U.S. patent application number 10/569417 was filed with the patent office on 2006-11-16 for reactive polymer-supporting porous film for battery seperator and use thereof.
Invention is credited to Shigeru Fujita, Keisuke Kii, Satoshi Nishikawa, Tatsuya Okuno, Yoshihiro Uetani.
Application Number | 20060257727 10/569417 |
Document ID | / |
Family ID | 34220646 |
Filed Date | 2006-11-16 |
United States Patent
Application |
20060257727 |
Kind Code |
A1 |
Uetani; Yoshihiro ; et
al. |
November 16, 2006 |
Reactive polymer-supporting porous film for battery seperator and
use thereof
Abstract
The invention provides a reactive polymer-supporting porous film
for use as a battery separator which comprises a porous substrate
film and a partially crosslinked reactive polymer supported on the
porous substrate film, the partially crosslinked reactive polymer
being obtained by the reaction of a crosslinkable polymer having at
least one reactive group selected from the group consisting of
3-oxetanyl group and epoxy group in the molecule with a
polycarboxylic acid. The reactive polymer-supporting porous film
for use as a battery separator has a separator and electrodes
sufficiently bonded to each other and low inner resistance so that
it is suitably used for production of battery excellent in high
rate performance. Further, the invention provides a method of
producing a battery which comprises placing the electrode/reactive
polymer-supporting porous film layered body in a battery container;
introducing an electrolytic solution containing a cationic
polymerization catalyst into the battery container thereby bonding
the porous film and the electrodes together.
Inventors: |
Uetani; Yoshihiro; (Osaka,
JP) ; Kii; Keisuke; (Osaka, JP) ; Fujita;
Shigeru; (Osaka, JP) ; Nishikawa; Satoshi;
(Osaka, JP) ; Okuno; Tatsuya; (Osaka, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
34220646 |
Appl. No.: |
10/569417 |
Filed: |
August 20, 2004 |
PCT Filed: |
August 20, 2004 |
PCT NO: |
PCT/JP04/12334 |
371 Date: |
February 23, 2006 |
Current U.S.
Class: |
429/144 ;
29/623.1; 427/243; 427/385.5; 428/480 |
Current CPC
Class: |
Y10T 29/49114 20150115;
H01M 10/058 20130101; H01M 50/449 20210101; H01M 10/052 20130101;
H01M 50/411 20210101; H01M 50/46 20210101; Y02E 60/10 20130101;
Y10T 29/49115 20150115; H01M 50/461 20210101; Y10T 428/31786
20150401; Y10T 29/49108 20150115 |
Class at
Publication: |
429/144 ;
428/480; 029/623.1; 427/243; 427/385.5 |
International
Class: |
H01M 2/16 20060101
H01M002/16; H01M 2/18 20060101 H01M002/18; B32B 27/08 20060101
B32B027/08; B32B 27/36 20060101 B32B027/36; H01M 10/04 20060101
H01M010/04; B05D 5/00 20060101 B05D005/00; B05D 3/00 20060101
B05D003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 26, 2003 |
JP |
2003-208808 |
Jul 21, 2004 |
JP |
2004-213380 |
Claims
1. A reactive polymer-supporting porous film for use as a battery
separator which comprises a porous substrate film and a partially
crosslinked reactive polymer supported on the porous substrate
film, the partially crosslinked reactive polymer being obtained by
the reaction of a crosslinkable polymer having at least one
reactive group selected from the group consisting of 3-oxetanyl
group and epoxy group in the molecule with a polycarboxylic
acid.
2. The reactive polymer-supporting porous film according to claim
1, wherein the crosslinkable polymer is a radical copolymer of at
least one radical polymerizable monomer selected from the group
consisting of 3-oxetanyl group-containing radical polymerizable
monomers and epoxy group-containing radical polymerizable monomers
with another radical polymerizable monomer.
3. The reactive polymer-supporting porous film according to claim
1, wherein the crosslinkable polymer is a radical copolymer of 5 to
50% by weight of a 3-oxetanyl group-containing radical
polymerizable monomer and/or an epoxy group-containing radical
polymerizable monomer with 95 to 50% by weight of another radical
polymerizable monomer.
4. The reactive polymer-supporting porous film according to claim
1, wherein the reactive polymer has insoluble matter in an amount
of 1 to 90%.
5. The reactive polymer-supporting porous film according to claim
2, wherein the 3-oxetanyl group-containing radical polymerizable
monomer is 3-oxetanyl group-containing (meth)acrylate represented
by the general formula (I) ##STR7## wherein R.sub.1 is a hydrogen
atom or a methyl and R.sub.2 is a hydrogen atom or an alkyl group
having 1 to 6 carbon atoms.
6. The reactive polymer-supporting porous film according to claim
2, wherein the epoxy group-containing radical polymerizable monomer
is an epoxy group-containing (meth)acrylate represented by the
general formula (II) ##STR8## wherein R.sub.3 is a hydrogen atom or
a methyl group and R.sub.4 is an epoxy group-containing group
represented by the formula (1) ##STR9##
7. The reactive polymer-supporting porous film according to claim
2, wherein said another radical polymerizable monomer is at least
one selected from the group consisting of (meth)acrylates
represented by the following general formula (III) ##STR10##
wherein R.sub.5 is a hydrogen atom or a methyl group; A is an
oxyalkylene group having 2 or 3 carbon atoms; R.sub.6 is an alkyl
group having 1 to 6 carbon atoms or a fluorinated alkyl group
having 1 to 6 carbon atoms; and n is an integer of 0 to 3; and
vinyl esters represented by the general formula (IV) ##STR11##
wherein R.sub.7 is a methyl or an ethyl group and R.sub.8 is a
hydrogen atom or a methyl group.
8. The reactive polymer-supporting porous film according to claim
1, wherein the crosslinkable polymer has a glass transition
temperature of 70.degree. C. or lower.
9. The reactive polymer-supporting porous film according to claim
1, wherein the porous substrate film has a thickness in a range of
3 to 50 .mu.m and a porosity in a range of 20 to 95%.
10. A method of producing a battery which comprises obtaining an
electrode/reactive polymer-supporting porous film layered body by
layering electrodes on the reactive polymer-supporting porous film
according to claim 1; placing the electrode/reactive
polymer-supporting porous film layered body in a battery container;
introducing an electrolytic solution containing a cationic
polymerization catalyst into the battery container so that at least
a portion of the reactive polymer is swelled or dissolved in the
electrolytic solution at least in the vicinity of the interface of
the porous film and the electrodes and cationic-polymerized thereby
gelling at least a portion of the electrolytic solution so that the
the electrodes are bonded to the porous film.
11. The method of producing a battery according to claim 10,
wherein the cationic polymerization catalyst is an onium salt.
12. The method of producing a battery according to claim 10,
wherein the electrolytic solution contains at least one selected
from the group consisting of lithium hexafluorophosphate and
lithium tetrafluoroborate as an electrolytic salt working also as a
cationic polymerization catalyst.
13. A method of producing the reactive polymer-supporting porous
film for use as a battery separator according to claim 1,
comprising supporting a crosslinkable polymer having at least one
reactive group selected from the group consisting of 3-oxetanyl
group and epoxy group in the molecule and a polycarboxylic acid on
a porous substrate film; reacting a part of the reactive groups
with the polycarboxylic acid thereby partially crosslinking the
crosslinkable polymer and forming the reactive polymer on the
porous substrate film.
14. The method of producing the reactive polymer-supporting porous
film according to claim 13, wherein the crosslinkable polymer and
the polycarboxylic acid are supported on a porous substrate film by
applying a solution containing the crosslinkable polymer and the
polycarboxylic acid to a release sheet; drying the solution to form
a crosslinkable polymer/polycarboxylic acid layer on the release
sheet; and transferring the layer to the porous substrate film from
the release sheet.
15. The method of producing the reactive polymer-supporting porous
film according to claim 14, wherein the crosslinkable polymer
having a glass transition temperature of 70.degree. C. or
lower/polycarboxylic acid layer is transferred to the porous
substrate film by heating at a temperature of 100.degree. C. or
lower.
16. An electrode/porous film layered adherent obtained by layering
electrodes on the reactive polymer-supporting porous film according
to claim 1 thereby obtaining an electrode/reactive
polymer-supporting porous film layered body and bonding the
electrodes to the reactive polymer-supporting porous film.
17. The electrode/porous film layered adherent according to claim
16, wherein the porous film has an area thermal shrinkage ratio of
20% or less after it has been heated at 150.degree. C. for 1 hour.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a reactive polymer-supporting
porous film for use as a battery separator which comprises a porous
substrate film and a partially crosslinked reactive polymer
supported thereon, and a method of producing a battery in which
electrodes are bonded to the separator using such a reactive
polymer-supporting porous film.
PRIOR ART
[0002] Recently, a lithium ion secondary battery having a high
energy density has been used widely as a power source for compact
portable electronic appliances such as a mobile phone, a note-type
personal computer and the like. Such a lithium ion secondary
battery is produced by laminating or rolling sheet type positive
and negative electrodes and, for example, a porous polyolefin film
together, placing the laminated or rolled body in a battery
container of, for example, a metal can, pouring an electrolytic
solution into the battery container, and air-tightly closing and
sealing the container.
[0003] However, in recent years, it is strongly required to make
such compact portable electronic appliances as mentioned above
further small and lightweight. Accordingly, it is also required to
make a lithium ion secondary battery further thin and lightweight
so that a laminate film battery container tends to be employed in
place of a conventional metal can type container.
[0004] When such a laminate film battery container is used,
pressure cannot be applied to the electrode faces so sufficiently
as to maintain the electric connection between a separator and
electrodes, as compared with a conventional metal can type
container. Therefore, there occurs a problem that the distance
between the electrodes is partially widened with the lapse of time
because of expansion or shrinkage of electrode active material at
the time of charging or discharging of battery, resulting in
increase of inner resistance of battery and hence deterioration of
battery performance. In addition, the inner resistance of battery
becomes uneven, also resulting in deterioration of battery
performance.
[0005] Further, in the case of producing a sheet-type battery with
a large surface area, the distance between electrodes cannot be
kept constant so that sufficiently high battery performance cannot
be obtained owing to the unevenness of the inner resistance of the
battery.
[0006] Accordingly, it has been proposed to bond electrodes to a
separator using adhesive resin layers composed of a mixed phase of
an electrolytic solution phase, a polymer gel layer containing an
electrolytic solution and a polymer solid phase to solve such
problems, as described in JP-A No. 10-177865. Also, it has been
proposed to produce a battery having electrodes and a separator
bonded to each other by applying a binder resin solution containing
a poly(vinylidene fluoride) resin as a main component to the
separator; laminating the electrodes to the separator and drying
the laminated body to form an electrode/separator laminated body;
placing the electrode/separator laminated body in a battery
container; and then pouring an electrolytic solution into the
battery container, as described in JP-A No. 10-189054.
[0007] Further, it has been also proposed to obtain a battery
having a separator bonded to positive and negative electrodes by
bonding the separator impregnated with an electrolytic solution to
the electrodes with porous adhesive resin layers and keeping the
electrolytic solution in the through holes of the porous adhesive
resin layers, as described in JP-A No. 10-172606.
[0008] However, according to the above-mentioned methods, since the
thickness of the adhesive resin layers must be thick to obtain
sufficient adhesion between the separator and the electrodes and
the amount of the electrolytic solution in relation to the adhesive
resin cannot be made high, the resulting battery has a problem that
inner resistance increases and desirable cycle properties and high
rate discharge property cannot be obtained.
[0009] On the other hand, a variety of methods of producing porous
films for use as a separator of a battery have already been known.
