JP6061563B2 - Aqueous electrode binder for secondary battery - Google Patents

Description

The present invention relates to an aqueous electrode binder for a secondary battery.

A secondary battery is a battery that can be repeatedly charged and discharged. With the recent increase in interest in environmental problems, the use is progressing not only in electronic devices such as mobile phones and laptop computers, but also in fields such as automobiles and airplanes. 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.
A lithium ion battery is mainly composed of a positive electrode, an electrolyte, a negative electrode, and a separator. Among these electrodes, an electrode in which an electrode composition is applied on a current collector is 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.
This is because PVDF is chemically and electrically stable, NMP is a solvent that is stable over time in which PVDF is dissolved, and lithium cobaltate that is commonly used as a positive electrode active material is hydrolyzed in water. This is because it is necessary to use an organic solvent.
However, the low molecular weight product of PVDF has insufficient adhesion, and the dissolution concentration is not high when the molecular weight is increased, and when the high molecular weight PVDF is used, it is difficult to increase the solid content concentration. Moreover, since NMP has a high boiling point, when NMP is used as a solvent, there is a problem that a large amount of energy is required for volatilization of the solvent when an electrode is formed. In addition, in recent years, an aqueous composition that does not use an organic solvent has been demanded for the electrode composition against the background of increasing interest in environmental problems.

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) (the solvent is N-methyl-2-pyrrolidone (NMP)) is used in the solvent system, and carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) are used in the water system. Is common.
Regarding the negative electrode composition, from the background described above, a solvent-based one and a water-based one have been studied. In normal aqueous systems, the binder is a water-soluble polymer that is responsible for dispersibility and viscosity adjustment functions typified by CMC, and the flexibility of the electrode typified by SBR and an emulsion as a binder that binds active material particles to each other. (Polymer particle aqueous dispersion) is used in combination.
As the water-soluble polymer as the binder for the negative electrode of the secondary battery, celluloses, polycarboxylic acid compounds and the like are mainly studied and exemplified.

Under such circumstances, various researches and developments have been made on electrode compositions and binders that can be used in electrode compositions.
As a secondary battery binder, an aqueous solution containing a specific amount of a structural unit derived from an ethylenically unsaturated carboxylic acid ester monomer and a structural unit derived from an ethylenically unsaturated carboxylate monomer, and having a specific weight average molecular weight The thing containing a functional polymer is disclosed (refer 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).

International Publication No. 2012/008539 JP 2002-203561 A

However, conventional binders for secondary batteries are not suitable for electrodes due to inadequate moisture absorption characteristics, complicated process management of electrode plates due to the ease of water retention, and insufficient adhesion. Peeling when bent is a problem.
In addition, in the inventions described in each of the above patent documents, there is room for improvement in order to ensure sufficient moisture absorption characteristics and adhesion.

The present invention has been made in view of the above circumstances, and has excellent moisture absorption characteristics and adhesiveness, and is suitably used as a water-soluble binder to be contained in a composition for forming a secondary battery electrode. An object of the present invention is to provide an aqueous electrode binder for a secondary battery.

The present inventors have conducted various studies on water-based electrode binders that can improve the moisture absorption characteristics and adhesion of the water-based electrode composition. And the content of the component derived from the compound having a specific proportion of the structural unit derived from the ethylenically unsaturated carboxylate monomer is less than the specific amount, and the weight average molecular weight is 500,000 or more It has been found that the use of a water-based electrode binder containing a water-soluble polymer can improve the hygroscopic properties and adhesion of the water-based electrode composition. In addition, since the content of the component derived from the low molecular weight compound having surface activity is less than a specific amount, the water-soluble polymer improves the adhesion of the water-soluble polymer, and further has a surface activity. As a result, the present inventors have found that the water absorption property of the water-soluble polymer is improved because there is no alkylene oxide chain derived from a compound having a function.
In addition, as the electrode binder has a lower hygroscopic property (more difficult to absorb water), it becomes easier to manage the process. Therefore, in this specification, the improvement of the hygroscopic property means that the hygroscopic property is lowered, and the hygroscopic property is improved. Excellent means low hygroscopicity.

That is, the present invention is an aqueous electrode binder for a secondary battery containing a water-soluble polymer, and the water-soluble polymer is an ethylenic resin based on 100% by mass of the total amount of structural units of the water-soluble polymer. The content of a component derived from a compound having a weight average molecular weight of 100,000 or less having a surfactant activity is 5 to 95% by mass, containing a structural unit derived from a saturated carboxylate monomer, and 0.5% by mass or less, and A water-based electrode binder for a secondary battery having a weight average molecular weight of 500,000 or more.

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 aqueous electrode binder for secondary batteries of the present invention (hereinafter also referred to as “aqueous electrode binder”) is an ethylenically unsaturated carboxylate monomer based on 100% by mass of the total amount of structural units of the water-soluble polymer. The content of a component derived from a compound having a weight-average molecular weight of 100,000 or less, containing 5 to 95% by mass of a derived structural unit, and having a surfactant activity is 0.5% by mass or less, and the weight-average molecular weight is 500,000 or more And a water-soluble polymer (hereinafter also referred to as “water-soluble polymer in the present invention” or simply “water-soluble polymer”).

The water-based electrode binder of the present invention may contain other components and other water-soluble polymers as long as such water-soluble polymers are contained.
In addition, it is preferable that the aqueous electrode binder of this invention contains 10-100 mass% of water-soluble polymers in this invention with respect to the said aqueous electrode binder whole quantity 100 mass% from an adhesive point, More preferably, it is 50. ˜100 mass%.
Moreover, the water-based electrode binder of the present invention may contain one type of the water-soluble polymer in the present invention, or may contain two or more types.

The structural unit derived from an ethylenically unsaturated carboxylate monomer (hereinafter also referred to as “structural unit (a)”), which is essential for the water-soluble polymer in the present invention, is an ethylenically unsaturated carboxylate single unit. This represents a structure in which the carbon-carbon double bond of the monomer is a single bond.
Examples of the ethylenically unsaturated carboxylate monomer include ethylenically unsaturated groups having 3 to 10 carbon atoms such as alkali metal salts such as (meth) acrylic acid, crotonic acid, and isocrotonic acid, ammonium salts, and organic amine salts. Monocarboxylic acid salt monomer; ethylenically unsaturated dicarboxylic acid having 4 to 10 carbon atoms such as alkali metal salts such as itaconic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid and glutaconic acid, ammonium salts and organic amine salts And acid salt monomers. Among these, salts of an ethylenically unsaturated monocarboxylic acid having 3 to 6 carbon atoms such as acrylic acid and methacrylic acid are preferable.
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 the compound that forms an organic amine salt include monoethanolamine, diethanolamine, triethanolamine, cyclohexylamine, and hydroxylamine. Of the above salts, lithium salts are preferred.
Thus, by using an ethylenically unsaturated carboxylate monomer, in particular, an alkali metal salt, an ammonium salt, or an organic amine salt of an ethylenically unsaturated carboxylic acid, the water-soluble polymer in the present invention. Can be prevented from swelling with respect to the electrolytic solution. As these ethylenically unsaturated carboxylate monomers, one type may be used, or two or more types may be used.

A part of the carboxylate having the ethylenically unsaturated carboxylate monomer is in the form of carboxylic acid (—COOH) as long as a water-soluble polymer can be synthesized by a polymerization method described later. Also good. In the case where 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, water From the viewpoint of solubility in water, the amount of carboxylic acid is preferably 50 mol% or less. More preferably, it is 40 mol% or less, More preferably, it is 30 mol% or less.

The water-soluble polymer in the present invention preferably contains a structural unit derived from an ethylenically unsaturated carboxylic acid ester monomer in addition to the structural unit (a).
The structural unit derived from the ethylenically unsaturated carboxylic acid ester monomer (hereinafter also referred to as “structural unit (b)”) is a single carbon-carbon double bond of the ethylenically unsaturated carboxylic acid ester monomer. It represents a bonded structure.
Examples of the ethylenically unsaturated carboxylic acid ester monomer include acrylic acid ester, methacrylic acid ester, and crotonic acid ester. Preferably, for example, the general formula (1);
_{CH 2 = CR-C (=} O) -OR '(1)
(In formula, R represents a hydrogen atom or a methyl group. R 'represents a C1-C10 alkyl group, a C3-C10 cycloalkyl group, or a C1-C10 hydroxyalkyl group. )
It is a compound represented by these.

