JP7031278B2 - Binder aqueous solution for lithium ion battery, electrode slurry for lithium ion battery and its manufacturing method, electrode for lithium ion battery, and lithium ion battery - Google Patents

Description

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

Lithium-ion batteries are small and 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, improvement of battery members such as electrodes has been studied for the purpose of further improving the performance of lithium ion batteries.

For both the positive and negative electrodes of a lithium-ion battery, a slurry obtained by dispersing an electrode active material and a binder resin in a solvent is applied on both sides of a current collector (for example, a metal foil), and the solvent is dried and removed to form an electrode. After forming the layer, it is produced by compression molding with a roll press machine or the like.

Regarding the binder resin, for example, Patent Document 1 discloses a technique of using poly (meth) acrylic acid as a binder for a negative electrode active material layer containing a silicon-based active material.

Japanese Unexamined Patent Publication No. 2007-115671

However, in the technique disclosed in Patent Document 1, since poly (meth) acrylic acid has low flexibility, it cannot follow the expansion and contraction of the active materials and separates the active materials from each other, so that the cycle characteristics are improved. There is room.

Therefore, the present invention is a binder aqueous solution for a lithium ion battery capable of preparing a slurry having excellent dispersion stability, and when a lithium ion battery is manufactured using the aqueous solution, electricity such as cycle characteristics of the lithium ion battery is obtained. An object of the present invention is to provide an aqueous binder solution for a lithium ion battery capable of improving the characteristics.

Another object of the present invention is to provide an electrode slurry for a lithium ion battery capable of improving electrical characteristics such as cycle characteristics of the lithium ion battery when manufacturing a lithium ion battery.

As a result of diligent studies to solve the above problems, the present inventor has found that the above problems can be solved by using a polymer having a specific composition, and has completed the present invention.

（式中、Ｒ^１は、水素原子又はメチル基であり、Ｒ^２は、メチレン基、エチレン基、又はプロピレン基であり、Ｒ^３は、水素原子又はメチル基であり、ｎは３以上の整数である。）で表されるマクロモノマーの重合物である、上記項目に記載のリチウムイオン電池用バインダー水溶液。
（項目３）
前記水溶性グラフトポリマー（Ｃ）を乾燥し、作成したフィルムのＨＡＺＥが３％以上である、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バインダー水溶液。
（項目４）
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バインダー水溶液、及び電極活物質（Ｄ）を含む、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（Ｄ）１００質量％に対し、前記水溶性グラフトポリマー（Ｃ）を１～１５質量％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）
前記電極活物質（Ｄ）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７）
幹ポリマー（Ａ）を構成する構成単位中、（メタ）アクリルアミド基含有化合物（ａ－１）に由来する構成単位の割合が５０質量％以上であり、枝ポリマー（Ｂ）を構成する構成単位中、３量体以上のポリアルキレングリコールエーテル（ｂ－１）に由来する構成単位の割合が９０質量％以上であり、幹ポリマー（Ａ）と枝ポリマー（Ｂ）がエステル結合で結合されている水溶性グラフトポリマー（Ｃ）、及び電極活物質（Ｄ）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８）
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９）
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１０）
上記項目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 disclosure provides the following items:
(Item 1)
Among the constituent units constituting the stem polymer (A), the proportion of the constituent units derived from the (meth) acrylamide group-containing compound (a-1) is 50% by mass or more, and among the constituent units constituting the branch polymer (B). The proportion of the structural unit derived from the trimeric or more polyalkylene glycol ether (b-1) is 90% by mass or more, and the stem polymer (A) and the branch polymer (B) are bonded by an ester bond. An aqueous solution of a binder for a lithium ion battery containing the sex graft polymer (C).
(Item 2)
The water-soluble graft polymer (C) is the same as the (meth) acrylamide group-containing compound (a-1) and the following general formula (1).

(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a methylene group, an ethylene group or a propylene group, R ³ is a hydrogen atom or a methyl group, and n is an integer of 3 or more. The aqueous binder solution for a lithium ion battery according to the above item, which is a polymer of the macromonomer represented by ().
(Item 3)
The binder aqueous solution for a lithium ion battery according to any one of the above items, wherein the film produced by drying the water-soluble graft polymer (C) has a HAZE of 3% or more.
(Item 4)
An electrode slurry for a lithium ion battery containing the aqueous binder solution for a lithium ion battery according to any one of the above items and the electrode active material (D).
(Item 5)
The electrode slurry for a lithium ion battery according to any one of the above items, which contains 1 to 15% by mass of the water-soluble graft polymer (C) with respect to 100% by mass of the electrode active material (D).
(Item 6)
The electrode slurry for a lithium ion battery according to any one of the above items, wherein the electrode active material (D) contains 5% by mass or more of silicon or silicon oxide covered with a carbon layer.
(Item 7)
Among the constituent units constituting the stem polymer (A), the proportion of the constituent units derived from the (meth) acrylamide group-containing compound (a-1) is 50% by mass or more, and among the constituent units constituting the branch polymer (B). The proportion of the structural unit derived from the trimeric or more polyalkylene glycol ether (b-1) is 90% by mass or more, and the stem polymer (A) and the branch polymer (B) are bonded by an ester bond. The method for producing an electrode slurry for a lithium ion battery according to any one of the above items, which comprises a step of mixing the sex graft polymer (C) and the electrode active material (D).
(Item 8)
An electrode for a lithium ion battery obtained by applying the electrode slurry for a lithium ion battery according to any one of the above items to a current collector and drying it.
(Item 9)
The electrode for a lithium ion battery according to the above item, wherein the current collector is a copper foil.
(Item 10)
A lithium ion battery comprising the electrodes for the lithium ion battery described in the above item.

In the electrode binder aqueous solution for the lithium ion battery and the electrode slurry for the lithium ion battery of the present invention, the aqueous solution and / Alternatively, a lithium ion battery having improved battery capacity sustainability can be obtained by using an electrode obtained from the above slurry.

Since the electrode for a lithium ion battery of the present invention is obtained by using the above-mentioned aqueous solution and / or the above-mentioned slurry containing the water-soluble graft polymer (C), it accompanies charge and discharge even when the battery capacity is increased. It provides a lithium-ion battery with little volume expansion and excellent durability of battery capacity.

Since the lithium ion battery of the present invention is equipped with the electrode according to the present invention, the battery capacity is excellent in sustainability.

[1. Binder aqueous solution for lithium-ion battery: Also called aqueous solution (1)]
In the present disclosure, the proportion of the structural unit derived from the (meth) acrylamide group-containing compound (a-1) in the structural units constituting the stem polymer (A) is 50% by mass or more, and constitutes the branch polymer (B). The proportion of the structural unit derived from the trimeric or more polyalkylene glycol ether (b-1) is 90% by mass or more, and the stem polymer (A) and the branch polymer (B) are bonded by an ester bond. Provided is an aqueous binder solution for a lithium ion battery containing the water-soluble graft polymer (C).

<1-1. Water-soluble graft polymer (C): Also referred to as (C) component>
In the present disclosure, "water-soluble" means that when 0.5 g of the compound is dissolved in 100 g of water at 25 ° C., the insoluble content is less than 0.5% by mass.

The chemical structure of the water-soluble graft polymer (C) is composed of a stem polymer (A), a branch polymer (B), and a binding site for binding them.

The water-soluble graft polymer (C) of the present invention can exert the functions of the stem polymer (A) and the branch polymer (B) separately. For example, the stem polymer (A) has mechanical strength, heat resistance, high cohesiveness, etc., and the branch polymer (B) relieves the stress generated as a result of the cohesive force of the stem polymer (A), and has flexibility. High adhesion can function.

In order for the graft structure to act efficiently, it is preferable to reduce the affinity between the stem polymer (A) and the branch polymer (B). For example, it is preferable that the hydrophilic unit composed of a functional group having high agglomerating property is used for the stem polymer (A), and the branch polymer (B) is a liquid polymer that is not compatible with the stem polymer (A).

（式中、Ｒ^Ａ１は水素又はメチル基である。）を有する化合物又はその塩を意味する。（ａ－１）成分は、単独で用いてもよいし、二種以上を併用してもよい。 <1-2. Stem polymer (A): Also referred to as (A) component>
In the present disclosure, the term "(meth) acrylamide group-containing compound (a-1)" refers to a (meth) acrylamide skeleton.

(In the formula, ^RA1 is a hydrogen or a methyl group) means a compound or a salt thereof. The component (a-1) may be used alone or in combination of two or more.

In the present disclosure, "(meth) acrylic" means "at least one selected from the group consisting of acrylic and methacrylic". Similarly, "(meth) acrylate" means "at least one selected from the group consisting of acrylates and methacrylates". Further, "(meth) acryloyl" means "at least one selected from the group consisting of acryloyl and methacryloyl".

（式中、Ｒ^Ａ１は水素又はメチル基であり、Ｒ^Ａ２及びＲ^Ａ３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^Ａ２及びＲ^Ａ３が一緒になって環構造を形成する基であり、Ｒ^Ａ４及びＲ^Ａ５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。（メタ）アクリルアミド基含有化合物は、単独で用いてもよいし、二種以上を併用してもよい。 In one embodiment, the (meth) acrylamide group-containing compound has the following structural formula:

(In the formula, ^RA1 is a hydrogen or a methyl group, and ^RA2 and ^RA3 are independently hydrogen, substituted or unsubstituted alkyl groups, acetyl groups, or sulfonic acid groups, or ^RA2 and ^RA3 is a group that forms a ring structure together, and ^RA4 and ^RA5 are independently hydrogen, substituted or unsubstituted alkyl group, carboxyl group, hydroxy group, amino group (-NR ^a R). ^b (R ^a and R ^b are independently hydrogen or substituted or unsubstituted alkyl groups) (same below)), acetyl group, sulfonic acid group. Substituents of the substituted alkyl group are hydroxy group and amino. Examples include a group, an acetyl group, a sulfonic acid group, and the like. Further, as a group in which R ² and R ³ form a ring structure together, a morphoryl group and the like are exemplified.)
Represented by. The (meth) acrylamide group-containing compound may be used alone or in combination of two or more.

