U.S. patent application number 09/875039 was filed with the patent office on 2002-01-03 for electrolyte solution and secondary battery.
This patent application is currently assigned to NEC Corporation. Invention is credited to Bannai, Yutaka, Kumeuchi, Tomokazu, Ohyama, Norihide, Satoh, Masaharu, Shirakata, Masato, Yageta, Hiroshi.
Application Number | 20020001754 09/875039 |
Document ID | / |
Family ID | 26427649 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020001754 |
Kind Code |
A1 |
Satoh, Masaharu ; et
al. |
January 3, 2002 |
Electrolyte solution and secondary battery
Abstract
In a secondary battery wherein a positive electrode active
material layer 2 and a negative electrode active material layer 3
are allowed to face each other via an electrolyte solution 1, there
is used, as the electrolyte solution 1, a basic solvent containing
a halogenated polyolefin dissolved therein.
Inventors: |
Satoh, Masaharu; (Tokyo,
JP) ; Yageta, Hiroshi; (Tokyo, JP) ; Bannai,
Yutaka; (Tokyo, JP) ; Shirakata, Masato;
(Tokyo, JP) ; Ohyama, Norihide; (Tokyo, JP)
; Kumeuchi, Tomokazu; (Tokyo, JP) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Assignee: |
NEC Corporation
Tokyo
JP
|
Family ID: |
26427649 |
Appl. No.: |
09/875039 |
Filed: |
June 7, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09875039 |
Jun 7, 2001 |
|
|
|
09460768 |
Dec 14, 1999 |
|
|
|
Current U.S.
Class: |
429/303 ;
29/623.1; 429/324 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 10/0565 20130101; H01M 2300/0037 20130101; H01M 10/4235
20130101; Y10T 29/49108 20150115; H01M 10/0567 20130101; H01M
10/0525 20130101; H01M 10/0431 20130101; H01M 2300/0085 20130101;
H01M 10/052 20130101; H01M 2300/0025 20130101; H01M 4/60 20130101;
Y02P 70/50 20151101 |
Class at
Publication: |
429/303 ;
29/623.1; 429/324 |
International
Class: |
H01M 010/40 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 18, 1998 |
JP |
10-361002 |
Mar 29, 1999 |
JP |
11-086543 |
Claims
What is claimed is:
1. An electrolyte solution consisting of a basic solvent containing
an alkali metal salt and a halogenated polyolefin both dissolved
therein.
2. An electrolyte solution according to claim 1, wherein the
halogenated polyolefin is a fluorinated polyolefin.
3. An electrolyte solution according to claim 2, wherein the
fluorinated polyolefin is a copolymer containing a
tetrafluoroethylene.
4. An electrolyte solution according to claim 1, wherein the
halogenated polyolefin is contained in a concentration of 0.1 to
20% by weight.
5. An electrolyte solution according to claim 1, wherein the basic
solvent further contains an aliphatic polyolefin dissolved
therein.
6. An electrolyte solution according to claim 5, wherein the
aliphatic polyolefin is a saturated hydrocarbon having a carbon
chain length of 6 to 24.
7. An electrolyte solution according to claim 5, wherein the
aliphatic polyolefin is contained in a concentration smaller than
that of the halogenated polyolefin.
8. A secondary battery using an alkali metal ion as a charge
carrier and having a structure in which a positive electrode and a
negative electrode are adjacent to each other via an electrolyte
solution, in which secondary battery the electrolyte solution
consists of a basic solvent containing an alkali metal salt and a
halogenated polyolefin both dissolved therein.
9. A secondary battery according to claim 8, wherein the
halogenated polyolefin is a fluorinated polyolefin.
10. A secondary battery according to claim 9, wherein the
fluorinated polyolefin is a copolymer containing a
tetrafluoroethylene.
11. A secondary battery according to claim 8, wherein the
halogenated polyolefin is contained in a concentration of 0.1 to
20% by weight.
12. A secondary battery according to claim 8, wherein the basic
solvent further contains an aliphatic polyolefin dissolved
therein.
13. A secondary battery according to claim 8, wherein the aliphatic
polyolefin is a saturated hydrocarbon having a carbon chain length
of 6 to 24.
14. A secondary battery according to claim 12, wherein the
aliphatic polyolefin is contained in a concentration smaller than
that of the halogenated polyolefin.
15. A secondary battery having a structure in which a positive
electrode layer and a negative electrode layer are laminated via a
separator and a liquid electrolyte is allowed to be present between
the positive electrode layer and the negative electrode layer, in
which secondary battery the liquid electrolyte is a plastisol
containing an electrolyte salt.
16. A secondary battery according to claim 15, wherein the
plastisol is a dispersion of a halogenated polyolefin in a
plasticizer.
17. A secondary battery according to claim 16, wherein the
halogenated polyolefin is a fluorinated polyolefin.
18. A secondary battery according to claim 16, wherein the
halogenated polyolefin is a copolymer containing
tetrafluoroethylene.
19. A process for producing a secondary battery, which comprises: a
step of laminating a positive electrode layer and a negative
electrode layer via a separator, a step of introducing a plastisol
containing an electrolyte salt, between the positive electrode
layer and the negative electrode layer, a step of applying a
voltage between the positive electrode layer and the negative
electrode layer to heat part of the plastisol, and a step of
cooling the plastisol.
20. A process according to claim 19, wherein the plastisol is a
dispersion of a halogenated polyolefin in a plasticizer.
21. A process according to claim 20, wherein the halogenated
polyolefin is a fluorinated polyolefin.
22. A process according to claim 20, wherein the halogenated
polyolefin is a copolymer containing tetrafluoroethylene.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electrolyte solution, a
secondary battery using the electrolyte solution, and a secondary
battery using a plastisol as a liquid electrolyte.
[0003] 2. Description of the Related Art
[0004] As the market for notebook personal computer, portable
telephone, etc. has expanded rapidly, the requirement for batteries
used therein, having a high output and excellent stability has
increased. To respond to the requirement, there have been developed
secondary batteries which use an alkali metal ion (e.g. lithium
ion) as a charge carrier and utilize an electrochemical reaction
associated with the donation and acceptance of the above ion.
[0005] Such batteries using an alkali metal ion need to use a
non-aqueous electrolyte solution and, therefore, have had a
possibility of reduced battery properties caused by liquid leakage
and vaporization. Hence, there have been used, as the solvent for
the electrolyte solution, high-boiling basic solvents such as
ethylene carbonate, propylene carbonate, diethyl carbonate,
dimethyl carbonate, .gamma.-butyrolactone and the like, singly or
in combination. With these solvents, however, it has been
impossible to completely eliminate the possibility of reduced
battery properties caused by liquid leakage and/or vaporization. A
stable and highly safe electrolyte solution has been required also
for electrochemical apparatuses such as electric double layer
capacitor, electrolytic capacitor, various sensors and the like;
however, no completely satisfactory electrolyte solution has been
developed.