Examples of R ′ in the general formula (1) 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, a cyclohexyl group, and the like. 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, from the viewpoint of stability at the time of soap-free emulsion polymerization described later, those having high hydrophobicity are preferable, that is, alkyl groups having 1 to 10 carbon atoms and cycloalkyl groups having 3 to 10 carbon atoms are preferable. . More preferably, they are a C1-C8 alkyl group and a C3-C8 cycloalkyl group, More preferably, they are a C1-C6 alkyl group. When R ′ in the general formula (1) is an alkyl group, the glass transition temperature (Tg) of the resulting water-soluble polymer is preferably reduced. R ′ is particularly preferably an alkyl group having 1 to 4 carbon atoms, and most preferably an alkyl group having 1 to 2 carbon atoms. When the alkyl group has 1 to 4 carbon atoms, the copolymer with the ethylenically unsaturated carboxylate monomer is easily dissolved in water.
As these ethylenically unsaturated carboxylic acid ester monomers, one type may be used, or two or more types may be used.

The water-soluble polymer in the present invention may contain a structural unit derived from another polymerizable monomer in addition to the structural unit (a) and the structural unit (b).
The structural unit derived from the other polymerizable monomer (hereinafter also referred to as “structural unit (c)”) is a single bond of the carbon-carbon double bond of the other polymerizable monomer. It represents the structure.
Other polymerizable monomers include, for example, styrene monomers such as styrene, α-methylstyrene, and ethyl vinylbenzene; (meth) acrylic acid amide, N, N-dimethyl (meth) acrylamide and the like ( (Meth) acrylamide monomers; polyfunctional allyl monomers such as vinyl acetate and diallyl phthalate; polyfunctional acrylates such as 1,6-hexanediol diacrylate; Examples thereof include (meth) acrylic esters having a polyalkylene oxide group and vinyl compounds having a hydrophobic group such as 30 alkyl groups.
Among these, other polymerizable monomers are preferably styrene monomers, (meth) acrylamide monomers, polyfunctional allyl monomers, and polyfunctional acrylates.
As these other polymerizable monomers, one type may be used, or two or more types may be used.

The content ratio of the structural unit (a) in the water-soluble polymer in the present invention is 5 to 95% by mass with respect to 100% by mass of the total amount of the structural units of the water-soluble polymer. When the structural unit (a) is within this range, the water-soluble polymer in the present invention can be easily produced by soap-free emulsion polymerization, and the solubility of the produced polymer in water ( It is possible to express water solubility. On the other hand, if the structural unit (a) is less than 5% by mass, the solubility in water may be insufficient and a uniform solution may not be obtained. If it exceeds 95% by mass, production by soap-free emulsion polymerization becomes difficult. There is a fear. As a content rate of the structural unit (a) in the water-soluble polymer in this invention, Preferably it is 20-80 mass%, More preferably, it is 30-60 mass%.

The content ratio of the structural unit (b) in the water-soluble polymer in the present invention is preferably 5 to 95% by mass with respect to 100% by mass of the total amount of the structural units of the water-soluble polymer. When the structural unit (b) is within this range, the water-soluble polymer in the present invention can be easily produced by soap-free emulsion polymerization. On the other hand, when the structural unit (b) exceeds 95% by mass, the solubility in water may be insufficient and a uniform solution may not be obtained. When the structural unit (b) is less than 5% by mass, production by soap-free emulsion polymerization becomes difficult. There is a fear. As a content rate of the structural unit (b) in the water-soluble polymer in this invention, Preferably it is 20-80 mass%, More preferably, it is 40-70 mass%.
In the case where the structural unit (b) is a structural unit derived from the ethylenically unsaturated carboxylic acid ester monomer represented by the general formula (1), the ethylenically unsaturated carboxylic acid ester monomer is A monomer having an ester structure portion, that is, a structure portion represented by —C (═O) —OR ′ in the general formula (1), which is a hydrophobic monomer but contains a polar group . For this reason, at the time of soap-free emulsion polymerization, it tends to be the core of emulsion droplets, but when it is neutralized with an alkali metal salt, ammonium salt, organic amine salt, etc. after polymerization, it dissolves uniformly in water. It will be easier. Therefore, the water-soluble polymer preferably contains 5 to 95% by mass of a structural unit (structural unit (b)) derived from an ethylenically unsaturated carboxylic acid ester monomer.

When the water-soluble polymer in the present invention contains the structural unit (c), the content is preferably 20% by mass or less with respect to 100% by mass of the total amount of the structural units of the water-soluble polymer. More preferably, it is 10 mass% or less, More preferably, it is 5 mass% or less.

That is, as the ratio of each structural unit in the water-soluble polymer in the present invention, when the total amount of the structural units of the water-soluble polymer is 100% by mass, ((a) ethylenically unsaturated carboxylate monomer Body-derived structural unit) / ((b) structural unit derived from ethylenically unsaturated carboxylic acid ester monomer) / ((c) structural unit derived from other polymerizable monomer) = 5 to 95% by mass / 5 to 95% by mass / 0 to 20% by mass is preferable.

Since the water-soluble polymer in the present invention contains the hydrophobic part and the polar part in a balanced manner as described above, the water-soluble polymer is excellent in dispersion stability of the positive electrode active material, the conductive auxiliary agent, etc. And a binder for preparing a positive electrode aqueous composition for a secondary battery in which a conductive auxiliary agent and the like are dispersed.

The water-soluble polymer needs to have a weight average molecular weight of 500,000 or more. When the weight average molecular weight is less than 500,000, the dispersibility and viscosity adjusting ability required for a water-soluble polymer can be expressed, but there is a possibility that it is not sufficient for improving the binding property between particles. In addition to dispersibility and viscosity adjustment function, further binding by improving flexibility by using ethylenically unsaturated carboxylic acid ester monomer and improving strength by increasing the molecular weight to a weight average molecular weight of 500,000 or more Can also be improved. Preferably it is 700,000-2 million, More preferably, it is 900,000-1,800,000.
A weight average molecular weight can be measured by the gel permeation chromatography method (GPC method) as described in the Example mentioned later.

The water-soluble polymer preferably has a viscosity of 100 mPa · s or more at 25 ° C., pH 7, and a non-volatile content of 2% by mass as measured in accordance with JIS K 7117-1, from the viewpoint of viscosity adjusting ability. More preferably, it is 500-20,000 mPa * s, More preferably, it is 1000-10,000 mPa * s.

The water-soluble polymer preferably has a total light transmittance of 90% or more in a 2% by mass non-volatile solution from the viewpoint of uniformity and transparency. More preferably, it is 95-100%, More preferably, it is 97-100%.
The total light transmittance can be measured using a haze meter (product name “NDH5000”, manufactured by Nippon Denshoku Industries Co., Ltd.).

In addition, 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 haze can be measured using a haze meter (product name “NDH5000”, manufactured by Nippon Denshoku Industries Co., Ltd.).

In the water-soluble polymer, the content of a component derived from a compound having a surface active ability and a weight average molecular weight of 100,000 or less is 0.5 mass based on 100 mass% of the total amount of structural units of the water-soluble polymer. % Or less. From the viewpoint of adhesion and moisture absorption properties, it is preferably 0.3% by mass or less, more preferably 0.1% by mass or less, and particularly preferably 0% by mass.
In addition, “a compound having a surface active ability and a weight average molecular weight of 100,000 or less” means a compound having both a hydrophilic part and a hydrophobic part and having a weight average molecular weight of 100,000 or less. Among the compounds having active ability, compounds having a weight average molecular weight of 100,000 or less can be mentioned.
The weight average molecular weight can be measured by the same method as described above.

Examples of the compound having surface activity include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants.
Examples of the anionic surfactant include polyoxyalkylene alkyl ether sulfate, polyoxyalkyl ether sulfate, polyoxyalkylene alkyl phenyl ether sulfate, polyoxyalkylene carboxylic ester sulfate, alkyl allyl polyether Examples thereof include sulfate ester salts such as sulfate, sulfonate and phosphate ester salts.
Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl aryl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, fatty acid monoglycerides such as glycerol monolaurate, and polyoxyethyleneoxypropylene Examples thereof include polymers, condensation products of ethylene oxide and fatty acid amines, amides or acids.
Examples of the cationic surfactant include alkyl pyridinyl chloride and alkyl ammonium chloride.
Examples of the amphoteric surfactant include lauryl petaine, stearyl petaine, lauryl dimethylamine oxide and the like.