Examples of the alkyl group include a linear alkyl group, a branched alkyl group, a cycloalkyl group and the like.

The linear alkyl group can be expressed by the general formula of −C _n H _{2n + 1} (n is an integer of 1 or more). The linear alkyl group includes a methyl group, an ethyl group, a propylene group, an n-butylene group, an n-pentylene group, an n-hexylene group, an n-heptylene group, an n-octylene group, an n-nonylene group, an n-decamethylene group and the like. Is exemplified.

A branched alkyl group is a group in which at least one hydrogen of a linear alkyl group is substituted with an alkyl group. Examples of the branched alkyl group include a diethylpentyl group, a trimethylbutyl group, a trimethylpentyl group, a trimethylhexyl group (trimethylhexamethyl group) and the like.

Examples of the cycloalkyl group include a monocyclic cycloalkyl group, a crosslinked ring cycloalkyl group, and a condensed ring cycloalkyl group.

In the present disclosure, a single ring means a cyclic structure having no bridging structure inside formed by a covalent bond of carbon. Further, a fused ring means a cyclic structure in which two or more monocycles share two atoms (that is, only one side of each ring is shared (condensed) with each other). A crosslinked ring means a cyclic structure in which two or more monocycles share three or more atoms.

Examples of the monocyclic cycloalkyl group include a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclodecyl group, a 3,5,5-trimethylcyclohexyl group and the like.

Examples of the crosslinked ring cycloalkyl group include a tricyclodecyl group, an adamantyl group, a norbornyl group and the like.

Examples of the fused ring cycloalkyl group include a bicyclodecyl group.

The above (meth) acrylamide group-containing compound (a) contains an N-unsubstituted (meth) acrylamide skeleton-containing monomer, an N-uni-substituted (meth) acrylamide skeleton-containing monomer, and an N, N-disubstituted (meth) acrylamide skeleton-containing monomer. Monomers and the like are exemplified.
Examples of the N-unsubstituted (meth) acrylamide skeleton-containing monomer include (meth) acrylamide and maleic acid amide.
N-monosubstituted (meth) acrylamide skeleton-containing monomers include N-isopropyl (meth) acrylamide, N-methylol (meth) acrylamide, diacetone (meth) acrylamide (meth) acrylamide t-butylsulfonic acid, and hydroxyethyl (meth) acrylamide. Etc. are exemplified.
N-disubstituted (meth) acrylamide skeleton-containing monomers include N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, and (meth) acryloylmorpholine. Etc. are exemplified.

Examples of the salt include dimethylaminopropyl (meth) acrylamide methyl chloride quaternary salt, dimethylaminoethyl (meth) acrylate benzyl chloride quaternary salt and the like. Among these, when (meth) acrylamide, particularly acrylamide, is used, it is possible to prepare a binder having high water solubility, high dispersibility of the slurry, and high binding property between the electrode active materials.

As described above, the chemical structure of the water-soluble graft polymer (C) is composed of a stem polymer (A), a branch polymer (B), and a binding site for binding them. Here, in the present disclosure, the binding site is defined as not included in either (A) or (B).

The upper limit of the proportion of the structural unit derived from the (meth) acrylamide group-containing compound (a-1) contained in 100% by mass of the monomer constituting the stem polymer (A) is 100, 99.95, 99.8. , 99.7, 99.2, 95, 90, 85, 80, 75, 70, 65% by mass, etc., and the lower limit is 99.8, 99.7, 99.2, 95, 90, 85, 80. , 75, 70, 65, 60, 55, 50% by mass and the like. The range of the ratio of the structural units can be set as appropriate (for example, by selecting from the upper and lower limit values). In one embodiment, the proportion of the structural unit is preferably 50% by mass or more, more preferably 55.0 to 99.8% by mass, and 60.0 to 99.7% by mass. Is particularly preferable. By including the structural unit derived from the (meth) acrylamide group-containing compound (a-1) in the above range, the dispersibility of the electrode active material is improved, and a uniform electrode layer can be produced, so that structural defects are eliminated. By including a structural unit derived from a (meth) acrylamide group-containing compound in the above range, the polymer has good oxidation resistance and reduction resistance, and thus deteriorates at high voltage. Is suppressed and shows good charge / discharge durability characteristics.

<Monomers other than the component (a-1): Also referred to as the component (a-2)>
The stem polymer (A) may contain a structural unit derived from a monomer (component (a-2)) other than the component (a-1) as long as the desired effect of the present invention is not impaired. The component (a-2) may be used alone or in combination of two or more. The component (a-2) is an acid group-containing monomer such as unsaturated carboxylic acid, unsaturated sulfonic acid, and unsaturated phosphoric acid, unsaturated carboxylic acid ester, α, β-unsaturated nitrile compound, conjugated diene compound, and the like. Aromatic vinyl compounds and the like are exemplified.

Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid and salts thereof. The amount of the unsaturated carboxylic acid used is not particularly limited, but in consideration of the reaction with the above component (a-1), less than 40 mol% (for example, 30, 20, 19, 15) with respect to 100 mol% of the monomer group. 10, 5, 1 mol% or less) is preferable.

The unsaturated sulfonic acid is α, β-ethylenic unsaturated sulfonic acid such as vinyl sulfonic acid, styrene sulfonic acid, (meth) allyl sulfonic acid; (meth) acrylamide t-butyl sulfonic acid, 2- (meth) acrylamide- Examples thereof include 2-methylpropanesulfonic acid, 2- (meth) acrylamide-2-hydroxypropanesulfonic acid, 3-sulfopropane (meth) acrylic acid ester, bis- (3-sulfopropyl) itaconic acid ester, and salts thereof. Will be done. The amount of unsaturated sulfonic acid used is not particularly limited, but in consideration of the reaction with the above component (a-1), the upper limit of the content of 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 mol% and the like are exemplified, and the lower limit is 30, 20, 19, 15, 10, 5, 1 , 0.5, 0.1, 0.05, 0.02, 0.01 mol% and the like. The content range may be set as appropriate (eg, selected from the upper and lower limit values).

The unsaturated phosphoric acid monomer is vinylphosphonic acid, vinyl phosphate, bis ((meth) acryloxyethyl) phosphate, diphenyl-2- (meth) acryloyloxyethyl phosphate, dibutyl-2- (meth) acryloyloxy. Examples thereof include ethyl phosphate, dioctyl-2- (meth) acryloyloxyethyl phosphate, monomethyl-2- (meth) acryloyloxyethyl phosphate, 3- (meth) acryloxy-2-hydroxypropane phosphate and salts thereof. To. The amount of the acid group-containing monomer such as unsaturated phosphoric acid used is not particularly limited, but considering the reaction with the above component (a-1), it is less than 40 mol% (for example) with respect to 100 mol% of the monomer group. 30, 20, 19, 15, 10, 5, 1 mol% or less) is preferable.

In one embodiment, the amount of the acid group-containing monomer such as unsaturated carboxylic acid, unsaturated sulfonic acid, and unsaturated phosphoric acid used is less than 40 mol% (for example, 30) with respect to 100 mol% of the monomer group. 20, 19, 15, 10, 5, 1 less than 1 mol%) is preferred.

The unsaturated carboxylic acid ester is preferably a (meth) acrylic acid ester. Examples of the (meth) acrylic acid ester include a linear (meth) acrylic acid ester, a branched (meth) acrylic acid ester, an alicyclic (meth) acrylic acid ester, and a substituted (meth) acrylic acid ester.

The linear (meth) acrylate ester is methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, n-amyl (meth) acrylate. , (Meta) hexyl acrylate, (meth) n-octyl acrylate, nonyl (meth) acrylate, decyl (meth) acrylate and the like are exemplified.

Examples of the branched (meth) acrylic acid ester include (meth) acrylic acid i-propyl, (meth) acrylic acid i-butyl, (meth) acrylic acid i-amyl, and (meth) acrylic acid 2-ethylhexyl.

Examples of the alicyclic (meth) acrylic acid ester include cyclohexyl (meth) acrylic acid.

The substituted (meth) acrylic acid ester is glycidyl (meth) acrylate, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, ethylene glycol (meth) acrylate, ethylene glycol di (meth) acrylate, di. (Meta) propylene glycol acrylate, tri (meth) trimethylolpropane acrylate, tetra (meth) pentaerythritol acrylate, hexa (meth) dipentaerythritol acrylate, allyl (meth) acrylate, di (meth) acrylate Ethylene and the like are exemplified.

The amount of the unsaturated carboxylic acid ester used is not particularly limited, but by using the unsaturated carboxylic acid ester, curling of the electrode due to a decrease in the glass transition temperature of the water-soluble graft polymer (C) of the present invention can be suppressed. On the other hand, considering the cycle characteristics of the lithium ion battery of the present invention, the amount of the unsaturated carboxylic acid ester used is less than 40 mol% with respect to 100 mol% of the monomer group (for example, 30, 20, 19, 15, 10, 5). Less than 1 mol%) is preferred.

