JP7238379B2 - Thermally crosslinkable binder aqueous solution for lithium ion battery, electrode slurry for lithium ion battery and method for producing the same, electrode for lithium ion battery, and lithium ion battery - Google Patents

Description

The present disclosure relates to a thermally crosslinkable binder aqueous solution for lithium ion batteries, an electrode slurry for lithium ion batteries and a method for producing the same, an electrode for lithium ion batteries, and a lithium ion battery.

Lithium ion batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvements in battery members such as electrodes have been studied for the purpose of further improving the performance of lithium ion batteries.

For both the positive electrode and the negative electrode of a lithium ion battery, an electrode active material and a binder resin are dispersed in a solvent to form a slurry, which is coated on both sides of a current collector (for example, a metal foil), and the solvent is removed by drying to form an electrode. After forming the layers, it is manufactured by compression molding with a roll press machine or the like.

Lithium ion battery slurries mainly contain an active material, a binder and a solvent. Binders have generally been polyvinylidene fluoride (PVdF) as a binder resin dissolved in organic solvents such as N-methyl-2-pyrrolidone (NMP), and styrene as a binder resin for particulate resins in aqueous dispersions. A butadiene-based emulsion (SBR latex) is used.

In recent years, various electrode active materials have been proposed for lithium ion battery electrodes from the viewpoint of increasing battery capacity. However, depending on the electrode active material, it is easy to expand and contract with charging and discharging. Therefore, lithium-ion battery electrodes, which tend to expand and contract with charging and discharging, undergo volume changes (spring-back properties) from the initial stage of repeated charging and discharging. can be easily lowered.

Therefore, in the field, studies have been made to solve the above problems with binder resins. For example, it is proposed that good charge-discharge characteristics can be obtained by using polyacrylamide (Patent Documents 1 and 2) as a binder for water-soluble resins. It is In addition, it has been proposed to add a cross-linking agent to a particulate resin, which is a binder resin, to suppress expansion and contraction of an active material due to charging and discharging (Patent Document 3). The cross-linking agent usually causes a cross-linking reaction in the drying process after the slurry composition is applied to the current collector, and forms cross-links between particles of the particulate resin.

Japanese Unexamined Patent Application Publication No. 2015-118908 JP 2015-106488 A WO2015/098507

However, the polyacrylamides of Patent Documents 1 and 2 cannot have a high molecular weight that makes the binder resin insoluble in water, from the viewpoint of ensuring water solubility. As a result, there is a problem that the resistance to springback caused by the expansion of the active material is insufficient.

In some cases, the combined use of the cross-linking agent described in Patent Document 3 does not exhibit the effect even if a large amount is added. In such a case, if a large amount of a cross-linking agent is added in order to exhibit the effect of the cross-linking agent, for example, resistance to springback, the adhesion of the electrode active material layer to the current collector will rather decrease, resulting in poor high-temperature cycle characteristics. There is room for further improvement because the desired effect may not be obtained.

Furthermore, binder compositions containing a cross-linking agent and a particulate binder may deteriorate during storage between preparation and use, and may not exhibit desired performance. For example, during the storage period after preparation, unintended cross-linking may proceed, resulting in increased viscosity and decreased reactivity of the cross-linking agent.

Therefore, the problem to be solved by the present invention is a slurry for a lithium ion battery that can impart battery characteristics such as good electrode adhesion and springback resistance to a lithium ion battery, and a thermal bridge for a lithium ion battery that can produce the slurry An object of the present invention is to provide an aqueous binder solution.

As a result of intensive studies aimed at solving the above problems, the present inventors have found that the above problems can be achieved by using an aqueous binder solution containing, as a main component, poly(meth)acrylamide having predetermined physical properties and containing a predetermined unsaturated monomer. was found to be able to solve the problem, and the present invention was completed.

＜式中、Ｒ^１は水素原子又はメチル基を表し、Ｒ^２は置換若しくは非置換の炭素数が１～５のオキシアルキレン基、一般式（２）：

（式中、ｑは１～３の整数であり、ｎは１以上の整数である。）
で示されるポリオキシアルキレン基、

又はこれらの組合せを表す。＞
（項目３）
上記項目のいずれか１項に記載のリチウムイオン電池用熱架橋性バインダー水溶液と、電極活物質（Ｂ）を含む、リチウムイオン電池用電極スラリー。
（項目４）
前記電極活物質（Ｂ）１００質量％に対し、前記リチウムイオン電池用熱架橋性バインダー水溶液に含まれる水酸基含有水溶性ポリ（メタ）アクリルアミド（Ａ）が１～１５質量％である、上記項目に記載のリチウムイオン電池用電極スラリー。
（項目５）
前記電極活物質（Ｂ）が炭素層で覆われたシリコン又はシリコンオキサイドを５質量％以上含む、上記項目のいずれか１項に記載のリチウムイオン電池用電極スラリー。
（項目６）
単量体群１００モル％に対して、
（メタ）アクリルアミド基含有化合物（ａ）を３０～９５モル％、
水酸基含有（メタ）アクリルエステル（ｂ）を５～５０モル％含む単量体群の重合物であり、硬化物のゲル分率が２０％以上である
水酸基含有水溶性ポリ（メタ）アクリルアミド（Ａ）、及び電極活物質（Ｂ）を混合する工程を含む、上記項目のいずれか１項に記載のリチウムイオン電池用電極スラリーの製造方法。
（項目７）
上記項目のいずれか１項に記載のリチウムイオン電池用電極スラリーを集電体に塗布し乾燥させることにより得られる、リチウムイオン電池用電極。
（項目８）
前記集電体が銅箔である、上記項目に記載のリチウムイオン電池用電極。
（項目９）
８０～２００℃で乾燥する工程により得られる、上記項目のいずれか１項に記載のリチウムイオン電池用電極。
（項目１０）
上記項目のいずれか１項に記載のリチウムイオン電池用電極を含む、リチウムイオン電池。 The following items are provided by this disclosure.
(Item 1)
With respect to 100 mol% of the monomer group,
30 to 95 mol% of the (meth)acrylamide group-containing compound (a),
It is a polymer of a monomer group containing 5 to 50 mol% of a hydroxyl group-containing (meth)acrylic ester (b), and the gel fraction of the cured product is 20% or more.
An aqueous thermally crosslinkable binder solution for a lithium ion battery, containing a hydroxyl group-containing water-soluble poly(meth)acrylamide (A).
(Item 2)
The aqueous thermally crosslinkable binder solution for lithium ion batteries according to the above items, wherein the hydroxyl group-containing (meth)acrylic ester (b) is represented by the following general formula (1).
General formula (1):

<wherein R ¹ represents a hydrogen atom or a methyl group, R ² represents a substituted or unsubstituted oxyalkylene group having 1 to 5 carbon atoms, general formula (2):

(Wherein, q is an integer of 1 to 3, and n is an integer of 1 or more.)
A polyoxyalkylene group represented by

or a combination thereof. ＞
(Item 3)
An electrode slurry for lithium ion batteries, comprising the thermally crosslinkable binder aqueous solution for lithium ion batteries according to any one of the above items and an electrode active material (B).
(Item 4)
The above item, wherein the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) contained in the aqueous thermally crosslinkable binder solution for a lithium ion battery is 1 to 15% by mass with respect to 100% by mass of the electrode active material (B). An electrode slurry for a lithium ion battery as described.
(Item 5)
The electrode slurry for a lithium ion battery according to any one of the above items, wherein the electrode active material (B) contains 5% by mass or more of silicon or silicon oxide covered with a carbon layer.
(Item 6)
With respect to 100 mol% of the monomer group,
30 to 95 mol% of the (meth)acrylamide group-containing compound (a),
Hydroxyl-containing water-soluble poly(meth)acrylamide (A), which is a polymer of a monomer group containing 5 to 50 mol% of a hydroxyl-containing (meth)acryl ester (b) and having a cured product gel fraction of 20% or more. ), and a step of mixing the electrode active material (B).
(Item 7)
A lithium ion battery electrode obtained by coating a current collector with the lithium ion battery electrode slurry according to any one of the above items and drying the slurry.
(Item 8)
The lithium ion battery electrode according to the above items, wherein the current collector is a copper foil.
(Item 9)
The lithium ion battery electrode according to any one of the above items, which is obtained by a step of drying at 80 to 200°C.
(Item 10)
A lithium ion battery comprising the lithium ion battery electrode according to any one of the above items.

Since the lithium ion battery electrode slurry of the present invention contains the hydroxyl group-containing water-soluble poly(meth)acrylamide (A), it has excellent storage stability. Moreover, since it has thermal crosslinkability, it is possible to obtain a lithium ion battery with improved springback resistance by using an electrode obtained from the slurry.

Since the lithium ion battery electrode of the present invention is obtained using the slurry containing the hydroxyl group-containing water-soluble poly(meth)acrylamide (A), thermal crosslinking proceeds to increase the battery capacity. Also provides a lithium ion battery with excellent springback resistance.

Since the lithium ion battery of the present invention is equipped with the electrode of the present invention, it is excellent in springback resistance.

Throughout the present disclosure, the range of numerical values for each physical property value, content, etc. can be set as appropriate (for example, by selecting from the upper and lower limit values described in each item below). Specifically, for the numerical value α, when the upper limit of the numerical value α is A1, A2, A3, etc., and the lower limit of the numerical value α is B1, B2, B3, etc., the range of the numerical value α is A1 or less, A2 or less, A3 or less, B1 or more, B2 or more, B3 or more, A1-B1, A1-B2, A1-B3, A2-B1, A2-B2, A2-B3, A3-B1, A3-B2, A3-B3 etc. are exemplified.

[1. Thermally crosslinkable binder aqueous solution for lithium ion battery (also referred to as aqueous solution (1))]
In the present disclosure, with respect to 100 mol% of the monomer group,
30 to 95 mol% of the (meth)acrylamide group-containing compound (a),
Hydroxyl-containing water-soluble poly(meth)acrylamide (hydroxyl-containing water-soluble poly(meth)acrylamide ( Provided is an aqueous thermally crosslinkable binder solution for lithium ion batteries comprising A).

<(Meth)acrylamide group-containing compound (a) (hereinafter also referred to as component (a))>
In the present disclosure, "(meth)acrylamide group-containing compound" means a compound having a (meth)acrylamide group. As the (meth)acrylamide group-containing compound, various known compounds can be used without particular limitation, and may be used alone or in combination of two or more.

