WO2021215380A1

WO2021215380A1 - Carboxyl group-containing crosslinked polymer or salt thereof, and use thereof

Info

Publication number: WO2021215380A1
Application number: PCT/JP2021/015807
Authority: WO
Inventors: 朋子仲野; 篤史西脇; 直彦斎藤
Original assignee: 東亞合成株式会社
Priority date: 2020-04-23
Filing date: 2021-04-19
Publication date: 2021-10-28
Also published as: JPWO2021215380A1

Abstract

The present invention provides a carboxyl group-containing crosslinked polymer or a salt thereof, which can achieve both coatability and coating film performance of a composition containing the crosslinked polymer or the salt thereof.　The carboxyl group-containing crosslinked polymer or the salt thereof is provided such that the non-uniform network structure size Ξ of the crosslinked polymer is at most 80, as calculated by curve fitting, with equation (1), the scattering intensity curve I (q) which is obtained by measuring a 1 mass% aqueous solution of the crosslinked polymer neutralized to a neutralization degree of 50-100 mol% through a small-angle X-ray scattering method (measuring temperature: 25.0±0.1°C). I(q): Intensity of scattered radiation Ξ: Non-uniform network structure size of crosslinked polymer A: Fitting parameter B: Fitting parameter q: Scattering vector q*: Distance between charged groups L: Electrostatic shielding length of polymer chain m: Fitting parameter

Description

Carboxyl group-containing crosslinked polymer or salt thereof and its use

The present invention relates to a carboxyl group-containing crosslinked polymer or a salt thereof, and its use.

Carboxyl group-containing polymers are used in various applications such as thickeners and viscosity modifiers for cosmetics, binders for non-aqueous electrolyte secondary battery electrodes, sedimentation inhibitors for pigments, and dispersion stabilizers for metal powders. ing.
Among these uses, as a thickener for cosmetics, when the carboxyl group-containing polymer is linear, it has a spinnability and feels sticky, but as the degree of cross-linking is increased, the spinnability becomes higher. It has the characteristic that it decreases and you can feel the freshness. Therefore, in cosmetics that do not require spinnability and require freshness, a carboxyl group-containing crosslinked polymer is often used because of the advantage that high viscosity can be obtained with a small amount of use.

Further, as a binder for a non-aqueous electrolyte secondary battery electrode, a carboxyl group-containing crosslinked polymer is often used because of the advantages of being able to impart good binding properties and cycle characteristics.
Here, as the applications of various secondary batteries such as nickel hydrogen secondary batteries, lithium ion secondary batteries, and electric double layer capacitors 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 defects, a binder is used to firmly bond the active materials (bonding property), the size of the active material is reduced to alleviate the stress associated with swelling and shrinkage, and the addition of an electrolytic solution is performed. Studies are being conducted to improve durability by devising agents.

Under such circumstances, it has been reported that an acrylic acid-based polymer is effective as a binder that has good cycle characteristics and is effective in improving the durability of the negative electrode mixture layer using a silicon-based active material. 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 using an active material containing silicon. It is disclosed that it exhibits various cycle characteristics. Patent Document 2 discloses a crosslinked acrylic acid-based polymer having a specific particle size in a 1% NaCl aqueous solution.

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

According to the studies by the inventors, the microcrosslinked acrylic acid system disclosed in

Patent Documents

1 and 2 as a binder of particles in the slurry (for example, a binder of the active material in the lithium ion secondary battery electrode slurry). When a polymer is used, the fine cross-linking of the acrylic acid-based polymer can enhance the binding property between the particles in the slurry, while the spread of the polymer in water is increased and the viscosity is increased even with a small amount of addition. There is a limit to the reduction of the slurry viscosity, and there is a problem that the coatability and the coating performance (for example, the cycle characteristics of the lithium ion secondary battery) cannot be compatible with each other.

Further, the binders for secondary battery electrodes disclosed in

Patent Documents

1 and 2 can all impart good cycle characteristics and binding properties, but as the performance of the secondary battery is improved, the cycle characteristics become more favorable. There is an increasing demand for improveable binders.
Furthermore, the secondary battery electrode is generally obtained by applying a composition for an electrode mixture layer containing an active material and a binder (hereinafter, also referred to as “electrode slurry”) to the surface of an electrode current collector and drying it. At this time, it is advantageous to increase the solid content concentration of the electrode slurry from the viewpoint of increasing the drying efficiency of the electrode slurry and improving the productivity of the electrode. However, usually, as the solid content concentration increases, it becomes difficult to ensure good coatability. As described above, the binders disclosed in

Patent Documents

1 and 2 have a large increase in viscosity even when added in a small amount, so that it is difficult to increase the solid content concentration.

The present invention has been made in view of such circumstances, and an object of the present invention is to achieve both coatability and coating performance of a composition containing a carboxyl group-containing crosslinked polymer or a salt thereof. It is to provide a crosslinked polymer or a salt thereof.
Furthermore, when the solid content concentration of the composition for the electrode mixture layer is higher than before, it is possible to obtain a secondary battery that exhibits excellent cycle characteristics while ensuring coatability by reducing the viscosity of the electrode slurry. It is to provide a binder for a secondary battery electrode that can be made. In addition, the present invention also provides a composition for a secondary battery electrode mixture layer containing the above binder, a secondary battery electrode obtained by using the composition, and a secondary battery.

As a result of diligent studies to solve the above problems, the present inventors have found that the non-uniform network structure size obtained by measurement by the small-angle X-ray scattering method is a specific value or less, or a carboxyl group-containing crosslinked polymer or a crosslinked polymer thereof. The present invention has been completed by finding that by using a salt, excellent coating performance can be exhibited while ensuring the coatability of the crosslinked polymer or a composition containing the salt thereof.
Furthermore, when the solid content concentration of the composition for the secondary battery electrode mixture layer containing the binder for the secondary battery electrode containing the carboxyl group-containing crosslinked polymer or a salt thereof, the active material and water is high, the composition may be used. , The non-uniform network structure size obtained by the small angle X-ray scattering method measurement is less than a specific value. By containing a carboxyl group-containing crosslinked polymer or a salt thereof, the coatability is ensured by reducing the viscosity of the electrode slurry. At the same time, they have found that a secondary battery exhibiting excellent cycle characteristics can be obtained, and have completed the present invention.

The present invention is as follows.
[1] The above-mentioned crosslinked polymer containing a carboxyl group or a salt thereof, which has been neutralized to a degree of neutralization of 50 to 100 mol% by a small-angle X-ray scattering method (measurement temperature: 25.0 ± 0.1 ° C.). Non-uniform network structure size of the crosslinked polymer calculated by curve fitting with the following formula (1) to the scattering intensity curve I (q) obtained by measuring a 1% by mass concentration aqueous solution of the crosslinked polymer. A carboxyl group-containing crosslinked polymer or a salt thereof, wherein Ξ (hereinafter, also referred to as “Ξ1”) is 80 or less.

[2] A 5% by mass aqueous solution of the crosslinked polymer neutralized to a degree of neutralization of 50 to 100 mol% by the small angle X-ray scattering method (measurement temperature: 25.0 ± 0.1 ° C.) with the above Ξ1. The non-uniform network structure size Ξ (hereinafter, also referred to as “Ξ5”) of the crosslinked polymer, which is calculated by curve fitting with the above formula (1) with respect to the scattering intensity curve I (q) obtained by measuring. .) The carboxyl group-containing crosslinked polymer or salt thereof according to [1], wherein the difference ΔΞ (Ξ1-Ξ5) is 50 or less.
[3] The crosslinked polymer according to [1] or [2], wherein the crosslinked polymer contains 50% by mass or more and 100% by mass or less of structural units derived from an ethylenically unsaturated carboxylic acid monomer with respect to all the structural units. Carboxyl group-containing crosslinked polymer or a salt thereof.
[4] The crosslinked polymer is crosslinked with a crosslinkable monomer, and the amount of the crosslinkable monomer used is 0.1 mass by mass with respect to 100 parts by mass of the total amount of the non-crosslinkable monomer. The carboxyl group-containing crosslinked polymer according to any one of [1] to [3] or a salt thereof, which is not more than parts and not more than 2.0 parts by mass.
[5] The crosslinked polymer or a salt thereof is neutralized to a degree of neutralization of 80 to 100 mol%, and then the particle size measured in an aqueous medium is 0.1 μm or more and 5.0 μm or less in terms of volume-based median diameter. The carboxyl group-containing crosslinked polymer according to any one of [1] to [4] or a salt thereof.
[6] The carboxyl group-containing crosslinked polymer or salt thereof according to any one of [1] to [5], wherein the crosslinked polymer or a salt thereof has a water swelling degree of 20 or more and 80 or less at pH 8.
[7] A binder for a secondary battery electrode, which comprises the carboxyl group-containing crosslinked polymer according to any one of [1] to [6] or a salt thereof.
[8] The composition for a secondary battery electrode mixture layer containing the binder for the secondary battery electrode, the active material, and water according to [7].
[9] A secondary battery electrode comprising a mixture layer formed from the composition for the secondary battery electrode mixture layer according to [8] on the surface of a current collector.
[10] A secondary battery including the secondary battery electrode according to [9].

According to the carboxyl group-containing crosslinked polymer of the present invention or a salt thereof, the coatability and the coating film performance of the composition containing the crosslinked polymer or the salt thereof can be compatible with each other.
Furthermore, according to the binder for the secondary battery electrode containing the carboxyl group-containing crosslinked polymer of the present invention or a salt thereof, the viscosity of the electrode slurry is higher than the conventional one when the solid content concentration of the composition for the electrode mixture layer is higher. It is possible to obtain a secondary battery that exhibits excellent cycle characteristics while ensuring coatability by reducing the amount.

It is a schematic diagram showing the non-uniform network structure size Ξ (dotted line part) of the crosslinked polymer, and it means that the value of Ξ in the left figure is smaller than that in the right figure. It is a figure which shows the scattering intensity curve I (q) obtained by the small-angle X-ray scattering method of the carboxyl group-containing crosslinked polymer salt R-2 (1 mass% concentration aqueous solution and 5 mass% concentration aqueous solution). It is a figure which shows the scattering intensity curve I (q) obtained by the small-angle X-ray scattering method of the carboxyl group-containing crosslinked polymer salt R-17 (1 mass% concentration aqueous solution and 5 mass% concentration aqueous solution). It is a figure which shows the apparatus used for measuring the water swelling degree of a crosslinked polymer or a salt thereof.

The carboxyl group-containing crosslinked polymer of the present invention or a salt thereof (hereinafter, also referred to as “the present crosslinked polymer”) has a degree of neutralization by a small angle X-ray scattering method (measurement temperature: 25.0 ± 0.1 ° C.). Calculated by curve fitting with the above formula (1) to the scattering intensity curve I (q) obtained by measuring a 1% by mass concentration aqueous solution of the present crosslinked polymer neutralized to 50 to 100 mol%. , The non-uniform network structure size Ξ (Ξ1) of this crosslinked polymer is 80 or less. Ξ will be described in detail in "3. Characteristics of the Crosslinked Polymer" and "Examples" described later.