The α, β-unsaturated nitrile compound can be suitably used for the purpose of imparting flexibility to the electrode of the present invention. Examples of the α, β-unsaturated nitrile compound include (meth) acrylonitrile, α-chlor (meth) acrylonitrile, α-ethyl (meth) acrylonitrile, and vinylidene cyanide. Of these, (meth) acrylonitrile is preferred, and acrylonitrile is particularly preferred. The amount of the α, β-unsaturated nitrile compound used is not particularly limited, but less than 40 mol% (for example, less than 30, 20, 19, 15, 10, 5, 1 mol%) with respect to 100 mol% of the monomer group. preferable. When it is 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 graft polymer (C) component in water, and exhibits the flexibility. It will be easier to make it.

Conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, substituted linear conjugated pentadiene, substituted. And side chain conjugated hexadiene and the like are exemplified. The amount of the conjugated diene compound used is not particularly limited, but from the viewpoint of the cycle characteristics of the lithium ion battery according to the present invention, less than 10 mol% of the 100 mol% of the monomer group is preferable, and 0 mol% is more preferable.

Examples of the aromatic vinyl compound include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorstyrene, and divinylbenzene. The amount of the aromatic vinyl compound used is not particularly limited, but from the viewpoint of the cycle characteristics of the lithium ion battery according to the present invention, less than 10 mol% of the 100 mol% of the monomer group is preferable, and 0 mol% is more preferable. ..

Other than acid group-containing monomers such as unsaturated carboxylic acid, unsaturated sulfonic acid, and unsaturated phosphoric acid, unsaturated carboxylic acid ester, α, β-unsaturated nitrile compound, conjugated diene compound, and aromatic vinyl compound ( The ratio of the a-2) component to the monomer group is less than 10 mol%, less than 5 mol%, less than 1 mol%, less than 0.1 mol%, 0. Less than 01 mol%, less than 10% by weight, less than 5% by weight, less than 1% by weight, less than 0.5% by weight, less than 0.1% by weight, 0.01 with respect to 100% by weight of the compound group. Less than% by mass.

(Physical characteristics of stem polymer (A))
Hereinafter, the physical characteristics of the stem polymer (A) will be described. For the physical characteristics of the stem polymer (A) below, the amount (meth) acrylamide group-containing compound (a-1) required for synthesizing the stem polymer (A) alone (for example, the water-soluble graft polymer (C)) is used. (Polymer etc. synthesized by the above).

The weight average molecular weight (Mw) of the stem polymer (A) is not particularly limited, but the upper limit thereof is 6 million, 5.5 million, 5 million, 4.5 million, 4 million, 3.5 million, 3 million, 2.5 million, 2 million, 150. 10,000, 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. are exemplified, and the lower limit is 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, 65 Examples include 10,000, 600,000, 550,000, 500,000, 450,000, 400,000, 350,000, 300,000, 250,000, 200,000, 150,000, 100,000 and the like. The range of the weight average molecular weight (Mw) can be appropriately set (for example, selected from the upper and lower limit values). In one embodiment, it is preferably 100,000 to 6 million, more preferably 200,000 to 6 million, from the viewpoint of dispersion stability of the slurry for lithium ion battery electrodes.

The weight average molecular weight (Mw) of the stem polymer (A) is not particularly limited, but the upper limit thereof is 6 million, 5.5 million, 5 million, 4.5 million, 4 million, 3.5 million, 3 million, 2.5 million, 2 million, 150. 10,000, 1,000,000, 950,000, 900,000, 850,000, 800,000, 750,000, 700,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, 300,000, 200,000, 100,000, 50,000 etc. are exemplified, and the lower limit is 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, 85. Examples include 10,000, 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, 10,000, etc. To. The range of the number average molecular weight (Mn) can be appropriately set (for example, selected from the upper and lower limit values). In one embodiment, the number average molecular weight (Mn) of the stem polymer (A) is preferably 10,000 or more.

The weight average molecular weight and the number average molecular weight are determined as polyacrylic acid equivalent values measured under an appropriate solvent by, for example, gel permeation chromatography (GPC) (the same applies hereinafter).

The B-type viscosity of the stem polymer (A) is not particularly limited, but the upper limit thereof 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., and the lower limit is 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, 500, 100 mPa · s and the like are exemplified. The range of the B-type viscosity can be appropriately set (for example, selected from the upper and lower limit values). In one embodiment, the B-type viscosity range is preferably 1 to 100,000 mPa · s. The B-type viscosity is measured by a B-type viscometer such as the product name "B-type viscometer model BM" manufactured by Toki Sangyo Co., Ltd. (the same applies hereinafter).

The pH of the aqueous solution containing the stem polymer (A) is not particularly limited, but is preferably pH 2 to 13 (25 ° C.), more preferably pH 3 to 12, from the viewpoint of solution stability.

The glass transition point of the stem polymer (A) is not particularly limited, but is preferably 70 ° C. or higher (80 ° C. or higher, 90 ° C. or higher, etc.), and 100 ° C. or higher (125 ° C. or higher, 150 ° C. or higher) from the viewpoint of mechanical strength and heat resistance. The above, etc.) are more preferable.

The glass transition temperature of the stem polymer (A) can be adjusted by the combination of (a-1) and the monomer (a-2). In the stem polymer (A) using the (meth) acrylamide group-containing compound (a-1) and the monomer (a-2), the glass transition temperature thereof is homozygous to (a-1) or (a-2). It can be obtained from the glass transition temperature (Tg) (absolute temperature: K) of the polymer and the mass fraction of the monomer (a-2) based on the Fox formula shown below.
1 / Tg = (W ₁ / Tg ₁ ) + (W ₂ / Tg ₂ ) + (W ₃ / Tg ₃ ) + ... + (W _n / Tg _n )
[In the formula, Tg is the glass transition temperature (K) of the polymer to be obtained, W ₁ to W _n are mass fractions of each monomer, and Tg ₁ to Tg _n are homopolymers of each monomer. Indicates the glass transition temperature (K) of

For example, the glass transition temperature is 165 ° C for acrylamide homopolymers, 106 ° C for acrylic acid homopolymers, 126 ° C for methyl methacrylate homopolymers, and 105 ° C for acrylonitrile homopolymers. The compositions of (a-1) and (a-2) constituting the stem polymer (A) having a desired glass transition temperature can be determined. The glass transition temperature of the monomeric homopolymer is raised from -100 ° C to 300 ° C by DSC (differential scanning calorimetry device), DTA (differential thermal analysis device), TMA (thermomechanical measurement device), etc. It can be measured under the condition of allowing the temperature to rise (heating rate 10 ° C./min.). In addition, the values described in the literature can also be used. Examples of the literature include "Chemistry Handbook Basics II, Chemical Society of Japan (Revised 5th Edition)", p325, and the like.

<1-3. Branch polymer (B): Also called component (B)>
The branch polymer (B) of the water-soluble graft polymer (C) of the present invention is directly linked to the stem polymer (A) via a binding site, and is a compound (b-) containing a trimer or more of a polyalkylene glycol ether group. 1) is included in the constituent unit. The branch polymer (B) may be used alone or in combination of two or more. Examples of such a branch polymer (B) include polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like. As such a branch polymer, a commonly used one can be used, and the present invention is not particularly limited.

In the present disclosure, the term "trimeric or higher polyalkylene glycol ether group" is used.
-(RO) _n-
(In the formula, R is an alkylene group and n is an integer of 3 or more).

Examples of the alkylene group include a linear alkylene group, a branched alkylene group, and a cycloalkylene group.

The linear alkylene group can be expressed by the general formula of-(CH ₂ ) _n- (n is an integer of 1 or more). Examples of the linear alkylene group include a methylene group, an ethylene group, a propylene group, an n-butylene group, an n-pentylene group and the like.

A branched alkylene group is a group in which at least one hydrogen of a linear alkylene group is substituted with an alkyl group. The branched alkylene group is 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, or a methylbutylene group. Etc. are exemplified.

Examples of the cycloalkylene group include a monocyclic cycloalkylene group, a crosslinked ring cycloalkylene group, and a fused ring cycloalkylene group.

Examples of the monocyclic cycloalkylene group include a cyclopentylene group and the like.

（式中、Ｒ^１は、水素原子又はメチル基であり、Ｒ^２は、メチレン基、エチレン基、又はプロピレン基であり、Ｒ^３は、水素原子又はメチル基であり、ｎは３以上の整数である。）
で表わされる。 In one embodiment, the macromonomer having a trimer or more of the polyalkylene glycol ether (b-1) is described in the following general formula (1).

(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a methylene group, an ethylene group or a propylene group, R ³ is a hydrogen atom or a methyl group, and n is an integer of 3 or more. Is.)
It is represented by.

The macromonomers having an ethylene glycol group described above are polyethylene glycol-mono (meth) acrylate, methoxypolyethylene glycol-mono (meth) acrylate, octoxypolyethylene glycol-polypropylene glycol-mono (meth) acrylate, and stearoxy-polyethylene glycol-. Examples thereof include mono (meth) acrylate, phenoxypolyethylene glycol-mono (meth) acrylate, phenoxypolyethylene glycol-mono (meth) acrylate, and phenoxypolyethylene glycol-polypropylene glycol-mono (meth) acrylate.
Examples of the macromonomer having a propylene glycol group include polypropylene glycol-mono (meth) acrylate and polyethylene glycol-propylene glycol-mono (meth) acrylate.
Among these macromonomers, polyethylene glycol-mono (meth) acrylate is preferable because it can easily carry out radical polymerization.

The ratio of the structural units derived from the trimeric or more polyalkylene glycol ether (b-1) constituting the branch polymer (B) is not particularly limited. The upper limit of the proportion of the structural units derived from the trimer or more of the polyalkylene glycol ether (b-1) constituting the branch polymer (B) is 100, 99, 98 with respect to 100% by mass of the branch polymer (B). , 97, 96, 95, 94, 93, 92, 91% by mass and the like, and the lower limit is 99, 98, 97, 96, 95, 94, 93, 92, 91, 90% by mass and the like. .. The range of the ratio of the structural units can be set as appropriate (for example, by selecting from the upper and lower limit values). In one embodiment, the proportion range of the building blocks is preferably 90 to 100% by weight, more preferably 91 to 99% by weight. If it is 90% by mass or more, it is sufficient to separate and exert the functions of the stem polymer (A) and the branch polymer (B), and the electrode adhesion, which is the effect of the present invention, is improved.