By way of example, a method has been known in which polyolefin film
is produced and is drawn at a high ratio to provide a porous film,
as described in JP-A No. 09-012756. However, a battery separator
making use of such a highly drawn porous film is considerably
shrunk in the high temperature environments just in the case of
abnormal temperature increase by inner short circuit of battery,
and in some cases, there occurs a problem that the separator does
not work as a partitioning wall between the electrodes.
[0010] Accordingly, it is regarded to be a very important issue to
suppress thermal shrinkage of a battery separator in the high
temperature environments in order to improve safety of a battery.
In this regard, a method has been proposed in which a ultrahigh
molecular weight polyethylene and a plasticizer are melted and
kneaded, and extruded out of a die into sheet, followed by
extracting and removing the plasticizer from the sheet, to obtain a
porous film for use as a battery separator which is suppressed in
thermal shrinkage in the high temperature environments, as
described in JP-A No. 05-310989. However, on the contrary to the
aforesaid methods, the porous film obtained by this method has not
been drawn so that a problem arises that it has an insufficient
strength.
[0011] Furthermore, as described above, when a battery having
adhesive resin layers between the separator and the electrodes, in
which the separator and the electrodes are bonded to each other, is
put under the high temperature environments, the strength of the
adhesive resin layers is decreased so that thermal shrinkage of the
separator inevitably occurs.
[0012] The invention has been accomplished to solve the
above-mentioned problems in the production of a battery having
electrodes bonded to a separator. Accordingly, it is an object of
the invention to provide a reactive polymer-supporting porous film
suitable for use as a separator in the producing a battery that has
sufficient adhesion between electrodes and a separator, low inner
resistance, and high rate performance. It is also an object of the
invention to provide a method for producing a battery using such a
reactive polymer-supporting porous film.
DISCLOSURE OF THE INVENTION
[0013] The invention provides a reactive polymer-supporting porous
film for use as a battery separator which comprises a porous
substrate film and a partially crosslinked reactive polymer
supported thereon, the partially crosslinked reactive polymer being
obtained by the reaction of a crosslinkable polymer having at least
one reactive group selected from the group consisting of 3-oxetanyl
group and epoxy group in the molecule with a polycarboxylic
acid.
[0014] The invention also provides a method of producing such a
reactive polymer-supporting porous film for use as a battery
separator which comprises supporting a crosslinkable polymer having
at least one reactive group selected from the group consisting of
3-oxetanyl group and epoxy group in the molecule and a
polycarboxylic acid on a porous substrate film; reacting a part of
the reactive groups with the polycarboxylic acid thereby partially
crosslinking the crosslinkable polymer and forming the reactive
polymer on the porous substrate film.
[0015] The invention further provides a method of producing a
battery which comprises obtaining an electrode/reactive
polymer-supporting porous film layered body by layering electrodes
on such a reactive polymer-supporting porous film as mentioned
above; placing the electrode/reactive polymer-supporting porous
film layered body in a battery container; introducing an
electrolytic solution containing a cationic polymerization catalyst
into the battery container so that at least a portion of the
reactive polymer is swelled or dissolved in the electrolytic
solution at least in the vicinity of the interface of the porous
film and the electrodes to cause cationic polymerization of the
remaining reactive groups of the reactive polymer and further
crosslinking of the reactive polymer thereby gelling at least a
portion of the electrolytic solution so that the electrodes are
bonded to the porous film.
BRIEF DESCRIPTION OF THE DRAWING
[0016] FIG. 1 is a view showing a separator (porous film)/electrode
adherent and an apparatus for measuring the area thermal shrinkage
in examples.
BEST MODE FOR CARRYING OUT THE INVENTION
[0017] A reactive polymer-supporting porous film for use as a
battery separator of the invention comprises a porous substrate
film and a partially crosslinked reactive polymer supported
thereon, the partially crosslinked reactive polymer being obtained
by the reaction of a crosslinkable polymer having at least one
reactive group selected from the group consisting of 3-oxetanyl
group and epoxy group in the molecule with a polycarboxylic
acid.
[0018] The porous substrate film used has a thickness preferably in
a range of 3 to 50 .mu.m. When the porous film has a thickness of
less than 3 .mu.m, it has an insufficient strength so that when it
is used as a separator in a battery, inner short circuit may
possibly be caused. On the other hand, when the porous film has a
thickness of more than 50 .mu.m, it makes the distance between the
electrodes too large in a resulting battery thereby undesirably
increasing the inner resistance.
[0019] In addition, the porous substrate film used has fine pores
having an average pore diameter of 0.01 to 5 .mu.m and a porosity
in a range of 20 to 95%, preferably 30 to 90%, and most preferably
35 to 85%. When the porous substrate film has a so small porosity,
the resulting battery has decreased ionic conducting channels and
thus fails to have sufficient performance if it is used as a
separator in a battery. On the other hand, when the porous
substrate film has a so large porosity, it has an insufficient
strength for use as a separator in a battery. If such a porous
substrate film is to have a sufficient strength as a separator, the
film used must be thick, which results in undesirable increase of
inner resistance of battery,
[0020] Further, the porous substrate film used has an air
permeability preferably of 1500 s/100 cc or less, more preferably
1000 s/100 cc or less. When the porous substrate film used has a
too large air permeability, it has a too small ionic conductivity
for use as a separator in a battery so that it fails to provide a
high performance battery. The porous substrate film used has a
piercing strength preferably of 1 N or more. When the porous
substrate film having a piercing strength of smaller than 1 N is
used as a separator and pressure is applied between the electrodes,
it is torn and inner short circuit may take place.
[0021] According to the invention, any porous film may be used as
the porous substrate film with no particular limitation so long as
it has such properties as mentioned above. However, in
consideration of solvent resistance and redox resistance, a porous
film of polyolefin resin such as polyethylene or polypropylene is
preferred. Among the exemplified above, a porous film made of
polyethylene is particularly preferred since it melts when being
heated and closes the fine pores so that it provides so-called shut
down function to a battery. In this connection, the polyethylene
may include not only homopolymers of ethylene but also copolymers
of ethylene with an .alpha.-olefin such as propylene, butane or
hexene. Further, a laminate film of a porous film of
polytetrafluoroethylene, polyimide and the like with the
above-mentioned polyolefin porous film is also excellent in the
heat resistance and therefore is used preferably as the porous
substrate film.
[0022] According to the invention, the crosslinkable polymer refers
to a polymer having at least one reactive group selected from the
group consisting of 3-oxetanyl group and epoxy group in the
molecule. It is preferably a radical copolymer of 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 an epoxy group with another
radical polymerizable monomer.
[0023] In particular, the crosslinkable polymer is preferably a
polymer having 3-oxetanyl and epoxy groups in the molecule, or a
polymer having epoxy groups in the molecule. Accordingly, such a
crosslinkable polymer can be obtained preferably either by radical
copolymerization of a radical polymerizable monomer having
3-oxetanyl group and a radical polymerizable monomer having an
epoxy group with another radical polymerizable monomer or by
radical copolymerization of a radical polymerizable monomer having
epoxy groups with another radical polymerizable monomer.
[0024] As already known, either 3-oxetanyl or epoxy group reacts on
one hand with carboxyl groups and on the other hand it is
cation-polymerizable. Therefore, according to the invention, at
first a crosslinkable polymer having at least one reactive group
selected from the group consisting of 3-oxetanyl group and epoxy
groups in the molecule is reacted with a polycarboxylic acid making
use of such reactive groups to obtain a partially crosslinked
reactive polymer, and then the crosslinked reactive polymer is
supported on the porous substrate film thereby to provide a
reactive polymer-supporting porous film for use as a battery
separator.
[0025] Further, according to the invention, as described
hereinafter, electrodes are layered on such a reactive
polymer-supporting porous film to provide an electrode/reactive
polymer-supporting porous film layered body, and then layered body
is immersed in an electrolytic solution containing a cationic
polymerization catalyst, preferably an electrolyte working also as
a cation polymerization catalyst, so that at least a portion of the
crosslinkable polymer that has been partially crosslinked or the
resulting reactive polymer on the porous film is swollen or
dissolved in the electrolytic solution and then diffused thereinto,
followed by being further crosslinked by cationic polymerization of
the remaining reactive groups. This causes gelation of the
electrolytic solution in the vicinity of the interface of the
porous film and the electrodes and consequently, the electrodes and
the porous film are bonded together.
[0026] When the crosslinkable polymer having at least one reactive
group selected from the group consisting of 3-oxetanyl group and
epoxy group in the molecule is prepared, a 3-oxetanyl
group-containing radical-polymerizable monomer and/or an epoxy
group-containing radical-polymerizable monomer is used in terms of
total amount of these monomers in an amount of 5 to 50% by weight,
preferably 10 to 30% by weight of the total monomers used.
Accordingly, when a crosslinkable polymer having 3-oxetanyl group
is prepared, the 3-oxetanyl group-containing radical-polymerizable
monomer is used in an amount of 5 to 50% by weight, preferably 10
to 30% by weight, of the total monomers used. Similarly, when a
crosslinkable polymer having epoxy group is obtained, the epoxy
group-containing radical-polymerizable monomer is used in an amount
of 5 to 50% by weight, preferably 10 to 30% by weight, of the total
monomers used.
[0027] On the other hand, when a crosslinkable polymer having both
3-oxetanyl and epoxy groups in the molecule is prepared by radical
copolymerization of both of a 3-oxetanyl group-containing
radical-polymerizable monomer and an epoxy group-containing
radical-polymerizable monomer with another radical-polymerizable
monomer, the total amount of the 3-oxetanyl group-containing
radical-polymerizable monomer and the epoxy group-containing
radical-polymerizable monomer is in a range of 5 to 50% by weight,
preferably in a range of 10 to 30% by weight, of the total monomers
used. In this case, it is preferred that the epoxy group-containing
radical-polymerizable monomer is used in an amount of 90% by weight
or less of the total of the 3-oxetanyl group-containing
radical-polymerizable monomer and the epoxy group-containing
radical-polymerizable monomer.
[0028] In the preparation of a 3-oxetanyl group-containing
crosslinkable polymer or an epoxy group-containing crosslinkable
polymer, when the total amount of the 3-oxetanyl group-containing
radical-polymerizable monomer and the epoxy group-containing
radical-polymerizable monomer is less than 5% by weight of the
total monomers used, the amount of the crosslinkable polymer needed
for gelation of the electrolytic solution increases, so that the
performance of the resulting battery is adversely affected, as
described above. On the other hand, when it exceeds 50% by weight,
the formed gel is deteriorated in retention of the electrolytic
solution, thereby to lower the adhesion strength between the
electrodes and separator in the resulting battery.
[0029] According to the invention, a 3-oxetanyl group-containing
(meth)acrylate represented by the general formula (I) ##STR1##
wherein R.sub.1 is a hydrogen atom or a methyl group, and R.sub.2
is a hydrogen atom or an alkyl having 1 to 6 carbon atoms, is
preferably used as the 3-oxetanyl group-containing radical
polymerizable-monomer.
[0030] Examples of the 3-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)acrylate, and
3-hexyl-3-oxetanylmethyl(meth)acrylate. These (meth)acrylates may
be used alone or in combination of two or more of these. In the
invention, (meth)acrylate means acrylate or methacrylate.
[0031] In turn, an epoxy group-containing (meth)acrylate
represented by the general formula (II) ##STR2## wherein R.sub.3 is
a hydrogen atom or a methyl group and R.sub.4 is an epoxy
group-containing group represented by the following formula (1)
##STR3## is preferably used as the epoxy group-containing radical
polymerizable monomer.
[0032] Examples of the epoxy group-containing (meth)acrylate
include 3,4-epoxycyclohexylmethyl(meth)acrylate and
glycidyl(meth)acrylate. These (meth)acrylates are used alone or in
combination of two or more of these.
