WO2010134465A1 - Fluorine-containing binder - Google Patents

Abstract

Disclosed is a binder which is capable of finely and uniformly dispersing an electrode active material, a conductive assistant and a binder, and is also capable of providing an electrode composite layer that has high workability and a low risk of placing a burden on the environment or damaging the health of human beings. Also disclosed is an aqueous paste which is used for the production of an electrode for an electrical storage element. Specifically disclosed is a binder which is blended into an aqueous paste of an electrode material that is used for the production of an electrode for an electrical storage element. The binder is composed of a polymer which is selected from among fluorine-containing olefin copolymers having a hydrophilic group in a side chain and linear hydrophilic polymers having a hydrophobic fluorine-containing organic group at both ends, and has a fluorine content of 3-60% by mass and a number average molecular weight of 1,000-1,000,000.

Description

Fluorine-containing binder

The present invention relates to a binder for an electrode material used for manufacturing an electrode of a power storage device, a paste-like composition containing the binder, the electrode material, and water, and an electrode using the paste-like composition It relates to the manufacturing method. This electrode is used as an electrode of a storage element such as a lithium ion battery, a lithium polymer battery, a nickel metal hydride battery, or a capacitor.

Storage elements of various mechanisms and forms are widely used as energy sources for mobile devices, in-vehicle storage / discharge systems / energy sources, power storage systems, and the like. These elements are required to have characteristics such as high output, high energy density, reliability that can be used stably even in various environments such as low temperature and high temperature, and safety even in an unexpected situation. Conventionally, studies for improving these characteristics have been on the improvement of the main material that plays a role. However, it is also extremely important to study an element structure that can fully exhibit the characteristics of the material, particularly an element structure for realizing an electrode composite structure.

The electrode of the electricity storage element is composed of a composite of at least an electrode active material having a main function, a conductive additive, a binder and the like. In the formation of composites, the technology of supporting the electrode active material, which is powder particles, and the conductive additive as finely and as homogeneously as possible, and supporting them in as little binder as possible. This is important in order to maximize the properties of the material. Composite formation is performed by preparing a paste in which each electrode constituent material is dispersed in a medium, and applying and drying the paste on a current collector. Conventionally, an organic solvent has been used as a medium for preparing the paste. In order to support the electrode constituent material using a small amount of the polymer for the binder, it has been considered preferable to use a polymer solution (Patent Document 1).

On the other hand, water-based pastes that use water as a medium have been proposed in the past, and it was expected that the environmental burden and cost could be greatly reduced in terms of materials, equipment, and equipment operation. However, conductive carbon materials that are usually used as conductive aids are hydrophobic and are extremely difficult to disperse in water. Therefore, it has not been possible to produce electrodes with good battery characteristics from aqueous pastes. In addition, in the case of non-aqueous power storage elements, since the intrusion of water greatly impairs the element characteristics, it has been considered not to bring water into the manufacturing process.

In order to solve this problem, ammonium perfluorooctanoate (hereinafter referred to as APFO), which is an emulsifier used in the production of an aqueous fluoropolymer dispersion, and carboxymethyl cellulose (hereinafter referred to as CMC) coexist. It has been proposed that a conductive carbonaceous material is finely dispersed in water (see Patent Document 2). In this case, an aqueous paste in which the electrode forming material is uniformly dispersed can be prepared. Since an electrode manufactured from such an aqueous paste can exhibit good electric storage element characteristics, an electrode manufactured from an aqueous paste has been adopted in electric storage elements such as lithium batteries, lithium ion batteries, and electric double layer capacitors. I came.

However, PFOAs typified by APFO (in this specification, PFOAs include APFO and ammonium perfluorooctane sulfonate, and perfluoroalkanoic acid and salts thereof and perfluoroalkanesulfonic acid and salts thereof which are similar to these. It was found that fluorinated surfactants such as, etc.) have high in vivo persistence and accumulation. Although there are still many unclear points about the toxicity and danger of PFOAs remaining in the living body to the human body, it is required not to use them as much as possible because they are compounds that do not exist in nature. For this reason, in the production of an aqueous dispersion of a fluoropolymer, after emulsion polymerization using PFOAs, a hydrocarbon-based surfactant such as sodium lauryl sulfate or polyoxyethylene alkyl ether is added to the resulting emulsion of the fluoropolymer. In addition, after stabilization, a technique has been developed in which PFOAs are removed to obtain a fluoropolymer aqueous dispersion having a significantly low PFOA content.

However, an aqueous paste using a fluorine-containing polymer aqueous dispersion containing a small amount of PFOA as a binder cannot be applied to the surface of the current collector as a result of abnormally thickening of the paste. There has been a problem that it is not possible to form an electrode composite layer that is excellent in workability such as winding and that can exhibit good characteristics of an electric storage element.

Japanese Patent Publication No. 08-4007 Japanese Patent Publication No. 07-40485

The present invention overcomes the above-mentioned problems of the prior art, enables electrode materials such as electrode active materials and conductive assistants to be finely and uniformly dispersed, and the obtained electrode composite layer has high workability, and has an environmental load and It is an object of the present invention to provide a binder having a low risk of damaging human health, a paste-like composition containing the binder, an electrode material, and water, and a method for producing an electrode using the paste-like composition. To do.

The present inventor has intensively studied to achieve the above-mentioned problems. As a result, fluorine-containing oligomers and polymers that are dissolved in water and / or micro-dispersed in water form a structure called self-assembly. The present inventors have found that the problem can be solved and have completed the present invention. That is, this invention provides the manufacturing method of the binder which has the following structures, a paste-form composition, and an electrode.
[1] A fluorine content of 3 to 60% by mass selected from a fluorine-containing olefin copolymer having a hydrophilic group in the side chain or a linear hydrophilic polymer having a hydrophobic fluorine-containing organic group at both ends. , A binder for electrode materials, comprising a polymer having a number average molecular weight of 1,000 to 1,000,000.
[2] The fluorine-containing olefin copolymer is at least one unit selected from tetrafluoroethylene and chlorotrifluoroethylene units, a hydroxyl group and a —COOX group (X is a hydrogen atom or a cation). The binder according to [1], which is a copolymer comprising a unit having one kind of hydrophilic group.
[3] A linear polymer chain in which the hydrophilic polymer includes a unit having at least one hydrophilic group selected from a hydroxyl group and a —COOX group (X is a hydrogen atom or a cation), and the linear polymer. The binder according to [1], which is a polymer having a hydrophobic fluorine-containing organic group derived from a polymerization initiator or a chain transfer agent present at both ends of the chain.
[4] The bond according to [1] or [3], wherein the hydrophobic fluorine-containing organic group has a perfluoroalkyl group having 3 or more carbon atoms, which may have an etheric oxygen atom between carbon atoms. Dressing.
[5] A pasty composition comprising the binder according to any one of [1] to [4], an electrode material, and water.
[6] The paste composition according to [5], further comprising polytetrafluoroethylene.
[7] The paste composition according to [5] or [6], wherein the electrode material is at least one selected from a metal compound and a carbon material.
[8] The paste composition according to any one of [5] to [7], wherein the electrode material is a material for an electrode of a storage element.
[9] A method for producing an electrode for a storage element, wherein the paste composition according to any one of [5] to [8] is applied to a current collector and dried.
[10] The method for producing an electrode according to [9], wherein the storage element is a lithium ion secondary battery, a nickel hydride secondary battery, or an electric double layer capacitor.

When the binder of the present invention is placed in water, it forms a structure called so-called self-assembly, and exhibits a function of being dissolved in water and / or microscopically dispersed in water. Self-organization also has a function of incorporating a hydrophobic material arranged in the vicinity into the structure and dispersing it in water. In particular, a compound containing fluorine in a hydrophobic group is excellent in this function, and even incorporates acetylene black, which is widely used as a conductive aid and is very hydrophobic and difficult to disperse in water, and is incorporated into water. It has the effect of being uniformly dispersed in the inside. Thus, the paste-like composition manufactured using the binder of the present invention is an electrode composite that maintains a state in which a plurality of finely divided components are uniformly dispersed even after being applied onto a current collector. Layers can be formed. The obtained electrode has excellent adhesion to the current collector, excellent solvent resistance and heat resistance, high workability, and finely divided electrode active material, conductive additive and binder are homogeneous. Therefore, it functions to perform smooth interfacial charge transfer reaction, ionic conduction, and electronic conduction, and has the effect of exhibiting good storage element characteristics. Moreover, it is not necessary to use PFOAs having in vivo residue and accumulation in the paste-like composition of the present invention.

The binder of the present invention is also self-organized with binders such as polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber, etc., which have been used as a binder for power storage element electrodes, and that are very hydrophobic. Incorporated into a structured structure, it is also refined into water and dispersed uniformly. Therefore, the binder of the present invention is not only a binder but also exhibits an effect of functioning as a dispersant or stabilizer for an aqueous paste.

