JP2006348280A - Porous film and laminated porous film - Google Patents

Abstract

An object of the present invention is to provide a porous film and a laminated porous film that provide a separator capable of obtaining a battery and a capacitor having good long-term storage stability without impairing high heat resistance.
A polymer having a thermal decomposition starting temperature of 200 ° C. or higher and a raw material monomer thereof are contained, and the proportion of the raw material monomer is 0.05% by weight or more and 5% by weight based on the total weight of the polymer and the raw material monomer. % Porous film or less. The porous film as described above, wherein the polymer having a thermal decomposition starting temperature of 200 ° C. or higher is a nitrogen-containing aromatic polymer. A laminated porous film obtained by laminating the porous film and a porous film containing a thermoplastic resin in contact with each other.
[Selection figure] None

Description

  The present invention relates to a porous film and a laminated porous film. More specifically, the present invention relates to a porous film and a laminated porous film used for a separator.

  The porous film and the laminated porous film are used as separators used for batteries, capacitors and the like. The battery mainly includes electrodes such as a positive electrode and a negative electrode, an electrolytic solution, and a separator. The separator is required to exhibit high heat resistance, and as a separator exhibiting high heat resistance, a separator made of a synthetic resin containing a polyimide resin as a main component has been proposed (for example, see Patent Document 1). .)

JP-A-62-37871 (first page to second page)

However, batteries and capacitors having conventional separators have not been sufficient for long-term storage stability.
An object of the present invention is to provide a porous film and a laminated porous film that provide a separator capable of obtaining a battery and a capacitor having good long-term storage stability without impairing high heat resistance.

    As a result of intensive studies to solve the above problems, the present inventors have reached the present invention.

That is, the present invention provides the following <1> to <16>.
<1> A polymer having a thermal decomposition start temperature of 200 ° C. or higher and a raw material monomer thereof, and the proportion of the raw material monomer is 0.05% by weight or more and 5% by weight in the total weight of the polymer and the raw material monomer A porous film characterized by:
<2> The porous film according to <1>, wherein the polymer having a thermal decomposition starting temperature of 200 ° C. or higher is a nitrogen-containing aromatic polymer.
<3> The porous film according to <2>, wherein the nitrogen-containing aromatic polymer is an aromatic polyimide.
<4> The porous film according to <2>, wherein the nitrogen-containing aromatic polymer is an aromatic polyamideimide.
<5> The porous film according to any one of <1> to <4>, further containing an organic powder and / or an inorganic powder.
<6> The porous film according to any one of <1> to <4>, further containing alumina.
<7> A laminated porous film obtained by laminating the porous film according to any one of <1> to <6> and a porous film containing a thermoplastic resin.
<8> The laminated porous film according to <7>, wherein the thermoplastic resin is polyethylene.
<9> The laminated porous film according to <7> or <8>, wherein the non-porous temperature is less than 180 ° C.
<10> A separator comprising the porous film according to any one of <1> to <6>.
<11> A separator comprising the laminated porous film according to any one of <7> to <9>.
<12> The separator according to <10> or <11>, wherein the porosity is 20% by volume or more and 90% by volume or less.
<13> The separator according to any one of <10> to <12>, wherein the air permeability according to the Gurley method is 20 seconds / 100 cc or more and 2000 seconds / 100 cc.
<14> A battery comprising the separator according to any one of <10> to <13>.
<15> A lithium secondary battery comprising the separator according to any one of <10> to <13>.
<16> A capacitor comprising the separator according to any one of <10> to <13>.

  Since the battery and the capacitor obtained using the separator made of the porous film and the separator made of the laminated porous film of the present invention are excellent in long-term storage stability, the present invention is extremely useful industrially.

The present invention is described in detail below.
The porous film of the present invention contains a polymer having a thermal decomposition starting temperature of 200 ° C. or higher and a raw material monomer thereof, and the proportion of the raw material monomer is 0.05% in the total weight of the polymer and the raw material monomer. % Or more and 5% by weight or less. The ratio of the raw material monomer is preferably 0.08 wt% or more and 1 wt% or less, more preferably 0.1 wt% or more and 0.5 wt% or less in the total weight. If the ratio of the raw material monomer exceeds 5% by weight in the total weight, it is not preferable because long-term storage stability of a battery and a capacitor having a separator made of a porous film tends to be lowered. In addition, when the proportion of the raw material monomer is less than 0.05% by weight in the total weight, when producing a battery and a capacitor having a separator made of a porous film, the adhesion between the separator and the electrode tends to be insufficient. It is not preferable.

  Examples of the polymer having a thermal decomposition starting temperature of 200 ° C. or higher include oxygen-containing aromatic polymers such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene isophthalate, and nitrogen-containing aromatic polymers described later. Polyethylene terephthalate is obtained by condensation polymerization using ethylene glycol and terephthalic acid as raw materials monomers, polybutylene terephthalate is obtained by condensation polymerization using butylene glycol and terephthalic acid as raw material monomers, polyethylene isophthalate is It can be obtained by condensation polymerization using ethylene glycol and isophthalic acid as raw material monomers. As a raw material monomer, terephthalic acid dichloride may be used instead of terephthalic acid, or isophthalic acid dichloride may be used instead of isophthalic acid.

  The thermal decomposition starting temperature of these polymers is more preferably 220 ° C. or higher, further preferably 300 ° C. or higher. When the thermal decomposition starting temperature is less than 200 ° C., when the separator made of the porous film of the present invention is used for a battery, the battery insulation may not be maintained when the battery internal temperature rises due to a battery short circuit or the like. Among these polymers having a thermal decomposition starting temperature of 200 ° C. or higher, a nitrogen-containing aromatic polymer is preferable from the viewpoint of operability.

  As the nitrogen-containing aromatic polymer, an aromatic polymer containing an amide-imide group, an imide group is used in order to further improve the long-term storage stability of a battery and a capacitor having a separator made of the porous film of the present invention. Aromatic polymers containing, aromatic polymers containing ester groups and imide groups, aromatic polymers containing ester groups and amide groups are preferred, among these, aromatic polyamideimides, aromatic polyimides, aromatics Polyester amide is more preferable, and aromatic polyamide imide and aromatic polyimide are still more preferable.

