JP2014175055A - Porous film for secondary battery, slurry for secondary battery porous film, method of manufacturing porous film for secondary battery, electrode for secondary battery, separator for secondary battery, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous film for a secondary battery having small thermal shrinkage rate and excellent thermal shrinkage resistance, capable of improving battery performance such as rate characteristics of the secondary battery configured using the porous film for the secondary battery.SOLUTION: A porous film for a secondary battery contains a non-conductive particle, a water-soluble polymer, and a binder. The non-conductive particle is an organic fine particle. The binder contains an acrylic polymer containing a fluorine-based polymer and (meth) acrylic acid alkyl ester monomer unit.

Description

  The present invention relates to a porous film for a secondary battery, a slurry for a secondary battery porous film, a method for producing a porous film for a secondary battery, a secondary battery electrode using the porous film for a secondary battery, and a secondary battery. The present invention relates to a battery separator and a secondary battery.

  Secondary batteries, particularly lithium ion secondary batteries, are small and light, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. In the lithium ion secondary battery, a separator is generally used to prevent a short circuit between the positive electrode and the negative electrode. A normal separator is made of a polyolefin-based material such as polyethylene or polypropylene, and has a physical property of melting at 200 ° C. or lower. Therefore, when a battery becomes high temperature, there exists a possibility that a separator may cause volume changes, such as shrinkage | contraction and a fusion | melting. Such a phenomenon may cause a short circuit between the positive electrode and the negative electrode, release of electric energy, and the like.

Therefore, it has been proposed to provide a porous film that can improve the heat resistance and strength of the separator and the electrodes (positive electrode and negative electrode). Such porous films include those formed by binding non-conductive particles such as organic fine particles and inorganic fine particles with a binder. Here, among non-conductive particles, organic fine particles are less likely to adversely affect battery performance by mixing moisture and metal ions into the porous film compared to inorganic fine particles. From the viewpoint of battery performance, Suitable for use in porous membranes.
However, the porous film containing organic fine particles has a problem that the strength is low and the performance of preventing a short circuit of the battery under a high temperature use environment is low. In addition, since it is difficult to make the film thickness distribution and the strength distribution uniform in the porous film containing organic fine particles, partial cracking is likely to occur, and the porous film is cut and curved during the production of the secondary battery. Powdering (dropping of fine powder from the porous film) was liable to occur. And when powder omission etc. arise, there existed a problem that the performance of secondary batteries, such as cycling characteristics, fell, for example.

  Therefore, conventionally, techniques have been proposed for porous films containing organic fine particles to improve the performance of preventing battery short-circuiting in a high-temperature environment and to make the film thickness and strength distribution uniform (for example, Patent Documents). 1). According to Patent Document 1, by setting the shape factor of the organic fine particles contained in the porous membrane for a secondary battery, the coefficient of variation of the shape factor, and the particle size within a predetermined range, the possibility of a short circuit at a high temperature is low. Thus, a porous film for a secondary battery having a uniform film thickness and strength distribution can be obtained.

International Publication No. 2012/020737

  However, in recent years, there has been a demand for higher performance of secondary batteries. Specifically, in a secondary battery using a porous film containing organic fine particles, the thermal contraction rate of the porous film is reduced (that is, the heat shrinkage is increased), and the occurrence of a short circuit of the battery in a high temperature environment is prevented. There is a demand for further suppressing the safety of the secondary battery. There is also a demand for further improving battery performance such as rate characteristics.

  In view of such points, the present invention is a porous film for a secondary battery having a small heat shrinkage rate and excellent heat shrinkage resistance, such as a rate characteristic of a secondary battery configured using the porous film for a secondary battery. It aims at providing the porous film for secondary batteries which can improve battery performance. Moreover, an object of this invention is to provide the manufacturing method of the slurry for secondary battery porous films which provides this porous film for secondary batteries, and the porous film for secondary batteries. Furthermore, an object of this invention is to provide the electrode for secondary batteries, the separator for secondary batteries, and a secondary battery which have this porous membrane for secondary batteries.

  The present inventor has intensively studied for the purpose of solving the above problems. And this inventor uses a binder containing a fluorine-type polymer and a predetermined acrylic polymer as a binder used for manufacture of the porous membrane for secondary batteries, and is non-conductive in the porous membrane for secondary batteries. The present inventors have found that a homogeneous porous film can be obtained by uniformly dispersing contained components such as conductive particles and a binder. Further, the present inventor has found that the porous film for a secondary battery using a binder containing a fluorine-based polymer and a predetermined acrylic polymer has a small heat shrinkage rate, and uses the porous film for a secondary battery. The present invention was completed by confirming that the rate characteristics of the secondary battery constructed as described above could be improved.

  That is, the present invention aims to advantageously solve the above-mentioned problems, and the porous membrane for a secondary battery of the present invention includes non-conductive particles, a water-soluble polymer and a binder, and the non-conductive The conductive particles are organic fine particles, and the binder contains a fluoropolymer and an acrylic polymer containing a (meth) acrylic acid alkyl ester monomer unit. Thus, in a porous membrane for a secondary battery using organic fine particles as non-conductive particles, a binder containing a fluorine-based polymer and an acrylic polymer containing a (meth) acrylic acid alkyl ester monomer unit is provided. By using it, the heat shrinkage resistance of the porous membrane for a secondary battery can be improved, and the rate characteristics of a secondary battery configured using the porous membrane for a secondary battery can be improved.

  Here, as for the porous film for secondary batteries of this invention, it is preferable that the said acrylic polymer has an acidic functional group. This is because, when the acrylic polymer has an acidic functional group, an effect of improving the adhesion of the porous film to the substrate and the binding force as a binder can be expected.

  In the porous membrane for a secondary battery of the present invention, the acidic functional group is preferably at least one selected from a carboxylic acid group and a sulfonic acid group. This is because when the acrylic polymer has at least one of a carboxylic acid group and a sulfonic acid group, the adhesion of the porous membrane to the substrate and the binding force as a binder can be further improved.

  Moreover, this invention aims at solving the said subject advantageously, The slurry for secondary battery porous films of this invention contains a nonelectroconductive particle, a water-soluble polymer, a binder, and water, The nonconductive particles are organic fine particles, and the binder contains a fluoropolymer and an acrylic polymer containing a (meth) acrylic acid alkyl ester monomer unit. If such a slurry for a porous membrane containing organic fine particles as non-conductive particles and containing a fluorine-based polymer as a binder and an acrylic polymer containing a (meth) acrylic acid alkyl ester monomer unit is used. In addition, it is possible to form a porous film for a secondary battery that has high heat shrinkage resistance and can improve the rate characteristics of the secondary battery when used for manufacturing a secondary battery.

  Here, in the slurry for a secondary battery porous membrane of the present invention, the acrylic polymer preferably has an acidic functional group. Since the acrylic polymer has an acidic functional group, the binding force as a binder can be improved, and the base of the porous membrane for a secondary battery obtained by applying the slurry for the porous membrane to the substrate and drying it. This is because the adhesion to the material can be improved.

  In the slurry for a secondary battery porous membrane of the present invention, the acidic functional group is preferably at least one selected from a carboxylic acid group and a sulfonic acid group. When the acrylic polymer has at least one of a carboxylic acid group and a sulfonic acid group, the binding force as a binder can be further improved, and a secondary film obtained by applying a slurry for a porous film to a substrate and drying it This is because the adhesion of the battery porous membrane to the substrate can be further improved.

  Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and the method for producing a porous film for a secondary battery according to the present invention is based on any of the above-mentioned slurry for a secondary battery porous film. The method includes a step of applying a slurry layer on a material and a step of drying the slurry layer. By applying the slurry for a secondary battery porous membrane as described above onto a substrate and drying to produce a porous membrane for a secondary battery, the heat-resistant shrinkage is high, and it was used for the production of a secondary battery. In this case, a porous film for a secondary battery that can improve the rate characteristics of the secondary battery is obtained.

  Furthermore, this invention aims to solve the above-mentioned problem advantageously, and the electrode for a secondary battery of the present invention is attached to the current collector and the current collector and is used for the electrode mixture layer. An electrode mixture layer containing a binder and an electrode active material, and any one of the above-described porous membrane for a secondary battery formed on the surface of the electrode mixture layer. When the secondary battery electrode has the secondary battery porous film as described above, the safety and rate characteristics of the secondary battery including the secondary battery electrode can be improved.

  Furthermore, this invention aims at solving the said subject advantageously, The separator for secondary batteries of this invention is the above-mentioned secondary formed in the surface of the organic separator and the said organic separator. Any of the porous membranes for batteries is provided. When the secondary battery separator has the secondary battery porous film as described above, the safety and rate characteristics of the secondary battery including the secondary battery separator can be improved.

  Furthermore, this invention aims at solving the said subject advantageously, The secondary battery of this invention is a secondary battery containing a positive electrode, a negative electrode, a separator, and electrolyte solution, Comprising: The said positive electrode, At least one of the negative electrode and the separator has any one of the above-described porous membrane for a secondary battery. When at least one of the positive electrode, the negative electrode, and the separator of the secondary battery has the above-described porous film for a secondary battery, the safety and rate characteristics of the secondary battery can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, in the porous film for secondary batteries, while reducing a thermal contraction rate, the secondary characteristic which can improve the rate characteristic of the secondary battery comprised using the said porous film for secondary batteries, A porous membrane for a battery can be provided. Moreover, according to this invention, the manufacturing method of the slurry for secondary battery porous films which provides this porous film for secondary batteries, and the porous film for secondary batteries can be provided. Furthermore, according to the present invention, it is possible to provide a secondary battery electrode, a secondary battery separator, and a secondary battery having such a secondary battery porous membrane.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the slurry for a secondary battery porous membrane of the present invention is used when forming a porous membrane for a secondary battery. And the manufacturing method of the porous membrane for secondary batteries of this invention prepares the slurry for secondary battery porous membranes of this invention, and when manufacturing the porous membrane for secondary batteries from the said slurry for secondary battery porous membranes Can be used.
The secondary battery electrode, the secondary battery separator, and the secondary battery of the present invention are characterized by using the porous film for a secondary battery of the present invention.

