Binder Aqueous Solution for Lithium-Ion Batteries, Anode Slurry for Lithium-Ion Batteries, Anode for Lithium-Ion Batteries, and Lithium-Ion Batteries

Abstract

To provide a binder aqueous solution for a lithium-ion battery, a negative electrode slurry for a lithium-ion battery, a negative electrode for a lithium-ion battery, and a lithium-ion battery.SOLUTION: The binder aqueous solution for a lithium-ion battery is a polymer of a monomer group containing 15 to 99.9 mole% unsaturated carboxylic acid or its inorganic salt for 100 mole% of the monomer group. The binder aqueous solution for a lithium-ion battery includes a water-soluble polymer (A) with a glass transition temperature of 110°C or less and a partially hydrolyzed condensation product of amino group-containing trialkoxysilane (B). The pH is 5 or higher.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to an aqueous binder solution for a lithium-ion battery, a negative electrode slurry for a lithium-ion battery, a negative electrode for a lithium-ion battery, and a lithium-ion battery.

Background Art

[0002] Lithium-ion batteries are small, lightweight, have a high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvements in battery components such as electrodes have been studied for the purpose of further improving the performance of lithium-ion batteries.

[0003] Both the positive electrode and the negative electrode of a lithium-ion battery are produced by dispersing an electrode active material and a binder resin in a solvent to form a slurry, applying the slurry on both sides of a current collector (for example, a metal foil), drying and removing the solvent to form an electrode layer, and then compression molding this with a roll press or the like.

[0004] In recent years, various electrode active materials have been proposed for lithium-ion battery electrodes from the viewpoint of increasing the battery capacity. However, depending on the electrode active material, it is likely to expand and contract during charge and discharge. Therefore, a lithium-ion battery electrode that is likely to expand and contract during charge and discharge causes a volume change from the initial stage of repeated charge and discharge, and easily degrades electrical characteristics such as the cycle characteristics of a lithium-ion battery using this.

[0005] Therefore, in this field, studies have been made to solve the above problems with a binder resin. For example, it has been proposed that good charge and discharge characteristics can be obtained by using polyacrylamide (Patent Documents 1 and 2) as a binder of a water-soluble resin. In addition, it has been proposed to suppress expansion by adding a cross-linking agent to a particulate resin that is a binder resin against expansion and contraction accompanying charge and discharge of an active material (Patent Document 3). The cross-linking agent usually causes a cross-linking reaction in the drying process after applying the slurry composition to the current collector, and forms cross-links between the particles of the particulate resin and the like.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, when cross-linking is carried out using a cross-linking agent, the flexibility of the binder resin decreases, and as a result, there may occur a problem that the electrode flexibility decreases. Also, in the prior art, the dispersion stability and storage stability of the slurry were not sufficient. Further, it is also required of the binder to endow a lithium-ion battery with a good discharge capacity retention rate.

[0008] Therefore, one of the problems to be solved by the present invention is to provide an aqueous binder solution for a lithium-ion battery that can endow a lithium-ion battery with a good discharge capacity retention rate, endow a negative electrode with good flexibility, and endow a slurry with good dispersion stability and storage stability. Another problem to be solved by the present invention is to provide a negative electrode slurry for a lithium-ion battery that can endow a lithium-ion battery with a good discharge capacity retention rate, endow a negative electrode with good flexibility, and has good dispersion stability and storage stability.

Means for Solving the Problems

[0009] As a result of intensive studies, the present inventors have found that the above problems can be solved.

[0010] The following items are provided by the present disclosure. (Item 1) With respect to 100 mol% of the monomer group, A polymer of a monomer group containing 15 to 99.9 mol% of an unsaturated carboxylic acid or an inorganic salt thereof, A water-soluble polymer (A) having a glass transition temperature of 110°C or lower, and A hydrolysis partial condensate (B) of an amino group-containing trialkoxysilane, An aqueous binder solution for a lithium-ion battery having a pH of 5 or higher. (Item 2) The aqueous binder solution for a lithium-ion battery according to the above item, containing 15 to 60 mol% of hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms with respect to 100 mol% of the monomer group. (Item 3) The aqueous binder solution for a lithium-ion battery according to any one of the above items, wherein the molar ratio (amino group / carboxyl group) of the amino group of the hydrolysis partial condensate (B) of the amino group-containing trialkoxysilane to the carboxyl group of the water-soluble polymer (A) is 0.05 or higher. (Item 4) With respect to 100 mol% of the monomer group, A polymer of a monomer group containing 15 to 99.9 mol% of an unsaturated carboxylic acid or an inorganic salt thereof, A water-soluble polymer (A) having a glass transition temperature of 110°C or lower, A hydrolysis partial condensate (B) of an amino group-containing trialkoxysilane, A negative electrode active material (C), and A conductive carbon assistant (D) having a zeta potential of 0 mV or higher at pH 5 to 7, A negative electrode slurry for a lithium-ion battery. (Item 5) A negative electrode for a lithium-ion battery obtained by applying the negative electrode slurry for a lithium-ion battery according to the above item to a current collector and drying and curing it. (Item 6) A lithium-ion battery including the negative electrode for a lithium-ion battery according to the above item.