  The number average molecular weight of the nitrogen-containing aromatic polymer is 2000 or more, preferably 5000 or more and 50000 or less. If the number average molecular weight of the polymer is less than 2,000, the strength of the porous film of the present invention may be lowered, which causes a problem in the safety of a battery and a capacitor having a separator made of the porous film. There is a case. Moreover, when the number average molecular weight of this polymer exceeds 50000, the solubility at the time of making it melt | dissolve in the below-mentioned polar organic solvent may not be enough.

  Examples of the aromatic polyamideimide include those obtained by condensation polymerization using aromatic dicarboxylic acid and aromatic diisocyanate as raw material monomers, and aromatic diacid anhydride and aromatic diisocyanate as raw material monomers. Those obtained from condensation polymerization are mentioned. Specific examples of the aromatic dicarboxylic acid include isophthalic acid and terephthalic acid. Specific examples of the aromatic dianhydride include trimellitic anhydride. Specific examples of the aromatic diisocyanate include 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, orthotolylane diisocyanate, m-xylene diisocyanate, and the like.

  Examples of the aromatic polyimide include those obtained from these condensation polymerizations using an aromatic dianhydride and a diamine as raw material monomers. Specific examples of the aromatic dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone Examples thereof include tetracarboxylic dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, and the like. Specific examples of the diamine include oxydianiline, paraphenylenediamine, benzophenonediamine, 3,3'-methylenedianiline, 3,3'-diaminobenzophenone, 3,3'-diaminobenzosulfone, and the like.

  Examples of the aromatic polyester amide include those obtained from condensation polymerization using aromatic carboxylic acid chloride and aromatic amine as raw material monomers, and those obtained from condensation polymerization using aromatic alcohol and aromatic amine. Things.

  The porous film of the present invention preferably further contains an organic powder and / or an inorganic powder. In this case, the porosity of the obtained porous film can be controlled by changing the addition amount of the organic powder and / or the inorganic powder. The particle size of the organic powder and / or inorganic powder is preferably 1.0 μm or less in terms of average particle size of primary particles from the viewpoint of maintaining the strength characteristics and smoothness of the porous film, from the viewpoint of operability. , 0.01 μm or more is preferable. The addition amount of the organic powder and / or inorganic powder is preferably 20% by weight or more and 95% by weight or less, more preferably, based on the total weight of the porous film, from the viewpoint of maintaining the strength characteristics of the porous film. 30% by weight or more and 91% by weight or less. Examples of the shape of the organic powder and / or inorganic powder include a spherical shape and a rod shape, and a spherical shape is preferable.

Examples of the organic powder include, for example, styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, methyl acrylate, and the like, or two or more kinds of copolymers, polytetrafluoroethylene, 4 Fluorine-based resins such as fluorinated ethylene-6 fluorinated propylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride; melamine resin; urea resin; polyolefin; powder made of organic matter such as polymethacrylate It is done. The organic powder may be used alone or in combination of two or more. Among these organic powders, polytetrafluoroethylene is preferable from the viewpoint of chemical stability.
Examples of the inorganic powder include powders made of inorganic materials such as metal oxides, metal nitrides, metal carbides, metal hydroxides, carbonates, sulfates, and specific examples include alumina, silica, The powder which consists of titanium dioxide or calcium carbonate etc. is mentioned. The inorganic powder may be used alone or in combination of two or more. Among these inorganic powders, alumina is preferable from the viewpoint of chemical stability.

  Further, the present invention is a laminated porous film in which the above porous film and a porous film containing a thermoplastic resin are laminated in contact with each other. As the thermoplastic resin, polyethylene such as low density polyethylene, high density polyethylene, linear polyethylene or the like, or a low molecular weight wax thereof, or polyolefin such as polypropylene is preferably used. Moreover, these polyolefins can be used in mixture of 2 or more types.

  The laminated porous film of the present invention preferably has a non-porous temperature of less than 180 ° C. In this case, the non-porous temperature refers to a temperature at which ions and / or electrons cannot substantially move between the electrodes in the battery and the capacitor when the pores of the laminated porous film are closed.

  The separator of the present invention is characterized by comprising the porous film of the present invention or the laminated porous film of the present invention.

  The porosity of the separator of the present invention is preferably 20% by volume to 90% by volume, and more preferably 30% by volume to 80% by volume. If the porosity is less than 20% by volume, the ion permeability and / or electrolyte impregnation of the separator may be reduced, and the performance of the obtained battery and capacitor, such as load characteristics and cycle characteristics, may be reduced. May end up. On the other hand, when the porosity exceeds 90% by volume, the strength of the separator may be lowered, and the insulation properties of the obtained battery and capacitor may not be maintained. The porosity can be determined by the method described later.

  The air permeability of the separator of the present invention is preferably 20 seconds / 100 cc or more and 2000 seconds / 100 cc as measured by the Gurley method. If the air permeability is less than 20 seconds / 100 cc, the strength of the separator may decrease, and the resulting battery and capacitor may not be able to maintain insulation. Moreover, when the air permeability exceeds 2000 seconds / 100 cc, the ion permeability and / or electrolyte impregnation of the separator may be deteriorated, and performance such as load characteristics and cycle characteristics of the obtained battery and capacitor may be deteriorated. It may decrease. The air permeability by the Gurley method can be obtained by the method described later.

  The thickness of the separator is preferably 5 μm to 100 μm, more preferably 5 μm to 50 μm, and still more preferably 5 μm to 30 μm. When the thickness is less than 5 μm, the strength of the separator is lowered and handling may be difficult. On the other hand, when the thickness exceeds 100 μm, the electric capacity of the obtained battery and capacitor tends to decrease due to the increase in volume of the separator.

  The laminated porous film of the present invention may be laminated so that at least one layer of the porous film of the present invention and at least one layer of the porous film containing a thermoplastic resin are in contact with each other. The above may be laminated.

Next, the method for producing the porous film of the present invention will be described by taking as an example the case of producing a porous film containing a nitrogen-containing aromatic polymer and its raw material monomer.
The nitrogen-containing aromatic polymer in the present invention can be obtained by condensation polymerization of two or more raw material monomers. The raw material monomer includes impurities present in the raw material monomer. Examples of the impurities include 1) raw material monomers modified by oxygen, moisture, etc. 2) raw materials used in preparing raw material monomers, and the like. If these impurities do not have a condensation polymerization bond, they will be present as raw material monomers in the resulting porous film without condensation polymerization. The amount of impurities in the raw material monomer is preferably 0.05% by weight or more and less than 5% by weight, and more preferably 0.08% by weight or more and less than 1% by weight. Even when the reactivity of the condensation polymerization between the raw material monomers is low, the raw material monomers do not react and exist in the porous film.

