JP2003017123A - Polymer film for solid electrolyte, and manufacturing method of the same, solid electrolyte film and lithium ion secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a polymer film for solid electro lyte obtained by immersing the polymer film for the solid electrolyte in electro lyte liquid, which hardly generates distortion or wrinkle on a solid electrolyte film when immersed, and to provide a cell restrained from the deposition of electrolyte component by using such a solid electrolyte film as an electrolyte of the cell. SOLUTION: At the manufacturing method of the polymer film for the solid electrolyte, not the material with large coefficient of linear expansion like PET, but the material with small coefficient of linear expansion like metal as Al or Ni, is used as a base material 1 on which, the liquid including a polymer 2 is painted.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polymer film for solid electrolyte, a method for producing the same, a solid electrolyte film and a lithium ion secondary battery.

[0002]

2. Description of the Related Art As a battery for an electronic device such as a portable telephone or a personal computer, a solid electrolyte battery such as a so-called lithium-ion secondary battery which is free from liquid leakage is used. The solid electrolyte battery has a basic structure in which a solid electrolyte having the functions of both a separator and an electrolyte is interposed between a positive electrode and a negative electrode. In the case of batteries for electronic devices, from the viewpoint of miniaturization and weight reduction, those obtained by impregnating a polymer of an organic compound with an electrolyte solution to form a gel (these are referred to as solid electrolyte films) are known. There is. These solid electrolyte films are prepared by coating a polymer-containing liquid prepared by dissolving and dispersing a raw material polymer in a solvent onto a plastic substrate such as polyethylene terephthalate (PET) or polypropylene (PP) having solvent resistance and heat resistance. Then, after solidification by heating and cooling, the polymer film for a solid electrolyte is prepared by peeling from the plastic substrate and then impregnated with an electrolytic solution in which a lithium salt is dissolved to obtain a solid electrolyte film.

A problem of a battery using such a polymer film for a solid electrolyte impregnated with an electrolyte solution as an electrolyte is that an electrolyte component is deposited on the surface of a negative electrode. For example, in a lithium ion secondary battery using carbon for the negative electrode and a composite oxide of lithium and a transition metal such as cobalt for the positive electrode, metallic lithium may be deposited on the surface of the negative electrode. When such a deposit grows, it breaks through the solid electrolyte film and contacts with the positive electrode to cause an internal short circuit, which causes the cycle life of the battery to be shortened.Therefore, it is desired to provide a battery in which the deposition of the electrolyte component is suppressed. There is.

The cause of deposition of such an electrolyte component has not been known so far, and has been a major obstacle to the development of solid electrolyte batteries. As a result of a detailed investigation of the shape of the precipitate, the generation site, etc., the present inventors found for the first time that the non-uniform contact between the electrode and the electrolyte, which was conventionally overlooked, is the cause of the precipitation of the electrolyte component. . Therefore, in order to prevent the precipitation of the electrolyte component, it is necessary to realize a uniform contact between the electrode and the electrolyte. Therefore, it is strongly desired that the solid electrolyte film is free from distortion and wrinkles. However, when the solid electrolyte film is manufactured by the above-described method, it is the actual situation that distortion and wrinkles are likely to occur when the polymer film for solid electrolyte separated from the substrate is immersed in the electrolyte solution.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a method for producing a solid electrolyte film free from (or extremely few) distortion and wrinkles, and using such a solid electrolyte film as an electrolyte for a battery, An object of the present invention is to provide a lithium ion secondary battery in which precipitation of components is suppressed.

[0006]

Means for Solving the Problems With respect to the above problems, the present inventors have focused on the residual stress of the polymer film for solid electrolyte resulting from the expansion and contraction of the base material due to heat when producing the polymer film for solid electrolyte. As a result of doing research,
The present invention has been completed having the following features.

(1) A solid electrolyte including a step of coating a polymer-containing liquid on a base material made of a material having a linear expansion coefficient of 5 × 10 ^-5 K ^-1 or less, and peeling from the base material after solidification of the polymer. For producing polymer film for automobile. (2) The method for producing a polymer film for a solid electrolyte as described in (1) above, wherein the material having a linear expansion coefficient of 5 × 10 ⁻⁵ K ⁻¹ or less is a metal. (3) The method for producing a polymer film for a solid electrolyte according to (2), wherein the metal is Al, Ni, Fe, or an alloy containing at least one of these metals. (4) A polymer film for a solid electrolyte manufactured by the manufacturing method according to any one of (1) to (3) above. (5) A solid electrolyte film obtained by impregnating the polymer film for solid electrolyte according to (4) above with an electrolytic solution in which a lithium salt is dissolved. (6) A lithium ion secondary battery containing the solid electrolyte film as described in (5) above.

