JP7215348B2 - Thermally crosslinkable binder aqueous solution for lithium ion battery, electrode thermally crosslinkable slurry for lithium ion battery, 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, a thermally crosslinkable electrode slurry for lithium ion batteries, 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. Based on this background, the properties required for the binder include slurry dispersibility of the active material particles, adhesion between the active material particles, and adhesion between the electrode active material layer containing the active material particles and the current collector. characteristics, cycle characteristics of the produced battery, and the like.

Therefore, in the art, development and investigation of binder resins satisfying the above-described performance requirements have been made. For example, Patent Document 1 proposes a copolymer of an acrylic acid derivative (salt) and an acrylonitrile derivative. On the other hand, as a positive electrode binder, polyvinylidene fluoride (hereinafter abbreviated as “PVDF”) and the like are frequently used. Since this binder resin is a fluorine-based resin, it is dissolved in a solvent containing an organic solvent such as N-methyl-2-pyrrolidone (NMP) and used as a binder resin slurry.

JP 2015-115109 A Japanese Patent No. 3067544

However, the technique disclosed in Patent Literature 1 requires a large amount of an acrylic acid derivative (salt), and therefore has a high hygroscopicity, which poses a problem that a large amount of water remains in the resulting electrode. Due to the water remaining when the battery is made, there is a high possibility that a large amount of gas will be generated due to electrolysis. In addition, electrode adhesion and cycle performance were still insufficient.

In the technology disclosed in Patent Document 2, since an organic solvent such as NMP is used as a solvent, the environmental load during coating and drying is reduced compared to the case of using a water-based solvent in mass production due to future increase in demand. extremely large.

Therefore, the problem to be solved by the present invention is to have good slurry storage stability, and to be able to impart good adhesion, springback suppressing ability and discharge capacity maintenance to the electrode, and good volume expansion suppressing ability It is an object of the present invention to provide a thermally crosslinkable slurry for a lithium ion battery negative electrode capable of imparting to a lithium ion battery and a thermally crosslinkable binder aqueous solution for a lithium ion battery capable of producing the slurry.

As a result of intensive studies to solve the above problems, the present inventors found that the above problems can be solved by using an aqueous binder solution containing poly(meth)acrylamide having a predetermined unsaturated monomer as a constituent component. I have perfected my invention.

The following items are provided by this disclosure.
(Item 1)
With respect to 100 mol% of the monomer group,
20 to 85 mol% of the (meth)acrylamide group-containing compound (a),
10 to 50 mol% of one or more unsaturated acids or inorganic salts thereof (b) selected from the group consisting of unsaturated carboxylic acids and unsaturated sulfonic acids, and 5 hydroxybutyl (meth)acrylates (c) An aqueous solution of a thermally crosslinkable binder for a lithium ion battery, containing water-soluble poly(meth)acrylamide (A) which is a polymer of a monomer group containing up to 30 mol %.
(Item 2)
Substance ratio of the (meth)acrylamide group-containing compound (a) and the hydroxybutyl (meth)acrylate (c) contained in the monomer group [substance amount of component (a)/substance of component (c) Amount] is 1 or more.
(Item 3)
A thermally crosslinkable slurry for a lithium ion battery negative electrode, comprising the thermally crosslinkable binder aqueous solution for a lithium ion battery according to any one of the above items and a negative electrode active material.
(Item 4)
A lithium ion battery negative electrode obtained by applying the thermally crosslinkable slurry for a lithium ion battery negative electrode according to any one of the above items to a current collector, followed by drying and curing.
(Item 5)
A lithium ion battery comprising the negative electrode for a lithium ion battery as described above.

In the present disclosure, one or more of the features described above may be provided in further combinations in addition to the explicit combinations.

The thermally crosslinkable slurry for a lithium ion battery negative electrode of the present invention has excellent slurry storage stability. In addition, the lithium ion battery negative electrode of the present invention has excellent adhesion, springback suppression ability, and discharge capacity maintenance ability. Furthermore, the lithium-ion battery of the present invention has excellent capacity to suppress volumetric expansion.

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 A1, A2, A3, A4 (with A1>A2>A3>A4), etc. are exemplified as the upper and lower limits of the numerical value α, the range of the numerical value α is A1 or less, Examples include A2 or less, A3 or less, A2 or more, A3 or more, A4 or more, A1 to A2, A1 to A3, A1 to A4, A2 to A3, A2 to A4, A3 to A4.

[Aqueous solution of thermally crosslinkable binder for lithium ion battery: also referred to as aqueous solution]
In the present disclosure, with respect to 100 mol% of the monomer group,
20 to 85 mol% of the (meth)acrylamide group-containing compound (a),
10 to 50 mol% of one or more unsaturated acids or inorganic salts thereof (b) selected from the group consisting of unsaturated carboxylic acids and unsaturated sulfonic acids, and 5 hydroxybutyl (meth)acrylates (c) Provided is an aqueous thermally crosslinkable binder solution for lithium ion batteries, containing water-soluble poly(meth)acrylamide (A), which is a polymer of a monomer group containing up to 30 mol %.

