JP2015018776A - Binder for aqueous electrode composition for battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder for electrode composition for battery having a dispersion/viscosity adjustment function and available as a one liquid binder, in which sufficient adhesion of electrode can be expressed with a small amount of binder.SOLUTION: In a binder for electrode composition forming the electrode of a battery, a water-soluble polymer contains for total 100 mass% of structural unit of the water-soluble polymer (a) 50-80 mass% of structural unit derived from ethylenic unsaturated carboxylic acid salt monomer, and (b) 20-50 mass% of structural unit derived from ethylenic unsaturated carboxylic acid ester monomer. The water-soluble polymer has a viscosity of 100-20,000 mPa s at 25°C, pH7, and 2 mass% of non-volatile component.

Description

  The present invention relates to a binder for a battery aqueous electrode composition, a conductivity imparting agent, a battery aqueous electrode composition, a battery electrode, and a battery. More specifically, it relates to a lithium ion battery application.

  A battery is a device that generates electric power by converting chemical energy of a substance by a chemical reaction. Among them, the secondary battery is a battery that can be charged by converting electric energy into chemical energy by flowing a current in a direction opposite to that during discharging, and can be repeatedly charged and discharged. With the increasing interest in environmental problems in recent years, the use of secondary batteries has been advanced in mobile applications such as mobile phones and PDAs (personal digital assistants) and in-vehicle applications such as automobiles. In response to the increasing demand for such secondary batteries, research is being actively conducted. In particular, light-weight, small, and high-energy density lithium ion batteries among secondary batteries are attracting attention from various industries, and are actively developed. Moreover, since it is necessary to endure vibration etc. in a vehicle-mounted application, development of the battery which has an electrode with good base-material adhesiveness is calculated | required.

  A lithium ion battery is mainly composed of a positive electrode, an electrolyte, a negative electrode, and a separator. Of these, an electrode in which an electrode composition is coated on a current collector is usually used.

Among the electrode compositions, the positive electrode composition used for forming the positive electrode mainly comprises a positive electrode active material, a conductive additive, a binder, and a solvent. Polyvinylidene fluoride (PVdF) is generally used as the binder, and N-methyl-2-pyrrolidone (NMP) is generally used as the solvent. However, in recent years, an aqueous system that does not use an organic solvent has been demanded for the electrode composition against the background of increasing interest in environmental problems.
Under such circumstances, various researches and developments have been made on positive electrode compositions and binders that can be used for positive electrode compositions.

  On the other hand, among the electrode compositions, the negative electrode composition used for forming the negative electrode mainly comprises a negative electrode active material, a binder, and a solvent. As the binder, polyvinylidene fluoride (PVdF) (solvent is N-methyl-2-pyrrolidone (NMP)) in a solvent system, and water-solubility that has a dispersibility and viscosity adjustment function represented by carboxymethylcellulose (CMC) in an aqueous system. It is common to use an emulsion (an aqueous dispersion of polymer particles) in combination as a binder that binds the flexibility of the polymer and the active material particles represented by styrene butadiene rubber (SBR) with a polymer. is there. The negative electrode composition has also been studied from a solvent system to an aqueous system from the background described above. It is disclosed that by using polyvinylidene fluoride having a relatively high degree of polymerization as a secondary battery binder, a powdered electrode material can be held in a smaller amount than in the past. (See Patent Document 1). Moreover, the thickener for lithium ion secondary batteries negative electrode which consists of a copolymer obtained by copolymerizing a (meth) acrylic-acid polyoxyalkylene ether compound and ethylenically unsaturated carboxylic acid as a composition for secondary battery negative electrodes Is disclosed. (See Patent Document 2)

Japanese Patent No. 3703582 JP 2002-203561 A

  Examples of one-pack binders include solvent-based polymers using high molecular weight polyvinylidene fluoride, but the adhesion of the vinylidene fluoride itself to the current collector is low, so that it adheres to the substrate. There is an inadequate aspect in terms of sex, which is a problem.

On the other hand, in water systems, use a water-soluble polymer that is responsible for dispersibility and viscosity adjustment, and an emulsion (water dispersion of polymer particles) as a binder to bind electrode flexibility and active material particles. However, the problem which becomes complicated in a process remains.
The present invention has been made in view of the above situation, and can be suitably used as an aqueous binder composition for an aqueous binder used in a composition for forming an electrode for a battery that exhibits excellent electrode peel strength. The object is to provide a binder.

  The present inventors have made various studies on binders for electrode compositions that require both dispersibility, binding properties, and flexibility of electrodes, and in particular, binders for electrode compositions that can be used in a one-part system. . The electrode composition binder contains a water-soluble polymer, and (a) a structural unit derived from an ethylenically unsaturated carboxylate monomer is added to 100% by mass of the total amount of structural units of the water-soluble polymer. 50 to 80% by mass, (b) 20 to 50% by mass of a structural unit derived from an ethylenically unsaturated carboxylic acid ester monomer, and the viscosity of the aqueous solution at 25 ° C., pH 7 and nonvolatile content of 2% by mass is 100 mPa · s or more. It has been found that the use of an electrode binder containing a water-soluble polymer characterized by the fact that the electrode composition has a dispersion / viscosity adjusting function, has good binding properties, and can be highly solidified.

  When the water-soluble polymer of the present invention has the above-described configuration, the viscosity of the electrode composition can be easily adjusted, and the stability of the slurry can be increased. Furthermore, the water-soluble polymer of the present invention preferably contains (c) a structural unit derived from a polyfunctional unsaturated monomer. When the slurry is formed by crosslinking the polymer, the binding property is improved and the thixotropy can be imparted. In addition, by producing such a water-soluble polymer by emulsion polymerization using seed particles, it is possible to easily produce a polymer having a relatively high molecular weight, and by making it water-soluble using a salt, it is inexpensive. The inventors have found that they can be easily produced, and have reached the present invention.

  That is, the present invention is an aqueous electrode binder for a secondary battery containing a water-soluble polymer, wherein the water-soluble polymer is (a) based on 100% by mass of the total amount of structural units of the water-soluble polymer. 50) 80-80% by mass of structural units derived from ethylenically unsaturated carboxylate monomer, and (b) a water-soluble polymer containing 20-50% by mass of structural units derived from ethylenically unsaturated carboxylic acid ester monomer. In addition, the secondary electrode is a water-based electrode binder for a secondary battery in which the viscosity of an aqueous solution having a nonvolatile content of 2% by mass at 25 ° C. is 100 mPa · s to 20,000 mPa · s.

