U.S. patent application number 10/724882 was filed with the patent office on 2004-08-12 for crosslinking polymer-supported porous film for battery separator and method for producing battery using the same.
This patent application is currently assigned to NITTO DENKO CORPORATION. Invention is credited to Kii, Keisuke, Nishikawa, Satoshi, Uetani, Yoshihiro.
Application Number | 20040157118 10/724882 |
Document ID | / |
Family ID | 32752513 |
Filed Date | 2004-08-12 |
United States Patent
Application |
20040157118 |
Kind Code |
A1 |
Uetani, Yoshihiro ; et
al. |
August 12, 2004 |
Crosslinking polymer-supported porous film for battery separator
and method for producing battery using the same
Abstract
A porous film having a crosslinking polymer supported thereon,
which can preferably be used for producing a gel electrolyte
battery having sufficient adhesion between the electrodes and the
separator, low internal resistance and high rate performance, and
which can function as a separator in a battery, and a method for
producing a gel electrolyte battery using such a crosslinking
polymer-supported porous film. The crosslinking polymer-supported
porous film for battery separator comprises a porous film substrate
having supported thereon a crosslinking polymer having plural
cation-polymerizable functional groups in the molecule. The method
for producing a battery, includes the steps of: laminating
electrodes on the crosslinking polymer-supported porous film to
prepare a laminate of crosslinking polymer-supported porous
film/electrodes; placing the laminate in a battery container; and
pouring an electrolyte solution containing a cation polymerization
catalyst in the battery container to induce cation polymerization
and crosslinking of the crosslinking polymer, thereby at least
partially gelling the electrolyte solution to adhere the porous
film and the electrodes.
Inventors: |
Uetani, Yoshihiro;
(Ibaraki-shi, JP) ; Kii, Keisuke; (Ibaraki-shi,
JP) ; Nishikawa, Satoshi; (Takatsuki-shi,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
NITTO DENKO CORPORATION
SUNSTAR ENGINEERING INC.
|
Family ID: |
32752513 |
Appl. No.: |
10/724882 |
Filed: |
December 2, 2003 |
Current U.S.
Class: |
429/144 ;
29/623.3; 429/253 |
Current CPC
Class: |
H01M 10/0565 20130101;
B32B 27/30 20130101; B32B 2323/10 20130101; H01M 50/42 20210101;
B32B 2323/04 20130101; H01M 50/449 20210101; H01M 2300/0082
20130101; H01M 2300/0085 20130101; B32B 2379/08 20130101; Y02P
70/50 20151101; B32B 2327/18 20130101; H01M 50/411 20210101; H01M
50/46 20210101; H01M 50/491 20210101; Y10T 29/49112 20150115; H01M
50/406 20210101; B32B 27/32 20130101; H01M 50/417 20210101; B32B
27/08 20130101; B32B 2305/026 20130101; H01M 10/052 20130101; Y02E
60/10 20130101; H01M 50/403 20210101 |
Class at
Publication: |
429/144 ;
429/253; 029/623.3 |
International
Class: |
H01M 002/16; H01M
002/18; H01M 010/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 2, 2002 |
JP |
P. 2002-350223 |
Claims
What is claimed is:
1. A crosslinking polymer-supported porous film for battery
separator, comprising a porous film substrate having supported
thereon a crosslinking polymer having plural cation-polymerizable
functional groups in the molecule.
2. The crosslinking polymer-supported porous film as claimed in
claim 1, wherein the crosslinking polymer has a plurality of at
least one cation polymerizable functional group selected from the
group consisting of 3-oxetanyl group and epoxy group.
3. The crosslinking polymer-supported porous film as claimed in
claim 1, wherein the crosslinking polymer is a radical copolymer
comprising at least one radical-polymerizable monomer selected from
the group consisting of a radical-polymerizable monomer having
3-oxetanyl group and a radical-polymerizable monomer having epoxy
group, and other radical-polymerizable monomer.
4. The crosslinking polymer-supported porous film as claimed in
claim 1, wherein the crosslinking polymer is a radical copolymer
comprising 5-50% by weight of a radical-polymerizable monomer
having 3-oxetanyl group and other radical-polymerizable
monomer.
5. The crosslinking polymer-supported porous film as claimed in
claim 1, wherein the crosslinking polymer is a radical copolymer
comprising 5-50% by weight of a radical-polymerizable monomer
having epoxy group and other radical-polymerizable monomer.
6. The crosslinking polymer-supported porous film as claimed in
claim 3, wherein the radical-polymerizable monomer having
3-oxetanyl group is 3-oxetanyl group-containing (meth)acrylate
represented by the following formula (I): 7wherein R.sub.1
represents hydrogen atom or methyl group; and R.sub.2 represents
hydrogen atom or an alkyl group having 1-6 carbon atoms.
7. The crosslinking polymer-supported porous film as claimed in
claim 3, wherein the radical-polymerizable monomer having epoxy
group is epoxy group-containing (meth)acrylate represented by the
following formula (II): 8wherein R.sub.3 represents hydrogen atom
or methyl group; and R.sub.4 represents an epoxy group-containing
group represented by the following formula (1) or (2): 9
8. The crosslinking polymer-supported porous film as claimed in
claim 3, wherein the other radical-polymerizable monomer is at
least one monomer selected from the group consisting of
(meth)acrylate represented by the following formula (III):
10wherein R.sub.5 represents hydrogen atom or methyl group; A
represents an oxyalkylene group having 2 or 3 carbon atoms; R.sub.6
represents an alkyl group having 1-6 carbon atoms or a fluorinated
alkyl group having 1-6 carbon atoms; and n is an integer of 0-3,
and vinyl ester represented by the following formula (IV):
11wherein R.sub.7 represents methyl group or ethyl group; and
R.sub.8 represents hydrogen atom or methyl group.
9. The crosslinking polymer-supported porous film as claimed in
claim 1, wherein the porous film substrate has a thickness of 3-50
.mu.m and a porosity of 20-95%.
10. A method for producing a battery, comprising: laminating
electrodes on the crosslinking polymer-supported porous film as
claimed in claim 1 to prepare a laminate of crosslinking
polymer-supported porous film/electrodes, placing the laminate in a
battery container, and pouring an electrolyte solution containing a
cation polymerization catalyst in the battery container to induce
cation polymerization and crosslinking of the crosslinking polymer,
thereby at least partially gelling the electrolyte solution to
adhere the porous film and the electrodes.
