U.S. patent application number 16/385520 was filed with the patent office on 2019-08-08 for separator and battery.
The applicant listed for this patent is MURATA MANUFACTURING CO., LTD.. Invention is credited to Kazuki CHIBA, Masatake HAYASHI, Atsushi KAJITA, Yukako TESHIMA.
Application Number | 20190245184 16/385520 |
Document ID | / |
Family ID | 44099765 |
Filed Date | 2019-08-08 |
![](/patent/app/20190245184/US20190245184A1-20190808-D00000.png)
![](/patent/app/20190245184/US20190245184A1-20190808-D00001.png)
![](/patent/app/20190245184/US20190245184A1-20190808-D00002.png)
![](/patent/app/20190245184/US20190245184A1-20190808-D00003.png)
![](/patent/app/20190245184/US20190245184A1-20190808-D00004.png)
United States Patent
Application |
20190245184 |
Kind Code |
A1 |
CHIBA; Kazuki ; et
al. |
August 8, 2019 |
SEPARATOR AND BATTERY
Abstract
A separator includes a first layer that has a first principal
face and a second principal face, and a second layer that is formed
on at least one of the first principal face and the second
principal face. The first layer is a microporous membrane including
a first polymer resin, and the second layer is a microporous
membrane including inorganic particles having an electrically
insulating property and a second polymer resin.
Inventors: |
CHIBA; Kazuki; (Kyoto,
JP) ; KAJITA; Atsushi; (Kyoto, JP) ; TESHIMA;
Yukako; (Kyoto, JP) ; HAYASHI; Masatake;
(Kyoto, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MURATA MANUFACTURING CO., LTD. |
Kyoto |
|
JP |
|
|
Family ID: |
44099765 |
Appl. No.: |
16/385520 |
Filed: |
April 16, 2019 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12959638 |
Dec 3, 2010 |
10312491 |
|
|
16385520 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 2250/40 20130101;
H01M 2/1653 20130101; H01M 2/1686 20130101; B32B 2255/26 20130101;
B32B 1/08 20130101; H01M 10/0525 20130101; B32B 2307/724 20130101;
B32B 15/085 20130101; H01M 2/145 20130101; B32B 2307/50 20130101;
B32B 2457/10 20130101; H01M 10/0431 20130101; B32B 2255/10
20130101; H01M 2/166 20130101; H01M 2/28 20130101; H01M 2/18
20130101 |
International
Class: |
H01M 2/16 20060101
H01M002/16; B32B 15/085 20060101 B32B015/085; H01M 2/18 20060101
H01M002/18; H01M 2/28 20060101 H01M002/28; H01M 10/04 20060101
H01M010/04; B32B 1/08 20060101 B32B001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 4, 2009 |
JP |
2009-277071 |
Claims
1. A battery comprising: a positive electrode; a negative
electrode; an electrolyte; and a separator, wherein the separator
includes a first resin layer having a first principal face and a
second principal face, and a second resin layer provided on at
least one of the first principal face and the second principal
face; wherein the second resin layer includes inorganic particles,
wherein an average particle diameter D20 of the inorganic particles
is larger than an average pore diameter of pores opening onto a
surface of the first resin layer, wherein the average particle
diameter D20 of the inorganic particles ranges from 0.13 .mu.m to
2.10 .mu.m.
2. The battery according to claim 1, wherein the average particle
diameter D20 of the inorganic particles ranges from 0.13 .mu.m to
0.80 .mu.m.
3. The battery according to claim 2, wherein the average particle
diameter D20 of the inorganic particles ranges from 0.13 .mu.m to
0.21 .mu.m.
4. The battery according to claim 1, wherein a volume fraction of
the inorganic particles in the second resin layer is equal to or
greater than 60 vol % and equal to or lower than 90 vol %.
5. The battery according to claim 4, wherein a volume fraction of
the inorganic particles in the second resin layer is equal to or
greater than 82 vol % and equal to or lower than 90 vol %.
6. The battery according to claim 1, wherein the inorganic
particles includes one or more of alumina, silica, zirconia, and
titania.
7. The battery according to claim 1, wherein an average particle
diameter D90 of the inorganic particles ranges from 2.00 .mu.m to
5.00 .mu.m.
8. The battery according to claim 1, wherein an average particle
diameter D90 of the inorganic particles is equal to or less than
1/3 of a thickness of the first resin layer.
9. The battery according to claim 1, wherein a thickness of the
first resin layer is equal to or greater than 10.0 .mu.m and less
than 30.0 .mu.m.
10. The battery according to claim 1, wherein the average pore
diameter of the pores ranges from 0.03 .mu.m to 0.10 .mu.m.
11. The battery according to claim 10, wherein the average pore
diameter of the pores ranges from 0.03 .mu.m to 0.05 .mu.m.
12. The battery according to claim 1, wherein the first resin layer
includes one or both of polyethylene and polypropylene.
13. The battery according to claim 1, wherein the second resin
layer includes one or more of polyvinylidene fluoride,
polyhexafluoropropylene, polysiloxane, polyvinyl alcohol,
polyacrylic acid, polymethacrylate, styrene-butadiene rubber, and
nitrile butadiene rubber.
14. The battery according to claim 1, wherein the second resin
layers are formed on both of the first principal face and the
second principal face of the first resin layer.
15. The battery according to claim 1, wherein the second resin
layer has a fibrillated mesh-shaped structure with the inorganic
particles being separately dispersed.
16. The battery according to claim 1, wherein the second resin
layer comprises fibrils having an average diameter of equal to or
less than 1 .mu.m.
17. The battery according to claim 1, wherein an area density per
unit area of the second resin layer is equal to or greater than 0.2
mg/cm.sup.2 and equal to or less than 1.8 mg/cm.sup.2.
18. The battery according to claim 1, wherein a difference between
air permeability of the separator and air permeability of the first
layer is equal to or less than 60 sec/100 ml.
19. The battery according to claim 1, wherein an air-permeability
rising rate of air permeability at a time when pressure is applied
to the separator for two minutes at 60.degree. C. under 50
kgf/cm.sup.2 with respect to air permeability before the pressure
load to the separator is equal to or lower than 35%.
20. The battery according to claim 1, wherein the positive
electrode, the negative electrode and the separator are stacked and
wound to constitute a wound electrode body, and an outer end of the
separator is exposed on the periphery of the wound electrode
body.
21. The battery according to claim 1, wherein an open-circuit
voltage in a fully-charged state is in the range of 4.2 V to 4.6
V.
22. An electronic apparatus comprising the battery according to
claim 1.
23. A separator comprising: a first resin layer having a first
principal face and a second principal face, and a second resin
layer provided on at least one of the first principal face and the
second principal face; wherein the second resin layer includes
inorganic particles, wherein an average particle diameter D20 of
the inorganic particles is larger than an average pore diameter of
pores opening onto a surface of the first resin layer, wherein the
average particle diameter D20 of the inorganic particles ranges
from 0.13 .mu.m to 2.10 .mu.m.
24. The separator according to claim 23, wherein the average
particle diameter D20 of the inorganic particles ranges from 0.13
.mu.m to 0.80 .mu.m.
25. The separator according to claim 24, wherein the average
particle diameter D20 of the inorganic particles ranges from 0.13
.mu.m to 0.21 .mu.m.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S.
application Ser. No. 12/959,638, filed on Dec. 3, 2010, which
application claims priority to Japanese Priority Patent Application
JP 2009-277071 filed in the Japan Patent Office on Dec. 4, 2009,
the entire contents of which is hereby incorporated by
reference.
BACKGROUND
[0002] The present application relates to a separator and a battery
including the separator, and more particularly, to a
lamination-type separator.
[0003] Owing to the noticeable recent development of mobile
electronic technology, electronic apparatuses such as cellular
phones and notebook computers are recognized as basic technologies
that support an advanced information society. Research and
development in implementing a high level of functionality of such
electronic apparatuses has been vigorously advanced, and the power
consumption of these electronic apparatuses has increased in
proportion thereto. On the other hand, long-term driving force is
necessary for these electronic apparatuses. Accordingly,
implementation of a high energy density of a secondary battery that
is a driving power source thereof is necessarily desired. In
addition, from the viewpoint of the volume occupied, the mass, and
the like of a battery built into these electronic apparatuses, it
is desirable that the energy density of the battery is as high as
it possibly can be. Accordingly, currently, lithium-ion secondary
batteries with a superior energy density are built into most
apparatuses.
[0004] In the lithium-ion secondary battery, by opposing a positive
electrode and a negative electrode through a separator, both safety
and battery capability are implemented. However, considering the
implementation of high capacity and high safety, in the related art
it is difficult to obtain sufficient capability only by using a
polyolefin microporous membrane. In other words, in a battery in
which high capacity is implemented in accordance with an increase
in the functionality of the electronic apparatus, the thickness of
an electrode layer is increased. Accordingly, the expansion of the
negative electrode increases at the time of the charging process.
At this time, pressure is applied to the inside of a cell, the
pores of the separator are crushed so as to decrease ion
permeability. Therefore, in a case where compression resistance is
low, it is difficult to obtain adequate battery
characteristics.
[0005] Meanwhile, for example as in JP-A-2008-4536, there is
disclosed the technology of employing a separator that has a
dynamic hardness DH of 1000 or higher at a time when the indenter
load reaches 12 kgf/cm.sup.2 in the composite membrane that is
acquired by forming a coating layer formed from a polymer porous
body having heat resistance on at least one face of a polyolefin
microporous membrane.
SUMMARY
[0006] As the thickness of the negative electrode mixture increases
in accordance with the increase in capacity, the pressure applied
to the inside of the battery further increases. However, in
JP-A-2008-4536, it has not been checked whether the separator
maintains its pores in the state in which a load of the separator
is equal to or greater than 12 kgf/cm2.
[0007] Thus, it is desirable to provide a separator that can
maintain the pores of the separator even in a case where expansion
of the electrode occurs in accordance with charging/discharging and
a battery including this separator.
[0008] According to an, there is provided a separator including: a
first layer that has a first principal face and a second principal
face; and a second layer that is formed on at least one of the
first principal face and the second principal face. The first layer
is a microporous membrane including a polymer resin, and the second
layer is a microporous membrane including inorganic particles
having an electrically insulating property and a polymer resin.
[0009] According to another, there is provided a battery including:
a positive electrode; a negative electrode; an electrolyte; and a
separator. The separator includes a first layer that has a first
principal face and a second principal face and a second layer that
is formed on at least one of the first principal face and the
second principal face. The first layer is a microporous membrane
including a polymer resin, and the second layer is a microporous
membrane including inorganic particles having an electrically
insulating property and a polymer resin.
[0010] In the above-described separator, it is preferable that a
difference between air permeability of the separator and air
permeability of the first layer is equal to or less than 60 sec/100
ml, and an air-permeability rising rate of air permeability at a
time when pressure is applied to the separator for two minutes at
60.degree. C. under 50 kgf/cm.sup.2 with respect to air
permeability before the pressure load is equal to or lower than
35%. In order to implement this kind of separator, it is preferable
that an average particle diameter D20 of the inorganic particles is
larger than an average pore diameter of the pores opening onto a
surface of the first layer, and the average pore diameter of the
pores opening onto the surface of the first layer is equal to or
greater than 0.03 .mu.m and equal to or less than 2.00 .mu.m.
[0011] According to an embodiment, the pressure resistance is
improved, and the inorganic particles are not allowed to break into
the pores formed on the surface of the first layer. Accordingly, it
is difficult to crush the pores of the first layer of the
separator. Therefore, both high ion permeability and high pressure
resistance can be achieved.
[0012] According to an embodiment, the separator that can implement
both pressure resistance and ion permeability can be achieved.
Therefore, a battery that has a high degree of safety and superior
battery characteristics can be achieved.
[0013] Additional features and advantages are described herein, and
will be apparent from the following Detailed Description and the
figures.
BRIEF DESCRIPTION OF THE FIGURES
[0014] FIG. 1 is a cross-sectional view representing a
configuration example of a nonaqueous electrolyte secondary battery
according to a first.
[0015] FIG. 2 is an enlarged cross-sectional view of a part of a
wound electrode body shown in FIG. 1.
[0016] FIG. 3 is a cross-sectional view representing a
configuration example of a separator according to the first.
[0017] FIG. 4 is an exploded perspective view representing a
configuration example of a nonaqueous electrolyte secondary battery
according to a second.
[0018] FIG. 5 is a cross-sectional view of a wound electrode body,
which is shown in FIG. 4, taken along line VI-VI.
DETAILED DESCRIPTION
[0019] Embodiments of the present application will be described
below in detail with reference to the drawings.
[0020] (1) First Embodiment (Example of Cylinder-Type Battery)
[0021] (2) Second Embodiment (Example of Flat-Type Battery)
1. First Embodiment
[0022] Configuration of Battery
[0023] FIG. 1 is a cross-sectional view representing a
configuration example of a nonaqueous electrolyte secondary battery
according to the first. This nonaqueous electrolyte secondary
battery is a so-called a lithium ion secondary battery in which the
capacity of a negative electrode is represented by a capacitance
component according to intercalation or release of lithium (Li)
that is an electrode reaction material. The nonaqueous electrolyte
secondary battery is of a so-called cylinder type and has a wound
electrode body 20 in which one pair of strip-shaped positive
electrodes 21 and a strip-shaped negative electrode 22 are stacked
and wound with separators 23 interleaved therebetween inside a
battery can 11 having a substantially hollow column shape. The
wound electrode body 20 is in a state where the separator 23, the
negative electrode 22, the separator 23 and the positive electrode
21 are stacked in this order and wound, and the end of the
separator 23 in the outer side is exposed on the periphery of the
wound electrode body 20 and faces the inner wall of the battery can
11.
