JP2010140684A - Binder for battery electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery having an excellent discharge performance and charge and discharge cycle characteristics by using a binder which has a good binding force and hardly forms a coating defect on an electrode mainly in the field of a secondary battery. <P>SOLUTION: The binder for battery electrode is a copolymer latex which is obtained by emulsion polymerization of a monomer that is constructed of 20-40 wt.% aliphatic conjugated diene, 2-30 wt.% (meta) acrylic ester, 0.1-10 wt.% ethylenic unsaturated carboxylic acid, 20-77.9 wt.% and ethylenic unsaturated monomer capable of copolymerization with these. Out of the ethylenic unsaturated carboxylic acid, when the amount of use of the ethylenic unsaturated carboxylic acid is A (wt.%) and the amount of use of the ethylenic unsaturated mono-carboxylic acid is B (wt.%), A/B>3 is satisfied (provided that, B≠0). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a binder for a secondary battery electrode excellent in charge / discharge cycle characteristics.

In recent years, electronic devices have become increasingly smaller. Lithium ion secondary batteries that use conductive carbonaceous materials that store and release lithium ions as electrodes, and nickel metal hydride batteries that use hydrogen storage alloys as negative electrodes, are lightweight and have high energy density. It is becoming increasingly important as a power source. Each of these secondary battery electrodes has a structure in which an active material is applied on a metal substrate, and a polymer binder is usually used as a binder for adhering the active material to the metal substrate. This polymer binder is required to have adhesiveness with an active material, stability in an electrochemical environment, and the like. In the case of a lithium ion battery, a fluorine-based polymer such as polyvinylidene fluoride has been used in this field. However, when an electrode film is formed, conductivity is hindered and adhesion between the current collector and the electrode film is prevented. There are problems such as insufficient strength. In addition, when a fluorine-based polymer is used for the negative electrode, which is a reducing condition, there are problems such as insufficient stability and a decrease in cycle performance of the secondary battery, and improvement of these problems is desired. . For this reason, development of non-fluorine polymers has been carried out. For example, JP-A-5-74461 (Patent Document 1) and JP-A-11-25989 (Patent Document 2) describe diene polymers having a specific composition, which are sufficient for solving the above problems. Instead, further improvements were sought.
JP-A-5-74461 Japanese Patent Laid-Open No. 11-25989

  An object of the present invention is to obtain a battery having good discharge performance, charge / discharge cycle characteristics, etc. by using a binder that has a good binding force and hardly causes a coating defect in an electrode, mainly in the field of secondary batteries. It is in.

  As a result of intensive studies in view of the above-mentioned circumstances, the present inventors have found that as an ethylenically unsaturated carboxylic acid monomer used for a battery electrode binder, an ethylenically unsaturated dicarboxylic acid monomer and an ethylenic monomer. By using unsaturated monocarboxylic acid monomer at a specific ratio, an electrode with high chemical stability, few coating defects, and excellent binding strength can be obtained. The inventors have found that a battery having good electric characteristics such as cycle characteristics can be obtained, and have completed the present invention.

  That is, the present invention includes an aliphatic conjugated diene monomer 20 to 40% by weight, a (meth) acrylic acid ester monomer 2 to 30% by weight, and an ethylenically unsaturated carboxylic acid monomer 0.1 to 10%. A copolymer latex obtained by emulsion polymerization of a monomer comprising 20% by weight and 20 to 77.9% by weight of an ethylenically unsaturated monomer copolymerizable therewith, comprising the above ethylenically unsaturated Of the carboxylic acid monomers, the amount of ethylenically unsaturated dicarboxylic acid monomer used is A (% by weight), and the amount of ethylenically unsaturated monocarboxylic acid monomer used is B (% by weight). In this case, a battery electrode binder is provided in which A / B> 3 (B ≠ 0).

  By using the battery electrode binder of the present invention, an electrode having high chemical stability, few coating defects, and excellent binding strength is obtained. As a result, electrical characteristics such as charge / discharge cycle characteristics are obtained. Therefore, it is possible to obtain a battery with good quality, which is extremely useful.

