JP2024009777A - Binder for secondary battery electrode and use of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder for a lithium-ion secondary electrode that excels in dispersibility of electrode slurry and exhibits high cycle characteristics.

SOLUTION: The binder for a lithium-ion secondary electrode includes polymeric particles. The polymeric particles include a fragment polymer. In the fragment polymer, a ratio (B/A) of a maximum absorbance B from 1650 cm^-1 to 1750 cm^-1 to a maximum absorbance A from 1550 cm^-1 to 1650 cm^-1 in the absorption band in the infrared spectrum is 0 to 1.5.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a binder for secondary battery electrodes and its use.

Conventionally, in order to improve the cycle characteristics of lithium ion secondary batteries, attempts have been made to improve the binder used to form the electrode mixture layer. For example, polymers obtained from styrene, ethylenically unsaturated carboxylic acid esters, ethylenically unsaturated carboxylic acids, etc. (Patent Document 1), and styrene-butadiene-based polymers (Patent Document 2) have been proposed.

International Publication No. 2015/045522 International Publication No. 2013/191080

However, in either case, the dispersibility of the electrode slurry was not sufficient, and the cycle characteristics of the resulting lithium ion secondary battery were sometimes insufficient. Therefore, an object of the present invention is to provide a binder for lithium ion secondary battery electrodes (also referred to as a binder for lithium ion secondary electrodes) that has excellent dispersibility in electrode slurry and exhibits high cycle characteristics.

In order to achieve the above object, the present inventors conducted various studies and came up with the present invention. That is, the present invention is as follows.
[1] A binder for a lithium ion secondary electrode containing polymer particles,
The ratio (B/A) of the maximum absorbance B of 1650 cm ^-1 to 1750 cm ^-1 to the maximum absorbance A of 1550 cm ^-1 to 1650 cm ^-1 in the absorption band in the infrared spectrum of the polymer particles is 0 to 1. A binder for a lithium ion secondary electrode, comprising a fragment polymer having a composition of .5.
[2] The binder for a lithium ion secondary electrode according to [1], wherein the fragment polymer has a ratio of maximum absorbance B to maximum absorbance A (B/A) of 0 to 1.0.
[3] The binder for a lithium ion secondary electrode according to [1], wherein the polymer particles contain 0.1 to 60% by mass of the fragment polymer.
[4] The binder for a lithium ion secondary electrode according to [1] or [2], wherein the polymer particles have a core-shell structure.
[5] The binder for a lithium ion secondary electrode according to any one of [1] to [3], wherein the polymer particles have a volume average particle diameter of 0.01 to 5 μm.

According to the present disclosure, it is possible to provide a binder for secondary battery electrodes in which the slurry for electrodes has high dispersibility and excellent cycle characteristics.

The present invention will be explained in detail below. Note that a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

[binder]
The binder of the present disclosure has polymer particles.

<Polymer particles>
The polymer particles of the present disclosure may include particles with a single layer structure or particles with a multilayer structure, but preferably include particles with at least a multilayer structure. In the case of a multilayer structure, for example, it may be a core-shell particle composed of a core part and a shell part provided outside the core part. The core-shell structure tends to make it easier to uniformly disperse the negative electrode active material described below, and tends to further improve cycle characteristics when a binder containing the polymer particles is used in an electrode.

The polymer particles of the present disclosure preferably have a structural unit derived from a crosslinkable monomer. Note that in this specification, the structural unit derived from a crosslinkable monomer refers to a structural unit having the same structure as the structure formed by polymerization of the crosslinkable monomer, and usually, the structural unit derived from the crosslinkable monomer This is a structure in which the carbon-carbon double bond contained in is replaced by a carbon-carbon single bond and two bonds bonded to each carbon. Note that the structural unit derived from the crosslinkable monomer does not need to be a structural unit actually formed by polymerization of the crosslinkable monomer, but may be a structure formed by polymerization of the crosslinkable monomer. If the structure is the same as that of the crosslinkable monomer, even if it is a structural unit formed by a method other than polymerization (for example, a structural unit formed by a reaction after polymerization), it is derived from the crosslinkable monomer. Included in the structural unit.

The crosslinking monomer may be any monomer having crosslinking properties, such as a monomer having two or more ethylenically unsaturated bonds. The polyfunctional ethylenically unsaturated monomer is a monomer having two or more ethylenically unsaturated bonds at its terminal, that is, a monomer having two or more CH ₂ =C< groups. is preferred. For example, CH ₂ =CH- group, CH ₂ =CH-O- group, CH ₂ =CH-CH ₂ -O- group, CH ₂ =C(CH ₃ )-CH ₂ -O- group, CH ₂ =CH -CH ₂ -CH ₂ -O- group, CH ₂ =C(CH ₃ )-CH ₂ -CH ₂ -O- group, CH ₂ =CH-CO-O- group, CH ₂ =C(CH ₃ )- Examples include compounds containing two or more ethylenic carbon double bonds of one or more selected from CO--O- groups and CH ₂ ═CH--CO--NH- groups. The CH ₂ =CH- group etc. exemplified above may be bonded to a di- or trivalent or higher hydrocarbon group to form a crosslinkable monomer, or may be bonded to a polyhydric alcohol (polyhydric alkyl alcohol, polyether It is preferable to form a crosslinkable monomer by bonding to a group in which two or three or more hydroxyl groups (including compounds having two or more hydroxyl groups such as polyol) are substituted with a bond.

The crosslinkable monomer (hereinafter sometimes referred to as polyfunctional ethylenic monomer) preferably has a molecular weight of 50 or more and 1000 or less, more preferably 100 or more and 400 or less.

Examples of the crosslinkable monomer include hydrocarbon crosslinkable monomers, divinyl ether monomers, diallyl ether monomers, polyvalent (meth)acrylic acid esters, and the like.

Examples of the hydrocarbon crosslinking monomer include aromatic hydrocarbon crosslinking monomers such as divinylbenzene, trivinylbenzene, divinylnaphthalene, divinyltoluene, and divinylxylene; cyclic hydrocarbon crosslinking monomers such as trivinylcyclohexane; Examples include alicyclic hydrocarbon crosslinking monomers (for example, alicyclic hydrocarbon crosslinking monomers); chain hydrocarbon crosslinking monomers such as 1,3-butadiene;

Examples of the divinyl ether monomer include dialkylene glycol divinyl ether (preferably diC _1-4 alkylene glycol divinyl ether) such as diethylene glycol divinyl ether, dipropylene glycol divinyl ether, and dibutylene glycol divinyl ether; polyethylene glycol Examples include polyalkylene glycol divinyl ether (preferably polyC _1-4 alkylene glycol divinyl ether) such as divinyl ether, polypropylene glycol divinyl ether, and polybutylene glycol divinyl ether. The number of repeating alkylene glycol units in the polyalkylene glycol divinyl ether is not particularly limited, but is preferably from 3 to 10, more preferably from 3 to 5.

Examples of the diallyl ether monomer include dialkylene glycol diallyl ether (preferably diC _1-4 alkylene glycol diallyl ether) such as diethylene glycol diallyl ether, dipropylene glycol diallyl ether, and dibutylene glycol diallyl ether; polyethylene glycol Examples include polyalkylene glycol diallyl ether (preferably polyC _1-4 alkylene glycol diallyl ether) such as diallyl ether, polypropylene glycol diallyl ether, and polybutylene glycol diallyl ether. The number of repeating alkylene glycol units in the polyalkylene glycol diallyl ether is not particularly limited, but is preferably from 3 to 10, more preferably from 3 to 5.

Examples of polyvalent (meth)acrylic esters include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and 1,6- (Meth)acrylic acid diesters of mono-, di-, or polyalkylene glycols such as hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate; trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate (meth)acrylic acid triesters of polyols such as; (meth)acrylic acid tetraesters of polyols such as pentaerythritol tetra(meth)acrylate; (meth)acrylic acid pentaesters of polyols such as dipentaerythritol penta(meth)acrylate ; (meth)acrylic acid hexaester of polyol such as dipentaerythritol hexa(meth)acrylate; and the like.

The polymer particles may contain one type of structural unit derived from a crosslinkable monomer, or may contain two or more types of structural units.

As the crosslinkable monomer, preferably a hydrocarbon crosslinkable monomer or a polyvalent (meth)acrylic acid ester. In particular, aromatic hydrocarbon crosslinkable monomers and polyvalent methacrylic acid esters are more preferable from the viewpoint of suppressing elution of polymer particles into solvents and further enhancing the effects of the present application, and divinylbenzene and monoalkylene glycol methacrylic acid esters are more preferable. More preferred are acid diesters.
Further, when the polymer particles of the present disclosure have a multilayer structure, it is preferable that the inner layer such as the core portion has a structural unit derived from polyvalent methacrylic acid ester, and the outermost layer such as the shell portion has an aromatic hydrocarbon layer. It is preferable to have a structural unit derived from a crosslinkable monomer.

The proportion of structural units derived from crosslinkable monomers contained in the polymer particles of the present disclosure is preferably 10% by mass or less, more preferably 8% by mass or less, and 6% by mass or less. It is more preferable that the amount is present, and even more preferably 3% by mass or less. On the other hand, it is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, even more preferably 0.04% by mass or more, even more preferably 0.1% by mass or more. .

The polymer particles of the present disclosure preferably have a structural unit derived from a monofunctional ethylenically unsaturated monomer.