[0006] Secondary batteries using a liquid electrolyte have, in some
cases, a structure in which an active material layer for positive
electrode and an active material layer for negative electrode are
separated by a separator made of a porous film and the resulting
combination of two electrodes and a separator is wound a plurality
of times or piled in a plurality of layers. A liquid electrolyte is
introduced between the positive electrode and the negative
electrode. In such batteries, the film-shaped separator has
functions of (1) preventing the contact of two electrode active
materials with each other and (2), when, for example, an abnormally
large current flows and Joule's heat is generated, melting and
plugging the pores which are the passages of ion. In recent years,
as electronic appliances have become smaller and come to possess a
higher performance, the secondary batteries used therein have
become smaller and come to possess a higher output and a higher
capacity; therefore, when short-circuiting arises in the batteries,
a large current may be generated and may break the film-shaped
separator of battery. In recent years, in response to the
requirement for smaller battery, there has come to be often
employed a thin battery having such a structure that a combination
of a positive electrode active material layer, a negative electrode
active material layer and a separator is wound a plurality of times
and then crushed. In such a battery, however, the separator
receives a large pressure and breaks very easily. The breakage of
separator may invite short-circuiting and make charging impossible,
or may produce firing or fuming. Therefore, in such a battery, it
has been necessary as a measure for possible short-circuiting, to
provide a protective circuit or a fuse at the outside of the
battery. Thus, in secondary batteries which use a liquid
electrolyte and wherein a positive electrode and a negative
electrode are separated from each other by a separator film, there
have been rooms for improvement, as mentioned above.
[0007] Meanwhile, it has been investigated to use a solvent-free
polymer solid electrolyte or a polymer gel electrolyte low in
solvent content, in order to prevent the reduction in battery
properties caused by liquid leakage and vaporization and further
prevent the occurrence of short-circuiting and the firing or fuming
caused by heat generation. In such a battery constitution, no
separator film is required and, therefore, the breakage of
separator film and resultant occurrence of short-circuiting, etc.
can be eliminated. As the polymer solid electrolyte, there are
known those obtained by dissolving a metal salt in a polymer having
a polyether segment (e.g. polyethylene oxide) or in a crosslinking
product of the polymer.
[0008] In U.S. Pat. No. 4,303,748 is disclosed an
electricity-generating device of charge and discharge type, which
uses, as the electrolyte, a solid solution obtained by dissolving
an ionic substance in a polymer having an ethylene oxide main
chain. In JP-A-8-7924 is disclosed an ion-conductive polymer
obtained by crosslinking a polymer having a polyether segment, with
acryloyl group or the like. Further, investigations have been made
on polymer gel electrolytes wherein a polymer is allowed to contain
an organic solvent for improved ionic conductivity. For example, in
JP-B-61-23947 is disclosed a polymer gel electrolyte comprising a
polymer (e.g. polyvinylidene fluoride), a group I or II metal salt
and an organic solvent having solubility for both the polymer and
the metal salt. In U.S. Pat. No. 5,296,318 is disclosed a polymer
gel electrolyte obtained by impregnating a
hexafluoropropylene-vinylidene fluoride copolymer film with a
solution (an organic solvent containing a lithium salt). Also in
JP-A-5-109310 is disclosed a method for producing a complex wherein
an alkali metal-containing solution is infiltrated into the inside
of a crosslinked polymer, by mixing a polymer having a
crosslinkable polyether segment, an alkali metal salt and a solvent
capable of dissolving the metal salt, molding the mixture, and
applying a light, a radiation or the like to the molded material to
give rise to crosslinking. Investigations have also been made on
polymer gel electrolytes using a combination of two or more kinds
of polymers. For example, in JP-A-58-75779 is disclosed a battery
constituted by at least one kind of polymer selected from a
polyvinylidene fluoride, a polymethyl methacrylate and other
particular polymers, a lithium salt, a particular organic solvent,
a metal lithium negative electrode and a positive electrode
consisting of a particular inorganic compound. In JP-A-9-971618 is
disclosed a polymer gel electrolyte obtained by preparing a mixture
or solution of a polymer sparingly soluble in an organic
electrolytic solution and a polymer soluble in the organic
electrolytic solution, making the mixture or solution into a
polymer alloy film, and impregnating the film with the organic
electrolytic solution to give rise to gelation. Therein are shown,
as an example of the polymer sparingly soluble in the organic
electrolytic solution, a polyvinylidene fluoride and, as an example
of the polymer soluble in the organic electrolytic solution, a
polyethylene oxide. In these polymer solid electrolytes and polymer
gel electrolytes, however, as compared with liquid electrolytes,
ionic conductivity is low and it is difficult to obtain a high
output.
[0009] As mentioned above, with a liquid electrolyte, although a
high ionic conductivity is obtained, it is difficult to completely
eliminate the possible liquid leakage and vaporization from the
very small flaws of sealed container. Therefore, in batteries which
use an alkali metal ion as a charge carrier and wherein a positive
electrode and a negative electrode are adjacent via an electrolytic
solution, it has been impossible to completely eliminate the
possible reduction in battery properties, caused by liquid leakage
and vaporization; further, there has been a risk that the separator
film breaks easily and short-circuiting takes place between the
positive electrode and the negative electrode, making charging
impossible and inducing firing or fuming.
[0010] Meanwhile, with polymer solid electrolytes containing no
solvent or with polymer gel electrolytes containing a solvent in a
low concentration, although the risk of short-circuiting is low, no
sufficiently high ionic conductivity is obtained, making it
difficult to obtain a secondary battery of high output.
[0011] In view of the above situation, it is an object of the
present invention to provide a secondary battery which is free from
liquid leakage and vaporization, maintains sufficiently high ionic
conductivity, hardly causes short-circuiting or the like, and is
highly stable.
SUMMARY OF THE INVENTION
[0012] According to the present invention, there is provided an
electrolyte solution consisting of a basic solvent containing an
alkali metal salt and a halogenated polyolefin both dissolved
therein.
[0013] According to the present invention, it is possible to obtain
an electrolyte solution high in ionic conductivity and excellent in
stability and safety. Containing an alkali metal salt and a
halogenated polyolefin both dissolved, the present electrolyte
solution is substantially free from liquid leakage or vaporization
and has high ionic conductivity.
[0014] According to the present invention, there is also provided a
secondary battery using an alkali metal ion as a charge carrier and
having a structure in which a positive electrode and a negative
electrode are adjacent to each other via an electrolyte solution,
in which secondary battery the electrolyte solution consists of a
basic solvent containing an alkali metal salt and a halogenated
polyolefin both dissolved therein.
[0015] Using the above-mentioned electrolyte solution of the
present invention, the above secondary battery has a high output
density and high safety.
[0016] According to the present invention, there is further
provided a secondary battery having a structure in which a positive
electrode layer and a negative electrode layer are laminated via a
separator and a liquid electrolyte is allowed to be present between
the positive electrode layer and the negative electrode layer, in
which secondary battery the liquid electrolyte is a plastisol
containing an electrolyte salt.
[0017] According to the present invention, there is also provided a
process for producing a secondary battery, which comprises:
[0018] a step of laminating a positive electrode layer and a
negative electrode layer via a separator,
[0019] a step of introducing a plastisol containing an electrolyte
salt, between the positive electrode layer and the negative
electrode layer,
[0020] a step of applying a voltage between the positive electrode
layer and the negative electrode layer to heat part of the
plastisol, and
[0021] a step of cooling the plastisol.
[0022] The above secondary battery is characterized in that it uses
a plastisol as a liquid electrolyte. "Plastisol" refers to a
paste-like sol having fluidity, obtained by dispersing a
thermoplastic resin powder in a plasticizer, as defined in, for
example, "New Polymer Dictionary (edited by Polymer
Dictionary-Editing Committee of The Society of Polymer Science,
Japan, published from Asakura Shoten in 1988)". In the plastisol,
the most part of the thermoplastic resin powder is not dissolved
and is dispersed in the plasticizer. When the plastisol is heated
to a certain temperature or higher, the thermoplastic resin powder
dissolves in the plasticizer and, when the plastisol is then
cooled, a polymer gel is formed. This unique property of plastisol
is utilized in the present invention.