(Secondary battery porous membrane)
The porous membrane for a secondary battery of the present invention is a porous membrane for a secondary battery containing non-conductive particles, a water-soluble polymer and a binder, wherein the non-conductive particles are organic fine particles, and the binder is a fluorine-based polymer. It contains a coalescence and an acrylic polymer containing a (meth) acrylic acid alkyl ester monomer unit.
The porous membrane for a secondary battery according to the present invention uses an organic fine particle as non-conductive particles, and an acrylic polymer containing a fluoropolymer as a binder and a (meth) acrylic acid alkyl ester monomer unit. Is used together, and the uniformity of the porous film is high. Moreover, while being excellent in heat-resistant shrinkage, the rate characteristic of the secondary battery comprised using the said porous film for secondary batteries can be improved.

<Non-conductive particles>
As the non-conductive particles, for example, known organic fine particles that exist stably in an environment where a secondary battery such as a lithium ion secondary battery is used and are electrochemically stable can be used.
Here, when the organic fine particles are used as the non-conductive particles, it is possible to suppress the deterioration of the battery performance by suppressing the mixing of metal ions as compared with the case of using the inorganic fine particles. In addition, organic fine particles usually have a lower specific gravity than inorganic fine particles and are excellent in dispersibility in the slurry for a secondary battery porous film used for forming a porous film. Evenly dispersed in the porous film.

As the organic fine particles, particles composed of various polymers can be used, but a polymer synthesized using a polymerizable monomer having a vinyl group is preferably used.
The polymerizable monomer having a vinyl group is not particularly limited, and styrene such as styrene, α-methylstyrene, p-methylstyrene, p-chlorostyrene, chloromethylstyrene, or a derivative thereof; vinyl chloride; acetic acid Vinyl esters such as vinyl and vinyl propionate; unsaturated nitriles such as acrylonitrile; (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylic (Meth) acrylic acid or its ester derivatives such as 2-ethylhexyl acid, stearyl (meth) acrylate; monofunctional monomers such as conjugated dienes such as butadiene and isoprene, divinylbenzene, trimethylolpropane diacrylate , Trimethylolpropane trimethacrylate, tetramethylo Propane tetra (meth) acrylate, polyfunctional monomers such as ethylene glycol dimethacrylate. Among these, divinylbenzene and ethylene glycol dimethacrylate are preferable as the polymerizable monomer having a vinyl group from the viewpoint of improving heat resistance. These polymerizable monomers may be used independently and may be used together 2 or more types.
In the present application, “(meth) acrylic acid” means acrylic acid and / or methacrylic acid, and “(meth) acrylate” means acrylate and / or methacrylate.

In addition, the polymer which comprises organic fine particles may have monomers other than the polymerizable monomer which has a vinyl group.
As the monomer other than the polymerizable monomer having a vinyl group, any monomer copolymerizable with the polymerizable monomer having a vinyl group can be used. Specifically, monomers other than the polymerizable monomer having a vinyl group include a monomer having a carboxyl group, a monomer having a sulfonic acid group, a monomer having a hydroxyl group, and an amide. Examples thereof include monomers containing a group, cationic monomers, monomers containing a cyano group, monomers containing an epoxy group, and polar group-containing monomers such as salts thereof. These monomers may be used alone or in combination of two or more.

  Here, it is preferable that the content rate of the polymerizable monomer unit which has a vinyl group in the polymer which comprises organic fine particles is 65-100 mass%. By making the content ratio of the polymerizable monomer unit having a vinyl group 65% by mass or more, the heat resistance of the porous film containing the organic fine particles can be improved.

<Method for producing non-conductive particles>
The organic fine particles as non-conductive particles contained in the porous membrane for a secondary battery of the present invention are the above-mentioned monomer or a mixture of monomers (hereinafter sometimes referred to as “monomer composition”). Can be obtained by polymerization by a known polymerization method such as dispersion polymerization, emulsion polymerization, or microsuspension polymerization. Among these, as the polymerization method, dispersion polymerization and emulsion polymerization are preferable, and dispersion polymerization is particularly preferable. By using these polymerization methods, it is possible to form organic fine particles that are uniform and have good dispersibility in the slurry for the porous membrane of the secondary battery used for the preparation of the porous membrane. The uniformity of the porous film can be improved.

  Here, examples of the medium that can be used for the polymerization of the monomer composition include water, an organic solvent, and a mixture thereof. As the organic solvent, those which are inert to radical polymerization and do not inhibit the polymerization of monomers can be used. Specific examples of the organic solvent include alcohols such as methanol, ethanol, propanol, cyclohexanol and octanol, esters such as dibutyl phthalate and dioctyl phthalate, ketones such as cyclohexanone, polyvinyl pyrrolidone and a mixture thereof. .

In addition to the monomer composition and the medium, optional components can be added to the polymerization reaction system. Specifically, components such as a polymerization initiator, a suspension protective agent, and a surfactant can be added.
As the polymerization initiator, a general water-soluble radical polymerization initiator or an oil-soluble radical polymerization initiator can be used. Examples of the water-soluble radical initiator include potassium persulfate, sodium persulfate, cumene hydroperoxide, hydrogen peroxide, or a redox initiator based on a combination of these reducing agents. Examples of oil-soluble polymerization initiators include benzoyl peroxide, α, α′-azobisisobutyronitrile, t-butylperoxy-2-ethylhexanoate, 3,5,5-trimethylhexanoyl peroxide. An oxide etc. can be mentioned. Of the oil-soluble polymerization initiators, α, α′-azobisisobutyronitrile can be preferably used.
Examples of the suspension protective agent include polyvinyl alcohol, carboxymethyl cellulose, sodium polyacrylate, and a fine powder inorganic compound.
As the surfactant, a normal one can be used, and examples thereof include anionic emulsifiers such as sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium dialkylsulfosuccinate, and a formalin condensate of naphthalenesulfonic acid. Furthermore, nonionic surfactants such as polyoxyethylene nonylphenyl ether, polyethylene glycol monostearate, sorbitan monostearate can be used in combination.

Here, in the case of preparing organic fine particles using emulsion polymerization, polymerization (seed polymerization) may be performed using seed particles. When seed polymerization is performed, seed particles prepared in advance may be used, or by first polymerizing a part of the monomer contained in the emulsion containing the monomer composition. The formed seed polymer may be used as seed particles. In seed polymerization, the organic particles are prepared by absorbing the monomer in the seed particles and then performing polymerization.
When a seed polymer formed by previously polymerizing a part of the monomer contained in the emulsion is used as seed particles, the polymerization of the seed polymer may be performed in a plurality of stages. Specifically, for example, the seed polymer A is formed by using a part of the monomer constituting the monomer composition, and the seed polymer A is separated from the monomer constituting the monomer composition. A larger seed polymer B can be formed by using a part of the polymer, and organic fine particles can be formed by using the seed polymer B and the remainder of the monomer constituting the monomer composition.

  The organic fine particles are preferably monodispersed fine particles having a volume average particle diameter of 0.1 to 1.0 μm. The particle diameter of the organic fine particles can be freely designed according to the particle diameter of the seed particles and the mixing ratio of the polymerizable monomer and the seed particles. Both the organic fine particles and the binder described below are present as fine particles, which differ in that the organic fine particles do not have a binding property, whereas the binder has a binding property.

<Water-soluble polymer>
The water-soluble polymer used in the present invention functions as a thickener for the slurry for the secondary battery porous membrane used for forming the porous membrane, and dissolves in water, but in the electrolyte of the secondary battery. On the other hand, it is a polymer compound that does not dissolve. Here, the polymer being water-soluble means that the insoluble content is less than 0.5% by mass when 0.5 g of the polymer is dissolved in 100 g of water at 25 ° C.
Examples of water-soluble polymers include cellulose polymers such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose, and ammonium salts and alkali metal salts of these cellulose polymers; modified or unmodified polyvinyl alcohol, acrylic acid or acrylic Polyvinyl alcohols such as copolymers of acid salts and vinyl alcohol, maleic anhydride, maleic acid or copolymers of fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide without a hydrophobic moiety, polyvinyl pyrrolidone, Modified polyacrylic acid, oxidized starch, phosphate starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride, and the like can be used. Among these, from the viewpoint of the stability of the slurry for the secondary battery porous membrane, the water-soluble polymer is preferably carboxymethyl cellulose and methyl cellulose, and more preferably carboxymethyl cellulose. These water-soluble polymers may be used alone or in combination of two or more.