[0024] The battery can 11 is composed of iron (Fe) plated with
nickel (Ni). One end of the battery can 11 is closed, and the other
end thereof is open. Inside the battery can 11, an electrolytic
solution is injected so that the separator 23 is impregnated with
the electrolytic solution. In addition, one pair of insulating
plates 12 and 13 is disposed perpendicular to the winding
peripheral face so as to interpose the wound electrode body 20
therebetween.
[0025] In the open end of the battery can 11, a battery cover 14
and a safety valve mechanism 15 and a positive temperature
coefficient device (PTC device) 16 disposed inside the battery
cover 14 are installed upon being caulked through a sealing gasket
17. Accordingly, the inside of the battery can 11 is hermetically
sealed. The battery cover 14 is composed of, for example, a
material that is the same as that of the battery can 11. The safety
valve mechanism 15 is electrically connected to the battery cover
14. Thus, when internal pressure of the battery reaches a
predetermined or higher level due to an internal short circuit,
heating from the exterior, or the like, a disk plate 15A is
reversed, thereby cutting off the electrical connection between the
battery cover 14 and the wound electrode body 20. The sealing
gasket 17 is composed of, for example, an insulating material, and
the surface thereof is coated with asphalt.
[0026] For example, a center pin 24 is inserted in the center of
the wound electrode body 20. A positive electrode lead 25 made of
aluminum (Al) or the like is connected to the positive electrode 21
of the wound electrode body 20; and a negative electrode lead 26
made of nickel or the like is connected to the negative electrode
22 of the wound electrode body 20. The positive electrode lead 25
extends from the wound electrode body 20 with one end thereof being
fixed to the end of the positive electrode 21 in the wound center
side while the other end thereof is welded to the safety valve
mechanism 15, whereby the positive electrode lead 25 is
electrically connected to the battery cover 14; and the negative
electrode lead 26 extends from the wound electrode body 20 with one
end thereof being fixed to the end of the negative electrode 22 in
the outer side while the other end thereof is welded to the battery
can 11, whereby the negative electrode lead 26 is electrically
connected to the battery can 11.
[0027] FIG. 2 is an enlarged cross-sectional view of a part of the
wound electrode body 20 shown in FIG. 1. FIG. 3 is a
cross-sectional view representing a configuration example of the
separator. Hereinafter, the positive electrode 21, the negative
electrode 22, the separator 23, and the electrolytic solution
configuring a secondary battery according to an will be
sequentially described with reference to FIGS. 2 and 3.
[0028] Positive Electrode
[0029] The positive electrode 21 has a structure in which, for
example, positive electrode active material layers 21B are disposed
on the both sides of a positive electrode collector 21A. Although
not shown in the figure, the positive electrode active material
layer 21B may be disposed on only one side of the positive
electrode collector 21A. The positive electrode collector 21A is
formed of a metal foil such as an aluminum foil. The positive
electrode active material layers 21B are disposed on the positive
electrode collector 21A except for both ends of the positive
electrode collector 21A. The positive electrode lead 25 is
connected to the positive electrode collector 21A of the positive
electrode 21 in a portion where the the positive electrode active
material layer 21B is not disposed and the positive electrode
collector 21A is exposed.
[0030] The positive electrode active material layer 21B is composed
so as to contain, for example, one or two or more types of
materials composing the positive electrode capable of intercalating
and releasing lithium as a positive electrode active material. As
necessary, the positive electrode active material layer 21B is
composed so as to contain a conductive material such as graphite
and a binder such as polyvinylidene fluoride.
[0031] As a material composing the positive electrode that is
capable of intercalating and releasing lithium, for example, a
lithium-containing compound such as a lithium oxide, lithium
phosphate, lithium sulfide, or an interlayer compound containing
lithium may be appropriately used. In addition, two or more types
of the above-described materials may be used in a mixed manner. In
order to increase the energy density, a lithium-containing compound
containing lithium, a transition metal element, and oxygen (O) is
preferably used, and the above-described lithium-containing
material containing at least one selected from a group consisting
of cobalt (Co), nickel (Ni), manganese (Mn), and iron (Fe) as the
transition metal element is more preferably used. As examples of
such a lithium-containing compound, there are a lithium composite
oxide having a structure of a layered rock salt type represented in
Formula (1), Formula (2), or Formula (3), a lithium composite oxide
having a structure of a spinel type represented in Formula (4), and
a lithium composite phosphate having a structure of an olivine type
represented in Formula (5). In particular, there are
LiNi.sub.0.50Co.sub.0.20Mn.sub.0.30O.sub.2, Li.sub.aCoO.sub.2
(a=1), Li.sub.bNiO.sub.2 (b=1),
Li.sub.c1Ni.sub.c2Co.sub.1-c2O.sub.2(c1=1 and 0<c2<1),
LidMn.sub.2O.sub.4(d=1) and LieFePO.sub.4 (e=1).
Li.sub.fMn.sub.(1-g-h)Ni.sub.gM1.sub.hO.sub.(2-j)F.sub.k (1)
[0032] (In the formula, M1 represents at least one selected from
the group of cobalt (Co), magnesium (Mg), aluminum (Al), boron (B),
titanium (Ti), vanadium (V), chrome (Cr), iron (Fe), copper (Cu),
zinc (Zn), zirconium (Zr), molybdenum (Mo), tin (Sn), calcium (Ca),
strontium (Sr), and tungsten (W), f, g, h, j, and k are values in
the respective ranges of 0.8.ltoreq.f.ltoreq.1.2, 0<g<0.5,
0.ltoreq.h.ltoreq.0.5, g+h<1, -0.1.ltoreq.j.ltoreq.0.2, and
0.ltoreq.k.ltoreq.0.1, and the composition of lithium changes
depending on a charged or discharged state, and the value of f
represents a value in a completed discharged state.).
Li.sub.mNi.sub.(1-n)M2.sub.nO.sub.(2-p)F.sub.q (2)
[0033] (In the formula, M2 represents at least one selected from
the group of cobalt (Co), manganese (Mn), magnesium (Mg), aluminum
(Al), boron (B), titanium (Ti), vanadium (V), chrome (Cr), iron
(Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium
(Ca), strontium (Sr), and tungsten (W), m, n, p, and q are values
in the respective ranges of 0.8.ltoreq.m.ltoreq.1.2,
0.005.ltoreq.n.ltoreq.0.5, 0.1.ltoreq.p.ltoreq.0.2, and
0.ltoreq.q.ltoreq.0.1, and the composition of lithium changes
depending on a charged or discharged state, and the value of m
represents a value in a completed discharged state.).
Li.sub.fCo.sub.(1-s)M3.sub.sO.sub.(2-t)F.sub.u (3)
[0034] (In the formula, M3 represents at least one selected from
the group of nickel (Ni), manganese (Mn), magnesium (Mg), aluminum
(Al), boron (B), titanium (Ti), vanadium (V), chrome (Cr), iron
(Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium
(Ca), strontium (Sr), and tungsten (W), r, s, t, and u are values
in the respective ranges of 0.8.ltoreq.r.ltoreq.1.2,
0.ltoreq.s.ltoreq.0.5, 0.1.ltoreq.t.ltoreq.0.2, and
0.ltoreq.u.ltoreq.0.1, and the composition of lithium changes
depending on a charged or discharged state, and the value of r
represents a value in a completed discharged state.).
Li.sub.vMn.sub.2-wM4wOxFy (4)
[0035] (In the formula, M4 represents at least one selected from
the group of cobalt (Co), nickel (Ni), magnesium (Mg), aluminum
(Al), boron (B), titanium (Ti), vanadium (V), chrome (Cr), iron
(Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium
(Ca), strontium (Sr), and tungsten (W), v, w, x, and y are values
in the respective ranges of 0.9.ltoreq.v.ltoreq.1.1,
0.ltoreq.w.ltoreq.0.6, 3.7.ltoreq.x.ltoreq.4.1, and
0.ltoreq.y.ltoreq.0.1, and the composition of lithium changes
depending on a charged or discharged state, and the value of v
represents a value in a completed discharged state.).
Li.sub.zM.sub.5PO.sub.4 (5)
[0036] (In the formula, M5 represents at least one selected from
the group of cobalt (Co), manganese (Mn), iron (Fe), nickel (Ni),
magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium
(V), niobium (Nb), copper (Cu), zinc (Zn), molybdenum (Mo), calcium
(Ca), strontium (Sr), tungsten (W), and zirconium (Zr), z is a
value in the range of 0.9<z<1.1, and the composition of
lithium changes depending on a charged or discharged state, and the
value of z represents a value in a completed discharged
state.).
[0037] As a material composing the positive electrode that is
capable of intercalating and releasing lithium, other than the
above-described materials, there are inorganic compounds such
MnO.sub.2, V.sub.2O.sub.5, V.sub.6O.sub.13, NiS, and MoS that do
not contain lithium.
[0038] [Negative Electrode]
[0039] The negative electrode 22 has, for example, a structure in
which negative electrode active material layers 22B are disposed on
both sides of a negative electrode collector 22A. Although not
shown in the figure, the negative electrode active material layer
22B may be disposed on only one side of the negative electrode
collector 22A. The negative electrode collector 22A is formed of a
metal foil such as a copper foil. The negative electrode active
material layers 22B are disposed on the negative electrode
collector 22A except for both ends of the negative electrode
collector 22A. The negative electrode lead 26 is connected to the
negative electrode collector 22A of the negative electrode 22 in a
portion where the negative electrode active material layer 22B is
not disposed and the negative electrode collector 22A is
exposed.
[0040] The negative electrode active material layer 22B is composed
so as to contain, for example, one or two or more types of a
material composing the negative electrode that is capable of
intercalating and releasing lithium as a negative electrode active
material. As necessary, the negative electrode active material
layer 22B is composed so as to contain a binder, similarly to the
positive electrode active material layer 21B.
[0041] In this secondary battery, the electrochemical equivalent of
the material composing the negative electrode that is capable of
intercalating and releasing lithium is larger than that of the
positive electrode 21. Accordingly, in the middle of a charging
process, lithium metal is not deposited in the negative electrode
22.
[0042] For example, this secondary battery is designed such that an
open circuit voltage (that is, a battery voltage) at the time when
the secondary battery is fully charged is in the range of 4.2 V to
4.6 V, and is preferably in the range of 4.25 V to 4.5 V. In a case
where the open circuit voltage is designed to be in the range of
4.25 V to 4.5 V, expansion of the electrode is larger than that of
a battery having an open circuit voltage of 4.20 V. Accordingly, a
noticeable effect of employing a separator according to an is
acquired. In addition, in a case where the open circuit voltage is
designed to be in the range of 4.25 V to 4.5 V, the amount of
discharge of lithium per unit mass increases for the same positive
electrode active material. Accordingly, the amounts of the positive
electrode active material and the negative electrode active
material are adjusted in accordance with the amount of discharge of
lithium. Therefore, a high energy density can be acquired.
[0043] As a material composing the negative electrode that is
capable of intercalating and releasing lithium, for example, there
is a carbon material such as non-graphitizable carbon,
graphitizable carbon, graphite, pyrolytic carbons, cokes, glassy
carbons, an organic polymer compound sintered body, a carbon fiber,
or an activated charcoal. Among these, as the cokes, there are
pitch coke, needle coke, petroleum coke, and the like. Here, the
organic polymer compound sintered body refers to a material that is
acquired by calcining a polymer material such as a phenolic resin
or a furan resin at an appropriate temperature so as to be
carbonized. Some of the organic polymer compound sintered bodies
are classified as non-graphitizable carbon or graphitizable carbon.
As the polymer material, there is polyacetylene or polypyrrole, or
the like. According to these carbon materials, there is very little
change in the crystal structure, which occurs at the time of
charging or discharging, a large amount of electricity charged and
discharged can be acquired, and good cycle characteristics can be
acquired. Thus, the carbon materials are preferably used.
Especially, since graphite has a high electrochemical equivalent
and provides a high energy density, graphite is preferably used. In
addition, since the non-graphitizable carbon provides superior
characteristics, the non-graphitizable carbon can be preferably
used. Furthermore, since a material that has low
charging/discharging electric potentials, in particular,
charging/discharging electric potentials that are close to those of
lithium metal can easily implement a high energy density of a
battery, such a material is preferably used.
[0044] As a material composing the negative electrode that is
capable of intercalating and releasing lithium, there is a material
that can intercalate and release lithium and contains at least one
of a metal element and a metalloid element as its constituent
element. By using such a material, a high energy density can be
acquired. In particular, when the material is used together with a
carbon material, superior cycle characteristics can be acquired
together with acquiring a high energy density, which is more
preferable. The material composing the negative electrode may be a
simple substance, an alloy, or a compound of a metal element or a
metalloid element, and may be a material that has a facet of one or
two or more of the above-described elements in at least a part
thereof. In the description here, an alloy includes a material
containing one or more metal elements and one or more metalloid
elements in addition to a material formed from two or more metal
elements. Furthermore, the alloy may contain a non-metallic
element. The structure thereof may be a solid solution, eutectic
(eutectic mixture), an intermetallic compound, or a structure in
which two or more of such structures coexist.
[0045] As a metal element or a metalloid element composing such a
negative electrode material, for example, there is magnesium (Mg),
boron (B), aluminum (Al), gallium (Ga), indium (In), silicon (Si),
germanium (Ge), tin (Sn), lead (Pb), bismuth (Bi), cadmium (Cd),
silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y),
palladium (Pd), or platinum (Pt). Such element may be crystalline
or amorphous.
[0046] The material composing the negative electrode preferably
contains a metal element or a metalloid element of group 4B in the
short-period periodical table, and more preferably contains at
least one of silicon (Si) and tin (Sn) as its constituent element.