The binder of the present invention also has an effect of exhibiting excellent adhesion with a small addition amount because the hydrophilic group bears strong adhesion with the current collector. This effect can also be applied to conventional fluorine-based binders that have been considered to have low adhesion, and when used in combination with the binder of the present invention, has the effect of imparting strong adhesion.

Furthermore, since the binder of the present invention has a high affinity with the electrolyte solution, the electrolyte solution spreads deep into the electrode composite, without interfering with the interfacial charge transfer reaction in rapid charge / discharge, or unevenly distributing the active region, It also has the effect of achieving high load characteristics and power, and a long battery life.

In this specification, acrylate and methacrylate are collectively referred to as (meth) acrylate. The same applies to (meth) acrylic acid and the like.

The binder of the present invention has a fluorine content selected from a fluorine-containing olefin copolymer having a hydrophilic group in the side chain or a linear hydrophilic polymer having a hydrophobic fluorine-containing organic group at both ends. It is characterized by comprising a polymer having 3 to 60% by mass and a number average molecular weight of 1,000 to 1,000,000.

The fluorine-containing olefin copolymer having a hydrophilic group in the side chain in the present invention is a copolymer having a unit of a fluorine-containing olefin and a unit having a hydrophilic group in the side chain, and further copolymerization if necessary. It may be a copolymer further having other possible monomer units.

The fluorine-containing olefin in the present invention includes vinyl fluoride, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, bromotrifluoroethylene, tetrafluoroethylene, pentafluoropropylene, hexafluoropropylene and other α-olefins, and the following general formula Examples include perfluoro (alkyl vinyl ethers) and perfluoro (alkyloxyalkyl vinyl ethers) represented by (1), 1-bromo-1,1,2,2-tetrafluoroethyl trifluorovinyl ether, and others. it can.
CF ₂ = C (OR ^f1 ) _n F _2-n (1)
In the formula, R ^f1 is a perfluoroalkyl group having 1 to 18 carbon atoms or a perfluoroalkyloxyalkyl group containing one or more ether bonds in the molecule, n is 1 or 2, and any carbon chain is It may have a linear, branched or cyclic structure.

_{Further, CH 2 = CH (CF 2} ) 2 Br, CH 2 = CHOCH 2 (CF 2) 2 H, CH 2 = CHOCH 2 (CF 2) 4 H, CH 2 = CHO (CH 2) 2 (CF 2) fluorine-containing monomer such as _{6 F} can be preferably used in the present invention. In particular, chlorotrifluoroethylene and tetrafluoroethylene are preferable because they are stable thermally and electrochemically and have excellent durability.

The unit having a hydrophilic group in the side chain in the fluorinated olefin copolymer is a monomer having a hydrophilic functional group such as a hydroxyl group, a carboxylic acid group, a sulfonic acid group, a phosphoric acid group or an amino group, or a hydrophilic group such as an oxyethylene chain. A hydrophilic functional group obtained by converting a monomer unit having an ionic chain, a monomer unit having a group that can be converted into these hydrophilic functional groups into a hydrophilic functional group by a treatment such as hydrolysis. A unit obtained by reacting ethylene oxide or the like with a monomer unit having a group having a group capable of introducing a hydrophilic chain (such as a hydroxyl group) or the like, and introducing a hydrophilic chain. A copolymer obtained by copolymerizing a monomer having a group that can be converted into a hydrophilic functional group with a fluorine-containing olefin, converts the group that can be converted into a hydrophilic functional group into a hydrophilic functional group, and is used in the present invention. Conversion into a fluorinated olefin copolymer having a hydrophilic group in the chain. For example, a copolymer having an unsaturated carboxylic acid unit such as a (meth) acrylic acid unit by hydrolyzing a copolymer having an unsaturated carboxylic acid ester unit such as a (meth) acrylic acid ester. Coalescence can be obtained. Moreover, the copolymer which has a unit of a hydroxyl-containing monomer can be made to react with ethylene oxide, and the copolymer which has a polyoxyethylene chain in a side chain can be obtained.

Specific examples of the monomer include the following compounds.
2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 3-hydroxybutyl vinyl ether, 2-hydroxy-2-methylpropyl vinyl ether, 5-hydroxypentyl vinyl ether, 6-hydroxyhexyl Hydroxyl-containing alkyl vinyl ethers such as vinyl ether.
2-hydroxyethyl (meth) allyl ether, 3-hydroxypropyl (meth) allyl ether, 2-hydroxypropyl (meth) allyl ether, 4-hydroxybutyl (meth) allyl ether, 3-hydroxybutyl (meth) allyl ether, Hydroxyl-containing alkyl allyl ethers such as 2-hydroxy-2-methylpropyl (meth) allyl ether, 5-hydroxypentyl (meth) allyl ether, and 6-hydroxyhexyl (meth) allyl ether.
Vinyl-2,2-dimethylpropanoate, vinyl-2,2-dimethylbutanoate, vinyl-2,2-dimethylpentanoate, vinyl-2,2-dimethylhexanoate, vinyl-2-ethyl- 2-methylbutanoate, vinyl-2-ethyl-2-methylpentanoate, vinyl-3-chloro-2,2-dimethylpropanoate, and other branched aliphatic carboxylates. Vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl crotonate, vinyl stearate, monovinyl adipate, monovinyl succinate, other branched aliphatic vinyl carboxylates Aliphatic vinyl carboxylates and derivatives thereof other than those.
Vinyl esters of cyclic carboxylic acids such as vinyl cyclohexanecarboxylate, vinyl methylcyclohexanecarboxylate, vinyl benzoate, vinyl p-tert-butylbenzoate, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate And (meth) acrylic acid esters such as cyclohexyl (meth) acrylate.
4-vinyloxycarbonylmethyl-2-oxo-1,3-dioxolane, 4-methyl 4-vinyloxycarbonylmethyl-2-oxo-1,3-dioxolane, 4- (1-propenyl) oxycarbonylmethyl-2- Oxo-1,3-dioxolane, 4-methyl-4- (1-propenyl) oxycarbonylmethyl-2-oxo-1,3-dioxolane, 4-vinyloxymethyl-2-oxo-1,3-dioxolane, 4 -Methyl-4-vinyloxymethyl-2-oxo-1,3-dioxolane, 4- (1-propenyl) oxymethyl-2-oxo-1,3-dioxolane, 4-methyl-4- (1-propenyl) Vinyl monomers containing a 2-oxo-1,3-dioxolane group such as oxymethyl-2-oxo-1,3-dioxolane;
Polyoxyethylene glycol mono (meth) acrylate, polyoxypropylene glycol mono (meth) acrylate, (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, maleic anhydride, itaconic anhydride, pentenoic acid, hexene Acid, heptenoic acid, octenoic acid, nonenic acid, decenoic acid, undecenoic acid, 3-allyloxypropionic acid, allyloxyvaleric acid, (meth) allylsulfonic acid, vinylsulfonic acid, styrenesulfonic acid, butyl (meth) acrylate 4-sulfonic acid, (meth) acrylooxybenzenesulfonic acid, butylacrylamidesulfonic acid, 2-acryl-2-acrylamido-2-methylpropanesulfonic acid, phosphooxyethyl (meth) acrylate, phosphooxypolyoxyethylene glycol (Meth) acrylate, phosphonate oxy poly polypropylene glycol (meth) acrylate, vinyl phosphoric acid, allyl phosphoric acid, propenyl phosphoric acid, acrylamide and the like derivatives thereof.

In particular, the unit having a hydrophilic group in the side chain is preferably a unit having at least one hydrophilic group selected from a hydroxyl group and a —COOX group (X is a hydrogen atom or a cation) in the side chain. This unit is obtained using a monomer having a hydroxyl group, a monomer having a —COOH group, a monomer having a group capable of becoming a hydroxyl group upon hydrolysis, and a monomer having a group capable of becoming a —COOH group upon hydrolysis. Further, by converting the hydrogen atom of the —COOH group in the copolymer to a cation, a unit having a —COOX group in which X is a cation can be obtained. In addition, when converting the group which can be converted into a hydrophilic functional group into a hydrophilic functional group after manufacture of a copolymer, it is not necessary to convert all the groups which can be converted into a hydrophilic functional group into a hydrophilic functional group.

The hydrophilic group of the above monomer is usually a nonion or an anion in the polymer, but it is also possible to convert the hydrophilic group into a cation after polymerization. In addition, a copolymerizable monomer that becomes a cation by normal or simple treatment can also be used. For example, alkylaminoalkyl (meth) acrylates such as N-dimethylaminoethyl (meth) acrylate, alkylaminohydroxyalkyl (meth) acrylates, alkylaminoalkyl (meth) acrylamides, aziridiniethyl (meth) acrylate, pyrrolidinylethyl ( Examples include meth) acrylate, piperidinylethyl (meth) acrylate, vinylpyridine, vinylimidazole, allylamine, vinylamine, and derivatives thereof.