The number average degree of polymerization of the nitrogen-containing aromatic polymer in the present invention can be controlled by the molar ratio of one raw material monomer and the other raw material monomer used during the condensation polymerization. At this time, it is preferable that one raw material monomer is slightly excessive with respect to the other raw material monomer. That is, by making the number of moles of one raw material monomer excessive with respect to the number of moles of the other raw material monomer, the amount of raw material monomer in the porous film can be controlled, and the number average molecular weight can be controlled. Can do. Theoretically, the relationship of the following formula (1) is established between the target number average molecular weight (n) and the used molar ratio (d). When the used molar ratio (d) increases, the number average molecular weight ( n) tends to be small, and as a result, the raw material monomer concentration in the polymer tends to be high. The molar ratio used is preferably 1.01 or more and 1.05 or less, and more preferably 1.02 or more and 1.04 or less.
d = (n + 1) / n (1)

The porous film of the present invention is produced, for example, by a method including the following steps (a) to (e).
(A) A nitrogen-containing aromatic polymer and its raw material monomer are dissolved in a polar organic solvent to prepare a solution containing the nitrogen-containing aromatic polymer and its raw material monomer.
(B) The solution obtained in step (a) is applied to the surface of the substrate to form a coating film.
(C) The nitrogen-containing aromatic polymer and its raw material monomer are precipitated from the coating film obtained in step (b) to obtain a wet coating film.
(D) The wet coating film obtained in the step (c) is peeled from the substrate, and the polar organic solvent contained in the wet coating film is removed.
(E) The coating film after removing the polar organic solvent obtained in the step (d) is dried to obtain a porous film.

  In the step (a), the concentration of the nitrogen-containing aromatic polymer and the raw material monomer in the solution is preferably 0.5% by weight to 80% by weight. When the concentration is less than 0.5% by weight, the strength of the obtained porous film may not be sufficient, and the insulation properties of the resulting battery may not be maintained. If the concentration exceeds 80% by weight, the solution viscosity is high and the fluidity is lost, which may be undesirable in terms of production such as coating. Examples of the polar organic solvent include a polar amide solvent or a polar urea solvent. Examples of the polar amide solvent include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone and the like. Examples of the polar urea solvent include N, N, N ′, N′-tetramethylurea and the like. Among these, N-methyl-2-pyrrolidone is preferable in terms of chemical stability.

  In the step (b), the solution obtained in the step (a) is applied to the surface of a base material such as a base film, a steel belt, a roll, or a drum to form a coating film. As the base film, for example, polyethylene terephthalate, paper whose surface has been subjected to mold release treatment, or the like is used. Further, as the steel belt, a corrosion-resistant belt whose surface is mirror-finished is preferably used. Further, as the roll or drum, a corrosion-resistant one whose surface is mirror-finished is preferably used. Examples of the coating method include coating methods such as knife, blade, bar, gravure, and die. Coating of bars, knives and the like is simple, but industrially, die coating having a structure in which the solution does not come into contact with outside air is preferable.

In the step (c), the nitrogen-containing aromatic polymer and its raw material monomer are precipitated from the coating film obtained in the step (b) to obtain a wet coating film. As the deposition method, since the wet coating film becomes porous, specifically, the following 1) and 2) are preferable.
1) The coating film obtained in step (b) is preferably placed in an atmosphere controlled at a temperature of 20 ° C. or higher and a predetermined humidity to precipitate a nitrogen-containing aromatic polymer and its raw material monomer, and wet coating How to get a membrane.
2) The coating film obtained in step (b) is immersed in a poor solvent (a solvent in which the nitrogen-containing aromatic polymer cannot be dissolved) to precipitate the nitrogen-containing aromatic polymer and its raw material monomer, and wet coating Method to obtain a film.
In addition, the atmosphere controlled to the predetermined humidity in the above 1) may be a dry atmosphere having a relative humidity of 5% or less, or may be a humid atmosphere having a relative humidity of 30% to 95%.

In the step (d), the polar organic solvent contained in the wet coating film obtained in the step (c) is removed. Specific examples of the removal method include the following 1 ′) or 2 ′).
1 ′) A method of removing a polar organic solvent by bringing a wet coating film into contact with a solvent such as water, an aqueous solution or an alcohol-based solution that can dissolve the polar organic solvent.
2 ′) A method of removing the polar organic solvent by heating the wet coating film.
In the method 1 ′), when water is used, it is preferable to use ion-exchanged water in which metal ions are reduced. In method 2 ′), the heating temperature is preferably below the melting temperature or below the decomposition temperature. For the removal, it is preferable to completely remove the polar organic solvent, but a part of the polar organic solvent may remain. Method 1 ′) is preferred because in step (a), inorganic salts contained as additives in the polar organic solvent and inorganic salts generated as by-products during condensation polymerization can be removed.

  In the step (e), the wet coated film obtained in the step (d) is preferably dried at a temperature lower than the melting temperature or lower than the decomposition temperature to obtain the porous film of the present invention.

  In order to contain the organic powder and / or inorganic powder in the porous film of the present invention, in the step (a), the organic powder and / or inorganic powder is a solution containing a nitrogen-containing aromatic polymer and its raw material monomer. It may be added to and dispersed. Examples of the dispersing device include a pressure disperser (gorin homogenizer, nanomizer) and the like.

  Next, a method for producing the laminated porous film of the present invention will be described.

  As a manufacturing method of the porous film containing a thermoplastic resin, it can manufacture by the method etc. which are disclosed by Unexamined-Japanese-Patent No. 2003-105120, for example.

The laminated porous film of the present invention is produced, for example, by a method including the following steps (f) to (j).
(F) A nitrogen-containing aromatic polymer and its raw material monomer are dissolved in a polar organic solvent to prepare a solution containing the nitrogen-containing aromatic polymer and its raw material monomer.
(G) The solution obtained in step (f) is applied to the surface of a porous film containing a thermoplastic resin to form a coating film.
(H) A nitrogen-containing aromatic polymer and its raw material monomer are precipitated from the coating film obtained in the step (g) to form a wet coating film.
(I) The polar organic solvent contained in the wet coating film obtained in the step (h) is removed.
(J) The coated film after removal of the polar organic solvent obtained in step (i) is dried to obtain a laminated porous film.

  Step (f) can be carried out in the same manner as in the above step (a).