<(Meth)acrylamide group-containing compound (a): 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. Examples of branched alkyl groups include i-propyl, i-butyl, s-butyl, t-butyl, diethylpentyl, trimethylbutyl, trimethylpentyl and trimethylhexyl groups.

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 and lower limits of the content of the (meth)acrylamide group-containing compound in 100 mol% of the monomer group are 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25. , 20 mol % and the like are exemplified. In one embodiment, the content range is preferably 20 to 85 mol %.

The upper and lower limits of the content of the (meth)acrylamide group-containing compound with respect to 100% by mass of the monomer group are 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 12 mass. % etc. are exemplified. In one embodiment, the content of the (meth)acrylamide group-containing compound is preferably 12 to 70% by mass with respect to 100% by mass of the monomer group.

<One or more unsaturated acids or inorganic salts thereof (b) selected from the group consisting of unsaturated carboxylic acids and unsaturated sulfonic acids: also referred to as component (b)>
As the component (b), various known components can be used without particular limitation, and may be used alone or in combination of two or more.

Examples of unsaturated carboxylic acids include (meth)acrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid.

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- Examples include 2-methylpropanesulfonic acid, 2-(meth)acrylamido-2-hydroxypropanesulfonic acid, 3-sulfopropane (meth)acrylic acid ester, bis-(3-sulfopropyl) itaconic acid ester and the like.

Inorganic salts are exemplified by alkali metal salts, alkaline earth metal salts and the like.

Alkali metals are exemplified by lithium, sodium, potassium and the like.

Alkaline earth metals are exemplified by magnesium, calcium and the like.

The upper and lower limits of the content of one or more unsaturated acids or inorganic salts thereof (b) selected from the group consisting of unsaturated carboxylic acids and unsaturated sulfonic acids with respect to 100% by mass of the monomer group are 50, 45, 40, 35, 30, 25, 20, 15, 10 mol % and the like are exemplified. In one embodiment, the content of one or more unsaturated acids or inorganic salts thereof (b) selected from the group consisting of unsaturated carboxylic acids and unsaturated sulfonic acids with respect to 100% by mass of the monomer group is 10 ~50 mol% is preferred.

The upper and lower limits of the content of one or more unsaturated acids or inorganic salts thereof (b) selected from the group consisting of unsaturated carboxylic acids and unsaturated sulfonic acids with respect to 100% by mass of the monomer group are 50, 45, 40, 35, 30, 25, 20, 15, 10, 5% by mass and the like are exemplified. In one embodiment, the content of one or more unsaturated acids or inorganic salts thereof (b) selected from the group consisting of unsaturated carboxylic acids and unsaturated sulfonic acids with respect to 100% by mass of the monomer group is 5 ~50% by mass is preferred.

<Hydroxybutyl (meth)acrylate (c): Also referred to as component (c)>
As the component (c), various known components can be used without particular limitation, and may be used alone or in combination of two or more.

Component (c) is 1-hydroxybutyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, (meth)acrylic 1-hydroxy-1-methyl-propyl acid, 2-hydroxy-1-methyl-propyl (meth)acrylate, 3-hydroxy-1-methyl-propyl (meth)acrylate, 1-ethyl-(meth)acrylate 2-hydroxyethyl, 1-hydroxy-2-methyl-propyl (meth)acrylate, 2-hydroxy-2-methyl-propyl (meth)acrylate, 3-hydroxy-2-methyl-propyl (meth)acrylate, Examples include 1,1-dimethyl-2-hydroxyethyl (meth)acrylate.

The upper and lower limits of the content of hydroxybutyl (meth)acrylate (c) with respect to 100 mol % of the monomer group are exemplified by 30, 25, 20, 15, 10, 5 mol % and the like. In one embodiment, the above content is preferably 5 to 30 mol %.

The upper and lower limits of the content of hydroxybutyl (meth)acrylate (c) with respect to 100% by mass of the monomer group are exemplified by 50, 45, 40, 35, 30, 25, 20, 15, 10, 5% by mass, etc. be done. In one embodiment, the content of hydroxybutyl (meth)acrylate (c) is preferably 5 to 50% by mass with respect to 100% by mass of the monomer group.

The upper and lower limits of the substance amount ratio of the (a) component and the (b) component [substance amount of component (a)/substance amount of component (b)] contained in the monomer group are 8.5, 8, 7.5, 7, 6.5, 6, 5.5, 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.5, 0.4 and the like are exemplified. In one embodiment, the substance amount ratio of the (a) component and the (b) component contained in the monomer group [substance amount of component (a)/substance amount of component (b))] is 0.4 to 8.5 is preferred.