The binder for a battery electrode composition of the present invention is characterized by containing a water-soluble polymer having the above-described structure, and when it is made into an aqueous electrode composition, it has a dispersing function and can form a uniform electrode. To. Furthermore, the electrode obtained by the battery electrode composition using such a binder for battery electrode composition has excellent adhesion to the current collector. Moreover, since the dispersibility is good and high solid differentiation is possible, the load for removing the solvent during drying can be reduced. And by having a dispersibility and a viscosity adjustment function, it can be used not only as a two-component binder but also as a one-component binder, and the process can be shortened as compared with a two-component binder. As a result, it can be suitably used as a composition for forming an electrode for a battery.
The present invention is described in detail below.

In addition, the form which combined two or more each preferable form of this invention described below is also a preferable form of this invention.
The water-based electrode binder for secondary batteries of the present invention (hereinafter also referred to as “electrode binder”) includes a water-soluble polymer, and the water-soluble polymer has a total amount of 100% by mass of the structural unit of the water-soluble polymer. On the other hand, (a) 50-80 mass% of structural units derived from ethylenically unsaturated carboxylate monomer, and (b) 20-50 mass% of structural units derived from ethylenically unsaturated carboxylic acid ester monomer. A water-soluble polymer containing 25 ° C., pH 7, and a 2% by weight non-volatile solution having a viscosity of 100 mPa · s to 20,000 mPa · s. The water-based binder for secondary batteries of the present invention may contain other components and other polymers as long as such a polymer is contained. However, the aqueous electrode binder for secondary batteries of the present invention preferably contains 10 to 100% by mass of the water-soluble polymer of the present invention with respect to 100% by mass of the total amount of secondary electrode aqueous electrode binder. More preferably, it is 30 mass% or more. Here, the mass of the binder refers to the mass of the solid content in the binder.
Moreover, the binder for battery electrode compositions of this invention may contain 1 type of the water-soluble polymer of this invention, and may contain 2 or more types.

  The structural unit derived from the ethylenically unsaturated carboxylate monomer (a) which is essential for the water-soluble polymer of the present invention is a carbon-carbon double bond of the ethylenically unsaturated carboxylate monomer. Is a structure with a single bond.

Examples of the ethylenically unsaturated carboxylate monomer include, for example, (meth) acrylic acid, crotonic acid, isocrotonic acid and the like, an ethylenically unsaturated monocarboxylate monomer having 3 to 10 carbon atoms; itaconic acid, malee Examples thereof include ethylenically unsaturated dicarboxylate monomers having 4 to 10 carbon atoms such as acid, fumaric acid, citraconic acid, mesaconic acid and glutaconic acid. Among these, salts of unsaturated monocarboxylic acids having 3 to 6 carbon atoms such as acrylic acid and methacrylic acid are preferable.
By containing 50% by mass or more of the ethylenically unsaturated carboxylate monomer, it is possible to suppress swelling with respect to the electrolytic solution when an electrode is prepared using the water-soluble polymer as an electrode binder. The electrolyte solution resistance can be made sufficient. The volume swelling rate in the electrolytic solution test is preferably 200% or less, more preferably 150% or less. In addition, the volume swelling rate is usually 100% or more.

Examples of the salt that forms the salt of the ethylenically unsaturated carboxylic acid include the following examples.
Examples of the alkali metal that forms the alkali metal salt include lithium, sodium, and potassium.
Ammonia etc. are mentioned as a compound which forms the said ammonium salt.
Examples of compounds that form organic amine salts include monoethanolamine, diethanolamine, triethanolamine, cyclohexylamine, and hydroxylamine.
Of the above salts, an alkali metal salt is preferable, and lithium is more preferable. As these ethylenically unsaturated carboxylate monomers, one type may be used, or two or more types may be used.

  A part of the ethylenically unsaturated carboxylate monomer may be in the form of carboxylic acid (—COOH) as long as a water-soluble polymer can be synthesized by a polymerization method described later. When a part of the carboxylate salt of the ethylenically unsaturated carboxylate monomer is a carboxylic acid, among the carboxylate salts of the ethylenically unsaturated carboxylate monomer, It is preferable that what is a form is 50 mol% or less. More preferably, it is 40 mol% or less, More preferably, it is 30 mol% or less. When the amount of the carboxylic acid is 50 mol% or more, the compatibility with water is insufficient and there is a possibility that a uniform aqueous solution is not obtained.

The structural unit derived from the ethylenically unsaturated carboxylic acid ester monomer (hereinafter referred to as “structural unit (b)”) included as essential in the water-soluble polymer of the present invention is an ethylenically unsaturated carboxylic acid ester. This represents a structure in which the carbon-carbon double bond of the monomer is a single bond.
Examples of the ethylenically unsaturated carboxylic acid ester monomer include acrylic acid esters, methacrylic acid esters, and crotonic acid esters. Preferably, for example, the general formula (1);
CH2 = CR-C (= O) -OR '(1)
(Wherein R represents a hydrogen atom or a methyl group. R ′ represents an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, and a hydroxylalkyl group having 1 to 10 carbon atoms). It is a compound represented.
Examples of R ′ in the general formula (I) include alkyl groups having 1 to 10 carbon atoms such as a methyl group, an ethyl group, a propyl group, a butyl group, an octyl group, and a 2-ethylhexyl group; a cyclopentyl group and a cyclohexyl group. A cycloalkyl group having 3 to 10 carbon atoms, and a hydroxyalkyl group having 1 to 10 carbon atoms such as a hydroxyethyl group, a hydroxypropyl group, and a hydroxybutyl group.
Among these, an alkyl group having 1 to 10 carbon atoms and a cycloalkyl group having 3 to 10 carbon atoms are preferable from the viewpoint of stability during emulsion polymerization described later. The alkyl group having 1 to 10 carbon atoms is preferable because the glass transition temperature (Tg) of the obtained water-soluble polymer is lowered. R is preferably hydrogen. That is, the ethylenically unsaturated carboxylic acid ester monomer is preferably an acrylic acid ester.

  The content ratio of the structural unit (a) in the water-soluble polymer of the present invention is 50 to 80% by mass. It becomes possible to express solubility in water by setting it to 50% by mass or more, and increasing the polar group can increase the binding property with a filler component such as an active material or a conductive aid or a current collector. it can. When the content ratio of the structural unit (a) is 80% by mass or more, the dispersibility in the electrode composition may be insufficient. Moreover, when it is 50 mass% or less, there exists a possibility that adhesiveness with a collector may become inadequate. Dispersibility can be improved by including 80 mass% or less and other components. The content ratio of the structural unit (a) in the water-soluble polymer of the present invention is more preferably 55 to 70% by mass.