[0023] Being a liquid electrolyte, the plastisol has high ionic
conductivity as compared with a gel or solid electrolyte. As
mentioned previously, in secondary batteries using a conventional
liquid electrolyte, Joule's heat is generated when an abnormally
large current flows inside the battery, causing separator'
breakage, etc. In contrast, in the secondary battery of the present
invention using a plastisol which becomes a gel upon generation of
Joule's heat, a polymer gel is formed at the sites where an
abnormally large current flows. By the formation of this polymer
gel, the sites where breakage tends to occur, are reinforced, and
the sites already having breakage are automatically repaired; and
the short-circuiting inside battery can be effectively prevented
when an abnormally large current appears. Thus, in spite of using a
liquid electrolyte, good stability and good safety can be realized
in the present secondary battery.
[0024] Moreover, since the plastisol has a low vapor pressure and a
high viscosity as compared with ordinary liquid electrolytes, there
is neither leakage nor vaporization of electrolytic solution;
therefore, from this point as well can be achieved improvement in
stability and safety.
[0025] The process for production of secondary battery according to
the present invention is characterized in that it uses a plastisol
as a liquid electrolyte and has a step of applying a voltage
between a positive electrode layer and a negative electrode layer
to heat part of the plastisol. In a state that a voltage is applied
between the electrodes, a current density distribution appears in
the separator, microscopically speaking. The sites of high current
density correspond to sites which easily break during the use of
battery; at such sites, Joule's heat appears and the plastisol
becomes a solution. Hence, by conducting cooling after the above
step, a polymer gel is formed selectively at the above sites and
reinforcement of the sites is made. In this case, only part of the
plastisol becomes a polymer gel and the most part of the plastisol
maintains a sol form and constitutes the electrolyte of secondary
battery. The plastisol constituting the electrolyte of secondary
battery functions, as mentioned previously, so as to prevent the
breakage of separator when an abnormally large current flows.
[0026] Thus, the secondary battery produced by the process of the
present invention, using a plastisol as an electrolyte has not only
a self-repairing function but also a function of beforehand
reinforcing sites of separator which may easily break, and can
effectively prevent the breakage of separator which may occur when
an abnormally large current flows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a sectional view showing an example of the
constitution of the secondary battery of the present invention.
[0028] FIG. 2 is a sectional view showing an example of the
constitution of the secondary battery of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] First, description is made on the electrolyte solution
consisting of a basic solvent containing an alkali metal salt and a
halogenated polyolefin both dissolved therein, as well as on the
battery using the electrolyte solution.
[0030] In the present invention, the halogenated polyolefin is a
polyolefin having halogen substituent such as F, Cl, Br or the
like, and is preferably a fluorinated polyolefin such as
polyvinylidene fluoride, polyhexafluoropropylene,
polytetrafluoroethylene or the like from the standpoint of the
stability, and particularly preferably a copolymer containing a
tetrafluoroethylene. In the present invention, the fluorinated
polyolefin includes a copolymer, a graft copolymer and a block
copolymer all containing repeating units of fluorinated olefin, and
composite materials of one of these copolymers and other polymer.
The copolymer containing a tetrafluoroethylene includes a
copolymer, a graft copolymer and a block copolymer all containing
at least repeating units of tetrafluoroethylene, and composite
materials of one of these copolymers and other polymer.
[0031] In the present invention, the basic solvent has no
particular restriction as to the kind as long as it is a
proton-accepting solvent, but a non-aqueous basic solvent is
preferred from the standpoint of the effect of the present
invention. Examples of the basic solvent are ethylene carbonate,
propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl
ethyl carbonate, .gamma.-butyrolactone, N,N'-dimethylformamide,
dimethyl sulfoxide, N-methylpyrrolidone and m-cresol. In the
present invention, these solvents can be used singly or in
combination of two or more kinds.
[0032] The electrolyte solution of the present invention is a
solution of an alkali metal salt and a halogenated polyolefin
dissolved in a basic solvent, and, since being a solution, has a
feature of having high ionic conductivity as compared with gel or
solid electrolytes. Further, the electrolyte solution of the
present invention, as compared with an electrolyte solution
containing no halogenated polyolefin, has about the same ionic
conductivity but has low vapor pressure and high viscosity;
therefore, has a feature of causing substantially no liquid leakage
or vaporization. Hence, in the electrolyte solution of the present
invention, it is necessary that at least part of the halogenated
polyolefin is dissolved completely, and it is preferred that no
part of the halogenated polyolefin is in a gel or solid form. From
this standpoint, the concentration of the halogenated polyolefin is
preferably 0.1 to 20% by weight. When the concentration of the
halogenated polyolefin is smaller than 0.1% by weight, the effect
of reduced vapor pressure and increased viscosity is small. When
the concentration is larger than 20% by weight, gelation or
solidification proceeds easily and it is difficult to obtain
stability. In the present invention, an aliphatic polyolefin may be
used in order to increase the solubility of halogenated polyolefin
and the stability of halogenated polyolefin solution. As the
aliphatic polyolefin, there can be mentioned straight chain or
branched chain saturated or unsaturated hydrocarbon compounds. From
the standpoint of the effect of the present invention, a saturated
hydrocarbon having a carbon chain length of 6 to 24 is preferred.
When the carbon chain length is 5 or smaller, the aliphatic
polyolefin per se has a vapor pressure, reduces the viscosity of
solution, and does not increase the stability of halogenated
polyolefin solution. When the carbon chain length is 25 or larger,
the aliphatic polyolefin allows the electrolyte solution to cause
gelation and have reduced ionic conductivity. A concentration of
the aliphatic polyolefin larger than that of the halogenated
polyolefin impairs the ionic conductivity of electrolyte solution;
therefore, the concentration of the aliphatic polyolefin is
preferably smaller than that of the halogenated polyolefin.
[0033] As to the process for production of the electrolyte solution
of the present invention, there is no particular restriction. The
present electrolyte solution can be produced by adding a basic
solvent to an alkali metal salt and a halogenated polyolefin and
giving rise to dissolution, or by dissolving an alkali metal salt
and a halogenated polyolefin separately in a basic solvent and
mixing the two solutions, or by dissolving a halogenated polyolefin
in a basic solvent and then adding thereto an alkali metal salt.
The electrolyte solution can also be produced by dissolving a
halogenated polyolefin in a low-boiling organic solvent such as
tetrahydrofuran or the like, then adding a high-boiling basic
solvent, and removing the low-boiling solvent alone by vacuum
distillation or the like. In the present invention, there is no
particular restriction, either, as to the method for dissolving the
halogenated polyolefin, etc., and it is possible to use an ordinary
means such as agitating blade, homogenizer or the like. It is also
possible to conduct dissolution while applying an ultrasonic wave
or at a high temperature and a high pressure using an
autoclave.
[0034] The secondary battery of the present invention has a
structure in which at least an positive electrode and a negative
electrode are adjacent via an electrolyte solution, and uses an
alkali metal ion (e.g. Li ion) as a charge carrier. The secondary
battery is characterized in that the electrolyte solution consists
of a basic solvent containing an alkali metal salt and a
halogenated polyolefin both dissolved therein.