Furthermore, the binder for a secondary battery electrode containing the crosslinked polymer or a salt thereof (hereinafter, also referred to as “the binder”) is a composition for a secondary battery electrode mixture layer by mixing with an active material and water. (Hereinafter, also referred to as "the present composition"). The above composition is in a slurry state that can be applied to a current collector. The secondary battery electrode of the present invention can be obtained by forming a mixture layer formed from the above composition on the surface of a current collector such as a copper foil or an aluminum foil. Here, when this binder is used in a composition for a secondary battery electrode mixture layer containing a silicon-based active material described later as an active material, the effect of the present invention is particularly large, which is preferable.

Hereinafter, each of the present crosslinked polymer, the present binder, the composition for the secondary battery electrode mixture layer obtained by using the present binder, the secondary battery electrode, and the secondary battery will be described in detail.
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.

1. 1. Structural unit of this crosslinked polymer <Structural unit derived from ethylenically unsaturated carboxylic acid monomer>
The crosslinked polymer has a structural unit derived from an ethylenically unsaturated carboxylic acid monomer (hereinafter, also referred to as “component (a)”), and is a single amount containing an ethylenically unsaturated carboxylic acid monomer. The body component can be introduced into the polymer by precipitation polymerization or dispersion polymerization. Since the crosslinked polymer has a carboxyl group by having such a structural unit, the adhesiveness to the current collector is improved, and the lithium ion desolvation effect and the ionic conductivity are excellent, so that the resistance is small. , An electrode having 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.

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 carboxyl groups such as monohydroxyethyl succinate (meth) acrylate, ω-carboxy-caprolactone mono (meth) acrylate, β-carboxyethyl (meth) acrylate, or (partial) thereof. ) Alkali 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 carboxyl group content can be obtained.

The content of the component (a) in the present crosslinked polymer is not particularly limited, but may be, for example, 10% by mass or more and 100% by mass or less with respect to all the structural units of the present crosslinked 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. When the lower limit is 50% by mass or more, the dispersion stability of the present composition becomes good and a higher binding force can be obtained, which is preferable, and it may be 60% by mass or more, or 70% by mass or more. It may be 80% by mass or more. Further, the upper limit is, for example, 99.9% by mass or less, for example, 99.5% by mass or less, for example, 99% by mass or less, for example, 98% by mass or less, and for example, 95% by mass. It is less than or equal to, for example, 90% by mass or less, and for example, 80% by mass or less. The range may be a range in which such a lower limit and an upper limit are appropriately combined, and is, for example, 10% 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. It can be 50% by mass or more and 99.9% by mass or less, and can be, for example, 50% by mass or more and 99% by mass or less, and can be, for example, 50% by mass or more and 98% by mass or less.

<Other structural units>
In addition to the component (a), the crosslinked polymer may contain a structural unit derived from another ethylenically unsaturated monomer copolymerizable with the component (hereinafter, also referred to as “component (b)”). can. The component (b) includes, for example, an ethylenically unsaturated monomer compound having an anionic group other than a carboxyl group such as a sulfonic acid group and a phosphoric acid group, or a nonionic ethylenically unsaturated monomer. The structural unit from which it is derived can be mentioned. These structural units are ethylenically unsaturated monomer compounds having anionic groups other than carboxyl groups such as sulfonic acid groups and phosphoric acid groups, or monomers containing nonionic ethylenically unsaturated monomers. Can be introduced by copolymerizing.

The ratio of the component (b) can be 0% by mass or more and 90% by mass or less with respect to all the structural units of the present crosslinked polymer. The ratio of the component (b) may be 1% by mass or more and 60% by mass or less, 2% by mass or more and 50% by mass or less, and 5% by mass or more and 40% by mass or less. It may be 10% by mass or more and 30% by mass or less. Further, when the component (b) is contained in an amount of 1% by mass or more with respect to all the structural units of the crosslinked polymer, the affinity for the electrolytic solution is improved, so that the effect of improving the lithium ion conductivity can be expected.

As the component (b), among the above, structural units derived from nonionic ethylenically unsaturated monomers are preferable from the viewpoint of obtaining electrodes having good bending resistance, and nonionic ethylenically unsaturated monomers are preferable. Examples of the monomer include (meth) acrylamide and its derivatives, a nitrile group-containing ethylenically unsaturated monomer, an alicyclic structure-containing ethylenically unsaturated monomer, and the like.

Examples of the (meth) acrylamide derivative include N-alkyl (meth) acrylamide compounds such as isopropyl (meth) acrylamide and t-butyl (meth) acrylamide; Nn-butoxymethyl (meth) acrylamide and N-isobutoxymethyl. N-alkoxyalkyl (meth) acrylamide compounds such as (meth) acrylamide; N, N-dialkyl (meth) acrylamide compounds such as dimethyl (meth) acrylamide and diethyl (meth) acrylamide include one of them. It may be used alone or in combination of two or more.

Examples of the nitrile group-containing ethylenically unsaturated monomer include (meth) achlorinitrile; (meth) cyanomethyl acrylate, (meth) cyanoethyl acrylate and other (meth) acrylate cyanoalkyl ester compounds; 4-cyanostyrene. , 4-Cyano-α-methylstyrene and other unsaturated aromatic compounds containing cyano groups; examples thereof include vinylidene cyanide, and one of these may be used alone or in combination of two or more. You may use it. Among the above, acrylonitrile is preferable because it has a high nitrile group content.

Examples of the alicyclic structure-containing ethylenically unsaturated monomer include cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, t-butylcyclohexyl (meth) acrylate, and (meth). ) Cyclodecyl acrylate and cyclododecyl (meth) acrylate and other aliphatic substituents may have (meth) cycloalkyl acrylate; isobornyl (meth) acrylate, adamantyl (meth) acrylate, (meth). ) Dicyclopentenyl acrylate, dicyclopentenyloxyethyl (meth) acrylate, dicyclopentanyl (meth) acrylate, and cyclohexanedimethanol mono (meth) acrylate and cyclodecanedimethanol mono (meth) acrylate, etc. Cycloalkyl polyalcohol mono (meth) acrylate and the like can be mentioned, and one of these may be used alone, or two or more thereof may be used in combination.

The crosslinked polymer or a salt thereof has excellent binder binding properties, and is an amount of (meth) acrylamide and its derivatives, a nitrile group-containing ethylenically unsaturated monomer, and an alicyclic structure-containing ethylenically unsaturated monomer. It is preferable to include a structural unit derived from a body or the like. 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. , Can exhibit good binding properties to active materials. As a result, a solid and well-integrated electrode mixture layer can be obtained. Therefore, the above-mentioned "hydrophobic ethylenically unsaturated monomer having a solubility in water of 1 g / 100 ml or less" is particularly selected. An alicyclic structure-containing ethylenically unsaturated monomer is preferable.

Further, as the other nonionic ethylenically unsaturated monomer, for example, (meth) acrylic acid ester may be used. Examples of the (meth) acrylic acid ester include (meth) methyl acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and the like. Meta) Acrylic acid alkyl ester compound;
Aromatic (meth) acrylic acid ester compounds such as (meth) phenyl acrylate, (meth) phenylmethyl acrylate, and (meth) phenylethyl acrylate;
Examples thereof include (meth) acrylic acid alkoxyalkyl ester compounds such as 2-methoxyethyl (meth) acrylic acid and 2-ethoxyethyl (meth) acrylic acid, and one of these may be used alone. Two or more types may be used in combination.

From the viewpoint of binding property to the active material and cycle characteristics, an aromatic (meth) acrylic acid ester compound can be preferably used. Compounds having an ether bond, such as (meth) acrylic acid alkoxyalkyl esters such as 2-methoxyethyl (meth) acrylate and 2-ethoxyethyl (meth) acrylate, from the viewpoint of further improving lithium ion conductivity and high-rate characteristics. 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 due to its high polymerization rate and the binding force of the binder is improved. 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.

The crosslinked polymer may be in the form of a salt in which some or all of the carboxyl groups contained in the polymer are neutralized. The type of salt is not particularly limited, but alkali metal salts such as lithium salt, sodium salt and potassium salt; alkaline earth metal salts such as calcium salt and barium salt; other metal salts such as magnesium salt and aluminum salt; ammonium. Examples thereof include salts and organic 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.

The present crosslinked polymer is a crosslinked polymer having a crosslinked structure. The cross-linking method in the present cross-linked polymer is not particularly limited, and examples thereof include the following methods.
1) Copolymerization of crosslinkable monomers 2) Utilizing chain transfer to polymer chains during radical polymerization 3) After synthesizing a polymer having a reactive functional group, post-crosslinking is performed by adding a crosslinking agent as necessary. Since the present crosslinked polymer has a crosslinked structure, the crosslinked polymer or the binder containing a salt thereof can have an excellent binding force. Among the above, the method by copolymerization of crosslinkable monomers is preferable because the operation is simple and the degree of crosslinking can be easily controlled.

<Crosslinkable monomer>
Examples of the crosslinkable monomer include 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. Can be 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, ( Meta) 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. Among these, a polyfunctional alkenyl compound is preferable because a uniform crosslinked structure can be easily obtained, and a polyfunctional allyl ether compound having two or more allyl ether groups in the molecule is particularly preferable.

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) acrylate; trimethylol propantri (meth) acrylate, tri (meth) acrylate of trimethyl propanethylene oxide modified product, glycerin tri (meth) acrylate, pentaerythritol tri (meth) Tri (meth) acrylates of trivalent or higher polyhydric alcohols such as meta) acrylates and pentaerythritol tetra (meth) acrylates, poly (meth) acrylates such as tetra (meth) acrylates; Bisamides and the like 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 monomer having a self-crosslinkable 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.

When the present crosslinked polymer is crosslinked with a crosslinkable monomer, the amount of the crosslinkable monomer used is the total amount of monomers other than the crosslinkable monomer (non-crosslinkable monomer). It is preferably 0.05 parts by mass or more and 5.0 parts by mass or less, more preferably 0.1 parts by mass or more and 5.0 parts by mass or less, and further preferably 0.2 parts by mass or more with respect to 100 parts by mass. It is 4.0 parts by mass or less, more preferably 0.3 parts by mass or more and 3.0 parts by mass or less. When the amount of the crosslinkable monomer used is 0.05 parts by mass or more, it is preferable in that the binding property and the stability of the electrode slurry are improved. If it is 5.0 parts by mass or less, the stability of precipitation polymerization or dispersion polymerization tends to be high.
Similarly, the amount of the crosslinkable monomer used may be 0.02 to 1.7 mol% with respect to the total amount of the monomers other than the crosslinkable monomer (non-crosslinkable monomer). It is preferably 0.10 to 1.0 mol%, more preferably 0.10 to 1.0 mol%.