[0011] In the present disclosure, the above-described one or more features may be provided in combination in addition to the explicitly stated combinations. Effect of the Invention

[0012] The aqueous binder solution for lithium ion batteries according to the present embodiment can impart excellent dispersion stability and storage stability to the negative electrode slurry for lithium ion batteries. The negative electrode slurry for lithium ion batteries according to the present embodiment has excellent dispersion stability and storage stability. Furthermore, the negative electrode according to the present embodiment has excellent flexibility. And the lithium ion battery according to the present embodiment has an excellent discharge capacity retention rate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Throughout this disclosure, the range of the values of the physical properties, contents, etc. may be set as appropriate (for example, by selecting from the upper and lower limit values described in each item below). Specifically, when A4, A3, A2, A1 (where A4>A3>A2>A1) are exemplified as the upper and lower limits of the value α, the range of the value α is exemplified as A4 or less, A3 or less, A2 or less, A1 or more, A2 or more, A3 or more, A1 to A2, A1 to A3, A1 to A4, A2 to A3, A2 to A4, A3 to A4, etc.

[0014] [Aqueous binder solution for lithium-ion batteries: also called aqueous solution] The present disclosure relates to a monomer group having a molecular weight of 100 mol %. A polymer of a monomer group containing 15 to 99.9 mol % of an unsaturated carboxylic acid or an inorganic salt thereof, A water-soluble polymer (A) having a glass transition temperature of 110° C. or less, and Contains a hydrolysis partial condensate (B) of an amino group-containing trialkoxysilane, Provided is an aqueous binder solution for lithium ion batteries having a pH of 5 or more.

[0015] <Water-soluble polymer: also referred to as component (A)> The component (A) may be used alone or in combination of two or more types.

[0016] 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 matter is less than 0.5 mass% (less than 2.5 mg).

[0017] When the component (A) is not water-soluble, it does not dissolve in water and thus does not form an aqueous solution in the first place. As a result, the component (A) does not contribute to the slurry dispersion. In addition, it is not possible to impart the viscosity necessary for coating the current collector to the slurry.

[0018] When 0.5 g of the component (A) is dissolved in 100 g of water, examples of the insoluble matter of the component (A) include less than 0.5, 0.4, 0.3, 0.2, 0.1 mass%, and 0 mass%.

[0019] 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 acrylate and methacrylate". Also, "(meth)acryloyl" means "at least one selected from the group consisting of acryloyl and methacryloyl".

[0020] (unsaturated carboxylic acid or its inorganic salt) The unsaturated carboxylic acid or its inorganic salt may be used alone or in combination of two or more.

[0021] Examples of the unsaturated carboxylic acid include (meth)acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, etc. Among these, when (meth)acrylic acid, particularly acrylic acid, is used, a binder with high interaction with the electrode active material and the conductive carbon assistant and good slurry dispersibility can be provided.

[0022] Examples of the inorganic salt include alkali metal salts and alkaline earth metal salts. In the present disclosure, an inorganic salt of an organic substance (for example, an inorganic salt of one or more unsaturated acids selected from the group consisting of unsaturated carboxylic acids and unsaturated sulfonic acids, or an inorganic salt of the component (A), etc.) refers to a salt in which the cation part is a metal cation.

[0023] Examples of the alkali metal include lithium, sodium, potassium, etc.

[0024] Examples of the alkaline earth metal include magnesium, calcium, etc.

[0025] The upper and lower limits of the content of the unsaturated carboxylic acid or its inorganic salt with respect to 100 mol% of the monomer group are exemplified by 99.9, 99, 95, 90, 89.95, 85, 80, 75, 70, 65, 60, 59.95, 55, 50, 45, 40, 36.7, 35, 30, 25, 20, 15 mol%, etc. In one embodiment, the above content is preferably 15 to 99.9 mol%.