[0035] In the secondary battery of the present invention, there is
no particular restriction as to the positive electrode active
material as long as it absorbs positive ion or releases negative
ion during discharge. As the positive electrode active material in
the present invention, there can be used known positive electrode
active materials for secondary battery, such as metal oxide (e.g.
LiMnO.sub.2, LiMn.sub.2O.sub.4, LiCoO.sub.2 or LiNiO.sub.2),
conductive polymer or its derivative (e.g. polyacetylene,
polyaniline, polypyrrole, polythiophene or polyparaphenylene),
disulfide compound represented by general formula
(R--S.sub.m).sub.n (R is an aliphatic or aromatic hydrocarbon; S is
sulfur; m is an integer of 1 or larger; and n is an integer of 1 or
larger) (e.g. dithioglycol, 2,5-dimercapto-1,3,4-thiadiazole or
S-triazine-2,4,6-trithiol), and the like. In the present invention,
the positive electrode active material may be mixed with an
appropriate binder and/or an appropriate functional material to
form a positive electrode. As the binder, there can be mentioned,
for example, a halogen-containing polymer such as polyvinylidene
fluoride or the like. As the functional material, there can be
mentioned a conductive polymer for securing electronic conductivity
(e.g. acetylene black, polypyrrole or polyaniline), a polymer
electrolyte for securing ionic conductivity, a composite material
thereof, etc. In the secondary battery of the present invention,
there is no particular restriction as to the negative electrode
active material as long as it can occlude and release cation. As
the negative electrode active material, there can be used those
negative electrode active materials for secondary battery, such as
natural graphite, crystalline carbon (e.g. graphitized carbon)
obtained by treating coal, petroleum pitch or the like at high
temperatures), amorphous carbon obtained by heat-treating coal,
petroleum pitch coke, acetylene pitch coke or the like, metallic
lithium, lithium alloy (e.g. AlLi) and the like.
[0036] In the secondary battery of the present invention, it is
possible to use a thin-film or reticulate collector composed of
stainless steel, copper, nickel, aluminum or the like. It is also
possible to use, as in conventional batteries, a separator
consisting of a porous thermoplastic resin film or the like,
between the positive electrode and the negative electrode.
[0037] The secondary battery of the present invention can be used
in a form of cylinder, prism, coin, sheet or the like, but the form
is not restricted thereto. There is no particular restriction,
either, as to the process for production of the secondary battery
of the present invention. The present secondary battery can be
produced by a known process for production of secondary battery,
for example, by winding a positive electrode sheet, a separator, a
negative electrode sheet, etc. a plurality of times, inserting the
wound material into a case, dropping thereinto the electrolyte
solution of the present invention, and conducting sealing.
[0038] The electrolyte solution of the present invention is
constituted by a basic solvent containing an alkali metal salt and
a halogenated polyolefin both dissolved therein. Containing a
halogenated polyolefin, the electrolyte solution has a high
viscosity and is high in solvent holdablity, and yet has
sufficiently high ionic conductivity. In the present invention,
therefore, there can be obtained a secondary battery which is low
in the possible reduction in battery properties caused by liquid
leakage and vaporization and further low in internal resistance and
high in output.
[0039] Next, description is made on the embodiment of the present
invention with reference to FIG. 1.
[0040] FIG. 1 shows a general structure of the present secondary
battery using an electrolyte solution consisting of a basic solvent
containing an alkali metal salt and a halogenated polyolefin both
dissolved therein. In FIG. 1, a positive electrode active material
layer 2 and a negative electrode active material layer 3 are
located so as to face each other via an electrolyte solution 1. At
the back side of the positive electrode active material layer 2 is
provided a positive electrode collector 4; at the back side of the
negative electrode active material layer 3 is provided a negative
electrode collector 5; at the side is provided a sealing member 6.
Since the electrolyte solution is a basic solvent containing a
halogenated polyolefin dissolved therein, the battery is low in the
possible reduction in battery properties caused by liquid leakage
and vaporization, low in internal resistance, and high in
output.
[0041] Next, description is made on the secondary battery using a
plastisol and the process for production of the battery.
[0042] An example of the embodiment of the secondary battery using
a plastisol, of the present invention is shown in FIG. 2. In the
secondary battery shown in FIG. 2, a positive electrode layer 12
and a negative electrode layer 13 are laminated via a separator 17,
and a plastisol 11 is filled between the positive electrode layer
12 and the negative electrode layer 13. The plastisol 11 is sealed
by a sealing member 16; at the back sides of the positive electrode
layer 12 and the negative electrode layer 13 are provided a
positive electrode collector 14 and a negative electrode collector
15, respectively. It is preferred that a plastisol is introduced
between a separator and a positive electrode layer and also between
the separator and a negative electrode layer, as in the secondary
battery of FIG. 2; however, the plastisol may be introduced only
between the separator and the positive electrode layer or between
the separator and the negative electrode layer.
[0043] In the present invention, the plastisol is a dispersion of a
thermoplastic resin in a plasticizer. As the thermoplastic resin,
there are preferably used, from the standpoint of, for example, the
stability to the solvent of electrolyte solution, resins containing
a polyolefin having halogen substituent such as F, Cl, Br or the
like, for example, a halogenated polyolefin such as polyvinyl
chloride, polyvinylidene chloride, polyvinylidene fluoride,
polyhexafluoropropylene, polytetrafluoroethylene,
polychlorotrifluoroethylene or the like.
[0044] Of these, preferred are resins containing a fluorinated
polyolefin such as polyvinylidene fluoride, hexafluoropropylene,
polytetrafluoroethylene, polychlorotrifluoroethylene or the like;
particularly preferred is a copolymer containing
tetrafluoroethylene. By using such a resin, the sites of separator
which tends to cause breakage when an abnormally large current
flows, are reinforced quickly; and the sites of separator already
having breakage are repaired quickly. A polymer gel consisting of
the above resin has good resistance to large current. Therefore,
short-circuiting occurring inside the battery can be prevented more
effectively. Incidentally, the "copolymer containing
tetrafluoroethylene" refers to s copolymer containing
tetrafluoroethylene as a constituent monomer, and is a copolymer
obtained by copolymerizing tetrafluoroethylene and other monomer.
In this case, the other monomer is preferred to be also a
fluorine-containing monomer. An example of the copolymer containing
tetrafluoroethylene is a copolymer of vinylidene fluoride and
tetrafluoroethylene.
[0045] In the present invention, it is possible to add, to the
plastisol, additives such as heat stabilizer, viscosity
controlling-agent and the like, as necessary. In the present
invention, it is also possible to use the thermoplastic resin in
combination with a thermosetting resin as necessary, or to
crystallize or crosslink part of the thermoplastic resin for
insolubilization as necessary. In the present invention, there is
no particular restriction as to the plasticizer, and any material
capable of plasticizing the thermosetting resin can be used.
However, a solvent is preferred from the standpoint of easiness of
production of the present secondary battery. Preferred as the
solvent are highly polar basic solvents usable in the electrolytic
solution of secondary battery, such as ethylene carbonate,
propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl
ethyl carbonate, .gamma.-butyrolactone, N,N'-dimethylformamide,
dimethyl sulfoxide, N-methylpyrrolidone, m-cresol and the like. In
the present invention, these basic solvents can be used as the
plasticizer singly or in combination of two or more kinds.
