JPWO2020090695A1 - Binder for secondary battery electrode and its use - Google Patents

Abstract

In order to achieve both binding properties in the secondary battery electrode and suppression of electrode slurry viscosity, a non-crosslinked structural unit and a crosslinked structural unit are provided, and the non-crosslinked structural unit is an ethylenically unsaturated carboxylic acid monomer. The crosslinked structural unit contains a non-crosslinked structural unit derived from the crosslinked structural unit, and the crosslinked structural unit contains a crosslinked structural unit derived from a crosslinkable monomer having two or more (meth) acryloyl groups in one molecule and having a hydroxyl group. A secondary battery electrode binder having a polymer or a salt thereof is provided.

Description

The present specification relates to a binder for a secondary battery electrode and its use.
(Cross-reference of related applications)
This application is a related application of Japanese Patent Application No. 2018-205228, which is a Japanese patent application filed on October 31, 2018, and claims priority based on this Japanese application. It is incorporated herein by reference.

As the secondary battery, various power storage devices such as a nickel hydrogen secondary battery, a lithium ion secondary battery, and an electric double layer capacitor have been put into practical use. The electrodes used in these secondary batteries are produced by applying, drying, or the like on a current collector a composition for forming an electrode mixture layer containing an active material, a binder, and the like. For example, in a lithium ion secondary battery, an aqueous binder containing styrene-butadiene rubber (SBR) latex and carboxymethyl cellulose (CMC) is used as the binder used in the negative electrode mixture layer composition.

On the other hand, as the applications of various secondary batteries expand, the demand for improving energy density, reliability and durability tends to increase. For example, for the purpose of increasing the electric capacity of a lithium ion secondary battery, specifications for using a silicon-based active material as a negative electrode active material are increasing. However, it is known that the volume of a silicon-based active material changes significantly during charging and discharging, and the electrode mixture layer peels off or falls off as it is used repeatedly, resulting in a decrease in battery capacity and cycle characteristics. There was a problem that (durability) deteriorated. In order to suppress such a defect, it is generally effective to improve the binder's binding property, and for the purpose of improving the durability, studies on improving the binder's binding property have been conducted.

As a binder having good binding properties and exerting an effect of improving durability, a binder using the above acrylic acid-based polymer has been proposed. In Patent Document 1, by using a polymer obtained by cross-linking polyacrylic acid with a specific cross-linking agent as a binder, the electrode structure is not destroyed even when an active material containing silicon is used. It is stated that it can be provided. Patent Document 2 describes an electrode obtained by using a crosslinked polymer having a carboxy group or a salt thereof and a binder containing a polymer having a sufficiently small particle size when dispersed in salt water after neutralization. It is described that it exhibits excellent binding properties.

International Publication No. 2014/060407 International Publication No. 2017/073589

All of the binders disclosed in the patent documents can impart good binding properties, but as the performance of the secondary battery is improved, an electrode mixture layer having even higher binding properties is required. It has become. Further, when the amount of the binder is increased in order to improve the binding property, the slurry viscosity of the electrode mixture layer composition is increased and the coatability is lowered. Therefore, there is a demand for a binder capable of reducing the slurry viscosity.

The present specification provides a binder capable of improving the binding property and reducing the viscosity of the slurry for the electrode mixture layer, and the use thereof.

As a result of various studies focusing on crosslinkable monomers to improve the binding property without increasing the slurry viscosity, the present inventors have found two or more (meth) acryloyl groups having high radical reactivity. It was found that the above-mentioned problems can be solved by using a crosslinked polymer using a crosslinkable monomer having a hydroxyl group as well as having a hydroxyl group. According to the present specification, the following means are provided based on such findings.

[1] A secondary battery electrode binder having a crosslinked polymer or a salt thereof.
The crosslinked polymer or a salt thereof comprises a non-crosslinked structural unit and a crosslinked structural unit.
The non-crosslinked structural unit includes a non-crosslinked structural unit derived from an ethylenically unsaturated carboxylic acid monomer.
The crosslinked structural unit contains a crosslinked structural unit derived from a crosslinkable monomer having two or more (meth) acryloyl groups in one molecule and having a hydroxyl group.
binder.
[2] The binder according to [1], which contains 30% by mass or more and 100% by mass or less of the non-crosslinked structural unit derived from the ethylenically unsaturated monomer with respect to the total amount of the non-crosslinked structural unit.
[3] A composition for a secondary battery electrode.
The binder for the secondary battery electrode according to [1] or [2],
With active material
water and,
Composition containing.
[4] A secondary battery electrode
The binder for the secondary battery electrode according to [1] or [2],
With active material
Electrode containing.
[5] Further, the electrode according to [4], wherein the active material is a silicon-containing substance.
[6] A method for manufacturing a binder for a secondary battery electrode.
A step of polymerizing a monomer composition containing an ethylenically unsaturated carboxylic acid monomer and a crosslinkable monomer having two or more (meth) acryloyl groups in one molecule and having a hydroxyl group. ,
A manufacturing method.

The binder for a secondary battery electrode disclosed in the present specification (hereinafter, also simply referred to as the present binder) may contain a crosslinked polymer or a salt thereof (hereinafter, also simply referred to as the present polymer). The present polymer comprises a non-crosslinked structural unit and a crosslinked structural unit, the non-crosslinked structural unit contains a non-crosslinked structural unit derived from an ethylenically unsaturated monomer, and the crosslinked structural unit is contained in one molecule. Can contain a crosslinked structural unit derived from a crosslinkable monomer having two or more (meth) acryloyl groups and having a hydroxyl group.

Since this polymer has a carboxylic acid as a non-crosslinked structural unit, it is a binder having good binding properties. In addition, the present polymer contains a crosslinked structural unit derived from a crosslinkable monomer having two or more (meth) acryloyl groups as the crosslinked structural unit. Since such a crosslinkable monomer has a relatively high radical polymerizable property, a crosslinked structural unit is formed relatively uniformly from the inside of the polymer particles to the surface portion. In other words, it is considered that the excessive increase in the cross-linking density on the surface of the present polymer particles obtained by the cross-linking polymerization can be suppressed, and as a result, the degree of swelling of the surface of the present polymer particles in water is relatively high, and the active material or It is considered that the adhesion area with the current collector can be secured and the binder containing the present polymer particles exhibits good binding properties.

Further, since the present polymer has a hydroxyl group in the crosslinked structural unit, the degree of swelling of the present polymer particles is suppressed by the interaction (hydrogen bond, etc.) by the hydroxyl groups in the polymer particles, and the increase in slurry viscosity is suppressed. can do.

Since the composition for the secondary battery electrode contains the present binder, it is easy to apply. In addition, the secondary battery electrode containing the present binder exhibits excellent binding properties. Further, according to the method for producing the present binder, the composition for the secondary battery electrode, and the method for producing the secondary battery electrode, it is possible to provide an electrode having excellent binding property by suppressing an increase in viscosity during preparation of the electrode slurry. can.

The binder contains the polymer, and can be mixed with an active material and water to form a composition for a secondary battery electrode (electrode mixture layer composition, hereinafter simply referred to as the composition). can do. The present composition may be in a slurry state that can be applied to the current collector, or may be prepared in a wet powder state so that it can be pressed on the surface of the current collector. A secondary battery electrode disclosed in the present specification by forming a mixture layer formed from the present composition on the surface of a current collector such as a copper foil or an aluminum foil (hereinafter, also simply referred to as the present electrode). Is obtained.

Hereinafter, in addition to the present binder, typical and non-limiting specific examples of the present composition, the method for producing the present binder, the method for producing the present composition, the method for producing the present electrode, etc. will be described in detail with reference to the drawings as appropriate. explain. This detailed description is intended to provide those skilled in the art with details for implementing the preferred examples of the present disclosure and is not intended to limit the scope of the present disclosure. In addition, the additional features disclosed below may be used separately or together with other features and disclosures to provide a further improved "binder for secondary battery electrodes and their use".

In addition, the combination of features and processes disclosed in the following detailed description is not essential in carrying out the present disclosure in the broadest sense, and is particularly for explaining typical specific examples of the present disclosure. It is to be described. In addition, the various features of the above and below representative examples, as well as the various features of those described in the independent and dependent claims, are described herein in providing additional and useful embodiments of the present disclosure. It does not have to be combined according to the specific examples given or in the order listed.