[0026] The upper and lower limits of the content of the unsaturated carboxylic acid or its inorganic salt with respect to 100% by mass of the monomer group are exemplified by 99.9, 99, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 36.7, 35, 30, 25, 20, 15, 10, 5% by mass, etc. In one embodiment, the above content is preferably 5 to 99.9% by mass.

[0027] (Hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms) In one embodiment, the above monomer group may include a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms. The hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms may be used alone or in combination of two or more.

[0028] In the present disclosure, the "hydroxyalkyl group having 2 to 4 carbon atoms" refers to a group in which one of the hydrogen atoms constituting the alkyl group having 2 to 4 carbon atoms is substituted with a hydroxy group.

[0029] Hydroxyalkyl (meth) acrylates having a hydroxyalkyl group with 2 to 4 carbon atoms include 1-hydroxyethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 1-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxy-1-methylethyl (meth) acrylate, 1-hydroxy-2-methylethyl (meth) acrylate, 1-hydroxybutyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 1-hydroxy-1-methyl-propyl (meth) acrylate, 2-hydroxy-1-methyl-propyl (meth) acrylate, 3-hydroxy-1-methyl-propyl (meth) acrylate, 1-ethyl-2-hydroxyethyl (meth) acrylate, 1-hydroxy-2-methyl-propyl (meth) acrylate, 2-hydroxy-2-methyl-propyl (meth) acrylate, 3-hydroxy-2-methyl-propyl (meth) acrylate, 1,1-dimethyl-2-hydroxyethyl (meth) acrylate, and the like.

[0030] Among these, when 2-hydroxyethyl (meth) acrylate, particularly 2-hydroxyethyl acrylate, is used, it is possible to provide a binder that not only reduces water absorption while maintaining water solubility, but also reduces irreversible capacity and imparts good flexibility to the electrode.

[0031] Examples of the upper and lower limits of the content of hydroxyalkyl (meth) acrylate having a hydroxyalkyl group with 2 to 4 carbon atoms relative to 100 mol% of the monomer group include 60, 56, 55, 50, 45, 40, 35, 30, 28.5, 25, 20, 15, 10, 5, 0 mol%, etc. In one embodiment, the above content is preferably 0 to 60 mol%, more preferably 15 to 60 mol%.

[0032] The upper and lower limits of the content of hydroxyalkyl (meth)acrylate having a hydroxyalkyl group with 2 to 4 carbon atoms with respect to 100% by mass of the monomer group are exemplified by 80, 75, 70, 65, 60, 55, 50, 45, 40, 36.7, 35, 30, 25, 20, 15, 10, 5, 0% by mass, etc. In one embodiment, the above content is preferably 0 to 80% by mass.

[0033] ((Meth)acrylamide group-containing compound) In one embodiment, the monomer group may include a (meth)acrylamide group-containing compound. In the present disclosure, the “(meth)acrylamide group-containing compound” means a compound having a (meth)acrylamide group. The (meth)acrylamide group-containing compound may be used alone or in combination of two or more.

[0034] In one embodiment, the (meth)acrylamide group-containing compound has the following structural formula [Chemical formula] (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 and R 3 are each independently a hydrogen atom, a substituted or unsubstituted alkyl group, or an acetyl group, or R 2 and R 3 together form a group forming a ring structure, R 4 and R 5 are each independently a hydrogen atom, a substituted or unsubstituted alkyl group, a hydroxy group, an amino group (-NR a R b (R a and R b are each independently a hydrogen atom or a substituted or unsubstituted alkyl group)), an acetyl group. Examples of the substituent of the substituted alkyl group include a hydroxy group, an amino group, an acetyl group, etc. Further, the group in which R 2 and R 3 together form a ring structure is exemplified by a morpholyl group, etc.). is represented by.

[0035] Examples of the alkyl group include a linear alkyl group, a branched alkyl group, and a cycloalkyl group.

[0036] The linear alkyl group is -C n H 2n+1 (where n is an integer of 1 or more). Examples of the linear alkyl group include a methyl group, an ethyl group, a propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, and an n-decyl group.

[0037] The branched alkyl group is a group in which at least one hydrogen of the linear alkyl group is substituted by an alkyl group. Examples of the branched alkyl group include an i-propyl group, an i-butyl group, an s-butyl group, a t-butyl group, a diethylpentyl group, a trimethylbutyl group, a trimethylpentyl group, and a trimethylhexyl group.

