JP7137954B2 - METHOD FOR MANUFACTURING BATTERY ELECTRODE COMPOSITION - Google Patents

Description

The present invention relates to a method for producing a battery electrode composition.

In recent years, electronic devices have been getting smaller and smaller, and because of their light weight and high energy density, secondary batteries are gaining importance as the central power source for portable electronic devices such as mobile phones and laptop computers. there is A battery electrode has a structure in which an active material is applied onto a metal substrate (hereinafter referred to as a current collector), and the active material is bound to the current collector using a battery electrode binder. The battery electrode binder is required to have dispersibility of the battery electrode composition, binding property with the active material, resistance to the electrolytic solution, stability in the electrochemical environment, and the like. In the case of secondary batteries, conventionally, a fluorine-based polymer such as polyvinylidene fluoride is dissolved in a solvent such as N-methyl-2-pyrrolidone and used as a binder for battery electrodes. A water-based binder is recommended.

For example, Patent Document 1 states that it is possible to provide a battery with excellent cycle characteristics and high-temperature retention performance by using a styrene-butadiene latex with a specific composition and a specific gel content and a water-soluble polymer. Further, Patent Document 2 proposes to improve the rate characteristics and cycle characteristics by improving the dispersibility of the battery electrode composition by using a battery electrode binder to which a specific functional group is added. there is However, in any technology, the cycle characteristics are still not sufficient to satisfy the market demands for longer life.

JP-A-5-74461

International publication WO2006/101182

Provided is a method for producing a battery electrode composition that improves the cycle characteristics of the resulting battery by improving the coverage of an active material with a particulate binder that is a battery electrode binder.

In the present invention, in producing a battery electrode composition containing an active material, a particulate binder, and a water-soluble polymer, the total amount of the water-soluble polymer is added before adding the particulate binder to the composition. characterized by not

According to the present invention, the coverage of the active material by the particulate binder is improved, and as a result, a battery with good cycle characteristics can be provided.

Preferred embodiments of the present invention are described in detail below. However, the present invention is not limited to the following embodiments.

In the present invention, in producing a battery electrode composition containing an active material, a particulate binder, and a water-soluble polymer, the total amount of the water-soluble polymer is added before adding the particulate binder to the composition. characterized by not

Specifically, in producing the composition for a battery electrode, kneading is performed in a state in which the active material and a part of the water-soluble polymer are contained (hereinafter also referred to as the first step), and then a particulate binder is added. addition (hereinafter also referred to as the second step), and the remainder of the water-soluble polymer is added and kneaded to produce a battery electrode composition.
The remainder of the water-soluble polymer may be added simultaneously with the particulate binder in the second step, or may be added after the addition of the particulate binder in the third step.

The water-soluble polymer may be added in two or more portions before starting to add the particulate binder to the composition, but the total amount used may be added before the total amount of the particulate binder is added to the composition. If added, the effect of improving the coverage of the active material cannot be obtained.

In the first step, the water-soluble polymer is preferably contained in an amount of 3% by mass or more and 60% by mass or less of the total amount used from the viewpoint of improving the dispersibility of the battery electrode composition and the coverage of the active material. . It is more preferably 5% by mass or more and 50% by mass or less, and most preferably 8% by mass or more and 40% by mass or less.

A battery electrode composition in the present invention contains an active material, a particulate binder, and a water-soluble polymer.
The particulate binder is preferably contained in an amount of 0.1 to 10 parts by weight (solid content), more preferably 0.3 to 7 parts by weight, based on 100 parts by weight (solid content) of the active material. If it is less than 0.1 part by weight, the binding force tends to be poor, and if it is more than 10 parts by weight, the overvoltage tends to rise significantly and the cycle characteristics tend to be poor when the battery is assembled.
It is preferable to contain 0.05 to 5 parts by weight (solid content) of the water-soluble polymer with respect to 100 parts by weight (solid content) of the active material, and 0.05 to 5 parts by weight (solid content). It is more preferable to contain 5 to 4 parts by weight (solid content). If it is less than 0.05 parts by weight, the binding strength tends to be poor, and if it exceeds 4 parts by weight, the cycle characteristics tend to be poor.