[0033] The aforesaid another radical polymerizable monomer that is
copolymerized with the 3-oxetanyl group-containing radical
polymerizable monomer and/or the epoxy group-containing radical
polymerizable monomer is preferably at least one selected from the
group consisting of (meth)acrylates represented by the general
formula (III) ##STR4## wherein R.sub.5 is a hydrogen atom or a
methyl group; A is an oxyalkylene group having 2 or 3 carbon atoms
(preferably oxyethylene or oxypropylene group); R.sub.6 is an alkyl
group having 1 to 6 carbon atoms or a fluoroalkyl group having 1 to
6 carbon atoms; and n is an integer of 0 to 3; and vinyl esters
represented by the general formula (IV) ##STR5## wherein R.sub.7 is
a methyl group or an ethyl group and R.sub.5 is a hydrogen atom or
a methyl group.
[0034] Examples of the (meth)acrylates represented by the general
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.
[0035] Other than the exemplified above, the following can be
mentioned as the aforesaid another radical polymerizable monomer in
which n is an integer of 0 to 3. ##STR6##
[0036] Among the (meth)acrylates represented by the general formula
(III), there may be mentioned ethyl acrylate, butyl acrylate,
propyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate and
dodecyl acrylate as examples of the said another radical
polymerizable monomer which can adjust the glass transition
temperature of the resulting reactive polymer to be 70.degree. C.
or less as mentioned above.
[0037] Examples of the above-mentioned vinyl esters represented by
the general formula (IV) include vinyl acetate and vinyl
propionate.
[0038] As described above, the crosslinkable polymer having at
least one reactive group selected from the group consisting of
3-oxetanyl group and epoxy group can be obtained as a radical
copolymer preferably by radical copolymerization of at least one
radical polymerizable monomer selected from the group consisting of
3-oxetanyl group-containing radical polymerizable monomers and
epoxy group-containing radical polymerizable monomers with another
radical polymerizable monomer using a radical polymerization
initiator. The radical copolymerization may be carried out by any
polymerization method such as solution polymerization, bulk
polymerization, suspension polymerization or emulsion
polymerization. In terms of the easiness of polymerization,
adjustment of molecular weight, and post-treatment, solution
polymerization or suspension polymerization is preferably
employed.
[0039] The radical polymerization initiator used is not
particularly limited. For example, 2,2'-azobis(isobutyronitrile),
diemthyl-2,2'-azobis(2-methylpropionate), benzoyl peroxide or
lauroyl peroxide can be used. In the radical copolymerization, if
necessary, a molecular weight adjusting agent such as mercaptan may
be used.
[0040] It is preferred that the crosslinkable polymer has a weight
average molecular weight of 10,000 or more. When the weight average
molecular weight of the crosslinkable polymer is less than 10,000,
a large quantity of the crosslinkable polymer is required for
gelation of the electrolytic solution, so that the performance of
the battery obtained may be deteriorated. On the other hand, the
upper limit of the weight average molecular weight of the
crosslinkable polymer is not particularly limited, however it is
about 3,000,000 so that it keeps the electrolytic solution in the
form of gel and preferably about 2,500,000. It is particularly
preferred that the crosslinkable polymer has a weight average
molecular weight in a range of 100,000 to 2,000,000.
[0041] The above-mentioned crosslinkable polymer having at least
one reactive group selected from the group consisting of 3-oxetanyl
group and epoxy groups in the molecule are already known, as
described in JP-A Nos. 2001-176555 and 2002-110245.
[0042] The reactive polymer-supporting porous film for use as a
battery separator of the invention comprises a porous substrate
film and a reactive polymer supported thereon, the reactive polymer
being obtained by reacting the above-mentioned crosslinkable
polymer with a polycarboxylic acid so that it is partially
crosslinked. The crosslinking of the crosslinkable polymer by the
reaction thereof with a polycarboxylic acid is carried out by the
reaction of 3-oxetanyl and/or epoxy groups of the crosslinkable
polymer with the polycarboxylic acid (i.e., carboxyl groups) as
described in JP-A Nos. 11-43540 and 11-116663. According to the
invention, the crosslinkable polymer is reacted with the
polycarboxylic acid making use of the reactivity of 3-oxetanyl and
epoxy groups, thereby partially crosslinking the crosslinkable
polymer and obtaining the reactive polymer.
[0043] The polycarboxylic acid used in the invention to partially
crosslink the crosslinkable polymer is an organic compound having
two or more carboxyl groups in the molecule, preferably 2 to 6
carboxyl groups, and more preferably 2 to 4 carboxyl groups.
[0044] Examples of dicarboxylic acid having two carboxylic groups
in the molecule include straight chain aliphatic saturated
dicarboxylic acids having 2 to 20 carbon atoms such as oxalic acid,
malonic acid, succinic acid, glutaric acid, adipic acid, pimellic
acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid,
dodecanoic acid, tridecanoic acid, tetradecanoic acid,
pentadecanoic acid, hexadecanoic acid, octadecanoic acid,
nonadecanoic acid and eicosanoic acid; branched aliphatic saturated
dicarboxylic acids having 3 to 20 carbon atoms such as
methylmalonic acid, ethylmalonic acid, n-propylmalonic acid,
n-butylmalonic acid, methylsuccinic acid, ethyl succinic acid,
2,4-diethylglutaric acid and 1,1,3,5-tetramethyloctylsuccinic acid;
straight chain or branched aliphatic unsaturated dicarboxylic acids
such as maleic acid, fumaric acid, citraconic acid,
.gamma.-methylcitraconic acid, mesaconic acid,
.gamma.-methylmesaconic acid, itaconic acid and glutaconic acid;
hexahydrophthalic acid; hexahydroisophthalic acid;
tetrahydrophthalic acids such as hexahydroterephthalic acid,
methylhexahydroxyphthalic acid, methylhexaisophthalic acid,
methylhexahydroterephthalic acid, cyclohexene-1,2-dicarboxylic
acid, cyclohexene-1,6-dicarboxylic acid,
cyclohexene-3,4-dicarboxylic acid and cyclohexene-4,5-dicarboxylic
acid; tetrahydroisophthalic acids such as
cyclohexene-1,3-dicarboxylic acid, cyclohexene-1,5-dicarboxylic
acid and cyclohexene-3,5-dicarboxylic acid; tetrahydroterephthalic
acids such as cyclohexene-1,4-dicarboxylic acid and
cyclohexene-3,6-dicarboxylic acid; dihydrophthalic acids such as
1,3-cyclohexadiene-1,2-dicarboxylic acid,
1,3-cyclohexadiene-1,6-dicarboxylic acid,
1,3-cyclohexadiene-2,3-dicarboxylic acid,
1,3-cyclohexadiene-5,6-dicarboxylic acid,
1,4-cyclohexadiene-1,2-dicarboxylic acid and
1,4-cyclohexadiene-1,6-dicarboxylic acid; dihydroisophthalic acids
such as 1,3-cyclohexadiene-1,3-dicarboxylic acid and
1,3-cyclohexadiene-3,5-dicarboxylic acid; dihydroterephthalic acids
such as 1,3-cyclohexadiene-1,4-dicarboxylic acid,
1,3-cyclohexadiene-2,5-dicarboxylic acid,
1,4-cyclohexadiene-1,4-dicarboxylic acid and
1,4-cyclohexadiene-3,6-dicarboxylic acid; saturated or unsaturated
carboxylic acids such as methyltetrahydrophthalic acid,
endomethylenetetrahydrophthalic acid,
endocis-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid,
methyl-endocis-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid;
chlorendic acid; phthalic acid; terephthalic acid; isophthalic
acid; 3-alkylphthalic acids such as 3-methylphthalic acid,
3-ethylphthalic acid, 3-n-propylphthalic acid, 3-isopropylphthalic
acid, 3-n-butylphthalic acid, 3-isobutylphthalic acid,
3-sec-butylphthalic acid and 3-tert-butylphthalic acid;
4-alkylphthalic acids such as 4-methylphthalic acid,
4-ethylphthalic acid, 4-n-propylphthalic acid, 4-isopropylphthalic
acid, 4-n-butylphthalic acid, 4-isobutylphthalic acid,
4-sec-butylphthalic acid and 4-tert-butylphthalic acid;
2-alkylphthalic acids such as 2-methylisophthalic acid,
2-ethylisophthalic acid, 2-n-propylphthalic acid,
2-isopropylphthalic acid, 2-n-butylphthalic acid,
2-isobutylphthalic acid, 2-sec-butylphthalic acid and
2-tert-butylphthalic acid; 4-alkylisophthalic acids such as
4-methylisophthalic acid, 4-ethylisophthalic acid,
4-n-propylisophthalic acid, 4-isopropylisophthalic acid,
4-n-butylisophthalic acid, 4-isobutylisophthalic acid,
4-sec-butylisophthalic acid, and 4-tert-butylisophthalic acid;
5-alkylisophthalic acids such as 5-methylisophthalic acid,
5-ethylisophthalic acid, 5-n-propylisophthalic acid,
5-isopropylisophthalic acid, 5-n-butylisophthalic acid,
5-isobutylisophthalic acid, 5-sec-butylisophthalic acid and
5-tert-butylisophthalic acid; alkylterephthalic acids such as
methylterephthalic acid, ethylterephthalic acid,
n-propylterephthalic acid, isopropylterephthalic acid,
n-butylterephthalic acid, isobutylterephthalic acid,
sec-butylterephthalic acid and tert-butylterephthalic acid;
aromatic dicarboxylic acids such as naphthalene-1,2-dicarboxylic
acid, naphthalene-1,3-dicarboxylic acid,
naphthalene-1,4-dicarboxylic acid, naphthalene-1,5-dicarboxylic
acid, naphthalene-1,6-dicarboxylic acid,
naphthalene-1,7-dicarboxylic acid, naphthalene-1,8-dicarboxylic
acid, naphthalene-2,3-dicarboxylic acid,
naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic
acid, anthracene-1,3-dicarboxylic acid, anthracene-1,4-dicarboxylic
acid, anthracene-1,5-dicarboxylic acid, anthracene-1,9-dicarboxylic
acid, anthracene-2,3-dicarboxylic acid and
anthracene-9,10-dicarboxylic acid; and
2,2'-bis(carboxyphenyl)hexafluoropropane.
[0045] Examples of polycarboxylic acids having three or more
carboxyl groups in the molecule include aliphatic tricarboxylic
acids such as tricarballylic acid, citric acid, isocitric acid, and
aconitic acid; aromatic tricarboxylic acids such as hemellitic acid
and trimellitic acid; aliphatic tetracarboxylic acids having 4 to
13 carbon atoms such as 1,2,3,4-butanetetracarboxylic acid;
alicyclic tetracarboxylic acids such as maleated
methylcyclohexenetetracarboxylic acid; aromatic tetracarboxylic
acids such as mellophanic acid, prehnitic acid, pyromellitic acid,
and benzophenonetetracarboxylic acid; hexahydromellitic acid,
benzenepentacarboxylic acid, and mellitic acid.
[0046] Polyol esters of the above-mentioned polycarboxylic acids
and polyols, preferably diol esters of dicarboxylic acids and
diols, preferably (poly)alkylene glycols and polymethylenediols may
be used also as the polycarboxylic acid. Ethylene glycol diadipate
can be exemplified as the diol esters.
[0047] Further, the polycarboxylic acid may be a polymer carboxylic
acid having a plurality of carboxyl groups in the molecule.
Examples of such polymer carboxylic acids include copolymers of
(meth)acrylic acid and (meth)acrylic acid esters.