[0038] Examples of the cycloalkyl group include a monocyclic cycloalkyl group, a bridged-ring cycloalkyl group, and a fused-ring cycloalkyl group.

[0039] In the present disclosure, a monocyclic ring means a cyclic structure formed by covalent bonds of carbon and having no bridging structure inside. Further, a fused ring means a cyclic structure in which two or more monocyclic rings share two atoms (that is, each ring shares only one side with each other (condenses)). A bridged ring means a cyclic structure in which two or more monocyclic rings share three or more atoms.

[0040] Examples of the monocyclic cycloalkyl group include a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclodecyl group, and a 3,5,5-trimethylcyclohexyl group.

[0041] Examples of the bridged-ring cycloalkyl group include a tricyclodecyl group, an adamantyl group, and a norbornyl group.

[0042] Examples of the fused-ring cycloalkyl group include a bicyclodecyl group.

[0043] The above (meth)acrylamide group-containing compound includes, for example, (meth)acrylamide, N-isopropyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N-methylol(meth)acrylamide, diacetone(meth)acrylamide, maleic acid amide, (meth)acryloylmorpholine, hydroxyethyl(meth)acrylamide, and salts thereof. Examples of the above salts include quaternary salts of dimethylaminopropyl(meth)acrylamide methyl chloride and quaternary salts of dimethylaminoethyl(meth)acrylate benzyl chloride. Among these, when using (meth)acrylamide, particularly acrylamide, not only can the water absorption be reduced while maintaining water solubility, but also the irreversible capacity can be reduced, and the interaction with the electrode active material is high, enabling the production of a binder with high dispersibility of the slurry and high binding property between the electrode active materials inside the electrode.

[0044] The upper and lower limits of the content of the (meth)acrylamide group-containing compound with respect to 100 mol% of the monomer group are, for example, 90, 89.95, 85, 80, 75, 70, 69.8, 65, 60, 59.95, 55, 50, 45, 40, 35, 34.6, 30, 25, 20, 15, 10, 5, 4, 3.8, 3, 2, 1, 0 mol%, etc. In one embodiment, the above content is preferably 0 to 90 mol%.

[0045] The upper and lower limits of the content of the (meth)acrylamide group-containing compound with respect to 100 mass% of the monomer group are, for example, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 0 mass%, etc. In one embodiment, the above content is preferably 0 to 90 mass%.

[0046] (Unsaturated sulfonic acid) In one embodiment, the above monomer group may include an unsaturated sulfonic acid. The unsaturated sulfonic acid may be used alone or in combination of two or more.

[0047] Unsaturated sulfonic acids include α,β-ethylenically unsaturated sulfonic acids such as vinylsulfonic acid, styrenesulfonic acid, (meth)allylsulfonic acid; (meth)acrylamido t-butylsulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, 2-(meth)acrylamido-2-hydroxypropanesulfonic acid, 3-sulfopropyl (meth)acrylate, bis-(3-sulfopropyl) itaconate, and the like.

[0048] Examples of the upper and lower limits of the content of unsaturated sulfonic acid relative to 100 mol% of the monomer group include 20, 17, 15, 13, 10, 9, 7, 5, 4, 2, 1, 0.9, 0.7, 0.5, 0.3, 0.2, 0.1, 0.09, 0.07, 0.05, 0.03, 0.01, 0 mol%, etc. In one embodiment, the above content is preferably 0 to 20 mol%.

[0049] Examples of the upper and lower limits of the content of unsaturated sulfonic acid relative to 100 mass% of the monomer group include 30, 25, 20, 17, 15, 13, 10, 9, 7, 5, 4, 2, 1, 0.9, 0.7, 0.5, 0.3, 0.2, 0.1, 0.09, 0.07, 0.05, 0.03, 0.01, 0 mass%, etc. In one embodiment, the above content is preferably 0 to 30 mass%.

[0050] (Unsaturated phosphoric acid) In one embodiment, the monomer group may contain unsaturated phosphoric acid. Unsaturated phosphoric acid may be used alone or in combination of two or more.

[0051] Examples of unsaturated phosphoric acids include vinylphosphonic acid, vinyl phosphate, bis((meth)acryloxyethyl) phosphate, diphenyl-2-(meth)acryloyloxyethyl phosphate, dibutyl-2-(meth)acryloyloxyethyl phosphate, dioctyl-2-(meth)acryloyloxyethyl phosphate, monomethyl-2-(meth)acryloyloxyethyl phosphate, 3-(meth)acryloxy-2-hydroxypropylphosphoric acid, and the like.

