having a
rectangular portion in which the active material layer 111 and the
insulating layer 112 are formed on the entire surface of the
current collector 110 and an extension portion 110a made of the
current collector 110 extending from the rectangular portion by an
appropriate method such as punching. The electrode is thereby
obtained. The cutting step may be carried out so as to obtain a
desired shape by one time of processing or it may be carried out so
as to obtain a desired shape by a plurality of times of
processing.
[0121] Note that the current collector 110 having the active
material layer 111 and the insulating layer 112 formed thereon is
often wound around a roll and stored and/or transported until the
next process. As described above, in the laminated structure of the
current collector 110, the active material layer 111, and the
insulating layer 112, peeling occurs between the current collector
110 and the active material layer 111 and its peeling strength is
10 mN/mm or more when the 90.degree. peeling test is carried out.
Therefore, it is possible to suppress peeling of the active
material layer 111 from the current collector 110 and peeling of
the insulating layer 112 from the active material layer 111 even
when wound on a roll.
[0122] Although the present invention has been described with
reference to one embodiment, the present invention is not limited
to the above-described embodiments, and can be arbitrarily changed
within the scope of the technical idea of the present
invention.
[0123] For example, in the above embodiment, in order to apply the
active material layer 111 and the insulating layer 112, a die
coater 210 having two die heads 211 and 212 with discharge openings
211a and 212a as shown in FIG. 6 was used. However, as shown in
FIG. 7, the active material layer 111 and the insulating layer 112
can be applied to the current collector 110 by using a die coater
220 having a single die head 221 with two discharge openings 221a
and 221b.
[0124] The two discharge openings 221a and 221b are arranged at
intervals in the rotation direction of the backup roller 201, that
is, the feed direction of the current collector 110. The slurry for
the active material layer is applied by the discharge opening 221a
located on the upstream side in the feed direction of the current
collector 110 and the slurry for the insulating layer is applied by
the discharge opening 221b located on the downstream side.
Therefore, the slurry for the active material layer and the slurry
for the insulating layer are discharged respectively from the two
discharge openings 221a and 221b, thereby it is possible to obtain
a structure that the active material layer 111 is intermittently
applied to the surface of the current collector 110 and the
insulating layer 112 is applied with a part of the active material
layer 111 exposed.
[0125] Furthermore, in the above embodiment, the case where the
active material layer 111 and the insulating layer 112 are applied
to one side of the current collector 110 has been described.
However, it is possible to manufacture an electrode having the
active material layer 111 and the insulating layer 112 on both
surface of the current collector 110 by applying the active
material layer 111 and the insulating layer 112 on the other side
of the current collector 110 in a similar manner.
[0126] Further, the battery obtained by the present invention can
be used in various uses. Some examples are described below.
[Battery Pack]
[0127] A plurality of batteries can be combined to form a battery
pack. For example, the battery pack may have a configuration in
which two or more batteries according to the present embodiment are
connected in series and/or in parallel. The series number and
parallel number of the batteries can be appropriately selected
according to the intended voltage and capacity of the battery
pack.
[Vehicle]
[0128] The above-described battery or the battery pack thereof can
be used for a vehicle. Examples of vehicles that can use batteries
or assembled batteries include hybrid vehicles, fuel cell vehicles,
and electric vehicles (four-wheel vehicles (commercial vehicles
such as passenger cars, trucks and buses, and mini-vehicles, etc.),
motorcycles (motorbike and tricycles). Note that the vehicle
according to the present embodiment is not limited to an
automobile, and the battery can also be used as various power
sources for other vehicles, for example, transportations such as
electric trains. As an example of such a vehicle, FIG. 8 shows a
schematic diagram of an electric vehicle. The electric vehicle 200
shown in FIG. 8 has a battery pack 210 configured to satisfy the
required voltage and capacity by connecting a plurality of the
above-described batteries in series and in parallel.
