JPH11306859A - Manufacture of polymer solid electrolyte, polymer solid electrolyte, lithium secondary battery and electric double layer capacitor using the same, and their manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a polymer solid electrolyte capable of producing even battery element bodies on the atmosphere, and having reliability, improved safety, and high conductivity, and to provide a polymer solid electrolyte, a lithium secondary battery and an electric double layer capaci tor using it. SOLUTION: This polymer solid electrolyte is manufactured by including imidazolium salt represented by the formula and lithium salt in the matrix of a fluoric high polymer compound on the atmosphere. In the formula, R1 , R2 and R3 respectively represents an alkyl or a hydrogen atom, and A<-> represents one of (RSO2 )3 C<-> , (RSO2 )2 N- , RSO3 <-> , BF4 <-> , PF6 <-> , AsF6 <-> , and ClO4 <-> . R represents a perfluoroalkyl having 1-3 carbons, and when there are plural Rs, they may be identical with each other or may be different from each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid polymer electrolyte, and a lithium secondary battery and an electric double layer capacitor using the same.

[0002]

2. Description of the Related Art In recent years, demand for secondary batteries has been steadily expanding from large industrial batteries to small consumer batteries.
2. Description of the Related Art As electronic devices have become smaller, lighter, and more sophisticated due to advances in electronics, development of secondary batteries having both high energy density and long cycle life has been desired.

[0003] Liquids are generally used as the electrolyte of currently used batteries. However, if the electrolyte can be made solid, the solidification of the battery can be achieved, and liquid leakage can be prevented and a sheet structure can be formed. Becomes For this reason, batteries using solid electrolytes have attracted attention as next-generation batteries.
In particular, if all-solidification of lithium-ion secondary batteries and the like, which are now widely used in notebook computers and mobile phones, is realized, not only small batteries but also secondary batteries for power load leveling, It is expected that application development will be accelerated even for large batteries such as secondary batteries for electric vehicles.

When such a solid electrolyte is used, a ceramic material, a polymer material, or a composite material thereof has been proposed. Above all, a gel electrolyte plasticized using a polymer electrolyte and an electrolyte solution has both high liquid-based electrical conductivity and high polymer-based plasticity, and is considered promising as a solid electrolyte.

An example in which a gel polymer solid electrolyte is used in a battery has been disclosed, and US Pat. No. 5,296,3.
No. 18, No. 5,418,091 and the like also provide practical systems.

Some of such gel-like polymer solid electrolytes (hereinafter, referred to as “gel electrolytes”) have a conductivity close to that of a liquid and exhibit a value of 10 ⁻³ S · cm ⁻¹ level.

For example, US Pat. No. 5,296,318 discloses a copolymer of vinylidene fluoride (VDF) and 8 to 25% by weight of propylene hexafluoride (HFP) [P
(VDF-HFP)] discloses a gel electrolyte containing 20 to 70% by weight of a solution in which a lithium salt is dissolved. The conductivity of this gel electrolyte reaches 10 ⁻³ S · cm ⁻¹ .

[0008] However, such a gel electrolyte is
Since it contains the same electrolytic solution as in the solution system, liquid leakage is likely to occur, and the organic solvent tends to volatilize from the gel electrolyte, thus lacking long-term reliability. Further, since the organic solvent is flammable, there is a problem in safety, though not as much as in the solution system.

Furthermore, since the incorporation of moisture into the organic electrolyte significantly deteriorates the battery characteristics, the production of the gel electrolyte must be carried out in a special environment in which moisture is controlled such as a dew point minus several tens of degrees. When manufacturing a gel electrolyte industrially, it is necessary to maintain all processes in a dry atmosphere, which requires a large amount of capital investment and maintenance cost, and inventory management in the process is not easy. There is a demand for a high-performance gel electrolyte that can be produced with low-cost equipment and has high productivity, and a method for producing the same.

Attempts have also been made to use molten salts as electrolytes.

For example, a complex of an aromatic quaternary ammonium halide such as N-butylpyridinium and an aluminum halide has been proposed (Takahashi, Electrochemistry, 59).
Vol. 14, p. 1991). However, this has the problem of corrosion by halide ions. There is also a problem with stability.

