WO2020090695A1 - Binder for secondary battery electrodes, and use thereof - Google Patents

Abstract

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

Description

Binder for secondary battery electrode and use thereof

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 filed on Oct. 31, 2018, and claims the priority right based on this Japanese application. Incorporated herein by reference.

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

On the other hand, as the use of various secondary batteries expands, demands for improving energy density, reliability and durability tend to increase. For example, specifications for using a silicon-based active material as the negative electrode active material are increasing in order to increase the electric capacity of the lithium-ion secondary battery. However, it is known that the volume change of a silicon-based active material during charge / discharge is large, and peeling or dropping of the electrode mixture layer occurs as it is repeatedly used, and as a result, the capacity of the battery decreases and the cycle characteristics There was a problem that (durability) deteriorates. In order to suppress such a problem, it is generally effective to enhance the binding property of the binder, and for the purpose of improving the durability, studies on improving the binding property of the binder have been conducted.

A binder using the above acrylic acid-based polymer has been proposed as a binder having good binding properties and an effect of improving durability. In Patent Document 1, by using a polymer obtained by crosslinking 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 described that it can be provided. Patent Document 2 discloses a crosslinked polymer having a carboxy group or a salt thereof, which is obtained by using 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. 2014/065407 International Publication No. 2017/073589

The binders disclosed in each patent document are all capable of imparting good binding properties, but as the performance of the secondary battery is improved, an electrode mixture layer having 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 becomes high and the coatability is deteriorated. Therefore, there is a demand for a binder that can reduce the viscosity of the slurry.

The present specification provides a binder that can improve the binding property and reduce the viscosity of the slurry for the electrode mixture layer, and the use thereof.

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

[1] A secondary battery electrode binder having a crosslinked polymer or a salt thereof, comprising:
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 cross-linking structural unit has two or more (meth) acryloyl groups in one molecule, and includes a cross-linking structural unit derived from a cross-linkable monomer having a hydroxyl group,
binder.
[2] The binder according to [1], which contains the non-crosslinking structural unit derived from the ethylenically unsaturated monomer in an amount of 30% by mass or more and 100% by mass or less based on the total amount of the non-crosslinking structural unit.
[3] A composition for a secondary battery electrode, comprising:
A binder for a secondary battery electrode according to [1] or [2],
Active material,
water and,
A composition containing:
[4] A secondary battery electrode,
A binder for a secondary battery electrode according to [1] or [2],
Active material,
An electrode containing.
[5] The electrode according to [4], wherein the active material is a silicon-containing material.
[6] A method for manufacturing a binder for a secondary battery electrode, comprising:
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 ,
And a manufacturing method.

The secondary battery electrode binder (hereinafter, simply referred to as the binder) disclosed in the present specification can include a crosslinked polymer or a salt thereof (hereinafter, 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 includes a non-crosslinked structural unit derived from an ethylenically unsaturated monomer, the crosslinked structural unit in one molecule Can have 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 in the non-crosslinked structural unit, it becomes a binder with good binding properties. Further, the present polymer contains, in the cross-linking structural unit, a cross-linking structural unit derived from a cross-linking monomer having two or more (meth) acryloyl groups. Since such a crosslinkable monomer has a relatively high radical polymerizability, a crosslinked structural unit is formed relatively uniformly from the inside of the polymer particle to the surface portion. In other words, it is considered that the cross-linking density of the present polymer particle surface obtained by cross-linking polymerization can be suppressed from being excessively increased, and as a result, the degree of swelling of the present polymer particle surface in water is relatively high, and the active material or It is considered that the adhesive 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 cross-linking structural unit, the swelling degree of the present polymer particle is suppressed by the interaction (hydrogen bond etc.) due to the hydroxyl group in the polymer particle, and the increase of slurry viscosity is suppressed. can do.

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

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

Hereinafter, other than the present binder, representative and non-limiting specific examples of the present composition, a method for producing the present binder, a method for producing the present composition, a method for producing the present electrode, etc. will be described in detail with reference to the drawings as appropriate. explain. This detailed description is merely intended to present 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. Also, the additional features disclosed below can be used separately from or together with other features or disclosures to provide a further improved "binder for secondary battery electrodes and use thereof".

Further, the combination of features and steps disclosed in the following detailed description is not essential in carrying out the present disclosure in the broadest sense, and is only for describing a representative specific example of the present disclosure. It is described. Furthermore, various features of the exemplary embodiments above and below, as well as those set forth in the independent and dependent claims, are described herein in providing additional and useful embodiments of the present disclosure. It is not necessary to combine them according to the specific examples described or in the order listed.

All the features described in the present specification and / or the claims are, apart from the configuration of the features described in the examples and / or the claims, individually as a limitation to the disclosure at the time of filing the application and specific matters claimed, And are intended to be disclosed independently of each other. Furthermore, all numerical ranges and statements regarding groups or groups are intended to disclose the disclosure as originally filed and as limitations on the specific matter claimed, as well as intermediate constructions thereof.

In the present 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 include the polymer, that is, 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 of the binder component, for example 60% by mass or more, for example 70% by mass or more, for example 80% by mass or more, and for example 90% by mass or more. It is contained, for example, 95% by mass or more, and for example, 100% by mass.

<Structural unit of cross-linked polymer>
<Non-crosslinked structural unit>
The polymer has a non-crosslinked structural unit and a crosslinked structural unit. The non-crosslinking structural unit is not particularly limited, and includes structural units derived from various non-crosslinking monomers that can be used in the crosslinked polymer that can be used as the binder of the secondary battery electrode, as the noncrosslinking structural unit. be able to.