The fluorine-containing olefin copolymer may have other monomer units in addition to the above-described two monomer units. Other monomers include those represented by the general formula (2): CH ₂ ═CHOR ² (wherein R ² is an alkyl group having 1 to 18 carbon atoms or an alkyloxyalkyl group containing at least one ether bond, The chain may also have a linear, branched or cyclic structure, and may be an alkyloxyalkyl group partially substituted with a halogen other than fluorine.) Alkyl vinyl ethers, ethylene, propylene, butene-1, vinyl chloride, vinylidene chloride, styrene, α-methylstyrene, vinyl toluene, acrylonitrile, cyanostyrene, and the like can be used. As the other monomer, a monomer represented by the general formula (2) is particularly preferable.

Moreover, an epoxy group-containing monomer such as a monomer represented by the following general formula (3) can also be used.

In the formula, R ³ is a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms, R ⁴ is an alkyl group having 1 to 18 carbon atoms, R ⁵ is an alkyl group having 1 to 18 carbon atoms, or epoxycyclohexanemethylene It is a group. a is an integer of 0 to 10, b is an integer of 0 to 5, c is 0 or 1, b is 0 when a is 1 to 10, and a is 0 when b is 1 to 4.

The fluorine-containing olefin copolymer having a hydrophilic group in the side chain in the present invention has a fluorine content of 3 to 60% by mass. More preferably, it is 10 to 55% by mass. The unit having a hydrophilic group needs to be at least 10 mol% in order to exhibit dispersibility, and is preferably 10 to 50 mol% based on all units.

The number average molecular weight M _n is a value measured by gel permeation chromatography (hereinafter referred to as GPC) using polystyrene as a standard substance. _Mn of the fluorinated olefin copolymer having a hydrophilic group in the side chain of the present invention is preferably from 1,000 to 1,000,000, more preferably from 1500 to 600,000. It is preferable that M _n is 1000 or more because good adhesion can be exhibited and the accumulation in the human body is reduced. Moreover, even if _Mn exceeds 1000000, the characteristics useful for the present invention do not remarkably increase, but rather the handling is often more difficult. Therefore, _Mn is more preferably 1000000 or less.

The production of the copolymer in the present invention is not particularly limited, and various conventionally known production methods such as solution polymerization, emulsion polymerization, suspension polymerization, bulk polymerization and the like can be used. The solution polymerization and the emulsion polymerization are preferable.

The polymerization initiator includes diacyl peroxides such as benzoyl peroxide and acetyl peroxide, various ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide, hydroperoxides such as hydrogen peroxide and cumene hydroperoxide, Dialkyl peroxides such as dibutyl peroxide and dicumyl peroxide, alkyl peroxy esters such as butyl peroxyacetate and butyl peroxypivalate, azo compounds such as azobisisobutyronitrile and azobisisovaleronitrile Or persulfates such as potassium persulfate and ammonium persulfate can be used.

The amount of the polymerization initiator used is determined depending on the type of polymerization initiator used, the polymerization conditions, and the like, but is usually about 0.1 to 0.5% by mass based on the total amount of monomers. It is general and is preferably used in the present invention.

The polymerization temperature is often determined by the type of initiator used, but it is usually preferably from 10 ° C to 90 ° C because it is easy to handle. The polymerization pressure is usually from 0 to 100 kg / cm ² · G, preferably from 1 to 50 kg / cm ² · G, since it is easy to operate.

The solvent used for the polymerization is not particularly limited as long as various monomers, a polymerization initiator, or an emulsifier is soluble, and examples thereof include the following solvents. These solvents can be preferably used alone or as a mixed medium using two or more kinds in combination.
Aromatic hydrocarbons such as benzene, xylene and toluene. Aliphatic hydrocarbons such as heptane, hexane, and octane. Cycloaliphatic hydrocarbons such as cyclopentane, cyclohexane, methylcyclohexane and ethylcyclohexane;
Alcohols such as methanol, ethanol, propanol, butanol, pentanol, hexanol, octanol, 2-ethylhexanol, cyclohexanol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether.
Ethers such as dimethoxyethane, tetrahydrofuran, dioxane, isopropyl ether; Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone, cyclohexanone and isophorone. Esters such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate, ethylene glycol monomethyl ether acetate, and ethylene glycol monoethyl acetate.
Chloroform, methylene chloride, carbon tetrachloride, chlorodifluoromethane, trichloroethane, tetrachloroethane, tetrafluoroethane, chloropentafluoroethane, dichloropentafluoropropane, trifluoromethoxydifluoroethyl ether, difluoroethyl ether, methylchlorohexafluoropropyl Halogenated hydrocarbons such as ether.
Mineral spirit, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, ethylene carbonate, water, etc.

The linear hydrophilic polymer having a hydrophobic fluorine-containing organic group at both ends in the present invention is present at both ends of a linear polymer chain containing a unit having a hydrophilic group and the linear polymer chain. It is a polymer having a hydrophobic fluorine-containing organic group derived from a polymerization initiator or a chain transfer agent.

The hydrophobic fluorine-containing organic group derived from the polymerization initiator present at both ends of the linear polymer chain is represented by the following general formula (4) because it is easily available and relatively easy to handle. Fluoroalkanoyl peroxide is preferred.
R ^f6 C (═O) OOC (═O) R ^f7 (4)
(In the formula, R ^f6 and R ^f7 have a perfluoroalkyl group having 3 or more carbon atoms which may have an etheric oxygen atom between carbon atoms, or an etheric oxygen atom between carbon atoms. Or a fluorine-containing alkyl group in which a part of fluorine atoms is replaced by a hydrogen atom or a chlorine atom, and any carbon chain may have a linear, branched or cyclic structure. ) Particularly preferred is a perfluoroalkyl group having 3 or more carbon atoms which may have an etheric oxygen atom between carbon atoms.

The fluoroalkanoyl peroxide can be easily produced by a known method in which an acyl halide having a fluoroalkyl group is reacted with a hydrogen peroxide solution in a fluorine-containing solvent to which an alkali such as sodium hydroxide is added. Specifically, diperfluorobutyryl peroxide, diperfluoroheptanoyl peroxide, diperfluoro-2-methyl-3-oxahexanoyl peroxide, diperfluoro-2-methyl-3-oxanonanoyl peroxide, diperfluoroperoxide -2,5-dimethyl-3,6-dioxanonanoyl, diperfluoro-2,5,8-trimethyl-3,6,9-trioxadodecanoyl peroxide, etc., all of which are examples of the polymerization of the present invention It can be suitably used as an initiator.

The unit having a hydrophilic group in the linear polymer chain containing a unit having a hydrophilic group is the same unit as the unit having a hydrophilic group in the side chain in the fluorine-containing olefin copolymer. This unit is a unit obtained by modifying a radical polymerizable monomer unit or a radical polymerizable monomer unit as described above. Furthermore, the linear polymer chain may be a linear polymer chain having a hydrophilic unit such as an oxyethylene group (for example, a polyoxyethylene chain). The linear polymer chain containing a unit having a hydrophilic group preferably has a radical polymerizable monomer unit or a unit obtained by modifying it. Moreover, the linear polymer chain containing the unit which has a hydrophilic group may have units other than the unit which has a hydrophilic group.

The unit having a hydrophilic group in the linear polymer chain containing a unit having a hydrophilic group has, in particular, at least one hydrophilic group selected from a hydroxyl group and a —COOX group (X is a hydrogen atom or a cation). Units are preferred. This unit is obtained using a monomer having a hydroxyl group, a monomer having a —COOH group, a monomer having a group capable of becoming a hydroxyl group upon hydrolysis, and a monomer having a group capable of becoming a —COOH group upon hydrolysis. Further, a unit having a —COOX group in which X is a cation can be obtained by converting a hydrogen atom of a —COOH group in a linear polymer into a cation. In addition, when a group that can be converted to a hydrophilic functional group after the production of the polymer is converted to a hydrophilic functional group, as long as the polymer after the conversion becomes sufficiently hydrophilic, all the groups that can be converted to the hydrophilic functional group There is no need to convert to a hydrophilic functional group.

As the hydrophobic fluorine-containing organic group derived from the chain transfer agent present at both ends of the linear polymer chain, thiols having a polyfluoroalkyl group can be used. Examples thereof include polyfluoromercaptan having 1 to 14 carbon atoms.

In the present invention, the _Mn of the linear hydrophilic polymer having a hydrophobic fluorine-containing organic group at both ends is preferably from 1,000 to 1,000,000, more preferably from 1500 to 100,000. It is preferable that M _n is 1000 or more because good adhesion can be exhibited and the accumulation in the human body is reduced. Moreover, even if _Mn exceeds 1000000, the characteristics useful for the present invention do not remarkably increase, but rather the handling is often more difficult. Therefore, _Mn is more preferably 1000000 or less.

In the present invention, the linear hydrophilic polymer having hydrophobic fluorine-containing organic groups at both ends has a fluorine content of 3 to 60% by mass. More preferably, it is 10 to 55% by mass. Further, the unit having a hydrophilic group needs to be at least 35 mol% or more, preferably 35 to 99 mol% with respect to the total polymerization units in order to exhibit dispersibility.