The lithium ion secondary battery produced by using the solid electrolyte film obtained from the polymer film for a solid electrolyte in which the generation of wrinkles as described above is not only able to suppress the intended deposition of lithium, but also As will be described later, high-rate charging / discharging became possible, and the effect of improving the characteristics at low temperatures was obtained.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A method for producing a polymer film for a solid electrolyte according to the present invention will be described with reference to FIG. 1 (schematic diagram of a polymer film for a solid electrolyte coated on a substrate). The greatest feature of the present invention is that the material of the base material 1 is
Conventional PET (coefficient of linear expansion 6.5 × 10 ^-5 K ^-1 ), PP
A material having a small linear expansion coefficient is used instead of a material having a large linear expansion coefficient (the coefficient of linear expansion is 7 to 10 × 10 ⁻⁵ K ⁻¹ ).

Here, the coefficient of linear expansion refers to β in the following formula 1, and is a value measured by the method described in JIS K7197.

Β = (1 / l ₀ )  (dl / dθ) However, lengths at Celsius temperatures of 0 ° C. and θ are l ₀ and l, respectively.

The linear expansion coefficient of the substrate 1 used in the present invention is 5 × 10 ^-5 K ^-1 or less, preferably 2.5 × 10 ^-5 K ^-1.
It is the following. Examples of the material of the base material 1 include a metal (whether a simple substance or an alloy). These may be pure, may contain impurities, or may be a mixture of a plurality of materials, as long as they have the above-mentioned linear expansion coefficient when used as a base material. From the viewpoint of solvent resistance and the like, preferably a metal (including an alloy), more preferably a metal is A
1, Ni, Fe, or an alloy containing any of these, preferably aluminum (having a linear expansion coefficient of 2.4 × 10 ⁻⁵ K ⁻¹ ), stainless steel (SUS304,
A linear expansion coefficient of 1.2 × 10 ⁻⁵ K ⁻¹ ) and nickel (a linear expansion coefficient of 1.3 × 10 ⁻⁵ K ⁻¹ ) are used.

The shape of the substrate 1 is not particularly limited as long as it is compatible with the method for producing a polymer film for a solid electrolyte described below, but in the present invention for producing a polymer film for a solid electrolyte by coating, solidifying and peeling a polymer. , Substrate 1
Is preferably a long thin plate, for example, the width is 1 to 5c
m, the length is 1 to 100 cm, and the thickness is 10 to 20 μm.

The polymer film for a solid electrolyte according to the present invention is obtained by applying a polymer-containing liquid, which is a raw material for a polymer film for a solid electrolyte, onto a substrate 1 made of a material having a small linear expansion coefficient as described above, It is obtained by evaporating the solvent by heating and then solidifying the polymer 2 by cooling, and then peeling the solidified polymer 2 (FIG. 1). By using a material having a small linear expansion coefficient as the material of the base material 1, expansion and contraction of the base material 1 during heating and cooling is reduced, and residual stress in the polymer 2 is also reduced. Therefore, PET and PP
Strains and wrinkles that accompany the release of stress, which occur when the electrolyte solution is impregnated with a polymer solidified on a base material having a large linear expansion coefficient, are less likely to occur by the method according to the present invention.

The material of the polymer 2 which is the main component of the polymer film for solid electrolyte used in the present invention is not particularly limited as long as it can be used for the electrolyte of the battery. Here, what can be used for the electrolyte of the battery means that the polymer itself does not have ion conductivity, but the electrolyte solution permeates the polymer to acquire ion conductivity.

The material of the polymer 2 is preferably one having a high affinity for the electrolyte solution, such as polystyrene, polybutadiene and their copolymers, polyvinylidene fluoride, polyacrylonitrile, polyvinylpyrrolidone and polyvinylidene carbonate. Is mentioned.