The reason is that silicon (Si) and tin (Sn) have superior
capability of intercalating and releasing lithium (Li) and can
implement a high energy density.
[0047] In an alloy of tin (Sn), for example, at least one selected
from the group of silicon (Si), nickel (Ni), copper (Cu), iron
(Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), silver
(Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb)
and chrome (Cr) may be contained as a secondary constituent element
other than tin (Sn). In an alloy of silicon (Si), for example, at
least one selected from the group of tin (Sn), nickel (Ni), copper
(Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium
(In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi),
antimony (Sb) and chrome (Cr) may be contained as a secondary
constituent element other than silicon (Si).
[0048] In the compound of tin (Sn) or the compound of silicon (Si),
for example, oxygen (O) or carbon (C) may be contained. In addition
to tin (Sn) or silicon (Si), the above-described secondary
constituent element may be contained.
[0049] As examples of the material composing the negative electrode
that is capable of intercalating and releasing lithium, there are
other metal compounds and polymer materials. As examples of the
other metal compounds, oxides such as MnO.sub.2, V.sub.2O.sub.5,
and V.sub.6O.sub.13, sulfides such as NiS and MoS, and lithium
nitride such as LiN.sub.3. In addition, as examples of the polymer
material, there are polyacetylene, polyaniline, polypyrrole, and
the like.
[0050] Separator
[0051] FIG. 3 is a cross-sectional view representing a
configuration example of the separator 23. The separator 23 allows
lithium ions to pass through it while preventing formation of a
short circuit for a current, which is caused by a contact between
both the electrodes, by isolating the positive electrode 21 and the
negative electrode 22 from each other. The separator 23 includes a
first layer 23A that has first and second principal faces and a
second layer 23B that is formed on at least one of both the
principal faces of the first layer 23A. From the viewpoint of
improving safety, it is preferable that the second layers 23B are
formed on both the principal faces of the first layer 23A. In a
case where the second layer is formed on at least one face of the
first layer, it is preferable that the second layer is formed on a
face that faces an electrode having a higher degree of expansion.
Furthermore, in a case where the separator is applied to a
cylinder-type battery, the electrode expands to the outermost
peripheral side of the wound electrode body. Accordingly, it is
preferable that the second layer is disposed on the wound inner
side face of the separator. FIG. 3 represents an example in which
the second layers 23B are formed on both principal faces of the
first layer.
[0052] In the separator 23 according to an, a porous resin layer
configuring the separator 23 has a co-continuous phase structure so
as to have superior impregnability for an electrolytic solution. In
addition, the separator is porous so as to have superior ion
permeability. Furthermore, from the viewpoint of ion permeability,
pores are maintained even for 50 kgf/cm.sup.2 or higher. From this
viewpoint, the second layer that contains an inorganic material
that becomes a pressure buffer is formed.
[0053] Under heavy load, the pores are thought to be crushed thus
decreasing the ion permeability of the separator 23. The
characteristics of a battery are largely influenced by ion
permeability. Thus, as an evaluation index of a separator for a
change in the pressure of the inside of the battery, the
compression resistance of the separator is important. In addition,
a case where the pores of the first layer are clogged by inorganic
materials which decrease ion permeability may be considered. Thus,
according to an, in order to check ion permeability, air
permeability is measured so as to clarify the state of the pores,
and a superior separator structure having superior battery
characteristics is found. Hereinafter, the first layer and the
second layer will be described in detail.
[0054] First Layer
[0055] The first layer 23A is a microporous membrane that, for
example, has a polymer resin as its major ingredient. It is
preferable that a polyolefin-based resin is used as the polymer
resin. The reason for this is that the microporous membrane having
polyolefin as its major ingredient has a superior effect of
preventing formation of a short circuit and can achieve an
improvement in battery safety based on a shutdown effect. As the
polyolefin-based resin, it is preferable that a simple substance of
polypropylene or polyethylene or a mixture thereof is used. In
addition, other than polypropylene and polyethylene, a resin having
chemical stability can be used by being copolymerized or mixed with
polyethylene or polypropylene.
[0056] The average membrane thickness of the first layer 23A is
preferably in the range of 10.0 .mu.m to less than 30.0 .mu.m. In a
case where the average membrane thickness exceeds 30.0 .mu.m, the
ion permeability is degraded, whereby the battery characteristics
deteriorate. In addition, in such a case, the volume fraction of
the separator 23 that is occupied inside the battery becomes too
high, and the volume fraction of the active material is decreased,
whereby the capacity of the battery decreases. Furthermore, in the
case of the wound-type battery, it may be difficult to house the
wound electrode body 20 inside the battery can 11. On the other
hand, in a case where the average membrane thickness is less than
10.0 .mu.m, the mechanical strength becomes too low, whereby
inconvenience in battery winding or a decrease in battery safety
occurs.
[0057] It is preferable that the average diameter of the pores
opening onto the surface of the first layer 23A is in the range of
0.03 .mu.m to 2.00 .mu.m. In a case where the surface pore diameter
of the pores is less than 0.03 .mu.m, the ion permeability is
degraded, whereby the battery characteristics deteriorate. On the
other hand, in a case where the surface pore diameter of the pores
is equal to or greater than 2.00 .mu.m, the mechanical strength
becomes too low, whereby inconvenience in battery winding or a
decrease in battery safety occurs. In addition, inorganic particles
included in the second layer can easily enter into the pores,
whereby there is a concern that clogging may easily occur.
[0058] Second Layer
[0059] The second layer 23B of the separator 23 is a
multi-functional porous layer including inorganic particles having
an electrically insulating property and a polymer resin.
[0060] In this embodiment, the second layer 23B is formed on the
entire surface of each of the principal faces of the first layer
23A. Accordingly, the positive electrode 21 and the negative
electrode 22 of the wound electrode body 20 are interleaved between
the second layers 23B of the separators 23. The second layer 23B
formed on one principal face of the first layer 23A faces the
exposed portion of the positive electrode collector 21A and the
positive electrode lead 25 connected to the exposed portion of the
positive electrode collector 21A as well as the positive electrode
active material layer 21B of the positive electrode 21. The second
layer 23B formed on the other principal face of the first layer 23A
faces the exposed portion of the negative electrode collector 22A
and the negative electrode lead 26 connected to the exposed portion
of the positive electrode collector 22A as well as the negative
electrode active material layer 22B of the negative electrode 22.
Accordingly, none of the positive electrode collector 21A, the
negative electrode collector 22A, the positive electrode lead 25
and the negative electrode lead 26 faces the battery can 11
directly, but the second layer 23B of the separator 23 is
interleaved therebetween.
[0061] The polymer resin has a three-dimensional network structure
(a mesh-shaped structure) formed by continuous mutual connection.
It is preferable that the second layer 23B is, for example, in the
state of being fibrillated. In addition, it is preferable that
inorganic particles are carried inside the network structure.
[0062] By including the inorganic particles in the second layer
23B, the inorganic particles serve as a buffer for pressure,
whereby crushing of the pores of the first layer can be suppressed.
In addition, since the polymer resin has the three-dimensional
network structure formed by continuous mutual connection, the pore
spaces can be maintained in the second layer 23B by the second
layer 23B. Accordingly, deterioration of the battery
characteristics (cycle characteristics) can be suppressed without
degrading ion permeability, and flexibility can be provided,
whereby safety can be improved. In a case where the polymer resin
is fibrillated, when the average diameter of fibrils is equal to or
less than 1 .mu.m, particles that are sufficient for acquiring the
insulating property can be reliably carried even when the
composition ratio of an ingredient composing the fibril is low,
whereby safety can be improved.
[0063] The polymer resin is not particularly limited as long as it
can form a three-dimensional network structure acquired by mutual
continuous connection. It is preferable that the average molecular
weight of the polymer resin is in the range of 500,000 to
2,000,000. By configuring the average molecular weight to be equal
to or larger than 500,000, the above-described network structure
can be acquired. When the average molecular weight is equal to or
less than 500,000, particle maintaining force is low, and peel-off
of a layer containing the particles and the like occurs. As the
polymer resin, for example, a simple substance of
polyacrylonitrile, polyvinylidene fluoride, a copolymer of
vinylidene fluoride and hexafluoropropylene,
polytetrafluoroethylene, polyhexafluoropropylene, polyethylene
oxide, polypropylene oxide, polyphosphazene, polysiloxane,
polyvinyl acetate, polyvinyl alcohol, polymethylmethacrylate,
polyacrylic acid, polymethacrylate, styrene-butadiene rubber,
nitrile butadiene rubber, polystyrene, or polycarbonate or a
mixture containing two or more of the above-described materials can
be used.
[0064] As the polymer resin, from the viewpoint of electro-chemical
stability, polyacrylonitrile, polyvinylidene fluoride,
polyhexafluoropropylene, or polyethylene oxide is preferably used.
On the other hand, from the viewpoint of thermal stability and
electro-chemical stability, as the polymer resin, the fluorine
resin is preferably used. Furthermore, from the viewpoint of an
improvement in flexibility of the second layer 23B, as the polymer
resin, polyvinylidene fluoride is preferably used. When the
flexibility of the second layer 23B is improved, in a case where
there are impurities between the electrode and the separator 23, a
shape following property for the impurities of the second layer 23B
is improved, whereby safety is improved.
[0065] As the polymer resin, a heat resistant resin may be used. By
using the heat resistant resin, both the insulating property and
heat resistance can be acquired. As the heat resistant resin, from
the viewpoint of dimensional stability under a high-temperature
ambience, a resin that has high glass-transition temperature is
preferable. In addition, as the polymer resin, from the viewpoint
of decreasing a dimensional change or contraction due to fluidity,
a resin that has melting entropy and does not have a melting point
is preferably used. As such a resin, for example, there is a
polyamide having an aromatic backbone, a resin that has an aromatic
backbone and has imide bonding or a copolymer thereof.
[0066] The inorganic particles, for example, are inorganic
particles having an electrically insulating property. The inorganic
particles may have an electrically insulating property and are not
particularly limited. However, inorganic particles having an
inorganic oxide such as alumina, silica, zirconia, or titania as
its major ingredient are preferably used.
[0067] Regarding the average particle diameter of the inorganic
particles contained in the second layer 23B, the average particle
diameter D20, which is a 20% cumulative diameter on the basis of
the particle diameters, is greater than the average diameter of the
pores that open to the surface of the first layer. There is a
concern that the inorganic particles contained in the second layer
may break into the inside of the pores from the openings formed on
the surface of the first layer when the second layer is formed.
However, by configuring the average particle diameter D20 to be
greater than the average particle diameter of the pores opening
onto the surface of the first layer, the quantity of inorganic
particles breaking into the inside of the pores can be markedly
decreased.
[0068] In addition, regarding the average particle diameter of the
inorganic particles contained in the second layer 23B, the average
particle diameter D90, which is a 90% cumulative particle diameter,
is preferably equal to or less than 1/3 of the membrane thickness
of the first layer. When particles having a large particle diameter
are included as the inorganic particles, there is a concern that
damage or fracture occurs in the first layer due to the inorganic
particles. In addition, when inorganic particles having a large
particle diameter are included, there is a concern that the second
layer may not be formed near the large particles. The reason for
this is that a process of coating the second layer with, for
example, a coating material containing inorganic particles and a
polymer resin is performed, and the coating material does not
spread into the side area of each large particle in the coating
direction. Accordingly, by not including organic particles having
as large a diameter as possible, the second layer can be formed in
a stable manner.
[0069] It is preferable that the area density per the unit area of
the second layer 23B is equal to or greater than 0.2 mg/cm.sup.2
and equal to or lower than 1.8 mg/cm.sup.2. In a case where the
area density per the unit area is less than 0.2 mg/cm.sup.2,
short-time resistance is decreased so as to increase the amount of
heat generation at the time of formation of a short circuit,
whereby the safety thereof is degraded. In addition, uneven coating
or a coating break of the coating material occurs in the second
layer, and there is a concern that it is difficult to form a
separator according to an. On the other hand, in a case where the
area density per the unit area exceeds 1.8 mg/cm.sup.2, safety can
be secured. However, the thickness of the separator 23 is increased
so as to excessively increase the occupied volume fraction of the
separator 23 inside the battery and decrease the volume fraction of
the active material, whereby the capacity of the battery is
decreased, which is not preferable. Furthermore, in the case of a
cylinder-type battery, the component diameter of the wound
electrode body 20 is increased, and there is a concern that it is
difficult to insert the wound electrode body 20 into the battery
can 11.
[0070] It is preferable that the mixed amount (the volume fraction)
of the inorganic particles in the second layer 23B is equal to or
greater than 60 vol % and equal to or less than 95 vol %. In a case
where the mixed amount of the inorganic particles is less than 60
vol %, the pressure resistance of the separator is decreased, and
the mixed amount of the resin is large, whereby the pores formed on
the surface of the first layer may easily be crushed by the resin.
In addition, in a case where the mixed amount of the inorganic
particles is 0 vol %, the cycle characteristics are also degraded.
On the other hand, in a case where the mixed amount of the
inorganic particles exceeds 95 vol %, the particle maintaining
force of the resin is decreased. Accordingly, peeling-off, that is,
powdering of the inorganic particles occurs.
[0071] In such a separator 23, it is preferable that the amount of
change (that is, a difference between the air permeability before
formation of the second layer and the air permeability after the
formation of the second layer) in the air permeability after
formation of the second layer 23B is equal to or less than 60
sec/100 ml. The air permeability of the separator 23 in which the
second layer 23B is formed on the surface of the first layer 23A is
higher than the air permeability thereof in which only the first
layer 23A is disposed. However, it is preferable that the amount of
change in the air permeability after formation of the second layer
23B is small. As the number of the inorganic particles breaking
into the pores of the surface of the first layer increases, the
difference between the air permeability of the first layer only and
the air permeability after formation of the second layer increases.