2. Method for Producing the Crosslinked Polymer The crosslinked polymer is a monomer component containing the above ethylenically unsaturated carboxylic acid monomer in the presence of an exchange chain transfer mechanism type control agent (hereinafter, also referred to as “the present monomer”). It is obtained by precipitation polymerization or dispersion polymerization.
Here, precipitation polymerization is a method for producing a polymer by carrying out a polymerization reaction in a solvent that dissolves a 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.

Regarding the exchange chain transfer mechanism type control agent The exchange chain transfer mechanism type control agent according to the present invention includes a control agent (hereinafter, also referred to as “RAFT agent”) in the reversible addition-cleaving chain transfer polymerization method (RAFT method). In the iodine transfer polymerization method, the control agent in the polymerization method using an organic tellurium compound (TERP method), the control agent in the polymerization method using an organic antimony compound (SBRP method), and the polymerization method using an organic bismuth compound (BIRP method). Control agents and the like can be mentioned. As the exchange chain transfer mechanism type control agent, a polymer having a polymer chain of one or more kinds of vinyl-based monomers and a living radical polymerization active unit by the exchange chain transfer mechanism (hereinafter, simply "the first polymer"). A control agent other than the polymer can be used, which will be described in detail in paragraphs [0052] to [0078] described later. The first polymer and the control agent other than the polymer may be used alone or in combination.
Precipitation polymerization or dispersion polymerization of this monomer in the presence of an exchange chain transfer mechanism type control agent shortens the primary chain length, and the same chain length forms a uniform crosslinked structure. It is possible to increase the degree of water swelling of the polymer. Along with this, it is presumed that good coatability and excellent cycle characteristics can be achieved at the same time by reducing the viscosity of the electrode slurry.
Among these, the RAFT agent and the control agent in the iodine transfer polymerization method are preferable, and the RAFT agent is more preferable, because the crosslinked structure of the present crosslinked polymer can be made more uniform.

RAFT agents include a first polymer having a living radical polymerization active unit by a reversible addition-cleavage chain transfer method (detailed below) and / or a RAFT agent (dithioester) other than the first polymer. Compounds, xanthate compounds, trithiocarbonate compounds, dithiocarbamate compounds, etc.) can be used.
Specific examples of the RAFT agent other than the first polymer include 2-cyano-2-propylbenzodithioate, 2-phenyl-2-propylbenzodithioate, trithiocarbonate, and 2-cyano-. 2-propyldodecyltrithiocarbonate, 2- (dodecylthiocarbonothio oil thio) propionic acid, 3-((1-carboxyethylthio) carbonothio oil thio)) propionic acid, 2- (dodecylthio carbonothio oil thio) Methyl 2-methylpropanoate, 1,4-bis (n-dodecylsulfanylthiocarbonylsulfanylmethyl) benzene, dibenzyltrithiocarbonate, distyryltrithiocarbonate, dicumyltrithiocarbonate, cyanomethyl-N-methyl-N- Examples thereof include phenyldithiocarbamate.
Among the RAFT agents, those having trithiocarbonate in the molecule are particularly preferable in that the crosslinked structure of the present crosslinked polymer can be made more uniform.

As the control agent in the iodine transfer polymerization method, a first polymer having a living radical active unit by the iodine transfer polymerization method (detailed later) and / or a control agent other than the first polymer shall be used. Can be done.
Specific examples of the control agent other than the first polymer include alkyl groups such as methyl iodide, methylene iodide, iodoform, carbon tetraiodide, 1-phenylethyl iodide, and benzyl iodide. Pafluoroalkyl perfluoroalkyl iodide having 1 to 20 carbon atoms, ethyl 2-iodopropionate, methyl 2-iodoisobutyrate, ethyl 2-iodoisobutyrate, ethyl 2-iodo-2-phenylacetate, bis (2-iodine) Examples thereof include -2-phenylacetic acid) ethylene glycol, bis (2-iodoisobutyric acid) ethylene glycol, 1,5-diiodo-2,4-dimethylbenzene, and 2-iodopropionitrile.

The exchange chain transfer mechanism type control agent may be a monofunctional one having one active site, or a bifunctional or more agent having two or more active sites. A bifunctional or higher exchange chain transfer mechanism type control agent is one in which a polymer chain is extended in a bidirectional or higher direction. From the viewpoint of producing the present crosslinked polymer, it may be preferable to use a bifunctional or trifunctional or higher exchange chain transfer mechanism type control agent.

The amount of the exchange chain transfer mechanism type control agent used is 0.0001 to 0.50 mol% with respect to the total amount of the present monomer in that the crosslinked structure of the crosslinked polymer can be made more uniform. It is more preferable, it is more preferably 0.0001 to 0.40 mol%, further preferably 0.0001 to 0.30 mol%, and more preferably 0.0002 to 0.30 mol%. More preferred.

As the polymerization initiator used together with the exchange chain transfer mechanism type control agent, known polymerization initiators such as azo compounds, organic peroxides, and inorganic peroxides can be used, but are 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 the present 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.
Among the above-mentioned polymerization initiators, an azo compound is preferable because it is easy to handle for safety and side reactions during radical polymerization are unlikely to occur. Specific examples of the above azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), and 2,2'-azobis (4-methoxy-2, 4-Dimethylvaleronitrile), dimethyl-2,2'-azobis (2-methylpropionate), 2,2'-azobis (2-methylbutyronitrile), 1,1'-azobis (cyclohexane-1-) Carbonitrile), 2,2'-azobis [N- (2-propenyl) -2-methylpropionamide], 2,2'-azobis (N-butyl-2-methylpropionamide) and the like. Only one kind of the radical polymerization initiator may be used, or two or more kinds thereof may be used in combination.

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 monomer components used is 100 parts by mass. Further, 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.
The proportion of the polymerization initiator used is not particularly limited, but the amount of the polymerization initiator used per 1 mol of the exchange chain transfer mechanism type control agent is 0.5 mol from the viewpoint that the crosslinked structure of the present crosslinked polymer can be made uniform. It is preferably less than or equal to 0.2 mol or less. Further, from the viewpoint of stably performing the polymerization reaction, the lower limit of the amount of the polymerization initiator used with respect to 1 mol of the exchange chain transfer mechanism type control agent is 0.001 mol. Therefore, the amount of the polymerization initiator used with respect to 1 mol of the exchange chain transfer mechanism type control agent is preferably in the range of 0.001 mol or more and 0.5 mol or less, and more preferably in the range of 0.005 mol or more and 0.2 mol or less.

As the polymerization solvent, a solvent selected from water, various organic solvents and the like can be used 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. In the present invention, 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 present crosslinked polymer is difficult to secondary agglomerate (or even if secondary agglomeration occurs in an aqueous medium. Methyl ethyl ketone and acetonitrile are different in that they are easy to unravel), that a polymer with a small chain transfer constant and a large degree of polymerization (primary chain length) can be obtained, and that the operation is easy during the process neutralization described later. preferable.

Similarly, in order to allow the neutralization reaction to proceed stably and quickly in the process 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 20.0% by mass, more preferably 0.1 to 10.0% by mass, still more preferably 0.1 to 5% by mass based on the total mass of the medium. It is 0.0% by mass, more preferably 0.1 to 1.0% 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 20.0% 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.

The reaction temperature during the polymerization reaction in the presence of the exchange chain transfer mechanism type controller is preferably 30 ° C. or higher and 120 ° C. or lower, more preferably 40 ° C. or higher and 110 ° C. or lower, and further preferably 50 ° C. or higher and 100 ° C. or higher. It is below ° C. When the reaction temperature is 30 ° C. or higher, the polymerization reaction can proceed smoothly. On the other hand, when the reaction temperature is 120 ° C. or lower, side reactions can be suppressed and restrictions on the initiators and solvents that can be used are relaxed.

The crosslinked polymer dispersion obtained through the polymerization step can be obtained in a powder state by subjecting the dispersion to a reduced pressure and / or heat treatment in the drying step and distilling off the solvent. At this time, for the purpose of removing the unreacted monomer (and its salt) before the drying step, following the polymerization step, a solid-liquid separation step such as centrifugation and filtration, an organic solvent or an organic solvent / water. It is preferable to include a cleaning step using a mixed solvent.
When the above cleaning step is provided, even when the crosslinked polymer is secondarily agglutinated, it is easily unraveled at the time of use, and the remaining unreacted monomer is removed, so that the coating film performance is also good. Is shown.

In the production method of the present invention, when an unneutralized or partially neutralized salt is used as the ethylenically unsaturated carboxylic acid monomer, an alkaline compound is added to the dispersion of the crosslinked polymer obtained in the polymerization step to add weight. After neutralizing the coalescence (hereinafter, also referred to as "step neutralization"), the solvent may be removed in a drying step. Further, after obtaining the powder of the crosslinked polymer in an unneutralized or partially neutralized salt state, an alkaline compound is added when preparing the slurry composition to neutralize the polymer (hereinafter, "post-neutralization"). It may also be called). Of the above, process neutralization is preferable because the secondary aggregates tend to be easily disintegrated.

Here, as the exchange chain transfer mechanism type control agent, as described above, a polymerized chain (hereinafter, also simply referred to as “first monomer”) of one kind or two or more kinds of vinyl-based monomers (hereinafter, also simply referred to as “first monomer”) ( Hereinafter, a polymer (first polymer) having a living radical polymerization active unit by an exchange chain transfer mechanism and a “first polymer chain”) can be used.

In producing the present crosslinked polymer by polymerizing the present monomer in the presence of the first polymer, the first polymer is used as a starting point for the polymerization of the present monomer and the polymerization of the crosslinked polymer. The present crosslinked polymer, which can be used as a dispersion stabilizer in a solvent and has a polymer chain having a structural unit derived from the present monomer bonded to the polymer chain of the first polymer, is obtained as dispersed fine particles. Can be done. By doing so, the polymerization stability, that is, the aggregation of the present crosslinked polymer during the polymerization step is suppressed, the generation of coarse aggregated particles is suppressed, the particle size is small, and the particle size distribution is narrow. You can get coalescence.

In order to make the first polymer function as a dispersion stabilizer in producing the present crosslinked polymer by polymerizing the present monomer in the presence of the first polymer, for example, the first polymer is used. , 0.3 parts by mass or more and 50 parts by mass or less can be used with respect to 100 parts by mass of the total mass of this monomer. By using it in such a range, it is possible to produce the present crosslinked polymer mainly containing the present monomer while allowing the first polymer to function as a dispersion stabilizer. Further, if the amount of the first polymer is less than 0.3 parts by mass, it is difficult to obtain a sufficient dispersion stabilizing effect, and the particle size of the crosslinked polymer tends to exceed 0.3 μm, even if it exceeds 50 parts by mass. This is because it is difficult to improve the functionality as a dispersion stabilizer, and the effect of reducing the particle size of the crosslinked polymer is also reduced.

The first polymer can be used with respect to 100 parts by mass of the total mass of the present monomer, for example, 0.5 parts by mass or more, and for example, 1 part by mass or more. Further, the first polymer can be used, for example, 40 parts by mass or less, for example, 30 parts by mass or less, and for example, 20 parts by mass or less. The range of the amount of the first polymer used with respect to 100 parts by mass of the total mass of the present monomer can be set by appropriately combining the above upper limit and lower limit.