In the present invention, the polymer itself does not have ionic conductivity, but one which acquires ionic conductivity by the electrolyte solution penetrating into the polymer, among which a fluoropolymer having vinylidene fluoride as a main unit is particularly preferably used. To be The fluoropolymer having vinylidene fluoride as a main unit means a homopolymer of vinylidene fluoride, or a copolymer of vinylidene fluoride and a vinyl-based monomer having another fluorine atom, which may be used alone. It can also be used by mixing. Examples of other vinyl monomers having a fluorine atom include hexafluoropropylene, chlorotrifluoroethylene, and tetrafluoroethylene.
The form of the copolymer may be random or block. In the case of a copolymer, the proportion of vinylidene fluoride (unit thereof) is preferably 70 mol% or more,
Particularly preferably, it is 75 mol% or more.

The fluoropolymer having vinylidene fluoride as a main unit is a carboxyl group (--COO).
H), a sulfonic acid group (-SO ₂ OH), carboxylic acid ester group (-COOR), a carbamoyl group (-CON
H ₂ ) or a polymer of a vinyl-based monomer having a functional group composed of a phosphoric acid group (—PO (OH) ₂ ) or the like may be grafted (carboxylic ester group (—COOR)
The substituent R in is preferably a lower alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group and a butyl group. ). It is preferable to make the fluoropolymer into a polymer form in which a polymer containing such a functional group is grafted, because the adhesion of the polymer film to the positive electrode or the negative electrode of the battery is improved.

As the vinyl-based monomer having the functional group, a monomer composed of a compound having a carbon number of 4 or less in the portion excluding the functional group is suitable. As the carboxyl group-containing monomer, acrylic acid, methacrylic acid, crotonic acid,
Besides those having one carboxyl group such as vinyl acetic acid and allyl acetic acid, those having two or more carboxyl groups such as itaconic acid and maleic acid can also be used. As the sulfonic acid group-containing monomer, styrene sulfonic acid, vinyl sulfonic acid and the like are suitable. As the carboxylic acid ester group-containing monomer, methyl acrylate, butyl acrylate and the like are suitable. As the carbamoyl group-containing monomer, acrylamide or the like is suitable. As the phosphate group-containing monomer, triphenyl phosphate, tricresyl phosphate and the like are preferable. The degree of grafting is preferably 2 mol% to 20 mol% of the final weight, more preferably 3 mol% to 12 mol%, and 5 mol% to 10 mol%.
Are particularly preferred.

The polymer used in the present invention is
From the viewpoint of electrolyte retention, it is preferably porous,
Density is 0.60 to 1.3 g / cm ³ , preferably 0.7
It is good to set it to 0 to 0.80 g / cm ³ . When the density of the polymer is less than 0.60 g / cm ³ , problems such as difficulty in handling during assembly of the battery due to deterioration in mechanical strength may occur, and when the density is higher than 1.30 g / cm ³ , sufficient rate characteristics and This is because it is difficult to obtain the effect of improving low temperature characteristics.

The production of a polymer film for a solid electrolyte comprising a polymer of such a material comprises the steps of applying the polymer-containing liquid to the above-mentioned substrate, solidifying by heating and cooling, and then peeling from the substrate. Hereinafter, each step will be described.

The solvent for preparing the polymer-containing liquid is not particularly limited as long as it dissolves and disperses the polymer, and it may be a single substance or a mixture of two or more types of substances. Certain solvents (eg, octanol, 1-pentanol, 3-methyl-1-butanol,
2-methyl-1-butanol, 2-pentanol, 3-
It is preferable to combine pentanol, 2-methyl-2-butanol, 3-methyl-2-butanol, etc.) with a non-foaming solvent (eg, tetrahydrofuran (THF), dimethylacetamide, dimethylformamide, etc.). This is to cause the above-mentioned pores in the polymer that solidifies when the solvent evaporates. Among these combinations, a mixture of dimethylacetamide and octanol is preferably used.

The polymer-containing liquid used in the present invention is obtained by dissolving or dispersing the polymer raw material in the above-mentioned solvent. The concentration of the polymer in the contained liquid may be adjusted so that the viscosity is suitable for the coating method. Dissolution at the time of preparing the polymer-containing liquid may be performed by any method such as stirring. When bubbles are mixed in during mixing, or when dissolution and dispersion are insufficient and the concentration of the polymer raw material is non-uniform, it causes thickness variation of the polymer film for solid electrolyte.
It is desirable to let it stand for about 15 hours.