In other words, in order to suppress clogging of the separator 23
with the inorganic particles so as to maintain high ion
permeability, it is preferable that a difference between the air
permeability of the first layer only and the air permeability after
formation of the second layer is small.
[0072] Here, the air permeability can be measured, for example, by
using a Gurley-type densometer.
[0073] In addition, it is preferable that the air permeability (the
air permeability after the pressure load of the second layer) at a
time point when the separator after formation of the second layer
is placed at an environment of 60.degree. C. and then pressure of
50 kgf/cm.sup.2 is applied to the separator after the formation of
the second layer for over two minutes is equal to or lower than
35%. It is preferable that the rising rate of the air permeability
at a time when pressure is applied to the separator after the
formation of the second layer 23B is low. In a case where the
pressure is applied, as the pores of the separator 23 are crushed,
the rising rate of the air permeability at the time of the pressure
load decreases by as much. In other words, in order to maintain
high pressure resistance of the separator 23, it is preferable that
the rising rate of the air permeability in the air permeability
before the application of the pressure load and the air
permeability after application of the pressure load is low.
[0074] Electrolytic Solution
[0075] An electrolytic solution that is a liquid-phase electrolyte
is impregnated in the separator 23. The electrolytic solution
contains a solvent and an electrolyte salt that is dissolved in the
solvent.
[0076] As the solvent, cyclic ester carbonate such as ethylene
carbonate or propylene carbonate can be used. It is preferable that
one of ethylene carbonate and propylene carbonate, and more
particularly, a mixture of both ethylene carbonate and propylene
carbonate is used. The reason for this is that the cycle
characteristics can be improved.
[0077] As the solvent, it is preferable to mix chained ester
carbonate such as diethyl carbonate, dimethyl carbonate, ethyl
methyl carbonate, or methyl propyl carbonate into the
above-described cyclic ester carbonate. The reason for this is that
a high ionic conduction property can be acquired.
[0078] It is preferable that the solvent further contains 2,
4-difluoro anisole or vinylene carbonate. The reason for this is
that 2, 4-difluoro anisole can improve the amount of electricity
discharged, and vinylene carbonate can improve the cycle
characteristics. Accordingly, by using a solvent acquired by mixing
the above-described materials, the amount of electricity discharged
and the cycle characteristics can be improved, which is
preferable.
[0079] As examples of solvents other than the above-described
materials, there are butylene carbonate, .gamma.-butyrolactone,
.gamma.-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran,
2-methyltetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan,
methyl acetate, methyl propionate, acetonitrile, glutaronitrile,
adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile,
N,N-dimethyl formamide, N-methylpiroridinon, N-methyl oxazoridinon,
N,N-dimethylimidazolidinone, nitromethane, nitroethane, sulpholane,
dimethyl sulfoxide, trimethyl phosphate, and the like.
[0080] In addition, a compound acquired by substituting at least a
part of hydrogen of the above-described nonaqueous solvent with
fluorine may improve the reversibility of an electrode reaction
depending on the types of combined electrodes, which may be
preferable.
[0081] As an example of the electrolytic salt, there is lithium
salt. Thus, one type of the lithium salt may be used alone, or two
or more types of the lithium salt may be used by being mixed
together. As examples of the lithium salt, there are LiPF.sub.6,
LiBF.sub.4, LiAsF.sub.6, LiClO.sub.4, LiB(C.sub.6H.sub.5).sub.4,
LiCH.sub.3SO.sub.3, LiCF.sub.3SO.sub.3,
LiN(SO.sub.2CF.sub.3).sub.2, LiC(SO.sub.2CF.sub.3).sub.3,
LiAlCl.sub.4, LiSiF.sub.6, LiCl, difluoro[oxalato O, O'] lithium
borate, lithium-bis(oxalate)borate, LiBr, or the like. Among these
materials, LiPF.sub.6 is preferable in that a high ionic conduction
property can be acquired and the cycle characteristics can be
improved.
[0082] Method of Manufacturing Battery
[0083] Next, an example of a method of manufacturing a nonaqueous
electrolyte secondary battery according to the first will be
described.
[0084] First, for example, a positive electrode mixture is prepared
by mixing a positive electrode material, a conductive material, and
a binder, and the positive electrode mixture is dispersed into a
solvent medium such as N-methyl-2-pyrrolidone, whereby a positive
electrode mixture slurry having a past form is prepared. Next, a
positive electrode active material layer 21B is formed so as to
form a positive electrode 21 by coating the positive electrode
collector 21A with the positive electrode mixture slurry, drying
the solvent medium, and performing compression molding for the
coated positive electrode collector 21A by using a roll-pressing
machine or the like.
[0085] In addition, for example, a negative electrode mixture is
prepared by mixing a negative electrode active material and a
binder, and the negative electrode mixture is dispersed into a
solvent medium such as N-methyl-2-pyrrolidone, whereby a negative
electrode mixture slurry in a paste form is prepared. Next, a
negative electrode active material layer 22B is formed so as to
prepare a negative electrode 22 by coating the negative electrode
collector 22A with the negative electrode mixture slurry, drying
the solvent medium, and performing compression molding for the
coated negative electrode collector 22A by using a roll-pressing
machine or the like.
[0086] Next, a positive electrode lead 25 is installed to the
positive electrode collector 21A by performing a welding process or
the like, and a negative electrode lead 26 is installed to the
negative electrode collector 22A by performing a welding process or
the like. Next, the positive electrode 21 and the negative
electrode 22 are wound with separators 23 interleaved therebetween.
Next, the front end portion of the positive electrode lead 25 is
welded to a safety valve mechanism 15, and the front end portion of
the negative electrode lead 26 is welded to a battery can 11. Then,
the positive electrode 21 and the negative electrode 22 that have
been wound are housed inside the battery can 11 with one pair of
insulating plates 12 and 13 being interposed therebetween. Next,
after the positive electrode 21 and the negative electrode 22 are
housed inside the battery can 11, an electrolytic solution is
injected into the inside of the battery can 11 so as to impregnate
the separator 23. Next, the battery cover 14, the safety valve
mechanism 15, and a PTC device 16 are fixed in a caulking manner to
the end portion of the opening of the battery can 11 through a
sealing gasket 17. Accordingly, the secondary battery shown in FIG.
1 can be acquired.
[0087] In the secondary battery according to the first embodiment,
the open-circuit voltage in the fully-charged state is, for
example, in the range of 4.2 V to 4.6 V, and is preferably in the
range of 4.25 V to 4.5 V. The reason for this is that, in a case
where the open-circuit voltage is equal to or higher than 4.25 V,
the use rate of the positive electrode active material can be
increased, and more energy can be drawn out. In addition, in a case
where the open-circuit voltage is equal to or lower than 4.5 V,
oxidation of the separator 23, a chemical change of the
electrolytic solution, or the like can be suppressed.
[0088] In the secondary battery according to the first embodiment,
when a charging process is performed, lithium ions are released
from the positive electrode active material layer 21B and are
intercalated into the material composing the negative electrode
that is capable of intercalating and releasing lithium contained in
the negative electrode active material layer 22B through the
electrolytic solution. Next, when a discharging process is
performed, the lithium ions intercalated into the material
composing the negative electrode that is capable of intercalating
and releasing lithium contained in the negative electrode active
material layer 22B are released and are intercalated into the
positive electrode active material layer 21B through the
electrolytic solution.
[0089] According to the separator of the first embodiment, even
when the electrode is expanded in accordance with
charging/discharging of the battery, high pressure-resistance is
implemented, whereby a high ion permeability can be maintained
without crushing the pores of the separator. In contrast, according
to a single-layered polyolefin separator in related art, pores
thereof are crushed in accordance with the expansion of the
electrode, whereby the battery characteristics are degraded.
[0090] In addition, in the first embodiment, since the separator 23
resides on the outer periphery of the wound electrode body 20 and
the second layer 23B of the separator 23 is disposed thereon, the
inorganic particles intervene between the outer end of the negative
electrode 22 and the battery can 11. Therefore, a short circuit
between the wound electrode body 20 and the battery can 11 is
effectively prevented and a high degree of safety can be
achieved.
[0091] The wound electrode body 20 pushes the battery can 11 due to
the expansion of the wound electrode body 20 accompanying charging
of the battery. Further, when the lead (the negative electrode lead
26 in this embodiment) is disposed on the outer end of the positive
electrode 21 or the negative electrode 22 (the negative electrode
22 in this embodiment), stress is liable to be concentrated on the
edge of the lead. Therefore, there is a possibility that the outer
end of the separator 23 is damaged. However, in this embodiment,
since the inorganic particles in the second layer 23B of the
separator 23 face this portion, a risk of tearing of the separator
23 is reduced and a degree of safety is increased accordingly.
2. Second Embodiment
[0092] Configuration of Battery
[0093] FIG. 4 is an exploded perspective view representing a
configuration example of a nonaqueous electrolyte secondary battery
according to a second. In the secondary battery, a wound electrode
body 30, to which a positive electrode lead 31 and a negative
electrode lead 32 are installed, is housed inside a film-shaped
exterior member 40. Accordingly, miniaturization, light weight, and
thinness of the exterior member 40 can be implemented.
[0094] The positive electrode lead 31 and the negative electrode
lead 32 are disposed from the inside of the exterior member 40
toward the outside thereof, for example, so as to be derived in the
same direction. The positive electrode lead 31 and the negative
electrode lead 32 are composed of metal materials such as aluminum,
copper, nickel, and stainless steel and are respectively formed in
a thin plate shape or a mesh shape.
[0095] The exterior member 40, for example, is configured by an
aluminum-laminated film in a rectangular shape in which a nylon
film, an aluminum foil, and a polyethylene film are bonded together
in the mentioned order. In the exterior member 40, for example, the
polyethylene film side and the wound electrode body 30 are arranged
so as to face each other, and the outer frame portions thereof are
brought into close contact with each other by welding or by using
an adhesive agent. Between the exterior member 40 and the positive
electrode lead 31 and the negative electrode lead 32, an adhesive
film 41 that is used for preventing penetration of the outer air is
inserted. The adhesive film 41 is composed of a material that has
adhesiveness to the positive electrode lead 31 and the negative
electrode lead 32, for example, a polyolefin resin formed from
polyethylene, polypropylene, modified polyethylene, modified
polypropylene, or the like.
[0096] Instead of the above-described aluminum-laminated film, the
exterior member 40 may be configured by a laminated film having a
different structure, a polymer film formed from polypropylene or
the like, or a metal film.
[0097] FIG. 5 is a cross-sectional view of the wound electrode body
30, which is shown in FIG. 4, taken along line VI-VI. The wound
electrode body 30 is acquired by stacking a positive electrode 33
and a negative electrode 34 with separators 35 and electrolyte
layers 36 interleaved therebetween so as to be wound, and the
outermost circumferential portion thereof is protected by a
protection tape 37.
[0098] The positive electrode 33 has a structure in which a
positive electrode active material layer 33B is disposed on one
side or both sides of a positive electrode collector 33A. The
negative electrode 34 has a structure in which a negative electrode
active material layer 34B is disposed on one side or both sides of
a negative electrode collector 34A, and the negative electrode
active material layer 34B and the positive electrode active
material layer 33B are arranged so as to face each other. The
configurations of the positive electrode collector 33A, the
positive electrode active material layer 33B, the negative
electrode collector 34A, the negative electrode active material
layer 34B, and the separator 35 are the same as those of the
positive electrode collector 21A, the positive electrode active
material layer 21B, the negative electrode collector 22A, the
negative electrode active material layer 22B, and the separator 23
of the first embodiment.
[0099] The electrolyte layer 36 contains an electrolytic solution
and a polymer compound that becomes a maintaining body that
maintains the electrolytic solution and is formed as gel. The
gel-shaped electrolyte layer 36 can acquire high ion conductivity
and prevent leakage of the battery, which is preferable. The
composition of the electrolytic solution (that is, a solvent,
electrolyte salt, and the like) is the same as that of the
secondary battery according to the first embodiment. As examples of
the polymer compound, there are polyacrylonitrile, polyvinylidene
fluoride, a copolymer of vinylidene fluoride and
hexafluoropropylene, polytetrafluoroethylene,
polyhexafluoropropylene, polyethylene oxide, polypropylene oxide,
polyphosphazene, polysiloxane, polyvinyl acetate, polyvinyl
alcohol, polymethylmethacrylate, polyacrylic acid,
polymethacrylate, styrene-butadiene rubber, nitrile butadiene
rubber, polystyrene, and polycarbonate. Especially, from the
viewpoint of electro-chemical stability, polyacrylonitrile,
polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene
oxide is preferably used.
[0100] Method of Manufacturing Battery
[0101] Next, an example of a method of manufacturing a nonaqueous
electrolyte secondary battery according to the second will be
described.
[0102] First, the electrolyte layer 36 is formed by coating the
positive electrode 33 and the negative electrode 34 with a
precursor solution that contains the solvent, the electrolyte salt,
the polymer compound, and a mixed solvent medium and volatilizing
the mixed solvent medium. Thereafter, a positive electrode lead 31
is installed to the end portion of the positive electrode collector
33A by performing a welding process or the like, and a negative
electrode lead 32 is installed to the end portion of the negative
electrode collector 34A by performing a welding process or the
like. Next, the wound electrode body 30 is formed by stacking the
positive electrode 33 and the negative electrode 34, in which the
electrolyte layer 36 is formed, with the separators 35 interleaved
therebetween, then winding the stacked body in the direction of the
length thereof, and bonding the protection tape 37 to the outermost
circumferential portion thereof. Finally, for example, with the
wound electrode body 30 being pinched between the exterior members
40, the outer frame portions of the exterior members 40 are brought
into close contact with each other and are sealed by performing a
thermal welding process or the like. At that time, between the
positive and negative electrode leads 31 and 32 and the exterior
members 40, an adhesive film 41 is inserted. Accordingly, the
secondary battery shown in FIGS. 4 and 5 can be acquired.