The upper and lower limits of the substance amount ratio of the (a) component and the (c) component contained in the monomer group [substance amount of component (a)/substance amount of component (c))] are 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2.5, 2, 1.5, 1, 0.9, 0.6 and the like. In one embodiment, the substance amount ratio of the (a) component and the (c) component contained in the monomer group [substance amount of component (a)/substance amount of component (c)] is 0.6 to 17. is preferred, and 1 or more is more preferred. By setting the amount of the substance to 1 or more, it becomes easier to prevent an increase in the water absorption rate after crosslinking, and as a result, the amount of gas generated during the production of the battery can be reduced.

The upper and lower limits of the substance amount ratio between the (b) component and the (c) component contained in the monomer group [substance amount of component (b)/substance amount of component (c)] are 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.9, 0.5, 0.3 and the like are exemplified. In one embodiment, the substance amount ratio between the (b) component and the (c) component contained in the monomer group [substance amount of component (b)/substance amount of component (c)] is 0.3 to 10. is preferred.

The upper and lower limits of the mass ratio of component (a) to component (b) contained in the monomer group [mass of component (a)/mass of component (b)] are 14, 12, 10, 9, 7, 5, 3, 2, 1, 0.9, 0.7, 0.5, 0.3, 0.2 and the like are exemplified. In one embodiment, the mass ratio of component (a) to component (b) contained in the monomer group [mass of component (a)/mass of component (b)] is preferably 0.2 to 14. .

The upper and lower limits of the mass ratio of component (a) to component (c) contained in the monomer group [mass of component (a)/mass of component (c)] are 14, 12, 10, 9, 7, 5, 3, 2, 1, 0.9, 0.7, 0.5, 0.3, 0.2 and the like are exemplified. In one embodiment, the mass ratio of component (a) to component (c) contained in the monomer group [mass of component (a)/mass of component (c)] is preferably 0.2 to 14. .

The upper and lower limits of the mass ratio of component (b) to component (c) contained in the monomer group [mass of component (b)/mass of component (c)] are 10, 9, 7, 5, 3, 2, 1, 0.9, 0.7, 0.5, 0.3, 0.2, 0.1 and the like are exemplified. In one embodiment, the mass ratio of component (b) to component (c) contained in the monomer group [mass of component (b)/mass of component (c)] is preferably 0.1 to 10. .

<Monomers other than components (a), (b), and (c): also referred to as component (d)>
In the monomer group, a monomer (component (d)) that does not fall under any of components (a), (b), and (c) may be used unless the desired effects of the present invention are impaired. can be done. Component (c) may be used alone or in combination of two or more. Component (d) is a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group with 2 to 3 carbon atoms, unsaturated phosphoric acid, a hydroxyl group-free unsaturated carboxylic acid ester, an α,β-unsaturated nitrile compound, and a conjugated diene compound. , aromatic vinyl compounds, and the like.

Hydroxyalkyl (meth)acrylates having a hydroxyalkyl group having 2 to 3 carbon atoms include 1-hydroxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 1-hydroxypropyl (meth)acrylate, ( 2-hydroxypropyl meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxy-1-methylethyl (meth)acrylate, 1-hydroxy-2-methylethyl (meth)acrylate and the like are exemplified. be.

The upper and lower limits of the content of hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 3 carbon atoms with respect to 100 mol% of the monomer group are 50, 45, 40, 35, 30, 25, 20, 15, Examples include 10 and 5 mol %. In one embodiment, the content of hydroxyalkyl (meth)acrylate having a hydroxyalkyl group with 2 to 3 carbon atoms is preferably 5 to 50 mol% with respect to 100 mol% of the monomer group.

The upper and lower limits of the content of hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 3 carbon atoms with respect to 100% by mass of the monomer group are 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5 mass % and the like are exemplified. In one embodiment, the content of hydroxyalkyl (meth)acrylate having a hydroxyalkyl group with 2 to 3 carbon atoms is preferably 5 to 70% by mass with respect to 100% by mass of the monomer group.

Unsaturated phosphoric acids include vinylphosphonic acid, vinyl phosphate, bis((meth)acryloxyethyl)phosphate, diphenyl-2-(meth)acryloyloxyethyl phosphate, dibutyl-2-(meth)acryloyloxyethyl phosphate, Examples include dioctyl-2-(meth)acryloyloxyethyl phosphate, monomethyl-2-(meth)acryloyloxyethyl phosphate, 3-(meth)acryloxy-2-hydroxypropane phosphate and salts thereof.

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 unsaturated phosphoric acid content 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).