[Power Storage Device]
[0129] The above-described battery or the battery pack thereof can
be used for a power storage device. Examples of the power storage
device using the secondary battery or the battery pack thereof
include a power storage device which is connected between a
commercial power supply supplied to an ordinary household and a
load such as a household electric appliance to use as a backup
power source or an auxiliary power source in case of power outage,
and a power storage device used for large-scale electric power
storage for stabilizing electric power output with large time
variation due to renewable energy such as photovoltaic power
generation. An example of such a power storage device is
schematically shown in FIG. 9. The power storage device 300 shown
in FIG. 9 has a battery pack 310 configured to satisfy a required
voltage and capacity by connecting a plurality of the
above-described batteries in series and in parallel.
[Others]
[0130] Furthermore, the above-described battery or the battery pack
thereof can be used as a power source of a mobile device such as a
mobile phone, a notebook computer and the like.
[0131] The present invention will be described with reference to
specific examples below. However, the present invention is not
limited to the following examples.
Example 1
(Preparation of Insulating Applied Positive Electrode)
[0132] LiNi.sub.0.8Mn.sub.0.15Co.sub.0.05, a carbon conductive
agent (acetylene black) and polyvinylidene fluoride (PVdF) as a
binder were dispersed in N-methyl-2-pyrrolidone at a weight ratio
of 90:5:5 to prepare a slurry for a positive electrode active
material layer. This slurry was applied to the surface of a
positive electrode current collector foil made of aluminum and
dried to form a positive electrode active material layer (PAM 1). A
positive electrode active material layer was similarly formed on
the back surface of the positive electrode current collector
foil.
[0133] Subsequently, alumina and polyvinylidene fluoride (PVdF) as
a binder were dispersed in N-methyl-2-pyrrolidone at a weight ratio
of 90:10 to prepare a slurry for an insulating layer. This was
applied to the positive electrode active material layer and dried
to form an insulating layer (INS 1). An insulating layer was
similarly formed on the positive electrode active material layer on
the back side of the positive electrode current collector foil.
Subsequently, the whole of the positive electrode current collector
foil, the positive electrode active material layer and the
insulating layer were compression-molded and further cut into a
predetermined shape to prepare a plurality of positive
electrodes.
(Measurement of Peeling Strength)
[0134] One of the obtained plurality of positive electrodes was cut
out as a sample having a width of 20 mm and a length of 100 mm, and
90.degree. peeling test was carried out using this sample under an
ambient temperature environment (15.degree. C. to 25.degree. C.).
The 90.degree. peeling test was carried out as follows. First, the
sample was fixed on the upper surface of a flat sample stage using
a double-sided tape (NWBB-20 manufactured by Nichiban Co., Ltd.)
having the same width as the sample so that the double-sided tape
was not peeled off. At that time, only the portion of the sample
from the one end to 80 mm in the length direction was fixed to the
sample stage, and the remaining portion of 20 mm length was not
fixed as a clamping margin. Next, the clamping margin of the sample
was held by a chuck, and in that state, the chuck was moved at a
speed of 100 mm/min in a direction away from the sample stage
perpendicular to the upper surface of the sample stage, the sample
was peeled off from the sample stage, and the maximum load at that
time was measured. For 90.degree. peeling test, a tensile and
compression tester (model number FGS-20TV, manufactured by Nidec
Shimpo Co., Ltd.) was used. In the 90.degree. peeling test, the
peeling strength and layer and location where peel was occurred was
determined. The peeling strength is a value converted into a force
per 1 mm width of a sample by dividing the maximum load measured
when the sample is peeled as described above by 20 mm which is the
width of the sample. The unit of the peeling strength is expressed
in Nm/mm.
(Preparation of Negative Electrode)
[0135] Natural graphite, sodium carboxymethyl methyl cellulose as a
thickener and styrene butadiene rubber as a binder were mixed in an
aqueous solution at a weight ratio of 97:1:2 to prepare a slurry
for a negative electrode active material layer. This was applied to
the surface of a negative electrode current collector foil made of
copper and dried to form a negative electrode active material layer
(NAM 1). A negative electrode active material layer was similarly
formed on the back surface of the negative electrode current
collector foil. Subsequently, the whole of negative electrode
current collector foil and the negative electrode active material
layer were compression-molded and further cut into a predetermined
shape to prepare a plurality of negative electrodes.
(Preparation of Electrolytic Solution)
[0136] For a non-aqueous solvent of the electrolytic solution, a
non-aqueous solvent obtained by mixing ethylene carbonate (EC) and
diethyl carbonate (DEC) in a volume ratio of 30:70 was used. As a
supporting salt, LiPF.sub.6 was dissolved so as to have a
concentration of 1 M.