  The content rate of the structural unit (b) in the water-soluble polymer of this invention is 20-50 mass%. In the case of 20% by mass or less, it may be difficult to produce the water-soluble polymer of the present invention by emulsion polymerization. The content ratio of the structural unit (b) in the water-soluble polymer of the present invention is preferably 25 to 48% by mass, and more preferably 30 to 45% by mass.

  The water-soluble polymer of the present invention may contain (c) a structural unit derived from a polyfunctional group-containing monomer as long as it contains the structural unit (a) and the structural unit (b) as essential. The structural unit derived from the polyfunctional group-containing monomer represents a structure in which at least one carbon-carbon double bond of the polyfunctional group-containing unsaturated monomer (c) is a single bond. The polyfunctional group-containing unsaturated monomer (c) may be any monomer having at least two polymerizable double bonds such as vinyl group, allyl group, (meth) acryloyl group in the molecule. For example, polyfunctional allylic monomers such as divinylbenzene and diallyl phthalate; 1,6-hexanediol diacrylate, polyethylene glycol diacrylate (average number of moles of ethylene oxide added n = 4, 9, 14, etc.), trimethylol Polyfunctional acrylates such as propane triacrylate are exemplified. Among these, bifunctional monomers such as diallyl phthalate and 1,6-hexanediol diacrylate are preferable because gelation of the water-soluble polymer hardly occurs. As these polyfunctional group containing monomers, 1 type may be used and 2 or more types may be used.

When the water-soluble polymer of the present invention contains (c) a structural unit derived from a polyfunctional group monomer, the content is preferably 0.01 to 5% by mass or less. When using 5 mass% or more, there exists a possibility that this water-soluble polymer may become easy to gelatinize. When gelled, dispersibility and slurry viscosity are poor, making it difficult to use as a binder. Moreover, 0.1-3 mass% is more preferable as a content rate. When the content ratio is 0.01% by mass or less, the effect of increasing the binding property by crosslinking is insufficient.
When the water-soluble polymer contains the structural unit (c), a mixed solution of monomers mixed with the structural unit (a) and the structural unit (b) is added to the polymerization system and incorporated into the water-soluble polymer. be able to.

  The water-soluble polymer of the present invention may contain a structural unit derived from another polymerizable monomer (d) as long as it contains the structural unit (a) and the structural unit (b) as essential. The structural unit derived from the other polymerizable monomer represents a structure in which the carbon-carbon double bond of the other polymerizable monomer is a single bond.

Examples of the other polymerizable monomer (d) include styrene monomers such as styrene, α-methylstyrene, and ethyl vinylbenzene; (meth) acrylic acid amide, N, N-dimethyl (meth) acrylamide. (Meth) acrylamide monomers such as nitrile compounds such as vinyl acetate and acrylonitrile. Further, a (meth) acrylic ester or vinyl compound having a polyalkylene oxide group having a hydrophobic group such as an alkyl group having 1 to 30 carbon atoms which may be halogenated at the terminal can also be used.
Among these, the polymerizable monomer (d) is preferably a styrene monomer or a (meth) acrylamide monomer. As these other polymerizable monomers (d), one type may be used, or two or more types may be used.

  That is, as a ratio of structural units in the water-soluble polymer of the present invention, when the total amount of structural units of the water-soluble polymer is 100% by mass, (a) a structure derived from an ethylenically unsaturated carboxylate monomer Unit / (b) Structural unit derived from ethylenically unsaturated carboxylic acid ester monomer / (c) Structural unit derived from polyfunctional group-containing monomer / (d) Structural unit derived from other polymerizable structural unit = What is 50-80 mass% / 20-50 mass% / 0-5 mass% / 0-15 mass% is preferable. More preferably, (a) / (b) / (c) / (d) = 50 to 80% by mass / 20 to 50% by mass / 0.01 to 3% by mass / 0 to 15% by mass.

  The water-soluble polymer can be produced by polymerizing each monomer component derived from the structural unit contained in the polymer. The method for polymerizing the monomer component is not particularly limited, and examples thereof include emulsion polymerization, reverse phase suspension polymerization, suspension polymerization, solution polymerization, aqueous solution polymerization, and bulk polymerization. Among these polymerization methods, the emulsion polymerization method is preferable.

  The above-mentioned emulsion polymerization method is a method in which polymerization proceeds in a micelle, so that a high molecular weight copolymer can be easily polymerized at a high concentration, and the viscosity of the polymerization solution is low and the workability is excellent. The water-soluble polymer is prepared as an aqueous dispersion by an emulsion polymerization method, and is easily manufactured by neutralizing with a salt (alkali metal, ammonia, organic amine, etc.) and solubilizing (homogenizing). This can be done and has advantages in terms of production costs.

  The emulsion polymerization may or may not use an emulsifier. In the case where an emulsifier is not used, the emulsion polymerization is, for example, a soap-free polymerization method (does not use a compound having surface active ability or polymerizes using a trace amount of a compound having surface active ability), a seed polymerization method described later, etc. Emulsion polymerization. When an emulsifier is used, the emulsifier is not particularly limited. For example, an anionic surfactant, a nonionic surfactant, a cationic surfactant, an amphoteric surfactant, a polymer surfactant, and a surfactant of these surfactants. Examples thereof include a reactive surfactant having a radical polymerizable unsaturated group in the structure. In particular, reactive surfactants can incorporate surfactants into the polymer structure by virtue of their polymerizable unsaturated groups, and reduce the surfactant components that are present free in aqueous solutions when made into aqueous solutions. Can do. These emulsifiers may be used alone or in combination of two or more.

  A polymerization initiator can be used for the polymerization of the monomer components. As the polymerization initiator, those usually used as a polymerization initiator can be used, and are not particularly limited as long as they generate radical molecules by heat. When emulsion polymerization is performed as a polymerization method, a water-soluble initiator is preferably used. Examples of the polymerization initiator include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; 2,2′-azobis (2-amidinopropane) dihydrochloride, 4,4′-azobis (4-cyano). Water-soluble azo compounds such as pentanoic acid; thermal decomposition initiators such as hydrogen peroxide; hydrogen peroxide and ascorbic acid, t-butyl hydroperoxide and rongalite, potassium persulfate and metal salts, ammonium persulfate and sodium bisulfite And the like, and the like. These polymerization initiators can use 1 type (s) or 2 or more types.

  As the usage-amount of the said polymerization initiator, it is preferable that it is 0.05-2 mass parts with respect to 100 mass parts of total amounts of the monomer component with which it uses for a polymerization reaction. More preferably, it is 0.1-1 mass part.

  In the emulsion polymerization, a chain transfer agent may be used to adjust the molecular weight. Examples of chain transfer agents include, but are not limited to, halogenated substituted alkanes, alkyl mercaptans, thioesters, alcohols, and the like. These chain transfer agents may be used alone or in combination of two or more. The chain transfer agent is preferably used in an amount of 0 to 1 part by mass with respect to 100 parts by mass of the total amount of monomer components used for the polymerization reaction.

