JP2009266612A - Binder for lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a binder for an electrode of a lithium ion battery having excellent adhesive characteristics and excellent cycle characteristics when used in the lithium ion battery. <P>SOLUTION: The binder and a binder slurry composition for a lithium battery having a higher adhesive strength than that in the prior art, and excellent cycle characteristics is composed of multilayer structural polymer particles having at least two layers having a thermal plastic resin layer (A) having at least a glutaric anhydride structural unit and a glass transition temperature of 120-200°C on its outermost layer, and, in its interior, at least one layer of rubber component layer (B) with acrylic acid alkyl ester unit 50 to 99.9 pts.mass and other single functional units 50-0.1 pts.mass. A mass ratio between the rubber component layer (B) and the thermal plastic resin layer (A) is 50/50 to 90/10 in (B)/(A). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a binder for a lithium ion secondary battery and use thereof.

  In recent years, mobile terminals such as mobile phones and notebook computers have been widely used. In particular, the development of a secondary battery as a power source is important. As these secondary batteries, lithium ion secondary batteries are frequently used. The basic structure of a lithium ion secondary battery is composed of an electrolyte / gel electrolyte that dissolves lithium ions, two electrodes, a positive electrode and a negative electrode, and an active material for the positive electrode and the negative electrode.

  Mobile terminals are required to be further reduced in size, weight, thickness, and performance. Under such circumstances, movements for thickness reduction and size reduction are also required for lithium batteries.

In order to improve the performance of a battery, it is important to improve the performance of each component used in the battery. In addition to examining the active material and the current collector itself, the electrode is used to hold the active material on the current collector. It is also important to examine polymers that serve as binders.
Usually, this binder is mixed with water or an organic liquid to form a binder composition, and the composition is applied to a current collector and dried to produce an electrode. As such a binder composition, at least a polyurethane (Patent Document 1), a polymer using butadiene, acrylonitrile, styrene or the like as a raw material (Patent Document 2), or a fluorine-based resin such as polyvinylidene fluoride (hereinafter referred to as PVDF) is used as a binder. What is used as is known (Patent Document 3).

  Fluorine-based resins have low adhesion to active materials and metal current collectors, and it is necessary to add a large amount of a binder, covering the surface of the active material and causing the problem of reducing battery characteristics.

  In order to solve the above-mentioned problem of adhesive strength, a polyurethane-based binder has been presented, but this also does not solve the problem of covering the surface of the active material and deteriorating battery characteristics.

  On the other hand, in the case of a polymer using butadiene, acrylonitrile, styrene or the like as a raw material, since the main chain has a double bond, particularly in butadiene or the like, the double bond portion is oxidized and deteriorated by repeated charge and discharge, In addition, since the binder gradually dissolves due to heat generation at the electrode portion, there is a problem that the active material is easily removed from the metal current collector, and the battery capacity is reduced.

  On the other hand, in Patent Document 4, this problem is avoided by using multi-layer structured particles. However, in this multilayer structure particle, only the difference in glass transition temperature between the central layer and other layers is described. At this time, the glass transition temperature of the outermost layer is not a sufficient temperature, and there is a problem that the binder is dissolved by the heat generation of the electrode part as described above, and the active material is easily dropped.

Under such circumstances, there has been a high demand for the development of a multilayer structure particle type binder that does not cover the surface of the active material, has high adhesion, and does not dissolve the binder due to heat generation at the electrode portion.
JP 2007-200957 A JP 2007-173047 A JP 2004-47460 A International Publication No. 98/39808 Pamphlet

  The present invention relates to a secondary battery capable of improving the high-rate discharge characteristics and cycle characteristics of a secondary battery in a binder for a lithium ion secondary battery, having sufficient adhesion to a metal assembly and an active material. It is to provide a binder.

  As a result of intensive studies on the above-mentioned problems of the prior art, the present inventors have disclosed good dispersibility in thermoplastic resins, excellent heat resistance and retention stability disclosed in JP-A-2007-169626. The present inventors have newly found that specific multilayer structure particles useful as additives for optical materials are also useful as binders for lithium ion secondary batteries.

That is, the present invention
(1) The outermost layer has a thermoplastic resin layer (A) having at least a glutaric anhydride structural unit represented by the following general formula (1) and having a glass transition temperature of 120 ° C. or higher and 200 ° C. or lower; Two or more rubber component layers (B) having at least one or more acrylic acid alkyl ester units of 50 to 99.9 parts by mass and other monofunctional units of 50 to 0.1 parts by mass The mass ratio of the rubber component layer (B) and the thermoplastic resin layer (A) is 50/50 to 90/10 in (B) / (A). A binder for a lithium ion secondary battery comprising multilayer polymer particles characterized by