[0048] The reactive polymer-supporting porous film for use as a
battery separator of the invention comprises a porous substrate
film and a reactive polymer supported thereon, wherein the reactive
polymer is formed by reacting the above-mentioned crosslinkable
polymer with the above-mentioned polycarboxylic acid so that it is
partially crosslinked. A method of supporting the reactive polymer
on the porous substrate film is not particularly limited. For
example, a crosslinkable polymer is dissolved in an appropriate
solvent such as acetone, ethyl acetate or butyl acetate together
with a polycarboxylic acid, and then either the resulting solution
is applied to a porous substrate film or a porous substrate film is
impregnated with the solution by casting or spray coating, followed
by drying the film to remove the solvent used therefrom, thereby
supporting the reactive polymer on the porous film. Then, the
porous substrate film thus supporting the crosslinkable polymer and
the polycarboxylic acid is heated to an appropriate temperature to
cause the reaction of the crosslinkable polymer with the
polycarboxylic acid to partially crosslink the crosslinkable
polymer as described above. In this way, the reactive
polymer-supporting porous film for use as a battery separator of
the invention is obtained.
[0049] If necessary, an onium salt may be supported as a catalyst
together with the crosslinkable polymer and the polycarboxylic acid
on the porous substrate film. As the onium salts, those which are
exemplified later may be used.
[0050] The means or method of supporting the reactive polymer
obtained by partially crosslinking the crosslinkable polymer with
the polycarboxylic acid on the porous substrate film is not limited
to those as above exemplified. For example, as another method, a
solution of the crosslinkable polymer is applied to a porous
substrate film, and after the film is dried, a solution of the
polycarboxylic acid is applied to the porous substrate film or the
porous substrate film is impregnated with the solution, followed by
heating the film at an appropriate temperature. As a further
method, a crosslinkable polymer is reacted with a polycarboxylic
acid in a solvent and is partially crosslinked to provide a
reactive polymer, and thereafter a solution containing the reactive
polymer is applied to a porous substrate film and the film is
dried. As a still further method, a crosslinkable polymer is
reacted with a polycarboxylic acid in a solvent and is partially
crosslinked to provide a reactive polymer, and thereafter a
solution containing the reactive polymer is applied to a release
paper, and then the reactive polymer is transferred to a substrate
porous film from the release paper.
[0051] However, one of the particularly preferred methods according
to the invention is as follows. A solution containing both of the
crosslinkable polymer and the polycarboxylic acid is applied to
release sheet and dried to form a crosslinkable
polymer/polycarboxylic acid layer on the release sheet. Thereafter,
the release sheet is layered on a porous substrate film and is
heated under pressure to transfer the crosslinkable
polymer/polycarboxylic acid layer to the porous substrate film.
Then, the crosslinkable polymer/polycarboxylic acid layer on the
porous film is heated to an appropriate temperature so that a
reactive polymer is formed on the porous substrate film.
[0052] Particularly, a crosslinkable polymer having a glass
transition temperature preferably of 70.degree. C. or less can be
obtained by copolymerizing at least one radical polymerizable
monomer selected from the group consisting of 3-oxetanyl
group-containing radical polymerizable monomers and epoxy
group-containing radical polymerizable monomers with a suitably
selected another radical polymerizable monomer as mentioned
hereinbefore. Therefore, when a crosslinkable
polymer/polycarboxylic acid layer is formed on release sheet using
such a crosslinkable polymer as described above, the layer can be
transferred to a porous substrate film by heating the layer at a
temperature of not less than the glass transition temperature of
the crosslinkable polymer and of not more than 100.degree. C. under
pressure without causing any damage to the porous substrate film.
The crosslinkable polymer/polycarboxylic acid layer thus
transferred to the porous substrate film is heated at an
appropriate temperature to readily form a layer of reactive polymer
on the porous substrate film.
[0053] When the crosslinkable polymer/polycarboxylic acid layer on
the release sheet is transferred to a porous substrate film, it is
preferred to adjust the heating temperature at 100.degree. C. or
less so as not to cause deformation or melting of the porous
substrate film. Accordingly, the glass transition temperature of
the crosslinkable polymer is preferably in a range of 20 to
60.degree. C.
[0054] As the above-mentioned release sheet, a polypropylene resin
sheet is a typical one, however it is not particularly limited and
sheets made of polyethylene terephthalate, polyethylene, vinyl
chloride, and engineering plastics; paper (particularly,
resin-impregnated paper); synthetic paper; and their laminates may
be usable. These sheets may be surface-treated in the rear faces
with silicone or long chain alkyl type compounds, if necessary.
[0055] When the crosslinkable polymer/polycarboxylic acid layer is
formed on a porous substrate film by transferring the crosslinkable
polymer/polycarboxylic acid layer from a release sheet to a porous
substrate film in such a manner as mentioned above, the
crosslinkable polymer/polycarboxylic acid layer can be reliably
formed on the surface of the porous substrate film since the
crosslinkable polymer or the crosslinkable polymer/polycarboxylic
acid is prevented from penetrating the fine pores of the porous
film, and accordingly without closing the fine pores of porous
substrate film, unlike the case of applying a solution of the
crosslinkable polymer or a solution of the crosslinkable
polymer/polycarboxylic acid to the surface of the porous substrate
film.
[0056] According to the invention, it is preferred that the
reactive polymer obtained by partially crosslinking the
crosslinkable polymer has an insoluble matter in a proportion of 1
to 90%, preferably 3 to 75%, and most preferably 10 to 65% based on
the weight of reactive polymer. The proportion of insoluble matter
means, as described later, the amount of the reactive polymer
remaining on the porous substrate film when the porous film
supporting the reactive polymer is immersed in a mixture of
ethylene carbonate/diethyl carbonate (1/1 ratio by volume) at a
room temperature for 2 hours under stirring and further immersed in
ethyl methyl carbonate.
[0057] Such a reactive polymer having an insoluble matter in a
proportion of 1 to 90% can be obtained usually by reacting the
crosslinkable polymer with a polycarboxylic acid to partially
crosslink the crosslinkable polymer in a manner in which a
polycarboxylic acid is used so that the amount of the carboxyl
groups of the polycarboxylic acid used is in a range of 0.01 to 1.0
parts by mole, preferably 0.05 to 0.8 parts by mole, and
particularly preferably 0.1 to 0.7 parts by mole to one part by
mole of the reactive groups of the crosslinkable polymer, and in
addition, by appropriately adjusting the conditions under which the
crosslinkable polymer and the polycarboxylic acid are reacted under
heating. In this manner, a reactive polymer having a desired
proportion of insoluble matter can be obtained. However, the method
is not particularly limited.
[0058] By way of example, a reactive polymer having an insoluble
matter in a proportion of 1-90% can be obtained by using a
polycarboxylic acid in an amount that the molar ratio of the
carboxyl group of the polycarboxylic acid to the reactive groups of
the crosslinkable polymer is 0.5-1.0 parts by mole, and heating and
reacting the crosslinkable polymer with the polycarboxylic acid at
a temperature of 50.degree. C. usually over a period of 10 to 500
hours, preferably over 12 to 250 hours.
[0059] When the proportion of insoluble matter in the reactive
polymer is less than 1% and electrodes are pressure-adhered to a
porous film supporting such a reactive polymer thereon to provide
an electrode/porous film layered body and the body is immersed in
an electrolytic solution, a large portion of the reactive polymer
is dissolved and diffused in the electrolytic solution. Therefore,
even if the reactive polymer is cation-polymerized and further
crosslinked in the electrolytic solution, effective adhesion
between the electrodes and the porous film cannot be obtained, as
described later. On the other hand, when the proportion of
insoluble matter in the reactive polymer is more than 90% and the
resulting electrode/porous film layered body is immersed in an
electrolytic solution, the reactive polymer is insufficiently
swollen, so that the resulting battery containing such an
electrode/porous film layered adherent formed of the reactive
polymer has high inner resistance and is adversely affected in the
battery performance.
[0060] The reactive polymer is obtained by reacting the
crosslinkable polymer with the polycarboxylic acid so that it is
partially crosslinked to have insoluble matter in such an amount as
mentioned above. Thus, the reactive polymer is suppressed from
dissolving in an electrolytic solution and diffusing thereinto when
it is immersed therein. Therefore, when an electrode/porous film
layered body is obtained by supporting such a reactive polymer on
the porous film and layering the electrodes thereon, and then it is
placed in a battery container, an electrolytic solution containing
an electrolyte and a cationic polymerization catalyst is poured
into the battery container, only a portion of the reactive polymer
of the above-mentioned electrode/porous film layered body is
swollen or dissolved in the electrolytic solution in the vicinity
of the interface of the porous film and the electrodes. Thus, the
reactive polymer is cation-polymerized and further crosslinked by
the cationic polymerization catalyst, preferably an electrolyte
working also as a cationic polymerization catalyst in the
electrolytic solution, making use of the remaining reactive groups
which have not been used in the partial crosslinking by the
polycarboxylic acid, thereby the electrolytic solution is gelled
and the electrodes are firmly and closely bonded to the porous
film. In this manner, an electrode/porous film (that is a separator
of the battery obtained) layered adherent can be obtained in a
resulting battery.
[0061] That is, according to the invention, the partially
crosslinked reactive polymer has an insoluble matter in the
above-mentioned range and accordingly when it is immersed in an
electrolytic solution, dissolution or diffusion thereof in the
electrolytic solution is prevented or suppressed and the reactive
polymer is efficiently used for bonding of the porous film to the
electrodes, so that the electrodes and the porous film are stably
and more firmly bonded to each other by using a relatively small
amount of the reactive polymer.
[0062] Further, according to a preferred embodiment of the
invention, a reactive polymer-supporting porous film that is
readily wetted with an electrolytic solution can be obtained, or
that is excellent in wettability with an electrolytic solution. The
use of such a reactive polymer-supporting porous film in the
production of a battery increases the production efficiency. Herein
the invention, the wettability with an electrolytic solution of the
reactive polymer-supporting porous film is the degree of the
easiness with which the reactive polymer-supporting porous film is
wetted or impregnated with an electrolytic solution, as described
in detail later.
[0063] According to a preferred embodiment of the invention, as
described above, when a reactive polymer-carrying porous film is
obtained by forming a crosslinkable polymer by radical
copolymerization of a 3-oxetanyl group-containing (meth)acrylate
and/or an epoxy group-containing (meth)acrylate with another
(meth)acrylate; obtaining a reactive polymer by partially
crosslinking the crosslinkable polymer; and supporting the reactive
polymer on a porous film, the ratio of the acrylate monomer as the
above-mentioned (meth)acrylate monomers is increased and the amount
of the insoluble matter in the reactive polymer obtained, that is,
the crosslinking density of the reactive polymer obtained, is so
adjusted that it is not excessively increased, and thereby the
reactive polymer-supporting porous film excellent in wettability
with the electrolytic solution can be obtained. Therefore, it is
believed that when a reactive polymer has not an excess
crosslinking density and it has flexible molecular chains, and when
as it has a low glass transition temperature, or the mobility of
the polymer chains is more significant, and as the affinity to the
electrolytic solution used in the production of a battery is
higher, the reactive polymer is more readily wetted with an
electrolytic solution.
[0064] As described above, when the reactive polymer-supporting
porous film is readily wetted with an electrolytic solution and
when a layered body composed of sheet-like positive and negative
electrodes and a separator placed therebetween or a cylindrically
rolled body of such a layered body is placed in a battery can and
an electrolytic solution is poured into the battery can, the
electrolytic solution quickly wet or penetrates the entire body of
the separator and spreads in the separator and accordingly, the
productivity of the battery production can be heightened. Further,
in such a manner, the electrolytic solution spreads in the entire
body of the separator and contributes to the bonding of the
electrodes and the porous film to firmly bond them together.
