JP2014116265A - Binder composition for lithium ion secondary battery negative electrode, slurry composition for lithium ion secondary battery negative electrode, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder composition for a lithium ion secondary battery negative electrode capable of obtaining a lithium ion secondary battery having excellent in cycle characteristics and low temperature output characteristics.SOLUTION: A binder composition for a lithium ion secondary battery electrode contains: polymer particles (A) containing a (meth)acrylate compound and polyfunctional thiol compound, and produced by polymerizing a monomer composition (a) having 0.001 pts.wt to 10 pts.wt of content of polyfunctional thiol compound with respect to (meth)acrylate compound of 100 pts.wt, in aqueous medium; and a solvent.

Description

  The present invention relates to a binder composition for a lithium ion secondary battery electrode, a slurry composition for a lithium ion secondary battery electrode, an electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

  In recent years, portable terminals such as notebook computers, mobile phones, and PDAs (Personal Digital Assistants) have been widely used. Lithium ion secondary batteries are frequently used as secondary batteries used as power sources for these portable terminals. Mobile terminals are required to have more comfortable portability, and are rapidly becoming smaller, thinner, lighter, and higher performance. As a result, mobile terminals are used in various places. In addition, secondary batteries are also required to be smaller, thinner, lighter, and have higher performance as with mobile terminals.

  In order to improve the performance of secondary batteries, improvements to electrodes, electrolytes, and other battery members have been studied. Of these electrodes, the electrode active material is usually mixed with a liquid composition in which a polymer serving as a binder is dispersed or dissolved in a solvent to obtain a slurry composition, and this slurry composition is applied to a current collector. And dried. In the electrode manufactured by such a method, it has been attempted in the past to improve the performance of the secondary battery by devising the binder (Patent Document 1).

  In addition, techniques such as Patent Documents 2 to 5 are also known.

JP 2012-14920 A JP-A-1994-306109 JP 2006-196464 A JP 2004-152654 A Japanese Patent Laid-Open No. 08-157777

However, the demand for the performance of lithium ion secondary batteries has recently become increasingly high, and in particular, improvement of cycle characteristics and discharge rate characteristics is particularly required.
The present invention was devised in view of the above problems, and a binder composition for a lithium ion secondary battery electrode and a slurry for a lithium ion secondary battery electrode from which a lithium ion secondary battery excellent in cycle characteristics and discharge rate characteristics can be obtained. It is an object of the present invention to provide a composition, an electrode for a lithium ion secondary battery, and a lithium ion secondary battery having excellent cycle characteristics and discharge rate characteristics.

As a result of intensive studies to solve the above problems, the present inventor obtained by polymerizing a monomer composition (a) containing a (meth) acrylic acid ester compound and a predetermined amount of a polyfunctional thiol compound in an aqueous medium. It was found that a lithium ion secondary battery excellent in cycle characteristics and discharge rate characteristics can be realized by using a binder composition for a lithium ion secondary battery electrode containing the polymer particles (A) obtained and a solvent. Completed the invention.
That is, the present invention is as follows.

[1] A single amount containing a (meth) acrylic acid ester compound and a polyfunctional thiol compound, wherein the ratio of the polyfunctional thiol compound to 100 parts by weight of the (meth) acrylic acid ester compound is 0.001 part by weight to 10 parts by weight. The binder composition for lithium ion secondary battery electrodes containing the polymer particle (A) obtained by superposing | polymerizing a body composition (a) in an aqueous medium, and a solvent.
[2] The lithium ion secondary compound according to [1], wherein the monomer composition (a) includes a polymerizable monomer copolymerizable with the (meth) acrylic acid ester compound or the polyfunctional thiol compound. Binder composition for secondary battery electrode.
[3] A slurry composition for a lithium ion secondary battery electrode, comprising the binder composition for a lithium ion secondary battery electrode according to [1] or [2] and an electrode active material.
[4] The slurry composition for a lithium ion secondary battery electrode according to [3], wherein the electrode active material is a positive electrode active material.
[5] The slurry composition for a lithium ion secondary battery electrode according to [3], wherein the electrode active material is a negative electrode active material.
[6] The lithium ion secondary according to [5], comprising polymer particles (B) obtained by polymerizing a monomer composition (b) containing an aromatic vinyl compound and a conjugated diene compound in an aqueous medium. A slurry composition for battery electrodes.
[7] The slurry composition for a lithium ion secondary battery electrode according to any one of [3] to [6], further including a water-soluble polymer.
[8] For a lithium ion secondary battery obtained by applying the slurry composition for a lithium ion secondary battery electrode according to any one of [3] to [7] onto a current collector and drying it. electrode.
[9] A positive electrode, a negative electrode, and an electrolyte solution are provided.
A lithium ion secondary battery, wherein the positive electrode or the negative electrode is an electrode for a lithium ion secondary battery according to [8].

According to the binder composition for a lithium ion secondary battery electrode, the slurry composition for a lithium ion secondary battery electrode, and the electrode for a lithium ion secondary battery of the present invention, a lithium ion secondary battery excellent in cycle characteristics and discharge rate characteristics is obtained. can get.
The lithium ion secondary battery of the present invention is excellent in cycle characteristics and discharge rate characteristics.

  Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and can be implemented with any modifications without departing from the scope of the claims of the present invention and its equivalents.

  In the following description, (meth) acrylic acid means acrylic acid or methacrylic acid. Moreover, (meth) acrylate means an acrylate or a methacrylate. Furthermore, (meth) acrylonitrile means acrylonitrile or methacrylonitrile.

  Furthermore, that a substance is water-soluble means that an insoluble content is less than 0.5% by weight when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C. Further, that a certain substance is water-insoluble means that an insoluble content is 90% by weight or more when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C.

[1. Binder composition for lithium ion secondary battery electrode]
The binder composition for a lithium ion secondary battery electrode of the present invention (hereinafter sometimes referred to as “binder composition” as appropriate) includes polymer particles (A) and a solvent. Hereinafter, the binder composition will be described for each of the negative electrode and the positive electrode.

[1.1. Binder composition for negative electrode]
The binder composition for a negative electrode includes polymer particles (A) for a negative electrode and a solvent.

[1.1.1. Polymer particles for negative electrode (A)]
The polymer particles (A) are polymer particles obtained by polymerizing a monomer composition (a) containing a (meth) acrylic acid ester compound and a polyfunctional thiol compound in an aqueous medium.

((Meth) acrylic acid ester compound)
The (meth) acrylic acid ester compound is one of the monomers of the polymer particles (A). In this case, only the acrylic ester compound may be used, only the methacrylic ester compound may be used, or an acrylic ester compound and a methacrylic ester compound may be used in combination. The structural unit formed by polymerizing the (meth) acrylic acid ester compound has high strength and flexibility, and can enhance the binding properties of the polymer particles (A).

  Examples of (meth) acrylic acid ester compounds include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, and nonyl acrylate. , Alkyl acrylate esters such as decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, 2-ethylhexyl acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate; 2- (perfluorobutyl) ethyl acrylate, 2 2- (perfluoroalkyl) ethyl acrylate such as-(perfluoropentyl) ethyl acrylate; Methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, tridecyl methacrylate, Methacrylic acid alkyl esters such as n-tetradecyl methacrylate, stearyl methacrylate, 2-ethylhexyl methacrylate; 2- (perfluorobutyl) ethyl methacrylate, 2- (perfluoropentyl) ethyl methacrylate, 2- (perfluoroalkyl) ethyl methacrylate, etc. Of 2- (perfluoroalkyl) ethyl methacrylate; Jill acrylate; benzyl methacrylate; and the like. Among these, from the viewpoint of excellent yield of polymer particles (A), various properties of the negative electrode for secondary battery and secondary battery, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t- It preferably contains at least one selected from the group consisting of butyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, and t-butyl methacrylate, methyl acrylate, ethyl acrylate, n- It contains at least one selected from the group consisting of butyl acrylate, t-butyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and t-butyl methacrylate. It is particularly preferred. Moreover, a (meth) acrylic acid ester compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  When the polymer particles (A) are used in the binder composition for a negative electrode, the proportion of the (meth) acrylic acid ester compound in the monomer composition (a) is preferably 40% by weight or more, more preferably 50% by weight. Above, particularly preferably 60% by weight or more, preferably 95% by weight or less, more preferably 90% by weight or less, and particularly preferably 85% by weight or less. By setting the ratio of the (meth) acrylic acid ester compound to be equal to or higher than the lower limit of the above range, the binding property between the polymer particles (A) and the negative electrode active material or current collector can be further improved. Moreover, the slurry composition excellent in stability can be obtained by making it below an upper limit.

(Polyfunctional thiol compound)
A polyfunctional thiol compound refers to a compound having two or more mercapto groups (-SH groups) per molecule. The polyfunctional thiol compound can function as a chain transfer agent when the monomer composition (a) is polymerized. For this reason, in the obtained polymer particle (A), a crosslinked structure or a branched structure derived from a polyfunctional thiol compound is usually formed as its molecular structure. Due to such a crosslinked structure or branched structure, the resulting polymer particles (A) are excellent in toughness. Moreover, the polarity of polymer particle (A) can be enlarged with the sulfur atom which a polyfunctional thiol compound has. Thereby, the binding property of the polymer particles (A) to the electrode active material and the current collector can be improved. Moreover, the ion conductivity of a polymer particle (A) can be improved because a polymer particle (A) contains the sulfur atom originating in a polyfunctional thiol compound. Further, the polarity of the mercapto group can increase the affinity of the polymer particles (A) for water, so that the polymer particles (A) can be stably dispersed in a solvent such as water, and the binder composition and The stability of the slurry composition for lithium ion secondary battery electrodes (hereinafter sometimes referred to as “slurry composition” as appropriate) can be improved. Furthermore, the affinity of the polymer particles (A) with respect to the polar solvent is improved by the polarity of the mercapto group, so that the wettability of the polymer particles (A) with respect to the electrolytic solution can be improved.

  Examples of polyfunctional thiol compounds include mercapto groups per molecule such as 1,4-bis (3-mercaptobutyryloxy) butane and tetraethylene glycol bis (3-mercaptopropionate) (EGMP-4). 2 bifunctional thiol compounds; trimethylolpropane tris (3-mercaptobutyrate), trimethylolethane tris (3-mercaptobutyrate), 1,3,5-tris (3-mercaptobutyloxyethyl) -1, 3,5-triazine-2,4,6 (1H, 3H, 5H) -trione, trimethylolpropane tris (3-mercaptopropionate) (TMMP), tris-[(3-mercaptopropionyloxy) -ethyl] -Mercapto groups per molecule, such as isocyanurate (TEMPIC) A trifunctional thiol compound having three; a tetrafunctional thiol compound having four mercapto groups per molecule, such as pentaerythritol tetrakis (3-mercaptobutyrate), pentaerythritol tetrakis (3-mercaptopropionate) (PEMP); 6-functional thiol compound having 6 mercapto groups per molecule, such as dipentaerythritol hexakis (3-mercaptopropionate) (DPMP). Moreover, a polyfunctional thiol compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  As the polyfunctional thiol compound, those having 3 or more mercapto groups per molecule are preferable from the viewpoint of preventing swelling of the electrode active material layer due to charge / discharge. Further, from the viewpoint of enhancing the binding property between the polymer particles (A), the electrode active material and the current collector, those having 4 or less mercapto groups per molecule are preferable. Therefore, among the polyfunctional thiol compounds described above, trifunctional thiol compounds and tetrafunctional thiol compounds are preferable.

  When the polymer particles (A) are used in the negative electrode binder composition, the ratio of the polyfunctional thiol compound in the monomer composition (a) is usually 0 with respect to 100 parts by weight of the (meth) acrylate compound. 0.001 part by weight or more, preferably 0.01 part by weight or more, more preferably 0.1 part by weight or more, and usually 10 parts by weight or less, preferably 5 parts by weight or less, more preferably 3 parts by weight or less. By making the ratio of a polyfunctional thiol compound more than the lower limit of the said range, the binding property of a polymer particle (A), an electrode active material, and a collector can be improved. Moreover, the swelling of the electrode active material layer accompanying charging / discharging can be prevented by setting it as an upper limit or less.

(Any polymerizable monomer)
When the polymer particles (A) are used in a binder composition for a negative electrode, the monomer composition (a) is an arbitrary polymerizable monomer that can be copolymerized with a (meth) acrylate compound and a polyfunctional thiol compound. May contain body. Arbitrary polymerizable monomers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Examples thereof include a polyfunctional vinyl compound, a monomer having a hydrophilic group, and a monomer having a reactive functional group.

・ Polyfunctional vinyl compounds:
A polyfunctional vinyl compound refers to a compound having two or more vinyl groups per molecule. In the polymer particles (A), usually, a crosslinked structure or a branched structure is formed by this polyfunctional vinyl compound. Due to such a crosslinked structure or branched structure, the resulting polymer particles (A) are excellent in toughness and strength. Thereby, the binding property of the polymer particles (A) can be improved and the binding force of the negative electrode active material by the polymer particles (A) can be improved, so that the cutting of the conductive path due to charge / discharge can be suppressed. Therefore, it is possible to effectively improve the cycle characteristics of the lithium ion secondary battery.

  Examples of the polyfunctional vinyl compound include divinylbenzene, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, and 1,6-hexanediol. A bifunctional vinyl compound having two vinyl groups per molecule, such as di (meth) acrylate and diallyl phthalate; trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, aliphatic tri (meth) acrylate, Trifunctional vinyl compounds having three vinyl groups per molecule such as trivinylcyclohexane; pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate Tetrafunctional vinyl compounds having four vinyl groups per molecule such as aliphatic tetra (meth) acrylate; vinyl groups per molecule such as dipentaerythritol penta (meth) acrylate and dipentaerythritol hexa (meth) acrylate And (meth) acrylates having a polyester skeleton, a urethane skeleton or a phosphazene skeleton, and having two or more vinyl groups per molecule. Moreover, a polyfunctional vinyl compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  When the polymer particles (A) are used in the negative electrode binder composition, the ratio of the polyfunctional vinyl compound in the monomer composition (a) is preferably 100 parts by weight of the (meth) acrylate compound. 0.001 part by weight or more, more preferably 0.01 part by weight or more, particularly preferably 0.05 part by weight or more, preferably 10 parts by weight or less, more preferably 5 parts by weight or less, particularly preferably 3 parts by weight. It is as follows. By setting the ratio of the polyfunctional vinyl compound to be equal to or higher than the lower limit of the above range, the binding property between the electrode active material layer and the current collector can be enhanced. Moreover, the swelling of the electrode active material layer by charging / discharging can be effectively suppressed by being below an upper limit.

・ Monomer having a hydrophilic group:
Moreover, as an arbitrary polymerizable monomer, the monomer which has a hydrophilic group is mentioned, for example. Here, examples of the hydrophilic group include a carboxy group (—COOH group), a hydroxyl group (—OH group), a sulfonic acid group (—SO ₃ H group), —PO ₃ H ₂ group, —PO (OH) (OR ) Group (R represents a hydrocarbon group), a lower polyoxyalkylene group, and the like.