In the linear hydrophilic polymer having a hydrophobic fluorine-containing organic group at both ends in the present invention, a hydrophilic polymer having a low molecular weight can be obtained if the molar ratio of fluoroalkanoyl peroxide is high. If the molar ratio of alkanoyl is low, a hydrophilic polymer having a large molecular weight can be obtained. The radical polymerizable monomer can be used in combination of two or more monomers. Two or more types of fluoroalkanoyl peroxide can be used in combination, but fluoroalkanoyl peroxide is not practical because the decomposition start temperature differs depending on the type. Although the reaction temperature depends on the fluoroalkanoyl peroxide used, it is usually from −20 ° C. to 150 ° C., preferably from 0 ° C. to 100 ° C., because normal pressure can be used with relatively simple equipment. . The reaction time is usually 30 minutes to 50 hours, but it is practical to set it to 1 to 10 hours.

The hydrophilic polymer in the present invention can be obtained by reacting fluoroalkanoyl peroxide and a radical polymerizable monomer in the absence of a solvent. However, it is preferable to use an organic solvent or the like as the reaction solvent because the reaction is easily controlled stably from the start to the end of the reaction. Examples of the reaction solvent include a series of solvents presented as the polymerization solvent and others, and these can be used alone or as an arbitrary mixed solvent of two or more kinds.

A polymer obtained by reacting a fluoroalkanoyl peroxide and a radical polymerizable monomer can be used as it is as the binder of the present invention. However, depending on the selected radically polymerizable monomer, the dispersibility in water can be further enhanced by acid treatment or alkali treatment. As the usable acid, either an inorganic acid or an organic acid can be used. Examples include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, citric acid, boric acid, hydrofluoric acid, acetic acid, butyric acid, trichloroacetic acid, trifluoroacetic acid, methanesulfonic acid, trifluoromethanesulfonic acid, toluenesulfonic acid, and the like. An inorganic alkali or an organic base can also be used as the alkali. For example, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, pyridine, triethylamine, tributylamine, lutidine, triethanolamine and the like can be exemplified. The acid treatment and alkali treatment are usually preferably performed using an acid or alkali solution because the reaction is easy to control. Examples of the solvent used in these solutions include general-purpose organic solvents such as water, methanol, ethanol, xylene, toluene, benzene, and acetonitrile. The amount of acid or alkali used is preferably 0.01 to 1000 parts by weight with respect to 1 part by weight of the polymer. The reaction temperature is preferably −20 ° C. to 250 ° C., and the reaction time is preferably in the range of 1 minute to 48 hours because it is easy to control.

The fluorine-containing olefin copolymer and the hydrophilic polymer can be produced by charging the monomers, polymerization initiators, polymerization media, and other total amounts into a reaction vessel and copolymerizing them. Furthermore, it can be produced by copolymerizing a part of the monomers or other monomers, polymerization initiators, etc., or by supplying them sequentially or continuously to the reaction vessel. Although it is often observed that the produced copolymer does not dissolve in the polymerization solvent, there is no problem in using it as the binder of the present invention.

The binder of the present invention is provided as an aqueous solution or aqueous dispersion of the polymer. When the polymerization solvent or the polymerization dispersion medium is water, the polymer aqueous solution or polymer aqueous dispersion after polymerization can be used as it is as the binder of the present invention. On the other hand, a polymerization method using an organic solvent as a polymerization solvent or a polymerization dispersion medium is also widely used. In the case of a solution or dispersion using such an organic solvent as a medium, it can be used as the binder of the present invention by converting it into a solution or dispersion using water as a medium. A technique for converting a solution or dispersion using an organic solvent as a medium to a solution or dispersion of an aqueous medium is also known and can be applied to the present invention. For example, firstly, a solution or dispersion is prepared by adding water to an organic medium solution or dispersion and mixing, and then the organic medium is removed by a method such as distillation under reduced pressure to convert it into an aqueous medium solution or dispersion. It can be suitably used in the present invention.

In order to improve the solubility in water and the dispersibility in water, for example, in the case of a carboxyl group-containing polymer, it is more effective to use a type neutralized with a salt thereof rather than a carboxylic acid type. However, in the case of a monomer having a carboxyl group, the neutralization type monomer generally has low polymerization reactivity. Therefore, it is possible to obtain a copolymer having a wide composition by using a carboxylic acid type monomer or a hydroxyl group-containing monomer which is easily copolymerized. The polymer thus obtained can be modified in an organic solvent to obtain the binder of the present invention.

The copolymer containing a hydroxyl group is characterized in that it exhibits a desirable characteristic such as being hydrophilic per se or improving adhesion to a current collector. However, at least a part of the hydroxyl group is acid-modified, so that the hydrophilicity is further increased and the solubility and dispersibility in water can be improved. Acid modification is performed by reacting a hydroxyl group with an anhydride of a dibasic acid and esterifying it. Dibasic acid anhydrides include succinic anhydride, glutaric anhydride, itaconic anhydride, adipic anhydride, cyclohexanedicarboxylic anhydride, cyclhexene dicarboxylic anhydride, phthalic anhydride, naphthalic anhydride, maleic anhydride, etc. It can be exemplified and is preferably used in the present invention.

As the solvent for esterification, the organic solvent itself used in the polymerization reaction may be added, or other solvents selected in consideration of the solubility of the hydroxyl group-containing binder and dibasic acid anhydride may be added. Is possible. In the esterification step, a catalyst can be used in combination. As the catalyst, metal salts of carboxylic acids, alkali metal hydroxides, alkali metal carbonates, quaternary ammonium salts, tertiary amines and the like are generally used. The esterification temperature is in the range of room temperature to 150 ° C., but it is generally carried out at 50 to 100 ° C., which is easy to control the reaction. Although the reaction time depends on the temperature and the catalyst, it is generally several minutes to several hours for the same reason.

The neutralization of the carboxylic acid can be performed by reacting a carboxyl group-containing polymer with a basic compound. In the present invention, it can be freely selected from a wide range of basic compounds, but since it is difficult to remain in the formed electrode composite, it can be selected from amines, imines and the like. Particularly preferred. Examples of such basic compounds include the following compounds. Primary, secondary or tertiary alkylamines such as monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoisopropylamine, diisopropylamine, triisopropylamine, monobutylamine, dibutylamine and the like. Alkanolamines such as monoisopropanolamine, dimethylaminoethanol, diethylaminoethanol and methyldiethanolamine. Diamines such as ethylenediamine, propylenediamine, tetramethylenediamine and hexamethylenediamine. Alkyleneimines such as ethyleneimine and propyleneimine. Ammonia, piperazine, morpholine, pyrazine, pyridine.

The neutralization reaction is performed by adding a basic compound or a basic compound solution to an organic dispersion of a carboxyl group-containing binder. The proportion of the carboxyl group in the fluorinated olefin copolymer to be neutralized is generally 30 to 100 mol%, but it can be increased to 50 to 100 mol% because the solubility or dispersibility in water can be further improved. Preferably there is.

When the polymer medium is an organic solution or an organic dispersion, it is then converted into an aqueous solution or dispersion and applied to the binder of the present invention. As described above, the aqueous solution or dispersion can be converted into an aqueous solution or dispersion by adding water to the organic solution or dispersion of the polymer to dissolve or disperse it, and then distilling off the organic solvent under reduced pressure. Alternatively, it can be converted to an aqueous dispersion. The removal of the organic solvent is generally 50 to 100% by mass, preferably 90 to 100% by mass, more preferably.

The binder of the present invention can be used alone or in combination with other binders. When used alone, it is preferable because the hydrophilic group of the binder has an affinity for the electrolyte and the supply of the electrolyte into the electrode composite proceeds smoothly. As other binders, polymers such as crystalline resins, amorphous resins, rubbers, and elastomers can be used regardless of the content of fluorine. For example, polymers that do not contain fluorine include natural rubber, styrene butadiene copolymer, acrylic modified styrene butadiene copolymer, vinyl acetate copolymer, nitrile butyl rubber, hydrogenated nitrile butyl rubber, acrylic rubber, epichlorohydrin, polyurethane, etc. Synthetic resins such as rubber / elastomers, (meth) acrylic resin, vinyl resin, polyolefin, polycarbonate, nylon, and polyimide can be used.

As the other binder in the present invention, a fluorine-containing polymer is more preferable. The fluorine-containing polymer is not particularly limited as long as it is a fluorine-containing polymer obtained by polymerizing a fluorine-containing monomer. Examples of fluorine-containing monomers include tetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, perfluoro (alkyl vinyl ethers) and perfluoro (alkyloxyalkyl vinyl ethers) represented by the general formula (1), and chlorotrifluoroethylene. Fluorine-containing monomers of at least one or a combination of two or more selected from
Preferably, polytetrafluoroethylene (PTFE) obtained by polymerization of tetrafluoroethylene, which has excellent powder binding properties and does not hinder ion migration, is preferable.