All features described herein and / or claims are, separately, as a limitation to the disclosure at the time of filing and the specific matters claimed, apart from the composition of the features described in the examples and / or claims. And it is intended to be disclosed independently of each other. In addition, all numerical ranges and statements relating to groups or groups are made with the intention of disclosing their intermediate composition as a limitation to the disclosure at the time of filing and the specific matters claimed.

In addition, in this specification, "(meth) acrylic" means acrylic and / or methacrylic, and "(meth) acrylate" means acrylate and / or methacrylate. Further, the “(meth) acryloyl group” means an acryloyl group and / or a methacryloyl group.

<Binder>
The binder may contain the polymer, i.e., a crosslinked polymer or a salt thereof. The present binder may contain only the present polymer, or may contain other binder components as described later. Preferably, the present polymer is contained in an amount of 50% by mass or more, for example, 60% by mass or more, for example, 70% by mass or more, and for example, 80% by mass or more, and for example, 90% by mass or more. It contains, for example, 95% by mass or more, and also contains, for example, 100% by mass.

<Structural unit of crosslinked polymer>
<Non-crosslinked structural unit>
The present polymer has a non-crosslinked structural unit and a crosslinked structural unit. The non-crosslinked structural unit is not particularly limited, and a structural unit derived from various non-crosslinkable monomers that can be used in a crosslinked polymer that can be used as a binder for a secondary battery electrode is provided as the non-crosslinked structural unit. be able to.

As the non-crosslinked structural unit, for example, a structural unit derived from an ethylenically unsaturated carboxylic acid monomer (hereinafter, also referred to as “component (a)”) can be included. By having a carboxy group as a structural unit, the adhesiveness to the current collector is improved, and the lithium ion desolvation effect and ionic conductivity are excellent, so that an electrode having low resistance and excellent high rate characteristics can be obtained. .. Further, since water swelling property is imparted, the dispersion stability of the active material or the like in the present composition can be enhanced. The structural unit can be introduced into the present polymer, for example, by polymerizing a monomer containing an ethylenically unsaturated carboxylic acid monomer. Alternatively, it can also be obtained by (co) polymerizing a (meth) acrylic acid ester monomer and then hydrolyzing it. Further, after polymerizing (meth) acrylamide, (meth) acrylonitrile or the like, the polymer may be treated with a strong alkali, or the present polymer having a hydroxyl group may be reacted with an acid anhydride.

Examples of the ethylenically unsaturated carboxylic acid monomer include (meth) acrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid; and (meth) acrylamide alkyl such as (meth) acrylamide hexane acid and (meth) acrylamide dodecanoic acid. Carboxylic acid; ethylenically unsaturated monomers having carboxy groups such as monohydroxyethyl succinate (meth) acrylate, ω-carboxy-caprolactone mono (meth) acrylate, β-carboxyethyl (meth) acrylate, or (partial) thereof. ) Alkaline neutralized products may be mentioned, and one of these may be used alone, or two or more thereof may be used in combination. Among the above, a compound having an acryloyl group as a polymerizable functional group is preferable, and acrylic acid is particularly preferable, in that a polymer having a long primary chain length can be obtained due to a high polymerization rate and the binder has a good binding force. be. When acrylic acid is used as the ethylenically unsaturated carboxylic acid monomer, a polymer having a high carboxy group content can be obtained.

The ethylenically unsaturated carboxylic acid monomer may be free with respect to the carboxy group, or at least a part thereof may be a salt. The type of salt is not particularly limited, but alkali metal salts such as lithium, sodium and potassium; alkaline earth metal salts such as calcium salt and barium salt; other metal salts such as magnesium salt and aluminum salt; ammonium salt and organic Examples include amine salts. Among these, alkali metal salts and magnesium salts are preferable, and alkali metal salts are more preferable, from the viewpoint that adverse effects on battery characteristics are unlikely to occur. A particularly preferred alkali metal salt is a lithium salt.

The content of the component (a) in the present polymer is not particularly limited, but may be, for example, 10% by mass or more and 100% by mass or less with respect to the total amount of the non-crosslinked structural units of the present polymer. By containing the component (a) in such a range, excellent adhesiveness to the current collector can be easily ensured. The lower limit is, for example, 20% by mass or more, for example, 30% by mass or more, and for example, 40% by mass or more. The lower limit may be 50% by mass or more, for example, 60% by mass or more, for example, 70% by mass or more, and for example, 80% by mass or more. When it is 30% by mass or more, the adhesiveness to the current collector can be ensured, and since it has a good lithium ion desolvation effect and ionic conductivity, an electrode having excellent high rate characteristics can be obtained. Further, the water swelling property can enhance the dispersion stability of the active material or the like in the present composition. (A) Such effects tend to be improved by increasing the content of the component.

Further, the upper limit is 100% by mass, and 100% by mass may be preferable, but for example, it is 99% by mass or less, for example 98% by mass or less, and for example 95% by mass or less. For example, it is 90% by mass or less.

The range of the component (a) may be a range in which such a lower limit and an upper limit are appropriately combined, and for example, it is 10% by mass or more and 100% by mass or less with respect to the total amount of the non-crosslinked structural units of the present polymer. Yes, for example, 20% by mass or more and 100% by mass or less, and for example, 30% by mass or more and 100% by mass or less, and for example, 50% by mass or more and 100% by mass or less, and for example, 60% by mass or more. , 100% by mass or less, and can be, for example, 70% by mass or more and 100% by mass or less. If the ratio of the component (a) to all the structural units is less than 10% by mass, the dispersion stability, the binding property and the durability as a battery may be insufficient.

The content of the component (a) with respect to the total amount of the non-crosslinked structural units can also be obtained, for example, as the content of the ethylenically unsaturated carboxylic acid monomer with respect to the total amount of the non-crosslinked monomers used in the present polymer.

<Other structural units>
In addition to the component (a), the present polymer may contain a structural unit derived from another ethylenically unsaturated monomer copolymerizable with the component (hereinafter, also referred to as “component (b)”). .. Examples of the component (b) include an ethylenically unsaturated monomer compound having an anionic group other than a carboxy group such as a sulfonic acid group and a phosphoric acid group, a nonionic ethylenically unsaturated monomer, and the like. The structural unit from which it is derived can be mentioned. These structural units are ethylenically unsaturated monomer compounds having anionic groups other than carboxy groups such as sulfonic acid groups and phosphoric acid groups, or monomers containing nonionic ethylenically unsaturated monomers. Can be introduced by copolymerizing. Among these, as the component (b), a structural unit derived from a nonionic ethylenically unsaturated monomer is preferable from the viewpoint of obtaining an electrode having good bending resistance, and the binder binding property and slurry viscosity are preferable. (Meta) acrylamide and its derivatives are preferable in that Further, when a structural unit derived from a hydrophobic ethylenically unsaturated monomer having a solubility in water of 1 g / 100 ml or less is introduced as the component (b), a strong interaction with the electrode material can be achieved. It can exhibit good binding properties to active materials. This is preferable because a solid and well-integrated electrode mixture layer can be obtained. In particular, a structural unit derived from an alicyclic structure-containing ethylenically unsaturated monomer is preferable.

As the nonionic ethylenically unsaturated monomer, (meth) acrylamide and its derivative are preferable in terms of excellent binder binding property and slurry viscosity. Examples of the (meth) acrylamide derivative include N-alkyls such as isopropyl (meth) acrylamide, t-butyl (meth) acrylamide, Nn-butoxymethyl (meth) acrylamide, and N-isobutoxymethyl (meth) acrylamide. Meta) acrylamide compounds; N, N-dialkyl (meth) acrylamide compounds such as dimethyl (meth) acrylamide and diethyl (meth) acrylamide can be mentioned, and one of these may be used alone or two. The above may be used in combination.

The ratio of (meth) acrylamide and the component (b) which is a derivative thereof can be, for example, 0% by mass or more and 90% by mass or less with respect to the total amount of the non-crosslinked structural units. The proportion of the component (b) is also, for example, 1% by mass or more, 70% by mass or less, for example, 2% by mass or more, 60% by mass or less, and for example, 5% by mass or more, 50% by mass or less, and for example, 10% by mass or more. , 30% by mass or less. Further, when the component (b) is contained in an amount of 1% by mass or more based on the total amount of the non-crosslinked structural units, the affinity for the electrolytic solution is improved, so that the effect of improving the lithium ion conductivity can be expected. Further, when it contains 70% by mass or less with respect to the total amount of the non-crosslinked structural units, it may be useful for suppressing the viscosity of the slurry.