In the present invention, this polymer-containing liquid is applied onto the above-mentioned substrate having a small linear expansion coefficient. The coating method is not particularly limited, for example, direct coating using a device such as a blade knife type coating machine, indirect coating using a device such as a reverse roll, the accuracy of the thickness at the time of coating is It is preferable in terms of high price. As the thickness of coating,
The thickness of the polymer film for solid electrolyte after drying is 1 μm
˜50 μm, more preferably 10 μm to 30 μm.

After coating the polymer-containing liquid on the substrate,
The polymer-containing liquid is dried by heating in a batch type or continuous type hot air oven or the like. The temperature and heating time at this time may be determined so that the polymer has a desired density depending on the solvent. As an example of drying conditions, dimethylacetamide 85
For a polymer-containing liquid consisting of 1 part by weight, 15 parts by weight of octanol, and 15 parts by weight of polyvinylidene fluoride, a drying furnace having a furnace length of 10 m and a temperature of 70 to 100 ° C. is used at 0.1 m / mi.
Examples of the heating method include heating by passing m. However, the present invention is not limited to this condition.

As described above, during the heating for drying, there is a concern that the base material coated with the polymer-containing liquid may thermally expand. However, since the manufacturing method according to the present invention uses the base material made of a material having a small linear expansion coefficient, the thermal expansion of the base material becomes extremely small. For this reason, the stress on the polymer becomes very small, and it is possible to prevent the solid electrolyte film from being distorted or wrinkled.

After evaporation of the solvent, the solution is allowed to cool to near room temperature and then the solidified polymer film for solid electrolyte is peeled from the substrate. Any peeling method can be used as long as it does not cause scratches or tears on the polymer film for solid electrolyte. Examples of the peeling method include mechanical peeling using a winding machine and peeling by immersing in a liquid, but the invention is not limited thereto. Further, the polymer film for solid electrolyte is used after being cut to a predetermined size, but the polymer film for solid electrolyte may be cut after peeling or may be cut together with the substrate before peeling.

Next, the impregnation of the polymer film for solid electrolyte into the electrolyte solution will be described in the order of the electrolyte constituting the electrolyte solution, the solvent, and the method for impregnating the polymer film for solid electrolyte.

As the electrolyte, any of those known in the art can be used. When the battery is a lithium ion secondary battery, LiClO ₄ , LiBF ₄ , L
_{iPF 6, LiAsF 6, LiAlCl 4} , Li (CF 3 S
One or more selected from O ₂ ) ₂ N and the like are preferably used. Further, as the solvent, which dissolves the electrolyte and permeates the polymer film for solid electrolyte, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl sulfoxide, sulfolane, γ-butyrolactone , 1,2-dimethoxyethane, N, N-dimethylformamide, tetrahydrofuran, 1,3-dioxolane, 2-methyltetrahydrofuran, diethyl ether and the like are exemplified, and one kind or a mixture of two or more kinds thereof is used. The electrolyte concentration in the electrolyte solution is preferably 0.1 mol / l to 2 mol /
1, more preferably 0.5 mol / l to 1.5 mol / l. When the concentration of the electrolyte is less than 0.1 mol / l, the battery capacity cannot be sufficiently obtained due to a decrease in ionic conductivity,
Further, there is a problem that the high rate characteristic is significantly deteriorated, which is not preferable. On the other hand, if the concentration exceeds 2 mol / l, the viscosity is remarkably increased, and the high rate characteristics and the low temperature characteristics are deteriorated, which is not preferable.

When a mixed solvent is used as the compatible solvent, it particularly contains at least one selected from diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), and further ethylene carbonate (EC).
And a mixture containing propylene carbonate (PC) and dimethyl carbonate (DMC) is suitable. The mixing ratio of each component constituting such a mixture is preferably 25% by volume to 50% by volume, and 30% by volume to 35% by volume in at least one selected from diethyl carbonate and ethylmethyl carbonate. More preferable. In ethylene carbonate, the mixing ratio is preferably 4% by volume to 20% by volume, and 6% by volume to
More preferably, it is 18% by volume. In propylene carbonate, the mixing ratio is preferably 3% by volume to 17% by volume, and more preferably 5% by volume to 15% by volume. Further, in dimethyl carbonate, the mixing ratio is preferably more than 40% by volume and 60% by volume or less, and more preferably 45% by volume to 55% by volume.