In the present disclosure, "(meth)acryl" means "at least one selected from the group consisting of acryl and methacryl." Similarly, "(meth)acrylate" means "at least one selected from the group consisting of acrylate and methacrylate". "(Meth)acryloyl" means "at least one selected from the group consisting of acryloyl and methacryloyl".

（式中、Ｒ^１は水素又はメチル基であり、Ｒ^２及びＲ^３はそれぞれ独立して、水素、置換若しくは非置換のアルキル基、アセチル基、又はスルホン酸基であるか、或いはＲ^２及びＲ^３が一緒になって環構造を形成する基であり、Ｒ^４及びＲ^５はそれぞれ独立して、水素、置換若しくは非置換のアルキル基、カルボキシル基、ヒドロキシ基、アミノ基（－ＮＲ^ａＲ^ｂ（Ｒ^ａ及びＲ^ｂはそれぞれ独立して水素又は置換若しくは非置換のアルキル基である）（以下同様））、アセチル基、スルホン酸基である。置換アルキル基の置換基はヒドロキシ基、アミノ基、アセチル基、スルホン酸基等が例示される。また、Ｒ^２及びＲ^３が一緒になって環構造を形成する基は、モルホリル基等が例示される。）
により表される。 In one embodiment, the (meth)acrylamide group-containing compound has the following structural formula

(wherein R ¹ is hydrogen or a methyl group, R ² and R ³ are each independently hydrogen, a substituted or unsubstituted alkyl group, an acetyl group, or a sulfonic acid group, or R ² and R ³ is a group that together forms a ring structure, R ⁴ and R ⁵ are each independently hydrogen, a substituted or unsubstituted alkyl group, a carboxyl group, a hydroxy group, an amino group (-NR ^a R ^b (R ^a and R ^b are each independently hydrogen or a substituted or unsubstituted alkyl group) (the same shall apply hereinafter)), acetyl group, sulfonic acid group Substituents of the substituted alkyl group are hydroxy group, amino group, acetyl group, sulfonic acid group, etc. Also, the group in which ^R2 and ^R3 together form a ring structure is exemplified by morpholyl group, etc.)
is represented by

Alkyl groups are exemplified by linear alkyl groups, branched alkyl groups, cycloalkyl groups and the like.

A straight-chain alkyl group is represented by a general formula of -C _n H _2n+1 (n is an integer of 1 or more). Linear alkyl groups include methyl group, ethyl group, propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decamethyl group, etc. are exemplified.

A branched alkyl group is a group in which at least one hydrogen of a straight-chain alkyl group has been replaced by an alkyl group. Branched alkyl groups are exemplified by diethylpentyl, trimethylbutyl, trimethylpentyl, trimethylhexyl and the like.

The cycloalkyl group is exemplified by a monocyclic cycloalkyl group, a bridged ring cycloalkyl group, a condensed ring cycloalkyl group and the like.

In the present disclosure, monocyclic means a cyclic structure with no internal bridging structure formed by covalent carbon bonds. Fused rings also refer to cyclic structures in which two or more single rings share two atoms (ie, each ring shares (condenses) only one edge with each other). Bridged ring means a cyclic structure in which two or more single rings share three or more atoms.

Monocyclic cycloalkyl groups are exemplified by cyclopentyl, cyclohexyl, cycloheptyl, cyclodecyl and 3,5,5-trimethylcyclohexyl groups.

The bridging ring cycloalkyl group is exemplified by a tricyclodecyl group, an adamantyl group, a norbornyl group and the like.

The condensed ring cycloalkyl group is exemplified by a bicyclodecyl group and the like.

The (meth)acrylamide group-containing compound (a) includes (meth)acrylamide, N-isopropyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N- dimethylaminopropyl (meth)acrylamide, N-methylol (meth)acrylamide, diacetone (meth)acrylamide, maleic acid amide, (meth)acrylamide t-butylsulfonic acid, (meth)acryloylmorpholine, hydroxyethyl (meth)acrylamide, and salts thereof and the like, and the above salts are exemplified by dimethylaminopropyl(meth)acrylamide methyl chloride quaternary salt, dimethylaminoethyl(meth)acrylate benzyl chloride quaternary salt and the like. Among these, (meth)acrylamide, especially acrylamide, is highly water-soluble, has a high interaction with the electrode active material, and is a binder with high slurry dispersibility and binding between the electrode active materials inside the electrode. can be made.

The upper limit of the content of the (meth)acrylamide group-containing compound in 100 mol% of the monomer group is exemplified by 95, 90, 80, 70, 60, 59, 50, 40, 35 mol%, etc., and the lower limit is , 90, 80, 70, 60, 59, 50, 40, 35, 30 mol %, and the like. In one embodiment, the lower limit of the content is preferably 30 mol% or more. The content range is preferably 30 to 95 mol%, more preferably 30 to 93 mol%, and particularly preferably 30 to 90 mol%. By setting the above content, the dispersibility of the electrode active material and filler is improved, and it is possible to produce a uniform electrode active material layer and protective film, which eliminates structural defects and exhibits good charge-discharge characteristics. , the oxidation resistance of the polymer is improved, so deterioration at high voltage is suppressed and good charge-discharge durability characteristics are exhibited, but the present invention is not intended to be limited to this.

The upper limit of the content of the (meth)acrylamide group-containing compound with respect to 100% by mass of the monomer group is exemplified by 80, 75, 70, 60, 50, 40, 30, 25% by mass, etc., and the lower limit is 75, Examples include 70, 60, 50, 40, 30, 25, 20% by mass. In one embodiment, the content of the (meth)acrylamide group-containing compound with respect to 100% by mass of the monomer group is preferably 20 to 80% by mass.

<Hydroxyl group-containing (meth)acrylic ester (b) (also referred to as component (b))>
In the present disclosure, "hydroxyl group-containing (meth)acrylic ester" means a compound having a hydroxyl group and a (meth)acrylic acid ester group. Various known hydroxyl group-containing (meth)acrylic esters can be used without particular limitation, and may be used alone or in combination of two or more.

＜式中、Ｒ^１は水素原子又はメチル基を表し、Ｒ^２は置換若しくは非置換の炭素数が１～５のオキシアルキレン基、一般式（２）：

（式中、ｑは１～３の整数であり、ｎは１以上の整数である。）
で示されるポリオキシアルキレン基、

又はこれらの組合せを表す。＞
で表わされる水酸基含有（メタ）アクリルエステル（ｂ）、特に（メタ）アクリル酸ヒドロキシエチル、ポリエチレングリコール－モノ（メタ）アクリレートは入手が容易であることと、これらを用いると水溶性が高い水酸基含有水溶性ポリ（メタ）アクリルアミド（Ａ）を合成できることから好ましい。 The hydroxyl group-containing (meth)acrylic ester (b) includes hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, and (meth)acrylic acid 3. - hydroxy-1-adamantyl, 1,4-cyclohexanedimethanol mono (meth) acrylate, glycerin mono (meth) acrylate, glycerin di (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, tri ( Examples include pentaerythritol meth)acrylate, polyethylene glycol-mono(meth)acrylate, polypropylene glycol-mono(meth)acrylate, polyethylene glycol-propylene glycol-mono(meth)acrylate and the like.
Among these, general formula (1):

<wherein R ¹ represents a hydrogen atom or a methyl group, R ² represents a substituted or unsubstituted oxyalkylene group having 1 to 5 carbon atoms, general formula (2):

(Wherein, q is an integer of 1 to 3, and n is an integer of 1 or more.)
A polyoxyalkylene group represented by

or a combination thereof. ＞
Hydroxyl group-containing (meth) acrylic ester (b) represented by, especially hydroxyethyl (meth) acrylate, polyethylene glycol - mono (meth) acrylate is easy to obtain, and when these are used, water-soluble high hydroxyl group-containing It is preferable because water-soluble poly(meth)acrylamide (A) can be synthesized.

The alkylene group is exemplified by a linear alkylene group, a branched alkylene group, a cycloalkylene group and the like.

A straight-chain alkylene group can be represented by the general formula —(CH ₂ ) _n — (n is an integer of 1 or more). The linear alkylene group is exemplified by a methylene group, ethylene group, propylene group, n-butylene group, n-pentylene group and the like.

A branched alkylene group is a group in which at least one hydrogen of a linear alkylene group has been replaced by an alkyl group. A branched alkylene group includes a methylmethylene group, an ethylmethylene group, a propylmethylene group, a butylmethylene group, a methylethylene group, an ethylethylene group, a propylethylene group, a methylpropylene group, a 2-ethylpropylene group, a dimethylpropylene group, and a methylbutylene group. etc. are exemplified.

The cycloalkylene group is exemplified by a monocyclic cycloalkylene group, a bridged ring cycloalkylene group, a condensed ring cycloalkylene group and the like.

A monocyclic cycloalkylene group is exemplified by a cyclopentylene group and the like.

In one embodiment, the upper limit of the content of the hydroxyl group-containing (meth)acrylic ester (b) with respect to 100 mol% of the monomer group is 50, 48, 45, 40, 30, 20, 10, 5.5, Examples include 5.1 mol %, and the lower limits include 48, 45, 40, 30, 20, 10, 5.5, 5.1, 5 mol % and the like. In one embodiment, the content is preferably 5 to 50 mol%, more preferably 5.5 to 48 mol%. By setting the content of the hydroxyl group-containing (meth)acrylic ester (b) to 100 mol% of the monomer group within the above range, thermal crosslinking sufficiently proceeds, and an aqueous solution of a thermally crosslinkable binder or a thermally crosslinkable electrode slurry is obtained. It is considered that the effect of springback resistance during charge and discharge can be exhibited while ensuring the storage stability of the present invention, but the present invention is not intended to be limited to this.

The upper limit of the content of the hydroxyl group-containing (meth) acrylic ester (b) with respect to 100% by mass of the monomer group is exemplified by 70, 65, 60, 50, 40, 30, 20, 15% by mass, etc., and the lower limit is , 65, 60, 50, 40, 30, 20, 15, 10% by mass, and the like. In one embodiment, the content of the hydroxyl group-containing (meth)acrylic ester (b) is preferably 10 to 70% by mass with respect to 100% by mass of the monomer group.