  Examples of the monomer having a carboxy group as a hydrophilic group include monocarboxylic acid and derivatives thereof; dicarboxylic acid and derivatives thereof, and acid anhydrides and derivatives thereof. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid. Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, β-diaminoacrylic acid Etc. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like. Examples of the acid anhydride of dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride and the like. Examples of dicarboxylic acid derivatives include halogenated maleic acids such as chloromaleic acid, dichloromaleic acid, and fluoromaleic acid; methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, methylallyl maleate, diphenylmaleate, nonylmaleate, And maleate esters such as decyl maleate, dodecyl maleate, octadecyl maleate and fluoroalkyl maleate.

Examples of the monomer having a hydroxyl group as a hydrophilic group include ethylenically unsaturated alcohols such as (meth) allyl alcohol, 3-buten-1-ol, and 5-hexen-1-ol; acrylic acid-2-hydroxy Ethyl, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, di-2 itaconate - such as hydroxypropyl, alkanol esters of ethylenically unsaturated carboxylic acids; formula ^{_{CH 2 = CR 1 -COO- (C}} n H 2n O) m -H (m is an integer of 2 to 9, n is 2 represents to 4 integer, R ¹ is represented by the representative.) hydrogen or a methyl group, a polyalkylene glycol and a (meth) acrylic acid Esters; mono (meth) acrylic esters of dihydroxy esters of dicarboxylic acids, such as 2-hydroxyethyl-2 ′-(meth) acryloyloxyphthalate, 2-hydroxyethyl-2 ′-(meth) acryloyloxysuccinate Vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; (meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl-3-hydroxypropyl ether; Examples of alkylene glycol such as (meth) allyl-2-hydroxybutyl ether, (meth) allyl-3-hydroxybutyl ether, (meth) allyl-4-hydroxybutyl ether, (meth) allyl-6-hydroxyhexyl ether (Meth) allyl ethers; polyoxyalkylene glycol (meth) monoallyl ethers such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether; glycerin mono (meth) allyl ether, (meth) allyl Mono (meth) allyl ethers of halogens and hydroxy substituents of (poly) alkylene glycols, such as 2-chloro-3-hydroxypropyl ether, (meth) allyl-2-hydroxy-3-chloropropyl ether; eugenol, iso Mono (meth) allyl ethers of polyhydric phenols such as eugenol and halogen-substituted products thereof; alkylene glycols such as (meth) allyl-2-hydroxyethylthioether and (meth) allyl-2-hydroxypropylthioether ( Data) allyl thioether compound; and the like.

  Examples of the monomer having a sulfonic acid group as a hydrophilic group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, (meth) acrylic acid-2-ethyl sulfonate, 2 -Acrylamide-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, etc. are mentioned.

Examples of the monomer having a —PO ₃ H ₂ group or —PO (OH) (OR) group (R represents a hydrocarbon group) as the hydrophilic group include, for example, phosphate-2- (meth) acryloyloxy phosphate Examples include ethyl, methyl-2- (meth) acryloyloxyethyl phosphate, and ethyl phosphate- (meth) acryloyloxyethyl phosphate.

Examples of the monomer having a lower polyoxyalkylene group as a hydrophilic group include poly (alkylene oxide) such as poly (ethylene oxide).
Moreover, the monomer which has a hydrophilic group may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  When the polymer particles (A) are used in the negative electrode binder composition, the proportion of the monomer having a hydrophilic group in the monomer composition (a) is preferably 2% by weight or more, more preferably 3% by weight. % Or more, particularly preferably 5% by weight or more, preferably 20% by weight or less, more preferably 15% by weight or less, and particularly preferably 10% by weight or less. By making the ratio of the monomer having a hydrophilic group equal to or higher than the lower limit of the above range, the binding property between the polymer particles (A) and the negative electrode active material or current collector can be further improved. Moreover, the binder composition excellent in lithium ion conductivity can be obtained. Moreover, the particle stability at the time of superposition | polymerization of a polymer particle (A) can be made excellent by making it into an upper limit or less.

-Monomers having reactive functional groups:
As an arbitrary polymerizable monomer, the monomer which has a reactive functional group is mentioned, for example. Here, examples of the reactive functional group include a thermally crosslinkable group. Examples of the monomer having a heat-crosslinkable crosslinkable group include a monomer having an epoxy group, a monomer having an N-methylolamide group, a monomer having an oxetanyl group, and a monomer having an oxazoline group. Examples include the body. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The proportion of the monomer having a reactive functional group in the monomer composition (a) is preferably 0.1% by weight or more, preferably 10% by weight or less, more preferably 5% by weight or less. By keeping the ratio of the monomer having a reactive functional group within the above range, elution of the polymer particles (A) into the electrolytic solution is suppressed, and an excellent swelling suppressing effect is obtained.

・ Other monomers:
Furthermore, as an arbitrary polymerizable monomer, for example, styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl Styrene monomers such as styrene and divinylbenzene; amide monomers such as acrylamide and methacrylamide; α, β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; olefins such as ethylene and propylene; butadiene, Diene-based monomers such as isoprene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether Of vinyl ethers; vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; heterocycle-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine, and vinyl imidazole; It is done. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

(Method for producing polymer particles (A) for negative electrode)
The polymer particles (A) can be obtained by polymerizing the monomer composition (a) described above in an aqueous medium. Since the monomer contained in the monomer composition (a) is polymerized by polymerization, the polymer particles (A) are obtained in a state of being dispersed in the aqueous medium.

  The aqueous medium may be any as long as the desired polymer particles (A) can be obtained, but usually the boiling point at normal pressure is usually 80 ° C. or higher, preferably 100 ° C. or higher, and usually 350 ° C. or lower, preferably Uses an aqueous medium of 300 ° C. or lower. Examples of such an aqueous medium include water; ketones such as diacetone alcohol and γ-butyrolactone; alcohols such as ethyl alcohol, isopropyl alcohol and normal propyl alcohol; propylene glycol monomethyl ether, methyl cellosolve, ethyl cellosolve, ethylene Glycol ethers such as glycol tertiary butyl ether, butyl cellosolve, 3-methoxy-3-methyl-1-butanol, ethylene glycol monopropyl ether, diethylene glycol monobutyl pyrether, triethylene glycol monobutyl ether, dipropylene glycol monomethyl ether; Examples include ethers such as 3-dioxolane, 1,4-dioxolane, and tetrahydrofuran. Among these, water is particularly preferable from the viewpoint that it is not flammable and a dispersion of polymer particles (A) can be easily obtained. In addition, one type of aqueous medium may be used alone, or two or more types may be used in combination at any ratio. For example, water may be used as the main solvent, and an aqueous medium other than water described above may be mixed and used within a range in which the dispersion state of the polymer particles (A) can be ensured.

The polymerization method of the monomer composition (a) is not limited as long as the desired polymer particles (A) can be obtained, but the polymerization is usually carried out by an emulsion polymerization method. In emulsion polymerization, the monomer composition (a) is polymerized in an aqueous medium, preferably in the presence of an emulsifier.
Any emulsifier can be used as long as the desired polymer particles (A) can be obtained. Examples thereof include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium dodecyldiphenyl ether disulfonate, sodium dialkyl ester sulfonate succinate and the like. Is mentioned. Further, for example, a reactive emulsifier having an unsaturated bond may be used. Among them, sodium dodecyl diphenyl ether disulfonate is preferable from the viewpoint of versatility during production and less foaming. Moreover, an emulsifier may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The amount of the emulsifier is arbitrary as long as the desired polymer particles (A) can be obtained. 15 parts by weight or more, particularly preferably 0.2 parts by weight or more, preferably 10.0 parts by weight or less, more preferably 5 parts by weight or less, and particularly preferably 2.5 parts by weight or less. By keeping the amount of the emulsifier within the above range, the polymerization reaction can proceed stably.

  In the polymerization reaction, a polymerization initiator is usually used. Any polymerization initiator can be used as long as the desired polymer particles (A) are obtained. Examples thereof include sodium persulfate (NaPS), ammonium persulfate (APS), and potassium persulfate (KPS). Is mentioned. Of these, sodium persulfate and ammonium persulfate are preferable, and ammonium persulfate is more preferable. By using ammonium persulfate or sodium persulfate as a polymerization initiator, it is possible to suppress a decrease in cycle characteristics of the obtained lithium ion secondary battery.

  The amount of the polymerization initiator is arbitrary as long as the desired polymer particles (A) can be obtained, and is preferably 0.5 parts by weight or more, more preferably, 100 parts by weight of the monomer composition (a). It is 0.6 parts by weight or more, particularly preferably 0.7 parts by weight or more, preferably 2.5 parts by weight or less, more preferably 2.0 parts by weight or less, and particularly preferably 1.5 parts by weight or less. By keeping the amount of the polymerization initiator in the above range, it is possible to prevent the binder composition and the slurry composition from thickening and obtain a stable binder composition and slurry composition.

  When the monomer composition (a) is polymerized, the polymerization system may contain a molecular weight modifier or a chain transfer agent. However, the above-mentioned polyfunctional thiol compound is not included in the molecular weight modifier or the chain transfer agent. Examples of the molecular weight adjusting agent or chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan; dimethylxanthogen disulfide Xanthogen compounds such as diisopropylxanthogen disulfide; terpinolene; thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide; 2,6-di-t-butyl-4-methylphenol, styrenated phenol Phenolic compounds such as allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide; Cholic acid, thiomalate, 2-ethylhexyl thioglycolate, diphenylethylene, alpha-methyl styrene dimer; and the like. Among these, from the viewpoint of suppressing side reactions, alkyl mercaptans are preferable, and t-dodecyl mercaptan is more preferable. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The amount of the molecular weight modifier or chain transfer agent is arbitrary as long as the desired polymer particles (A) can be obtained, and preferably 0 parts by weight or more and 5 parts by weight with respect to 100 parts by weight of the monomer composition (a). Part or less, more preferably 0 part by weight or more and 2.0 parts by weight or less.

  Further, when the monomer composition (a) is polymerized, the polymerization system may contain a surfactant. The type of the surfactant is arbitrary as long as the desired polymer particles (A) can be obtained, and is any one of an anionic surfactant, a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant. Also good. For example, examples of the anionic surfactant include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecyl sulfate, ammonium dodecyl sulfate, sodium octyl sulfate, sodium decyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium Sulfate salts of higher alcohols such as octadecyl sulfate; alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, sodium laurylbenzenesulfonate, sodium hexadecylbenzenesulfonate; sodium laurylsulfonate, sodium dodecylsulfonate, tetradecylsulfonic acid Aliphatic sulfonates such as sodium; etc. And the like. Moreover, surfactant may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The amount of the surfactant is arbitrary as long as the desired polymer particles (A) are obtained, and is preferably 0.5 parts by weight or more, more preferably 100 parts by weight of the monomer composition (a). 1 part by weight or more, preferably 10 parts by weight or less, more preferably 5 parts by weight or less.

  Further, when the monomer composition (a) is polymerized, the polymerization system may contain any additive other than those described above as long as the desired polymer particles (A) are obtained. Good. Examples of optional additives include pH adjusters such as sodium hydroxide and ammonia; dispersants; chelating agents; oxygen scavengers; builders; seed latexes for particle size adjustment. In particular, emulsion polymerization using a seed latex is preferable. The seed latex refers to a dispersion of fine particles (seed particles) that become the core of the reaction during emulsion polymerization. The fine particles often have a particle size of 100 nm or less. The fine particles are not particularly limited, and for example, general-purpose polymer particles such as an acrylic polymer can be used. By using seed latex, polymer particles (A) having a relatively uniform particle diameter can be obtained. Moreover, arbitrary additives may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  When the monomer composition (a) is polymerized, the polymerization temperature and polymerization time can be arbitrarily selected depending on the polymerization method and the type of polymerization initiator. Usually, the polymerization temperature is about 30 ° C. or more, and the polymerization time is about 0.5 to 30 hours.

By the polymerization, a dispersion liquid containing an aqueous medium and polymer particles (A) dispersed in the aqueous medium is obtained. At this time, the obtained dispersion is mixed with, for example, alkali metal (for example, Li, Na, K, Rb, Cs) hydroxide, ammonia, inorganic ammonium compound (for example, NH ₄ Cl), organic amine compound (for example, ethanol). The pH may be adjusted by mixing with a basic aqueous solution containing amine, diethylamine and the like. At this time, the pH after adjustment is preferably 5 or more, preferably 10 or less, more preferably 9 or less. Especially, adjustment of pH with an alkali metal hydroxide is preferable because the binding property between the current collector and the electrode active material layer can be improved.

  The obtained polymer particles (A) may be taken out from the aqueous medium. However, usually, the polymer particles (A) dispersed in the aqueous medium are used for the production of the binder composition or the slurry composition without being taken out from the aqueous medium.

(Physical properties of polymer particles (A) for negative electrode)
In the binder composition for a negative electrode, the number average particle diameter of the polymer particles (A) is preferably 50 nm or more, more preferably 70 nm or more, preferably 500 nm or less, more preferably 400 nm or less. By keeping the number average particle diameter of the polymer particles (A) within the above range, the strength and flexibility of the electrode can be improved.

  In the binder composition for a negative electrode, the gel amount of the polymer particles (A) is preferably 70% or more, more preferably 80% or more, preferably 98% or less, more preferably 95% or less. Here, the gel amount of the polymer particles (A) is a value representing the weight ratio of components insoluble in tetrahydrofuran in the polymer particles (A). The gel amount of the polymer particles (A) can be an index indicating the degree of crosslinking of the polymer particles (A). By setting the gel amount of the polymer particles (A) to be equal to or higher than the lower limit of the above range, swelling of the polymer particles (A) into the electrolytic solution can be suppressed and swelling of the electrodes can be prevented. Moreover, it can prevent that a polymer particle (A) becomes too soft, and can make binding property high. Moreover, since it can prevent that a polymer particle (A) becomes too hard by setting it as an upper limit or less, a binding property can also be made high by this. Therefore, the binding property between the electrode active material layer and the current collector can be improved, and battery characteristics such as cycle characteristics can be improved.

The method for measuring the gel amount of the polymer particles (A) is as follows.
A dispersion containing polymer particles (A) and an aqueous medium is prepared, and the dispersion is dried in an environment of 50% humidity and 23 ° C. to 25 ° C. to produce a film having a thickness of 3 ± 0.3 mm. The produced film is cut into 5 mm squares to prepare film pieces. About 1 g of these film pieces is precisely weighed. Let the weight of the precisely weighed film piece be W0. This film piece is immersed in 100 g of tetrahydrofuran (THF) for 24 hours. Thereafter, the film piece is lifted from THF. The pulled film piece is vacuum-dried at 105 ° C. for 3 hours, and its weight (insoluble content weight) W1 is measured. Then, the gel amount (%) is calculated according to the following formula.
Gel amount (%) = W1 / W0 × 100

  The gel amount of the polymer particles can be controlled by adjusting, for example, the type and amount of the monomer; the polymerization temperature of the polymer particle; the type and amount of the molecular weight modifier or the chain transfer agent.