(Preparation of Battery)
[0137] The positive electrode and the negative electrode were
laminated via the base of the separator to prepare an electrode
assembly. As the separator, a microporous separator made of
polypropylene and having a thickness of 25 .mu.m was used. The size
of the electrode assembly was adjusted so that the initial charge
capacity of the cell was 1 Ah. Terminals for taking out current
were connected to each of the laminated positive electrode and
negative electrode, and they were accommodated in a casing package
which is a laminated film of aluminum and resin. After injecting
the electrolytic solution into the casing, the casing was sealed
under reduced pressure. A battery was prepared by the above
steps.
(160.degree. C. Heating Test)
[0138] After the prepared battery was charged to 4.2 V, heating
test at 160.degree. C. was carried out. The heating rate was
10.degree. C./min, and the temperature was maintained for 30
minutes after reaching 160.degree. C.
Example 2
[0139] A positive electrode having an insulating layer was prepared
in the same manner as Example 1 expect that the positive electrode
active material was changed from LiNi.sub.0.8Mn.sub.0.15Co.sub.0.05
that was used in Example 1 to LiNi.sub.0.8Ta.sub.0.15Al.sub.0.05
and that a positive active material layer (PAM 2) was formed using
this positive active material. Further, a battery was prepared in
the same manner as Example 1 except that the above positive
electrode was used. The peeling test of the prepared positive
electrode and the 160.degree. C. heating test of the prepared
battery were carried out in the same manner as Example 1.
Example 3
[0140] A positive electrode having an insulating layer was prepared
in the same manner as Example 1 except that the positive electrode
active material was changed from LiNi.sub.0.8Mn.sub.0.15Co.sub.0.05
that was used in Example 1 to LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2 and
that a positive electrode active material layer (PAM 3) was formed
using this positive electrode active material. Further, a battery
was prepared in the same manner as Example 1 except that this
positive electrode was used. The peeling test of the prepared
positive electrode and the 160.degree. C. heating test of the
prepared battery were carried out in the same manner as Example
1.
Example 4
(Preparation of Insulation Coated Negative Electrode)
[0141] Graphite, sodium carboxymethyl methyl cellulose as a
thickener and styrene butadiene rubber as a binder were mixed in an
aqueous solution at a weight ratio of 97:1:2 to prepare a slurry
for a negative electrode active material layer. The slurry was
applied to the surface of a negative electrode current collector
foil made of copper and dried to form a negative electrode active
material layer (NAM 1). A negative electrode active material layer
was similarly formed on the back surface of the negative electrode
current collector foil. Subsequently, the negative electrode active
material layers formed on both sides of the negative electrode
current collector foil were compression-molded.
[0142] Subsequently, alumina and polyvinylidene fluoride (PVdF) as
a binder were dispersed in N-methyl-2-pyrrolidone at a weight ratio
of 90:10 to prepare a slurry for an insulating layer. This slurry
was applied to the negative electrode active material layer and
dried to form an insulating layer (INS 1). An insulating layer was
similarly formed on the negative electrode active material layer on
the back side of the negative electrode current collector foil.
Next, the insulating layers formed on both sides of the negative
electrode current collector foil were compression-molded and
further cut into a predetermined shape to prepare a plurality of
negative electrodes. For the prepared negative electrode, the
peeling test was carried out in the same manner as Example 1.
(Preparation of Positive Electrode)
[0143] LiNi.sub.0.8Mn.sub.0.15Co.sub.0.05, a carbon conductive
agent (acetylene black) and polyvinylidene fluoride (PVdF) as a
binder were dispersed in N-methyl-2-pyrrolidone at a weight ratio
of 90:5:5 to prepare a slurry for a positive electrode active
material layer. This slurry was applied to the surface of a
positive electrode current collector foil made of aluminum and
dried to form a positive electrode active material layer (PAM 1). A
positive electrode active material layer was similarly formed on
the back surface of the positive electrode current collector foil.
Subsequently, the whole of the positive electrode current collector
foil and the positive electrode active material layer was
compression-molded and further cut into a predetermined shape to
prepare a plurality of positive electrodes.