<Monomers other than components (a) and (b) (also referred to as component (c))>
In the above monomer group, monomers other than components (a) and (b) (component (c)) can be used as long as the desired effects of the present invention are not impaired. Component (c) may be used alone or in combination of two or more. Component (c) includes acid group-containing monomers such as unsaturated carboxylic acids, unsaturated sulfonic acids, and unsaturated phosphoric acids, hydroxyl group-free unsaturated carboxylic acid esters, α,β-unsaturated nitrile compounds, and conjugated diene compounds. , aromatic vinyl compounds, and the like.

Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid and salts thereof.

The content of the unsaturated carboxylic acid is not particularly limited, but considering the reaction with the component (b), less than 45 mol% relative to 100 mol% of the monomer group (e.g., 42, 41, 40, 30, 20, 19, 15, 10, 5, less than 1 mol %, 0 mol %) are preferred.

In one embodiment, the content of the unsaturated carboxylic acid is less than 45% by mass (e.g., 42, 41, 40, 30, 20, 19, 15, 10, 5, 1 mass%) relative to 100% by mass of the monomer group. %, 0% by mass) is preferred.

Unsaturated sulfonic acids include α,β-ethylenically unsaturated sulfonic acids such as vinylsulfonic acid, styrenesulfonic acid, (meth)allylsulfonic acid; (meth)acrylamide t-butylsulfonic acid, 2-(meth)acrylamide- 2-methylpropanesulfonic acid, 2-(meth)acrylamido-2-hydroxypropanesulfonic acid, 3-sulfopropane (meth)acrylic acid ester, bis-(3-sulfopropyl) itaconic acid ester and salts thereof, etc. be done. The content of the unsaturated sulfonic acid is not particularly limited, but considering the reaction with the component (b), the upper limit of the content of the unsaturated sulfonic acid with respect to 100 mol% of the monomer group is 40, 30, 20, 19, 15, 10, 5, 1, 0.5, 0.1, 0.05, 0.02, 0.01 mol%, etc., and the lower limit is 30, 20, 19, 15, 10, 5 , 1, 0.5, 0.1, 0.05, 0.02, 0.01, 0 mol %, and the like.

The upper limit of the unsaturated sulfonic acid content relative to 100% by mass of the monomer group is 40, 30, 20, 19, 15, 10, 5, 1, 0.5, 0.1, 0.05, 0.02. , 0.01% by mass, etc., and the lower limits are 30, 20, 19, 15, 10, 5, 1, 0.5, 0.1, 0.05, 0.02, 0.01, 0 mass % etc. are exemplified.

Unsaturated phosphoric acid monomers include vinyl phosphonic acid, vinyl phosphate, bis((meth)acryloxyethyl)phosphate, diphenyl-2-(meth)acryloyloxyethyl phosphate, dibutyl-2-(meth)acryloyloxy Ethyl phosphate, dioctyl-2-(meth)acryloyloxyethyl phosphate, monomethyl-2-(meth)acryloyloxyethyl phosphate, 3-(meth)acryloxy-2-hydroxypropane phosphate and salts thereof are exemplified. be. The content of the unsaturated phosphoric acid is not particularly limited, but considering the reaction with the component (b), less than 40 mol% (for example, 30, 20, 19, 15, 10, 100 mol% of the monomer group) 5, less than 1 mol %, 0 mol %) are preferred.

The content of the unsaturated phosphoric acid monomer relative to 100% by mass of the monomer group is preferably less than 40% by mass (eg, less than 30, 20, 19, 15, 10, 5, 1% by mass, 0% by mass).

In one embodiment, the content of acid group-containing monomers such as unsaturated carboxylic acids, unsaturated sulfonic acids, and unsaturated phosphoric acids relative to 100 mol% of the monomer group is less than 40 mol% (e.g., 30, 20 , 19, 15, 10, 5, less than 1 mol %, 0 mol %).

In one embodiment, the content of acid group-containing monomers such as unsaturated carboxylic acids, unsaturated sulfonic acids, and unsaturated phosphoric acids relative to 100% by mass of the monomer group is less than 40% by mass (e.g., 30, 20 , 19, 15, 10, 5, less than 1% by weight, 0% by weight).

The hydroxyl-free unsaturated carboxylic acid ester is preferably a hydroxyl-free (meth)acrylic acid ester. Hydroxyl-free (meth)acrylates include hydroxyl-free linear (meth)acrylates, hydroxyl-free branched (meth)acrylates, hydroxyl-free alicyclic (meth)acrylates, and hydroxyl-free substituted (Meth)acrylic acid ester and the like are exemplified.

Hydroxyl group-free linear (meth) acrylic acid esters include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, and (meth) acrylic acid. Examples include n-amyl, hexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, and decyl (meth)acrylate.

Examples of hydroxyl-free branched (meth)acrylates include i-propyl (meth)acrylate, i-butyl (meth)acrylate, i-amyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and the like. be done.

The hydroxyl-free alicyclic (meth)acrylic acid ester is exemplified by cyclohexyl (meth)acrylate.

The content of the hydroxyl-free unsaturated carboxylic acid ester is not particularly limited, but the use of the hydroxyl-free unsaturated carboxylic acid ester reduces the glass transition temperature of the hydroxyl-containing water-soluble poly(meth)acrylamide (A) of the present invention. It is possible to suppress the curling of the electrodes due to On the other hand, considering the springback resistance of the lithium ion battery of the present invention, the content of the hydroxyl-free unsaturated carboxylic acid ester is less than 40 mol% (for example, 30, 20, 19, 100 mol% of the monomer group). 15, 10, 5, less than 1 mol %, 0 mol %) are preferred.

In one embodiment, the content of the hydroxyl-free unsaturated carboxylic acid ester relative to 100% by mass of the monomer group is less than 40% by mass (for example, 30, 20, 19, 15, 10, 5, less than 1% by mass, 0 % by mass) is preferred.

An α,β-unsaturated nitrile compound can be preferably used for the purpose of imparting flexibility to the electrode of the present invention. The α,β-unsaturated nitrile compounds are exemplified by (meth)acrylonitrile, α-chloro(meth)acrylonitrile, α-ethyl(meth)acrylonitrile, vinylidene cyanide and the like. Among these, (meth)acrylonitrile is preferred, and acrylonitrile is particularly preferred. The content of the α,β-unsaturated nitrile compound is not particularly limited, but less than 40 mol% (for example, 30, 20, 19, 15, 10, 5, less than 1 mol%, 0 mol %) is preferred. By being less than 40 mol% with respect to 100 mol% of the monomer group, the electrode layer of the slurry becomes uniform while maintaining the solubility in water of the hydroxyl group-containing water-soluble poly(meth)acrylamide (A). Makes it easier to be flexible.

In one embodiment, the content of the α,β-unsaturated nitrile compound with respect to 100% by mass of the monomer group is less than 40% by mass (for example, less than 30, 20, 19, 15, 10, 5, 1% by mass, 0% by mass) is preferred.

Conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadiene, substituted and side chain conjugated hexadiene. The content of the conjugated diene compound is not particularly limited, but from the viewpoint of springback resistance of the lithium ion battery according to the present invention, it is preferably less than 10 mol%, more preferably 0 mol%, out of 100 mol% of the monomer group. preferable.

In one embodiment, the content of the conjugated diene compound with respect to 100% by mass of the monomer group is preferably less than 10% by mass, more preferably 0% by mass.

Examples of aromatic vinyl compounds include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene and the like. The content of the aromatic vinyl compound is not particularly limited, but from the viewpoint of the springback resistance of the lithium ion battery according to the present invention, it is preferably less than 10 mol% of 100 mol% of the monomer group, and 0 mol%. more preferred.

In one embodiment, the content of the aromatic vinyl compound relative to 100% by mass of the monomer group is preferably less than 10% by mass, more preferably 0% by mass.

( The proportion of component c) in the monomer group is less than 10 mol%, less than 5 mol%, less than 1 mol%, less than 0.1 mol%, and 0.01 mol with respect to 100 mol% of the monomer group. %, less than 0 mol%, relative to 100% by mass of the monomer group, less than 10% by mass, less than 5% by mass, less than 1% by mass, less than 0.5% by mass, less than 0.1% by mass, 0 Less than 0.01% by weight, 0% by weight.

<Method for producing hydroxyl group-containing water-soluble poly(meth)acrylamide (A)>
Hydroxyl group-containing water-soluble poly(meth)acrylamide (A) can be synthesized by various known polymerization methods, preferably radical polymerization method. The polymerization reaction is carried out by adding a radical polymerization initiator and, if necessary, a chain transfer agent to a monomer mixture containing (a) component, (b) component, and optionally (c) component, and stirring. The reaction temperature may be about 50 to 100°C. The reaction time is not particularly limited, and is preferably about 1 to 10 hours.

Various known radical polymerization initiators can be used without particular limitation. The radical polymerization initiator is a persulfate such as potassium persulfate and ammonium persulfate; a redox polymerization initiator obtained by combining the above persulfate with a reducing agent such as sodium hydrogen sulfite; 2,2'-azobis-2-amidino Examples include azo initiators such as propane dihydrochloride. The amount of the radical polymerization initiator used is not particularly limited, but is preferably 0.05 to 5.00% by mass, and 0.1 to 3.0% by mass with respect to 100% by mass of the monomer group that provides component (A). more preferred.

Prior to the radical polymerization reaction and/or when water-solubilizing the obtained component (A), for the purpose of improving production stability, common solvents such as ammonia, organic amines, potassium hydroxide, sodium hydroxide, lithium hydroxide, etc. A neutralizing agent may be used to adjust the pH of the reaction solution. In that case, the pH is preferably 2-11. For the same purpose, it is also possible to use EDTA or a salt thereof, which is a metal ion sealant.

When the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) has an acid group, the neutralization rate (100% neutralization rate is included in the hydroxyl group-containing water-soluble poly(meth)acrylamide (A)) The neutralization rate of 50% is half the number of moles of the acid component contained in the hydroxyl group-containing water-soluble poly(meth)acrylamide (A). neutralized with alkali) can be adjusted and used. Although the neutralization rate when dispersing the electrode active material is not particularly limited, it is preferably 70 to 120%, more preferably 80 to 120% after forming the coating layer and the like. By setting the neutralization rate after the coating layer is produced within the above range, most of the acid is neutralized, which is preferable because it does not bind to Li ions or the like in the battery to cause a decrease in capacity. Examples of neutralized salts include Li salts, Na salts, K salts, ammonium salts, Mg salts, Ca salts, Zn salts, Al salts and the like.

