JP2012238488A - Electrode binder, electrode, and lithium ion secondary battery including the electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that solubility resistance against an electrolyte of an obtained electrode is not always satisfactorily enough in conventional binders for a lithium ion secondary battery.SOLUTION: An electrode binder contains a polymer A and/or a polymer B. Polymer A: a copolymer including a structural unit derived from α-olefin having 2-4 carbon atoms, a structural unit derived from fatty acid vinyl, a structural unit derived from a vinyl monomer containing a cross linking group, and a structural unit derived from an α,β-unsaturated carboxylic acid Polymer, and B: a polymer including a structural unit represented by formula (1)

Description

  The present invention relates to an electrode binder, an electrode, a lithium ion secondary battery having the electrode, and the like.

  Since lithium ion secondary batteries store a large amount of accumulated electricity, they are actively used in recent years, for example, in the fields of portable devices, electric power, automobiles, and the like. Patent Document 1 describes a copolymer of ethylene and vinyl acetate as a binder for a lithium ion secondary battery electrode.

International Publication No. 2010/150902

  In the conventional binder for lithium ion secondary battery electrodes, the electrolytic solution dissolution resistance of the obtained electrode may not always be sufficiently satisfied.

〔２〕電極用バインダー１００重量部あたり、重合体Ａの含有量が３０〜７０重量部であり、重合体Ｂの含有量が３０〜７０重量部である〔１〕記載の電極用バインダー。
〔３〕重合体Ａを含有し、該重合体Ａに含まれるα−オレフィンに由来する構造単位が、エチレンに由来する構造単位である〔１〕又は〔２〕記載の電極用バインダー。
〔４〕重合体Ａを含有し、該重合体Ａに含まれる脂肪酸ビニルに由来する構造単位が、酢酸ビニルに由来する構造単位である〔１〕〜〔３〕のいずれか記載の電極用バインダー。
〔５〕重合体Ａを含有し、該重合体Ａに含まれる架橋性基含有ビニルモノマーに由来する構造単位が、Ｎ−メチロールアクリルアミドに由来する構造単位である〔１〕〜〔４〕のいずれか記載の電極用バインダー。
〔６〕重合体Ａを含有し、該重合体Ａに含まれるα，β−不飽和カルボン酸に由来する構造単位が、アクリル酸に由来する構造単位である〔１〕〜〔５〕のいずれか記載の電極用バインダー。
〔７〕重合体Ｂを含有し、該重合体Ｂが、さらに炭素数２〜４のα−オレフィンに由来する構造単位を含む共重合体である〔１〕〜〔６〕のいずれか記載の電極用バインダー。
〔８〕重合体Ｂ１００重量部あたり、炭素数２〜４のα−オレフィンに由来する構造単位の含有量が０〜５０重量部であり、式（１）で表される構造単位の含有量が５０〜１００重量部である〔７〕記載の電極用バインダー。
〔９〕〔１〕〜〔８〕のいずれか記載の電極用バインダーを含有することを特徴とする電極。
〔１０〕〔９〕記載の電極を有することを特徴とするリチウムイオン二次電池。 The present invention includes the following inventions.
[1] A binder for electrodes containing the polymer A and / or the polymer B.
Polymer A: Structural unit derived from α-olefin having 2 to 4 carbon atoms, structural unit derived from fatty acid vinyl, structural unit derived from crosslinkable group-containing vinyl monomer, and α, β-unsaturated carboxylic acid A polymer containing a structural unit represented by formula (1)

[2] The electrode binder according to [1], wherein the content of the polymer A is 30 to 70 parts by weight and the content of the polymer B is 30 to 70 parts by weight per 100 parts by weight of the electrode binder.
[3] The binder for an electrode according to [1] or [2], which contains the polymer A, and the structural unit derived from the α-olefin contained in the polymer A is a structural unit derived from ethylene.
[4] The binder for an electrode according to any one of [1] to [3], which contains the polymer A and the structural unit derived from the fatty acid vinyl contained in the polymer A is a structural unit derived from vinyl acetate. .
[5] Any of [1] to [4], wherein the structural unit derived from the crosslinkable group-containing vinyl monomer contained in the polymer A is derived from N-methylolacrylamide. A binder for an electrode as described above.
[6] Any of [1] to [5], which contains polymer A and the structural unit derived from α, β-unsaturated carboxylic acid contained in polymer A is a structural unit derived from acrylic acid A binder for an electrode as described above.
[7] The polymer B is contained, and the polymer B is a copolymer further containing a structural unit derived from an α-olefin having 2 to 4 carbon atoms. Electrode binder.
[8] The content of the structural unit derived from the α-olefin having 2 to 4 carbon atoms is 0 to 50 parts by weight per 100 parts by weight of the polymer B, and the content of the structural unit represented by the formula (1) is [7] The electrode binder according to [7], which is 50 to 100 parts by weight.
[9] An electrode comprising the electrode binder according to any one of [1] to [8].
[10] A lithium ion secondary battery comprising the electrode according to [9].

