JP6988888B2 - Binder for non-aqueous electrolyte secondary battery electrode, its manufacturing method, and its application - Google Patents

Description

The present invention relates to a binder for a non-aqueous electrolyte secondary battery electrode that can be used for a lithium ion secondary battery or the like and its use, and a method for producing a carboxyl group-containing crosslinked polymer or a salt thereof used for the binder.

As a non-aqueous electrolyte secondary battery, for example, a lithium ion secondary battery is well known. The non-aqueous electrolyte secondary battery electrode is produced by applying, drying, or the like on a current collector a composition for forming an electrode mixture layer containing an active material, a binder, and the like. As the binder used in the negative electrode mixture layer composition, an aqueous binder containing styrene-butadiene rubber (SBR) latex and carboxymethyl cellulose (CMC) is used. Further, as a binder having excellent dispersibility and binding property, a binder containing an aqueous acrylic acid polymer solution or an aqueous dispersion is known. On the other hand, as a binder used for the positive electrode mixture layer, a solution of polyvinylidene fluoride (PVDF) in N-methyl-2-pyrrolidone (NMP) is widely used. However, against the background of increasing environmental awareness in recent years, there is an increasing demand for water-based composition that does not use an organic solvent even for the positive electrode mixture layer composition.

On the other hand, as the use of lithium ion secondary batteries expands, the demand for improved energy density, reliability and durability tends to increase. For this reason, studies have been conducted on improving the binding property of the binder for the purpose of suppressing peeling or falling off of the electrode mixture layer and improving durability (Patent Documents 1 to 3).
For example, Patent Document 1 discloses an acrylic acid polymer crosslinked with polyalkenyl ether as a binder for forming a negative electrode coating film of a lithium ion secondary battery. Patent Document 2 contains a structural unit derived from an ethylenically unsaturated carboxylic acid salt monomer and a structural unit derived from an ethylenically unsaturated carboxylic acid ester monomer, and contains a water-soluble polymer having a specific aqueous solution viscosity. A water-based electrode binder for a secondary battery is disclosed. Patent Document 3 discloses an aqueous dispersion having a specific viscosity and containing a salt of a crosslinked polymer containing a structural unit derived from an ethylenically unsaturated carboxylate monomer.

Japanese Unexamined Patent Publication No. 2000-294247 JP-A-2015-18776 International Publication No. 2016/158939

Patent Document 1 discloses that crosslinked polyacrylic acid is used as a binder, but improvement in bending resistance and the like of the obtained electrode has been desired. The binder described in Patent Document 2 is good in terms of flexibility, but is not sufficiently satisfactory in terms of binding properties. Further, even with the binder described in Patent Document 3, there is room for further improvement in binding property.

The present disclosure has been made in view of such circumstances, and is an aqueous binder for a non-aqueous electrolyte secondary battery having both excellent binding properties and flexibility, a polymer used for the binder, or a salt thereof. Provides a manufacturing method for. The present disclosure also provides a composition for a non-aqueous electrolyte secondary battery electrode mixture layer and a non-aqueous electrolyte secondary battery electrode obtained by using the above binder.

As a result of diligent studies to solve the above problems, the present inventors have found that a crosslinked polymer having a carboxyl group and a substituent having an alicyclic structure or a binder containing a salt thereof is well bound to an electrode active material or the like. It was found that the electrode mixture layer containing the binder showed excellent binding properties. The present invention has been completed based on these findings.

The present invention is as follows.
[1] A binder for a non-aqueous electrolyte secondary battery electrode containing a crosslinked polymer or a salt thereof.
The crosslinked polymer has 50 to 99% by mass of a structural unit derived from an ethylenically unsaturated carboxylic acid monomer and a structural unit derived from an ethylenically unsaturated monomer containing an alicyclic structure with respect to all the structural units thereof. A binder for non-aqueous electrolyte secondary battery electrodes containing 1 to 50% by mass.
[2] The crosslinked polymer 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 to 10 μm in terms of volume-based median size. ] The non-aqueous electrolyte secondary battery electrode binder according to.
[3] The binder for a non-aqueous electrolyte secondary battery electrode according to the above [1] or [2], wherein the alicyclic structure-containing ethylenically unsaturated monomer has an acryloyl group as a polymerizable functional group.
[4] The crosslinked polymer is crosslinked with a crosslinkable monomer, and the amount of the crosslinkable monomer used is 0.02 to 0.7 with respect to the total amount of the non-crosslinkable monomer. The binder for a non-aqueous electrolyte secondary battery electrode according to any one of the above [1] to [3], which is mol%.
[5] A method for producing a crosslinked polymer or a salt thereof used for a binder for a non-aqueous electrolyte secondary battery electrode.
A polymerization step of precipitating and polymerizing a monomer component containing 50 to 99% by mass of an ethylenically unsaturated carboxylic acid monomer and 1 to 50% by mass of a structural unit derived from an ethylenically unsaturated monomer containing an alicyclic structure. The method for producing the crosslinked polymer or a salt thereof.
[6] The crosslinked polymer 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 to 10 μm in terms of volume-based median diameter. [5] The method for producing a crosslinked polymer or a salt thereof according to the above.
[7] The method for producing a crosslinked polymer or a salt thereof according to the above [5] or [6], which uses a polymerization medium containing acetonitrile in the polymerization step.
[8] A drying step is provided after the polymerization step.
Any of the above [5] to [7], which comprises a step of adding an alkaline compound to the polymer dispersion obtained by the polymerization step to neutralize the polymer after the polymerization step and before the drying step. The method for producing a crosslinked polymer or a salt thereof according to the above.
[9] The composition for a non-aqueous electrolyte secondary battery electrode mixture layer containing the binder, active material and water according to any one of the above [1] to [4].
[10] The composition for a non-aqueous electrolyte secondary battery electrode mixture layer according to the above [9], which further contains a styrene / butadiene latex as a binder.
[11] The composition for a water electrolyte secondary battery electrode mixture layer according to the above [9] or [10], which comprises a carbon-based material or a silicon-based material as a negative electrode active material.
[12] The composition for a water electrolyte secondary battery electrode mixture layer according to the above [9] or [10], which contains a lithium-containing metal oxide as a positive electrode active material.
[13] A non-aqueous electrolyte having a mixture layer formed from the composition for the non-aqueous electrolyte secondary battery electrode mixture layer according to any one of [9] to [12] above on the surface of the current collector. Secondary battery electrode.

The binder for a non-aqueous electrolyte secondary battery electrode of the present invention exhibits excellent binding properties to an electrode active material and the like, and is also excellent in flexibility. In addition, the binder can exhibit good adhesiveness to the current collector. Therefore, the electrode mixture layer containing the binder and the electrode provided with the binder are excellent in binding property and can maintain their integrity. Further, deterioration of the electrode mixture layer due to volume change and shape change of the active material due to charge / discharge is suppressed, and it becomes possible to obtain a secondary battery having high durability (cycle characteristics).

Since the composition for the electrode mixture layer of the non-aqueous electrolyte secondary battery of the present invention has good binding property to the electrode material and good adhesion to the current collector, the electrode mixture layer having good integrity can be obtained. It is possible to obtain a non-aqueous electrolyte secondary battery electrode that can be formed and has good electrode characteristics.