[0046] In the present invention, as the electrolyte salt contained
in the plastisol, there can be used known electrolyte salts for
secondary battery. As the electrolyte salt, there can be mentioned
salts composed of a cation of alkali metal (e.g. Li, K or Na) and
an anion of halogen-containing compound [e.g. C10.sub.4.sup.-,
BF.sub.4.sup.-, PF.sub.6.sup.-, CF.sub.3SO.sub.3.sup.-,
(CF.sub.3SO.sub.2).sub.2N.sup.-,
(C.sub.2F.sub.5SO.sub.2).sub.2N.sup.-,
(CF.sub.3SO.sub.2).sub.3C.sup.- or
(C.sub.2F.sub.5SO.sub.2).sub.3C.sup.-]. In the present invention,
these electrolyte salts can be used singly or in combination of two
or more kinds.
[0047] In the secondary battery of the present invention, there is
no particular restriction as to the positive electrode active
material as long as it absorbs positive ion or releases negative
ion during discharge. As the positive electrode active material in
the present invention, there can be used known positive electrode
active materials for secondary battery, such as metal oxide (e.g.
LiMnO.sub.2, LiMn.sub.2O.sub.4, LiCoO.sub.2 or LiNiO.sub.2),
conductive polymer or its derivative (e.g. polyacetylene,
polyaniline, polypyrrole, polythiophene or polyparaphenylene),
disulfide compound represented by general formula (R--S.sub.m)n (R
is an aliphatic or aromatic hydrocarbon; S is sulfur; m is an
integer of 1 or larger; and n is an integer of 1 or larger) (e.g.
dithioglycol, 2,5-dimercapto-1,3,4-thiadiazole or
S-triazine-2,4,6-trithi- ol), and the like. In the present
invention, the positive electrode active material may be mixed with
an appropriate binder and/or an appropriate functional material to
form a positive electrode. As the binder, there can be mentioned,
for example, a halogen-containing polymer such as polyvinylidene
fluoride or the like. As the functional material, there can be
mentioned a conductive polymer for securing electronic conductivity
(e.g. acetylene black, polypyrrole or polyaniline), a polymer
electrolyte for securing ionic conductivity, a composite material
thereof, etc. In the secondary battery of the present invention,
there is no particular restriction as to the negative electrode
active material as long as it can occlude and release cation. As
the negative electrode active material, there can be used known
negative electrode active materials for secondary battery, such as
natural graphite, crystalline carbon (e.g. graphitized carbon)
obtained by treating coal, petroleum pitch or the like at high
temperatures), amorphous carbon obtained by heat-treating coal,
petroleum pitch coke, acetylene pitch coke or the like, metallic
lithium, lithium alloy (e.g. AlLi) and the like.
[0048] In the secondary battery of the present invention, it is
possible to use a thin-film or reticulate collector composed of
stainless steel, copper, nickel, aluminum or the like. In the
present invention, the above-mentioned positive electrode and
negative electrode are laminated via a separator made of a porous
thermoplastic resin film or the like. As the material for the
separator, there can be used known materials such as polyethylene,
polypropylene and the like.
[0049] In the present invention, there is no particular restriction
as to the method for production of the plastisol containing an
electrolyte salt. The plastisol can be produced by mixing an alkali
metal salt and a thermoplastic resin with a basic solvent, or by
mixing an alkali metal salt and a thermoplastic resin separately
with a basic solvent and mixing the two mixtures, or by dispersing
a thermoplastic resin in a basic solvent and adding thereto an
alkali metal salt, or by allowing a thermoplastic resin to swell
using a low-boiling organic solvent, adding thereto a high-boiling
basic solvent, and removing only the low-boiling organic solvent by
vacuum distillation or the like. In the present invention, there is
no particular restriction, either, as to the method for dispersing
the thermoplastic resin or the like, and an ordinary means such
agitating blade, homogenizer or the like can be used. Dispersion
may also be conducted while applying an ultrasonic wave, or at a
high temperature at a high pressure using an autoclave.
[0050] The secondary battery of the present invention can be
produced by introducing a plastisol containing an electrolyte salt,
at least between a separator and a positive electrode or between
the separator and a negative electrode. After the introduction of
the plastisol, it is preferred to apply a voltage between the
positive electrode layer and the negative electrode layer to heat
part of the plastisol. Thereby, an excess current flows through the
sites of short-circuiting or the sites which may cause
short-circuiting and the plastisol at these sites are melted by the
Joule's heat generated. By cooling, a polymer gel of low ionic
conductivity is formed at the sites of short-circuiting or the
sites which may cause short-circuiting, and these sites are
repaired or reinforced. At the time of voltage application, the
plastisol may be heated as a supplementary means. The heating
temperature is preferably lower than the melting point of the
plastisol, for example, about 30 to 90.degree. C. There is no
particular restriction as to the voltage applied between the
positive electrode and the negative electrode but is, for example,
4 to 10 V.
[0051] In the present invention, as the methods for lamination of
electrodes, taking out of lead, outer packaging, etc., there can be
used those known in the production of secondary battery.
[0052] The secondary battery of the present invention can be used
in a form of cylinder, prism, coin, sheet or the like, but the form
is not restricted thereto. The present secondary battery can be
produced and used by winding or laminating a positive electrode
sheet, a separator, a negative electrode sheet, etc., inserting the
resulting material into a case, dropping thereinto a plastisol
containing an electrolyte salt, and conducting outer packaging with
a known material such as metal case, resin case, laminate film or
the like.
[0053] The detail of the present invention is described
specifically below by way of Examples. However, the present
invention is in no way restricted to these Examples.
EXAMPLE 1
[0054] In a glass vessel was placed 0.115 g, 2.3 g, 5.75 g, 23 g or
34.5 g of a vinylidene fluoride-tetrafluoroethylene copolymer
(Kynar 7201 produced by Elf Atochem Japan, copolymerization
ratio=70/30). Thereto was added 50 ml of tetrahydrofuran. The
mixture was stirred at room temperature for 2 hours to obtain 5
kinds of solutions. To each solution was added 100 g of an ethylene
carbonate-propylene carbonate mixed solution (mixing ratio=50/50).
Each mixture was subjected to vacuum distillation at 65.degree. C.
to remove tetrahydrofuran, whereby were produced 5 kinds of
solutions different in concentration of vinylidene
fluoride-tetrafluoroethylene copolymer. To each solution was added
15 g of LiPF.sub.6, and the mixture was stirred for dissolution to
produce 5 kinds of electrolyte solutions containing 0.1% by weight,
2% by weight, 5% by weight, 20% by weight or 30% by weight of a
vinylidene fluoride-tetrafluoroethylene copolymer.
[0055] In each electrolyte solution consisting of an ethylene
carbonate-propylene carbonate mixture containing LiPF.sub.6 and a
vinylidene fluoride-tetrafluoroethylene copolymer both dissolved
therein were dipped two mirror-polished platinum-blocked electrodes
of 10 mm in diameter. The electrodes were connected to an
electrochemical work station (Model 1604 of CH Instruments), and
the electrolyte solution was measured for ionic conductivity at a
frequency range of 0.1 Hz to 100 KHz at a voltage of 0.1 V. Each
electrolyte solution was also measured for viscosity using a B type
viscometer. Further, in order to examine the degree of leakage of
each electrolyte solution, a filter paper (No. 5A) was fitted to a
Kiriyama funnel; each electrolyte solution was poured into the
funnel; and vacuum filtration was conducted at 1 mmHg for 5 minutes
and the volume of the filtrate obtained was measured. The ionic
conductivity, viscosity and amount of filtrate obtained for each
electrolyte solution are shown in Table 1.