In addition, a reactive surfactant having a radically polymerizable unsaturated group in the structure of the surfactant used in the process of producing the water-soluble polymer as a “component derived from a compound having surface active ability” is also used. included. Reactive surfactants can incorporate surfactants into the polymer structure by virtue of their polymerizable unsaturated groups and, when made into aqueous solutions, reduce the surfactant components that are free and present in the aqueous solution. Although it is difficult to completely eliminate the free component of the reactive surfactant which is not highly reactive, the hygroscopic property may be lowered by the alkylene oxide chain contained in the general reactive surfactant. There is.
Examples of the reactive surfactant include Latemul PD (manufactured by Kao Corporation), Adekaria Soap SR (manufactured by Adeka Company), Aqualon HS (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Aqualon KH (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) Elminol RS (manufactured by Sanyo Chemical Co., Ltd.) and the like.
When using these compounds having surface active ability in the range of 0.5 mass% or less, one type may be used, or two or more types may be used.

The “component derived from a compound having surface active ability” is not incorporated in the water soluble polymer itself but present in the water soluble polymer when the compound having surface active ability is a non-reactive surfactant. Therefore, there is a possibility of adversely affecting the adhesion. In addition, even when the compound having surface active ability is a reactive surfactant, it is not easy to completely eliminate the free component, and the free component may adversely affect the adhesion, and the water-soluble polymer Even when incorporated, there is a possibility that the hygroscopic property may be lowered by the alkylene oxide chain contained.

In the water-soluble polymer in the present invention, the content of the chain transfer agent is preferably less than 0.1% by mass with respect to 100% by mass of the total amount of structural units of the water-soluble polymer. When the content of the chain transfer agent is 0.1% by mass or more, a large amount of a low molecular weight compound is generated, and the adhesion may be insufficient. More preferably, it is 0.01 mass% or less, Most preferably, it is 0 mass%.
The chain transfer agent is not particularly limited as long as it is a commonly used chain transfer agent, and examples thereof include halogenated substituted alkanes, alkyl mercaptans, thioesters, and alcohols. When these chain transfer agents are used, one kind or two or more kinds can be used.

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

In the soap-free emulsion polymerization method, an oligomer radical having a radical and an ionic group at the end of the polymerization initiator is obtained by adding a monomer and a polymerization initiator into a solvent (water or the like) and contacting them. Is formed to form particle nuclei, a monomer enters the particle nuclei, a polymerization reaction proceeds, and the particles grow to become resin particles (polymer particles). Therefore, the soap-free emulsion polymerization method is a method in which a high molecular weight copolymer can be easily polymerized at a high concentration and the viscosity of the polymerization solution is low. In addition, it is preferable to use a hydrophobic monomer because the oligomer radicals are easily insolubilized in water. Further, a water-soluble polymer having a weight average molecular weight of 500,000 or more can be prepared as a resin particle dispersion by a soap-free emulsion polymerization method, and neutralized with an alkali metal salt, ammonium salt, organic amine salt or the like as described later. By taking the step of solubilization (homogenization), the production can be carried out easily, which is advantageous in terms of production cost.

Further, in such soap-free emulsion polymerization, the generated resin particles are dispersed and stabilized by the ionic group at the end of the polymerization initiator. For this reason, the soap-free emulsion polymerization can be carried out without using a compound having surface activity or using a very small amount of a compound having surface activity. As described above, in the water-soluble polymer of the present invention, the content of a component derived from a compound having a surface active ability and a weight average molecular weight of 100,000 or less is required to be 0.5% by mass or less. The free emulsion polymerization is preferably performed without using a compound having surface activity.
As described above, the amount of the compound having surface activity in soap-free emulsion polymerization is preferably 0 to 0.3% by mass, more preferably 100% by mass, more preferably 100% by mass of the total amount of monomer components to be subjected to the polymerization reaction. It is 0-0.1 mass%, Most preferably, it is 0 mass%.

Also, soap-free emulsion polymerization can be performed using seed particles. In this case, the seed particles absorb the monomer subjected to the polymerization reaction, and the resin particles grow. Therefore, since the monomer hardly reacts in the aqueous solution, it is difficult to form a low molecular weight product, which is preferable from the viewpoint of adhesion.
As the seed particles, known resin particles can be used. As the composition (component) of the seed particles, as described above, since the seed particles absorb the monomer and the resin particles grow, those having a similar composition to the water-soluble polymer to be produced are preferable.

A polymerization initiator can be used for the polymerization of the monomer components. As the polymerization initiator, those usually used can be used, and are not particularly limited as long as they generate radical molecules by heat. When performing soap-free emulsion polymerization 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 may be used alone or in combination of two or more.
As the usage-amount of the said polymerization initiator, it is preferable from an adhesive point 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 soap-free emulsion polymerization, a chain transfer agent may be used to adjust the molecular weight. However, it is necessary to use it so that a weight average molecular weight may be 500,000 or more.
The type of chain transfer agent is as described above.
The amount of the chain transfer agent used is preferably 0 to 1% by mass with respect to 100% by mass of the total amount of monomer components used for the polymerization reaction from the viewpoint of adhesion. More preferably, it is 0-0.5 mass%.

In addition, when performing soap-free emulsion polymerization, a hydrophilic solvent, an additive, or the like can be added within a range that does not adversely affect the resulting copolymer.
Examples of the hydrophilic solvent include alcohols, tetrahydrofuran, N-methylpyrrolidone, acetone and the like.
Examples of the additive include organic salts, inorganic salts, pH buffering agents, and the like.

Although it does not specifically limit about the polymerization temperature in the said soap free emulsion polymerization, Preferably it is 20-100 degreeC, More preferably, it is 50-90 degreeC.
The polymerization time in the soap-free emulsion polymerization is not particularly limited, but is preferably 1 to 10 hours, more preferably 1.5 to 8 hours in consideration of productivity.

The method of adding each monomer component to the soap-free emulsion polymerization reaction system is not particularly limited, and a batch polymerization method, a monomer component dropping method, a power feed method, a seed method, a multistage addition method, or the like is used. Can do.

The nonvolatile content of the resin particle dispersion obtained after the soap-free emulsion polymerization reaction is preferably 5 to 60%. When the non-volatile content is within the above range, it is easy to maintain the fluidity and dispersion stability of the obtained resin particle dispersion, and it is also preferable from the viewpoint of the production efficiency of the target polymer. On the other hand, if the nonvolatile content exceeds 60%, the viscosity of the resin particle dispersion is too high, so that the dispersion stability cannot be maintained and aggregation may occur. If the non-volatile content is less than 5%, the concentration of the polymerization system is low, the reaction may take time, and the production efficiency may deteriorate from the viewpoint of the production amount of the target polymer.
In the present specification, the polymer forming the resin particle dispersion is also referred to as resin particles.

It is preferable from the viewpoint of workability that the resin particles have a viscosity of 0.01 to 100 mPa · s measured at 25 ° C. and a 2% by weight non-volatile solution, measured according to JIS K7117-1. More preferably, it is 0.01-50 mPa * s, More preferably, it is 0.01-10 mPa * s.

The average particle diameter of the resin particles 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 resin particles is within the above range, the viscosity becomes too high, or the possibility that the dispersion stability cannot be maintained and agglomeration can be reduced. On the other hand, if the particle diameter of the resin particles is less than 10 nm, the viscosity of the resin particle dispersion may be too high, or the dispersion stability may not be maintained, and aggregation may occur. If the particle diameter exceeds 1 μm, the dispersion stability of the resin particles may be increased. It may be difficult to maintain sex.
The average particle size of the resin particles can be measured by a dynamic light scattering type particle size measuring device.

The water-soluble polymer in the present invention is preferably obtained by neutralizing the resin particles obtained by the above method with an alkali metal salt, ammonium salt, organic amine salt or the like.
Examples of the alkali metal salt include salts of lithium, sodium, potassium and the like. In order to neutralize with these metal salts, an aqueous solution of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, lithium carbonate or the like can be used, preferably Lithium hydroxide, lithium hydrogen carbonate, lithium carbonate.
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.

Neutralization is preferably 50% or more of the theoretical carboxylic acid content, more preferably 65% or more. The pH after neutralization is preferably 6 or more, more preferably 6.2 or more. The pH is preferably 9 or less.
The pH can be measured as a value at 25 ° C. using a glass electrode type hydrogen ion meter F-21 (product name, manufactured by HORIBA, Ltd.).