The binder for a non-aqueous electrolyte secondary battery electrode of the present invention contains a crosslinked polymer or a salt thereof, and can be mixed with an active material and water to form an electrode mixture layer composition. The above composition may be in a slurry state that can be applied to the current collector, or may be prepared in a wet powder state so that it can be pressed on the surface of the current collector. The non-aqueous electrolyte 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.

The following is a method for producing a binder for a non-aqueous electrolyte secondary battery electrode of the present invention and a crosslinked polymer used for the binder, and a composition for a non-aqueous electrolyte secondary battery electrode mixture layer obtained by using the binder. And each of the non-aqueous electrolyte secondary battery electrodes 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.

<Binder>
The binder of the present invention contains a crosslinked polymer having a carboxyl group or a salt thereof. The crosslinked polymer having a carboxyl group or a salt thereof has a structural unit derived from an ethylenically unsaturated carboxylic acid and a structural unit derived from an ethylenically unsaturated monomer containing an alicyclic structure.

<Structural unit of crosslinked polymer>
<Structural unit derived from ethylenically unsaturated carboxylic acid monomer>
The crosslinked polymer can have a structural unit derived from an ethylenically unsaturated carboxylic acid monomer (hereinafter, also referred to as “component (a)”). When the crosslinked polymer has a carboxyl group due to 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 and the high rate is obtained. An electrode with excellent characteristics can be obtained. Further, since water swelling property is imparted, the dispersion stability of the active material or the like in the mixture layer composition can be enhanced.
The component (a) can be introduced into a crosslinked polymer, for example, by polymerizing a monomer containing an ethylenically unsaturated carboxylic acid monomer. Alternatively, it can also be obtained by (co) polymerizing a (meth) acrylic acid ester monomer and then hydrolyzing it. Further, after polymerizing (meth) acrylamide, (meth) acrylonitrile or the like, it may be treated with a strong alkali, or it may be a method of reacting an acid anhydride with a polymer having a hydroxyl group.

Examples of the ethylenically unsaturated carboxylic acid monomer include (meth) acrylic acid; (meth) acrylamide alkylcarboxylic acid such as (meth) acrylamide hexane acid and (meth) acrylamide dodecanoic acid; and monohydroxyethyl succinate (meth) acrylate. , Ω-carboxy-caprolactone mono (meth) acrylate, β-carboxyethyl (meth) acrylate and other ethylenically unsaturated monomers having a carboxyl group or (partially) alkaline neutralized products thereof. One of the above may be used alone, or two or more of them 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 crosslinked polymer is not particularly limited, but may be, for example, 50% by mass or more and 99% by mass or less with respect to all the structural units of the 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, 60% by mass or more, for example, 70% by mass or more, and for example, 80% by mass or more. The upper limit is, for example, 98% by mass or less, for example, 95% by mass or less, and for example, 90% by mass or less. The range may be a range in which these lower and upper limits are appropriately combined, and is, for example, 60% by mass or more and 98% by mass or less, for example, 70% by mass or more and 95% by mass or less, and for example, 80% by mass. It can be% or more and 90% by mass or less. If the ratio of the component (a) to all the structural units is less than 50% by mass, the dispersion stability, the binding property and the durability as a battery may be insufficient.

<Structural unit derived from alicyclic structure-containing ethylenically unsaturated monomer>
The crosslinked polymer of the present invention can have a structural unit derived from an alicyclic structure-containing ethylenically unsaturated monomer (hereinafter, also referred to as “component (b)”) in addition to the component (a). The component (b) can exhibit a strong interaction with the electrode material and can exhibit good binding property to the active material. This makes it possible to obtain a solid and well-integrated electrode mixture layer. The component (b) can be introduced into the crosslinked polymer, for example, by polymerizing an ethylenically unsaturated monomer having a substituent having an alicyclic structure.

Examples of the ethylenically unsaturated monomer having a substituent having an alicyclic structure include cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, and t (meth) acrylate. -A (meth) acrylic acid cycloalkyl ester which may have an aliphatic substituent such as butylcyclohexyl, cyclodecyl (meth) acrylate and cyclododecyl (meth) acrylate; (meth) isobornyl acrylate, (meth). Adamanthyl acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, dicyclopentanyl (meth) acrylate, and cyclohexanedimethanol mono (meth) acrylate and cyclodecanedimethanol mono Cycloalkyl polyalcohol mono (meth) acrylates such as (meth) acrylates may be mentioned, and one of these may be used alone or in combination of two or more. Among the above, a compound having an acryloyl group as a polymerizable functional group is preferable in that a polymer having a long primary chain length can be obtained because the polymerization rate is high and the binding force of the binder is good.

The content of the component (b) in the crosslinked polymer is not particularly limited, but may be, for example, 1% by mass or more and 50% by mass or less with respect to all the structural units of the crosslinked polymer. The lower limit is, for example, 2% by mass or more, for example, 5% by mass or more, and for example, 10% by mass or more. Further, the upper limit is, for example, 40% by mass or less, for example, 30% by mass or less, and for example, 20% by mass or less. The range may be a range in which these lower and upper limits are appropriately combined, and is, for example, 2% by mass or more and 40% by mass or less, for example, 5% by mass or more and 30% by mass or less, and for example, 10% by mass. It can be% or more and 20% by mass or less. If the ratio of the component (b) to all the structural units is less than 1% by mass, the binding property to the electrode active material may be insufficient. Further, if it exceeds 50% by mass, the amount of the component (a) cannot be sufficiently secured, and the dispersion stability, the binding property and the durability as a battery may be insufficient.

<Other structural units>
The crosslinked polymer is a structural unit derived from other ethylenically unsaturated monomers copolymerizable with the component (a) and the component (b) (hereinafter, also referred to as “component (c)”). Can be included. Examples of the component (c) include 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. Among these, as the component (c), a structural unit derived from a nonionic ethylenically unsaturated monomer is preferable from the viewpoint of obtaining an electrode having good bending resistance.

The ratio of the component (c) can be 0% by mass or more and 40% by mass or less with respect to all the structural units of the crosslinked polymer. The ratio of the component (c) may be 1% by mass or more and 30% by mass or less, or 5% by mass or more and 20% by mass or less. Like the component (b), the component (c) can improve the binding property with the active material. Further, when the component (c) is contained in an amount of 1% by mass or more with respect to all the structural units of the crosslinked polymer, a mixture layer having higher flexibility can be obtained, so that it is easy to obtain an electrode having excellent bending resistance. Further, since the affinity for the electrolytic solution is improved, the effect of improving the lithium ion conductivity can be expected.

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

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, and 2-ethylhexyl (meth) acrylate. Meta) Acrylic acid alkyl ester compound;
(Meta) Acrylic acid aralkyl ester compounds such as (meth) phenyl acrylate, (meth) phenylmethyl acrylate, (meth) phenylethyl acrylate;
(Meta) Acrylic Acid Alkoxy Alkyl Ester Compounds such as 2-Methoxyethyl (Meta) Acrylic Acid and ethoxyethyl (Meta) Acrylic Acid;
Examples thereof include (meth) acrylic acid hydroxyalkyl ester compounds such as (meth) hydroxyethyl acrylate, (meth) hydroxypropyl acrylate and (meth) hydroxybutyl acrylate, and one of them is used alone. It may be used in combination of 2 or more types. From the viewpoint of adhesion to the active material and cycle characteristics, the (meth) acrylic acid aralkyl ester compound can be preferably used.