[0103] In addition, the secondary battery may be prepared as
follows. First, a positive electrode 33 and a negative electrode 34
are prepared as described above, and a positive electrode lead 31
and a negative electrode lead 32 are installed to the positive
electrode 33 and the negative electrode 34. Next, a wound body,
which is a precursor of a wound electrode body 30, is formed by
stacking the positive electrode 33 and the negative electrode 34
with separators 35 interleaved therebetween, then winding the
stacked body, and bonding a protection tape 37 to the outermost
circumferential portion thereof. Next, the wound body is pinched
between the exterior members 40, and the outer circumferential
portion except for one side is thermally welded so as to form a
pouch shape, and the wound body is housed inside the exterior
members 40. Next, an electrolyte composition material that contains
a solvent, an electrolyte salt, a monomer that is a raw material of
the polymer compound, a polymerization initiator, and other
materials such as a polymerization inhibitor are prepared as
necessary, and the electrolyte composition material is injected
into the inside of the exterior members 40.
[0104] After the electrolyte composition material is injected, the
opening portion of the exterior portions 40 is thermally welded
under a vacuum atmosphere so as to be sealed. Next, the monomer is
polymerized by applying heat thereto so as to form as a polymer
compound, whereby an electrolyte layer 36 as gel is formed. The
secondary battery shown in FIG. 4 can be acquired by performing the
above-described process.
[0105] The operations and advantages of the nonaqueous electrolyte
secondary battery according to the second embodiment are the same
as those of the nonaqueous electrolyte secondary battery according
to the first embodiment.
EXAMPLES
Example 1
[0106] In Example 1, regarding a separator in which a second layer
is disposed on the surface of a first layer serving as a base
member, batteries were manufactured by employing separators that
were prepared by changing the average pore diameter of the pores
formed on the surface of the first layer and the average particle
diameter D20 of the inorganic particles mixed into the second
layer, and the separators and the battery characteristics were
evaluated.
Example 1-1
[0107] Preparation of Separator
[0108] Preparation of Coating Material
[0109] First, a polyvinylidene fluoride (PVdF) resin having an
average molecular weight of about 1,000,000 was dissolved into
N-methyl-2-pyrrolidone (NMP) so as to be 2 wt %. Next, in the
obtained PVdF/NMP solution, alumina particles having an average
particle diameter D20 of 0.21 .mu.m and an average particle
diameter D90 of 3.18 .mu.m as the inorganic particles were input at
the volume ratio PVdF:alumina particles=5:95 (volume fraction 95.0
vol %). Then, after the solution was agitated until a uniform
slurry was formed, a coating process was performed by performing a
mesh pass. The volume fraction was acquired by using the following
equation by using the volume ratio of the inorganic particles and
the volume ratio of the resin.
Volume fraction Ratio [vol %]=((Volume Ratio of Inorganic
Particles)/(Volume Ratio of Inorganic Particles+Volume Ratio of
Resin)).times.100
[0110] <Coating Process>
[0111] Next, both sides of the polyethylene microporous membrane
(first layer) in which the average pore diameter of a plurality of
pores exposed on the surface was 0.05 .mu.m were coated in a table
coater with the above-described coating material in a thickness of
16 .mu.m. At this time, the coating material is adjusted such that
the area density is 0.60 mg/cm.sup.2. Next, second layers
containing the alumina particles were formed on both sides of the
polyethylene microporous membrane as the first layer by performing
phase separation through a water bath and then performing a drying
process. As a result, a separator was acquired.
Example 1-2
[0112] A separator was prepared in the same manner as in Example
1-1 except for adjusting the mixed amount of the alumina particles
to be 90.0 vol % at the time of preparation of the coating
material.
Example 1-3
[0113] A separator was prepared in the same manner as in Example
1-1 except for adjusting the mixed amount of the alumina particles
to be 82.0 vol % at the time of preparation of the coating
material.
Example 1-4
[0114] A separator was prepared in the same manner as in Example
1-1 except for adjusting the mixed amount of the alumina particles
to be 69.0 vol % at the time of preparation of the coating
material.
Example 1-5
[0115] A separator was prepared in the same manner as in Example
1-1 except for adjusting the mixed amount of the alumina particles
to be 60.0 vol % at the time of preparation of the coating
material.
Example 1-6
[0116] A separator was prepared in the same manner as in Example
1-1 except for using silica particles having an average particle
diameter D20 of 0.80 .mu.m and an average particle diameter D90 of
2.00 .mu.m as the inorganic particles that were mixed at the time
of preparation of the coating material.
Example 1-7
[0117] A separator was prepared in the same manner as in Example
1-1 except for using a polyethylene microporous membrane having an
average pore diameter of a plurality of pores exposed on the
surface to be 0.10 .mu.m as the first layer, using silica particles
having an average particle diameter D20 of 2.10 .mu.m and an
average particle diameter D90 of 5.00 .mu.m as the inorganic
particles that were mixed at the time of preparation of the coating
material, and adjusting the mixed amount of the silica particles to
be 90.0 vol %.
Example 1-8
[0118] A separator was prepared in the same manner as in Example
1-1 except for using a polyethylene microporous membrane having an
average pore diameter of a plurality of pores exposed on the
surface to be 0.50 .mu.m as the first layer, using silica particles
having an average particle diameter D20 of 2.10 .mu.m and an
average particle diameter D90 of 5.00 .mu.m as the inorganic
particles that were mixed at the time of preparation of the coating
material, and adjusting the mixed amount of the silica particles to
be 90.0 vol %.
Example 1-9
[0119] A separator was prepared in the same manner as in Example
1-1 except for using a polyethylene microporous membrane having an
average pore diameter of a plurality of pores exposed on the
surface to be 1.50 .mu.m as the first layer, using silica particles
having an average particle diameter D20 of 2.10 .mu.m and an
average particle diameter D90 of 5.00 .mu.m as the inorganic
particles that were mixed at the time of preparation of the coating
material, and adjusting the mixed amount of the silica particles to
be 90.0 vol %.
Example 1-10
[0120] A separator was prepared in the same manner as in Example
1-1 except for using a polyethylene microporous membrane having an
average pore diameter of a plurality of pores exposed on the
surface to be 2.00 .mu.m as the first layer, using silica particles
having an average particle diameter D20 of 2.10 .mu.m and an
average particle diameter D90 of 5.00 .mu.m as the inorganic
particles that were mixed at the time of preparation of the coating
material, and adjusting the mixed amount of the silica particles to
be 90.0 vol %.
Comparative Example 1-1
[0121] A separator was prepared in the same manner as in Example
1-1 except for using a polyethylene microporous membrane having an
average pore diameter of a plurality of pores exposed on the
surface to be 0.21 .mu.m as the first layer.
Comparative Example 1-2
[0122] A separator was prepared in the same manner as in Example
1-1 except for using a polyethylene microporous membrane having an
average pore diameter of a plurality of pores exposed on the
surface to be 0.21 .mu.m as the first layer and adjusting the mixed
amount of alumina particles to be 90.0 vol % at the time of
preparation of the coating material.
Comparative Example 1-3
[0123] A separator was prepared in the same manner as in Example
1-1 except for using a polyethylene microporous membrane having an
average pore diameter of a plurality of pores exposed on the
surface to be 0.21 .mu.m as the first layer and adjusting the mixed
amount of alumina particles to be 82.0 vol % at the time of
preparation of the coating material.
Comparative Example 1-4
[0124] A separator was prepared in the same manner as in Example
1-1 except for using a polyethylene microporous membrane having an
average pore diameter of a plurality of pores exposed on the
surface to be 0.21 .mu.m as the first layer and adjusting the mixed
amount of alumina particles to be 69.0 vol % at the time of
preparation of the coating material.
Comparative Example 1-5
[0125] A separator was prepared in the same manner as in Example
1-1 except for using a polyethylene microporous membrane having an
average pore diameter of a plurality of pores exposed on the
surface to be 0.21 .mu.m as the first layer and adjusting the mixed
amount of alumina particles to be 60.0 vol % at the time of
preparation of the coating material.
Comparative Example 1-6
[0126] A separator was prepared in the same manner as in Example
1-1 except for using a polyethylene microporous membrane having an
average pore diameter of a plurality of pores exposed on the
surface to be 2.20 .mu.m as the first layer and mixing silica
particles having an average particle diameter D20 of 2.10 .mu.m and
an average particle diameter D90 of 5.00 .mu.m so as to adjust the
mixed amount of silica particles to be 90.0 vol % at the time of
preparation of the coating material.
Comparative Example 1-7
[0127] A separator was prepared in the same manner as in Example
1-1 except for not disposing the second layer.
[0128] Evaluation
[0129] (a) Difference of Air Permeability of Separator
[0130] The air permeability of the first layer before formation of
the second layer was measured. Subsequently, the air permeability
of the separator after formation of the second layer was measured
in the same manner as that for measurement of the first layer.
Then, a difference between the air permeability of the first layer
and the air permeability of the second layer was calculated by
using the following equation.
Difference of Air Permeability [sec/100 ml]=Air Permeability of
First Layer-Air Permeability of Second Layer
[0131] Here, the air permeability was measured by using a
Gurley-type densometer (manufactured by ToYo Seiki Co., Ltd.).
[0132] (b) Air Permeability Rising Rate of Separator
[0133] The separator after formation of the second layer is placed
under an ambience of 60.degree. C., and the air permeability (the
air permeability after the pressure load of the second layer) at a
time point when pressure of 50 kgf/cm.sup.2 was applied to the
separator after the formation of the second layer for two minutes.
Then, the air permeability rising rate after the pressure load
under the above-described condition was calculated by using the
following equation.
[0134] Air Permeability Rising Rate [%]=(Air Permeability After
Pressure Load of Second Layer-Air Permeability of Second Layer)/Air
Permeability of Second Layer
[0135] In addition, in a measurement test of an air permeability
rising rate, the degree of clogging at a time point when a load of
50 kgf/cm.sup.2 is applied can be measured. As the air permeability
rising rate at constant pressure is increased, the degree of
crushing the pores in the case of application of the pressure can
be determined to increase.
[0136] (c) Capacity Maintaining Rate
[0137] Cylinder-type batteries were manufactured by employing the
above-described separators, and the capacity maintaining rates at
the 100th cycle were measured. The cylinder-type batteries of the
examples and the comparative examples were placed in a constant
temperature bath at 25.degree. C. and were charged with a constant
current of 0.2 C. Then, the cylinder-type batteries were switched
to constant voltage charging at a time point when the battery
voltage becomes 4.2 V. Thereafter, constant current charging with a
discharge current of 0.2 C was performed until the battery voltage
becomes 3.0 V, and then the amount of electricity discharged
(first-time capacity) was measured.
[0138] Under the above-described charging/discharging conditions,
100 cycles of charging/discharging were repeated, and the amount of
electricity discharged at the 100th cycle was measured. The
capacity maintaining rate at the 100th cycle was calculated by
using the following equation.
Capacity Maintaining Rate [%]=(Amount of Electricity Discharged at
the 100th Cycle/First-Time Capacity).times.100
[0139] In addition, the cylinder-type battery was prepared as
follows.
[0140] Preparation of Cylinder-Type Battery
[0141] Preparation of Positive Electrode
[0142] Lithium cobalt oxide (LiCoO.sub.2) 92 wt % as a positive
electrode active material, graphite powders 5 wt % as a conductive
material, and polyvinylidene fluoride (PVdF) 3 wt % as a binder
were uniformed mixed together, and the mixture is dispersed into
N-methyl-2-piroridinon (NMP), whereby a positive electrode mixture
in a slurry state was prepared. Then, both sides of an aluminum
foil that becomes a positive electrode collector were uniformly
coated with the positive electrode mixture, and the coated aluminum
foil was decompressed and dried at 100.degree. C. for 24 hours,
whereby a positive electrode active material layer was formed.
Subsequently, the positive electrode active material layer was
pressed and molded so as to be a positive electrode sheet by a roll
pressing machine.
[0143] Preparation of Negative Electrode
[0144] Synthetic graphite 91 wt % and polyvinylidene fluoride
(PVdF) 9 wt % were uniformed mixed together, and the mixture is
dispersed into N-methyl-2-piroridinon (NMP), whereby a negative
electrode mixture in a slurry state was prepared. Next, both sides
of a copper foil that becomes a negative electrode collector were
uniformly coated with the negative electrode mixture, and the
coated copper foil was decompressed and dried at 120.degree. C. for
24 hours, whereby a negative electrode active material layer was
formed. Subsequently, the negative electrode active material layer
was pressed and molded so as to be a negative electrode sheet by a
roll pressing machine.
[0145] Preparation of Electrolytic Solution
[0146] An electrolytic solution that contains a mixed solvent
acquired by mixing ethylene carbonate (EC), ethyl methyl carbonate
(EMC), and dimethyl carbonate (DMC) at a volume ratio of 2:2:6 as
an electrolytic solution and lithium hexafluorophosphate
(LiPF.sub.6) as a electrolyte salt was used. The density of lithium
hexafluorophosphate (LiPF.sub.6) in the electrolytic solution was 1
mol/dm.sup.3.