<Physical properties of hydroxyl group-containing water-soluble poly(meth)acrylamide (A)>
In the present disclosure, "water-soluble" means that the insoluble matter is less than 0.5% by mass when 0.5 g of the compound is dissolved in 100 g of water at 25°C.

The glass transition point of the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) is not particularly limited, but is preferably 0°C or higher (10°C or higher, 20°C or higher, etc.), and from the viewpoint of mechanical strength and heat resistance, 30°C or higher. (40° C. or higher, 45° C. or higher, etc.) is more preferable.

The glass transition temperature of the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) is the combination of the (meth)acrylamide group-containing compound (a), the hydroxyl group-containing (meth)acrylic ester (b), and the copolymer monomer (c). can be adjusted by In the hydroxyl group-containing water-soluble poly(meth)acrylamide (A), the glass transition temperature is the following: (meth)acrylamide group-containing compound (a), hydroxyl group-containing (meth)acrylic ester (b), copolymer monomer (c) can be obtained from the glass transition temperature (Tg) (absolute temperature: K) of the homopolymer of and their mass fractions based on the following Fox formula.
1/Tg=( _W1 / _Tg1 )+( _W2 / _Tg2 )+( _W3 / _Tg3 )+...+( _Wn / _Tgn )
[In the formula, Tg is the glass transition temperature (K) of the polymer to be determined, W ₁ to W _n are the mass fractions of each monomer, and Tg ₁ to Tg _n are homopolymers of each monomer. Shows the glass transition temperature (K) of]

For example, the glass transition temperature is 165° C. for acrylamide homopolymer, 106° C. for acrylic acid homopolymer, −15° C. for hydroxyethyl acrylate homopolymer, and 105° C. for acrylonitrile homopolymer. A (meth)acrylamide group-containing compound (a), a hydroxyl group-containing (meth)acrylic ester (b), and a copolymer monomer, which constitute the backbone polymer (A) having a desired glass transition temperature. The composition of (c) can be determined. The glass transition temperature of the homopolymer of the monomer is raised from -100°C to 300°C by DSC (differential scanning calorimeter), DTA (differential thermal analyzer), TMA (thermo-mechanical analyzer), or the like. It can be measured under the conditions (heating rate of 10° C./min.). Moreover, the value described in literature can also be used. The literature is exemplified by "Kagaku Binran Basic Edition II, The Chemical Society of Japan (revised 5th edition)", p.325, and the like.

The gel fraction of the cured product of hydroxyl group-containing water-soluble poly(meth)acrylamide (A) is not particularly limited, but the upper limit of the gel fraction of component (A) is 99.9%, 95%, 90%, and 80%. , 70%, 60%, 50%, 40%, 30%, 25%, etc. are exemplified, and the lower limits are 95%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 25% %, 20% and the like are exemplified. In one embodiment, it is preferably 20% or more, more preferably 25% or more, from the viewpoint of the springback resistance development effect accompanying charge-discharge cycles. The gel fraction of the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) is calculated by the following formula: gel fraction (%) = {insoluble residue in water (g) / mass of solid resin (g)} x 100
It is a value calculated by

In one embodiment, the curing conditions for the cured product are exemplified by 120° C. and 4 hours.

The gel fraction is measured, for example, as follows. An appropriate amount (e.g., 10 g) of a thermally crosslinkable binder aqueous solution for lithium ion batteries containing a hydroxyl group-containing water-soluble poly(meth)acrylamide (A), an appropriate container (e.g., an ointment can (manufactured by Sogo Rikagaku Glass Co., Ltd., product After drying under appropriate drying conditions (e.g., circulating air dryer (manufactured by Advantech Toyo Co., Ltd., trade name "air constant temperature dryer DSR420DA") at 120 ° C. for 4 hours), A solid resin after thermal cross-linking is obtained. The mass of the solid resin is accurately measured at 25° C. with an appropriate mass meter (for example, manufactured by Sartorius Japan Co., Ltd., trade name “Standard Balance CPA324S”). The measured solid resin is transferred to a suitable container (e.g. 300 mL beaker) containing an appropriate amount (e.g. 150 mL) of pure water and placed in water under appropriate conditions (e.g. 25°C for 3 hours) with an appropriate magnetic stirrer (e.g. Tokyo Rikaki Co., Ltd., product name "strong magnetic stirrer RCX-1000D") after immersion in a stirred condition, appropriate equipment (for example, Kiriyama funnel (manufactured by Kiriyama Seisakusho Co., Ltd., product name "Kiriyama funnel SB- 60") and a suction bell (manufactured by Kiriyama Seisakusho Co., Ltd., trade name "Shukan Kane VKB-200"), and filtered under reduced pressure with filter paper (manufactured by Kiriyama Seisakusho Co., Ltd., "No. 50B"). After that, the insoluble residue remaining on the filter paper is dried under appropriate conditions (e.g., 120 ° C. for 3 hours) in an appropriate dryer (e.g., the above air circulation dryer), and the mass of the insoluble residue is reduced to an appropriate temperature (e.g., 25° C.) with an appropriate mass meter (for example, the above-mentioned mass meter), and calculate the gel fraction of the resin after thermal crosslinking of the water-soluble battery binder from the above formula.

Mechanism Hydroxyl group-containing water-soluble poly(meth)acrylamide (A) contains amide groups derived from (meth)acrylamide group-containing compound (a) and hydroxyl groups derived from hydroxyl group-containing (meth)acrylic ester (b). there is Thermal cross-linking proceeds by forming chemical bonds with heat. As a result, the gel fraction is expressed by being insolubilized in water. Since amide groups and hydroxyl groups are present independently in a binder solution for a lithium ion battery or an electrode slurry for a lithium ion battery, which will be described later, storage stability of an aqueous solution or slurry stability can be demonstrated. Note that this mechanism is just one theory, and the present invention is not limited to this.

The thermal crosslinking of the hydroxyl-containing water-soluble poly(meth)acrylamide (A) is due to the amide group derived from the (meth)acrylamide-containing compound (a) and the hydroxyl group derived from the hydroxyl-containing (meth)acrylic ester (b). Conceivable. The molar ratio of amide groups to hydroxyl groups (amide groups/hydroxyl groups) in the hydroxyl-containing water-soluble poly(meth)acrylamide (A) is not particularly limited, but an excess of amide groups is preferred. The upper limit of the molar ratio of the amide group to the hydroxyl group (amide group/hydroxyl group) is 19, 18, 17.5, 15, 12.5, 10, 9, 7.5, 5, 2.5, 1.2, etc. are exemplified, and the lower limits are exemplified by 18, 17.5, 15, 12.5, 10, 9, 7.5, 5, 2.5, 1.2, 1.0, and the like. In one embodiment, the amide group/hydroxyl group ratio is preferably 1.0 to 19.0, more preferably 1.2 to 18.0. By satisfying the above, it is considered that the effect of exhibiting springback resistance accompanying charge-discharge cycles can be obtained without impairing the adhesion of the active material layer to the current collector, but the present invention is limited to this. is not intended to be

The weight average molecular weight (Mw) of the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) is not particularly limited, but the upper limit is 6 million, 5.5 million, 5 million, 4.5 million, 4 million, 3.5 million, 3 million, 2.5 million, 2 million, 1.5 million, 1 million, 950,000, 900,000, 850,000, 800,000, 750,000, 700,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, etc. and the lower limits are 5.5 million, 5 million, 4.5 million, 4 million, 3.5 million, 3 million, 2.9 million, 2.5 million, 2 million, 1.5 million, 1 million, 950,000, 900,000, 850,000, 800,000, 750,000, 700,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, 350,000, 300,000 and the like are exemplified. In one embodiment, it is preferably 300,000 to 6,000,000, more preferably 350,000 to 6,000,000 from the viewpoint of the dispersion stability of the lithium ion battery electrode slurry.

The number average molecular weight (Mn) of the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) is not particularly limited, but its upper limit is 6 million, 5.5 million, 5 million, 4.5 million, 4 million, 3.5 million, 3 million, 2.5 million, 2 million, 1.5 million, 1 million, 950 thousand, 900 thousand, 850 thousand, 800 thousand, 750 thousand, 700 thousand, 650 thousand, 600 thousand, 550 thousand, 500 thousand, 450 thousand, 400 thousand, 300 thousand , 200,000, 100,000, 50,000, etc. are exemplified, and the lower limits are 5.5 million, 5 million, 4.5 million, 4 million, 3.5 million, 3 million, 2.9 million, 2.5 million, 2 million, 1.5 million, 1 million, 950,000, 900,000, 850,000, 800,000, 750,000, 700,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, 350,000, 300,000, 200,000, 100,000, 50,000 , 10,000, etc. are exemplified. In one embodiment, the number average molecular weight (Mn) of the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) is preferably 10,000 or more.

The weight-average molecular weight and number-average molecular weight can be determined, for example, as polyacrylic acid conversion values measured under an appropriate solvent by gel permeation chromatography (GPC).

The upper limit of the molecular weight distribution (Mw/Mn) of the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) is 15, 14, 13, 11, 10, 9, 7.5, 5, 4, 3, 2.9, Examples include 2.5, 2, 1.5, etc., and the lower limits are 14, 13, 11, 10, 9, 7.5, 5, 4, 3, 2.9, 2.5, 2, 1.5. , 1.1, and the like. In one embodiment, the molecular weight distribution (Mw/Mn) of the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) is preferably 1.1-15.

The B-type viscosity of the aqueous solution containing the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) is not particularly limited, but the upper limit is 100,000, 90,000, 80,000, 70,000, 60,000, 50,000, 40,000, 30,000, 20,000, 10,000, 9000, 8000, 7000, 6000, 5000, 4000, 3000, 2000 mPa s, etc. are exemplified, and the lower limits are 90,000, 80,000, 70,000, 60,000, 50,000, 4 10,000, 30,000, 20,000, 10,000, 9000, 8000, 7000, 6000, 5000, 4000, 3000, 2000, 1000 mPa·s and the like. In one embodiment, the B-type viscosity range is preferably from 1000 to 100,000 mPa·s. The B-type viscosity is measured by a B-type viscometer such as "B-type viscometer model BM" manufactured by Toki Sangyo Co., Ltd.