JP-A-8-245493 discloses a room-temperature molten salt obtained by mixing an aliphatic quaternary ammonium salt of an organic carboxylic acid and a lithium salt. But,
This product can also be produced only in a special environment in which moisture is controlled such as in a nitrogen atmosphere. Furthermore, the ionic conductivity is 10 ⁻⁴ S · cm ⁻¹ or less, which is too low for practical use.

Further, as an electrolyte, a polymer compound composite obtained by solidifying a room temperature molten salt with a polymer compound has been proposed.

For example, N which is known as a room temperature molten salt
-Immobilization of a complex of butylpyridinium halide and aluminum halide with a polymer compound has been proposed (Watanabe et al., JCSChem. Commun., 929, 199).
3). However, this has the problem of corrosion by halide ions. There is also a problem with stability.

JP-A-8-245828 discloses a polymer compound complex obtained by solidifying a room temperature molten salt comprising a mixture of an aliphatic quaternary ammonium salt of an organic carboxylic acid and a lithium salt with a polymer compound. Have been. However, this can also be produced only in a special environment where moisture is controlled such as in a nitrogen atmosphere. Furthermore, the ionic conductivity is 10 ⁻⁴ S · cm ⁻¹ or less, which is too low for practical use.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a solid polymer electrolyte having higher reliability, higher safety, and higher electric conductivity, which can produce a battery element in the air. And a lithium secondary battery and an electric double layer capacitor using the same.

[0017]

This and other objects are achieved by the present invention described below. (1) A polymer solid electrolyte obtained by mixing an imidazolium salt and a lithium salt represented by the following general formula (I) in a matrix of a fluorine-based polymer compound in the atmosphere to obtain a polymer solid electrolyte Production method.

[0018]

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(In the general formula (I), R ₁ , R ₂ and R ₃ each represent an alkyl group or a hydrogen atom, and A ⁻ represents (RSO ₂ ) ₃ C ⁻ , (RSO ₂ ) ₂ N ⁻ , RSO ₃ ^- , B
Represents any of F ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ and ClO ₄ ⁻ , and R represents a perfluoroalkyl group having 1 to 3 carbon atoms, and when a plurality of Rs are present, they may be the same or different from each other . (2) The lithium salt is LiC (RSO ₂ ) ₃ , LiN
(RSO ₂ ) ₂ , LiRSO ₃ , (R represents a perfluoroalkyl group having 1 to 3 carbon atoms and may be the same or different when a plurality of Rs exist.) LiBF ₄ , LiPF ₆ , LiAsF ₆ and LiClO ₄
The method for producing a solid polymer electrolyte according to the above (1), which is at least one of the above. (3) The method for producing a solid polymer electrolyte according to the above (1) or (2), wherein the fluorine-based polymer compound is a homopolymer or a copolymer of vinylidene fluoride. (4) The method for producing a solid polymer electrolyte according to any one of the above (1) to (3), wherein a mixing ratio of the imidazolium salt and the lithium salt is 10: 1 to 1: 2 in molar ratio. (5) The method for producing a solid polymer electrolyte according to any one of the above (1) to (4), wherein the fluorine-based polymer compound is formed into a microporous film. (6) A solid polymer electrolyte produced by the method for producing a solid polymer electrolyte according to any one of the above (1) to (5). (7) A lithium secondary battery having the polymer solid electrolyte according to (6). (8) The method for producing a lithium secondary battery according to (7), wherein the battery element having the solid polymer electrolyte and the electrode according to (6) is produced in the air, and then water is removed. (9) An electric double layer capacitor having the polymer solid electrolyte according to (6). (10) The method for producing an electric double layer capacitor according to the above (8), wherein the electric double layer capacitor comprising the polymer solid electrolyte and the electrode according to the above (6) is produced in the atmosphere, and then water is removed.

[0020]

According to the process for producing a solid polymer electrolyte of the present invention, an imidazolium salt and a lithium salt represented by the following general formula (I) are contained in a matrix of a fluoropolymer compound in the atmosphere. To obtain a solid polymer electrolyte. The imidazolium molten salt is stable even in a water-containing atmosphere, has a negligible vapor pressure at room temperature, and has a high boiling point / decomposition temperature. After producing a battery element in which these are combined in the air, the water can be removed by heating under reduced pressure and drying. As a result, the manufacturing process of batteries and the like can be significantly simplified, which is industrially very advantageous.