Method for Producing First Polymer By polymerizing a monomer composition containing the first monomer in the presence of a known exchange chain transfer mechanism type control agent, a structural unit derived from the first monomer It is possible to obtain a first polymer having a first polymer chain having the above and a living polymerization active unit by an exchange chain transfer mechanism.

The polymerization conditions for producing the first polymer are well known to those skilled in the art, and examples of the polymerization process include various processes such as bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization. Considering that it is a polymerization starting point in the production of coalescence and that it functions as a dispersion stabilizer, solution polymerization can be used, for example. Further, the polymerization conditions such as the type of the exchange chain transfer mechanism control agent, the type and amount of the polymerization initiator, the polymerization solvent, and the reaction temperature are described in the above paragraphs [0040] to [0043] and [0045] to [0049]. The amount of the exchange chain transfer mechanism control agent used is appropriately adjusted according to the number average molecular weight (Mn) of the target first polymer.
As the exchange chain transfer mechanism control agent, a RAFT agent and a control agent in the iodine transfer polymerization method are preferable in that the molecular weight distribution of the first polymer can be reduced.
Further, the concentration at the time of producing the first polymer is not particularly limited with respect to the total mass of the amount charged such as the polymerization solvent and the first monomer, but is, for example, 10% by mass or more and 80% by mass. % Or less, for example, 15% by mass or more and 70% by mass or less, and for example, 20% by mass or more and 70% by mass or less.

Typically, when a monofunctional exchange chain transfer mechanism type control agent is used, a living polymerization active unit is provided at the end of the first polymerization chain, and the exchange chain transfer mechanism type having two or more functionalitys is used. When a control agent is used, it is branched in two or more directions with the living polymerization active unit as a base point, and each of them is provided with a first polymerization chain. In any of the embodiments, when another polymerized chain is provided, the other polymerized chain is directly bonded to the living polymerization active unit, and the first polymerization is carried out more distally to the living polymerization active unit. The first polymerized chain is bonded to the distal end of the other polymerized chain so that the chain is provided.

The first polymer may also include two or more first polymerized chains. For example, after performing living radical polymerization or the like using one or more first monomers of a certain composition, one or more first monomers of another composition are used. By carrying out living radical polymerization or the like, a first polymer having a first polymerization chain (block) having a structural unit derived from the first monomer having a different composition can be obtained.

The number average molecular weight (Mn) of the first polymer is not particularly limited, but is, for example, 3,000 or more, for example, 5,000 or more, and for example, 7,000 or more. Also, for example, 8,000 or more, and for example, 10,000 or more. Further, the Mn is 50,000 or less, for example, 30,000 or less, and for example, 25,000 or less, and for example, 20,000 or less, and for example, 15,000 or less. And, for example, 14,000 or less, and for example, 12,000 or less. The range of Mn can be set by appropriately combining the above-mentioned lower limit and upper limit, and is, for example, 5,000 or more and 25,000 or less, and for example, 10,000 or more and 25,000 or less. For example, it is 10,000 or more and 15,000 or less, and for example, 10,000 or more and 14,000 or less.

The weight average molecular weight (Mw) of the first polymer is not particularly limited, but is, for example, 5,000 or more, for example, 7,000 or more, and for example, 9,000 or more. Also, for example, 10,000 or more, for example, 13,000 or more, and for example, 15,000 or more. Further, the Mw is 60,000 or less, for example, 55,000 or less, and for example, 50,000 or less, and for example, 45,000 or less, and for example, 40,000 or less. And, for example, 36,000 or less, and for example, 35,000 or less, and for example, 30,000 or less, and for example, 25,000 or less. The range of Mw can be set by appropriately combining the above-mentioned lower limit and upper limit, and is, for example, 1,000 or more and 40,000 or less, and for example, 10,000 or more and 35,000 or less. For example, it is 10,000 or more and 30,000 or less, and for example, 15,000 or more and 25,000 or less.

Both Mw and Mn of the first polymer can be measured by gel permeation chromatography using polystyrene as a standard substance. As for the details of the chromatography conditions, the conditions disclosed in the subsequent examples can be adopted.

The molecular weight distribution (Mw / Mn) of the first polymer is not particularly limited, but is, for example, 2.5 or less, for example, 2.4 or less, and for example, 2.3 or less. Yes, for example 2.0 or less, and for example 1.6 or less, and for example 1.5 or less, and for example 1.4 or less, and for example 1.3 or less. be. Further, the molecular weight distribution is, for example, 1.1 or more, for example, 1.2 or more, and for example, 1.3 or more, and for example, 1.4 or more, and for example, 1.5 or more. Is. The range of the molecular weight distribution can be set by appropriately combining the above-mentioned lower limit and upper limit. For example, 1.1 or more and 2.5 or less, for example, 1.1 or more and 2.4 or less, and for example, 1 It can be 1 or more and 2.3 or less, and for example, 1.1 or more and 2.0 or less.

The smaller the molecular weight distribution of the first polymer, the smaller the particle size of the obtained crosslinked polymer tends to be. The molecular weight distribution is preferably 2.4 or less, and in order to obtain the present crosslinked polymer having a smaller particle size, it is preferably 1.7 or less, and more preferably 1. It is 6 or less, and more preferably 1.4 or less.

<First monomer>
Examples of the first monomer include styrenes, (meth) acrylonitrile compounds, maleimide compounds, unsaturated acid anhydrides and unsaturated carboxylic acid compounds. One or a combination of two or more of these can be used.

Styrenes include styrene and its derivatives. Specific compounds include styrene, α-methylstyrene, β-methylstyrene, vinyltoluene, vinylxylene, vinylnaphthalene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o-ethylstyrene, and m-. Ethylstyrene, p-ethylstyrene, pn-butylstyrene, p-isobutylstyrene, pt-butylstyrene, o-methoxystyrene, m-methoxystyrene, p-methoxystyrene, o-chloromethylstyrene, p- Examples thereof include chloromethylstyrene, o-chlorostyrene, p-chlorostyrene, o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, divinylbenzene, etc., and one or more of these may be used. can. Among these, styrene, o-methoxystyrene, m-methoxystyrene, p-methoxystyrene, o-hydroxystyrene, m-hydroxystyrene, and p-hydroxystyrene are preferable from the viewpoint of polymerizable property.

Examples of the (meth) acrylonitrile compound include (meth) acrylonitrile, acrylonitrile, α-methylacrylonitrile, and the like. For example, acrylonitrile is used.

As the maleimide compound, the maleimide compound includes a maleimide and an N-substituted maleimide compound. Specific examples of the N-substituted maleimide compound include N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, N-isopropylmaleimide, Nn-butylmaleimide, N-isobutylmaleimide, and N-tert-butyl. N-alkyl-substituted maleimide compounds such as maleimide, N-pentylmaleimide, N-hexylmaleimide, N-heptylmaleimide, N-octylmaleimide, N-laurylmaleimide, N-stearylmaleimide; N-cyclopentylmaleimide, N-cyclohexylmaleimide, etc. N-Cycloalkyl-substituted maleimide compounds; N-phenylmaleimide, N- (4-hydroxyphenyl) maleimide, N- (4-acetylphenyl) maleimide, N- (4-methoxyphenyl) maleimide, N- (4-ethoxy) Examples thereof include N-aryl-substituted maleimide compounds such as phenyl) maleimide, N- (4-chlorophenyl) maleimide, N- (4-bromophenyl) maleimide, and N-benzylmaleimide, and one or more of these. Can be used. For example, N-phenylmaleimide is used.

Further, examples of the unsaturated acid anhydride include maleic anhydride, itaconic anhydride, citraconic anhydride and the like, and one or more of these can be used.

Examples of unsaturated carboxylic acid compounds include (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, citraconic acid, silicic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, maleic anhydride, and anhydrous. Examples thereof include unsaturated dicarboxylic acids such as itaconic acid and citraconic anhydride, and monoalkyl esters of unsaturated dicarboxylic acids, and one or more of them can be used.

Among these, the first monomer preferably contains, for example, at least styrenes. This is because styrenes are easy to carry out in the living room and can impart appropriate hydrophobicity and affinity to organic solvents. It is possible to impart hydrophobicity or affinity to an organic solvent to the first polymerized chain. By doing so, for example, when the present crosslinked polymer is produced by the dispersion polymerization method in a polar organic solvent, the first polymer tends to be present on the surface layer of the present crosslinked polymer. The dispersion stability of the crosslinked polymer is improved.

Styrene is, for example, 20% by mass or more of the total mass of the first monomer. This is because if the content is 20% by mass or more, the living polymerization is facilitated, and an appropriate hydrophobicity and an affinity for an organic solvent can be appropriately imparted. Further, for example, it is 30% by mass or more, and for example, 35% by mass or more, and for example, 40% by mass or more, and for example, 50% by mass or more, and for example, 60% by mass or more. Further, for example, it is 65% by mass or more, for example, 70% by mass or more, and for example, 75% by mass or more. Further, the styrenes are 100% by mass or less of the total mass, and are, for example, 95% by mass or less, and are, for example, 90% by mass or less, and are, for example, 85% by mass or less, and are, for example,. It is 80% by mass or less, and for example, 75% by mass or less. The range of the styrenes with respect to the total mass can be set by appropriately combining the above-mentioned lower limit and upper limit, and is, for example, 20% by mass or more and 95% by mass or less, and for example, 30% by mass or more and 75% by mass or more. And, for example, 35% by mass or more and 85% by mass or less.

The (meth) acrylonitrile compound, maleimide compound, acid anhydride and unsaturated carboxylic acid compound can be used alone, and it is preferable to use one or more of these four types in combination with styrenes. This is because all of these four types can maintain, regulate or impart the hydrophobicity or organic solvent affinity of the first polymerized chain. Among them, one or more of (meth) acrylonitrile compounds such as acrylonitrile, maleimide compounds such as N-phenylmaleimide, and acid anhydrides. Of these, a combination of styrene and acrylonitrile, styrene and N-phenylmaleimide and the like is preferable. The unsaturated carboxylic acid compound is preferable in that the polarity of the first polymer can be easily changed.

When used in combination with styrenes, the total amount of these one or more first monomers other than styrenes is the first monomer for polymerizing the first polymerized chain (first). It is, for example, 20% by mass or more of the total mass of the first monomer unit of the polymerized chain). Further, for example, it is 25% by mass or more, and for example, 30% by mass or more, and for example, 35% by mass or more, and for example, 40% by mass or more, and for example, 50% by mass or more. Further, for example, it is 60% by mass or more. The (meth) acrylonitrile compound is 80% by mass or less of the total mass, and is, for example, 75% by mass or less, and is, for example, 70% by mass or less, and is, for example, 65% by mass or less. Further, for example, it is 60% by mass or less, for example, 55% by mass or less, and for example, 50% by mass or less. The range of the styrenes with respect to the total mass can be set by appropriately combining the above lower limit and upper limit, and is, for example, 20% by mass or more and 65% by mass or less, and for example, 25% by mass or more and 50% by mass or more. It is as follows.