[0052] Examples of the upper and lower limits of the content of unsaturated phosphoric acid relative to 100 mol% of the monomer group include 10, 9, 7, 5, 4, 2, 1, 0.9, 0.7, 0.5, 0.3, 0.2, 0.1, 0.09, 0.07, 0.05, 0.03, 0.01, 0 mol%, etc. In one embodiment, the above content is preferably 0 to 10 mol%.

[0053] Examples of the upper and lower limits of the content of unsaturated phosphoric acid relative to 100 mass% of the monomer group include 20, 17, 15, 13, 10, 9, 7, 5, 4, 2, 1, 0.9, 0.7, 0.5, 0.3, 0.2, 0.1, 0.09, 0.07, 0.05, 0.03, 0.01, 0 mass%, etc. In one embodiment, the above content is preferably 0 to 20 mass%.

[0054] (α,β-unsaturated nitrile) In one embodiment, the above monomer group may contain α,β-unsaturated nitrile. The α,β-unsaturated nitrile may be used alone or in combination of two or more. The α,β-unsaturated nitrile can be preferably used for the purpose of imparting flexibility to the electrode.

[0055] Examples of the α,β-unsaturated nitrile include (meth)acrylonitrile, α-chloro(meth)acrylonitrile, α-ethyl(meth)acrylonitrile, vinylidene cyanide, etc. Among these, (meth)acrylonitrile is preferable, and acrylonitrile is particularly preferable.

[0056] Examples of the upper and lower limits of the content of α,β-unsaturated nitrile relative to 100 mol% of the monomer group include 40, 35, 30, 25, 20, 15, 10, 5, 0 mol%, etc. In one embodiment, the above content is preferably 0 to 40 mol%.

[0057] Examples of the upper and lower limits of the content of α,β-unsaturated nitrile relative to 100 mass% of the monomer group include 30, 25, 20, 15, 10, 5, 0 mass%, etc. In one embodiment, the above content is preferably 0 to 30 mass%.

[0058] <Monomer other than any of the above: Also referred to as other components> Among the above monomer groups, monomers (other components) that are not any of unsaturated carboxylic acids or their inorganic salts, hydroxyalkyl (meth)acrylates having a hydroxyalkyl group with 2 to 4 carbon atoms, (meth)acrylamide group-containing compounds, unsaturated sulfonic acids, unsaturated phosphoric acids, and α,β-unsaturated nitriles can be used as long as the desired effects of the present invention are not impaired. As the other components, various known ones may be used alone or in combination of two or more.

[0059] Examples of the other components include hydroxyl group-free unsaturated carboxylic acid esters, conjugated dienes, aromatic vinyl compounds, etc.

[0060] The hydroxyl group-free unsaturated carboxylic acid ester is preferably a hydroxyl group-free (meth)acrylic acid ester. Examples of the hydroxyl group-free (meth)acrylic acid ester include hydroxyl group-free linear (meth)acrylic acid esters, hydroxyl group-free branched (meth)acrylic acid esters, hydroxyl group-free alicyclic (meth)acrylic acid esters, hydroxyl group-free alkoxyalkyl (meth)acrylates, etc.

[0061] Examples of the hydroxyl group-free linear (meth)acrylic acid ester include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-amyl (meth)acrylate, hexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, etc.

[0062] Examples of the hydroxyl group-free branched (meth)acrylic acid ester include i-propyl (meth)acrylate, i-butyl (meth)acrylate, i-amyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, etc.

[0063] Examples of the hydroxyl group-free alicyclic (meth)acrylic acid ester include cyclohexyl (meth)acrylate, etc.

[0064] The hydroxyl group-free alkoxyalkyl (meth)acrylate includes methoxymethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 1-methoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 2-methoxypropyl (meth)acrylate, 1-methoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 2-methoxybutyl (meth)acrylate, 1-methoxybutyl (meth)acrylate, ethoxymethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 1-ethoxyethyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 2-ethoxypropyl (meth)acrylate, 1-ethoxypropyl (meth)acrylate, propoxymethyl (meth)acrylate, 2-propoxyethyl (meth)acrylate, 1-propoxyethyl (meth)acrylate, butoxymethyl (meth)acrylate, etc. are exemplified.