Further, since the polymer solid electrolyte to be produced is a gel electrolyte, it has characteristics of an all-solid-state battery or an electric double layer capacitor such as prevention of liquid leakage and formation of a sheet.

This polymer solid electrolyte is composed of a conventional electrolytic solution,
That is, since it does not contain an organic solvent, there is no problem such as liquid leakage or volatilization, and reliability and durability are high. Further, there is no problem of corrosion as in aluminum halide which is conventionally known as a component of a room temperature molten salt.

Moreover, the molten salt using the imidazolium salt is stable as compared with other compounds, in addition to containing no flammable component. Therefore, the electrolyte is nonflammable and has high safety.

The electric conductivity of the solid polymer electrolyte of the present invention is 10 ⁻⁴ to 10 ⁻² S · cm ⁻¹ , which is equivalent to that of a conventional gel electrolyte and that is close to that of a liquid.

The present inventors have already proposed using a mixture of a polymer of an imidazolium derivative and a lithium salt (lithium bis (trifluoromethanesulfonimide)) for the electrolyte (October 1997; Molecular Symposium). However, at present, this electrolyte has an ionic conductivity of about 10 ⁻⁴ S · cm ⁻¹ or less. In order to be put to practical use in the future, a thin film or further improvement in conductivity is left as an issue. ing.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a solid polymer electrolyte according to the present invention is characterized in that an imidazolium salt represented by the following general formula (I) and a lithium salt To obtain a solid polymer electrolyte.

[0027]

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In the general formula (I), R ₁ , R ₂ and R
₃ each represent an alkyl group or a hydrogen atom, A ^- is ^{_{(RSO 2) 3 C -,}} (RSO 2) 2 N -, RSO 3 -, B
Represents any of F ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ and ClO ₄ ⁻ . R represents a C1-C3 perfluoroalkyl group, and when two or more R exist, they may be mutually the same or different.

The imidazolium molten salt can very well impregnate the fluoropolymer compound. Therefore, a highly reliable and safer battery that does not contain a conventional electrolytic solution can be manufactured. Further, the molten salt using this imidazolium salt is more stable than other compounds. Therefore, it is nonflammable as an electrolyte and has high safety.

First, the imidazolium salt used in the present invention will be described.

In the general formula (I), R ₁ , R ₂ and R
₃ represents an alkyl group or a hydrogen atom, respectively. The alkyl group preferably has a total of 1 to 5 carbon atoms, particularly preferably a total of 1 to 3 carbon atoms, and more preferably a methyl group or an ethyl group. The alkyl group may be linear or branched.

Preferably, at least one of R _{1 to} R ₃ is an alkyl group. In particular, it is preferable that R ₁ and R ₃ are an alkyl group, and R ₂ is a hydrogen atom. R _{1 to} R ₃
May be the same or different.

[0033] A ^- is ^{_{(RSO 2) 3 C -,}} (RSO 2)
_{^{2 N -, RSO 3 -,}} BF 4 -, PF 6 -, AsF 6 - and Cl
O ₄ ^- is either. R represents a perfluoroalkyl group having 1 to 3 carbon atoms. R is preferably a perfluoromethyl group. When a plurality of Rs are present, they may be the same or different.

[0034] A ^- The _{particularly, (CF 3 SO 2) 2} N -
Is particularly preferred.

Hereinafter, specific examples of the imidazolium salt represented by the general formula (I) will be shown, but the present invention is not limited thereto. In addition, Chemical formula 4, Chemical formula 5, Chemical formula 6, Chemical formula 7 are represented using the notation of the general formula (I) of Chemical formula 3.

[0036]

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[0037]

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[0038]

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[0039]

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Of these, a so-called asymmetric imidazolium salt in which R ₁ and R ₃ are different is particularly preferred.

The imidazolium salt is obtained from JSWilkes et al.,
J. Chem. Soc., Chem. Commun., 965, 1992, VRKoch et a
l., J. Electrochem. Soc., 142 , L116, 1995, VRKoch
etal., J. Electrochem. Soc., 143 , 798, 1996 and the like.

The solid polymer electrolyte of the present invention is obtained by containing a lithium salt together with the above-mentioned imidazolium salt in a matrix of a fluoropolymer compound.