The upper limit of the pH (25° C.) of the aqueous solution containing the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) is 13, 12, 11, 10, 9, 8, 7, 6.9, 6.5, 6, 5. .9, 5.6, 5.5, 5.4, 5, 4.5, 4, 3, 2.5, etc., and the lower limits are 12, 11, 10, 9, 8, 7, 6. 9, 6.5, 6, 5.9, 5.6, 5.5, 5.4, 5, 4.5, 4, 3, 2.5, 2 and the like are exemplified. In one embodiment, the pH (25° C.) of the aqueous solution containing the hydroxyl-containing water-soluble poly(meth)acrylamide (A) is preferably pH 2 to 13, more preferably pH 2 to 9, from the viewpoint of solution stability, and pH 2 to A pH of 7 is more preferred, and a pH of less than 7 is particularly preferred. The pH of the aqueous solution can be measured at 25° C. using a glass electrode pH meter (for example, product name “pH meter D-52” manufactured by Horiba, Ltd.).

The upper limit of the content of the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) with respect to 100% by mass of the aqueous binder solution for lithium ion batteries is 20, 19, 15, 14, 12, 10, 9, 7, 6% by mass, etc. The lower limit is exemplified by 19, 15, 14, 12, 10, 9, 7, 6, 5% by mass. In one embodiment, the content of the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) with respect to 100% by mass of the aqueous binder solution for lithium ion batteries is preferably 5 to 20% by mass.

<Additive>
The aqueous binder solution for lithium ion batteries may contain, as additives, agents that are neither the component (A) nor water. Examples of additives include dispersants, leveling agents, antioxidants, thickeners, dispersions (emulsions), cross-linking agents, hydroxysilyl compounds and the like. The content of the additive is exemplified by 0 to 5% by mass, less than 1% by mass, less than 0.1% by mass, less than 0.01% by mass, etc. with respect to 100% by mass of component (A). %, 0 to 5% by mass, less than 1% by mass, less than 0.1% by mass, less than 0.01% by mass, and 0% by mass.

The dispersant can be selected according to the electrode active material to be used, and examples thereof include anionic dispersants, cationic dispersants, nonionic dispersants, polymeric dispersants, and the like.

Examples of the leveling agent include surfactants such as alkyl-based surfactants, silicon-based surfactants, fluorine-based surfactants, and metal-based surfactants. By using a surfactant, repelling that occurs during coating can be prevented, and the smoothness of the slurry layer (coating layer) can be improved.

Examples of antioxidants include phenol compounds, hydroquinone compounds, organic phosphorus compounds, sulfur compounds, phenylenediamine compounds, polymer-type phenol compounds, and the like. A polymer-type phenol compound is a polymer having a phenol structure in its molecule. The weight average molecular weight of the polymer-type phenol compound is preferably 200-1000, more preferably 600-700.

Thickeners include cellulosic polymers such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, ammonium salts and alkali metal salts thereof; (modified) poly(meth)acrylic acid and ammonium salts and alkali metal salts thereof; (modified) Polyvinyl alcohols such as polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, modified poly Examples include acrylic acid, oxidized starch, phosphate starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydrides, and the like.

Dispersions (emulsions) include styrene-butadiene copolymer latex, polystyrene polymer latex, polybutadiene polymer latex, acrylonitrile-butadiene copolymer latex, polyurethane polymer latex, and polymethyl methacrylate polymer latex. , methyl methacrylate-butadiene copolymer latex, polyacrylate polymer latex, vinyl chloride polymer latex, vinyl acetate polymer emulsion, vinyl acetate-ethylene copolymer emulsion, polyethylene emulsion, carboxy-modified styrene-butadiene copolymer Polymerized resin emulsion, acrylic resin emulsion, polyethylene, polypropylene, polyethylene terephthalate, polyamide (PA), polyimide (PI), polyamideimide (PAI), aromatic polyamide, alginic acid and its salts, polyvinylidene fluoride (PVDF), polytetrafluoro Ethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE) and the like are exemplified. .

Crosslinking agents include formaldehyde, glyoxal, hexamethylenetetramine, urea formaldehyde resins, methylolmelamine resins, carbodiimide compounds, polyfunctional epoxy compounds, oxazoline compounds, polyfunctional hydrazide compounds, isocyanate compounds, melamine compounds, urea compounds, and mixtures thereof. exemplified.

A hydroxysilyl compound means a compound having a structure in which a hydroxy group (--OH) is directly bonded to a silicon atom, and a trihydroxysilyl compound means a compound having a trihydroxysilyl group (--Si(OH) ₃ ). and a tetrahydroxysilyl compound means a compound represented by Si(OH) ₄ . In one embodiment, the trihydroxysilyl compound has the general formula RSi(OH) ₃
(In the formula, R represents a substituted or unsubstituted alkyl group, vinyl group, or (meth)acryloxy group, and the substituents include an amino group, a mercapto group, a glycidoxy group, a (meth)acryloxy group, an epoxy group, and the like. exemplified). The hydroxysilyl compound is preferably prepared by hydrolyzing a silane coupling agent or tetraalkoxysilane. The hydroxysilyl compound may be partially polycondensed as long as it does not lose its water-solubility. As the silane coupling agent, a commonly used silane coupling agent can be used. A silane coupling agent is not particularly limited. A hydroxysilyl compound produced from a silane coupling agent may be used alone or in combination of two or more. In one embodiment, the hydroxysilyl compound comprises trihydroxysilylpropylamine. Trialkoxysilanes include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2 (aminoethyl) 3-aminopropyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropyltriethoxysilane. , 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, vinyl Examples include trimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, tetrahydroxysilane and the like. Tetraalkoxysilane is exemplified by tetramethoxysilane, tetramethoxysilane oligomer, tetraethoxysilane, tetraethoxysilane oligomer and the like. Among these, 3-aminopropyltrimethoxysilane is preferably used to produce the hydroxysilyl compound from the viewpoint of stability and electrolyte resistance.

Examples of additives other than the above include at least one compound selected from the group consisting of unsaturated carboxylic acids, unsaturated amides, and salts thereof.

The aqueous thermally crosslinkable binder solution for lithium ion batteries can be used as both an aqueous thermally crosslinkable binder solution for lithium ion battery negative electrodes and an aqueous thermally crosslinkable binder solution for lithium ion battery positive electrodes.

[2. Electrode slurry for lithium-ion batteries]
The present disclosure provides an electrode slurry for a lithium ion battery, containing the above aqueous solution of a thermally crosslinkable binder for a lithium ion battery and an electrode active material (B).

<Electrode active material (B) (also referred to as component (B))>
The electrode active material is not particularly limited as long as it can reversibly absorb and release lithium, and may be used alone or in combination of two or more. As the electrode active material, an appropriate material can be appropriately selected depending on the type of the target electricity storage device. Examples of the electrode active material include carbon materials, silicon materials, oxides containing lithium atoms, lead compounds, tin compounds, arsenic compounds, antimony compounds, and materials that alloy with lithium such as aluminum compounds. Since the carbon material and the material alloyed with lithium have a large coefficient of volume expansion during charging of the battery, the effects of the present invention can be remarkably exhibited.

The above carbon materials include graphite (also known as graphite, exemplified by natural graphite, artificial graphite, etc.), which is highly crystalline carbon, low crystalline carbon (soft carbon, hard carbon), carbon black (ketjen black, acetylene black). , channel black, lamp black, oil furnace black, thermal black, etc.), fullerenes, carbon nanotubes, carbon nanofibers, carbon nanohorns, carbon fibrils, mesocarbon microbeads (MCMB), pitch-based carbon fibers, and the like.

In addition to silicon, silicon oxide, and silicon alloys, _the silicon _materials include SiC, _SiOxCy (0<x≦3, 0<y≦5 ₎ , _Si3N4 , _Si2N2O , _SiOx (0 <x ≤ 2) silicon oxide composites (for example, materials described in JP-A-2004-185810 and JP-A-2005-259697), JP-A-2004-185810 described A silicon material or the like is exemplified. Silicon materials described in Japanese Patent No. 5390336 and Japanese Patent No. 5903761 may also be used.

The silicon oxide is preferably a silicon oxide represented by a composition formula of SiO _x (0<x<2, preferably 0.1≦x≦1).

The silicon alloy is preferably an alloy of silicon and at least one transition metal selected from the group consisting of titanium, zirconium, nickel, copper, iron and molybdenum. Silicon alloys of these transition metals are preferred because they have high electronic conductivity and high strength. Silicon alloys are more preferably silicon-nickel alloys or silicon-titanium alloys, and particularly preferably silicon-titanium alloys. The content of silicon in the silicon alloy is preferably 10 mol % or more, more preferably 20 to 70 mol %, based on 100 mol % of the metal element in the alloy. Note that the silicon material may be monocrystalline, polycrystalline, or amorphous.

Moreover, when using a silicon material as an electrode active material, you may use electrode active materials other than a silicon material together. Such an electrode active material includes the above-described carbon materials; conductive polymers such as polyacene; A _X B _Y O _Z (A is an alkali metal or transition metal; At least one selected from metals, O represents an oxygen atom, and X, Y and Z are 0.05<X<1.10, 0.85<Y<4.00, 1.5<Z<5. is a number in the range of 00.) and other metal oxides. When a silicon material is used as the electrode active material, it is preferable to use a carbon material together because the volume change associated with the absorption and release of lithium is small.

The above oxides containing lithium atoms include ternary nickel-cobalt lithium manganate, lithium-manganese composite oxides (LiMn ₂ O ₄ etc.), lithium-nickel composite oxides (LiNiO ₂ etc.), lithium-cobalt composite oxides. ( _LiCoO2, etc.), lithium- _iron composite oxides ( _LiFeO2, etc.), lithium-nickel-manganese composite oxides (LiNi0.5Mn0.5O2 _{, etc.} ), lithium-nickel-cobalt composite oxides (LiNi _0.8 Co _0.2 O ₂ etc.), lithium-transition metal phosphate compounds (LiFePO ₄ etc.), and lithium-transition metal sulfate compounds (Li _x Fe ₂ (SO ₄ ) ₃ ), lithium-titanium composite oxides Lithium-transition metal composite oxides such as (lithium titanate: Li ₄ Ti ₅ O ₁₂ ) and other conventionally known electrode active materials are exemplified.