Therefore, the porous film keeps a small area thermal shrinkage
ratio. It is generally 20% or less and preferably 15% or less even
if a battery is put under a high temperature condition of
150.degree. C.
[0065] As described above, the reactive polymer-supporting porous
film of the invention is preferably usable for the production of
battery. Hereinafter, a method for production of a battery
according to the invention using the reactive polymer-supporting
porous film will be described.
[0066] Although differing depending on batteries, an electrode to
be used, that is a positive electrode or a negative electrode, is
generally formed in a sheet-like form by firmly bonding and
supporting an active material and a conductive agent if necessary
and on a conductive substrate by using a binder resin.
[0067] At first, sheet-like electrodes described above are layered
on the reactive polymer-supporting porous film, or the layered
product is rolled to obtain an electrode/reactive
polymer-supporting porous film layered body. The layered body is
placed in a battery container such as a metal can or a can made of
a laminate film and if necessary, terminals are welded, and then a
prescribed amount of an electrolytic solution containing a cationic
polymerization catalyst dissolved therein is poured into the
battery container and the battery container is air-tightly closed
and sealed to give a battery having a separator firmly bonded to
electrodes formed in such a manner as follows.
[0068] When an electrolytic solution is poured into the battery
container, at least a portion of the reactive polymer supported on
the reactive polymer-supporting porous film is swollen in the
vicinity of the interface of the porous film and the electrodes in
the electrolytic solution, or dissolved or diffused in the
electrolytic solution, to cause the cationic polymerization and
further crosslinking of the reactive polymer. Thus, at least a part
of the electrolytic solution is made gel thereby bonding porous
film to the electrodes firmly.
[0069] As clear from the foregoing, the reactive polymer causes
gelation of the electrolytic solution at least in the vicinity of
the interface between the porous film and the electrodes when it is
crosslinked by cationic polymerization and works so as to bond the
electrodes and the porous film.
[0070] Although depending on the structure and the supported amount
as well as the type and the amount of the cationic polymerization
catalyst used, the reactive polymer can be polymerized and
crosslinked at a normal temperature, however the cationic
polymerization can be promoted by heating. In the case the cationic
polymerization is carried out under heating, it is carried out
usually at a temperature of 40 to 100.degree. C. for 0.5 to 24
hours in consideration of balance with the heat resistance of the
materials composing the battery and the productivity. Further, when
a battery is manufactured in such a manner as mentioned above, the
resulting content in the battery container may be left standing at
a normal temperature for several hours in order to swell the
reactive polymer, or dissolve and diffuse the polymer in an amount
sufficient to bond the porous film to the electrodes after the
electrolytic solution is poured into the battery container, The
electrode/reactive polymer-supporting porous film layered body is
sufficient if the electrodes are layered on the reactive
polymer-supporting porous film. Accordingly, depending on the
structure and the form of the battery, the electrode/reactive
polymer-supporting porous film layered body may have various
layered structures such as a negative electrode/porous
film/positive electrode or a negative electrode/porous
film/positive electrode/porous film.
[0071] The electrolytic solution is a solution comprised of an
electrolytic salt dissolved in an appropriate solvent. Examples of
the electrolytic salt include salts comprising: cationic components
such as hydrogen; alkali metals such as lithium, sodium and
potassium; alkaline earth metals such as calcium and strontinum;
and tertiary or quaternary ammoniums; and anionic components such
as inorganic acids such as hydrochloric acid, nitric acid,
phosphoric acid, sulfuric acid, borofluoric acid, hydrofluoric
acid, hexafluorophosphoric acid, and perchloric acid and organic
acids such as carboxylic acid, organic sulfonic acid, and
fluorine-substituted organic sulfonic acid. Among them, an
electrolytic salt containing an alkali metal in as a cationic
component is preferably used.
[0072] Practical examples of the electrolytic salt containing an
alkali metal ion as a cationic component are alkali metal
perchlorates such as lithium perchlorate, sodium perchlorate, and
potassium perchlorate; alkali metal tetrafluoroborates such as
lithium tetrafluoroborate, sodium tetrafluoroborate, and potassium
tetrafluoroborate; alkali metal hexafluorophosphates such as
lithium hexafluorophosphate and potassium hexafluorophosphate;
alkali metal trifluoroacetates such as lithium trifluoroacetate;
and alkali metal trifluoromethanesulfonates such as lithium
trifluoromethanesulfonate.
[0073] In particular, when a lithium ion secondary battery is to be
obtained according to the invention, lithium hexafluorophosphate,
lithium tetrafluoroborate, and lithium perchlorate are used
preferably as an electrolytic salt.
[0074] The solvent used to dissolve the electrolytic salt may be
any solvents if they can dissolve the electrolytic salts. For
example, non-aqueous solvents used include cyclic esters such as
ethylene carbonate, propylene carbonate, butylene carbonate, and
y-butyrolactone; ethers such as tetrahydrofuran and
dimethoxyethane; and chain type esters such as dimethyl carbonate,
diethyl carbonate and ethyl methyl carbonate. These solvents may be
used alone or in combination of two or more.
[0075] Although being suitably determined in accordance with the
type and the amount of the solvent used, the amount of the
electrolytic salt is adjusted usually to be 1 to 50% by weight in
the resulting electrolytic solution.
[0076] In the invention, an onium salt is preferably used as a
cationic polymerization catalyst. Examples of the onium salt are
those comprising cationic components such as ammonium, phosphonium,
arsonium, stibonium and iodonium, and anionic components such as
tetrafluoroborate, hexafluorophosphate, trifluoromethanesulfonate,
and perchlorate.
[0077] Among the above-exemplified electrolytic salts, lithium
tetrafluoroborate and lithium hexafluorophosphate are preferred
since they work themselves as cationic polymerization catalysts as
well as the electrolytic salts. In this case, either one of lithium
tetrafluoroborate and lithium hexafluorophosphate may be used or
both of them may be used in combination.
INDUSTRIAL APPLICABILITY
[0078] The reactive polymer-supporting porous film for use as a
battery separator of the invention comprises a porous substrate
film and a reactive polymer supported thereon, the reactive polymer
being obtained by reacting some of reactive groups of a
crosslinkable polymer having at least one reactive group selected
from the group consisting of 3-oxetanyl groups and epoxy groups
with a polycarboxylic acid so that it is partially crosslinked.
[0079] Accordingly, electrodes are layered on the reactive
polymer-supporting porous film to obtain an electrode/reactive
polymer-supporting porous film layered body; the layered body is
placed in a battery container; an electrolytic solution containing
a cationic polymerization catalyst is poured into the battery
container; at least a portion of the reactive polymer is swollen or
dissolved at least in the vicinity of the interface of the porous
film and the electrodes in the electrolytic solution; the remaining
reactive groups of the reactive polymer are cation-polymerized so
that it is further crosslinked and at least a portion of the
electrolytic solution is gelled, thereby firmly bonding the porous
film and the electrodes each other to form an electrode/porous film
adherent.
[0080] Since the reactive polymer in the reactive
polymer-supporting porous film of the invention is previously
partially crosslinked, when the electrode/reactive
polymer-supporting porous film layered body is immersed in an
electrolytic solution, dissolution and diffusion of the reactive
polymer from the electrode/reactive polymer-supporting porous film
layered body into the electrolytic solution are suppressed while
the reactive polymer is swollen in the electrolytic solution. As a
result, even a small amount of the reactive polymer can bond the
porous film (separator) firmly to the electrodes. The porous film
is excellent in the ion permeability and satisfactorily functions
as a separator. Further, the reactive polymer is prevented from
excess dissolution and diffusion so that it does not cause any
adverse effect on the electrolytic solution.
[0081] According to a preferred embodiment of the invention, a
layer of the crosslinkable polymer can be transferred to and
supported on a porous substrate film at a relatively low
temperature. Then, the reactive polymer-supporting porous film
having the reactive polymer reliably on the surface can be readily
obtained by. partially crosslinking the crosslinkable polymer.
Further according to the invention, the reactive polymer-supporting
porous film is readily wetted with an electrolytic solution so that
the use of such a reactive polymer-supporting porous film for
production of a battery increases the productivity of the
battery.
[0082] Consequently, according to the invention, not only an
electrode/separator layered adherent in which electrodes and a
separator are firmly bonded together can be formed in situ in the
course of production of battery, but also a battery having low
inner resistance and excellent in high rate performance can be
obtained easily at a high productivity.
EXAMPLES
[0083] The invention will be explained in more detail below by way
of Examples, but the invention is not limited to these Examples at
all. The physical properties of porous substrate films and the
battery performance are evaluated as described below.
(Thickness of Porous Substrate Film)
[0084] The thickness of a porous substrate film was measured by
measuring the porous film with a 1/10000 mm thickness gauge and a
scanning electron microscopic photograph with 10,000 magnification
of the cross-section of the porous film.
(Porosity of Porous Substrate Film)
[0085] The porosity of a porous substrate film was calculated from
the weight W (g) per unit surface area S (cm.sup.2), the average
thickness t (cm) of the porous film and the density d (g/cm.sup.3)
of the resin forming the porous film according to the following
equation: Porosity(%)=(1-(W/S/t/d)).times.100 (Air Permeability of
Porous Substrate Film)
[0086] It is measured according to JIS P 8117.
(Piercing Strength)
[0087] The piercing test was carried out by using a compressing
tester KES-G5 manufactured by Kato Tech. Co., Ltd. The maximum load
was read from the load fluctuation curve obtained by the
measurement and represented as the piercing strength. Using a
needle with a diameter of 1.0 mm and a curvature diameter of the
tip end of 0.5 mm, the test was carried out at a speed of 2
cm/s.
(Proportion of Insoluble Matter in Reactive Polymer)
[0088] A reactive polymer-supporting porous film supporting a
reactive polymer with a known weight A was weighed to measure the
weight B. After the reactive polymer-supporting porous film was
immersed in a mixture of ethylene carbonate/diethyl carbonate (1/1
ratio by volume) at a room temperature for 2 hours, the film was
immersed in ethyl methyl carbonate and washed and dried.
Thereafter, the reactive polymer-supporting porous film treated in
such a manner was weighed to measure the weight C. The proportion
of insoluble matter in the reactive polymer was calculated
according to the following equation: Proportion of insoluble
matter(%)=((A-(B-C))/A).times.100 (Wettability of Reactive
Polymer-Supporting Porous Film with Electrolytic Solution)
[0089] After a reactive polymer-supporting porous film is immersed
in an electrolytic solution obtained by dissolving 1.0 mol/L of
lithium hexafluorophosphate in a mixture of ethylene
carbonate/diethyl carbonate (1/1 ratio by weight) for a prescribed
period, it was taken out of the electrolytic solution and
immediately sandwiched between two platinum electrodes and
subjected to resistance measurement by applying 1 KHz a.c. current.
The immersion time was variously changed and the 1 KHz a.c.
resistance was measured to find such immersion time for which the
resistance becomes the minimum and thus evaluate the wettability
with electrolytic solution in terms of time (s).
(Glass Transition Temperature of Crosslinkable Polymer)
[0090] The glass transition temperature of a crosslinkable polymer
was measured as follows. A solution of the crosslinkable polymer
was cast on release paper and dried to obtain a sheet of the
polymer with a thickness of 0.2 to 0.5 mm and width of 5 mm. The
glass transition temperature of the sheet was measured using DMS
120 manufactured by Seiko Instruments Inc. under the conditions of
chuck distance 10 mm and 10 KHz in bending mode. The heating speed
was 5.degree. C./min and the temperature range was in a range of 20
to 200.degree. C. The glass transition temperature was calculated
from the peak temperature of tan .delta..