  If the binder for electrodes of this invention is used, the electrode excellent in electrolyte solution resistance can be obtained.

Hereinafter, the present invention will be described in detail.
The electrode binder of the present invention contains polymer A and / or polymer B.
Polymer A: Structural unit derived from α-olefin having 2 to 4 carbon atoms, structural unit derived from fatty acid vinyl, structural unit derived from crosslinkable group-containing vinyl monomer, and α, β-unsaturated carboxylic acid A polymer containing a structural unit represented by formula (1)

Examples of the α-olefin having 2 to 4 carbon atoms in the polymer A include ethylene, propylene, 1-butene and the like.
In the polymer A, structural units derived from a plurality of types of α-olefins may be contained.
As the structural unit derived from an α-olefin having 2 to 4 carbon atoms, a structural unit derived from ethylene is preferable.
The content of the structural unit derived from the α-olefin in the polymer A is preferably in the range of 10 to 40 parts by weight per 100 parts by weight of the polymer A.

  As the fatty acid vinyl in the polymer A, for example, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl laurate, vinyl caproate, vinyl stearate, vinyl palmitate, vinyl versatate, etc., preferably Examples thereof include vinyl esters of 2 to 4 fatty acids. As a structural unit derived from fatty acid vinyl, a structural unit derived from vinyl acetate is more preferable.

  The content of the structural unit derived from the fatty acid vinyl in the polymer A is preferably in the range of 2 to 90 parts by weight and more preferably in the range of 3 to 60 parts by weight per 100 parts by weight of the polymer A.

The crosslinkable group in the polymer A is a functional group capable of causing a crosslinking reaction under heating conditions, acidic or alkaline conditions, and the like, for example, methoxymethylcarbamoyl group, ethoxymethylcarbamoyl group, propoxymethyl. C3-C6 alkoxymethylcarbamoyl groups such as carbamoyl group, butoxymethylcarbamoyl group, isobutoxymethylcarbamoyl group, t-butoxymethylcarbamoyl group; glycidyl group; methylolcarbamoyl group;
Examples of the crosslinkable group-containing vinyl monomer include Nn-butoxymethylacrylamide, glycidyl acrylate, glycidyl methacrylate, and N-methylolacrylamide. The structural unit derived from the crosslinkable group-containing vinyl monomer is preferably a structural unit derived from N-methylolacrylamide.

  The content of the structural unit derived from the crosslinkable group-containing vinyl monomer in the polymer A is preferably in the range of 0.1 to 10 parts by weight and more preferably in the range of 1 to 5 parts by weight per 100 parts by weight of the polymer A.

  Examples of the α, β-unsaturated carboxylic acid in the polymer A include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid. As the structural unit derived from α, β-unsaturated carboxylic acid, a structural unit derived from acrylic acid is preferred.

  The content of the structural unit derived from the α, β-unsaturated carboxylic acid in the polymer A is preferably in the range of 0.1 to 10 parts by weight, and in the range of 0.1 to 1 part by weight per 100 parts by weight of the polymer A. Is more preferable.

In addition to the structural unit derived from α-olefin in polymer A, the structural unit derived from fatty acid vinyl, the structural unit derived from the crosslinkable group-containing vinyl monomer, and the structural unit derived from α, β-unsaturated carboxylic acid Furthermore, a structural unit derived from an α, β-unsaturated carboxylic acid alkyl ester, a structural unit derived from acrylamide, a structural unit derived from methacrylamide, a structural unit derived from a triallyl ester of benzenetricarboxylic acid, triallyl isocyanate Structural units derived from α-olefin, fatty acid vinyl, crosslinkable group-containing vinyl monomer, and addition-polymerizable monomers other than α, β-unsaturated carboxylic acid, such as structural units derived from May be.
Examples of the α, β-unsaturated carboxylic acid alkyl ester include those having 1 to 16 carbon atoms such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, lauryl acrylate, and the like. Acrylic acid alkyl ester having an alkyl group; ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, octyl methacrylate, methacrylic acid alkyl ester having a C 1-16 alkyl group such as lauryl methacrylate; Dialkyl maleate having an alkyl group having 1 to 16 carbon atoms such as dimethyl acid, diethyl maleate, dibutyl maleate, dioctyl maleate, dilauryl maleate; dimethyl fumarate, diethyl fumarate, dibu fumarate Dialkyl fumarate having an alkyl group having 1 to 16 carbon atoms such as til, dioctyl fumarate, dilauryl fumarate; 1 carbon atom such as diethyl itaconate, dibutyl itaconate, dihexyl itaconate, dioctyl itaconate, dilauryl itaconate, etc. Itaconic acid dialkyl ester having ˜16 alkyl groups.