<First polymerized chain>
The first polymerized chain may be a polymerized chain containing only the first monomer described above, but if necessary, other vinyl-based monomers other than the above may be used as the first monomer. be able to. For example, known vinyl-based monomers such as (meth) acrylic acid esters such as (meth) acrylic acid and alkyl (meth) acrylic acid can be used.
It should be noted that these other monomers are, for example, 10% by mass or less, for example, 5% by mass or less, for example, 3% by mass or less, or, for example, the total mass of the monomers constituting the first polymerized chain. 1, 1% by mass or less, and for example, 0.5% by mass or less.

Further, the first polymer may include a block (another polymer chain) different from that of the first polymer chain. Such other polymerized chains may be added, for example, in another synthetic step after the formation of the first polymerized chain. In this case, a radical polymerization initiator and another vinyl-based monomer are continuously or newly supplied to the first polymer having the first polymer chain to have a composition different from that of the first polymer chain. It is possible to obtain a first polymer having another polymer chain (block) composed of units derived from a monomer other than the first monomer. By being provided so as to be directly linked to the living radical active unit, which will be described later, and to be linked to the first polymerized chain, a part of the monomer common to the present monomer used in the present crosslinked polymer can be partially linked in advance. It can be provided in the first polymer.

<Living radical polymerization active unit>
Since the first polymer has a living radical polymerization active unit by an exchange chain transfer mechanism, it can be used as a solubility or dispersion stabilizer in the polymerization solvent of the first polymer in the precipitation polymerization or dispersion polymerization of this monomer. Various monomers can be selected for the function of.

As the exchange chain transfer mechanism of the living radical polymerization active unit in the first polymer, a reversible addition-cleavage chain transfer polymerization method (RAFT method), an iodine transfer polymerization method, a polymerization method using an organic tellurium compound (TERP method), and the like. Examples thereof include a polymerization method using an organic antimony compound (SBRP method) and a polymerization method using an organic bismuth compound (BIRP method). Among these, the RAFT method and the iodine transfer polymerization method are preferable, and the RAFT method is more preferable, because the particle size of the crosslinked polymer can be reduced.

3. 3. Characteristics of the present crosslinked polymer <Non-uniform network structure size of the present crosslinked polymer>
The crosslinked polymer or a salt thereof is 1% by mass of the crosslinked polymer neutralized to a neutralization degree of 50 to 100 mol% by a small-angle X-ray scattering method (measurement temperature: 25.0 ± 0.1 ° C.). The non-uniform network structure size Ξ (Ξ1) of the crosslinked polymer calculated by curve fitting with the following formula (1) is 80 or less with respect to the scattering intensity curve I (q) obtained by measuring the concentrated aqueous solution. Is.

Here, the above equation (1) is a correlation between the “Lorentz square model” (Shibayama M. et al., Macromolecules 2009, 42, 1344) capable of describing the non-uniform structure of cross-linking and the electrolyte derived from the carboxyl group. This is a combination of "broad peak models" (Shibayama M. et al., Journal of Chemistry Physics 2018, 149, 163301-) that can describe.

Ξ1 is the coatability and coating performance of the composition containing the crosslinked polymer or a salt thereof (in the case of a composition containing a binder for a secondary battery electrode containing the crosslinked polymer or a salt thereof, an active material and water). Is 80 or less, preferably 70 or less, more preferably 60 or less, further preferably 50 or less, and more preferably 40 or less, from the viewpoint of excellent coatability and cycle characteristics. Is more preferable.
Further, from the above viewpoint, 5 of the crosslinked polymer neutralized to a degree of neutralization of 50 to 100 mol% by the above-mentioned Ξ1 and the small-angle X-ray scattering method (measurement temperature: 25.0 ± 0.1 ° C.). The non-uniform network structure size Ξ (Ξ5) of the crosslinked polymer calculated by curve fitting with the above formula (1) with respect to the scattering intensity curve I (q) obtained by measuring the mass% concentration aqueous solution. The difference ΔΞ (Ξ1-Ξ5) is preferably 50 or less, more preferably 30 or less, further preferably 20 or less, further preferably 10 or less, and 5.0 or less. Is even more preferable.
Here, Ξ1 and Ξ5 are obtained by a method according to the method described in Examples.

<Aqueous viscosity of this crosslinked polymer>
The crosslinked polymer or a salt thereof preferably has a viscosity of 100 mPa · s or more in a 2% by mass aqueous solution thereof. When the viscosity of the 2% by mass aqueous solution is 100 mPa · s or more, the storage stability of the composition containing the crosslinked polymer is high, and excellent binding property can be exhibited. The viscosity of the 2 mass% concentration aqueous solution may be 1,000 mPa · s or more, 10,000 mPa · s or more, or 50,000 mPa · s or more. It is obtained by uniformly dissolving or dispersing the present crosslinked polymer or a salt thereof in an amount to be a concentration in water, and then measuring the B-type viscosity (25 ° C.) at 12 rpm according to the method described in Examples.

The crosslinked polymer or a salt thereof absorbs water and becomes swollen in water. In general, when the crosslinked polymer has an appropriate degree of crosslinkage, the larger the amount of hydrophilic groups contained in the crosslinked polymer, the easier it is for the crosslinked polymer to absorb water and swell. Regarding the degree of cross-linking, the lower the degree of cross-linking, the easier it is for the cross-linked polymer to swell. However, even if the number of cross-linking points is the same, the larger the molecular weight (primary chain length), the more cross-linking points that contribute to the formation of the three-dimensional network, so that the cross-linked polymer is less likely to swell. Therefore, the viscosity of the crosslinked polymer aqueous solution can be adjusted by adjusting the amount of hydrophilic groups of the crosslinked polymer, the number of crosslinked points, the primary chain length, and the like. At this time, the number of the cross-linking points can be adjusted by, for example, the amount of the cross-linking monomer used, the chain transfer reaction to the polymer chain, the post-crosslinking reaction, and the like. Further, the primary chain length of the polymer can be adjusted by setting conditions related to the amount of radicals generated such as the initiator and the polymerization temperature, and selecting the polymerization solvent in consideration of chain transfer and the like.

<Particle size of this crosslinked polymer>
In the present composition, the crosslinked polymer does not exist as a mass (secondary agglomerate) having a large particle size, but is well dispersed as water-swelled particles having an appropriate particle size. A binder containing the above is preferable because it can exhibit good binding performance.

In this crosslinked polymer, the particle size (water-swelling particle size) when a crosslinked polymer having a degree of neutralization based on a carboxyl group of 80 to 100 mol% is dispersed in water is a volume-based median diameter. It is preferably in the range of 0.1 μm or more and 5.0 μm or less. The more preferable range of the particle size is 0.1 μm or more and 4.0 μm or less, the more preferable range is 0.1 μm or more and 3.0 μm or less, and the more preferable range is 0.2 μm or more and 3.0 μm or less. Yes, and even more preferable ranges are 0.3 μm or more and 3.0 μm or less. When the particle size is in the range of 0.1 μm or more and 5.0 μm or less, the composition is uniformly present in a suitable size in the present composition, so that the present composition is highly stable and exhibits excellent binding properties. It becomes possible to do. If the particle size exceeds 5.0 μm, the binding property may be insufficient as described above. In addition, there is a risk that the coatability will be insufficient because it is difficult to obtain a smooth coated surface. On the other hand, when the particle size is less than 0.1 μm, there is concern from the viewpoint of stable manufacturability.

In the present crosslinked polymer, acid groups such as a carboxyl group derived from an ethylenically unsaturated carboxylic acid monomer are neutralized so that the degree of neutralization is 20 mol% or more 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 mol% or more, further preferably 70 mol% or more, still more preferably 75 mol% or more, still more preferably 80 mol% or more, and particularly preferably. It is 85 mol% or more. The upper limit of the degree of neutralization is 100 mol%, and may be 98 mol% or 95 mol%. The range of the degree of neutralization may be appropriately combined with the above lower limit value and upper limit value, and may be, for example, 50 mol% or more and 100 mol% or less, or 75 mol% or more and 100 mol% or less. , 80 mol% or more and 100 mol% or less. When the degree of neutralization is 20 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 carboxyl group and a neutralizing agent used for neutralization. The degree of neutralization was determined by measuring the IR of the crosslinked polymer or a salt thereof after drying the crosslinked polymer or a salt thereof at 80 ° C. for 3 hours under reduced pressure, and measuring the peak derived from the C = O group of the carboxylic acid and the C = of the carboxylate. It can be confirmed from the intensity ratio of the peak derived from the O group.

<Water swelling degree of this crosslinked polymer>
In this specification, the water swelling degree of the dry crosslinked polymer or a salt thereof by weight "(W _{A) g",} and the cross-linked polymer or a salt thereof of water absorbed when the saturation swelling with water since the amount "(W _{B) g",} it is calculated based on the following equation.
(Water swelling _{_{degree) = {(W A) +}} (W B)} / (W A)

The crosslinked polymer or a salt thereof preferably has a water swelling degree of 20 or more and 80 or less at pH 8. When the degree of water swelling is within the above range, the crosslinked polymer or a salt thereof swells appropriately in an aqueous medium, so that a sufficient adhesive area to the active material and the current collector is provided when forming the electrode mixture layer. It becomes possible to secure it, and the binding property tends to be good. The degree of water swelling may be, for example, 21 or more, 23 or more, 25 or more, 27 or more, or 30 or more. When the degree of water swelling is 20 or more, the crosslinked polymer or a salt thereof spreads on the surface of the active material or the current collector, and a sufficient adhesive area can be secured, so that good binding property can be obtained. The upper limit of the degree of water swelling at pH 8 may be 75 or less, 70 or less, 65 or less, 60 or less, or 55 or less. When the degree of water swelling exceeds 60, the viscosity of the composition for the electrode mixture layer (electrode slurry) containing the crosslinked polymer or a salt thereof tends to increase, resulting in insufficient uniformity of the mixture layer, which is sufficient. Cohesiveness may not be obtained. In addition, the coatability of the electrode slurry may decrease. The range of the degree of water swelling at pH 8 can be set by appropriately combining the above upper limit value and lower limit value, and is, for example, 23 or more and 70 or less, and for example, 25 or more and 65 or less, and for example, 25. It is 55 or less.
The degree of water swelling at pH 8 can be obtained by measuring the degree of swelling of the crosslinked polymer or a salt thereof in water at pH 8. As the water having a pH of 8, for example, ion-exchanged water can be used, and the pH value may be adjusted by using an appropriate acid or alkali, a buffer solution or the like, if necessary. The pH at the time of measurement is, for example, in the range of 8.0 ± 0.5, preferably in the range of 8.0 ± 0.3, more preferably in the range of 8.0 ± 0.2, and further. It is preferably in the range of 8.0 ± 0.1.