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. curl can be suppressed. 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 of the water-soluble poly(meth)acrylamide (A) in water, and the flexibility It becomes easier to demonstrate

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 ratio of component (d) other than the unsaturated phosphoric acid, unsaturated carboxylic acid ester, α,β-unsaturated nitrile compound, conjugated diene compound, and aromatic vinyl compound to the monomer group is 100 in the monomer group. Per mol%, less than 10 mol%, less than 5 mol%, less than 1 mol%, less than 0.1 mol%, less than 0.01 mol%, 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, less than 0.01% by mass, and 0% by mass.

<Method for producing thermally crosslinkable binder aqueous solution for lithium ion battery>
In one embodiment, the aqueous thermally crosslinkable binder solution for a lithium ion battery contains 20 to 85 mol% of the (meth)acrylamide group-containing compound (a) and an unsaturated carboxylic acid with respect to 100 mol% of the monomer group. , and one or more unsaturated acids or inorganic salts thereof selected from the group consisting of unsaturated sulfonic acids (b) 10 to 50 mol%, and hydroxybutyl (meth)acrylate (c) 5 to 30 mol% It can be produced by a production method including a step of obtaining a water-soluble poly(meth)acrylamide (A) that is a polymer of the monomer group containing.

Water-soluble poly(meth)acrylamide (A) can be synthesized by various known polymerization methods, preferably radical polymerization method. In the polymerization reaction, a radical polymerization initiator and optionally a chain transfer agent are added to a monomer mixed liquid containing components (a), (b), (c) and optionally (d), The reaction may be carried out at a reaction temperature of about 50 to 100° C. while stirring. 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 5.0% 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 water-soluble poly(meth)acrylamide (A) has an acid group, depending on the application, the neutralization rate (a neutralization rate of 100% is the acid component contained in the water-soluble poly(meth)acrylamide (A)). A neutralization rate of 50% means neutralization with half the number of moles of alkali relative to the acid component contained in the water-soluble poly(meth)acrylamide (A). ) can be adjusted and used. The neutralization rate when dispersing the electrode active material is not particularly limited. In one embodiment, it is preferably 70 to 95% after forming a coating layer or the like. It is preferably 70% or more from the viewpoint of preventing a decrease in initial capacity, and preferably 95% or less from the viewpoint of preventing hydrolysis. Examples of neutralized salts include Li salts, Na salts, K salts, ammonium salts, Mg salts, Ca salts, Zn salts, Al salts and the like.

In one embodiment, water-soluble poly(meth)acrylamide (A) is preferably an inorganic salt. Examples of inorganic salts include those mentioned above.

<Physical properties of 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.

Although the glass transition point of the water-soluble poly(meth)acrylamide (A) is not particularly limited, it 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, it is 30°C or higher (40°C or higher). ° C. or higher, 45 ° C. or higher, etc.) is more preferable.

The glass transition temperature of water-soluble poly(meth)acrylamide (A) can be adjusted by a combination of monomers. The glass transition temperature of the water-soluble poly(meth)acrylamide (A) is calculated from the glass transition temperature (Tg) (absolute temperature: K) of the homopolymer of the monomers and their mass fractions according to the following Fox formula: can be determined based on
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. The composition of the monomers making up the backbone polymer (A) with the desired glass transition temperature can be determined so as to obtain the backbone polymer (A). 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 water-soluble poly(meth)acrylamide (A) is not particularly limited, but the upper and lower limits of the gel fraction of component (A) are 99.9%, 95%, 90% and 85% , 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20% and the like. In one embodiment, it is preferably 20% or more, more preferably 25% or more, from the viewpoint of the effect of exhibiting springback resistance during charge-discharge cycles.

The gel fraction of the 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 water-soluble poly(meth)acrylamide (A), an appropriate container (e.g., an ointment can (manufactured by Sogo Rikagaku Glass Co., Ltd., trade name " Ointment cans made of tin”))) and dried under appropriate drying conditions (for example, circulating air dryer (manufactured by Advantech Toyo Co., Ltd., trade name “air constant temperature dryer DSR420DA”) at 120 ° C. for 4 hours), and then thermally crosslinked. A solid resin 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.

The thermal crosslinking of the water-soluble poly(meth)acrylamide (A) is believed to be due to the amide group derived from the (meth)acrylamide group-containing compound (a) and the hydroxyl group derived from the hydroxyl group-containing (meth)acrylic ester (b). . The molar ratio of amide groups to hydroxyl groups (amide groups/hydroxyl groups) in the water-soluble poly(meth)acrylamide (A) is not particularly limited, but excess amide groups are preferred. The upper and lower limits of the molar ratio between the amide group and the hydroxyl group (amide group/hydroxyl group) are 19, 18, 17.5, 15, 12.5, 10, 9, 7.5, 5, 2.5, 1. 2, 1.0, etc. are exemplified. 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 water-soluble poly(meth)acrylamide (A) is not particularly limited, but its upper and lower limits are 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, 350 thousand , 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 thermally crosslinkable slurry for lithium ion battery negative electrode.