As mentioned above, the structural unit derived from a monofunctional ethylenically unsaturated monomer refers to a structural unit having the same structure as the structure formed by polymerization of a monofunctional ethylenically unsaturated monomer, and usually , a structure in which a carbon-carbon unsaturated double bond contained in a monofunctional ethylenically unsaturated monomer is replaced with a carbon-carbon single bond and two bonds bonded to each carbon. Note that the structural unit derived from the monofunctional ethylenically unsaturated monomer does not need to be a structural unit actually formed by polymerization of the monofunctional ethylenically unsaturated monomer; If the structure is the same as that formed by the polymerization of a saturated monomer, it is a structural unit formed by a method other than the polymerization of a monofunctional ethylenically unsaturated monomer (for example, a structural unit formed by a reaction after polymerization). Structural units) are included in the structural units derived from monomers. For example, in the case of methyl acrylate (CH ₂ =CH(-COOCH ₃ )), the structural unit derived from methyl acrylate can be represented by -CH ₂ -CH(-COOCH ₃ )-.

The monofunctional ethylenically unsaturated monomer of the present disclosure preferably contains a polar functional group (hereinafter referred to as a polar functional group). Although the polar functional group is not particularly limited, examples thereof include a carboxy group, an amide group, a nitrile group, an amino group, a hydroxyl group, an epoxy group, and a polyoxyethylene group. Preferred are a carboxyl group, an amide group, a nitrile group, and a hydroxyl group. Here, in this specification, the carboxy group is a group containing a "-C(=O)O" structure, such as -COOH, -COOX (X is an alkali metal atom, an alkaline earth metal atom, or ammonium) , -COO-R (R is a hydrocarbon group such as an alkyl group). That is, monofunctional ethylenically unsaturated monomers having a carboxyl group as a polar functional group include carboxylic acids; esters of carboxylic acids; carboxylic acid salts with alkali metals, alkaline earth metals, ammonia and amines, etc. . Note that the monofunctional ethylenically unsaturated monomer of the present disclosure may have one type of polar functional group, or may have two or more types of polar functional groups.

An ethylenically unsaturated monomer having a carboxyl group (however, a monomer having at least one group selected from the group consisting of an amide group, a nitrile group, an amino group, a hydroxyl group, an epoxy group, and a polyoxyethylene group) (preferably not included) include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2 - (meth)acrylic monomers such as ethylhexyl (meth)acrylate and lauryl (meth)acrylate (preferably (meth)acrylic acid alkyl ester monomers); (meth)acrylic acid, maleic acid, fumaric acid, Carboxylic acid monomers such as crotonic acid, itaconic acid, maleic anhydride; alkali metal salts of carboxylic acid monomers, alkaline earth metal salts of carboxylic acid monomers, ammonium of carboxylic acid monomers Examples include salts of carboxylic acid monomers such as salts; vinyl ester monomers such as vinyl acetate and vinyl propionate. In addition, in the salt of the carboxylic acid monomer, specific examples of the alkali metal atom and ammonium that form the salt with the carboxylic acid monomer are the same as the examples of the alkali metal atom and ammonium represented by R ¹ described below. The preferred embodiments are also the same.

The ethylenically unsaturated monomer having a carboxy group is preferably a (meth)acrylic monomer, a carboxylic acid monomer, or a salt of a carboxylic acid monomer, more preferably methyl acrylate, Acrylic monomers such as ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate; acrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, anhydride Examples include carboxylic acid monomers (a) such as maleic acid, and salts of carboxylic acid monomers (a). In particular, from the viewpoint of further improving cycle characteristics, the polymer particles of the present disclosure have a structural unit derived from acrylic acid and/or a salt of acrylic acid as a structural unit derived from an ethylenically unsaturated monomer having a carboxy group. It is more preferable to have a structural unit derived from a salt of acrylic acid. The structural unit derived from the salt of acrylic acid can be obtained by (co)polymerizing an acrylic monomer, and then adding an alkali metal hydroxide, an alkaline earth metal hydroxide, or a basic substance such as ammonia or amine. It is preferable to introduce the ester group into the polymer particles of the present disclosure by hydrolyzing the ester group with . Further, the structural unit derived from acrylic acid is preferably introduced into the polymer particles of the present disclosure by appropriately adding an acid to perform neutralization after the hydrolysis. Note that the structural unit derived from acrylic acid and the structural unit derived from a salt of acrylic acid are used in the polymer particles of the present disclosure when they have a single-layer structure, and when they have a multilayer structure, such as in the shell part, etc. Preferably, it is included in the outer shell layer.
The ethylenic inorganic compound having a carboxy group contained in the polymer particles (preferably, the polymer particles have a single-layer structure, or the outermost layer of the shell part when the polymer particles have a multi-layer structure) In 100 mol% of structural units derived from saturated monomers, the total proportion of structural units derived from acrylic acid and structural units derived from salts of acrylic acid (particularly the proportion of structural units derived from salts of acrylic acid) is, for example, 15 to 100. The mol% is preferably 30 to 100 mol%, more preferably 40 to 100 mol%, and even more preferably 70 to 100 mol%.

Examples of the ethylenically unsaturated monomer having an amide group include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, dimethylaminoethyl(meth)acrylamide, and N-vinylpyrrolidone. Preferred are acrylamide, N,N-dimethylacrylamide, dimethylaminoethylacrylamide, and N-vinylpyrrolidone, and more preferred are N,N-dimethylacrylamide and N-vinylpyrrolidone.

Examples of the ethylenically unsaturated monomer having a nitrile group include (meth)acrylonitrile, and preferably acrylonitrile.

Examples of the ethylenically unsaturated monomer having an amino group include amino group-containing (meth)acrylic acid alkyl esters such as N,N-dimethylaminomethyl (meth)acrylate and N,N-dimethylaminoethyl (meth)acrylate. Examples include monomers.

Examples of ethylenically unsaturated monomers having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, - Hydroxyl group-containing (meth)acrylic acid alkyl ester monomers such as hydroxybutyl (meth)acrylate; examples include monomers represented by the general formula (2) described below, preferably those represented by the general formula (2). The monomer represented.

Examples of the ethylenically unsaturated monomer having an epoxy group include epoxy group-containing (meth)acrylic acid alkyl ester monomers such as glycidyl (meth)acrylate.

Examples of the ethylenically unsaturated monomer having a polyoxyethylene group include ethylene glycol methoxy (meth)acrylate, diethylene glycol methoxy (meth)acrylate, and the like.

When using a monomer represented by the following general formula (2) as the monofunctional ethylenically unsaturated monomer, the polymer particles of the present disclosure include a structural unit represented by the following general formula (1). It will be held.

（一般式（２）中、Ｒ¹は、炭素数１～４のアルキル基、水素原子、アルカリ金属原子、アルカリ土類金属原子、またはアンモニウムを表す。）

(In general formula (2), R ¹ represents an alkyl group having 1 to 4 carbon atoms, a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or ammonium.)

（一般式（１）中、Ｒ¹は、炭素数１～４のアルキル基、水素原子、アルカリ金属原子、アルカリ土類金属原子、またはアンモニウムを表す。）

(In general formula (1), R ¹ represents an alkyl group having 1 to 4 carbon atoms, a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or ammonium.)

The polymer particles of the present disclosure include a structural unit represented by general formula (1) as a structural unit derived from the monofunctional ethylenically unsaturated monomer of the present disclosure, from the viewpoint of strengthening the binding force to a current collector. It is more preferable to have. In addition, when the polymer particle has a multilayer structure, it is preferable that at least the outermost layer such as the shell portion has a structural unit represented by the general formula (1).

The alkyl group having 1 to 4 carbon atoms represented by R ¹ above is preferably an alkyl group having 1 to 2 carbon atoms, and more preferably an alkyl group having 1 carbon number (methyl group).

The alkali metal atom represented by R ¹ is preferably lithium, sodium, or potassium, more preferably sodium or potassium, and even more preferably sodium.

The alkaline earth metal atom represented by R ¹ is preferably calcium or magnesium, and more preferably calcium.

The ammonium represented by R ¹ is defined to include not only NH ⁴⁺ but also organic ammonium. Examples of organic ammonium include quaternary ammonium such as tetraalkylammonium (preferably tetraC _1-10 alkylammonium) such as tetramethylammonium and tetrabutylammonium; ammonium), etc. As R ¹ , ammonia or ammonium formed by protonation of an amine is preferred. The amines include trialkylamines (preferably tri-C _1-10 alkyl amines) such as trimethylamine, triethylamine, and tributylamine; hydroxyalkylamines (preferably di- or tri(hydroxyC _1-10 ) such as diethanolamine and triethanolamine); hydroxyalkylamines are preferred.

In addition, when R ¹ is an alkali metal atom, it corresponds to a salt of a carboxyl group and an alkali metal, and when R ¹ is ammonium, it corresponds to a salt of a carboxyl group and ammonium. In addition, when R ¹ is an alkaline earth metal atom, it corresponds to a salt of two molecules of carboxy groups and one molecule of alkaline earth metal atom, that is, in formula (1) or formula (2), R ¹ The number of alkaline earth metal atoms represented is 1/2.