(Measurement of Area Thermal Shrinkage Ratio of Separator (Porous
Film)/Electrode Layered Adherent)
[0091] Each of the positive electrode/porous film/negative
electrode layered bodies obtained in production of a reference
battery, the respective examples and comparative examples was
punched in a prescribed size and was immersed in an electrolytic
solution obtained by dissolving 1.0 mol/L of lithium
hexafluorophosphate in a mixture of ethylene carbonate/diethyl
carbonate (1/1 ratio by weight) to obtain samples.
[0092] As shown in FIG. 1, a cylindrical container 1 made of SUS
having an O-ring 3 in a circular upper end face 2 of the
circumferential wall was prepared. A sample 4 was placed in the
bottom of the container and a weight 5 was put on so as to apply a
pressure of 9 g/m.sup.2 and then a cover 6 was put on the cover to
close the container. The container containing the sample in such a
manner was placed in an oven at 150.degree. C. for 1 hour and then
gradually cooled. The sample was taken out of the container. The
separator (porous film) of the sample was peeled from the positive
and negative electrodes and the surface area of the peeled film was
read by a scanner and compared with the surface area of the porous
film before heating to measure the area thermal shrinkage
ratio.
Reference Example 1
(Preparation of Electrode Sheet)
[0093] 85 parts by weight of lithium cobaltate (CELLSEAD C-10,
manufactured by Nippon Chemical Industrial Co., Ltd.) as an anode
active material, 10 parts by weight of acetylene black (DENKA
BLACK, manufactured by Denki Kagaku Kogyo K.K.) as a conduction aid
and 5 parts by weight of vinylidene fluoride resin (KF POLYMER
L#1120, manufacture by Kureha Chemical Industry Co., Ltd.) as a
binder were mixed together. The resulting mixture was then mixed
with N-methyl-2-pyrrolidone to prepare a slurry of a solid content
of 15% by weight. The slurry was applied in a thickness of 200
.mu.m to a 20 .mu.m-thick aluminum foil (a collector) and the
resulting aluminum foil was vacuum dried at 80.degree. C. for 1
hour and at 120.degree. C. for 2 hours and then pressed by a roll
press to obtain a positive electrode sheet having an active
material layer with a thickness of 100 .mu.m.
[0094] 80 parts by weight of mesocarbon microbeads (MCMB 6-28,
manufactured by Osaka Gas Chemicals Co., Ltd.) as a cathode active
material, 10 parts by weight of acetylene black (DENKA BLACK,
manufactured by Denki Kagaku Kogyo K.K.) as a conduction aid and 10
parts by weight of vinylidene fluoride resin (KF POLYMER L#1120,
manufacture by Kureha Chemical Industry Co., Ltd.) as a binder were
mixed together. The resulting mixture was then mixed with
N-methyl-2-pyrrolidone to prepare a slurry of a solid content of
15% by weight. The slurry was applied in a thickness of 200 .mu.m
to a 20 .mu.m-thick copper foil (a collector) and the resulting
copper foil was vacuum dried at 80.degree. C. for 1 hour and at
120.degree. C. for 2 hours and then pressed by a roll press to
obtain a negative electrode sheet having an active material layer
with a thickness of 100 .mu.m.
(Production of Reference Battery)
[0095] The negative electrode sheet obtained in Reference Example
1, a porous film (separator) made of polyethylene having a
thickness of 16 .mu.m, a porosity of 40%, an air permeability of
300 s/100 cc and a piercing strength 3.0 N and positive electrode
sheet obtained in the Reference Example 1 were layered in this
order to obtain a positive electrode/porous film/negative electrode
layered body. The layered body was placed in an aluminum laminate
package and then an electrolytic solution obtained by dissolving
1.0 mol/L of lithium hexafluorophosphate in a mixed solvent of
ethylene carbonate/diethyl carbonate (1/1 ratio by weight) was
poured into the package and then the package was sealed to assembly
a lithium ion secondary battery. The battery was charged and
discharged three times at a rate of 0.1 CmA and then charged at a
rate of 0.1 CmA, and thereafter discharged at a rate of 1 CmA to
measure the 1 CmA discharge capacity A.
[0096] The wettability of the above-mentioned separator in terms of
time as measured in such a manner as mentioned hereinbefore was 5
seconds. The area thermal shrinkage ratio of the separator as
measured by the aforesaid method was 72%.
Discharging Performance of Batteries of Examples and Comparative
Examples
[0097] Each of the laminate film lithium ion secondary batteries
obtained by the following Examples and Comparative Examples was
charged and discharged each three times at a rate of 0.1 CmA and
then charged at a rate of 0.1 CmA and thereafter discharged at a
rate of 1 CmA to measure the 1 CmA discharge capacity B. The
battery performance was evaluated on the basis of the percentage
(%) of the discharge capacity B to the discharge capacity A of the
above-mentioned reference battery.
Production Example 1
(Production of Crosslinkable Polymer A (Composed of 5% by Weight of
3,4-epoxycyclohexylmethyl Acrylate Monomer Component, 20% by Weight
of 3-oxetanyl Group-Containing Monomer Component and 75% by Weight
of Methyl Methacrylate Monomer Component))
[0098] 60.0 g of methyl methacrylate, 16.0 g of
3-ethyl-3-oxetanylmethyl methacrylate, 4.0 g of
3,4-epoxycyclohexylmethyl acrylate, 226.6 g of ethylene carbonate
and 0.15 g 2,2'-azobis(isobutyronitrile) were placed in a 500 mL
capacity three-necked flask equipped with a refluxing condenser and
stirred and mixed for 30 minutes while nitrogen gas was introduced
into the flask. Then the resulting mixture was heated to 70.degree.
C. and radical polymerization was carried out over 8 hours at the
temperature. The resulting reaction mixture was cooled to
40.degree. C. 226.6 g of diethyl carbonate and 0.15 g of
2,2'-azobis(isobutyronitrile) were added to the reaction mixture
and the resulting mixture was again heated to 70.degree. C. to
carry out radical polymerization at the temperature for another 8
hours. Then the resulting reaction mixture was cooled to 40.degree.
C. to obtain a solution of a polymer in a concentration of 15% by
weight in a solvent of ethylene carbonate/diethyl carbonate
mixture.
[0099] While being stirred by a high speed mixer, 100 g of the
polymer solution was poured into 600 mL of methanol to precipitate
the polymer. The polymer was separated by filtration and washed
several times with methanol, placed in a drying tube, and dried by
passing dried nitrogen gas (having a dew point -150.degree. C. or
lower) obtained by evaporation of liquefied nitrogen through the
tube and then by further drying in vacuo in a desiccator for 6
hours, thereby obtaining a crosslinkable polymer A.
[0100] The thus obtained crosslinkable polymer A was found to be
white powder and was found to have a weight average molecular
weight of 344,400 and a number average molecular weight of 174,500
as measured by GPC (gel permeation chromatography). The
crosslinkable polymer A was also found to have a glass transition
temperature of 116.degree. C. as measured by DSC (differential
scanning calorimetry).
Production Example 2
(Production of Crosslinkable Polymer B (Composed of 25% by Weight
of 3,4-epoxycyclohexylmethyl Acrylate Monomer Component and 75% by
Weight of Methyl Methacrylate Monomer Component))
[0101] 60.0 g of methyl methacrylate, 20.0 g of
3,4-epoxycyclohexylmethyl acrylate, 226.6 g of ethylene carbonate
and 0.24 g of 2,2'-azobis(isobutyronitrile) were placed in a 500 mL
capacity three-necked flask equipped with a refluxing condenser and
stirred and mixed for 30 minutes while nitrogen gas was introduced
into the flask. The mixture was heated to 70.degree. C. and radical
polymerization was carried out at the temperature over 8 hours. The
resulting reaction mixture was cooled to 40.degree. C. 226.6 g of
diethyl carbonate and 0.24 g of 2,2'-azobis(isobutyronitrile) were
added to the reaction mixture and the resulting mixture was again
heated to 70.degree. C. for carrying out radical polymerization at
the temperature for another 8 hours. The resulting reaction mixture
was cooled to 40.degree. C. thereby to obtain a solution of a
polymer in a concentration of 15% by weight in a solvent of
ethylene carbonate/diethyl carbonate mixture.
[0102] 100 g of the polymer solution was treated in the same manner
as Production Example 1 to obtain a crosslinkable polymer B. It was
white powder and was found to have a weight average molecular
weight of 429,100 and a number average molecular weight of 133,600
as measured by GPC and a glass transition temperature of 93.degree.
C.
Production Example 3
[0103] (Production of Crosslinkable Polymer C (Composed of 5% by
Weight of 3,4-epoxycyclohexylmethyl Acrylate Monomer Component, 20%
by Weight of 3-oxetanyl Group-Containing Monomer Component, 37.5%
by Weight of Methyl Methacrylate Monomer Component and 37.5% by
Weight of n-butyl Acrylate Monomer Component))
[0104] 0.05 g of partially saponified polyvinyl alcohol (having a
polymerization degree of 2,000 and a saponification degree of 78 to
87 mole %), 2.0 g of completely saponified polyvinyl alcohol
(having a polymerization degree of 2,000 and a saponification
degree of 98.5 to 99.4 mole %) and 210.0 g of ion exchanged water
were placed in a 500 mL capacity three-necked flask equipped with a
refluxing condenser. While nitrogen gas was introduced into the
flask, the mixture was heated to 95.degree. C. and, after the
above-mentioned polyvinyl alcohols were completely dissolved, the
mixture was cooled to about 30.degree. C. Then 30.0 g of methyl
methacrylate, 4.0 g of 3,4-epoxy-cyclohexylmethyl acrylate, 16.0 g
of 3-ethyl-3-oxetanylmethyl methacrylate, 30.0 g of n-butyl
acrylate, 0.4 g of 2,2'-azobis(isobutyronitrile) and 2.5 g of 1.0%
by weight solution solution of n-dodecanethiol in diethyl carbonate
as a solvent were placed in the flask and stirred and mixed for 30
minutes while nitrogen gas was introduced into the flask. Then the
mixture was heated to 70.degree. C. for carrying out radical
polymerization for 5 hours.
[0105] After the reaction mixture obtained in this way was filtered
using a 500 mesh filtration net and washed with water, the filtered
product was placed in a 500 mL capacity three-necked flask and
mixed with 300 mL of ion exchanged water. The mixture was heated to
95.degree. C. while being stirred and washed with hot water to
remove the remaining polyvinyl alcohols. The resulting product was
filtered using a 500 mesh filtration net and washed with water and
again washed with hot water and water repeatedly. Then the product
obtained was washed with methanol to remove the remaining water and
then dried in vacuo to obtain a crosslinkable polymer C as white
and fine granule. It was found to have a weight average molecular
weight of 281,600 and a number average molecular weight of 108,700
as measured by GPC. It was also found to have a glass transition
temperature of 43.degree. C. as measured by DSC.
Production Example 4
[0106] (Production of Crosslinkable Polymer D (Composed of 5% by
Weight of 3,4-epoxycyclohexylmethyl Acrylate Monomer Component, 20%
by Weight of 3-oxetanyl Group-Containing Monomer Component, 50% by
Weight of Methyl Methacrylate Monomer Component and 25% by Weight
of n-butyl Acrylate Monomer Component))
[0107] In the same manner as Production Example 3, partially
saponified polyvinyl alcohol and completely saponified polyvinyl
alcohol were dissolved in ion exchanged water under heating and
then cooled to prepare a solution. 40.0 g of methyl methacrylate,
4.0 g of 3,4-epoxycyclohexylmethyl acrylate, 16.0 g of
3-ethyl-3-oxetanylmethyl methacrylate, 20.0 g of n-butyl acrylate,
0.4 g of 2,2'-azobis(isobutyronitrile) and 6.0 g of 1.0% by weight
solution of n-dodecanethiol in a solvent of ethylene carbonate were
added to the solution. The resulting mixture was stirred and mixed
for 30 minutes while nitrogen gas was introduced thereinto. The
mixture was then heated to 70.degree. C. and radical polymerization
was carried out for 5 hours at the temperature. Thereafter, in the
same manner as Production Example 3, the resulting reaction mixture
was washed with hot water, water, and methanol in this order, and
then dried in vacuo to provide a crosslinkable polymer D as white
and fine granule.