In at least one selected from diethyl carbonate and ethyl methyl carbonate,
If the mixing ratio is less than 25% by volume, the freezing point of the solution in which the salt (electrolyte) is dissolved rises, and the internal resistance of the battery increases, especially at low temperatures of -20 ° C or lower, and the charge / discharge cycle characteristics and The low temperature characteristics tend to deteriorate. on the other hand,
If the mixing ratio exceeds 50% by volume, the viscosity of the solution in which the salt (electrolyte) is dissolved increases and the internal resistance of the battery increases,
The charge / discharge cycle characteristics tend to deteriorate.

In ethylene carbonate, if the mixing ratio is less than 4% by volume, it is difficult to form a stable film on the surface of the negative electrode plate, and the cycle characteristics tend to deteriorate.
If the mixing ratio exceeds 20% by volume, the viscosity of the solution in which the salt (electrolyte) is dissolved increases, the internal resistance of the battery increases, and the charge / discharge cycle characteristics tend to deteriorate.

In the case of propylene carbonate, if the mixing ratio is less than 3% by volume, the effect of suppressing the increase in impedance due to charge / discharge cycles becomes small and the cycle characteristics tend to deteriorate, so that the mixing ratio becomes 17% by volume. When it exceeds, the viscosity of the solution in which the salt (electrolyte) is dissolved increases, the internal resistance of the battery increases, and the charge-discharge cycle characteristics tend to deteriorate.

When the mixing ratio of dimethyl carbonate is 40% by volume or less, the viscosity of the solution in which the salt (electrolyte) is dissolved increases, the internal resistance of the battery increases, and the charge-discharge cycle characteristics tend to deteriorate. And the above mixing ratio is 6
If it exceeds 0% by volume, the freezing point of the solution in which the salt (electrolyte) is dissolved rises, and the internal resistance of the battery increases and the cycle characteristics and low temperature characteristics tend to deteriorate, especially at low temperatures of -20 ° C or lower. Becomes

In addition to the above-mentioned solvent, tetraethylene glycol dimethyl ether, N-, for the purpose of preventing crystallization of the solution at the operating temperature of the battery (especially when using at low temperature).
Methyl-pyrrolidone (1-methyl-2-pyrrolidone),
It is preferable to use a plasticizer such as ethylene glycol dimethyl ether or diethylene glycol dimethyl ether. Addition of a plasticizer further prevents crystallization of the electrolyte from the electrolyte solution infiltrated into the polymer,
The present invention can be made more effective.

The method of impregnating the polymer film for solid electrolyte with the electrolyte solution is not particularly limited. After impregnating the electrolyte solution with the polymer film for solid electrolyte, the battery described below may be assembled, but considering that the polymer film gels after impregnation, from the viewpoint of ease of processing,
It is preferable that the battery is assembled using the polymer film for solid electrolyte before impregnation and then impregnated with the electrolyte solution.

The solid electrolyte film of the present invention can be applied to various conventionally known lithium ion secondary batteries. For example, a strip-shaped positive electrode (sheet) and a negative electrode (sheet) are interposed with a strip-shaped solid electrolyte film of substantially the same size, and these three members are wound in a spiral shape along the length direction. A wound body is formed by rotating the wound body, and the wound body is housed in an exterior material (so-called wound type), or between a rectangular positive electrode (sheet) and a negative electrode (sheet) having substantially the same size. An example is a form (so-called laminated type) in which a laminated structure is formed by repeating one or two or more units (cells) in which a rectangular solid electrolyte film is sandwiched, and the laminated structure is housed in an exterior material. To be Further, as one variation of the laminated type, a laminated structure formed by laminating a positive electrode bagging body in which a rectangular positive electrode (sheet) is surrounded by a bag-shaped solid electrolyte film and a rectangular negative electrode (sheet) is laminated. The form (so-called bag type) accommodated in the exterior material can be mentioned. In such a bag type, since the positive electrode sheet is completely surrounded by the bag-shaped solid electrolyte film, there is no physical contact between the positive electrode (sheet) and the negative electrode (sheet), and the positive electrode sheet and the negative electrode sheet are completely insulated. There is an advantage that you can. As a method for forming the solid electrolyte film into a bag shape, various methods that have been widely used in the art can be cited. For example, a method of heating the outer peripheral portion of the solid electrolyte film bent to an appropriate size using a device such as a heat press, a heat sealer, or a vacuum heat press to fix the outer peripheral portion,
Examples thereof include a method of pressurizing the outer peripheral portion using a device such as a press roll, a method of applying pressure while heating the outer peripheral portion using a heat press, a hot roll press, a vacuum press, and the like.