In addition to the fluorine-containing monomer, one or more of copolymerizable monomers such as alkyl vinyl ethers and alkyloxyalkyl vinyl ethers represented by the general formula (2), ethylene and propylene may be copolymerized. Good.

Other copolymerizable monomers include 1-bromo-1,1,2,2-tetrafluoroethyl trifluorovinyl ether, vinyl crotonic acid, vinyl (meth) acrylate, maleic anhydride, itaconic anhydride, maleic acid, Examples include itaconic acid. In the present invention, the fluorine-containing crystalline polymer and the fluorine-containing amorphous polymer obtained from these monomers can be used alone or in combination of two or more.

The binder of the electrode material of the present invention is composed of the fluorine-containing olefin copolymer and the hydrophilic polymer. This electrode material is a material used for manufacturing a positive electrode or a negative electrode of a power storage element. The binder for an electrode material of the present invention is suitable as a binder for producing a paste-like composition containing an electrode material and a liquid medium. In particular, it is suitable as a binder for producing a paste-like composition containing an electrode material and an aqueous medium. The present invention is also a paste-like composition comprising the above-mentioned electrode material binder, electrode material and water. Hereinafter, a paste-like composition containing a binder, an electrode material, and an aqueous medium, which is characterized by containing an aqueous medium, is also referred to as an aqueous paste.

As the electrode material, an electrode active material or a conductive additive selected from metal compounds and carbon materials can be used as appropriate.

As the electrode active material in the present invention, for example, metal oxides, metal sulfides, conductive organic compounds and the like are generally used as the positive electrode active material of lithium batteries. In particular, metal oxides such as lithium metal composite oxide and lithium metal phosphoolivine are preferable because stable battery characteristics can be expressed over a long period of time. These metal oxides are sometimes used as a composite oxide of Li and another metal, but are also used as a composite oxide composed of Li and other metals. For example, in the case of lithium nickel composite oxides, LiNiO ₂ is hardly used as a positive electrode of a lithium ion battery as it is, and a part of lithium or nickel is Co, Mn, Al, B, Cr, Cu, F, Fe, A material substituted with one or more elements selected from Ga, Mg, Mo, Nb, O, Sn, Ti, V, Zn, Zr, and the like is preferable.

As the negative electrode active material of lithium batteries, materials such as graphite-based carbon, non-graphite-based carbon, or metal-based materials can be preferably applied. For example, natural graphite, artificial graphite, coal-based coke, petroleum-based coke, coal-based pitch carbide, petroleum-based pitch carbide, needle coke, pitch coke, furnace black, acetylene black, carbon fiber, etc. are suitably used as the carbon material. . In addition, carbides such as phenol resin and cellulose and partially graphitized products of these carbides are also preferably used. Metal systems such as tin, silicon, titanium, metal nitride, lithium, and lithium alloys are also preferably used. Furthermore, lithium titanium composite oxide and other oxide systems are also preferably used.

Activated carbon is suitably used as the electrode active material for the electric double layer capacitor. For the purpose of increasing load characteristics and capacitance, modified activated carbon such as activated carbon treated with boric acid is also preferably used.

As an electrode active material for a nickel metal hydride battery, a nickel hydroxide in which nickel hydroxide or cobalt oxide is combined with the positive electrode is preferably used, and a nickel-based or titanium-based hydrogen storage alloy is preferably used for the negative electrode.

The average particle diameter of the electrode active material is usually preferably from 0.05 to 500 μm, more preferably from 0.1 to 100 μm. In the paste-like composition, the content of the electrode active material in the paste-like composition is not limited, but is generally preferably 5 to 65% by mass, and preferably 20 to 55% by mass with respect to the total amount of the paste-like composition. % Is more preferable. Even if the amount is less than 5% by mass, the formed electrode itself has no problem in characteristics, but it is not preferable because of low productivity and inefficiency.

Effective conductive aids in the present invention include graphites such as natural graphite and artificial graphite, carbon blacks such as thermal black, furnace black, channel black, lamp black and acetylene black, ketjen black, needle coke, and carbon fiber. Carbon nanotubes, carbon nanocoils and the like are preferably used. The average particle size of the conductive aid is usually preferably 3 to 1000 nm, more preferably 5 to 200 nm. In the case of a fibrous carbon material, the length is preferably 100 μm or less because it is easy to handle. The content of the conductive additive in the paste-like composition is determined according to the type and characteristics of the electrode active material, but the content of the conductive auxiliary is usually 0 with respect to the amount of the electrode active material. 0.01 to 15% by mass is preferable, and 0.1 to 12% by mass is more preferable.

The main material responsible for the characteristics of the storage element is an electrode active material. Therefore, materials other than the electrode active material that do not contribute to the storage capacity are preferably added in the minimum amount capable of expressing the required function.

In addition, the paste-like composition of the present invention is mixed with a dispersion stabilizer and / or a thickening agent of the paste-like composition such as methylcelluloses, carboxymethylcelluloses, crown ethers, dextrins, and water-soluble dietary fibers. May be. The mixing amount of the dispersion stabilizer and / or thickener is preferably 0.01 to 10% by mass with respect to the total amount of the paste-like composition.

The aqueous medium used in the aqueous paste (that is, the paste-like composition containing the aqueous medium) may be water such as ion-exchanged water. For the purpose of improving the adhesion between the electrode composite and the current collector, the aqueous medium As an aqueous medium, a water-soluble compound having a boiling point higher than that of water can be used. Examples of the water-soluble compound having a higher boiling point than water include organic solvents such as dimethylformamide, dimethylacetamide, dimethyl sulfoxide, tetramethylene sulfone, N-methylpyrrolidone, ethylene glycols, propylene glycols, and glycerin. In general, the content of the organic solvent is preferably 0 to 50% by mass, more preferably 0 to 20% by mass with respect to the total amount of water and the organic solvent. The content ratio of the aqueous medium is preferably 30 to 90% by mass, more preferably 40 to 75% by mass with respect to the total amount of the aqueous paste.

The production of the aqueous paste of the present invention is carried out by further mixing a binder, an electrode active material, a conductive auxiliary agent and an aqueous medium with the above-mentioned other components as necessary. When an aqueous dispersion or aqueous solution is used as the binder, since an aqueous medium is already contained, another aqueous medium may not be added, or another aqueous medium may be added.

The method for producing a storage element electrode using the aqueous paste of the present invention is not limited in any way, and can be produced using a general general technique or other techniques. However, an electrode manufacturing method using an aqueous process is preferred because it takes advantage of the property of being easily dissolved or dispersed in water. In the aqueous process, an aqueous paste in which all materials constituting the electrode are dispersed in an aqueous medium is formed and mixed homogeneously, and an electrode composite is formed by applying and drying on a current collector to produce an electrode for a storage element. Is done. The content of the binder for forming the electrode composite is determined according to the type and characteristics of the electrode active material, and is 0.01 to 15% by mass with respect to the amount of the electrode active material. The same applies to the binder of the present invention. When the amount of the binder is less than 0.01% by mass, it is difficult to form an electrode composite in which a conductive auxiliary agent such as carbon and an active material are uniformly arranged, or even if an electrode can be formed, it is not preferable to maintain a uniform arrangement. The storage element characteristics cannot be expressed. On the other hand, even if the binder exceeds 15% by mass, there is no remarkable defect in electrode formation, but there is no effect commensurate with the content. Rather, a high content of a material that does not have a power storage function deteriorates the characteristics of the power storage device. Let The main material responsible for the characteristics of the storage element is an electrode active material. Therefore, materials other than the electrode active material that do not contribute to the storage capacity are preferably added in the minimum amount capable of expressing the required function. More preferably, the content is 0.1 to 12% by mass.

Examples of a method for forming a storage element electrode from a paste-like composition include a method in which a paste-like composition of the present invention is applied to a current collector, dried and heat-treated. The viscosity of the water-based paste that is preferable for application to the current collector depends on the application method, but is generally preferably 100 to 10,000 mPa · S. If the viscosity is less than 100 mPa · S, it may be difficult to maintain the form of the coating film, and it is difficult to control the film thickness. On the other hand, when the viscosity is greater than 10,000 mPa · S, it is not preferable because unevenness is generated in the coating film and uniform molding becomes difficult. The viscosity of the aqueous paste is more preferably 300 to 8000 mPa · S, and further preferably 500 to 6000 mPa · S. Within these ranges, the film thickness can be easily controlled and a uniform coating film can be formed.

As the current collector, an aluminum foil is used for a positive electrode of a lithium ion battery, a copper foil or an aluminum foil is used for a negative electrode, an aluminum foil is used for a capacitor electrode, a nickel foil or a nickel mesh is used for a nickel metal hydride battery electrode. A good electrode composite layer can be formed on any of these current collectors from the aqueous paste of the present invention. A good coating film can be formed on other current collectors.

The aqueous paste of the present invention is suitable for forming an electrode composite layer of a storage element. As the storage element, primary batteries such as lithium batteries such as lithium ion batteries, lithium polymer batteries, and lithium primary batteries, nickel hydride batteries, secondary batteries, and capacitors such as electric double layer capacitors are suitable.