11. The method for producing battery as claimed claim 10, wherein
the cation polymerization catalyst is an onium salt.
12. The method for producing battery as claimed in claim 10,
wherein the electrolyte solution contains at least one member
selected from the group consisting of lithium hexafluorophosphate
and lithium tetrafluoroborate, as an electrolyte salt further
functioning as a cation polymerization catalyst.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a crosslinking
polymer-supported porous film for battery separator, comprising a
porous film substrate having supported thereon a crosslinking
polymer having plural cation-polymerizable functional groups in the
molecule, and a method for producing a battery by adhering
electrodes to a separator using the crosslinking polymer-supported
porous film.
DESCRIPTION OF THE RELATED ART
[0002] In recent years, lithium ion secondary batteries with high
energy density have been widely used as a power source of
small-type hand-held electronic devices such as cell phone and
laptop personal computer. Such lithium ion secondary batteries are
produced by a process including a step of laminating or winding,
for example, a polyolefin resin-porous film on or around positive
and negative electrodes in a sheet form to place the resulting
laminate in a battery container made of, for example, a metal can,
a step of pouring an electrolyte solution in the battery container,
and a step of sealing the battery container or sealing the opening
of the battery container.
[0003] However, very strong demands for downsizing such small-type
hand-held electronic devices as described above into small weight
have prevailed recently. Lithium ion secondary batteries of a
thinner type and a smaller weight have been desired. Therefore,
battery containers of laminate seal type are now used in place of
the conventional metal can containers.
[0004] Compared with the conventional metal can containers, such
battery containers of laminate seal type have the following
disadvantages. Because face pressure for maintaining the electric
connection between the separator and the electrodes cannot
sufficiently be applied to the face of the electrodes, the distance
between the electrodes partially gets longer over time due to the
expansion and shrinkage of electrode active substances during the
charge or discharge of the battery. Thus, the internal resistance
of the battery increases, involving deterioration of the battery
performance. Additionally, the occurrence of resistance variation
inside the battery also disadvantageously deteriorates the battery
performance.
[0005] In the case of producing a sheet-like battery of a large
area, the distance between the electrodes cannot be fixed, so that
satisfactory battery performance cannot be obtained due to the
resulting resistance variation inside the battery.
[0006] To overcome the above-described problems, it has
conventionally been proposed to join electrodes and a separator by
an adhesive resin layer comprising an electrolyte solution phase, a
polymer gel layer containing an electrolyte solution and a polymer
solid phase (for example, JP-A-10-177865). It is further proposed
to obtain a battery comprising electrodes adhered to a separator,
by coating a separator with a binder resin solution containing a
poly(vinylidene fluoride) resin as the main component, superposing
electrodes thereon, followed by drying to prepare a battery
laminate, charging the battery laminate in a battery container, and
pouring an electrolyte solution in the battery container (for
example, JP-A-10-189054).
[0007] It is also proposed to obtain a battery comprising
electrodes adhered to a separator, by joining a separator
impregnated with an electrolyte solution to positive and negative
electrodes through a porous adhesive resin layer for closely
contacting those, and holding the electrolyte solution in the
through holes (for example, JP-A-10-172606).
[0008] According to those processes, however, thickness of the
adhesive resin layer must increase in order to obtain sufficient
adhesive force between the separators and the electrodes. Further,
because the amount of the electrolyte solution relative to the
adhesive resin cannot increase, the internal resistance of the
resulting batteries is high, so that satisfactory cycle performance
and high-rate discharge performance cannot be obtained, which is
disadvantageous.
SUMMARY OF THE INVENTION
[0009] The invention has been made to overcome the problems in the
production of batteries by adhering electrodes to separators.
[0010] Accordingly, one object of the present invention is to
provide a surface-treated porous film having a polymer supported
thereon, for a battery separator, which can suitably be used for
the production of a battery having sufficient adhesiveness between
electrodes and a separator, low internal resistance and high-rate
performance.
[0011] Another object of the present invention is to provide a
method for producing a battery using the surface-treated porous
film.
[0012] According to the present invention, there is provided a
crosslinking polymer-supported porous film for battery separator,
comprising a porous film substrate having supported thereon a
crosslinking polymer having plural cation-polymerizable functional
groups in the molecule.
[0013] According to the present invention, there is further
provided a method for producing a battery, comprising:
[0014] laminating electrodes on the crosslinking polymer-supported
porous film to prepare a laminate of crosslinking polymer-supported
porous film/electrodes,
[0015] placing the laminate in a battery container, and
[0016] pouring an electrolyte solution containing a cation
polymerization catalyst in the battery container to induce cation
polymerization and crosslinking of the crosslinking polymer,
thereby at least partially gelling the electrolyte solution to
adhere the porous film and the electrodes.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The crosslinking polymer-supported porous film for battery
separator in accordance with the present invention comprises a
porous film substrate having supported thereon a crosslinking
polymer having plural cation-polymerizable functional groups in the
molecule.
[0018] The porous film substrate has a thickness of preferably 3-50
.mu.m. If the porous film has a thickness less than 3 .mu.m, the
film strength is insufficient, and when such a porous film is used
as the battery separator, the electrodes may cause internal short
circuit. On the other hand, when the porous film has a thickness
exceeding 50 .mu.m, the battery using such a porous film as the
separator has too large distance between the electrodes, so that
the internal resistance of the battery is excessive.
[0019] The porous film substrate used has pores having a mean pore
diameter of 0.01-5 .mu.m and a porosity of 20-95%, preferably
30-90%, and more preferably 40-85%. When the porosity ratio is too
low, such a porous film when used as a battery separator causes
reduction in ionic conduction paths so that sufficient battery
performance cannot be obtained. On the other hand, when the
porosity ratio is too high, the strength of the film when used as a
battery separator is insufficient. In such a case, a porous film
substrate having further large thickness has to be used in order to
obtain the required strength. This results in unfavorable increase
in the internal resistance of the battery.