In the lithium ion secondary battery using the solid electrolyte film of the present invention, the positive electrode (sheet) and the negative electrode (sheet) are known positive electrode (sheet) and negative electrode (sheet) for lithium ion secondary battery, respectively. )
Can be used. As a preferred example, for example, a positive electrode active material composition or a negative electrode active material composition obtained by mixing a positive electrode active material or a negative electrode active material with a conductive material, a binder, or the like is applied onto a current collector, and dried and rolled. Then, the thing formed by forming a positive electrode active material layer or a negative electrode active material layer is mentioned.

As the positive electrode active material, Li-Co type composite oxide, Li-Mn type composite oxide, Li-Ni type composite oxide and the like can be used, and among them, they are chemically stable and easy to handle. In addition, since it is possible to manufacture a high capacity secondary battery,
It is preferable to use lithium cobalt oxide (LiCoO ₂ ).
As the conductive material, artificial or natural graphite, or granular carbon material such as carbon black such as Ketjen black, acetylene black, oil furnace black, and Extra conductive furnace black (granular, scaly, spherical, pseudo Spheres, lumps, whiskers, etc. are included and are not particularly limited) can be used. Further, as the binder in the positive electrode (sheet), polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, ethylene-propylene-diene polymer, etc. can be used. In the positive electrode active material composition, the total amount of the positive electrode active material, the conductive material and the binder deposited is 100.
3 to 15 parts by weight of the conductive material and 1 part of the binder with respect to parts by weight
It is preferable that the composition is blended in an amount of about 10 to 10 parts by weight.

As the current collector, a foil or a perforated foil made of a conductive metal can be used, and its thickness may be about 5 to 100 μm. As a material for the positive electrode current collector, copper, nickel, silver, stainless steel or the like is used.

The positive electrode (sheet) and the negative electrode (sheet) are
It can be manufactured according to a known method. For example, a positive electrode (sheet) is prepared by mixing and processing a positive electrode active material, a conductive material, and a binder, dispersing it in an organic solvent such as N-methylpyrrolidone to form a paste, applying it on the positive electrode current collector, and drying it. It can be obtained by applying pressure and cutting into an appropriate shape.

In the present invention, as the battery exterior material,
In addition to metal cans such as cylindrical cans, rectangular cans, and button-shaped cans, sheet-shaped exterior materials such as laminated films are used. As the laminate film, one having a thermoplastic resin laminate layer such as polyester or polypropylene formed on at least one surface of a metal foil such as copper or aluminum is preferable.
Examples of the metal foil include aluminum, copper, iron and the like. Examples of the resin include thermoplastic resins such as polyester and polypropylene. As long as it has such a thermoplastic resin layer, it can be sealed only by covering the wound body or the laminated structure with the outer periphery and heat-sealing the peripheral edge thereof, and the battery manufacturing operation is simple. The thickness of the metal foil is preferably 1
0 to 100 μm, more preferably 20 to 70 μm, the thickness of the resin layer is preferably 5 to 100 μm, more preferably 10 to 50 μm, and the total thickness is preferably 20 to 200 μm, more preferably 40.
˜150 μm.

In the battery according to the present invention, a lid of a battery can,
Safety structure, electrode terminals (lead terminals in sheet batteries)
As various constituent members not mentioned above such as the above, existing members and members to be developed in the future can be used.