The present invention is described in detail below.
The monomer composition of the copolymer latex in the present invention is 20 to 40% by weight of an aliphatic conjugated diene monomer, 2 to 30% by weight of a (meth) acrylic acid ester monomer, and an ethylenically unsaturated carboxylic acid. It is composed of 0.1 to 10% by weight of a monomer and 20 to 77.9% by weight of an ethylenically unsaturated monomer copolymerizable therewith.

  Examples of the aliphatic conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, Examples thereof include substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes and the like, and one or more kinds can be used. 1,3-butadiene is particularly preferable.

  The aliphatic conjugated diene monomer needs to be used in the range of 20 to 40% by weight in all monomers. If the aliphatic conjugated diene monomer is less than 20% by weight, the properties as a binder are not exhibited, which is not preferable. On the other hand, when the amount of the aliphatic conjugated diene monomer exceeds 40% by weight, the binder covers the surface of the active material more than necessary, which is not preferable. More preferably, it is 22 to 38% by weight.

  Examples of the (meth) acrylic acid ester monomer include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, 2-ethylhexyl acrylate, and the like. it can. Particularly preferred is methyl methacrylate.

  The (meth) acrylic acid ester-based monomer needs to be used in the range of 2 to 30% by weight in all monomers. If the (meth) acrylic acid ester monomer is less than 2% by weight, the properties as a binder are not exhibited, which is not preferable. On the other hand, if the (meth) acrylic acid ester monomer exceeds 30% by weight, the polymerization stability of the copolymer is lowered, which is not preferable. Preferably it is 5-25 weight%, More preferably, it is 10-20 weight%.

Among the ethylenically unsaturated carboxylic acid monomers used in the present invention, examples of the ethylenically unsaturated dicarboxylic acid monomer include itaconic acid, fumaric acid, and maleic acid. These may be used alone or in combination of two or more.
Examples of the ethylenically unsaturated monocarboxylic acid monomer include acrylic acid and methacrylic acid. These may be used alone or in combination of two or more.
These ethylenically unsaturated carboxylic acid monomers need to be used in the range of 0.1 to 10% by weight. If the ethylenically unsaturated carboxylic acid monomer is less than 0.1% by weight, the chemical stability of the copolymer is inferior, which is not preferable. On the other hand, when the ethylenically unsaturated carboxylic acid monomer exceeds 10% by weight, the viscosity of the copolymer becomes high and handling becomes difficult. Preferably it is 0.3-7 weight%, More preferably, it is 0.5-5 weight%.

  As the ethylenically unsaturated carboxylic acid monomer used in the copolymer latex of the present invention, an ethylenically unsaturated dicarboxylic acid monomer (% by weight) / ethylenically unsaturated monocarboxylic acid monomer The ratio (% by weight) needs to exceed 3. When the ratio of ethylenically unsaturated dicarboxylic acid monomer (wt%) / ethylenically unsaturated monocarboxylic acid monomer (wt%) is 3 or less, the electrode coating composition has poor mechanical stability and is Cause work defects. Preferably it is 3.1 or more.

  Examples of the copolymerizable ethylenically unsaturated monomer used in the present invention include vinyl cyanide monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, such as styrene, Aromatic vinyl monomers such as α-methylstyrene, for example, ethylenically unsaturated carboxylic acid amide monomers such as acrylamide, methacryloamide, N, N-dimethylacrylamide, N-methylolacrylamide, for example acetic acid Carboxylic acid vinyl esters such as vinyl, for example, ethylenically unsaturated amine monomers such as methylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, 2-vinylpyridine, etc. Two or more kinds can be used.

  The gel content of the copolymer latex in the present invention needs to be 60% by weight or more. If it is less than 60% by weight, the desired binding force and chemical stability of the electrode coating composition cannot be obtained. Preferably it is 70 weight% or more, More preferably, it is 80 weight% or more.

  The number average particle diameter of the copolymer latex is not particularly limited, but is preferably 0.4 μm or less. More preferably, it is 0.35 μm or less, and the most preferable copolymer latex has a number average particle diameter of 0.05 to 0.30 μm.

  In emulsion polymerization of the copolymer latex of the present invention, a conventional emulsifier, polymerization initiator, reducing agent, chain transfer agent, redox catalyst, hydrocarbon solvent, electrolyte, polymerization accelerator, chelating agent, etc. are used. be able to.