The shape of the electrode active material is not particularly limited, and may be any shape such as particulate or thin film, but is preferably particulate. The average particle size of the electrode active material is not particularly limited, but the upper limit is 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 4, 3, 2.9, 2, 1, 0 0.5, 0.1 μm, etc., and the lower limits are 45, 40, 35, 30, 25, 20, 15, 10, 5, 4, 3, 2.9, 2, 1, 0.5, 0.5 μm, etc. 1 μm and the like are exemplified. In one embodiment, it is preferably 0.1-50 μm. If the thickness is 0.1 μm or more, the handleability is good, and if the thickness is 50 μm or less, electrode coating is easy. It is more preferably 0.1 to 45 μm, still more preferably 1 to 10 μm, and particularly preferably about 5 μm. A uniform and thin coating film can be formed when the content is in such a range, which is preferable. In addition, the “particle size” in the present disclosure means the maximum distance among the distances between any two points on the contour line of the particle. In addition, unless otherwise specified, the value of "average particle size" is the number of particles observed in several to several tens of fields of view using observation means such as scanning electron microscope (SEM) and transmission electron microscope (TEM). A value calculated as an average value of particle diameters shall be adopted.

In order to exhibit the effect of the present invention remarkably, the carbon material and/or the material to be alloyed with lithium is preferably 50% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass in the electrode active material. % or more, particularly preferably 100% by mass.

In one embodiment, the content of silicon or silicon oxide covered with a carbon layer in the electrode active material is 5% by mass or more (for example, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 100% by mass) preferable.

The upper limit of the content of component (A) with respect to 100% by mass of the slurry of the present invention is 15, 14, 12, 10, 9, 7, 5, 4, 3, 2, 1, 0.9, 0.6 mass %, and the lower limit is exemplified by 14, 12, 10, 9, 7, 5, 4, 3, 2, 1, 0.9, 0.6, 0.5% by mass. In one embodiment, the content of component (A) is preferably 0.5 to 10% by mass with respect to 100% by mass of the slurry of the present invention.

The content of the component (A) in the slurry of the present invention is not particularly limited, but the upper limit of the content of the component (A) with respect to 100% by mass of the component (B) is 15, 14, 11, 10, 9, 5, About 4 and 2% by mass are exemplified, and the lower limits are exemplified by about 14, 11, 10, 9, 5, 4, 2 and 1% by mass. In one embodiment, the content of component (A) is preferably about 1 to 15% by mass with respect to 100% by mass of component (B).

In addition, although the content of the component (B) in the slurry of the present invention is not particularly limited, the upper limit of the content of the component (B) with respect to 100% by mass of the slurry of the present invention is 65, 60, 55, 50, 45, 40, 35, 30, 25% by mass and the like are exemplified, and the lower limit is exemplified by 60, 55, 50, 45, 40, 35, 30, 25, 20% by mass and the like. In one embodiment, the content of component (B) is preferably 20 to 65% by mass with respect to 100% by mass of the slurry of the present invention.

In the lithium ion battery electrode slurry of the present invention, a binder other than the hydroxyl-containing water-soluble poly(meth)acrylamide (A) may be used. Acrylamide (A) is preferably 90% by mass or more (95, 99% by mass or more, 100% by mass, etc.).

(Slurry viscosity adjusting solvent)
Various known slurry viscosity adjusting solvents can be used without any particular limitation, and may be used alone or in combination of two or more. Examples of the solvent include ether solvents, ketone solvents, alcohol solvents, amide solvents, water and the like. Ether solvents are exemplified by dioxane, tetrahydrofuran (THF) and the like. Ketone solvents are exemplified by acetone, methyl ethyl ketone (MEK) and the like. Alcohol solvents are exemplified by methanol, ethanol, 2-propanol, isopropyl alcohol and the like. Amide solvents are exemplified by N-methyl-2-pyrrolidone (NMP) and the like.

Attempts have been made to thermally crosslink the binder resin in the electrode by adding a crosslinking agent to the binder or slurry, coating the slurry on a current collector, and drying it (for example, see International Publication No. 2015/098507. listed materials, etc.). This has the effect of suppressing expansion of the active material layer due to charge/discharge cycles by cross-linking the binder resin in the electrode. Also in the thermally crosslinkable binder solution of the present invention, the thermal crosslinking of the binder resin in the electrode has the effect of suppressing the expansion of the active material layer due to charge/discharge cycles. The heat-crosslinkable binder solution of the present invention or the heat-crosslinkable electrode slurry using the heat-crosslinkable binder solution has excellent storage stability. The method for evaluating storage stability is to measure the solution viscosity of the prepared thermally crosslinkable binder solution or thermally crosslinkable electrode slurry with a Brookfield viscometer, store it in an oven heated to 40 ° C. for 3 days, and after storage The solution viscosity of can be evaluated by measuring the Brookfield viscometer again and confirming the presence or absence of viscosity change.

<Additive>
The slurry may contain, as additives, agents other than the components (A), (B), and water. The content of the additive is exemplified by 0 to 5% by mass, less than 1% by mass, less than 0.1% by mass, less than 0.01% by mass, and 0% by mass with respect to 100% by mass of the slurry. Examples of additives include those mentioned above.

The lithium ion battery electrode slurry can be used as both a lithium ion battery negative electrode slurry and a lithium ion battery positive electrode slurry.

[3. Method for producing electrode slurry for lithium ion battery]
In the present disclosure, with respect to 100 mol% of the monomer group,
30 to 95 mol% of the (meth)acrylamide group-containing compound (a),
Hydroxyl-containing water-soluble poly(meth)acrylamide (A), which is a polymer of a monomer group containing 5 to 50 mol% of a hydroxyl-containing (meth)acryl ester (b) and having a cured product gel fraction of 20% or more. ), and mixing the electrode active material (B).

The method for producing the slurry of the present invention includes a method of mixing an aqueous solution of component (A) (the aqueous binder solution for a lithium ion battery) and an electrode active material, and mixing components (A), (B), and water separately. A method is exemplified. In addition, the order of mixing in the above method is not particularly limited. Examples of slurry mixing means include ball mills, sand mills, pigment dispersers, grinders, ultrasonic dispersers, homogenizers, planetary mixers, Hobart mixers, and the like.

[4. Electrodes for lithium-ion batteries]
The present disclosure provides a lithium ion battery electrode obtained by coating a current collector with a lithium ion battery electrode slurry and drying the slurry.

The coating means is not particularly limited, and conventionally known coating devices such as a comma coater, gravure coater, micro gravure coater, die coater, and bar coater are exemplified.

The drying means is not particularly limited, and the temperature is preferably about 80 to 200° C., more preferably about 90 to 180° C., and the atmosphere may be dry air or an inert atmosphere. By drying at an appropriate temperature, the crosslinking of hydroxyl group-containing water-soluble poly(meth)acrylamide (A), which is a heat-crosslinkable binder for lithium-ion batteries, proceeds, and springback resistance associated with charge-discharge cycles is exhibited. .

Although the thickness of the electrode (cured coating film) is not particularly limited, it is preferably about 5 μm to 300 μm, more preferably about 10 μm to 250 μm. By setting the content in the above range, it becomes easy to obtain a sufficient Li intercalation/deintercalation function for a high-density current value.

Various known current collectors can be used without particular limitation. The material of the current collector is not particularly limited, and examples thereof include metal materials such as copper, iron, aluminum, nickel, stainless steel, and nickel-plated steel, and carbon materials such as carbon cloth and carbon paper. The shape of the current collector is not particularly limited, and examples thereof include a metal foil, a metal cylinder, a metal coil, a metal plate, etc. in the case of a metal material, and a carbon plate, a carbon thin film, a carbon cylinder, etc. in the case of a carbon material. Among them, when the electrode active material is used for the negative electrode, copper foil is preferable as the current collector because it is currently used in industrialized products.

The lithium ion battery electrode can be used as both a lithium ion battery negative electrode and a lithium ion battery positive electrode.

[5. Lithium-ion battery]
The present disclosure provides a lithium ion battery including the lithium ion battery electrode described above. The batteries also include, but are not limited to, electrolyte solutions, separators, positive electrodes, and packaging materials.

The electrolyte solution is exemplified by a non-aqueous electrolytic solution in which a supporting electrolyte is dissolved in a non-aqueous solvent. In addition, the non-aqueous electrolytic solution may contain a film-forming agent.

Various known non-aqueous solvents can be used without particular limitation, and may be used alone or in combination of two or more. Non-aqueous solvents include chain carbonate solvents such as diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate; cyclic carbonate solvents such as ethylene carbonate, propylene carbonate and butylene carbonate; chain ether solvents such as 1,2-dimethoxyethane; Cyclic ether solvents such as 2-methyltetrahydrofuran, sulfolane and 1,3-dioxolane; Chain ester solvents such as methyl formate, methyl acetate and methyl propionate; Cyclic ester solvents such as γ-butyrolactone and γ-valerolactone; are exemplified. Among these, a combination of a mixed solvent containing a cyclic carbonate and a chain carbonate is preferable.

A lithium salt is used as the supporting electrolyte. Various known lithium salts can be used without particular limitation, and may be used alone or in combination of two or more. Supporting electrolytes include _LiPF6 , LiAsF6, _{LiBF4 , LiSbF6} , _LiAlCl4 , _{LiClO4 , CF3SO3Li , C4F9SO3Li , CF3COOLi} , ( _CF3CO ) _2NLi , (CF _3SO2 ) _{2NLi ,} ( _C2F5SO2 ) _NLi and the like are exemplified _. Among them, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li, which are easily soluble in a solvent and exhibit a high degree of dissociation, are preferable. Since the lithium ion conductivity increases with the use of a supporting electrolyte having a higher degree of dissociation, the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

Various known film-forming agents can be used without particular limitation, and may be used alone or in combination of two or more. Film-forming agents include carbonate compounds such as vinylene carbonate, vinylethylene carbonate, vinylethyl carbonate, methylphenyl carbonate, fluoroethylene carbonate and difluoroethylene carbonate; alkene sulfides such as ethylene sulfide and propylene sulfide; 1,3-propanesultone, 1 ,4-butane sultone and other sultone compounds; maleic anhydride, succinic anhydride and other acid anhydrides, and the like. The content of the film-forming agent in the electrolyte solution is not particularly limited, but is preferably 10% by mass or less, 8% by mass or less, 5% by mass or less, and 2% by mass or less in this order. When the content is 10% by mass or less, the advantages of the film-forming agent, such as suppression of initial irreversible capacity and improvement of low-temperature characteristics and rate characteristics, can be easily obtained.