When the polymer particles of the present disclosure have a plurality of structural units represented by the general formula (1), R ¹ contained in the plurality of general formulas (1) may be the same or different. You can leave it there. If they are all the same, R ¹ is preferably a hydrogen atom, an alkali metal atom, or ammonium, and more preferably an alkali metal atom or ammonium. When different R ¹ exists, R ¹ is preferably a combination of one or more selected from hydrogen atoms, alkali metal atoms, and ammonium and an alkyl group having 1 to 4 carbon atoms; A combination of one or more of the above and an alkyl group having 1 to 4 carbon atoms is more preferable. In 100 mol% of the total R ¹ contained in the polymer particles (preferably, the polymer particles have a single layer structure, or the outermost layer such as a shell part when the polymer particles have a multilayer structure). , hydrogen atoms, alkali metal atoms, and ammonium (preferably one or more selected from alkali metal atoms and ammonium), the proportion of R ¹ is, for example, 20 to 100 mol%, preferably 40 to The content is 100 mol%, more preferably 50 to 100 mol%, even more preferably 70 to 100 mol%.

The structural unit represented by the above general formula (1) may be formed by the monomer represented by the above general formula (2) via a polymerization reaction, but it may also be formed by other methods. good. For example, in the general formula (2), a monomer in which R ¹ is an alkyl group having 1 to 4 carbon atoms is polymerized, and then an alkali metal hydroxide, an alkaline earth metal hydroxide, a base such as ammonia or an amine, etc. By hydrolyzing the ester group by adding a chemical substance, even if R ¹ forms an alkali metal structural unit, an alkaline earth metal structural unit, or an ammonium structural unit in the above general formula (1), good. Further, by neutralizing by appropriately adding an acid after hydrolysis, a structural unit in which R ¹ is a hydrogen atom in the above general formula (1) may be formed.

As described above, the polymer particles contain one or more structural units represented by general formula (1) (i.e., structural units derived from a monomer represented by general formula (2)). But that's fine. When two or more types of R ¹ are included, it may be formed by polymerizing two or more types of monomers represented by the above general formula (2), and the above where R ¹ is an alkyl group having 1 to 4 carbon atoms. It may be formed by partially hydrolyzing the ester group or hydrolyzing it with two or more basic substances after polymerizing the monomer represented by the general formula (2).

The polymer particles of the present disclosure may contain one type of structural unit derived from a monofunctional ethylenically unsaturated monomer, or may contain two or more types of structural units.

The polymer particles of the present disclosure preferably contain 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more of the structural unit represented by the above general formula (1). . On the other hand, the polymer particles of the present disclosure preferably contain 99.9% by mass or less, more preferably 99% by mass or less, and 90% by mass or less of the structural unit represented by the above general formula (1). It is even more preferable.

The structural unit derived from the monofunctional ethylenically unsaturated monomer is preferably a structural unit derived from an ethylenically unsaturated monomer having a carboxy group, or a structural unit represented by general formula (1).
In particular, when the polymer particles of the present disclosure have a single layer structure, the outermost layer such as the shell portion when the polymer particles have a multilayer structure are derived from an ethylenically unsaturated monomer having a carboxy group. The structural unit preferably has a structural unit derived from at least one monomer selected from acrylic acid alkyl ester, acrylic acid, and salts of acrylic acid, and acrylic acid C _1-8 alkyl ester, acrylic acid It is more preferable to have a structural unit derived from at least one monomer selected from an alkali metal salt of and an ammonium salt of acrylic acid.
In addition, in the case where the polymer particles of the present disclosure have a multilayer structure, the inner layer such as the core portion has a structural unit derived from an alkyl (meth)acrylate ester as a structural unit derived from an ethylenically unsaturated monomer having a carboxy group. It is preferable to have a structural unit derived from (meth)acrylic acid C _1-8 alkyl ester, and it is more preferable to have a structural unit derived from acrylic acid C _1-8 alkyl ester, from the viewpoint of easy adjustment of physical properties such as hardness. It is more preferable to have a structural unit and a structural unit derived from methacrylic acid C _1-8 alkyl ester.

In the polymer particles of the present disclosure, out of 100% by mass of structural units derived from monofunctional ethylenically unsaturated monomers, structural units derived from ethylenically unsaturated monomers having a carboxyl group and those represented by general formula (1) The total content of structural units is, for example, 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even if it is 100% by mass. good.
Further, the content of the structural unit represented by the general formula (1) with respect to 100 parts by mass of the structural unit derived from the ethylenically unsaturated monomer having a carboxyl group is preferably 0 to 100 parts by mass, more preferably is 5 to 70 parts by weight, more preferably 10 to 50 parts by weight.

The polymer particles of the present disclosure include structural units derived from monomers other than the monomers exemplified above (hereinafter referred to as "other monomers") as structural units derived from monofunctional ethylenically unsaturated monomers. may contain one or more types of structural units (also referred to as "structural units derived from"). The structural unit derived from other monomers refers to a structural unit in which at least one carbon-carbon double bond of the other monomer is replaced with a carbon-carbon single bond.

The structural unit derived from other monomers can be formed, for example, by radical polymerization of other monomers. In addition, the structural unit derived from other monomers may have the same structure as that of the other monomer in which the carbon-carbon double bond is replaced with a carbon-carbon single bond, and may be formed by polymerization of the other monomer. The structural unit is not limited to the structural unit, and may be, for example, a structural unit formed by a reaction after polymerization.

Other monomers include, but are not particularly limited to, styrene monomers such as styrene, α-methylstyrene, p-methylstyrene, tert-butylstyrene, chlorostyrene, and vinyltoluene; vinyltrimethoxysilane, vinyltriethoxy Silane, vinyltri(methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, 2-styrylethyltrimethoxysilane, vinyltrichlorosilane, γ-(meth)acryloyloxypropylhydroxysilane, γ-(meth)acryloyl Silane group-containing monomers such as oxypropylmethylhydroxysilane; fluorine atom-containing monomers such as trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, and octafluoropentyl (meth)acrylate; 2,2, Photo-stabilizing monomers such as 6,6-tetramethylpiperidine-4-(meth)acrylate; UV-absorbing monomers such as benzotriazole-based UV-absorbing monomers and benzophenone-based UV-absorbing monomers; Examples include.

The polymer particles of the present disclosure may contain one or more types of structural units derived from a monofunctional ethylenically unsaturated monomer, or may have two or more types of structural units.

The polymer particles of the present disclosure preferably have a structural unit derived from a crosslinkable monomer and a structural unit derived from a monofunctional ethylenically unsaturated monomer, and the structural unit derived from a crosslinkable monomer and a carboxyl group. It is more preferable to have a structural unit derived from an ethylenically unsaturated monomer and/or a structural unit represented by the general formula (1), and a structural unit derived from a crosslinkable monomer, an ethylenic unit having a carboxy group. It is more preferable to have a structural unit derived from an unsaturated monomer and a structural unit represented by general formula (1). In particular, it is preferable that the polymer particles of the present disclosure have a single layer structure, and the outermost layer of the shell portion or the like when the polymer particles have a multilayer structure have the above composition.

The content ratio of the structural unit derived from the crosslinkable monomer in the polymer particle of the present disclosure has a single layer structure, or in the outermost layer such as the shell part when the polymer particle has a multilayer structure, The amount is preferably 0.01 to 10% by weight, more preferably 0.02 to 8% by weight, even more preferably 0.04 to 6% by weight, even more preferably 0.1 to 3% by weight.
Originating from the ethylenically unsaturated monomer having a carboxy group in the outermost shell layer of the polymer particle of the present disclosure, such as a shell part when the polymer particle has a single layer structure or a multilayer structure The content of structural units is preferably 20 to 99.99% by mass, more preferably 30 to 99.96% by mass, and even more preferably 40 to 85% by mass.
Content ratio of the structural unit represented by general formula (1) in the polymer particles of the present disclosure when they have a single-layer structure, or in the outermost layer of the shell portion when they have a multi-layer structure is preferably 0 to 75% by weight, more preferably 15 to 65% by weight, even more preferably 30 to 60% by weight.
Further, in the case where the polymer particles of the present disclosure have a single-layer structure, or in the outermost layer of the shell part or the like when the polymer particles have a multi-layer structure, the polymer particles derived from an ethylenically unsaturated monomer having a carboxy group The content of the structural unit represented by general formula (1) with respect to 100 parts by mass of structural units is preferably 0 to 200 parts by mass, more preferably 50 to 150 parts by mass.
The polymer particles of the present disclosure have a structural unit derived from a crosslinkable monomer, a carboxyl group, in the outermost layer of the shell portion, etc., when the polymer particles have a single layer structure, or when they have a multilayer structure. The total proportion of the structural unit derived from the ethylenically unsaturated monomer and the structural unit represented by general formula (1) is, for example, 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass. The content is more preferably 95% by mass or more, and may be 100% by mass.

In addition, when the polymer particles of the present disclosure have a multilayer structure, the composition of the inner layer such as the core part is not particularly limited, but may include structural units derived from a crosslinkable monomer and structures derived from a monofunctional ethylenically unsaturated monomer. unit, more preferably a structural unit derived from a crosslinkable monomer and a structural unit derived from an ethylenically unsaturated monomer having a carboxyl group, and a structural unit derived from a crosslinkable monomer and ( It is more preferable to have a structural unit derived from a meth)acrylic acid alkyl ester (particularly a (meth)acrylic acid C _1-8 alkyl ester), and a structural unit derived from a crosslinking monomer, an acrylic acid C _1-8 alkyl ester. It is even more preferable to have a structural unit derived from a methacrylic acid C _1-8 alkyl ester.
When the polymer particles of the present disclosure have a multilayer structure, the proportion of structural units derived from crosslinkable monomers in the inner layer such as the core portion is preferably 0.01 to 20% by mass, more preferably The amount is 0.04 to 10% by weight, more preferably 0.1 to 6% by weight, even more preferably 0.3 to 3% by weight.
When the polymer particles of the present disclosure have a multilayer structure, the proportion of the structural unit derived from the ethylenically unsaturated monomer having a carboxy group in the inner layer such as the core portion is preferably 50 to 99.99% by mass, and more preferably Preferably 70 to 99.96% by mass, more preferably 80 to 99.9% by mass, even more preferably 90 to 99.7% by mass. Core when the polymer particles of the present disclosure have a multilayer structure. In the case where _{the inner} layer of _the Unit: Structural unit derived from methacrylic acid C _1-8 alkyl ester) is preferably 10:90 to 90:10, more preferably 30:70 to 70:30.
When the polymer particles of the present disclosure have a multilayer structure, the total proportion of the structural units derived from the crosslinkable monomer and the structural units derived from the ethylenically unsaturated monomer having a carboxyl group in the inner layer such as the core part is: For example, it is 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and may be 100% by mass.