  The step (g) can be carried out in the same manner as in the above step (b) except that the solution obtained in the step (f) is coated on the porous film containing a thermoplastic resin.

  Step (h) can be carried out in the same manner as in the above step (c).

  Step (i) can be carried out in the same manner as the above step (d).

  Step (j) can be carried out in the same manner as in the above step (e).

  In order to contain the organic powder and / or inorganic powder in the laminated porous film of the present invention, in the step (f), the organic powder and / or inorganic powder contains the nitrogen-containing aromatic polymer and its raw material monomer. What is necessary is just to add to a solution and disperse | distribute. Examples of the dispersing device include a pressure disperser (gorin homogenizer, nanomizer) and the like.

The present invention also relates to a battery having the separator of the present invention.
Next, a battery having the separator of the present invention will be described by taking a lithium secondary battery as an example of the battery.

  As the lithium secondary battery, for example, a known technique disclosed in JP-A-2002-054394 can be used. That is, by laminating and winding a positive electrode sheet in which a positive electrode mixture is applied to a positive electrode current collector, a negative electrode sheet in which a negative electrode electrode material is applied to a negative electrode current collector, and the separator of the present invention. After the obtained electrode group is accommodated in a battery can, it can be manufactured by impregnating an electrolytic solution composed of a non-aqueous organic solvent containing an electrolyte.

  As the shape of the electrode group, for example, a shape in which the cross section when the electrode group is cut in a direction perpendicular to the winding axis is a circle, an ellipse, a rectangle, a rectangle with rounded corners, etc. Can be mentioned. In addition, examples of the shape of the battery include a paper shape, a coin shape, a cylindrical shape, and a square shape.

  As the positive electrode sheet, a material obtained by applying a positive electrode mixture containing a positive electrode active material, a conductive material and a binder to a positive electrode current collector is usually used. The electrode mixture for positive electrode preferably includes a material capable of doping and dedoping lithium ions as a positive electrode active material, a carbonaceous material as a conductive material, and a thermoplastic resin as a binder.

Specific examples of the positive electrode active material include lithium composite oxides containing at least one transition metal such as V, Mn, Fe, Co, and Ni, and preferably have a high average discharge potential. , Lithium cobaltate, lithium nickelate, composite oxides based on α-NaFeO ₂ type structure such as a part of nickel of lithium nickelate substituted with other elements such as Mn, spinel such as lithium manganese spinel Examples include complex oxides having a mold structure as a base material.

  Examples of the binder include thermoplastic resins, and specifically, polyvinylidene fluoride, vinylidene fluoride copolymer, polytetrafluoroethylene, and tetrafluoroethylene-hexafluoropropylene copolymer. , Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, thermoplastic polyimide, carboxymethylcellulose, polyethylene, polypropylene, etc. Can be mentioned.

  Examples of the conductive agent include a carbonaceous material, specifically, natural graphite, artificial graphite, coke, carbon black, and the like, and a mixture of two or more of these may be used. .

Examples of the positive electrode current collector include Al and stainless steel, and Al is preferable from the viewpoints of light weight, low cost, and ease of processing.
As a method of applying the positive electrode mixture to the positive electrode current collector, a method of pressure molding, pasting the positive electrode mixture using a solvent, etc., applying it on the positive electrode collector, drying and pressing Examples of the method include pressure bonding.

As the negative electrode sheet, a negative electrode mixture containing a material capable of doping and dedoping lithium ions can be used, or a lithium metal, a lithium alloy, or the like can be used. Specific examples of materials that can be removed include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired organic polymer compounds. It is also possible to use chalcogen compounds such as oxides and sulfides that can be doped / undoped with lithium ions at a lower potential. As the carbonaceous material, a carbonaceous material mainly composed of graphite such as natural graphite or artificial graphite is preferable because of high potential flatness and low average discharge potential. The shape of the carbonaceous material may be, for example, a flake shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, or an aggregate of fine powder.
In the case where the electrolyte solution does not contain the later-described ethylene carbonate, the use of a negative electrode mixture containing polyethylene carbonate is preferable because the cycle characteristics and large current discharge characteristics of the resulting battery may be improved.

  The negative electrode mixture may contain a binder as necessary. Examples of the binder include thermoplastic resins. Specifically, polyvinylidene fluoride, a copolymer of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene-terolafluoroethylene, Examples thereof include thermoplastic polyimide, carboxymethyl cellulose, polyethylene, and polypropylene.

  As chalcogen compounds such as oxides and sulfides used as a material capable of doping and dedoping lithium ions contained in the electrode mixture for the negative electrode, the elements of Groups 13, 14, and 15 in the periodic table are mainly used. Examples include crystalline or amorphous oxides, chalcogen compounds such as sulfides, and specific examples include amorphous compounds mainly composed of tin oxide. Also in these cases, a carbonaceous material as a conductive material and a thermoplastic resin as a binder can be added as necessary.

Examples of the negative electrode current collector used for the negative electrode sheet include Cu, Ni, and stainless steel. Cu is preferable in that it is difficult to form an alloy with lithium and it can be easily processed into a thin film.
The method for applying the electrode mixture for the negative electrode to the negative electrode current collector is the same as that for the positive electrode. It is pasted into a paste using a method by pressure molding, a solvent, etc., dried and pressed. Examples of the method include pressure bonding.

As the electrolytic solution, for example, an electrolytic solution in which a lithium salt is dissolved in an organic solvent can be used. Examples of the lithium salt include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LIBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , Examples thereof include lower aliphatic lithium carboxylic acid salts and LiAlCl _4, and a mixture of two or more of these may be used. The lithium salt is selected from the group consisting of fluorine-containing LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ and LiC (SO ₂ CF ₃ ) ₃ among these. It is preferable to use those containing at least one kind.

  Examples of the organic solvent used in the electrolytic solution include propylene carbonate, ethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, 1,2 Carbonates such as di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, Ethers such as 2-methyltetrahydrofuran; esters such as methyl formate, methyl acetate and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N Amides such as N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone, or fluorine substituents are introduced into the above organic solvents These compounds may be mentioned, and two or more of these may be mixed and used. Among these, a mixed solvent containing carbonates is preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate, or a mixed solvent of cyclic carbonate and ethers is more preferable. The mixed solvent of cyclic carbonate and non-cyclic carbonate includes a wide operating temperature range, excellent load characteristics, and natural graphite and artificial graphite as materials capable of doping and dedoping lithium ions contained in the electrode mixture for negative electrodes When a graphite material such as is used, a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferable in that it is hardly decomposable. Examples of the cyclic carbonate include ethylene carbonate, and examples of the non-cyclic carbonate include dimethyl carbonate and ethyl methyl carbonate.