[0020] The porous film has an air permeability of 1,500 seconds/100
cc or smaller, and preferably 1,000 second/100 cc or smaller. When
the permeability is too high, such a film when used as a battery
separator has low ionic conductivity, so that sufficient battery
performance cannot be obtained. Further, the porous film substrate
preferably has a puncture strength of 1N or more. When the puncture
strength is less than 1N, the substrate breaks when the face
pressure is applied to between the electrodes, which may cause
internal short circuit.
[0021] According to the present invention, the porous film
substrate is not particularly limited so long as it has the
above-described properties. Considering solvent resistance and
redox resistance, a porous film comprising polyolefin resins such
as polyethylene and polypropylene is preferably used. Of those,
polyethylene resin film is particularly preferably used as the
porous film for the reason that the film has a property such that
when heated, the resin melts and clogs the pores, thereby giving a
so-called shutdown function to the battery. The polyethylene resin
used herein includes not only ethylene homopolymer but also
copolymers of ethylene with .alpha.-olefins such as propylene,
butene and hexene. Further, laminate films of porous films such as
polytetrafluoroethylene and polyimide with the polyolefin resin
porous film have excellent heat resistance. Therefore, such
laminate films are also preferably used as the porous film
substrate in the present invention.
[0022] The crosslinking polymer-supported porous film for battery
separator in accordance with the present invention comprises the
above-described porous film substrate having supported thereon a
crosslinking polymer having plural cation-polymerizable functional
groups in the molecule.
[0023] The crosslinking polymer used in the present invention
preferably is polymers having a plurality of at least one
cation-polymerizable functional group selected from 3-oxetanyl
group and epoxy group (2-oxysilanyl group) in the molecule. The
crosslinking polymer particularly preferably used is a polymer
having plural 3-oxetanyl groups in the molecule (hereinafter
referred to as "3-oxetanyl group-containing crosslinking polymer"
for simplicity) or a polymer having plural epoxy groups in the
molecule (hereinafter referred to as "epoxy group-containing
crosslinking polymer" for simplicity). Such 3-oxetanyl
group-containing crosslinking polymer and epoxy group-containing
crosslinking polymer are described in, for example,
JP-A-2001-176555 and JP-A-2002-110245.
[0024] The 3-oxetanyl group-containing crosslinking polymer is
preferably a radical copolymer of a radical-polymerizable monomer
having 3-oxetanyl group (hereinafter referred to as "3-oxetanyl
group-containing radical-polymerizable monomer" for simplicity)
with other radical-polymerizable monomer. Similarly, the epoxy
group-containing crosslinking polymer is preferably a radical
copolymer of a radical-polymerizable monomer with epoxy group
(hereinafter referred to as "epoxy group-containing
radical-polymerizable monomer" for simplicity) with other
radical-polymerizable monomer.
[0025] The 3-oxetanyl group-containing radical-polymerizable
monomer preferably used is 3-oxetanyl group-containing
(meth)acrylate represented by the following formula (I): 1
[0026] wherein R.sub.1 represents hydrogen atom or methyl group;
and R.sub.2 represents hydrogen atom or an alkyl group having 1-6
carbon atoms.
[0027] Examples of the 2-oxetanyl group-containing (meth)acrylate
include 3-oxetanylmethyl(meth)acrylate,
3-methyl-3-oxetanylmethyl(meth)acrylate,
3-ethyl-3-oxetanylmethyl(meth)acrylate,
3-butyl-3-oxetanylmethyl(meth)acr- ylate, and
3-hexyl-3-oxetanylmethyl(meth)acrylate. These (meth)acrylates can
be used alone or as mixtures of two or more thereof. The term
"(meth)acrylate" used herein means acrylate or methacrylate.
[0028] The epoxy group-containing radical-polymerizable monomer
preferably used is an epoxy group-containing (meth)acrylate
represented by the following formula (II): 2
[0029] wherein R.sub.3 represents hydrogen atom or methyl group;
and R.sub.4 represents an epoxy group-containing group represented
by the following formula (1) or (2): 3
[0030] Examples of the epoxy group-containing (meth)acrylate
include 3,4-epoxycyclohexylmethyl(meth)acrylate, and
glycidyl(meth)acrylate. These (meth)acrylates can be used alone or
as mixtures of two or more thereof.
[0031] The other radical-polymerizable monomer to be copolymerized
with such 3-oxetanyl group-containing radical-polymerizable monomer
or epoxy group-containing radical-polymerizable monomer is
preferably at least one selected from (meth)acrylates represented
by the following formula (III): 4
[0032] wherein R.sub.5 represents hydrogen atom or methyl group; A
represents an oxyalkylene group having 2 or 3 carbon atoms
(preferably, oxyethylene group or oxypropylene group): R.sub.6
represents an alkyl group having 1-6 carbon atoms or a fluorinated
alkyl group having 1-6 carbon atoms; and n is an integer of 0-3,
and
[0033] vinyl ester represented by the following formula (IV): 5
[0034] wherein R.sub.7 represents methyl group or ethyl group; and
R.sub.8 represents hydrogen atom or methyl group.
[0035] Examples of the (meth)acrylate represented by the formula
(III) include methyl(meth)acrylate, ethyl(meth)acrylate,
propyl(meth)acrylate, butyl(meth)acrylate,
2,2,2-trifluoroethyl(meth)acrylate, and
2,2,3,3-tetrafluoropropyl(meth)acrylate. Other than those, for
example, compounds represented by the following formulae can be
used. 6
[0036] wherein n is an integer of 0-3.
[0037] Examples of the vinyl ester represented by the formula (IV)
include vinyl acetate and vinyl propionate.
[0038] The 3-oxetanyl group-containing crosslinking polymers and
the epoxy group-containing crosslinking polymers are preferably
obtained as radical copolymers via radical copolymerization of the
3-oxetanyl group-containing radical-polymerizable monomer or the
epoxy group-containing radical-polymerizable monomer with other
radical-polymerizable monomer using radical polymerization
initiators as described above. The radical copolymerization can be
conducted by any polymerization processes such as solution
polymerization, bulk polymerization, suspension polymerization or
emulsion polymerization. From the standpoints of ease of
polymerization, molecular weight adjustment and post-treatment, the
radical copolymerization is preferably conducted by solution
polymerization or suspension polymerization.