In addition, as the nonionic ethylenically unsaturated monomer, for example, (meth) acrylic acid ester may be used. Examples of the (meth) acrylic acid ester include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. (Meta) acrylic acid alkyl ester compounds; (meth) acrylic acid cycloalkyl ester compounds such as (meth) acrylic acid cyclohexyl, (meth) acrylic acid methylcyclohexyl; (meth) acrylic acid 2-methoxyethyl, (meth) acrylic acid (Meta) acrylic acid alkoxyalkyl ester compounds such as ethoxyethyl; (meth) acrylic acid hydroxyalkyl ester compounds such as (meth) acrylic acid hydroxyethyl, (meth) acrylic acid hydroxypropyl and (meth) acrylic acid hydroxybutyl One of these may be used alone, or two or more thereof may be used in combination. When a (meth) acrylic acid ester is used as the nonionic ethylenically unsaturated monomer, the ratio of the structural units derived from the (meth) acrylic acid ester is the total amount of the non-crosslinked structural units of the present polymer. , It is preferably 1 to 30% by mass, more preferably 5 to 30% by mass, and further preferably 10 to 30% by mass. Further, in this case, the ratio of the component (a) is preferably 70 to 99% by mass, more preferably 70 to 95% by mass, and further preferably 70 to 70% by mass with respect to the total structural units of the present polymer. It is 90% by mass.

Among the above, ethers such as (meth) acrylate alkoxyalkyls such as 2-methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate are used because they have high lithium ion conductivity and higher high-rate characteristics. A compound having a bond is preferable, and 2-methoxyethyl (meth) acrylate is more preferable.

Among the nonionic ethylenically unsaturated monomers, a compound having an acryloyl group is preferable in that a polymer having a long primary chain length can be obtained because the polymerization rate is high and the binding force of the binder is good. Further, as the nonionic ethylenically unsaturated monomer, a compound having a homopolymer glass transition temperature (Tg) of 0 ° C. or lower is preferable in terms of improving the bending resistance of the obtained electrode.

<Cross-linked structural unit>
This polymer has a crosslinked structural unit derived from a crosslinkable monomer having two or more (meth) acryloyl groups in one molecule and a hydroxyl group as a crosslinked structural unit (hereinafter, “component (c)”). Also referred to as).

(C) The two or more (meth) acryloyl groups that the component can have include two or more methacryloyl groups, one or more acryloyl groups, one or more methacryloyl groups, two or more acryloyl groups, and the like. can do. Although not particularly limited, for example, 2 or more and 6 or less (meth) acryloyl groups, for example, 2 or more and 5 or less (meth) acryloyl groups, and for example, 2 or more and 4 or less (meth) acryloyl groups. ) Acryloyl groups, for example, 2 or more and 3 or less (meth) acryloyl groups, and for example, 2 (meth) acryloyl groups can be provided.

The (meth) acryloyl group can reduce the degree of swelling in water by lowering the crosslink density of the particle surface of the present polymer. From the viewpoint of improving the binding property, the (meth) acryloyl group contained in the component (c) is more preferably a methacryloyl group. Therefore, when the component (c) is a bifunctionalized compound having two (meth) acryloyl groups, the component (c) is, for example, a dimethacryloyl group in a preferable order from the viewpoint of improving the binding property. , Methacryloyl group, acryloyl group, diacryloyl group. Further, the (meth) acryloyl group contained in the component (c) is more preferably an acryloyl group from the viewpoint of the viscosity of the mixture layer composition (slurry). Therefore, the bifunctional compound includes, for example, a diacryloyl group, a methacryloyl group and an acryloyl group, and a dimethacryloyl group in a preferable order from the viewpoint of suppressing slurry viscosity. In addition to the binding property and slurry viscosity intended as a binder for a secondary battery electrode, the number and combination of (meth) acryloyl groups in the component (c) can be appropriately selected in consideration of the amount of crosslinked structural units.

The number of hydroxyl groups that the component (c) can have is not particularly limited as long as it is 1 or more, but is, for example, 1 or more and 3 or less, and for example, 1 or more and 2 or less. For example, one. It is considered that the more hydroxyl groups there are, the greater the interaction within the polymer particles tends to be. In addition to the slurry viscosity intended as the binder for the secondary battery electrode, the number of hydroxyl groups in the component (c) can be appropriately selected in consideration of the amount of crosslinked structural units.

The component (c) is not particularly limited, but is, for example, trimethylolpropane di (meth) acrylate, pentaerythritol di or tri (meth) acrylate, dipentaerythritol di, tri, tetra or penta (meth). ) Acrylate, glycerindi (meth) acrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate and the like can be used. As the component (c), only one kind may be used, but two or more kinds may be used in combination.

The component (c) is not particularly limited, but is, for example, 0.01 part by mass or more and 20 parts by mass or less when the total amount of the non-crosslinked structural unit is 100 parts by mass. If it is less than 0.01 parts by mass, the binding property cannot be obtained and the slurry viscosity becomes too high, and if it exceeds 20 parts by mass, the binding property cannot be obtained. The component (c) is also, for example, 0.02 parts by mass or more, for example 0.04 parts by mass or more, for example 0.05 parts by mass or more, and for example 0.1 parts by mass or more. Further, for example, it is 0.2 parts by mass or more. The component (c) is also, for example, 15 parts by mass or less, for example, 12 parts by mass or less, for example, 10 parts by mass or less, for example, 9 parts by mass or less, and for example, 7 parts by mass or less. , For example, 5 parts by mass or less, for example, 3 parts by mass or less, and for example, 2 parts by mass or less, or 1 part by mass or less. The range of the preferable content of the component (c) can be appropriately combined with the upper limit and the lower limit thereof, and is, for example, 0.1 part by mass or more and 15 parts by mass or less, and for example, 0.1 part by mass or more and 10 parts by mass. It is, for example, 0.2 parts by mass or more and 9 parts by mass or less, for example, 0.2 parts by mass or more and 7 parts by mass or less, and for example, 0.2 parts by mass or more and 5 parts by mass or less. Further, for example, it is 0.2 parts by mass or more and 2 parts by mass or less, and for example, 0.2 parts by mass or more and 1 part by mass or less.

The present polymer may also include a crosslinked structural unit other than the component (c). Such a crosslinked structural unit is a structure derived from a polyfunctional polymerizable monomer having two or more polymerizable unsaturated groups, a monomer having a self-crosslinkable crosslinkable functional group such as a hydrolyzable silyl group, and the like. The unit is mentioned. The polyfunctional polymerizable monomer is a compound having two or more polymerizable functional groups such as a (meth) acryloyl group and an alkenyl group in the molecule, and is a polyfunctional (meth) acrylate compound, a polyfunctional alkenyl compound, and (meth). ) Examples thereof include compounds having both an acryloyl group and an alkenyl group. These compounds may be used alone or in combination of two or more.

Examples of the polyfunctional (meth) acrylate compound include ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and polypropylene glycol di (meth) acrylate. Di (meth) acrylates of dihydric alcohols such as meta) acrylates; trimethylol propantri (meth) acrylates, tri (meth) acrylates of modified trimethylolpropane ethylene oxide, glycerin tri (meth) acrylates, pentaerythritol tetra (meth). Tri (meth) acrylates of trivalent or higher valent alcohols such as meta) acrylates, poly (meth) acrylates such as tetra (meth) acrylates; bisamides such as methylene bisacrylamide and hydroxyethylene bisacrylamide can be mentioned. ..

Examples of the polyfunctional alkenyl compound include polyfunctional allyl ether compounds such as trimethylolpropanediallyl ether, trimethylolpropanetriallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, tetraallyloxyethane, and polyallyl saccharose; diallyl phthalate and the like. Polyfunctional allyl compound; Examples thereof include polyfunctional vinyl compounds such as divinylbenzene.

Compounds having both (meth) acryloyl group and alkenyl group include allyl (meth) acrylate, isopropenyl (meth) acrylate, butenyl (meth) acrylate, pentenyl (meth) acrylate, and (meth) acrylate. 2- (2-Vinyloxyethoxy) ethyl and the like can be mentioned.

Specific examples of the above-mentioned monomer having a crosslinkable functional group include a hydrolyzable silyl group-containing vinyl monomer, N-methylol (meth) acrylamide, N-methoxyalkyl (meth) acrylate and the like. Can be mentioned. These compounds can be used alone or in combination of two or more.