(In the above formula, R ¹ and R ² are the same or different and represent any one selected from a hydrogen atom and an alkyl group having 1 to 5 carbon atoms.)
(2) A binder slurry composition for a lithium ion secondary battery, wherein the binder described in (1) is a dispersion in which a boiling point at normal pressure is dispersed in a dispersion medium having a temperature of 80 ° C to 350 ° C or less,
(3) (I) (i) an unsaturated carboxylic acid alkyl ester unit, (ii) a thermoplastic resin layer (A) which is a copolymer having an unsaturated carboxylic acid unit in the outermost layer, and at least the inside Multilayer structure polymer particle comprising two or more layers having a rubber component layer having 50 to 99.9 parts by weight of one or more alkyl acrylate units and 50 to 0.1 parts by weight of other monofunctional units (II) Disperse the precursor in a dispersion medium having a boiling point of 80 ° C. to 350 ° C. at atmospheric pressure,
(III) By heating to 100 ° C. or higher,
(IV) Multilayer structure polymer particles having a thermoplastic resin layer (A) having a glutaric anhydride unit represented by the general formula (1) are generated. (1) or (2) Method for producing binder slurry composition for lithium ion secondary battery,
(4) A slurry for a lithium ion secondary battery electrode containing the binder slurry composition according to (2) or the binder slurry composition obtained from the production method according to (3) and an active material,
It is.

  According to the present invention, a secondary battery binder that has sufficient adhesion to a metal current collector, a positive electrode active material, and a negative electrode active material, and can improve high rate discharge characteristics and cycle characteristics of a secondary battery. Can be obtained.

  Hereinafter, the present invention will be described in detail.

  The binder for a lithium ion secondary battery of the present invention is a multilayer structure polymer particle. Among the multilayered polymer particles, the copolymer component forming the outermost layer is required to have at least a glutaric anhydride structural unit represented by the following general formula (1).

In this case, in the above ^formula, R 1, ^{R 2} represents either hydrogen atoms, selected from alkyl groups of 1 to 5 carbon atoms. These may be the same or different.
Among these, a hydrogen atom, a methyl group, an ethyl group, and an isopropyl group are preferable, a hydrogen atom, a methyl group, and an ethyl group are more preferable, and a hydrogen atom and a methyl group are particularly preferable.

  In the multilayer structure polymer of the present invention, the copolymer component other than the glutaric anhydride structural unit is not particularly limited as long as it is composed of a polymer component having thermoplasticity.

  In the multilayer structure polymer of the present invention, the copolymer component other than the glutaric anhydride structural unit may contain other thermoplastic copolymer components as long as the object of the present invention is not impaired.

  The thermoplastic copolymer component includes the cyclic structural unit represented by the general formula (1), an unsaturated carboxylic acid alkyl ester unit, an unsaturated carboxylic acid unit, an unsaturated glycidyl group-containing unit, and an unsaturated dicarboxylic anhydride unit. And polymers containing one or more units selected from aliphatic vinyl units, aromatic vinyl units, vinyl cyanide units, maleimide units, unsaturated dicarboxylic acid units, and other vinyl units. Among them, a polymer containing an unsaturated carboxylic acid alkyl ester unit is preferable, and in addition, a cyclic structural unit represented by the general formula (1), an unsaturated glycidyl group-containing unit, an unsaturated carboxylic acid unit, and an unsaturated group. A polymer containing at least one unit selected from dicarboxylic anhydride units, α-hydroxymethyl unsaturated carboxylic acid alkyl ester units, and α-hydroxymethyl unsaturated carboxylic acid units is more preferable.

  Although it does not specifically limit as a monomer used as the raw material of an unsaturated carboxylic acid alkylester unit, Acrylic acid alkylester or methacrylic acid alkylester is used preferably. Specifically, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate , T-butyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, stearyl acrylate, stearyl methacrylate, octadecyl acrylate , Octadecyl methacrylate, phenyl acrylate, phenyl methacrylate, benzyl acrylate, benzyl methacrylate, chloromethyl acrylate, chloromethyl methacrylate, 2-chloroethyl acrylate, methacrylic acid -Chloroethyl, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 2,3,4,5,6-pentahydroxyhexyl acrylate, methacrylic acid 2 , 3,4,5,6-pentahydroxyhexyl, 2,3,4,5-tetrahydroxypentyl acrylate, 2,3,4,5-tetrahydroxypentyl methacrylate, aminoethyl acrylate, propylamino acrylate Examples include ethyl, dimethylaminoethyl methacrylate, ethylaminopropyl methacrylate, phenylaminoethyl methacrylate, and cyclohexylaminoethyl methacrylate. From the viewpoint that the effect of improving the charge / discharge characteristics is great, methyl acrylate or methyl methacrylate is preferably used. These units can be used alone or in combination of two or more.

  There is no restriction | limiting in particular as an unsaturated carboxylic acid monomer, The hydrolyzate of acrylic acid, methacrylic acid, maleic acid, and also maleic anhydride etc. are mentioned. In particular, acrylic acid and methacrylic acid are preferable from the viewpoint of excellent thermal stability, and methacrylic acid is more preferable. These can be used alone or in combination.