[0039] The radical polymerization initiators are not particularly
limited, and examples thereof include N,N'-azobisisobutyronitrile,
dimethyl N,N'-azobis(2-methylpropionate), benzoyl peroxide, and
lauroyl peroxide. If required and necessary, chain transfer agents
such as mercaptan can be used in this radical copolymerization.
[0040] According to the present invention, at least a part of the
crosslinking polymer supported on a porous film is swollen in an
electrolyte solution or dissolves in an electrolyte solution at
least around the interface between the porous film and electrodes
to crosslink by cation polymerization and gel the electrolyte
solution around the interface between the porous film and the
electrodes, thereby adhering the electrodes to the porous film, as
described hereinafter. Therefore, the gel formed by the
crosslinking polymer together with the electrolyte solution is
required to be one capable of adhering the electrodes and the
porous film to each other.
[0041] In producing the 3-oxetanyl group-containing crosslinking
polymer or the epoxy group-containing crosslinking polymer, the
3-oxetanyl group-containing radical-polymerizable monomer or the
3-epoxy group-containing radical-polymerizable monomer is used in
an amount such that the respective total amount is 5-50% by weight,
preferably 10-30% by weight, based on the weight of the whole
monomers used. Therefore, in the case of producing the 3-oxetanyl
group-containing crosslinking polymer, the 3-oxetanyl
group-containing radical-polymerizable monomer is used in an amount
of 5-50% by weight, preferably 10-30% by weight, based on the
weight of the whole monomers used. Similarly, in the case of
producing the epoxy group-containing crosslinking polymer, the
epoxy group-containing radical-polymerizable monomer is used in an
amount of 5-50% by weight, preferably 10-30% by weight, based on
the weight of the whole monomers used.
[0042] In the case of producing a crosslinking polymer containing
3-oxetanyl group and epoxy group by using 3-oxetanyl
group-containing radical-polymerizable monomer and epoxy
group-containing radical-polymerizable monomer in combination and
copolymerizing those monomers with other radical-polymerizable
monomer, those monomers are used in an amount such that its total
amount is 5-50% by weight, preferably 10-30% by weight, based on
the weight of the whole monomers used. In this case of the combined
use, the proportion of the epoxy group-containing
radical-polymerizable monomer is 90% by weight or less based on the
weight of the total amount of the 3-oxetanyl group-containing
radical-polymerizable monomer and epoxy group-containing
radical-polymerizable monomer.
[0043] In producing the 3-oxetanyl group-containing crosslinking
polymer, epoxy group-containing crosslinking polymer or
crosslinking polymer containing 3-oxetanyl group and epoxy group,
if the amount of the 3-oxetanyl group-containing
radical-polymerizable monomer, the amount of the epoxy
group-containing radical-polymerizable monomer or the total amount
of 3-oxetanyl group-containing radical-polymerizable monomer and
epoxy group-containing radical-polymerizable monomer is less than
5% by weight based on the weight of the whole monomers used, the
amount of the respective crosslinking polymer required for the
gelation of the electrolyte solution increases as described above.
As a result, the performance of the resulting battery deteriorates.
On the other hand, if the respective amount is more than 50% by
weight, the property to maintain the electrolyte solution in a form
of a gel deteriorates. As a result, the adhesiveness between the
electrodes and the separator in the resulting battery
deteriorates.
[0044] The 3-oxetanyl group and/or epoxy group-containing
crosslinking polymer preferably has a weight average molecular
weight of 10,000 or more. If the weight average molecular weight is
smaller than 10,000, a larger amount of the crosslinking polymers
is required for the gelation of the electrolyte solution, resulting
in deterioration of the performance of the battery obtained. The
upper limit of the weight average molecular weight is not
particularly limited. However, the upper limit is about 3,000,000,
and preferably 2,500,000, so as to maintain the electrolyte
solution in the gel form. The 3-oxetanyl group and/or epoxy
group-containing crosslinking polymer further preferably has a
weight average molecular weight of 100,000-2,000,000.
[0045] A method of supporting the crosslinking polymer on the
porous film is not particularly limited. For example, the
crosslinking polymer is dissolved in an appropriate organic solvent
such as acetone, ethyl acetate or butyl acetate to prepare a
crosslinking polymer solution, this solution is applied to the
surface of a porous film by casting or spray coating, or a porous
film is dipped in the crosslinking polymer solution, and the porous
film thus treated is dried to remove the organic solvent.
[0046] Another method is that the crosslinking polymer is molded
into a film by melt extrusion, and this film is laminated on the
porous film substrate by thermal lamination and the like.
[0047] The method for producing a battery using the thus obtained
crosslinking polymer-supported porous film according to the present
invention is described below.
[0048] Electrodes are laminated on or are wound around the
crosslinking polymer-supported porous film, and preferably,
electrodes and the crosslinking polymer-supported porous film are
heat bonded, to obtain a laminate of electrodes/crosslinking
polymer-supported porous film. The laminate is placed in a battery
container comprising a metal can or a laminate film. If required
and necessary, terminals are welded. A given amount of an
electrolyte solution having a cation polymerization catalyst
dissolved therein is poured in the battery container. The battery
container is sealed or the opening of the battery container is
sealed. At least a part of the crosslinking polymer supported on
the porous film is swollen at least around the interface between
the porous film and the electrodes in the electrolyte solution or
dissolves in the electrolyte solution. The crosslinking polymer is
crosslinked by cation polymerization to gel at least a part of the
electrolyte solution, thereby adhering the electrodes and the
porous film. Thus, a battery in which the electrodes are strongly
adhered to the porous film as a separator can be obtained.
[0049] The crosslinking polymer can satisfactorily function to
adhere the electrodes to the porous film by the crosslinking
thereof via cation polymerization. Therefore, the crosslinking
polymer is not required to gel the whole electrolyte solution.
[0050] The crosslinking polymer can be cation polymerized at
ordinary temperature for crosslinking, although depending on the
structure thereof, the amount of the crosslinking polymer supported
on the porous film, and the type and amount of the cation
polymerization catalyst. The cation polymerization can be promoted
by heating. In this case, heating is generally conducted at a
temperature of about 40-100.degree. C. for about 0.5-24 hours,
although depending on the thermal resistance of materials
constituting the battery and productivity of the battery. To swell
or dissolve the polymer in an amount sufficient to adhere the
electrodes to the porous film, the battery container may be allowed
to stand at ordinary temperature for about several hours after
pouring the electrolyte solution in the battery container.