  Examples of emulsifiers that can be used in the production of the copolymer latex of the present invention include sulfate esters of higher alcohols, alkylbenzene sulfonates, alkyl diphenyl ether sulfonates, aliphatic sulfonates, aliphatic carboxylates, and nonionic surfactants. Nonionic surfactants such as anionic surfactants such as sulfuric acid ester salts of polyethylene or alkyl ester type, alkyl phenyl ether type, alkyl ether type of polyethylene glycol, and the like, and one or more of these should be used Can do. In particular, alkylbenzene sulfonate and alkyl diphenyl ether sulfonate are preferable.

  As the polymerization initiator, water-soluble polymerization initiators such as potassium persulfate, sodium persulfate, ammonium persulfate, cumene hydroperoxide, benzoyl peroxide, t-butyl hydroperoxide, acetyl peroxide, diisopropylbenzene hydroperoxide, An oil-soluble polymerization initiator such as 1,1,3,3-tetramethylbutyl hydroperoxide can be appropriately used. In particular, water-soluble polymerization initiators such as potassium persulfate, sodium persulfate and ammonium persulfate and oil-soluble polymerization initiators of cumene hydroperoxide are preferred.

  Specific examples of the reducing agent preferably used in the present invention include sulfite, bisulfite, pyrosulfite, nitrite, nithionate, thiosulfate, formaldehyde sulfonate, benzaldehyde sulfonate, Examples thereof include carboxylic acids such as L-ascorbic acid, tartaric acid and citric acid, further reducing sugars such as dextrose and saccharose, and amines such as dimethylaniline and triethanolamine. L-ascorbic acid is particularly preferable.

  Examples of the chain transfer agent that can be used for the production of the copolymer latex of the present invention include alkyls such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan. Xanthogen compounds such as mercaptan, dimethylxanthogen disulfide, diisopropylxanthogen disulfide, terpinolene, thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide, 2,6-di-t-butyl-4 -Halogenation of phenolic compounds such as methylphenol and styrenated phenol, allyl compounds such as allyl alcohol, dichloromethane, dibromomethane, carbon tetrabromide, etc. Hydrogenated compounds, vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexylthioglyco A rate, (alpha) -methylstyrene dimer, etc. are mentioned, These can be used 1 type (s) or 2 or more types. In particular, n-octyl mercaptan and t-dodecyl mercaptan are preferable. The amount of these chain transfer agents is not particularly limited, but is usually 0 to 5 parts by weight with respect to 100 parts by weight of the monomer.

  In the polymerization, unsaturated hydrocarbons such as pentene, hexene, heptene, cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene, and 1-methylcyclohexene may be used. In particular, cyclohexene, which has a moderately low boiling point and can be easily recovered and reused after the completion of polymerization by steam distillation or the like, is preferable from the viewpoint of environmental problems although it differs from the object of the present invention.

  Furthermore, anti-aging agents, preservatives, dispersants, thickeners and the like can be appropriately added to the copolymer latex as necessary.

  As the polymerization method in the present invention, any one of single-stage polymerization, two-stage polymerization, multi-stage polymerization, seed polymerization, power feed polymerization and the like may be adopted. Further, the addition method of various components in the polymerization method of the present invention is not particularly limited, and any of a batch addition method, a divided addition method, and a continuous addition method can be employed.

The binder for battery electrodes of this invention is mix | blended with each active material of a positive electrode and a negative electrode, and is used as a composition for battery electrodes. The type of active material is not particularly limited. For example, in the case of a non-aqueous electrolyte secondary battery, graphite, carbon fiber, resin-fired carbon, linear graphite hybrid, coke, pyrolytic gas-layer-grown carbon, furfuryl alcohol resin Carbonaceous materials such as calcined carbon, polyacene organic semiconductors, mesocarbon microbeads, mesophase pitch carbon, graphite whiskers, pseudo-isotropic carbon, calcined natural materials, and pulverized products thereof, transitions such as MnO2 and V2O5 Examples include metal oxides, lithium-containing composite oxides such as LiCoO ₂ , LiMnO ₂ , and LiNiO ₂ , and one kind or a mixture of two or more kinds can be used.