[0108] It was found to have a weight average molecular weight of
224,200 and a number average molecular weight of 79,800 as measured
GPC. It was also found to have a glass transition temperature of
41.degree. C. as measured by DSC.
Production Example 5
[0109] (Production of Crosslinkable Polymer E (Composed of 5% by
Weight of 3,4-epoxycyclohexylmethyl Acrylate Monomer Component, 20%
by Weight of 3-oxetanyl Group-Containing Monomer Component, 37.5%
by Weight of Methyl Methacrylate Monomer Component and 37.5% by
Weight of Ethyl Acrylate Monomer Component))
[0110] 30.0 g of methyl methacrylate, 4.0 g of
3,4-epoxycyclohexylmethyl acrylate, 16.0 g of
3-ethyl-3-oxetanyl-methyl methacrylate, 30.0 g of ethyl acrylate,
150.0 g of ethyl acetate and 0.15 g of
2,2'-azobis(isobutyronitrile) were placed in a 500 mL capacity
three-necked flask equipped with a refluxing condenser and stirred
and mixed for 30 minutes while nitrogen gas was introduced into the
flask. The mixture was heated to 70.degree. C. to carry out radical
polymerization. After one hour, radical polymerization started
simultaneously with increase of the viscosity of the reaction
mixture and the polymerization was carried out for 8 hours. After
the reaction mixture was cooled to about 40.degree. C., 0.15 g of
2,2'-azobis(isobutyronitrile) was added to the reaction mixture,
and it was again heated to 70.degree. C. to carry out radical
polymerization for another 8 hours. Thereafter, the resulting
reaction mixture was cooled to 40.degree. C. and 90 g of ethyl
acetate was added thereto and stirred and mixed until the mixture
became entirely uniform to obtain an ethyl acetate solution of
crosslinkable polymer E (having a concentration of 33.3% by
weight). The crosslinkable polymer E was found having a weight
average molecular weight of 70,200 and a number average molecular
weight of 35,000 as measured by GPC. The glass transition
temperature was found to be 47.degree. C. by DSC.
Example 1
[0111] The crosslinkable polymer A was added to ethyl acetate and
stirred at room temperature so that it is dissolved therein to
obtain a solution of the crosslinkable polymer A in a concentration
of 10% by weight. Separately, an ethanol solution of adipic acid in
a concentration of 10% by weight was prepared. The solution of
adipic acid was gradually dropwise added to the solution of the
crosslinkable polymer A while it was stirred to prepare a mixed
solution of the crosslinkable polymer A and adipic acid. The molar
ratio of the carboxyl groups of adipic acid to the reactive groups
of the crosslinkable polymer A was adjusted to be 0.5.
[0112] The mixed solution of the crosslinkable polymer A and adipic
acid was applied to both surfaces of a porous substrate film made
of polyethylene resin (having a thickness of 16 .mu.m, a porosity
of 40%, an air permeability of 300 s/100 cc, a piercing strength of
3.0 N) with a wire bar (#7). The film was then heated at 50.degree.
C. to evaporate ethyl acetate and ethanol to obtain a crosslinkable
polymer-supporting porous film in which each of the surfaces of the
porous film supported the crosslinkable polymer in an amout of 2.2
g/m.sup.2. The crosslinkable polymer-supporting porous film was
then placed in a thermostat at a temperature of 50.degree. C. for
48 hours to react the crosslinkable polymer supported on the porous
film with adipic acid and partially crosslink the crosslinkable
polymer thereby providing a reactive polymer-supporting porous
film. The proportion of insoluble matter in the reactive polymer in
the reactive polymer-supporting porous film was found to be 19%.
The wettability of the reactive polymer-supporting porous film with
the aforesaid electrolytic solution as measured in terms of time
(hereinafter simply referred to as wettability) was 10 minute.
[0113] The negative electrode sheet obtained in the Reference
Example 1, the reactive polymer-supporting porous film obtained
above and the positive electrode sheet obtained in the Reference
Example 1 were layered in this order to obtain a
separator/electrode layered body. The layered body was placed in an
aluminum laminate package and an electrolytic solution obtained by
dissolving 1.0 mol/L of lithium hexafluorophosphate in a mixture of
ethylene carbonate/diethyl carbonate (1/1 ratio by weight) was
poured into the package and then the package was sealed. The
package was heated at 70.degree. C. for 7 hours to allow the
reactive polymer to carry out cationic polymerization so that it
was crosslinked thereby a portion of the electrolytic solution was
gelled while the porous film (separator) was bonded to the
electrode sheets to provide a laminate battery.
[0114] The 1 CmA discharge capacity of the battery was 97% of the
discharge capacity of the reference battery. The battery was
disassembled and the adhesion strength of the electrode sheets and
the separator was measured to find that it was 0.22 N/cm for the
positive electrode and 0.10 N/cm for the negative electrode. The
surface thermal shrinkage ratio of the separator in the
separator/electrode layered adherent obtained by using the
above-mentioned reactive polymer-supporting porous film was
2.0%.
Example 2
[0115] A reactive polymer-supporting porous film was obtained in
the same manner as Example 1, except that the crosslinkable polymer
B was used in place of the crosslinkable polymer A. The molar ratio
of the carboxyl groups of adipic acid to the reactive groups of the
crosslinkable polymer A was adjusted to be 0.5. The proportion of
insoluble matter in the reactive polymer in the reactive
polymer-supporting porous film was 30%. The wettability of the
reactive polymer-supporting porous film was 20 minute.
[0116] A laminate battery was obtained in the same manner as
Example 1 by using the reactive polymer-supporting porous film
obtained above. The 1 CmA discharge capacity of the battery was 93%
of the discharge capacity of the reference battery. The battery was
disassembled and the adhesion strength of the electrode sheets and
the separator was measured to find that it was 0.20 N/cm for the
positive electrode and 0.10 N/cm for the negative electrode. The
surface thermal shrinkage ratio of the separator in the
separator/electrode layered adherent obtained by using the reactive
polymer-supporting porous film was 2.5%.
Example 3
[0117] A crosslinkable polymer-supporting porous film was obtained
in the same manner as Example 1, and a reactive polymer-supporting
porous film was obtained in the same manner as Example 1, except
that the crosslinkable polymer-supporting porous film was placed in
a thermostat at a temperature of 50.degree. C. for 12 hours. The
proportion of insoluble matter in the reactive polymer in the
reactive polymer-supporting porous film was 3.0%. The wettability
of the reactive polymer-supporting porous film was 5 minute.
[0118] A laminate battery was obtained in the same manner as
Example 1 by using the reactive polymer-supporting porous film
obtained above. The 1 CmA discharge capacity of the battery was 90%
of the discharge capacity of the reference battery. The battery was
disassembled and the adhesion strength of the electrode sheets and
the separator was measured to find that it was 0.20 N/cm for the
positive electrode and 0.26 N/cm for the negative electrode. The
surface thermal shrinkage ratio of the separator in the
separator/electrode layered adherent obtained by using the reactive
polymer-supporting porous film was 1.5%.
Example 4
[0119] A reactive polymer-supporting porous film was obtained in
the same manner as Example 1, except that the crosslinkable polymer
B was used in place of the crosslinkable polymer A and the molar
ratio of the carboxyl groups of adipic acid to the reactive groups
of the crosslinkable polymer was adjusted to be 1.0. The proportion
of insoluble matter in the reactive polymer in the reactive
polymer-supporting porous film was found to be 80%. The wettability
of the reactive polymer-supporting porous film was found to be 35
minute.
[0120] A laminate battery was obtained in the same manner as
Example 1 by using the above-mentioned reactive polymer-supporting
porous film. The 1 CmA discharge capacity of the battery was found
to be 89% of the discharge capacity of the reference battery. The
battery was disassembled and the adhesion strength of the electrode
sheets and the separator was measured to find that it was 0.10 N/cm
for the positive electrode and 0.05 N/cm for the negative
electrode. The surface thermal shrinkage ratio of the separator in
the separator/electrode layered adherent obtained by using the
above-mentioned reactive polymer-supporting porous film was
5.0%.
Example 5
[0121] The crosslinkable polymer C was dissolved in ethyl acetate
at room temperature to obtain a solution of the crosslinkable
polymer C in a concentration of 10% by weight. Separately, an
ethanol solution of adipic acid in a concentration of 5% by weight
was prepared. The solution of adipic acid was gradually dropwise
added to the above-mentioned solution of crosslinkable polymer C
while it was stirred, thereby preparing a mixed solution of the
crosslinkable polymer C and adipic acid. The molar ratio of the
carboxyl groups of adipic acid to the reactive groups of the
crosslinkable polymer was adjusted to be 0.5.
[0122] The mixed solution of the crosslinkable polymer and adipic
acid was applied to a release paper by a wire bar (#7) and then
heated at 50.degree. C. to evaporate ethyl acetate and ethanol to
form a crosslinkable polymer C/adipic acid layer on the release
paper. The release paper was laminated on both surfaces of a porous
substrate film made of polyethylene (having a thickness of 16
.mu.m, a porosity of 40%, an air permeability of 300 s/100 cc, and
a piercing strength of 3.0 N) in such a manner that the
crosslinkable polymer C/adipic acid layer on the release paper was
brought into contact with the film. The thus obtained laminate was
passed through a hot roll at 70.degree. C. and then the release
papers were removed from the laminate to provide a crosslinkable
polymer-supporting porous film which supported the crosslinkable
polymer in an amount of 1.5 g/m.sup.2 for each surface.
[0123] The crosslinkable polymer-supporting porous film was then
placed in a thermostat at 50.degree. C. for 48 hours so that the
crosslinkable polymer supported on the porous film was reacted with
adipic acid and was partially crosslinked to provide a reactive
polymer-supporting porous film. The proportion of insoluble matter
in the reactive polymer in the reactive polymer-supporting porous
film was found to be 59%. The electrolytic solution immersion time
of the reactive polymer-supporting porous film was found to be 10
second.
[0124] A laminate battery was obtained in the same manner as
Example 1 by using the above-mentioned reactive polymer-supporting
porous film. The 1 CmA discharge capacity of the battery was found
to be 97% of the discharge capacity of the reference battery. The
battery was disassembled and the adhesion strength of the electrode
sheets and the separator was measured to find that it was 0.15 N/cm
for the positive electrode and 0.25 N/cm for the negative
electrode. The surface thermal shrinkage ratio of the separator in
the separator/electrode layered adherent obtained by using the
above-mentioned reactive polymer-supporting porous film was found
to be 1.5%.
Example 6
[0125] The crosslinkable polymer C was dissolved in ethyl acetate
at room temperature to obtain a solution of the crosslinkable
polymer C in a concentration of 10% by weight. Separately, an
ethanol solution of adipic acid in a concentration of 10% by weight
was prepared. The solution of adipic acid was gradually dropwise
added to the above-mentioned solution of the crosslinkable polymer
C while it was stirred thereby to prepare a mixed solution of the
crosslinkable polymer C and adipic acid. The molar ratio of the
carboxyl groups of adipic acid to the reactive groups of the
crosslinkable polymer was adjusted to be 0.5.