[0051] The laminate of the electrodes/crosslinking
polymer-supported porous film is satisfactory as long as the
electrodes are simply laminated on the crosslinking
polymer-supported porous film. Therefore, for example, negative
electrode/porous film/positive electrode, negative electrode/porous
film/positive electrode/porous film, and the like can be used as
the laminate of the electrodes/crosslinking polymer-supported
porous film according to the structure and form of the battery.
[0052] The electrolyte solution is a solution prepared by
dissolving an electrolyte salt in an appropriate organic solvent.
The electrolyte salt that can be used is, for example, salts
comprising a cation component and an anion component. The cation
component is derived from, for example, hydrogen, alkali metals
(such as lithium, sodium or potassium), alkaline earth metals (such
as calcium or strontium), or tertiary or quaternary ammonium ions.
The anion component is derived from, for example, inorganic acids
(such as hydrochloric acid, nitric acid, phosphoric acid, sulfuric
acid, fluoroboric acid, hydrofluoric acid, hexafluorophosphoric
acid or perchloric acid), or organic acids (such as carboxylic
acid, organic sulfonic acid or fluorine-substituted organic
sulfonic acid). Of those, electrolyte salts containing alkali metal
ions as cation components are particularly preferably used.
[0053] Examples of the electrolyte salts containing alkali metal
salts as cation components include alkali metal perchlorates, such
as lithium perchlorate, sodium perchlorate or potassium
perchlorate; alkali metal tetrafluoroborates, such as lithium
tetrafluoroborate, sodium tetrafluoroborate or potassium
tetrafluoroborate; alkali metal hexafluorophosphatets, such as
lithium hexafluorophosphate or potassium hexafluorophosphate;
alkali metal trifluoroacetates, such as lithium trifluoroacetate;
and alkali metal trifluoromethanesulfonates, such as lithium
trifluoromethanesulfonate.
[0054] In particular, in the case of producing lithium ion
secondary battery in accordance with the present invention, lithium
hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate
or the like is suitably used as the electrolyte salt.
[0055] The solvent used for the above electrolyte salts can be any
solvent so long as it can dissolve the electrolyte salt.
Representative example of the solvent is a non-aqueous solvent, and
examples thereof include cyclic esters such as ethylene carbonate,
propylene carbonate, butylene carbonate or .gamma.-butyrolactone;
ethers such as tetrahydrofuran or dimethoxyethane; and chain esters
such as dimethyl carbonate, diethyl carbonate or ethyl methyl
carbonate. Those can be used alone or as mixtures of two or more
thereof.
[0056] The amount of the electrolyte salts used is appropriately
determined depending on the type and amount of a solvent used. The
electrolyte salts are generally used in an amount such that the
resulting gel electrolyte has the electrolyte salt concentration of
1-50% by weight.
[0057] Onium salts are preferably used as the cation polymerization
catalyst. Examples of the onium salt includes onium salts
comprising cation components such as ammonium ion, phosphonium ion,
arsonium ion, stibonium ion or iodonium ion, and anion components
such as tetrafluoroborate, hexafluorophosphate,
trifluoromethanesulfonate or perchlorate.
[0058] Of those electrolyte salts, lithium tetrafluoroborate and
lithium hexafluorophosphate per se function as a cation
polymerization catalyst. Therefore, those are particularly
preferably used as an electrolyte salt functioning as both
electrolyte salt and cation polymerization initiator. In this case,
lithium tetrafluoroborate and lithium hexafluorophosphate may be
used alone or as a mixture thereof.
[0059] The present invention is described in more detail by
reference to the following Examples, but it should be understood
that the invention is not construed as being limited thereto.
Unless otherwise indicated, all parts are by weight.
[0060] Properties of a porous film substrate and battery properties
are evaluated as follows.
[0061] Thickness of Porous Film
[0062] The thickness of a porous film was determined by measurement
with a {fraction (1/10,000)} mm thickness gauge and based on a
scanning type electron micrograph (magnification: 10,000) of a
cross section of a porous film.
[0063] Porosity of Porous Film
[0064] Based on the weight "W" (g) per unit area "S" (cm.sup.2) of
porous film, the mean thickness "t" (cm) thereof, and the density
"d" (g/cm.sup.3) of a resin constituting a porous film, the
porosity was calculated by the following equation:
Porosity (%)=[1-(100 W/S/t/d)].times.100
[0065] Air Permeability of Porous Film
[0066] The permeability was determined according to JIS P 8117.
[0067] Puncture Strength
[0068] Puncture test was conducted with a compression tester KES-G5
manufactured by Kato Tech K.K. The maximum load was read from a
load-deformation curve obtained from the measurement and was
defined as puncture strength. A needle used had a diameter of 1.0
mm and a radius of curvature at the tip of 0.5 mm, and the needle
was penetrated at a rate of 2 cm/second.
REFERENCE EXAMPLE 1
[0069] Preparation of Electrode Sheet
[0070] 85 Parts of lithium cobalt oxide as a positive electrode
active material (Cell Seed C-10 manufactured by Nippon Chemical
Industrial Co., Ltd.), 10 parts of acetylene black as a conductive
auxiliary agent (Denka Black manufactured by Denki Kagaku Kogyo
Kabushiki Kaisha) and 5 parts of a vinylidene fluoride resin as a
binder (KF polymer L #1120 manufactured by Kureha Chemical
Industry, Co., Ltd.) were mixed together. Using
N-methyl-2-pyrrolidone, a slurry of the resulting mixture was
prepared so as to have a solid concentration of 15% by weight. The
slurry was applied to one side of a 20 .mu.m thick aluminum foil
(current collector) at a build-up of 200 .mu.m, dried at 80.degree.
C. for 1 hour and then at 120.degree. C. for 2 hours, and pressed
with a roll press, to prepare a positive electrode sheet having an
active material layer thickness of 100 .mu.m.