  The monomer used as the raw material for the unsaturated glycidyl group-containing unit is not particularly limited, but is glycidyl acrylate, glycidyl methacrylate, glycidyl itaconate, diglycidyl itaconate, allyl glycidyl ether, styrene-4-glycidyl ether. And glycidyl styrene or glycidyl methacrylate is preferably used from the viewpoint that the effect of improving impact resistance is great. These units can be used alone or in combination of two or more.

  Examples of the monomer used as the raw material for the unsaturated dicarboxylic acid anhydride unit include maleic anhydride, itaconic anhydride, glutaconic anhydride, citraconic anhydride, and aconitic anhydride, which have a large effect of improving impact resistance. From this viewpoint, maleic anhydride is preferably used. These units can be used alone or in combination of two or more.

  As a monomer used as a raw material for the aliphatic vinyl unit, ethylene, propylene, butadiene, or the like can be used.

  Examples of monomers used as raw materials for aromatic vinyl units include styrene, α-methylstyrene, 1-vinylnaphthalene, 4-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl- 4-Benzylstyrene, 4- (phenylbutyl) styrene, halogenated styrene and the like can be used.

  Acrylonitrile, methacrylonitrile, ethacrylonitrile, or the like can be used as a monomer as a raw material for the vinyl cyanide unit.

  As monomers for the raw material of the maleimide unit, maleimide, N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-isopropylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N- (p-bromo) Phenyl) maleimide and N- (chlorophenyl) maleimide can be used.

  As a monomer used as a raw material for the unsaturated dicarboxylic acid unit, maleic acid, maleic acid monoethyl ester, itaconic acid, phthalic acid, and the like can be used.

  Other monomers that can be used as starting materials for vinyl units include acrylamide, methacrylamide, N-methylacrylamide, butoxymethylacrylamide, N-propylmethacrylamide, N-vinyldiethylamine, N-acetylvinylamine, allylamine, methallylamine, N-methylallylamine, p-aminostyrene, 2-isopropenyl-oxazoline, 2-vinyl-oxazoline, 2-acryloyl-oxazoline, 2-styryl-oxazoline, and the like can be used. These monomers can be used alone or in combination of two or more.

  Of the copolymers obtained from these monomers, among the copolymers forming the outermost layer, the glass transition temperature is preferably 120 ° C. or higher and 200 ° C. or lower. More preferably, it is 120 degreeC or more and 180 or less, More preferably, it is 130 degreeC or more and 150 or less.

  The content of the glutaric anhydride structural unit represented by the general formula (1) in the thermoplastic resin layer (A) in the multilayer polymer particle of the present invention is preferably 100 masses of the thermoplastic resin layer (A). It is 10-50 mass parts in a part, More preferably, it is 15-30 mass parts. When it is less than 10 parts by mass, the glass transition temperature tends to be low. When the glass transition temperature is less than 120 degrees, in the use of the lithium ion secondary battery, the active material is likely to fall off from the binder metal current collector, and the cycle characteristics of the lithium ion secondary battery are likely to deteriorate. In addition, when the glass transition temperature exceeds 200 ° C., it does not serve as a binder for the metal current collector and the active material, and thus is preferably within this range.

  The rubber component layer (B) in the multilayer structure polymer particles of the present invention is a rubber composed of 50 to 99.9 parts by mass of alkyl acrylate units and 50 to 0.1 parts by mass of other monofunctional units. It consists of a polymer exhibiting the following characteristics. Specific examples of the alkyl acrylate monomer unit used to form the rubber component layer (B) include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, methacryl N-propyl acid, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isoptyl acrylate, isobutyl methacrylate, t-butyl acrylate, t-butyl methacrylate, n-pentyl acrylate , N-pentyl methacrylate, isopentyl acrylate, isopentyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, cyclohexyl acrylate, cyclohexane methacrylate Xylyl, dodecyl acrylate, dodecyl methacrylate, stearyl acrylate, stearyl methacrylate, octadecyl acrylate, octadecyl methacrylate, phenyl acrylate, phenyl methacrylate, benzyl acrylate, benzyl methacrylate, chloromethyl acrylate, chloro methacrylate Methyl, 2-chloroethyl acrylate, 2-chloroethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 2,3,4, acrylic acid 5,6-pentahydroxyhexyl, 2,3,4,5,6-pentahydroxyhexyl methacrylate, 2,3,4,5-tetrahydroxypentyl acrylate, 2,3,4, methacrylate -Tetrahydroxypentyl, aminoethyl acrylate, propylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethylaminopropyl methacrylate, phenylaminoethyl methacrylate, cyclohexylaminoethyl methacrylate, etc., especially n-butyl acrylate preferable. If the amount of the alkyl acrylate ester is less than 50% by weight, the rubber elasticity of the multilayer polymer particles is lowered, and the adhesive strength and flexibility as a binder may be inferior. On the other hand, if it exceeds 99.9% by weight, the structure of the multi-layered polymer particles is not formed. These can be used alone or in combination of two or more thereof.