  The content of the structural unit derived from the addition-polymerizable monomer other than the α-olefin, fatty acid vinyl, crosslinkable group-containing vinyl monomer, and α, β-unsaturated carboxylic acid in the polymer A is the polymer A100. For example, about 0 to 85 parts by weight can be mentioned per part by weight.

  As the polymer A, a copolymer containing a structural unit derived from ethylene, a structural unit derived from vinyl acetate, a structural unit derived from N-methylolacrylamide, and a structural unit derived from acrylic acid is preferable.

The polymer B is a polymer containing a structural unit represented by the above formula (1) (hereinafter sometimes referred to as the structural unit (1)), and is so-called polyvinyl which substantially consists of the structural unit (1). Although alcohol may be sufficient, structural units other than structural unit (1) may be contained.
As content of the structural unit (1) in the copolymer B, the range of 20-100 weight part is preferable with respect to 100 weight part of copolymer B, and the range of 50-100 weight part is more preferable.

As the structural unit other than the structural unit (1), a structural unit derived from an α-olefin having 2 to 4 carbon atoms, a structural unit derived from an α, β-unsaturated carboxylic acid alkyl ester, a structural unit derived from acrylamide, Examples include a structural unit derived from methacrylamide, a structural unit derived from a triallyl ester of benzenetricarboxylic acid, and a structural unit derived from triallyl isocyanate. The polymer B is preferably a copolymer containing a structural unit derived from an α-olefin having 2 to 4 carbon atoms. Examples of the α-olefin having 2 to 4 carbon atoms include ethylene, propylene, 1-butene and the like.
The copolymer B may contain structural units derived from a plurality of types of α-olefins.
The structural unit derived from α-olefin is preferably a structural unit derived from ethylene.
As content of the structural unit derived from the alpha olefin in the polymer B, the range of 0-80 weight part is preferable per 100 weight part of polymers B, and the range of 0-50 weight part is more preferable.

  In the electrode binder of the present invention, the polymer A and the polymer B may be used singly or as a mixture thereof. It is preferable that the content of the polymer A is 30 to 70 parts by weight and the content of the polymer B is 30 to 70 parts by weight per 100 parts by weight of the electrode binder. The mixing method in the case of mixing and using the polymer A and the polymer B is arbitrary, Furthermore, you may mix another polymer well-known as a binder for electrodes.

  The polymer A is preferably dispersed in water and used as the binder for an electrode of the present invention, for example, in the state of an emulsion (hereinafter sometimes referred to as the present emulsion).

The emulsion is preferably obtained by dispersing the polymer A with an emulsifier.
Examples of the emulsifier include anionic surfactants such as sodium alkylbenzene sulfonate and alkyl sulfosuccinate; polyvinyl alcohol, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene fatty acid ester Nonionic surfactants such as oxyethylene sorbitan fatty acid ester and polyoxyethylene-polyoxypropylene block copolymer; water-soluble polymers such as hydroxyethyl cellulose;
As content of the emulsifier in this emulsion, 0.5-5 weight% etc. can be mentioned, for example, Preferably, 1-3 weight% etc. are mentioned, for example.

  Examples of the method for producing this emulsion include sodium bisulfite, sodium thiosulfate, sodium pyrosulfite, Rongalite, ferrous chloride and other reducing agents, vinyl chloride, the above emulsifier, water, and, if necessary, addition polymerization. Monomers are mixed in a pressure-resistant reactor, then the air in the reactor is replaced with nitrogen, and α-olefin, fatty acid vinyl, and, if necessary, addition polymerization can be performed under a pressure of 5 to 150 atm. For example, a method of stirring the monomer at about 10 to 80 ° C. while sequentially injecting an oxidizing agent such as hydrogen peroxide, potassium persulfate, or ammonium persulfate in an aqueous solution while adding monomers sequentially can be exemplified.

The electrode of the present invention contains the electrode binder, such as a dry battery, a piezoelectric element sensor, an electric double layer capacitor, a lithium ion capacitor, a lithium ion secondary battery, a sodium ion secondary battery, and a fuel cell. It can be used for electrodes and the like.
Hereinafter, the electrode of the present invention will be described using the negative electrode of a lithium ion secondary battery as an example.