Since the composite electrode manufactured using the binder of the present invention can realize a structure in which an electrode active material, a conductive additive, a binder, and other composite components are finely and homogeneously arranged as described above, it is smooth. Can develop a positive charge transfer reaction. A power storage device having such features has a large charge / discharge capacity and high energy density, and can realize excellent cycle characteristics, high load characteristics, low temperature characteristics, high temperature characteristics, and safety. In particular, it is possible to achieve both high energy density and high load characteristics with high power and highly reliable safety, so that high output, high energy density, high reliability and safety can be realized even in medium and large-sized devices.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

(1) Synthesis of aqueous dispersion (A) of fluorine-containing olefin copolymer having a hydrophilic group in the side chain 3.1 g of ethyl vinyl ether (hereinafter referred to as EVE), cyclohexyl vinyl ether (hereinafter referred to as CHVE) in a 250 mL pressure-resistant polymerization tank 26.9 g, 4-hydroxybutyl vinyl ether (hereinafter referred to as HBVE) 19.8 g, methyl ethyl ketone (hereinafter referred to as MEK) 67 g, and t-butyl peroxypivalate 0.6 g were charged and cooled. After deaeration, the nitrogen gas pressurization operation is repeated to remove dissolved air, and then 50.3 g of tetrafluoroethylene (hereinafter referred to as TFE) is charged, the polymerization reaction is performed at 50 ° C., and the residual pressure purge is performed after 24 hours. Then, the polymerization reaction was completed. Next, after adding 2 g of Kyoward 500SH consisting of a double salt of magnesium and aluminum (hydrotalcite consisting of a double salt of magnesium and aluminum, manufactured by Kyowa Chemical Industry Co., Ltd.) and stirring for 30 minutes at room temperature, the solid content was removed. A solution having a polymer concentration of 60.3% by mass was obtained. The polymer had a fluorine content of 29.5% by mass and a number average molecular weight of 10,000.

To 166 g of this polymer solution, 1.8 g of succinic anhydride and 0.05 g of triethylamine were added, esterified at 70 ° C. for 6 hours, 1.3 g of triethylamine was added, and the mixture was stirred at 30 ° C. for 20 minutes to remove the carboxylic acid. Partial neutralization. Subsequently, 145 g of ion-exchanged water was slowly added with stirring, and then MEK was distilled off under reduced pressure to obtain a fluorine-containing copolymer aqueous solution (A) having a polymer concentration of 40.5% by mass. The MEK remaining in the aqueous solution (A) was less than 0.3% by mass based on the total amount of the aqueous solution from gas chromatographic analysis.

(2) Synthesis of aqueous dispersion (B) of fluorine-containing olefin copolymer having a hydrophilic group in the side chain 10.3 g of EVE, 16.7 g of CHVE, 15.4 g of HBVE, 10-undecenoic acid (hereinafter, referred to as 250 mL) 4.9 g, MEK 67 g, t-butyl peroxypivalate 0.6 g, and Kyoward 500 SH 2 g are charged, and after cooling, degassing, and nitrogen gas pressurization are repeated to remove dissolved air, and then chloro After charging 52.2 g of trifluoroethylene (hereinafter referred to as CTFE) and carrying out the polymerization reaction at 50 ° C., purging the residual pressure after 24 hours to complete the polymerization reaction, and removing the solid content, the polymer concentration 60. A 3% by weight solution was obtained. The polymer had a fluorine content of 20.2 mass% and a polystyrene-reduced number average molecular weight by GPC of 11,000.

To 1.67 g of this polymer solution, 1.85 g of triethylamine was added for neutralization, and 145 g of ion-exchanged water was slowly added with stirring. Subsequently, MEK was distilled off under reduced pressure to obtain a fluorine-containing copolymer aqueous solution (B) having a polymer concentration of 40% by mass. MEK remaining in the aqueous solution (B) was less than 0.4% by mass relative to the total amount of the aqueous solution.

(3) Synthesis of linear hydrophilic polymer aqueous solution (C) having hydrophobic fluorine-containing organic groups at both ends In a mixed solution of 1.7 g of vinyl acetate and 4.3 g of acrylic acid, 300 g of dichloropentafluoropropane (trade name: Asahi) in which 9.9 g of fluoroalkanoyl peroxide in which R ^f6 and R ^f7 are —CF (CF ₃ ) OCF ₂ CF (CF ₃ ) O (CF ₂ ) ₃ F was dissolved Clean AK225 (Asahi Glass Co., Ltd.) solution was added and reacted at 30 ° C. under a nitrogen stream. After 7 hours, the product was dissolved in methanol, purified by precipitation in hexane, dried, and after 9.5 ml of 40% by weight aqueous sodium hydroxide solution was slowly added dropwise to the methanol solution of the obtained purified product. A white precipitate was obtained. When this white precipitate was washed with methanol and dried, vinyl alcohol having both —CF (CF ₃ ) OCF ₂ CF (CF ₃ ) O (CF ₂ ) ₃ F at both ends of the molecular chain and acrylic acid (molar ratio of 1 pair) Thus, 5.3 g of a fluorine-containing copolymer having a fluorine content of 5.9% by mass and a number average molecular weight of 11,000 was obtained. When this was dissolved in pure water, 202 g of a fluorine-containing copolymer aqueous solution (C) having a polymer concentration of 2.6% by mass was obtained.

(4) Synthesis of linear hydrophilic polymer aqueous solution (D) having hydrophobic fluorine-containing organic groups at both ends. ^Rf6 and ^Rf7 in the general formula (4) are converted to —CF ( A solution of 300 g of dichloropentafluoropropane (trade name: Asahiklin AK225) in which 14.9 g of fluoroalkanoyl peroxide as CF ₃ ) O (CF ₂ ) ₆ F was dissolved was added at 30 ° C. under a nitrogen stream. Reacted. After 7 hours, the product was dissolved in methanol and then precipitated and purified in hexane. When dried, it was polyacrylic acid having —CF (CF ₃ ) O (CF ₂ ) ₆ F at both ends of the molecular chain. As a result, 5.2 g of a fluorine-containing copolymer having a fluorine content of 29.2% by mass and a number average molecular weight of 1950 was obtained. When this was dissolved in pure water, 101 g of a fluorine-containing copolymer aqueous solution (D) having a polymer concentration of 5.1% by mass was obtained.

(5) Synthesis of linear hydrophilic polymer aqueous solution (E) having hydrophobic fluorine-containing organic groups at both ends 3.0 g vinyl acetate and 9.9 g acrylic acid, R ^f6 and R in the general formula (4) When treated in the same manner as in Example (3) except that 6.5 g of fluoroalkanoyl peroxide whose ^f7 is —CF (CF ₃ ) O (CF ₂ ) ₆ F and 18 ml of 40% by mass aqueous sodium hydroxide solution were used. A copolymer of vinyl alcohol and acrylic acid (molar ratio 1 to 3) having —CF (CF ₃ ) O (CF ₂ ) ₆ F at both ends of the molecular chain, the fluorine content is 2.5 mass%, the number average 4.5 g of a fluorine-containing copolymer having a molecular weight of 17000 was obtained. When this was dissolved in pure water, 210 g of a fluorine-containing copolymer aqueous solution (E) having a polymer concentration of 2.1% by mass was obtained.

(6) Synthesis of linear hydrophilic polymer aqueous solution (F) having hydrophobic fluorine-containing organic groups at both ends 1.5 g of acrylic acid, R ^f6 and R ^f7 in formula (4) are —CF (CF ₃ ) When treated in the same manner as in Example (4) except that 21.5 g of fluoroalkanoyl peroxide as O (CF ₂ ) ₆ F was used, both ends of the molecular chain were —CF (CF ₃ ) O (CF ₂ ) _{As a result,} 7.7 g of a fluorine-containing copolymer having ₆ F and a fluorine content of 63.3 mass% and a number average molecular weight of 900 was obtained. When this was dissolved in pure water, 25 g of a fluorine-containing copolymer aqueous solution (G) having an oligomer concentration of 30.2% by mass was obtained.

(7) Preparation of polytetrafluoroethylene aqueous dispersion (G) Paraffin wax 736 g, ultrapure water 59 L, and APFO 15 g were charged into a 100 L pressure-resistant polymerization tank. After raising the temperature to 70 ° C., purging with nitrogen and then degassing, TFE was introduced to an internal pressure of 1.9 MPa while stirring. 1 L of 0.5 mass% disuccinic acid peroxide aqueous solution was injected into this to initiate polymerization. The polymerization was carried out for 45 minutes while maintaining the polymerization pressure at 1.9 MPa while supplying TFE, and then the temperature was raised to 90 ° C., and 1 L of a 2.5 mass% APFO aqueous solution was added and continued for 95 minutes. Agglomerates, paraffin and the like are removed from the obtained emulsion, and an aqueous dispersion having a polytetrafluoroethylene (hereinafter referred to as PTFE) content of 26.0% by mass and an APFO content of 0.05% by mass 25. 1 kg was obtained.