The non-crosslinked structural unit may have, for example, a structural unit derived from an ethylenically unsaturated carboxylic acid monomer (hereinafter, also referred to as “component (a)”). By having a carboxy group in the structural unit, the adhesion to the current collector is improved, and since the lithium ion desolvation effect and the ionic conductivity are excellent, the resistance is small, and an electrode having excellent high rate characteristics can be obtained. .. Further, since water swelling property is imparted, dispersion stability of the active material and the like in the present composition can be enhanced. The above structural unit can be introduced into the present polymer by, for example, 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. Moreover, after polymerizing (meth) acrylamide, (meth) acrylonitrile, etc., it may be treated with a strong alkali or a method of reacting an acid anhydride with the main polymer having a hydroxyl group.

Examples of the ethylenically unsaturated carboxylic acid monomer include (meth) acrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid; (meth) acrylamidoalkyl acid such as (meth) acrylamidohexanoic acid and (meth) acrylamidododecanoic acid. Carboxylic acid; ethylenically unsaturated monomers having a carboxy group such as succinic acid monohydroxyethyl (meth) acrylate, ω-carboxy-caprolactone mono (meth) acrylate, β-carboxyethyl (meth) acrylate or the like (part thereof) ) Alkali-neutralized products are mentioned, and one of them may be used alone, or two or more thereof may be used in combination. Among the above, a polymer having a long primary chain length is obtained because of a high polymerization rate, and a compound having an acryloyl group as a polymerizable functional group is preferable in that the binding force of the binder is good, and acrylic acid is particularly preferable. is there. When acrylic acid is used as the ethylenically unsaturated carboxylic acid monomer, a polymer having a high carboxy group content can be obtained.

The carboxy group of the ethylenically unsaturated carboxylic acid monomer may be free 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 salt Examples thereof include amine salts. Among these, alkali metal salts and magnesium salts are preferable, and alkali metal salts are more preferable, because they are unlikely to adversely affect battery characteristics. 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 based on 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 secured, and a good lithium ion desolvation effect and ion conductivity are provided, so that an electrode having excellent high rate characteristics can be obtained. Further, the water swelling property can enhance the dispersion stability of the active material and the like in the present composition. Such an effect tends to be improved by increasing the content of the component (a).

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

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

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

<Other structural units>
The present polymer may contain, in addition to the component (a), a structural unit derived from another ethylenically unsaturated monomer copolymerizable therewith (hereinafter, also referred to as “component (b)”). .. Examples of the component (b) include ethylenically unsaturated monomer compounds having anionic groups other than carboxy groups such as sulfonic acid groups and phosphoric acid groups, or nonionic ethylenically unsaturated monomers. The structural unit from which it is derived is included. 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 binding property of the binder and the slurry viscosity. (Meth) acrylamide and its derivatives are preferred because of their excellent properties. 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), strong interaction with the electrode material can be achieved, Good binding properties can be exhibited for the active material. This is preferable because it is possible to obtain a firm and good electrode mixture layer. A structural unit derived from an alicyclic structure-containing ethylenically unsaturated monomer is particularly preferable.

(Meth) acrylamide and its derivatives are preferable as the nonionic ethylenically unsaturated monomer because of their excellent binder binding properties and slurry viscosity. Examples of the (meth) acrylamide derivative include N-alkyl (s) such as isopropyl (meth) acrylamide, t-butyl (meth) acrylamide, Nn-butoxymethyl (meth) acrylamide, N-isobutoxymethyl (meth) acrylamide. (Meth) acrylamide compound; N, N-dialkyl (meth) acrylamide compounds such as dimethyl (meth) acrylamide, diethyl (meth) acrylamide, etc. may be mentioned, and one of these may be used alone, or two of them may be used. The above may be used in combination.

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

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. (Meth) acrylic acid alkyl ester compound; (meth) acrylic acid cycloalkyl ester such as (meth) acrylic acid cyclohexyl, (meth) acrylic acid methylcyclohexyl, etc .; (meth) acrylic acid 2-methoxyethyl, (meth) acrylic acid (Meth) acrylic acid alkoxyalkyl ester compounds such as ethoxyethyl; hydroxymethacrylic acid hydroxyalkyl ester compounds such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate and hydroxybutyl (meth) acrylate Named You may be using one of these alone or may be used in combination of two or more. 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 based on the total amount of the non-crosslinked structural units of the present polymer. , Preferably 1 to 30% by mass, more preferably 5 to 30% by mass, and further preferably 10 to 30% by mass. 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 99% by mass based on the total structural units of the present polymer. It is 90% by mass.

Among the above, since the lithium ion conductivity is high and the high rate property is further improved, (meth) acrylic acid alkoxyalkyls such as 2-methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate, ethers, etc. 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 of its high polymerization rate and the binding force of the binder is good. As the nonionic ethylenically unsaturated monomer, a compound having a homopolymer glass transition temperature (Tg) of 0 ° C. or lower is preferable in that the obtained electrode has good bending resistance.

<Crosslinked structural unit>
The present polymer has, as a cross-linking structural unit, two or more (meth) acryloyl groups in one molecule, and a cross-linking structural unit derived from a cross-linkable monomer having a hydroxyl group (hereinafter, referred to as “(c) component”). Also referred to as).