As the active material used in the battery electrode composition of the present invention, known materials can be used. For example, the positive electrode active material of the non-aqueous electrolyte secondary battery is not particularly limited, but transition metal oxides such as MnO2, MoO3, V2O5, V6O13, Fe2O3, and Fe3O4, LiCoO2, LiMnO2, LiNiO2, LMO2 (here, M contains two or more kinds of Ni, Mn, Co, AL, etc.); Spinel structure, composite metal oxides having an olivine structure such as LiFePO4, lithium-excess composite oxides such as Li2MnO3, transition metal sulfides such as TiS2, TiS3, MoS3 and FeS2, and metal fluorides such as CuF2 and NiF2. be done. These can be used individually by 1 type or in combination of 2 or more types.

For example, negative electrode active materials for non-aqueous electrolyte secondary batteries include carbon fluoride, graphite, carbon fiber, resin baked carbon, linear graphite hybrid, coke, pyrolytic vapor growth carbon, furfuryl alcohol resin baked carbon. , mesocarbon microbeads, mesophase pitch-based carbon, graphite whiskers, pseudo-isotropic carbon, sintered natural materials, and conductive carbonaceous materials such as pulverized products thereof, polyacene-based organic semiconductors, polyacetylene, poly-p- Examples include conductive polymers such as phenylene, and composite materials containing simple metals such as silicon and tin, metal oxides, or metal alloys thereof. These can be used individually by 1 type or in combination of 2 or more types.

For example, as the active material of the lithium ion capacitor electrode, graphite, soft carbon, hard carbon, carbon materials such as coke, polyacene-based organic semiconductor (PAS), and the like can be used.

For example, activated carbon, activated carbon fiber, silica, alumina, etc. can be used as the active material of the electric double layer capacitor electrode.

The particulate binder used in the battery electrode composition of the present invention acts as a binder that binds the active material particles together and the active material and the current collector in the battery electrode composition.

Although the type of particulate binder is not particularly limited, conjugated diene-based copolymers such as styrene/butadiene copolymers, acrylonitrile/butadiene copolymers, methyl methacrylate/butadiene copolymers, and vinylpyridine/butadiene copolymers can be used. Aqueous dispersions of copolymers, acrylic polymers, vinyl acetate polymers, ethylene/vinyl acetate copolymers, chloroprene polymers, natural rubber, etc., may be used alone or in combination of two or more. .
From the viewpoint of the dispersibility and binding strength of the battery electrode composition, the above copolymer preferably contains a structural unit derived from an ethylenically unsaturated carboxylic acid monomer. Such a copolymer is obtained by copolymerizing an ethylenically unsaturated carboxylic acid monomer with another monomer copolymerizable with the ethylenically unsaturated carboxylic acid monomer. Among them, by using a copolymer containing 5% by mass or more and 35% by mass or less of structural units derived from an ethylenically unsaturated carboxylic acid monomer, the coatability of the active material can be further improved.

Examples of the ethylenically unsaturated carboxylic acid monomers include ethylenically unsaturated monocarboxylic acid monomers such as acrylic acid and methacrylic acid, and ethylenically unsaturated dicarboxylic acids such as itaconic acid, fumaric acid and maleic acid. system monomers and the like. These may be used singly or in combination of two or more.

Other monomers copolymerizable with ethylenically unsaturated carboxylic acid monomers include aliphatic conjugated diene-based monomers, aromatic vinyl-based monomers, vinyl cyanide-based monomers, unsaturated carboxylic acid monomers, acid alkyl ester-based monomers, hydroxyalkyl group-containing unsaturated monomers, unsaturated carboxylic acid amide monomers, polyfunctional ethylenically unsaturated monomers containing two or more unsaturated double bonds, and the like. can be used alone or in combination of two or more.