The hydrolyzable silyl group-containing vinyl monomer is not particularly limited as long as it is a vinyl monomer having at least one hydrolyzable silyl group. For example, vinyl silanes such as vinyl trimethoxysilane, vinyl triethoxysilane, vinyl methyl dimethoxysilane, vinyl dimethyl methoxysilanen; silyl such as trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate, methyldimethoxysilylpropyl acrylate and the like. Group-containing acrylic acid esters; silyl group-containing methacrylate esters such as trimethoxysilylpropyl methacrylate, triethoxysilylpropyl methacrylate, methyldimethoxysilylpropyl methacrylate, dimethylmethoxysilylpropyl methacrylate; trimethoxysilylpropyl vinyl ether and the like. Cyril group-containing vinyl ethers; Examples thereof include silyl group-containing vinyl esters such as trimethoxysilyl undecanoate vinyl.

The crosslinked structural unit other than the component (c) is not particularly limited, but for example, 0.1 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the total amount of the non-crosslinkable monomer. Can be prepared. The structural unit may be 0.2 parts by mass, 3.0 parts by mass or less, 0.3 parts by mass, 2.0 parts by mass or less, 0.5 parts by mass, 1.0 parts by mass. It may be less than a part by mass.

<Neutralization degree>
In the present polymer, acid groups such as a carboxy group derived from an ethylenically unsaturated carboxylic acid monomer are neutralized so that the degree of neutralization is 20 to 100 mol% in the present composition, and the mode of the salt is It is preferable to use as. The degree of neutralization is more preferably 50 to 100 mol%, for example, 60 mol% or more, for example 65 mol% or more, for example 70 mol% or more, for example 75 mol% or more, and for example 80 mol% or more. Also, for example, 85 mol% or more, for example 90 mol% or more, and for example 95 mol% or more. When the degree of neutralization is 50 mol% or more, the water swelling property is good and the dispersion stabilizing effect is easily obtained, which is preferable.

In the present specification, the degree of neutralization can be calculated by calculation from the charged values of a monomer having an acid group such as a carboxy group and a neutralizing agent used for neutralization. The degree of neutralization was determined by measuring the IR of the polymer after drying the polymer at 80 ° C. for 3 hours under reduced pressure conditions, and measuring the peak derived from the C = O group of the carboxylic acid and the C = O group of the carboxylic acid salt. It can be confirmed from the intensity ratio of the peak of.

<Manufacturing method of crosslinked polymer or salt thereof / Manufacturing method of binder for secondary battery electrode>
The present polymer, which is a binder component of the present binder, can be produced by the following preparatory step (polymerization step). The method for producing the present polymer described below can also be carried out as a method for producing the present binder.

<Preparation process>
The preparation step is a step of preparing the present polymer. This is a step (polymerization step) of obtaining the present polymer or obtaining the present polymer by polymerization. The polymerization step is a step of polymerizing a monomer composition containing at least the non-crosslinkable monomer derived from the above-mentioned component (a) and the crosslinkable monomer derived from the component (c). Is.

<Polymerization process>
<Polymerization method>
Known polymerization methods such as solution polymerization, precipitation polymerization, suspension polymerization, and emulsion polymerization can be used for this polymer, but precipitation polymerization and suspension polymerization (reverse phase suspension polymerization) can be used in terms of productivity. ) Is preferable. Non-uniform polymerization methods such as precipitation polymerization, suspension polymerization, and emulsion polymerization are preferable in terms of obtaining better performance in terms of binding properties, and among them, polymer fine particles having a small particle size having excellent uniformity can be obtained. The precipitation polymerization method is more preferable because it is easy. Precipitation polymerization is a method for producing a polymer by carrying out a polymerization reaction in a solvent that dissolves an unsaturated monomer as a raw material but does not substantially dissolve the polymer to be produced. As the polymerization progresses, the polymer particles become larger due to aggregation and growth, and a dispersion liquid of the polymer particles in which the primary particles of several tens of nm to several hundreds nm are secondarily aggregated to several μm to several tens of μm can be obtained. Dispersion stabilizers can also be used to control the particle size of the polymer. The secondary aggregation can also be suppressed by selecting a dispersion stabilizer, a polymerization solvent, or the like. In general, precipitation polymerization in which secondary agglutination is suppressed is also called dispersion polymerization.

<Polymerization solvent>
In the case of precipitation polymerization, a solvent selected from water, various organic solvents and the like can be used as the polymerization solvent in consideration of the type of monomer used and the like. In order to obtain a polymer having a longer primary chain length, it is preferable to use a solvent having a small chain transfer constant.

Specific examples of the polymerization solvent include water-soluble solvents such as methanol, t-butyl alcohol, acetone, methyl ethyl ketone, acetonitrile and tetrahydrofuran, as well as benzene, ethyl acetate, dichloroethane, n-hexane, cyclohexane and n-heptane. , One of these can be used alone or in combination of two or more. Alternatively, it may be used as a mixed solvent of these and water. As used herein, the water-soluble solvent refers to a solvent having a solubility in water at 20 ° C. of more than 10 g / 100 ml. Of the above, the formation of coarse particles and adhesion to the reactor are small and the polymerization stability is good, and the precipitated polymer fine particles are difficult to secondary agglomerate (or even if secondary agglomeration occurs, they dissolve in the aqueous medium. Methyl ethyl ketone and acetonitrile are preferable because they are easy to use), a polymer having a small chain transfer constant and a large degree of polymerization (primary chain length) can be obtained, and the operation is easy during the step neutralization described later. ..

Similarly, in order to allow the neutralization reaction to proceed stably and rapidly in the step neutralization, it is preferable to add a small amount of a highly polar solvent to the polymerization solvent. Such highly polar solvents preferably include water and methanol. The amount of the highly polar solvent used is preferably 0.05 to 10.0% by mass, more preferably 0.1 to 5.0% by mass, still more preferably 0.1 to 1 based on the total mass of the medium. It is 0.0% by mass. When the proportion of the highly polar solvent is 0.05% by mass or more, the effect on the neutralization reaction is recognized, and when it is 10.0% by mass or less, no adverse effect on the polymerization reaction is observed. Further, in the polymerization of highly hydrophilic ethylenically unsaturated carboxylic acid monomer such as acrylic acid, the polymerization rate is improved when a highly polar solvent is added, and it becomes easy to obtain a polymer having a long primary chain length. Among the highly polar solvents, water is particularly preferable because it has a large effect of improving the polymerization rate.

<Monomer and its usage amount>
In this production method, for example, the ethylenically unsaturated carboxylic acid monomer from which the component (a) is derived is 10% by mass or more, 100% by mass or less, and ( b) A monomer containing 0% by mass or more and 90% by mass or less of another ethylenically unsaturated monomer from which the component is derived, and a crosslinkable monomer from which the component (c) is derived is non-crosslinkable. It is preferable to include a polymerization step of polymerizing a monomer composition containing 0.01 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the monomer. By the above polymerization step, the component (a) is introduced into the polymer in an amount of 10% by mass or more and 100% by mass or less, and the component (b) is contained in an amount of 0% by mass or more and 90% by mass or less based on the non-crosslinked structural unit. be introduced. The amount of the ethylenically unsaturated carboxylic acid monomer from which the component (a) is derived and the other ethylenically unsaturated monomer from which the component (b) is derived is the content with respect to the non-crosslinked structural unit already described. It is set appropriately to correspond. Further, the amount of the crosslinkable monomer from which the component (c) is derived is also appropriately set so as to correspond to the content of the component (c) already described.

The ethylenically unsaturated carboxylic acid monomer may be in an unneutralized state, or may be in a salt state in which at least a part thereof is neutralized. From the viewpoint of polymerization rate and binding property, the neutralization degree of the ethylenically unsaturated carboxylic acid monomer is, for example, 10 mol% or less, for example, 5 mol% or less, and is preferably unneutralized. ..

According to the present specification, such a monomer composition is a suitable composition for producing a binder for a secondary battery electrode.

The total concentration of the monomers in the polymerization step may be, for example, 2.0% by mass or more, for example 4.0% by mass or more, and for example about 10.0% by mass or more, but from the viewpoint of binding property. Preferably, it is, for example, 10.0% by mass or more, and for example, 13.0% by mass or more. As will be described later, when the polymerization step is carried out in the presence of a basic compound, the polymerization reaction can be stably carried out even at a high monomer concentration. The monomer concentration is more preferably 15.0% by mass or more, further preferably 17.0% by mass or more, and even more preferably 19.0% by mass or more. The monomer concentration is still more preferably 20.0% by mass or more, even more preferably 22.0% by mass or more, and even more preferably 25.0% by mass or more. In general, the higher the monomer concentration at the time of polymerization, the higher the molecular weight can be, and a polymer having a long primary chain length can be produced. Since this polymer is a microcrosslinked polymer in which a polymer having a sufficiently long primary chain length is appropriately crosslinked, it is analytically difficult to directly measure the primary chain length. Generally, it is known that the primary chain length of a polymer correlates with the solution viscosity, but in the case of this polymer, the solution viscosity also varies depending on the degree of cross-linking. Therefore, it is very difficult to define the present polymer obtained by the above method by the structure or characteristics of the present polymer. In the present specification, the “monomer concentration” indicates the monomer concentration in the reaction solution at the time when the polymerization is started.