  In the binder composition for the negative electrode, the glass transition temperature of the polymer particles (A) is preferably −80 ° C. or higher, more preferably −70 ° C. or higher, particularly preferably −60 ° C. or higher, preferably 20 ° C. or lower. More preferably, it is 10 ° C. or less, particularly preferably 0 ° C. or less. By setting the glass transition temperature of the polymer particles (A) to be equal to or higher than the lower limit of the above range, it is possible to suppress the swelling of the electrode during charging and improve the cycle characteristics. Moreover, since the binding property of a polymer particle (A) can be improved by setting it as an upper limit or less, a cycle characteristic can also be improved by this.

The glass transition temperature of the polymer particles (A) can be measured by a differential scanning calorimetry measurement method (DSC measurement method). In this case, the glass transition temperature of the polymer particles (A) is usually measured as a single peak glass transition temperature. A specific method for measuring the glass transition temperature is as follows.
A dispersion containing polymer particles (A) in an aqueous medium is prepared, and this dispersion is dried in an environment of 50% humidity and 23 ° C. to 25 ° C. for 3 days to produce a film. The film is dried in a hot air oven at 120 ° C. for 1 hour. Thereafter, the dried film can be measured using a differential scanning calorimeter, for example, according to JIS K7121. As the differential scanning calorimeter, for example, DSC6220SII manufactured by Nanotechnology can be used. The measurement conditions can be set at a measurement temperature of −100 ° C. to 180 ° C. and a temperature increase rate of 5 ° C./min.

  The glass transition temperature of the polymer particles can be controlled, for example, by adjusting the type and amount of the monomer.

[1.1.2. Solvent of binder composition for negative electrode]
The binder composition contains a solvent in addition to the polymer particles (A) described above. Usually, in the binder composition, the polymer particles (A) are dispersed in a solvent, and the binder composition is a fluid composition. As this solvent, the same solvent as that used in the production of the polymer particles (A) can be used. Among these, it is preferable to use water. Moreover, a solvent may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The amount of the solvent in the binder composition is such that the solid content concentration of the binder composition is usually 15% by weight or more, preferably 20% by weight or more, more preferably 30% by weight or more, and usually 70% by weight or less, preferably 65%. It is made to be not more than wt%, more preferably not more than 60 wt%. When the solid content concentration is within this range, the workability in producing the slurry composition is good. Here, the solid content of the composition means a component that remains without being evaporated when the composition is dried to remove the liquid.

[1.1.3. Optional component of binder composition for negative electrode]
Unless the effect of this invention is impaired remarkably, a binder composition may contain arbitrary components other than a polymer particle (A) and a solvent. When the example of the arbitrary component which the binder composition for negative electrodes may contain is given, the example similar to the arbitrary component which the slurry composition for negative electrodes of this invention mentioned later may contain is mentioned. Moreover, the binder composition may contain any component alone, or may contain two or more components in combination at any ratio.

[1.1.4. Method for producing binder composition for negative electrode]
There is no restriction | limiting in the manufacturing method of the binder composition for negative electrodes. For example, when the aqueous medium used at the time of producing the polymer particles (A) is used as a solvent for the binder composition, a dispersion containing the polymer particles (A) obtained by producing the polymer particles (A) is used. It may be used as a binder composition. In addition, for example, when a liquid other than the aqueous medium used in the production of the polymer particles (A) is used as a solvent for the binder composition, the polymer particles (A) obtained by the production of the polymer particles (A) Substrate may be subjected to solvent substitution. Further, for example, the polymer particles (A) are taken out from the dispersion containing the polymer particles (A) obtained by the production of the polymer particles (A), and the taken out polymer particles (A) are mixed with a desired solvent. May be.

[1.2. Binder composition for positive electrode]
The binder composition for a positive electrode includes polymer particles (A) for a positive electrode and a solvent.

[1.2.1. Polymer particles for positive electrode (A)]
The polymer particle (A) for the positive electrode is obtained by mixing the monomer composition (a) containing the (meth) acrylic acid ester compound and the polyfunctional thiol compound in the aqueous medium, like the polymer particle (A) for the negative electrode. It is the particle | grains of the polymer obtained by superposing | polymerizing with.

((Meth) acrylic acid ester compound)
The (meth) acrylic acid ester compound may use only the acrylic acid ester compound, or may use only the methacrylic acid ester compound, as described in the section of the binder composition for the negative electrode. And a methacrylic acid ester compound may be used in combination. By using the (meth) acrylic acid ester compound, the same advantage as the (meth) acrylic acid ester compound described in the section of the binder composition for the negative electrode can be obtained.

  Examples of the (meth) acrylic acid ester compound include the same examples as those given in the section of the negative electrode binder composition. Moreover, a (meth) acrylic acid ester compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  When the polymer particles (A) are used in a positive electrode binder composition, among the (meth) acrylic acid ester compounds, those having 2 or more carbon atoms in the alkyl group bonded to the non-carbonyl oxygen atom are preferable. 4 or more are more preferable, 8 or more are particularly preferable, 13 or less are preferable, and 10 or less are more preferable. By using such a (meth) acrylic acid ester compound, polymer particles (A) that can be appropriately swollen into the electrolyte without being eluted into the electrolyte can be realized, so that the conductivity of lithium ions in the electrode active material layer can be realized. Can be high. Further, in the polymer particles (A) using such a (meth) acrylic acid ester compound, the electrode active material is unlikely to cause bridging and aggregation by the polymer particles (A) in the electrode active material layer. From this point of view, specific examples of (meth) acrylic acid ester compounds suitable for positive electrode applications include ethyl acrylate, butyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, and lauryl acrylate. In particular, octyl acrylate, 2-ethylhexyl acrylate, and nonyl acrylate are preferable. These may be used alone or in combination of two or more at any ratio.

  Moreover, when using polymer particle (A) in the binder composition for positive electrodes, the ratio of the (meth) acrylic acid ester compound in a monomer composition (a) becomes like this. Preferably it is 50 weight% or more, More preferably, it is 60. % By weight or more, preferably 95% by weight or less, more preferably 90% by weight or less. By setting the ratio of the (meth) acrylic acid ester compound to be equal to or higher than the lower limit of the above range, the binding property between the polymer particles (A), the negative electrode active material and the current collector can be further increased. Moreover, the binder composition excellent in lithium ion conductivity can be obtained. Moreover, the particle stability at the time of superposition | polymerization of a polymer particle (A) can be made excellent by making it into an upper limit or less.

(Polyfunctional thiol compound)
As a polyfunctional thiol compound, the thing similar to the description in the term of the binder composition for negative electrodes can be used. By using a polyfunctional thiol compound, the advantage by the polyfunctional thiol compound similar to having demonstrated by the term of the binder composition for negative electrodes is acquired.

  As a polyfunctional thiol compound, the same example as what was mentioned by the term of the binder composition for negative electrodes is mentioned, for example. Moreover, a polyfunctional thiol compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In the positive electrode application, as in the negative electrode application, the polyfunctional thiol compound preferably has three or more mercapto groups per molecule from the viewpoint of preventing swelling of the electrode active material layer accompanying charge / discharge. . Further, from the viewpoint of enhancing the binding property between the polymer particles (A), the electrode active material and the current collector, those having 4 or less mercapto groups per molecule are preferable. Therefore, among the polyfunctional thiol compounds described above, trifunctional thiol compounds and tetrafunctional thiol compounds are preferable.

  When the polymer particles (A) are used in the positive electrode binder composition, the ratio of the polyfunctional thiol compound in the monomer composition (a) is usually 0 with respect to 100 parts by weight of the (meth) acrylic acid ester compound. 0.001 part by weight or more, preferably 0.01 part by weight or more, more preferably 0.1 part by weight or more, and usually 10 parts by weight or less, preferably 5 parts by weight or less, more preferably 3 parts by weight or less. By making the ratio of a polyfunctional thiol compound more than the lower limit of the said range, the binding property of a polymer particle (A), an electrode active material, and a collector can be improved. Moreover, the swelling of the electrode active material layer accompanying charging / discharging can be prevented by setting it as an upper limit or less.

(Any polymerizable monomer)
When the polymer particles (A) are used in a positive electrode binder composition, the monomer composition (a) is an arbitrary polymerizable monomer that can be copolymerized with a (meth) acrylate compound and a polyfunctional thiol compound. May contain body. Arbitrary polymerizable monomers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Examples thereof include a polyfunctional vinyl compound, a vinyl monomer having an acidic group, a monomer having a reactive functional group, and an α, β-unsaturated nitrile compound.

・ Polyfunctional vinyl compounds:
As a polyfunctional vinyl compound, the same thing as the description in the term of the binder composition for negative electrodes can be used. By using the polyfunctional vinyl compound, advantages similar to those explained in the section of the binder composition for the negative electrode can be obtained.

  As a polyfunctional vinyl compound, the same example as what was mentioned by the term of the binder composition for negative electrodes is mentioned, for example. Moreover, a polyfunctional vinyl compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  When the polymer particles (A) are used in the binder composition for the positive electrode, the ratio of the polyfunctional vinyl compound in the monomer composition (a) is preferably based on 100 parts by weight of the (meth) acrylic acid ester compound. It is 0.01 parts by weight or more, more preferably 0.05 parts by weight or more, preferably 5 parts by weight or less, more preferably 3 parts by weight or less. By setting the ratio of the polyfunctional vinyl compound to be equal to or higher than the lower limit of the above range, the binding property between the electrode active material layer and the current collector can be enhanced. Moreover, the swelling of the electrode active material layer by charging / discharging can be effectively suppressed by being below an upper limit.

・ Vinyl monomer having acidic group:
In the vinyl monomer having an acidic group, examples of the acidic group include the same hydrophilic groups as those mentioned in the section of the binder composition for a negative electrode.
Examples of the monomer having an acidic group include the same examples as those of the monomer having a hydrophilic group mentioned in the section of the binder composition for a negative electrode.
Here, the monomer which has an acidic group may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In particular, when the polymer particles (A) are used in a binder composition for a positive electrode, the adhesiveness to the current collector is excellent, and cobalt ions and manganese ions eluted from the positive electrode active material can be efficiently captured. For this reason, a monomer having a carboxy group is preferable, for example, a monocarboxylic acid having a carboxy group having 5 or less carbon atoms such as acrylic acid and methacrylic acid, and 5 carbon atoms such as maleic acid and itaconic acid. The following dicarboxylic acids having two carboxy groups are preferred. Acrylic acid and methacrylic acid are preferred from the viewpoint of high storage stability of the polymer particles (A).

  Further, when the polymer particles (A) are used in the binder composition for the positive electrode, the ratio of the vinyl monomer having an acidic group in the monomer composition (a) is preferably 1% by weight or more, more preferably It is 1.5% by weight or more, preferably 4% by weight or less, more preferably 3% by weight or less, and particularly preferably 2.5% by weight or less. By setting the ratio of the monomer having an acidic group to be equal to or higher than the lower limit of the above range, the binding property of the polymer particles (A) can be improved and the electrode active material can be prevented from falling off from the current collector. Moreover, by making it into an upper limit or less, the capture | acquisition of lithium ion by the acidic group which a polymer particle (A) contains can be prevented, and an output characteristic and cycling characteristics can be improved.

-Monomers having reactive functional groups:
As the monomer having a reactive functional group, those described in the section of the binder composition for the negative electrode can be used. Here, the monomer which has a reactive functional group may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  When the polymer particles (A) are used in the binder composition for the positive electrode, the ratio of the monomer having a reactive functional group in the monomer composition (a) is preferably 0.1% by weight or more, Preferably it is 10 weight% or less, More preferably, it is 5 weight% or less. By keeping the ratio of the monomer having a reactive functional group within the above range, elution of the polymer particles (A) into the electrolytic solution is suppressed, and an excellent swelling suppressing effect is obtained.

Α, β-unsaturated nitrile compound:
The binder composition for positive electrodes may contain, for example, an α, β-unsaturated nitrile compound as an optional polymerizable monomer. By using the α, β-unsaturated nitrile compound, the degree of swelling of the polymer particles (A) into the electrolytic solution can be appropriately controlled, and the oxidation resistance can be enhanced. Examples of the α, β-unsaturated nitrile compound include acrylonitrile and methacrylonitrile. Moreover, an alpha, beta-unsaturated nitrile compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  When the polymer particles (A) are used in a positive electrode binder composition, the proportion of the α, β-unsaturated nitrile compound in the monomer composition (a) is preferably 3% by weight or more, more preferably 5% by weight. % Or more, preferably 40% by weight or less, more preferably 30% by weight or less. By making the ratio of the α, β-unsaturated nitrile compound equal to or higher than the lower limit of the above range, the oxidation resistance of the polymer particles (A) can be improved. Moreover, the swelling property to the electrolyte solution of a polymer particle (A) can be moderately controlled by making it into an upper limit or less.

(Method for producing polymer particles (A) for positive electrode)
The polymer particles (A) for the positive electrode can be obtained by polymerizing the monomer composition (a) described above in an aqueous medium, like the polymer particles (A) for the negative electrode. At this time, the type and amount of the aqueous solvent, the polymerization method, the types and amounts of additives (for example, emulsifier, polymerization initiator, molecular weight modifier, chain transfer agent, surfactant, etc.) that can be used during the polymerization, and the reaction conditions, It can be performed in the same manner as the production method of the polymer particles (A) for the negative electrode.

  The monomer contained in the monomer composition (a) is polymerized by polymerization. Thereby, the dispersion liquid containing an aqueous medium and the polymer particle (A) disperse | distributed in the said aqueous medium is obtained. Under the present circumstances, you may adjust pH of the obtained dispersion liquid like the manufacturing method of the polymer particle (A) for negative electrodes. At this time, the pH after adjustment is preferably 5 or more, preferably 10 or less, more preferably 9 or less. Especially, adjustment of pH with an alkali metal hydroxide is preferable because the binding property between the current collector and the electrode active material layer can be improved.

  The obtained polymer particles (A) may be taken out from the aqueous medium. However, usually, the polymer particles (A) dispersed in the aqueous medium are used for the production of the binder composition or the slurry composition without being taken out from the aqueous medium.

(Physical properties of polymer particles (A) for positive electrode)
In the positive electrode binder composition, the number average particle diameter of the polymer particles (A) is preferably 50 nm or more, more preferably 70 nm or more, preferably 500 nm or less, more preferably 400 nm or less. By keeping the number average particle diameter of the polymer particles (A) within the above range, the strength and flexibility of the electrode can be improved.

  In the binder composition for the positive electrode, the glass transition temperature of the polymer particles (A) is preferably −60 ° C. or higher, more preferably −50 ° C. or higher, particularly preferably −40 ° C. or higher, preferably 40 ° C. or lower. More preferably, it is 30 degrees C or less, Most preferably, it is 20 degrees C or less. By setting the glass transition temperature of the polymer particles (A) to be equal to or higher than the lower limit of the above range, it is possible to suppress electrode swelling during charging and improve cycle characteristics. Moreover, since the binding property of a polymer particle (A) can be improved by setting it as an upper limit or less, a cycle characteristic can also be improved by this.