  In addition, the compounding quantity of the water-soluble polymer in the slurry for secondary battery porous membranes of this invention is 5-30 mass parts normally per 100 mass parts of organic fine particles, Preferably it is 10-20 mass parts. When the blending amount of the water-soluble polymer is within the above range, the stability of the slurry for the secondary battery porous membrane is improved. If the blending amount of the water-soluble polymer is below the above range, the viscosity of the slurry for the secondary battery porous membrane is insufficient and the stability of the slurry is lowered, and conversely, the blending amount of the water-soluble polymer exceeds the above range. For example, when the porous membrane for a secondary battery is used, the permeability of ions in the electrolytic solution is deteriorated, and the battery characteristics may be deteriorated.

<Binder>
The binder contained in the porous membrane for a secondary battery of the present invention is
A fluoropolymer (a),
An acrylic polymer (b) containing a (meth) acrylic acid alkyl ester monomer unit;
Containing. Thus, the binder in the slurry for a secondary battery porous film used for forming a porous film when a fluoropolymer and an acrylic polymer containing a (meth) acrylic acid alkyl ester monomer unit are used in combination as a binder. In the porous membrane for a secondary battery using organic fine particles as non-conductive particles, the uniformity of the porous membrane can be improved. Further, by using this binder, the heat shrinkage resistance of the porous film can be improved, and the rate characteristics of a secondary battery configured using the secondary battery porous film can be improved. In the present invention, “comprising a monomer unit” means that a structural unit derived from a monomer is contained in a polymer obtained using the monomer.

  The fluoropolymer (a) used in the present invention is not particularly limited as long as it is a polymer containing a fluorine atom, but a polymer containing at least one of a vinylidene fluoride unit and a hexafluoropropylene unit is preferable, More preferred are polymers containing both vinylidene fluoride units and propylene hexafluoride units.

  The content ratio of the vinylidene fluoride unit in the fluoropolymer (a) used in the present invention is preferably 50 to 100% by mass, more preferably 55 to 100% by mass, and further preferably 60 to 100% by mass. It is. By setting the content ratio of the vinylidene fluoride unit in the above range, the binding force as a binder can be further enhanced while improving the compatibility with the acrylic polymer (b).

  The content ratio of the hexafluoropropylene unit in the fluoropolymer (a) used in the present invention is preferably 0 to 50% by mass, more preferably 0 to 45% by mass, and further preferably 0 to 40% by mass. %. By containing a hexafluoropropylene unit, a binder having excellent flexibility can be obtained, and the heat shrinkage resistance of the porous film can be further improved. In addition, when the content rate of a hexafluoropropylene unit exceeds 50 mass%, there exists a possibility that the crystallinity of a binder may fall and the cycling characteristics of the secondary battery using this porous film for secondary batteries may fall.

In addition, the fluorine-based polymer (a) may have a monomer unit other than the vinylidene fluoride unit and the hexafluoropropylene unit. As such other monomer, For example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i- (meth) acrylate Butyl, n-amyl (meth) acrylate, i-amyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, (meth) N-nonyl acrylate, n-decyl (meth) acrylate, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, trimethylol group (Meth) acrylic acid alkyl esters such as pantri (meth) acrylate, pentaerythritol tetra (meth) acrylate and dipentaerythritol hexa (meth) acrylate; aromatic vinyl compounds such as styrene, α-methylstyrene and divinylbenzene; acetic acid Vinyl esters such as vinyl and vinyl propionate; vinyl halide compounds such as vinyl fluoride, tetrafluoroethylene, vinyl chloride and vinylidene chloride; conjugated dienes such as butadiene, isoprene and chloroprene, ethylene, carboxyl groups, Examples thereof include unsaturated monomers containing a specific functional group such as a carboxylic acid anhydride group, an amide group, an amino group, a cyano group, an epoxy group, a vinyl group, and a sulfonic acid group.
Here, when these other monomers are contained, the content ratio of the units of the other monomers is:
It is necessary to be 25% by weight or less, and more preferably 20% by weight or less.

  Moreover, the acrylic polymer (b) used by this invention is a polymer different from a fluorine-type polymer (a), and is a polymer containing a (meth) acrylic-acid alkylester monomer unit. Specifically, examples of the acrylic polymer (b) include a polymer containing a (meth) acrylic acid alkyl ester monomer unit and not containing a fluorine atom.

  The (meth) acrylic acid alkyl ester monomer forming the (meth) acrylic acid alkyl ester monomer unit includes methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, (meth ) Isopropyl acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isopentyl (meth) acrylate, isooctyl (meth) acrylate , Isobonyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, tridecyl (meth) acrylate, and the like.

  These alkyl (meth) acrylates can be used alone or in combination of two or more. Among these, n-butyl (meth) acrylate, (meta), because the cycle characteristics of a secondary battery using a porous film can be improved by setting the degree of swelling of the binder to the electrolyte to an appropriate level. ) Ethyl acrylate and 2-ethylhexyl (meth) acrylate are preferred, and n-butyl (meth) acrylate is more preferred.

  The content ratio of the (meth) acrylic acid alkyl ester unit in the acrylic polymer (b) is preferably 40 to 99% by mass, more preferably 50 to 90% by mass, and further preferably 70 to 85% by mass. . By setting the content ratio of the (meth) acrylic acid alkyl ester unit within the above range, the liquid retaining property (swellability) of the acrylic polymer (b) with respect to the electrolytic solution can be improved. The cycle characteristics of the secondary battery when used in the secondary battery can be made more excellent.

  In addition, the acrylic polymer (b) used in the present invention has an acidic functional group from the viewpoint that adhesion to an organic separator or an electrode mixture layer and a binding force as a binder can be improved. preferable. In the present invention, the method for introducing an acidic functional group into the acrylic polymer (b) is not particularly limited, but can be copolymerized with the above-mentioned (meth) acrylic acid alkyl ester monomer, and the acidic functional group is A preferred method is to use a monomer having a monomer unit having an acidic functional group in the acrylic polymer (b) of the present invention. In addition, the monomer having an acidic functional group used in the present invention is not particularly limited. However, the monomer having a carboxylic acid group is highly effective in improving the adhesion to a current collector and the binding force as a binder. And at least one selected from a monomer having a sulfonic acid group and a monomer having a phosphoric acid group, preferably selected from a monomer having a carboxylic acid group and a monomer having a sulfonic acid group At least one is preferred.

  Specific examples of the monomer having a carboxylic acid group include monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, and β-trans-aryloxyacrylic. Derivatives of monocarboxylic acids such as acids, α-chloro-β-E-methoxyacrylic acid, β-diaminoacrylic acid; dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid; maleic anhydride, acrylic anhydride, methyl Dicarboxylic acid anhydrides such as maleic anhydride and dimethylmaleic anhydride; methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, diphenylmaleate, nonylmaleate, maleate Decyl acid, dodecyl maleate, octane maleate Examples thereof include derivatives of dicarboxylic acids such as decyl and fluoroalkyl maleate. These may be used alone or in combination of two or more. Among these, acrylic acid, methacrylic acid and itaconic acid are preferable, acrylic acid and methacrylic acid are more preferable, and acrylic acid is particularly preferable.

  Specific examples of the monomer having a sulfonic acid group include sulfonic acid group-containing monomers such as vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfoethyl methacrylate, sulfopropyl methacrylate, and sulfobutyl methacrylate. A sulfonic acid group-containing compound having no functional group other than an acid group; an amide group such as 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 2-hydroxy-3-acrylamidopropanesulfonic acid, and a sulfonic acid group; A compound containing; a compound containing a hydroxyl group and a sulfonic acid group such as 3-allyloxy-2-hydroxypropanesulfonic acid (HAPS); and the like. These lithium salts, sodium salts, potassium salts, and the like can also be used. These may be used alone or in combination of two or more. Among these, a compound containing an amide group and a sulfonic acid group is preferable, and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) is more preferable.

  Specific examples of the monomer having a phosphoric acid group include: 2-acryloyloxyethyl phosphate, 2-methacryloyloxyethyl phosphate, methyl-2-acryloyloxyethyl phosphate, methyl-2-methacryloyloxy phosphate Examples thereof include ethyl, ethyl phosphate-acryloyloxyethyl phosphate, and ethyl phosphate-methacryloyloxyethyl. These may be used alone or in combination of two or more. Among these, 2-methacryloyloxyethyl phosphate is preferable.

  Among the above-mentioned monomers, acrylic acid, methacrylic acid, itaconic acid and 2-acrylamide- are examples of the monomer having an acidic functional group from the viewpoint that the effect of improving the adhesion to the current collector and the binding force as a binder is high. 2-methylpropanesulfonic acid (AMPS) is preferred, acrylic acid, methacrylic acid and AMPS are more preferred, and acrylic acid and AMPS are particularly preferred.

  The content ratio of the monomer unit having an acidic functional group in the acrylic polymer (b) used in the present invention is preferably 0.5 to 10% by mass, more preferably based on the total monomer units. Is 1 to 8% by mass, more preferably 1 to 6% by mass. By making the content rate of the monomer unit which has an acidic functional group into the said range, the improvement effect of the adhesiveness as a collector and the binding force as a binder can be exhibited appropriately. In addition, when the content rate of the monomer unit which has an acidic functional group exceeds 10 mass%, there exists a possibility that stability of a binder may fall. On the other hand, when the content ratio of the monomer unit having an acidic functional group is less than 0.5% by mass, the binding force as a binder may be insufficient.

  The acrylic polymer (b) is a copolymer of the above-described (meth) acrylic acid alkyl ester and a monomer copolymerizable with the (meth) acrylic acid alkyl ester other than the monomer having an acidic functional group. Such a copolymerizable monomer may be a nitrile group-containing monomer, an aromatic vinyl monomer, or a (meth) acrylic acid other than a (meth) acrylic acid alkyl ester. Examples include esters.