A person skilled in the art can adjust the degree of water swelling by controlling the composition and structure of the crosslinked polymer or a salt thereof. For example, the degree of water swelling can be increased by introducing an acidic functional group or a highly hydrophilic structural unit into the crosslinked polymer. Further, by lowering the degree of cross-linking of the cross-linked polymer, the degree of water swelling is usually increased.

4. Composition for secondary battery electrode mixture layer The composition for secondary battery electrode mixture layer of the present invention contains the present binder, active material and water.
The amount of the binder used in the composition is, for example, 0.1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the total amount of the active material. The amount used is, for example, 0.2 parts by mass or more and 10 parts by mass or less, for example, 0.3 parts by mass or more and 8 parts by mass or less, and for example, 0.4 parts by mass or more and 5 parts by mass or less. .. When the amount of the binder used is 0.1 parts by mass or more, sufficient binding property can be obtained. In addition, the dispersion stability of the active material and the like can be ensured, and a uniform mixture layer can be formed. When the amount of the binder used is 20 parts by mass or less, the composition does not have a high viscosity, and the coatability to the current collector can be ensured. As a result, a mixture layer having a uniform and smooth surface can be formed.

Among the above active materials, a lithium salt of a transition metal oxide can be used as the positive electrode active material, and for example, a layered rock salt type and a spinel type lithium-containing metal oxide 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 {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 crosslinked polymer which has not been neutralized or partially neutralized as the binder. Further, the amount of the unneutralized or partially neutralized present crosslinked polymer used is such that the amount of unneutralized carboxyl groups of the present crosslinked polymer is equal to or more than the amount of alkali eluted from the active material. It is preferable to use it.

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. Is preferable. 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 parts by mass with respect to 100 parts by mass of the total amount of the active material from the viewpoint of achieving both conductivity and energy density, and for example, 0. It can be 2 to 10 parts by 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, Also, 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 or a metal oxide 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.

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 parts by mass or less with respect to 100 parts by mass of the total amount of the active material, and for example, 5 from the viewpoint of energy density. It is less than a part by mass.

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.

This composition uses water as a 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 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. , 25-60% by mass, and can be, for example, 35-60% by mass.

The present composition may further contain other binder components such as styrene-butadiene rubber (SBR) -based latex, carboxymethyl cellulose (CMC), acrylic-based latex, and polyvinylidene fluoride-based latex. When other binder components are used in combination, the amount used may be, for example, 0.1 to 5 parts by mass or less, and for example, 0.1 to 2 parts by mass, based on 100 parts by mass of the total amount of the active material. It can be less than or equal to parts, and can be, for example, 0.1 to 1 part by mass or less. If the amount of the other binder component used exceeds 5 parts by mass, the resistance increases and the high rate characteristics may become insufficient. Among the above, SBR-based latex and CMC are preferable, and SBR-based latex and CMC are more preferable in combination because they are excellent in the balance between binding property and bending resistance.

The SBR latex is an aqueous dispersion of a copolymer having a structural unit derived from an aromatic vinyl monomer such as styrene and a structural unit derived from an aliphatic conjugated diene monomer such as 1,3-butadiene. Show the body. Examples of the aromatic vinyl monomer include α-methylstyrene, vinyltoluene, divinylbenzene and the like in addition to styrene, and one or more of these can be used. The structural unit derived from the aromatic vinyl monomer in the copolymer can be, for example, in the range of 20 to 70% by mass, and for example, 30 to 60, mainly from the viewpoint of binding property. It can be in the range of% by mass.
As the above-mentioned aliphatic conjugated diene-based monomer, in addition to 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3- Butadiene and the like can be mentioned, and one or more of these can be used. The structural unit derived from the aliphatic conjugated diene-based monomer in the copolymer is, for example, 30 to 70% by mass in that the binding property of the binder and the flexibility of the obtained electrode are good. It can be in the range of 40 to 60% by mass, for example.
In addition to the above-mentioned monomers, styrene / butadiene-based monomers include nitrile group-containing monomers such as (meth) acrylonitrile and (meth) as other monomers in order to further improve performance such as binding properties. ) A carboxyl group-containing monomer such as acrylic acid, itanconic acid, and maleic acid, and an ester group-containing monomer such as methyl (meth) acrylate may be used as the copolymerization monomer.
The structural unit derived from the other monomer in the copolymer can be, for example, in the range of 0 to 30% by mass, or can be, for example, in the range of 0 to 20% by mass.

The CMC refers to a substitute obtained by substituting a nonionic cellulosic semi-synthetic polymer compound with a carboxymethyl group and a salt thereof. Examples of the nonionic cellulose-based semi-synthetic polymer compound include alkyl celluloses such as methyl cellulose, methyl ethyl cellulose, ethyl cellulose, and microcrystallin cellulose;
Examples thereof include hydroxyethyl cellulose, hydroxybutyl methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose stearoxy ether, carboxymethyl hydroxyethyl cellulose, alkyl hydroxyethyl cellulose, hydroxyalkyl cellulose such as nonoxynyl hydroxyethyl cellulose and the like.

The composition for the secondary battery electrode mixture layer of the present invention 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, powder components such as an active material, a conductive additive and a binder are dry-blended and then mixed with a dispersion medium such as water. However, the method of dispersion 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 pH of the slurry is not particularly limited as long as the effects of the present invention are exhibited, but is preferably less than 12.5. For example, when CMC is blended, there is little concern about hydrolysis thereof, and 11.5. It is more preferably less than 10.5 and even more preferably less than 10.5. The viscosity of the slurry is not particularly limited as long as the effect of the present invention is exhibited, but the B-type viscosity (25 ° C.) at 20 rpm can be, for example, in the range of 100 to 6,000 mPa · s, and for example. , 500 to 5,000 mPa · s, or, for example, the range of 1,000 to 4,000 mPa · s. When the viscosity of the slurry is within the above range, good coatability can be ensured.

5. Secondary battery electrode The secondary battery electrode of the present invention is provided with a mixture layer formed from the composition for the mixture layer of the secondary battery electrode of the present invention 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.

6. Secondary battery A secondary battery can be manufactured by providing the secondary battery electrode of the present invention with a separator and an electrolytic solution. The electrolytic solution may be in the form of a liquid or in the form of a gel.
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 electrolytic solution, a known one that is generally used depending on the type of active material can be used. In a lithium ion secondary battery, specific solvents include cyclic carbonates having a high dielectric constant and a high dissolving ability of an electrolyte such as propylene carbonate and ethylene carbonate, and low-viscosity chains such as ethylmethyl carbonate, dimethyl carbonate and diethyl carbonate. Examples thereof include form carbonates, which can be used alone or as a mixed solvent. The electrolytic solution is used by dissolving lithium salts such as _{LiPF 6} , LiSbF ₆ , LiBF ₄ , LiClO ₄ , and LiAlO _{4 in these solvents.} In the nickel-metal hydride secondary battery, an aqueous potassium hydroxide solution can be used as the electrolytic solution. 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 secondary battery provided with the electrode having the mixture layer formed from the composition for the mixture layer for the secondary battery electrode containing the binder for the secondary battery electrode disclosed in the present specification It is suitable for in-vehicle secondary batteries and the like because it exhibits good durability (cycle characteristics) even after repeated charging and discharging.

Hereinafter, the present invention will be specifically described based on Examples. The present invention is not limited to these examples. In the following, "parts" and "%" mean parts by mass and% by mass unless otherwise specified.

<< Evaluation of carboxyl group-containing crosslinked polymer (salt) >>
(Measurement of non-uniform network structure size Ξ of crosslinked polymer by small-angle X-ray scattering method)
1. 1. Preparation method of measurement sample <1> Preparation of 1 mass% concentration aqueous solution 0.5 g of carboxyl group-containing crosslinked polymer salt powder and 49.5 g of ion-exchanged water are weighed in a 100 cc container, and a rotating / revolving stirrer (sinky). It was set in Awatori Rentaro AR-250) manufactured by the company. Next, stirring (rotation speed 2000 rpm / revolution speed 800 rpm, 7 minutes) and defoaming (rotation speed 2200 rpm / revolution speed 60 rpm, 1 minute) treatment were performed to obtain 1 mass of the carboxyl group-containing crosslinked polymer salt swollen in water. A% concentration aqueous solution was prepared.
<2> Preparation of 5% by mass aqueous solution Weigh 2.5 g of carboxyl group-containing crosslinked polymer salt powder and 47.5 g of ion-exchanged water in a 100 cc container, and perform the same operation as in <1> to 5 mass. A% concentration aqueous solution was prepared.

2. Method of Small-angle X-ray Scattering Measurement <1> Equipment Small-angle X-ray scattering measurement was carried out using SAXSpoint 2.0 manufactured by Anton Pearl Co., Ltd. As the X-ray source, a Primux100 micro microfocus X-ray source was used (Cu Kα ray having a wavelength of 1.542 Å). As the detector, a 2D EIGER2R series HPC detector was used.
The distance between the measurement sample and the detector is 3.0 m, which ^{realizes a measurable q range of 0.015 to 4.0 Å -1} (scattering vector q is determined by q = 4π / λsinθ and is determined by q = 4π / λsinθ. 2θ is the scattering angle).
The measurements were performed at a temperature of 25.0 ° C. and controlled by a Pertier element with an accuracy of 0.1 ° C. The raw scatter data was corrected for cell and silver behenate scatter using relative transmittance.

<2> Measurement method 1. Inject the 1% by mass aqueous solution and the 5% by mass aqueous solution obtained in After reducing the scattering and adjusting the exposure time so that the detector was not damaged by strong X-rays, the sample was irradiated with X-rays to obtain a two-dimensional scattered image of the sample.
Next, the background was corrected from the two-dimensional scattered image of the sample obtained in the above procedure. Specifically, a two-dimensional scattering image of the background obtained by performing the same operation as the above procedure in the absence of the sample is obtained, and the two-dimensional scattering image of the sample is used to obtain the background two-dimensional scattering image using image processing software (Igor Pro8). The two-dimensional scattering image was subtracted to obtain a two-dimensional scattering image for analysis. Ring-shaped scattering was confirmed in the two-dimensional scattering image for analysis.

<3> Analysis method The two-dimensional scattering image for analysis was converted into a one-dimensional scattering spectrum. Specifically, the two-dimensional scattering image for analysis is read into X-ray data processing software (Igor Pro8) and integrated over all directional angles, so that the horizontal axis is the scattering vector q (Å ^-1 ) and the vertical axis is the vertical axis. A one-dimensional scattering spectrum (scattering intensity curve I (q)) was obtained. Next, as the baseline correction, the minimum value of the scattering intensity in the analysis target region was obtained, and the minimum value was subtracted over the entire region to perform the baseline correction.
The obtained corrected one-dimensional scattering profile was fitted using the following formula (1) to determine Ξ (Ξ1) in a 1% by mass aqueous solution and Ξ (Ξ5) in a 5% by mass aqueous solution. In the following formula (1), Ξ means the structural size of the non-uniform network of the crosslinked polymer, and as shown in FIG. 1, when there is a portion having a dense degree of crosslink, the size is described by Ξ. ..
Waveform separation software (Igor Pro8) was used for fitting.