  The present invention also relates to a capacitor having the separator of the present invention. The capacitor having the separator of the present invention can be manufactured by using a known technique as disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-106327.

  An example of the capacitor is an electric double layer capacitor. The capacitor is composed of an electrode, a separator, and an electrolytic solution, and an electrolyte dissolved in the electrolytic solution is adsorbed on the electrode and formed between the electrolyte and the electrode. It is a capacitor that stores electrical energy at the interface (electric double layer).

Carbon electrodes are used for electrodes for capacitors, and activated carbon, carbon black, polyacene, etc. can be used. Generally, micropores (pore diameter is usually obtained by carbonizing and activating raw materials such as coconut shells) Activated carbon having pores of 20 μm or less). The total pore volume of the activated carbon is usually less than 0.95 ml / g, preferably 0.5 ml / g or more and 0.93 ml / g or less. If the total pore volume is less than 0.95 ml / g, it is preferable because the electrostatic capacity per unit volume is improved. Activated carbon is usually pulverized to an average particle size of 50 μm or less, preferably 30 μm or less, particularly preferably 10 μm or less. By finely pulverizing the activated carbon, the bulk density of the electrode can be improved and the internal resistance can be reduced.
In addition, activated carbon having almost no alkali metal or alkaline earth metal content, that is, a metal content of 100 ppm or less is not polarized by the metal content, and many electric double layers are formed. Therefore, it is preferably used as an electrode. Usually, the electrode further contains a binder, a conductive agent and the like so that it can be easily formed as an electrode.

  As a method for producing an electrode, a mixture containing activated carbon, a binder, a conductive agent and the like is usually formed on a current collector. Specifically, for example, a method in which a mixed slurry obtained by adding a solvent to activated carbon, a binder, a conductive agent, etc. is applied to or dipped in a current collector by a doctor blade method or the like, and dried, for example, activated carbon, a binder, a conductive agent. A method in which a sheet obtained by kneading, shaping and drying by adding a solvent to the current collector is bonded to the current collector surface via a conductive adhesive, followed by pressing and heat treatment drying, for example, activated carbon, binder, conductive And a method of forming a mixture of an agent and a liquid lubricant on a current collector, removing the liquid lubricant, and then stretching the obtained sheet-like molded product in a uniaxial or multiaxial direction. It is done. When making an electrode into a sheet form, the thickness is about 50-1000 micrometers.

  Examples of the material for the current collector used for the electrode for the capacitor include metals such as nickel, aluminum, titanium, copper, gold, silver, platinum, aluminum alloy, and stainless steel, such as carbon material, nickel on activated carbon fiber, Conductive agent applied to resin formed by plasma spraying or arc spraying of aluminum, zinc, copper, tin, lead or alloys thereof, such as rubber, styrene-ethylene-butylene-styrene copolymer (SEBS), etc. Examples thereof include a dispersed conductive film. Particularly preferred is aluminum which is lightweight, excellent in electrical conductivity and electrochemically stable.

  Examples of the conductive agent used for the electrode for the capacitor include graphite, carbon black, acetylene black, ketjen black, conductive carbon such as activated carbon different from the present invention; natural graphite, thermally expanded graphite, scaly graphite, expanded Graphite-based conductive agents such as graphite; carbon fibers such as vapor-grown carbon fibers; metal fine particles or metal fibers such as aluminum, nickel, copper, silver, gold, and platinum; conductive metal oxides such as ruthenium oxide and titanium oxide; Examples thereof include conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyacene. Carbon black, acetylene black, and ketjen black are particularly preferable in that the conductivity is effectively improved in a small amount. The compounding amount of the conductive agent in the electrode is usually about 5 to 50 parts by weight, preferably about 10 to 30 parts by weight with respect to 100 parts by weight of the activated carbon of the present invention.

  As said binder used for the electrode for capacitors, the polymer of a fluorine compound is mentioned, for example, As a fluorine compound, fluorinated alkyl (C1-C18) (meth) acrylate, perfluoroalkyl ( (Meth) acrylate, perfluoroalkyl-substituted alkyl (meth) acrylate, perfluorooxyalkyl (meth) acrylate, fluorinated alkyl (1 to 18 carbon atoms) crotonate, fluorinated alkyl (1 to 18 carbon atoms) malate and fumarate, fluorine Alkyl fluorinated (1-18 carbon atoms) itaconate, fluorinated alkyl-substituted olefins (about 2-10 carbon atoms, about 1-17 fluorine atoms), tetrafluoroethylene, trifluoroethylene, vinylidene fluoride, hexafluoropropylene, etc. Can be mentioned. In addition, addition polymers of monomers containing ethylenic double bonds that do not contain fluorine atoms, starch, methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylhydroxyethylcellulose, nitrocellulose, etc. And polysaccharides thereof; phenol resin; melamine resin; polyurethane resin; urea resin: polyimide resin; polyamideimide resin; petroleum pitch; As the binder, a polymer of a fluorine compound is preferable, and polytetrafluoroethylene which is a polymer of tetrafluoroethylene is particularly preferable. A plurality of types of binders may be used as the binder. As a compounding quantity of the binder in an electrode, it is about 0.5-30 weight part normally with respect to 100 weight part of activated carbon, Preferably it is about 2-30 weight part.

  Electrolytes dissolved in the electrolyte for capacitors are roughly classified into inorganic electrolytes and organic electrolytes. Examples of the inorganic electrolyte include acids such as sulfuric acid, hydrochloric acid and perchloric acid, bases such as sodium hydroxide, potassium hydroxide, lithium hydroxide and tetraalkylammonium hydroxide, salts such as sodium chloride and sodium sulfate, etc. Is mentioned. Among inorganic electrolytes, an aqueous sulfuric acid solution is preferable because of its excellent stability and low corrosiveness to the materials constituting the electric double layer capacitor. The concentration of the inorganic electrolyte is usually about 0.2 to 5 mol (electrolyte) / L (electrolytic solution), and preferably about 1 to 2 mol (electrolyte) / L (electrolytic solution). When the concentration is 0.2 to 5 mol / L, ion conductivity in the electrolytic solution can be ensured. The inorganic electrolyte is usually mixed with water and used as an electrolytic solution.