(Physical characteristics of branch polymer (B))
The weight average molecular weight (Mw) of the branch polymer (B) is not particularly limited, but the upper limit of the weight average molecular weight (Mw) is 2 million, 1.5 million, 1 million, 950,000, 900,000, 850,000, 800,000, 75. Examples include 10,000, 700,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, 300,000, 100,000, 10,000, 100, 500, 250, 150, etc., and the lower limit is 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, 100,000, 10,000 , 100, 500, 250, 150, 100 and the like are exemplified. The range of the weight average molecular weight (Mw) can be appropriately set (for example, selected from the upper and lower limit values). In one embodiment, it is preferably 1 to 2 million, more preferably 1.5 to 1.5 million, from the viewpoint of dispersion stability of the slurry for lithium ion battery electrodes.

The upper limit of the number average molecular weight (Mn) of the branch polymer (B) is 1 million, 950,000, 900,000, 850,000, 800,000, 750,000, 700,000, 650,000, 600,000, 550,000, 500,000, 45. 10,000, 400,000, 300,000, 200,000, 100,000, 50,000, 10,000, 1,000, 500, 250, 100, etc. are exemplified, and the lower limit is 800,000, 750,000, 700,000, 650,000, 600,000, etc. 550,000, 500,000, 450,000, 400,000, 350,000, 300,000, 200,000, 100,000, 50,000, 10,000, 1,000, 500, 250, 100, 50 and the like are exemplified. The range of the number average molecular weight (Mn) can be appropriately set (for example, selected from the upper and lower limit values). In one embodiment, the number average molecular weight (Mn) of the branch polymer (B) is preferably 50 or more.

The B-type viscosity of the branch polymer (B) is not particularly limited, but the upper limit thereof 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, 1000, 750, 500, 250, 100, 50, 25, 10 mPa · s, etc., and the lower limit is 90,000, 80,000, 70,000, 6 10,000, 50,000, 40,000, 30,000, 20,000, 10,000, 9000, 8000, 7000, 6000, 5000, 4000, 3000, 2000, 1000, 750, 500, 250, 100, 50, 25, 10, 1 mPa -S and the like are exemplified. The range of the B-type viscosity can be appropriately set (for example, selected from the upper and lower limit values). In one embodiment, the B-type viscosity range is preferably 10,000 to 100,000 mPa · s.

The pH of the aqueous solution containing the branch polymer (B) is not particularly limited, but is preferably pH 2 to 13 (25 ° C.), more preferably pH 3 to 12 (25 ° C.) from the viewpoint of solution stability.

The glass transition point of the branch polymer (B) is not particularly limited, but it may be a glass transition point lower than that in a room temperature environment, and more preferably 10 ° C. or lower (5 ° C. or lower, etc.). The glass transition temperature of the branch polymer (B) can be adjusted by the type of the polyalkylene glycol ether (b-1) of the trimer or more. In the branch polymer (B), the glass transition temperature can be determined based on the Fox formula.

For example, the glass transition temperature is -67 ° C for polyethylene glycol homopolymers, -73 ° C for polypropylene glycol homopolymers, -78 ° C for polypropylene glycol homopolymers, and -95 ° C for polytetramethylene glycol homopolymers. .. The composition of (b-1) constituting the branch polymer (B) having the desired glass transition temperature can be determined so that the branch polymer (B) can be obtained.

In the water-soluble graft polymer (C), the stem polymer (A) has a structural unit derived from the (meth) acrylamide group-containing compound (a-1), and the branch polymer (B) has a trimer or more of a polyalkylene glycol ether ( The upper limit of the ratio of the constituent units derived from b-1) (the amount of substance of the component (a-1) / the amount of substance of the component (b-1)) is 2000, 1900, 1750, 1500, 1250, 1000, 750, 500, 250, 100, 80 and the like are exemplified, and the lower limit is 1900, 1750, 1500, 1250, 1000, 750, 500, 250, 100, 80, 75 and the like. The range of the above ratio can be set as appropriate (for example, by selecting from the above upper and lower limit values). In one embodiment, the ratio of the structural unit derived from the component (a-1) to the structural unit derived from the component (b-1) (amount of substance of the component (a-1) / substance of the component (b-1)). The amount) is preferably 75 to 2000.

<1-4. Binding site>
The binding site of the present invention contains an ester group and binds the stem polymer (A) and the branch polymer (B) by a covalent bond. The binding site is not particularly limited as long as it has an ester bond, and is derived from a double bond such as an acrylic residue, a methacrylic residue, an allyl residue, and a vinyl residue for reacting with the stem polymer (A). It is preferable to have a polymerization residue to be used. The ester bond can also be used to bond with the alkylene glycol ether group contained in the branch polymer (B).

（式中、Ｒ^１は、水素原子又はメチル基であり、Ｒ^２は、メチレン基、エチレン基、又はプロピレン基であり、Ｒ^３は、水素原子又はメチル基であり、ｎは３以上の整数である。）
上記四角で囲んだ部分となる。 The binding site is, for example, when the water-soluble graft polymer (C) is synthesized using the macromonomer represented by the above general formula (1).

(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a methylene group, an ethylene group or a propylene group, R ³ is a hydrogen atom or a methyl group, and n is an integer of 3 or more. Is.)
It is the part surrounded by the above square.

<1-5. Method for Producing Water-Soluble Graft Polymer (C)>
The water-soluble graft polymer (C) used in the present invention is synthesized by (1) a method of copolymerizing so as to form a branched structure, (2) a method of modifying the obtained polymer to form a branched structure, or the like. be able to. Among them, the method (1) is preferable because the desired structure can be obtained in one step.

As the method of copolymerizing so as to form the (1) branched structure, a method of obtaining a graft polymer by a chain transfer reaction by polymerizing a graft monomer in the presence of a stem polymer by a known polymerization method is exemplified. Further, a graft polymer can also be obtained by introducing a functional group capable of generating radicals or ions into the stem polymer and initiating the polymerization reaction of the graft monomer from the functional group. In addition, a branch polymer obtained by polymerizing a graft monomer capable of forming a branched structure at the time of polymerization by a known polymerization method may be added to the stem polymer by a radical addition reaction or the like.

Among these, the method of adding a branched polymer obtained by polymerizing a graft monomer capable of forming a branched structure at the time of polymerization by a known polymerization method to a stem polymer by a radical addition reaction or the like is the easiest to control the structure. It is preferable because it is easy to stabilize the slurry for the lithium ion battery electrode described later. Specifically, a method of copolymerizing using a macromonomer as a branch polymer is exemplified.

The macromonomer can be easily obtained as a water-soluble graft polymer (C) by polymerizing at the same time as the monomer constituting the stem polymer (A). The macromonomer may be used alone or in combination of two or more. As the macromonomer, a commonly used one can be used, and the macromonomer is not particularly limited.

As the radical polymerization initiator, various known radical polymerization initiators are used without particular limitation. The radical polymerization initiator is a persulfate such as potassium persulfate and ammonium persulfate; a redox-based polymerization initiator that combines the above persulfate and a reducing agent such as sodium hydrogen sulfite; 2,2'-azobis-2-amidino. An azo-based initiator such as propane dihydrochloride is exemplified. The amount of the radical polymerization initiator used is not particularly limited, but is preferably about 0.05 to 5.00% by mass, preferably 0.1 to 3.0% by mass, based on 100% by mass of the monomer group giving the component (C). The degree is more preferable.

Ammonia, organic amines, potassium hydroxide, sodium hydroxide, lithium hydroxide, etc. are generally used for the purpose of improving production stability before the radical polymerization reaction and / or when the obtained component (C) is solubilized in water. The pH of the reaction solution may be adjusted with a neutralizing agent. In that case, the pH is preferably adjusted to the range of about 2 to 11. It is also possible to use EDTA, which is a metal ion encapsulant, or a salt thereof, for the same purpose.

The polymerization temperature at the time of radical polymerization is not particularly limited, and is preferably about 50 to 100 ° C. The polymerization time is not particularly limited, and is preferably about 1 to 10 hours.

When the water-soluble graft polymer (C) has an acid group, the neutralization rate is appropriately determined according to the application (the neutralization rate of 100% is based on the same number of moles of alkali as the acid component contained in the water-soluble graft polymer (C). It indicates that it is neutralized. A neutralization rate of 50% indicates that it was neutralized by half the number of moles of alkali with respect to the acid component contained in the water-soluble graft polymer (C)). can. The neutralization rate when the electrode active material is dispersed is not particularly limited, but is preferably 70 to 120%, more preferably 80 to 120% after the formation of the coating layer or the like. By setting the neutralization rate after producing the coating layer within the above range, most of the acid is in a neutralized state, and it is preferable because it does not bind to Li ions or the like in the battery and cause a capacity decrease. Examples of the neutralized salt include Li salt, Na salt, K salt, ammonium salt, Mg salt, Ca salt, Zn salt, Al salt and the like.

<1-6. Physical characteristics of water-soluble graft polymer (C)>
The weight average molecular weight (Mw) of the water-soluble graft polymer (C) is not particularly limited, but the upper limit thereof 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. 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. The range of the weight average molecular weight (Mw) can be appropriately set (for example, selected from the upper and lower limit values). In one embodiment, the weight average molecular weight (Mw) of the water-soluble graft polymer (C) is preferably 300,000 to 6 million, more preferably 350,000 to 600, from the viewpoint of dispersion stability of the slurry for lithium ion battery electrodes. It is 10,000.