[1.2.2. Solvent of binder composition for positive electrode]
The binder composition contains a solvent in addition to the polymer particles (A) described above. The solvent for the positive electrode binder composition can be the same as the negative electrode binder composition in any of the types and amounts.

[1.2.3. Arbitrary component of binder composition for positive electrode]
Unless the effect of this invention is impaired remarkably, a binder composition may contain arbitrary components other than a polymer particle (A) and a solvent. When the example of the arbitrary components which the binder composition for positive electrodes may contain is given, the example similar to the arbitrary components which the slurry composition for positive electrodes of this invention mentioned later may contain is mentioned. Moreover, the binder composition may contain any component alone, or may contain two or more components in combination at any ratio.

[1.2.4. Method for producing binder composition for positive electrode]
There is no restriction | limiting in the manufacturing method of the binder composition of this invention. For example, the binder composition for the positive electrode can be produced in the same manner as the binder composition for the negative electrode.

[2. Slurry composition for lithium ion secondary battery electrode]
The lithium ion secondary battery electrode slurry composition of the present invention includes the above-described binder composition and electrode active material. That is, the slurry composition of this invention contains a polymer particle (A), an electrode active material, and a solvent. Hereinafter, the slurry composition will be described for each of the negative electrode and the positive electrode.

[2.1. Slurry composition for negative electrode]
The slurry composition for negative electrodes contains the negative electrode active material which is an electrode active material for negative electrodes, the polymer particle (A) for negative electrodes, and a solvent.

[2.1.1. Negative electrode active material]
The negative electrode active material is an electrode active material for a negative electrode, and is a material that can transfer electrons in the negative electrode of a lithium ion secondary battery. As such a negative electrode active material, a material that can occlude and release lithium is usually used.

  An example of a suitable negative electrode active material is a negative electrode active material formed of carbon. Examples of the negative electrode active material formed of carbon include natural graphite, artificial graphite, and carbon black. Among them, graphite such as artificial graphite and natural graphite is preferable, and natural graphite is particularly preferable.

  Another example of a suitable negative electrode active material is a negative electrode active material containing a metal. In particular, a negative electrode active material containing at least one selected from the group consisting of tin, silicon, germanium and lead is preferable. The negative electrode active material containing these elements can reduce the irreversible capacity.

  Among the negative electrode active materials containing these metals, a negative electrode active material containing silicon is preferable. By using a negative electrode active material containing silicon, the electric capacity of the lithium ion secondary battery can be increased. In general, a negative electrode active material containing silicon expands and contracts greatly (for example, about 5 times) with charge and discharge. However, in a negative electrode produced using the slurry composition of the present invention, a negative electrode active material containing silicon is used. It is possible to effectively suppress a decrease in battery performance due to the expansion and contraction of the substance.

Examples of the negative electrode active material containing silicon include a compound containing silicon and silicon metal. The compound containing silicon is a compound of silicon and another element, and examples thereof include SiO, SiO ₂ , SiO _x (0.01 ≦ x <2), SiC, and SiOC. Among these, SiO _x , SiOC, and SiC are preferable, SiO _x and SiOC are more preferable from the viewpoint of battery life, and SiO _x is particularly preferable from the viewpoint of suppressing swelling of the negative electrode. Here, SiO _x is a compound that can be formed from one or both of SiO and SiO ₂ and metallic silicon. This SiO _x can be produced, for example, by cooling and precipitating silicon monoxide gas generated by heating a mixture of SiO ₂ and metal silicon.

Among the negative electrode active materials, silicon-containing compounds and graphite are preferable because of a good balance between high capacity and life characteristics of the lithium ion secondary battery. More preferred are graphite, SiO _x , SiOC and SiC, and particularly preferred are graphite and SiO _x .

  Further, when a silicon-containing compound is used as the negative electrode active material, the ratio of the silicon-containing compound in the negative electrode active material is preferably 1% by weight or more, more preferably 5% by weight or more, and particularly preferably 10% by weight. % Or more, preferably 50% by weight or less, more preferably 40% by weight or less, and particularly preferably 30% by weight or less. The capacity of the lithium ion secondary battery can be increased by setting the ratio of the compound containing silicon to the lower limit value or more of the above range. Moreover, the swelling of a negative electrode can be suppressed by making it below an upper limit.

  Moreover, a negative electrode active material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, two or more kinds of the negative electrode active materials may be used in combination. Among these, it is preferable to use a negative electrode active material containing a combination of a negative electrode active material containing silicon and a negative electrode active material formed of carbon. When a combination of a negative electrode active material containing silicon and a negative electrode active material formed of carbon is used as the negative electrode active material, insertion and desorption of Li into the negative electrode active material containing silicon occurs at a high potential, and the low It is presumed that Li is inserted into and desorbed from the negative electrode active material formed of carbon at a potential. For this reason, since expansion and contraction are suppressed, the cycle characteristics of the lithium ion secondary battery can be improved.

  In the case where a negative electrode active material containing silicon and a negative electrode active material formed of carbon are used in combination, a negative electrode active material in which silicon and conductive carbon are combined may be used. By combining silicon and conductive carbon, swelling of the negative electrode active material itself can be suppressed. As a method of compounding, for example, a method of compounding a negative electrode active material containing silicon by coating with conductive carbon; and compounding by granulating a mixture containing a negative electrode active material containing silicon and conductive carbon And the like.

  The weight ratio of the negative electrode active material formed of carbon and the negative electrode active material containing silicon (“weight of negative electrode active material formed of carbon” / “weight of negative electrode active material containing silicon”) is preferably 50 / 50 or more, more preferably 70/30 or more, preferably 97/3 or less, more preferably 90/10 or less. Thereby, the cycling characteristics of a lithium ion secondary battery can be improved.

  The negative electrode active material is preferably sized in the form of particles. Here, when the shape of the negative electrode active material particles is spherical, a higher-density electrode can be formed at the time of forming the electrode.

  The volume average particle diameter of the particles of the negative electrode active material is appropriately selected in consideration of other constituent requirements of the secondary battery, preferably 0.1 μm or more, more preferably 1 μm or more, particularly preferably 5 μm or more, preferably Is 100 μm or less, more preferably 50 μm or less, and particularly preferably 20 μm or less. Here, the volume average particle diameter is a particle diameter at which the cumulative volume calculated from the small diameter side is 50% in the particle size distribution measured by the laser diffraction method.

The specific surface area of the negative electrode active material is usually 2 m ² / g or more, preferably 3 m ² / g or more, more preferably 5 m ² / g or more, and usually 20 m ² / g or less, preferably from the viewpoint of improving the output density. It is 15 m ² / g or less, more preferably 10 m ² / g or less. The specific surface area of the negative electrode active material can be measured by, for example, the BET method.

  The amount of the negative electrode active material is such that the ratio of the negative electrode active material in the electrode active material layer is preferably 90% by weight or more, more preferably 95% by weight or more, and preferably 99.9% by weight or less, more preferably 99% by weight. %. Thereby, the capacity | capacitance of a lithium ion secondary battery can be enlarged, and the softness | flexibility of a negative electrode and the binding property of a collector and an electrode active material layer can be improved.

[2.1.2. Polymer particle (A)]
In the negative electrode slurry composition, the polymer particles (A) described above in the section of the binder composition are used as the polymer particles (A). The polymer particles (A) are usually dispersed in the slurry composition. In particular, when an aqueous medium such as water is used as the solvent, the polymer particles (A) can be highly dispersed in the aqueous medium because the affinity of the polymer particles (A) to the aqueous medium is good. Therefore, the applicability of the slurry composition to the current collector can be improved.

  The amount of the polymer particles (A) in the slurry composition for the negative electrode is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, particularly preferably 0 with respect to 100 parts by weight of the negative electrode active material. 0.8 parts by weight or more, preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and particularly preferably 4 parts by weight or less. When the amount of the polymer particles (A) is within the above range, it is possible to stably prevent the negative electrode active material from dropping from the negative electrode without inhibiting the battery reaction.

[2.1.3. solvent]
As the solvent for the slurry composition, the same solvent as that for the binder composition can be usually used. Of these, water is preferred. Moreover, a solvent may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The amount of the solvent in the negative electrode slurry composition is preferably adjusted so that the slurry composition has a viscosity suitable for coating. Specifically, the concentration of the solid content of the slurry composition is preferably 40% by weight or more, more preferably 45% by weight or more, preferably 70% by weight or less, more preferably 65% by weight or less. Used by adjusting.

[2.1.4. Polymer particles (B)]
The slurry composition for the negative electrode may further contain polymer particles other than the polymer particles (A) in addition to the polymer particles (A), the electrode active material and the solvent. Especially, it is preferable that the slurry composition for negative electrodes contains a polymer particle (B). Here, the polymer particles (B) are polymer particles obtained by polymerizing a monomer composition (b) containing an aromatic vinyl compound and a conjugated diene compound in an aqueous medium. Combining the polymer particles (B) with the polymer particles (A) can suppress swelling of the electrode plate during charging and discharging of the negative electrode.

(Aromatic vinyl compound)
The aromatic vinyl compound is one of the monomers of the polymer particles (B). Since the structural unit formed by polymerizing the aromatic vinyl compound has high rigidity, the rigidity of the polymer particles (B) can be increased by using the aromatic vinyl compound. For this reason, the breaking strength of the polymer particles (B) can be improved. In addition, since the polymer particles (B) have high rigidity, even when the negative electrode active material repeatedly expands and contracts with charge and discharge, the polymer particles (B) do not impair contact with the negative electrode active material. It can contact the negative electrode active material. Therefore, the binding property of the polymer particles (B) to the negative electrode active material can be enhanced. In particular, when the charge and discharge are repeated, the effect of improving the binding property is remarkable. Further, since the polymer particles (B) have high rigidity, the negative electrode active material moved by the stress generated by expansion and contraction can be returned to the original position with a strong force. Therefore, even if the negative electrode active material repeatedly expands and contracts, the electrode active material layer can be made difficult to expand.

  Examples of the aromatic vinyl compound include styrene compounds such as styrene, α-methylstyrene, β-methylstyrene, pt-butylstyrene, and chlorostyrene. Moreover, an aromatic vinyl compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In the monomer composition (b), the proportion of the aromatic vinyl compound is preferably 10% by weight or more, more preferably 20% by weight or more, particularly preferably 40% by weight or more, preferably 90% by weight or less, More preferably, it is 80 weight% or less, Most preferably, it is 70 weight% or less. By setting the ratio of the aromatic vinyl compound to be equal to or higher than the lower limit of the above range, the swelling of the electrode active material layer due to charge / discharge can be effectively suppressed. Moreover, the binding property of a polymer particle (B) can be effectively improved by setting it as an upper limit or less.

(Conjugated diene compounds)
The conjugated diene compound is one of the monomers of the polymer particles (B). Since the structural unit formed by polymerizing the conjugated diene compound is flexible, the polymer particles (B) can be made flexible by using the conjugated diene compound. Furthermore, the binding property of the polymer particles (B) can be improved.

  Examples of the conjugated diene compound include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, piperylene and the like. Among these, 1,3-butadiene, isoprene and 2,3-dimethyl-1,3-butadiene are preferable, and 1,3-butadiene is particularly preferable. Moreover, a conjugated diene compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In the monomer composition (b), the proportion of the conjugated diene compound is preferably 10% by weight or more, more preferably 20% by weight or more, particularly preferably 30% by weight or more, and preferably 90% by weight or less. Preferably it is 80 weight% or less, Most preferably, it is 60 weight% or less. By keeping the ratio of the aromatic vinyl compound within the above range, swelling of the electrode active material layer due to charge / discharge can be effectively suppressed. Moreover, the binding property of the polymer particles (B) can be effectively increased.

  The weight ratio of the aromatic vinyl compound to the conjugated diene compound (aromatic vinyl compound / conjugated diene compound) is preferably 42/58 or more, more preferably 49/51 or more, and particularly preferably 55/45 or more. , Preferably 87/13 or less, more preferably 80/20 or less, and particularly preferably 70/30 or less. By setting the weight ratio to be equal to or higher than the lower limit of the range, it is possible to effectively suppress swelling of the electrode active material layer due to charge / discharge. Moreover, by making it below an upper limit, a negative electrode can be made flexible and the crack of a negative electrode can be suppressed.

(Any polymerizable monomer)
The monomer composition (b) may further contain any polymerizable monomer copolymerizable with the aromatic vinyl compound and the conjugated diene compound. Arbitrary polymerizable monomers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Examples of such an optional polymerizable monomer include a polyfunctional vinyl compound, an ethylenically unsaturated carboxylic acid monomer, and a hydroxyl group-containing monomer.

・ Polyfunctional vinyl compounds:
As a polyfunctional vinyl compound, the thing similar to what was mentioned in description of monomer composition (a) is mentioned, for example. In the polymer particles (B), a crosslinked structure or a branched structure is usually formed by a polyfunctional vinyl compound. Such a crosslinked structure or branched structure can improve the toughness of the polymer particles (B). Furthermore, since the binding property of the polymer particles (B) can be improved, cutting of the conductive path due to charge / discharge can be suppressed. Therefore, it is possible to effectively improve the cycle characteristics of the lithium ion secondary battery. Here, a polyfunctional vinyl compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In the monomer composition (b), the proportion of the polyfunctional vinyl compound is preferably 0.001 part by weight or more, more preferably 0.01 parts by weight with respect to 100 parts by weight of the total of the aromatic vinyl compound and the conjugated diene compound. It is at least 10 parts by weight, more preferably at most 5 parts by weight, particularly preferably at most 3 parts by weight. By setting the ratio of the polyfunctional vinyl compound to be equal to or higher than the lower limit of the above range, the binding property between the electrode active material layer and the current collector can be effectively enhanced. Moreover, the swelling of the electrode active material layer by charging / discharging can be effectively suppressed by being below an upper limit.

・ Ethylenically unsaturated carboxylic acid monomer:
Since the ethylenically unsaturated carboxylic acid monomer has a carboxy group (—COOH group), the polymer particles (B) have high polarity by using the ethylenically unsaturated carboxylic acid monomer. Thereby, the binding property of the polymer particles (B) can be further enhanced. Moreover, since the structural unit formed by polymerizing the ethylenically unsaturated carboxylic acid monomer has high strength, the strength of the polymer particles (B) is increased by using the ethylenically unsaturated carboxylic acid monomer. Thus, the binding property of the electrode active material layer to the current collector can be enhanced. Moreover, since the affinity with respect to the water of polymer particle (B) can be improved with the polarity which a carboxy group has, if an ethylenically unsaturated carboxylic acid monomer unit is used, polymer particles will be used in a solvent such as water. (B) can be stably dispersed to improve the stability of the slurry composition. Furthermore, since the affinity of the polymer particles (B) with respect to the polar solvent is improved by the polarity of the carboxy group, the wettability of the polymer particles (B) with respect to the electrolytic solution can be improved.