  Examples of the nitrile group-containing monomer include acrylonitrile; α-halogenoacrylonitrile such as α-chloroacrylonitrile and α-bromoacrylonitrile; α-alkylacrylonitrile such as methacrylonitrile; Among these, acrylonitrile and methacrylonitrile are preferable, and acrylonitrile is more preferable because the binding force as a binder can be further increased. The nitrile group-containing monomer may be used alone or in combination of two or more.

  The content ratio of the nitrile group-containing monomer unit in the acrylic polymer (b) is preferably 30% by mass or less, more preferably 3 to 25% by mass, and further preferably 5 to 20% by mass. By setting the content ratio of the nitrile group-containing monomer unit in the above range, the binding force as a binder can be further increased, and thereby the cycle characteristics of the secondary battery when the porous film is used in the secondary battery. Can be made more excellent. Moreover, the peel strength between the porous film and the substrate can be increased. In addition, when the content rate of the nitrile group containing monomer unit in an acrylic polymer (b) exceeds 30 mass%, there exists a possibility that stability of a binder may fall.

  Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, m-methylstyrene, p-methylstyrene, o-chlorostyrene, p-chlorostyrene, and divinylbenzene. Among these, styrene and α-methylstyrene are preferable, and styrene is particularly preferable. The aromatic vinyl monomer may be used alone or in combination of two or more.

  The content ratio of the aromatic vinyl monomer unit in the acrylic polymer (b) is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, and further preferably 1 to 10% by mass. %. In addition, when the content ratio of the aromatic vinyl monomer unit in the acrylic polymer (b) exceeds 20% by mass, the binder becomes hard and the heat shrinkability of the secondary battery porous membrane of the present invention may be reduced. If the amount is less than 0.5% by mass, the binding property of the binder is lowered, and the peel strength of the porous film may be lowered.

  In addition, (meth) acrylic acid esters other than (meth) acrylic acid alkyl esters include butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydipropylene glycol (meth) acrylate, and (meth) acrylic. Ether group-containing (meth) acrylic acid esters such as methoxypolyethylene glycol acid, phenoxyethyl (meth) acrylate, and tetrahydrofurfuryl (meth) acrylate; (meth) acrylic acid-2-hydroxyethyl, (meth) acrylic acid- Hydroxyl group-containing (meth) acrylic acid esters such as 2-hydroxypropyl, (meth) acrylic acid-2-hydroxy-3-phenoxypropyl, 2- (meth) acryloyloxyethyl-2-hydroxyethylphthalic acid; (Meta) acryloyloxy Carboxylic acid-containing (meth) acrylic acid esters such as 2- (meth) acryloyloxyethyl phthalic acid; fluorine-containing (meth) acrylic acid esters such as (meth) acrylic perfluorooctylethyl; (meth) Phosphoric acid group-containing (meth) acrylic acid ester such as ethyl acrylate phosphate; Epoxy group-containing (meth) acrylic acid ester such as glycidyl (meth) acrylate; Amino group content such as dimethylaminoethyl (meth) acrylate ( (Meth) acrylic acid ester; and the like.

  The content ratio of the (meth) acrylic acid ester monomer unit other than the (meth) acrylic acid alkyl ester in the acrylic polymer (b) is preferably 7% by mass or less, more preferably 1 to 5% by mass, More preferably, it is 1.5-4 mass%. By making the content ratio of (meth) acrylic acid ester monomer units other than (meth) acrylic acid alkyl ester within the above range, the slurry for porous film used for forming the porous film can be made dispersible in non-conductive particles. It is possible to obtain a good slurry that is excellent and has no sedimentation.

  Further, the acrylic polymer (b) may be a copolymer of other monomers copolymerizable with the above-mentioned monomers. Examples of such other monomers include: Examples thereof include carboxylic acid esters having two or more carbon-carbon double bonds, amide monomers, olefins, diene monomers, vinyl ketones, and heterocyclic ring-containing vinyl compounds.

<Method for producing binder>
As long as the binder contained in the porous membrane for a secondary battery of the present invention contains a fluoropolymer (a) and an acrylic polymer (b) containing a (meth) acrylic acid alkyl ester monomer unit. In addition, the fluoropolymer (a) and the acrylic polymer (b) may be prepared individually and mixed (polymer mixture), or the fluoropolymer (a) and the acrylic polymer. It may be composed of a composite polymer obtained by combining (b). Note that it is preferable to use a composite polymer as the binder because a binder having high stability and good dispersibility in the slurry for the porous film used for forming the porous film can be obtained. That is, if the binder is a composite polymer of the fluoropolymer (a) and the acrylic polymer (b), the uniformity of the porous film and the heat shrinkage can be improved, and the secondary battery The rate characteristic of the secondary battery configured using the porous film for a battery can be improved.

  In addition, it is preferable to set it as 10-90 mass parts with respect to 100 mass parts of the whole binder, and, as for the quantity of the acrylic polymer (b) in a binder, it is more preferable to set it as 30-70 mass parts. This is because by setting the content range of the acrylic polymer (b) in the above range, the binding force as a binder can be made sufficient, and thereby, favorable rate characteristics can be expressed. The weight ratio of the fluoropolymer (a) to the acrylic polymer (b) is preferably 10/90 to 90/10, more preferably 30/70 to 70/30. In addition, the form of the binder is not particularly limited, but a binder having a particle shape is preferable, and it is particularly preferable that the binder can exist in a state in which the particle state is maintained even in the porous film. This is because the non-conductive particles can be satisfactorily bound. Furthermore, when the form of the binder is particulate, the number average particle diameter is preferably 50 to 500 nm, more preferably 70 to 400 nm, and particularly preferably 100 to 250 nm. Furthermore, the glass transition temperature (Tg) of the binder is preferably −50 to 25 ° C., more preferably −45 to 15 ° C., and particularly preferably −40 to 5 ° C.

<Method for producing polymer mixture>
Here, the production method of the fluoropolymer (a) in the case where the fluoropolymer (a) and the acrylic polymer (b) are separately prepared is not particularly limited. It can manufacture by superposing | polymerizing by the emulsion polymerization method which uses as a dispersion medium.

  The emulsifier used in the emulsion polymerization is not particularly limited, and any of an anionic surfactant, a nonionic surfactant, and a cationic surfactant can be used. Such emulsifiers include, for example, 2- (1-allyl) -4-nonylphenoxypolyethylene glycol sulfate ammonium. The addition amount of the emulsifier can be arbitrarily set, and is usually about 0.01 to 10 parts by mass with respect to 100 parts by mass of the total amount of monomers used for polymerization.

  Examples of the polymerization initiator used for the polymerization include lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexanoylper Organic peroxides such as oxide, azo compounds such as α, α′-azobisisobutyronitrile, ammonium persulfate, potassium persulfate and the like can be mentioned.

  The method for producing the acrylic polymer (b) in the case where the fluoropolymer (a) and the acrylic polymer (b) are separately prepared is not particularly limited, but each monomer described above is treated with water as a dispersion medium. A method of polymerizing by an emulsion polymerization method is preferred. As the emulsifier and the polymerization initiator used in the emulsion polymerization, the same ones as the above-mentioned fluoropolymer (a) can be used.

<Method for producing composite polymer>
In addition, the composite polymer of the fluoropolymer (a) and the acrylic polymer (b) is a polymer obtained by polymerizing any one of the fluoropolymer (a) and the acrylic polymer (b) in advance. And a method for polymerizing the other polymer in the presence of the polymer, a monomer for obtaining the fluoropolymer (a), and a monomer for obtaining the acrylic polymer (b) In the same reaction vessel, and a method of polymerizing simultaneously, and a method of converting a solution containing a fluoropolymer into an aqueous dispersion. The emulsifier and the polymerization initiator used for the polymerization can be the same as the above-described fluoropolymer (a).

  And the content rate of the binder containing the fluoropolymer (a) and the acrylic polymer (b) in the porous membrane for a secondary battery of the present invention is preferably 1 to 20 masses with respect to 100 mass parts of the organic fine particles. Parts, more preferably 5 to 15 parts by mass. By making the content rate of a binder into the said range, it is possible to improve the high temperature short circuit-proof property and battery performance of the secondary battery comprised using the porous film for secondary batteries of this invention. When the content of the binder for the porous film in the porous film for the secondary battery is less than 1 part by mass with respect to 100 parts by mass of the organic fine particles, the strength of the porous film for the secondary battery becomes insufficient and the porous film for the secondary battery A short circuit is likely to occur in the secondary battery configured using the. On the other hand, when the content ratio of the binder in the secondary battery porous film exceeds 20 parts by mass with respect to 100 parts by mass of the organic fine particles, the porosity of the secondary battery porous film decreases, and the secondary battery porous film There is a possibility that the battery performance of the secondary battery configured using the battery becomes insufficient.

<Optional component>
In addition, the porous membrane for a secondary battery according to the present invention includes a heavy metal supplement compound, a dispersing agent, a leveling agent, an antioxidant, an antifoaming agent, an electrolytic solution additive and the like described in International Publication No. 2012/020737. Can be added.