When the polymer particles of the present disclosure are core-shell particles, the mass ratio of the core part to the shell part (core part:shell part) is preferably 10:90 to 90:10, more preferably 30:70 to 70:30. It is.

The polymer particles of the present disclosure may be at least partially hydrolyzed, as described above. Here, the phrase "at least partially hydrolyzed" means that the polymer particles are either a partial hydrolyzate, a complete hydrolyzate, or a hydrolyzed neutralized product thereof. For example, in the case of methyl acrylate (CH ₂ =CH(-COO-CH ₃ )), the partial hydrolyzate is CH ₂ =CH(-COO-CH ₃ ) and CH ₂ =CH(-COO-H ) and structural units derived from

The at least partially hydrolyzed polymer particles contained in the polymer particles of the present disclosure are preferably 0.1% by mass or more, more preferably 1% by mass or more, based on the total amount of the polymer particles. and more preferably 10% by mass or more. On the other hand, the content is preferably 100% by mass or less, more preferably 99.99% by mass or less, even more preferably 90% by mass or less, even more preferably 85% by mass or less.

The polymer particles of the present disclosure may be polymer particles in which all polymer particles are completely hydrolyzed (ie, polymer particles with a hydrolysis rate of 100%).
The hydrolysis rate of the polymer particles of the present disclosure is preferably 10 to 100%, more preferably 40 to 100%, and even more preferably 80 to 100%, from the viewpoint of further improving cycle characteristics. The hydrolysis rate is calculated based on the amount of the basic substance added to 100 mol% of the structural unit derived from the hydrolyzable monomer contained in the outermost shell (the entire particle if it is a single layer). can do. Examples of hydrolyzable monomers include acrylic monomers such as acrylic acid alkyl ester monomers, monomers represented by general formula (2), and the like.

The volume average particle diameter of the polymer particles of the present disclosure is preferably 10 nm to 5 μm or 0.01 to 5 μm, more preferably 25 nm to 3 μm, even more preferably 50 nm to 2 μm, and even more preferably 100 nm to 1 μm. It is particularly preferable that Note that the volume average particle diameter can be measured, for example, by a dynamic light scattering method.

The content of the polymer particles of the present disclosure is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, based on the total amount of the binder of the present disclosure. On the other hand, the content is preferably 99% by mass or less, more preferably 95% by mass or less, still more preferably 90% by mass or less.
Further, the content of the polymer particles of the present disclosure is, for example, 50 to 100% by mass, preferably 80 to 100% by mass, more preferably 90 to 100% by mass, based on 100% by mass of the solid content of the binder of the present disclosure. More preferably, it is 95 to 100% by mass.

Note that in this specification, the solid content (nonvolatile content) refers to components excluding the solvent. A known method can be used to calculate the solid content (non-volatile content). Using the total mass of the target sample (if the solid content of the binder, the binder) and the mass of volatile components, calculate the following: It may be calculated according to formula A. Approximately 1 g of the target sample is weighed, dried with hot air at a temperature of 120°C for 30 minutes, the resulting residue is defined as solid content (nonvolatile content), and calculated according to formula B below. You may.
Formula A: [solid content in sample (mass%)] = ([total sample mass - mass of volatile components] ÷ [total sample mass]) x 100
Formula B: [solid content in sample (mass%)] = ([mass of sample after drying] ÷ [mass of sample before drying]) x 100

The polymer particles of the present disclosure are suitably used as a binder for lithium ion secondary electrodes (also referred to as lithium secondary electrodes), and by utilizing their good dispersibility, they can be used, for example, in semiconductor abrasives, ceramic It can also be applied in various fields such as coatings, thermoplastic resins, thermosetting resins, various films, catalyst carriers, insulation materials, and low-reflection materials.

<Fragment polymer>
The binders of the present disclosure include fragment polymers. The fragment polymer of the present disclosure (hereinafter sometimes referred to as fragment) has an absorption peak in the range of 1550 cm ^-1 to 1650 cm ^-1 as an absorption band in an infrared absorption spectrum. Here, the absorbance of the maximum absorption peak in the above absorption band is defined as the maximum absorbance (A).

The fragment polymer of the present disclosure preferably has an absorption peak in the range of 1650 cm ^-1 to 1750 cm ^-1 as an absorption band in the infrared absorption spectrum. Here, the absorbance of the maximum absorption peak in the above absorption band is defined as the maximum absorbance (B).

The fragment polymer of the present disclosure preferably has a ratio (B/A) of maximum absorbance B to maximum absorbance (A) of, for example, 1.5 or less, preferably 1 or less, or 1.0 or less, More preferably it is 0.9 or less, still more preferably 0.8 or less. On the other hand, it is preferably 0.001 or more, more preferably 0.01, and still more preferably 0.1.
The method for adjusting the ratio (B/A) of the maximum absorbance B to the maximum absorbance (A) is not particularly limited, but for example, in the production of polymer particles containing fragment polymers, the value can be adjusted by increasing the hydrolysis rate. Can be made smaller.

The absorption band in which the maximum absorbance (A) of the fragment polymer of the present disclosure exists is preferably from 1550 cm ^-1 to 1650 cm ^-1 , more preferably from 1555 cm ^-1 to 1645 cm ^-1 . The absorption band in which the maximum absorbance (B) of the fragment polymer of the present disclosure exists is preferably from 1650 cm ^-1 to 1750 cm ^-1 , more preferably from 1655 cm ^-1 to 1745 cm ^-1 .

The weight average molecular weight of the fragment polymer of the present disclosure is preferably 500 or more, more preferably 1000 or more, and still more preferably 1500 or more. On the other hand, it is preferably 500,000 or less, more preferably 250,000 or less, and still more preferably 100,000 or less. The weight average molecular weight of the fragment polymers of the present disclosure can be measured using gel permeation chromatography (GPC).

The fragment polymer of the present disclosure is preferably 0.1% by mass or more based on the total amount of the binder of the present disclosure (preferably 100% by mass of the polymer particles or the total amount of solid content of the binder), The content is more preferably 0.2% by mass or more, and still more preferably 0.3% by mass or more. On the other hand, the content is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. By adjusting the content of the fragment polymer within the above range, the density of the polymer particles can be increased, and high cycle characteristics tend to be exhibited.

The form of the fragment polymer in the binder of the present disclosure is not particularly limited, and it may be localized (preferably dispersed) in the form of particles such as spherical, cylindrical, plate-like, irregularly shaped, etc., or it may be in a dissolved state. may exist.

When the fragment polymer has a particle shape, the volume average particle diameter of the fragment polymer is preferably 1/7 or more, more preferably 1/6 or more with respect to the volume average particle diameter of the polymer particles of the present disclosure. Yes, and more preferably 1/5 or more. On the other hand, it is preferably 2/3 or less, more preferably 5/8 or less, and even more preferably 3/5 or less.

The composition of the fragment polymer of the present disclosure is the same as the composition exemplified for the polymer particles, and its preferred embodiments are also the same.

The fragment polymer of the present disclosure preferably has a structural unit represented by the above general formula (1). The structural unit represented by the above general formula (1) may be formed by a polymerization reaction of the monomer represented by the above general formula (2), but may also be formed by other methods. Specific examples of the structural unit represented by general formula (1) and the monomer represented by general formula (2) include the above-mentioned structural units and monomers.

The fragment polymer of the present disclosure may have a multilayer structure, for example, a polymer composed of a core portion and a shell portion provided outside the core portion.

Fragment polymers of the present disclosure may include hydrolyzed polymers.

The fragment polymer of the present disclosure can be obtained by a known method. For example, fragment polymers can be separated by filtration by filtering an aqueous solution containing the polymer particles of the present disclosure. More specifically, a fragment polymer can be obtained by removing the solvent from a filtrate obtained by filtering an aqueous solution containing the polymer particles of the present disclosure, such as by heating and drying. The filtration method is not particularly limited, but includes microfiltration (MF), ultrafiltration (UF), reverse osmosis (RO), and the like. In the filtration, the opening diameter corresponds to 1/7 to 2/3 (preferably 1/6 to 5/8, more preferably 1/5 to 3/5) of the volume average particle diameter of the polymer particles. It is preferable to separate by filtration using a filter.

The drying conditions for the filtrate are not particularly limited, but the drying temperature is, for example, 80 to 180°C, preferably 100 to 150°C, and the drying time is, for example, 30 minutes to 20 hours, preferably 3 hours to 10 hours. It is.

The fragment polymer of the present disclosure can be obtained by microfiltration when the volume average particle diameter of the polymer particles is 0.05 to 10 μm. The opening diameter of the microfiltration membrane is not particularly limited, but is preferably 0.05 to 10 μm, more preferably 0.06 to 9 μm, and even more preferably 0.07 to 8 μm.