  The copolymer latex in the present invention is used as a binder for battery electrodes, and acts as a binder between electrode active material particles and between an electrode active material and a current collector. In this case, the copolymer latex is contained in an amount of 0.1 to 10 parts by weight, preferably 1 to 7 parts by weight in solid content with respect to 100 parts by weight of the conductive carbonaceous material. Can be prepared as If the amount of the copolymer latex of the present invention is less than 0.1 parts by weight, good adhesion to a current collector or the like cannot be obtained, and if it exceeds 10 parts by weight, the overvoltage significantly increases when assembled as a battery. It tends to adversely affect battery characteristics.

  If necessary, various additives such as a water-soluble thickener may be added to the electrode composition containing the battery electrode binder of the present invention. Examples include water-soluble thickeners such as carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, casein, hexametaphosphate soda, tripolyphosphate soda, pyrophosphate soda , Dispersants such as sodium polyacrylate, and nonionic and anionic surfactants as latex stabilizers.

  The electrode composition of the present invention is applied to a current collector, dried and used as a battery electrode. Further, as a method for applying the electrode composition of the present invention to a current collector, any coater head such as a reverse roll method, a comma bar method, a gravure method, an air knife method can be used, and a drying method is allowed to stand, A blower dryer, a hot air dryer, an infrared heater, a far infrared heater, or the like can be used. The drying temperature is usually 100 ° C. or higher.

  Current collectors, separators, non-aqueous electrolytes, terminals, insulators, battery containers, etc. used when manufacturing a battery made using the battery electrode binder of the present invention are used without particular limitations. Is possible.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples, unless the summary is changed. In the examples, parts and percentages indicating percentages are based on weight. In addition, various physical properties in the examples were evaluated by the following methods.

The number average number average particle size particle size measurement of the copolymer latex was measured by dynamic light scattering method. In the measurement, FPAR-1000 manufactured by Otsuka Electronics Co., Ltd. was used.

Measurement of gel content of copolymer latex A latex film is prepared at room temperature. Thereafter, about 1 g of the latex film is weighed and placed in 400 cc of toluene to swell and dissolve for 48 hours. Thereafter, this was filtered through a 300-mesh wire mesh, and the toluene insoluble portion captured by the wire mesh was dried and weighed, and the ratio of the weight to the weight of the first latex film was calculated as a gel content in wt%.

<Example 1>
Preparation of copolymer latex 1 (example of the present invention)
Add each monomer, t-dodecyl mercaptan, α-methylstyrene dimer, sodium alkyldiphenyl ether disulfonate, and pure water to 60 ° C. in a pressure-resistant polymerization reactor under a nitrogen atmosphere in a nitrogen atmosphere. After raising the temperature, potassium persulfate was added to initiate polymerization. The polymerization was stopped 9 hours after the initiation of polymerization, and the pH was adjusted to 7 with an aqueous lithium hydroxide solution. Thereafter, steam distillation is performed at 90 ° C. for 15 hours to remove unreacted monomers and other low-boiling compounds, thereby obtaining a copolymer latex 1 having the number average particle diameter and gel content shown in Table 3. It was.

<Example 2>
Preparation of copolymer latex 2 (example of the present invention)
After adding each monomer, t-dodecyl mercaptan, cyclohexene, sodium dodecylbenzenesulfonate and pure water shown in addition 1 of Table 1 to a pressure-resistant polymerization reactor and raising the temperature to 50 ° C. Then, potassium persulfate was added to initiate polymerization. Three hours after the start of polymerization, each monomer, t-dodecyl mercaptan, sodium dodecylbenzenesulfonate and pure water shown in addition 1 in Table 1 were added, the temperature of the polymerization reaction vessel was raised to 60 ° C., and polymerization was continued. did. The polymerization was stopped 12 hours after the start of the polymerization, and the pH was adjusted to 7.5 with an aqueous sodium hydroxide solution. Thereafter, steam distillation is performed at 90 ° C. for 15 hours to remove unreacted monomers and other low-boiling compounds to obtain a copolymer latex 2 having a number average particle diameter and a gel content shown in Table 3. It was.