From the viewpoint of further improving lithium ion conductivity and high rate characteristics, compounds having an ether bond such as (meth) acrylate alkoxyalkyls such as 2-methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate are preferable. , 2-Methoxyethyl (meth) acrylate is more preferred.

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

The crosslinked polymer may be a salt. The type of salt is not particularly limited, but is limited to alkali metal salts such as lithium, sodium and potassium; alkaline earth metal salts such as calcium salt and barium salt; other metal salts such as magnesium salt and aluminum salt; ammonium salt and organic. Examples include amine salts. Among these, alkali metal salts and magnesium salts are preferable, and alkali metal salts are more preferable, from the viewpoint that adverse effects on battery characteristics are unlikely to occur. Particularly preferred alkali metal salts are lithium salts and sodium salts. From the viewpoint of low temperature characteristics, lithium salts are suitable.

<Aspects of crosslinked polymer>
The cross-linking method in the cross-linked polymer of the present invention 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. 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 a plurality of 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) acrylates; trimethylol propanetri (meth) acrylates, tri (meth) acrylates of modified trimethylol propaneethylene oxide oxides, glycerin tri (meth) acrylates, pentaerythritol tris (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, tetraallyloxyetane, and polyallyl saccharose; diallyl phthalate and the like. Polyfunctional allyl compound; Polyfunctional vinyl compound such as divinylbenzene and the like can be mentioned.

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

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

The hydrolyzable silyl group-containing vinyl monomer is not particularly limited as long as it is a vinyl monomer having at least one hydrolyzable silyl group. For example, vinyl silanes such as vinyl trimethoxysilane, vinyl triethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilanen; silyls such as trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate, methyldimethoxysilylpropyl acrylate and the like. Group-containing acrylic acid esters; silyl group-containing methacrylic 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 crosslinked polymer is crosslinked by a crosslinkable monomer, the amount of the crosslinkable monomer used is the total amount of the monomers other than the crosslinkable monomer (non-crosslinkable monomer). On the other hand, it is preferably 0.02 to 0.7 mol%, more preferably 0.03 to 0.4 mol%. When the amount of the crosslinkable monomer used is 0.02 mol% or more, it is preferable in that the binding property and the stability of the mixture layer slurry are improved. If it is 0.7 mol% or less, the stability of the crosslinked polymer tends to be high.

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

The crosslinked polymer of the present invention or a salt thereof has a degree of neutralization based on the carboxyl group of the crosslinked polymer of 80 to 100 mol%, and the particle size when dispersed in water is the volume-based median diameter. It is preferably in the range of 0.1 to 10 μm. A more preferable range of the particle size is 0.2 to 5.0 μm, and a more preferable range is 0.5 to 3.0 μm. When the particle size is in the range of 0.1 to 10 μm, it is uniformly present in the mixture layer composition in a suitable size, so that the mixture layer composition is highly stable and exhibits excellent binding properties. It becomes possible to do. If the particle size exceeds 10 μm, the binding property may be insufficient as described above. On the other hand, when the particle size is less than 0.1 μm, there is concern from the viewpoint of stable manufacturability.

If the crosslinked polymer is unneutralized or has a neutralization degree of less than 80 mol%, neutralize it to a neutralization degree of 80 to 100 mol% with an alkali metal hydroxide or the like, and measure the particle size when dispersed in water. do it. In general, the crosslinked polymer or a salt thereof often exists as agglomerated particles in which primary particles are associated and aggregated in the state of powder or solution (dispersion liquid). When the particle size when dispersed in water is in the above range, the crosslinked polymer or a salt thereof has extremely excellent dispersibility, and is neutralized to a degree of neutralization of 80 to 100 mol% to be water. By dispersing, the agglomerated particles are disintegrated, and even if it is a dispersion of almost primary particles or a secondary agglomerate, the particle size is within the range of 0.1 to 10 μm, and a stable dispersed state is formed. be.

In general, the longer the length of the polymer chain (primary chain length) of the crosslinked polymer, the greater the toughness, the higher the binding property, and the higher the viscosity of the aqueous dispersion. Further, the crosslinked polymer (salt) obtained by subjecting a polymer having a long primary chain length to a relatively small amount of crosslinks exists as a microgel body swollen in water in water. In the composition for the electrode mixture layer of the present invention, the thickening effect and the dispersion stabilizing effect are exhibited by the interaction of the microgel bodies. The interaction of microgels varies depending on the degree of water swelling of the microgels and the strength of the microgels, which are affected by the degree of cross-linking of the crosslinked polymer. If the degree of cross-linking is too low, the strength of the microgel may be insufficient, and the dispersion stabilizing effect and the binding property may be insufficient. On the other hand, if the degree of cross-linking is too high, the degree of swelling of the microgel may be insufficient, and the dispersion stabilizing effect and the binding property may be insufficient. That is, it is desirable that the crosslinked polymer is a microcrosslinked polymer obtained by appropriately cross-linking a polymer having a sufficiently long primary chain length.

The crosslinked polymer or a salt thereof is neutralized with an acid group such as a carboxyl group derived from an ethylenically unsaturated carboxylic acid monomer so that the degree of neutralization is 20 to 100 mol% in the mixture layer composition. It is preferable to use it as an embodiment of a salt. The degree of neutralization is more preferably 50 to 100 mol%, further preferably 60 to 95 mol%. 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 measured by IR measurement of the crosslinked polymer or a salt thereof after drying at 80 ° C. for 3 hours under reduced pressure conditions, and the peak derived from the C = O group of the carboxylic acid and the C = of the carboxylic acid Li =. It can be confirmed from the intensity ratio of the peak derived from the O group.

<Method for producing crosslinked polymer or salt thereof>
As the crosslinked polymer, known polymerization methods such as solution polymerization, precipitation polymerization, suspension polymerization, and reverse phase emulsion polymerization can be used, but in terms of productivity, precipitation polymerization and suspension polymerization (reverse phase polymerization) can be used. (Suspension polymerization) is preferable. The precipitation polymerization method is more preferable in that better performance can be obtained in terms of binding property and the like.
Precipitation polymerization is a method for producing a polymer by carrying out a polymerization reaction in a solvent that dissolves an unsaturated monomer as a raw material but does not substantially dissolve the polymer to be produced. As the polymerization progresses, the polymer particles become larger due to aggregation and growth, and a dispersion liquid of the polymer particles in which the primary particles of several tens of nm to several hundred 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 aggregation is suppressed is also called dispersion polymerization.

In the case of precipitation polymerization, a solvent selected from water, various organic solvents and the like can be used as the polymerization solvent in consideration of the type of the monomer to be 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, acetonitrile and tetrahydrofuran, as well as benzene, ethyl acetate, dichloroethane, n-hexane, cyclohexane and n-heptane. 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 polymer fine particles are difficult to secondary agglomerate (or even if secondary agglomeration occurs, they dissolve in the aqueous medium. Acetonitrile is preferable because it is easy), a polymer having a small chain transfer constant and a large degree of polymerization (primary chain length) can be obtained, and it is easy to operate during step neutralization described later.