  Moreover, as other monofunctional units, monofunctional units other than the alkyl acrylate ester can be used. For example, styrene, α-methylstyrene, 1-vinylnaphthalene, 3-methylstyrene, 4- Aromatic vinyl monomers such as propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4- (phenylbutyl) styrene, halogenated styrene; acrylonitrile, methacrylonitrile, etc. Vinyl cyanide monomer; butadiene, isoprene, 2,3-dimethylbutadiene, 2-methyl-3-ethylbutadiene, 1,3-pentadiene, 3-methyl-1,3-pentadiene, 2-ethyl-1, 3-pentadiene, 1,3-hexadiene, 2-methyl-1,3-hexadiene, 3,4 Dimethyl-1,3-hexadiene, 1,3-heptadiene, 3-methyl-1,3-heptadiene, 1,3-octadiene, cyclopentadiene, chloroprene, conjugated diene monomers and the like of myrcene, and the like. Preferred rubbers include, for example, acrylic units such as ethyl acrylate units and butyl acrylate units, styrene units such as styrene units and α-methylstyrene units, nitrile units such as acrylonitrile units and methacrylonitrile units, and butadiene. It is a rubber composed of conjugated diene units such as units and isoprene units. A rubber composed of a combination of two or more of these components is also preferred.

  In addition to these components, rubber obtained by crosslinking a copolymer composed of a polyfunctional monomer is also preferable. Examples of the polyfunctional monomer include allyl methacrylate, allyl acrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl malate, divinyl adipate, divinylbenzene ethylene glycol dimethacrylate, divinylbenzene ethylene glycol diacrylate. , Diethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetramethacrylate, tetramethylolmethane tetraacrylate, dipropylene glycol dimethacrylate And dipropylene glycol Over diacrylate, and these two or more kinds may be used in combination.

  The multilayer structure polymer particle of the present invention has at least one rubber component layer (B) inside and at least the thermoplastic resin component layer (A) as an outermost layer. The number of layers constituting the multilayer structure polymer particle of the present invention may be two or more, and may be composed of three layers or four or more layers.

  The total weight ratio of the layer (B) and the layer (A) is in the range of 50/50 to 90/10 in (B) / (A). When the ratio of the layer (B) is smaller than this range, the copolymerization system at the time of forming the thermoplastic resin component layer (A) is inferior, and the adhesiveness as a binder is also lowered, which is not preferable. On the contrary, when the ratio of the layer (B) is larger than this range, the heat resistance becomes insufficient.

  The multilayer structure polymer particles in the present invention are obtained by using a known polymerization method such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization, so that (i) an unsaturated carboxylic acid alkyl ester unit in the outermost layer, (ii) The thermoplastic resin layer (A) which is a copolymer having an unsaturated carboxylic acid unit, and at least one or more layers of alkyl acrylate units of 50 to 99.9 parts by mass and other monofunctional units It is produced by making a multilayer structure polymer particle precursor composed of two or more layers having a rubber component layer having 50 to 0.1 parts by mass and subsequently forming a glutaric anhydride skeleton in the outermost layer.

  For example, in emulsion polymerization, deionized water, an emulsifier, and a polymerization initiator are added to a reaction vessel, and then each monomer and a crosslinking agent are added alone or in a mixture of two or more, and polymerized at a predetermined temperature. It is preferable. The temperature of emulsion polymerization is not necessarily limited, but a general range is 0 ° C to 100 ° C. Examples of the emulsifier used herein include aliphatic alkali metal salts such as sodium oleate, sodium laurate, and sodium stearate; sulfate esters of aliphatic alcohols such as sodium lauryl sulfate; and rosinates such as potassium rosinate. An alkylallylsulfonic acid such as dodecylbenzenesulfonic acid, and the like, and these are used in a combination of one or two or more. As a polymerization initiator used in emulsion polymerization, a radical polymerization initiator is generally used. As specific examples of the radical polymerization initiator, peroxides such as persulfate, azobisisobutyronitrile, and benzoyl peroxide can be used alone. In addition, as a radical polymerization initiator, a redox initiator using a combination of organic hydroperoxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, paramentane hydroperoxide and a reducing agent such as a transition metal salt is used. can do.

  Moreover, a chain transfer agent can be used as needed. Specific examples include mercaptans such as n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, mercaptoethanol, and the like; Mixtures; halogenated hydrocarbons such as chloroform and carbon tetrachloride. Among these, alkyl mercaptans such as n-octyl mercaptan are preferable.