In the soap-free emulsion polymerization described above, the compound having the surface-active ability described above is not used, or even when it is used, the amount used is a small amount compared to ordinary emulsion polymerization, so the resin particles obtained by soap-free emulsion polymerization Water-soluble polymer obtained by neutralizing with alkali metal salt, ammonium salt, organic amine salt, etc. contains low molecular weight components such as free emulsifiers (emulsifiers not incorporated into the polymer structure) Is extremely small.
Thus, it is also possible that the water-soluble polymer is obtained by neutralizing resin particles synthesized by soap-free emulsion polymerization with an alkali metal salt, ammonium salt, organic amine salt, or the like. This is one of the preferred embodiments.
Specifically, the water-soluble polymer is ethylenic in an aqueous solution under the condition that the content of a compound having a surface activity is 0.5% by mass or less with respect to 100% by mass of all monomer components. It is obtained by neutralizing a resin particle dispersion obtained by polymerizing an unsaturated carboxylic acid monomer with at least one selected from the group consisting of alkali metal salts, ammonium salts, and organic amine salts. It is also one of the preferred embodiments of the present invention.
Here, the “ethylenically unsaturated carboxylic acid monomer” means one containing both the above-mentioned ethylenically unsaturated carboxylate monomer and ethylenically unsaturated carboxylic acid ester monomer.

Next, the conductivity imparting agent of the present invention will be described.
The conductivity-imparting agent of the present invention is characterized by containing the above-described water-based polymer binder for secondary batteries of the present invention, a conductive assistant, and water as essential components. The conductivity-imparting agent of the present invention may contain one of these essential components, or two or more of them.

The conductive auxiliary agent 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-like carbon, and graphite. Among these, carbon black such as ketjen black and acetylene black is preferable. Ketjen Black has a hollow shell structure and is easy to form a conductive network. Therefore, compared with conventional carbon black, it is preferable because the equivalent performance is exhibited with an addition amount of about half. In addition, acetylene black is preferable by using a high-purity acetylene gas because the generated carbon black has very few impurities and crystallites on the surface are developed.

The conductive auxiliary agent preferably has an average particle size of 1 μm or less. When a positive electrode is formed from a positive electrode aqueous composition prepared using the conductivity-imparting agent of the present invention by using a conductive additive having an average particle diameter of 1 μm or less, and the formed positive electrode is used as a positive electrode of a battery In addition, a positive electrode having excellent electrical characteristics such as output characteristics can be obtained. The average particle diameter is more preferably 0.01 to 0.8 μm, and further preferably 0.03 to 0.5 μm.
The average particle diameter of the conductive assistant can be measured by a dynamic light scattering particle size distribution meter (conducting assistant refractive index is set to 2.0).

If necessary, a dispersant can be further used for the conductivity imparting agent of the present invention. By using a dispersant, the viscosity can be reduced, and the solid content in the case of a positive electrode aqueous composition mixed with a positive electrode active material or the like can be set high.
There are no particular restrictions on the dispersant, and anionic surfactants, nonionic surfactants, cationic surfactants; copolymers of styrene and maleic acid (including half ester copolymers-ammonium salts) and the like Various dispersing agents such as a molecular dispersing agent can be used.

When a positive electrode active material particle mixed with a positive electrode active material or the like is obtained by further using a dispersant in combination with the water-soluble polymer in the present invention to improve the uniform dispersion stability of the conductive additive, the positive electrode active material particles The contact resistance between them can be reduced, and good conductivity of the positive electrode film can be achieved.

The present invention further relates to a secondary battery positive electrode aqueous composition containing the above-mentioned water-soluble polymer, the secondary battery aqueous electrode binder of the present invention, a positive electrode active material, and water as essential components. One of these essential components may be included, or two or more thereof may be included. Furthermore, the positive electrode aqueous composition for secondary battery of the present invention may contain a conductive additive.

In the positive electrode aqueous composition for a secondary battery of the present invention, the water-soluble polymer and the conductive auxiliary agent described above can be used.
The positive electrode active material used in the aqueous electrode composition for secondary batteries 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 the compound that can occlude and release lithium ions include lithium-containing metal oxides. Examples of the metal oxides include lithium cobaltate, lithium iron phosphate, lithium manganese phosphate, lithium manganate, lithium nickelate, A ternary compound represented by a compound having an olivine structure, LiNi _1-xy Co _x Mn _y O ₂ or LiNi _1-xy Co _x Al _y O ₂ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) Transition metal oxides such as system oxides, solid solution materials incorporating a plurality of transition metals (electrochemically inactive layered Li ₂ MnO ₃ and electrochemically active layered LiMO (M = Co, Ni Solid solution) with transition metals such as
As these positive electrode active materials, 1 type may be used and 2 or more types may be used.

The positive electrode active material used in the aqueous electrode composition for secondary batteries of the present invention preferably contains a compound having an olivine structure. That is, it is one of the preferred embodiments of the present invention that the positive electrode active material is a positive electrode active material containing a compound having an olivine structure.

The compound having an olivine structure is represented by the following formula:
LixAyDzPO ₄
(However, A represents one or more selected from the group consisting of Cr, Mn, Fe, Co, Ni and Cu. D represents Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, It represents one or more selected from the group consisting of In, Si, Ge, Sc, Y and rare earth elements, where x, y and z are 0 <x <2, 0 <y <1.5, 0 ≦ z <1. Represents a number satisfying .5.)
It is a compound which has a structure represented by these.
This compound forms a (PO ₄ ) ^3- polyanion by bonding an oxygen atom in the structure to phosphorus, and since oxygen is immobilized in the crystal structure, no combustion reaction takes place in principle. . For this reason, since the electrode active material containing this compound will be excellent in safety | security, it can be used suitably especially for the use to a medium sized power supply.
The component A is preferably Fe, Mn, or Ni, and particularly preferably Fe. The D component is preferably Mg, Ca, Ti, or Al.
As the compound having the olivine structure, lithium iron phosphate and lithium manganese phosphate are preferable. More preferably, it is lithium iron phosphate.

Further, as the positive electrode active material, it is preferable to use a material whose surface is partially or entirely coated with carbon in order to supplement conductivity. The surface coating with carbon can suppress deterioration in an aqueous system.
20 mass parts or less are preferable with respect to 100 mass parts of positive electrode active materials, and, as for content of the carbon which coat | covers a positive electrode active material, 10 mass parts or less are more preferable.

In the positive electrode aqueous composition of the present invention, the content of the compound having an olivine structure is preferably 70 parts by mass or more with respect to 100 parts by mass of the entire positive electrode active material. More preferably, it is 90 parts by mass or more, and most preferably, the positive electrode active material consists only of a compound having an olivine structure.

The positive electrode active material is preferably a positive electrode active material containing lithium iron phosphate as a main component. Among the compounds having the olivine structure, lithium iron phosphate is more preferable, and the main component of the positive electrode active material is preferable. Lithium iron phosphate has high stability against overcharge and uses abundant resources such as iron and phosphoric acid, so that it is inexpensive and preferable in terms of production cost. Further, lithium iron phosphate is not a high voltage system and has a low load on the binder.
“Containing lithium iron phosphate as a main component” means that the content of lithium iron phosphate with respect to 100% by mass of the whole positive electrode active material is 50% by mass or more, preferably 80% by mass or more. 90% by mass or more is more preferable. Most preferably, the positive electrode active material is made of lithium iron phosphate.

In the positive electrode aqueous composition for secondary batteries of the present invention, an emulsion may be used as a binder such as a positive electrode active material and a conductive additive.
Although it does not specifically limit as said emulsion, Non-fluorine-type polymers, such as a (meth) acrylic-type polymer, a nitrile-type polymer, and a diene polymer; PVDF, PTFE (polytetrafluoroethylene), (meth) acryl-modified fluorine-type polymer, etc. Fluorinated polymer (fluorine-containing polymer); Unlike a water-soluble polymer, the emulsion is preferably excellent in binding properties and flexibility (film flexibility) between particles. For this reason, (meth) acrylic polymers, nitrile polymers, and (meth) acryl-modified fluoropolymers are preferred.