Similarly, in order to allow the neutralization reaction to proceed stably and rapidly 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 10.0% by mass, more preferably 0.1 to 5.0% by mass, still more preferably 0.1 to 1 by mass, based on the total mass of the medium. It is 0.0% by mass. If the proportion of the highly polar solvent is 0.05% by mass or more, the effect on the neutralization reaction is recognized, and if it is 10.0% by mass or less, no adverse effect on the polymerization reaction is observed. Further, in the polymerization of a 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.

In this production method, the ethylenically unsaturated carboxylic acid monomer from which the component (a) is derived is 50% by mass or more and 99% by mass or less, and the alicyclic structure-containing ethylenically unsaturated monomer from which the component (b) is derived. It is preferable to include a polymerization step of precipitating and polymerizing a monomer component containing 1% by mass or more and 50% by mass or less of the weight. By the polymerization step, the crosslinked polymer contains 50 to 99% by mass of the structural unit (component (a)) derived from the ethylenically unsaturated carboxylic acid monomer, and the alicyclic structure-containing ethylenically unsaturated monomer. 1 to 50% by mass of the structural unit (component (b)) derived from the above is introduced. The amount of the ethylenically unsaturated carboxylic acid monomer used is, for example, 60% by mass or more and 98% by mass or less, and for example, 70% by mass or more and 95% by mass or less, and for example, 80% by mass or more and 90% by mass or less. It is less than mass%. The amount of the alicyclic structure-containing ethylenically unsaturated monomer used is, for example, 2% by mass or more and 40% by mass or less, and for example, 5% by mass or more and 30% by mass or less, and for example, 10%. It is 20% by mass or more and 20% by mass or less.
The ethylenically unsaturated carboxylic acid monomer may be in an unneutralized state or in a neutralized salt state. Further, it may be in the state of a partially neutralized salt in which a part of the ethylenically unsaturated carboxylic acid monomer used is neutralized. Since the polymerization rate is high, the degree of neutralization of the ethylenically unsaturated carboxylic acid monomer is preferably 10 mol% or less, preferably 5 mol%, in that a polymer having a high molecular weight and excellent binding properties can be obtained. The following is more preferable, and it is further preferable that it is unneutralized.

In this production method, in addition to the ethylenically unsaturated carboxylic acid monomer and the alicyclic structure-containing ethylenically unsaturated monomer, other ethylenically unsaturated monomers copolymerizable therewith are used as monomers. It may be included as an ingredient. Examples of the other ethylenically unsaturated monomer include 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, and a nonionic ethylenically. Examples include unsaturated monomers. The other ethylenically unsaturated monomer may be contained in an amount of 0% by mass or more and 40% by mass or less with respect to the total amount of the monomer components, or may be 1% by mass or more and 30% by mass or less, or 5% by mass. It may be 20% by mass or less. Among these, structural units derived from nonionic ethylenically unsaturated monomers are preferable from the viewpoint of obtaining an electrode having good bending resistance.

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

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

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

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

The preferable amount of the polymerization initiator to be 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 concentration of the monomer component at the time of polymerization is preferably high from the viewpoint of obtaining a polymer having a longer primary chain length. However, if the concentration of the monomer component is too high, the aggregation of the polymer particles tends to proceed, and it becomes difficult to control the heat of polymerization, which may cause the polymerization reaction to run away. Therefore, the monomer concentration at the start of polymerization is generally in the range of about 2 to 30% by mass, preferably in the range of 5 to 30% by mass.
The polymerization temperature is preferably 0 to 100 ° C, more preferably 20 to 80 ° C, although it depends on conditions such as the type and concentration of the monomer used. The polymerization temperature may be constant or may change during the polymerization reaction. The polymerization time is preferably 1 minute to 20 hours, more preferably 1 hour to 10 hours.

The crosslinked polymer dispersion obtained through the polymerization step can be obtained in a powder state by subjecting it to reduced pressure and / or heat treatment in the drying step and distilling off the solvent. At this time, prior to the drying step, for the purpose of removing unreacted monomers (and salts thereof), impurities derived from the initiator, etc., the polymerization step is followed by a solid-liquid separation step such as centrifugation and filtration, and water. , It is preferable to include a cleaning step using the same solvent as methanol or a polymerization solvent. When the above cleaning step is provided, even when the crosslinked polymer is secondarily aggregated, it is easily unraveled at the time of use, and the remaining unreacted monomer is removed, which is good in terms of binding property and battery characteristics. Shows excellent performance.

In this production method, when an unneutralized or partially neutralized salt is used as the ethylenically unsaturated carboxylic acid monomer, an alkaline compound is added to the polymer dispersion obtained in the polymerization step to neutralize the polymer. After (hereinafter, also referred to as “step neutralization”), the solvent may be removed in the 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 electrode mixture layer slurry to neutralize the polymer (hereinafter, “after”. It may also be called "neutralization"). Of the above, process neutralization is preferable because secondary aggregates tend to be easily disintegrated.

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

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

Among the above active materials, the lithium salt of the transition metal oxide is mainly used as the positive electrode active material, and for example, layered rock salt type and spinel type lithium-containing metal oxides can be used. Specific compounds of the positive electrode active material of layered rock-salt, lithium cobaltate, lithium nickelate, _{and, NCM {Li (Ni x,} Co y, Mn z), x + y + z = 1} called ternary and NCA {Li (Ni _1-ab Co _a Al _b )} and the like can be mentioned. Examples of the spinel-type positive electrode active material include lithium manganate and the like. Phosphate, silicate, sulfur and the like are used in addition to the oxide, and examples of the phosphate 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 exhibits alkalinity 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), 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 an unneutralized or partially neutralized crosslinked polymer as the binder. The amount of the unneutralized or partially neutralized crosslinked polymer used should be such that the amount of unneutralized carboxyl groups in the crosslinked polymer is equal to or greater than the amount of alkali eluted from the active material. Is preferable.

Since all positive electrode active materials have low electrical conductivity, they are generally used by adding a conductive auxiliary agent. Examples of the conductive auxiliary agent include carbon-based materials such as carbon black, carbon nanotubes, carbon fibers, graphite fine powder, and carbon fibers. Among these, carbon black, carbon nanotubes, and carbon fibers are easy to obtain excellent conductivity. , Are preferred. Further, as the carbon black, Ketjen black and acetylene black are preferable. As the conductive auxiliary agent, one of the above may be used alone, or two or more of them may be used in combination. The amount of the conductive auxiliary agent used can be, for example, 0.2 to 20% by mass, and for example, 0.2 to 10% by mass, based on the total amount of the active material from the viewpoint of achieving both conductivity and energy density. It can be mass%. Further, as the positive electrode active material, a material having a surface coating 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, graphite such as natural graphite and artificial graphite, and graphite. Hard carbon is more preferred. Further, in the case of graphite, spherical graphite is preferably used from the viewpoint of battery performance, and the preferable range of the particle size thereof is, for example, 1 to 20 μm, and for example, 5 to 15 μm. Further, in order to increase the energy density, a metal such as silicon or tin that can occlude lithium, a metal oxide, or the like can be used as the negative electrode active material. Among them, silicon has a higher capacity than graphite, and is an active material made of a silicon-based material such as silicon, a silicon alloy, and a silicon oxide such as silicon monoxide (SiO) (hereinafter, also referred to as "silicon-based active material"). Can be used. However, while the silicon-based active material has a high capacity, the volume change due to charge / discharge is large. Therefore, it is preferable to use it in combination with the above carbon-based active material. In this case, if the amount of the silicon-based active material is large, the electrode material may be disintegrated and the cycle characteristics (durability) may be significantly deteriorated. From such a viewpoint, when a silicon-based active material is used in combination, the amount used is, for example, 60% by mass or less, and for example, 30% by mass or less, based on the carbon-based active material.