A separator is an article interposed between a positive electrode and a negative electrode, and is used to prevent short circuits between the electrodes. Specifically, porous separators such as porous membranes and non-woven fabrics can be preferably used, and they are impregnated with the non-aqueous electrolytic solution before use. Polyolefin such as polyethylene or polypropylene, polyethersulfone, or the like is used as the material of the separator, and polyolefin is preferred.

In addition, when a lithium ion battery is produced using a negative electrode produced using the lithium ion battery electrode slurry as the negative electrode and a positive electrode produced without using the lithium ion battery electrode slurry as the positive electrode, the positive electrode is various. A known one can be used without particular limitation. The positive electrode is prepared by mixing a positive electrode active material, a conductive agent, and a positive electrode binder with an organic solvent to prepare a slurry, applying the prepared slurry to a positive electrode current collector, drying, and pressing, and the like. exemplified.

The positive electrode active material is exemplified by an inorganic positive electrode active material and an organic positive electrode active material. Examples of inorganic positive electrode active materials include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. Examples of the transition metals include Fe, Co, Ni, Mn, and Al. Inorganic compounds used for the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiNi _1/2 Mn _3/2 O ₄ , LiCo _1/3 Ni _1/3 Mn _1/ Lithium-containing composite metal oxides such _{as 3O2} , Li[ _{Li0.1Al0.1Mn1.8} ] _O4 and _LiFeVO4 ; Transition _metal sulfides such _{as TiS2} , _TiS3 and amorphous _MoS2 transition metal oxides such as Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MoO ₃ , V ₂ O ₅ and V ₆ O ₁₃ ; These compounds may be partially elementally substituted. The organic positive electrode active material is exemplified by conductive polymers such as polyacetylene and poly-p-phenylene. An iron-based oxide having poor electrical conductivity may be used as an electrode active material covered with a carbon material by allowing a carbon source material to exist during reduction firing. Also, these compounds may be partially element-substituted. Among these, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiNi _1/2 Mn _3/2 O ₄ , LiCo _1/3 Ni _{1/ 3Mn1 / 3O2 , Li} [ _{Li0.1Al0.1Mn1.8} ] _O4 are preferred.

Conductive agents include fibrous carbon such as vapor-grown carbon fiber (VGCF), carbon nanotube (CNT), carbon nanofiber (CNF), graphite particles, carbon black such as acetylene black, ketjen black, and furnace black; average Fine powders of Cu, Ni, Al, Si or alloys thereof having a particle size of 10 μm or less are exemplified.

As the positive electrode binder, various known binders can be used without particular limitation, and may be used alone or in combination of two or more. Positive electrode binders include fluorine-based resins (polyvinylidene fluoride, polytetrafluoroethylene, etc.), polyolefins (polyethylene, polypropylene, etc.), polymers with unsaturated bonds (styrene-butadiene rubber, isoprene rubber, butadiene rubber, etc.), acrylic Examples include acid-based polymers (acrylic acid copolymers, methacrylic acid copolymers, etc.).

The positive electrode current collector is exemplified by aluminum foil, stainless steel foil, and the like.

The form of the lithium ion battery is not particularly limited. Examples of the form of the lithium ion battery include a cylinder type in which a sheet electrode and a separator are spirally formed, a cylinder type with an inside-out structure in which a pellet electrode and a separator are combined, a coin type in which a pellet electrode and a separator are laminated, and the like. Moreover, by housing the batteries of these forms in an arbitrary exterior case, they can be used in arbitrary shapes such as coin-shaped, cylindrical, and rectangular.

The method for manufacturing the lithium ion battery is not particularly limited, and the battery may be assembled by an appropriate procedure according to the structure of the battery. A method for manufacturing a lithium ion battery is exemplified by the method described in JP-A-2013-089437. A battery can be manufactured by placing a negative electrode on an exterior case, providing an electrolytic solution and a separator thereon, placing a positive electrode so as to face the negative electrode, and fixing them with a gasket and a sealing plate.

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these. In the examples, "%" indicates "% by mass" and "parts" indicates "parts by mass" unless otherwise specified.

1. (A) Component Production Example 1-1
A reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was charged with 1,020 g of ion-exchanged water, 250 g (1.76 mol) of 50% acrylamide aqueous solution, and 22.4 g (0.108 mol) of acrylamide t-butylsulfonic acid. ), 33.9 g (0.292 mol) of 2-hydroxyethyl acrylate, and 0.34 g (0.0022 mol) of sodium methallylsulfonate were added, and after removing oxygen in the reaction system with nitrogen gas, the temperature was raised to 50°C. I warmed up. 1.8 g of 2,2′-azobis-2-amidinopropane dihydrochloride (product name “NC-32” manufactured by Nippo Chemical Co., Ltd.) and 50 g of deionized water were added thereto, and the temperature was raised to 80° C. for 3 A time reaction was carried out to obtain an aqueous solution containing hydroxyl group-containing water-soluble polyacrylamide.

Examples 1-2 to 1-9
An aqueous solution containing a hydroxyl group-containing water-soluble polyacrylamide was prepared in the same manner as in Example 1-1, except that the monomer composition and the amount of the initiator were changed to those shown in Table 1.

Comparative Example 1-1
A reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was charged with 1,000 g of ion-exchanged water, 380 g (2.67 mol) of a 50% acrylamide aqueous solution, and 0.42 g (0.0027 mol) of sodium methallylsulfonate. was introduced, nitrogen gas was passed through the reaction system to remove oxygen, and then the temperature was raised to 50°C. 1.9 g of 2,2′-azobis-2-amidinopropane dihydrochloride (product name “NC-32” manufactured by Nippo Chemical Co., Ltd.) and 50 g of deionized water were added thereto, and the temperature was raised to 80° C. for 3 A time reaction was carried out to obtain an aqueous solution containing polyacrylamide.

Comparative Examples 1-2 to 1-3
An aqueous solution containing water-soluble poly(meth)acrylamide was prepared in the same manner as in Comparative Example 1-1, except that the monomer composition and the amount of the initiator in Comparative Example 1-1 were changed to those shown in Table 1. .

Comparative Example 1-4
A reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was charged with 990 g of ion-exchanged water, 190 g (1.34 mol) of a 50% acrylamide aqueous solution, 80.4 g (0.892 mol) of 80% acrylic acid, After adding 0.35 g (0.0022 mol) of sodium methallylsulfonate and removing oxygen in the reaction system through nitrogen gas, the temperature was raised to 50°C. 1.6 g of 2,2′-azobis-2-amidinopropane dihydrochloride (product name “NC-32” manufactured by Nippo Chemical Co., Ltd.) and 50 g of deionized water were added thereto, and the temperature was raised to 80° C. for 3 A time reaction was performed. After cooling to room temperature, 14.8 g of a carbodiimide compound (“Carbodilite V-02” by Nisshinbo Chemical Co., Ltd.) was added to obtain an aqueous solution containing polyacrylamide and a cross-linking agent.

B-type Viscosity The viscosity of each aqueous binder solution was measured at 25° C. under the following conditions using a B-type viscometer (product name “B-type viscometer model BM” manufactured by Toki Sangyo Co., Ltd.).
When the viscosity is 100,000 to 20,000 mPa·s: No. When 4 rotors are used, the rotation speed is 6 rpm, and the viscosity is less than 20,000 mPa·s: No. 3 rotors, 6 rpm.

Weight-Average Molecular Weight The weight-average molecular weight was obtained as a value converted to polyacrylic acid measured under 0.2M phosphate buffer/acetonitrile solution (90/10, pH 8.0) by gel permeation chromatography (GPC). HLC-8220 (manufactured by Tosoh Corporation) was used as the GPC apparatus, and SB-806M-HQ (manufactured by SHODEX) was used as the column.

Gel fraction 10 g of an aqueous solution of a thermally crosslinkable binder for lithium ion batteries containing a hydroxyl group-containing water-soluble poly(meth)acrylamide (A) was placed in an ointment can (manufactured by Sogo Rikagaku Glass Co., Ltd., trade name "ointment can tinplate"). After drying at 120° C. for 4 hours with an air circulating dryer (manufactured by Advantec Toyo Co., Ltd., trade name: constant temperature air dryer DSR420DA), a solid resin after thermal cross-linking was obtained. The mass of the solid resin was accurately measured at 25° C. with a mass meter (manufactured by Sartorius Japan K.K., trade name “Standard Balance CPA324S”). Transfer the measured solid resin to a container (300 mL beaker) containing 150 mL of pure water, and immerse in water at 25 ° C. for 3 hours with a magnetic stirrer (manufactured by Tokyo Rikakikai Co., Ltd., trade name "strong magnetic stirrer RCX-1000D"). After immersion under the conditions of stirring using, Kiriyama funnel (manufactured by Kiriyama Seisakusho Co., Ltd., trade name “Kiriyama funnel SB-60”) and a suction bell (manufactured by Kiriyama Seisakusho Co., Ltd., trade name “Suction bell VKB-200”) was filtered under reduced pressure with filter paper (manufactured by Kiriyama Seisakusho Co., Ltd., "No. 50B"). Then, after drying the insoluble residue remaining on the filter paper at 120 ° C. for 3 hours with the above-mentioned air circulation dryer, the mass of the insoluble residue is accurately measured at 25 ° C. with the above-mentioned mass meter, The gel fraction of the resin after thermal crosslinking of the binder for a battery was calculated.
Gel fraction (%) = {insoluble residue (g) / mass of solid resin (g)} x 100