[0126] The mixed solution of the crosslinkable polymer and adipic
acid was applied to a release paper by a wire bar (#3) and heated
at 50.degree. C. to evaporate ethyl acetate and ethanol to form a
crosslinkable polymer C/adipic acid layer on the release paper. The
release paper was laminated on both surfaces of a porous substrate
film made of polyethylene (having a thickness of 16 .mu.m, a
porosity of 40%, an air permeability of 300 s/100 cc, and a
piercing strength of 3.0 N) in such a manner that the crosslinkable
polymer C/adipic acid layer on the release paper was brought into
contact with the film. The thus obtained laminate was passed
through a hot roll at 70.degree. C. and then the release papers
were removed from the laminate to provide a crosslinkable
polymer-supporting porous film which supported the crosslinkable
polymer in an amount of 0.6 g/m.sup.2 for each surface.
[0127] The above-mentioned crosslinkable polymer-supporting porous
film was placed in a thermostat at 50.degree. C. for 48 hours so
that the crosslinkable polymer supported on the porous film was
reacted with adipic acid and was partially crosslinked thereby to
provide a reactive polymer-supporting porous film. The proportion
of insoluble matter in the reactive polymer in the reactive
polymer-supporting porous film was found to be 46%. The wettability
of the reactive polymer-supporting porous film was found to be 10
second.
[0128] The negative electrode sheet obtained in the aforesaid
Reference Example 1, the above-mentioned reactive
polymer-supporting porous film, and positive electrode sheet
obtained in the aforesaid Reference Example 1 were layered in this
order to obtain a separator/electrode layered body. It was pressed
with a pressure of 5 kgf/cm.sup.2 at a temperature of 80.degree. C.
for 2 minutes to pressure-adhere and temporarily adhere the
positive and negative electrode sheets to the reactive
polymer-supporting porous film and obtain a negative
electrode/porous film/positive electrode layered body.
[0129] The thus obtained separator/electrode layered body was
placed in an aluminum laminate package and an electrolytic solution
of lithium hexafluorophosphate in a concentration of 1.0 mol/L in a
mixture of ethylene carbonate/diethyl carbonate (1/1 ratio by
weight) was poured into the package and then the package was
sealed. Thereafter the package was heated at 70.degree. C. for 7
hours so that the reactive polymer was allowed to carry out
cationic polymerization and crosslinked while a portion of the
electrolytic solution was gelled thereby the porous film
(separator) was bonded to the electrode sheets to provide a
laminate battery.
[0130] The 1 CmA discharge capacity of the battery was found to be
87% of the discharge capacity of the reference battery. The battery
was disassembled and the adhesion strength of the electrode sheets
and the separator was measured to find that it was 0.12 N/cm for
the positive electrode and 0.41 N/cm for the negative electrode.
The surface thermal shrinkage ratio of the separator in the
separator/electrode adherent obtained by using the above-mentioned
reactive polymer-supporting porous film was found to be 1.5%.
Example 7
[0131] A reactive polymer-supporting porous film was obtained in
the same manner as Example 5, except that the crosslinkable polymer
D was used in place of the crosslinkable polymer C and the
crosslinkable polymer-supporting porous film was placed in a
thermostat at 50.degree. C. for 60 hours. The molar ratio of the
carboxyl groups of adipic acid to the reactive groups of the
crosslinkable polymer was adjusted to be 0.5. The proportion of
insoluble matter in the reactive polymer in the reactive
polymer-supporting porous film was 65%. The wettability of the
reactive polymer-supporting porous film was 10 second.
[0132] A laminate battery was obtained in the same manner as
Example 1 by using the above-mentioned reactive polymer-supporting
porous film. The 1 CmA discharge capacity of the battery was found
to be 97% of the discharge capacity of the reference battery. The
battery was disassembled and the adhesion strength of the electrode
sheets and the separator was measured to find that it was 0.18 N/cm
for the positive electrode and 0.20 N/cm for the negative
electrode. The surface thermal shrinkage ratio of the separator in
the separator/electrode adherent obtained by using the
above-mentioned reactive polymer-supporting porous film was found
to be 2.0%.
Example 8
[0133] Ethyl acetate was added to the ethyl acetate solution of the
crosslinkable polymer E in a concentration of 33.3% by weight
obtained in Production Example 5 to obtain a 10% by weight solution
of the crosslinkable polymer E. A reactive polymer-supporting
porous film was obtained in the same manner as Example 5, except
that the ethyl acetate solution of the crosslinkable polymer E in a
concentration of 10% by weight was used in place of the ethyl
acetate solution of the crosslinkable polymer C in a concentration
of 10% by weight and the crosslinkable polymer was applied to the
substrate film made of polyethylene in an amount of 2.0 g/m.sup.2
per one surface as well as the crosslinkable polymer-supporting
porous film was placed in a thermostat at 50.degree. C. for 160
hours. The molar ratio of the carboxyl groups of adipic acid to the
reactive groups of the crosslinkable polymer was adjusted to be
0.5. The proportion of insoluble matter in the reactive polymer in
the reactive polymer-supporting porous film was 49%. The
wettability of the reactive polymer-supporting porous film was 10
second.
[0134] A laminate battery was obtained in the same manner as
Example 1 by using the above-mentioned reactive polymer-supporting
porous film. The 1 CmA discharge capacity of the battery was found
to be 92% of the discharge capacity of the reference battery. The
battery was disassembled and the adhesion strength of the electrode
sheets and the separator was measured to find that it was 0.09 N/cm
for the positive electrode and 0.08 N/cm for the negative
electrode. The surface thermal shrinkage ratio of the separator in
the separator/electrode layered adherent obtained by using the
above-mentioned reactive polymer-supporting porous film was
6.0%.
Example 9
[0135] The crosslinkable polymer D was dissolved in ethyl acetate
at room temperature to obtain a solution of crosslinkable polymer D
in a concentration of 10% by weight. Separately, an ethyl acetate
solution of 10% by weight of 2,4-diethylglutaric acid was prepared.
The ethyl acetate solution of 2,4-diethylglutaric acid was
gradually dropwise added to the solution of crosslinkable polymer D
while it was stirred to prepare a mixed solution of the
crosslinkable polymer D and 2,4-diethylglutaric acid. The molar
ratio of the carboxyl groups of 2,4-diethylglutaric acid to the
reactive groups of the crosslinkable polymer was adjusted to be
0.2.
[0136] The mixed solution of the crosslinkable polymer D and
2,4-diethylglutaric acid was applied to a release paper by a wire
bar (#7) and heated at 50.degree. C. to evaporate ethyl acetate to
form a crosslinkable polymer D/2,4-diethylglutaric acid layer on
the release paper. The release paper was laminated on both surfaces
of a porous substrate film made of polyethylene (having a thickness
16 .mu.m, a porosity of 40%, an air permeability of 300 s/100 cc, a
piercing strength of 3.0 N) in a manner that the crosslinkable
polymer D/2,4-diethylglutaric acid layer on the release paper was
brought into contact with the film.
[0137] The obtained laminate was passed through a hot roll at
70.degree. C. and then the release papers were removed from the
laminate to obtain a crosslinkable polymer-supporting porous film
carrying the crosslinkable polymer in a coating ratio of 2.0
g/m.sup.2 for each surface.
[0138] The crosslinkable polymer-supporting porous film was placed
in a thermostat at 50.degree. C. for 96 hours so that the
crosslinkable polymer supported on the porous film was reacted with
2,4-diethylglutaric acid and partially crosslinked, thereby to
obtain a reactive polymer-supporting porous film. The proportion of
insoluble matter in the reactive polymer in the reactive
polymer-supporting porous film was 41%. The wettability of the
reactive polymer-supporting porous film was 10 second.
[0139] A laminate battery was obtained in the same manner as
Example 1 using the above-mentioned reactive polymer-supporting
porous film. The 1 CmA discharge capacity of the battery was 95% of
the discharge capacity of the reference battery. The battery was
disassembled and the adhesion strength of the electrode sheets and
the separator was measured to find that it was 0.17 N/cm for the
positive electrode and 0.15 N/cm for the negative electrode. The
surface thermal shrinkage ratio of the separator in the
separator/electrode adherent obtained by using the above-mentioned
reactive polymer-supporting porous film was 4.0%.
Comparative Example 1
[0140] A 10% by weight polymer solution was prepared by dissolving
poly(vinylidene fluoride/hexafluoropropylene) copolymer (KYNAR
2801, manufactured by Elf Atochem.) in N-methyl-2-pyrrolidone. The
polymer solution was applied to both surfaces of a porous substrate
film made of polyethylene (having a thickness of 16 .mu.m, a
porosity of 40%, an air permeability of 300 s/100 cc, a piercing
strength of 3.0 N) by a wire bar (#20) and then heated at
60.degree. C. to evaporate N-methyl-2-pyrrolidone to obtain a
porous film made of polyethylene and carrying poly(vinylidene
fluoride/hexafluoropropylene) copolymer on both surfaces. The
wettability of the poly(vinylidene fluoride/hexafluoropropylene)
copolymer-supporting porous film was 5 minutes.
[0141] The negative electrode sheet obtained in the aforesaid
Reference Example 1, the porous film made of polyethylene and
supporting the poly(vinylidene fluoride/hexafluoropropylene)
copolymer obtained above and the positive electrode sheet obtained
in the aforesaid Reference Example 1 were laminated in this order
and bonded together under a pressure of 50 kfg/cm.sup.2 at a
temperature of 80.degree. C. for one minute to obtain a
separator/electrode layered body. The separator/electrode layered
body was placed in an aluminum laminate package and an electrolytic
solution obtained by dissolving 1.0 mol/L of lithium
hexafluorophosphate in a mixed solvent of ethylene
carbonate/diethyl carbonate (1/1 ratio by weight) was poured into
the package and then the package was sealed to obtain a laminate
battery.
[0142] The 1 CmA discharge capacity of the battery was 85% of the
discharge capacity of the reference battery. The battery was
disassembled and the adhesion strength of the electrode sheets and
the separator was measured to find that it was 0.20 N/cm for the
positive electrode and 0.09 N/cm for the negative electrode. The
surface thermal shrinkage ratio of the separator in the
separator/electrode layered adherent obtained by using the
above-mentioned porous film supporting the poly(vinylidene
fluoride/hexafluoropropylene) copolymer was 30%.
Comparative Example 2
[0143] A laminate battery was obtained in the same manner as
Comparative Example 1, except that a solution of poly(vinylidene
fluoride/hexafluoropropylene) copolymer in a concentration of 5% by
weight was used. The 1 CmA discharge capacity of the battery was
96% of the discharge capacity of the reference battery. The battery
was disassembled and the adhesion strength of the electrode sheets
and the separator was measured to find that it was 0.05 N/cm for
the positive electrode and 0.0 N/cm for the negative electrode. The
wettability of the porous film supporting poly(vinylidene
fluoride/hexafluoropropylene) copolymer obtained by this
Comparative Example was 30 second and the surface thermal shrinkage
ratio of the separator in the separator/electrode layered adherent
obtained by using the above-mentioned porous film supporting
poly(vinylidene fluoride/hexafluoropropylene) copolymer was
60%.
[0144] Accordingly, the use of a reactive polymer-supporting porous
film of the invention makes it possible to obtain a battery in
which electrodes are firmly bonded to a separator and the separator
is scarcely shrunk even in the high temperature environments and
which is thus excellent in the safety. Further, as it is clear in
Examples 5 to 9, the reactive polymer-supporting porous films
according to preferred embodiments of the invention are excellent
in the wettability with an electrolytic solution and shorten the
time required for producing batteries and increase the productivity
of batteries.
* * * * *