The lithium salt is LiC (RSO ₂ ) ₃ , Li
N (RSO ₂ ) ₂ , LiRSO ₃ , LiBF ₄ , LiP
It is preferable to use F ₆ , LiAsF ₆ and LiClO ₄ . R represents a perfluoroalkyl group having 1 to 3 carbon atoms. R is preferably a perfluoromethyl group. When a plurality of Rs are present, they may be the same or different.

As the lithium salt, LiN (CF
₃ SO ₂ ) ₂ is preferred.

As the lithium salt, one kind may be used alone, or two or more kinds may be used in combination. When two or more kinds are used in combination, the mixing ratio is arbitrary.

The mixing ratio of the imidazolium salt and the lithium salt is from 10: 1 to 1: 2, especially from 4: 1 to 1:
It is preferably 1. If the amount of the imidazolium salt is larger than this, the melting point becomes high and it is not practical.
If the amount of the lithium salt is smaller than this, the lithium ion conductivity is lowered, and it is not practical.

The solid polymer electrolyte obtained in the present invention is obtained by impregnating a fluoropolymer compound with an imidazolium salt and a lithium salt.

Examples of the fluorine-based polymer compound include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-ethylene trifluoride chloride (CTFE) copolymer [P (VDF
-CTFE)], vinylidene fluoride-hexafluoropropylene fluororubber, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene fluororubber [P
(VDF-TFE-HFP)], vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether fluororubber, and the like. These vinylidene fluoride (VDF) polymers preferably have a vinylidene fluoride content of 50% by weight or more, especially 70% by weight or more. Among them, polyvinylidene fluoride, a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), a copolymer of vinylidene fluoride and ethylene chloride trifluoride [P (VDF-CTFE)] Is particularly preferred. By making it a copolymer, the crystallinity becomes low,
It becomes easy to impregnate the room temperature molten salt, and it becomes easy to hold it.

The VDF-CTFE copolymer is available from, for example, Central Glass Co., Ltd. under the trade name “Sefuralsoft (G15).
0, G180) ”from Solvay Japan Limited under the trade name“ Solef 31508 ”. In addition, VDF-HFP copolymers are trade names “KynarFlex2750 (VDF: HFP = 85: 15wt%)” and “KynaFlex
rFlex2801 (VDF: HFP = 90: 10wt%) ”and other product names from Solvay Japan Ltd.“ Solef 11008 ”,“ Solef 1 ”
1010 "," Solef 21508 "," Solef 2151 "
0 "and the like.

Next, a method for producing a solid polymer electrolyte will be described. The production takes place in the atmosphere, unlike conventional ones. Since the incorporation of water into the organic electrolyte significantly deteriorates the battery characteristics, the conventional gel electrolyte requires 5 pp of water for all processes.
It had to be done in a special environment of less than m.
Since the imidazolium molten salt is stable in the atmosphere containing water and has a high boiling point / decomposition temperature, the gel electrolyte of the present invention produces a polymer solid electrolyte, an electrode, and a battery element body combining these in the atmosphere. After that, moisture can be removed by heating under reduced pressure. As a result, the manufacturing process of batteries and the like can be significantly simplified, which is industrially very advantageous.

First, a polymer compound is dissolved in a solvent.
The solvent at this time may be appropriately selected from various solvents in which the polymer can be dissolved, and for example, acetone, tetrahydrofuran, methyl acetate and the like are preferably used. The concentration of the polymer in the solvent is preferably 5 to 40% by weight. In the dissolution method, it is preferable to stir while heating to room temperature or 100 ° C. or lower.

Then, a room temperature molten salt is added to the polymer solution. The content of the room temperature molten salt composed of the imidazolium salt and the lithium salt is as follows: polymer: room temperature molten salt = 5 by weight ratio.
0:50 to 20:80 is preferred.

A mixed solution of a polymer solution and a room temperature molten salt (referred to as “gel electrolyte solution”) is applied on a substrate. This substrate may be any smooth material. For example, polyester film, glass, polytetrafluoroethylene film and the like can be mentioned. The means for applying the gel electrolyte solution to the substrate is not particularly limited, and may be appropriately determined according to the material and shape of the substrate. Generally, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a screen printing method, and the like are used. Thereafter, if necessary, a rolling treatment is performed by a flat plate press, a calender roll, or the like.

Then, the solvent in which the polymer was dissolved is evaporated to obtain a gel electrolyte film. The temperature at which the solvent is evaporated may be room temperature, but may be heated.