As a method for producing an electrode, a mixture containing a negative electrode active material, the electrode binder, and the like is usually formed on a current collector. Specifically, for example, a method in which a mixed slurry obtained by adding water or the like to the negative electrode active material and the electrode binder is applied or immersed in a current collector by a doctor blade method or the like, and dried, for example, the negative electrode active material and the above-mentioned A method in which water is added to an electrode binder, etc., kneaded, molded, dried, and a sheet obtained by bonding to a current collector surface via a conductive adhesive and the like, followed by pressing and heat treatment drying, for example, a negative electrode active material And a method comprising subjecting the obtained sheet-like molded product to a uniaxial or multiaxial orientation after molding a mixture comprising the electrode binder and the like on a current collector.
When making an electrode into a sheet form, the thickness is about 5-1000 micrometers normally.

Here, the negative electrode active material has conductivity that can occlude and release lithium ions. For example, silicon oxide such as SiO ₂ , non-graphitizable carbon, coke, natural graphite, Examples thereof include carbon materials such as artificial graphite.

Examples of the current collector material include metals such as nickel, aluminum, titanium, copper, gold, silver, platinum, aluminum alloys, and stainless steel, such as carbon materials or activated carbon fibers, nickel, aluminum, zinc, copper, and tin. Formed by plasma spraying or arc spraying of lead or an alloy thereof, for example, a conductive film in which a conductive agent is dispersed in a resin such as rubber or styrene-ethylene-butylene-styrene copolymer (SEBS) Is mentioned.
Examples of the shape of the current collector include a foil, a flat plate, a mesh, a net, a lath, a punching or an emboss, or a combination thereof (for example, a mesh flat). .
Concavities and convexities may be formed on the surface of the current collector by etching.

  The blending amount of the electrode binder in the electrode is, for example, about 0.1 to 30 parts by weight, preferably about 0.6 to 15 parts by weight with respect to 100 parts by weight of the negative electrode active material. Here, the weight part of the binder for electrodes means the weight part of the component excluding water, so-called solid content, and can be measured according to JIS K-6828.

The electrode may contain a conductive agent as necessary. Examples of the conductive agent include conductive carbon such as graphite, carbon black, acetylene black, ketjen black and activated carbon; graphite-based conductive agent such as natural graphite, thermally expanded graphite, scale-like graphite, and expanded graphite; vapor grown carbon fiber Carbon fiber such as aluminum, nickel, copper, silver, gold, platinum, etc .; conductive metal oxide such as ruthenium oxide or titanium oxide; conductivity such as polyaniline, polypyrrole, polythiophene, polyacetylene, polyacene Examples include polymers.
Carbon black, acetylene black and ketjen black are preferred in that the conductivity is effectively improved with a small amount.
The compounding amount of the conductive agent in the electrode can be, for example, about 0 to 50 parts by weight, preferably, for example, about 0 to 30 parts by weight with respect to 100 parts by weight of the negative electrode active material.

  The electrode of the present invention is excellent in electrolyte solution resistance. Here, “excellent in electrolytic solution resistance” means, for example, that dissolution of the binder for an electrode in the electrolytic solution is suppressed.

A lithium ion secondary battery having the electrode will be described below. The lithium ion secondary battery includes, for example, a positive electrode, a separator, an electrolytic solution, a negative electrode, and the like, and lithium is oxidized and reduced at both the positive electrode and the negative electrode to store and release electric energy.
As the lithium ion secondary battery, for example, the negative electrode is the electrode, and the positive electrode is a lithium ion secondary battery made of lithium metal or a metal oxide containing lithium.

The positive electrode is a material in which a mixture containing a material capable of doping and dedoping lithium ions, a conductive material and a binder is supported on a current collector.
Specific examples of materials that can be doped and dedoped with lithium ions include lithium composite oxides and lithium foils containing at least one transition metal such as V, Mn, Fe, Co, and Ni. Among them, an α-NaFeO ₂ type structure such as a cobalt / lithium composite oxide, a composite metal of nickel and a transition metal other than nickel, or lithium containing aluminum is preferably used as a base material in that the average discharge potential is high. And lithium composite oxides based on a spinel structure such as a layered lithium composite oxide and lithium manganese spinel. In addition, lithium foil (lithium metal) was used for the positive electrode of the lithium ion secondary battery for carbon material evaluation of this patent.
Examples of the binder contained in the positive electrode include a polymer of a fluorine compound. Examples of the fluorine compound include fluorinated alkyl (C1-18) (meth) acrylate, perfluoroalkyl (meth) acrylate [for example, perfluorododecyl (meth) acrylate, perfluoro n-octyl (meth) acrylate, Perfluoro n-butyl (meth) acrylate], perfluoroalkyl-substituted alkyl (meth) acrylate [for example, perfluorohexylethyl (meth) acrylate, perfluorooctylethyl (meth) acrylate], perfluorooxyalkyl (meth) acrylate [ For example, perfluorododecyloxyethyl (meth) acrylate and perfluorodecyloxyethyl (meth) acrylate, etc.], fluorinated alkyl (C1-C18) crotonate, fluorinated alkyl (carbon Number 1-18) Malate and fumarate, fluorinated alkyl (carbon number 1-18) itaconate, fluorinated alkyl-substituted olefin (about 2-10 carbon atoms, about 1-17 fluorine atoms) such as perfluorohexylethylene, carbon Examples thereof include fluorinated olefins, tetrafluoroethylene, trifluoroethylene, vinylidene fluoride, hexafluoropropylene and the like in which fluorine atoms are bonded to double bond carbons of about 2 to 10 and about 1 to 20 fluorine atoms.