  Examples of the ethylenically unsaturated carboxylic acid monomer include unsaturated monocarboxylic acid and derivatives thereof, unsaturated dicarboxylic acid and acid anhydrides thereof, and derivatives thereof. Examples of unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of unsaturated monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and β -Diamino acrylic acid etc. are mentioned. Examples of unsaturated dicarboxylic acids include maleic acid, fumaric acid, itaconic acid, and the like. Examples of unsaturated dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Examples of derivatives of unsaturated dicarboxylic acids include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, methylallyl maleate; and diphenyl maleate, nonyl maleate, maleate And maleic acid esters such as decyl acid, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate. Among these, from the viewpoint of improving the stability of the polymer particles (B) in the slurry composition, unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid, and unsaturated acids such as maleic acid, fumaric acid, and itaconic acid. Dicarboxylic acids are preferred, acrylic acid, methacrylic acid and itaconic acid are more preferred, and itaconic acid is particularly preferred. Moreover, an ethylenically unsaturated carboxylic acid monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The ethylenically unsaturated carboxylic acid monomer usually affects the gel amount and glass transition temperature of the polymer particles (B). From the viewpoint of keeping the gel amount and the glass transition temperature of the polymer particles (B) within an appropriate range, in the monomer composition (b), the ratio of the ethylenically unsaturated carboxylic acid monomer is the aromatic vinyl compound and Preferably it is 0.1 weight part or more with respect to a total of 100 weight part of a conjugated diene compound, More preferably, it is 0.5 weight part or more, Preferably it is 6 weight part or less, More preferably, it is 5 weight part or less. By keeping the ratio of the ethylenically unsaturated carboxylic acid monomer within the above range, the binding property between the current collector and the electrode active material layer can be improved, and the negative electrode strength can be improved. As a result, a lithium ion secondary battery having excellent cycle characteristics can be obtained.

・ Hydroxyl group-containing monomer:
Since the hydroxyl group-containing monomer has a hydroxyl group (—OH group), the polymer particles (B) have high polarity by using the hydroxyl group-containing monomer. Thereby, the binding property of the polymer particles (B) to the negative electrode active material and the current collector can be further enhanced. For this reason, the binding property of the electrode active material layer to the current collector can be effectively enhanced by using the hydroxyl group-containing monomer. Moreover, the affinity with respect to the water of a polymer particle (B) can be improved with the polarity which a hydroxyl group has. Therefore, when a hydroxyl group-containing monomer is used, the polymer particles (B) can be more stably dispersed in a solvent such as water, and the stability of the slurry composition can be improved. Furthermore, since the affinity of the polymer particles (B) to the polar solvent is improved by the polarity of the hydroxyl group, the wettability of the polymer particles (B) to the electrolytic solution can be further improved.

  Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl acrylate, 2-hydroxy methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, and 3-chloro-2-hydroxypropyl methacrylate. Hydroxyalkyl acrylates such as di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, and 2-hydroxyethyl methyl fumarate; Examples thereof include monoallyl ethers of polyhydric alcohols. Of these, hydroxyalkyl acrylate is preferable, and 2-hydroxyethyl acrylate is particularly preferable. Moreover, a hydroxyl-containing monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In the monomer composition (b), the proportion of the hydroxyl group-containing monomer is preferably 0.1 parts by weight or more, more preferably 0.00 parts by weight relative to 100 parts by weight of the total of the aromatic vinyl compound and the conjugated diene compound. 5 parts by weight or more, preferably 10 parts by weight or less, more preferably 5 parts by weight or less. The wettability with respect to the electrolyte solution of a polymer particle (B) can be improved by making the ratio of a hydroxyl-containing monomer more than the lower limit of the said range. Moreover, the stability at the time of manufacture of a polymer particle (B) and the wettability with respect to electrolyte solution can be made compatible by making it below an upper limit.

・ Other polymerizable monomers:
The monomer composition (b) contains a monomer other than the above-described polyfunctional vinyl compound, ethylenically unsaturated carboxylic acid monomer, and hydroxyl group-containing monomer as an optional polymerizable monomer. Also good. Examples thereof include nitrile group-containing monomers such as acrylonitrile and methacrylonitrile; acrylamide monomers such as acrylamide, N-methylolacrylamide, and N-butoxymethylacrylamide; methacrylamide, N-methylolmethacrylamide, and N-butoxy. Methacrylamide monomers such as methyl methacrylamide; Glycidyl group-containing monomers such as glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether; Monomers containing sulfonic acid groups such as sodium styrenesulfonate and acrylamidomethylpropanesulfonic acid Body; amino group-containing methacrylic monomers such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; alkoxy groups such as methoxypolyethylene glycol monomethacrylate Tacrylic acid monomer; (meth) acrylic acid-2,2,2-trifluoroethyl, (meth) acrylic acid-β- (perfluorooctyl) ethyl, (meth) acrylic acid-2,2,3 3-tetrafluoropropyl, (meth) acrylic acid-2,2,3,4,4,4-hexafluorobutyl, (meth) acrylic acid-1H, 1H, 9H-perfluoro-1-nonyl, (meth) Acrylic acid-1H, 1H, 11H-perfluoroundecyl, perfluorooctyl (meth) acrylate, (meth) acrylic acid-3- [4- [1-trifluoromethyl-2,2-bis [bis (tri Fluorine-containing acrylic acids such as (fluoro) perfluoroalkyl esters such as (meth) acrylic acid such as fluoromethyl) fluoromethyl] ethynyloxy] benzooxy] -2-hydroxypropyl Monomeric monomers or fluorine-containing methacrylic acid monomers; unsaturated dicarboxylic acid monoesters such as monooctyl maleate, monobutyl maleate, monooctyl itaconate; and the like. Furthermore, as an arbitrary polymerizable monomer, for example, monomers listed in “Polymer Latex (New Polymer Library 26) (Polymer Press, First Edition) P131 to P134” can be mentioned. Among these, a nitrile group-containing monomer, an alkoxy group-containing methacrylic acid monomer, and a fluorine-containing acrylic acid monomer are preferable. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  In the monomer composition (b), the total ratio of any polymerizable monomer such as a polyfunctional vinyl compound, an ethylenically unsaturated carboxylic acid monomer, a hydroxyl group-containing monomer, etc. is preferably 0.00. It is 001% by weight or more, more preferably 0.1% by weight or more, particularly preferably 1% by weight or more, preferably 10% by weight or less, more preferably 8% by weight or less, and particularly preferably 5% by weight or less. By setting the ratio of the arbitrary polymerizable monomer to the lower limit value or more of the above range, the binding property between the polymer particles (B), the negative electrode active material and the current collector can be improved. Moreover, the stability of a slurry composition can be improved by making it into an upper limit or less.

-Production method of polymer particles (B):
The polymer particles (B) can be obtained by polymerizing the monomer composition (b) described above in an aqueous medium, similarly to the polymer particles (A) for the negative electrode. At this time, the type and amount of the aqueous solvent, the polymerization method, the types and amounts of additives (for example, emulsifier, polymerization initiator, molecular weight modifier, chain transfer agent, surfactant, etc.) that can be used during the polymerization, and the reaction conditions, It can be performed in the same manner as the production method of the polymer particles (A) for the negative electrode.

  The monomer contained in the monomer composition (b) is polymerized by polymerization. Thereby, the dispersion liquid containing an aqueous medium and the polymer particle (B) disperse | distributed in the said aqueous medium is obtained. Under the present circumstances, you may adjust pH of the obtained dispersion liquid like the manufacturing method of the polymer particle (A) for negative electrodes. At this time, the pH after adjustment is preferably 5 or more, preferably 10 or less, more preferably 9 or less. Especially, adjustment of pH with an alkali metal hydroxide is preferable because the binding property between the current collector and the electrode active material layer can be improved.

  The obtained polymer particles (B) may be taken out from the aqueous medium. However, normally, the polymer particles (B) dispersed in the aqueous medium are used for the production of the slurry composition without being taken out from the aqueous medium.

-Physical properties of polymer particles (B):
The number average particle diameter of the polymer particles (B) is preferably 50 nm or more, more preferably 70 nm or more, preferably 500 nm or less, more preferably 400 nm or less. By keeping the number average particle diameter of the polymer particles (B) within the above range, the strength and flexibility of the negative electrode can be improved.

  The amount of gel insoluble in tetrahydrofuran of the polymer particles (B) is preferably 70% or more, more preferably 80% or more, particularly preferably 85% or more, preferably 98% or less, more preferably 95% or less, Particularly preferably, it is 93% or less. By setting the gel amount of the polymer particles (B) to be equal to or greater than the lower limit of the above range, swelling of the polymer particles (B) into the electrolyte can be suppressed and swelling of the electrodes can be prevented. Moreover, it can prevent that a polymer particle (B) becomes too soft, and can make binding property high. Moreover, since it can prevent that a polymer particle (B) becomes hard too much by setting it as an upper limit or less, a binding property can also be made high by this. Therefore, the binding property between the electrode active material layer and the current collector can be improved, and battery characteristics such as cycle characteristics can be improved.

  The glass transition temperature of the polymer particles (B) is preferably −30 ° C. or higher, more preferably −20 ° C. or higher, particularly preferably −10 ° C. or higher, preferably 60 ° C. or lower, more preferably 40 ° C. or lower, Especially preferably, it is 30 degrees C or less. By setting the glass transition temperature of the polymer particles (B) to be equal to or higher than the lower limit of the above range, swelling of the electrode during charging can be suppressed, and cycle characteristics can be improved. Moreover, since the binding property of a polymer particle (B) can be improved by setting it as an upper limit or less, a cycle characteristic can also be improved by this.

-Amount of polymer particles (B):
The amount of the polymer particles (B) is preferably 100 parts by weight or more, more preferably 500 parts by weight or more, preferably 2000 parts by weight or less, more preferably 100 parts by weight of the polymer particles (A). 1500 parts by weight or less. By setting the amount of the polymer particles (B) to be not less than the lower limit of the above range, the negative electrode active material and the current collector can be stably held in the electrode active material layer. Moreover, the swelling of the electrode plate in charging / discharging can be suppressed by making it below an upper limit.

[2.1.5. Water-soluble polymer]
The slurry composition for the negative electrode preferably further contains a water-soluble polymer. When an aqueous medium such as water is used as a solvent, a part of the water-soluble polymer is liberated in the solvent, but another part is adsorbed on the surface of particles such as an electrode active material. Since the surface of the particles is covered with a stable layer by the water-soluble polymer thus adsorbed, the dispersibility of the particles in the aqueous medium can be improved. Thereby, since the dispersibility of particles, such as an electrode active material, in an electrode active material layer can also be improved, the swelling of the electrode by charging / discharging can be suppressed. Further, the binding property between the electrode active material layer and the current collector can be enhanced. Furthermore, the cycle characteristics of the lithium ion secondary battery can be improved by these actions.

  Examples of the water-soluble polymer include water-soluble polysaccharides, sodium polyacrylate, polyethyleneimine, polyvinyl alcohol, polyvinyl pyrrolidone and the like. Of these, water-soluble polysaccharides are preferable, and carboxymethyl cellulose is particularly preferable. Here, carboxymethylcellulose may be used in the form of a salt such as a sodium salt or an ammonium salt. Moreover, a water-soluble polymer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The molecular weight of the water-soluble polymer varies depending on the polymer used, but when a B-type viscometer at 25 ° C. is used, the 1% by weight aqueous solution viscosity is preferably 500 mPa · s or more, more preferably 1000 mPa · s or more. More preferably, it is 1500 mPa · s or more, particularly preferably 2000 mPa · s or more, preferably 10000 mPa · s or less, more preferably 9000 mPa · s or less, and particularly preferably 8000 mPa · s or less. By setting it to the lower limit of the above range or more, the surface active property of the electrode active material is excellent, a stable negative electrode slurry composition is obtained, and a lithium ion secondary battery excellent in cycle characteristics and the like is obtained. Moreover, by making it into an upper limit or less, it is excellent in the fluidity | liquidity of the slurry composition for negative electrodes, and excellent in a coating characteristic.

  The amount of the water-soluble polymer is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, preferably 5 parts by weight or less, more preferably 3 parts by weight with respect to 100 parts by weight of the electrode active material. Less than parts by weight. By making the amount of the water-soluble polymer not less than the lower limit of the above range, the dispersibility of particles such as an electrode active material can be enhanced in the slurry composition. Moreover, the low temperature output characteristic of a lithium ion secondary battery can be improved by making it into an upper limit or less.

[2.1.6. Arbitrary ingredients]
The slurry composition for the negative electrode contains optional components in addition to the negative electrode active material, polymer particles (A), solvent, polymer particles (B) and water-soluble polymer as long as the effects of the present invention are not significantly impaired. May be included. Examples thereof include a conductive material, a reinforcing material, a leveling agent, nanoparticles, an electrolytic solution additive, and the like. Moreover, these components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The conductive material is a component that can improve electrical contact between the electrode active materials. By including a conductive material, the discharge rate characteristics of the lithium ion secondary battery can be improved.
Examples of the conductive material include furnace black, acetylene black, ketjen black, carbon black, graphite, vapor grown carbon fiber, and conductive carbon such as carbon nanotube. A conductive material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
The amount of the conductive material is preferably 1 to 20 parts by weight, more preferably 1 to 10 parts by weight, with respect to 100 parts by weight of the electrode active material.

As the reinforcing material, for example, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used. A reinforcing material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. By using the reinforcing material, a tough and flexible negative electrode can be obtained, and a lithium ion secondary battery exhibiting excellent long-term cycle characteristics can be realized.
The amount of the reinforcing material is usually 0.01 parts by weight or more, preferably 1 part by weight or more, and usually 20 parts by weight or less, preferably 10 parts by weight or less with respect to 100 parts by weight of the electrode active material. By setting the amount of the reinforcing material in the above range, the lithium ion secondary battery can exhibit high capacity and high load characteristics.

Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants. A leveling agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. By using the leveling agent, it is possible to prevent the repelling that occurs during the application of the slurry composition or to improve the smoothness of the electrode. Moreover, by containing a surfactant, the dispersibility of particles such as an electrode active material in the slurry composition can be improved, and the smoothness of the resulting electrode can be improved.
The amount of the leveling agent is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. When the leveling agent is within the above range, the productivity, smoothness, and battery characteristics during electrode production are excellent.

Examples of the nanoparticles include particles such as fumed silica and fumed alumina. One kind of nanoparticles may be used alone, or two or more kinds of nanoparticles may be used in combination at any ratio. When nanoparticles are included, the thixotropy of the slurry composition can be adjusted, so that the leveling property of the resulting electrode can be improved.
The amount of the nanoparticles is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. When the nanoparticles are in the above range, the stability and productivity of the slurry composition can be improved, and high battery characteristics can be realized.

Examples of the electrolytic solution additive include vinylene carbonate. One electrolyte solution additive may be used alone, or two or more electrolyte solution additives may be used in combination at any ratio. By using the electrolytic solution additive, for example, decomposition of the electrolytic solution can be suppressed.
The amount of the electrolytic solution additive is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. By setting the amount of the electrolytic solution additive in the above range, a secondary battery excellent in cycle characteristics and high temperature characteristics can be realized.