The two or more (meth) acryloyl groups that the component (c) may have include two or more methacryloyl groups, one or more acryloyl groups and one or more methacryloyl groups, two or more acryloyl groups. can do. It is not particularly limited, but is, for example, 2 or more and 6 or less (meth) acryloyl group, and is, for example, 2 or more and 5 or less (meth) acryloyl group, or, for example, 2 or more and 4 or less (meth ) An acryloyl group, for example, 2 or more and 3 or less (meth) acryloyl groups, for example, 2 (meth) acryloyl groups can be provided.

The (meth) acryloyl group can reduce the crosslink density on the particle surface of the present polymer and reduce the degree of swelling in water. 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 difunctionalized compound having two (meth) acryloyl groups, the components (c) are, for example, from the viewpoint of improving the binding property, preferred dimethacryloyl groups. , A methacryloyl group, an acryloyl group, and a diacryloyl group. 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. The number and combination of (meth) acryloyl groups in the component (c) can be appropriately selected in consideration of the binding property and slurry viscosity intended as a binder for secondary battery electrodes, as well as the amount of the crosslinking structural unit.

The number of hydroxyl groups that the component (c) can have is not particularly limited as long as it is 1 or more, and is, for example, 1 or more and 3 or less, or, for example, 1 or more and 2 or less, and For example, one. It is considered that as the number of hydroxyl groups increases, the interaction within the polymer particles tends to increase. The number of hydroxyl groups in the component (c) can be appropriately selected in consideration of the viscosity of the slurry intended as the binder for the secondary battery electrode and the like, as well as the amount of the cross-linking structural unit.

The component (c) is not particularly limited, and examples thereof include trimethylolpropane di (meth) acrylate, pentaerythritol di- or tri (meth) acrylate, dipentaerythritol di-, tri-, tetra- or penta- (meta). ) Acrylate, glycerin di (meth) acrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate and the like can be used. As the component (c), only one type may be used, but two or more types 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 units is 100 parts by mass. If it is less than 0.01 parts by mass, the binding property will not be obtained and the viscosity of the slurry will be too high. If it exceeds 20 parts by mass, the binding property will not be obtained. The component (c) is, for example, 0.02 parts by mass or more, and 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, 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. Also, for example, 5 parts by mass or less, and 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 preferable range of the content of the component (c) may be a combination of the upper limit and the lower limit thereof, but 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. Parts or less, for example 0.2 parts by mass or more and 9 parts by mass or less, and 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, it is, for example, 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 have a cross-linking structural unit other than the component (c). The cross-linking structural unit is derived from a polyfunctional polymerizable monomer having two or more polymerizable unsaturated groups and a monomer having a self-crosslinkable crosslinkable functional group such as a hydrolyzable silyl group. 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, (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, polypropylene glycol di ( Di (meth) acrylates of dihydric alcohols such as (meth) acrylate; trimethylolpropane tri (meth) acrylate, trimethylolpropane ethylene oxide modified tri (meth) acrylate, glycerin tri (meth) acrylate, pentaerythritol tetra ( Poly (meth) acrylates such as tri (meth) acrylates of trihydric or higher polyhydric alcohols such as (meth) acrylates, tetra (meth) acrylates; methylenebisacrylamide, hydro Shi ethylene bisacrylamide bisamides such as and the like.

Examples of the polyfunctional alkenyl compound include trimethylolpropane diallyl ether, trimethylolpropane triallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, tetraallyloxyethane, polyallyl saccharose and the like; diallyl phthalate and the like. Examples of the polyfunctional allyl compound: a polyfunctional vinyl compound such as divinylbenzene.

Examples of the compound having both a (meth) acryloyl group and an alkenyl group include allyl (meth) acrylate, isopropenyl (meth) acrylate, butenyl (meth) acrylate, pentenyl (meth) acrylate, and (meth) acrylic acid. 2- (2-vinyloxyethoxy) ethyl and the like can be mentioned.

Specific examples of the monomer having a crosslinkable functional group capable of self-crosslinking include hydrolyzable silyl group-containing vinyl monomer, N-methylol (meth) acrylamide, N-methoxyalkyl (meth) acrylate and the like. Is mentioned. These compounds may 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 trimethoxy silane, vinyl triethoxy silane, vinyl methyl dimethoxy silane, vinyl dimethyl methoxy silane; silyl triacrylate such as trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate, methyldimethoxysilylpropyl acrylate, etc. Group-containing acrylic acid esters; trimethoxysilylpropyl methacrylate, triethoxysilylpropyl methacrylate, methyldimethoxysilylpropyl methacrylate, dimethylmethoxysilylpropyl methacrylate, etc. silyl group-containing methacrylates; trimethoxysilylpropyl vinyl ether, etc. Examples of the silyl group-containing vinyl ethers include silyl group-containing vinyl esters such as trimethoxysilyl vinyl undecanoate.

The cross-linking structural unit other than the component (c) is not particularly limited, but is, 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-crosslinking monomers. 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 part by mass. It may be less than or equal to parts 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 in the composition is 20 to 100 mol%, and a salt form is obtained. It is preferable to use as. The above-mentioned degree of neutralization is more preferably 50 to 100 mol%, for example 60 mol% or more, also for example 65 mol% or more, for example 70 mol% or more, for example 75 mol% or more, for example 80 mol% or more. And, for example, 85 mol% or more, also 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 from the charged values of the monomer having an acid group such as a carboxy group and the neutralizing agent used for neutralization. The degree of neutralization was determined by IR measurement of the powder obtained by drying the present polymer at 80 ° C. for 3 hours under reduced pressure, and the peak derived from the C═O group of the carboxylic acid and the C═O group of the carboxylate. It can be confirmed from the intensity ratio of the peak.