Examples of the organic electrolyte include BO ₃ ³⁻ , F ⁻ , PF ₆ ⁻ , BF ₄ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , ClO ₄ ⁻ , AlF ₄ ⁻ , AlCl ₄ ⁻ , TaF ₆ ⁻ and NbF _6. A combination of an inorganic anion such as ⁻ , SiF ₆ ²⁻ , CN ⁻ , F (HF) ⁿ⁻ (wherein n represents a numerical value of 1 or more and 4 or less) and an organic cation described later; Combinations with organic cations, and combinations with organic anions and inorganic cations such as lithium ions, sodium ions, potassium ions, hydrogen ions, and the like can be mentioned.

The organic cation is a cationic organic compound, and examples thereof include an organic quaternary ammonium cation and an organic quaternary phosphonium cation. An organic quaternary ammonium cation consists of an alkyl group (1-20 carbon atoms), a cycloalkyl group (6-20 carbon atoms), an aryl group (6-20 carbon atoms), and an aralkyl group (7-20 carbon atoms). A quaternary ammonium cation in which a hydrocarbon group selected from the group is substituted with a nitrogen atom, and an organic quaternary phosphonium cation is a quaternary phosphonium cation in which the same hydrocarbon group as described above is substituted with a phosphorus atom. is there. A hydroxyl group, amino group, nitro group, cyano group, carboxyl group, ether group, aldehyde group, or the like may be bonded to the substituted hydrocarbon group. As the organic cation, an organic quaternary ammonium cation is preferable, and among them, an imidazolium cation is preferable. Particularly, 1-ethyl-3-methylimidazolium (EMI ⁺ ) has a capacitance per unit volume. This is preferable because it tends to increase.

The organic anion is an anion containing a hydrocarbon group which may have a substituent, for example, N (SO ₂ R _f ) ²⁻ , C (SO ₂ R _f ) ³⁻ , R _f COO ⁻ , And an anion selected from the group consisting of R _f SO ³⁻ (R _f represents a C 1-12 perfluoroalkyl group), and organic acids (carboxylic acid, organic sulfonic acid, organic phosphoric acid) shown below ) Or an anion obtained by removing an active hydrogen atom from phenol. As the anion, an inorganic anion is preferable, and BF ₄ ⁻ , AsF ₆ ⁻ , and SbF ₆ ⁻ are particularly preferable. Among them, BF ₄ ⁻ is preferable because the capacitance tends to be improved.

  The organic polar solvent contained in the electrolytic solution is a solvent mainly comprising at least one selected from the group consisting of carbonates, lactones and sulfoxides, preferably propylene carbonate, ethylene carbonate, butylene carbonate, It is a solvent containing at least one selected from the group consisting of sulfolane, 3-methylsulfolane, acetonitrile, dimethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, ethylene glycol and diethyl carbonate as a main component. Particularly preferred is a solvent comprising at least one selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyrolactone, and sulfolane as a main component. Here, “main component” means that the compound occupies 50% by weight or more, preferably 70% by weight or more of the solvent. The higher the content of the organic polar solvent, the longer the capacitor. Durability and operating voltage can be improved. The organic polar solvent for dissolving the electrolyte may be a mixture of two or more different solvents.

  As a method for producing a capacitor using the capacitor electrode, the electrolytic solution, and the separator of the present invention, for example, a pair of sheet electrodes are wound through the separator of the present invention to produce an electrode group, A method in which the electrode group is impregnated with an electrolytic solution and accommodated in a bottomed cylindrical case, a rectangular electrode and a rectangular separator of the present invention are alternately laminated to produce an electrode group, and the electrode group is electrolyzed. A method of impregnating with a liquid and storing it in a bottomed rectangular case can be given.

  EXAMPLES Next, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples. The tests and evaluations in the examples and comparative examples were performed as follows.

(1) Measurement of raw material monomer amount The obtained porous film is dissolved in dimethylacetamide, a solution containing a nitrogen-containing aromatic polymer and the raw material monomer at a predetermined concentration is prepared, and a gel permeation chromatography (GPC) measuring device. The raw material monomer weight% was quantified using a calibration curve method.
(2) Porosity A sample of the obtained porous film or laminated porous film was cut into a square having a side length of 10 cm, and weight W (g) and thickness D (cm) were measured. The weight (Wi) of each layer in the sample is obtained, and the volume of each layer is obtained from Wi and the true specific gravity (g / cm ³ ) of the material of each layer. The rate (volume%) was determined.
Porosity (volume%) = 100 × {1- (W1 / true specific gravity 1 + W2 / true specific gravity 2 +. + Wn / true specific gravity n) / (10 × 10 × D)} (2)
(3) Measurement of air permeability by Gurley method The obtained porous film or laminated porous film was measured with a digital timer type Gurley type densometer manufactured by Yasuda Seiki Seisakusho Co., Ltd. based on JIS P8117.
(4) Thickness measurement The thickness of the obtained porous film or laminated porous film was measured according to JIS standard K7130 (1992).