(Preparation of Battery)
[0144] After preparation of the negative electrode and the positive
electrode, an electrolytic solution and a battery were prepared in
the same manner as Example 1. Using the prepared battery, the
160.degree. C. heating test was carried out under the same
conditions as Example 1.
Example 5
[0145] Graphite and polyacrylic acid as a binder were mixed in an
aqueous solution at a weight ratio of 95:5 to prepare a slurry for
a negative electrode active material layer. A negative electrode
was prepared in the same manner as Example 4 except that the
negative electrode active material layer (NAM 2) was formed using
this slurry, and the peeling test of the negative electrode was
carried out. In addition, a battery was prepared in the same manner
as Example 4 except that the above negative electrode was used, and
the 160.degree. C. heating test was carried out.
Example 6
[0146] Graphite, Si and polyacrylic acid as a binder were mixed in
an aqueous solution at a weight ratio of 92:3:5 to prepare a slurry
for a negative electrode active material layer. A negative
electrode was prepared in the same manner as Example 4 except that
the negative electrode active material layer (NAM 3) was formed
using this slurry, and the peeling test was carried out. In
addition, a battery was prepared in the same manner as Example 4
except that the above negative electrode was used, and the
160.degree. C. heating test was carried out.
Example 7
[0147] Alumina and polyacrylic acid (PAA) as a binder were mixed in
an aqueous solution at a weight ratio of 93:7 to prepare a slurry
for an insulating layer. A negative electrode was prepared in the
same manner as Example 4 except that the negative electrode
insulating layer (INS 2) was formed using this slurry, and the
peeling test was carried out. In addition, a battery was prepared
in the same manner as Example 4 except that the above negative
electrode was used, and the 160.degree. C. heating test was carried
out.
Example 8
[0148] Graphite and polyvinylidene fluoride (PVdF) as a binder were
dispersed in N-methyl-2-pyrrolidone at a weight ratio of 95:5 to
prepare a slurry for a negative electrode active material. This
slurry was applied to the surface of a negative electrode current
collector foil made of copper and dried to form a negative
electrode active material layer (NAM 4). A negative electrode
active material layer was similarly formed on the back surface of
the negative electrode current collector foil.
[0149] Subsequently, alumina and polyimide as a binder were
dispersed in N-methyl-2-pyrrolidone at a weight ratio of 90:10 to
prepare a slurry for an insulating layer. This slurry was applied
to the negative electrode active material layer and dried to form
an insulating layer (INS 3). An insulating layer was similarly
formed on the negative electrode active material layer on the back
side of the negative electrode current collector foil. Next, the
whole of the negative electrode current collector foil, the
negative electrode active material layer and the insulating layer
were compression-molded and further cut into a predetermined shape
to prepare a plurality of negative electrodes. For the prepared
negative electrode, the peeling test was carried out in the same
manner as Example 4. In addition, a battery was prepared in the
same manner as in Example 4 except that the above negative
electrode was used, and the 160.degree. C. heating test was carried
out.
Example 9
[0150] Graphite, SiO and polyacrylic acid as a binder were mixed in
an aqueous solution at a weight ratio of 28:67:5 to prepare a
slurry for a negative electrode active material layer. A negative
electrode was prepared in the same manner as Example 4 except that
the negative electrode active material layer (NAM 4) was formed
using this slurry, and the peeling test was carried out. In
addition, a battery was prepared in the same manner as Example 4
except that the above negative electrode was used, and the
160.degree. C. hearing test was carried out.
Comparative Example 1
[0151] Graphite, sodium carboxymethyl methyl cellulose as a
thickener, and styrene butadiene rubber as a binder were mixed in
an aqueous solution at a weight ratio of 97.6:1.2:1.2 to prepare a
slurry for a negative electrode active material layer. A negative
electrode was prepared in the same manner as Example 4 except that
the negative electrode active material layer (NAM 5) was formed
using this slurry, and the peeling test of the negative electrode
was carried out. In addition, a battery was prepared in the same
manner as Example 4 except that the above negative electrode was
used, and the 160.degree. C. heating test was carried out.