The room temperature molten salt may be mixed at the time of preparing the gel electrolyte solution as described above. Alternatively, a film not containing the room temperature molten salt may be prepared in advance and then impregnated with the room temperature molten salt.

In order to increase film strength and swelling property,
A filler such as silica or alumina may be added to the gel electrolyte. There is no particular limitation on the material, particle size, shape, and filling amount of the filler to be added, but the ionic conductivity of the solid electrolyte decreases with the filling amount.
% Is preferable.

The polymer compound is preferably formed into a microporous film by a known method. For example, US Pat. No. 5,418,
No. 091, a method of adding a plasticizer to a polymer solution, applying this to a substrate, and then evaporating the solvent to form a microporous film may be used. Alternatively, a microporous film may be formed by using a swellable polymer film and impregnating with a room temperature molten salt. Other methods include using a polymer blend exhibiting sea-island type phase separation, making a hole with a needle, or applying an electron beam.

The pore diameter of the polymer microporous membrane is 0.005 to 5
μm, particularly preferably 0.01 to 0.5 μm. A film having a porosity in the range of 20 to 90%, particularly 35 to 70% is practically preferable.

The thickness of the solid polymer electrolyte of the present invention is usually 5 to 200 μm.

The thus obtained solid polymer electrolyte of the present invention has an electric conductivity of 10 ⁻⁴ to 10 ⁻² S · cm ⁻¹ , which is equivalent to that of a conventional gel electrolyte and close to that of a liquid.

The structure of the lithium secondary battery using the gel electrolyte of the present invention is not particularly limited, but is applied to a stacked battery, a cylindrical battery and the like.

The electrode combined with the gel electrolyte is
Preferably, a composition of an electrode active material, a gel electrolyte, and if necessary, a conductive additive is used.

For the negative electrode, a negative electrode active material such as a carbon material, lithium metal, lithium alloy or oxide material is used. For the positive electrode, an oxide or carbon material capable of intercalating / deintercalating lithium ions is used. It is preferable to use such a positive electrode active material as described above. By using such an electrode, a lithium secondary battery having excellent characteristics can be obtained.

The carbon material used as the electrode active material may be appropriately selected from, for example, mesocarbon microbeads (MCMB), natural or artificial graphite, resin fired carbon material, carbon black, carbon fiber and the like. These are used as powders. Above all, graphite is preferred, and its average particle size is preferably 1 to 30 μm, particularly preferably 5 to 25 μm.

As the oxide capable of intercalating / deintercalating lithium ions, a composite oxide containing lithium is preferable. For example, LiCoO ₂ , LiM
_{n 2 O 4, LiNiO 2,} LiV 2 O 4 and the like.
The average particle diameter of these oxide powders is preferably about 1 to 40 μm.

A conductive assistant is added to the electrode as necessary. Preferred examples of the conductive auxiliary agent include metals such as graphite, carbon black, carbon fiber, nickel, aluminum, copper, and silver. Particularly, graphite and carbon black are preferable.

The electrode composition of the positive electrode is as follows: active material: conductive auxiliary agent: gel electrolyte = 30 to 90: 3 to 10: 1 by weight.
The range of 0 to 70 is preferable. In the negative electrode, active material: conductive auxiliary agent: gel electrolyte = 30 to 90: 0 to 10: 1 by weight ratio.
A range from 0 to 70 is preferred.

In the present invention, the above-mentioned negative electrode active material and / or positive electrode active material, preferably both active materials, are preferably mixed in the above-mentioned gel electrolyte and adhered to the surface of the current collector.

In the production of the electrode, first, an active material and, if necessary, a conductive auxiliary are dispersed in a gel electrolyte solution to prepare a coating solution.

Then, this electrode coating solution is applied to the current collector. The means for applying is not particularly limited, and may be determined as appropriate according to the material and shape of the current collector. Generally, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a screen printing method, and the like are used.
Thereafter, if necessary, a rolling treatment is performed by a flat plate press, a calender roll, or the like.

The current collector may be appropriately selected from ordinary current collectors according to the shape of the device used by the battery, the method of disposing the current collector in the case, and the like. Generally, aluminum or the like is used for the positive electrode, and copper, nickel, or the like is used for the negative electrode.
Note that a metal foil, a metal mesh, or the like is generally used as the current collector. Although the metal mesh has a smaller contact resistance with the electrode than the metal foil, in the case of the gel electrolyte of the present invention, the metal foil has a sufficiently small contact resistance.