・ＡＭ：アクリルアミド（三菱ケミカル株式会社製 「５０％アクリルアミド」）
・ＡＴＢＳ：アクリルアミドｔ－ブチルスルホン酸（東亞合成株式会社製 「ＡＴＢＳ」）
・ＴＢＡＡ：ｔ－ブチルアクリルアミド（ＭＣＣユニテック株式会社製 「Ｎ－ｔ－ブチルアクリルアミド」）
・ＤＭＡＡ：Ｎ，Ｎ－ジメチル（メタ）アクリルアミド（ＫＪケミカルズ株式会社製 「ＤＭＡＡ」）
・ＨＥＡ：アクリル酸２－ヒドロキシエチル（大阪有機化学工業株式会社製 「ＨＥＡ」）
・ＧＬＭ：グリセリンモノメタクリレート（日油株式会社製 「ブレンマー ＧＬＭ」）
・ＰＥ－９０：ポリエチレングリコールモノメタクリレート（日油株式会社製 「ブレンマー ＰＥ－９０」）
・ＰＥ－２００：ポリエチレングリコールモノメタクリレート（日油株式会社製 「ブレンマー ＰＥ－２００」）
・ＡＡ：アクリル酸（大阪有機化学工業株式会社製 「８０％アクリル酸」）
・ＡＮ：アクリロニトリル（三菱ケミカル株式会社製 「アクリロニトリル」）
・ＳＭＡＳ：メタリルスルホン酸ナトリウム
・カルボジイミド：カルボジイミド化合物（日清紡ケミカル株式会社「カルボジライトＶ－０２」）

・ AM: Acrylamide ("50% acrylamide" manufactured by Mitsubishi Chemical Corporation)
・ ATBS: acrylamide t-butyl sulfonic acid ("ATBS" manufactured by Toagosei Co., Ltd.)
・ TBAA: t-butyl acrylamide ("Nt-butyl acrylamide" manufactured by MCC Unitech Co., Ltd.)
・ DMAA: N, N-dimethyl (meth) acrylamide ("DMAA" manufactured by KJ Chemicals Co., Ltd.)
・ HEA: 2-hydroxyethyl acrylate ("HEA" manufactured by Osaka Organic Chemical Industry Co., Ltd.)
・ GLM: Glycerin monomethacrylate ("Blemmer GLM" manufactured by NOF Corporation)
・ PE-90: Polyethylene glycol monomethacrylate (“Blenmar PE-90” manufactured by NOF Corporation)
・ PE-200: Polyethylene glycol monomethacrylate (manufactured by NOF Corporation "Blemmer PE-200")
・ AA: Acrylic acid (“80% acrylic acid” manufactured by Osaka Organic Chemical Industry Co., Ltd.)
・ AN: Acrylonitrile ("Acrylonitrile" manufactured by Mitsubishi Chemical Corporation)
・SMAS: Sodium methallyl sulfonate ・Carbodiimide: Carbodiimide compound (Nisshinbo Chemical Co., Ltd. “Carbodilite V-02”)

2. Production of electrode slurry, cell production and evaluation Example 2-1
Using a commercially available rotation-revolution mixer (product name “Awatori Mixer”, manufactured by Thinky Co., Ltd.), the hydroxyl-containing water-soluble poly(meth)acrylamide obtained in Example 1-1 ( A) containing 7 parts by mass of a thermally crosslinkable binder aqueous solution for lithium ion batteries in terms of solid content, 50 parts by mass of silicon particles having a D50 of 5 μm, and natural graphite (product name “Z- 5F”) was mixed with 50 parts by mass. Ion-exchanged water was added thereto so that the solid content concentration was 40%, and the container was set in the mixer. After kneading at 2000 rpm for 10 minutes, defoaming was performed for 1 minute to obtain a slurry for electrodes.

Examples 2-2 to 2-11, Comparative Examples 2-1 to 2-4
A slurry was prepared in the same manner as in Example 2-1 except that the composition in Example 2-1 was changed to that shown in Table 2.

<Calculation of springback rate>
The resulting slurry was uniformly applied to the surface of a current collector made of copper foil by a doctor blade method so that the film thickness after drying was 25 μm, dried at 80° C. for 1 hour, and dried at 150° C./vacuum for 2 hours. An electrode was obtained by heat treatment for a period of time. After that, the film (electrode active material layer) was pressed with a roll press machine so that the density of the film (electrode active material layer) was 1.5 g/cm ³ to obtain an electrode. Using the obtained electrode, a lithium half-cell was produced by the following procedure, charge/discharge measurement was performed, and springback ratio was calculated.

<Storage stability test of electrode slurry>
After measuring the viscosity (unit: mPa·s) of the electrode slurry with a Brookfield viscometer, it was stored in an oven heated to 40° C. for 3 days. After storage, the viscosity was measured again with a Brookfield viscometer, and the change in viscosity was calculated by the following formula and evaluated according to the following evaluation criteria.
Viscosity change (%) = (viscosity of electrode slurry after storage)/(viscosity of electrode slurry before storage) x 100
A: Less than 110% B: 110% or more and less than 120% C: 120% or more and less than 130% D: 130% or more

<Assembly of lithium half cell>
In an argon-purged glove box, the above electrode was punched to a diameter of 16 mm and placed inside the packing on the Al lower lid of a test cell (manufactured by Nippon Thomcell Co., Ltd.). Next, a separator made of a polypropylene porous film punched to a diameter of 24 mm (manufactured by CS TECH CO., LTD, trade name “Selion P2010”) was placed, and an electrolytic solution was injected so as not to enter air. A piece of metallic lithium foil punched to 16 mm was placed. After that, a disk made of SUS and a leaf spring were put on the plate so as to press the electrode and metallic lithium uniformly. The electrolytic solution used here is a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol/L in a solvent of ethylene carbonate/ethyl methyl carbonate=1/1 (mass ratio).

<Charge/discharge measurement>
The lithium half cell was placed in a constant temperature bath at 25° C., charging was started at a constant current (0.1 C), and charging was completed (cutoff) when the voltage reached 0.01 V. Then, discharge was started at a constant current (0.1 C), and charge/discharge was repeated 30 times, with discharge being completed (cutoff) when the voltage reached 1.0V.
In the above measurement conditions, "1 C" indicates a current value at which discharge is completed in 1 hour when a cell having a certain electric capacity is discharged at a constant current. For example, "0.1 C" means a current value at which discharge is completed in 10 hours, and "10 C" means a current value at which discharge is completed in 0.1 hour.

<Measurement of springback rate>
After the charge-discharge cycle test was performed at room temperature (25° C.) for 30 cycles, the lithium half-cell was disassembled and the electrode thickness was measured. The springback ratio of the electrode was obtained by the following formula.
Springback rate = {(electrode thickness after 30 cycles - current collector thickness) / (electrode thickness before charging and discharging - current collector thickness)} x 100-100 (%)

As is clear from Table 2, both the electrode slurry prepared using the aqueous binder solution of Example and the lithium half cell prepared from this electrode slurry evaluated the storage stability and springback rate of the electrode slurry. there were.

Claims (9)

With respect to 100 mol% of the monomer group,
30 to 95 mol% of the (meth)acrylamide group-containing compound (a),
It is a polymer of a monomer group containing 5 to 50 mol% of a hydroxyl group-containing (meth)acrylic ester (b), and the gel fraction of the cured product measured by the following procedure is 20% or more.
including a hydroxyl group-containing water-soluble poly (meth) acrylamide (A),
An aqueous thermally crosslinkable binder solution for lithium ion batteries, which has a pH of less than 7.
<Method for measuring gel fraction of cured product>
(1) Put 10 g of a thermally crosslinkable binder aqueous solution for lithium ion batteries containing a hydroxyl group-containing water-soluble poly(meth)acrylamide (A) in an ointment can and dry it at 120 ° C. for 4 hours in a circulating dryer. A solid resin is obtained.
(2) Measure the mass of the solid resin at 25° C. using a mass meter.
(3) Transfer the measured solid resin to a 300 mL beaker containing 150 mL of pure water, immerse in water at 25 ° C. for 3 hours under the conditions of stirring using a magnetic stirrer, then filter paper using a Kiriyama funnel and a suction bell. Filter under reduced pressure.
(4) After that, after drying the insoluble residue remaining on the filter paper at 120 ° C. for 3 hours with the above-mentioned air circulation dryer, the mass of the insoluble residue is accurately measured at 25 ° C. using the above-mentioned mass meter, The gel fraction of the resin after thermal crosslinking of the water-soluble battery binder is calculated from the following formula.
Gel fraction (%) = {insoluble residue (g) / mass of solid resin (g)} x 100 2. The aqueous thermally crosslinkable binder solution for lithium ion batteries according to claim 1, wherein the hydroxyl group-containing (meth)acrylic ester (b) is represented by the following general formula (1).
General formula (1):

<wherein R ¹ represents a hydrogen atom or a methyl group, R ² represents a substituted or unsubstituted oxyalkylene group having 1 to 5 carbon atoms, general formula (2):

(Wherein, q is an integer of 1 to 3, 2q is an integer twice as large as q, and n is an integer of 1 or more.)
A polyoxyalkylene group represented by

or a combination thereof. ＞ An electrode slurry for lithium ion batteries, comprising the thermally crosslinkable binder aqueous solution for lithium ion batteries according to claim 1 or 2 and an electrode active material (B). Claim 3, wherein the hydroxyl group-containing water-soluble poly(meth)acrylamide (A) contained in the aqueous thermally crosslinkable binder solution for a lithium ion battery is 1 to 15% by mass with respect to 100% by mass of the electrode active material (B). The electrode slurry for a lithium ion battery according to 1. 5. The electrode slurry for a lithium ion battery according to claim 3, wherein said electrode active material (B) contains 5% by mass or more of silicon covered with a carbon layer or silicon oxide covered with a carbon layer. With respect to 100 mol% of the monomer group,
30 to 95 mol% of the (meth)acrylamide group-containing compound (a),
Hydroxyl-containing water-soluble poly(meth)acrylamide (A), which is a polymer of a monomer group containing 5 to 50 mol% of a hydroxyl-containing (meth)acryl ester (b) and having a cured product gel fraction of 20% or more. ), and the step of mixing the electrode active material (B). A lithium ion battery electrode comprising a current collector and a dried lithium ion battery electrode slurry according to any one of claims 3 to 5. 8. The electrode for a lithium ion battery according to claim 7, wherein said current collector is copper foil. A lithium ion battery comprising the lithium ion battery electrode according to any one of claims 7 and 8.