The fragment polymer of the present disclosure can be obtained by ultrafiltration when the volume average particle diameter of the polymer particles is 0.001 to 0.05 μm. The opening diameter of the ultrafiltration membrane is not particularly limited, but it is preferably 0.001 to 0.05 μm, more preferably 0.002 to 0.06 μm, and even more preferably 0.003 to 0.07 μm. It is. The fragment polymer of the present disclosure can be obtained by reverse osmosis when the volume average particle diameter of the polymer particles is 0.001 μm or less.

When separating the fragment polymer by microfiltration, specifically, the following method may be employed. That is, 700 g of an aqueous solution containing the polymer particles of the present disclosure is concentrated by discharging 350 mL of the treated liquid using a microfiltration module (for example, Microza MF manufactured by Asahi Kasei Chemicals Co., Ltd.), and 350 mL of the solution is added to the obtained concentrated liquid. Repeat adding water 7 times. Then, a fragment polymer may be obtained by collecting all of the discharged processing liquid and heating and drying the collected processing liquid under the above-mentioned drying conditions. The solid content of the aqueous solution containing the polymer particles is preferably 3 to 30% by mass, more preferably 5 to 20% by mass.

<Other ingredients>
The binder of the present disclosure preferably includes a mixture in which polymer particles containing the fragment polymer described above are dispersed in water (hereinafter sometimes referred to as a water dispersion).

The binder of the present disclosure may contain polymer particles obtained by drying an aqueous dispersion. The drying method is not particularly limited, and examples thereof include heat drying, reduced pressure drying, spray drying, and the like.

The binder of the present disclosure may contain any component other than the polymer particles containing the fragment polymer described above. Examples include solvents, dispersants, thickeners, wetting agents, pH adjusters, stabilizers, surfactants, antioxidants, and polymerization inhibitors.

Examples of the solvent include water; alcohols such as methanol, ethanol, isopyl alcohol, and hexanol; ketones such as acetone and 2-butanone; and acetic acid esters such as methyl acetate, ethyl acetate, and butyl acetate. Preferably, the aqueous solvent described below is preferred, and water is particularly preferred. The content of the solvent is not particularly limited, but is, for example, 20 to 88% by weight, preferably 50 to 96% by weight, and more preferably 70 to 95% by weight based on 100% by weight of the binder of the present disclosure.

[Binder manufacturing method]
The binder of the present disclosure can be manufactured by, for example, polymerizing raw material monomer components such as a crosslinkable monomer or a monofunctional ethylenically unsaturated monomer in an aqueous solvent and then obtaining polymer particles. I can do it. After polymerization, the polymer may be produced by performing hydrolysis as described below to obtain a polymer.

<Polymerization method>
Examples of polymerization methods include suspension polymerization, emulsion polymerization, and dispersion polymerization. Among these, emulsion polymerization is preferred, in which a (radical) polymerization reaction is carried out by dispersing the raw material monomer components in a reaction solvent (e.g., an aqueous solvent) in the presence of an emulsifier, and specifically, for producing the polymer particles of the present invention. The method preferably includes emulsion polymerization in which at least one monomer represented by the above formula (2) is dispersed in an aqueous solvent and a polymerization reaction is performed in the presence of an emulsifier. Emulsion polymerization may be performed in only one stage or in multiple stages.

The emulsifier may be used alone or in combination of two or more, and may be a non-reactive surfactant or a reactive surfactant having a radically polymerizable group in its structure.

Non-reactive surfactants include anionic and nonionic surfactants. Examples of anionic surfactants include fatty acid salts, alkyl (allyl) sulfonates, alkyl sulfate salts, polyoxyethylene alkyl (phenyl) ether sulfates, etc., and examples of nonionic surfactants include polyoxyethylene Examples include alkyl (phenyl) ether, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene polyoxypropylene block polymer, and the like.

The reactive surfactant includes anionic and nonionic surfactants. Examples of the anionic reactive surfactant include, but are not limited to, ether sulfate type reactive surfactants and phosphate ester type reactive surfactants.

The amount of the emulsifier is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.3 parts by mass or more, based on 100 parts by mass of the raw material monomer components in total. , is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, still more preferably 5 parts by mass or less, particularly preferably 3 parts by mass or less.

In the present disclosure, the aqueous solvent includes water alone or a mixed solvent of water and a water-miscible organic solvent, but water alone is preferable. An aqueous solvent typically refers to a solvent in which the content of water exceeds 50% by volume. As water, ion exchange water (deionized water), distilled water, pure water, etc. can be used. As the water-miscible organic solvent, an organic solvent (lower alcohol such as C _1-4 alkyl alcohol, etc.) that can be uniformly mixed with water can be used. From the viewpoint of preventing the organic solvent from remaining in the polymer as much as possible, an aqueous solvent in which 80% by volume or more of the aqueous solvent is water is preferable, an aqueous solvent in which 90% by volume or more in the aqueous solvent is water is more preferable; An aqueous solvent in which 95% by volume or more of the solvent is water is more preferred, an aqueous solvent consisting essentially of water (an aqueous solvent in which 99.5% by volume or more is water) is particularly preferred, and water alone is most preferred. .

When polymerizing the raw material monomer components, methods such as using a polymerization initiator, irradiating ultraviolet rays or radiation, or applying heat are used, and it is preferable to use a polymerization initiator. A polymerization initiator that combines an oxidizing agent and a reducing agent (redox type polymerization initiator) is preferable from the viewpoint of efficiently reacting the components and sufficiently reducing the amount of residual monomer.

The reaction temperature during the polymerization reaction is not particularly limited, and is usually preferably 30°C or higher, more preferably 50°C or higher, and preferably 100°C or lower, more preferably 95°C or lower. If the reaction temperature is within this range, the polymerization reaction can be easily controlled.

<Hydrolysis method>
The polymer particles of the present disclosure are produced by polymerizing raw monomer components containing a monofunctional ethylenically unsaturated monomer and, for example, a crosslinking monomer in an aqueous solvent as described above. It may be produced by obtaining an aqueous dispersion containing the particles and then partially or completely hydrolyzing it.

The polymer particles of the present disclosure can be hydrolyzed by, for example, adding a basic aqueous solution such as an aqueous sodium hydroxide solution, an aqueous calcium hydroxide solution, an aqueous ammonia solution, or an aqueous cyclohexylamine solution to an aqueous dispersion containing the polymer particles. It can be performed. Furthermore, partial or complete neutralization can be achieved by appropriately adding an acid to the hydrolyzed solution. By performing hydrolysis and neutralization, for example, the group corresponding to R ¹ in the above general formula (1) can be converted into a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or ammonium. The pH and hydrophilicity of the polymer can be adjusted by adjusting the amount of acid or base used during polymerization, hydrolysis, and neutralization, and by adjusting the proportion of monomer units in which R ¹ is a hydrogen atom. This tends to strengthen the binding force to the current collector.

The aqueous dispersion containing polymer particles obtained by the above-mentioned polymerization method and hydrolysis method contains a fragment polymer. Therefore, the aqueous dispersion containing polymer particles obtained by the above method may be used as it is as a binder resin, or after filtering the aqueous dispersion containing polymer particles to separate the fragments, A binder may be prepared by mixing the obtained fragment polymer with separately produced polymer particles (preferably an aqueous dispersion containing polymer particles).

[Composition for lithium ion electrode]
The composition for a lithium ion electrode (also referred to as an electrode slurry) of the present disclosure may contain a binder containing the polymer particles (hereinafter sometimes referred to as binder 1) and a negative electrode active material. By using Binder 1, the cycle characteristics of the obtained lithium secondary battery can be improved, probably because the dispersibility of the lithium ion electrode composition is improved. The content of the binder 1 is not particularly limited, but the amount of polymer particles contained in the binder 1 is 1 based on the total amount of the lithium ion electrode composition (preferably, the total amount of solid content of the lithium ion electrode composition). The content is preferably at least 1.5% by mass, more preferably at least 1.5% by mass, and still more preferably at least 2% by mass. On the other hand, the content is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less. By including it in the above range, high cycle characteristics tend to be easily exhibited.

Note that the binder component contained in the composition for a lithium ion electrode may include a binder other than the above-mentioned binder 1 (hereinafter sometimes referred to as binder 2). As the binder 2, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene; synthetic rubbers such as styrene-butadiene rubber, nitrile butadiene rubber, methyl methacrylate butadiene rubber, and chloroprene rubber; polyamide resins such as polyamideimide; polyethylene , polyolefin resins such as polypropylene; poly(meth)acrylic resins such as polyacrylamide and polymethyl methacrylate; polyacrylic acid; cellulose resins such as methyl cellulose, ethyl cellulose, triethyl cellulose, carboxymethyl cellulose, and aminoethyl cellulose; ethylene vinyl alcohol, Examples include vinyl alcohol resins such as polyvinyl alcohol, among which cellulose resins are preferred. These binders 2 may be used alone or in combination of two or more. Furthermore, during the production of the negative electrode, these binders may be in a state dissolved in a solvent or in a state dispersed in a solvent.

The content of Binder 1 is, for example, 30 to 100% by weight, preferably 50 to 95% by weight, and more preferably 60 to 90% by weight, based on 100% by weight of the total amount of Binder 1 and Binder 2.

[Negative electrode active material]
Examples of the negative electrode active material of the present disclosure include negative electrode active materials containing silicon (hereinafter sometimes referred to as silicon-based negative electrode active materials), carbon materials, composite metal oxides (however, they do not contain silicon atoms), lithium alloys, etc. It will be done.