<Method for producing crosslinked polymer or salt thereof / Method for producing binder for secondary battery electrode>
The present polymer, which is a binder component of the present binder, can be produced by the following preparation 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 of obtaining the present polymer or obtaining the present polymer by polymerization (polymerization step). The polymerization step is a step of polymerizing a monomer composition containing at least the non-crosslinkable monomer from which the component (a) is derived and the crosslinkable monomer from which the component (c) is derived. Is.

<Polymerization process>
<Polymerization method>
For the present polymer, known polymerization methods such as solution polymerization, precipitation polymerization, suspension polymerization, and emulsion polymerization can be used, but from the viewpoint of productivity, precipitation polymerization and suspension polymerization (reverse phase suspension polymerization) ) Is preferred. In terms of obtaining better performance with respect to binding properties, etc., a heterogeneous polymerization method such as precipitation polymerization, suspension polymerization, or emulsion polymerization is preferable, and among them, polymer fine particles having a small particle size excellent in uniformity are obtained. The precipitation polymerization method is more preferable because it is easy. Precipitation polymerization is a method of producing a polymer by carrying out a polymerization reaction in a solvent that dissolves an unsaturated monomer that is a raw material but does not substantially dissolve a produced polymer. As the polymerization progresses, the polymer particles become larger due to aggregation and growth, and a dispersion liquid of polymer particles in which primary particles of several tens nm to several hundreds nm are secondarily aggregated to several μm to several tens μm is obtained. Dispersion stabilizers can also be used to control the particle size of the polymer. The secondary aggregation can be suppressed by selecting a dispersion stabilizer or a polymerization solvent. Generally, precipitation polymerization in which secondary aggregation 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 to be used. 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 polymerization solvents 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. These can be used alone or in combination of two or more. Alternatively, they may be used as a mixed solvent of these and water. In the present specification, the water-soluble solvent refers to a solvent having a solubility in water at 20 ° C of more than 10 g / 100 ml. Among the above, the formation of coarse particles and the small adhesion to the reactor are good and the polymerization stability is good, and the precipitated polymer particles are difficult to secondary aggregate (or even if secondary aggregation occurs, it is unraveled in an aqueous medium). Methyl ethyl ketone and acetonitrile are preferable in that they are easy), a polymer having a small chain transfer constant and a large degree of polymerization (primary chain length) can be obtained, and that the operation is easy at the time of the step neutralization described later. ..

Similarly, in the process neutralization, it is preferable to add a small amount of a highly polar solvent to the polymerization solvent so that the neutralization reaction proceeds stably and quickly. As such a highly polar solvent, water and methanol are preferably mentioned. 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, and further preferably 0.1 to 1 based on the total mass of the medium. It is 0.0 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. In addition, in the polymerization of highly hydrophilic ethylenically unsaturated carboxylic acid monomer such as acrylic acid, when a highly polar solvent is added, the polymerization rate is improved, and a polymer having a long primary chain length is easily obtained. Among the highly polar solvents, water is particularly preferable because it has a large effect of improving the polymerization rate.

<Monomer and amount used>
In the present production method, for example, with respect to the total amount of non-crosslinkable monomers, the amount of the ethylenically unsaturated carboxylic acid monomer from which the component (a) is derived is 10% by mass or more and 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 non-crosslinkable monomer from the crosslinkable monomer from which the component (c) is derived. It is preferable to include a polymerization step of polymerizing a monomer composition containing 0.01 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the monomer. By the polymerization step, the component (a) is introduced into the present polymer in an amount of 10% by mass or more and 100% by mass or less, and the component (b) is 0% by mass or more and 90% by mass or less with respect to 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 amount of the other ethylenically unsaturated monomer from which the component (b) is derived are the same as those described above with respect to the content of the non-crosslinked structural unit. It is appropriately set 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 a non-neutralized state, or may be in a salt state in which at least a part thereof is neutralized. From the viewpoint of the polymerization rate and the binding property, the degree of neutralization of the ethylenically unsaturated carboxylic acid monomer is, for example, 10 mol% or less, and for example, 5 mol% or less, and it is preferably unneutralized. ..

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

The total concentration of 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 10.0% by mass or more, but from the viewpoint of binding property. Preferably, it is, for example, 10.0 mass% or more, and for example, 13.0 mass% or more. As will be described later, when the polymerization step is performed in the presence of a basic compound, the polymerization reaction can be stably performed 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 further preferably 19.0% by mass or more. The monomer concentration is 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. Generally, the higher the monomer concentration at the time of polymerization, the higher the molecular weight can be made, and the polymer having a long primary chain length can be produced. Since the present polymer is a finely crosslinked polymer obtained by appropriately crosslinking a polymer having a sufficiently long primary chain length, it is analytically difficult to directly measure the primary chain length. It is generally known that the primary chain length of a polymer correlates with the solution viscosity, but in the case of the present polymer, the solution viscosity also varies depending on the degree of crosslinking. 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” refers to the monomer concentration in the reaction liquid at the time of starting the polymerization.

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

<Use of basic compound>
In the present production method, the polymerization step may be carried out in the presence of a 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 even when the monomer concentration is high, the main composition The coalesced product can be manufactured stably.

By performing the polymerization reaction in the presence of a base compound, the polymerization reaction can be stably performed even under a high monomer concentration condition of, for example, more than 13.0 mass%. A polymer obtained by polymerizing at such a high monomer concentration has a high molecular weight (because of its long primary chain length) and is therefore excellent in binding property.