The upper limit of the number average molecular weight (Mn) of the water-soluble graft polymer (C) component 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, 100. 10,000, 950,000, 900,000, 850,000, 800,000, 750,000, 700,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, 300,000, 200,000, 100,000, 50,000, etc. The lower limit is 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, 80. Examples include 10,000, 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, and 10,000. The range of the number average molecular weight (Mn) can be appropriately set (for example, selected from the upper and lower limit values). In one embodiment, the number average molecular weight (Mn) of the water-soluble graft polymer (C) is preferably 10,000 or more.

The B-type viscosity of the water-soluble graft polymer (C) is not particularly limited, but the upper limit thereof 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., and the lower limit is 90,000, 80,000, 70,000, 60,000, 50,000, 40,000, 30,000, 20,000, etc. Examples thereof include 10,000, 9000, 8000, 7000, 6000, 5000, 4000, 3000, 2000, 1000 mPa · s and the like. The range of the B-type viscosity can be appropriately set (for example, selected from the upper and lower limit values). In one embodiment, the B-type viscosity range is preferably 1000 to 100,000 mPa · s.

The pH of the aqueous solution containing the water-soluble graft polymer (C) is not particularly limited, but is preferably pH 2 to 13 (25 ° C.), more preferably pH 3 to 12, from the viewpoint of solution stability.

The water-soluble graft polymer (C) is a polymer of monomers in which the stem polymer (A) exhibits mechanical strength, heat resistance, and high cohesiveness due to a segment having a high glass transition point, and is a branch polymer. In (B), it is preferable that the segment having a low glass transition point functions for stress relaxation, flexibility, and high adhesion. Here, the glass transition point of the stem polymer (A) is preferably 70 ° C. or higher (80 ° C. or higher, 90 ° C. or higher, etc.), more preferably 100 ° C. or higher (125 ° C. or higher, 150 ° C. or higher, etc.). It is preferable from the viewpoint of mechanical strength and heat resistance. The branch polymer (B) may have a glass transition point lower than that in a room temperature environment, and is more preferably 10 ° C. or lower (5 ° C. or lower, etc.). The effect of the present invention can be achieved by including the constituent unit derived from the (meth) acrylamide group-containing compound in the main constituent component of the stem polymer (A) and the constituent unit derived from the alkylene glycol ether in the main constituent component of the branch polymer (B). It is expressed.

<1-7. Film of water-soluble graft polymer (C)>
The water-soluble graft polymer (C) of the present invention preferably has a microphase-separated structure in which the stem polymer (A) is a continuous layer and the branch polymer (B) is a domain. As a method for confirming having this phase-separated structure, a method for measuring HAZE of a film is exemplified. The film of the water-soluble graft polymer (C) is prepared by applying an aqueous solution containing (C) on a flat glass plate and preparing the film in a smooth air dryer at 80 ° C. so that the film thickness becomes 100 to 250 μm. It is preferable to obtain it. Here, the HAZE of the produced film can be measured by a turbidity meter "NDH-2000 (manufactured by Nippon Denshoku Industries Co., Ltd.)".

The HAZE of the film is 3% or more (for example, 5% or more, 10% or more, 25% or more, 50% or more, 75% or more, 90% or more, 97.5% or more, 99% or more, etc.). Is preferable. A HAZE of the film below 3% suggests that the stem polymer (A) and the branch polymer (B) are compatible. On the other hand, a film HAZE higher than 3% suggests that the stem polymer (A) and the branch polymer (B) are not compatible (microphase separated). In this case, since the film has a low affinity in which the segment having a high glass transition point and the segment having a low glass transition point are separated, it is derived from the segment having a low glass transition point when an internal stress is applied to the film. It relieves stress due to its flexibility, and also exhibits high strength and high heat resistance derived from segments with high glass transition points.
As a result, the obtained lithium-ion secondary battery has a segment with a low glass transition point, so that the electrode adhesion is high, and the internal stress due to swelling in the electrode can be alleviated during the charge / discharge cycle, so that a high glass transition point can be achieved. It is expected that the cycle characteristics will be improved by the segment.

<1-8. Additives>
The aqueous binder solution for a lithium ion battery may contain an agent that does not correspond to either the component (C) or water as an additive. Examples of the additive include a dispersant, a leveling agent, an antioxidant, a thickener, a dispersion (emulsion), a cross-linking agent, a hydroxysilyl compound 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 the component (A), and 100% by mass of the aqueous solution. %, 0 to 5% by mass, less than 1% by mass, less than 0.1% by mass, less than 0.01% by mass, 0% by mass and the like are exemplified.

The dispersant can be selected according to the electrode active material (D) to be used, and examples thereof include anionic dispersants, cationic dispersants, nonionic dispersants, and polymer dispersants.

Examples of the leveling agent include alkyl-based surfactants, silicon-based surfactants, fluorine-based surfactants, and surfactants such as metal-based surfactants. By using a surfactant, it is possible to prevent repelling generated during coating and improve the smoothness of the layer (coating layer) of the slurry.

Examples of the antioxidant include a phenol compound, a hydroquinone compound, an organic phosphorus compound, a sulfur compound, a phenylenediamine compound, and a polymer type phenol compound. The polymer-type phenol compound is a polymer having a phenol structure in the molecule, and a polymer-type phenol compound having a weight average molecular weight of preferably 200 or more, more preferably 600 or more, preferably 1000 or less, and more preferably 700 or less is preferable. Used.

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

The dispersion (emulsion) includes styrene-butadiene polymer latex, polystyrene polymer latex, polybutadiene polymer latex, acrylonitrile-butadiene copolymer latex, polyurethane polymer latex, and polymethylmethacrylate polymer latex. , Methyl methacrylate-butadiene polymer latex, polyacrylate polymer latex, vinyl chloride polymer latex, vinyl acetate polymer emulsion, vinyl acetate-ethylene copolymer emulsion, polyethylene emulsion, carboxy-modified styrene butadiene 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 Examples thereof include ethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and ethylene-tetrafluoroethylene copolymer (ETFE). ..

The cross-linking agent includes formaldehyde, glyoxal, hexamethylenetetramine, ureaformaldehyde resin, methylolmelamine resin, carbodiimide compound, polyfunctional epoxy compound, oxazoline compound, polyfunctional hydrazide compound, isocyanate compound, melamine compound, urea compound, and a mixture thereof. Illustrated.

The 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 is a compound having a trihydroxysilyl group (-Si (OH) ₃ ). The tetrahydroxysilyl compound means a compound represented by Si (OH) ₄ . In one embodiment, the trihydroxysilyl compound is the following general formula RSi (OH) ₃
(In the formula, R represents a substituted or unsubstituted alkyl group, vinyl group, or (meth) acryloxy group, and the above-mentioned substituents include an amino group, a mercapto group, a glycidoxy group, a (meth) acryloxy group, an epoxy group and the like. It is a compound represented by (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 the water solubility is not lost. As the silane coupling agent, a commonly used silane coupling agent can be used. The silane coupling agent is not particularly limited. The hydroxysilyl compound produced from the silane coupling agent may be used alone or in combination of two or more. In one embodiment, the hydroxysilyl compound comprises trihydroxysilylpropylamine. The trialkoxysilanes are 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-isoxapropyltriethoxysilane, vinyl Examples thereof include trimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, and tetrahydroxysilane. Examples of the tetraalkoxysilane include tetramethoxysilane, tetramethoxysilane oligomer, tetraethoxysilane, and tetraethoxysilane oligomer. Of these, from the viewpoint of stability with the water-soluble graft polymer (C) and electrolytic solution resistance, it is preferable to produce a hydroxysilyl compound using 3-aminopropyltrimethoxysilane.

[2. Lithium-ion battery electrode slurry]
The present disclosure provides a slurry for a lithium ion battery electrode containing the above-mentioned aqueous binder for a lithium ion battery and the electrode active material (D).

In the present disclosure, "slurry" means a suspension of liquid and solid particles.

<2-1. Electrode active material (D) (also referred to as (D) component)>
The electrode active material is not particularly limited as long as it can reversibly store and release lithium, and an appropriate material can be appropriately selected depending on the type of the target power storage device. The electrode active material may be used alone or in combination of two or more kinds of electrode active materials. 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 alloying with lithium have a large volume expansion rate when the battery is charged, the effect of the present invention can be remarkably exhibited.

The carbon materials are graphite (also referred to as graphite, natural graphite, artificial graphite, etc.) which is a high crystalline carbon, low crystalline carbon (soft carbon, hard carbon), carbon black (ketchen black, acetylene black, etc.). , Channel black, lamp black, oil furnace black, thermal black, etc.), fullerene, 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, SiO _x Cy (0 <x ≦ 3, 0 < _y ≦ 5), Si ₃ N ₄ , Si ₂ N ₂ O, SiO _x . Described in the silicon oxide complex represented by (0 <x≤2) (for example, the materials described in JP-A-2004-185810 and JP-A-2005-25969), JP-A-2004-185810. The silicon material used is exemplified. Further, the silicon materials described in Japanese Patent No. 5390336 and Japanese Patent No. 5903761 may be used.

The silicon oxide is preferably a silicon oxide represented by the composition formula 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 preferably used because they have high electron conductivity and high strength. As the silicon alloy, it is more preferable to use a silicon-nickel alloy or a silicon-titanium alloy, and it is particularly preferable to use a silicon-titanium alloy. The content ratio of silicon in the silicon alloy is preferably 10 mol% or more, more preferably 20 to 70 mol%, based on all the metal elements in the alloy. The silicon material may be single crystal, polycrystal or amorphous.