[0056] Of the above 5 kinds of electrolyte solutions, the
electrolyte solution containing 5% by weight of a vinylidene
fluoride-tetrafluoroethy- lene copolymer was used to produce a
secondary battery. First, there were mixed lithium cobaltate having
an average particle diameter of 5 .mu.m, acetylene black, a
polyvinylidene fluoride and N-methyl-2-pyrrolidone at a weight
ratio of 10:1:1:30 to obtain a dispersion. The dispersion was
uniformly coated on one side of an aluminum foil by a wire bar
method, followed by vacuum-drying at 100.degree. C. for 2 hours to
remove the solvent. The thin layer obtained was cut into an
appropriate size to produce a positive electrode layer having a
capacity of about 25 mAh. On this positive electrode layer was
laminated a separator film made of a polyethylene, having a
thickness of 25 .mu.m and a porosity of 50%. On the laminated film
was cast a slurry obtained by mixing a polyvinylidene fluoride,
N-methyl-2-pyrrolidone, a petroleum coke powder and acetylene black
at a weight ratio of 1:30:20:1; the coated slurry was made uniform
by a wire bar method; and vacuum drying was conducted at
100.degree. C. for 2 hours to produce a negative electrode layer.
Then, on the negative electrode layer was placed, as a collector, a
copper foil having the same area as the aluminum foil of positive
electrode; the resulting material was wound a plurality of times
and accommodated in a metal case. Lastly, into the metal case was
dropped the electrolyte solution containing 10% by weight of a
vinylidene fluoride-tetrafluoroethylene copolymer; and the metal
case was sealed with an adhesive to complete a secondary battery.
The secondary battery was subjected to a charge-discharge test. As
a result, the charge-discharge efficiency was 99% or more at a
discharge rate of 2.5 mA and 95% even at a discharge rate of 25 mA.
Further, even at -10.degree. C, a good charge-discharge efficiency
of 60% was obtained at a discharge rate of 2.5 mA. A
charge-discharge test was repeated 100 times at a constant current
of 5 mA between 4.1 V and 2.0 V. As a result, there was
substantially no change in capacity, and good properties were
observed.
Comparative Example 1
[0057] In the same glass vessel as used in Example 1 was placed 100
g of an ethylene carbonate-propylene carbonate mixed solution
(mixing ratio=50/50) alone. Thereto was added 15 g of LiPF.sub.6.
The mixture was stirred for dissolution to produce an electrolyte
solution.
[0058] The electrolyte solution was measured for ionic conductivity
in the same manner as in Example 1. The electrolyte solution was
also measured for viscosity and amount of filtrate. The results are
shown in Table 1 together with the results of Example 1. As
compared with Example 1, the ionic conductivity was about
equivalent, but the viscosity was small and the amount of filtrate
was striking large. Therefore, the secondary battery using the
above electrolyte solution was found to have (1) a high possibility
of liquid leakage when the battery has come to possess flaws in
sealing and (2) inferior safety.
EXAMPLE 2
[0059] Five kinds of solutions containing a vinylidene
fluoride-hexafluoropropylene copolymer (Kynar 2801 produced by Elf
Atochem Japan, copolymerization ratio=90/10) in different
concentrations were produced in the same manner as in Example 1
except that the vinylidene fluoride-tetrafluoroethylene copolymer
used in Example 1 was replaced by the above vinylidene
fluoride-hexafluoropropylene copolymer. In the same manner as in
Example 1, 15 g of LiPF.sub.6 was added to each solution and the
mixture was stirred for dissolution to produce 5 kinds of
electrolyte solutions containing 0.1% by weight, 2% by weight, 5%
by weight, 20% by weight or 30% by weight of a vinylidene
fluoride-hexafluoropropylene copolymer.
[0060] The electrolyte solutions were measured for ionic
conductivity in the same manner as in Example 1. The electrolyte
solutions were also measured for viscosity and amount of filtrate.
The results are shown in Table 1 together with the results of
Example Next, of the above electrolyte solutions, the electrolyte
solution containing 20% by weight of a vinylidene
fluoride-hexafluoropropylene copolymer was used to produce a
secondary battery. First, a positive electrode layer having a
capacity of about 25 mAh was produced in the same manner as in
Example 1. On this positive electrode layer was laminated a
separator film in the same manner as in Example 1, after which a
negative electrode layer was formed in the same manner as in
Example 1. Then, a copper foil was placed on the negative electrode
layer in the same manner as in Example 1. The resulting material
was wound a plurality of times and accommodated in a metal case.
Lastly, into the metal case was dropped the electrolyte solution
containing 20% by weight of a vinylidene fluoride-hexafluoroprop-
ylene copolymer; and the metal case was sealed with an adhesive to
complete a secondary battery. The secondary battery was subjected
to a charge-discharge test. As a result, the charge-discharge
efficiency was 99% or more at a discharge rate of 2.5 mA and 96%
even at a discharge rate of 25 mA. Further, even at -10.degree. C.,
a good charge-discharge efficiency of 75% was obtained at a
discharge rate of 2.5 mA. A charge-discharge test was repeated 100
times at a constant current of 5 mA between 4.1 V and 2.0 V. As a
result, there was substantially no change in capacity, and good
properties were observed.
EXAMPLE 3
[0061] Five kinds of solutions containing a vinylidene
fluoride-chlorotrifluoroethylene copolymer (copolymerization
ratio=90/10) in different concentrations were produced in the same
manner as in Example 1 except that the vinylidene
fluoride-tetrafluoroethylene copolymer used in Example 1 was
replaced by the above vinylidene fluoride-chlorotrifluoroethylene
copolymer. In the same manner as in Example 1, 15 g of LiPF.sub.6
was added to each solution and the mixture was stirred for
dissolution to produce 5 kinds of electrolyte solutions containing
0.1% by weight, 2% by weight, 5% by weight, 20% by weight or 30% by
weight of a vinylidene fluoride-chlorotrifluoroethylene
copolymer.
[0062] The electrolyte solutions were measured for ionic
conductivity in the same manner as in Example 1. The electrolyte
solutions were also measured for viscosity and amount of filtrate.
The results are shown in Table 1 together with the results of
Example Next, of the above electrolyte solutions, the electrolyte
solution containing 20% by weight of a vinylidene
fluoride-chlorotrifluoroethylene copolymer was used to produce a
secondary battery. First, a positive electrode layer having a
capacity of about 25 mAh was produced in the same manner as in
Example 1. On this positive electrode layer was laminated a
separator film in the same manner as in Example 1, after which a
negative electrode layer was formed in the same manner as in
Example 1. Then, a copper foil was placed on the negative electrode
layer in the same manner as in Example 1. The resulting material
was wound a plurality of times and accommodated in a metal case.
Lastly, into the metal case was dropped the electrolyte solution
containing 20% by weight of a vinylidene fluoride-chlorotrifluor-
oethylene copolymer; and the metal case was sealed with an adhesive
to complete a secondary battery. The secondary battery was
subjected to a charge-discharge test. As a result, the
charge-discharge efficiency was 99% or more at a discharge rate of
2.5 mA and 95% even at a discharge rate of 25 mA. Further, even at
-10.degree. C., a good charge-discharge efficiency of 72% was
obtained at a discharge rate of 2.5 mA. A charge-discharge test was
repeated 100 times at a constant current of 5 mA between 4.1 V and
2.0 V. As a result, there was substantially no change in capacity,
and good properties were observed.