The binder containing the crosslinked polymer of the present invention is a structural unit (component (a)) in which the crosslinked polymer is derived from an ethylenically unsaturated carboxylic acid monomer, and an alicyclic structure-containing ethylenically unsaturated monomer. It has both of the derived structural units (component (b)). Here, the component (a) has a high affinity for a silicon-based active material and exhibits good binding properties. Further, as described above, the component (b) has an excellent effect of improving the binding property to the carbon-based active material and the like. Therefore, the binder of the present invention exhibits excellent binding properties even when a high-capacity type active material using a carbon-based active material and a silicon-based active material in combination is used, and thus the durability of the obtained electrode can be improved. It is also considered to be effective.

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

When the composition for the non-aqueous electrolyte secondary battery electrode mixture layer is in a slurry state, the amount of the active material used is, for example, in the range of 10 to 75% by mass with respect to the total amount of the composition, and for example, 30 to 30 to It is in the range of 65% by mass. 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 composition can be ensured, and a uniform mixture layer can be formed.

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

The composition for the electrode mixture layer of the non-aqueous electrolyte secondary battery 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 solvents such as tetrahydrofuran and N-methylpyrrolidone. It may be used as a mixed solvent with. 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 for the electrode mixture layer is put into a slurry state that can be applied, the content of the medium containing water in the entire composition is from the viewpoint of the coatability of the slurry, the energy cost required for drying, and the productivity. Therefore, it can be, for example, in the range of 25 to 90% by mass, and can be, for example, 35 to 70% by mass. Further, in the case of a pressable wet powder state, the content of the medium can be, for example, in the range of 3 to 40% by mass from the viewpoint of the uniformity of the mixture layer after pressing, and for example, 10 It can be in the range of ~ 30% by mass.

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

The styrene / butadiene latex is 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. Shows an aqueous dispersion. 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 60% by mass, and for example, 30 to 50, mainly from the viewpoint of binding property. It can be in the range of% by mass.

Examples of the aliphatic conjugated diene-based monomer include 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 2-chloro-1,3-in addition to 1,3-butadiene. 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 binder binding property 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, the styrene / butadiene-based latex includes nitrile group-containing monomers such as (meth) acrylonitrile and (meth) as other monomers in order to further improve the performance such as binding property. ) A carboxyl group-containing monomer such as acrylic acid, itanconic acid, and maleic acid 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, and can be, for example, in the range of 0 to 20% by mass.

The composition for a non-aqueous electrolyte secondary battery electrode mixture layer of the present invention contains the above-mentioned active material, water and a binder as essential constituents, and by mixing the respective components using known means. can get. The mixing method of each component is not particularly limited, and a known method can be adopted. However, after dry-blending powder components such as an active material, a conductive additive, and crosslinked polymer particles which are binders, water is used. A method of mixing with a dispersion medium such as the above and dispersing and kneading is preferable. When the composition for the electrode mixture layer is obtained in a slurry state, it is preferable to finish the slurry without dispersion failure or aggregation. As the mixing means, a known mixer such as a planetary mixer, a thin film swirl mixer, or a self-revolving mixer can be used, but a thin film swirl mixer is used because a good dispersion state can be obtained in a short time. It is preferable to do this. When using a thin film swirl mixer, it is preferable to pre-disperse in advance with a stirrer such as a disper. The viscosity of the slurry can be, for example, 500 to 100,000 mPa · s, or 1,000 to 50,000 mPa · s, for example, as the B-type viscosity at 60 rpm. can.

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

<Electrodes for non-aqueous electrolyte secondary batteries>
The electrode for a non-aqueous electrolyte secondary battery of the present invention comprises a mixture layer formed from the composition for the electrode mixture layer on the surface of a current collector such as copper or aluminum. The mixture layer is formed by applying the composition for an electrode mixture layer of the present invention to the surface of a current collector and then drying and removing a medium such as water. The method for applying the mixture layer 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 are adopted. be able to. 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 die press, a roll press or the like. By compressing, the active material and the binder are 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, and the thickness of the mixture layer after compression is generally about 4 to 200 μm.

By providing the electrode for the non-aqueous electrolyte secondary battery of the present invention with a separator and a non-aqueous electrolyte solution, a non-aqueous electrolyte secondary battery can be manufactured.
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 film having good ion permeability and mechanical strength. As a specific material, polyolefins such as polyethylene and polypropylene, polytetrafluoroethylene and the like can be used.

As the non-aqueous electrolyte solution, known ones generally used for non-aqueous electrolyte secondary batteries can be used. Specific examples of the solvent include cyclic carbonates having a high dielectric constant and a high dissolving ability of an electrolyte such as propylene carbonate and ethylene carbonate, and chain carbonates having a low viscosity such as ethylmethyl carbonate, dimethyl carbonate and diethyl carbonate. , These can be used alone or as a mixed solvent. The non-aqueous electrolyte solution is used by dissolving lithium salts such as _{LiPF 6} , LiSbF ₆ , LiBF ₄ , LiClO ₄ , and LiAlO _{4 in these solvents.} The non-aqueous electrolyte 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 non-aqueous electrolyte secondary battery electrode binder disclosed in the present specification exhibits excellent adhesion to the electrode material and excellent adhesion to the current collector in the mixture layer. Therefore, it is expected that the non-aqueous electrolyte secondary battery equipped with the electrodes obtained by using the above binder can secure good integrity and show good durability (cycle characteristics) even after repeated charging and discharging. Therefore, it is suitable for an in-vehicle secondary battery or the like.

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.