Comparative Example 2
[0152] Alumina and polyvinylidene fluoride (PVdF) as a binder were
dispersed in N-methyl-2-pyrrolidone at a weight ratio of 97:3 to
prepare a slurry for an insulating layer. A positive electrode was
prepared in the same manner as Example 1 except that the insulating
layer (INS 4) of the positive electrode was formed using this
slurry, and the peeling test was carried out. In addition, a
battery was prepared in the same manner as Example 1 except that
the above positive electrode was used, and the 160.degree. C.
heating test was carried out.
Comparative Example 3
[0153] A positive electrode was prepared in the same manner as
Example 1 except that an insulating layer (INS 5) for a positive
electrode was formed by using a slurry for the insulating layer in
which alumina and polyvinylidene fluoride (PVdF) as a binder were
dispersed in N-methyl-2-pyrrolidone at a weight ratio of 92:8, and
that a drying process and a compression-molding process ware added
after a slurry for a positive electrode active material layer was
applied to both surfaces of the positive electrode current
collector foil The peeling test was carried out on the prepared
positive electrode. In addition, a battery was prepared in the same
manner as Example 1 except that the above positive electrode was
used, and the 160.degree. C. heating test was carried out.
[0154] Table 1 shows the layer configurations of the positive
electrode and the negative electrode, the results of the peeling
test and the results of the 160.degree. C. heating test of Examples
1 to 8 and Comparative Examples 1 to 3.
TABLE-US-00001 TABLE 1 Electrode having insulating layer Applying
Peeling Positive Negative Insulation Peeled Strength 160.degree. C.
Electrode Electrode Layer Portion (mN/mm) Heating Test Example 1
Al/CAM1/INS1 Cu/NAM1 before CCF-AML 21 No smoking/ compression
firing Example 2 Al/CAM2/INS1 Cu/NAM1 before CCF-AML 18 No smoking/
compression firing Example 3 Al/CAM3/INS1 Cu/NAM1 before CCF-AML 20
No smoking/ compression firing Example 4 Al/CAM1 Cu/NAM1/INS1 after
CCF-AML 15 No smoking/ compression firing Example 5 Al/CAM1
Cu/NAM2/INS1 after CCF-AML 12 No smoking/ compression firing
Example 6 Al/CAM1 Cu/NAM3/INS1 after CCF-AML 11 No smoking/
compression firing Example 7 Al/CAM1 Cu/NAM1/INS2 after CCF-AML 15
No smoking/ compression firing Example 8 Al/CAM1 Cu/NAM4/INS3
before CCF-AML 30 No smoking/ compression firing Example 9 Al/CAM1
Cu/NAM4/INS1 After CCF-AML 35 No smoking/ compression firing
Comparative Al/CAM1 Cu/NAM5/INS1 after CCF-AML 9.2 Smoking Example
1 compression Comparative Al/CAM1/INS4 Cu/NAM1 before AML-IL 10
Smoking Example 2 compression Comparative Al/CAM1/INS5 Cu/NAM1
after AML-IL 12 Smoking Example 3 compression
[0155] In Table 1, the column of the positive electrode represents
the material of "positive electrode current collector foil/positive
electrode active material layer/insulating layer". Similarly, the
column of the negative electrode represents the material of
"negative electrode current collector foil/negative electrode
active material layer/insulating layer". The details of PAM 1 to
PAM 3, NAM 1 to NAM 5 and INS 1 to INS 5 are as described in the
above-mentioned Examples 1 to 9 and Comparative Examples 1 to
3.
[0156] In each of Examples 1 to 9, peeling occurred between the
current collector foil and the active material layer in the peel
test, and the peeling strength thereof was 10 mN/mm or more.
Furthermore, smoking and firing from the battery were not confirmed
in the 160.degree. C. heating test. On the other hand, in
Comparative Examples 2 and 3, although the peeling strength was 10
mN/mm or more, peeling occurred between the active material layer
and the insulating layer, and smoke was generated from the battery
in the 160.degree. C. heating test. In Comparative Example 1,
peeling occurred between the current collector foil and the active
material layer as in Examples 1 to 8, but the peeling strength was
relatively small as 9.2 mN/mm, and smoking was generated in the
heating test. From the above, it was found that smoking and heat
generation can be effectively suppressed even though the
temperature of the battery is high by configuring the electrode
having the insulating layer further on the active material layer
such that peeling occurs between the current collector foil and the
active material layer and its peeling strength is 10 mN/mm or more
when 90.degree. peeling test was carried out.