Then, the solvent is evaporated to form an electrode. The coating thickness is preferably about 50 to 400 μm.

As described above, when the electrode contains the same gel electrolyte as the gel electrolyte, the adhesion to the gel electrolyte is improved, and the internal resistance is reduced. When lithium metal or lithium alloy is used as the negative electrode active material, the composition of the negative electrode active material and the gel electrolyte may not be used.

The positive electrode, the gel electrolyte, and the negative electrode thus obtained are laminated in this order and pressed to form a battery body.

The polymer solid electrolyte, the electrode, and the battery element obtained by combining the solid electrolyte and the electrode thus manufactured in the atmosphere can be dried by heating under reduced pressure to remove water. The degree of vacuum at this time is preferably 10 to 10 ^-5 Pa, particularly preferably 1 to 10 ^-3 Pa. The temperature is preferably from 25 to 120C, particularly preferably from 40 to 90C. The drying time is preferably 0.1 to 8 hours, particularly preferably 1 to 3 hours. Drying is preferably performed in an atmosphere of an inert gas such as Ar.

After the battery element is dried, the battery element is sealed in an outer package in an environment having a water content of 5 ppm or less to obtain a lithium secondary battery. At this time, it is preferable to be in an atmosphere of an inert gas such as Ar. Thus, even when the battery element is manufactured in the air, the same battery characteristics as those obtained when all the processes are performed in an environment having a water content of 5 ppm or less can be obtained, and the manufacturing process can be significantly simplified. It is very advantageous in terms of quality.

Further, the polymer solid electrolyte and electrode of the present invention are also effective for electric double layer capacitors. This also enables the electric double layer capacitor to be manufactured in the atmosphere, so that the manufacturing process can be remarkably simplified, which is industrially very advantageous.

The current collector used for the polarizable electrode may be a conductive rubber such as a conductive butyl rubber or the like, or may be formed by spraying a metal such as aluminum or nickel. A metal mesh may be provided.

The electric double layer capacitor is obtained by combining the above-mentioned polarizable electrode and a gel electrolyte.

As the insulating gasket, an insulator such as polypropylene or butyl rubber may be used.

The structure of the electric double layer capacitor in which the gel electrolyte of the present invention is used is not particularly limited. Usually, a pair of polarizable electrodes are arranged via the gel electrolyte, and the polarizable electrode and the periphery of the gel electrolyte are usually arranged. An insulating gasket is arranged in the part. Such an electric double layer capacitor may be any type called a coin type, a paper type, a laminated type, or the like.

[0082]

EXAMPLES Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention.

Example 1 The following gel electrolyte was used.

Polymer matrix PVDF Kynar 2801 (manufactured by Elf Atochem) (copolymer of polyvinylidene fluoride and propylene hexafluoride) Room temperature molten salt (abbreviated as IL) The following 1,3-dimethylimidazolium bis Fluoromethylsulfonyl) imide (DMIIm) and LiN
Mixture with (CF ₃ SO ₂ ) ₂ DMIIm: LiN (CF ₃ SO ₂ ) ₂ = 2: 1 (molar ratio) Solvent Acetone (abbreviated as Ac)

[0085]

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Each of the above components was converted to PVDF: I by weight.
L: Ac = 3: 7: 5, weighed, heated to 50 ° C and dissolved to prepare a gel electrolyte solution.

This gel electrolyte solution was applied to a polyethylene terephthalate (PET) film to a width of 50 mm with an applicator having a gap of 0.8 mm. And from room temperature to 5
Acetone was evaporated in the range of 0 ° C. to obtain a gel electrolyte sheet.

LiCoO ₂ was used as a positive electrode active material, and acetylene black was used as a conductive additive. These were added to the gel electrolyte solution in a weight ratio of gel electrolyte solution: L
The mixture was weighed so that iCoO ₂ : acetylene black = 10: 8: 1, and the cathode active material and the conductive additive were dispersed and mixed in the gel electrolyte solution using a homogenizer at room temperature to prepare a slurry for the cathode. The obtained slurry was applied to tantalum foil by metal mask printing and dried to obtain a positive electrode sheet.
The thickness of this electrode was 0.15 mm.