[0147] Assembly of Battery
[0148] A positive electrode lead was installed to the positive
electrode collector prepared as described above by performing a
welding process or the like, and a negative electrode lead was
installed to the negative electrode collector by performing a
welding process. Next, the positive electrode and the negative
electrode are wound with separators therebetween. The front end
portion of the positive electrode lead is welded to a safety valve
mechanism, and the front end portion of the negative electrode lead
is welded to a battery can. Then, the positive electrode and the
negative electrode that have been wound are housed inside the
battery can with one pair of insulating plates being interposed
therebetween. After the positive electrode and the negative
electrode are housed inside the battery can, an electrolytic
solution is injected into the inside of the battery can so as to
impregnate the separator. Thereafter, by caulking the battery can
with the battery cover through a gasket, a cylinder-type battery
having size 18650 could be acquired. In Table 1 shown below, the
evaluation results are represented.
TABLE-US-00001 TABLE 1 First Layer Second Layer Average Average
Average Air Surface Particle Particle Particle Permeability Air
Thick- Pore Diameter Diameter Mixed Difference Permeability
Capacity ness Diameter Resin Inorganic D20 D90 Amount [Sec/ Rising
Rate Maintaining Material [.mu.m] [.mu.m] Material Particle [.mu.m]
[.mu.m] [Vol %] 100 ml] [%] Rate Example 1-1 Polyethylene 16.0 0.05
PVdF Alumina 0.21 3.18 95.0 10 10 .largecircle. Example 1-2
Polyethylene 16.0 0.05 PVdF Alumina 0.21 3.18 90.0 10 15
.largecircle. Example 1-3 Polyethylene 16.0 0.05 PVdF Alumina 0.21
3.18 82.0 10 18 .largecircle. Example 1-4 Polyethylene 16.0 0.05
PVdF Alumina 0.21 3.18 69.0 10 28 .largecircle. Example 1-5
Polyethylene 16.0 0.05 PVdF Alumina 0.21 3.18 60.0 10 35
.largecircle. Example 1-6 Polyethylene 16.0 0.05 PVdF Silica 0.80
2.00 95.0 10 10 .largecircle. Example 1-7 Polyethylene 16.0 0.10
PVdF Silica 2.10 5.00 90.0 10 8 .largecircle. Example 1-8
Polyethylene 16.0 0.50 PVdF Silica 2.10 5.00 90.0 10 8
.largecircle. Example 1-9 Polyethylene 16.0 1.50 PVdF Silica 2.10
5.00 90.0 10 6 .largecircle. Example 1-10 Polyethylene 16.0 2.00
PVdF Silica 2.10 5.00 90.0 10 6 .largecircle. Comparative
Polyethylene 16.0 0.21 PVdF Alumina 0.21 3.18 95.0 70 37 X Example
1-1 Comparative Polyethylene 16.0 0.21 PVdF Alumina 0.21 3.18 90.0
70 38 X Example 1-2 Comparative Polyethylene 16.0 0.21 PVdF Alumina
0.21 3.18 82.0 70 39 X Example 1-3 Comparative Polyethylene 16.0
0.21 PVdF Alumina 0.21 3.18 69.0 70 41 X Example 1-4 Comparative
Polyethylene 16.0 0.21 PVdF Alumina 0.21 3.18 60.0 70 43 X Example
1-5 Comparative Polyethylene 16.0 2.20 PVdF Silica 2.10 5.00 90.0
100 45 X Example 1-6 Comparative Polyethylene 16.0 0.05 -- -- -- --
-- 10 50 X Example 1-7
[0149] In Table 1, a case where the capacity maintaining rate is
equal to or greater than 80% is denoted by "o", and a case where
the capacity maintaining rate is less than 80% is denoted by
"x".
[0150] As is apparent from Table 1, in Examples 1-1 to 1-10
employing a separator in which a second layer containing inorganic
particles having an average particle diameter D20 larger than the
average pore diameter of pores of the surface of the first layer is
formed, the capacity maintaining rate was equal to or greater than
80%.
[0151] In contrast, in Comparative Examples 1-1 to 1-6 employing a
separator in which a second layer containing inorganic particles
having an average particle diameter equivalent to the average pore
diameter of the pores of the surface of the first layer is formed,
the capacity maintaining rate was less than 80%.
[0152] In addition, also in Comparative Example 1-7 in which a
second layer is not disposed, the capacity maintaining rate was
decreased. It is thought that the reason for this is a decrease in
the ion permeability that is caused by crushing of the holes of the
first layer, that is, a polyethylene microporous membrane as a
separator due to expansion of the electrode.
[0153] In each comparative example, since the particle diameter of
the inorganic particles contained in the second layer is small on
the whole, the number of the inorganic particles breaking into the
pores opening onto the surface of the first layer in a coating
process of a coating material was increased. Accordingly, the
opening diameter of the first layer decreases or the pores opening
onto the surface were clogged, whereby the ion permeability was
decreased.
[0154] According to a separator of an, the second layer containing
inorganic particles is formed on the surface of the first layer.
Accordingly, the air permeability after formation of the second
layer is higher than that of the first layer. Accordingly, as the
number of the inorganic particles breaking into the pores of the
surface of the first layer is increased, a difference between the
air permeability of the first layer only and the air permeability
of the separator after formation of the second layer increases. In
other words, it is known that, in order to maintain high ion
permeability, the difference between the air permeability of the
first layer only and the air permeability of the separator after
the formation of the second layer is desired to be decreased.
[0155] As is apparent from Table 1, in each comparative example
employing a separator in which the difference of the air
permeability was 70 sec/100 ml, the capacity maintaining rate was
decreased. Accordingly, it was found that the difference of the air
permeability is desired to be equal to or less than 60 sec/100 ml.
Similarly, it was found that, from the viewpoint of the air
permeability rising rate, the air permeability rising rate is
desired to be equal or less than 35%.
Example 2
[0156] In Example 2, batteries were prepared by employing
separators that were prepared by changing the average pore diameter
of the pores of the surface of the first layer, and the separators
and the battery characteristics were evaluated.
Example 2-1
[0157] Preparation of Separator
[0158] Preparation of Coating Material
[0159] First, as the inorganic particles dispersed into a
polyvinylidene fluoride (PVdF) resin, alumina particles having an
average particle diameter D20 of 0.21 .mu.m and an average particle
diameter D90 of 3.18 .mu.m were used, and the mixed amount of the
alumina particles is adjusted to 90.0 vol % so as to be used as the
coating material.
[0160] Coating Process
[0161] Next, both sides of the polyethylene microporous membrane
(first layer) in which the average pore diameter of a plurality of
pores exposed on the surface was 0.05 .mu.m were coated in a table
coater with the above-described coating material in a thickness of
16 .mu.m. At this time, the coating material is adjusted such that
the area density is 0.60 mg/cm2. Next, second layers containing the
alumina particles were formed on both sides of the polyethylene
microporous membrane as the first layer by performing phase
separation through a water bath and then performing a drying
process. As a result, a separator was acquired.
Example 2-2
[0162] A separator was prepared in the same manner as Example 2-1
except for using a polyethylene microporous membrane having a
thickness of 9.0 .mu.m, in which an average pore diameter of a
plurality of pores exposed to the surface was 0.04 .mu.m, as the
first layer and using silica particles having an average particle
diameter D20 of 0.13 .mu.m and an average particle diameter D90 of
2.48 .mu.m as the inorganic particles that were mixed at the time
of preparation of the coating material.
Example 2-3
[0163] A separator was prepared in the same manner as Example 2-1
except for using a polyethylene microporous membrane having a
thickness of 12.0 .mu.m, in which an average pore diameter of a
plurality of pores exposed to the surface was 0.03 .mu.m, as the
first layer and using silica particles having an average particle
diameter D20 of 0.13 .mu.m and an average particle diameter D90 of
2.48 .mu.m as the inorganic particles that were mixed at the time
of preparation of the coating material.
Example 2-4
[0164] A separator was prepared in the same manner as Example 2-1
except for using a polyethylene microporous membrane, in which an
average pore diameter of a plurality of pores exposed to the
surface was 0.10 .mu.m, as the first layer and using silica
particles having an average particle diameter D20 of 2.10 .mu.m and
an average particle diameter D90 of 5.00 .mu.m as the inorganic
particles that were mixed at the time of preparation of the coating
material.
Example 2-5
[0165] A separator was prepared in the same manner as Example 2-1
except for using a polyethylene microporous membrane, in which an
average pore diameter of a plurality of pores exposed to the
surface was 0.50 .mu.m, as the first layer and using silica
particles having an average particle diameter D20 of 2.10 .mu.m and
an average particle diameter D90 of 5.00 .mu.m as the inorganic
particles that were mixed at the time of preparation of the coating
material.
Example 2-6
[0166] A separator was prepared in the same manner as Example 2-1
except for using a polyethylene microporous membrane, in which an
average pore diameter of a plurality of pores exposed to the
surface was 1.50 .mu.m, as the first layer and using silica
particles having an average particle diameter D20 of 2.10 .mu.m and
an average particle diameter D90 of 5.00 .mu.m as the inorganic
particles that were mixed at the time of preparation of the coating
material.
Example 2-7
[0167] A separator was prepared in the same manner as Example 2-1
except for using a polyethylene microporous membrane, in which an
average pore diameter of a plurality of pores exposed to the
surface was 2.00 .mu.m, as the first layer and using silica
particles having an average particle diameter D20 of 2.10 .mu.m and
an average particle diameter D90 of 5.00 .mu.m as the inorganic
particles that were mixed at the time of preparation of the coating
material.
Comparative Example 2-1
[0168] A separator was prepared in the same manner as Example 2-1
except for using a polyethylene microporous membrane, in which an
average pore diameter of a plurality of pores exposed to the
surface was 0.01 .mu.m, as the first layer and using silica
particles having an average particle diameter D20 of 2.10 .mu.m and
an average particle diameter D90 of 5.00 .mu.m as the inorganic
particles that were mixed at the time of preparation of the coating
material.
Comparative Example 2-2
[0169] A separator was prepared in the same manner as Example 2-1
except for using a polyethylene microporous membrane, in which an
average pore diameter of a plurality of pores exposed to the
surface was 2.20 .mu.m, as the first layer and using silica
particles having an average particle diameter D20 of 3.00 .mu.m and
an average particle diameter D90 of 5.00 .mu.m as the inorganic
particles that were mixed at the time of preparation of the coating
material.
[0170] Evaluation
[0171] Similarly to Example 1, the following were calculated.
[0172] (a) Difference of Air Permeability of Separator
Difference of Air Permeability [sec/100 ml]=Air Permeability of
First Layer-Air Permeability of Second Layer
[0173] (b) Air Permeability Rising Rate of Separator
Air Permeability Rising Rate [%]=(Air Permeability of Second
Layer-Air Permeability of First Layer)/Air Permeability of First
Layer
[0174] (c) Capacity Maintaining Rate
Capacity Maintaining Rate [%]=(Amount of Electricity Discharged at
the 100th Cycle/First-Time Capacity).times.100
[0175] In Table 2 shown below, the evaluation results are
represented.
TABLE-US-00002 TABLE 2 First Layer Second Layer Average Average
Average Air Surface Particle Particle Permeability Air Thick- Pore
Diameter Diameter Difference Permeability Capacity ness Diameter
Resin Inorganic D20 D90 [Sec/ Rising Maintaining Material [.mu.m]
[.mu.m] Material Particle [.mu.m] [.mu.m] 100 ml] Rate [%] Problem
Rate Example 2-1 Polyethylene 16.0 0.05 PVdF Alumina 0.21 3.18 10
15 -- .largecircle. Example 2-2 Polyethylene 9.0 0.04 PVdF Silica
0.13 2.48 10 12 -- .largecircle. Example 2-3 Polyethylene 12.0 0.03
PVdF Silica 0.13 2.48 10 10 -- .largecircle. Example 2-4
Polyethylene 16.0 0.10 PVdF Silica 2.10 5.00 10 8 -- .largecircle.
Example 2-5 Polyethylene 16.0 0.50 PVdF Silica 2.10 5.00 10 8 --
.largecircle. Example 2-6 Polyethylene 16.0 1.50 PVdF Silica 2.10
5.00 10 6 -- .largecircle. Example 2-7 Polyethylene 16.0 2.00 PVdF
Silica 2.10 5.00 10 6 -- .largecircle. Comparative Polyethylene
16.0 0.01 PVdF Silica 2.10 5.00 10 7 -- X Example 2-1 Comparative
Polyethylene 16.0 2.20 PVdF Silica 3.00 5.00 10 10 Broken --
Example 2-2 Separator
[0176] In Table 2, a case where the capacity maintaining rate is
equal to or greater than 80% is denoted by "o", and a case where
the capacity maintaining rate is less than 80% is denoted by
"x".
[0177] In Example 2, the separator, in which the second layer
containing inorganic particles having the average particle diameter
D20 larger than the average pore diameter of the pores of the
surface of the first layer was formed, was employed. As is apparent
from Table 2, in a case where the average pore diameter of the
first layer is equal to or greater than 0.03 .mu.m and equal to or
less than 2.00 .mu.m as in Examples 2-1 to 2-7, the capacity
maintaining rate was equal to or greater than 80%.
[0178] In contrast, it was found that, in a case where the average
pore diameter of the pores of the surface of the first layer was
too small as being 0.01 .mu.m, as in Comparative Example 2-1, the
capacity maintaining rate was decreased regardless of the average
particle diameter D20 of the inorganic particles contained in the
second layer. In such a case, since the ion permeability is
decreased regardless of clogging of the pores with inorganic
particles, the battery capability was decreased. On the other hand,
in a case where the average pore diameter of the pores of the
surface of the first layer was too large as being 2.20 .mu.m, as in
Comparative Example 2-2, the strength of the first layer serving as
a base member is remarkably decreased, whereby the separator was
broken when the wound electrode body was prepared. In addition,
since deposition of lithium dendrite occurs at the time of the
charging process, even in a case where a cylinder-type battery
could be prepared, a short circuit was formed due to the lithium
dendrite.