Particularly in the positive electrode, the emulsion of a polymer having a structure in which a fluorine-containing polymer is (meth) acryl-modified is a chemically and electrically stable property possessed by the fluorine-containing polymer. Since the low binding property which is a fault, the low adhesiveness of the obtained coating film, and the hard brittleness of the coating film can be improved by modifying with acrylic, it is preferable. In addition, vinylidene fluoride polymers such as PVDF and fluorine-containing polymers such as PTFE are polymers having crystallinity, but particles having an IPN structure in which a (meth) acrylic polymer is contained in the fluorine-containing polymer. By making it, crystallinity is lowered, and there is an effect of lowering the film forming temperature of the emulsion.
The emulsion preferably contains 60 to 100% by mass of the (meth) acryl-modified fluorine-containing polymer with respect to 100% by mass of the total amount of the emulsion. More preferably, it is 80-100 mass%, More preferably, it is 90-100 mass%. Most preferably, it is 100% by mass, that is, the emulsion is made of a (meth) acryl-modified fluorine-containing polymer.

The ratio of the fluorine-containing polymer portion to the (meth) acrylic polymer portion in the (meth) acryl-modified fluorine-containing polymer emulsion is fluorine-containing polymer / (meth) acrylic polymer (mass ratio). 50/50 to 95/5 is preferable. More preferably, it is 60 / 40-90 / 10.

The fluorine-containing polymer is preferably a vinylidene fluoride polymer. The vinylidene fluoride-based polymer is a polymer having crystallinity, but it can be reduced in crystallinity by modifying it with (meth) acryl, improving the binding property and flexibility of the resin, and A great effect can be obtained in terms of lowering the film forming temperature. Therefore, by using a (meth) acrylic modified vinylidene fluoride polymer, the chemical and electrical stability of the fluorine-containing polymer as a binder for secondary batteries, and (meth) acrylic modification As a result, the excellent binding property and flexibility, and the effect of lowering the film-forming temperature can be exhibited more sufficiently. The vinylidene fluoride polymer may be produced using only vinylidene fluoride as a raw material, or may be obtained by copolymerization of vinylidene fluoride and other monomers, It is preferably obtained by copolymerization of vinylidene fluoride and another monomer. By copolymerizing with other monomers, the crystallinity of the vinylidene fluoride-based polymer can be lowered and acrylic modification can be facilitated.

Other monomers to be copolymerized with the vinylidene fluoride (VDF) are not particularly limited. For example, perfluorovinyl ethers such as tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoropropyl vinyl ether, and the like. Chlorotrifluoroethylene (CTFE); and the like. These 1 type (s) or 2 or more types can be used. Among these, hexafluoropropylene (HFP) and perfluoroalkyl vinyl ethers are preferable.

The emulsion of the (meth) acryl-modified fluorine-containing polymer is, for example, (meth) acrylic acid and / or (meth) acrylic acid ester in the presence of water-dispersed particles of the fluorine-containing polymer, and as necessary. A monomer component containing an unsaturated monomer having a functional group such as carboxylic acid or sulfonic acid can be obtained by a general polymerization method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization.

In the positive electrode aqueous composition for secondary battery of the present invention, the content (% by mass) of the water-soluble polymer in the solid content of the positive electrode aqueous composition is 0.2% with respect to 100% of the solid content of the positive electrode aqueous composition. It is preferable to be -5.0%. More preferably, it is 0.3 to 3.0%. With such a content ratio, it is possible to make the output characteristics and electrical characteristics excellent when the electrode formed from the positive electrode aqueous composition is used as the positive electrode of the battery.
In the positive electrode aqueous composition for secondary battery of the present invention, the content (mass%) of the positive electrode active material in the solid content of the positive electrode aqueous composition is 70-98. 8% is preferable. More preferably, it is 80 to 98.7%. With such a content ratio, it is possible to make the output characteristics and electrical characteristics excellent when the electrode formed from the positive electrode aqueous composition is used as the positive electrode of the battery.
In the positive electrode aqueous composition for secondary batteries of the present invention, the content (% by mass) of the conductive additive in the solid content of the positive electrode aqueous composition is 1 to 20% with respect to 100% of the solid content of the positive electrode aqueous composition. It is preferable that More preferably, it is 2 to 10%. With such a content ratio, it is possible to make the output characteristics and electrical characteristics excellent when the electrode formed from the positive electrode aqueous composition is used as the positive electrode of the battery.
In the positive electrode aqueous composition for secondary batteries of the present invention, the content (mass%) of the emulsion in the solid content of the positive electrode aqueous composition is 0 to 10% with respect to 100% of the solid content of the positive electrode aqueous composition. It is preferable. More preferably, it is 0 to 6.0%. With such a content ratio, it is possible to make the output characteristics and electrical characteristics excellent when the electrode formed from the positive electrode aqueous composition is used as the positive electrode of the battery.
The positive electrode aqueous composition for a secondary battery of the present invention may contain other components. The other components here refer to components other than the above-described water-soluble polymer, positive electrode active material, conductive additive, and emulsion, and include a dispersant and the like.

The positive electrode aqueous composition for secondary batteries of the present invention preferably has a viscosity of 1 to 20 Pa · s. When the viscosity of the positive electrode composition for a secondary battery 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 2-12 Pa.s, More preferably, it is 3-10 Pa.s, Most preferably, it is 4-7 Pa.s.
The viscosity of the aqueous electrode composition for secondary batteries can be measured with a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) and 30 rpm.

Moreover, it is preferable that the positive electrode aqueous composition for secondary batteries of this invention has a thixo value of 2.5-8. When it is less than 2.5, the coating liquid flows and becomes easy to repel, and when it exceeds 8, the coating liquid does not have fluidity and is difficult to apply. More preferably, it is 3-7.5, Most preferably, it is 3.5-7.
The thixo value can be obtained by measuring the viscosity at 25 ± 1 ° C., 6 rpm and 60 rpm with a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) and dividing the viscosity at 6 rpm by the viscosity at 60 rpm.

The positive electrode aqueous composition for secondary batteries 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 (eg, aluminum) is hardly corroded, and the battery performance of the material can be fully expressed.
pH measurement can measure the value of 25 degreeC using the glass electrode type hydrogen ion thermometer F-21 (made by Horiba Ltd.).

When the positive electrode aqueous composition for secondary batteries of the present invention contains the above-mentioned water-soluble polymer, positive electrode active material, conductive additive, emulsion and water, the method for producing the positive electrode aqueous composition is as follows. As long as the conductive aid is uniformly dispersed, there is no particular limitation. For example, a water-soluble polymer dissolved in water as a solvent may optionally be added with a dispersant, further mixed with a conductive aid, and dispersed using beads, a ball mill, a stirring mixer, etc. It is preferable to adjust the imparting agent, add a positive electrode active material to the solution, perform the same dispersion treatment, and further mix the emulsion to obtain a positive electrode composition for a secondary battery. 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.

The positive electrode water-based composition for secondary batteries of the present invention has a structural unit derived from an ethylenically unsaturated carboxylate monomer in an amount of 5 to 95% by mass based on 100% by mass of the total amount of structural units of the water-soluble polymer. Including a water-soluble polymer having a surface active ability of a component derived from a compound having a weight average molecular weight of 100,000 or less and having a weight average molecular weight of 500,000 or more and a weight average molecular weight of 0.5% or less Furthermore, it is preferable that the material further contains a positive electrode active material and a conductive assistant.
Thereby, the dispersion stability of filler components, such as a positive electrode active material and a conductive support agent, is ensured, and also it becomes excellent in the formation capability of a coating film, adhesiveness with a base material, and flexibility. And the positive electrode formed from such a positive electrode aqueous composition can exhibit sufficient performance as a positive electrode for secondary batteries.

A positive electrode for a secondary battery formed using such a positive electrode aqueous composition for a secondary battery of the present invention is also one aspect of the present invention. Furthermore, the secondary battery comprised using such a positive electrode for secondary batteries is also contained in this invention.
Moreover, it forms using the water-system electrode binder for secondary batteries of this invention containing the water-soluble polymer mentioned above, the positive electrode for secondary batteries containing a positive electrode active material, and the electroconductivity imparting agent of this invention. A positive electrode for a secondary battery is also one aspect of the present invention. And the secondary battery comprised using these positive electrodes for secondary batteries is also contained in this invention.