The basic compound is a so-called alkaline compound, and either an inorganic basic compound or an organic basic 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, alkali metals such as sodium carbonate and potassium carbonate. Examples thereof include alkali metal hydrogencarbonates such as metal carbonates, sodium hydrogencarbonate and potassium hydrogencarbonate. These 1 type (s) or 2 or more types can be used. As the organic base compound, in addition to ammonia, for example, monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monobutylamine, dibutylamine, tributylamine, monohexylamine, dihexylamine, trihexylamine, trioctylamine. And N-alkyl-substituted amines such as tridodecylamine; (ethyl) alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, propanolamine, dimethylethanolamine and N, N-dimethylethanolamine; pyridine, piperidine, piperazine, Cyclic amines such as 1,8-bis (dimethylamino) naphthalene, morpholine and diazabicycloundecene (DBU); diethylene tria Emissions, N, N-organic amine compounds such as dimethylbenzylamine, and the like, may be used alone or two or more of these. Among these, organic amine compounds excluding ammonia are 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 base compound, the polymerization stability can be improved, and the polymerization reaction proceeds smoothly even under a high monomer concentration condition. 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. is there. The amount of the base compound used may be 0.3 mol% or more, or may be 0.5 mol% or more. Further, 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 a base compound in an amount of 4.0 mol% or less, the polymerization stability can be improved, and the polymerization reaction proceeds smoothly even under a high monomer concentration condition. 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, further preferably 1.0 mol% or less. is there. 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 basic 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 are not particularly limited. The use conditions can be adjusted by a known method such as thermal initiation, redox initiation using a reducing agent in combination, UV initiation, etc., so that an appropriate amount of radicals is generated. In order to obtain a crosslinked polymer having a long primary chain length, it is preferable to set the conditions so that the radical generation amount is smaller within a range where the production time is allowed.

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

Examples of the organic peroxide include 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane (trade name “Pertetra A” manufactured by NOF CORPORATION), 1,1-di (t- Hexylperoxy) cyclohexane (the same “Perhexa HC”), 1,1-di (t-butylperoxy) cyclohexane (the same “Perhexa C”), n-butyl-4,4-di (t-butylperoxy) Valerate (the same "Perhexa V"), 2,2-di (t-butylperoxy) butane (the same "Perhexa 22"), t-butyl hydroperoxide (the same "Perbutyl H"), cumene hydroperoxide (Japan Oil company, trade name "Park Mill H"), 1,1,3,3-tetramethylbutyl hydroperoxide (the same "Per octa H"), t-butyl cumyl peroxide (the same) Perbutyl C ”), di-t-butyl peroxide (the same“ perbutyl D ”), di-t-hexyl peroxide (the same“ perhexyl D ”), di (3,5,5-trimethylhexanoyl) peroxide ( "Perloyl 355"), dilauroyl peroxide ("Perloyl L"), bis (4-t-butylcyclohexyl) peroxydicarbonate ("Perloyl TCP"), di-2-ethylhexyl peroxydicarbonate ( "Perloyl OPP"), di-sec-butyl peroxydicarbonate ("Perloyl SBP"), cumyl peroxyneodecanoate ("Perkyl ND"), 1,1,3,3-tetramethylbutyl Peroxyneodecanoate (same as "Perocta ND"), t-hexyl peroxyneodeca Ate (the same “perhexyl ND”), t-butyl peroxy neodecanoate (the same “perbutyl ND”), t-butyl peroxy neoheptanoate (the same “perbutyl NHP”), t-hexyl peroxypivalate (The same "Perhexyl PV"), t-butyl peroxypivalate (the same "Perbutyl PV"), 2,5-dimethyl-2,5-di (2-ethylhexanoyl) hexane (the same "Perhexa 250"), 1,1,3,3-Tetramethylbutylperoxy-2-ethylhexanoate (the same "Perocta O"), t-hexyl peroxy-2-ethylhexanoate (the same "Perhexyl O"), t- Butyl peroxy-2-ethylhexanoate (the same "perbutyl O"), t-butyl peroxylaurate (the same "perbutyl L"), t-bu Cylperoxy-3,5,5-trimethylhexanoate (the same "Perbutyl 355"), t-hexyl peroxyisopropyl monocarbonate (the same "Perhexyl I"), t-butyl peroxyisopropyl monocarbonate (the same "Perbutyl I") ), T-butylperoxy-2-ethylhexyl monocarbonate (the same “perbutyl E”), t-butyl peroxyacetate (the same “perbutyl A”), t-hexyl peroxybenzoate (the same “perhexyl Z”) and t -Butyl peroxybenzoate (the same "perbutyl Z") and the like, and one or more of them can be used.

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

The preferred amount of the polymerization initiator used is, for example, 0.001 to 2 parts by mass, or 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 part 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., though 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 period of 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, a solid-liquid separation step such as centrifugation and filtration, water, methanol, acetonitrile or polymerization. It is preferable to include a washing step using the same solvent as the solvent. When the above washing step is provided, even when the present polymer is secondarily aggregated, it is easy to unravel during 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 the present 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 by the polymerization step to neutralize the polymer. After performing the step (hereinafter, also referred to as "step neutralization"), the solvent may be removed in the above-mentioned drying step to obtain the solid state polymer. Further, after the drying step is carried out in the unneutralized or partially neutralized salt state to obtain a solid state main polymer 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, the step neutralization is preferable because the secondary aggregate tends to be easily loosened.