  In the present invention, the thermoplastic resin layer (A) in the multilayer polymer particle precursor is preferably a copolymer of (i) an unsaturated carboxylic acid alkyl ester unit and (ii) an unsaturated carboxylic acid unit. . The preferred ratio is that the monomer mixture is 100 parts by mass, the unsaturated carboxylic acid monomer (ii) is 15 to 50 parts by mass, more preferably 20 to 45 parts by mass, the unsaturated carboxylic acid alkyl ester unit ( i) is preferably 50 to 85 parts by mass, more preferably 55 to 80 parts by mass. When the unsaturated carboxylic acid unit is less than 15 parts by mass, the amount of the glutaric anhydride structural unit represented by the general formula (1) generated by the subsequent heat cyclization is reduced, and the heat resistance improvement effect is small. Tend to be. On the other hand, when the unsaturated carboxylic acid unit exceeds 50 parts by mass, a large amount of the unsaturated carboxylic acid unit tends to remain after the cyclization reaction by heating, and the residence stability tends to decrease.

  After the emulsion polymerization, separation and acquisition of the produced multilayer structure polymer particle precursor from the polymerization reaction system can be performed according to a known method. As a known separation and acquisition method, for example, an acid precipitation method, a salting out method, a spray drying method, a freeze coagulation method, or the like can be employed.

  In the present invention, multilayer structure polymer particles can be produced by heating a multilayer structure polymer particle precursor to cause an intramolecular cyclization reaction by dealcoholization and / or dehydration. In this case, typically, the copolymer is heated to dehydrate the carboxyl group of two (ii) unsaturated carboxylic acid units, or is adjacent to (ii) an unsaturated carboxylic acid unit (i ) Removal of alcohol from unsaturated carboxylic acid alkyl ester units yields one unit of the glutaric anhydride structural unit.

  The multilayer structure polymer particle precursor thus obtained is subsequently subjected to a step of generating a glutaric anhydride skeleton unit.

  For the step of generating the glutaric anhydride skeleton unit, the aqueous dispersion obtained in the multilayer polymer particle precursor step may be used as it is, but in order to reduce the mixing of emulsifiers, salts, etc., a generally known method is used. After being isolated in a solid state using an acid precipitation method, salting-out method, spray drying method, freeze-thaw coagulation method, etc., and after being dispersed in a dispersion medium having a boiling point of 80 to 350 ° C. at normal pressure Alternatively, it may be subjected to a step of generating a glutaric anhydride skeleton unit.

  In the step of generating a glutaric anhydride skeleton unit, it can be generated by heating in a solid state, but preferably in a dispersion medium having a boiling point of 80 ° C. to 350 ° C. at normal pressure after isolation into a solid state. After being dispersed. This method is preferable from the viewpoint that it is easy to obtain a final dispersion as a binder composition and that the fusion of the multilayer structure polymer particles can be prevented.

  The following are illustrated as a solvent whose boiling point of a normal pressure is 80 to 350 degreeC. The number in parentheses after the name of the dispersion medium is the boiling point (° C.) at atmospheric pressure, and is a value obtained by rounding off or rounding off after the decimal point. hydrocarbons such as n-dodecane (216), decahydronaphthalene (189-191) and tetralin (207); alcohols such as 2-ethyl-1-hexanol (184) and 1-nonanol (214); 197), ketones such as acetophenone (202) and isophorone (215); benzyl acetate (213), isopentyl butyrate (184), γ-butyrolactone (204), methyl lactate (143), ethyl lactate (154) and butyl lactate Esters such as (185); amines such as o-toluidine (200), m-toluidine (204) and p-toluidine (201); N-methyl-2-pyrrolidone (202), N, N-dimethylacetamide (194) and amides such as dimethylformamide (153) ; And dimethyl sulfoxide (189) and sulfoxides, sulfones such as sulfolane (287), and the like. As the dispersion medium, N-methyl-2-pyrrolidone, methyl lactate, and ethyl lactate are particularly preferable.

  The step of producing a glutaric anhydride skeleton unit can be produced by the following method. That is, a glutaric anhydride skeleton unit is generated by heating the above-mentioned aqueous dispersion, a solid state and a state in which the boiling point at normal pressure is dispersed in a dispersion medium having a boiling point of 80 to 350 ° C. be able to.

  In addition, when heating a water dispersion or a state in which the boiling point is dispersed in a dispersion medium having a boiling point of 80 ° C. to 350 ° C. or less, it is usually performed in a known heating reaction tank or pressure-resistant heating reactor. it can. At this time, the reaction is preferably performed in an inert gas such as nitrogen, argon or helium. The pressure may be either normal pressure or increased pressure. However, when productivity is taken into consideration, it is preferable to carry out under normal pressure or an autogenous pressure generated by heating the solvent.

  The reaction temperature in this method is 100 ° C. or higher and 280 ° C. or lower, more preferably 120 ° C. or higher and 200 ° C. or lower, and further preferably 120 ° C. or higher and 180 ° C. or lower. If it is this temperature, decomposition | disassembly of the copolymer which comprises multilayer structure polymer particle is suppressed, and a glutaric anhydride skeleton unit can be produced | generated efficiently.