[0044]

Example 1 As a raw material for a polymer film for a solid electrolyte, 30 g of polyvinylidene fluoride was dissolved in 170 g of dimethylacetamide. To this solution, 30 g of octanol was gradually mixed over 1 hour, and 12
Let stand for more than an hour. An aluminum foil (rolled aluminum foil, thickness 20 μm) was prepared as a base material for coating. The solution was applied to this substrate by direct coating with a doctor blade, and the solvent was volatilized by passing through a drying oven (120 ° C., oven length 10 m) at 0.1 m / mim. By this operation, a polymer film for solid electrolyte having a density of 0.8 g / cm ³ or less was obtained. By adjusting the interval between the blades according to the viscosity of the solution, a polymer film for solid electrolyte of 20 μm and a polymer film for solid electrolyte of 30 μm were obtained.

This polymer film for solid electrolyte was cut into 10 cm × 10 cm together with the substrate, and after cutting, dimethoxyethane was impregnated and peeled from the substrate. Electrolyte (LiP
A tray (15 cm) containing 100 cc of a solution prepared by dissolving F ₆ in a 1: 1 (volume ratio) mixed solvent of ethylene carbonate and ethylmethyl carbonate at a concentration of 1.0 mol / l).
W × 15 cmD × 5 cmH) was prepared, and the polymer film for solid electrolyte separated from the substrate was immersed. It was investigated whether wrinkles would occur at this time. In the investigation, the presence or absence of shrinkage of the polymer film for solid electrolyte due to the occurrence of wrinkles was visually determined.

Example 2 Thickness of 1 as a base material for coating a polymer-containing liquid as a raw material for a polymer film for solid electrolyte
By the same operation as in Example 1 except that a 4 μm aluminum foil was used, the presence or absence of shrinkage of the polymer film for solid electrolyte due to the generation of wrinkles was investigated.

[Comparative Example 1] Thickness of 5 as a base material for coating a polymer-containing liquid as a raw material of a polymer film for solid electrolyte.
By the same operation as in Example 1 except that a polyethylene terephthalate film having a thickness of 0 μm was used, the presence or absence of shrinkage of the polymer film for solid electrolyte due to the generation of wrinkles was investigated. The results of Example 1, Example 2 and Comparative Example are summarized in Table 1.

[0048]

[Table 1]

According to Table 1, the base material is PE having a large coefficient of linear expansion.
It was revealed that by replacing T with a metal (aluminum) having a small linear expansion coefficient, it is possible to prevent wrinkles from being generated in the polymer film for solid electrolyte at the time of dipping in the electrolytic solution during the production of the solid electrolyte film. Further, it was confirmed that this effect was maintained even if the polymer film for solid electrolyte was thinned.

Next, the characteristics of the battery using the polymer film for solid electrolyte according to the present invention were evaluated.

(Production of Polymer Film for Solid Electrolyte) [Examples 3 and 4 and Comparative Example 2] In Example 3, Example 4 and Comparative Example 2, Examples 1 and 2 and Comparative Example 1 were obtained, respectively. A polymer film for solid electrolyte was prepared, the following lithium ion secondary batteries were assembled, and the following tests were performed for each.

(Production of Positive Electrode Sheet) 90 parts by weight of lithium cobalt oxide granular material as a positive electrode active material, 5 parts by weight of polyvinylidene fluoride as a binder, 5 parts by weight of artificial graphite as a conductive agent and N-methyl. Pyrrolidone 70
Parts by weight were mixed to form a slurry. This slurry was applied on both sides of a strip-shaped aluminum foil (thickness 20 μm) as a positive electrode current collector, dried, and then rolled (rolling temperature 25
C., rolling rate 30%), and a positive electrode sheet (width: 30 m) having a positive electrode active material composition layer (thickness: 70 μm) in which the amount of the active material deposited on one surface of the aluminum foil is 20 mg / cm ^2.
m, length 50 mm) was produced.

(Preparation of Negative Electrode Sheet) 95 parts by weight of graphitized carbon fiber, 5 parts by weight of polyvinylidene fluoride, and 60 parts by weight of N-methylpyrrolidone were mixed to prepare a slurry. This slurry was applied to both sides of a strip-shaped copper foil (thickness 14 μm) as a negative electrode current collector, dried, and then subjected to rolling treatment (rolling temperature 100 ° C., rolling rate 20%) to obtain active material per side of the copper foil. A strip-shaped negative electrode (width 32 mm, length 52 mm) having a negative electrode active material composition layer (thickness 75 μm) having an adhesion amount of 10 mg / cm ² was prepared.