Other examples of the binder include monomer addition polymers containing an ethylenic double bond that does not contain a fluorine atom. Examples of such monomers include (cyclo) alkyl (C1-22) (meth) acrylate [for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (Meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, octadecyl (meth) acrylate, etc.]; aromatic ring-containing (meth) acrylate [for example, benzyl (Meth) acrylate, phenylethyl (meth) acrylate, etc.]; mono (meth) acrylate of alkylene glycol or dialkylene glycol (alkylene group having 2 to 4 carbon atoms) [for example, 2-hydroxyethyl (meth) acrylate, 2- Hi Roxypropyl (meth) acrylate, diethylene glycol mono (meth) acrylate]; (poly) glycerin (degree of polymerization 1 to 4) mono (meth) acrylate; polyfunctional (meth) acrylate [for example, (poly) ethylene glycol (degree of polymerization 1) ~ 100) di (meth) acrylate, (poly) propylene glycol (degree of polymerization 1-100) di (meth) acrylate, 2,2-bis (4-hydroxyethylphenyl) propane di (meth) acrylate, trimethylolpropane tri ( (Meth) acrylate monomers such as (meth) acrylate]; (meth) acrylamide (meth) acrylamide, (meth) acrylamide derivatives [eg, N-methylol (meth) acrylamide, diacetone acrylamide, etc.] Acrylamide monomer; ) Cyano group-containing monomers such as acrylonitrile, 2-cyanoethyl (meth) acrylate, 2-cyanoethylacrylamide; styrene and styrene derivatives having 7 to 18 carbon atoms [for example, α-methylstyrene, vinyltoluene, p-hydroxystyrene and Styrene monomers such as divinylbenzene] Diene monomers such as alkadienes having 4 to 12 carbon atoms [for example, butadiene, isoprene, chloroprene, etc.]; Carboxylic acid (2 to 12 carbon atoms) vinyl esters [for example, , Vinyl acetate, vinyl propionate, vinyl butyrate and vinyl octoate, etc.], carboxylic acid (2 to 12 carbon atoms) (meth) allyl ester [for example, (meth) allyl acetate, (meth) allyl propionate and octanoic acid ( Alkenyl ester monomers such as (meth) allyl etc.]; Epoxy group-containing monomers such as zir (meth) acrylate and (meth) allyl glycidyl ether; monoolefins having 2 to 12 carbon atoms [for example, ethylene, propylene, 1-butene, 1-octene and 1-dodecene, etc.] Monoolefins; chlorine, bromine or iodine atom-containing monomers, halogen atom-containing monomers other than fluorine such as vinyl chloride and vinylidene chloride; (meth) acrylic acid such as acrylic acid and methacrylic acid; butadiene, isoprene, etc. Examples thereof include a conjugated double bond-containing monomer.
The addition polymer may be, for example, a copolymer such as a styrene / butadiene copolymer or an ethylene / propylene copolymer. Moreover, the carboxylic acid vinyl ester polymer may be partially or completely saponified, such as polyvinyl alcohol.
The binder may be a copolymer of a fluorine compound and a monomer containing an ethylenic double bond not containing a fluorine atom.

  Examples of the conductive material included in the positive electrode include natural graphite, artificial graphite, cokes, and carbon black. As the conductive material, each may be used alone, or for example, a composite conductive material system in which artificial graphite and carbon black are mixed and used may be selected.

Examples of the electrolytic solution used in the lithium ion battery of the present invention include a non-aqueous electrolytic solution in which a lithium salt is dissolved in an organic solvent. Lithium salts include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , One or a mixture of two or more of lower aliphatic carboxylic acid lithium salts, LiAlCl _{4 and the} like can be mentioned.
The lithium salt is selected from the group consisting of LiPF ₆ containing fluorine, LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiC (CF ₃ SO ₂ ) ₃ among these. It is preferable to use one containing at least one selected from the above.