<Method for producing porous membrane for secondary battery>
As a method for producing a porous membrane for a secondary battery of the present invention, 1) a slurry for porous membrane containing organic fine particles as non-conductive particles, a water-soluble polymer, a binder and water is applied on a predetermined substrate. A slurry layer, and then drying the slurry layer; 2) immersing the substrate in a slurry for porous membrane containing organic fine particles, water-soluble polymer, binder and water as non-conductive particles, and then drying this Method; Among these, the method 1) is preferable because the thickness of the porous film can be easily controlled. Hereinafter, the method 1) will be described as a method for producing a porous membrane for a secondary battery of the present invention.

<Slurry for porous membrane>
The slurry for a porous membrane of the present invention contains the binder produced as described above, organic fine particles as non-conductive particles, a water-soluble polymer, and water. In the porous membrane slurry of the present invention, it is of course possible to use a mixed medium of water and a water-soluble solvent (for example, lower alcohol) as a dispersion medium.
The solid content concentration of the slurry for the porous membrane can be appropriately adjusted to a concentration at which the slurry can be applied and immersed and has a fluid viscosity, but is generally about 10 to 50% by mass. It is.
Components other than the solid content in the slurry are components that volatilize upon drying, and in addition to a dispersion medium such as water, for example, a medium in which these are dissolved or dispersed during the preparation and addition of non-conductive particles and a binder. Including.
Since the slurry for a porous membrane of the present invention is for forming the porous membrane for a secondary battery of the present invention, non-conductive particles, a binder, and a water-soluble polymer in the total solid content of the slurry for a porous membrane. And the content rate of an arbitrary component (component mentioned above as an arbitrary component of a porous film) can be made into the ratio as having mentioned above about the porous film of this invention.
In addition to the above-mentioned optional components as the non-conductive particles, binder, water-soluble polymer, water, and optional components of the porous membrane, the slurry for the porous membrane further has functions such as dispersing agent and electrolyte decomposition suppression. Arbitrary components, such as an electrolyte solution additive, may be included. These are not particularly limited as long as they do not affect the battery reaction.

The method for producing the slurry for the porous membrane is not particularly limited, and can be obtained by mixing the non-conductive particles, the binder, the water-soluble polymer, and water and optional components added as necessary.
The mixing device is not particularly limited as long as it can uniformly mix the above components, and a homomixer, a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or the like is used. However, it is particularly preferable to use a homomixer that can add an appropriate dispersion share.
The viscosity of the slurry for the porous membrane is preferably 10 mPa · s to 10,000 mPa · s, more preferably 50 to 500 mPa · s, from the viewpoints of uniform coatability and slurry aging stability. The viscosity is a value measured using a B-type viscometer at 25 ° C. and a rotation speed of 60 rpm.

In the present invention, the porous film has a film-like shape. The porous membrane may be an article that can maintain its shape as a membrane independently (that is, without being supported by a substrate). However, the porous film may be a layer formed on a substrate that does not independently maintain the shape of the film. In the present invention, the porous membrane can usually be the latter. The composite of the porous membrane and the substrate used for forming the porous membrane can be used as it is, for example, as a separator or an electrode in a battery.
In a certain aspect of the method for producing a porous membrane of the present invention, the substrate is a component in the battery, and it is a preferable component having the porous membrane. Specifically, it is preferable to use a secondary battery electrode or an organic separator as a base material and form a porous film thereon.
In the method for producing a porous membrane of the present invention, the porous membrane may be formed on a substrate other than the electrode and the organic separator. When the porous film of the present invention is formed on a substrate other than an electrode or an organic separator, it is used by peeling the porous film from the substrate and laminating it directly on the electrode or the organic separator when assembling the battery directly. I can do it. In this case, an appropriate release film such as a known release film can be used as the substrate.

  The method for applying and drying the slurry for the porous film onto the substrate is not particularly limited. Examples thereof include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. Among them, the dip method and the gravure method are preferable in that a uniform porous film can be obtained. Examples of the method for drying the slurry layer obtained by coating include drying by warm air, hot air, low-humidity air, vacuum drying, and (dry) drying by irradiation with infrared rays, electron beams, or the like.

  The drying temperature of the slurry layer obtained by coating can be changed depending on the type of medium used. In order to completely remove the medium, for example, in the case of using a low-volatility medium such as N-methylpyrrolidone, the medium may be dried at a high temperature of 120 ° C. or higher with a blower-type dryer. Conversely, when a highly volatile medium is used, it can be dried at a low temperature of 100 ° C. or lower. When forming a porous film on the organic separator mentioned later, since it is necessary to dry without causing shrinkage of the organic separator, drying at a low temperature of 100 ° C. or lower is preferable.

  The film thickness of the obtained porous film is not particularly limited, and is appropriately set according to the use or application field of the porous film. However, if the film is too thin, a uniform film cannot be formed. 1 to 10 μm is preferable, and 2 to 7 μm is more preferable, because the capacity per volume (weight) of the resin is reduced.

<Electrode for secondary battery>
The electrode for a secondary battery according to the present invention includes a current collector, an electrode mixture layer that adheres to the current collector and includes an electrode mixture layer binder and an electrode active material, and a surface of the electrode mixture layer. And the formed porous membrane for a secondary battery of the present invention. Since this secondary battery electrode has the porous film for a secondary battery of the present invention, the safety and rate characteristics of the secondary battery including the secondary battery electrode can be improved.

<Current collector>
The current collector is not particularly limited as long as it has electrical conductivity and is electrochemically durable. For example, the current collector can be made of a material described in International Publication No. 2012/020737.

<Electrode mixture layer>
The electrode mixture layer includes an electrode active material and a binder (binder for the electrode mixture layer). By including the binder, the binding property of the electrode mixture layer in the electrode is improved, the strength against the mechanical force applied during the process of winding the electrode is increased, and the active material in the electrode is increased. Since it becomes difficult to detach, the risk of a short circuit due to the detachment is reduced.

What is necessary is just to select the electrode active material used for the electrode for secondary batteries of this invention according to the secondary battery in which an electrode is utilized, or the kind (positive electrode or negative electrode) of an electrode. Examples of the secondary battery include a lithium ion secondary battery and a nickel hydride secondary battery.
When the electrode for a secondary battery of the present invention is used for an electrode of a lithium ion secondary battery or a nickel metal hydride battery, an electrode active material described in International Publication No. 2012/020737 can be used.
As the binder for the electrode mixture layer, for example, various resin components and soft polymer components described in International Publication No. 2012/020737 can be used at the adjusted viscosity and ratio described in the pamphlet. .
The formation of the electrode mixture layer on the current collector can be performed using a known method. Moreover, formation of the porous film on the electrode mixture layer can be performed as described above.

<Separator for secondary battery>
The separator for secondary batteries of this invention has an organic separator and the porous film for secondary batteries of this invention formed in the surface of an organic separator. Since this secondary battery separator has the porous film for secondary batteries of the present invention, the safety and rate characteristics of the secondary battery using the secondary battery separator can be improved.
As an organic separator, well-known things, such as a separator containing polyolefin resin, such as polyethylene and a polypropylene, and an aromatic polyamide resin, are used. The organic separator can be obtained, for example, according to the description in WO2012 / 020737.
The separator of the present invention may have a porous film only on one side of the organic separator, or may have a porous film on both sides of the organic separator.
The porous film can be formed on the organic separator as described above.

<Secondary battery>
The secondary battery of the present invention is a secondary battery including a positive electrode, a negative electrode, a separator, and an electrolytic solution, and at least one of the positive electrode, the negative electrode, and the separator has a porous film for a secondary battery. In this secondary battery, safety and rate characteristics can be improved by having the porous membrane for a secondary battery of the present invention.
Secondary batteries include lithium ion secondary batteries, nickel metal hydride secondary batteries, etc., but safety improvement is most demanded and the effect of introducing a porous film is the highest, and in addition, improvement of rate characteristics is cited as an issue. Therefore, a lithium ion secondary battery is preferable. Hereinafter, the case where the porous film of the present invention is used for a lithium ion secondary battery will be described.

<Electrolyte for secondary battery>
As the electrolytic solution for the lithium ion secondary battery, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is used. As the organic solvent and the supporting electrolyte, for example, organic solvents and lithium salts described in International Publication No. 2012/020737 can be used.

<Separator and electrode>
As the separator, the separator of the present invention having a porous film can be used, but when at least one of the positive electrode and the negative electrode has the porous film of the present invention, other separators can also be used. For example, what was illustrated above as an organic separator can be used as a separator as it is.
As the positive electrode and the negative electrode, the electrode for the secondary battery of the present invention having a porous film can be used. However, when any one of the electrodes or the separator has the porous film of the present invention, the other electrode is used. You can also. For example, the above-described laminate composed of the current collector and the electrode mixture layer adhering thereto can be used as an electrode as it is.
However, in the secondary battery of the present invention, at least one, preferably all of the positive electrode, the negative electrode, and the separator have the porous film of the present invention.

  As a specific method for producing a lithium ion secondary battery, a positive electrode and a negative electrode are overlapped via a separator, and this is wound into a battery container according to the shape of the battery. The method of injecting and sealing is mentioned. The porous film of the present invention is formed on any one of a positive electrode, a negative electrode, and a separator. In addition, lamination with only a porous film is possible. If necessary, an extra metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate and the like can be inserted to prevent an increase in pressure inside the battery and overcharge / discharge. The shape of the battery may be any of a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. In the following description, “%” and “part” representing amounts are based on mass unless otherwise specified.
In Examples and Comparative Examples, the following methods are used for the heat shrinkability, uniformity, and peel strength of the secondary battery porous membrane, and the rate characteristics of the secondary battery using the secondary battery porous membrane, respectively. And evaluated.