(Water swelling degree at pH 8)
The degree of water swelling at pH 8 was measured by the following method. The measuring device is shown in FIG.
The measuring device is composed of <1> to <3> in FIG.
<1> It is composed of a burette 1, a pinch cock 2, a silicon tube 3 and a polytetrafluoroethylene tube 4 having a branch tube for venting air.
<2> A support cylinder 8 having a large number of holes on the bottom surface is installed on the funnel 5, and a filter paper 10 for an apparatus is installed on the support cylinder 8.
<3> The sample 6 (measurement sample) of the crosslinked polymer or a salt thereof is sandwiched between two sample fixing filter papers 7, and the sample fixing filter paper is fixed by the adhesive tape 9. All the filter papers used are ADVANTEC No. 2. The inner diameter is 55 mm.
<1> and <2> are connected by a silicon tube 3.
Further, the heights of the funnel 5 and the support cylinder 8 are fixed with respect to the burette 1, and the lower end of the polytetrafluoroethylene tube 4 installed inside the burette branch pipe and the bottom surface of the support cylinder 8 are at the same height. (Dotted line in FIG. 1).

The measuring method will be described below.
The pinch cock 2 in <1> is removed, ion-exchanged water is poured from the upper part of the burette 1 through the silicon tube 3, and the burette 1 to the filter paper 10 for the device are filled with the ion-exchanged water 12. Next, the pinch cock 2 is closed, and air is removed from the polytetrafluoroethylene tube 4 connected to the burette branch pipe with a rubber stopper. In this way, the ion-exchanged water 12 is continuously supplied from the burette 1 to the filter paper 10 for the apparatus.
Next, after removing the excess ion-exchanged water 12 oozing from the filter paper 10 for the device, the reading (a) of the scale of the burette 1 is recorded.
Weigh 0.1 to 0.2 g of the dry powder of the measurement sample, and place it evenly on the center of the sample fixing filter paper 7 as shown in <3>. The sample is sandwiched between another filter paper, and the two filter papers are fastened with the adhesive tape 9 to fix the sample. The filter paper on which the sample is fixed is placed on the device filter paper 10 shown in <2>.
Next, the reading (b) of the scale of the burette 1 is recorded 30 minutes after the lid 11 is placed on the filter paper 10 for the device.
The total (c) of the water absorption of the measurement sample and the water absorption of the two sample fixing filter papers 7 is obtained by (ab). By the same operation, the water absorption amount (d) of only two filter papers 7 containing no sample of the crosslinked polymer or a salt thereof is measured.
The above operation was performed, and the degree of water swelling was calculated from the following formula. As the solid content used in the calculation, the value measured by the method described later was used.
Water swelling degree = {dry weight of measurement sample (g) + (cd)} / {dry weight of measurement sample (g)}
However, the dry weight (g) of the measurement sample = the weight (g) of the measurement sample × (solid content (%) ÷ 100)

Here, the method for measuring the solid content will be described below.
Approximately 0.5 g of the sample is collected in a weighing bottle [weight of the weighing bottle = B (g)] whose weight has been measured in advance, and the entire weighing bottle is accurately weighed [W ₀ (g)]. The sample was placed in a windless dryer together with the weighing bottle, dried at 155 ° C. for 45 minutes, and the weight at that time was measured together with the weighing bottle [W ₁ (g)], and the solid content was determined by the following formula.
Solid content (%) = (W _1- B) / (W _0- B) x 100

(Measurement of particle size (water-swelling particle size) in water medium)
0.25 g of the carboxyl group-containing crosslinked polymer salt powder and 49.75 g of ion-exchanged water were weighed in a 100 cc container and set in a rotating / revolving stirrer (Awatori Rentaro AR-250, manufactured by Shinky). Next, stirring (rotation speed 2,000 rpm / revolution speed 800 rpm, 7 minutes) and defoaming (rotation speed 2,200 rpm / revolution speed 60 rpm, 1 minute) are performed, and the carboxyl group-containing crosslinked polymer salt swells in water. A hydrogel in a state of being prepared was prepared.
Next, the particle size distribution of the hydrogel was measured with a laser diffraction / scattering particle size distribution meter (Microtrack MT-3300EXII, manufactured by Microtrac Bell) using ion-exchanged water as a dispersion medium. When an amount of hydrogel capable of obtaining an appropriate scattered light intensity was added to the place where an excessive amount of dispersion medium was circulated with respect to the hydrogel, the particle size distribution shape measured after several minutes became stable. As soon as the stability was confirmed, the particle size distribution was measured to obtain a volume-based median diameter (D50) as a representative value of the particle size.

(Measurement of viscosity of 2% by mass aqueous solution)
2.0 parts of the carboxyl group-containing crosslinked polymer salt powder and 98 parts of the ion-exchanged water were weighed in a container and set in a rotating / revolving stirrer (Awatori Rentaro AR-250, manufactured by Shinky). Next, stirring (rotation speed 2,000 rpm / revolution speed 800 rpm, 7 minutes) and defoaming (rotation speed 2,200 rpm / revolution speed 60 rpm, 1 minute) were repeated until there were no unswelled powdery parts, and carboxyl group-containing cross-linking was performed. A hydrogel fine particle dispersion in which the polymer salt was swollen in water was prepared. After adjusting each of the obtained hydrogel fine particle dispersions to 25 ° C. ± 1 ° C., the viscosity at a rotor speed of 12 rpm was measured using a B-type viscometer (TVB-10 manufactured by Toki Sangyo Co., Ltd.).

≪Synthesis of the first polymer≫
(Polymer 1)
2.0 parts of RAFT agent (dibenzyltrithiocarbonate: DBTTC), 2,2'-azobis (2-methylbutylonitrile) (2-methylbutylonitrile) in a reactor equipped with a stirrer, thermometer, reflux condenser and nitrogen introduction tube. Japan Finechem Co., Ltd., trade name "ABN-E") 0.410 parts, styrene (St) 75 parts, acrylonitrile (AN) 25 parts, and anisole 67 parts were charged, sufficiently degassed by nitrogen bubbling, and at 80 ° C. Polymerization was started in a constant temperature bath. After 4 hours, the reaction was stopped by cooling to room temperature. The above polymerization solution was reprecipitated and purified from methanol / water = 90/10 (vоl%) and vacuum dried to obtain a polymer 1. As a result of the test by gas chromatography, the reaction rate of the obtained polymer 1 was 72%. The molecular weight of the polymer 1 was Mn11,900, Mw15,500, and Mw / Mn was 1.30. Styrene and acrylonitrile correspond to the first monomer.

(Method for measuring the molecular weight of the first polymer)
The molecular weight of the first polymer was measured by gel permeation chromatography (GPC). That is, a polystyrene-equivalent number average molecular weight (Mn) and a weight average molecular weight (Mw) were obtained by THF-based GPC. Moreover, the molecular weight distribution (Mw / Mn) was calculated from the obtained values. The GPC was performed under the following conditions.

Column: Tosoh TSKgel SuperMultipore HZ-M x 4 Solvent: Tetrahydrofuran Temperature: 40 ° C
Detector: RI
Flow velocity: 600 μL / min

<< Production of crosslinked polymer salt containing carboxyl group >>
(Production Example 1: Production of Carboxyl Group-Containing 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"), 0.001 part of DBTTC, trimethylolpropane diallyl ether (manufactured by Daiso, trade name "Neoallyl T"). -20 ") 0.90 parts and 1.0 mol% of triethylamine 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%. Cooling of the reaction solution is started 12 hours after the polymerization start point, and after the internal temperature is lowered to 25 ° C., _{a powder of lithium hydroxide / monohydrate (hereinafter referred to as “LiOH / H 2} O”) is used. 52.4 parts were 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 carboxyl group-containing 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 washing operation of precipitating the polymer particles by centrifugation to remove the supernatant was repeated twice. The precipitate was recovered and dried at 80 ° C. for 3 hours under reduced pressure conditions to remove volatile components to obtain a powder of the carboxyl group-containing polymer salt R-1. Since the carboxyl group-containing polymer salt R-1 has hygroscopicity, it was stored in a container having a water vapor barrier property. The powder of the carboxyl group-containing 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. , 90 mol% equal to the calculated value from the preparation. The degree of water swelling was 36.4, the particle size in the aqueous medium was 1.72 μm, and the viscosity of the 2% by mass aqueous solution was 9,110 mPa · s.

(Production Examples 2 to 15 and Comparative Production Examples 1 to 2: Carboxyl group-containing crosslinked polymer salts R-2 to R-17)
The same operation as in Production Example 1 was carried out except that the amounts of the monomer, the crosslinkable monomer and the neutralizing agent were as shown in Table 1, and the carboxyl group-containing crosslinked polymer salts R-2 to R were carried out. A polymerization reaction solution containing -17 was obtained.
Next, the same operations as in Production Example 1 were carried out for each polymerization reaction solution to obtain powdery carboxyl group-containing crosslinked polymer salts R-2 to R-17. Each carboxyl group-containing crosslinked polymer salt was sealed and stored in a container having a water vapor barrier property. Table 1 shows the degree of water swelling of R-2 to R-17, the particle size in the aqueous medium, and the viscosity of the 2% by mass aqueous solution. Incidentally, the particle diameter in an aqueous medium of R-3 (degree of neutralization 70 mol%) was measured after adjusting the neutralization degree of 90 mol% by LiOH · _{H 2} O.

(Small-angle X-ray scattering measurement)
An example of the small-angle X-ray scattering measurement result is shown in FIG. 1 (Production Example 2: R-2, Comparative Production Example 2: R-17).
In each sample, a broad peak was observed in the vicinity of ^{q of 0.03 to 0.10 Å -1 in} a 1% by mass aqueous solution. This is a peak due to scattering of charged groups derived from carboxyl groups existing inside the particles in which the hydrogel fine particles are dispersed in water.
On the other hand, in the 5% by mass aqueous solution, a peak was observed in the vicinity of ^{q 0.07 to 0.20 Å -1.} It can be considered that this is because the hydrogel fine particles were densely packed in water and the structure was apparently uniform, so that the peak derived from the cross-linking was confirmed.