  When the multilayer structure polymer in which the glutaric anhydride skeleton unit is formed is obtained in a solid state, it is dispersed in a suitable solvent as a binder slurry. Suitable dispersions include hydrocarbons such as n-dodecane, decahydronaphthalene and tetralin; alcohols such as 2-ethyl-1-hexanol and 1-nonanol; ketones such as holon, acetophenone and isophorone; benzyl acetate , Esters such as isopentyl butyrate, γ-butyrolactone, methyl lactate, ethyl lactate and butyl lactate; amines such as o-toluidine, m-toluidine and p-toluidine; N-methyl-2-pyrrolidone, N, N-dimethyl Amides such as acetamide and dimethylformamide; and sulfoxide sulfones such as dimethyl sulfoxide and sulfolane. As the dispersion medium, N-methyl-2-pyrrolidone, methyl lactate, and ethyl lactate are particularly preferable.

  The active material constituting the electrode slurry for the lithium ion secondary battery of the present invention is composed of a positive electrode active material for the positive electrode and a negative electrode active material for the negative electrode. The positive electrode active material is a carbon material such as carbon black, amorphous whisker carbon, or graphite, and the negative electrode active material is a metal lithium, a lithium alloy, a carbon material that can dope / dedo lithium ions, lithium ions Tin oxide, niobium oxide, vanadium oxide, titanium oxide that can be doped / dedoped with lithium ions, or silicon that can be doped / dedoped with lithium ions, lithium Any transition metal nitride capable of doping and dedoping ions can be used. Among these, a carbon material that can dope / dedope lithium ions is preferable. Such a carbon material may be graphite or amorphous carbon, and activated carbon, carbon fiber, carbon black, mesocarbon microbeads, natural graphite and the like are used.

Examples of the positive electrode active material include transition metal oxides or transition metal sulfides such as MoS ₂ , TiS ₂ , MnO ₂ , and V ₂ O ₅ , LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _x Co _{(1 -x) O} 2 _(where, X is 0 or more, indicating the real number 1 below.) composite oxide consisting of lithium, such as a transition metal, polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole / polyaniline composite Examples thereof include conductive polymer materials such as body. Among these, a composite oxide composed of lithium and a transition metal is particularly preferable. When the negative electrode is lithium metal or a lithium alloy, a carbon material can also be used as the positive electrode. As the positive electrode, a mixture of lithium and transition metal composite oxide and a carbon material can be used.

  The lithium ion secondary battery electrode binder and binder slurry and lithium ion secondary battery electrode slurry thus obtained have higher heat resistance and are useful as binder properties than previously developed. In addition, when applied to a lithium ion secondary battery electrode, the electrode has highly efficient charge / discharge performance and excellent recycling characteristics.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these Examples.

(Reference Example 1)
Under a nitrogen atmosphere, 157 parts by mass of deionized water and 1 part by mass of Latemul E-118B (manufactured by Kao Corporation) and 0.2 part by mass of sodium pyrophosphate as an emulsifier were added to a polymerization vessel equipped with a stirring blade and a cooling tube. Heated to ° C. Next, 60 parts by mass of n-butyl acrylate and 21 parts by mass of styrene are added at the same temperature, 0.1 part by mass of potassium persulfate, 4 parts by mass of 1,4-butanediol diacrylate, 2 parts by mass of allyl methacrylate, sodium pyrophosphate Polymerization was performed by adding 0.2 parts by mass and 0.1 parts by mass of potassium persulfate dropwise over 4 hours. After completion of the dropwise addition, the reaction was continued for another hour, and it was confirmed by gas chromatography that all the raw materials had been consumed, and a copolymer latex was obtained.

  Further, the obtained copolymer latex was mixed with 35 parts by weight of deionized water, 2 parts by weight of Latemul E-118B, 25 parts by weight of methyl methacrylate, 10 parts by weight of methacrylic acid, 0.1 part by weight of sodium pyrophosphate, 0 parts of potassium persulfate. .1 part by mass was added dropwise over 2 hours. After completion of the dropwise addition, the reaction was continued for further 1 hour, and it was confirmed by gas chromatography that all the raw materials had been consumed, and a multilayer structure polymer latex was obtained.

  The multilayer structure polymer particle precursor in the form of agglomerated powder was obtained by salting out, washing and drying from the multilayer structure polymer latex.

(Reference Examples 2, 3, 4)
A multilayer polymer particle precursor was obtained in the same manner as in Reference Example 1 except that the monomer composition added during the first and second stage polymerizations was changed. Table 1 shows the monomer composition.