[0157] Here, in the Comparative Examples 2 and 3, a mechanism in
which smoke was generated in the heating test will be considered.
In Comparative Examples 2 and 3, peeling occurred between the
active material layer and the insulating layer, which means that
the adhesion force between the active material layer and the
insulating layer is lower than the adhesion force between active
material layer and the current collecting foil. In the heating
test, the positive electrode, the negative electrode and the
separator are heated, and a shrinking force in the in-plane
direction is exerted on the separator by heating. At the same time,
contracting force acts also on the positive electrode and the
negative electrode that are in contact with the separator so as to
be pulled by the separator. By this contracting force, in the
negative electrode, the insulating layer is peeled from the active
material layer so as to be pulled by the separator and the active
material layer is partially exposed. As a result, it is considered
that a short circuit occurred between the positive electrode and
the negative electrode, resulting in smoking.
[0158] Some or all of the above embodiments may also be described
as follows, but the disclosure of the present application is not
limited to the following further exemplary embodiments.
Further Exemplary Embodiment 1
[0159] An electrode for a battery comprising:
[0160] a current collector (110),
[0161] an active material layer (111) formed on at least one
surface of the current collector (110),
[0162] an insulating layer (112) formed on a surface of the active
material layer (111), and
[0163] wherein peeling occurs between the current collector (110)
and the active material layer (111) and a peeling strength thereof
is 10 mN/mm or more when a 90.degree. peeling test is carried out
at a peeling rate of 100 mm/min.
Further Exemplary Embodiment 2
[0164] The electrode according to Further exemplary embodiment 1,
wherein the current collector (110) and the active material layer
(111) are the current collector (110) for a positive electrode.
Further Exemplary Embodiment 3
[0165] The electrode according to Further exemplary embodiment 2,
wherein the active material layer (111) for the positive electrode
includes polyvinylidene fluoride as a binder.
Further Exemplary Embodiment 4
[0166] The electrode according to Further exemplary embodiment 1,
wherein the current collector (110) and the active material layer
(111) are the current collector (110) and the active material layer
(111) for a negative electrode.
Further Exemplary Embodiment 5
[0167] The electrode according to Further exemplary embodiment 4,
wherein the active material layer (111) for the negative electrode
includes at least one of styrene butadiene rubber, polyacrylic acid
and polyvinylidene fluoride as a binder.
Further Exemplary Embodiment 6
[0168] The electrode according to any one of Further exemplary
embodiments 1 to 5, wherein the active material layer (111)
includes N-methyl-2-pyrrolidone.
Further Exemplary Embodiment 7
[0169] A battery comprising:
[0170] at least one positive electrode (11),
[0171] at least one negative electrode (12) disposed to face the
positive electrode (11), and
[0172] wherein at least one of the positive electrode (11) and the
negative electrode (12) includes a current collector (110), an
active material layer (111) formed on at least one surface of the
current collector (110), and an insulating layer (112) formed on a
surface of the active material layer (111), and peeling occurs
between the current collector (110) and the active material layer
(111) and a peeling strength thereof is 10 mN/mm or more when a
90.degree. peeling test is carried out at a peeling rate of 100
mm/min.
Further Exemplary Embodiment 8
[0173] The battery according to Further exemplary embodiment 7,
wherein the positive electrode (11) and the negative electrode (12)
are disposed to face each other with the insulating layer (112)
interposed therebetween.
Further Exemplary Embodiment 9
[0174] The battery according to Further exemplary embodiment 7 or
8, further comprising a separator (13) disposed between the
positive electrode (11) and the negative electrode (12).
Further Exemplary Embodiment 10
[0175] The battery according to any one of Further exemplary
embodiments 7 to 9, wherein the active material layer (111)
includes polyvinylidene fluoride as a binder.
Further Exemplary Embodiment 11
[0176] The battery according to any one of Further exemplary
embodiments 7 to 10, wherein the active material layer (111)
includes N-methyl-2-pyrrolidone.