<Heat shrinkability>
A separator for a secondary battery (a separator with a porous film) or an electrode (an electrode with a porous film) is cut into a width of 10 cm and a length of 10 cm to obtain a test piece. After leaving the test piece in an oven adjusted to a temperature of 150 ° C. for 1 hour, the length of each side was measured, and the shrinkage rate of the side having the largest shrinkage rate was evaluated as the thermal shrinkage rate according to the following criteria. The smaller the heat shrinkage rate, the higher the heat shrinkage resistance and the better the safety of the secondary battery.
A: Heat shrinkage rate is less than 3.0% B: Heat shrinkage rate is 3.0% or more and less than 5.0% C: Heat shrinkage rate is 5.0% or more and less than 10.0% D: Heat shrinkage rate is 10 0.0% or more

<Uniformity of porous film>
A separator with a porous film or an electrode with a porous film was cut into a width of 6 cm and a length of 1 m, and the thickness of the cut-out separator with a porous film or an electrode with a porous film was 20 points every 3 cm in the width direction and every 5 cm in the length direction. Measurement was made at 60 points, and the film thickness variation was calculated from the standard deviation and average value of the film thickness based on the following formula, and evaluated according to the following criteria.

ここで、ｘは膜厚の平均値、ｎは測定数を示す。
Ａ：膜厚のばらつきが３％未満
Ｂ：膜厚のばらつきが３％以上〜１０％未満
Ｃ：膜厚のばらつきが１０％以上

Here, x represents an average value of the film thickness, and n represents the number of measurements.
A: Variation in film thickness is less than 3% B: Variation in film thickness is 3% or more and less than 10% C: Variation in film thickness is 10% or more

<Peel strength test>
A separator with a porous membrane or an electrode with a porous membrane is cut into a rectangle with a length of 100 mm and a width of 10 mm to form a test piece, and cellophane tape (specified in JIS Z1522) is applied to the porous membrane surface with the porous membrane surface down. The stress was measured when one end of the separator with the porous membrane or the electrode with the porous membrane was pulled in the vertical direction at a pulling rate of 50 mm / min and peeled off (the cellophane tape was fixed to the test stand). The measurement was performed three times, the average value was obtained, and this was taken as the peel strength. It shows that the binding strength to the base material (organic separator or electrode) of a porous membrane layer is so large that peel strength is large, ie, adhesive strength is large.
A: Peel strength is 100 N / m or more B: Peel strength is 75 N / m or more and less than 100 N / m C: Peel strength is 50 N / m or more and less than 75 N / m D: Peel strength is 25 N / m or more and less than 50 N / m E: Peel strength is less than 25 N / m

<Rate characteristics>
Using a 10-cell full-cell coin type battery in which the porous membrane for a secondary battery of the present invention is applied to an organic separator or electrode, the battery is charged to 4.2 V at a constant current of 0.1 C at 25 ° C. A charge / discharge cycle for discharging to 3.0 V with a constant current of 1.0 and a charge / discharge cycle for charging to 4.2 V with a constant current of 0.1 C and discharging to 3.0 V with a constant current of 1.0 C were performed, respectively. The ratio of the discharge capacity at 1.0 C to the discharge capacity at 0.1 C was calculated as a percentage to obtain charge / discharge rate characteristics, and the determination was made according to the following criteria. It shows that internal resistance is so small that this value is large, and high-speed charge / discharge is possible.
A: The charge / discharge rate characteristic is 80% or more.
B: The charge / discharge rate characteristics are 70% or more and less than 80%.
C: The charge / discharge rate characteristics are 60% or more and less than 70%.
D: The charge / discharge rate characteristic is 50% or more and less than 60%.
E: The charge / discharge rate characteristic is less than 50%.

<Example 1>
(Manufacture of non-conductive particles)
In a reactor, 100 parts of divinylbenzene (manufactured by Dow Chemical Co., Ltd., product name: divinylbenzene 55 (55% effective, 41% by weight of ethylvinylbenzene and 4% by weight of p-diethylbenzene)), polyvinylpyrrolidone 20 parts, 5.0 parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl O) as a polymerization initiator, 1100 parts of methanol, 70 ° C. under nitrogen gas atmosphere For 24 hours. This obtained the nonelectroconductive particle which consists of organic fine particles with a high monodispersity of a volume average particle diameter of 670 nm.

(Manufacture of binder)
The interior of an autoclave with an internal volume of about 6 liters equipped with an electromagnetic stirrer was sufficiently purged with nitrogen, then charged with 2.5 liters of deoxygenated pure water and 25 g of ammonium perfluorodecanoate as an emulsifier, and stirred at 350 rpm. The temperature was raised to 60 ° C. Next, a mixed gas composed of 44.2% by mass of vinylidene fluoride (VDF) and 55.8% by mass of propylene hexafluoride (HFP) was charged until the internal pressure reached 20 kg / cm ² . Thereafter, 25 g of Freon 113 solution containing 20% by mass of diisopropyl peroxydicarbonate as a polymerization initiator was injected using nitrogen gas to initiate polymerization. During the polymerization, a mixed gas composed of 60.2% by mass of vinylidene fluoride and 39.8% by mass of propylene hexafluoride was sequentially injected to maintain the internal pressure at 20 kg / cm ² . Further, since the polymerization rate decreased with the progress of the polymerization, after the lapse of 3 hours, the same amount of the polymerization initiator as that of the previous one was injected using nitrogen gas, and the reaction was further continued for 3 hours. The reaction liquid was cooled and the stirring was stopped, and the reaction was stopped by releasing unreacted monomers to obtain an aqueous dispersion of a fluoropolymer. When the content ratio of the vinylidene fluoride unit and the hexafluoropropylene unit contained in the obtained fluoropolymer was analyzed by ¹ H-NMR, the content ratio of the vinylidene fluoride unit was 60% by mass, The content ratio of the hexafluoropropylene unit was 40% by mass.

  After the inside of the 7-liter separable flask was sufficiently purged with nitrogen, 100 parts of an aqueous dispersion of the obtained fluoropolymer (in terms of solid content) and 2- (1-allyl) -4-nonyl as an emulsifier 3 parts of phenoxypolyethyleneglycol sulfate ammonium was charged and the temperature was raised to 75 ° C. Next, 60% by mass of n-butyl acrylate, 30% by mass of methyl methacrylate, 6% by mass of styrene, 3% by mass of 2-acrylamido-2-methylpropanesulfonic acid, 1% by mass of glycidyl methacrylate, and an appropriate amount of water And stirred at 75 ° C. for 30 minutes. Thereafter, 0.5 part by mass of sodium persulfate was added as a polymerization initiator, and polymerization was carried out at 85 to 95 ° C. for 2 hours. Aqueous dispersion of a binder containing a composite polymer having a volume average particle size of 200 nm containing a fluoropolymer and an acrylic polymer having a (meth) acrylic acid alkyl ester monomer unit by cooling to stop the reaction Got the body.

(Manufacture of slurry for secondary battery porous membrane)
An aqueous dispersion of non-conductive particles obtained as described above, an aqueous dispersion of a binder containing a composite polymer containing a fluoropolymer and an acrylic polymer, and carboxymethylcellulose (Daicel) as a water-soluble polymer Chemical Co., Ltd., trade name: Daicel 1220), solid content weight ratio is non-conductive particles: water-soluble polymer: binder = 83.1: 12.3: 4.6 (the ratio is different. Conductive particles: water-soluble polymer: binder = 83.1: 4.6: 12.3) were mixed in water to obtain a slurry for porous membrane.

(Manufacture of separator with porous membrane)
A single-layer polypropylene organic separator (porosity 55%, thickness 25 μm) produced by a dry method was prepared, and the secondary battery porous material obtained as described above was formed on one surface of the polypropylene organic separator. The slurry for film | membrane was formed by apply | coating using the wire bar so that the thickness after drying might be set to 5 micrometers. Next, the formed slurry layer was dried at 110 ° C. for 20 minutes to form a porous film. And the same operation was performed also on the other surface of the organic separator made of polypropylene, whereby a porous film was formed in the same manner, and a separator with a porous film having a porous film on both surfaces was obtained.

(Manufacture of positive electrode)
95 parts of lithium manganate having a spinel structure as a positive electrode active material and a polyvinylidene fluoride (KF-1100, manufactured by Kureha Chemical Industry Co., Ltd.) as a positive electrode binder (a binder for a positive electrode mixture layer) in terms of solid content In addition, 2 parts of acetylene black and 20 parts of N-methylpyrrolidone were added and mixed with a planetary mixer to obtain a positive electrode slurry. Then, the obtained positive electrode slurry was applied to one side of an aluminum foil having a thickness of 18 μm as a current collector, dried at 120 ° C. for 3 hours, and then roll-pressed to form a positive electrode mixture layer having a total thickness of 100 μm. The positive electrode which has was obtained.

(Manufacture of negative electrode)
98 parts of graphite as a negative electrode active material (volume average particle diameter 20 μm, specific surface area 4.2 m ² / g) and styrene-butadiene rubber (glass transition temperature: binder for negative electrode mixture layer) as negative electrode binder −10 ° C.) so as to be 1 part in terms of solid content, and these are mixed. Then, 1.0 part of carboxymethyl cellulose and water as a dispersion medium are added to the resulting mixture, and these are added to the planetary plate. The slurry for negative electrodes was obtained by mixing with a Lee mixer. The obtained negative electrode slurry was applied to one side of a 18 μm thick copper foil as a current collector, dried at 120 ° C. for 3 hours, and then roll-pressed to form a negative electrode mixture layer having a total thickness of 60 μm. The negative electrode which has this was obtained.