The present invention further provides a secondary battery negative electrode aqueous composition containing the above-described water-soluble polymer, the secondary battery aqueous electrode binder of the present invention, a negative electrode active material, and water as essential components. The negative electrode aqueous composition for secondary batteries of the present invention may contain one of these essential components, or two or more of them. Furthermore, the secondary battery aqueous electrode binder of the present invention containing the water-soluble polymer described above, a negative electrode for a secondary battery containing a negative electrode active material, and such a negative electrode for a secondary battery. Such secondary batteries are also included in the present invention.

In the negative electrode aqueous composition for secondary battery of the present invention, the above-mentioned water-soluble polymer can be used. Examples of the negative electrode active material used in the negative electrode aqueous composition for secondary batteries of the present invention include carbon materials such as graphite, natural graphite, and artificial graphite; polyacene conductive polymers; complex metal oxides such as lithium titanate; lithium alloys Etc. are exemplified. A carbon material is preferable.
Note that “the negative electrode active material contains a carbon-based negative electrode material as a main component” means that the carbon-based negative electrode material is included by 50% by mass or more with respect to 100% by mass of the total amount of the negative electrode active material. As a content rate of the carbon type negative electrode material in a negative electrode active material, Preferably it is 70-100 mass%, More preferably, it is 80-100 mass%. Particularly preferably, the negative electrode active material is made of a carbon-based negative electrode material.

The negative electrode aqueous composition for a secondary battery of the present invention may contain an emulsion, a conductive additive, a dispersant, a thickener, and the like as necessary. Especially, it is preferable to use the emulsion which can provide a softness | flexibility as a further binder component. Although the emulsion to be used is not particularly limited, the same emulsion as that contained in the positive electrode aqueous composition for secondary battery of the present invention described above, a diene polymer, or the like can be used.

A carbon-based negative electrode material as a negative electrode active material, a water-based electrode binder for a secondary battery of the present invention containing the water-soluble polymer described above, and a negative electrode composition containing water are the most preferred embodiments of the present invention. .

When using the negative electrode aqueous composition for secondary batteries of the present invention as a material for forming a negative electrode, the content (% by mass) of the water-soluble polymer in the solid content of the composition is 100% of the solid content in the composition. It is preferable that it is 0.3 to 2%. With such a content ratio, it is possible to improve output characteristics and electrical characteristics when an electrode formed from the negative electrode aqueous composition is used as a negative electrode of a battery. More preferably, it is 0.5 to 1.5%.
When using the negative electrode aqueous composition for secondary batteries of the present invention as a material for forming a negative electrode, the content ratio (% by mass) of the negative electrode active material in the solid content of 100% is 85 to 99.7%. It is preferable. With such a content ratio, it is possible to improve output characteristics and electrical characteristics when an electrode formed from the negative electrode aqueous composition is used as a negative electrode of a battery. More preferably, it is 90 to 99.5%.
Moreover, it is preferable that the content rate (mass%) of the conductive support agent in 100% of solid content of the composition in the negative electrode aqueous composition for secondary batteries is 0-10%. More preferably, it is 0 to 5%.
It is preferable that the content rate (mass%) of the emulsion in the solid content 100% of the composition in the negative electrode aqueous composition for secondary batteries is 0 to 9%. More preferably, it is 0 to 3%.
The negative electrode aqueous composition for secondary batteries of the present invention may contain other components. The “other components” referred to here mean components other than the binder, such as a negative electrode active material, a conductive aid, a water-soluble polymer, and an emulsion, and include a dispersant, a thickener, and the like.

The viscosity, thixo value and pH of the negative electrode aqueous composition for secondary battery of the present invention are preferably the same as the viscosity, thixo value and pH of the above-described positive electrode aqueous composition for secondary battery of the present invention, respectively.

When the negative electrode aqueous composition for secondary battery of the present invention comprises the above-mentioned water-soluble polymer aqueous electrode binder for secondary battery, negative electrode active material, emulsion, and water, the negative electrode aqueous composition The method for producing the product is not particularly limited as long as the negative electrode active material is uniformly dispersed, but a water-soluble resin dissolved in water as a solvent, and optionally a dispersant to obtain a uniform aqueous solution, Furthermore, it is preferable to mix a conductive additive as necessary and disperse using a bead, a ball mill, a stirring type mixer, or the like, and mix an emulsion therein to obtain a 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 negative electrode aqueous composition for a secondary battery of the present invention contains 5 to 95 structural units derived from an ethylenically unsaturated carboxylate monomer with respect to 100% by mass of the total amount of structural units of the water-soluble polymer. A water-soluble polymer containing a mass%, having a surface active ability and having a component derived from a compound having a weight average molecular weight of 100,000 or less and having a weight average molecular weight of 0.5 million or less and a weight average molecular weight of 500,000 or more is used. And further containing a negative electrode active material.
Thereby, the dispersion stability of the negative electrode active material is ensured, and further, the formed coating film can be formed, and the adhesion with the base material and the flexibility are excellent. And the negative electrode formed from such a negative electrode aqueous composition can exhibit sufficient performance as a negative electrode for secondary batteries.

The negative electrode for a secondary battery obtained from such a negative electrode aqueous composition for a secondary battery of the present invention is also one aspect of the present invention. Furthermore, a secondary battery constructed using such a negative electrode for a secondary battery is also one aspect of the present invention.

When the positive electrode active material is LiFePO ₄ , the secondary battery configured using the positive electrode for the secondary battery of the present invention preferably has an initial discharge capacity of 120 mAh / g or more from the viewpoint of battery performance. More preferably, it is 130 mAh / g or more. When the positive electrode active material is a ternary system of nickel cobalt lithium manganate, the initial discharge capacity is preferably 130 mAh / g or more. More preferably, it is 140 mAh / g or more.
In addition, the said initial stage discharge capacity can be measured by the method etc. which are described in the below-mentioned Example, for example.

A secondary battery configured using the positive electrode for a secondary battery according to the present invention has an electric capacity retention rate of 100 cycles after 100 cycles of charging and discharging (also simply referred to as “100 cycle maintenance rate”). The above is preferable. More preferably, it is 90% or more. By confirming the maintenance rate of 100 cycles, it can be confirmed that there is no problem as a binder. The electric capacity of the secondary battery can be measured by a charge / discharge evaluation apparatus.

Since the water-based electrode binder for secondary batteries of the present invention contains a water-soluble polymer having the above-described configuration, it has excellent moisture absorption characteristics and adhesion. Since the positive electrode aqueous composition for the secondary battery and the negative electrode aqueous composition for the secondary battery using such an aqueous electrode binder for the secondary battery enable uniform electrode formation, the positive electrode for the secondary battery and the secondary battery It can be suitably used as a composition for forming a negative electrode for a battery.

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” and “%” means “% by mass”.

In the following examples and comparative examples, the physical properties of the resin particle dispersion, the water-soluble polymer or its aqueous solution, and the electrode binder were evaluated by the following measuring methods.
<Nonvolatile content measurement>
About 1 g of the resin particle dispersion was weighed in an aluminum dish, dried in a hot air dryer at 150 ° C. for 20 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 measurement>
The viscosity of the resin particle dispersion was measured at 25 ° C. according to JIS K 7117-1 using TVB-10 (manufactured by Toki Sangyo Co., Ltd.) after adjusting the resin particle dispersion to 2% nonvolatile content.
The viscosity of the water-soluble polymer aqueous solution was measured at 25 ° C. using a TVB-10 (manufactured by Toki Sangyo Co., Ltd.) at 25 ° C. using a TVB-10 (manufactured by Toki Sangyo Co., Ltd.). did.
<Weight average molecular weight measurement>
A water-soluble polymer was dissolved in an eluent so that the non-volatile content of the measurement object was 0.2% by mass, and filtered through a filter, and measured under the following conditions.
Measuring equipment: GPC manufactured by Tosoh Corporation (model number: HLC-8120)
Molecular weight column: TSKgel GMHXL (manufactured by Tosoh Corporation)
Eluent: Tetrahydrofuran (THF)
Standard material for calibration curve: Polystyrene

<Total light transmittance measurement>
Using a haze meter (model number; NDH5000) manufactured by Nippon Denshoku Co., Ltd., a water-soluble polymer aqueous solution having a nonvolatile content of 2% by mass was placed in a quartz cell having a depth of 10 mm, and the total light transmittance was measured.
<Moisture absorption measurement>
About 50 g of the water-soluble polymer was weighed in an aluminum dish, dried with a hot air dryer at 100 ° C. for 2 hours, and then pulverized with a pulverizer. Then, after drying overnight at 80 ° C. with a vacuum dryer, about 1 g of powder was weighed on an aluminum dish under dry conditions to obtain an initial weight. Thereafter, the sample was allowed to stand at 23 ° C. and 65% RH for 4 hours, then weighed, and the moisture absorption rate was determined by the following formula.
Moisture absorption (%) = ((mass after 4 hours) − (initial mass)) / (initial mass)