  Although there is no limitation in particular about the polymerization temperature in the said emulsion polymerization, Preferably it is 20-100 degreeC, More preferably, it is 50-90 degreeC. The polymerization time is not particularly limited, but is preferably 1 to 10 hours in consideration of productivity.

  When emulsion polymerization is performed, a hydrophilic solvent, an additive, or the like can be added within a range that does not adversely affect the resulting copolymer.

  The method for adding each monomer component to the emulsion polymerization reaction system is not particularly limited, and a batch polymerization method, a monomer component dropping method, a pre-emulsion method, a power feed method, a seed method, a multistage addition method, or the like is used. be able to. Among these polymerization methods, a seed method using seed particles is preferable. In ordinary emulsion polymerization, monomers are emulsified to form micelles, and monomer radicals enter the micelles, and polymerization proceeds in the micelles. When there are many relatively hydrophilic monomers such as acid monomers, it is difficult to form micelles. When seed particles are used, even in the case of a relatively highly hydrophilic monomer in the seed particles, it is easy to absorb, and the reaction in the micelle can proceed. Using seed particles is one of the preferred embodiments of the present invention. More preferably, the seed particles are made of a resin that can be uniformly dissolved in water by neutralization in the same manner as the water-soluble resin of the present invention. The resin that is uniformly dissolved in water by neutralization has a high acid value, and the absorption of the acid monomer used to produce the water-soluble resin of the present invention is likely to occur, so that the polymerization can be performed quickly. Can do.

  The non-volatile content of the aqueous dispersion obtained after the emulsion polymerization reaction is preferably 15 to 60%. When the non-volatile content is in the range of 15 to 60%, it becomes easy to maintain the fluidity and dispersion stability of the aqueous dispersion (emulsion) obtained. Moreover, it is preferable also from the point of the production efficiency of the target polymer. On the other hand, if the non-volatile content exceeds 60%, the viscosity of the aqueous dispersion is too high, so that the dispersion stability may not be maintained and aggregation may occur. If the non-volatile content is less than 15%, the concentration of the polymerization system is low. The reaction may take time, and the production efficiency deteriorates from the viewpoint of the production amount of the target polymer.

  The average particle size of the polymer particles contained in the aqueous dispersion is not particularly limited, but is preferably 10 nm to 1 μm, and more preferably 30 to 500 nm. When the particle diameter of the polymer particles contained in the aqueous dispersion is in this range, the possibility that the viscosity becomes too high or the dispersion stability cannot be maintained and the particles are aggregated can be lowered. On the other hand, when the particle size of the polymer particles contained in the aqueous dispersion is less than 10 nm, the viscosity of the aqueous dispersion may become too high, or the dispersion stability may not be maintained, and aggregation may occur. If it exceeds, it becomes difficult to maintain the dispersion stability of the polymer particles. The average particle size of the polymer particles contained in the aqueous dispersion can be measured by a dynamic light scattering type particle size measuring device.

  The water-soluble polymer of the present invention is preferably obtained by neutralizing polymer particles (aqueous dispersion) obtained by the above method with an alkali metal salt, ammonium salt, organic amine salt or the like. The alkali metal salt is a salt of lithium, sodium, potassium or the like. In order to neutralize with these metal salts, aqueous solutions of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, lithium carbonate and the like can be used. In order to neutralize with an ammonium salt, an aqueous solution of ammonia or the like can be used. In order to neutralize with an organic amine salt, an aqueous solution of monoethanolamine, diethanolamine, triethanolamine, cyclohexylamine, hydroxylamine or the like can be used, preferably monoethanolamine, diethanolamine, or triethanolamine. Of the above salts, an alkali metal salt is particularly preferable, and among them, lithium hydroxide, lithium hydrogen carbonate, and lithium carbonate are more preferable. By neutralizing with these metal salts, it becomes a uniform aqueous solution and becomes a transparent solution in appearance.

  As said neutralization reaction, it is preferable to neutralize 60-150% of carboxylic acid which the structural unit derived from the ethylenically unsaturated carboxylic acid monomer in the said water-soluble polymer has with a metal salt. The neutralization rate is more preferably 65 to 110%, and still more preferably 70 to 100%.

  The neutralization rate is provided for the neutralization reaction with respect to the amount of carboxylic acid in the structural unit derived from the ethylenically unsaturated carboxylic acid monomer in the polymer particles (aqueous dispersion) subjected to the neutralization reaction. It is defined by the ratio of the amount of metal salt charged. Therefore, when the amount of carboxylic acid is more than the amount of carboxylic acid and the metal salt is charged excessively, the neutralization rate exceeds 100%.

  In the neutralization reaction, the pH of the aqueous solution containing the neutralized polymer particles (aqueous solution containing the water-soluble polymer) is preferably 6 or more. More preferably, it is 7 or more. Moreover, as an upper limit of pH, it is preferable not to exceed 9. The pH can be determined by measuring a value at 25 ° C. using a glass electrode type hydrogen ion meter F-21 (product name, manufactured by Horiba, Ltd.).

  Thus, it is also one of the preferred embodiments of the present invention that the water-soluble polymer of the present invention is obtained by neutralizing polymer particles synthesized by emulsion polymerization with an alkali metal salt. It is.

  The transparent solution means a solution having a total light transmittance of 90 to 100% when the water-soluble polymer contained in the solution has a nonvolatile content of 2% by mass. That is, the water-soluble polymer has a total light transmittance of 90 to 100% in an aqueous solution adjusted to a nonvolatile content of 2% by mass. The total light transmittance is preferably 95% or more, and more preferably 97% or more. The water-soluble polymer preferably has a haze of an aqueous solution adjusted to 2% by mass of nonvolatile content of 3% or less, more preferably 1% or less. The total light transmittance and haze can be measured by a method similar to the example using a haze meter (model number “NDH5000”, manufactured by Nippon Denshoku Industries Co., Ltd.).

  An aqueous solution having a nonvolatile content of 2% by mass prepared using the water-soluble polymer has a viscosity at 25 ° C. and pH 7 of 100 mPa · s or more. When the viscosity is 100 mPa · s or less, the binding property may be insufficient when an electrode is formed. More preferably, it is 200 mPa · s or more. Moreover, it is preferable that it is 20,000 mPa * s or less from the point of handling, More preferably, it is 15,000 mPa * s or less. The viscosity can be measured using TVB-10 (manufactured by Toki Sangyo Co., Ltd.) at 25 ± 1 ° C. and 30 rpm.