[0065] The hydroxyl group-free unsaturated carboxylic acid ester can be preferably used for the purpose of imparting flexibility to the electrode. From the above viewpoints, the content of the hydroxyl group-free unsaturated carboxylic acid ester with respect to 100 mol% of the above monomer group is preferably less than 30 mol% (for example, less than 25, 20, 19, 15, 10, 5, 1 mol%, 0 mol%).

[0066] Also, the content of the hydroxyl group-free unsaturated carboxylic acid ester with respect to 100% by mass of the above monomer group is preferably 30% by mass or less (for example, less than 25, 20, 19, 15, 10, 5, 1% by mass, 0% by mass).

[0067] The conjugated diene includes 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadiene, substituted and side-chain conjugated hexadiene, etc. are exemplified.

[0068] The content of the conjugated diene with respect to 100 mol% of the above monomer group is preferably less than 10 mol%, more preferably 0 mol%, from the viewpoint of the cycle characteristics of the lithium-ion battery.

[0069] Examples of the upper and lower limits of the content of the conjugated diene with respect to 100% by mass of the above monomer group include 30, 20, 10, 5, 1, 0% by mass, etc. In one embodiment, the above content is preferably 0 to 30% by mass.

[0070] Examples of the aromatic vinyl compound include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, etc.

[0071] The content of the aromatic vinyl compound with respect to 100 mol% of the above monomer group is preferably less than 10 mol%, more preferably 0 mol%, from the viewpoint of the cycle characteristics of the lithium-ion battery.

[0072] Examples of the upper and lower limits of the content of the aromatic vinyl compound with respect to 100% by mass of the above monomer group include 30, 20, 10, 5, 1, 0% by mass, etc. In one embodiment, the above content is preferably 0 to 30% by mass.

[0073] Examples of the ratio of other components other than the above hydroxyl group-free unsaturated carboxylic acid ester, the above conjugated diene, and the above aromatic vinyl compound in the above monomer group are less than 10 mol%, less than 5 mol%, less than 2 mol%, less than 1 mol%, less than 0.9 mol%, less than 0.5 mol%, less than 0.4 mol%, less than 0.3 mol%, less than 0.1 mol%, less than 0.05 mol%, less than 0.01 mol%, 0 mol%, etc. with respect to 100 mol% of the above monomer group. Also, examples with respect to 100% by mass of the above monomer group are less than 10% by mass, less than 9% by mass, less than 7% by mass, less than 5% by mass, less than 4% by mass, less than 2% by mass, less than 1% by mass, less than 0.9% by mass, less than 0.5% by mass, less than 0.4% by mass, less than 0.3% by mass, less than 0.1% by mass, less than 0.05% by mass, less than 0.01% by mass, 0% by mass, etc.

[0074] <Production method of component (A)> (Component (A) can be synthesized by various known polymerization methods, preferably radical polymerization. Specifically, a radical polymerization initiator and, if necessary, a chain transfer agent are added to a monomer mixture containing the component, and the polymerization reaction is preferably carried out at a reaction temperature of 50 to 100 °C while stirring. The reaction time is not particularly limited, and 1 to 10 hours is preferred.)

[0075] For the radical polymerization initiator, various known ones can be used without particular limitation. Examples of the radical polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate; redox polymerization initiators obtained by combining the above persulfates with reducing agents such as sodium bisulfite; azo initiators such as 2,2'-azobis-2-amidinopropane dihydrochloride, etc. The amount of the radical polymerization initiator used is not particularly limited, but is preferably 0.05 to 5.0% by mass, more preferably 0.1 to 3.0% by mass, based on 100% by mass of the monomer group that gives component (A).

[0076] For the purpose of improving production stability, the pH of the reaction solution may be adjusted with a general neutralizing agent such as ammonia, organic amine, potassium hydroxide, sodium hydroxide, lithium hydroxide, etc. before the radical polymerization reaction and / or when solubilizing the obtained component (A). In that case, the pH is preferably 2 to 11. Also, for the same purpose, it is possible to use ethylenediaminetetraacetic acid (EDTA) or its salts, etc., which are metal ion sequestering agents.)

[0077] <Physical properties of component (A)> From the viewpoint of suppressing the generation of cracks and curling of the electrode, the glass transition temperature of component (A) is 110 °C or lower.) Examples of the upper and lower limits of the glass transition temperature of component (A) include 110, 105, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10 °C, etc. In one embodiment, considering the discharge capacity retention rate, the glass transition temperature of component (A) is preferably 10 to 110 °C.)