[0071] 80 Parts of mesocarbon microbeads as a negative electrode
active material (MCMB 6-28 manufactured by Osaka Gas Chemical Co.,
Ltd.), 10 parts of acetylene black as a conductive auxiliary agent
(Denka Black manufactured by Denki Kagaku Kogyo Kabushiki Kaisha)
and 10 parts of a vinylidene fluoride resin as a binder (KF polymer
L #1120 manufactured by Kureha Chemical Industry, Co., Ltd.) were
mixed. Using N-methyl-2-pyrrolidone, a slurry of the resulting
mixture was prepared so as to have a solid concentration of 15% by
weight. The slurry was applied to one side of a 20 .mu.m thick
copper foil (current collector) at a build-up of 200 .mu.m, dried
at 80.degree. C. for 1 hour and then at 120.degree. C. for 2 hours,
and pressed with a roll press, to prepare a negative electrode
sheet having an active material layer thickness of 100 .mu.m.
[0072] Preparation of Reference Battery
[0073] A polyethylene resin-made porous film (separator) having a
thickness of 16 .mu.m, a porosity of 40%, an air permeability of
300 second/100 cc and a puncture strength of 3.0N was provided. The
negative sheet obtained in Reference Example 1, the porous film
provided above and the positive electrode sheet obtained in
Reference Example 1 were laminated in this order. The resulting
laminate was placed in an aluminum laminate package. An electrolyte
solution containing an ethylene carbonate/diethyl carbonate (1:1 in
weight ratio) mixed solvent dissolving lithium hexafluorophosphate
therein at a concentration of 1.0 mol/liter was poured into the
package. The package was sealed to assemble a lithium ion secondary
battery. The battery was charged and discharged at a rate of 0.2
CmA three times. Subsequently, the battery was further charged at
0.2 CmA and then discharged at 2 CmA, to determine the 2
CmA-discharge capacity A.
[0074] Discharge Characteristics of Batteries of Examples or
Comparative Examples
[0075] Coin-type lithium ion secondary batteries obtained in the
following Examples and Comparative Examples were charged and
discharged at a rate of 0.2 CmA three times. Subsequently, the
batteries were further charged at 0.2 CmA and then discharged at 2
CmA, to determine the 2 CmA-discharge capacity B/. Battery
characteristics were evaluated on the basis of the percentage (%)
of the discharge capacity B to the discharge capacity A of the
reference battery.
PRODUCTION EXAMPLE 1
[0076] Production of 3-oxetanyl Group-Containing Crosslinking
Polymer A (Weight Average Molecular Weight: 518,000 and Content of
3-oxetanyl Group-Containing Monomer Content: 25% by Weight)
[0077] 60.0 g of methyl methacrylate, 20.0 g of
3-ethyl-3-oxetanylmethyl methacrylate, 158.0 g of ethyl acetate and
0.16 g of N,N'-azobisisobutyronitrile were placed in a 500 ml
three-necked flask equipped with a reflux condenser, and mixed for
30 minutes under stirring while introducing nitrogen gas. Radical
polymerization was initiated at 60.degree. C. When about 2 hours
passed, the viscosity of the reaction mixture began to increase.
The reaction mixture was further polymerized for additional 8
hours. The reaction mixture was cooled to about 10.degree. C., and
0.16 g of azobisbutyronitrile was added thereto. The resulting
mixture was again heated to 70.degree. C., and polymerization was
conducted for 8 hours.
[0078] After completion of the reaction, the reaction mixture was
cooled to about 40.degree. C., and 295 g of ethyl acetate was added
thereto. The resulting mixture was mixed under stirring until the
mixture became wholly homogenous, thereby obtaining an ethyl
acetate solution of the oxetanyl group-containing crosslinking
polymer A (concentration: 15% by weight).
[0079] 100 g of the polymer solution was introduced in 600 ml of
methanol under stirring with a high-speed mixer to precipitate the
polymer. The polymer was filtered off and recovered. After rinsing
the polymer with methanol several times, the polymer was dried in a
drying tube while flowing dry nitrogen gas (a dew point:
-150.degree. C. or lower) prepared by vaporizing liquid nitrogen,
and was further dried in a desiccator in vacuum for 6 hours, to
obtain 3-oxetanyl group-containing crosslinking polymer A in white
powder. As a result of molecular weight measurement by GPC, the
polymer had a weight average molecular weight of 518,000 and a
number average molecular weight of 231,000.
PRODUCTION EXAMPLE 2
[0080] Production of 3-oxetanyl Group-Containing Crosslinking
Polymer B (Weight Average Molecular Weight: 253,000 and Content of
3-oxetanyl Group-Containing Monomer Component: 15% by Weight)
[0081] In the same manner as in the Production Example 1, 68.0 g of
methyl methacrylate, 12.0 g of 3-ethyl-3-oxetanylmethyl
methacrylate, 158.0 g of ethyl acetate and 0.15 g of
N,N'-azobisisobutyronitrile were placed in a 500 ml three-necked
flask equipped with a reflux condenser, and mixed for 30 minutes
under stirring while introducing nitrogen gas. Radical
polymerization was initiated at 70.degree. C. When about 1.5 hours
passed, the viscosity of the reaction mixture began to increase.
The reaction mixture was further polymerized for additional 8
hours. The reaction mixture was cooled to about 40.degree. C., and
0.15 g of azobisbutyronitrile was added thereto. The resulting
mixture was again heated to 70.degree. C., and polymerization was
conducted for 8 hours.
[0082] After completion of the reaction, the reaction mixture was
cooled to about 40.degree. C., and 162 g of ethyl acetate was added
thereto. The resulting mixture was mixed under stirring until the
mixture was wholly homogenous, thereby obtaining an ethyl acetate
solution of the oxetanyl group-containing crosslinking polymer B
(concentration: 20% by weight).
[0083] In the same manner as in the Production Example 1, a polymer
was precipitated from the polymer solution, and the polymer was
filtered off and recovered. After rinsing the polymer several
times, the polymer was dried to obtain 3-oxetanyl group-containing
crosslinking polymer B in white powder. As a result of molecular
weight measurement by GPC, the polymer had a weight average
molecular weight of 253,000 and a number average molecular weight
of 147,000.