To this aqueous dispersion, 0.2 kg of a nonionic surfactant mainly composed of polyoxyethylene (average polymerization degree 9) lauryl ether was added and dissolved, and 0.3 kg of an anion exchange resin (Diaion WA—manufactured by Mitsubishi Chemical) was dissolved. 30) was dispersed and stirred for 24 hours, followed by filtration to remove the anion exchange resin. To the filtrate was added 0.04 kg of 28% by mass aqueous ammonia, concentrated by a phase separation method at 80 ° C. for 10 hours, and after removing the supernatant, 15 g of ammonium perfluorohexanoate (hereinafter referred to as APFH) was newly added. In addition, PTFE aqueous dispersion (G) 10.5 kg having a PTFE content of 59.7% by mass, an APFH content of 0.15% by mass, and an APFO content of 0.01% by mass was obtained.

(8) Preparation of TFE-propylene copolymer aqueous dispersion (H) 1.5 L of ion exchange water, 40 g of disodium hydrogenphosphate dodecahydrate, 0.5 g of sodium hydroxide, 198 g of grade butanol, 8 g of sodium lauryl sulfate (hereinafter referred to as SLS), and 2.5 g of ammonium persulfate were charged and dissolved. Subsequently, 200 g of an aqueous solution in which 0.4 g of ethylenediaminetetraacetic acid disodium salt dihydrate and 0.3 g of ferrous sulfate heptahydrate were dissolved was added, and then the TFE with a molar ratio of 85/15 was stirred. / Propylene (hereinafter referred to as Pr) mixed gas was charged to an internal pressure of 2.5 MPa, and 2.5% by mass of Rongalite aqueous solution was added to initiate polymerization. The polymerization was carried out for 5.5 hours while maintaining a polymerization pressure of 2.5 MPa while additionally supplying 800 g of a TFE / Pr mixed gas having a molar ratio of 56/44. Aggregates and the like were removed from the obtained emulsion to obtain 2520 g of an aqueous TFE-Pr copolymer dispersion (H) having a TFE / Pr copolymer content of 30.8% by mass.

(9) Preparation of positive electrode active material for lithium ion battery (I) [lithium (nickel / manganese / cobalt) composite oxide] 3.3 mol of nickel oxide prepared by firing nickel carbonate at 700 ° C. for 15 hours in the air Then, 3.3 mol of manganese dioxide prepared by baking manganese carbonate at 700 ° C. for 15 hours in the air, 3.3 mol of cobalt oxyhydroxide having low crystallinity, and 5.1 mol of lithium carbonate were dispersed in pure water, The beads were milled with zirconia beads having a diameter of 0.1 mm for 2 hours and then spray-dried to obtain a dry powder. This was calcined in the atmosphere at 850 ° C. for 15 hours to obtain a lithium (nickel / manganese / cobalt) composite oxide having an average particle size of 3.6 μm.

(10) Preparation of lithium ion battery positive electrode active material (J) [lithium iron phosphate] 313.1 g of 85% phosphoric acid was diluted with 1000 g of pure water. While stirring this aqueous phosphoric acid solution, 100.3 g of lithium carbonate was added and dissolved to obtain an aqueous solution of lithium phosphate. To this aqueous solution, iron oxyhydroxide having a molecular weight of 92.4 per equivalent of iron was added, and 400 g of pure water was further added to obtain an aqueous paste as a raw material for lithium iron phosphate. This paste was subjected to bead mill treatment for 1 hour using zirconia beads having a diameter of 0.5 mm, and then an aqueous solution prepared by dissolving 51.4 g of dextrin having an average molecular weight of 8500 in 115 g of pure water was dissolved and spray-dried to obtain a dry powder. Got. The dry powder was heated to 600 ° C. at a temperature rising rate of 5 ° C./min while supplying 5% hydrogen containing nitrogen gas at a flow rate of 0.8 liter / min, and kept at 600 ° C. for 5 hours. Cooling was performed at a temperature lowering rate setting of ° C./min to obtain lithium iron phosphate having an average particle diameter of 4.2 μm.

(11) Preparation of Lithium Ion Battery Negative Electrode Active Material (K) [Disproportionated Silicon] 240 g of silicon monoxide having an average particle size of 0.38 μm was added to 630 g of pure water, stirred, and spray-dried from the obtained paste. A dry powder was prepared. While supplying this dry powder at a flow rate of 1 liter / min of argon gas, it is heated to 1200 ° C. at a temperature increase rate of 5 ° C./min, held at 1200 ° C. for 5 hours, and then a temperature decrease rate of −5 ° C./min is set. To obtain disproportionated silicon having an average particle diameter of 4.2 μm.

(12) Boron-modified acetylene black (L)
The obtained boron-modified acetylene black (L) had a boron content of 1.07% by mass and a carbon content of 95.3% by mass, and had characteristics that were easier to adapt to water than general-purpose acetylene black. This boron-modified acetylene black (L) is sprayed into a tube furnace controlled at 750 to 800 ° C. at a feed rate of acetylene gas of 200 liters / hour and trimethyl borate of 30 ml / hour, and boron-containing acetylene black is obtained. The boron-containing acetylene black is obtained by treating at 2800 ° C. in an argon atmosphere.

In addition, lithium cobalt composite oxide and spinel-type lithium manganese composite oxide, which are positive electrode active materials for lithium ion secondary batteries, are synthesized by existing methods, and natural graphite, nickel hydrogen, which are negative electrode active materials for lithium ion secondary batteries. Commercially available products were used for nickel hydroxide as a positive electrode active material for secondary batteries and activated carbon as an electrode active material for electric double layer capacitors.

(Example 1) (Example)
While adding 2.3 g of acetylene black to 75 g of ion-exchanged water to which 0.91 g of the aqueous dispersion (A) of the fluorinated copolymer was added, the three-one motor equipped with the disk turbine blades was rotated at a speed of 450 rpm. Stir for minutes to disperse. To this, 2.49 g of an aqueous polytetrafluoroethylene dispersion (G) (the sum of the polymer components of (A) and (G) corresponds to 1.85 g) and a commercially available lithium cobalt composite dispersed in 25 g of ion-exchanged water 60 g of oxide was added and stirred for 1 minute in the same manner as above to obtain an aqueous paste (1). In the obtained aqueous paste (1), the electrode active material, the conductive auxiliary agent, and the binder were finely and uniformly dispersed.

<Adhesion evaluation>
Subsequently, the aqueous paste (1) was applied onto the aluminum sheet, dried at 120 ° C. for 2 hours, heat-treated at 200 ° C. for 10 minutes and roll-press-rolled to adjust the electrode composite layer thickness to 120 μm. A test piece cut out to a size of 2 cm in width and 10 cm in length from the obtained electrode plate was bent 100 times along a round bar having a diameter of 2 mm, and the strength of the electrode composite layer and the electrode active material holding power were examined. Adhesion with the current collector (aluminum sheet) is determined by the number of meshes remaining by peeling off the adhesive tape ("Serotape (registered trademark)") after lightly cutting it into a 100 square grid. Measured and evaluated. The results are shown in Table 1. From Table 1, the positive electrode plate for a lithium ion battery formed from the aqueous paste (1) had good electrode active material carrying power and adhesion with the current collector.

<Battery special evaluation>
Next, a lead wire is attached to each of the positive electrode plate obtained by punching out the electrode plate to a predetermined size and the negative electrode plate obtained by cutting out lithium foil to a predetermined size, and stored in a stainless steel cell case via a polyolefin-based separator, An electrolyte solution in which 1 mol / liter of lithium hexafluorophosphate was dissolved in a mixed solution of ethylene carbonate and diethylene carbonate was injected to obtain a model cell of a lithium secondary battery. Attach the model cell charge and discharge tester, corresponds to the charge coulometry 0.6 mA / cm ² was charged to a battery voltage 4.3V, the discharge coulometric 2.0mA ^/ cm 2 (1.25C rate at 25 ° C. Table 1 also shows the results of repeating 100 cycles of charging and discharging for discharging until 2.0 V. From Table 1, it was found that this model cell was a lithium secondary battery with good storage element characteristics.

(Example 2) (Example)
A storage element electrode was formed in the same manner as in Example 1 except that 0.93 g of the aqueous solution (B) of the fluorinated copolymer was used instead of 0.91 g of the aqueous dispersion (A) of the fluorinated copolymer. An aqueous paste (2) was obtained, an electrode plate was prepared, and the strength of the electrode composite layer, the electrode active material holding power, and the adhesion with the current collector were examined. As a result, it was found that the positive electrode plate for a lithium ion battery formed from the aqueous paste (2) has a good electrode active material supporting force and an adhesive force with the current collector.

The results of battery evaluation of model cells assembled in the same manner as in Example 1 are also shown. From the table, it was found that this model cell was a lithium secondary battery with good power storage device characteristics.