The upper limit of the monomer concentration varies depending on the type of monomer and solvent used, the polymerization method, various polymerization conditions, etc., but if the heat of the polymerization reaction can be removed, the amount of precipitation polymerization is approximately 40 mass. %, About 50% by mass in suspension polymerization, and about 70% by mass in emulsion polymerization.

<Use of base compounds>
In this production method, the polymerization step may be carried out in the presence of the basic compound. The binder containing the present polymer thus obtained can exhibit high binding properties. Further, when a monomer composition containing an ethylenically unsaturated carboxylic acid monomer is polymerized in the presence of a basic compound, the polymerization stability is improved and the main weight is improved even at a high monomer concentration. The coalescence can be stably produced.

By carrying out the polymerization reaction in the presence of a basic compound, the polymerization reaction can be stably carried out even under high monomer concentration conditions such as exceeding 13.0% by mass. The polymer obtained by polymerizing at such a high monomer concentration has a high molecular weight (because the primary chain length is long), and therefore has excellent binding properties.

The base compound is a so-called alkaline compound, and either an inorganic base compound or an organic base compound may be used. Examples of the inorganic base compound include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide, and alkalis such as sodium carbonate and potassium carbonate. Examples thereof include alkali metal hydrogen carbonates such as metal carbonates, sodium hydrogen carbonates and potassium hydrogen carbonates. One or more of these can be used. Examples of organic base compounds include ammonia, for example, monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monobutylamine, dibutylamine, tributylamine, monohexylamine, dihexylamine, trihexylamine, and trioctylamine. And N-alkyl substituted amines such as tridodecylamine; (alkyl) alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, propanolamine, dimethylethanolamine and N, N-dimethylethanolamine; Cyclic amines such as 1,8-bis (dimethylamino) naphthalene, morpholin and diazabicycloundecene (DBU); organic amine compounds such as diethylenetriamine, N, N-dimethylbenzylamine and one of these. Alternatively, two or more types can be used. Among these, an organic amine compound excluding ammonia is preferable from the viewpoint of binding property.

When a base compound is used in the polymerization step, it is preferable to use 0.001 mol% or more of the base compound with respect to the ethylenically unsaturated carboxylic acid monomer. By carrying out the polymerization reaction in the presence of 0.001 mol% or more of the basic compound, the polymerization stability can be improved, and the polymerization reaction proceeds smoothly even under high monomer concentration conditions. The amount of the base compound used with respect to the ethylenically unsaturated carboxylic acid monomer is preferably 0.01 mol% or more, more preferably 0.03 mol% or more, still more preferably 0.05 mol% or more. be. The amount of the basic compound used may be 0.3 mol% or more, or 0.5 mol% or more. The upper limit of the amount of the basic compound used is preferably 4.0 mol% or less. By carrying out the polymerization reaction in the presence of 4.0 mol% or less of the basic compound, the polymerization stability can be improved, and the polymerization reaction proceeds smoothly even under high monomer concentration conditions. The amount of the base compound used with respect to the ethylenically unsaturated carboxylic acid monomer is preferably 3.0 mol% or less, more preferably 2.0 mol% or less, still more preferably 1.0 mol% or less. be. In this specification, the amount of the base compound used represents the molar concentration of the base compound used with respect to the ethylenically unsaturated carboxylic acid monomer, and does not mean the degree of neutralization. That is, the valence of the base compound used is not considered.

<Polymerization initiator>
As the polymerization initiator, known polymerization initiators such as azo compounds, organic peroxides, and inorganic peroxides can be used, but the polymerization initiator is not particularly limited. The conditions of use can be adjusted by known methods such as heat initiation, redox initiation with a reducing agent, and UV initiation so that the amount of radicals generated is appropriate. In order to obtain a crosslinked polymer having a long primary chain length, it is preferable to set the conditions so that the amount of radicals generated is smaller within the allowable range of the production time.

Examples of the azo compound include 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (N-butyl-2-methylpropionamide), and 2- (tert-butylazo) -2. -Cyanopropane, 2,2'-azobis (2,4,4-trimethylpentane), 2,2'-azobis (2-methylpropane) and the like, and one or more of these are used. be able to.

Examples of the organic peroxide include 2,2-bis (4,5-di-t-butylperoxycyclohexyl) propane (manufactured by Nichiyu Co., Ltd., trade name "Pertetra A") and 1,1-di (t-). Hexylperoxy) cyclohexane (same as "perhexa HC"), 1,1-di (t-butylperoxy) cyclohexane (same as "perhexa C"), n-butyl-4,4-di (t-butylperoxy) Valerate (“Perhexa V”), 2,2-di (t-Butyl Peroxy) Butan (“Perhexa 22”), t-Butyl Hydroperoxide (“Per Butyl H”), Kumen Hydroperoxide (Japan) Made by Yuyu Co., Ltd., trade name "Park Mill H"), 1,1,3,3-tetramethylbutylhydroperoxide ("Perocta H"), t-butylcumyl peroxide ("Perbutyl C"), di- t-Butyl peroxide (“Perbutyl D”), di-t-hexyl peroxide (“Perhexyl D”), di (3,5,5-trimethylhexanoyl) peroxide (“Perloyl355”), Dilauroyl peroxide (“Parloyl L”), Bis (4-t-butylcyclohexyl) peroxydicarbonate (“Parloyl TCP”), Di-2-ethylhexyl peroxydicarbonate (“Parloyl OPP”), Di-sec-Butylperoxydicarbonate (“Parloyl SBP”), Cumylperoxyneodecanoate (“Parkmill ND”), 1,1,3,3-Tetramethylbutylperoxyneodecanoate (1,1,3,3-tetramethylbutylperoxyneodecanoate) The same "Perocta ND"), t-hexyl peroxyneodecanoate (the same "Perhexyl ND"), t-butylperoxyneodecanoate (the same "Perbutyl ND"), t-butylperoxyneoheptanoate (Same as "Perbutyl NHP"), t-hexyl peroxypivalate (same as "Perhexyl PV"), t-butyl peroxypivalate (same as "Perbutyl PV"), 2,5-dimethyl-2,5-di (same as "Perbutyl PV") 2-Ethylhexanoyl) hexane (“Perhexa 250”), 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate (“Perocta O”), t-hexylperoxy-2 -Ethylhexanoate ("Perhexyl O"), t-Butylperoxy-2-ethylhexanoate ("Perbutyl O"), t-Butyl peroxylaurate ("Perbutyl L"), t- Butyl Luperoxy-3,5,5-trimethylhexanoate (“Perbutyl 355”), t-hexyl peroxyisopropyl monocarbonate (“Perhexyl I”), t-butyl peroxyisopropyl monocarbonate (“Perbutyl I”) ), T-Butylperoxy-2-ethylhexyl monocarbonate (“Perbutyl E”), t-Butylperoxyacetate (“Perbutyl A”), t-hexyl peroxybenzoate (“Perhexyl Z”) and t. -Butyl peroxybenzoate (the same "perbutyl Z") and the like can be mentioned, and one or more of these can be used.

Examples of the inorganic peroxide include potassium persulfate, sodium persulfate, ammonium persulfate and the like. When starting redox, sodium sulfite, sodium thiosulfate, sodium formaldehyde sulfoxylate, ascorbic acid, sulfurous acid gas (SO ₂ ), ferrous sulfate and the like can be used as the reducing agent.

The preferable amount of the polymerization initiator used is, for example, 0.001 to 2 parts by mass, and for example 0.005 to 1 part by mass, when the total amount of the monomers used is 100 parts by mass. For example, it is 0.01 to 0.1 parts by mass. When the amount of the polymerization initiator used is 0.001 part by mass or more, the polymerization reaction can be stably carried out, and when it is 2 parts by mass or less, a polymer having a long primary chain length can be easily obtained.