EXAMPLE 4
[0063] n-Decane was added, in a concentration of 2% by weight, to
each of the three different electrolyte solutions produced in
Examples 1 to 3, each consisting of an ethylene carbonate-propylene
carbonate mixed solution (mixing ratio=50/50) containing 15 g of
LiPF.sub.6 and 20% by weight of a vinylidene
fluoride-tetrafluoroethylene copolymer, a vinylidene
fluoride-hexafluoropropylene copolymer or a vinylidene
fluoride-chlorotrifluoroethylene copolymer.
[0064] The above-obtained electrolyte solutions were measured for
ionic conductivity in the same manner as in Example 1. The
electrolyte solutions were also measured for viscosity and amount
of filtrate. The results are shown in Table 2.
[0065] Next, the above 3 kinds of electrolyte solutions were used
to produce three kinds of secondary batteries. First, a positive
electrode layer having a capacity of about 25 mAh was produced in
the same manner as in Example 1. On this positive electrode layer
was laminated a separator film in the same manner as in Example 1,
after which a negative electrode layer was formed in the same
manner as in Example 1. Then, a copper foil was placed on the
negative electrode layer in the same manner as in Example 1. The
resulting material was wound a plurality of times and accommodated
in a metal case. Lastly, into the metal case was dropped the
electrolyte solution containing a vinylidene
fluoride-tetrafluoroethy- lene copolymer and n-decane; and the
metal case was sealed with an adhesive to complete a secondary
battery. There were also produced two secondary batteries using a
vinylidene fluoride-hexafluoropropylene copolymer or a vinylidene
fluoride-chlorotrifluoroethylene copolymer in place of the
vinylidene fluoride-tetrafluoroethylene copolymer. The three
secondary batteries were subjected to a charge-discharge test. As a
result, the charge-discharge efficiencies were each 99% or more at
a discharge rate of 2.5 mA and 95% or more even at a discharge rate
of 25 mA. Further, even at -10.degree. C., good charge-discharge
efficiencies of 70% or more were obtained at a discharge rate of
2.5 mA. A charge-discharge test was repeated 100 times at a
constant current of 5 mA between 4.1 V and 2.0 V. As a result,
there was substantially no change in capacity and good properties
were observed, in all the secondary batteries.
[0066] The electrolyte solution of the present invention can be
used as an electrolytic solution not only for secondary battery but
also for electrochemical apparatuses such as primary battery,
electric double layer capacitor, electrolytic capacitor, various
sensors and the like.
1 TABLE 1 Polymer Ionic concen- conduc- Vis- Amount of tration
tivity cosity filtrate Polymer (wt. %) (mS/cm) (cps) (wt. %)
Example 1 Vinylidene 0.1 12.1 180 23 fluoride- 2 12.3 340 18
tetrafluoro- 5 12.1 410 15 ethylene 20 10.5 1600 5 copolymer 30 7.5
3500 5 Example 2 Vinylidene 0.1 12.5 220 18 fluoride- 2 11.2 480 19
hexafluoro- 5 12.3 800 12 propylene 20 11.5 3500 4 copolymer 30 8.8
7000 3 Example 3 Vinylidene 0.1 12.8 200 20 fluoride- 2 12.0 400 16
chlorotri- 5 11.9 650 13 fluoroethylene 20 9.2 1900 5 copolymer 30
6.8 4500 5 Comparative Not used 0 13.2 150 45 Example 1
[0067]
2TABLE 2 Ionic conductivity Viscosity Amount of Polymer (mS/cm)
(cps) filtrate (wt. %) Vinylidene fluoride- 10.5 1800 2
tetrafluoroethylene copolymer Vinylidene fluoride- 11.5 4100 2
hexafluoropropylene copolymer Vinylidene fluoride- 9.2 2200 2
chlorotrifluoroethylene copolymer
EXAMPLE 5
[0068] In a glass vessel was placed 0.115 g, 2.3 g, 5.75 g, 23 g or
34.5 g of a vinylidene fluoride-tetrafluoroethylene copolymer
powder (Kynar 7201 produced by Elf Atochem Japan, copolymerization
molar ratio=70/30). Thereto was added 100 g of an ethylene
carbonate-propylene carbonate mixed solution (mixing ratio=50/50).
Each mixture was stirred to produce 5 kinds of plastisols
containing a vinylidene fluoride-tetrafluoroethylen- e copolymer in
a dispersed form. To each plastisol was added 15 g of LiPF.sub.6,
and the mixture was stirred for dissolution to produce 5 kinds of
electrolyte plastisols containing 0.1% by weight, 2% by weight, 5%
by weight, 20% by weight or 30% by weight of a vinylidene
fluoride-tetrafluoroethylene copolymer.
[0069] In each electrolyte plastisol produced above were dipped two
mirror-polished platinum-blocked electrodes of 10 mm in diameter.
The electrodes were connected to an electrochemical work station
(Model 1604 of CH Instruments), and the electrolyte plastisol was
measured for ionic conductivity at a frequency range of 0.1 Hz to
100 KHz at a voltage of 0.1 V. The results obtained are shown in
Table 3.
3 TABLE 3 Polymer Ionic concentration conductivity Polymer (wt. %)
(mS/cm) Example 5 Vinylidene 0.1 13.2 fluoride- 2 13.1 tetrafluoro-
5 12.9 ethylene 20 12.9 copolymer 30 12.6 Example 6 Vinylidene 0.1
13.0 fluoride- 2 12.5 hexafluoro- 5 12.1 propylene 20 11.8
copolymer 30 11.5 Example 7 Vinylidene 0.1 13.2 fluoride- 2 13.0
chlorotri- 5 12.8 fluoroethylene 20 12.0 copolymer 30 12.1
Comparative Not used 0 13.2 Example 2
[0070] Of the above 5 kinds of electrolyte plastisols, the
electrolyte plastisol containing 5% by weight of a vinylidene
fluoride-tetrafluoroeth- ylene copolymer was used to produce a
secondary battery. First, there were mixed lithium cobaltate having
an average particle diameter of 5 .mu.m, acetylene black, a
polyvinylidene fluoride and N-methyl-2-pyrrolidone at a weight
ratio of 10:1:1:30 to obtain a dispersion. The dispersion was
uniformly coated on one side of an aluminum foil by a wire bar
method, followed by vacuum-drying at 100.degree. C. for 2 hours to
remove the solvent. The thin layer obtained was cut into an
appropriate size to produce a positive electrode layer having a
capacity of about 25 mAh. On this positive electrode layer was
laminated a separator film having a thickness of 25 .mu.m and a
porosity of 50%, made of a polyethylene having, at various
locations, holes of 0.1 mm in diameter forcibly formed as flaws. On
the laminated film was cast a slurry obtained by mixing a
polyvinylidene fluoride, N-methyl-2-pyrrolidone, a petroleum coke
powder and acetylene black at a weight ratio of 1:30:20:1; the
coated slurry was made uniform by a wire bar method; and vacuum
drying was conducted at 100.degree. C. for 2 hours to produce a
negative electrode layer. Then, on the negative electrode layer was
placed, as a collector, a copper foil having the same area as the
aluminum foil of positive electrode; the resulting material was
wound a plurality of times and accommodated in a metal case.