The alkaline compound that can be used in the neutralization step such as the step neutralization is not particularly limited, but various alkaline compounds that can be used in the polymerization step 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 is preferable because it gives the Li salt of the present polymer.

<Composition for Secondary Battery Electrode and Manufacturing Method Thereof>
The composition is a composition for an electrode (mixture layer) of a secondary battery, and can contain a binder containing the polymer, an active material, and water. 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 based on 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. .. When the amount of the present polymer and its salt used is less than 0.1% by mass, sufficient binding property may not be obtained. In addition, the dispersion stability of the active material and the like becomes insufficient, which may reduce the uniformity of the formed mixture layer. On the other hand, when the amount of the present polymer and its salt used exceeds 20% by mass, the composition of the electrode mixture layer may have a high viscosity and the coatability on the current collector may be deteriorated. As a result, the obtained mixture layer may have bumps or irregularities, which may adversely affect the electrode characteristics.

The present specification also provides 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 adhesiveness to the current collector and thus the binding property of the mixture layer are extremely high. The agent layer can be obtained, and as a result, the durability of the battery is improved. Further, the present polymer and its salt exhibit a sufficiently high binding property with respect to the active material even in a small amount (for example, 5% by mass or less), and since they have a carboxy anion, they have low interfacial resistance and excellent high rate characteristics. The electrode is obtained.

Of the above active materials, a lithium salt of a transition metal oxide is mainly used as the positive electrode active material, and for example, layered rock salt type and spinel type lithium-containing metal oxides can be used. Specific compounds of the positive electrode active material of layered rock-salt, lithium cobaltate, lithium nickelate, _{and, NCM {Li (Ni x,} Co y, Mn z), x + y + z = 1} called ternary and NCA Examples include {Li (Ni _1-ab Co _a Al _b )} and the like. Examples of the spinel-type positive electrode active material include lithium manganate. In addition to oxides, phosphates, silicates, sulfur, and the like are used. Examples of phosphates include olivine-type lithium iron phosphate. As the positive electrode active material, one of the above may be used alone, or two or more of them may be used in combination as a mixture or composite.

Note that when a positive electrode active material containing a layered rock salt type lithium-containing metal oxide is dispersed in water, the lithium ions on the surface of the active material and hydrogen ions in the water are exchanged, so that the dispersion liquid shows alkaline. Therefore, aluminum foil (Al), which is a general positive electrode current collector material, may be corroded. In such a case, it is preferable to neutralize the alkali component eluted from the active material by using the unneutralized or partially neutralized main polymer as the binder. The amount of the unneutralized or partially neutralized polymer used is such that the amount of unneutralized carboxy groups of the polymer is equivalent to or more than the amount of alkali eluted from the active material. Is preferred.

Since all positive electrode active materials have low electrical conductivity, they are generally used with a conductive additive added. Examples of the conductive aid include carbon-based materials such as carbon black, carbon nanotubes, carbon fibers, graphite fine powder, and carbon fibers. Among them, carbon black, carbon nanotubes, and carbon fibers are easy to obtain excellent conductivity. , Are preferred. Moreover, as the carbon black, Ketjen black and acetylene black are preferable. As the conductive auxiliary agent, one type described above 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 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 surface-coated carbon-based material having conductivity 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 more of these may be used in combination. Among these, active materials composed 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 Hard carbon is more preferred. In the case of graphite, spheroidized graphite is preferably used from the viewpoint of battery performance, and the preferable particle size range is, for example, 1 to 20 μm and, for example, 5 to 15 μm. Further, in order to increase the energy density, a metal or metal oxide capable of occluding lithium such as silicon or tin can be used as the negative electrode active material. Among them, silicon has a higher capacity than graphite, and active materials made of silicon-based materials such as silicon, silicon alloys and silicon oxides such as silicon monoxide (SiO) (hereinafter, also referred to as “silicon-based active material”). Can be used. However, the above silicon-based active material has a high capacity, but on the other hand, the volume change due to charge and discharge is large. Therefore, it is preferable to use the carbon-based active material together. In this case, if the amount of the silicon-based active material added is large, the electrode material may be collapsed, and the cycle characteristics (durability) may be significantly reduced. From such a point of view, when the silicon-based active material is used in combination, the amount thereof 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 the silicon-based active material and exhibits a good binding property. Therefore, the present binder exhibits excellent binding properties even when a high-capacity type active material containing a silicon-based active material is used, and thus is also effective for 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 auxiliary agent. When a conductive auxiliary agent is added for the purpose of further reducing resistance, the amount used is, for example, 10% by mass or less and 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 in the range of, for example, 10 to 75% by mass, or in the range of 30 to 65% by mass, based on the total amount of the composition. When the amount of the active material used is 10% by mass or more, migration of the binder and the like can be suppressed, and it is also advantageous in terms of medium drying cost. On the other hand, when the content is 75% by mass or less, the fluidity and coatability of the composition can be secured, 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 in the range of, for example, 60 to 97% by mass, or 70 to 90% by mass, based on the total amount of the present composition. It is a range. 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 additive be as small as possible within the range in which the required binding property and conductivity are ensured.

The composition uses water as a medium. For the purpose of adjusting the properties and drying properties of the composition, lower alcohols such as methanol and ethanol, carbonates such as ethylene carbonate, ketones such as acetone, water-soluble organic compounds such as tetrahydrofuran and N-methylpyrrolidone. It may be a mixed solvent with a solvent. The proportion of water in the mixed 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 the coatability of the slurry, and the energy cost required for drying, from the viewpoint of productivity, for example, The amount can be in the range of 25 to 90% by mass, and can be, for example, 35 to 70% by mass. In addition, in the case of a wettable powder that can be pressed, 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. It can be in the range of up to 30% by mass.