  Examples of the organic solvent used in the electrolytic solution of the present invention include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, 1,2-di Carbonates such as (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2- Ethers such as methyltetrahydrofuran; Esters such as methyl formate, methyl acetate and γ-butyrolactone; Nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethylacetate Amides such as amide; Carbamates such as 3-methyl-2-oxazolidone; Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone, or those obtained by introducing a fluorine substituent into the above organic solvent Usually, a mixture of two or more of these is used.

The separator plays a role of separating the working electrode and the counter electrode and holding the electrolytic solution, and an insulating film having a large ion permeability and a predetermined mechanical strength is used.
Examples of the separator include, for example, paper making such as viscose rayon or natural cellulose, mixed paper obtained by making fibers such as cellulose and polyester, electrolytic paper, kraft paper, manila paper, polyethylene non-woven fabric, polypropylene non-woven fabric, polyester non-woven fabric, glass Fiber, porous polyethylene, porous polypropylene, porous polyester, aramid fiber, polybutylene terephthalate nonwoven fabric, para-type wholly aromatic polyamide, vinylidene fluoride, tetrafluoroethylene, copolymer of vinylidene fluoride and propylene hexafluoride , Non-woven fabrics such as fluorine-containing resins such as fluoro rubber, or porous membranes.
The separator may be a molded product made of ceramic powder particles such as silica and the binder. The molded article is usually formed integrally with the working electrode and the counter electrode. Moreover, about the separator using polyethylene, a polypropylene, etc., in order to improve hydrophilicity, you may mix surfactant and a silica particle. Furthermore, the separator may contain an organic solvent such as acetone and a plasticizer such as dibutyl phthalate (DBP).

As the separator, a proton conductive polymer may be used.
As separators, in particular, electrolytic paper, viscose rayon or natural cellulose paper, kraft paper, manila paper, mixed paper obtained by making cellulose or polyester fibers, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyester nonwoven fabric, manila hemp sheet, glass A fiber sheet or the like is preferable.
The pore diameter of the separator is usually about 0.01 to 10 μm. The thickness of the separator is usually about 1 to 300 μm, preferably about 5 to 30 μm.
The separator may be a laminate of separators having different porosity. In particular, a separator composed of a polyolefin porous membrane and a polyester resin porous membrane is suitable.

  Hereinafter, the present invention will be described in more detail with reference to examples. Parts and% in the examples mean weight basis unless otherwise specified.

[Residual vinyl acetate monomer]
The residual vinyl acetate monomer was diluted with 10 ml of sample with 25 ml distilled water, titrated with a bromine-potassium bromide aqueous solution until the color did not disappear, and calculated from the following formula.
Residual vinyl acetate monomer (%) = (A × N × 0.043) / S × 100
[In the formula, A represents the volume (ml) of bromine-potassium bromide aqueous solution.
N represents the specified number of bromine-potassium bromide aqueous solution.
S represents the mass (g) of the sample. ]

[Solid content]
The solid content was measured by a measuring method according to JIS K-6828.

[Glass-transition temperature]
The glass transition temperature ([Tg], unit: ° C.) was measured for a differential scanning calorimetry curve under the following conditions using a differential scanning calorimeter (Exstar 6000 manufactured by Seiko Instruments Inc.).
<Measurement conditions>
The temperature of the sample is lowered from 20 ° C. to −100 ° C. at 10 ° C./min, and when it reaches −100 ° C., the temperature is raised to 100 ° C. at 10 ° C./min.

[viscosity]
The viscosity (unit: mPa · s) of the emulsion was measured using a Brookfield viscometer under the conditions of 25 ° C. and 60 rpm.