Further Exemplary Embodiment 12
[0177] A method for manufacturing an electrode for a battery, the
method comprising;
[0178] forming an active material layer (111) on at least one
surface of a current collector (110),
[0179] forming an insulating layer (112) such that the insulating
layer (112) is finally laminated on a surface of the active
material layer (111), and
[0180] wherein at least one of a material of the active material
layer (111), a formation condition of the active material layer
(111), a material of the insulating layer (112) and a formation
condition of the insulating layer (112) is determined such that
peeling occurs between the current collector (110) and the active
material layer (111) and a peeling strength thereof is 10 mN/mm or
more when a 90.degree. peeling test is carried out at a peeling
rate of 100 mm/min.
Further Exemplary Embodiment 13
[0181] The method for manufacturing the electrode according to
Further exemplary embodiment 12,
[0182] wherein the step of forming the active material layer (111)
comprises:
[0183] applying a mixture for the active material layer in which an
active material and a binder are dispersed in a solvent,
[0184] drying the mixture for the active material layer after the
mixture is applied, and
[0185] compression-molding the mixture for the active material
layer after the mixture is dried, and
[0186] wherein the step of forming the insulating layer (112)
comprises:
[0187] applying a mixture for the insulating layer in which an
insulating material and a binder are dispersed in a solvent,
[0188] drying the mixture for the insulating layer after the
mixture is applied, and
[0189] compression-molding the mixture for the insulating layer
after the mixture is dried.
Further Exemplary Embodiment 14
[0190] The method for manufacturing the electrode according to
Further exemplary embodiment 13,
[0191] wherein the step of applying the mixture for the active
material layer,
[0192] the step of drying the mixture for the active material
layer,
[0193] the step of compression-molding the mixture for the active
material layer,
[0194] the step of applying the mixture for the insulating
layer,
[0195] the step of drying the mixture for the insulating layer
and
[0196] the step of compression-molding the mixture for the
insulating layer
[0197] are carried out in this order.
Further Exemplary Embodiment 15
[0198] The method for manufacturing the electrode according to
Further exemplary embodiment 13,
[0199] wherein the step of applying the mixture for the active
material layer,
[0200] the step of drying the mixture for the active material
layer,
[0201] the step of applying the mixture for the insulating layer
and
[0202] the step of drying the mixture for the insulating layer
[0203] are carried out in this order, and
[0204] wherein the step of compression-molding the mixture for the
active material layer and the step of compression-molding the
mixture for the insulating layer are carried out simultaneously
after the step of drying the mixture for the insulating layer.
Further Exemplary Embodiment 16
[0205] The method for manufacturing the electrode according to
Further exemplary embodiment 13,
[0206] wherein the step of applying the mixture for the active
material layer and
[0207] the step of applying the mixture for the insulating
layer
[0208] are carried out in this order,
[0209] the step of drying the mixture for the active material layer
and the step of drying the mixture for the insulating layer are
carried out simultaneously after the step of applying the mixture
for the insulating layer, and
[0210] the step of compression-molding the mixture for the active
material layer and the step of compression-molding the mixture for
the insulating layer are carried out simultaneously thereafter.
Further Exemplary Embodiment 17
[0211] The method for manufacturing the electrode according to any
one of Further exemplary embodiments 13 to 16, wherein the mixture
for the active material layer includes polyvinylidene fluoride as
the binder.
Further Exemplary Embodiment 18
[0212] The method for manufacturing the electrode according to any
one of Further exemplary embodiments 13 to 17, wherein the mixture
for the active material layer includes N-methyl-2-pyrrolidone as
the solvent.
EXPLANATION OF SYMBOLS
[0213] 1 Battery [0214] 10 Electrode assembly [0215] 10a Positive
electrode tab [0216] 10b Negative electrode tab [0217] 11 Positive
electrode [0218] 12 Negative electrode [0219] 13 Separator [0220]
21, 22 Casing member [0221] 31 Positive electrode terminal [0222]
32 Negative electrode terminal [0223] 110 Current collector [0224]
110a Extended portion [0225] 111 Active material layer [0226] 112
Insulating layer [0227] 201 Backup roller [0228] 210, 220 Die
coater [0229] 211, 212, 221 Die head [0230] 211a, 212a, 221a
Discharge opening
* * * * *