The binder component contained in the composition may be composed only of the polymer, but in addition to this, a styrene / butadiene latex (SBR), an acrylic latex, a polyvinylidene fluoride latex, or the like. You may use together other binder components. When the other binder component is used in combination, the amount thereof can 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 can be, for example, 0.1 to 1% by mass or less. If the amount of the other binder component used exceeds 5% by mass, the resistance may increase and the high rate property may become insufficient. Among the above, a styrene / butadiene-based latex is preferable because it has an excellent balance of binding property and flex resistance.

The present composition has the above-mentioned active material, water and binder as essential constituent components, and can be obtained by mixing the components using a known means. The mixing method of each component is not particularly limited, and a known method can be adopted. After dry blending the powder components such as the active material, the conductive auxiliary agent and the polymer as a binder, water, etc. The method of mixing with the dispersion medium of (1) and dispersing and kneading is preferable. When the present composition is obtained in the form of a slurry, it is preferable to finish it into a slurry free from poor dispersion and aggregation. As the mixing means, a known mixer such as a planetary mixer, a thin film swirling mixer and a revolving mixer can be used, but a thin film swirling mixer is used in that a good dispersion state can be obtained in a short time. It is preferable to carry out. When a thin film swirling mixer is used, it is preferable to carry out preliminary dispersion with a stirrer such as a disper in advance.

The viscosity of the slurry of the present composition can be in the range of, for example, 500 to 100,000 mPa · s as a shear viscosity at a shear rate of 60 s ⁻¹ at 25 ° C., and can be, 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, and further preferably 500 to 6,000 mPa · s. s, more preferably 500 to 5,000 mPa · s, still more preferably 500 to 4,000 mPa · s, still more preferably 500 to 3,000 mPa · s. .S, more preferably 500 to 2,000 mPas, still more preferably 500 to 1,800 mPas, and still more preferably 500 to 1,700 mPas. s, preferably 500 to 1,600 mPa · s, and more preferably 500 to 1,500 m. It is a · s.

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

<Secondary battery electrode>
The present electrode comprises a mixture layer formed of 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 on the surface of the current collector and then removing a medium such as water by drying. The method of applying the present composition is not particularly limited, and a known method 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 may be adopted. it can. Further, the drying can be performed by a known method such as blowing hot air, reducing pressure, (far) infrared rays, or microwave irradiation. Usually, the mixture layer obtained after drying is subjected to compression treatment by a die press, a roll press or the like. By compressing, the active material and the binder can be brought into close contact, 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.

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

As the non-aqueous electrolyte, a known one generally used for secondary batteries can be used. Specific solvents include cyclic carbonates having high permittivity and high electrolyte dissolving ability such as propylene carbonate and ethylene carbonate, and low-viscosity chain carbonates such as ethylmethyl carbonate, dimethyl carbonate and diethyl carbonate. , And these can be used alone or as a mixed solvent. The non-aqueous electrolytic solution is used by dissolving a lithium salt such as LiPF ₆ , LiSbF ₆ , LiBF ₄ , LiClO ₄ , and LiAlO ₄ in these solvents. The secondary battery is obtained by accommodating a positive electrode plate and a negative electrode plate, which are partitioned by a separator, in a spiral or laminated structure in a case or the like.

As described above, the binder for secondary battery electrodes disclosed in the present specification can achieve both excellent binding properties and reduction in viscosity of the mixture layer slurry. A secondary battery provided with an electrode obtained by using the above binder is expected to be able to secure good integrity and to exhibit good durability (cycle characteristics) even after repeated charge and discharge. It is suitable for secondary batteries and the like.

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

<Production Example of the Polymer>
<Production Example 1: Production of crosslinked polymer salt R-1>
For the polymerization, a reactor equipped with a stirring blade, a thermometer, a reflux condenser and a nitrogen introduction tube was used. 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 (Kyoeisha Chemical Co., Ltd., light ester G- 201P) 0.20 part and triethylamine corresponding to 1.0 mol% based on the above AA were charged. After sufficiently replacing the inside of the reactor with nitrogen, it was heated to raise the internal temperature to 55 ° C. 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”) was used as a polymerization initiator. When 0.040 part was added, white turbidity was observed in the reaction solution, and this point was used as the polymerization initiation point. The monomer concentration was calculated to be 15.0%.

The polymerization reaction was continued while adjusting the external temperature (water bath temperature) to maintain the internal temperature at 55 ° C, and the internal temperature was raised to 65 ° C when 6 hours passed from the polymerization initiation point. The internal temperature was maintained at 65 ° C., cooling of the reaction solution was started 12 hours after the reaction start point, and after the internal temperature dropped to 25 ° C., lithium hydroxide monohydrate (hereinafter, referred to as “LiOH - 52.5 parts powder of _{H 2} O "hereinafter) was added. After the addition, stirring was continued for 12 hours at room temperature to obtain a slurry-like polymerization reaction liquid 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 liquid was centrifuged to precipitate polymer particles, and the supernatant was removed. After that, the procedure of redispersing the precipitate in the same weight of acetonitrile as the polymerization reaction solution and then allowing the polymer particles to settle 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 matter, thereby obtaining a powder of crosslinked polymer salt R-1. Since the cross-linked polymer salt R-1 has a hygroscopic property, it was sealed and stored in a container having a water vapor barrier property. The powder of the crosslinked polymer salt R-1 was subjected to IR measurement, 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. 90 mol% 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 amounts of the respective raw materials charged were as shown in Table 1 to obtain a polymerization reaction liquid containing the crosslinked polymer salts R-2 to R-15. Then, the same operation as in Production Example 1 was carried out for each polymerization reaction liquid to obtain powdery 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 Production Example 9, a sodium salt of a crosslinked polymer (neutralization degree: 90 mol%) was obtained by using NaOH instead of the LiOH.H ₂ O powder.