Examples of silicon-based negative electrode active materials include silicon (Si), alloys containing silicon, carbides containing silicon, nitrides containing silicon, and oxides containing silicon. Specifically, Si, _SiB4 , _SiB6 , _Mg2Si , Ni2Si, _TiSi2 , _MoSi2 , CoSi2, _NiSi2 , _CaSi2 , _{CrSi2 , Cu5Si} , _FeSi2 , _{MnSi2 ,} NbSi _{2 , TaSi2 , VSi2} , _WSi2 , ZnSi2, SiC, _{Si3N4 , Si2N2O} , _SiOx (0<x≦2), _SnSiOx , and LiSiO. Among them, from the viewpoint of improving the cycle characteristics of the lithium ion secondary battery, oxides containing silicon are preferred, more preferably SiO _x (0<x≦2), and even more preferably silicon monoxide (SiO). .

Examples of carbon materials include graphite, carbon black, fullerene, carbon nanotubes, carbon nanofibers, carbon nanohorns, carbon fibrils, and the like.

Examples of the composite metal oxide include polyacene-based conductive polymers, lithium titanate, and the like.

The negative electrode active materials of the present disclosure may be used alone or in combination of two or more. More preferably, two or more types are used.

Among these, the negative electrode active material of the present disclosure preferably includes a silicon-based negative electrode active material, and includes a silicon-based negative electrode active material and other negative electrode active materials (specifically, carbon materials, composite metal oxides, and lithium alloys). It is more preferable to include at least one selected type of active material, and even more preferably to include a silicon-based negative electrode active material and a carbon material.

The content of silicon (preferably silicon-based negative electrode active material) is preferably 5% by mass or more, more preferably 7% by mass or more, based on the total amount of negative electrode active material from the viewpoint of dispersibility, and Preferably it is 10% by mass or more. On the other hand, the content is preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 70% by mass or less.

The composition for a lithium ion electrode of the present disclosure preferably contains a negative electrode active material in an amount of 85% by mass or more, more preferably 90% by mass or more based on the total solid content of the composition for a lithium ion electrode. and more preferably 95% by mass or more. On the other hand, the content is preferably 99% by mass or less, more preferably 98% by mass or less, still more preferably 97% by mass or less.

The composition for a lithium ion electrode (preferably the composition for a negative electrode of a lithium ion secondary battery) of the present disclosure may contain other components. Other ingredients include conductive aids, solvents, dispersants, thickeners, film-forming aids, wetting agents, pH adjusters, stabilizers, polymerization inhibitors, surfactants, adhesion promoters, fillers, and oxidation agents. Examples include inhibitors, antistatic agents, dyes, and pigments.

As the conductive aid, conductive carbon is preferable because it tends to improve the output of the lithium ion secondary battery. Examples of the conductive carbon include carbon black, fibrous carbon, and graphite, but carbon black is more preferred. Specific examples of carbon black include Ketjen black, acetylene black, and the like. The number of conductive aids may be one type, or two or more types may be used in combination.

The content of the conductive additive is determined by the total amount of the lithium ion electrode composition (preferably the lithium ion secondary battery negative electrode composition) from the viewpoint of improving the output characteristics and electrical characteristics of the lithium ion secondary battery. The content is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and still more preferably 1% by mass or more based on the total solid content of the lithium ion electrode composition. On the other hand, the content is preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less.
Further, the total content of the negative electrode active material and the conductive additive is preferably 86% by mass or more, more preferably 91% by mass or more, and even more preferably is 95% by mass or more. On the other hand, the total content is preferably 99% by mass or less, more preferably 98% by mass or less, still more preferably 97% by mass or less.

Examples of solvents include water; alcohols such as methanol, ethanol, isopyl alcohol, and hexanol; ketones such as acetone and 2-butanone; acetate esters such as methyl acetate, ethyl acetate, and butyl acetate; tetrahydrofuran, diethyl ether, etc. , 2-dimethylethane, diethylene glycol dimethyl ether, etc. Among them, water alone or a mixed solvent of water and a water-miscible organic solvent (lower alcohol such as C _1-4 alkyl alcohol, etc.) is preferred. In the case of a mixed solvent of water and a water-miscible organic solvent, the preferred embodiment of the volume ratio is the same as the preferred embodiment described for the aqueous solvent described above. The number of solvents may be one type, or two or more types may be used in combination.

The content of the solvent is preferably 20% by mass or more, more preferably 25% by mass or more, based on the total amount of the lithium ion electrode composition (preferably the lithium ion secondary battery negative electrode composition), and Preferably it is 30% by mass or more. On the other hand, the content is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

The pH at 25°C of the lithium ion electrode composition (preferably the lithium ion secondary battery negative electrode composition) of the present disclosure is preferably 5 or more, more preferably 5 or more, from the viewpoint of suppressing corrosion of the current collector. .5 or more, even more preferably 6 or more, still more preferably 6.5 or more. In addition, the pH at 25°C of the lithium ion electrode composition (preferably the lithium ion secondary battery negative electrode composition) is preferably 10 or less, more preferably 9 or less, from the viewpoint of suppressing corrosion of the current collector. , even more preferably 8 or less, still more preferably 7.5 or less.

The composition for a lithium ion electrode (preferably the composition for a negative electrode of a lithium ion secondary battery) of the present disclosure is capable of dispersing the active material and other components at a high concentration due to the specific polymer particles contained in the binder. , it becomes possible to save energy and improve electrode production.

[Lithium ion secondary battery negative electrode]
Electrodes for lithium ion secondary batteries include a positive electrode and a negative electrode. Although the electrode of the lithium ion secondary battery according to this embodiment can be used as any electrode, it can be preferably used as a negative electrode.

A negative electrode for a lithium ion secondary battery has a negative electrode composite layer formed from the above-mentioned lithium ion electrode composition (preferably a lithium ion secondary battery negative electrode composition) on a negative electrode current collector. Examples of metals used for the negative electrode current collector include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum. Among these, copper is preferred. Note that the shape and dimensions of the negative electrode current collector are not particularly limited.

[Method for manufacturing lithium ion secondary battery negative electrode]
The electrode of the lithium ion secondary battery according to the present embodiment can be prepared, for example, by applying the above-described composition for a lithium ion electrode (preferably a composition for a negative electrode of a lithium ion secondary battery) to a current collector, or It can be manufactured by immersing the material in a lithium ion electrode composition (preferably a lithium ion secondary battery negative electrode composition) and then drying it to form a negative electrode composite layer. The drying temperature is preferably 40°C or higher, more preferably 50°C or higher. On the other hand, the temperature is preferably 150°C or lower, more preferably 130°C or lower. If necessary, the electrode may be subjected to pressure treatment using, for example, a mold press, a roll press, or the like.

The negative electrode for a lithium ion secondary battery is also preferable in that its density before pressing is increased. The higher the dispersibility of the lithium ion electrode composition (electrode slurry), the higher the density before pressing tends to be. Furthermore, since the dispersibility of the lithium ion electrode composition is improved (that is, the density before pressing is increased), the cycle characteristics can be further improved. The density before pressing of the negative electrode for the lithium ion secondary battery is preferably 1.0 or more. Further, the upper limit of the density before pressing is not particularly limited, but is, for example, 1.3 or less. Note that the pre-press density can be measured by the following method. That is, a lithium ion electrode composition was coated on a current collector so that the coating weight after drying was 5.69 to 5.95 g/cm ² , dried with hot air at 60°C for 10 minutes, and then heated at 80°C. A vacuum drying process is performed for 10 hours to obtain a pre-press negative electrode. Thereafter, three circular pieces (Φ12 mm) are punched out from the unpressed negative electrode to obtain three negative electrode composite layers. The thickness and weight of each negative electrode composite material layer are measured, and the average value thereof is calculated. Then, the density before pressing (g/cm ³ ) may be calculated from the following (Formula 1). When measuring the thickness and weight of each negative electrode composite material layer, measure the thickness and weight of each negative electrode composite material layer three times, and calculate the average value of the three times for each negative electrode composite material layer. It is preferable to set the thickness and weight to .
Density before pressing (g/cm ³ )=Negative electrode composite layer weight (g)/{1.1304 (cm ² )×Negative electrode composite material thickness (cm)} (Formula 1)

[Lithium ion secondary battery]
The lithium ion secondary battery of the present disclosure includes a positive electrode and the negative electrode. More specifically, this lithium ion secondary battery includes a positive electrode, the negative electrode, a separator provided between the positive electrode and the negative electrode, and an exterior packaging together with the positive electrode, negative electrode, etc. while the separator is impregnated with the separator. and an electrolytic solution housed in the case.

The positive electrode is not particularly limited, and any known positive electrode may be used.

As the separator, for example, a film made of a polyolefin resin such as polyethylene or polypropylene, or a resin such as a fluororesin can be used.

As the electrolytic solution, an electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent can be used. A lithium salt is used as the supporting electrolyte. Examples of lithium salts include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi. , (FSO ₂ ) ₂ NLi, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, and the like. Examples of the organic solvent include carbonates such as dimethyl carbonate, ethylene carbonate, diethyl carbonate, propylene carbonate, butylene carbonate, methyl ethyl carbonate, and fluoroethylene carbonate, esters such as γ-butyrolactone and methyl formate, and 1,2-dimethoxyethane. and ethers such as tetrahydrofuran.
The concentration of the supporting electrolyte in the electrolytic solution is not particularly limited, but is preferably 0.5 to 2.5 mol/L, more preferably 0.8 to 1.5 mol/L.