<Example 3>
Preparation of copolymer latex 3 (example of the present invention)
In a pressure resistant polymerization reactor, each monomer shown in addition 1 in Table 1, n-octyl mercaptan, cyclohexene, sodium dodecylbenzenesulfonate, sodium alkyldiphenyl ether disulfonate, and pure water was added under a nitrogen atmosphere to 70. After the temperature was increased frequently, potassium persulfate was added to initiate polymerization. Two hours after the start of polymerization, each monomer, n-octyl mercaptan, sodium dodecylbenzenesulfonate, and pure water shown in addition 2 in Table 1 were added, and polymerization was continued. Further, 5 hours after the initiation of polymerization, each monomer, n-octyl mercaptan, sodium dodecylbenzenesulfonate and pure water shown in addition 3 in Table 1 were added, and polymerization was continued. Nine hours after the initiation of polymerization, diethylhydroxylamine shown in Table 1 was added as a polymerization terminator to terminate the polymerization, and the pH was adjusted to 8.0 with an aqueous potassium hydroxide solution. Thereafter, steam distillation was performed at 90 ° C. for 15 hours to remove unreacted monomers and other low-boiling compounds. Furthermore, pH was adjusted to about 8.5 with aqueous ammonia to obtain a copolymer latex 3 having a number average particle diameter and a gel content shown in Table 3.

<Example 4>
Preparation of copolymer latex 4 (example of the present invention)
Each monomer, t-dodecyl mercaptan, α-methylstyrene dimer, sodium dodecylbenzenesulfonate, sodium alkyldiphenyl ether disulfonate, pure water in a pressure-resistant polymerization reactor in a nitrogen atmosphere as shown in addition 1 in Table 1 Then, the temperature was raised to 30 ° C., and cumene hydroperoxide and L-ascorbic acid were added to initiate polymerization. After 20 hours from the start of polymerization, diethylhydroxylamine shown in Table 1 was added as a polymerization terminator to terminate the polymerization, and the pH was adjusted to 7 with an aqueous lithium hydroxide solution. Thereafter, steam distillation is performed at 90 ° C. for 15 hours to remove unreacted monomers and other low-boiling compounds, thereby obtaining a copolymer latex 4 having the number average particle diameter and gel content shown in Table 3. It was.

<Example 5>
Preparation of copolymer latex 5 (example of the present invention)
In a pressure-resistant polymerization reactor, in a nitrogen atmosphere, each monomer shown in addition 1 of Table 1, t-dodecyl mercaptan, sodium dodecylbenzenesulfonate, polyoxyethylene lauryl ether (Emulgen 109P manufactured by Kao Corporation), After adding pure water and raising the temperature to 60 ° C., potassium persulfate was added to initiate polymerization. The polymerization was stopped 9 hours after the initiation of polymerization, and the pH was adjusted to 7 with an aqueous lithium hydroxide solution. Thereafter, steam distillation is performed at 90 ° C. for 15 hours to remove unreacted monomers and other low-boiling compounds, thereby obtaining a copolymer latex 1 having the number average particle diameter and gel content shown in Table 3. It was.

<Comparative Examples 1-7>
Preparation of copolymer latex 6-12 (comparative example)
In the same manner as in Example 1, each monomer, t-dodecyl mercaptan, α-methylstyrene dimer, sodium alkyldiphenyl ether disulfonate, pure water shown in Table 2 under a nitrogen atmosphere was added to a pressure resistant polymerization reactor. Was added and the temperature was raised to 60 ° C., and then potassium persulfate was added to initiate polymerization. The polymerization was stopped 9 hours after the initiation of polymerization, and the pH was adjusted to 7 with an aqueous lithium hydroxide solution. Thereafter, steam distillation is performed at 90 ° C. for 15 hours to remove unreacted monomers and other low-boiling compounds, and copolymer latexes 6 to 12 having the number average particle diameter and gel content shown in Table 4 are used. Got.

Preparation of composition for negative electrode Natural graphite having an average particle size of 20 μm is used as the conductive carbonaceous material, and 2 parts by weight of carboxymethyl cellulose aqueous solution as a thickener is used as a thickener for 100 parts by weight of natural graphite. An appropriate amount of water was added and kneaded so that the combined latex had a solid content of 4 parts by weight and the total solid content was 40% to prepare a negative electrode composition.