The notations shown in Table 1 will be described below.
AA: acrylic acid DMAA: dimethylacrylamide HAPMA: 2-hydroxy-3-acryloyloxypropyl methacrylate (light ester G-201P, Kyoeisha Chemical Co., Ltd.)
GDMA: glycerin dimethacrylate (light ester G-101P, Kyoeisha Chemical)
EGDMA: Ethylene dimethacrylate (Fuji Film Wako Pure Chemical)
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 cross-linked polymer Li salt R-1 was weighed in 100 parts of natural graphite, mixed well in advance, 160 parts of ion-exchanged water was added and predispersed with a disper, and then thin film rotation type The main dispersion was performed for 15 seconds at a peripheral speed of 20 m / sec using a mixer (FM-56-30, manufactured by Primix Co., Ltd.) to obtain a slurry 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 measured at 25 ° C. using a cone plate (diameter 25 mm, cone angle 5 °) of CP25-5 using an Anton Paar Rheometer (Physica MCR301). The slurry viscosity at a shear rate of 60 s ^-1 was measured.

<90 ° peel strength (binding property)>
Using the variable applicator, the mixture layer composition was applied onto a copper foil (manufactured by Nippon Foil Co., Ltd.) having a thickness of 20 μm, and dried at 100 ° C. for 15 minutes in a ventilation dryer to form a mixture layer. Formed. Then, the mixture layer was rolled to a thickness of 70 ± 5 μm and a packing density of 1.70 ± 0.20 g / cm ³ to prepare a negative electrode. The negative electrode obtained above was cut into a strip having a width of 25 mm, and the mixture layer surface of the above sample was attached to a double-sided tape fixed on a horizontal surface to prepare a peel test sample. After the test sample was dried under reduced pressure at 60 ° C. overnight, 90 ° peeling was performed at a pulling speed of 50 mm / min, and the peel 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 in the same manner as in Example 1, except that the crosslinked polymer salt used as the active material and the binder was used as described in Table 2. In Examples 3 and 4, natural graphite and silicon particles were stirred for 1 hour at 400 rpm using a planetary ball mill (P-5, manufactured by FRITSCH), and the obtained mixture was crosslinked into powder form. 3.2 parts of Li salt R-2 was weighed and thoroughly mixed in advance, and then the same operation as in Example 1 was performed to prepare a mixture layer composition. The slurry viscosity and 90 ° peel strength of each mixture layer composition were evaluated. The results are shown in Table 2.

As shown in Table 2, Examples 1 to 15 using cross-linked polymers R-1 to R-13 using a cross-linkable monomer having two or more (meth) acryloyl groups and a hydroxyl group were combined. The viscosity of the agent layer slurry was 330 to 1800 mPa · s, showing extremely good viscosity. Further, the peel strengths of Examples 1 to 15 were 14.4 to 19.1 N / m, which showed 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 no 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, and the crosslinkable monomer having two allyl groups and having a hydroxyl group was used. In Comparative Example 3 in which the crosslinked polymer of Production Example 16 using a body was used, the binding property was low and the slurry viscosity was still high.

From the above, the ethylenically unsaturated carboxylic acid monomer and the crosslinkable monomer having two (meth) acryloyl groups and having a hydroxyl group are polymerized to derive the crosslinkable monomer. It was found that by providing the crosslinked structure, good binding properties and slurry viscosity can both be achieved.

Further, according to Examples 1 to 2, 5 to 7, the amount of the crosslinkable monomer used was about 0.1 to 10 parts based on 100 parts of the non-crosslinkable monomer, and the binding property was good. It is possible to obtain a crosslinked polymer, and 0.2 parts to 9 parts, 0.2 parts to 5 parts, 0.2 parts to 2 parts, and 0.2 parts to 1 part are more suitable for forming crosslinks. It was found that a polymer could be obtained. It was also found that the amount of the crosslinkable monomer used was about 0.1 to 10 parts to obtain a crosslinked polymer having a sufficiently low slurry viscosity.

Further, according to Examples 3 to 4, it was found that even when silicon particles were included as the active material, both stable binding property and slurry viscosity could be achieved. Furthermore, according to Example 8, even when 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 are obtained. I understood it.

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

Claims (6)

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 cross-linking structural unit has two or more (meth) acryloyl groups in one molecule, and includes a cross-linking structural unit derived from a cross-linkable monomer having a hydroxyl group,
   binder.
2. 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 unit.
3. A composition for a secondary battery electrode,
   A binder for a secondary battery electrode according to claim 1 or 2,
   Active material,
   water and,
   A composition containing:
4. A secondary battery electrode,
   A binder for a secondary battery electrode according to claim 1 or 2,
   Active material,
   An electrode containing.
5. Furthermore, the electrode according to claim 4, wherein the active material is a silicon-containing material.
6. A method for producing a binder for a secondary battery electrode, comprising:
   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 ,
   And a manufacturing method.