  In the water-soluble polymer of the present invention, the thixo value of the aqueous solution adjusted to 2% by mass of the nonvolatile content is preferably 1.2 to 4 at 25 ° C. and pH 7. When the thixo value is 1.2 or less, the dispersibility of the electrode composition may be insufficient when slurryed. Moreover, 4 or less is preferable from the point of handling, More preferably, it is 3.5 or less. By being in this range, it becomes easy to perform high solid differentiation of the slurry. The thixo value can be determined by dividing the viscosity measured under the condition of 25 ± 1 ° C. and 6 rpm using TVB-10 by the viscosity measured under the condition of 60 rpm.

  Next, the conductivity imparting agent of the present invention will be described. This invention is also the electroconductivity imparting agent which contains the binder for electrode compositions for secondary batteries of this invention, and a conductive support agent as an essential component. The conductivity-imparting agent of the present invention may contain one of these essential components, or two or more of them.

  The conductive assistant is used to increase the output of the lithium ion battery, and conductive carbon is mainly used. Examples of the conductive carbon include carbon black, fiber carbon, and graphite. Among these, carbon black such as ketjen black, acetylene black, and fiber-like carbon such as VGCF (manufactured by Showa Denko) are preferable. The conductivity can also be improved by using carbon black and fibrous carbon in combination.

  A dispersant may be further used in combination with the conductivity imparting agent of the present invention. When a dispersant is used, the dispersant is not particularly limited, and includes an anionic, nonionic or cationic surfactant, or a copolymer of styrene and maleic acid (half ester copolymer-ammonium salt). ), Various dispersants such as a polymer dispersant such as polyvinylpyrrolidone can be used. When using a dispersing agent, it can contain 5-20 mass% with respect to 100 mass% of conductive support agents.

The present invention is also a secondary battery aqueous electrode composition (hereinafter, also referred to as “electrode composition”) containing the secondary battery aqueous electrode binder, the electrode active material, and water as essential components. The aqueous electrode composition for a secondary battery of the present invention may contain one of these essential components, or may contain two or more of them.
The electrode composition of the present invention may be an aqueous positive electrode composition for secondary batteries (hereinafter also referred to as “positive electrode composition”), or an aqueous negative electrode composition for secondary batteries (hereinafter referred to as “negative electrode composition”). May be used).

  In the water-based positive electrode composition for secondary batteries of the present invention, the above-mentioned electrode binder and conductive additive can be used, and the electrode binder contains the above-mentioned water-soluble polymer. The positive electrode active material used in the positive electrode composition of the present invention is preferably a positive electrode active material capable of occluding and releasing lithium ions. By using such a positive electrode active material, it can be suitably used as a positive electrode of a lithium ion battery. Examples of compounds capable of inserting and extracting lithium ions include lithium-containing metal oxides, such as lithium cobaltate, olivine (lithium iron phosphate, lithium manganese phosphate), manganese (Lithium manganate), ternary system (lithium nickel manganese cobaltate), NCA system (lithium nickel cobalt aluminum composite oxide), and the like.

  In the positive electrode composition of the present invention, an emulsion may be used in combination as a binder such as a positive electrode active material or a conductive aid. The emulsion to be used is not particularly limited, but non-fluorinated polymers such as (meth) acrylic polymers, nitrile polymers, and diene polymers; fluorinated polymers such as PVdF and PTFE (polytetrafluoroethylene) (fluorine-containing polymers) And the like. Unlike the polymer, the emulsion is preferably excellent in the binding property between the particles and the flexibility (flexibility of the film). From this, (meth) acrylic polymers, nitrile polymers, or (meth) acryl-modified fluoropolymers are exemplified.

  In the aqueous positive electrode composition for secondary batteries of the present invention, the content of the electrode binder, positive electrode active material, conductive additive, emulsion, and other components other than these components in the solid content of the positive electrode composition (in solid content) (Mass ratio) is electrode binder / positive electrode active material / conductive aid / emulsion / other components = 0.2 to 3.0 / 70 to 98.8 / 1 to 20/0 to 10/0 to 5. Is preferred. With such a content ratio, it is possible to improve output characteristics and electrical characteristics when an electrode formed from the positive electrode composition is used as a positive electrode of a battery. More preferably, it is 0.3-2.5 / 80-98.3 / 1.5-10 / 0-6 / 0-2. In addition, the other components here refer to components other than the electrode binder, the positive electrode active material, the conductive additive, and the emulsion of the present invention, and include a dispersant, a preservative, and the like.

  The positive electrode composition of the present invention preferably has a viscosity of 1 to 20 Pa · s. When the viscosity of the positive electrode composition is in such a range, it is possible to ensure appropriate fluidity during coating, which is preferable in terms of workability. More preferably, it is 2-15 Pa.s. The viscosity of the positive electrode composition of the present invention can be measured by the same method as in Examples using TVB-10 (manufactured by Toki Sangyo Co., Ltd.).

  The battery positive electrode composition of the present invention preferably has a pH of 6 to 11 at 25 ° C. When the pH is in such a range, the current collector (for example, aluminum) is hardly corroded, and the battery performance of the material can be sufficiently exhibited. pH measurement can measure the value of 25 degreeC using the glass electrode type hydrogen ion thermometer F-21 (made by Horiba Ltd.).

  The water-based positive electrode composition for a secondary battery of the present invention contains a water-soluble polymer, a positive electrode active material, and water, and if necessary contains a conductive auxiliary, The positive electrode active material and the conductive additive are not particularly limited as long as they are uniformly dispersed, but a dispersant may optionally be added to the water-soluble polymer of the present invention dissolved in water as a solvent. Depending on the condition, the conductive additive is mixed and dispersed using a bead, ball mill, stirring type mixer or the like to adjust the conductivity imparting agent, and the positive electrode active material is added to the solution and the same dispersion treatment is performed. Is preferred. When mixing the emulsion, it is preferable to add to the above-described aqueous positive electrode composition for a secondary battery and mix. When the composition is prepared by such a procedure, it is preferable that the positive electrode active material and the conductive additive are sufficiently uniformly dispersed.

  In the negative electrode composition of the present invention, the electrode binder described above can be used. Examples of the negative electrode active material used in the battery electrode composition of the present invention include carbon materials such as graphite, natural graphite, and artificial graphite, polyacene conductive polymers, composite metal oxides such as lithium titanate, and lithium alloys. The A carbon material and lithium titanate are preferable. It is also one of the preferred embodiments of the present invention that the negative electrode active material contains a carbon-based negative electrode material or lithium titanate as a main component. Here, “the negative electrode active material contains a carbon-based negative electrode material or lithium titanate as a main component” means a group consisting of a carbon-based negative electrode material and lithium titanate with respect to 100% by mass of the total amount of the negative electrode active material. It represents that 50 mass% or more of at least 1 sort selected from more is included. The content ratio of at least one selected from the group consisting of a carbon-based negative electrode material and lithium titanate in the negative electrode active material is preferably 70 to 100% by mass, and more preferably 80 to 100% by mass. Particularly preferred is a form in which the negative electrode active material is at least one selected from the group consisting of a carbon-based negative electrode material and lithium titanate.