<Polymerization temperature, etc.>
The polymerization temperature is preferably 0 to 100 ° C., more preferably 20 to 80 ° C., although it depends on conditions such as the type and concentration of the monomer used. The polymerization temperature may be constant or may change during the polymerization reaction. The polymerization time is preferably 1 minute to 20 hours, more preferably 1 hour to 10 hours.

<Drying process, etc.>
Prior to the drying step, for the purpose of removing unreacted monomers or salts thereof, impurities derived from the initiator, etc., following the polymerization step, solid-liquid separation steps such as centrifugation and filtration, water, methanol, acetonitrile or polymerization It is preferable to include a cleaning step using the same solvent as the solvent. When the above cleaning step is provided, even when the present polymer is secondarily agglutinated, it is easily unraveled at the time of use, and the remaining unreacted monomer is removed, so that the binding property and the battery characteristics are improved. But it is advantageous.

<Neutralization process>
In this production method, when an unneutralized or partially neutralized salt is used as the ethylenically unsaturated carboxylic acid monomer, an alkaline compound is added to the polymer dispersion obtained in the polymerization step to neutralize the polymer. After carrying out the step (hereinafter, also referred to as “step neutralization”), the solvent may be removed in the drying step described above to obtain the present polymer in a solid state. Further, after the drying step is carried out in the unneutralized or partially neutralized salt state to obtain the present polymer in the solid state such as powder, an alkali for forming a salt when preparing the electrode mixture layer slurry. A step of adding a compound to neutralize the polymer (hereinafter, also referred to as “post-neutralization”) may be carried out. Of the above, process neutralization is preferable because the secondary aggregates tend to be easily disintegrated.

The alkaline compound that can be used in a neutralization step such as step neutralization is not particularly limited, but various alkaline compounds that can be used in the polymerization step as described above can be used. For example, LiOH, NaOH, KOH, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate and the like can be mentioned. From the viewpoint of battery performance when a Li salt is used, LiOH, which can obtain a Li salt of the present polymer, is preferable.

<Composition for secondary battery electrode and its manufacturing method>
The present composition is a composition for an electrode (mixture layer) of a secondary battery, and may contain a binder, an active material, and water containing the present polymer. The amount of the present polymer used in the present composition is, for example, 0.1% by mass or more and 20% by mass or less with respect to the total amount of the active material. The amount used is, for example, 0.2% by mass or more and 10% by mass or less, for example, 0.3% by mass or more and 8% by mass or less, and for example, 0.4% by mass or more and 5% by mass or less. .. If the amount of the polymer and its salt used is less than 0.1% by mass, sufficient binding properties may not be obtained. In addition, the dispersion stability of the active material or the like may become insufficient, and the uniformity of the formed mixture layer may decrease. On the other hand, when the amount of the present polymer and its salt used exceeds 20% by mass, the electrode mixture layer composition may have a high viscosity and the coatability to the current collector may be lowered. As a result, the obtained mixture layer may have lumps or irregularities, which may adversely affect the electrode characteristics.

According to the present specification, there is also provided a method for producing a composition for a secondary battery electrode, which comprises a step of preparing the present polymer and a step of preparing the present composition using the present polymer.

When the amount of the present polymer and its salt used is within the above range, the present composition having a sufficiently low slurry viscosity can be obtained, and the adhesion to the current collector and the binding property of the mixture layer are extremely high. An agent layer can be obtained, and as a result, the durability of the battery is improved. Further, the present polymer and its salt show sufficiently high binding property to the active material even in a small amount (for example, 5% by mass or less) and have a carboxy anion, so that the interfacial resistance is small and the high rate characteristics are excellent. The electrode is obtained.

Among the above active materials, lithium salts of transition metal oxides are mainly used as the positive electrode active materials, and for example, layered rock salt type and spinel type lithium-containing metal oxides can be used. Specific compounds of the layered rock salt type positive electrode active material include lithium cobalt oxide, lithium nickel oxide, and NCM {Li (Ni _x , Co _y , Mn _z ), x + y + z = 1} and NCA, which are called ternary systems. {Li (Ni _1-ab Co _a Al _b )} and the like can be mentioned. Moreover, as a spinel type positive electrode active material, lithium manganate and the like can be mentioned. In addition to oxides, phosphates, silicates, sulfur and the like are used, and examples of phosphates include olivine-type lithium iron phosphate and the like. As the positive electrode active material, one of the above may be used alone, or two or more thereof may be combined and used as a mixture or a composite.

When a positive electrode active material containing a layered rock salt type lithium-containing metal oxide is dispersed in water, the dispersion liquid becomes alkaline by exchanging lithium ions on the surface of the active material and hydrogen ions in water. Therefore, there is a risk that aluminum foil (Al) or the like, which is a general current collector material for positive electrodes, will be corroded. In such a case, it is preferable to neutralize the alkali content eluted from the active material by using the present polymer which has not been neutralized or partially neutralized as the binder. The amount of the unneutralized or partially neutralized present polymer used should be equal to or greater than the amount of alkali eluted from the active material in the amount of unneutralized carboxy groups of the present polymer. Is preferable.

Since all positive electrode active materials have low electrical conductivity, they are generally used by adding a conductive auxiliary agent. Examples of the conductive auxiliary agent include carbon-based materials such as carbon black, carbon nanotubes, carbon fibers, graphite fine powder, and carbon fibers. Among these, carbon black, carbon nanotubes, and carbon fibers are easy to obtain excellent conductivity. , Are preferred. Further, as the carbon black, Ketjen black and acetylene black are preferable. As the conductive auxiliary agent, one of the above types may be used alone, or two or more types may be used in combination. The amount of the conductive auxiliary agent used can be, for example, 0.2 to 20% by mass, and for example, 0.2 to 10% by mass, based on the total amount of the active material from the viewpoint of achieving both conductivity and energy density. It can be mass%. Further, as the positive electrode active material, a material whose surface is coated with a conductive carbon-based material may be used.

On the other hand, examples of the negative electrode active material include carbon-based materials, lithium metals, lithium alloys, metal oxides, and the like, and one or a combination of two or more of these can be used. Among these, active materials made of carbon-based materials such as natural graphite, artificial graphite, hard carbon and soft carbon (hereinafter, also referred to as "carbon-based active material") are preferable, and graphite such as natural graphite and artificial graphite, and graphite such as artificial graphite, and Hard carbon is more preferred. Further, in the case of graphite, spherical graphite is preferably used from the viewpoint of battery performance, and the preferable range of the particle size thereof is, for example, 1 to 20 μm, and for example, 5 to 15 μm. Further, in order to increase the energy density, a metal such as silicon or tin that can occlude lithium, a metal oxide, or the like can be used as the negative electrode active material. Among them, silicon has a higher capacity than graphite, and is an active material made of a silicon-based material such as silicon, a silicon alloy, and a silicon oxide such as silicon monoxide (SiO) (hereinafter, also referred to as "silicon-based active material"). ) Can be used. However, while the silicon-based active material has a high capacity, the volume change due to charging and discharging is large. Therefore, it is preferable to use it in combination with the above carbon-based active material. In this case, if the amount of the silicon-based active material is large, the electrode material may be disintegrated and the cycle characteristics (durability) may be significantly deteriorated. From such a viewpoint, when a silicon-based active material is used in combination, the amount used is, for example, 60% by mass or less, and for example, 30% by mass or less, based on the carbon-based active material.

The binder containing the present polymer has a structural unit (component (a)) in which the present polymer is derived from an ethylenically unsaturated carboxylic acid monomer. Here, the component (a) has a high affinity for a silicon-based active material and exhibits good binding properties. For this reason, this binder exhibits excellent binding properties even when a high-capacity type active material containing a silicon-based active material is used, and is therefore effective in improving the durability of the obtained electrode. Conceivable.

Since the carbon-based active material itself has good electrical conductivity, it is not always necessary to add a conductive additive. When a conductive additive is added for the purpose of further reducing resistance, the amount used is, for example, 10% by mass or less, and for example, 5% by weight or less, based on the total amount of the active material, from the viewpoint of energy density. Is.

When the composition is in a slurry state, the amount of the active material used is, for example, in the range of 10 to 75% by mass, and for example, in the range of 30 to 65% by mass, based on the total amount of the composition. If the amount of the active material used is 10% by mass or more, migration of the binder or the like can be suppressed, and the drying cost of the medium is also advantageous. On the other hand, if it is 75% by mass or less, the fluidity and coatability of the present composition can be ensured, and a uniform mixture layer can be formed.