(Production Example 1)
In a pressure vessel, 80 parts of water, 40 parts of vinyl acetate, 2.0 parts of hydroxyethyl cellulose, nonionic surfactant “Emulgen (registered trademark) 1135S-70” (manufactured by Kao Corporation), 1.5 parts, “Emulgen (registered) Trademark) 1108 "(manufactured by Kao Corporation) 1.0 part, 0.002 part of ferrous sulfate heptahydrate, 0.06 part of sodium acetate and 0.1 part of acetic acid were added. Next, the inside of the pressure vessel was replaced with nitrogen gas, the temperature inside the vessel was raised to 50 ° C., and then pressurized to 5.0 MPa with ethylene, and a 5.0% sodium persulfate aqueous solution was added at a rate of 1.1 parts / hour. Then, 7.0% sodium erythorbate aqueous solution was added to the pressure vessel for 5 hours at a rate of 0.7 parts / hour to initiate polymerization. Subsequently, after confirming that the liquid temperature in the pressure vessel had risen, 90 parts of vinyl acetate in which 1.3 parts of acrylic acid had been dissolved and 13.5 parts of a 1.9% N-methylolacrylamide aqueous solution were added over 4 hours. While maintaining the liquid temperature in the container at 50 ° C., when 5 hours have elapsed from the start of polymerization, the concentration of the sodium persulfate aqueous solution is switched to 8.0%, and the pressure vessel is 4 parts / hour. Was added for 1 hour, and when the residual vinyl acetate monomer became less than 1%, the pressure-resistant vessel was cooled to remove unreacted ethylene gas, and then the emulsion was taken out. The ethylene / vinyl acetate / acrylic acid / N-methylolacrylamide copolymer contained in the emulsion has 25 parts of ethylene units, 100% of vinyl acetate units, 57% solids, and a viscosity of 450 mPas. S and the glass transition temperature was 0 ° C.

(Production Example 2)
The emulsion was taken out in the same manner as in Production Example 1 except that the concentration of the 1.9% N-methylolacrylamide aqueous solution was changed to 3.8% in Production Example 1. The ethylene / vinyl acetate / acrylic acid / N-methylolacrylamide copolymer contained in the emulsion has 25 parts of ethylene units, 100% of vinyl acetate units, a solid content of 58%, and a viscosity of 550 mPa · s. s and the glass transition temperature was -2 ° C.

(Comparative Production Example 1)
In Production Example 1, the concentration of the 7.0% sodium erythorbate aqueous solution was changed to 5.0% and the concentration of the 8.0% sodium persulfate aqueous solution was changed to 6.0%, respectively, and 1.9% N-methylol was changed. The emulsion was taken out in the same manner as in (Production Example 1) except that no acrylamide aqueous solution was added. The ethylene / vinyl acetate / acrylic acid copolymer contained in the emulsion has 25 parts of ethylene units with respect to 100 parts of vinyl acetate units, a solid content of 58%, a viscosity of 400 mPa · s, and glass. The transition temperature was −5 ° C.

Example 1
As the polymer A, the emulsion obtained in Production Example 1 was used. As the polymer B, polyvinyl alcohol (PVA235 manufactured by Kuraray, ethylene: vinyl alcohol = 0: 100) was used. Both were mixed by the solid content ratio of polymer A: polymer B = 1: 2, and the binder for electrodes was obtained.

(Example 2)
As the polymer A, the emulsion obtained in Production Example 2 was used. As the polymer B, polyvinyl alcohol (PVA235 manufactured by Kuraray, ethylene: vinyl alcohol = 0: 100) was used. Both were mixed by the solid content ratio of polymer A: polymer B = 1: 2, and the binder for electrodes was obtained.

(Example 3)
The emulsion obtained in Production Example 2 was directly used as an electrode binder.

Example 4
The ethylene-vinyl alcohol copolymer (DT2904RB, manufactured by Nippon Synthetic Chemical, ethylene: vinyl alcohol = 29: 71), which is the polymer B, was used as an electrode binder as it was.

(Example 5)
After removing water from the emulsion obtained in Production Example 1, it was dissolved in N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP), and the NMP solution of polymer A was obtained at a solid content of 10.5%. Obtained. This solution and an NMP solution of polyvinyl alcohol as an NMP solution of polymer B (PVA235 manufactured by Kuraray, ethylene: vinyl alcohol = 0: 100, solid content 3.9%), polymer A: polymer B = 1: An electrode binder was obtained by mixing at a solid content ratio of 2.

(Example 6)
After removing water from the emulsion obtained in Production Example 2, it was dissolved in N-methyl-2-pyrrolidone to obtain an NMP solution of polymer A at a solid content of 10.1%. The solution and the same NMP solution of polyvinyl alcohol as that used in Example 5 as the NMP solution of polymer B were mixed at a solid content ratio of polymer A: polymer B = 1: 2 to form an electrode. A binder was obtained.

(Example 7)
After removing water from the emulsion obtained in Production Example 2, it was dissolved in N-methyl-2-pyrrolidone at a solid content of 10.1% to obtain an electrode binder.

(Comparative Example 1)
The emulsion obtained in the comparative production example was directly used as an electrode binder.

(Comparative Example 2)
After removing water from the emulsion obtained in the comparative production example, it was dissolved in N-methyl-2-pyrrolidone at a solid content of 10.1% to obtain an electrode binder.