[2.1.7. Method for producing slurry composition for negative electrode]
The slurry composition for the negative electrode is produced by mixing the negative electrode active material, the polymer particles (A) and the solvent, the polymer particles (B) used as necessary, the water-soluble polymer, and optional components. Yes. The specific procedure at this time is arbitrary. For example, a method of simultaneously mixing a negative electrode active material, polymer particles (A), polymer particles (B) and a water-soluble polymer in a solvent; a polymer in which a water-soluble polymer is dissolved in a solvent and then dispersed in the solvent A method of mixing particles (A) and polymer particles (B) and then mixing a negative electrode active material; mixing negative electrode active materials into polymer particles (A) and polymer particles (B) dispersed in a solvent And a method of mixing the mixture with a water-soluble polymer dissolved in a solvent.

  The apparatus used for mixing may be any apparatus that can uniformly mix the above components. Examples include bead mill, ball mill, roll mill, sand mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, fill mix and the like. Among these, it is particularly preferable to use a ball mill, a roll mill, a pigment disperser, a crusher, or a planetary mixer because dispersion at a high concentration is possible.

[2.2. Slurry composition for positive electrode]
The slurry composition for positive electrode contains the positive electrode active material which is an electrode active material for positive electrodes, the polymer particle (A) for positive electrodes, and a solvent.

[2.2.1. Cathode active material]
The positive electrode active material is an electrode active material for a positive electrode, and a material that can insert and desorb lithium ions can be used. Such positive electrode active materials are roughly classified into inorganic compounds and organic compounds.

Examples of the positive electrode active material made of an inorganic compound include transition metal oxides, transition metal sulfides, lithium-containing composite metal oxides of lithium and transition metals, and the like.
Examples of the transition metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.

Examples of the transition metal oxide include MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MoO _{3 and the} like. Among them, MnO, V ₂ O ₅ , V ₆ O ₁₃ , and TiO ₂ are preferable from the viewpoint of cycle stability and capacity.
Examples of the transition metal sulfide include TiS ₂ , TiS ₃ , amorphous MoS ₂ , FeS, and the like.

Examples of the lithium-containing composite metal oxide include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.
Examples of the lithium-containing composite metal oxide having a layered structure include lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), lithium composite oxide of Co—Ni—Mn, Ni—Mn— Examples thereof include a lithium composite oxide of Al and a lithium composite oxide of Ni—Co—Al.
Examples of the lithium-containing composite metal oxide having a spinel structure include Li [Mn _3/2 M _1/2 ] O _{4 in which} lithium manganate (LiMn ₂ O ₄ ) or a part of Mn is substituted with another transition metal. (Where M is Cr, Fe, Co, Ni, Cu, etc.).
Examples of the lithium-containing composite metal oxide having an olivine type structure include Li _X MPO ₄ (wherein M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti). Olivine type lithium phosphate compound represented by the formula: at least one selected from the group consisting of Al, Si, B and Mo, wherein X represents a number satisfying 0 ≦ X ≦ 2.

  Examples of the positive electrode active material made of an organic compound include conductive polymer compounds such as polyacetylene and poly-p-phenylene.

Moreover, you may use the positive electrode active material which consists of a composite material which combined the inorganic compound and the organic compound.
Alternatively, for example, a composite material covered with a carbon material may be produced by reducing and firing an iron-based oxide in the presence of a carbon source material, and the composite material may be used as a positive electrode active material. Iron-based oxides tend to have poor electrical conductivity, but can be used as a high-performance positive electrode active material by using a composite material as described above.
Furthermore, you may use as a positive electrode active material what carried out the element substitution of the said compound partially.
Moreover, you may use the mixture of said inorganic compound and organic compound as a positive electrode active material.
As the positive electrode active material, one type may be used alone, or two or more types may be used in combination at any ratio.

  The volume average particle diameter of the positive electrode active material particles is preferably 1 μm or more, more preferably 2 μm or more, preferably 50 μm or less, more preferably 30 μm or less. By setting the volume average particle diameter of the positive electrode active material particles in the above range, the amount of the binder in producing the electrode active material layer can be reduced, and the decrease in the capacity of the lithium ion secondary battery can be suppressed. Moreover, it becomes easy to adjust the viscosity of the slurry composition to an appropriate viscosity that is easy to apply, and a uniform positive electrode can be obtained.

  The amount of the positive electrode active material is such that the ratio of the positive electrode active material in the electrode active material layer is preferably 90% by weight or more, more preferably 95% by weight or more, preferably 99.9% by weight or less, more preferably 99% by weight. %. Thereby, the capacity | capacitance of a lithium ion secondary battery can be made high, and the softness | flexibility of a positive electrode and the binding property of a collector and an electrode active material layer can be improved.

[2.2.2. Polymer particle (A)]
In the positive electrode slurry composition, the positive electrode polymer particles (A) described above in the section of the binder composition are used as the polymer particles (A). The polymer particles (A) are usually dispersed in the slurry composition. In particular, when an aqueous medium such as water is used as the solvent, the polymer particles (A) can be highly dispersed in the aqueous medium because the affinity of the polymer particles (A) to the aqueous medium is good. Therefore, the applicability of the slurry composition to the current collector can be improved.

  The amount of the polymer particles (A) in the positive electrode slurry composition is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, particularly preferably 0, with respect to 100 parts by weight of the positive electrode active material. 0.5 parts by weight or more, preferably 10 parts by weight or less, more preferably 8 parts by weight or less, and particularly preferably 5 parts by weight or less. When the amount of the polymer particles (A) is within the above range, it is possible to stably prevent the positive electrode active material from dropping from the positive electrode without inhibiting the battery reaction.

[2.2.3. solvent]
The solvent of the slurry composition for the positive electrode can be the same as the slurry composition for the negative electrode, regardless of the type and amount.

[2.2.4. Water-soluble polymer]
The slurry composition for the positive electrode may further contain a water-soluble polymer. Thereby, the same advantage as the case where the slurry composition for negative electrodes contains a water-soluble polymer is acquired.
As the water-soluble polymer, the same type and weight average molecular weight as those described in the section of the slurry composition for the negative electrode can be used in the same amount. Moreover, a water-soluble polymer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[2.2.5. Arbitrary ingredients]
The slurry composition for the positive electrode can contain optional components in addition to the positive electrode active material, the polymer particles (A), the solvent, and the water-soluble polymer, as long as the effects of the present invention are not significantly impaired. As such an arbitrary component, the same thing as the slurry composition for negative electrodes can be used in the same quantity, for example. Moreover, these components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[2.2.6. Method for producing positive electrode slurry composition]
The slurry composition can be produced by mixing the positive electrode active material, the polymer particles (A) and the solvent, the water-soluble polymer used as necessary, and optional components. The specific procedure in this case is arbitrary, For example, it can manufacture in the same way as the slurry composition for negative electrodes.

[3. Electrode for lithium ion secondary battery]
An electrode can be manufactured by using the slurry composition of the present invention described above. The electrode includes a current collector and an electrode active material layer formed on the current collector. The electrode active material layer includes components such as the electrode active material and polymer particles (A) contained in the slurry composition. Such an electrode is usually excellent in the binding property between the current collector and the electrode active material layer. The reason why such excellent binding properties can be obtained is not clear, but according to the study of the present inventors, it is presumed as follows.
Since the polymer particles (A) functioning as a binder in the electrode active material layer have a large polarity due to sulfur atoms, they can cause a strong interaction with polar groups present on the surface of the electrode active material and the current collector. For this reason, polymer particle (A) can express high binding property with respect to an electrode active material and a collector. Further, the polymer particles (A) have strong toughness by having a crosslinked structure or a branched structure as a molecular structure. Also by this toughness, the polymer particles (A) can exhibit high binding properties to the electrode active material and the current collector. Therefore, it is considered that the binding property between the electrode active material layer and the current collector is excellent.

  Examples of the method for producing an electrode using the slurry composition include a production method including applying the slurry composition on a current collector and drying.

  As the current collector, one formed of a material having electrical conductivity and electrochemical durability is usually used. As a material for the current collector, a metal material is preferable since it has heat resistance. For example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, and the like can be given. Among these, copper is preferable as the current collector for the negative electrode. As the positive electrode current collector, aluminum is particularly preferable. One kind of the above materials may be used alone, or two or more kinds thereof may be used in combination at any ratio.

  The shape of the current collector is not particularly limited, and a sheet shape having a thickness of about 0.001 mm to 0.5 mm is preferable.

In order for the current collector to increase the adhesive strength with the electrode active material layer, the electrode active material layer (or the intermediate layer if there is an intermediate layer between the current collector and the electrode active material layer) It is preferable that the surface is subjected to a roughening treatment prior to the formation thereof. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, for example, abrasive cloth paper, abrasive wheels, emery buffs, wire brushes equipped with steel wires, etc., to which abrasive particles are fixed are used.
Further, an intermediate layer may be formed on the surface of the current collector in order to increase the adhesive strength between the current collector and the electrode active material layer or increase the conductivity.

  When apply | coating a slurry composition on a collector, it may apply | coat only to the single side | surface of a collector, and may apply | coat to both surfaces. The method for applying the slurry composition to the surface of the current collector is not particularly limited. Examples of the coating method include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

By applying the slurry composition, a film of the slurry composition is formed on the surface of the current collector. The slurry composition film is dried to remove a liquid such as a solvent, whereby an electrode active material layer is formed on the surface of the current collector.
Examples of the drying method include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying time is usually 5 to 30 minutes, and the drying temperature is usually 40 ° C to 180 ° C.

  In addition, after applying and drying the slurry composition on the surface of the current collector, the electrode active material layer may be subjected to pressure treatment using a press machine such as a die press or a roll press as necessary. preferable. By the pressure treatment, the porosity of the electrode active material layer can be lowered. The porosity is preferably 5% or more, more preferably 7% or more, preferably 30% or less, more preferably 20% or less. By setting the porosity to be equal to or higher than the lower limit value of the above range, a high volume capacity can be easily obtained, and the electrode active material layer can be made difficult to peel from the current collector. Moreover, high charging efficiency and discharge efficiency are obtained by setting it as an upper limit or less.

  Further, when the electrode active material layer contains a polymer that can be cured by a curing reaction such as a crosslinking reaction, the polymer may be cured at an appropriate time after the slurry composition is applied on the current collector. Good. For example, when the electrode active material layer includes a polymer having thermal crosslinkability, the heat treatment may be performed at 120 ° C. or more for 1 hour or more.

  By the method described above, an electrode for a lithium ion secondary battery including a current collector and an electrode active material layer formed on the current collector can be obtained.

In the obtained electrode, the amount of the electrode active material layer per unit area on the surface of the current collector can be arbitrarily set. In the negative electrode, the amount of the electrode active material layer per unit area on the surface of the current collector is preferably 6 mg / cm ² or more, more preferably 8 mg / cm ² or more, and particularly preferably 10 mg / cm ² or more. It is preferably 20 mg / cm ² or less, more preferably 18 mg / cm ² or less, and particularly preferably 16 mg / cm ² or less. In the positive electrode, the amount of the electrode active material layer per unit area on the surface of the current collector is preferably 15 mg / cm ² or more, more preferably 20 mg / cm ² or more, particularly preferably 25 mg / cm ² or more. Yes, preferably 70 mg / cm ² or less, more preferably 60 mg / cm ² or less, particularly preferably 50 mg / cm ² or less. By setting the amount of the electrode active material layer per unit area on the surface of the current collector to be equal to or greater than the lower limit of the above range, the capacity of the lithium ion secondary battery can be increased. Moreover, the lifetime characteristic of a lithium ion secondary battery can be made favorable by making it into an upper limit or less.

  From the viewpoint of setting the amount of the electrode active material layer per unit area within the above range, the thickness of the electrode active material layer in the negative electrode is usually 1 μm or more, preferably 5 μm or more, more preferably 30 μm or more, and usually 300 μm. Hereinafter, it is preferably 250 μm or less, more preferably 200 μm or less, and particularly preferably 100 μm or less. From the same viewpoint, the thickness of the electrode active material layer in the positive electrode is usually 5 μm or more, preferably 10 μm or more, and usually 300 μm or less, preferably 250 μm or less.

[4. Lithium ion secondary battery]
The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, and an electrolytic solution, and usually includes a separator. In the lithium ion secondary battery of the present invention, the positive electrode or the negative electrode is the electrode of the present invention. Under the present circumstances, the electrode of this invention may be used only as a negative electrode, the battery of this invention may be used only as a positive electrode, and the battery of this invention may be used as both a negative electrode and a positive electrode.

Since this lithium ion secondary battery is excellent in cycle characteristics, it has a long life. The reason why such excellent cycle characteristics are obtained is not necessarily clear, but according to the study of the present inventor, it is presumed as follows.
The polymer particles (A) functioning as a binder in the electrode active material layer have strong toughness and large polarity. For this reason, the polymer particles (A) have a high binding property to the electrode active material and the current collector. Therefore, even if the electrode active material repeatedly expands and contracts due to charge and discharge, the conductive path is hardly cut in the electrode.
Further, the polymer particles (A) have a high affinity for the aqueous medium and can be stably dispersed in the slurry composition. Therefore, since the polymer particles (A) can be highly dispersed even in the electrode active material layer obtained from this slurry composition, the strength of the electrode active material layer can be made uniform, and the starting point is a place where the strength is locally low. Damage can be prevented. Therefore, even if stress is generated in the electrode due to expansion and contraction of the electrode active material and heat generation due to charge and discharge, the conductive path is hardly cut due to breakage.
As described above, in the electrode of the present invention, the conductive path is hardly cut, so that the increase in resistance due to use is small. Therefore, it is considered that high cycle characteristics are obtained.

In addition, the lithium ion secondary battery of the present invention is excellent in discharge rate characteristics. The reason why such an excellent discharge rate characteristic is obtained is not necessarily clear, but according to the study of the present inventor, it is presumed as follows.
A polymer particle (A) is excellent in ion conductivity, for example by having a sulfur atom derived from a polyfunctional thiol compound. In addition, since the polymer particles (A) have a large polarity as described above, they have excellent affinity for polar solvents and thus excellent wettability for the electrolytic solution. Due to these actions, the electrode of the present invention has good ion conductivity, so that the resistance can be reduced. Furthermore, since the polymer particle (A) has a crosslinked structure or a branched structure, it is difficult to swell with respect to the electrolytic solution. Therefore, since the swelling of the electrode active material layer in the electrolytic solution can be suppressed, the resistance can also be reduced by this. Therefore, it is considered that high discharge rate characteristics are obtained by these actions.

  Moreover, normally, in the lithium ion secondary battery of this invention, even when charging / discharging is repeated, the swelling of an electrode can be suppressed. This is presumably because the swelling of the electrode is suppressed due to the high binding property between the current collector and the electrode active material layer and the high strength of the polymer particles (A).

  Furthermore, normally, in the lithium ion secondary battery of the present invention, it is possible to improve the binding property between the electrode and the separator. This is presumably because the affinity of the polymer particles (A) to the separator is increased because the polymer particles (A) have high polarity.

  In general, the lithium ion secondary battery of the present invention is excellent in low temperature output characteristics. This is presumably because the resistance of the electrode can be reduced by the action of the polyfunctional thiol compound as described above.