The number average molecular weight (Mn) of the water-soluble poly(meth)acrylamide (A) is not particularly limited, but the upper and lower limits are 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, 10,000 and the like are exemplified. In one embodiment, the water-soluble poly(meth)acrylamide (A) preferably has a number average molecular weight (Mn) of 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 and lower limits of the molecular weight distribution (Mw/Mn) of the water-soluble poly(meth)acrylamide (A) are 15, 14, 13, 11, 10, 9, 7.5, 5, 4, 3, 2.9, 2.5, 2, 1.5, 1.1 and the like are exemplified. In one embodiment, the molecular weight distribution (Mw/Mn) of the water-soluble poly(meth)acrylamide (A) is preferably 1.1-15.

The B-type viscosity of the aqueous solution containing the water-soluble poly(meth)acrylamide (A) is not particularly limited, but the upper and lower limits are 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, 1000 mPa·s and the like are exemplified. 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 and lower limits of the pH of the aqueous thermally crosslinkable binder solution for lithium ion batteries are 7, 6.9, 6.5, 6, 5.9, 5.6, 5.5, 5.4, 5.2, 5. .1, 5, etc. are exemplified. In one embodiment, the pH of the aqueous thermally crosslinkable binder solution for lithium ion batteries is preferably pH 5 to 7 from the viewpoint of solution stability.

The pH 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 and lower limits of the content of the water-soluble poly(meth)acrylamide (A) with respect to 100% by mass of the aqueous thermally crosslinkable binder solution for lithium ion batteries are 20, 19, 15, 14, 12, 10, 9, 7, 6, 5 mass % etc. are illustrated. In one embodiment, the content of the water-soluble poly(meth)acrylamide (A) with respect to 100% by mass of the aqueous thermally crosslinkable binder solution for lithium ion batteries is preferably 5 to 20% by mass.

Examples of the upper and lower limits of the water content with respect to 100% by mass of the aqueous thermally crosslinkable binder solution for lithium ion batteries are 95, 90, 85, 80% by mass, and the like. In one embodiment, the content of water is preferably 80 to 95% by mass with respect to 100% by mass of the aqueous thermally crosslinkable binder solution for lithium ion batteries.

The upper and lower limits of the mass ratio between the component (A) and water contained in the aqueous solution of the thermally crosslinkable binder for lithium ion batteries are exemplified by 0.25, 0.2, 0.15, 0.1, 0.05, and the like. be done. In one embodiment, the mass ratio of the component (A) and water contained in the aqueous thermally crosslinkable binder solution for lithium ion batteries is preferably 0.05 to 0.25.

<Additive>
The aqueous thermally crosslinkable binder solution for lithium ion batteries may contain, as an additive, an agent that does not correspond to either the component (A) or water. Examples of additives include dispersants, leveling agents, antioxidants, thickeners, particulate polymers, 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.

The particulate polymer includes styrene-butadiene copolymer latex, polystyrene polymer latex, polybutadiene polymer latex, acrylonitrile-butadiene copolymer latex, polyurethane polymer latex, 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 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), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), and the like. In one embodiment, the slurry is free of particulate polymer.

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. silane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, Examples include vinyltrimethoxysilane, 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 an aqueous thermally crosslinkable binder solution for lithium ion battery negative electrodes.

[Thermal crosslinkable slurry for lithium ion battery negative electrode: also referred to as slurry]
The present disclosure provides a thermally crosslinkable slurry for a lithium ion battery negative electrode, which contains the above aqueous solution of a thermally crosslinkable binder for a lithium ion battery and a negative electrode active material, and has a pH of 5 to 7.

The upper and lower limits of the pH of the thermally crosslinkable slurry for a lithium ion battery negative electrode are 7, 6.9, 6.5, 6, 5.9, 5.6, 5.5, 5.4, 5.2, 5. .1, 5, etc. are exemplified. In one embodiment, the pH of the thermally crosslinkable slurry for lithium ion battery negative electrode is preferably pH 5 to 7 from the viewpoint of solution stability.