[0179] From Example 2, it was found that the average pore diameter
of the pores of the surface of the first layer is preferably equal
to or greater than 0.03 .mu.m and equal to or less than 2.0
.mu.m.
Example 3
[0180] In Example 3, batteries were prepared by employing
separators that were prepared by changing the mixed amount of the
inorganic particles contained in the second layer, and the
separators and the battery characteristics were evaluated.
Example 3-1
[0181] Preparation of Separator
[0182] Preparation of Coating Material
[0183] First, as the inorganic particles dispersed into a
polyvinylidene fluoride (PVdF) resin, alumina particles having an
average particle diameter D20 of 0.21 .mu.m and an average particle
diameter D90 of 3.18 .mu.m were used, and the mixed amount of the
alumina particles is adjusted to 95.0 vol % so as to be used as the
coating material.
[0184] Coating Process
[0185] Next, both sides of the polyethylene microporous membrane
(first layer) in which the average pore diameter of a plurality of
pores exposed on the surface was 0.05 .mu.m were coated in a table
coater with the above-described coating material in a thickness of
16 .mu.m. At this time, the coating material is adjusted such that
the area density is 0.60 mg/cm2. Next, second layers containing the
alumina particles were formed on both sides of the polyethylene
microporous membrane as the first layer by performing phase
separation through a water bath and then performing a drying
process. As a result, a separator was acquired.
Example 3-2
[0186] A separator was prepared in the same manner as Example 3-1
except for configuring the mixed amount of the alumina particles to
be 90.0 vol %.
Example 3-3
[0187] A separator was prepared in the same manner as Example 3-1
except for configuring the mixed amount of the alumina particles to
be 82.0 vol %.
Example 3-4
[0188] A separator was prepared in the same manner as Example 3-1
except for configuring the mixed amount of the alumina particles to
be 69.0 vol %.
Example 3-5
[0189] A separator was prepared in the same manner as Example 3-1
except for configuring the mixed amount of the alumina particles to
be 60.0 vol %.
Example 3-6
[0190] A separator was prepared in the same manner as Example 3-1
except for using silica particles having an average particle
diameter D20 of 0.80 .mu.m and an average particle diameter D90 of
2.00 .mu.m as the inorganic particles that were mixed at the time
of preparation of the coating material.
Example 3-7
[0191] A separator was prepared in the same manner as Example 3-1
except for using silica particles having an average particle
diameter D20 of 2.10 .mu.m and an average particle diameter D90 of
5.00 .mu.m as the inorganic particles that were mixed at the time
of preparation of the coating material and configuring the mixed
amount of the silica particles to be 90.0 vol %.
Comparative Example 3-1
[0192] A separator was prepared in the same manner as Example 3-1
except for configuring the mixed amount of the alumina particles to
be 98.0 vol %.
Comparative Example 3-2
[0193] A separator was prepared in the same manner as Example 3-1
except for configuring the mixed amount of the alumina particles to
be 50.0 vol %.
[0194] Evaluation
[0195] Similarly to Example 1, the following were calculated.
[0196] (a) Difference of Air Permeability of Separator
[0197] Difference of Air Permeability [sec/100 ml]=Air Permeability
of First Layer-Air Permeability of Second Layer
[0198] (b) Air Permeability Rising Rate of Separator
[0199] Air Permeability Rising Rate [%]=(Air Permeability of Second
Layer-Air Permeability of First Layer)/Air Permeability of First
Layer
[0200] (c) Capacity Maintaining Rate
[0201] Capacity Maintaining Rate [%]=(Amount of Electricity
Discharged at the 100th Cycle/First-Time Capacity).times.100
[0202] In Table 3 shown below, the evaluation results are
represented.
TABLE-US-00003 TABLE 3 Second Layer Air Average Average Perme- Air
Particle Particle Particle ability Perme- Capacity First Layer
Diameter Diameter Mixed Difference ability Main- Thickness Resin
Inorganic D20 D90 Amount [Sec/ Rising taining Material [.mu.m]
Material Particle [.mu.m] [.mu.m] [Vol %] 100 ml] Rate [%] Problem
Rate Example 3-1 Polyethylene 16.0 PVdF Alumina 0.21 3.18 95.0 10
10 -- .largecircle. Example 3-2 Polyethylene 16.0 PVdF Alumina 0.21
3.18 90.0 10 15 -- .largecircle. Example 3-3 Polyethylene 16.0 PVdF
Alumina 0.21 3.18 82.0 10 18 -- .largecircle. Example 3-4
Polyethylene 16.0 PVdF Alumina 0.21 3.18 69.0 10 28 --
.largecircle. Example 3-5 Polyethylene 16.0 PVdF Alumina 0.21 3.18
60.0 10 35 -- .largecircle. Example 3-6 Polyethylene 16.0 PVdF
Silica 0.80 2.00 95.0 10 10 -- .largecircle. Example 3-7
Polyethylene 16.0 PVdF Silica 2.10 5.00 90.0 10 8 -- .largecircle.
Comparative Polyethylene 16.0 PVdF Alumina 0.21 3.18 98.0 -- --
Particle -- Example 3-1 Peeling-Off Comparative Polyethylene 16.0
PVdF Alumina 0.21 3.18 50.0 10 45 -- X Example 3-2
[0203] In Table 3, a case where the capacity maintaining rate is
equal to or greater than 80% is denoted by "o", and a case where
the capacity maintaining rate is less than 80% is denoted by
"x".
[0204] As is apparent from Table 3, in a case where the mixed
amount of the inorganic particles (alumina) is equal to or greater
than 60.0 vol % and equal to or less than 95.0 vol %, as in
Examples 3-1 to 3-7, the capacity maintaining rate was equal to or
greater than 80%.
[0205] In contrast, in a case where the mixed amount of the
inorganic particles was too large, as in Comparative Example 3-1,
peeling-off of the inorganic particles and the like occurred. On
the other hand, in a case where the mixed amount of the inorganic
particles was too small, as in Comparative Example 3-2, the amount
of mixed resin (PVdF) increased. Accordingly, the resin broke into
the pores from the surface of the first layer so as to clog the
pores. Therefore, the air permeability rising rate of the separator
become markedly high so as to decrease the ion permeability,
whereby the capacity maintaining rate was decreased.
[0206] From Example 3, it was found that, preferably, the mixed
amount of the inorganic particles in the second layer is equal to
or greater than 60.0 vol % and equal to or less than 95.0 vol
%.
Example 4
[0207] In Example 4, batteries were prepared by employing
separators that were prepared by changing the thickness of the
first layer, and the separators and the battery characteristics
were evaluated.
Example 4-1
[0208] [Preparation of Separator]
[0209] <Preparation of Coating Material>
[0210] First, as the inorganic particles dispersed into a
polyvinylidene fluoride (PVdF) resin, alumina particles having an
average particle diameter D20 of 0.21 .mu.m and an average particle
diameter D90 of 3.18 .mu.m were used, and the mixed amount of the
alumina particles is adjusted to 90.0 vol % so as to be used as the
coating material.
[0211] <Coating Proces>
[0212] Next, both sides of the polyethylene microporous membrane
(first layer) in which the average pore diameter of a plurality of
pores exposed on the surface was 0.05 .mu.m were coated in a table
coater with the above-described coating material in a thickness of
10 .mu.m. At this time, the coating material is adjusted such that
the area density is 0.60 mg/cm.sup.2. Next, second layers
containing the alumina particles were formed on both sides of the
polyethylene microporous membrane as the first layer by performing
phase separation through a water bath and then performing a drying
process. As a result, a separator was acquired.
Example 4-2
[0213] A separator was prepared in the same manner as Example 4-1
except for configuring the thickness of the first layer to be 12.0
.mu.m.
Example 4-3
[0214] A separator was prepared in the same manner as Example 4-1
except for configuring the thickness of the first layer to be 14.0
.mu.m.
Example 4-4
[0215] A separator was prepared in the same manner as Example 4-1
except for configuring the thickness of the first layer to be 16.0
.mu.m.
Example 4-5
[0216] A separator was prepared in the same manner as Example 4-1
except for configuring the thickness of the first layer to be 18.0
.mu.m.
Example 4-6
[0217] A separator was prepared in the same manner as Example 4-1
except for configuring the thickness of the first layer to be 20.0
.mu.m.
Example 4-7
[0218] A separator was prepared in the same manner as Example 4-1
except for configuring the thickness of the first layer to be 24.0
.mu.m.
Example 4-8
[0219] A separator was prepared in the same manner as Example 4-1
except for configuring the thickness of the first layer to be 28.0
.mu.m.
Comparative Example 4-1
[0220] A separator was prepared in the same manner as Example 4-1
except for configuring the thickness of the first layer to be 9.0
.mu.m.
Comparative Example 4-2
[0221] A separator was prepared in the same manner as Example 4-1
except for configuring the thickness of the first layer to be 30.0
.mu.m.
Comparative Example 4-3
[0222] A separator was prepared in the same manner as Example 4-1
except for configuring the thickness of the first layer to be 40.0
.mu.m.
[0223] [Evaluation]
[0224] Similarly to Example 1, the following were calculated.
[0225] (a) Difference of Air Permeability of Separator
Difference of Air Permeability [sec/100 ml]=Air Permeability of
First Layer-Air Permeability of Second Layer
[0226] (b) Air Permeability Rising Rate of Separator
Air Permeability Rising Rate [%]=(Air Permeability of Second
Layer-Air Permeability of First Layer)/Air Permeability of First
Layer
[0227] (c) Capacity Maintaining Rate
Capacity Maintaining Rate [%]=(Amount of Electricity Discharged at
the 100th Cycle/First-Time Capacity).times.100
[0228] In Table 4 shown below, the evaluation results are
represented.
TABLE-US-00004 TABLE 4 First Layer Second Layer Air Average Average
Average Perme- Air Surface Particle Particle ability Perme-
Capacity Thick- Pore Diameter Diameter Difference ability Main-
ness Diameter Resin Inorganic D20 D90 [Sec/ Rising taining Material
[.mu.m] [.mu.m] Material Particle [.mu.m] [.mu.m] 100 ml] Rate [%]
Problem Rate Example 4-1 Polyethylene 10.0 0.05 PVdF Alumina 0.21
3.18 10 7 -- .largecircle. Example 4-2 Polyethylene 12.0 0.05 PVdF
Alumina 0.21 3.18 10 8 -- .largecircle. Example 4-3 Polyethylene
14.0 0.05 PVdF Alumina 0.21 3.18 10 9 -- .largecircle. Example 4-4
Polyethylene 16.0 0.05 PVdF Alumina 0.21 3.18 10 10 --
.largecircle. Example 4-5 Polyethylene 18.0 0.05 PVdF Alumina 0.21
3.18 10 7 -- .largecircle. Example 4-6 Polyethylene 20.0 0.05 PVdF
Alumina 0.21 3.18 10 8 -- .largecircle. Example 4-7 Polyethylene
24.0 0.05 PVdF Alumina 0.21 3.18 10 8 -- .largecircle. Example 4-8
Polyethylene 28.0 0.05 PVdF Alumina 0.21 3.18 10 7 -- .largecircle.
Comparative Polyethylene 9.0 0.05 PVdF Alumina 0.21 3.18 -- --
Broken -- Example 4-1 Separator Comparative Polyethylene 30.0 0.05
PVdF Alumina 0.21 3.18 10 7 Increase in -- Example 4-2 Battery
Component Diameter Comparative Polyethylene 34.0 0.05 PVdF Alumina
0.21 3.18 10 7 Increase in -- Example 4-3 Battery Component
Diameter
[0229] In Table 4, a case where the capacity maintaining rate is
equal to or greater than 80% is denoted by "o", and a case where
the capacity maintaining rate is less than 80% is denoted by
"x".
[0230] As is apparent from Table 4, in a case where a separator in
which the thickness of the first layer was equal to or greater than
10.0 .mu.m and less than 30.0 .mu.m was employed, as in Examples
4-1 to 4-8, the capacity maintaining rate was equal to or greater
than 80%.
[0231] In contrast, in a case where the thickness of the first
layer was small as being 9.0 .mu.m, as in Comparative Example 4-1,
the strength of the separator was decreased, and the separator was
broken. On the other hand, in a case where the thickness of the
first layer is equal to or greater than 30.0 .mu.m, as in
Comparative Examples 4-2 and 4-3, the component diameter of a wound
electrode body prepared by being wound was increased, and
accordingly, it was difficult to insert the wound electrode body
into the battery can.
[0232] From Example 4, it was found that, preferably, the thickness
of the first layer was equal to or greater than 10.0 .mu.m and less
than 30.0 .mu.m.
Example 5
[0233] In Example 5, batteries were prepared by employing
separators that were prepared by changing the coating area density
of the coating material at the time of formation of the second
layer, and the separators and the battery characteristics were
evaluated.
Example 5-1
[0234] [Preparation of Separator]
[0235] <Preparation of Coating Material>
[0236] First, as the inorganic particles dispersed into a
polyvinylidene fluoride (PVdF) resin, alumina particles having an
average particle diameter D20 of 0.21 .mu.m and an average particle
diameter D90 of 3.18 .mu.m were used, and the mixed amount of the
alumina particles is adjusted to 90.0 vol % so as to be used as the
coating material.