When the present composition is prepared in a wet powder state, the amount of the active material used is, for example, in the range of 60 to 97% by mass, and for example, 70 to 90% by mass, based on the total amount of the present composition. The range. Further, from the viewpoint of energy density, it is preferable that the amount of non-volatile components other than the active material such as the binder and the conductive auxiliary agent is as small as possible within the range in which the necessary binding property and conductivity are guaranteed.

The composition uses water as the medium. Further, for the purpose of adjusting the properties and dryness of the composition, lower alcohols such as methanol and ethanol, carbonates such as ethylene carbonate, ketones such as acetone, and water-soluble organic substances such as tetrahydrofuran and N-methylpyrrolidone. It may be a mixed solvent with a solvent. The proportion of water in the mixing medium is, for example, 50% by mass or more, and for example, 70% by mass or more.

When the present composition is in a coatable slurry state, the content of the medium containing water in the entire composition is, for example, from the viewpoint of the coatability of the slurry, the energy cost required for drying, and the productivity. It can be in the range of 25-90% by mass, and can be, for example, 35-70% by mass. Further, in the case of a pressable wet powder state, the content of the medium can be, for example, in the range of 3 to 40% by mass from the viewpoint of the uniformity of the mixture layer after pressing, and for example, 10 It can be in the range of ~ 30% by mass.

The binder component contained in the present composition may consist only of the present polymer, but other than this, styrene / butadiene latex (SBR), acrylic latex, polyvinylidene fluoride latex and the like may be used. Other binder components may be used in combination. When other binder components are used in combination, the amount used may be, for example, 0.1 to 5% by mass or less, and for example, 0.1 to 2% by mass or less, based on the active material. And, for example, it can be 0.1 to 1% by mass or less. If the amount of the other binder component used exceeds 5% by mass, the resistance increases and the high rate characteristics may become insufficient. Among the above, styrene / butadiene latex is preferable because it has an excellent balance between binding property and bending resistance.

The present composition contains the above-mentioned active material, water and a binder as essential constituents, and can be obtained by mixing the respective components using known means. The mixing method of each component is not particularly limited, and a known method can be adopted. However, after dry blending the powder components such as the active material, the conductive additive and the present polymer which is a binder, water or the like is used. The method of mixing with the dispersion medium of the above and dispersing and kneading is preferable. When the present composition is obtained in a slurry state, it is preferable to finish the composition into a slurry having no poor dispersion or aggregation. As the mixing means, a known mixer such as a planetary mixer, a thin film swirl mixer, or a self-revolving mixer can be used, but a thin film swirl mixer is used because a good dispersion state can be obtained in a short time. It is preferable to do this. When using a thin film swirl mixer, it is preferable to pre-disperse in advance with a stirrer such as a disper.

The viscosity of the slurry of the present composition can be, for example, in the range of 500 to 100,000 mPa · s as the shear viscosity at a ^{shear rate of 60 s -1 at 25 ° C., and for example, 1,000 to 50,000 mPa · s.} It can be in the range of s. Further, for example, the slurry viscosity of the present composition is preferably in the range of 500 to 10,000 mPa · s, more preferably 500 to 7,000 mPa · s, still more preferably 500 to 6,000 mPa · s. It can be s, more preferably 500 to 5,000 mPa · s, even more preferably 500 to 4,000 mPa · s, and even more preferably 500 to 3,000 mPa · s. It can be s, more preferably 500 to 2,000 mPa · s, even more preferably 500 to 1,800 mPa · s, and even more preferably 500 to 1,700 mPa · s. It can be s, preferably 500 to 1,600 mPa · s, and preferably 500 to 1,500 mPa · s.

On the other hand, when the present composition is obtained in a wet powder state, it is preferable to knead the composition using a Henschel mixer, a blender, a planetary mixer, a twin-screw kneader or the like to a uniform state without uneven concentration.

<Secondary battery electrode>
The present electrode is provided with a mixture layer formed from the present composition on the surface of a current collector such as copper or aluminum. The mixture layer is formed by applying the present composition to the surface of the current collector and then drying and removing a medium such as water. The method for applying the present composition is not particularly limited, and known methods such as a doctor blade method, a dip method, a roll coating method, a comma coating method, a curtain coating method, a gravure coating method and an extrusion method can be adopted. can. Further, the drying can be performed by a known method such as blowing warm air, reducing the pressure, (far) infrared rays, and irradiating microwaves. Usually, the mixture layer obtained after drying is subjected to a compression treatment by a mold press, a roll press or the like. By compressing, the active material and the binder can be brought into close contact with each other, and the strength of the mixture layer and the adhesion to the current collector can be improved. The thickness of the mixture layer can be adjusted to, for example, about 30 to 80% before compression by compression, and the thickness of the mixture layer after compression is generally about 4 to 200 μm.

According to the present specification, the present invention includes a step of preparing the present polymer, a step of preparing the present composition using the present polymer, and a step of preparing a secondary battery electrode using the present composition. , A method for manufacturing a secondary battery electrode is also provided.

A secondary battery can be manufactured by providing the present electrode with a separator and a non-aqueous electrolytic solution. The separator is arranged between the positive electrode and the negative electrode of the battery, and plays a role of preventing a short circuit due to contact between the two electrodes and holding an electrolytic solution to ensure ionic conductivity. The separator is preferably a film-like insulating microporous membrane having good ion permeability and mechanical strength. As a specific material, polyolefins such as polyethylene and polypropylene, polytetrafluoroethylene and the like can be used.

As the non-aqueous electrolyte solution, known ones generally used for secondary batteries can be used. Specific examples of the solvent include cyclic carbonates having a high dielectric constant and a high dissolving ability of an electrolyte such as propylene carbonate and ethylene carbonate, and chain carbonates having a low viscosity such as ethylmethyl carbonate, dimethyl carbonate and diethyl carbonate. , These can be used alone or as a mixed solvent. The non-aqueous electrolyte solution is used by dissolving lithium salts such as _{LiPF 6} , LiSbF ₆ , LiBF ₄ , LiClO ₄ , and LiAlO _{4 in these solvents.} The secondary battery is obtained by forming a positive electrode plate and a negative electrode plate partitioned by a separator into a spiral or laminated structure and storing them in a case or the like.

As described above, the binder for the secondary battery electrode disclosed in the present specification can achieve both excellent binding properties and a decrease in the viscosity of the mixture layer slurry. A secondary battery provided with an electrode obtained by using the above binder is expected to ensure good integrity and exhibit good durability (cycle characteristics) even after repeated charging and discharging. For example, it is used for automobiles. Suitable for secondary batteries and the like.

Hereinafter, the production and use of the polymer disclosed in the present specification will be specifically exemplified and described, but the disclosure of the present specification is not limited to the following examples. Further, in the following, unless otherwise specified, "parts" and "%" shall mean parts by mass and% by mass unless otherwise specified.

<Production example of this polymer>
<Production Example 1: Production of crosslinked polymer salt R-1>
A reactor equipped with a stirring blade, a thermometer, a reflux condenser and a nitrogen introduction tube was used for the polymerization. In the reactor, 567 parts of acetonitrile, 2.20 parts of ion-exchanged water, 100 parts of acrylic acid (hereinafter referred to as "AA"), 2-hydroxy-3-acryloyloxypropyl methacrylate (manufactured by Kyoeisha Chemical Co., Ltd., light ester G- 201P) 0.20 part and triethylamine corresponding to 1.0 mol% with respect to the above AA were charged. After sufficiently replacing the inside of the reactor with nitrogen, the inside temperature was raised to 55 ° C. by heating. After confirming that the internal temperature was stable at 55 ° C., 2,2'-azobis (2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd., trade name "V-65") 0 as a polymerization initiator. When .040 parts were added, white turbidity was observed in the reaction solution, and this point was set as the polymerization initiation point. The monomer concentration was calculated to be 15.0%.

The polymerization reaction was continued while maintaining the internal temperature at 55 ° C. by adjusting the external temperature (water bath temperature), and the internal temperature was raised to 65 ° C. when 6 hours had passed from the polymerization initiation point. The internal temperature is maintained at 65 ° C., cooling of the reaction solution is started 12 hours after the reaction start point, and after the internal temperature drops to 25 ° C., lithium hydroxide monohydrate (hereinafter, “LiOH”). 52.5 parts of powder (referred to as "H _{2 O") was added.} After the addition, stirring was continued at room temperature for 12 hours to obtain a slurry-like polymerization reaction solution in which particles of the crosslinked polymer salt R-1 (Li salt, neutralization degree 90 mol%) were dispersed in a medium.