<Negative electrode active material>
The negative 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 negative electrode active material, an appropriate material can be appropriately selected depending on the type of the target electricity storage device. Examples of negative electrode active materials include carbon materials, silicon materials, oxides containing lithium atoms, lead compounds, tin compounds, arsenic compounds, antimony compounds, aluminum compounds, and other materials that are alloyed with lithium. 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 a negative electrode active material, you may use negative electrode active materials other than a silicon material together. Such a negative electrode active material includes the carbon materials described above; conductive _polymers such as _{polyacene ;} 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 negative electrode active material, it is preferable to use a carbon material in combination because the volume change accompanying the absorption and desorption 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 negative 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 negative electrode active material is not particularly limited, but the upper and lower limits are , 0.5, 0.1 μm, and the like. In one embodiment, the average particle size of the negative electrode active material is preferably 0.1 to 50 μm, more preferably 0.1 to 45 μm, even more preferably 1 to 10 μm, particularly preferably about 5 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. A uniform and thin coating film can be formed when the content is in such a range, which is preferable. In addition, the “particle diameter” 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 the "average particle size" is the number of particles observed in several to several tens of fields using observation means such as a scanning electron microscope (SEM) or a 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 negative 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 negative 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 and lower limits of the content of component (A) with respect to 100% by mass of the slurry are 15, 14, 12, 10, 9, 7, 5, 4, 3, 2, 1, 0.9, 0.6, 0.5 mass % etc. are illustrated. In one embodiment, the content of component (A) is preferably 0.5 to 15% by mass with respect to 100% by mass of the slurry of the present invention.

The upper and lower limits of the content of component (A) in the slurry are exemplified by about 15, 14, 11, 10, 9, 5, 4, 2, and 1% by mass relative to 100% by mass of the negative electrode active material. In one embodiment, the content of component (A) is preferably about 1 to 15% by mass with respect to 100% by mass of the negative electrode active material.

The upper and lower limits of the content of the negative electrode active material with respect to 100% by mass of the slurry are exemplified by 65, 60, 55, 50, 45, 40, 35, 30, 25, 20% by mass. In one embodiment, the content of the negative electrode active material is preferably 20 to 65% by mass with respect to 100% by mass of the slurry.

The upper and lower limits of water content with respect to 100% by mass of the slurry are exemplified by 79, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20% by mass. In one embodiment, the water content is preferably 20 to 79% by mass with respect to 100% by mass of the slurry.

A binder other than the water-soluble poly(meth)acrylamide (A) may be used in the slurry. In one embodiment, 90 wt% or more (95, 99 wt% or more, 100 wt%, etc.) of water-soluble poly(meth)acrylamide (A) in the total binder is preferred.

<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 an additive, an agent that does not fall under any of (A), the negative electrode active material, water, and the slurry viscosity adjusting solvent. 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 slurry, with respect to 100 mol% of the monomer group,
20 to 85 mol% of the (meth)acrylamide group-containing compound (a),
10 to 50 mol% of one or more unsaturated acids or inorganic salts thereof (b) selected from the group consisting of unsaturated carboxylic acids and unsaturated sulfonic acids, and 5 hydroxybutyl (meth)acrylates (c) It can be produced by a production method including a step of mixing water-soluble poly(meth)acrylamide (A), which is a polymer of a monomer group containing up to 30 mol %, and a negative electrode active material.

The method for producing the slurry of the present invention includes a method of mixing an aqueous solution of component (A) (the above aqueous solution of a thermally crosslinkable binder for a lithium ion battery) and a negative electrode active material, or a method of mixing component (A), a negative electrode active material, and water. A method of mixing separately 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.

[Lithium ion battery negative electrode]
The present disclosure provides a lithium ion battery negative electrode obtained by applying the thermally crosslinkable slurry for a lithium ion battery negative electrode to a current collector and drying and curing the slurry. The electrode has a dried and cured product of the thermally crosslinkable slurry for a lithium ion battery negative electrode on a current collector.

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. Drying at an appropriate temperature promotes cross-linking of the water-soluble poly(meth)acrylamide (A), which is a heat-crosslinkable binder for lithium ion batteries, and develops springback resistance associated with charge-discharge cycles.

Although the thickness of the electrode (cured coating film) is not particularly limited, it is preferably about 5 to 300 μm, more preferably about 10 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.

[Lithium-ion battery]
The present disclosure provides a lithium ion battery including the lithium ion battery negative electrode described above. In one embodiment, the battery includes an electrolyte solution, a separator, a positive electrode, and the like. These are not particularly limited.

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.

Various known positive electrodes 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 1,250 g of ion-exchanged water, 250 g (1.76 mol) of a 50% acrylamide aqueous solution, and 33.3 g (0.369 mol) of an 80% aqueous acrylic acid solution. , 47.9 g (0.332 mol) of 4-hydroxybutyl acrylate and 0.39 g (0.0025 mol) of sodium methallyl sulfonate are added, oxygen is removed from the reaction system through nitrogen gas, and the temperature is raised to 50°C. bottom. 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 water-soluble polyacrylamide.

Examples 1-2 to 1-8
An aqueous solution 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 in Example 1-1 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 1,200 g of ion-exchanged water, 210 g (1.48 mol) of a 50% acrylamide aqueous solution, and 88.9 g (0.986 mol) of an 80% aqueous acrylic acid solution. , 0.39 g (0.0025 mol) of sodium methallylsulfonate was added, and after oxygen was removed from 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 carried out to obtain an aqueous solution containing polyacrylamide.

Comparative Examples 1-2 to 1-5
An aqueous solution containing water-soluble polyacrylamide 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.