  In the negative electrode composition of the present invention, an emulsion, a conductive additive, a dispersant, a thickener and the like can be included as necessary. You may use together the emulsion which can provide a softness | flexibility as a binder component. Although the emulsion to be used is not specifically limited, the emulsion similar to the emulsion contained in the positive electrode composition of the present invention described above or a diene polymer can be used.

  A negative electrode composition containing a carbon-based negative electrode material or lithium titanate as the negative electrode active material, an electrode binder containing the water-soluble polymer of the present invention, and water is the most preferred embodiment of the present invention.

  When the aqueous negative electrode composition for secondary batteries of the present invention is used as a material for forming a negative electrode, the electrode binder, negative electrode active material, conductive additive, emulsion, and other components in the solid content of the composition ( The mass ratio in terms of solid content is preferably 0.3 to 4/85 to 99.7 / 0 to 10/0 to 10/0 to 5. With such a content ratio, it is possible to improve output characteristics and electrical characteristics when an electrode formed from the negative electrode composition is used as a negative electrode of a battery. More preferably, it is 0.5-2.5 / 90-99.5 / 0-5 / 0-3 / 0-3. In addition, the other components here mean components other than a binder like a negative electrode active material, a conductive support agent, a polymer, and an emulsion, and a dispersing agent, a thickener, a preservative, etc. are contained.

  The preferred range and measuring method of the viscosity and pH of the negative electrode composition of the present invention are the same as the preferred range and measuring method of the viscosity and pH of the positive electrode composition of the present invention described above, respectively.

  When the negative electrode composition of the present invention contains the water-based electrode binder for secondary batteries of the present invention containing the water-soluble polymer of the present invention, a negative electrode active material, and water, There is no particular limitation as long as the negative electrode active material is uniformly dispersed. A water-soluble polymer dissolved in water as a solvent and, if necessary, a dispersant is added to make a uniform aqueous solution, and further mixed with a conductive aid as necessary, using beads, a ball mill, a stirring type mixer, etc. It is preferable that the negative electrode active material is mixed therewith to obtain an aqueous negative electrode composition for a secondary battery. It is preferable to prepare the composition by such a procedure because the negative electrode active material is easily dispersed uniformly.

  The present invention is also a battery electrode containing the aqueous electrode binder for a secondary battery of the present invention and an electrode active material. The battery electrode of the present invention may contain one of these essential components, or two or more of them.

  This invention is also the battery electrode formed using the electroconductivity imparting agent of this invention, or the aqueous electrode composition for secondary batteries of this invention. The secondary battery electrode includes a secondary battery positive electrode or a secondary battery negative electrode. Preferred configurations of the secondary battery aqueous electrode binder, the electrode active material, the conductivity-imparting agent, and the secondary battery aqueous electrode composition used for the secondary battery electrode of the present invention are the above-described secondary battery aqueous electrode binders. , Electrode active material, conductivity-imparting agent, and preferred configurations of the secondary battery aqueous electrode composition.

  The present invention is also a secondary battery configured using the secondary battery electrode of the present invention. The preferable structure of the electrode for secondary batteries used for the battery of this invention is the same as the preferable structure of the electrode for secondary batteries mentioned above.

  The secondary battery constructed using the positive electrode for the secondary battery of the present invention has an initial discharge capacity of 120 mAh / in case where the positive electrode active material is lithium nickel manganese cobaltate (Ni: Co: Mn = 1: 1: 1). It is preferable that it is more than g. More preferably, it is 130 mAh / g or more. The initial discharge capacity can be measured by a method similar to the example using a charge / discharge measuring apparatus ACD-001 (product name, manufactured by Asuka Electronics Co., Ltd.).

  When the negative electrode active material is graphite, the secondary battery configured using the negative electrode for secondary battery of the present invention preferably has an initial discharge capacity of 250 mAh / g or more. More preferably, it is 300 mAh / g or more. The initial discharge capacity can be measured by a method similar to the example using a charge / discharge measuring apparatus ACD-001 (product name, manufactured by Asuka Electronics Co., Ltd.).

  The secondary battery constituted by using the positive electrode for a secondary battery of the present invention has an electric capacity retention rate after 50 cycles of repeated charging and discharging 50 times (also simply referred to as “50 cycle maintenance rate”) of 85% or more. It is preferable that More preferably, it is 95% or more. By confirming the maintenance rate of 50 cycles, it can be confirmed that there is no problem in initial characteristics as a binder. The electric capacity of the secondary battery can be measured by the same method as in the examples using a charge / discharge measuring device.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples. Unless otherwise specified, “part” means “part by mass”.

<Nonvolatile content of polymer solution>
About 1 g of the resin particle dispersion was weighed in an aluminum dish, dried in a hot air dryer at 150 ° C. for 30 minutes, and obtained from the mass before and after drying by the following formula.
Nonvolatile content (%) = {(mass after drying) / (mass before drying)} × 100
The nonvolatile content was determined in the same manner as above except that an aqueous solution of a water-soluble polymer was used instead of the resin particle dispersion.

<Viscosity of polymer solution>
The viscosity of the resin particle dispersion was measured at 25 ± 1 ° C. and 30 rpm using TVB-10 (manufactured by Toki Sangyo Co., Ltd.) after adjusting the resin particle dispersion to a non-volatile content of 2%.
The viscosity of the water-soluble polymer aqueous solution was measured at 25 ± 1 ° C. and 30 rpm using a TVB-10 (manufactured by Toki Sangyo Co., Ltd.) with a water-soluble polymer aqueous solution having a pH of 7 and a nonvolatile content of 2%.
Moreover, the viscosity of 6 rpm / 25 rpm of 25 ± 1 ° C. was defined as the thixo value.

<Total light transmittance measurement>
Using a haze meter (model number; NDH5000) manufactured by Nippon Denshoku Industries Co., Ltd., a water-soluble polymer aqueous solution having a nonvolatile content of 2% was put in a quartz cell having a depth of 10 mm, and the total light transmittance was measured.