[0078] (A) component's glass transition temperature is calculated as follows. Note that the glass transition temperature can be adjusted by the combination of monomers.

[0079] (1) When the constituent monomers of component (A) are known (A) component's glass transition temperature can be determined based on the following Fox's equation from the glass transition temperature (Tg) (absolute temperature: K) of the monomer's homopolymer and their mass fractions. 1 / Tg = (W1 / Tg1) + (W2 / Tg2) + (W3 / Tg3) + ··· + (W n / Tg n ) [In the formula, Tg is the glass transition temperature (K) of the polymer to be determined, W1~W n are the mass fractions of each monomer, and Tg1~Tg n are the glass transition temperatures (K) of the homopolymers of each monomer]

[0080] For example, the glass transition temperature is 165 °C for the homopolymer of acrylamide, 106 °C for the homopolymer of acrylic acid, -15 °C for the homopolymer of hydroxyethyl acrylate, and 105 °C for the homopolymer of acrylonitrile. The monomer composition can be determined so that component (A) having the desired glass transition temperature can be obtained. Note that the glass transition temperature of the monomer's homopolymer can be measured by a DSC (differential scanning calorimeter), DTA (differential thermal analyzer), TMA (thermomechanical analyzer), etc. under the condition of heating from -100 °C to 300 °C (heating rate 10 °C / min.). Also, the values described in the literature can be used. Examples of the literature are "Chemical Handbook, Basic Volume II, edited by the Chemical Society of Japan (Revised 5th Edition)", p325, etc.

[0081] (2) When the constituent monomers of component (A) are unknown (A) component's glass transition temperature is measured by a DSC (differential scanning calorimeter) under the condition of heating from -100 °C to 300 °C (heating rate 10 °C / min.).

[0082] (A) component's weight average molecular weight (Mw) is not particularly limited, but its upper and lower limits are exemplified by 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, 350,000, 300,000, etc. In one embodiment, from the perspective of the dispersion stability of the above slurry, it is preferably 300,000 to 6 million, more preferably 350,000 to 6 million.

[0083] (A) component's number average molecular weight (Mn) is not particularly limited, but its upper and lower limits are exemplified by 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, 350,000, 300,000, 200,000, 100,000, 50,000, 10,000, etc. In one embodiment, the number average molecular weight (Mn) of (A) component is preferably 10,000 or more.

[0084] The weight average molecular weight and the number average molecular weight can be determined as values in terms of polyacrylic acid measured under an appropriate solvent by, for example, gel permeation chromatography (GPC).

[0085] (A) component's upper and lower limits of molecular weight distribution (Mw / Mn) are exemplified by 15, 14, 13, 11, 10, 9, 7.5, 5, 4, 3, 2.9, 2.5, 2, 1.5, 1.1, etc. In one embodiment, (A) component's molecular weight distribution (Mw / Mn) is preferably 1.1 to 15.

[0086] (A) component's B-type viscosity of an aqueous solution containing 13% by mass is not particularly limited, but its upper and lower limits are exemplified by 100,000, 90,000, 80,000, 70,000, 60,000, 50,000, 45,000, 40,000, 30,000, 20,000, 10,000, 9,000, 8,000, 7,000, 6,000, 5,000, 4,000, 3,000, 2,000, 1,000, 900, 700, 500, 300, 200, 100 mPa·s, etc. In one embodiment, the range of the above B-type viscosity is preferably 100 to 100,000 mPa·s.

[0087] 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.

[0088] In one embodiment, the neutralization rate of the carboxyl group possessed by the component (A) is preferably 50% or more (for example, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, 95% or more, 100%). In the present disclosure, the neutralization rate of the carboxyl group means the rate at which the carboxyl group (-COOH) has become an acid group (-COO - ). The above neutralization rate can be adjusted with inorganic salts such as alkali metal salts and alkaline earth metal salts.

[0089] Examples of the upper and lower limits of the content of the component (A) with respect to 100% by mass of the aqueous binder solution for lithium ion batteries include 20, 19, 15, 14, 12, 10, 9, 7, 6, 5, 4, 3, 2, 1% by mass, etc. In one embodiment, the above content is preferably 1 to 20% by mass.

[0090] <Hydrolyzed partial condensate of amino group-containing trialkoxysilane (B): also referred to as component (B)> Component (B) may be used alone or in combination of two or more.