Aliphatic conjugated diene-based monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted Linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like can be mentioned, and one or two or more of them can be used. 1,3-Butadiene is particularly preferred.

Examples of the aromatic vinyl-based monomer include styrene, α-methylstyrene, methyl α-methylstyrene, vinyltoluene, divinylbenzene, and the like, and one or more of them can be used. Styrene is particularly preferred.

Vinyl cyanide monomers include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile and the like, and one or more of them can be used. Acrylonitrile and methacrylonitrile are particularly preferred.

Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, and dimethyl itaconate. , monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like, and one or more of them can be used. Methyl methacrylate and butyl acrylate are particularly preferred.

Hydroxyalkyl group-containing unsaturated monomers include, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di-(ethylene glycol) maleate, di-(ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis(2-hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate, etc., and one or two More than one species can be used. 2-Hydroxyethyl acrylate is preferred.

Examples of unsaturated carboxylic acid amide monomers include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N,N-dimethylacrylamide and the like, and one or more of them can be used. . Acrylamide, methacrylamide and N-methylolacrylamide are preferred.

Polyfunctional ethylenically unsaturated monomers containing two or more unsaturated double bonds include, for example, allyl methacrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth) Polyethylene glycol di(meth)acrylates such as acrylates, divinyl compounds such as divinylbenzene, and the like can be mentioned, and one or more of them can be used. Allyl methacrylate, ethylene glycol dimethacrylate, and divinylbenzene are preferred.

The polymerization method for copolymerizing the above-described monomers is not particularly limited, but the copolymer can be obtained, for example, by emulsion polymerization. In the case of emulsion polymerization, commonly used emulsifiers, polymerization initiators, reducing agents, redox catalysts, hydrocarbon solvents other than cyclic unsaturated hydrocarbons having one unsaturated bond in the ring, electrolytes, polymerization accelerators, chelates Polymerization auxiliaries such as agents and other auxiliaries, such as antioxidants, dispersants, thickeners, preservatives, etc., can be used if necessary.

The polymerization method is not particularly limited, and known polymerization methods such as batch polymerization, semi-batch polymerization and seed polymerization can be used. Also, the method of adding various components is not particularly limited, and a batch addition method, a divided addition method, a continuous addition method, a power feed method, or the like can be used. The solid content of the obtained aqueous dispersion of the copolymer is, for example, 35 to 55% by weight, preferably 40 to 50% by weight.

As the water-soluble polymer used in the battery electrode composition of the present invention, known ones can be mentioned. Examples thereof include cellulosics such as carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose and salts thereof, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, casein, etc. Among them, battery electrode composition It is preferable to add carboxymethylcellulose and/or a salt thereof from the viewpoint of the dispersion stability of the substance and the binding force of the battery electrode.

Further, in the battery electrode composition of the present invention, dispersants such as sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate and sodium polyacrylate, and various stabilizers such as nonionic and anionic surfactants. It may contain additives.

A battery electrode is obtained by coating a current collector with the battery electrode composition obtained by the production method of the present invention and drying it.
As a method for applying the composition for a battery electrode of the present invention to a current collector, any coater head such as a reverse roll method, a comma bar method, a gravure method, and an air knife method can be used. A fan dryer, warm air dryer, infrared heater, far infrared heater, etc. can be used.

Existing current collectors can be used without any particular restrictions for the current collector used in manufacturing the battery electrode.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples unless the gist thereof is changed. In the examples, parts and percentages indicating proportions are based on weight. Further, evaluation of physical properties in the examples was based on the following methods.