Thereafter, into the metal case was dropped the electrolyte
plastisol containing 5% by weight of a vinylidene
fluoride-tetrafluoroeth- ylene copolymer; and the metal case was
sealed with an adhesive to complete a secondary battery. Lastly,
the secondary battery was heated to 80.degree. C. and kept for 1
hour while applying a voltage of 4.3 V. The resulting secondary
battery was subjected to a charge-discharge test. As a result, the
charge-discharge efficiency was 99% or more at a discharge rate of
2.5 mA and 95% even at a discharge rate of 25 mA. Further, even at
-10.degree. C., a good charge-discharge efficiency of 60% was
obtained at a discharge rate of 2.5 mA. A charge-discharge test was
repeated 100 times at a constant current of 5 mA between 4.1 V and
2.0 V. As a result, there was substantially no change in capacity,
and good properties were observed. In this battery there was
observed neither incomplete voltage increase during charging nor
phenomenon (e.g. self-discharging) which seemed to be caused by
partial short-circuiting.
Comparative Example 2
[0071] In the same glass vessel as used in Example 5 was placed 100
g of an ethylene carbonate-propylene carbonate mixed solution
(mixing ratio=50/50) alone. Thereto was added 15 g of LiPF.sub.6.
The mixture was stirred for dissolution to produce an electrolyte
solution.
[0072] The electrolyte solution was measured for ionic conductivity
in the same manner as in Example 5. A positive electrode layer was
produced in the same manner as in Example 5. On this positive
electrode layer was laminated a separator film of 25 .mu.m in
thickness and 50% in porosity, made of a polyethylene having, at
various locations, holes of 0.1 mm in diameter forcibly formed as
flaws. Then, a negative electrode layer and a collector were formed
and the resulting material was wound a plurality of times and
accommodated in a metal case, in the same manner as in Example 5.
Thereafter, into the metal case was dropped the electrolyte
solution produced above, containing no vinylidene
fluoride-tetrafluoroethylene copolymer, and the metal case was
sealed with an adhesive to complete a secondary battery. This
secondary battery was subjected to a charge-discharge test. When
charging was conducted at a constant current of 2.5 mA, the voltage
did not increase to 4.1 V or higher and self-discharging was high;
therefore, the presence of internal short-circuiting was
predicted.
EXAMPLE 6
[0073] Five kinds of electrolyte plastisols containing 0.1% by
weight, 2% by weight, 5% by weight, 20% by weight or 30% by weight
of a vinylidene fluoride-hexafluoropropylene copolymer (Kynar 2801
produced by Elf Atochem Japan, copolymerization molar ratio=90/10)
were produced in the same manner as in Example 5 except that the
vinylidene fluoride-tetrafluoroethylene copolymer used in Example 5
was replaced by the above vinylidene fluoride-hexafluoropropylene
copolymer. In the same manner as in Example 5, 15 g of LiPF.sub.6
was added to each plastisol and the mixture was stirred for
dissolution to produce 5 kinds of electrolyte plastisols.
[0074] The electrolyte plastisols were measured for ionic
conductivity in the same manner as in Example 5. Of the above 5
kinds of electrolyte plastisols, the electrolyte plastisol
containing 20% by weight of a vinylidene
fluoride-hexafluoropropylene copolymer was used to produce a
secondary battery. First, a positive electrode layer was produced
in the same manner as in Example 5. On this positive electrode
layer was laminated a separator film having a thickness of 25 .mu.m
and a porosity of 50%, made of a polyethylene having, at various
locations, holes of 0.1 mm in diameter forcibly formed as flaws. A
negative electrode layer and a collector were produced in the same
manner as in Example 5, and the resulting material was wound a
plurality of times and accommodated in a metal case. Thereafter,
into the metal case was dropped the electrolyte plastisol
containing 20% by weight of a vinylidene
fluoride-hexafluoropropylene copolymer; and the metal case was
sealed with an adhesive to complete a secondary battery. Lastly,
the secondary battery was heated to 80.degree. C. and kept for 1
hour while applying a voltage of 4.3 V. The resulting secondary
battery was subjected to a charge-discharge test. As a result, the
charge-discharge efficiency was 99% or more at a discharge rate of
2.5 mA and 95% even at a discharge rate of 25 mA. Further, even at
-10.degree. C, a good charge-discharge efficiency of 60% was
obtained at a discharge rate of 2.5 mA. A charge-discharge test was
repeated 100 times at a constant current of 5 mA between 4.1 V and
2.0 V. As a result, there was substantially no change in capacity,
and good properties were observed. In this battery there was
observed neither incomplete voltage increase during charging nor
phenomenon (e.g. self-discharging) which seemed to be caused by
partial short-circuiting.
EXAMPLE 7
[0075] Five kinds of electrolyte plastisols containing 0.1% by
weight, 2% by weight, 5% by weight, 20% by weight or 30% by weight
of a vinylidene fluoride-chlorotrifluoroethylene copolymer
(copolymerization molar ratio=90/10) were produced in the same
manner as in Example 5 except that the vinylidene
fluoride-tetrafluoroethylene copolymer used in Example 5 was
replaced by the above vinylidene fluoride-chlorotrifluoroethylene
copolymer. In the same manner as in Example 5, 15 g of LiPF.sub.6
was added to each plastisol and the mixture was stirred for
dissolution to produce 5 kinds of electrolyte plastisols.
[0076] The electrolyte plastisols were measured for ionic
conductivity in the same manner as in Example 5. Of the above 5
kinds of electrolyte plastisols, the electrolyte plastisol
containing 20% by weight of a vinylidene
fluoride-chlorotrifluoroethylene copolymer was used to produce a
secondary battery. First, a positive electrode layer was produced
in the same manner as in Example 5. On this positive electrode
layer was laminated a separator film having a thickness of 25 .mu.m
and a porosity of 50%, made of a polyethylene having, at various
locations, holes of 0.1 mm in diameter forcibly formed as flaws. A
negative electrode layer and a collector were produced in the same
manner as in Example 5, and the resulting material was wound a
plurality of times and accommodated in a metal case. Thereafter,
into the metal case was dropped the electrolyte plastisol
containing 20% by weight of a vinylidene
fluoride-chlorotrifluoroethylene copolymer; and the metal case was
sealed with an adhesive to complete a secondary battery. Lastly,
the secondary battery was heated to 80.degree. C. and kept for 1
hour while applying a voltage of 4.3 V. The resulting secondary
battery was subjected to a charge-discharge test. As a result, the
charge-discharge efficiency was 99% or more at a discharge rate of
2.5 mA and 95% even at a discharge rate of 25 mA. Further, even at
-10.degree. C., a good charge-discharge efficiency of 60% was
obtained at a discharge rate of 2.5 mA. A charge-discharge test was
repeated 100 times at a constant current of 5 mA between 4.1 V and
2.0 V. As a result, there was substantially no change in capacity,
and good properties were observed. In this battery there was
observed neither incomplete voltage increase during charging nor
phenomenon (e.g. self-discharging) which seemed to be caused by
partial short-circuiting.
[0077] The electrolyte plastisol used in the secondary battery of
the present invention can be utilized as an electrolyte for primary
battery, electric double layer capacitor, electrolytic capacitor,
various sensors, etc.
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