PRODUCTION EXAMPLE 3
[0084] Production of 3-oxetanyl Group-Containing Crosslinking
Polymer C (Weight Average Molecular Weight: 167,000 and Content of
3-oxetanyl Group-Containing Monomer Component: 40% by Weight)
[0085] 48.0 g of methyl methacrylate, 32.0 g of
3-ethyl-3-oxetanylmethyl methacrylate, 58.0 g of ethyl acetate and
0.36 g of N,N'-azobisisobutyronitrile were charged in a 500 ml
three-neck flask equipped with a reflux condenser, for mixing were
placed in a 500 ml three-necked flask equipped with a reflux
condenser, and mixed for 30 minutes under stirring while
introducing nitrogen gas, in the same manner as in the Production
Example 1. Radical polymerization was initiated at 70.degree. C.
When about 1.5 hours passed, the viscosity of the reaction mixture
began to increase. The reaction mixture was further polymerized for
additional 8 hours. The reaction mixture was cooled to about
40.degree. C., and 0.36 g of azobisbutyronitrile was added thereto.
The resulting mixture was again heated to 70.degree. C., and
polymerization was conducted for 8 hours.
[0086] After completion of the reaction, the reaction mixture was
cooled to about 40.degree. C., and 82 g of ethyl acetate was added
thereto. The resulting mixture was mixed under stirring until the
mixture became wholly homogenous, thereby obtaining an ethyl
acetate solution of the oxetanyl group-containing crosslinking
polymer C (concentration: 25% by weight).
[0087] In the same manner as in the Production Example 1, the
polymer was precipitated from the polymer solution, filtered off
and recovered. After rinsing the polymer several times, the polymer
was dried to obtain 3-oxetanyl group-containing crosslinking
polymer C in white powder. As a result of molecular weight
measurement by GPC, the polymer had a weight average molecular
weight of 167,000 and a number average molecular weight of
80,000.
PRODUCTION EXAMPLE 4
[0088] Production of Epoxy Group-Containing Crosslinking Polymer D
(Weight Average Molecular Weight: 466,000 and Content of Epoxy
Group-Containing Monomer Component: 25% by Weight)
[0089] In the same manner as in the Production Example 1, 60.0 g of
methyl methacrylate, 20.0 g of 3,4-epoxycyclohexylmethyl
methacrylate, 158.0 g of ethyl acetate and 0.32 g of
N,N'-azobisisobutyronitrile were placed in a 500 ml three-necked
flask equipped with a reflux condenser, and mixed for 30 minutes
under stirring while introducing nitrogen gas. Radical
polymerization was initiated at 70.degree. C. When about one hour
passed, the viscosity of the reaction mixture began to increase.
The reaction mixture was further polymerized for additional 8
hours. The reaction mixture was cooled to about 40.degree. C., and
0.32 g of azobisbutyronitrile was added thereto. The resulting
mixture was again heated to 70.degree. C., and polymerization was
conducted for 8 hours.
[0090] After completion of the reaction, the reaction mixture was
cooled to about 40.degree. C., and 162 g of ethyl acetate was added
thereto. The resulting mixture was mixed under stirring until the
mixture became wholly homogenous, thereby obtaining an ethyl
acetate solution of the epoxy group-containing crosslinking polymer
D (concentration: 15% by weight).
[0091] In the same manner as in the Production Example 1, the
polymer was precipitated from the polymer solution, filtered off
and recovered. After rinsing the polymer several times, the polymer
was dried to obtain epoxy group-containing crosslinking polymer D
in white powder. As a result of molecular weight measurement by
GPC, the polymer had a weight average molecular weight of 466,000
and a number average molecular weight of 228,000.
PRODUCTION EXAMPLE 5
[0092] Production of 3-oxetanyl Group-Containing Crosslinking
Polymer E (Weight Average Molecular Weight: 812,400 and Content of
3-oxetanyl Group-Containing Monomer Component: 25% by Weight)
[0093] 2.0 g of completely saponified polyvinyl alcohol (weight
average molecular weight: 2,000 and degree of saponification: 99
mol %), 0.05 g of partially saponified polyvinyl alcohol (weight
average molecular weight: 2,000 and degree of saponification: 80
mol %) and 210 g of pure water were placed in a 500 ml three-necked
flask equipped with a reflux condenser, and stirred at 90.degree.
C. for 15 minutes to dissolve the polyvinyl alcohols. The resulting
solution was cooled to 40.degree. C.
[0094] A separately prepared mixture of 60.0 g of methyl
methacrylate, 20.0 g of 3-ethyl-3-oxetanylmethyl methacrylate, 0.15
g of a 10% solution of 1-dodecanethiol in ethyl acetate and 0.8 g
of N,N'-azobisisobutyronitr- ile was added to the polyvinyl alcohol
solution, and the resulting solution was mixed for 30 minutes under
stirring while introducing nitrogen gas. Radical polymerization of
the solution was conducted at 70.degree. C. for 8 hours while
stirring slightly strongly.
[0095] After completion of the reaction, the reaction mixture was
cooled to about 40.degree. C., followed by suction filtration and
drying, to obtain a polymer in spherical fine particle. The
polyvinyl alcohol attached to the polymer was rinsed off.
Specifically, the polymer was placed in a separate 500 ml flask,
and 400 ml of pure water was added thereto. The resulting mixture
was heated to 90.degree. C. At that temperature, the mixture was
stirred for about 15 minutes and then cooled to about 40.degree.
C., followed by suction filtration and rinsing with pure water.
After the rinsing procedure was repeated three times, suction
filtration and rinsing with pure water were conducted. Finally,
rinsing with methanol was conducted several times. The polymer was
dried in a drying tube while flowing dry nitrogen gas (a dew point:
-150.degree. C. or lower) prepared by vaporizing liquid nitrogen,
and further dried in a desiccator in vacuum for 6 hours, to obtain
3-oxetanyl group-containing crosslinking polymer E in white
spherical particle. As a result of molecular weight measurement by
GPC, the polymer had a weight average molecular weight of 821,400
and a number average molecular weight of 292,400.