Further, artificial graphite was used as a negative electrode active material. This was weighed with respect to the gel electrolyte solution so that gel electrolyte solution: artificial graphite = 2: 1 by weight ratio,
The negative electrode active material was dispersed and mixed in the gel electrolyte solution using a homogenizer at room temperature to prepare a negative electrode slurry. The obtained slurry is applied to copper foil by metal mask printing and dried,
A negative electrode sheet was obtained. The thickness of this electrode was 0.15 mm.

The positive electrode, the gel electrolyte and the negative electrode thus obtained were cut into a predetermined size, and the respective sheets were laminated in this order and pressed appropriately to obtain a battery element.

As described above, the steps up to the production of the battery element were performed in the air.

This battery element was left standing overnight at 90 ° C. at a degree of vacuum of 10 ⁻¹ Pa and a vacuum dryer connected to an argon glove box (water content: 3 ppm) having a dew point of −70 ° C. or less.
Water was removed. Then, the pressure was returned to the atmospheric pressure with dry argon.

Next, the battery element was transferred to an argon glove box and placed in an aluminum laminate pack. The lead portion was taken out and sealed with a polyolefin-based hot melt adhesive or the like to obtain a sheet-type lithium secondary battery.

After charging the battery at a constant current up to 4.15 V, the battery was discharged at a constant current up to 2.8 V, and the charge / discharge characteristics were measured. The current density was 20 mA / dm ² . As a result of the measurement, the capacity of this battery was 98 mAh.

Example 2 The following 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide (EMIIm) and LiN (CF
₃ SO ₂ ) ₂ (EMIIm: LiN (CF ₃ SO
₂ ) ₂ = 2: 1 (molar ratio)), except that a lithium secondary battery was produced in the same manner as in Example 1.

[0096]

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The charge / discharge characteristics of the obtained battery were measured in the same manner as in Example 1. The capacity of this battery was 103 mAh.

Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that a thermoplastic fluororesin was used for the polymer matrix. Specific examples of the thermoplastic fluororesin include trade name Cefralsoft (manufactured by Central Glass Co., Ltd .; a main chain consisting of a copolymer of vinylidene fluoride and chlorofluoroethylene, and a side chain consisting of polyvinylidene fluoride). ) Was used.

The charge / discharge characteristics of the obtained battery were measured in the same manner as in Example 1. The capacity of this battery was 100 mAh.

Example 4 A lithium secondary battery was manufactured in the same manner as in Example 2 except that a thermoplastic fluororesin was used for the polymer matrix. Specific examples of the thermoplastic fluororesin include trade name Cefralsoft (manufactured by Central Glass Co., Ltd .; a main chain composed of a copolymer of vinylidene fluoride and chlorofluoroethylene, and a side chain composed of polyvinylidene fluoride). ) Was used.

The charge / discharge characteristics of the obtained battery were measured in the same manner as in Example 1. The capacity of this battery was 104 mAh.

<Embodiment 5> Under the same conditions as in Embodiment 1, PV
An electrolyte was prepared with DF and acetone, the positive electrode and the negative electrode were laminated, and then impregnated with a molten salt to gel the polymer compound to prepare a lithium secondary battery.

The charge and discharge characteristics of the obtained battery were measured in the same manner as in Example 1. The capacity of this battery was 97 mAh.

<Embodiment 6> Under the same conditions as in Embodiment 2, PV
An electrolyte was prepared with DF and acetone, the positive electrode and the negative electrode were laminated, and then impregnated with a molten salt to gel the polymer compound to prepare a lithium secondary battery.

The charge / discharge characteristics of the obtained battery were measured in the same manner as in Example 1. The capacity of this battery was 101 mAh.

Example 7 An electrolyte was prepared from a thermoplastic fluororesin and acetone under the same conditions as in Example 3, and a positive electrode,
After laminating the negative electrode, the molten salt was impregnated, and the polymer compound was gelled to produce a lithium secondary battery.

The charge / discharge characteristics of the obtained battery were measured in the same manner as in Example 1. The capacity of this battery was 98 mAh.

Example 8 An electrolyte was prepared from a thermoplastic fluororesin and acetone under the same conditions as in Example 4, and a positive electrode,
After laminating the negative electrode, the molten salt was impregnated, and the polymer compound was gelled to produce a lithium secondary battery.