<Electrolytic solution resistance of water-soluble polymer>
A mold having a thickness of 3 mm was prepared on a Teflon (registered trademark) plate, and a water-soluble polymer was poured into the mold and dried to prepare a 20 mm square test piece. The obtained test piece was immersed in an electrolytic solution (EC / EMC = 3/7) for one day, and the vertical and horizontal lengths of the membrane were measured. In addition, the swelling rate indicates a value converted into a volume based on the vertical and horizontal increase / decrease rates, and indicates that the swelling rate is not changed when the swelling rate is 100%. For example, when it becomes 22 mm in each length and width by being immersed in electrolyte solution, a swelling rate will be 133%. The EC represents ethylene carbonate, and EMC represents ethyl methyl carbonate.

Synthesis of seed particle dispersion a Stirrer, thermometer, cooler, nitrogen inlet tube, four-necked separable flask equipped with dropping funnel, 292.1 parts by mass of ion-exchanged water, ammonium sulfonate of polyoxyethylene dodecyl ether 2.7 parts by weight of salt was added. While stirring at an internal temperature of 72 ° C., nitrogen was gently flowed to completely replace the inside of the reaction vessel with nitrogen. Next, 2.7 parts by mass of sulfonate of polyoxyethylene dodecyl ether was dissolved in 97.0 parts by mass of ion-exchanged water. As a monomer component of the polymer, a mixture of 72.0 parts by mass of methacrylic acid and 108 parts by mass of ethyl acrylate was added to prepare a pre-emulsion. Separately, 0.45 parts by mass of ammonium persulfate was dissolved in 44.5 parts by mass of ion-exchanged water to prepare an aqueous polymerization initiator solution. The temperature in the reaction vessel was kept at 72 ° C., and the pre-emulsion and the aqueous initiator solution were uniformly added dropwise over 2 hours. After completion of the dropwise addition, the internal temperature was kept at 72 ° C., and stirring was further continued for 1 hour, followed by cooling to complete the reaction, whereby a seed particle dispersion a having a nonvolatile content of 30% and a viscosity of 5 mPa · s was obtained.

In a four-necked separable flask equipped with a synthetic stirrer, thermometer, cooler, nitrogen inlet tube, and dropping funnel for water-soluble resin A, 610.9 parts by mass of ion-exchanged water, sulfonate of polyoxyethylene dodecyl ether 2 7 parts by mass and 18 parts by mass of seed particle dispersion a were added. While stirring at an internal temperature of 72 ° C., nitrogen was gently flowed to completely replace the inside of the reaction vessel with nitrogen. Next, 2.7 parts by mass of sulfonate of polyoxyethylene dodecyl ether was dissolved in 97.0 parts by mass of ion-exchanged water. As a monomer component of the polymer, a mixture of 117 parts by weight of methacrylic acid, 62.64 parts by weight of ethyl acrylate, and 0.36 parts by weight of 1,6-hexanediol acrylate was added to prepare a pre-emulsion. . Separately, 0.45 parts by mass of ammonium persulfate was dissolved in 44.5 parts by mass of ion-exchanged water to prepare an aqueous polymerization initiator solution. The temperature in the reaction vessel was kept at 72 ° C., and the pre-emulsion and the aqueous initiator solution were uniformly added dropwise over 2 hours. After completion of the dropwise addition, the internal temperature was kept at 72 ° C., and stirring was further continued for 1 hour, followed by cooling to complete the reaction to obtain a resin particle dispersion a having a nonvolatile content of 20%. . The resin particle dispersion a was diluted with water to adjust the nonvolatile content to 2%, and the viscosity was measured to be 3 mPa · s.
To the obtained resin particle dispersion a, a 5% lithium hydroxide monohydrate aqueous solution and ion-exchanged water were added and stirred to adjust pH to 7 to obtain a water-soluble resin A aqueous solution having a nonvolatile content of 2%. The obtained water-soluble resin A had a viscosity of 270 mPa · s, a thixo value of 1.5, and a total light transmittance of 99%. Further, the swelling resistance ratio of the polymer with respect to the electrolytic solution was 108%.

The monomer component of the synthetic polymer of the water-soluble resin B was changed to a mixture of 108 parts by weight of methacrylic acid, 53.82 parts by weight of ethyl acrylate, 18 parts by weight of butyl acrylate, and 0.18 parts by weight of diallyl phthalate. Was carried out in the same manner as in the synthesis of the water-soluble resin A.
The obtained resin particle dispersion b having a nonvolatile content of 20% was diluted with water to have a nonvolatile content of 2%, and the viscosity was measured to be 5 mPa · s.
To the obtained resin particle dispersion b, 5% lithium hydroxide monohydrate aqueous solution and ion-exchanged water were added and stirred to adjust to pH 7, thereby obtaining a water-soluble resin B aqueous solution having a nonvolatile content of 2%. The obtained water-soluble resin B had a viscosity of 260 mPa · s, a thixo value of 1.5, and a total light transmittance of 99%. Further, the swelling resistance ratio of the polymer with respect to the electrolytic solution was 108%.

<Viscosity of electrode composition>
The viscosity at 25 ± 1 ° C. and 30 rpm was measured using TVB-10 (manufactured by Toki Sangyo Co., Ltd.).
<PH of electrode composition>
The value at 25 ° C. was measured using a glass electrode type hydrogen ion concentration meter F-21 (product name, manufactured by Horiba, Ltd.).
<Evaluation of electrode formability>
Using a variable applicator, the positive electrode composition was applied by adjusting to a predetermined film thickness, and dried at 80 ° C. for 10 minutes to produce a positive electrode. The produced positive electrode was subjected to a bending test at φ10 mm and evaluated according to the following evaluation criteria.
Evaluation criteria:
○: No problem (no crack, no peeling, no crack).
Δ: There was no volume shrinkage crack during film formation, but cracking occurred when the electrode was bent.
X: Volume shrinkage cracks occurred during film formation.

<Evaluation of positive electrode electrical characteristics (initial discharge capacity, cycle characteristics)>
The positive electrode composition was applied using an applicator, dried at 80 ° C. for 10 minutes, and pressed at a linear pressure of 5 kN using a roll press.
Then, it dried under reduced pressure at 80 degreeC and produced the electrode sheet | seat with an electrode weight of 12 mg / cm3. Using the produced electrode sheet, a coin cell (CR2032) was produced as described below, and battery evaluation was performed under the following conditions using a charge / discharge measurement apparatus ACD-001 (product name, manufactured by Asuka Electronics Co., Ltd.).