≪Manufacturing of crosslinked polymer salt≫
(Production Example 1: Production of crosslinked polymer salt R-1)
A reactor equipped with a stirring blade, a thermometer, a reflux condenser and a nitrogen introduction tube was used for the polymerization.
In the reactor, 877 parts of acetonitrile, 3.50 parts of ion-exchanged water, 90 parts of acrylic acid (hereinafter referred to as "AA"), 10 parts of isobornyl acrylate (hereinafter referred to as "IBXA") and pentaerythritol triallyl ether (Daiso). Made by the company, trade name "Neoallyl P-30") 0.60 copies 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., when 0.0625 part of V-65 was added as a polymerization initiator, white turbidity was observed in the reaction solution, and this point was set as the polymerization initiation point. The polymerization reaction was continued while adjusting the outside temperature (water bath temperature) to maintain the inside temperature at 55 ° C., and when 6 hours had passed from the polymerization start point, 0.1 part of V-65 was added to adjust the inside temperature. The temperature was raised to 65 ° C. The internal temperature is maintained at 65 ° C., cooling of the reaction solution is started 12 hours after the reaction start point, and after the internal temperature drops to 25 ° C., lithium hydroxide monohydrate (hereinafter, “LiOH”) is started.・ H ₂49.9 parts of powder of "O") was added. After the addition, stirring was continued at room temperature for 12 hours to obtain a slurry-like polymerization reaction solution in which particles of the crosslinked polymer salt R-1 (Li salt, neutralization degree 95 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 and removing the supernatant was repeated twice. The sediment was recovered and dried at 80 ° C. for 3 hours under reduced pressure conditions to remove volatile components to obtain a powder of the crosslinked polymer salt R-1. Since the crosslinked polymer salt R-1 has hygroscopicity, it was sealed and stored in a container having a water vapor barrier property. The powder of the crosslinked polymer salt R-1 was measured by IR, and the degree of neutralization was determined from the intensity ratio of the peak derived from the C = O group of the carboxylic acid and the peak derived from the C = O of the carboxylic acid Li. It was 95 mol%, which was equal to the value calculated from.

(Measurement of average particle size of crosslinked polymer salt R-1 (Li neutralized product) in aqueous medium)
Weighing 0.25 g of the crosslinked polymer salt R-1 powder obtained above and 49.75 g of ion-exchanged water in a 100 cc container, a rotating / revolving stirrer (Sinky, Awatori Rentaro AR-250) ). 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 the crosslinked polymer salt R-1 (neutralization degree 95 mol%). A hydrogel swollen in water was prepared.
Next, the particle size distribution of the hydrogel was measured with a laser diffraction / scattering particle size distribution meter (Microtrac MT-3300EX2 manufactured by Nikkiso Co., Ltd.) using ion-exchanged water as a dispersion medium. When an excessive amount of the dispersion medium is circulated with respect to the hydrogel, an amount of the hydrogel that can obtain an appropriate scattered light intensity is added, and the dispersion medium is added, the particle size distribution shape measured after a few minutes is obtained. Stable. As soon as the stability was confirmed, the particle size distribution was measured based on the volume, and the median diameter (D50) was determined as the average particle diameter. It was 1.6 μm.

(Production Examples 2 to 16: Production of crosslinked polymers (salts) R-2 to R-16)
The same operation as in Production Example 1 was carried out except that the amount of each raw material charged was as shown in Table 1 or Table 2, to obtain powdery crosslinked polymers (salts) R-2 to R-16. R-14 to R-16 are unneutralized crosslinked polymers. Each crosslinked polymer (salt) was sealed and stored in a container having a water vapor barrier property.
For each of the obtained polymers (salts), the average particle size in an aqueous medium was measured in the same manner as in Production Example 1. The results are shown in Table 1 or Table 2. In the Production Example 5, by using a 48% NaOH instead of LiOH · H ₂ O. A crosslinked polymer Na salt (neutralization degree 95 mol%) was obtained. Further, the crosslinked polymer R-14~R-16 unneutralized is added LiOH · H ₂ O corresponding to the degree of neutralization 95 mol%, in an aqueous medium after the preparation of the crosslinked polymer salt The average particle size was measured. On the other hand, since the crosslinked polymer salt R-11 is highly swelled in water, the diffracted / scattered light required for the particle size measurement could not be obtained, and the measurement could not be performed.

In addition to the crosslinked polymers (salts) obtained in Production Examples 1 to 16 above, the average particle size of commercially available polymers was also measured in an aqueous medium. Details are shown below.

(Evaluation Example 1: Measurement of average particle size of commercially available non-crosslinked polymer Na salt)
An attempt was made to measure the average particle size in an aqueous medium of commercially available non-crosslinked sodium polyacrylate (Toagosei, Alonbis SX, completely neutralized product, Mw: 1 million or more) by the same operation as in Synthesis Example 1. In the case of non-crosslinked sodium polyacrylate, it could not be measured because it did not form a hydrogel. It is presumed that the diffracted / scattered light required for the measurement cannot be obtained.

(Evaluation Example 2: Measurement of average particle size of commercially available crosslinked polymer Na salt)
For commercially available cross-linked polyacrylic acid Na (manufactured by Toagosei, Leosic 270, completely neutralized product), an attempt was made to measure the average particle size in an aqueous medium by the same operation as in Synthesis Example 1, but the particles were highly swollen in water. Therefore, the diffracted / scattered light required for the particle size measurement could not be obtained, and the measurement could not be performed.

(Evaluation Example 3: Measurement of average particle size of commercially available crosslinked polymer)
For commercially available cross-linked polyacrylic acid (Carbopol 980, unneutralized product manufactured by Lubrizol), LiOH · H ₂ O corresponding to a neutralization degree of 95 mol% is added to prepare a cross-linked polymer salt, and then water is used. The average particle size in the medium was measured. However, due to the high degree of swelling in water, the diffracted / scattered light required for particle size measurement could not be obtained, and measurement was not possible.

Details of the compounds used in Tables 1 and 2 are shown below.
AA: Acrylic acid IBXA: Isobornyl acrylate FA-511AS: Dicyclopentenyl acrylate (Funkril FA-511AS, manufactured by Hitachi Chemical Co., Ltd.)
FA-513AS: Dicyclopentanyl acrylate (Funkril FA-513AS, manufactured by Hitachi Chemical Co., Ltd.)
CHDMMA: 1,4-Cyclohexanedimethanol monoacrylate (manufactured by Nihon Kasei)
CHA: Cyclohexyl acrylate CHMA: Cyclohexyl methacrylate SA: Stearyl acrylate AMA: Allyl methacrylate P-30: Pentaerythritol triallyl ether (manufactured by Daiso, trade name "Neoallyl P-30")
T-20: Trimethylolpropanediallyl ether (manufactured by Daiso, trade name "Neoallyl T-20")
AcN: Acetonitrile MeOH: Methanol V-65: 2,2'-azobis (2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd.)
ACVA: 4,4'-azobiscyanovaleric acid (manufactured by Otsuka Chemical Co., Ltd.)

(Evaluation of negative electrode)
Example 1-1
Graphite was used as the active material, and the crosslinked polymer salt R-1 was used as the binder.
100 parts of natural graphite (manufactured by Nippon Graphite Co., Ltd., trade name "CGB-10") and 3.2 parts of powdered crosslinked polymer Li salt R-1 were weighed and mixed well in advance. Next, 155 parts of ion-exchanged water was added and pre-dispersed with a disper, and then this dispersion was carried out for 15 seconds under the condition of a peripheral speed of 20 m / sec using a thin film swirl mixer (FM-56-30 manufactured by Primix Corporation). By doing so, a slurry-like composition for a negative electrode mixture layer having a solid content of 40% was obtained.
Using a variable applicator, apply the composition for the mixture layer on a copper foil (manufactured by Nippon Foil Co., Ltd.) with a thickness of 20 μm, and dry it in a ventilation dryer at 100 ° C for 10 minutes to mix the mixture. Formed a layer. Then, it was rolled so that the thickness of the mixture layer was 70 ± 5 μm and the packing density was 1.70 ± 0.05 g / cm ^3.