When a silicon material is used as the electrode active material, an electrode active material other than the silicon material may be used in combination. Electrode active materials other than silicon materials are the above carbon materials; conductive polymers such as polyacene; _{AX BYO Z} (A is an alkali metal or transition metal, B is cobalt, nickel, aluminum, tin, manganese, etc.) At least one selected from transition metals, O represents an oxygen atom, and X, Y and Z represent 0.05 <X <1.10, 0.85 <Y <4.00, 1.5 <Z <5, respectively. A composite metal oxide represented by (a number in the range of .00), other metal oxides, and the like are exemplified. Among these, when a silicon material is used as the electrode active material, it is preferable to use a carbon material in combination because the volume change due to occlusion and release of lithium is small.

The oxides containing lithium atoms are ternary lithium cobalt manganate, lithium-manganese composite oxide (LiMn ₂ O ₄ etc.), lithium-nickel composite oxide (LiNiO ₂ etc.), lithium-cobalt composite oxide. (LiCoO ₂ etc.), Lithium-iron composite oxide (LiFeO ₂ etc.), Lithium-nickel-manganese composite oxide (LiNi _0.5 Mn _0.5 O ₂ etc.), Lithium-nickel-cobalt composite oxide (LiNi) _0.8 Co _0.2 O ₂ etc.), Lithium-transition metal phosphate compound (LiFePO ₄ etc.), Lithium-transition metal sulfate compound (Li _x Fe ₂ (SO ₄ ) ₃ ), Lithium-titanium composite oxide Examples thereof include lithium-transition metal composite oxides such as (lithium titanate: Li ₄ Ti ₅ O1 ₂ ), and other conventionally known electrode active materials.

The shape of the electrode active material is not particularly limited and may be any shape such as a fine particle shape or a thin film shape, but is preferably a fine particle shape. The average particle size of the electrode active material is not particularly limited, but the upper limit thereof is 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 4, 3, 2.9, 2, 1, 0. .5, 0.1 μm, etc. are exemplified, and the lower limit is 45, 40, 35, 30, 25, 20, 15, 10, 5, 4, 3, 2.9, 2, 1, 0.5, 0. 1 μm and the like are exemplified. The range of the average particle size of the electrode active material can be appropriately set (for example, selected from the above upper and lower limit values). In one embodiment, it is preferably 0.1 to 50 μm. If it is 0.1 μm or more, the handleability is good, and if it is 50 μm or less, the electrode can be easily applied. It is more preferably 0.1 to 45 μm, further preferably 1 to 10 μm, and particularly preferably about 5 μm. It is preferable that the film is uniform and thin in such a range because a film can be formed. The "particle diameter" in the present disclosure means the maximum distance among the distances between any two points on the contour line of the particles. Unless otherwise specified, the value of "average particle size" is the value of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value of the particle size shall be adopted.

In one embodiment, from the viewpoint of significantly exerting the effect of the present invention, the carbon material and / or the material alloying with lithium is preferably 50% by mass or more, more preferably 80% by mass or more in the electrode active material. , More preferably 90% by mass or more, and particularly preferably 100% by mass.

The content of the component (D) in the slurry of the present invention is not particularly limited, but the solid content mass thereof is preferably about 1 to 15% by mass with respect to 100% by mass of the component (D). .. Further, a binder other than the water-soluble graft polymer (C) may be used in the electrode slurry for the lithium ion battery of the present invention, but the content ratio of the water-soluble graft polymer (C) in the total binder is 90. It is preferably mass% or more.

The ratio of the electrode active material used is preferably 1.5 to 14% by mass so that the water-soluble graft polymer (C) is 1 to 15% by mass with respect to 100% by mass of the electrode active material. It is more preferable to use it in a ratio such that, and it is further preferable to use it in a ratio such that it becomes 2 to 12% by mass. With such a content ratio, it is possible to manufacture an electrode having excellent adhesion, low electrode resistance, and excellent charge / discharge characteristics.

In one embodiment, the content of silicon or silicon oxide in the electrode active material is preferably 5% by mass or more with respect to 100% by mass of the electrode active material from the viewpoint of increasing the battery capacity of the lithium ion battery.

(Slurry viscosity adjusting solvent)
The slurry may contain a slurry viscosity adjusting solvent. The slurry viscosity adjusting solvent is not particularly limited, but may include a non-aqueous medium having a standard boiling point of 80 to 350 ° C. The slurry viscosity adjusting solvent may be used alone or in combination of two or more. Examples of slurry viscosity adjusting solvents are amide solvents such as N-methylpyrrolidone, dimethylformamide, N, N-dimethylacetamide; hydrocarbon solvents such as toluene, xylene, n-dodecane and tetralin; methanol, ethanol, 2-propanol, Alcohol solvents such as isopropyl alcohol, 2-ethyl-1-hexanol, 1-nonanol, lauryl alcohol; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, holon, acetophenone, isophorone; ether solvents such as dioxane, tetrahydrofuran (THF); acetic acid Ester solvents such as benzyl, isopentyl butyrate, methyl lactate, ethyl lactate, butyl lactate; amine solvents such as o-toluidine, m-toluidine, p-toluidine; lactones such as γ-butyrolactone and δ-butyrolactone; Sulfoxide-sulfone solvent; water and the like can be mentioned. Among these, N-methylpyrrolidone is preferable from the viewpoint of coating workability. The amount of the non-aqueous medium used is not particularly limited, but is usually about 0 to 10% by mass with respect to 100% by mass of the slurry of the present invention.

<2-2. Method for manufacturing electrode slurry for lithium-ion batteries>
In the present disclosure, the proportion of the structural unit derived from the (meth) acrylamide group-containing compound (a-1) in the structural units constituting the stem polymer (A) is 50% by mass or more, and constitutes the branch polymer (B). The proportion of the structural unit derived from the trimeric or more polyalkylene glycol ether (b-1) in the structural unit is 90% by mass or more, and the stem polymer (A) and the branch polymer (B) are bonded by an ester bond. Provided is a method for producing an electrode slurry for a lithium ion battery, which comprises a step of mixing the water-soluble graft polymer (C) and the electrode active material (D).

The method for producing a slurry of the present invention is a method of mixing an aqueous solution of the component (C) (the above-mentioned aqueous binder solution for a lithium ion battery) and an electrode active material, and separately mixing the component (C), the component (D), and water. The method of doing is exemplified. In the above method, the order of mixing is not particularly limited. Examples of the slurry mixing means include a ball mill, a sand mill, a pigment disperser, a grinder, an ultrasonic disperser, a homogenizer, a planetary mixer, a Hobart mixer and the like.

The electrode slurry for a lithium ion battery can be used as an electrode slurry for a negative electrode of a lithium ion battery or as an electrode slurry for a positive electrode of a lithium ion battery.

[3. Electrodes for lithium-ion batteries]
The electrode for a lithium ion battery is obtained by applying an electrode slurry for a lithium ion battery to a current collector and drying it.

The coating means is not particularly limited. Examples of the coating means include conventionally known coating devices such as a comma coater, a gravure coater, a microgravure coater, a die coater, and a bar coater.

The drying means is not particularly limited, and the temperature is preferably about 60 to 200 ° C, more preferably about 100 to 195 ° C. The dry atmosphere may be dry air or an inert atmosphere.

The thickness of the electrode (cured coating film) is not particularly limited, but is preferably about 5 μm to 300 μm, and more preferably about 10 μm to 250 μm. Within the above range, it becomes easy to obtain a sufficient Li storage / release function for a high-density current value.

As the current collector, various known ones can be used without particular limitation. The material is not particularly limited, and for example, a metal material such as copper, iron, aluminum, nickel, stainless steel, and nickel-plated steel, and a carbon material such as carbon cloth and carbon paper are used. The form of the current collector is also not particularly limited, and in the case of a metal material, a metal foil, a metal cylinder, a metal coil, a metal plate and the like are exemplified, and in the case of a carbon material, a carbon plate, a carbon thin film, a carbon cylinder and the like are exemplified. Among these, when the electrode active material is used for the negative electrode, copper foil is preferable as a current collector because it is currently used in industrialized products.

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

[4. Lithium-ion battery]
The present disclosure provides a lithium ion battery including the above electrode for a lithium ion battery. The battery also includes an electrolyte solution, a separator, and a packaging material, which are not particularly limited.

As the electrolyte solution, a non-aqueous electrolyte solution in which the supporting electrolyte is dissolved in a non-aqueous solvent is used. Further, the film-forming agent may be included in the non-aqueous electrolyte solution.

As the non-aqueous solvent, various known ones can be used without particular limitation. The non-aqueous solvent may be used alone or in combination of two or more. The non-aqueous solvent is a chain carbonate solvent such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate; a cyclic carbonate solvent such as ethylene carbonate, propylene carbonate, butylene carbonate; a chain ether solvent such as 1,2-dimethoxyethane; tetrahydrofuran, Cyclic ether solvents such as 2-methyltetratransferase, 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, acetonitrile and the like. Is exemplified. Among these non-aqueous solvents, 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 LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi can be used. , (CF ₃ CO) ₂ NLi, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi and the like are exemplified. Of these, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li, which are easily soluble in a solvent and show a high degree of dissociation, are preferable. These may be used alone or in combination of two or more. Since the lithium ion conductivity becomes higher as the supporting electrolyte having a higher degree of dissociation is used, the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

As the film forming agent, various known ones can be used without particular limitation. The film-forming agent is a carbonate compound such as vinylene carbonate, vinylethylene carbonate, vinylethyl carbonate, methylphenyl carbonate, fluoroethylene carbonate, difluoroethylene carbonate, alkenesulfide such as ethylenesulfide and propylenesulfide; 1,3-propanesulton, 1 , 4-Sulton compounds such as butane sulton; acid anhydrides such as maleic anhydride and succinic anhydride are exemplified. The amount of the film-forming agent used 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 amount used is 10% by mass or less, it becomes easy to obtain the advantages of the film forming agent, such as suppression of the initial irreversible capacity and improvement of low temperature characteristics and rate characteristics.