<Adhesion evaluation>
A sample obtained by coating a positive electrode aqueous composition with a dry film thickness of 50 μm on an aluminum foil was cut out to a width of 25 mm and a length of 100 mm, and the electrode surface was attached to an aluminum plate with a double-sided tape, under conditions of 23 ° C. and 65% RH, The peel strength at a peel direction of 180 ° and a peel speed of 5 mm / min was measured with a tensile tester (manufactured by Tester Sangyo Co., Ltd.).
<Initial capacity evaluation>
Using a charge / discharge measuring apparatus ACD-001 (manufactured by Asuka Electronics Co., Ltd.), a coin cell (CR2032) was produced and battery evaluation was performed. Other measurement conditions are as follows.
Positive electrode: Positive electrode aqueous composition obtained in the following Examples and Comparative Examples Negative electrode: Li foil electrolyte: 1 mol / L LiPF ₆ EC / EMC = 3/7 (manufactured by Kishida Chemical Co., Ltd.)
Charging conditions: 0.2C CC-CV Cut-off 4.3V
Discharge condition: 0.2C CC Cut-off 2.7V

Example 1
Into a four-separable flask equipped with a stirrer, a thermometer, a cooler, a nitrogen introduction tube, and a dropping funnel, 871.75 parts by mass of ion-exchanged water was added. While stirring at an internal temperature of 90 ° C., nitrogen was gently flowed to completely replace the inside of the reaction vessel with nitrogen. Next, an initiator aqueous solution obtained by mixing 0.55 parts of potassium persulfate with 10.45 parts by mass of ion-exchanged water was added, and after stirring for 5 minutes, 77 parts by mass of methacrylic acid, 98.3 parts by mass of ethyl acrylate, A mixed solution of 44 parts by mass of methyl acrylate and 0.66 parts by mass of 1,6-hexanediacrylate was uniformly added dropwise over 2 hours. After completion of the dropping, the internal temperature was kept at 85 ° C. and stirring was continued for 1 hour. Next, the reaction was terminated by cooling to obtain a resin particle dispersion a having a nonvolatile content of 19.5% and a nonvolatile content of 2% and a viscosity of 10 mPa · s or less. 5% lithium hydroxide / monohydrate aqueous solution (10.2 parts) and ion-exchanged water (127.8 parts) were added to the obtained resin particle dispersion a (15.4 parts / nonvolatile content 3 parts). To obtain a water-soluble polymer (1) aqueous solution having a pH of 7 and a nonvolatile content of 2%. The obtained water-soluble polymer (1) had a weight average molecular weight of 1,000,000, a viscosity of 2600 mPa · s, a total light transmittance of 96%, and a moisture absorption of 12.8%.
Next, 28.68 parts of ion-exchanged water and 12.5 parts of the water-soluble polymer (1) aqueous solution are mixed to obtain a homogeneous solution, and 1.5 parts of acetylene black HS-100 (manufactured by Denka) is added and mixed and dispersed. did. Furthermore, 23.0 parts of Cellseed NMC (manufactured by Nippon Kagaku Kogyo Co., Ltd.) were added and mixed and dispersed. Furthermore, 0.52 part of acrylic modified emulsion of vinylidene fluoride polymer (VDF-acrylic modified emulsion) (manufactured by Arkema) was added. In addition, it was mixed and dispersed to obtain a positive electrode aqueous composition (1). This positive electrode aqueous composition (1) was applied to an aluminum stay using an applicator and dried at 100 ° C. for 10 minutes and 150 ° C. for 60 minutes. The obtained positive electrode had an adhesion of 20 N / m and an initial capacity of 144 mAh / g.

(Example 2)
As a polymerizable monomer, instead of 77 parts by weight of methacrylic acid, 98.3 parts by weight of ethyl acrylate, 44 parts by weight of methyl acrylate, and 0.66 parts by weight of 1,6-hexanediacrylate, 99 parts by weight of methacrylic acid Polymerization was carried out in the same manner as in Example 1 except that 120.3 parts by mass of ethyl acrylate and 0.66 parts by mass of 1,6-hexanediacrylate were used, and the nonvolatile content was 19.5% and the nonvolatile content was 2%. Resin particle dispersion b having a viscosity of 10 mPa · s or less was obtained. 5% lithium hydroxide / monohydrate aqueous solution (10.2 parts) and ion-exchanged water (127.8 parts) were added to the obtained resin particle dispersion b (15.4 parts / nonvolatile content 3 parts). To obtain a water-soluble polymer (2) aqueous solution having a pH of 7 and a non-volatile content of 2%. The obtained water-soluble polymer (2) had a weight average molecular weight of 900,000, a viscosity of 2400 mPa · s, a total light transmittance of 98%, and a hygroscopicity of 13.6%.
Next, 28.68 parts of ion-exchanged water and 12.5 parts of water-soluble polymer (2) aqueous solution are mixed to obtain a homogeneous solution, and 1.5 parts of acetylene black HS-100 (manufactured by Denka) is added and mixed and dispersed. did. Furthermore, 23.0 parts of Cellseed NMC (manufactured by Nippon Kagaku Kogyo Co., Ltd.) were added and mixed and dispersed. Furthermore, 0.52 part of acrylic modified emulsion of vinylidene fluoride polymer (VDF-acrylic modified emulsion) (manufactured by Arkema) was added. In addition, it was mixed and dispersed to obtain a positive electrode aqueous composition (2). This positive electrode aqueous composition (2) was applied to an aluminum stay using an applicator and dried at 100 ° C. for 10 minutes and 150 ° C. for 60 minutes. The obtained positive electrode had an adhesion of 15 N / m and an initial capacity of 141 mAh / g.

(Example 3)
In a four-separable flask equipped with a stirrer, thermometer, cooler, nitrogen inlet tube, and dropping funnel, 33.1 parts by mass of the resin particle dispersion a prepared in Example 1 as seed particles and ion-exchanged water 868 are used. .15 parts by mass were charged. Thereafter, polymerization was performed in the same manner as in Example 2 to obtain a resin particle dispersion c having a non-volatile content of 19.5% and a non-volatile content of 2% and a viscosity of 10 mPa · s or less. 5% lithium hydroxide / monohydrate aqueous solution (10.2 parts) and ion-exchanged water (127.8 parts) were added to the obtained resin particle dispersion c (15.4 parts / nonvolatile content 3 parts). To obtain a water-soluble polymer (3) aqueous solution having a pH of 7 and a nonvolatile content of 2%. The obtained water-soluble polymer (3) had a weight average molecular weight of 1.1 million, a viscosity of 2700 mPa · s, a total light transmittance of 98%, and a hygroscopicity of 13.3%.
Next, 28.68 parts of ion-exchanged water and 12.5 parts of water-soluble polymer (3) aqueous solution are mixed to obtain a homogeneous solution, and 1.5 parts of acetylene black HS-100 (manufactured by Denka) is added and mixed and dispersed. did. Furthermore, 23.0 parts of Cellseed NMC (manufactured by Nippon Kagaku Kogyo Co., Ltd.) were added and mixed and dispersed. Furthermore, 0.52 part of acrylic modified emulsion of vinylidene fluoride polymer (VDF-acrylic modified emulsion) (manufactured by Arkema) was added. In addition, it was mixed and dispersed to obtain a positive electrode aqueous composition (3). This positive electrode aqueous composition (3) was applied to an aluminum stay using an applicator and dried at 100 ° C. for 10 minutes and 150 ° C. for 60 minutes. The obtained positive electrode had an adhesion of 23 N / m and an initial capacity of 151 mAh / g.