(5) Long-term storage stability evaluation of lithium secondary battery produced using the obtained separator (5-1) Production of positive electrode sheet Carboxymethyl cellulose, polytetrafluoroethylene, acetylene black, lithium cobaltate as positive electrode active material Powder and water were dispersed and kneaded to obtain an electrode mixture paste for positive electrode. The weight ratio of each component contained in this paste was 0.75: 4.55: 2.7: 92: 45 in a weight ratio of carboxymethylcellulose: polytetrafluoroethylene: acetylene black: lithium cobaltate powder: water. Met. The paste was applied to predetermined portions on both sides of a 20 μm thick Al foil serving as a positive electrode current collector, dried, roll-pressed, and slitted to obtain a positive electrode sheet. The length of the Al foil in the portion where the positive electrode mixture was not applied was 1.5 cm, and an aluminum lead was resistance welded to the portion where the positive electrode mixture was not applied.
(5-2) Production of Negative Electrode Sheet Carboxymethyl cellulose, natural graphite, artificial graphite and water were dispersed and kneaded to obtain a paste of an electrode mixture for negative electrode. The weight ratio of each component contained in this paste was 2.0: 58.8: 39.2: 122.8 in a weight ratio of carboxymethylcellulose: natural graphite: artificial graphite: water. The paste was applied to predetermined portions on both sides of a 12 μm-thick Cu foil serving as a negative electrode current collector, followed by drying, roll pressing, and slitting to obtain a negative electrode sheet. The length of the Cu foil in the portion where the negative electrode mixture was not applied was 1.5 cm, and a nickel lead was resistance welded to the portion where the negative electrode mixture was not applied.
(5-3) Production of Cylindrical Battery The positive electrode sheet, negative electrode sheet (negative electrode electrode mixture uncoated portion 30 cm) and separator produced as described above were arranged in the order of positive electrode sheet, separator, and negative electrode sheet. Moreover, it laminated | stacked so that the mixture uncoated part of a negative electrode might become the outermost periphery, and it wound up from one end, and was set as the electrode group.
The above electrode element is inserted into a battery can, and LiPF ₆ is dissolved in a mixed solution of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a volume ratio of 16:10:74 as a non-aqueous electrolyte solution so as to be 1 mol / liter. Using a battery lid that also serves as a positive electrode terminal, the lid was sealed through a gasket and sealed to obtain a 18650 size cylindrical battery. In addition, when using the laminated porous film of the present invention as the separator, it was laminated so that the positive electrode sheet and the porous film side of the present invention were in contact with each other, and the negative electrode sheet and the porous film side containing the thermoplastic resin were in contact with each other. .
(5-4) Test Method The cylindrical battery obtained as described above was subjected to a prescribed aging treatment so that the initial characteristics were obtained, and then the discharge capacity at 1C was measured and the battery was fully charged at 4.2V. Then, it preserve | saved for 4 weeks in a 60 degreeC thermostat. The battery taken out after 4 weeks is cooled to room temperature, and then the discharge capacity at 1C is measured again. The percentage of the discharge capacity before storage is defined as the recovery rate, which is an indicator of long-term storage stability. It was.
(5-5) Evaluation of adhesion between positive electrode sheet and separator Measure the maximum static friction force (kgf) generated by applying pressure from the positive electrode sheet side and pulling out only the separator with the positive electrode sheet and separator laminated. As a result, the adhesion between the positive electrode sheet and the separator was evaluated.

(6) Safety evaluation of lithium secondary battery produced from the obtained separator (6-1) Production of battery A cylindrical battery was produced by the same method as described in the long-term storage stability evaluation.
(6-2) Test method The following test was implemented as a safety test. A 18650 cylindrical battery charged at a constant current and a constant voltage of 4.3 V for 3 hours was fixed to a dedicated frame. A φ2.5 mm nail attached to a hydraulic press type nail piercing and testing machine was lowered to the center of the winding group at a speed of 5 mm / sec, and the behavior when the nail was penetrated through the battery can was observed.

Example 1 (Polyimide)
1. Preparation of slurry for coating 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride (impurity content 3.3 wt%) and 3,3′-diaminobenzophenone (impurity content 3.8 wt%) And 20 g of a product obtained by condensation polymerization of the above with 20 g of N-methyl-2-pyrrolidone dissolved in 80 g of N-methyl-2-pyrrolidone (Nippon Aerosil Co., Ltd .: Alumina C, average particle size 0.013 μm) was added, The mixture was mixed and treated three times with a nanomizer, and the resulting slurry was filtered through a 1000 mesh wire net and degassed under reduced pressure to obtain slurry A for coating.
2. Preparation of laminated porous film A PET film substrate having a thickness of 100 μm was wound on a drum having a diameter of 550 mm and a length of 350 mm. A polyethylene porous film having a thickness of 16 μm was wound on a PET film substrate. One side of the polyethylene porous film was fixed to the drum with tape. A weight of 0.6 kg was suspended on the other side so that a load was evenly applied to the substrate. A stainless steel coating bar having a diameter of 25 mm was arranged in parallel at the top of the drum so that the clearance from the drum was 0.01 mm. The drum was rotated and stopped so that the end of the polyethylene porous film fixed with the tape came between the drum and the coating bar. While supplying the coating slurry A prepared as described above onto the polyethylene porous film in front of the coating bar, the drum was rotated at 0.5 rpm, and coating was performed on the polyethylene porous film. The entire surface of the polyethylene porous film was coated, and the drum and the raw material monomer were precipitated by placing the drum in a 50% humidity atmosphere at 23 ° C. for 10 minutes while rotating the drum. After coating the slurry A for coating on a 100 μm PET film substrate and a polyethylene porous film, the deposited film is removed from the drum while being integrated and immersed in ion-exchanged water. Washed for 12 hours. After washing, the PET film substrate is taken, the obtained wet coating film is sandwiched between polyester cloths from both sides, and further sandwiched between aramid felts and placed on a 3 mm thick aluminum flat plate. A 1 mm nylon film was placed, the periphery was sealed with a sealant, and the interior was evacuated and dried at 70 ° C. for 6 hours to obtain a laminated porous film. The resulting porous porous film had a non-porous temperature of 140 ° C.
3. 2. Production of porous film The above-mentioned 2. except that the slurry for coating is applied on the PET film substrate without winding the polyethylene porous film. In the same manner, a porous film was produced. The obtained porous film was dissolved in dimethylacetamide, the alumina was removed by centrifugation, and the amount of raw material monomer was measured from the resulting solution. As a result, it was found to be 3% by weight. Moreover, the thermal decomposition temperature of the obtained porous film was 380 degreeC.
4). Evaluation of Separator The separator made of the obtained laminated porous film had a thickness of 22 μm, a porosity of 45% by volume, and an air permeability of 720 seconds / 100 cc. Further, when a cylindrical lithium secondary battery was produced using the separator and the long-term storage stability was examined, the recovery rate was 88.3%. Further, when the safety test of the battery was conducted, it was a gradual temperature increase that took 5 minutes or more to reach the maximum temperature when the nail penetrated.
5. Adhesion with electrode When the adhesion between the positive electrode sheet and the separator was examined, the maximum static frictional force was 1.0 kgf.