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 a thermally crosslinkable binder aqueous solution for lithium ion batteries 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") and circulated. After drying at 120° C. for 4 hours with a wind dryer (manufactured by Advantec Toyo Co., Ltd., trade name: constant temperature blower 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

Hygroscopicity 10 g of an aqueous binder solution for lithium ion batteries was dried for 12 hours in a 130°C circulating air dryer (product name “DRS420DA” manufactured by ADVANTEC). pulverized. The pulverized solid matter was placed in a vacuum dryer (manufactured by ADVANTEC, product name “VO-320P”) and vacuumed at 120° C. to a gauge pressure of 76 cmHg or less and dried for 12 hours. About 1 g of the obtained test piece was weighed in a petri dish, placed in a constant temperature and humidity machine (manufactured by ESPEC, product name "LH-113") and allowed to stand at 65° C. and 60% humidity for 3 hours, and the mass was measured.
Hygroscopicity = {(mass after 3 hours at 65°C and 60% humidity) / (mass immediately after drying)} x 100-100 (%)
Due to the low hygroscopicity of the binder for lithium ion batteries (water-soluble poly(meth)acrylamide), the amount of water remaining inside the lithium ion battery after fabrication is reduced.

・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」）
・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」）
・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」）
・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」）
・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」）
・ＨＰＡ：アクリル酸２－ヒドロキシプロピル
・ＨＢＡ：アクリル酸４－ヒドロキシブチル（三菱ケミカル株式会社製 「ＨＢＡ」）
・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

・ AM: Acrylamide ("50% acrylamide" manufactured by Mitsubishi Chemical Corporation)
・ DMAA: N, N-dimethyl (meth) acrylamide ("DMAA" manufactured by KJ Chemicals Co., Ltd.)
・ AA: Acrylic acid (“80% acrylic acid” manufactured by Osaka Organic Chemical Industry Co., Ltd.)
・ ATBS: acrylamide t-butyl sulfonic acid ("ATBS" manufactured by Toagosei Co., Ltd.)
・ HEA: 2-hydroxyethyl acrylate ("HEA" manufactured by Osaka Organic Chemical Industry Co., Ltd.)
・HPA: 2-hydroxypropyl acrylate ・HBA: 4-hydroxybutyl acrylate ("HBA" manufactured by Mitsubishi Chemical Corporation)
・ AN: Acrylonitrile ("Acrylonitrile" manufactured by Mitsubishi Chemical Corporation)
・SMAS: Sodium methallyl sulfonate

2. Production of electrode slurry, cell production and evaluation Example 2-1: Evaluation of electrode <Production of electrode slurry>
Using a commercially available rotation-revolution mixer (product name "Awatori Mixer", manufactured by Thinky Co., Ltd.), 5 parts by mass of the aqueous solution obtained in Production Example 1 in terms of solid content and D50 are added to a container dedicated to the mixer. 20 parts by mass of silicon monoxide particles (“CC powder”, manufactured by Osaka Titanium Technologies Co., Ltd.) with a (median diameter) of 5 μm, and 80 parts of natural graphite (product name “Z-5F” manufactured by Ito Graphite Industry Co., Ltd.) 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.

<Production of electrodes>
On the surface of a current collector made of copper foil, the lithium ion battery slurry was uniformly applied by a doctor blade method so that the film thickness after drying was 80 μm, dried at 150 ° C. for 30 minutes, and then dried at 150 ° C./ An electrode was obtained by heat treatment in vacuum for 120 minutes. 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.

<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 500 μL of an electrolytic solution was injected so as to prevent air from entering. A lithium half cell was assembled by placing a commercially available metallic lithium foil punched into a size of 16 mm and sealing the exterior body of the bipolar coin cell with screws. 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).

Examples 2-2 to 2-8, Comparative Examples 2-1 to 2-5
A lithium half cell was obtained 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.

<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

<Evaluation of electrode adhesion>
Electrode adhesion was evaluated as follows.
A test piece having a width of 2 cm and a length of 10 cm was cut out from the electrode and fixed with the coated surface facing up. Next, a 15 mm wide adhesive tape ("CELLOTAPE (registered trademark)" manufactured by Nichiban Co., Ltd.) (defined in JIS Z1522) was attached to the surface of the active material layer of the test piece while being pressed, and then subjected to 25°C conditions. Using a tensile tester ("Tensilon RTM-100" manufactured by A&D Co., Ltd.) below, the adhesive tape was peeled off from one end of the test piece at a speed of 30 mm / min in the 180 ° direction. Stress was measured. The measurement was performed 5 times, converted to a value per width of 15 mm, and the average value was calculated as the peel strength. The higher the peel strength, the higher the adhesive strength between the current collector and the active material layer or the adhesiveness between the active materials, indicating that the active material layer or the active materials are less likely to peel off from the current collector.