The separator is an article interposed between the positive electrode and the negative electrode, and is used to prevent a short circuit between the electrodes. Specifically, a porous separator such as a porous membrane or a non-woven fabric can be preferably used, and they are impregnated with the non-aqueous electrolyte solution and used. Examples of the material of the separator include polyolefins such as polyethylene and polypropylene, polyether sulfone and the like, and polyolefins are preferable.

When a lithium ion battery is manufactured using a negative electrode manufactured by using the electrode slurry for a lithium ion battery as a negative electrode and a positive electrode manufactured by not using the electrode slurry for a lithium ion battery as a positive electrode, various positive electrodes are used. Known ones can be used without particular limitation. For example, the positive electrode can be obtained by preparing a slurry by mixing a positive electrode active material, a conductive auxiliary material, and a binder for a positive electrode with an organic solvent, and applying, drying, and pressing the prepared slurry to a positive electrode current collector.

Examples of the positive electrode active material include an inorganic positive electrode active material and an organic positive electrode active material. Examples of the inorganic positive electrode active material include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. Examples of the transition metal include Fe, Co, Ni, Mn, Al and the like. The inorganic compounds used for the positive electrode active material are 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 ₃ O ₂ , Li [Li _0.1 Al _0.1 Mn _1.9 ] O ₄ , LiFeVO ₄ ; transition metal sulfides such as TiS ₂ , TiS ₃ , and amorphous MoS ₂ . Examples thereof include 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. Examples of the organic positive electrode active material include conductive polymers such as polyacetylene and poly-p-phenylene. The 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 be present at the time of reduction firing. Further, these compounds may be partially elementally substituted. Among these, in terms of practicality, electrical characteristics, and long life, 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 _1/3 O ₂ and Li [Li _0.1 Al _0.1 Mn _1.9 ] O ₄ are preferable. Examples of the conductive auxiliary material include those described above.

Binders for the positive electrode include fluororesins (polyfluorovinylidene, polytetrafluoroethylene, etc.), polyolefins (polyethylene, polypropylene, etc.), polymers having unsaturated bonds (styrene-butadiene rubber, isoprene rubber, butadiene rubber, etc.), acrylics. Examples thereof include acid-based polymers (acrylic acid copolymers, methacrylic acid copolymers, etc.). The binder for the positive electrode may be used alone or in combination of two or more.

Examples of the positive electrode current collector include aluminum foil and stainless steel foil.

The form of the lithium ion battery of the present invention 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 having an inside-out structure in which a pellet electrode and a separator are combined, and a coin type in which a pellet electrode and a separator are laminated. Further, by housing these types of batteries in an arbitrary outer case, they can be used in any shape such as a coin type, a cylindrical type, and a square type.

The method for producing the lithium ion battery of the present invention is not particularly limited, and the lithium ion battery may be assembled by an appropriate procedure according to the structure of the battery, and the method described in JP2013-089437 is exemplified. A negative electrode can be placed on the outer case, an electrolytic solution and a separator are provided on the negative electrode, a positive electrode is placed so as to face the negative electrode, and the battery is fixed by a gasket and a sealing plate to form a battery.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In the examples, unless otherwise specified, “%” indicates “% by mass” and “parts” indicates “parts by mass”.

(1) B-type viscosity The viscosity of each binder aqueous 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.).
In the case of viscosity of 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 used, rotation speed 6 rpm.

(2) Weight average molecular weight The weight average molecular weight is determined as a polyacrylic acid conversion value measured under 0.2 M phosphate buffer / acetonitrile solution (90/10, PH8.0) by gel permeation chromatography (GPC). rice field. The GPC apparatus used was HLC-8220 (manufactured by Tosoh Corporation), and the column used was SB-806M-HQ (manufactured by SHODEX).

(3) HAZE
HAZE uses a turbidity meter (product name "NDH-2000" manufactured by Nippon Denshoku Industries Co., Ltd.) to measure a laminate in which a film with a thickness of 100 to 250 μm is coated on a glass plate (normal glass, thickness 2 mm). did. This laminate is made by applying an aqueous solution containing a water-soluble graft polymer on a glass plate and drying it at 80 ° C for 2 hours with a smooth air dryer (manufactured by Advantech Toyo Co., Ltd., trade name "Blower constant temperature dryer DSR420DA"). did.

Example 1-1
Ion-exchanged water 1282 g, 50% acrylamide aqueous solution 300 g (2.10 mol), 80% acrylic acid aqueous solution 21.4 g (0.24 mol) in a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas introduction tube. , 9.1 g (0.008 mol, manufactured by Nichiyu, product name "Blemmer PME-1000") of polyalkylene glycol monomethacrylate and 0.19 g (0.0012 mol) of sodium methallyl sulfonate were added. After removing oxygen in the reaction system through nitrogen gas, the temperature was raised to 50 ° C. 1.79 g of 2,2'-azobis-2-amidinopropane dihydrochloride (product name "NC-32" manufactured by Nippoh Chemicals, Inc.) and 30 g of ion-exchanged water were added thereto, and the temperature was raised to 80 ° C. 3 The reaction was carried out for 0.0 hours. An aqueous solution containing a water-soluble graft polymer having a viscosity (25 ° C.) of 7,700 mPa · s was obtained.

Examples 1-2 to 1-5, Comparative Examples 1-1 to 1-3
In Example 1-1, an aqueous solution containing a water-soluble graft polymer was prepared in the same manner as in Example 1-1 except that the numerical value of the monomer composition was changed as shown in Table 1.

・ AM: Acrylamide (“50% Acrylamide” manufactured by Mitsubishi Chemical Corporation)
-ATBS: Acrylamide t-butyl sulfonic acid ("ATBS" manufactured by Toagosei Co., Ltd.)
・ Acrylic acid (“80% acrylic acid” manufactured by Osaka Organic Chemical Industry Co., Ltd.)
・ Acrylonitrile (“Acrylonitrile” manufactured by Mitsubishi Chemical Corporation)
SMAS: sodium methallyl sulfonate PME1000: polyalkylene glycol monomethacrylate (NOF CORPORATION "Blemmer PME-1000": n in the general formula (1) is about 23).
PME4000: Polyalkylene glycol monomethacrylate (“Blemmer PME-4000” manufactured by NOF CORPORATION: n in the general formula (1) is about 90).
-PE-90: Diethylene glycol monomethacrylate ("Blemmer PE-90" manufactured by NOF CORPORATION: n in the general formula (1) is about 2)

5. Production and Evaluation of Slurry for Electrodes Example 2-1
Using a commercially available rotation / revolution mixer (product name "Awatori Rentaro", manufactured by Shinky Co., Ltd.), 5 parts of the aqueous solution of the water-soluble graft polymer of Example 1-1 in terms of solid content was placed in a container dedicated to the mixer. And 10 parts of silicon particles having a D50 of 5 μm and 90 parts of natural graphite (product name “Z-5F” manufactured by Ito Graphite Industry Co., Ltd.) were mixed. Ion-exchanged water was added thereto so as to have a solid content concentration of 40%, and the container was set in the mixer. Then, after kneading at 2000 rpm for 10 minutes, defoaming was performed for 1 minute to obtain an electrode slurry.

Examples 2-2 to 2-6, Comparative Examples 2-1 to 2-3
In Example 2-1 the slurry for electrodes was obtained in the same manner except that the parts by weight of the binder and the active material were changed.

Comparative Example 2-4
An electrode slurry was obtained in the same manner as in Example 2-1 except that the binder was changed to an aqueous dispersion of SBR (styrene-butadiene polymer).

Comparative Example 2-5
An electrode slurry was obtained in the same manner as in Example 2-1 except that the binder was the aqueous solution obtained in Comparative Example 1-1 and the polyethylene glycol was changed to 50:50 in mass ratio (resin solid content).

<Slurry dispersity evaluation>
The dispersibility immediately after the slurry was prepared was visually evaluated according to the following criteria.
⊚: The whole is a homogeneous paste, there is no liquid separation, and no agglomerates are observed.
◯: The whole is a substantially homogeneous paste, and slight liquid separation is observed, but no agglomerates are observed.
Δ: A small amount of agglomerates and a slightly large amount of liquid separation are observed at the bottom of the container.
X: Many clay-like aggregates are observed at the bottom of the container, and many liquid separations are also observed.

<Evaluation of electrode condition>
The surface conditions of the electrodes obtained in Examples and Comparative Examples were visually evaluated according to the following criteria.
A: The surface is homogeneous as a whole, and no agglomerates are observed.
B: The entire surface is in a substantially homogeneous surface state, and the electrode layer has slight irregularities, but no aggregates are observed.
C: A large amount of agglomerates and many irregularities are observed in the electrode layer as a whole. In addition, abnormalities such as cracking and peeling between the current collector and the electrode layer are observed.

<Evaluation of electrode adhesion (peel strength)>
A test piece having a width of 2 cm and a length of 10 cm is cut out from the electrodes obtained in Examples and Comparative Examples, and fixed with the coated surface facing up. Next, an adhesive tape having a width of 15 mm (“Cellotape (registered trademark)” manufactured by Nichiban Co., Ltd.) (specified in JIS Z1522) was attached to the surface of the active material layer of the test piece while pressing it, and then the temperature was 25 ° C. When the adhesive tape was peeled off from one end of the test piece in the 180 ° direction at a speed of 30 mm / min using a tensile tester (“Tencilon RTM-100” manufactured by A & D Co., Ltd.) below. The stress was measured. The measurement was performed 5 times, converted into a value per 15 mm width, and the average value was calculated as the peel strength. The larger the peel strength, the higher the adhesion strength between the current collector and the active material layer or the binding property between the active materials, and the more difficult it is for the active material layer or the active materials to peel off from the current collector.