In the 1 mass% aqueous solution, the graph shown in FIG. 1 was fitted using the formula (1) with ^{q * = 0.053 Å -1} and L = 15.4 Å ^{-1, and in R-2,} For Ξ1 = 43.3 Å ^-1 , and for R-17, Ξ ¹ = 154.4 Å -1 was calculated. Further, in the 5 mass% aqueous solution, the graph shown in FIG. 1 was fitted using the formula (1) with ^{q * = 0.10 Å -1} and L = 10.0 Å ^{-1, R-2.} Then, Ξ5 = 41.6 Å ^-1 , and in R-17, Ξ 5 = 32.8 Å ^-1 .
In each case, Ξ1 shows a larger value than Ξ5. This is because in a 1% by mass aqueous solution, the hydrogel is not packed in water and is in a saturated swelling state capable of sufficiently absorbing water, so that the sparseness of the crosslinks becomes clearer and a large non-uniform network is formed. It can be considered that the structure size was observed.
On the other hand, in the 5% by mass aqueous solution, since the hydrogel is packed in water, the sparseness and density of the crosslinks are canceled out, so that the structure looks like a uniform mesh, resulting in a small non-uniform mesh structure size. It can be considered that it was observed. Therefore, ΔΞ (Ξ1-Ξ5) can be considered to indirectly indicate the degree of sparseness of the crosslinks. Considering from the result that R-2 showed a small value of Ξ in a 1% by mass aqueous solution and a small value of ΔΞ as compared with R-17, it is considered that R-2 has a more uniform crosslinked structure. be able to.
It should be noted that Ξ1, Ξ5 calculated by curve fitting the scattering intensity curve I (q) obtained by measuring R-1, R-3 to R-16 by small-angle X-ray scattering by the following formula (1). And ΔΞ are shown in Table 1.

Details of the compounds used in Table 1 are shown below.
AA: Acrylic acid IBXA: Isobornyl acrylate BM1430: 2- (Dodecylthiocarbonothio oilthio) Propionic acid IBME: 2-Methyl iodoisobutyrate T-20: Trimethylolpropane diallyl ether (manufactured by Daiso, trade name "Neoallyl T-" 20 "))
P-30: Pentaerythritol triallyl ether (manufactured by Daiso, trade name "Neoallyl P-30")
TEA: Triethylamine AcN: Acetonitrile V-65: 2,2'-azobis (2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd.)
LiOH ・ H ₂ O: Lithium hydroxide ・ Monohydrate Na ₂ CO ₃ : Sodium carbonate K ₂ CO ₃ : Potassium carbonate

<< Evaluation of composition containing carboxyl group-containing crosslinked polymer salt >>
(Example 1: Evaluation of composition containing carboxyl group-containing crosslinked polymer salt R-1)
<Preparation of slurry composition (composition for electrode mixture layer)>
Prepare a SiOx (0.8 <x <1.2) surface coated with 10% carbon by the CVD method (hereinafter referred to as "Si-based active material"), and prepare artificial graphite and Si-based active material. The mixture was used as the active material. As the binder, a mixture of the present crosslinked polymer salt R-1, styrene-butadiene rubber (SBR) -based latex, and carboxymethyl cellulose (CMC) was used.
Artificial graphite: Si-based active material: R-1: SBR: CMC = 90: 10: 1.0: using water as a diluting solvent so that the solid content concentration of the composition for the electrode mixture layer is 50% by mass. With a mass ratio of 1.0: 1.0 (solid content), T.I. K. The mixture was mixed for 2 hours using a hibis mix to prepare a slurry-state composition for an electrode mixture layer (electrode slurry) as a slurry composition. The viscosity of the electrode slurry was 3,670 mPa · s, which was a sufficiently low value.
An electrode was prepared using the obtained electrode slurry and evaluated. The specific procedure and evaluation method are shown below.

<Manufacturing of negative electrode plate>
The electrode slurry was applied to both sides of a copper foil (thickness: 20 μm) and dried to form a mixture layer. Then, after rolling so that the thickness of the mixture layer was 27 μm and the packing density was 1.3 g / cm ³ , the negative electrode electrode plate was obtained by punching 3 cm square.

(Applicability of electrode slurry)
The coatability of the electrode slurry in the production of the negative electrode electrode plate was evaluated based on the following criteria, and was evaluated as “⊚”.
<Evaluation criteria>
⊚: No abnormal appearance such as streaks or bumps is observed on the surface.
〇: Slight abnormalities in appearance such as streaks and bumps are observed on the surface.
Δ: Some appearance abnormalities such as streaks and bumps are observed on the surface.
X: Appearance abnormalities such as streaks and bumps are noticeably observed on the surface.

<Manufacturing of positive electrode plate>
In N-methylpyrrolidone (NMP) solvent, 100 parts of lithium iron phosphate (LFP) as the positive electrode active material, 0.2 parts of carbon nanotubes as the conductive agent, 2 parts of Ketjen black, and vapor layer carbon fiber (VGCF). ) 0.6 part was mixed and added, and polyvinylidene fluoride (PVDF) was mixed as a binder for the electrode composition to prepare a composition for a positive electrode. A mixture layer was formed by applying the positive electrode composition to an aluminum current collector (thickness: 15 μm) and drying it. Then, after rolling so that the thickness of the mixture layer was 88 μm and the packing density was 3.1 g / cm ³ , the mixture was punched 3 cm square to obtain a positive electrode plate.

<Making secondary batteries>
Using the positive electrode plate, the negative electrode plate, and the separator, a lithium ion secondary battery of a laminated cell was produced. _{As the electrolytic solution, one in which LiPF 6} was dissolved at a concentration of 1.0 mol / liter in a mixed solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (DEC) at a volume ratio of 25:75 was used.

(Coating film performance)
In this example, the performance of the coating film obtained from the electrode slurry was evaluated by measuring the cycle characteristics of the lithium ion secondary battery.
The lithium-ion secondary battery of the laminated cell produced above is charged / discharged at a charge / discharge rate of 0.2 C under the conditions of 2.7 to 3.4 V by CC discharge to obtain an initial capacity of C0. It was measured. Further, charging and discharging were repeated in an environment of 25 ° C., and the capacity C50 after 50 cycles was measured. The cycle characteristic (ΔC) calculated by the following formula was 91.8%, and the cycle characteristic based on the following criteria was evaluated as “◯”. The higher the value of ΔC, the better the cycle characteristics.
ΔC = C50 / C0 × 100 (%)
<Evaluation criteria>
⊚: Charge / discharge capacity retention rate is 95.0% or more 〇: Charge / discharge capacity retention rate is 90.0% or more and less than 95.0% Δ: Charge / discharge capacity retention rate is 85.0% or more and less than 90.0% × : Charge / discharge capacity retention rate is less than 85.0%

(Examples 2 to 15 and Comparative Examples 1 to 2)
An electrode slurry was prepared as a slurry composition by performing the same operation as in Example 1 except that the crosslinked polymer salt was as shown in Table 2, and the slurry viscosity was measured. In addition, the coatability of the electrode slurry and the cycle characteristics of the secondary battery obtained by using the electrode slurry were evaluated. The results are shown in Table 2.

≪Evaluation result≫
As is clear from the results of Examples 1 to 15, all the slurry compositions containing the crosslinked polymer salt of the present invention have good coatability and the coating performance of the composition (the present example). The cycle characteristics of the secondary battery provided with the electrodes obtained by using the composition) were also excellent.
Among these, when the water swelling degree and the particle size in the aqueous medium are the same (Examples 2, 12, and 13), as an exchange chain transfer mechanism type control agent, in reversible addition cleavage type chain transfer polymerization. When the control agent was used (Examples 2 and 12), the non-uniform network structure size Ξ1 was smaller than when the iodine transfer polymerization control agent was used (Example 13), and ΔΞ (Ξ1-Ξ5) was used. ) Is also a small value, so that the coating performance is excellent (in this embodiment, the charge / discharge capacity retention rate is high and the cycle characteristics are excellent).
On the other hand, in the case of a slurry composition containing a crosslinked polymer having a non-uniform network structure size Ξ1 of more than 80, either the coating film performance (cycle characteristics of the secondary battery) or the coatability was significantly inferior (). Comparative Examples 1 and 2).

Since the composition containing the carboxyl group-containing crosslinked polymer of the present invention or a salt thereof is excellent in both coatability and coating performance, it is a thickener for cosmetics, a viscosity modifier, and a non-aqueous electrolyte secondary battery electrode. It is expected to be applied to various applications such as binders for plastics, anti-settling agents for pigments, and dispersion stabilizers for metal powders.
Furthermore, a secondary battery provided with an electrode obtained by using a composition for a secondary battery electrode mixture layer containing a binder for a secondary battery electrode containing the carboxyl group-containing crosslinked polymer of the present invention or a salt thereof. Is expected to be applied to in-vehicle secondary batteries because it exhibits good durability (cycle characteristics). It is also useful for the use of active materials containing silicon, and is expected to contribute to increasing the capacity of batteries. Above all, it is useful for a non-aqueous electrolyte lithium ion secondary battery having a high energy density.

Claims

A carboxyl group-containing crosslinked polymer or a salt thereof.
It is obtained by measuring a 1% by mass concentration aqueous solution of the crosslinked polymer neutralized to a neutralization degree of 50 to 100 mol% by a small-angle X-ray scattering method (measurement temperature: 25.0 ± 0.1 ° C.). The non-uniform network structure size Ξ (hereinafter referred to as “Ξ1”) of the crosslinked polymer calculated by curve fitting with the following formula (1) with respect to the scattering intensity curve I (q) is 80 or less. A carboxyl group-containing crosslinked polymer or a salt thereof.
A 5% by mass aqueous solution of the crosslinked polymer neutralized to a neutralization degree of 50 to 100 mol% is measured by the small angle X-ray scattering method (measurement temperature: 25.0 ± 0.1 ° C.) with Ξ1. The difference in the non-uniform network structure size Ξ (hereinafter referred to as “Ξ5”) of the crosslinked polymer calculated by curve fitting with the above formula (1) with respect to the scattering intensity curve I (q) obtained. The carboxyl group-containing crosslinked polymer according to claim 1, or a salt thereof, wherein ΔΞ (Ξ1-Ξ5) is 50 or less.
The carboxyl group-containing crosslink according to claim 1 or 2, wherein the crosslinked polymer contains 50% by mass or more and 100% by mass or less of structural units derived from an ethylenically unsaturated carboxylic acid monomer with respect to all the structural units thereof. Polymer or salt thereof.
The crosslinked polymer is crosslinked with a crosslinkable monomer, and the amount of the crosslinkable monomer used is 0.1 part by mass or more with respect to 100 parts by mass of the total amount of the non-crosslinkable monomer. The carboxyl group-containing crosslinked polymer according to any one of claims 1 to 3, which is 0.0 parts by mass or less, or a salt thereof.
The crosslinked polymer or a salt thereof is neutralized to a degree of neutralization of 80 to 100 mol%, and then the particle size measured in an aqueous medium is 0.1 μm or more and 5.0 μm or less in terms of volume-based median diameter. The carboxyl group-containing crosslinked polymer according to any one of claims 1 to 4 or a salt thereof.
The carboxyl group-containing crosslinked polymer or salt thereof according to any one of claims 1 to 5, wherein the crosslinked polymer or a salt thereof has a water swelling degree of 20 or more and 80 or less at pH 8.
A binder for a secondary battery electrode containing the carboxyl group-containing crosslinked polymer according to any one of claims 1 to 6 or a salt thereof.
The composition for a secondary battery electrode mixture layer containing the binder for the secondary battery electrode, the active material, and water according to claim 7.
A secondary battery electrode comprising a mixture layer formed from the composition for the secondary battery electrode mixture layer according to claim 8 on the surface of a current collector.
A secondary battery including the secondary battery electrode according to claim 9.