As a result of visually observing the appearance of the obtained mixture layer and evaluating the coatability based on the following criteria, it was judged to be "○".
<Criteria for determining coatability>
◯: No abnormal appearance such as uneven streaks or bumps is observed on the surface.
Δ: Slightly abnormal appearance such as streaks and bumps is observed on the surface.
X: Appearance abnormalities such as streaks and bumps are noticeably observed on the surface.

<90 ° peel strength (bonding property)>
The negative electrode obtained above was cut into strips having a width of 25 mm to prepare a sample for a peeling test. The mixture layer surface of the above sample was attached to a double-sided tape fixed on a horizontal surface, peeled by 90 ° at a tensile speed of 50 mm / min, and the peel strength between the mixture layer and the copper foil was measured. The peel strength was as high as 16.0 N / m, which was good.

<Bending resistance>
Evaluation was performed using an electrode sample similar to the above 90 ° peel strength. The electrode sample was wound around a SUS rod having a diameter of 2.0 mm, the state of the curved mixture layer was observed, and the bending resistance was evaluated based on the following criteria. As a result, it was judged to be “◯”. The fact that no abnormal appearance is observed in this evaluation means that defective products are generated due to cracks, cracks, or chipping in the electrode mixture layer during the process of winding or processing the electrodes during battery manufacturing. It means that there is little risk of doing so.
◯: No abnormal appearance was observed in the mixture layer.
Δ: Fine cracks are observed in the mixture layer.
X: Clear cracks are observed in the mixture layer. Alternatively, a part of the mixture layer is peeled off.

Examples 1-2-1-10 and Comparative Examples 1-1-1-5
A mixture layer composition was prepared by performing the same operation as in Example 1-1 except that the crosslinked polymer salt used as the binder was used as shown in Table 3 or Table 4, and the coating property and 90 ° peel strength were obtained. And bending resistance were evaluated. In Comparative Examples 1-3 and 1-4, streaks were severely uneven during slurry coating, and an evaluable mixture layer could not be obtained. The results are shown in Table 3 or Table 4.

Example 2-1
Graphite was used as the active material, and a mixture of the crosslinked polymer salt R-1 and styrene / butadiene latex (SBR) was used as the binder.
100 parts of natural graphite (manufactured by Nippon Graphite Co., Ltd., trade name "CGB-10") and 2.2 parts of powdered crosslinked polymer Li salt R-1 were weighed and mixed well in advance. Next, 125 parts of ion-exchanged water was added and pre-dispersion was performed with a disper. After that, 2.06 parts (1.0 part as solid content) of styrene / butadiene latex (SBR) was added, and a peripheral speed of 20 m / sec was used using a thin film swirl mixer (FM-56-30 manufactured by Primix Corporation). By performing this dispersion for 15 seconds under the conditions, a slurry-like composition for a negative electrode mixture layer having a solid content of 45% was obtained. As the SBR, JSR's trade name "TRD2001" (active ingredient 48.5%, pH 7.8) was used.
Using a variable applicator, apply the composition for the mixture layer on a copper foil (manufactured by Nippon Foil Co., Ltd.) with a thickness of 20 μm, and dry it in a ventilation dryer at 100 ° C for 10 minutes to mix the mixture. Formed a layer. Then, it was rolled so that the thickness of the mixture layer was 70 ± 5 μm and the packing density was 1.60 ± 0.05 g / cm ^3. Similar to Example 1-1, coatability, 90 ° peel strength and bending resistance were evaluated. The results are shown in Table 5.

Example 2-2 and Comparative Examples 2-1 to 2-2
A mixture layer composition was prepared by performing the same operation as in Example 2-1 except that the crosslinked polymer salt used as the binder was used as shown in Table 5, and the coatability, 90 ° peel strength and bending resistance were obtained. Gender was evaluated. The results are shown in Table 5.

Example 3-1
Silicon particles and graphite were used as the negative electrode active material, and the crosslinked polymer salt R-1 was used as the binder.
20 parts of silicon particles (Sigma-Aldrich, Si nanopowder, particle diameter <100 nm), 80 parts of natural graphite (manufactured by Nippon Graphite Co., Ltd., trade name "CGB-10"), planetary ball mill (manufactured by FRITSCH Co., Ltd., P-5) Was stirred at 300 rpm for 1 hour. 3.2 parts of the powdered crosslinked polymer Li salt R-1 is weighed in the obtained mixture, mixed well in advance, 125 parts of ion-exchanged water is added, and predispersion is performed with a disper, and then a thin film swirl type is used. This dispersion was carried out for 15 seconds under the condition of a peripheral speed of 20 m / sec using a mixer (FM-56-30 manufactured by Primix Corporation) to obtain a slurry-like composition for a negative electrode mixture layer.
Using a variable applicator, apply the composition for the mixture layer on a copper foil (manufactured by Nippon Foil Co., Ltd.) with a thickness of 20 μm, and dry it in a ventilation dryer at 100 ° C for 15 minutes to mix the mixture. Formed a layer. Then, it was rolled so that the thickness of the mixture layer was 70 ± 5 μm and the packing density was 1.70 ± 0.05 g / cm ^3. Similar to Example 1-1, coatability, 90 ° peel strength and bending resistance were evaluated. The results are shown in Table 6.

Examples 3-3, Comparative Examples 3-1 and 3-3
A mixture layer composition was prepared by performing the same operation as in Example 3-1 except that the crosslinked polymer salt used as the binder was used as shown in Table 6, and the coatability, 90 ° peel strength and bending resistance were obtained. Gender was evaluated. The results are shown in Table 6.

Example 3-2
Silicon particles and graphite were used as the negative electrode active material, and a mixture of the crosslinked polymer salt R-1 and styrene / butadiene latex (SBR) was used as the binder.
20 parts of silicon particles (Sigma-Aldrich, Si nanopowder, particle diameter <100 nm), 80 parts of natural graphite (manufactured by Nippon Graphite Co., Ltd., trade name "CGB-10"), planetary ball mill (manufactured by FRITSCH Co., Ltd., P-5) Was stirred at 300 rpm for 1 hour. 2.2 parts of the powdered crosslinked polymer Li salt R-1 was weighed in the obtained mixture, mixed well in advance, and then 100 parts of ion-exchanged water was added and pre-dispersed with a disper. After that, 2.06 parts of TRD2001 (SBR) (1.0 part as solid content) was added, and this dispersion was performed under the condition of a peripheral speed of 20 m / sec using a thin film swirl mixer (FM-56-30 manufactured by Primix Corporation). Was carried out for 15 seconds to obtain a slurry-like composition for a negative electrode mixture layer.
The obtained composition for the negative electrode mixture layer was evaluated for coatability, 90 ° peel strength and bending resistance by the same method as in Example 3-1. The results are shown in Table 6.

Example 3-4, Comparative Example 3-2, 3-4
A mixture layer composition was prepared by performing the same operation as in Example 3-2 except that the crosslinked polymer salt used as the binder was used as shown in Table 6, and the coatability, 90 ° peel strength and bending resistance were obtained. Gender was evaluated. The results are shown in Table 6.