(Assembly of Battery) A polyvinylidene fluoride porous film was interposed between the positive electrode and the negative electrode, and the negative electrode was laminated on the outermost layer, and this was laminated with an electrolytic solution in an aluminum laminate film. It was sealed and the tab was taken out to make a cell. In addition, the polyvinylidene fluoride porous film here is a polyvinylidene fluoride porous film produced in Examples 3 and 4 and Comparative Example 2, and the electrolytic solution is Examples 1 and 2 and Comparative Example 1. It is the electrolytic solution used in.

(Low-temperature characteristic test) After charging the manufactured lithium-ion secondary battery at room temperature, this was -2.
Leave for 6 hours in 0 ° C. air atmosphere. In addition, charging is
The current was applied at a constant current of 1 C (600 mA) until the voltage reached 4.2 V, and then the current was applied at a constant voltage of 4.2 V until the total charging time reached 2.5 hours. Next, in this atmosphere of −20 ° C., 1 C (600 mAh) /
Discharge is performed at a cutoff voltage of 2.5 V, and the discharge capacity (mAh) at that time is obtained. Further, charge and discharge are performed under the same conditions even at room temperature (20 ° C.) to obtain the discharge capacity (mAh). Furthermore, the discharge capacity change rate was obtained by dividing the discharge capacity at −20 ° C. by the discharge capacity at room temperature.

(Cycle characteristic test) 1C (that is, 60)
Charge and discharge were repeated at a constant current of 0 mAh), and the number of cycles at which the discharge capacity retention ratio (%) to the discharge capacity was 80% or less was measured.

(Rate Characteristic Test) With respect to the manufactured lithium ion secondary battery, 2C charge / discharge was performed at room temperature (20 ° C.), and the ratio of the discharge capacity to the total capacity was calculated. The 2C is the discharge capacity of the lithium ion secondary battery (6
It refers to a constant current of 1200 mA for 00 mAh).

The results of the above tests are summarized in Table 2.

[0059]

[Table 2]

[0060]

By the method according to the present invention, it is possible to provide a solid electrolyte film free from wrinkles and distortions (or very few). This makes it possible to prevent the electrolyte from being deposited on the electrode surface due to the non-uniform contact between the negative electrode and the solid electrolyte film, and to manufacture a battery having a long cycle life. In addition, the battery obtained by using the solid electrolyte film according to the present invention also exhibits excellent effects in rate characteristics and low temperature characteristics. Since this effect is maintained even when the solid electrolyte film is thin, the solid electrolyte film can be made thinner and the battery can be made smaller.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a substrate coated with a polymer film for solid electrolyte.

[Explanation of symbols]

1 base material 2 polymer

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B29L 7:00 B29L 7:00 (72) Inventor Seiji Okada 4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Cable Industries Itami Works Co., Ltd. (72) Inventor's book to 4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Cable Industries, Ltd. Itami Works F-term (reference) 4F202 AA16 AB16 AE03 AG01 AH33 AJ02 AJ11 CA07 CB02 CK11 CM26 4F205 AA16 AB16 AE03 AG01 AH33 AJ02 AJ11 GA07 GB02 GC07 GE24 GN28 5G301 CA16 CA30 CD01 5H029 AJ12 AJ14 AK03 AL07 AM03 AM07 AM16 BJ12 CJ02 HJ14

Claims (6)

[Claims] 1. A solid electrolyte comprising a step of applying a polymer-containing liquid onto a base material made of a material having a linear expansion coefficient of 5 × 10 ⁻⁵ K ⁻¹ or less, and peeling from the base material after solidification of the polymer. Method for producing polymer film. 2. The method for producing a polymer film for a solid electrolyte according to claim 1, wherein the material having a linear expansion coefficient of 5 × 10 ⁻⁵ K ⁻¹ or less is a metal. 3. The method for producing a polymer film for a solid electrolyte according to claim 2, wherein the metal is Al, Ni, Fe, or an alloy containing at least one of these metals. 4. A polymer film for a solid electrolyte manufactured by the manufacturing method according to claim 1. 5. A solid electrolyte film obtained by impregnating the polymer film for solid electrolyte according to claim 4 with an electrolytic solution in which a lithium salt is dissolved. 6. A lithium ion secondary battery containing the solid electrolyte film according to claim 5.