Aggregate of electrode composition The electrode composition obtained as described above was coated on a glass plate with a wire bar (# 20). Aggregates in a 10 cm square in the middle of the coating were visually counted and evaluated as follows.
◎: 0 aggregates in 10 cm square ○: 1-3 aggregates in 10 cm square Δ: 4-10 aggregates in 10 cm square ×: 11 or more aggregates in 10 cm square

The negative electrode composition of the negative electrode prepared were each coated on both sides of a copper foil having a thickness of 20μm as the current collector, dried at 140 ° C. 20 min, and pressed at room temperature, the anode of the thickness of the coating layer is 80μm Got.

On the surface of the electrode sheet obtained in binding force above method of the electrode coating layer, the cross-cut by a cut from the active material layer to a depth reaching the collector aspect put each present 6 in 2mm intervals using a knife I made a cut. An adhesive tape was affixed to the cut and immediately peeled off, and the degree of dropout of the active material was evaluated from 5 points (no dropout) to 1 point (complete dropout) by visual judgment.

Preparation of positive electrode LiCoO ₂ as a positive electrode active material
100 parts by weight, 5 parts by weight of acetylene black as a conductive agent, 4 parts by weight of copolymer latex as a binder, and knead by adding an appropriate amount of water so that the total solid content is 40%. A positive electrode composition was prepared. The obtained slurry was used as a current collector to obtain a thickness of 20
After coating and drying on both sides of a μm aluminum foil, pressing was performed at room temperature to obtain a positive electrode having a coating layer thickness of 80 μm.

Preparation of batteries After welding lead plates to the ends of the positive and negative electrodes using the same type of copolymer latex, the positive electrode, a 30 μm thick porous polypropylene separator, the negative electrode, and the separator were laminated in this order. A wound body was wound in a spiral shape. The wound body is housed in a cylindrical battery can that also serves as a negative electrode terminal, the battery can and the negative electrode, the positive electrode terminal and the positive electrode are connected by a lead terminal, and ethylene carbonate and diethyl having a capacity ratio of 1: 1 in the battery can. After filling the prepared electrolyte solution by dissolving lithium hexafluorophosphate in a mixed solvent of carbonate so as to be 1 mol / l, a battery lid provided with a positive electrode terminal was caulked through a gasket to prepare a cylindrical battery.

Charge / Discharge Cycle Characteristics The process of charging to 4.2 V using the cylindrical battery obtained by the above method and discharging to 2.5 V at 10 mA was repeated 100 cycles. The capacity retention was calculated by the following formula and evaluated as follows.
Capacity retention (%) = (discharge capacity at the 100th cycle) / (discharge capacity at the first cycle)
A: Capacity retention exceeds 97% O: Capacity retention is 92 to 97%
Δ: Capacity retention is 85 to 92%
X: Capacity retention is less than 85%

  Ethylenically unsaturated dicarboxylic acid monomer / ethylenically unsaturated monocarboxylic acid monomer (wt% ratio), number average particle diameter, gel content, and aggregation of electrode composition of each copolymer latex Table 3 and Table 4 summarize the evaluation results of the product, the binding force of the electrode coating layer, and the charge / discharge cycle characteristics of the battery.

  As described above, the battery electrode binder of the present invention has high chemical stability, and by using this, an electrode having few coating defects and excellent binding strength can be obtained. A battery having good battery characteristics such as cycle characteristics can be obtained.

Claims (2)

Aliphatic conjugated diene monomer 20 to 40% by weight, (meth) acrylic acid ester monomer 2 to 30% by weight, ethylenically unsaturated carboxylic acid monomer 0.1 to 10% by weight, and these A copolymer latex obtained by emulsion polymerization of a monomer composed of 20 to 77.9% by weight of a copolymerizable ethylenically unsaturated monomer, comprising the above ethylenically unsaturated carboxylic acid monomer When the amount of ethylenically unsaturated dicarboxylic acid monomer used is A (% by weight) and the amount of ethylenically unsaturated monocarboxylic acid monomer used is B (% by weight), A / A binder for battery electrodes, wherein B> 3 (B ≠ 0). 2. The binder for battery electrodes according to claim 1, wherein the gel content is 60% by weight or more.