(Electrolytic solution resistance evaluation)
As the electrolytic solution dissolution resistance evaluation, the electrode binders obtained in Examples 5 to 7 and Comparative Example 2 were applied to aluminum cups and vacuum-dried at 120 ° C. for 8 hours. The So obtained film-shaped electrode binder (50 mg to 500 mg) was cut into 2cm square were weighed ^{W 1} of the sample. This sample was immersed in a mixed solution of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate (= 30: 35: 35) which is a kind of electrolytic solution. Those that did not dissolve after immersion for 24 hours were evaluated as ◯, and those that were dissolved were evaluated as ×. Moreover, what was not dissolved, and weighed W ² samples were taken out after 24 hours was calculated swelling degree (%) from the following equation.
Swelling degree (%) = (W ² −W ¹ ) / W ¹ × 100
Wherein, ^{W 1} represents the weight before immersion.
W ² represents the weight after 24 hours was immersed. ]

Example 9
(Example of electrode production)
As an active material, Li _1.04 Ni _0.47 Mn _0.48 Fe _0.05 O ₂ (crystal structure: R-3m, BET specific surface area: 8.5 m ² / g, average primary particle size: 200 nm) 92 parts As an electrode binder, 5 parts (solid content) of the emulsion obtained in Example 1 and 5 parts of a conductive material (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: HS100) are mixed, and N-methyl- 100 parts of 2-pyrrolidone was added and stirred with a stirrer (manufactured by PRIMIX, trade name: TK Fillmix) to obtain a composition for a lithium ion secondary battery electrode. The obtained composition for a lithium ion secondary battery electrode was applied at 8 mil onto a 20 μm thick aluminum current collector by a Baker type applicator using Tester Sangyo Co., Ltd. automatic coating apparatus I type PI-1210. And dried at 120 ° C. for 2 hours to obtain an electrode. The obtained electrode was vacuum-dried at 120 ° C. for 8 hours to obtain an electrode.

(Production example of lithium ion secondary battery)
After vacuum drying, in a CR2032 type (IEC / JIS standard) coin cell, the electrode as a positive electrode, lithium foil as a negative electrode, Pervio (registered trademark) manufactured by Sumitomo Chemical Co., Ltd., and a concentration of 1.0 mol / liter as an electrolyte LiPF ₆ / Ethylene carbonate, propylene carbonate, and a diethyl carbonate mixed solvent were used for assembly to obtain a lithium ion secondary battery.

(Initial accumulated electricity)
Toyo System Co., Ltd. TOSCAT-3100 charge / discharge evaluation device was used to charge the coin cell to 4.3 V at 25 ° C., 160 mA / g, 0.2 C, and discharge to 2.5 V at 160 mA / g once. When implemented, the integrated electricity amount was 130 mAh / g.

  If the binder for electrodes of this invention is used, the electrode excellent in electrolyte solution resistance can be obtained.

Claims (10)

The binder for electrodes containing the polymer A and / or the polymer B.
Polymer A: Structural unit derived from α-olefin having 2 to 4 carbon atoms, structural unit derived from fatty acid vinyl, structural unit derived from crosslinkable group-containing vinyl monomer, and α, β-unsaturated carboxylic acid A polymer containing a structural unit represented by formula (1)

  The binder for an electrode according to claim 1, wherein the content of the polymer A is 30 to 70 parts by weight and the content of the polymer B is 30 to 70 parts by weight per 100 parts by weight of the binder for an electrode.   The binder for an electrode according to claim 1 or 2, wherein the structural unit containing the polymer A and derived from an α-olefin contained in the polymer A is a structural unit derived from ethylene.   The binder for electrodes according to any one of claims 1 to 3, wherein the structural unit derived from fatty acid vinyl contained in the polymer A and derived from the fatty acid vinyl is a structural unit derived from vinyl acetate.   5. The electrode according to claim 1, wherein the structural unit containing the polymer A and derived from the crosslinkable group-containing vinyl monomer contained in the polymer A is a structural unit derived from N-methylolacrylamide. binder.   6. The electrode according to claim 1, wherein the structural unit containing the polymer A and derived from an α, β-unsaturated carboxylic acid contained in the polymer A is a structural unit derived from acrylic acid. binder.   The binder for electrodes according to any one of claims 1 to 6, which comprises a polymer B, and the polymer B further comprises a structural unit derived from an α-olefin having 2 to 4 carbon atoms.   The content of a structural unit derived from an α-olefin having 2 to 4 carbon atoms per 100 parts by weight of the polymer B is 0 to 50 parts by weight, and the content of the structural unit represented by the formula (1) is 50 to 100. The electrode binder according to claim 7, which is part by weight.   An electrode comprising the electrode binder according to claim 1.   A lithium ion secondary battery comprising the electrode according to claim 9.