(Example 3) (Example)
Formation of a storage element electrode in the same manner as in Example 1 except that 14.1 g of the aqueous solution (C) of the fluorinated copolymer was used instead of 0.91 g of the aqueous dispersion (A) of the fluorinated copolymer. An aqueous paste (3) was obtained, an electrode plate was prepared, and the strength of the electrode composite layer, the electrode active material holding power, and the adhesion with the current collector were examined. As a result, it was found that the positive electrode plate for a lithium ion battery formed from the aqueous paste (3) had a good electrode active material carrying power and an adhesive force with the current collector.

The results of battery evaluation of model cells assembled in the same manner as in Example 1 are also shown. From the table, it was found that this model cell was a lithium secondary battery with good power storage device characteristics.

(Example 4) (Comparative example)
An aqueous paste (4) was used in the same manner as in Example 1 except that 17.6 g of the aqueous solution (E) of the fluorinated copolymer was used instead of 0.91 g of the aqueous dispersion (A) of the fluorinated copolymer. ) Was prepared, but the paste had thickened into a gel, so that a homogeneous electrode composite layer could not be applied. This was judged to be due to insufficient dispersibility of the copolymer (E) having a small fluorine content.

(Example 5) (Comparative example)
An aqueous paste (5) was prepared in the same manner as in Example 1, except that 1.23 g of the aqueous solution (F) of the fluorinated copolymer was used instead of 0.91 g of the aqueous dispersion (A) of the fluorinated copolymer. The electrode plate was prepared, and the strength of the electrode composite layer, the electrode active material holding power, and the adhesion with the current collector were examined. As a result, it was found that the adhesion with the current collector was insufficient. This was considered to be because the molecular weight of the oligomer (F) was small, so that adhesion could not be expressed.

The results of battery evaluation of model cells assembled in the same manner as in Example 1 are also shown. From the table, it was found that this model cell does not have a practical life as a power storage element.

(Example 6) (Example)
An aqueous paste (6) for forming a storage element electrode was obtained in the same manner as in Example 1 except that 60 g of a commercially available spinel type lithium manganese composite oxide was used instead of 60 g of the lithium cobalt composite oxide, and an electrode plate was prepared. The strength of the electrode composite layer, the electrode active material holding power, and the adhesion with the current collector were examined. As a result, it was found that the positive electrode plate for a lithium ion battery formed from the water-based paste (6) had a good electrode active material carrying power and an adhesive force with the current collector.

(Example 7) (Example)
Instead of 0.91 g of the aqueous dispersion (A) of the fluorinated copolymer, 0.46 g of (A) is replaced with 2.49 g of the aqueous polytetrafluoroethylene dispersion (G), and 2 of (G) 0.8 g is replaced with 2.3 g of acetylene black, 2.3 g of boron-modified acetylene black (L) is replaced with 60 g of commercially available lithium cobalt composite oxide, and lithium (nickel / manganese / cobalt) composite oxide (I) A water-based paste for forming a storage element electrode (7) was obtained in the same manner as in Example 1 except that 60 g of was used, and an electrode plate was prepared. The strength of the electrode composite layer, the electrode active material holding power, and the current collector The adhesion with was investigated. As a result, it was found that the positive electrode plate for a lithium ion battery formed from the aqueous paste (7) has a good electrode active material supporting force and an adhesive force with the current collector.

(Example 8) (Example)
Example 6 except that 0.46 g of the aqueous dispersion (A) of the fluorinated copolymer and 2.8 g of the aqueous polytetrafluoroethylene dispersion (G) were used instead of 4.57 g of (A). In the same manner as above, an aqueous paste (8) was obtained, an electrode plate was prepared, and the strength of the electrode composite layer, the electrode active material holding power, and the adhesion with the current collector were examined. As a result, it was found that the positive electrode plate for a lithium ion battery formed from the aqueous paste (8) had a good electrode active material carrying force and an adhesive force with the current collector.

(Example 9) (Example)
Instead of 0.91 g of the aqueous solution (A) of the fluorinated copolymer, 3.63 g of the aqueous solution (D) of the fluorinated copolymer was replaced with 2.49 g of the aqueous polytetrafluoroethylene dispersion (G). Lithium (nickel / manganese / cobalt) composite oxidation (I) instead of 1.87 g of (G) and 1.84 g of TFE-propylene copolymer aqueous dispersion (H) in place of 60 g of commercially available lithium cobalt composite oxide An aqueous paste (9) was prepared in the same manner as in Example 1 except that 60 g of was used to obtain a positive electrode plate for a lithium ion battery. This electrode plate had good electrode active material carrying power and adhesion to the current collector.

(Example 10) (Example)
An aqueous paste (10) for forming a storage element electrode was obtained in the same manner as in Example 7 except that 60 g of lithium iron phosphate (J) was used instead of 60 g of lithium (nickel / manganese / cobalt) composite oxide (I). It prepared and obtained the positive electrode plate for lithium ion batteries. This electrode plate had good electrode active material carrying power and adhesion to the current collector.

The table also shows the results of battery evaluation of model cells assembled in the same manner as in Example 1. From the table, it was found that this model cell was a lithium secondary battery with good power storage device characteristics.

(Example 11) (Example)
An aqueous system was used in the same manner as in Example 1 except that 30 g of disproportionated silicon (K) and 30 g of commercially available natural graphite (average particle size: 3.3 μm) were used instead of 60 g of lithium cobalt composite oxide. A paste (11) was prepared to obtain a negative electrode plate for a lithium ion battery. This electrode plate had good electrode active material carrying power and adhesion to the current collector.

(Example 12) (Example)
An aqueous paste (12) was prepared in the same manner as in Example 1 except that 60 g of commercially available activated carbon (BET specific surface area of 2900 m ² / g) was used instead of 60 g of lithium cobalt composite oxide, and an electrode for an electric double layer capacitor I got a plate. This electrode plate had good electrode active material carrying power and adhesion to the current collector.

(Example 13) (Example)
Example 1 was used except that 5.0 g of cobalt oxyhydroxide was used instead of 2.3 g of acetylene black, and 60 g of commercially available nickel hydroxide (average particle size: 8.0 μm) was used instead of 60 g of lithium cobalt composite oxide. An aqueous paste (13) was prepared to obtain an electrode plate for a nickel metal hydride battery. This electrode plate had good electrode active material carrying power and adhesion to the current collector.

EVE: ethyl vinyl ether CHVE: cyclohexyl vinyl ether HBVE: 4-hydroxybutyl vinyl ether MEK: methyl ethyl ketone TFE: tetrafluoroethylene CTFE: chlorotrifluoroethylene

The present invention makes it possible to manufacture an electrode for a storage element, which has been conventionally manufactured using an organic solvent, using an aqueous process. Since the method of the present invention is also excellent in workability, it is possible to produce a homogeneously dispersed aqueous paste and an electrode plate with excellent adhesion to the current collector, which has high durability, long life, and high It is also suitably used in the manufacture of power storage elements that require power. Furthermore, the method of the present invention is also suitably used as a highly safe manufacturing process with a low risk of harming the environmental load and human health.

The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2009-119962 filed on May 18, 2009 are incorporated herein as the disclosure of the specification of the present invention. It is.

Claims (10)

1. Fluorine content of 3 to 60% by mass, number average selected from fluorine-containing olefin copolymer having hydrophilic group in side chain or linear hydrophilic polymer having hydrophobic fluorine-containing organic group at both ends A binder for electrode materials comprising a polymer having a molecular weight of 1,000 to 1,000,000.
2. The fluorine-containing olefin copolymer is at least one selected from a unit of at least one fluorine olefin selected from tetrafluoroethylene and chlorotrifluoroethylene, a hydroxyl group and a —COOX group (X is a hydrogen atom or a cation). The binder of Claim 1 which is a copolymer containing the unit which has a hydrophilic group.
3. The hydrophilic polymer includes a linear polymer chain containing a unit having at least one hydrophilic group selected from a hydroxyl group and a —COOX group (X is a hydrogen atom or a cation), and both the linear polymer chain and the linear polymer chain. The binder according to claim 1, which is a polymer having a hydrophobic fluorine-containing organic group derived from a polymerization initiator or a chain transfer agent present at a terminal.
4. The binder according to claim 1 or 3, wherein the hydrophobic fluorine-containing organic group has a perfluoroalkyl group having 3 or more carbon atoms which may have an etheric oxygen atom between carbon atoms.
5. A paste-like composition comprising the binder according to any one of claims 1 to 4, an electrode material, and water.
6. The paste composition according to claim 5, further comprising polytetrafluoroethylene.
7. The paste composition according to claim 5 or 6, wherein the electrode material comprises at least one selected from a metal compound and a carbon material.
8. The paste composition according to any one of claims 5 to 7, wherein the electrode material is a material for an electrode of a storage element.
9. A method for producing an electrode of a storage element, wherein the paste composition according to any one of claims 5 to 8 is applied to a current collector and dried.
10. The method for producing an electrode according to claim 9, wherein the storage element is a lithium ion secondary battery, a nickel hydride secondary battery or an electric double layer capacitor.