The obtained polymerization reaction solution was centrifuged to settle the polymer particles, and then the supernatant was removed. Then, after redispersing the precipitate in acetonitrile having the same weight as the polymerization reaction solution, the operation of precipitating the polymer particles by centrifugation and removing the supernatant was repeated twice. The precipitate was recovered and dried under reduced pressure at 80 ° C. for 3 hours to remove volatile components to obtain a powder of the crosslinked polymer salt R-1. Since the crosslinked polymer salt R-1 has hygroscopicity, it was stored in a container having a water vapor barrier property. The powder of the crosslinked polymer salt R-1 was measured by IR, and the degree of neutralization was determined from the intensity ratio of the peak derived from the C = O group of the carboxylic acid and the peak derived from the C = O of the carboxylic acid Li. It was 90 mol%, which was equal to the value calculated from.

<Production Examples 2 to 15: Production of crosslinked polymer salts R-2 to R-15>
The same operation as in Production Example 1 was carried out except that the amount of each raw material charged was as shown in Table 1, to obtain a polymerization reaction solution containing crosslinked polymer salts R-2 to R-15. Next, the same operations as in Production Example 1 were carried out for each polymerization reaction solution to obtain powdered crosslinked polymer salts R-2 to R-15. Each crosslinked polymer salt was sealed and stored in a container having a water vapor barrier property. In the production example 9, by using NaOH instead of powder LiOH · _{H 2} O, to obtain a crosslinked polymer Na salt (degree of neutralization 90 mol%).

The notations shown in Table 1 will be described below.
AA: DMAA acrylate: Dimethylacrylamide HAPMA: 2-Hydroxy-3-acryloyloxypropyl methacrylate (light ester G-201P, Kyoeisha Chemical Co., Ltd.)
GDMA: Glycerin dimethacrylate (light ester G-101P, Kyoeisha Chemical Co., Ltd.)
EGDMA: Ethylene dimethacrylate (Fujifilm Wako Pure Chemical Industries, Ltd.)
T-20: Trimethylolpropane diallyl ether (Osaka Soda)
TEA: Triethylamine AcCN: Acetonitrile V-65: 2,2'-azobis (2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd.)

<Example>
<Example 1>
3.2 parts of powdered crosslinked polymer Li salt R-1 is weighed in 100 parts of natural graphite, mixed well in advance, 160 parts of ion-exchanged water is added and pre-dispersed with a disper, and then a thin film swirl type is used. This dispersion was carried out for 15 seconds under the condition of a peripheral speed of 20 m / sec using a mixer (FM-56-30 manufactured by Primix Corporation) to obtain a slurry-like negative electrode mixture layer composition. The slurry concentration (solid content) was calculated to be 39.2%.

<Viscosity measurement of electrode slurry>
The negative electrode mixture layer composition (slurry) obtained above was prepared at 25 ° C. using a rheometer (Physica MCR301) manufactured by Anton Pearl Co., Ltd. on a CP25-5 cone plate (diameter 25 mm, cone angle 5 °). The slurry viscosity at a shear rate of 60s ^{-1 was measured.}

<90 ° peel strength (bonding property)>
Using a variable applicator, the mixture layer composition is applied onto a copper foil (manufactured by Nippon Foil Co., Ltd.) having a thickness of 20 μm, and dried in a ventilation dryer at 100 ° C. for 15 minutes to form a mixture layer. Was formed. Then, the mixture layer was rolled so that the thickness was 70 ± 5 μm and the packing density was 1.70 ± 0.20 g / cm ³ , and a negative electrode was prepared. The negative electrode obtained above was cut into strips having a width of 25 mm, and then the mixture layer surface of the sample was attached to a double-sided tape fixed on a horizontal surface to prepare a sample for a peeling test. The test sample was dried at 60 ° C. overnight under reduced pressure, and then peeled at 90 ° at a tensile speed of 50 mm / min, and the peeling strength between the mixture layer and the copper foil was measured. The peel strength was as high as 15.8 N / m, which was good.

<Examples 2 to 15, Comparative Examples 1 to 3>
A negative electrode mixture layer composition was prepared by the same operation as in Example 1 except that the crosslinked polymer salt used as the active material and the binder was used as shown in Table 2. In Examples 3 and 4, natural graphite and silicon particles were stirred at 400 rpm for 1 hour using a planetary ball mill (manufactured by FRITSCH, P-5), and a powdery crosslinked polymer was added to the obtained mixture. After weighing 3.2 parts of Li salt R-2 and mixing well in advance, a mixture layer composition was prepared by performing the same operation as in Example 1. The slurry viscosity and 90 ° peel strength were evaluated for each mixture layer composition. The results are shown in Table 2.

As shown in Table 2, Examples 1 to 15 using the crosslinked polymers R-1 to R-13 using the crosslinkable monomer having two or more (meth) acryloyl groups and a hydroxyl group are combined. The viscosity of the agent layer slurry was 330 to 1800 mPa · s, and showed extremely good viscosity. The peel strength of Examples 1 to 15 was 14.4 to 19.1 N / m, showing sufficient electrode binding property. On the other hand, in Comparative Example 1 using the polymer of Production Example 14 which was not crosslinked, a crosslinkable monomer having high viscosity but low binding property and having two acryloyl groups but not a hydroxyl group was used. In Comparative Example 2 using the crosslinked polymer of Production Example 15 used, the binding property was good, but the slurry viscosity was still considerably high, the crosslinkable single amount having two allyl groups and having a hydroxyl group. In Comparative Example 3 using the crosslinked polymer of Production Example 16 using the body, the binding property was low and the slurry viscosity was still high.

From the above, it is derived from such a crosslinkable monomer by polymerizing an ethylenically unsaturated carboxylic acid monomer and a crosslinkable monomer having two (meth) acryloyl groups and having a hydroxyl group. It was found that by providing a crosslinked structure, both good binding property and slurry viscosity can be achieved at the same time.

Further, according to Examples 1 to 2 and 5 to 7, the amount of the crosslinkable monomer used is about 0.1 to 10 parts with respect to 100 parts of the non-crosslinkable monomer, and the binding property is good. A crosslinked polymer can be obtained, and crosslinks with better binding properties are obtained in about 0.2 to 9 parts, 0.2 to 5 parts, 0.2 to 2 parts, and 0.2 to 1 part. It was found that a polymer could be obtained. It was also found that a crosslinked polymer having a sufficiently low slurry viscosity can be obtained when the amount of the crosslinkable monomer used is about 0.1 to 10 parts.

Further, according to Examples 3 to 4, it was found that even if silicon particles are contained as the active material, stable binding property and slurry viscosity can be achieved at the same time. Further, according to Example 8, even if the crosslinked polymer of Production Example 6 using a crosslinkable monomer having a structure different from that of Production Examples 1 to 5 is used, excellent binding property and slurry viscosity can be obtained. I understand.

Furthermore, according to Examples 9 to 12, stable binding property was observed regardless of the degree of salt neutralization (85%, 70% and 90%) and the type of salt to be neutralized (Li, Na, K). It was found that the slurry viscosity could be secured. Further, according to Examples 13 to 15, it was found that excellent binding property and slurry viscosity can be ensured even by using dimethylacrylamide as the non-crosslinkable monomer. The use of dimethylacrylamide also tended to lower the slurry viscosity.

Claims (6)

A secondary battery electrode binder having a crosslinked polymer or a salt thereof.
The crosslinked polymer or a salt thereof comprises a non-crosslinked structural unit and a crosslinked structural unit.
The non-crosslinked structural unit includes a non-crosslinked structural unit derived from an ethylenically unsaturated carboxylic acid monomer.
The crosslinked structural unit contains a crosslinked structural unit derived from a crosslinkable monomer having two or more (meth) acryloyl groups in one molecule and having a hydroxyl group.
binder. The binder according to claim 1, wherein the non-crosslinked structural unit derived from the ethylenically unsaturated monomer is contained in an amount of 30% by mass or more and 100% by mass or less based on the total amount of the non-crosslinked structural units. A composition for a secondary battery electrode
The binder for the secondary battery electrode according to claim 1 or 2,
With active material
water and,
Composition containing. It is a secondary battery electrode
The binder for the secondary battery electrode according to claim 1 or 2,
With active material
Electrode containing. The electrode according to claim 4, wherein the active material is a silicon-containing substance. A method for manufacturing a binder for a secondary battery electrode.
A step of polymerizing a monomer composition containing an ethylenically unsaturated carboxylic acid monomer and a crosslinkable monomer having two or more (meth) acryloyl groups in one molecule and having a hydroxyl group. ,
A manufacturing method.