[4.1. Electrolyte]
As the electrolytic solution, for example, a solution containing a solvent and a supporting electrolyte dissolved in the solvent can be used.
As the electrolyte, a lithium salt is usually used. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. Among these, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferably used because they are particularly soluble in a solvent and exhibit a high degree of dissociation. One of these may be used alone, or two or more of these may be used in combination at any ratio. Generally, the higher the dissociation of the supporting electrolyte, the higher the lithium ion conductivity. Therefore, the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

  The concentration of the supporting electrolyte in the electrolytic solution is preferably 1% by weight or more, more preferably 5% by weight or more, and preferably 30% by weight or less, more preferably 20% by weight or less. By keeping the amount of the supporting electrolyte within the above range, the ionic conductivity can be increased, and the charging characteristics and discharging characteristics of the lithium ion secondary battery can be improved.

  As a solvent used for the electrolytic solution, a solvent capable of dissolving the supporting electrolyte can be used. Examples of the solvent include alkyl carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (MEC); Examples include esters such as butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; and the like. In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferred because high ion conductivity is easily obtained and the use temperature range is wide. Moreover, a solvent may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. The lower the viscosity of the solvent used, the higher the lithium ion conductivity. Therefore, the lithium ion conductivity can be adjusted depending on the type of solvent.

  Moreover, electrolyte solution may contain the additive as needed. As the additive, for example, carbonate compounds such as vinylene carbonate (VC) are preferable. In addition, an additive may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Further, instead of the electrolyte solution described above, for example, a gel polymer electrolyte in which a polymer electrolyte such as polyethylene oxide or polyacrylonitrile is impregnated with the electrolyte; an inorganic solid electrolyte such as lithium sulfide, LiI, or Li ₃ N; Also good.

[4.2. separator]
As the separator, a porous substrate having a pore portion is usually used. Examples of separators include (a) a porous separator having pores, (b) a porous separator having a polymer coating layer formed on one or both sides, and (c) a porous resin coat containing inorganic ceramic powder. And a porous separator having a layer formed thereon. Examples of these include solid polymer electrolytes such as polypropylene, polyethylene, polyolefin, or aramid porous separators, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride hexafluoropropylene copolymers. Or a polymer film for a gel polymer electrolyte; a separator coated with a gelled polymer coat layer; a separator coated with a porous film layer composed of an inorganic filler and an inorganic filler dispersant; and the like.

[4.3. Manufacturing method of lithium ion secondary battery]
The manufacturing method of a lithium ion secondary battery is not specifically limited. For example, the negative electrode and the positive electrode may be overlapped via a separator, and this may be wound or folded according to the shape of the battery and placed in the battery container, and the electrolyte may be injected into the battery container and sealed. Furthermore, if necessary, for example, expanded metal; an overcurrent prevention element such as a fuse or a PTC element; a lead plate or the like may be inserted to prevent an increase in pressure inside the battery or overcharge / discharge. The shape of the battery may be any of, for example, a laminate cell type, a coin type, a button type, a sheet type, a cylindrical type, a square shape, and a flat type.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.
In the following description, “%” and “part” representing amounts are based on weight unless otherwise specified. In addition, the operations described below were performed under normal temperature and normal pressure conditions unless otherwise specified.

[Evaluation method]
(Measurement method of gel amount)
A binder composition containing polymer particles was prepared, and the binder composition was dried in an environment of 50% humidity and 23 ° C. to 25 ° C. to produce a film having a thickness of 3 ± 0.3 mm. The produced film was cut into 5 mm square to obtain a film piece. About 1 g of these film pieces was precisely weighed. Let the weight of the precisely weighed film piece be W0.
This film piece was immersed in 100 g of tetrahydrofuran (THF) for 24 hours. Then, the film piece was lifted from THF. The pulled film piece was vacuum-dried at 105 ° C. for 3 hours, and its weight (insoluble content weight) W1 was measured. The gel amount (%) was calculated according to the following formula.
Gel amount (%) = W1 / W0 × 100

(Measurement method of glass transition temperature)
A binder composition containing polymer particles was prepared, and this binder composition was dried in an environment of 50% humidity and 23 ° C. to 25 ° C. for 3 days to produce a film. The film was dried in a 120 ° C. hot air oven for 1 hour. Then, using the dried film as a sample, a differential scanning calorimeter (“DSC6220SII” manufactured by Nanotechnology Co., Ltd.) under measurement conditions of a measurement temperature of −100 ° C. to 180 ° C. and a heating rate of 5 ° C./min according to JIS K7121. )).

(Initial swelling of electrode)
For the laminated cell type lithium ion secondary batteries produced in the examples and comparative examples, the electrode thickness (excluding the thickness of the current collector) d0 was measured before assembling the electrodes. Moreover, after assembling the battery, the battery was allowed to stand for 5 hours, starting from the time when the electrolyte was injected into the battery exterior. Thereafter, the battery was charged and discharged by charging to 4.2 V and discharging to 3.0 V by a constant current method of 0.2 C. Further, the battery was charged to 4.2 V by a constant current method of 1C. Thereafter, the charged battery was disassembled, the electrode was taken out, and the electrode thickness d1 (excluding the current collector thickness) was measured. The change rate (initial swell characteristic) of the thickness (excluding the thickness of the current collector) with respect to the electrode before the production of the lithium ion secondary battery was calculated according to the following formula.
Initial swell characteristic of electrode = (d1−d0) / d0 × 100 (%)

The obtained initial bulging characteristics were determined according to the following criteria. A smaller value of the initial bulge characteristic indicates that the initial bulge of the electrode is suppressed.
A: Less than 30% B: 30% or more and less than 35% C: 35% or more and less than 40% D: 40% or more

(Bulge after electrode cycle)
For the laminated cell type lithium ion secondary batteries produced in the examples and comparative examples, the electrode thickness (excluding the current collector thickness) d0 was measured before assembling the batteries. Moreover, after assembling the battery, the battery was allowed to stand in an environment of 25 ° C. for 5 hours, starting from the time when the electrolyte was poured into the battery exterior. Thereafter, the battery was charged / discharged at a temperature of 25 ° C. and charged to 4.2 V by a constant current method of 0.2 C and discharged to 3.0 V. Furthermore, the charge / discharge operation of charging to 4.2 V and discharging to 3.0 V by a constant current method of 0.5 C in a 60 ° C. environment was repeated 100 cycles. Thereafter, the discharged battery was disassembled, the electrode was taken out, and the electrode thickness d2 (excluding the current collector thickness) was measured. The rate of change of the thickness (excluding the thickness of the current collector) with respect to the electrode before the production of the lithium ion secondary battery (the swelling characteristic after cycle) was calculated according to the following formula.
Swell characteristics after cycling of electrode = (d2−d0) / d0 × 100 (%)

The obtained post-cycle swelling characteristics were determined according to the following criteria. The smaller this value is, the more the post-cycle swelling of the electrode is suppressed.
A: Less than 10% B: 10% or more and less than 15% C: 15% or more and less than 20% D: 20% or more

(Cycle characteristics)
The laminated cell type lithium ion secondary batteries produced in the examples and comparative examples were allowed to stand for 5 hours in a 25 ° C. environment starting from the time when the electrolyte solution was poured into the exterior of the battery. Thereafter, in a 25 ° C. environment, a charge / discharge operation of charging to 4.2 V and discharging to 3.0 V was performed by a constant current method of 0.2 C. Furthermore, 100 cycles of charging / discharging operation of charging to 4.2 V and discharging to 3.0 V by a constant current method of 0.5 C under an environment of 60 ° C. At this time, the discharge capacity (initial discharge capacity) C1 at the time of charge / discharge at the first cycle and the discharge capacity C2 at the time of charge / discharge at the 100th cycle were measured. The capacity retention rate was calculated according to the following formula, and the cycle characteristics were evaluated based on this capacity retention rate.
Capacity maintenance rate = C2 / C1 x 100 (%)

The obtained capacity retention rate was determined according to the following criteria. Higher values indicate better cycle characteristics.
A: 80% or more B: 75% or more and less than 80% C: 70% or more and less than 75% D: Less than 70%

(Discharge rate characteristics)
The laminate cell type lithium ion secondary batteries produced in the examples and comparative examples were allowed to stand in an environment of 25 ° C. for 5 hours, starting from the time when the electrolyte solution was injected into the exterior of the battery. Thereafter, in a 25 ° C. environment, a charge / discharge operation of charging to 4.2 V and discharging to 3.0 V was performed by a constant current method of 0.2 C. Then, it charged to 4.2V by the constant current method of 0.2C in 25 degreeC environment. Thereafter, discharging was performed at a discharge rate of 0.2 C and 1.5 C in a 25 ° C. environment. The discharge capacity at a discharge rate of 0.2 C is C (0.2). The discharge capacity at a discharge rate of 1.5 C is C (1.5). The discharge rate characteristics were calculated according to the following formula.
Discharge rate characteristic = C (1.5) / C (0.2) × 100 (%)

The obtained discharge rate characteristics were determined according to the following criteria. It shows that it is excellent in the discharge rate characteristic, so that this value is large.
A: 80% or more B: 75% or more and less than 80% C: 70% or more and less than 75% D: Less than 70%

(Binding properties)
The secondary battery electrodes produced in the examples and comparative examples were cut into rectangles having a length of 100 mm and a width of 10 mm to obtain test pieces. A cellophane tape was attached to the surface of the electrode active material layer with the surface of the electrode active material layer facing down. At this time, a cellophane tape defined in JIS Z1522 was used. The cellophane tape was fixed to a horizontal test stand with the adhesive surface facing upward. Then, the stress when one end of the current collector was pulled vertically upward at a pulling speed of 50 mm / min and peeled was measured. This measurement was performed 3 times, the average value of the measured stress was calculated | required, and the said average value was made into peeling peel strength.

The obtained peel peel strength was determined according to the following criteria. The higher the peel peel strength, the greater the binding force of the electrode active material layer to the current collector, that is, the greater the adhesion strength.
A: 5 N / m or more B: 4 N / m or more and less than 5 N / m C: 3 N / m or more and less than 4 N / m D: Less than 3 N / m

[Example 1]
[1.1. Production of polymer particles (A) for negative electrode]
In a 5 MPa pressure vessel with a stirrer, 100 parts of butyl acrylate as a (meth) acrylic acid ester compound, 2 parts of acrylonitrile as an α, β-unsaturated nitrile compound, 2 parts of methacrylic acid as a monomer having a hydrophilic group, an amide group N-methylolacrylamide as a monomer, 1 part of allyl glycidyl ether as a monomer having a reactive functional group, 0.15 part of pentaerythritol tetrakis (3-mercaptobutyrate) as a polyfunctional thiol compound, lauryl sulfate as an emulsifier 4 parts of sodium, 150 parts of ion-exchanged water as a solvent, and 0.5 part of ammonium persulfate as a polymerization initiator were added and stirred sufficiently, and then heated to 80 ° C. to initiate polymerization.

  When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing polymer particles (A). A 5% aqueous sodium hydroxide solution was added to this mixture to adjust the pH to 7 to obtain a binder composition (A) containing the desired polymer particles (A). Using the obtained binder composition (A), the gel amount when the polymer particles (A) were immersed in THF and the glass transition temperature of the polymer particles (A) were measured by the method described above. As a result of the measurement, the gel amount was 93% and the glass transition temperature was −50 ° C.

[1.2. Production of polymer particles (B) for negative electrode]
In a 5 MPa pressure vessel equipped with a stirrer, 65 parts of styrene as an aromatic vinyl compound, 35 parts of 1,3-butadiene as a conjugated diene compound, 4 parts of itaconic acid as an ethylenically unsaturated carboxylic acid monomer, and 2 as a hydroxyl group-containing monomer -1 part hydroxyethyl acrylate, 0.3 part t-dodecyl mercaptan as a molecular weight regulator, 5 parts sodium dodecylbenzenesulfonate as an emulsifier, 150 parts ion-exchanged water as a solvent, and 1 part potassium persulfate as a polymerization initiator After sufficiently stirring, the polymerization was started by heating to 55 ° C.

  When the monomer consumption reached 95.0%, the reaction was stopped by cooling. A 5% aqueous sodium hydroxide solution was added to the aqueous dispersion containing the polymer thus obtained to adjust the pH to 8. Then, the unreacted monomer was removed by heating under reduced pressure. Furthermore, it cooled to 30 degrees C or less after that, and the binder composition (B) containing a polymer particle (B) was obtained. Using the obtained binder composition (B), the gel amount when the polymer particles (B) were immersed in THF and the glass transition temperature of the polymer particles (B) were measured by the method described above. As a result of the measurement, the gel amount was 93% and the glass transition temperature (Tg) was 10 ° C.

[1.3. Production of slurry composition for negative electrode]
In a planetary mixer, 90 parts of natural graphite as a negative electrode active material formed of carbon, 10 parts of SiO _x as a negative electrode active material containing silicon, 0.1 part of the binder composition (A) corresponding to the solid content, 1 part aqueous solution (B-type viscometer at 25 ° C.) of 1.0 part by weight of the binder composition (B) as a water-soluble polymer and a high molecular weight type carboxymethyl cellulose (“MAC800LC” manufactured by Nippon Paper Chemical Co., Ltd.) as a water-soluble polymer. The viscosity of 7800 mPa · s measured in step 1 was added in an amount corresponding to the solid content, and ion-exchanged water was added and mixed so that the total solid content concentration was 52%, thereby preparing a negative electrode slurry composition.

[1.4. (Manufacture of negative electrode)
The slurry composition for negative electrode was applied on a copper foil having a thickness of 20 μm, which is a current collector, with a comma coater. Coat-weight of the negative electrode slurry composition in this case, the solid content of the negative electrode slurry composition per unit area of the surface of the copper foil was set to be ^{11mg / cm 2 ~12mg / cm 2} . Thereafter, the applied negative electrode slurry composition was dried to form an electrode active material layer on the surface of the copper foil. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, the negative electrode original fabric was obtained by heat-processing at 120 degreeC for 2 minute (s). The raw by a roll press machine, the density of the negative electrode active material layer in the negative electrode is subjected to pressing so as to be ^{1.50g / cm 3 ~1.60g / cm 3} , and a negative electrode. A part was cut out from this negative electrode, and the thickness and binding property of the negative electrode were measured.

[1.5. Production of positive electrode)
In a planetary mixer, 100 parts by weight of LiCoO ₂ as a positive electrode active material, ₂ parts of acetylene black (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and polyvinylidene fluoride (PVDF; “KF-” manufactured by Kureha Chemical Co., Ltd.) as a binder 1100 ") 2 parts was added, and further, 2-methylpyrrhodone was added and mixed so that the total solid content concentration was 67% to prepare a slurry composition for positive electrode.

This positive electrode slurry composition was applied onto a 20 μm thick aluminum foil as a current collector by a comma coater. The coating amount of the positive electrode slurry composition at this time was such that the solid content of the positive electrode slurry composition per unit area of the surface of the aluminum foil was 30 mg / cm ² . Thereafter, the applied positive electrode slurry composition was dried to form an electrode active material layer on the surface of the aluminum foil. This drying was performed by conveying the aluminum foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a positive electrode raw material. After drying this raw material, it was pressed so that the density of the positive electrode active material layer in the positive electrode after being pressed by a roll press machine was 3.65 g / cm ^{3 to} 3.74 g / cm ³ to obtain a positive electrode.