Example 2 (Polyamideimide)
1. Preparation of Coating Slurry 2 g of a product obtained by condensation polymerization of trimellitic anhydride (impurity content 0.31% by weight) and 4,4′-diphenylmethane diisocyanate (impurity content 0.37% by weight) To a solution dissolved in 98 g of methyl-2-pyrrolidone, 10 g of alumina fine particles (manufactured by Nippon Aerosil Co., Ltd .: Alumina C, average particle size 0.013 μm) are added and mixed, and the resultant slurry is treated three times with a nanomizer. This was filtered through a 1000 mesh wire net and defoamed under reduced pressure to obtain slurry B for coating.
2. Production of Laminated Porous Film A stainless steel coating bar was placed in parallel so that the clearance from the drum was 0.015 mm, and the coating slurry B was used except that the coating slurry B was used. In the same manner, a laminated porous film was obtained. The resulting porous porous film had a non-porous temperature of 140 ° C.
3. 2. Production of porous film The above-mentioned 2. except that the slurry for coating is applied on the PET film substrate without winding the polyethylene porous film. In the same manner, a porous film was produced. The obtained porous film was dissolved in dimethylacetamide, the alumina was removed by centrifugation, and the amount of raw material monomer was measured from the resulting solution. As a result, it was found to be 0.3% by weight. Moreover, the thermal decomposition temperature of the obtained porous film was 380 degreeC.
4). Evaluation of Separator The separator made of the obtained laminated porous film had a thickness of 21 μm, a porosity of 50% by volume, and an air permeability of 680 seconds / 100 cc. A cylindrical lithium secondary battery was produced using the separator and its long-term storage stability was examined. The recovery rate was 91.0%. Further, when the safety test of the battery was conducted, it was a gradual temperature increase that took 5 minutes or more to reach the maximum temperature when the nail penetrated.
5. Adhesion with electrode When the adhesion between the positive electrode sheet and the separator was examined, the maximum static frictional force was 0.9 kgf.

Comparative Example 1 (Polyimide)
1. Preparation of slurry for coating 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic dianhydride (impurity content 8.8 wt%) and 3,3′-diaminobenzophenone (impurity content 9.2 wt%) And 20 g of a product obtained by condensation polymerization of the above with 20 g of N-methyl-2-pyrrolidone dissolved in 80 g of N-methyl-2-pyrrolidone (Nippon Aerosil Co., Ltd .: Alumina C, average particle size 0.013 μm) was added, The resultant slurry was mixed three times with a nanomizer, and the resulting slurry was filtered through a 1000 mesh wire net and defoamed under reduced pressure, and then used as a slurry C for coating.
2. Production of laminated porous film 1. In Example 1, except that the slurry C for coating was used. In the same manner, a laminated porous film was obtained. The resulting porous porous film had a non-porous temperature of 140 ° C.
3. 2. Production of porous film The above-mentioned 2. except that the slurry for coating is applied on the PET film substrate without winding the polyethylene porous film. In the same manner, a porous film was produced. The obtained porous film was dissolved in dimethylacetamide, the alumina was removed by centrifugation, and the amount of raw material monomer was measured from the resulting solution. As a result, it was found to be 8% by weight. Moreover, the thermal decomposition temperature of the obtained porous film was 350 degreeC.
4). Evaluation of Separator The separator made of the obtained laminated porous film had a thickness of 22 μm, a porosity of 50% by volume, and an air permeability of 700 seconds / 100 cc. A cylindrical lithium secondary battery was produced using the separator and its long-term storage stability was examined. The recovery rate was 75.5%.
5. Adhesiveness with electrode When the adhesiveness between the positive electrode sheet and the separator was examined, the maximum static frictional force was 1.1 kgf.

Comparative Example 2 (Polyimide)
1. Preparation of slurry for coating 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic dianhydride (impurity content 0.04 wt%) and 3,3′-diaminobenzophenone (impurity content 0.02 wt%) And 20 g of a product obtained by condensation polymerization of the above with 20 g of N-methyl-2-pyrrolidone dissolved in 80 g of N-methyl-2-pyrrolidone (Nippon Aerosil Co., Ltd .: Alumina C, average particle size 0.013 μm) was added, The resultant slurry was mixed three times with a nanomizer, and the resulting slurry was filtered through a 1000 mesh wire net and defoamed under reduced pressure, and then used as a coating slurry D.
2. Production of Laminated Porous Film 1. Except that the coating slurry D was used, In the same manner, a laminated porous film was obtained. The resulting porous porous film had a non-porous temperature of 140 ° C.
3. 2. Production of porous film The above-mentioned 2. except that the slurry for coating is applied on the PET film substrate without winding the polyethylene porous film. In the same manner, a porous film was produced. The obtained porous film was dissolved in dimethylacetamide, the alumina was removed by centrifugation, and the amount of raw material monomer was measured from the resulting solution. As a result, it was found to be 0.01% by weight. Moreover, the thermal decomposition temperature of the obtained porous film was 350 degreeC.
4). Evaluation of Separator The separator made of the obtained laminated porous film had a thickness of 22 μm, a porosity of 50% by volume, and an air permeability of 650 seconds / 100 cc. A cylindrical lithium secondary battery was produced using the separator and its long-term storage stability was examined. The recovery rate was 89.0%.
5. Adhesion with electrode When the adhesion between the positive electrode sheet and the separator was examined, the maximum static frictional force was 0.4 kgf.

Claims (16)

  A polymer having a thermal decomposition start temperature of 200 ° C. or higher and a raw material monomer thereof is contained, and the proportion of the raw material monomer is 0.05% by weight or more and 5% by weight or less in the total weight of the polymer and the raw material monomer. A porous film characterized by that.   The porous film according to claim 1, wherein the polymer having a thermal decomposition starting temperature of 200 ° C or higher is a nitrogen-containing aromatic polymer.   The porous film according to claim 2, wherein the nitrogen-containing aromatic polymer is an aromatic polyimide.   The porous film according to claim 2, wherein the nitrogen-containing aromatic polymer is an aromatic polyamideimide.   Furthermore, the porous film in any one of Claims 1-4 containing an organic powder and / or an inorganic powder.   Furthermore, the porous film in any one of Claims 1-4 containing an alumina.   A laminated porous film obtained by laminating the porous film according to claim 1 and a porous film containing a thermoplastic resin in contact with each other.   The laminated porous film according to claim 7, wherein the thermoplastic resin is polyethylene.   The laminated porous film according to claim 7 or 8, wherein the non-porous temperature is less than 180 ° C.   A separator comprising the porous film according to claim 1.   A separator comprising the laminated porous film according to claim 7.   The separator according to claim 10 or 11, wherein the porosity is 20% by volume or more and 90% by volume or less.   The separator according to any one of claims 10 to 12, which has an air permeability of 20 seconds / 100 cc or more and 2000 seconds / 100 cc by the Gurley method.   A battery comprising the separator according to claim 10.   A lithium secondary battery comprising the separator according to claim 10.   A capacitor comprising the separator according to claim 10.