Particulate binder A: carboxy-modified styrene-butadiene latex: containing 1% by mass of itaconic acid-derived structural units B: carboxy-modified styrene-butadiene latex: 2% by mass of itaconic acid-derived structural units and acrylic acid-derived structural units 4% by mass content

Negative electrode composition, production of negative electrode (Example 1)
Natural graphite with an average particle size of 20 μm is used as the negative electrode active material. 0.1 part by weight (solid content) of an aqueous solution of Cellogen EP (hereinafter referred to as CMC) was added, and an appropriate amount of water was added so that the solid content of the composition was 65%, followed by kneading. After sufficiently kneading, 2.0 parts by weight (solid content) of particulate binder A was added and kneaded. Subsequently, 0.9 parts by weight (solid content) of the CMC aqueous solution and an appropriate amount of water were added and kneaded so that the total solid content was 40%, to prepare a negative electrode composition. The negative electrode composition was applied to a copper foil having a thickness of 20 μm as a current collector and dried at 130° C. for 5 minutes to obtain a negative electrode sheet having a coating layer with a thickness of 60 μm.

(Examples 2 to 5 and Comparative Examples 1 and 2)
A negative electrode sheet was obtained in the same manner as in Example 1, except that the amount of the CMC aqueous solution added and the type and amount of the particulate binder added were changed as shown in Table 1. In Comparative Example 2, the dispersibility of the battery electrode composition was poor, and a part of the composition was aggregated.

Evaluation of Coverability of Active Material by Particulate Binder Since more of the surface of the active material is covered by the particulate binder, the cycle characteristics are improved when charging and discharging are repeated. In each of the obtained negative electrode sheets, the coatability of the active material with the copolymer latex was evaluated by the following method. That is, each of the negative electrode sheets (before rolling) obtained above was cut into 1 cm squares, dyed in an osmium tetroxide atmosphere, and then examined using a scanning electron microscope (manufactured by JEOL, trade name: JSM-6510LA). and observed at 5000 times. In the SEM observation image, the area where the particulate binder adhered on the active material was visually confirmed with respect to the area of the active material, and evaluated as follows. In addition, the most average image was selected from 8 screens of SEM observation images, and relative evaluation was performed. Table 1 shows the results.
Based on the degree of coverage of the particulate binder on the surface of the active material of Comparative Example 1,
A: The degree of coverage improved by 30% or more.
B: The degree of coverage improved by 20% or more and less than 30%.
C: The degree of coverage improved by 10% or more and less than 20%.
D: The degree of coverage was almost the same or decreased.

As described above, according to the present invention, it is possible to greatly improve the coverage of the active material with the particulate binder without impairing the dispersibility of the battery electrode composition, and thus provide a battery electrode with good cycle characteristics. be able to.

Claims (5)

In producing a battery electrode composition containing an active material, a particulate binder, and a water-soluble polymer , kneading is performed in a state in which a part of the aqueous solution of the active material and the water-soluble polymer is contained, and then particles A method for producing a battery electrode composition comprising adding and kneading a fine binder and the remainder of an aqueous solution of a water-soluble polymer (drying the mixture of the active material and the water-soluble polymer before adding the particulate binder). (Excluding the case where a coating layer containing a water-soluble polymer is formed on the surface of the active material) . Kneading is carried out in a state of containing 3% by mass or more and 60% by mass or less of the total amount of the aqueous solution of the active material and the water-soluble polymer, and then the rest of the aqueous solution of the particulate binder and the water-soluble polymer is added. 2. The method for producing a battery electrode composition according to claim 1 , comprising a step of kneading . Kneading is performed in a state in which 3% by mass or more and 50% by mass or less of the total amount of the aqueous solution of the active material and the water-soluble polymer is contained, and then the rest of the aqueous solution of the particulate binder and the water-soluble polymer is added. 3. The method for producing a battery electrode composition according to claim 1, comprising a step of kneading. The production of the battery electrode composition according to any one of claims 1 to 3, wherein the particulate binder comprises a styrene-butadiene copolymer containing a structural unit derived from an ethylenically unsaturated carboxylic acid monomer. Method. 5. The method for producing a battery electrode composition according to any one of claims 1 to 4, wherein the rest of the aqueous solution of the water-soluble polymer is added after finishing the addition of the particulate binder.