(Manufacture of secondary batteries)
On the inner bottom surface of a stainless steel coin-type outer container provided with a polypropylene packing, the separator with a porous film, the positive electrode, and the negative electrode obtained as described above were cut into circles with diameters of 18 mm, 13 mm, and 14 mm, respectively. In addition, a circular positive electrode with a diameter of 13 mm, an organic separator with a porous film with a diameter of 18 mm, and a circular negative electrode with a diameter of 14 mm were laminated in this order, and these were stored in a coin-type outer container. The positive electrode was placed so that the surface on the aluminum foil side faced the bottom surface side of the outer container, and the surface on the positive electrode mixture layer side faced the separator side with a porous film. The negative electrode was placed so that the surface on the negative electrode mixture layer side faced the separator with a porous film and the surface on the copper foil side faced upward.

(Evaluation)
About the obtained separator for secondary batteries with a porous film, peel strength, heat shrinkability, and the uniformity of the porous film were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery.

<Example 2>
A secondary battery was prepared in the same manner as in Example 1 except that 100 parts of ethylene glycol dimethacrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name: Light Ester EG) was used in place of divinylbenzene during the production of the non-conductive particles. A slurry for a porous membrane was prepared, and a separator with a porous membrane and a secondary battery were produced. And about the manufactured separator with a porous membrane, peel strength, heat-shrinkability, and the uniformity of the porous membrane were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery.

<Example 3>
A slurry for a secondary battery porous membrane was prepared in the same manner as in Example 1 except that methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., product name: Metrose SM) was used as the water-soluble polymer instead of carboxymethylcellulose. A separator with a porous membrane and a secondary battery were produced. And about the manufactured separator with a porous membrane, peel strength, heat-shrinkability, and the uniformity of the porous membrane were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery.

<Example 4>
When producing non-conductive particles, a seed polymer formed by first polymerizing a part of divinylbenzene is used as seed particles, the remaining divinylbenzene is absorbed by the seed particles, and then polymerized to perform organic fine particles. A porous membrane slurry for a secondary battery was prepared in the same manner as in Example 1 except that polymerization was performed by swelling seed polymerization (ie, polymerization was performed by swelling seed polymerization), and a separator with a porous membrane and a secondary battery were produced. And about the manufactured separator with a porous membrane, peel strength, heat-shrinkability, and the uniformity of the porous membrane were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery. Hereinafter, the manufacturing method of the nonelectroconductive particle by swelling seed polymerization is explained in full detail.

(Manufacture of non-conductive particles)
In a reactor equipped with a stirrer, 0.06 part of sodium dodecyl sulfate, 0.23 part of ammonium persulfate and 100 parts of ion-exchanged water were mixed to obtain a mixture, which was heated to 80 ° C.

  On the other hand, in a separate container, 93.8 parts of styrene, 2.0 parts of methacrylic acid, 2.0 parts of acrylonitrile, 1.0 part of allyl glycidyl ether, 1.2 parts of N-methylolacrylamide, 0.1 sodium dodecyl sulfate Part and 100 parts of ion-exchanged water were mixed to prepare a dispersion of a monomer mixture.

The dispersion of the monomer mixture was continuously added to the mixture obtained above over 4 hours and polymerized. The temperature of the reaction system during the addition of the monomer mixture dispersion was maintained at 80 ° C. After completion of the addition, the reaction was further continued at 90 ° C. for 3 hours.
Thereby, an aqueous dispersion of seed polymer particles having a volume average particle diameter of 370 nm was obtained.

  Next, in a reactor equipped with a stirrer, 20 parts of an aqueous dispersion of seed polymer particles based on solid content (that is, based on the weight of seed polymer particles) and divinylbenzene as a monomer (product name, manufactured by Dow Chemical Co., Ltd.) : 100 parts of divinylbenzene 55 (effective content 55%, the remainder includes 41% by weight of ethylvinylbenzene and 4% by weight of p-diethylbenzene), 1.0 part of sodium dodecylbenzenesulfonate, t-as a polymerization initiator 4.0 parts of butyl peroxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: perbutyl O) and 200 parts of ion-exchanged water were added and stirred at 35 ° C. for 12 hours. Thereby, the monomer and the polymerization initiator were completely absorbed in the seed polymer particles. Thereafter, this was polymerized at 90 ° C. for 5 hours. Thereafter, steam was introduced to remove unreacted monomers and initiator decomposition products. Thereby, an aqueous dispersion of non-conductive particles having a volume average particle diameter of 670 nm was obtained.

<Example 5>
(Manufacture of binder)
After the inside of the autoclave equipped with a stirrer was sufficiently purged with nitrogen, 250 parts of ion-exchanged water and 2.5 parts of ammonium perfluorodecanoate as an emulsifier were charged, and the temperature was raised to 60 ° C. while stirring at 350 rpm. Next, a mixed gas composed of 44.2% by mass of vinylidene fluoride and 55.8% by mass of propylene hexafluoride was charged until the internal pressure reached 20 kg / cm ² . Thereafter, 2.5 parts of a Freon 113 solution containing 20% of diisopropyl peroxydicarbonate as a polymerization initiator was injected using nitrogen gas to initiate polymerization. During the polymerization, a mixed gas consisting of 60.2 parts of vinylidene fluoride and 39.8 parts of propylene hexafluoride was sequentially injected to maintain the internal pressure at 20 kg / cm ² . Further, since the polymerization rate decreased with the progress of the polymerization, after the lapse of 3 hours, the same amount of the polymerization initiator as that of the previous one was injected using nitrogen gas, and the reaction was further continued for 3 hours. The reaction liquid was cooled and the stirring was stopped, and the reaction was stopped by releasing unreacted monomers to obtain an aqueous dispersion of a fluoropolymer. In addition, the volume average particle diameter of the obtained fluoropolymer was 160 nm. Further, 100 g of an aqueous dispersion of a fluoropolymer was coagulated with 1 liter of methanol and vacuum-dried at 60 ° C. for 12 hours to obtain a dry polymer. The composition of the obtained dry polymer was changed to ¹ H- As a result of NMR analysis, the composition of the fluoropolymer was 60% by mass of vinylidene fluoride and 40% by mass of propylene hexafluoride.

  After the inside of the 7-liter separable flask was sufficiently purged with nitrogen, 3 parts of 2- (1-allyl) -4-nonylphenoxypolyethylene glycol sulfate ammonium was charged as an emulsifier and heated to 75 ° C. Next, 60% by mass of n-butyl acrylate, 30% by mass of methyl methacrylate, 6% by mass of styrene, 3% by mass of 2-acrylamido-2-methylpropanesulfonic acid, 1% by mass of glycidyl methacrylate, and an appropriate amount of water And stirred at 75 ° C. for 30 minutes. Thereafter, 0.5 part by mass of sodium persulfate was added as a polymerization initiator, and polymerization was carried out at 85 to 95 ° C. for 2 hours. The reaction was stopped by cooling to obtain an aqueous dispersion of an acrylic polymer having a volume average particle diameter of 190 nm.

  The fluoropolymer and acrylic polymer obtained as described above were mixed at a ratio of 1: 1 to obtain a binder mixture. Using the obtained binder mixture, a slurry for a secondary battery porous membrane was prepared in the same manner as in Example 1 to produce a separator with a porous membrane and a secondary battery. And about the manufactured separator with a porous membrane, peel strength, heat-shrinkability, and the uniformity of the porous membrane were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery.

<Example 6>
When polymerizing the acrylic polymer contained in the composite polymer as a binder, 77.75% by mass of 2-ethylhexyl acrylate, 20.25% by mass of acrylonitrile, and 2-acrylamido-2-methyl are used as monomers. A slurry for a secondary battery porous membrane was prepared in the same manner as in Example 1 except that 2% by mass of propanesulfonic acid was used, and a separator with a porous membrane and a secondary battery were produced. And about the manufactured separator with a porous membrane, peel strength, heat-shrinkability, and the uniformity of the porous membrane were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery. The obtained composite polymer had a volume average particle size of 190 nm.

<Example 7>
When polymerizing an acrylic polymer contained in a composite polymer as a binder, n-butyl acrylate 41% by mass, ethyl acrylate 41.5% by mass, acrylonitrile 15% by mass, 2-acrylamido-2-methylpropane A slurry for a secondary battery porous membrane was prepared in the same manner as in Example 1 except that 0.5% by mass of sulfonic acid and 2% by mass of glycidyl methacrylate were used to produce a separator with a porous membrane and a secondary battery. . And about the manufactured separator with a porous membrane, peel strength, heat-shrinkability, and the uniformity of the porous membrane were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery. The obtained composite polymer had a volume average particle size of 190 nm.

<Example 8>
In the same manner as in Example 1, except that 100% by mass of vinylidene fluoride and no propylene hexafluoride were used when polymerizing the fluoropolymer contained in the composite polymer as a binder. A slurry for a secondary battery porous membrane was prepared, and a separator with a porous membrane and a secondary battery were produced. And about the manufactured separator with a porous membrane, peel strength, heat-shrinkability, and the uniformity of the porous membrane were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery. In addition, the volume average particle diameter of the obtained composite polymer was 210 nm.