The charge / discharge characteristics of the obtained battery were measured in the same manner as in Example 1. The capacity of this battery was 102 mAh.

<Comparative Example 1> In an argon glove box having a dew point of -70 ° C or less (water content: 3 ppm), a gel electrolyte was prepared in the same manner as in Example 1 by using a previously dried material.
A positive electrode and a negative electrode were manufactured, and a lithium secondary battery was manufactured.

The charge / discharge characteristics of the obtained battery were measured in the same manner as in Example 1. The capacity of this battery was 98 mAh.

<Comparative Example 2> In an argon glove box having a dew point of −70 ° C. or less (water content: 3 ppm), a gel electrolyte was prepared in the same manner as in Example 2 using a material previously dried.
A positive electrode and a negative electrode were manufactured, and a lithium secondary battery was manufactured.

The charge / discharge characteristics of the obtained battery were measured in the same manner as in Example 1. The capacity of this battery was 102 mAh.

Table 1 summarizes the results.

[0115]

[Table 1]

The lithium secondary battery using the gel electrolyte of the present invention, even when fabricated up to the battery element in the air, does not change in the subsequent water removal process, and has a dew point of −70 ° C. or less. Battery characteristics equivalent to those obtained when all the steps were performed in a glove box were obtained.

Further, the battery using the gel electrolyte of the present invention was able to obtain the same charge / discharge characteristics as the battery using the conventional gel electrolyte.

[0118]

As described above, according to the present invention, a method for producing a polymer solid electrolyte having higher reliability, higher safety and good electrical conductivity, which can produce even a battery element in the air, An electrolyte and a lithium secondary battery and an electric double layer capacitor using the same can be provided.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsu Maruyama 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor Makoto Kobayashi 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK (72) Inventor Kazuhide Oe 1-1-13 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation

Claims (10)

[Claims] 1. A polymer solid obtained by mixing an imidazolium salt and a lithium salt represented by the following general formula (I) in a matrix of a fluoropolymer compound in the atmosphere to obtain a polymer solid electrolyte. Manufacturing method of electrolyte. Embedded image (In the general formula (I), R ₁ , R ₂ and R ₃ each represent an alkyl group or a hydrogen atom, and A ⁻ represents (RSO ₂ ) ₃ C ⁻ , (RSO ₂ ) ₂ N ⁻ , RSO ₃ ⁻ ,
Represents any one of BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ and ClO ₄ ⁻ ; R represents a perfluoroalkyl group having 1 to 3 carbon atoms; and when a plurality of Rs are present, they may be the same or different from each other . ) 2. The method according to claim 1, wherein the lithium salt is LiC (RSO ₂ ) ₃ ,
LiN (RSO ₂ ) ₂ , LiRSO ₃ , (R represents a perfluoroalkyl group having 1 to 3 carbon atoms, and when there are a plurality of R, they may be the same or different.) LiBF ₄ , LiPF ₆ , LiAsF ₆ And LiClO ₄
2. The method for producing a solid polymer electrolyte according to claim 1, which is at least one of the following. 3. The method for producing a polymer solid electrolyte according to claim 1, wherein the fluorine-based polymer compound is a homopolymer or a copolymer of vinylidene fluoride. 4. The method for producing a solid polymer electrolyte according to claim 1, wherein the mixing ratio of the imidazolium salt and the lithium salt is from 10: 1 to 1: 2 in molar ratio. 5. The method for producing a solid polymer electrolyte according to claim 1, wherein said fluorine-based polymer compound is a microporous film. 6. A solid polymer electrolyte produced by the method for producing a solid polymer electrolyte according to claim 1. 7. A lithium secondary battery comprising the polymer solid electrolyte according to claim 6. 8. The method for manufacturing a lithium secondary battery according to claim 7, wherein the battery element having the polymer solid electrolyte and the electrode according to claim 6 is manufactured in the atmosphere, and thereafter, water is removed. 9. An electric double layer capacitor having the polymer solid electrolyte according to claim 6. 10. The method for manufacturing an electric double layer capacitor according to claim 8, wherein the electric double layer capacitor comprising the polymer solid electrolyte and the electrode according to claim 6 is manufactured in the atmosphere, and thereafter water is removed.