The lithium ion secondary battery according to this embodiment can be produced by, for example, stacking a positive electrode and a negative electrode with a separator in between, placing the obtained laminate in a battery container, and sealing the battery container by pouring an electrolyte into the battery container. , can be easily manufactured.

If necessary, an expanded metal, a fuse, an overcurrent prevention element such as a PTC element, a lead plate, etc. may be placed in the battery container to prevent pressure increase inside the battery and overcharging and discharging. Examples of the shape of the battery include a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, etc., but the present disclosure is not limited to these examples.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples. In addition, unless otherwise specified, "parts" shall mean "parts by mass" and "%" shall mean "% by mass."

<Volume average particle diameter>
The polymer particles diluted with ion-exchanged water (dilute solution) were measured using a light scattering particle size distribution analyzer ("Zetasizer Ultra" manufactured by Spectris), and the volume average of the polymer particles was determined by dynamic light scattering method. The particle diameter (nm) was determined. As the diluent, it is recommended to use a polymer particle aqueous dispersion diluted with ion-exchanged water so that the concentration of the polymer particles is 0.01 to 0.05% by mass.

<Solid content>
To determine the solid content of the aqueous polymer particle dispersion, weigh the sample (aqueous polymer particle dispersion) to approximately 1.0 g in a glass petri dish with a lid, and heat it with hot air at 120°C for 30 minutes with the lid open. After drying, the glass petri dish was quickly covered with a lid, and the solid content was calculated based on the following formula.
Solid content (%) of polymer particle aqueous dispersion = [{Mass of glass petri dish after drying (g) - Tare weight of glass petri dish (g)}] / [{Mass of glass petri dish before drying (g) - Tare weight of glass petri dish (g)}] x 100

<Evaluation of fragment polymer>
(1-1) Preparation of dried product (fragment polymer) of the treatment liquid. A dried product of the treatment liquid was obtained by drying the treatment liquid at 120° C. for 5 hours using a hot air dryer. Note that it is recommended that the treatment liquid be produced by the following method. That is, 700 g of the polymer particle aqueous dispersion obtained in each production example was concentrated by discharging 350 mL of the treatment liquid using a microfiltration module (manufactured by Asahi Kasei Chemicals, Microza MF, model: PSP-103). Adding 350 mL of water to the obtained concentrate is repeated 7 times. It is preferable to use the treatment liquid discharged at this time as the treatment liquid.
(1-2) Calculation of content of fragment polymer The content of fragment polymer was calculated from the following (Formula 2).
Fragment polymer content (%) = {dry product of treatment liquid (g)/solid content of polymer particle aqueous dispersion (g)} x 100 (Formula 2)
(1-3) Infrared absorption spectrum measurement The infrared absorption spectrum of the dried product (fragment polymer) obtained in (1-1) was measured (infrared total reflection measurement: ATR method) using a Thermo Nicolet manufactured by JASCO Corporation. Measurement was carried out using NEXUS-670 manufactured by Co., Ltd., equipped with a diamond crystal, at room temperature, with a resolution of 4 cm ^-1 , and with 32 integrations. In the obtained infrared absorption spectrum, the maximum absorbance in the absorption band range of 1550 cm ^-1 to 1650 cm ^-1 was designated as A, and the maximum absorbance in the absorption band range of 1650 cm ^-1 to 1750 cm ^-1 was designated as B. Then, the absorbance ratio B/A was determined.

[Synthesis of polymer particles]
<Manufacture example 1>
In a stainless steel reaction pot equipped with a stirrer, a thermometer, and a cooling tube, 684.8 parts by mass of deionized water and Adecaria Soap SR-20, an anionic reactive surfactant whose main component is an ether sulfate type ammonium salt, were placed. (active ingredient 100% by mass, manufactured by ADEKA) diluted with ion exchange water to 25.0% by mass of active ingredient (hereinafter referred to as "SR-20 (active ingredient 25.0% by mass)") 0.72 mass The internal temperature was raised to 75°C and maintained at the same temperature. In dropping funnel A, 67.2 parts by mass of methyl methacrylate (hereinafter referred to as "MMA"), 67.2 parts by mass of n-butyl acrylate (hereinafter referred to as "BA"), and 1,6-hexanediol dimethacrylate (hereinafter referred to as "16HX") were added. ), 11.3 parts by mass of SR-20 (25.0% by mass of active ingredient), and 123.7 parts by mass of deionized water, and placed in the dropping funnel A for dropping. Pre-emulsion A was prepared. In dropping funnel B, 149.7 parts by mass of methyl acrylate (hereinafter referred to as "MA") and 0.34 parts by mass of divinylbenzene (manufactured by Nippon Steel Chemical & Materials, divinylbenzene purity 81%, hereinafter referred to as "DVB810") , 12.0 parts by mass of SR-20 (active ingredient 25.0% by mass), 0.27 parts by mass of ammonia aqueous solution (concentration 28% by mass), and 137.7 parts by mass of deionized water were added to dropping funnel B. A pre-emulsion B for dropping was prepared in a container. 320 parts by mass of hydrogen peroxide solution (concentration 0.57% by mass) was charged into dropping funnel C. 320 parts by mass of an aqueous L-ascorbic acid solution (concentration 0.89% by mass) was charged into dropping funnel D.
Next, after purging the inside of the reaction vessel with nitrogen gas, 15.0 parts by mass of a mixed monomer composition of 7.5 parts by mass of MMA and 7.5 parts by mass of BA, hydrogen peroxide solution (concentration 0.48% by mass) 20 parts by mass and 20 parts by mass of an aqueous L-ascorbic acid solution (concentration 0.75% by mass) were added into the reaction vessel to perform an initial polymerization reaction. Subsequently, pre-emulsion A for dropping was added from dropping funnel A for 60 minutes, pre-emulsion B for dropping was added for 180 minutes from dropping funnel B, hydrogen peroxide solution was added for 240 minutes from dropping funnel C, and L-ascorbic acid aqueous solution was added from dropping funnel D. was added dropwise for 240 minutes. Note that the dropping pre-emulsion B started dropping immediately after the dropping of the dropping pre-emulsion A was completed. After completion of the dropping, the internal temperature of the reaction vessel was maintained at 75°C, and after aging by maintaining at the same temperature for 2 hours, the reaction solution was cooled to form a polymer particle aqueous dispersion in which polymer particles (1) were dispersed. (1a) was obtained. The solid content of the aqueous polymer particle dispersion (1a) was 13.94% by mass, and the volume average particle diameter of the polymer particles (1) was 191 nm.

<Manufacture example 2>
By mixing 700.0 parts by mass of the polymer particle aqueous dispersion (1a) and 117.6 parts by mass of an aqueous sodium hydroxide solution (concentration 20.0% by mass) as a basic aqueous solution, and stirring at 25 ° C. overnight. A polymer particle aqueous dispersion (2a) in which hydrolyzed polymer particles (2) were dispersed was obtained. At this time, the ratio of the number of moles of sodium hydroxide added to the number of moles of MA in the aqueous dispersion of polymer particles (1a) was 100%. Further, the solid content of the aqueous polymer particle dispersion (2a) was 13.59% by mass, and the volume average particle diameter of the polymer particles (2) was 644 nm.

<Manufacture example 3>
An aqueous polymer particle dispersion (3a) in which polymer particles (3) were dispersed was synthesized in the same manner as in Production Example 1, except that the ratio of the particle composition in Production Example 1 was changed as shown in Table 1. The solid content of the aqueous polymer particle dispersion (3a) was 14.49% by mass, and the volume average particle diameter of the polymer particles (3) was 166 nm. Note that RHMA in Table 1 represents methyl 2-hydroxymethylacrylate.

<Manufacture example 4>
By mixing 700.0 parts by mass of the polymer particle aqueous dispersion (3a) and 51.2 parts by mass of an aqueous sodium hydroxide solution (concentration 20.0% by mass) as a basic aqueous solution, and stirring at 25 ° C. overnight. An aqueous polymer particle dispersion (4a) in which partially hydrolyzed polymer particles (4) were dispersed was obtained. At this time, the ratio of the number of moles of sodium hydroxide added to the total number of moles of RHMA and MA in the aqueous dispersion of polymer particles (3a) was 50%. The solid content of the aqueous polymer particle dispersion (4a) was 12.09% by mass, and the volume average particle diameter of the polymer particles (4) was 548 nm.

<Manufacture example 5>
By mixing 700.0 parts by mass of the polymer particle aqueous dispersion (3a) and 102.4 parts by mass of an aqueous sodium hydroxide solution (concentration 20.0% by mass) as a basic aqueous solution, and stirring at 25 ° C. overnight. A polymer particle aqueous dispersion (5a) in which hydrolyzed polymer particles (5) were dispersed was obtained. At this time, the ratio of the number of moles of sodium hydroxide added to the total number of moles of RHMA and MA in the aqueous dispersion of polymer particles (3a) was 100%. The solid content of the aqueous polymer particle dispersion (5a) was 13.62% by mass, and the volume average particle diameter of the polymer particles (5) was 274 nm.