Example 4
Into a four-neck separable fresco equipped with a stirrer, a thermometer, a cooler, a nitrogen introducing tube, and a dropping funnel, 115 parts by mass of ion-exchanged water and 1.5 parts by mass of polyoxyethylene dodecyl ether sulfonate ammonium salt were added. . While stirring at an internal temperature of 68 ° C., nitrogen was gently flowed to completely replace the inside of the reaction vessel with nitrogen. Next, 1.5 parts by mass of sulfonate of polyoxyethylene dodecyl ether was dissolved in 92 parts by mass of ion-exchanged water. As a monomer component of the polymer, a mixture of 50 parts by mass of methacrylic acid, 30 parts by mass of ethyl acrylate, and 20 parts by mass of methyl acrylate was added to prepare a pre-emulsion. Separately, 0.23 parts by mass of ammonium persulfate was dissolved in 23 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 dropping, the dropping tank was washed with 8 parts by mass of ion-exchanged water and then charged into the reaction vessel. The internal temperature was kept at 72 ° C. and stirring was further continued for 1 hour, followed by cooling to complete the reaction, thereby producing alkali-soluble resin particles S-1 having a nonvolatile content of 30%. Subsequently, 21.5 parts by mass of S-1 and 879.75 parts by mass of ion-exchanged water as seed particles were added to a four-separable flask equipped with a separate stirrer, thermometer, cooler, nitrogen inlet tube, and dropping funnel. I put it in. Thereafter, polymerization was performed in the same manner as in Example 2 to obtain a resin particle dispersion d having a non-volatile content of 19.5% and a non-volatile content of 2% and a viscosity of 10 mPa · s or less. 5% lithium hydroxide / monohydrate aqueous solution (10.2 parts) and ion-exchanged water (127.8 parts) were added to the obtained resin particle dispersion d (15.4 parts / nonvolatile content 3 parts). To obtain a water-soluble polymer (4) aqueous solution having a pH of 7 and a non-volatile content of 2%. The obtained water-soluble polymer (4) had a weight average molecular weight of 1.1 million, a viscosity of 2600 mPa · s, a total light transmittance of 98%, and a hygroscopicity of 13.6%.
Next, 28.68 parts of ion-exchanged water and 12.5 parts of a water-soluble polymer (4) aqueous solution are mixed to obtain a uniform solution, and 1.5 parts of acetylene black HS-100 (manufactured by Denka) is added and mixed and dispersed. did. Furthermore, 23.0 parts of Cellseed NMC (manufactured by Nippon Kagaku Kogyo Co., Ltd.) were added and mixed and dispersed. Furthermore, 0.52 part of acrylic modified emulsion of vinylidene fluoride polymer (VDF-acrylic modified emulsion) (manufactured by Arkema) was added. In addition, it was mixed and dispersed to obtain a positive electrode aqueous composition (4). This positive electrode aqueous composition (4) was applied to an aluminum stay using an applicator and dried at 100 ° C. for 10 minutes and 150 ° C. for 60 minutes. The obtained positive electrode had an adhesion of 18 N / m and an initial capacity of 143 mAh / g.

(Comparative Example 1)
Into a four-neck separable fresco equipped with a stirrer, a thermometer, a cooler, a nitrogen introducing tube, and a dropping funnel, 115 parts by mass of ion-exchanged water and 1.5 parts by mass of polyoxyethylene dodecyl ether sulfonate ammonium salt were added. . While stirring at an internal temperature of 68 ° C., nitrogen was gently flowed to completely replace the inside of the reaction vessel with nitrogen. Next, 1.5 parts by mass of sulfonate of polyoxyethylene dodecyl ether was dissolved in 92 parts by mass of ion-exchanged water. As a monomer component of the polymer, a mixture of 35 parts by mass of methacrylic acid, 65 parts by mass of ethyl acrylate, and 0.3 parts by mass of t-dodecyl mercaptan was added to prepare a pre-emulsion. Separately, 0.23 parts by mass of ammonium persulfate was dissolved in 23 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 dropping, the dropping tank was washed with 8 parts by mass of ion-exchanged water and then charged into the reaction vessel. After maintaining the internal temperature at 72 ° C. and further stirring for 1 hour, the reaction was completed by cooling to obtain a resin particle dispersion e having a viscosity of 10 mPa · s or less at a nonvolatile content of 30% and a nonvolatile content of 2%. .
5% lithium hydroxide / monohydrate aqueous solution (10.2 parts) and ion-exchanged water (133.2 parts) were added to the obtained resin particle dispersion e (10 parts / nonvolatile content 3 parts) and stirred. As a result, a water-soluble polymer (5) aqueous solution having a pH of 7 and a nonvolatile content of 2% was obtained. The obtained water-soluble polymer (5) had a weight average molecular weight of 300,000, a viscosity of 80 mPa · s, a total light transmittance of 99%, and a hygroscopicity of 16.8%.
Next, 28.68 parts of ion-exchanged water and 12.5 parts of water-soluble polymer (5) aqueous solution are mixed to obtain a homogeneous solution, and 1.5 parts of acetylene black HS-100 (manufactured by Denka) is added and mixed and dispersed. did. Furthermore, 23.0 parts of Cellseed NMC (manufactured by Nippon Kagaku Kogyo Co., Ltd.) were added and mixed and dispersed. Furthermore, 0.52 part of acrylic modified emulsion of vinylidene fluoride polymer (VDF-acrylic modified emulsion) (manufactured by Arkema) was added. In addition, it was mixed and dispersed to obtain a positive electrode aqueous composition (5). This positive electrode aqueous composition (5) was applied to an aluminum stay using an applicator and dried at 100 ° C. for 10 minutes and 150 ° C. for 60 minutes. The obtained positive electrode had an adhesion of 5 N / m and an initial capacity of 138 mAh / g.

From the results of the above examples, the secondary battery aqueous electrode binder containing the water-soluble polymer in the present invention is excellent in hygroscopic properties, and the positive battery aqueous composition and secondary battery positive electrode using the binder. Is excellent in adhesion, and it can be seen that a secondary battery using the positive electrode has a large initial capacity. Further, when the aqueous electrode binder for secondary batteries containing the water-soluble polymer in the present invention is used for the negative electrode aqueous composition for secondary batteries and the negative electrode for secondary batteries, the positive electrode aqueous composition for secondary batteries is also used. The same results as those obtained when used for the positive electrode for the secondary battery are obtained.
In the above-described examples, it is considered that the mechanism of action in which the effects of excellent moisture absorption characteristics and adhesion described above are expressed by using the water-based electrode binder for secondary batteries containing the water-soluble polymer is the same. .
Therefore, it can be said from the results of the above-described embodiments that the present invention can be applied in the entire technical scope of the present invention and in various forms disclosed in the present specification, and can exhibit advantageous effects.

Claims (7)

A water-based electrode binder for a secondary battery containing a water-soluble polymer,
The water-soluble polymer contains 30 to 95% by weight of a structural unit derived from an ethylenically unsaturated carboxylate monomer with respect to 100% by weight of the total amount of structural units of the water-soluble polymer. The content of a component derived from a compound having a weight average molecular weight of 100,000 or less, which contains 5 to 70% by mass of a structural unit derived from an acid ester monomer and has a surface activity, is 0.5% by mass or less, and a weight average What der molecular weight of 500,000 or more was measured with JIS K 7117-1, 25 ℃, pH7 , the viscosity at a nonvolatile content 2% by weight aqueous solution is at 100 mPa · s or more, all of the non-volatiles 2% by weight aqueous solution secondary battery aqueous electrode binder light transmittance wherein der Rukoto 90%. A method for producing a water-based electrode binder for a secondary battery containing a water-soluble polymer,
The production method is carried out under the condition that the content of the compound having surface active ability is 0.5% by mass or less with respect to 100% by mass of the total monomer components, to 100% by mass of all the monomer components in the aqueous solution. A step of obtaining a resin particle dispersion by polymerizing a monomer component containing 30 to 95% by mass of an ethylenically unsaturated carboxylate monomer,
And a step of neutralizing the resin particle dispersion with at least one selected from the group consisting of alkali metal salts, ammonium salts, and organic amine salts to obtain a water-soluble polymer. A method for producing a system electrode binder. The electroconductivity imparting agent characterized by including the water-system electrode binder for secondary batteries of Claim 1 , a conductive support agent, and water as an essential component. A positive electrode aqueous composition for a secondary battery comprising the aqueous electrode binder for a secondary battery according to claim 1 , 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 claim 1 and a positive electrode active material. Conductivity imparting agent according to claim 3, or a positive electrode for a secondary battery characterized by being formed by using a secondary battery positive electrode aqueous composition according to claim 4. A secondary battery comprising the positive electrode for a secondary battery according to claim 5 .