<Coating Process>
[0237] Next, both sides of the polyethylene microporous membrane
(first layer) in which the average pore diameter of a plurality of
pores exposed on the surface was 0.05 .mu.m were coated in a table
coater with the above-described coating material in a thickness of
16 .mu.m. At this time, the coating material is adjusted such that
the area density is 0.20 mg/cm.sup.2. Next, second layers
containing the alumina particles were formed on both sides of the
polyethylene microporous membrane as the first layer by performing
phase separation through a water bath and then performing a drying
process. As a result, a separator was acquired.
Example 5-2
[0238] A separator was prepared in the same manner as Example 5-1
except for adjusting the coating area density of the coating
material to be 0.40 mg/cm.sup.2.
Example 5-3
[0239] A separator was prepared in the same manner as Example 5-1
except for adjusting the coating area density of the coating
material to be 0.60 mg/cm.sup.2.
Example 5-4
[0240] A separator was prepared in the same manner as Example 5-1
except for adjusting the coating area density of the coating
material to be 0.80 mg/cm.sup.2.
Example 5-5
[0241] A separator was prepared in the same manner as Example 5-1
except for adjusting the coating area density of the coating
material to be 1.80 mg/cm.sup.2.
Example 5-6
[0242] A separator was prepared in the same manner as Example 5-1
except for adjusting the mixed amount of the silica particles to be
95.0 vol % and the coating area density of the coating material to
be 0.60 mg/cm.sup.2 by using the silica particles having an average
particle diameter D20 of 0.80 .mu.m and an average particle
diameter D90 of 2.00 .mu.m as the inorganic particles that were
mixed at the time of preparation of the coating material.
Comparative Example 5-1
[0243] A separator was prepared in the same manner as Example 5-1
except for adjusting the coating area density of the coating
material to be 0.10 mg/cm.sup.2.
Comparative Example 5-2
[0244] A separator was prepared in the same manner as Example 5-1
except for adjusting the coating area density of the coating
material to be 2.00 mg/cm.sup.2.
Comparative Example 5-3
[0245] A separator was prepared in the same manner as Example 5-1
except for not disposing the second layer.
[0246] [Evaluation]
[0247] Similarly to Example 1, the following were calculated.
[0248] (a) Difference of Air Permeability of Separator
Difference of Air Permeability [sec/100 ml]=Air Permeability of
First Layer-Air Permeability of Second Layer
[0249] (b) Air Permeability Rising Rate of Separator
Air Permeability Rising Rate [%]=(Air Permeability of Second
Layer-Air Permeability of First Layer)/Air Permeability of First
Layer
[0250] (c) Capacity Maintaining Rate
Capacity Maintaining Rate [%]=(Amount of Electricity Discharged at
the 100th Cycle/First-Time Capacity).times.100
[0251] In Table 5 shown below, the evaluation results are
represented.
TABLE-US-00005 TABLE 5 Second Layer Average Average Air First Layer
Particle Particle Particle Coating Perme- Capacity Thick- Diameter
Diameter Mixed Area ability Main- ness Resin Inorganic D20 D90
Amount Density Rising Rate taining Material [.mu.m] Material
Particle [.mu.m] [.mu.m] [Vol %] [mg/cm.sup.2] [%] Problem Rate
Example 5-1 Polyethylene 16.0 PVdF Alumina 0.21 3.18 90.0 0.20 23
-- .largecircle. Example 5-2 Polyethylene 16.0 PVdF Alumina 0.21
3.18 90.0 0.40 20 -- .largecircle. Example 5-3 Polyethylene 16.0
PVdF Alumina 0.21 3.18 90.0 0.60 15 -- .largecircle. Example 5-4
Polyethylene 16.0 PVdF Alumina 0.21 3.18 90.0 0.80 10 --
.largecircle. Example 5-5 Polyethylene 16.0 PVdF Alumina 0.21 3.18
90.0 1.80 8 -- .largecircle. Example 5-6 Polyethylene 16.0 PVdF
Silica 0.80 2.00 95.0 0.60 10 -- .largecircle. Comparative
Polyethylene 16.0 PVdF Alumina 0.21 3.18 90.0 0.10 -- Uneven --
Example 5-1 Coating of Second Layer/ Broken Separator Comparative
Polyethylene 16.0 PVdF Alumina 0.21 3.18 90.0 2.00 8 Increase in --
Example 5-2 Battery Component Diameter Comparative Polyethylene
16.0 -- -- -- -- -- -- 50 -- X Example 5-3
[0252] In Table 5, a case where the capacity maintaining rate is
equal to or greater than 80% is denoted by "o", and a case where
the capacity maintaining rate is less than 80% is denoted by
"x".
[0253] As is apparent from Table 5, by adjusting the coating area
density of the second layer to be equal to or greater than 0.20
mg/cm.sup.2 and equal to or less than 1.80 mg/cm.sup.2, as in
Examples 5-1 to 5-6, in a case where the average pore diameter of
the first layer was equal to or greater than 0.03 .mu.m and equal
to or less than 2.00 .mu.m, the capacity maintaining rate was equal
to or greater than 80%.
[0254] In contrast, as in Comparative Example 5-1, in a case where
the coating area density of the second layer was low as being 0.10
mg/cm.sup.2, coating unevenness or coating breaking of the second
layer occurred. Accordingly, it was difficult to form a separator
according to an. On the other hand, as in Comparative Example 5-2,
in a case where the coating area density of the second layer was
high as being 2.00 mg/cm.sup.2, the component diameter of the wound
electrode body, which was prepared by being wound, increased.
Accordingly, it was difficult to insert the wound electrode body
into the battery can. Also in Comparative Example 5-3 in which the
second layer is not disposed, the capacity maintaining rate was
decreased. The reason for this is thought to be a decrease in the
ion permeability due to crushing of the holes of the polyethylene
microporous membrane as the first layer, that is, the separator,
which is caused by expansion of the electrode.
[0255] From Example 5, it was found that, preferably, the coating
area density of the second layer with respect to the surface of the
first layer was equal to or greater than 0.20 mg/cm.sup.2 and equal
to or lower than 1.8010 mg/cm.sup.2.
Example 6
[0256] In Example 6, batteries were prepared by employing
separators that were prepared by respectively changing the
thickness of the first layer and the average particle diameter D90
of the inorganic particles mixed into the second layer, and the
separators and the battery characteristics were evaluated.
Example 6-1
[0257] <Preparation of Coating Material>
[0258] First, as the inorganic particles dispersed into a
polyvinylidene fluoride (PVdF) resin, alumina particles having an
average particle diameter D20 of 0.21 .mu.m and an average particle
diameter D90 of 3.18 .mu.m were used, and the mixed amount of the
alumina particles is adjusted to 90.0 vol % so as to be used as the
coating material.
[0259] <Coating Process>
[0260] Next, both sides of the polyethylene microporous membrane
(first layer) in which the average pore diameter of a plurality of
pores exposed on the surface was 0.05 .mu.m were coated in a table
coater with the above-described coating material in a thickness of
16 .mu.m. At this time, the coating material is adjusted such that
the area density is 0.60 mg/cm.sup.2. Next, second layers
containing the alumina particles were formed on both sides of the
polyethylene microporous membrane as the first layer by performing
phase separation through a water bath and then performing a drying
process. As a result, a separator was acquired.
Example 6-2
[0261] A separator was prepared in the same manner as Example 6-1
except for configuring the thickness of the first layer to be 9.0
.mu.m and an average pore diameter of the surface of the first
layer to be 0.04 .mu.m and using silica particles having an average
particle diameter D20 of 0.13 .mu.m and an average particle
diameter D90 of 2.48 .mu.m as the inorganic particles mixed into
the second layer.
Example 6-3
[0262] A separator was prepared in the same manner as Example 6-1
except for configuring the thickness of the first layer to be 12.0
.mu.m and an average pore diameter of the surface of the first
layer to be 0.03 .mu.m and using silica particles having an average
particle diameter D20 of 0.13 .mu.m and an average particle
diameter D90 of 2.48 .mu.m as the inorganic particles mixed into
the second layer.
Example 6-4
[0263] A separator was prepared in the same manner as Example 6-1
except for configuring an average pore diameter of the surface of
the first layer to be 1.50 .mu.m and using silica particles having
an average particle diameter D20 of 2.10 .mu.m and an average
particle diameter D90 of 5.00 .mu.m as the inorganic particles
mixed into the second layer.
Comparative Example 6-1
[0264] A separator was prepared in the same manner as Example 6-1
except for configuring the thickness of the first layer to be 9.0
.mu.m.
Comparative Example 6-2
[0265] A separator was prepared in the same manner as Example 6-1
except for configuring the thickness of the first layer to be 9.0
.mu.m and the average pore diameter to be 0.04 .mu.m and using
silica particles having an average particle diameter D20 of 1.00
.mu.m and an average particle diameter D90 of 5.00 .mu.m as the
inorganic particles mixed into the second layer.
Comparative Example 6-3
[0266] A separator was prepared in the same manner as Example 6-1
except for configuring the thickness of the first layer to be 12.0
.mu.m and the average pore diameter to be 0.03 .mu.m and using
silica particles having an average particle diameter D20 of 1.00
.mu.m and an average particle diameter D90 of 5.00 .mu.m as the
inorganic particles mixed into the second layer.
[0267] [Evaluation]
[0268] Similarly to Example 1, the following were calculated.
[0269] (a) Difference of Air Permeability of Separator
Difference of Air Permeability [sec/100 ml]=Air Permeability of
First Layer-Air Permeability of Second Layer
[0270] (b) Air Permeability Rising Rate of Separator
Air Permeability Rising Rate [%]=(Air Permeability of Second
Layer-Air Permeability of First Layer)/Air Permeability of First
Layer
[0271] (c) Capacity Maintaining Rate
Capacity Maintaining Rate [%]=(Amount of Electricity Discharged at
the 100th Cycle/First-Time Capacity).times.100
[0272] In Table 6 shown below, the evaluation results are
represented.
TABLE-US-00006 TABLE 6 First Layer Second Layer Air Average Average
Average Perme- Air Surface Particle Particle ability Perme-
Capacity Thick- Pore Diameter Diameter Difference ability Main-
ness Diameter Resin Inorganic D20 D90 [Sec/ Rising Rate taining
Material [.mu.m] [.mu.m] Material Particle [.mu.m] [.mu.m] 100 ml]
[%] Problem Rate Example 6-1 Polyethylene 16.0 0.05 PVdF Alumina
0.21 3.18 10 15 -- .largecircle. Example 6-2 Polyethylene 9.0 0.04
PVdF Silica 0.13 2.48 10 12 -- .largecircle. Example 6-3
Polyethylene 12.0 0.03 PVdF Silica 0.13 2.48 10 10 -- .largecircle.
Example 6-4 Polyethylene 16.0 1.50 PVdF Silica 2.10 5.00 10 6 --
.largecircle. Comparative Polyethylene 9.0 0.05 PVdF Alumina 0.21
3.18 -- -- Broken -- Example 6-1 Separator Comparative Polyethylene
9.0 0.04 PVdF Silica 1.00 5.00 -- -- Cobwebbing -- Example 6-2 at
Time of Coating/ Broken Separator Comparative Polyethylene 12.0
0.03 PVdF Silica 1.00 5.00 -- -- Cobwebbing -- Example 6-3 at Time
of Coating
[0273] In Table 6, a case where the capacity maintaining rate is
equal to or greater than 80% is denoted by "o", and a case where
the capacity maintaining rate is less than 80% is denoted by
"x".
[0274] As is apparent from Table 6, as in Examples 6-1 to 6-4, in a
case where the average particle diameter D90 of the inorganic
particles contained in the second layer was equal to or less than
1/3 of the thickness of the first layer, there was no inconvenience
in preparing the wound electrode body, and the capacity maintaining
rate was equal to or greater than 80%.
[0275] In contrast, in a case where the average particle diameter
D90 of the inorganic particles contained in the second layer
exceeds 1/3 of the thickness of the first layer, the inorganic
particles of the second layer break through the first layer.
Accordingly, the separator is broken. In addition, since the
inorganic particles are too large, cobwebbing occurs, that is, a
portion (a portion in which coating is not spread on the side of
the inorganic particles) that is not coated with the coating
material is formed at the time of formation of the second layer.
Accordingly, it was difficult to prepare a separator according to
an.
[0276] From Example 6, it was found that, preferably, the average
particle diameter D90 of the inorganic particles is equal to or
less than 1/3 of the thickness of the first layer.
[0277] The configurations, the shapes, the materials, and the
numerical values described in the above-described embodiments are
merely examples. Thus, as necessary, a configuration, a shape, a
material, or a numerical value other than those may be used.
[0278] In addition, in the above-described embodiments, examples
are applied to a lithium ion battery are represented. However, the
embodiments are not limited to the type of battery, but may be
applied to any battery that has a separator. For example, an
embodiment can be applied to various batteries such as a nickel
hydrogen battery, a lithium cadmium battery, a lithium-manganese
dioxide battery, and a lithium-iron sulfide battery.
[0279] In addition, in the above-described embodiments, examples
are applied to a battery having a winding structure have been
described. However, the structure of the battery is not limited
thereto. Thus, an embodiment can be applied to a battery having a
structure in which a positive electrode and a negative electrode
are folded, a structure in which the positive electrode and the
negative electrode are overlapped, or the like.
[0280] In addition, in the above-described embodiments, examples
are applied to a battery having a cylinder shape or a flat shape
have been described. However, the shape of the battery is not
limited thereto. Thus, an embodiment can be applied to a battery
having a coin shape, a button shape, a corner shape, or the
like.
[0281] It should be understood that various changes and
modifications to the presently preferred embodiments described
herein will be apparent to those skilled in the art. Such changes
and modifications can be made without departing from the spirit and
scope and without diminishing its intended advantages. It is
therefore intended that such changes and modifications be covered
by the appended claims.
* * * * *