EXAMPLE 1
[0096] 10 g of the 3-oxetanyl group-containing crosslinking polymer
A was added to 90 g of ethyl acetate, and the resulting mixture was
stirred at room temperature to obtain a homogenous crosslinking
polymer solution. The crosslinking polymer solution was applied to
both sides of a polyethylene resin porous film substrate (film
thickness: 16 .mu.m, porosity: 40%, air permeability: 300
seconds/100 cc and puncture strength: 3.0 N) with a wire bar (#20),
and heat dried at 50.degree. C. to volatilize ethyl acetate. Thus,
a crosslinking polymer-supported porous film having the 3-oxetanyl
group-containing crosslinking polymer supported thereon at a
build-up of 2.5 .mu.m and a coating density of 3.0 g/m.sup.2 per
one side was obtained.
[0097] The negative electrode sheet obtained in the Reference
Example 1, the crosslinking polymer-supported porous film obtained
above and the positive electrode sheet obtained in the Reference
Example 1 were laminated in this order, and press bonded at a
temperature of 80.degree. C. under a pressure of 5 kg/cm.sup.2 for
1 minute. Thus, a laminate of the separator/electrodes was
obtained. The laminate of the separator/electrodes was placed in an
aluminum laminate package, and an electrolyte solution of an
ethylene carbonate/diethyl carbonate (1:1 in weight ratio) mixed
solvent dissolving lithium hexafluorophosphate at a concentration
of 1.0 mol/liter was poured in the package. The package was sealed.
The package was heated at 70.degree. C. for 7 hours to perform
cation polymerization and crosslinking of the 3-oxetanyl
group-containing polymer A, thereby adhering the electrode sheets
to the porous film (separator) and at the same time, partially
gelling the electrolyte solution. Thus, a laminate seal-type
battery was obtained.
[0098] The 2 CmA discharge capacity of this battery was 96% of the
discharge capacity of the reference battery. The battery was
disassembled to measure the adhesive force between the positive
electrode sheet and the separator. As a result, the adhesive force
was 0.20 N/cm.
EXAMPLE 2
[0099] A laminate seal-type battery was obtained in the same manner
as in Example 1 except for using the 3-oxetanyl group-containing
polymer B in place of the 3-oxetanyl group-containing polymer A.
The 2 CmA discharge capacity of this battery was 95% of the
discharge capacity of the reference battery. The battery was
disassembled to measure the adhesive force between the positive
electrode sheet and the separator. As a result, the adhesive force
was 0.25 N/cm.
EXAMPLE 3
[0100] A laminate seal-type battery was obtained in the same manner
as in Example 1 except for using the 3-oxetanyl group-containing
polymer C in place of the 3-oxetanyl group-containing polymer A.
The 2 CmA discharge capacity of this battery was 95% of the
discharge capacity of the reference battery. The battery was
disassembled to measure the adhesive force between the positive
electrode sheet and the separator. As a result, the adhesive force
was 0.20 N/cm.
EXAMPLE 4
[0101] A laminate seal-type battery was obtained in the same manner
as in Example 1 except for using the epoxy group-containing polymer
D in place of the 3-oxetanyl group-containing polymer A. The 2 CmA
discharge capacity of this battery was 93% of the discharge
capacity of the reference battery. The battery was disassembled to
measure the adhesive force between the positive electrode sheet and
the separator. As a result, the adhesive force was 0.30 N/cm.
EXAMPLE 5
[0102] A laminate seal-type battery was obtained in the same manner
as in Example 1 except for using the 3-oxetanyl group-containing
polymer E in place of the 3-oxetanyl group-containing polymer A.
The 2 CmA discharge capacity of this battery was 93% of the
discharge capacity of the reference battery. The battery was
disassembled to measure the adhesive strength between the positive
electrode sheet and the separator. As a result, the adhesive force
was 0.30 N/cm.
COMPARATIVE EXAMPLE 1
[0103] 10 g of poly(vinylidene fluoride/hexafluoropropylene)
copolymer (Kynar 2801 manufactured by Atofina Chemicals, Inc.) was
dissolved in 90 g of N-methyl-2-pyrrolidone to prepare a polymer
solution having a concentration of 10% by weight: The polymer
solution was applied to both sides of a polyethylene resin porous
film (film thickness: 16 .mu.m, porosity: 40%, air permeability: 30
seconds/100 cc and puncture strength: 3.0 N) with a wire bar (#20),
and heat dried at 60.degree. C. to volatilize
N-methyl-2-pyrrolidone. As a result, a polyethylene resin porous
film having the poly(vinylidene fluoride/hexafluoropropylene)
copolymer supported on both sides thereof was obtained.
[0104] The negative electrode sheet obtained in the Reference
Example 1, the porous film having the poly(vinylidene
fluoride/hexafluoropropylene) copolymer supported thereon obtained
above and the positive electrode sheet obtained in the Reference
Example 1 were laminated in this order, and press bonded at a
temperature of 80.degree. C. under a pressure of 5 kg/cm.sup.2 for
1 minute, to obtain a laminate of the separator/electrodes. The
laminate of the separator/electrodes was placed in an aluminum
laminate package, and an electrolyte solution of an ethylene
carbonate/diethyl carbonate (1:1 in weight ratio) mixed solvent
dissolving lithium hexafluorophosphate at a concentration of 1.0
mol/liter was poured in the package. The package was sealed to
obtain a laminate seal-type battery.
[0105] The 2 CmA discharge capacity of this battery was 70% of the
discharge capacity of the reference battery. The battery was
disassembled to measure the adhesive force between the positive
electrode sheet and the separator. As a result, the adhesive force
was 0.20 N/cm.
COMPARATIVE EXAMPLE 2
[0106] A laminate seal-type battery was obtained in the same manner
as in Comparative Example 1 except for changing the concentration
of the poly(vinylidene fluoride/hexafluoropropylene) copolymer
solution to 5% by weight. The 2 CmA discharge capacity of the
battery was 93% of the discharge capacity of the reference battery.
The battery was disassembled to measure the adhesive force between
the positive electrode sheet and the separator. As a result, the
adhesive force was 0.05 N/cm.
[0107] It should further be apparent to those skilled in the art
that various changes in form and detail of the invention as shown
and described above may be made. It is intended that such changes
be included within the spirit and scope of the claims appended
hereto.
[0108] This application is based on Japanese Patent Application No.
2002-350223 filed Dec. 2, 2002, the disclosure of which is
incorporated herein by reference in its entirety.
* * * * *