6. Manufacture and Evaluation of Lithium Ion Battery Electrodes The electrode slurry prepared in Example 2-1 is uniformly applied to the surface of a current collector made of copper foil by the doctor blade method so that the dried film thickness is 25 μm. Then, after drying at 60 ° C. for 30 minutes, heat treatment was performed at 150 ° C./vacuum for 120 minutes to obtain an electrode. Then, an electrode was obtained by press working with a roll press machine so that the density of the film (electrode active material layer) was 1.5 g / cm ³ .

7. Assembly and evaluation of lithium half cell (1) Assembly of lithium half cell In a glove box substituted with argon, the above electrodes are punched and molded to a diameter of 16 mm, and a two-pole coin cell (manufactured by Hosen Co., Ltd., trade name "HS Flat") It was placed on the cell "). Next, a separator made of a polypropylene porous membrane punched to a diameter of 24 mm (CS TECH CO., Made by LTD, trade name "Selion P2010") was placed, and further, 500 μL of an electrolytic solution was injected so as not to allow air to enter. A lithium half cell was assembled by placing a commercially available metallic lithium foil punched and molded to 16 mm and sealing the exterior body of the two-pole coin cell by closing it with a screw. The electrolytic solution used here is a solution in which LiPF ₆ is dissolved in a solvent of ethylene carbonate / ethylmethyl carbonate = 1/1 (mass ratio) at a concentration of 1 mol / L.

(2) Charge / discharge measurement Put the lithium half cell manufactured above in a constant temperature bath at 25 ° C, start charging at a constant current (0.1C), and complete charging (cutoff) when the voltage reaches 0.01V. ). Next, discharging was started at a constant current (0.1C), and charging / discharging was repeated 30 times with the time when the voltage reached 1.0 V as the discharge completion (cutoff).

(3) Evaluation of discharge capacity retention rate The discharge capacity retention rate was calculated from the following formula.
Discharge capacity retention rate = {(discharge capacity in the 30th cycle) / (discharge capacity in the 1st cycle)} x 100 (%)

In the above measurement conditions, "1C" indicates a current value at which a cell having a certain electric capacity is discharged with a constant current and the discharge is completed in 1 hour. For example, "0.1C" is a current value at which the discharge is completed over 10 hours, and "10C" is a current value at which the discharge is completed over 0.1 hours.

8. Preparation of Laminated Lithium Ion Battery A laminated lithium ion battery was manufactured as follows.
(1) Preparation of Negative Electrode The lithium ion battery electrode slurry of Example 2-1 was placed on a current collector made of copper foil and applied in a film form using a doctor blade. A lithium-ion battery electrode slurry coated on a current collector was dried at 80 ° C. for 20 minutes to volatilize and remove water, and then closely bonded by a roll press machine. At this time, the density of the electrode active material layer was set to 1.0 g / cm ² . The bonded material was heated at 120 ° C. for 2 hours in a vacuum dryer and cut into a predetermined shape (26 mm × 31 mm rectangular shape) to obtain a negative electrode having an electrode active material layer having a thickness of 15 μm.

(2) Preparation of positive electrode LiNi _0.5 Co _0.2 Mn _0.3 O ₂ as the positive electrode active material, acetylene black as the conductive auxiliary agent, and polyvinylidene fluoride (PVDF) as the binder, 88 parts by mass and 6 respectively. A 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 prepare a slurry for a positive electrode of a lithium ion battery. Next, an aluminum foil was prepared as a current collector for the positive electrode, a slurry for the positive electrode of a lithium ion battery was placed on the aluminum foil, and a film was applied using a doctor blade. The aluminum foil after applying the lithium ion battery positive electrode slurry was dried at 80 ° C. for 20 minutes to volatilize and remove NMP, and then closely joined 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 material was heated at 120 ° C. for 6 hours in a vacuum dryer and cut into a predetermined shape (25 mm × 30 mm rectangular shape) to obtain a positive electrode having a positive electrode active material layer having a thickness of about 45 μm.

(3) Preparation of Laminated Lithium Ion Battery A laminated lithium ion secondary battery was manufactured using the above positive and negative electrodes. Specifically, a rectangular sheet (27 x 32 mm, thickness 25 μm) of a separator (CS TECH CO., Made by LTD, trade name “Selion P2010”) made of a polypropylene porous film is sandwiched between the positive electrode and the negative electrode. It was made into a group of electrode plates. This group of plates was covered with a set of two laminated films, the three sides were sealed, and then the electrolytic solution was injected into the bag-shaped laminated film. As the electrolytic solution, a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethylmethyl carbonate = 1/1 (mass ratio) was used. Then, by sealing the remaining one side, a laminated lithium ion secondary battery was obtained in which the four sides were hermetically sealed and the electrode plate group and the electrolytic solution were sealed. The positive electrode and the negative electrode are provided with tabs that can be electrically connected to the outside, and a part of the tabs extends to the outside of the laminated lithium ion secondary battery. When the laminated lithium-ion battery produced in the above steps was energized, no operational problem occurred.

Regarding the lithium ion battery electrode slurry of Examples 2-2-2-6 and Comparative Examples 2-1 to 2-5, the lithium ion battery electrode slurry of Example 2-1 was replaced with Examples 2-2-2. -Evaluation was performed by the above procedure except that the lithium ion battery electrode slurrys of Comparative Examples 2-1 to 2-5 were used.

As is clear from Table 2, all of the electrode slurries of Examples 2-1 to 2-6 had a good evaluation of slurry dispersibility. In all the lithium half cell evaluations including the electrodes prepared using the electrode slurrys of Examples 2-1 to 2-6, the evaluation of the discharge capacity retention rate was good.

On the other hand, in the case of the electrode slurry containing the linear polymer (Comparative Example 2-1), the slurry dispersibility is inferior to that of the electrode slurry of the example, and cracks are formed on the prepared electrode surface. Occurred. Further, the discharge capacity retention rate of the lithium half cell containing the electrode prepared by using the electrode slurry of Comparative Example 2-1 was inferior to that of the example. An electrode slurry (Comparative Example 2-2) using a polymer having a low HAZE of a film, that is, a polymer in which a stem polymer (A) and a branch polymer (B) are compatible with each other, and an electrode containing a linear water-soluble polymer. The electrode condition of the electrode prepared from the slurry (Comparative Example 2-3) was poor, and peeling from the current collector and generation of cracks occurred, so that the discharge capacity retention rate was inferior to that of the example. The electrode slurry using the aqueous dispersion SBR (Comparative Example 2-4) had very poor dispersibility of the active material, and the electrode could not be produced. When the electrode slurry containing the binder (Comparative Example 2-5) in which the linear polymer and polyethylene glycol were mixed was used, the discharge capacity retention rate was inferior to that of the example because cracks were generated on the electrode surface. ..

Claims (10)

The proportion of the structural unit derived from the (meth) acrylamide group-containing compound (a-1) in the structural units constituting the stem polymer (A) is 50% by mass or more.
Among the structural units constituting the branch polymer (B), the proportion of the structural units derived from the trimeric or more polyalkylene glycol ether (b-1) is 90% by mass or more.
Contains a water-soluble graft polymer (C) in which the stem polymer (A) and the branch polymer (B) are bonded by an ester bond, and contains unsaturated sulfonic acid and / or a salt thereof in the water-soluble graft polymer (C). An aqueous solution of a binder for a lithium ion battery having an amount of less than 10 mol% . The water-soluble graft polymer (C) is the same as the (meth) acrylamide group-containing compound (a-1) and the following general formula (1).

(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a methylene group, an ethylene group or a propylene group, R ³ is a hydrogen atom or a methyl group, and n is an integer of 3 or more. The aqueous binder solution for a lithium ion battery according to claim 1, which is a polymer of the macromonomer represented by (1). The aqueous binder solution for a lithium ion battery according to claim 1 or 2, wherein the film produced by drying the water-soluble graft polymer (C) has a HAZE of 3% or more. An electrode slurry for a lithium ion battery containing the aqueous binder solution for a lithium ion battery according to any one of claims 1 to 3 and the electrode active material (D). The electrode slurry for a lithium ion battery according to claim 4, which contains 1 to 15% by mass of the water-soluble graft polymer (C) with respect to 100% by mass of the electrode active material (D). The electrode slurry for a lithium ion battery according to claim 4 or 5, wherein the electrode active material (D) contains 5% by mass or more of silicon or silicon oxide covered with a carbon layer. Among the constituent units constituting the stem polymer (A), the proportion of the constituent units derived from the (meth) acrylamide group-containing compound (a-1) is 50% by mass or more, and among the constituent units constituting the branch polymer (B). The proportion of the structural unit derived from the trimeric or more polyalkylene glycol ether (b-1) is 90% by mass or more, and the stem polymer (A) and the branch polymer (B) are bonded by an ester bond. The method for producing an electrode slurry for a lithium ion battery according to any one of claims 4 to 6, which comprises a step of mixing the sex graft polymer (C) and the electrode active material (D). An electrode for a lithium ion battery obtained by applying the electrode slurry for a lithium ion battery according to any one of claims 4 to 6 to a current collector and drying it. The electrode for a lithium ion battery according to claim 8, wherein the current collector is a copper foil. A lithium ion battery comprising the electrode for a lithium ion battery according to claim 9.