(Reference Example 5)
Under a nitrogen atmosphere, a polymerization vessel equipped with a stirring blade and a cooling tube, 150 parts by mass of deionized water, 2.5 parts by mass of sodium dodecylbenzenesulfonate (manufactured by Wako Pure Chemical Industries, Ltd.) as an emulsifier, 34 parts by mass of 1,3 butadiene Part, 20 parts by mass of styrene, 2 parts by mass of itaconic acid, 2 parts by mass of methyl methacrylate, 2 parts by mass of acrylonitrile and 0.5 parts by mass of divinylbenzene as a crosslinking agent were added and heated to 80 ° C. In order to perform the first stage polymerization, 0.01 parts by mass of potassium persulfate was added at the same temperature to initiate the polymerization. After 1 hour, it was confirmed by gas chromatography that all the monomers had been consumed. Next, in order to carry out the second stage polymerization, the obtained copolymer latex was added with 20 parts by mass of deionized water, 20 parts by mass of methyl methacrylate, 15 parts by mass of styrene, and 0.5 parts by mass of divinylbenzene over 2 hours. It was dripped. After completion of the dropwise addition, the reaction was continued for further 1 hour, and it was confirmed by gas chromatography that all the raw materials had been consumed, and a multilayer structure polymer latex was obtained.

<Outermost layer Tg measurement>
Using a differential scanning calorimeter (DSC-7 manufactured by Perkin Elmer), the measurement was performed at a temperature increase rate of 20 ° C./min in a nitrogen atmosphere.

<Confirmation of outermost glutaric acid skeleton formation>
Measured by an infrared spectrophotometer (Perkin Elmer Corp. System2000), the presence or absence of the absorption peak of 1800 cm ^-1 and 1760 cm ^-1 which is a characteristic peak of glutaric anhydride containing units, generation of glutaric anhydride containing units It was confirmed.

Example 1
The multilayer structure polymer particle precursor obtained in Reference Example 1 was placed in a vacuum oven and subjected to a heat treatment at 190 ° C. for 240 minutes and at a reduced pressure of 10 torr to obtain multilayer structure polymer particles. When the obtained polymer particles were confirmed with an infrared spectrophotometer, it was found that a peak indicating a glutaric anhydride skeleton was present. The multilayer polymer particles 15 g and N-methyl-2-pyrrolidone (hereinafter referred to as “NMP”) 285 g (manufactured by Kanto Chemical Co., Ltd., dehydrated grade) as an organic solvent were charged and stirred at a rotational speed of 500 min ⁻¹ for 170. And uniformly dissolved. Thereafter, the temperature was lowered to 30 ° C. to obtain a solution having a nonvolatile content of 5% by weight. When the obtained polymer particles were confirmed with an infrared spectrophotometer, it was found that a peak indicating a glutaric anhydride skeleton was present. This was used as the binder slurry composition of Example 1.

(Example 2)
1 g equipped with 15 g of layer-type multilayered polymer particle precursor obtained in Reference Example 1 and 285 g of NMP as organic solvent (manufactured by Kanto Chemical Co., Ltd., dehydrated grade) equipped with a stirrer, thermometer, and nitrogen gas inlet tube The solution was charged into a 0.0 liter glass autoclave and heated to 170 ° C. with stirring at a rotation speed of 500 min ⁻¹ in a nitrogen atmosphere to be uniformly dissolved. Thereafter, the temperature was lowered to 30 ° C. to obtain a solution having a nonvolatile content of 5% by weight. When the obtained polymer particles were confirmed with an infrared spectrophotometer, it was found that a peak indicating a glutaric anhydride skeleton was present. This was used as the binder slurry composition of Example 2.

(Comparative Examples 1-6)
Multilayer structure particle precursors (Comparative Examples 1, 2, 3, 4) prepared in Reference Examples 2, 3, 4, and 5 and SBR resin (BM400B manufactured by Nippon Zeon, Comparative Example 5) Fluorine resin (Kureha PVDF KF) For the binder of Polymer # 1120, Comparative Example 6), a binder slurry composition was prepared by the following method.

In a 1.0 liter glass autoclave equipped with a stirrer, a thermometer, and a nitrogen gas inlet tube, under a nitrogen atmosphere, 15 g of resin and 285 g of NMP (hereinafter referred to as NMP) as an organic solvent (Kanto Chemical Co., Ltd.) ), Dehydrated grade), and heated to 170 ° C. with stirring at a rotation speed of 500 min ⁻¹ to be uniformly dissolved. Thereafter, the temperature was lowered to 30 ° C. to obtain a solution having a nonvolatile content of 5% by weight.

<Creation of negative electrode>
40 g of the solution prepared in Examples 1 and 2 and Comparative Examples 1 to 6 was added to 98 parts by weight of natural graphite (LF18A, manufactured by Chuetsu Graphite Industries Co., Ltd.), and NMP for viscosity adjustment was further mixed to prepare a negative electrode mixture slurry. Was prepared. Next, this negative electrode mixture slurry was applied to a negative electrode current collector made of a strip-shaped copper foil having a thickness of 18 μm, dried, and compression molded to prepare a negative electrode having a thickness of 70 μm.

<Creation of positive electrode>
LiCoO ₂ (HLC-22 manufactured by Honjo FMC Energy System Co., Ltd.) 87 parts by mass, 8 parts by weight of graphite, 3 parts by mass of acetylene black and 40 g of the solution prepared in Examples 1 and 2 and Comparative Examples 1 to 6 were added. Further, NMP for viscosity adjustment was mixed to prepare a LiCoO ₂ mixture slurry. This LiCoO ₂ mixture slurry was applied to an aluminum foil having a thickness of 20 μm, dried, and compression molded to produce a positive electrode having a thickness of 70 μm.