<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 (%)

<Discharge capacity retention rate>
The discharge capacity retention rate was obtained from the following formula.
Discharge capacity retention rate = {(Discharge capacity at 30th cycle)/(Discharge capacity at 1st cycle)} x 100 (%)

<Manufacturing of laminated lithium-ion batteries>
In measuring the volume expansion coefficient, a laminate type lithium ion battery was manufactured as follows, and the operation was also checked.

<Manufacturing positive electrode for laminated lithium-ion battery>
LiNi _0.5 Co _0.2 Mn _0.3 O ₂ as a positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder, respectively, at 88 parts by mass, 6 parts by mass, and 6 parts by mass. were mixed, and this mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to produce a lithium ion battery positive electrode slurry for a laminate type lithium ion battery. Next, an aluminum foil was prepared as a current collector for the positive electrode, and the lithium ion battery positive electrode slurry for a laminate type lithium ion battery was placed on the aluminum foil and coated with a doctor blade to form a film. After applying the slurry for positive electrode of lithium ion battery for laminate type lithium ion battery, the aluminum foil was dried at 80° C. for 20 minutes to volatilize and remove NMP, and then closely bonded by a roll press machine. At this time, the density of the positive electrode active material layer was set to 3.2 g/cm ² . The bonded product was heated at 120° C. for 6 hours in a vacuum dryer and cut into a predetermined shape (rectangular shape of 25 mm×30 mm) to obtain a positive electrode having a positive electrode active material layer with a thickness of about 45 μm.

A laminated lithium ion secondary battery was produced using the positive electrode for a laminated lithium ion battery and the negative electrode obtained in Examples or Comparative Examples.
That is, a separator made of a polypropylene porous film (manufactured by CS TECH CO., LTD, trade name “Selion P2010”) was sandwiched between rectangular sheets (55 × 15 mm, thickness 25 μm) between the positive electrode and the negative electrode to form an electrode. It was made into a board group. This electrode plate assembly was dried at 100° C., 0.3 Pa for 24 hours, and the electrode plate assembly was covered with a set of two sheets of laminate film, and after sealing the three sides, the bag-like laminate film was used. electrolyte was injected. As an electrolytic solution, a solution in which LiPF ₆ was dissolved at a concentration of 1 mol/L in a solvent of ethylene carbonate/ethyl methyl carbonate=1/1 (mass ratio) was used. After that, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were airtightly sealed and the electrode plate group and the electrolytic solution were sealed. In addition, the positive electrode and the negative electrode have tabs that can be electrically connected to the outside, and a part of the tabs extends outside the laminate type lithium ion secondary battery. When the laminate type lithium ion battery manufactured by the above steps was energized, no problem occurred in operation.

<Volume expansion rate>
Using the above laminated lithium ion secondary battery, charge at a voltage of 2.5 to 4.2 V at 0.1 C at 25 ° C. When the voltage reaches 4.2 V, continue to a constant voltage (4.2 V). The charging was continued until the current value reached 0.01C, and the charging was completed (cutoff). A 1000 mL container was filled with water at 25° C., and the fully charged laminate type lithium ion battery was submerged, and the volume of overflowing water was defined as the volume of the laminate type lithium ion battery. After the laminated lithium ion battery was placed at 70° C. for 10 days, the volume was measured again.
Volumetric expansion rate = {(Volume after 10 days at 70°C after completion of charging)/(Volume immediately after completion of charging)} x 100-100 (%)

Claims (5)

With respect to 100 mol% of the monomer group,
20 to 85 mol% of the (meth)acrylamide group-containing compound (a),
10 to 50 mol% of one or more unsaturated acids or inorganic salts thereof (b) selected from the group consisting of unsaturated carboxylic acids and unsaturated sulfonic acids, and 5 hydroxybutyl (meth)acrylates (c) An aqueous solution of a thermally crosslinkable binder for a lithium ion battery, containing water-soluble poly(meth)acrylamide (A) which is a polymer of a monomer group containing up to 30 mol %. Substance amount ratio (molar ratio) between the (meth)acrylamide group-containing compound (a) and the hydroxybutyl (meth)acrylate (c) contained in the monomer group [substance amount of component (a)/(c 3. The aqueous thermally crosslinkable binder solution for a lithium ion battery according to claim 1, wherein the amount of substance of component )] is 1 or more. A thermally crosslinkable slurry for a lithium ion battery negative electrode, comprising the thermally crosslinkable binder aqueous solution for a lithium ion battery according to claim 1 or 2 and a negative electrode active material. A negative electrode for a lithium ion battery obtained by applying the thermally crosslinkable slurry for a lithium ion battery negative electrode according to claim 3 to a current collector, drying and curing the slurry. A lithium ion battery comprising the lithium ion battery negative electrode according to claim 4 .