(Evaluation of positive electrode)
Example 4-1
Lithium, nickel, cobalt, manganese, oxide (NCM) was used as the positive electrode active material, acetylene black (AB) was used as the conductive auxiliary agent, and the crosslinked polymer R-14 was used as the binder.
Weigh 93 parts of NCM111 (manufactured by Toda Kogyo, NM-3050), 7 parts of AB (manufactured by Electrochemical Industry, HS-100), and 1.5 parts of the powdered crosslinked polymer R-14 (unneutralized). After mixing well in advance, 101 parts of ion-exchanged water was added and pre-dispersion was performed with a disper, and then a thin film swirl mixer (FM-56-30 manufactured by Primix Corporation) was used under the condition of a peripheral speed of 20 m / sec. The dispersion was carried out for 15 seconds to obtain a slurry-like composition for a positive electrode mixture layer. In the composition for the positive electrode mixture layer, lithium ions are eluted from the NCM (exchanged with protons in water and alkalized), so that some (or all) of the carboxyl groups of the crosslinked polymer R-14 are medium. It is combined to form a lithium salt. The pH of the composition for the positive electrode mixture layer was 8.9.
Using a variable applicator, apply the composition for the mixture layer on an aluminum foil (manufactured by Nippon Foil Co., Ltd.) with a thickness of 15 μm, and dry it in a ventilation dryer at 100 ° C for 10 minutes to mix the mixture. Formed a layer. Then, it was rolled so that the thickness of the mixture layer was 80 ± 5 μm and the packing density was 2.90 ± 0.05 g / cm ^3. Similar to Example 1-1, coatability, 90 ° peel strength and bending resistance were evaluated. The results are shown in Table 7.

Examples 4-2 and Comparative Examples 4-1 to 4-2
A mixture layer composition was prepared by performing the same operation as in Example 4-1 except that the crosslinked polymer used as a binder was used as shown in Table 7, and the coatability, 90 ° peel strength and bending resistance were prepared. Was evaluated. The results are shown in Table 7.

Each example is an electrode mixture layer composition containing a binder for a non-aqueous electrolyte secondary battery electrode belonging to the present invention, and an electrode is produced using the same. The coatability of each mixture layer composition (slurry) is good, and the peel strength between the mixture layer of the obtained electrode and the current collector is high, and the bondability is excellent. Was shown. It was also confirmed that the bending resistance of the electrodes was at a satisfactory level.
Further, in the case of a crosslinked polymer (salt) containing a structural unit derived from an alicyclic structure-containing ethylenically unsaturated monomer having an acryloyl group as a polymerizable functional group, a methacryloyl-type alicyclic structure-containing ethylenically unsaturated simple substance is used. It showed higher peel strength as compared with the crosslinked polymer using the weight (Example 1-10).

On the other hand, the crosslinked polymers (salts) R-11, R-12, R-16 and each of the commercially available polymers have a polyacrylic acid structure. In the binder containing such a crosslinked polymer (salt), the peel strength of the mixture layer was low and the bending resistance of the electrode was insufficient (Comparative Examples 1-1, 1-2, 1-5, etc.). .. Further, the crosslinked polymer (salt) R-13 does not have a structural unit derived from the alicyclic structure-containing ethylenically unsaturated monomer, but the fluidity of the composition for the mixture layer is poor. The result was inferior in coatability.

The binder for a non-aqueous electrolyte secondary battery electrode of the present invention exhibits excellent binding properties in the mixture layer. Therefore, the non-aqueous electrolyte secondary battery provided with the electrode obtained by using the above binder has a high rate. It is expected to show good durability (cycle characteristics) even after repeated charging and discharging in, and is expected to be applied to in-vehicle secondary batteries. It is also useful for the use of active materials containing silicon or for thickening the electrode mixture layer, and is expected to contribute to increasing the capacity of batteries.
Further, the binder of the present invention can impart good bending resistance to the electrode mixture layer. Therefore, troubles during electrode manufacturing are reduced, which leads to improvement in yield.

Claims (13)

A binder for a non-aqueous electrolyte secondary battery electrode containing a crosslinked polymer or a salt thereof,
The crosslinked polymer has 50 to 99% by mass of a structural unit derived from an ethylenically unsaturated carboxylic acid monomer and a structural unit derived from an ethylenically unsaturated monomer containing an alicyclic structure with respect to all the structural units thereof. A binder for non-aqueous electrolyte secondary battery electrodes containing 1 to 50% by mass. The non-according to claim 1, wherein the crosslinked polymer has a particle size measured in an aqueous medium of 0.1 to 10 μm in terms of volume after being neutralized to a degree of neutralization of 80 to 100 mol%. Binder for water electrolyte secondary battery electrodes. The binder for a non-aqueous electrolyte secondary battery electrode according to claim 1 or 2, wherein the alicyclic structure-containing ethylenically unsaturated monomer has an acryloyl group as a polymerizable functional group. The crosslinked polymer is crosslinked with a crosslinkable monomer, and the amount of the crosslinkable monomer used is 0.02 to 0.7 mol% with respect to the total amount of the non-crosslinkable monomer. The binder for a non-aqueous electrolyte secondary battery electrode according to any one of claims 1 to 3. A method for producing a crosslinked polymer or a salt thereof used for a binder for a non-aqueous electrolyte secondary battery electrode.
A polymerization step of precipitating and polymerizing a monomer component containing 50 to 99% by mass of an ethylenically unsaturated carboxylic acid monomer and 1 to 50% by mass of a structural unit derived from an ethylenically unsaturated monomer containing an alicyclic structure. The method for producing the crosslinked polymer or a salt thereof. The crosslink according to claim 5, wherein the crosslinked polymer has a particle size measured in an aqueous medium after being neutralized to a degree of neutralization of 80 to 100 mol%, which is 0.1 to 10 μm in volume-based median diameter. A method for producing a polymer or a salt thereof. The method for producing a crosslinked polymer or a salt thereof according to claim 5 or 6, wherein a polymerization medium containing acetonitrile is used in the polymerization step. A drying step is provided after the polymerization step.
Any one of claims 5 to 7, further comprising a step of adding an alkaline compound to the polymer dispersion obtained by the polymerization step to neutralize the polymer after the polymerization step and before the drying step. The method for producing a crosslinked polymer or a salt thereof according to the above. The composition for a non-aqueous electrolyte secondary battery electrode mixture layer containing the binder, active material and water according to any one of claims 1 to 4. The composition for a non-aqueous electrolyte secondary battery electrode mixture layer according to claim 9, further comprising a styrene / butadiene latex as a binder. The composition for a water electrolyte secondary battery electrode mixture layer according to claim 9 or 10, which comprises a carbon-based material or a silicon-based material as the negative electrode active material. The composition for a water electrolyte secondary battery electrode mixture layer according to claim 9 or 10, which contains a lithium-containing metal oxide as a positive electrode active material. A non-aqueous electrolyte secondary battery electrode comprising a mixture layer formed from the composition for the non-aqueous electrolyte secondary battery electrode mixture layer according to any one of claims 9 to 12 on the surface of the current collector.