<Adhesion evaluation>
Each created electrode was cut into a width of 2.0 cm and a length of 10 cm, cellophane tape (registered trademark) was affixed to the electrode surface, the electrode was fixed, and the tape was 180 ° C. at a speed of 50 mm / min according to JISK6854-2. The strength (N / cm) when peeled in the direction was measured 5 times, and the adhesiveness was evaluated from the average value. The results are shown in Table 2.

<Adjustment of non-aqueous electrolyte>
As a non-aqueous solvent, a mixture of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) in a ratio of EC: MEC = 4: 6 (mass ratio) was used, and then LiPF6 as an electrolyte was dissolved to obtain an electrolyte concentration. Was adjusted to 1.0 mol / liter.

<Production of coin-type battery>
The above-described negative electrode as a negative electrode for a coin-type battery was punched into a disk shape having a diameter of 14 mm to obtain a coin-shaped negative electrode having a weight of 20 mg / 14 mmφ. Further, the above-mentioned positive electrode was punched out into a disk shape having a diameter of 13.5 mm as a positive electrode for a coin-type battery, and a coin-shaped positive electrode having a weight of 42 mg / 13.5 mmφ was obtained.

  The above-mentioned coin-shaped negative electrode, positive electrode, and separator made of a microporous polypropylene film having a thickness of 25 μm and a diameter of 16 mm are laminated in the negative electrode can of a stainless steel 2032 size battery can in this order: negative electrode, separator, positive electrode did. Thereafter, 0.04 ml of the non-aqueous electrolyte was injected into the separator, and then an aluminum plate (thickness 1.2 mm, diameter 16 mm) and a spring were stacked on the laminate. Finally, by covering the positive electrode can of the battery via a polypropylene gasket and caulking the can lid, the airtightness inside the battery was maintained, and a coin-type battery having a diameter of 20 mm and a height of 3.2 mm was produced. .

<Evaluation of battery cycle characteristics>
Using the coin battery made as described above, this battery was charged under the condition of a constant current of 0.5 mA and a constant voltage of 4.2 V until the current value at a constant voltage of 4.2 V was 0.05 mA, Thereafter, the battery was discharged under the condition of a constant current of 1 mA and a constant voltage of 3.0 V until the current value at a constant voltage of 3.0 V was 0.05 mA. This cycle was repeated 200 times, and the capacity% after 200 cycles with respect to the initial battery capacity was evaluated. Table 2 shows the evaluation results of the battery using each electrode.

  By using the heat-resistant multilayered polymer particles obtained by the present invention, it can be used as an electrode binder for lithium ion electrons having excellent adhesion. In particular, since it is excellent in heat resistance, it is possible to improve cycle characteristics, which has been a problem in the past. Furthermore, the present binder is not limited to these, and can be used as a binder for electric double-layer capacitors and electrolytic capacitors.

Claims (4)

The outermost layer has a thermoplastic resin layer (A) having at least a glutaric anhydride structural unit represented by the following general formula (1) and having a glass transition temperature of 120 ° C. or higher and 200 ° C. or lower, From two or more layers having a rubber component layer (B) having one or more layers of an alkyl acrylate unit of 50 to 99.9 parts by mass and other monofunctional units of 50 to 0.1 parts by mass The mass ratio of the rubber component layer (B) and the thermoplastic resin layer (A) is 50/50 to 90/10 in (B) / (A). A binder for a lithium ion secondary battery comprising multilayer polymer particles.

(In the above formula, R ¹ and R ² are the same or different and represent a hydrogen atom and an alkyl group having 1 to 5 carbon atoms.) A binder slurry composition for a lithium ion secondary battery comprising a dispersion in which the binder according to claim 1 is dispersed in a dispersion medium having a boiling point of 80 ° C to 350 ° C at normal pressure. (I) (i) an unsaturated carboxylic acid alkyl ester unit, (ii) a thermoplastic resin layer (A) that is a copolymer having an unsaturated carboxylic acid unit in the outermost layer, and at least one or more layers inside A multilayer polymer particle precursor composed of two or more layers having a rubber component layer having 50 to 99.9 parts by mass of acrylic acid alkyl ester units and 50 to 0.1 parts by mass of other monofunctional units (II) Disperse in a dispersion medium having a boiling point at normal pressure of 80 ° C. to 350 ° C. or less,
(III) By heating to 100 ° C. or higher,
(IV) The lithium polymer particles having a thermoplastic resin layer (A) having a glutaric anhydride unit represented by the general formula (1) are produced. The manufacturing method of the binder slurry composition for ion secondary batteries. The slurry for lithium ion secondary battery electrodes containing the binder slurry composition obtained from the binder slurry composition of Claim 2, or the manufacturing method of Claim 3, and an active material.