<Example 9>
(Manufacture of porous membrane electrode)
The slurry for the secondary battery porous membrane prepared in the same manner as in Example 1 is applied to the negative electrode mixture layer side surface of the negative electrode produced in the same manner as in Example 1 so that the porous membrane thickness after drying becomes 5 μm. The slurry layer was obtained by coating. The slurry layer was formed so that the negative electrode mixture layer was completely covered. And the formed slurry layer was dried at 110 degreeC for 10 minute (s), and the electrode with a porous film (negative electrode with a porous film) was obtained by making it into a porous film. In addition, the obtained electrode with a porous film had a layer structure of porous film / negative electrode mixture layer / copper foil. And about the manufactured electrode with a porous film, peel strength, heat-shrinkability, and the uniformity of the porous film were evaluated. In place of the separator with a porous membrane used in Example 1, an organic separator having no porous membrane (same as that used as an organic separator in Example 1) is used as a separator as it is, and is replaced with a negative electrode. A secondary battery was manufactured in the same manner as in Example 1 except that the negative electrode with a porous film obtained above was used. And the rate characteristic was evaluated about the manufactured secondary battery.

<Example 10>
In the same manner as in Example 1, except that 100% by mass of propylene hexafluoride was used and no vinylidene fluoride was used when polymerizing the fluoropolymer contained in the composite polymer as a binder. A slurry for a secondary battery porous membrane was prepared, and a separator with a porous membrane and a secondary battery were produced. And about the manufactured separator with a porous membrane, peel strength, heat-shrinkability, and the uniformity of the porous membrane were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery. In addition, the volume average particle diameter of the obtained composite polymer was 200 nm.

<Comparative Example 1>
A slurry for a secondary battery porous membrane was prepared in the same manner as in Example 1 except that the acrylic polymer was not polymerized (that is, not a composite polymer) during the production of the binder, and the fluoropolymer was used as it was as the binder. Thus, a separator with a porous film and a secondary battery were produced. And about the manufactured separator with a porous membrane, peel strength, heat-shrinkability, and the uniformity of the porous membrane were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery.

<Comparative example 2>
Example 1 except that the fluoropolymer was not polymerized (ie, not a composite polymer) during the production of the binder, and only an acrylic polymer polymerized in the same manner as the acrylic polymer of Example 5 was used as the binder. In the same manner as above, a slurry for a secondary battery porous membrane was prepared, and a separator with a porous membrane and a secondary battery were produced. And about the manufactured separator with a porous membrane, peel strength, heat-shrinkability, and the uniformity of the porous membrane were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery.

<Comparative Example 3>
Inorganic fine particles were used as non-conductive particles. The production method of the inorganic fine particles was as follows.

(Manufacture of inorganic fine particles)
Aluminum hydroxide having a volume average particle diameter of 2.8 μm obtained by the Bayer method was charged into a box-shaped mortar at a charging density of 0.61 g / cm ³ . This box-shaped mortar was placed in a furnace of a stationary electric furnace (“Siliconit Furnace” manufactured by Siliconit Takao Kogyo Co., Ltd.) and fired at a firing temperature of 1180 ° C. for 10 hours. Thereafter, the produced α-alumina particles were taken out of the furnace.

  A vibrating ball mill (“Vibrating Mill” manufactured by Chuo Kako Co., Ltd.) in which 7.8 kg of alumina balls having a diameter of 15 mm were accommodated in a 6-liter pot was prepared. The pot was filled with 1.0 kg of the above-mentioned α-alumina particles and 15 g of ethanol and pulverized for 36 hours to obtain α-alumina particles having a volume average particle diameter of 0.6 μm as inorganic fine particles.

  An aqueous dispersion of non-conductive particles which are inorganic fine particles obtained in this manner, a binder containing a composite polymer containing a fluoropolymer and an acrylic polymer obtained in the same manner as in Example 1. An aqueous dispersion and carboxymethyl cellulose (manufactured by Daicel Chemical Industries, trade name: Daicel 1220) have a solid content weight ratio of nonconductive particles: water-soluble polymer: binder = 307.8: 12.3: 4.6. The mixture was mixed in water to obtain a slurry for a porous membrane. Using the obtained slurry for a porous membrane, a separator with a porous membrane and a secondary battery were produced in the same manner as in Example 1. And about the manufactured separator with a porous membrane, peel strength, heat-shrinkability, and the uniformity of the porous membrane were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery.

<Comparative example 4>
An electrode with a porous film (negative electrode with a porous film) and a secondary battery were produced in the same manner as in Example 9 except that the slurry for porous film obtained in the same manner as in Comparative Example 1 was used. And about the manufactured electrode with a porous film, peel strength, heat-shrinkability, and the uniformity of the porous film were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery.

<Comparative Example 5>
An electrode with a porous film (negative electrode with a porous film) and a secondary battery were produced in the same manner as in Example 9 except that the slurry for porous film obtained in the same manner as in Comparative Example 2 was used. And about the manufactured electrode with a porous film, peel strength, heat-shrinkability, and the uniformity of the porous film were evaluated. Moreover, the rate characteristic was evaluated about the manufactured secondary battery.

  Table 1 shows the evaluation results for Examples 1 to 10 and Comparative Examples 1 to 5 described above.

From Table 1, the organic fine particles include non-conductive particles, a water-soluble polymer, and a binder, and the binder contains a fluorine-based polymer and an acrylic polymer including a (meth) acrylic acid alkyl ester monomer unit. In the separator and the electrode having the porous membrane for the secondary battery of Examples 1 to 10, the thermal shrinkage rate is small. Further, the separator or the electrode has high uniformity, and the secondary battery having the separator or the electrode has rate characteristics. Is found to be good. Moreover, it turns out that the separator and electrode which have the porous film for secondary batteries of Examples 1-10 are excellent also in peel strength.
On the other hand, in Comparative Examples 1 and 4 having a porous membrane for a secondary battery that does not contain an acrylic polymer containing a (meth) acrylic acid alkyl ester monomer unit, the uniformity and peel strength of the porous membrane are reduced. It can also be seen that the rate characteristics of the secondary battery are significantly deteriorated. Further, in Comparative Examples 2 and 5 in which the binder has a porous membrane for a secondary battery that does not contain a fluoropolymer, the uniformity, peel strength, and heat shrinkability of the porous membrane for the secondary battery are reduced and the secondary It turns out that the rate characteristic of a battery deteriorates remarkably. Moreover, it turns out that the uniformity of a porous film deteriorates in the comparative example 3 which used the inorganic fine particle as a nonelectroconductive particle.

  In particular, from Examples 1 and 5, by using a composite polymer of a fluoropolymer and an acrylic polymer containing a (meth) acrylic acid alkyl ester monomer unit as a binder, a porous membrane for a secondary battery It can be seen that the uniformity of the battery and the rate characteristics of the secondary battery are good. This is considered due to the fact that the stability of the binder is improved by using the composite polymer. Moreover, since Examples 6 and 7 do not contain styrene in the acrylic polymer constituting the binder, it is considered that the peel strength deteriorates. However, Examples 6 and 7 contain peel strength by containing acrylonitrile. Is considered to be well maintained. On the other hand, in Example 6, by not containing glycidyl methacrylate, it turns out that heat resistance falls and heat shrinkability falls. In Example 7, it can be seen that the use of ethyl acrylate as the acrylic polymer reduces the compatibility with the fluoropolymer and the rate characteristics. From Example 1 and Examples 8 and 10, the fluoropolymer is preferably a polymer containing at least one of a vinylidene fluoride unit and a propylene hexafluoride unit. The vinylidene fluoride unit and the hexafluoropropylene are preferable. It can be seen that polymers containing both units are more preferred.

Claims (10)

Including non-conductive particles, water-soluble polymer and binder,
The non-conductive particles are organic fine particles,
The porous membrane for secondary batteries in which the binder contains an acrylic polymer containing a fluorine-based polymer and a (meth) acrylic acid alkyl ester monomer unit.   The porous membrane for a secondary battery according to claim 1, wherein the acrylic polymer has an acidic functional group.   The porous membrane for a secondary battery according to claim 2, wherein the acidic functional group is at least one selected from a carboxylic acid group and a sulfonic acid group. Including non-conductive particles, water-soluble polymer, binder and water,
The non-conductive particles are organic fine particles,
The slurry for secondary battery porous films in which the binder contains an acrylic polymer containing a fluorine-based polymer and a (meth) acrylic acid alkyl ester monomer unit.   The slurry for a secondary battery porous film according to claim 4, wherein the acrylic polymer has an acidic functional group.   The slurry for a secondary battery porous membrane according to claim 5, wherein the acidic functional group is at least one selected from a carboxylic acid group and a sulfonic acid group. Applying the slurry for a secondary battery porous membrane according to any one of claims 4 to 6 on a substrate to form a slurry layer;
Drying the slurry layer;
The manufacturing method of the porous film for secondary batteries containing. A current collector,
An electrode mixture layer that adheres to the current collector and includes an electrode mixture layer binder and an electrode active material;
The electrode for secondary batteries provided with the porous film for secondary batteries in any one of Claims 1-3 formed in the surface of the said electrode mixture layer. An organic separator;
The separator for secondary batteries provided with the porous film for secondary batteries in any one of Claims 1-3 formed in the surface of the said organic separator.   A secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte solution, wherein at least one of the positive electrode, the negative electrode, and the separator has the porous membrane for a secondary battery according to any one of claims 1 to 3. Next battery.