[1.6. (Manufacture of lithium ion secondary batteries)
A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm; produced by a dry method; porosity 55%) was prepared. This separator was cut into a 5 × 5 cm ² square.

Subsequently, an aluminum packaging exterior was prepared as a battery exterior. The positive electrode was cut into a square of 4 × 4 cm ² and arranged so that the current collector-side surface was in contact with the aluminum packaging exterior. The square separator prepared above was placed on the surface of the electrode active material layer of the positive electrode. Further, the negative electrode was cut into a square of 4.2 × 4.2 cm ² and arranged on the separator so that the surface of the negative electrode on the electrode active material layer side faced the separator. This is filled with LiPF ₆ solution with a concentration of 1.0M as the electrolyte (solvent is a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 3/7 (volume ratio), vinylene carbonate 2% by volume (solvent ratio) as an additive). did. Furthermore, in order to seal the opening of the aluminum packaging material, heat sealing at 150 ° C. was performed to close the aluminum exterior, and a lithium ion secondary battery was manufactured.
With respect to the obtained lithium ion secondary battery, the initial swell characteristic, post-cycle swell characteristic, cycle characteristic, and discharge rate characteristic of the negative electrode were measured by the method described above.

[Example 2]
In step [1.1], 85 parts of butyl acrylate and 15 parts of ethyl acrylate were used as the (meth) acrylic acid ester compound.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 3]
In step [1.1], 70 parts of butyl acrylate and 30 parts of ethyl acrylate were used as the (meth) acrylic acid ester compound.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 4]
In step [1.1], 1,3,5-tris (3-mercaptobutyloxyethyl) -1,3,5-triazine- instead of pentaerythritol tetrakis (3-mercaptobutyrate) as a polyfunctional thiol compound 2,4,6 (1H, 3H, 5H) -trione was used.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 5]
In the step [1.1], 1,4-bis (3-mercaptobutyryloxy) butane was used in place of pentaerythritol tetrakis (3-mercaptobutyrate) as the polyfunctional thiol compound.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 6]
In step [1.1], the amount of pentaerythritol tetrakis (3-mercaptobutyrate) was changed to 0.05 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 7]
In step [1.1], the amount of pentaerythritol tetrakis (3-mercaptobutyrate) was changed to 4 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 8]
In step [1.1], the amount of pentaerythritol tetrakis (3-mercaptobutyrate) was changed to 8 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 9]
In the step [1.1], 0.1 parts of divinylbenzene as a polyfunctional vinyl compound was further added to the pressure vessel during the polymerization.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 10]
In the step [1.1], 0.1 parts of divinylbenzene as a polyfunctional vinyl compound was further added to the pressure vessel during the polymerization.
In Step [1.3], the amount of the binder composition (B) was changed to 2.5 parts corresponding to the solid content.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 11]
In the step [1.1], 0.1 parts of divinylbenzene as a polyfunctional vinyl compound was further added to the pressure vessel during the polymerization.
In step [1.3], the amount of the binder composition (B) was changed to 0.3 parts corresponding to the solid content.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 12]
In the step [1.1], 0.1 parts of divinylbenzene as a polyfunctional vinyl compound was further added to the pressure vessel during the polymerization.
In Step [1.3], the type of carboxymethyl cellulose was changed to “MAC200HC” (manufactured by Nippon Paper Chemical Co., Ltd.) (1% by weight aqueous solution viscosity measured at 25 ° C. with a B-type viscometer = 1200 mPa · s).
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 13]
In the step [1.1], 0.1 parts of divinylbenzene as a polyfunctional vinyl compound was further added to the pressure vessel during the polymerization.
In Step [1.3], the type of carboxymethyl cellulose was changed to “MAC350HC” (manufactured by Nippon Paper Chemicals Co., Ltd. (1 mass% aqueous solution viscosity measured with a B-type viscometer at 25 ° C. = 3100 mPa · s)).
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 14]
In step [1.3], the amount of natural graphite was changed to 100 parts, and SiO _x was not used.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 15]
In step [1.3], the amount of natural graphite was changed to 80 parts, and the amount of SiO _x was changed to 20 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 16]
In step [1.3], the amount of natural graphite was changed to 70 parts, and the amount of SiO _x was changed to 30 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 17]
In step [1.3], the amount of natural graphite was changed to 50 parts, and the amount of SiO _x was changed to 50 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 18]
In step [1.1], the amount of N-methylolacrylamide was changed to 0.5 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 19]
In step [1.1], the amount of N-methylolacrylamide was changed to 0.8 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 20]
[20.1. Production of polymer particles (A) for positive electrode]
In a 5 MPa pressure vessel with a stirrer, 100 parts of 2-ethylhexyl acrylate as a (meth) acrylic ester compound, 20 parts of acrylonitrile as an α, β-unsaturated nitrile compound, 2 parts of methacrylic acid as a monomer having an acidic group, polyfunctional 0.15 parts of pentaerythritol tetrakis (3-mercaptobutyrate) as a thiol compound, 0.1 part of divinylbenzene as a polyfunctional vinyl compound, 1 part of sodium lauryl sulfate as an emulsifier, 150 parts of ion-exchanged water as a solvent, and polymerization initiation After adding 0.2 parts of ammonium persulfate as an agent and stirring sufficiently, the mixture was heated to 55 ° C. to initiate polymerization.

  When the monomer consumption reached 95.0%, the reaction was stopped by cooling. A 5% aqueous sodium hydroxide solution was added to the aqueous dispersion containing the polymer thus obtained to adjust the pH to 10. Then, the unreacted monomer was removed by heating under reduced pressure. Furthermore, it cooled to 30 degrees C or less after that, and obtained the binder composition (C) containing the polymer particle (A) for positive electrodes. By using the obtained binder composition (C), the glass transition temperature of the polymer particles (A) was measured by the method described above. As a result of the measurement, the glass transition temperature (Tg) was −32 ° C.

[20.2. Production of slurry composition for positive electrode]
1. In a planetary mixer, 100 parts by weight of LiCoO ₂ as a positive electrode active material, ₂ parts of acetylene black (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and the binder composition (C) in an amount equivalent to 2. 5 parts, 1 part of a 1% aqueous solution of carboxymethyl cellulose (Nippon Paper Chemical Co., Ltd. “MAC200HC”) as a water-soluble polymer, and 1 part of carboxymethyl cellulose (Nippon Paper Chemical Co., Ltd. “MAC350HC”) A 1% aqueous solution was added in an amount corresponding to the solid content, and ion-exchanged water was further added and mixed so that the total solid content concentration was 67% to prepare a positive electrode slurry composition.

[20.3. Production of positive electrode)
The positive electrode slurry composition was applied onto an aluminum foil having a thickness of 20 μm as a current collector using a comma coater. The coating amount of the positive electrode slurry composition of this case, the solid content of the positive electrode slurry composition per unit area of the surface of the aluminum foil was coated to a ^{38mg / cm 2 ~40mg / cm 2} . Thereafter, the applied positive electrode slurry composition was dried to form an electrode active material layer on the surface of the aluminum foil. This drying was performed by conveying the aluminum foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a positive electrode raw material. This raw fabric was pressed with a roll press so that the positive electrode had a density of 3.65 g / cm ^{3 to} 3.74 g / cm ³ to obtain a positive electrode. A part was cut out from this positive electrode, and the thickness and binding property of the positive electrode were measured.

[20.4. (Manufacture of negative electrode)
In a planetary mixer, 100 parts by weight of natural graphite as a negative electrode active material, 1.0 part of the binder composition (B) produced in Example 1 as a binder in terms of solid content, and a high molecular weight type carboxymethyl cellulose as a water-soluble polymer 1 part aqueous solution of “MAC350HC” (manufactured by Nippon Paper Chemical Co., Ltd.) is added in an amount equivalent to the solid content, and ion-exchanged water is further added and mixed so that the total solid content concentration becomes 52%. Prepared.

This negative electrode slurry composition was applied on a copper foil having a thickness of 20 μm, which was a current collector, with a comma coater. The coating amount of the negative electrode slurry composition in this case, the solid content of the negative electrode slurry composition per unit area of the surface of the copper foil was set to be ^{11mg / cm 2 ~12mg / cm 2} . Thereafter, the applied negative electrode slurry composition was dried to form an electrode active material layer on the surface of the copper foil. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, the negative electrode original fabric was obtained by heat-processing at 120 degreeC for 2 minute (s). The raw by a roll press machine, the density of the negative electrode performs a press so as to be ^{1.50g / cm 3 ~1.60g / cm 3} , and a negative electrode.

[20.5. (Manufacture of lithium ion secondary batteries)
Step [1.6] of Example 1 except that the positive electrode manufactured in the above step [20.3] was used and the negative electrode manufactured in the above step [20.4] was used. ] A lithium ion secondary battery was manufactured in the same manner.
With respect to the obtained lithium ion secondary battery, the initial swell characteristic, post-cycle swell characteristic, cycle characteristic, battery capacity, and discharge rate characteristic of the positive electrode were measured by the method described above.

[Example 21]
In the step [20.1], 85 parts of 2-ethylhexyl acrylate and 15 parts of butyl acrylate were used as the (meth) acrylic acid ester compound.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 20.

[Example 22]
In step [20.1], 70 parts of 2-ethylhexyl acrylate and 30 parts of butyl acrylate were used as the (meth) acrylic acid ester compound.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 20.

[Example 23]
In step [20.2], LiMn ₂ O ₄ was used instead of LiCoO ₂ as the positive electrode active material.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 20.

[Example 24]
In step [20.2], LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used instead of LiCoO ₂ as the positive electrode active material.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 20.

[Example 25]
In step [20.1], the amount of pentaerythritol tetrakis (3-mercaptobutyrate) was changed to 0.05 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 20.

[Example 26]
In step [20.1], the amount of pentaerythritol tetrakis (3-mercaptobutyrate) was changed to 4 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 20.

[Example 27]
In step [20.1], the amount of pentaerythritol tetrakis (3-mercaptobutyrate) was changed to 8 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 20.

[Comparative Example 1]
In step [1.1], pentaerythritol tetrakis (3-mercaptobutyrate) was not used.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 2]
In step [1.1], the amount of pentaerythritol tetrakis (3-mercaptobutyrate) was changed to 15 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 3]
In step [1.1], 85 parts of butyl acrylate and 15 parts of ethyl acrylate were used as the (meth) acrylic acid ester compound, and pentaerythritol tetrakis (3-mercaptobutyrate) was not used.
In Step [1.3], the amount of natural graphite was changed to 100 parts, and SiO _x was not used.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 4]
In step [1.1], 70 parts of butyl acrylate and 30 parts of ethyl acrylate were used as the (meth) acrylic acid ester compound, and the amount of pentaerythritol tetrakis (3-mercaptobutyrate) was changed to 15 parts.
In Step [1.3], the amount of natural graphite was changed to 100 parts, and SiO _x was not used.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 5]
In step [20.1], pentaerythritol tetrakis (3-mercaptobutyrate) and divinylbenzene were not used.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 20.

[Comparative Example 6]
In step [20.1], the amount of pentaerythritol tetrakis (3-mercaptobutyrate) was changed to 15 parts, and divinylbenzene was not used.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 20.

[Comparative Example 7]
In step [20.1], 85 parts of 2-ethylhexyl acrylate and 15 parts of butyl acrylate were used as the (meth) acrylic acid ester compound, and pentaerythritol tetrakis (3-mercaptobutyrate) and divinylbenzene were used.
In Step [20.2], LiMn ₂ O ₄ was used instead of LiCoO ₂ as the positive electrode active material.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 20.

[Comparative Example 8]
In Step [20.1], 70 parts of 2-ethylhexyl acrylate and 30 parts of butyl acrylate were used as the (meth) acrylic acid ester compound, and pentaerythritol tetrakis (3-mercaptobutyrate) and divinylbenzene were used.
In Step [20.2], LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used instead of LiCoO ₂ as the positive electrode active material.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 20.

[result]
The results of Examples and Comparative Examples described above are shown in Tables 1 to 9 below.
In the table below, the terms of polymer particles (A) in Examples 1 to 19 and Comparative Examples 1 to 4 correspond to polymer particles (A) of the negative electrode. Moreover, the term of the polymer particle (A) of Examples 20-27 and Comparative Examples 5-8 respond | corresponds to the polymer particle (A) of a positive electrode.
In the table below, the meanings of the abbreviations are as follows.
PVDF: polyvinylidene fluoride SBR: styrene butadiene rubber BA: butyl acrylate EA: ethyl acrylate 2-EHA: 2-ethylhexyl acrylate LCO: LiCoO ₂
LMO: LiMn ₂ O ₄
NMC: LiNi _1/3 Co _1/3 Mn _1/3 O ₂

[Consideration]
As can be seen from the above table, the cycle characteristics and discharge rate characteristics superior to the comparative examples can be obtained in the examples. Therefore, it was confirmed that the present invention can realize a lithium ion secondary battery excellent in cycle characteristics and discharge rate characteristics.
Further, from the comparison between the above examples and comparative examples, the electrode according to the present invention is usually excellent in the binding property between the current collector and the electrode active material layer, and even after repeating the charge / discharge cycle. It turns out that it is hard to swell.

Claims (9)

  A monomer composition comprising a (meth) acrylate compound and a polyfunctional thiol compound, wherein the ratio of the polyfunctional thiol compound to 100 parts by weight of the (meth) acrylate compound is 0.001 to 10 parts by weight. The binder composition for lithium ion secondary battery electrodes containing the polymer particle (A) obtained by superposing | polymerizing (a) in an aqueous medium, and a solvent.   The lithium ion secondary battery electrode according to claim 1, wherein the monomer composition (a) includes a polymerizable monomer copolymerizable with the (meth) acrylic acid ester compound or the polyfunctional thiol compound. Binder composition.   A slurry composition for a lithium ion secondary battery electrode, comprising the binder composition for a lithium ion secondary battery electrode according to claim 1 or 2 and an electrode active material.   The slurry composition for lithium ion secondary battery electrodes according to claim 3, wherein the electrode active material is a positive electrode active material.   The slurry composition for a lithium ion secondary battery electrode according to claim 3, wherein the electrode active material is a negative electrode active material.   6. The lithium ion secondary battery electrode according to claim 5, comprising polymer particles (B) obtained by polymerizing a monomer composition (b) containing an aromatic vinyl compound and a conjugated diene compound in an aqueous medium. Slurry composition.   Furthermore, the slurry composition for lithium ion secondary battery electrodes as described in any one of Claims 3-6 containing a water-soluble polymer.   The electrode for lithium ion secondary batteries obtained by apply | coating the slurry composition for lithium ion secondary battery electrodes as described in any one of Claims 3-7 on a collector, and drying. Comprising a positive electrode, a negative electrode and an electrolyte;
The lithium ion secondary battery whose said positive electrode or the said negative electrode is an electrode for lithium ion secondary batteries of Claim 8.