<Manufacture example 6>
700 g of the polymer particle aqueous dispersion (4a) is concentrated by discharging 350 mL of the treatment liquid using an ultrafiltration module (manufactured by Asahi Kasei Chemicals, Microza MF, model: PSP-103), and 350 mL of water is added. It was purified by repeating this 7 times. A polymer particle aqueous dispersion (6a) with a reduced amount of fragment components was obtained from the polymer particle aqueous dispersion (4a). The solid content of the polymer particle aqueous dispersion (6a) was 7.6% by mass. Incidentally, it is preferable to refer to the minute components contained in the processing liquid when the processing liquid is processed through a filter having an opening corresponding to a volume average particle diameter of 2/3 to 1/7 as a fragment component.

<Manufacture example 7>
In Production Example 6, the aqueous polymer particle dispersion (5a) was used instead of the aqueous polymer particle dispersion (4a) for purification to obtain an aqueous polymer particle dispersion (7a). The solid content of the aqueous polymer particle dispersion (7a) was 8.35% by mass.

<Manufacture example 8>
In Production Example 6, the aqueous polymer particle dispersion (3a) was used instead of the aqueous polymer particle dispersion (4a) for purification, and the fragment polymer of the aqueous polymer particle dispersion (3a) discharged at this time was purified. A processing solution containing the above was obtained as processing solution (1). The treatment liquid (1) was concentrated to a concentration of 6.57% by mass by drying at 120° C. using a hot air dryer to obtain a treatment liquid (2). Polymer particle aqueous dispersion (8a) was prepared by mixing 468 parts by mass of polymer particle aqueous dispersion (6a) (concentration 7.6% by mass) and 232 parts by mass of treatment liquid (2) (concentration 6.57% by mass). ) was obtained. The solid content of the aqueous polymer particle dispersion (8a) was 7.26% by mass.

[Binder evaluation]
[Example 1]
(1-1) Preparation of slurry for electrodes Carboxymethyl cellulose (manufactured by Daicel FineChem Co., Ltd., product name "CMC Daicel 2200", hereinafter referred to as "CMC") was added to ion-exchanged water, and a stirring deaerator (manufactured by Shinky Co., Ltd., A CMC aqueous solution having a concentration of 2% by mass was prepared by stirring and mixing at 2000 rpm for 10 minutes using a Awatori Rentaro ARE-310). 50 parts by mass of the CMC aqueous solution obtained above, 80 parts by mass of negative electrode active material (1) (manufactured by Showa Denko Materials Co., Ltd., graphite active material, "MAGE"), negative electrode active material (2) (manufactured by Shin-Etsu Chemical Co., Ltd.) , silicon active material, "KSC-1265") 20 parts by mass, conductive aid (1) (manufactured by Showa Denko, graphitized carbon fiber, "VGCF-H") 2 parts by mass, conductive aid (2) (Denka) A predetermined amount of ion-exchanged water and 3 parts by mass of carbon black (manufactured by Denka Black, Inc., "Denka Black Powder Product") were added, and the mixture was stirred and mixed at 2000 rpm for 27 minutes using a stirring defoamer. Thereafter, by adding and mixing 22.08 parts by mass of the polymer aqueous dispersion (2a) (concentration 13.59% by mass) obtained in Production Example 2 (concentration 13.59% by mass) as a binder (2b) and a predetermined amount of ion-exchanged water. An electrode slurry (negative electrode composition) was prepared. At that time, the amount of ion-exchanged water to be added was adjusted so that the viscosity of the electrode slurry was 800±300 mPa·s. Table 2 shows the solid content of the electrode slurry.

(1-2) Density evaluation before pressing The electrode slurry obtained above was applied to a copper foil (manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd., thickness 16 μm) as a current collector, and the coating weight after drying was 5.69 μm. It was coated with an applicator to give a weight of ~5.95 g/cm ² , dried with hot air at 60°C for 10 minutes, and then vacuum-dried at 80°C for 10 hours to obtain a pre-pressed negative electrode. Thereafter, three circular pieces (Φ12 mm) were punched out from the unpressed negative electrode to obtain three negative electrode composite layers. The thickness and weight of each negative electrode composite material layer were measured, and the average value thereof was calculated. At that time, the thickness and weight of each negative electrode composite material layer were measured three times, and the average value of the three measurements was taken as the measured value of the thickness and weight of each negative electrode composite material layer. Then, the density before pressing (g/cm ³ ) was calculated from the following (Formula 1).
Density before pressing (g/cm ³ )=Negative electrode composite layer weight (g)/{1.1304 (cm ² )×Negative electrode composite material thickness (cm)} (Formula 1)
Table 2 shows the results of the density before pressing.

(1-3) Preparation of negative electrode for battery evaluation The electrode slurry obtained above was applied to a copper foil (manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd., thickness 16 μm) as a current collector, so that the coating weight after drying was It was coated with an applicator at a weight of 5.82 g/cm ² , dried with hot air at 60°C for 10 minutes, and then vacuum-dried at 80°C for 10 hours. Thereafter, the material was pressure-molded using a roll press machine until the density reached 1.5 g/cm ³ to obtain a negative electrode.

(1-4) Production of battery A lithium foil (manufactured by Honjo Kinzoku Co., Ltd., thickness 0.5 mm) was used as a positive electrode, the negative electrode obtained above, and a polyethylene separator (thickness 25 μm) were each placed in a circular shape (negative electrode Φ12 mm, lithium foil It was punched out into Φ15mm, separator Φ16mm). Using CR2032 coin battery parts (manufactured by Hosensha: case (made of SUS316L), cap (made of SUS316L), spacer (0.5 mm thick, made of SUS316L), wave washer (made of SUS316L), gasket (made of polypropylene)) Each coin-type lithium ion secondary battery was manufactured using the following procedure.
First, a cap with a gasket attached, lithium foil, and a separator were layered in this order. Next, ethylene carbonate (manufactured by Kishida Chemical Co., Ltd.): dimethyl carbonate (manufactured by Kishida Chemical Co., Ltd.): fluoroethylene carbonate (manufactured by Kishida Chemical Co., Ltd.): fluoroethylene carbonate (manufactured by Kishida Chemical Co., Ltd.) = 2:7:1 (volume ratio) solution was mixed with LiPF ₆ (manufactured by Stella Chemifa). The separator was impregnated with an electrolytic solution prepared by dissolving the following at a concentration of 1.0 mol/L. Then, place the negative electrode obtained above so that the negative electrode coated surface faces the lithium foil, stack the spacer, wave washer, and case on top of it in this order, and seal it with a crimping machine (manufactured by Hosensha). A coin-type lithium-ion secondary battery was fabricated using this method.

(1-5) Charge/discharge test The coin-type lithium ion secondary battery (designed capacity 3.73 mAh) obtained above was tested using a charge/discharge test device (manufactured by Asuka Electronics) in an environment at a temperature of 25°C. The capacity retention rate was measured. Constant current constant voltage discharge to 0.01V at 0.1C, constant current charge to 1.5V in the order of 0.1C, 0.1C, 0.2C, 1C, 2C, 0.1C, each charge/discharge. The charging/discharging test was sometimes conducted with a charging/discharging pause time of 10 minutes. Table 2 shows the capacity retention rate. It can be said that the higher the capacity retention rate, the better the cycle characteristics.

[Example 2]
Instead of the binder (2b), which is the aqueous polymer dispersion (2a) obtained in Production Example 2, the aqueous polymer dispersion (4a) obtained in Production Example 4 (concentration 12.09%) was used as the binder (2b). Evaluation was performed in the same manner as in Example 1, except that 24.81 parts by mass of 4b) was used.

[Example 3]
Instead of the binder (2b) which is the aqueous polymer dispersion (2a) obtained in Production Example 2, the aqueous polymer dispersion (7a) obtained in Production Example 7 (concentration 8.35%) was used as the binder (2b). Evaluation was performed in the same manner as in Example 1, except that 35.92 parts by mass of 7b) was used.

[Comparative example 1]
Instead of the binder (2b) which is the aqueous polymer dispersion (2a) obtained in Production Example 2, the aqueous polymer dispersion (1a) obtained in Production Example 1 (concentration 13.94%) was used as the binder (2b). Evaluation was performed in the same manner as in Example 1, except that 21.52 parts by mass of 1b) was used.

[Comparative example 2]
Instead of the binder (2b) which is the aqueous polymer dispersion (2a) obtained in Production Example 2, the aqueous polymer dispersion (8a) obtained in Production Example 8 (concentration 7.26%) was used as the binder (2b). Evaluation was performed in the same manner as in Example 1, except that 41.33 parts by mass of 8b) was used.

From the results in Tables 1 and 2, it is clear that the electrode slurry containing the binder for lithium secondary batteries of the present disclosure has excellent dispersibility, and the obtained lithium ion secondary batteries exhibit high cycle characteristics. became.

Claims (5)

A binder for a lithium ion secondary electrode containing polymer particles,
The ratio (B/A) of the maximum absorbance B of 1650 cm ^-1 to 1750 cm ^-1 to the maximum absorbance A of 1550 cm ^-1 to 1650 cm ^-1 in the absorption band in the infrared spectrum of the polymer particles is 0 to 1. A binder for a lithium ion secondary electrode, comprising a fragment polymer having a composition of .5. The binder for a lithium ion secondary electrode according to claim 1, wherein the ratio (B/A) of the maximum absorbance B to the maximum absorbance A of the fragment polymer is 0 to 1.0. The binder for a lithium ion secondary electrode according to claim 1, wherein the polymer particles contain 0.1 to 60% by mass of the fragment polymer. The binder for a lithium ion secondary electrode according to claim 1, wherein the polymer particles have a core-shell structure. The binder for a lithium ion secondary electrode according to claim 1, wherein the polymer particles have a volume average particle diameter of 0.01 to 5 μm.