<Cell creation conditions>
Positive electrode: Positive electrode composition negative electrode of Table 1: Li foil electrolyte solution: 1 mol% / L LiPF6 EC / EMC = 3/7 (manufactured by Kishida Chemical Co., Ltd.)
<Battery evaluation conditions>
Charging condition: 0.5C CC-CV Cut-off 4.3V
Discharge condition: 0.5C CC Cut-off 3.0V
<Measurement of peel strength>
The positive electrode composition was applied using an applicator, dried at 80 ° C. for 10 minutes, and pressed at a linear pressure of 5 kN using a roll press.
Then, it dried under reduced pressure at 80 degreeC and produced the electrode sheet | seat with an electrode weight of 12 mg / cm3. This sample was cut out to a width of 25 mm and a length of 100 mm, attached to an aluminum plate, and peel strength at a peel direction of 180 ° and a peel speed of 5 mm / min using a tensile tester (manufactured by Tester Sangyo Co., Ltd.) under 23 ° C. conditions. Was measured.

Example 1
To 25 parts by mass of water-soluble resin A, 1.5 parts by mass of acetylene black HS-100 (manufactured by Denki Kagaku Kogyo Co., Ltd.) was added and dispersed. Furthermore, 50 parts by mass of lithium nickel manganese cobaltate (Cell Seed NMC111, manufactured by Nippon Chemical Industry Co., Ltd.) was added and mixed and dispersed, and 6.1 parts by mass of ion-exchanged water was further added to obtain a positive electrode aqueous composition (1). . Using this positive electrode aqueous composition (1), an electrode was prepared according to the procedure described above. The obtained positive electrode had a 0.5C initial discharge capacity of 144 mAh / g and a capacity retention rate of 98.0% after 50 cycles. The peel strength was 17 N / m.

(Example 2)
The water-soluble resin A was changed to the water-soluble resin B, and paint was formed in the same manner as in Example 1 to produce a positive electrode. The physical properties of the obtained electrode are shown in Table 1.

(Comparative Example 1)
The water-soluble resin A was changed to a CMC aqueous solution (Serogen BSH-6, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and paint was formed in the same manner as in Example 1 to produce a positive electrode. The physical properties of the obtained electrode are shown in Table 1.

(Comparative Example 2)
The water-soluble resin A was changed to a PVdF solution (KF polymer L # 7208, manufactured by Kureha Co., Ltd.), and paint was formed in the same manner as in Example 1 to produce a positive electrode. The physical properties of the obtained electrode are shown in Table 1.
In Table 1, the column of the composition of each component is represented as “mass part added / solid content (part by mass)”. For example, the amount of the water-soluble resin A in Example 1, “25.00 / 0.75”, is 25.00 g of a 3% by mass water-soluble polymer solution, in which the water-soluble polymer (solid content) is 0. .75g is included. The physical properties of the water-soluble resins A and B (evaluation of viscosity and total light transmittance) are 2% solid content concentration obtained in the above (synthesis of water-soluble resin A) and (synthesis of water-soluble resin B). The measured values of the water-soluble resins A and B themselves are described. On the other hand, as shown in Table 1, the water-soluble resins A and B used to prepare the electrode composition in each example were adjusted to a solid content concentration of 3%.

From Table 1, by using the water-based resin of the present invention as an electrode binder, high solid differentiation was possible and good electrode peel strength was expressed.

  The binder for an electrode composition of the present invention can be used only with a water-soluble resin as in Examples 1 and 2 (one liquid), and the adhesion of the electrode is also ensured. Comparative Example 1 is an example in which CMC alone was used instead of the water-soluble polymer of the present invention, but the peel strength of the electrode was lower than that of the electrode binder of the present invention, and the initial discharge capacity was low. Comparative Example 2 is an example using PVdF, but sufficient peel strength cannot be expressed with the amount of binder examined this time.

  The battery electrode composition using the binder for battery electrode composition of the present invention enables uniform electrode formation and has a dispersibility and a viscosity adjusting function, so that it is not only a two-component binder, but also a single component. It can also be used as a system binder. Adhesiveness to the current collector can be expressed with a small amount of binder in a one-component system. Moreover, since it has a structural unit derived from an ethylenically unsaturated carboxylate monomer, the resistance to electrolyte solution is sufficiently good.

Claims (12)

A water-based electrode binder for a secondary battery containing a water-soluble polymer,
The water-soluble polymer is based on 100% by mass of the total amount of structural units of the water-soluble polymer.
(A) 50-80% by mass of a structural unit derived from an ethylenically unsaturated carboxylate monomer,
(B) containing 20 to 50 mass% of a structural unit derived from an ethylenically unsaturated carboxylic acid ester monomer,
An aqueous electrode binder for a secondary battery, wherein the water-soluble polymer has a viscosity of 100 to 20,000 mPa · s at 25 ° C., pH 7, and non-volatile content of 2 mass%. The ethylenically unsaturated carboxylic acid unsaturated carboxylic acid ester monomer is represented by the general formula (1);
CH2 = CR-C (= O) -OR '(1)
(In the formula, R represents a hydrogen atom or a methyl group. R ′ represents an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, and a hydroxylalkyl group having 1 to 10 carbon atoms. The water-based electrode binder for a secondary battery according to claim 1, wherein The water-soluble polymer is further based on 100% by mass of the total amount of structural units of the water-soluble polymer.
(C) 0.01-5 mass% of structural units derived from a polyfunctional group-containing unsaturated monomer are contained, The aqueous electrode binder for secondary batteries according to claim 1 or 2. The water-soluble polymer may be obtained by neutralizing a polymer synthesized by emulsion polymerization using seed particles with at least one salt selected from the group consisting of alkali metal salts, ammonium salts, and organic amine salts. The aqueous electrode binder for secondary batteries according to any one of claims 1 to 3. The electroconductivity imparting agent characterized by including the water-system electrode binder for secondary batteries in any one of Claims 1-4, a conductive support agent, and water as an essential component. A secondary battery positive electrode aqueous composition comprising the secondary battery aqueous electrode binder according to any one of claims 1 to 4, a positive electrode active material, and water as essential components. A positive electrode for a secondary battery comprising the aqueous electrode binder for a secondary battery according to any one of claims 1 to 4 and a positive electrode active material. It forms using the electroconductivity imparting agent of Claim 5, or the positive electrode aqueous composition for secondary batteries of Claim 6, The positive electrode for secondary batteries characterized by the above-mentioned. A secondary battery negative electrode aqueous composition comprising the secondary battery aqueous electrode binder according to any one of claims 1 to 4, a negative electrode active material, and water as essential components. A negative electrode for a secondary battery comprising the aqueous electrode binder for a secondary battery according to any one of claims 1 to 4 and a negative electrode active material. It obtains from the negative electrode aqueous composition for secondary batteries of Claim 9, The negative electrode for secondary batteries characterized by the above-mentioned. A secondary battery comprising the positive electrode for a secondary battery according to claim 7 and / or the negative electrode for a secondary battery according to claim 10 or 11.