[0091] In one embodiment, the amino group-containing trialkoxysilane has the following general formula

Chemical formula

[0092] Amino group (-NRam1 R am2 :R am1 ~R am2 Each of R, :R, and ~R is independently a hydrogen atom, an alkyl group, an aryl group, etc. Examples of the group having ) include an amino group-substituted alkyl group. An amino group-substituted alkyl group is a group in which one hydrogen atom constituting the alkyl group is substituted with an amino group.

[0093] Examples of the amino group-containing trialkoxysilane include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2(aminoethyl)3-aminopropyltrimethoxysilane, N-2(aminoethyl)3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and the like.

[0094] In the present disclosure, the "hydrolyzed partial condensate of trialkoxysilane" means a hydrolyzed condensate in which an alkoxy group is present. The residual ratio of the hydrolyzable group is not particularly limited. In the present disclosure, from the viewpoint of not being gelled, a hydrolyzed partial condensate of trialkoxysilane is used instead of a hydrolyzed complete condensate of trialkoxysilane. The hydrolyzed partial condensate of the amino group-containing trialkoxysilane means a hydrolyzed partial condensate of a trialkoxysilane having an amino group.

[0095] Examples of the upper and lower limits of the degree of condensation of the hydrolyzed partial condensate of the amino group-containing trialkoxysilane include 1000, 900, 800, 700, 600, 500, 400, 300, 200, 100, 90, 80, 70, 60, 50, 40, 30, 20, 19, 17, 15, 14, 13, 12, 11, 10, 9, 5, 3, 2, 1.7, 1.5, 1.4, 1.2, 1.1, 1.01, etc. In one embodiment, the degree of condensation of the hydrolyzed partial condensate of the amino group-containing trialkoxysilane is preferably from 1.01 to 1000, more preferably from 1.01 to 100.

[0096] The upper and lower limits of the weight average molecular weight of the hydrolyzed partial condensate of the amino group-containing trialkoxysilane are exemplified by 190,000, 170,000, 150,000, 130,000, 100,000, 90,000, 70,000, 50,000, 30,000, 20,000, 10,000, 9,000, 7,500, 5,000, 2,500, 1,000, 900, 750, 500, 250, 200, 175, 160, 150, 125, 110, 100, etc. In one embodiment, the weight average molecular weight is preferably 100 to 190,000.

[0097] The hydrolyzed partial condensate of the amino group-containing trialkoxysilane is obtained by hydrolyzing 100 parts by mass of the amino group-containing trialkoxysilane and partially condensing it in the presence of 0 to 5 parts by mass of an acid or base catalyst (preferably an acid catalyst). Specifically, while stirring the reaction solution containing the above components, it is preferable to carry out the reaction at a reaction temperature of 30 to 60 ° C for 0.5 to 5.0 hours.

[0098] Examples of the acid catalyst include nitric acid, hydrochloric acid, sulfurous acid, phosphoric acid, formic acid, acetic acid, etc.

[0099] Examples of the base catalyst include sodium hydroxide, lithium hydroxide, potassium hydroxide, calcium hydroxide, amine compounds, etc.

[0100] The upper and lower limits of the content of component (B) with respect to 100% by mass of the aqueous binder solution for lithium ion batteries are exemplified by 10, 9, 8, 7, 6, 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.5, 0.1, 0.09, 0.05, 0.03, 0.01% by mass, etc. In one embodiment, the above content is preferably 0.01 to 10% by mass.

[0101] The upper and lower limits of the mass ratio [(A) / (B)] of component (A) and component (B) contained in the aqueous binder solution for lithium ion batteries are exemplified by 2000, 1750, 1500, 1250, 1000, 750, 500, 250, 100, 75, 50, 25, 10, 5, 2, 1, etc. In one embodiment, the above mass ratio [(A) / (B)] is preferably 1 to 2000.

[0102] The upper and lower limits of the molar ratio (amino group / carboxyl group) of the amino group contained in the hydrolyzed partial condensate (B) of the above amino group-containing trialkoxysilane and the carboxyl group contained in the above water-soluble polymer (A) are 500, 475, 450, 425, 400, 375, 350, 325, 300, 275, 250, 225, 200, 175, 150, 125, 100, 75, 50, 25, 20, 15, 10, 9, 7, 5, 2, 1, 0.9, 0.5, 0.2, 0.1, 0.05, etc. are exemplified. In one embodiment, the above molar ratio is preferably 0.05 or more, and more preferably 0.05 to 500.

[0103] <Water> Examples of water include ultrapure water, pure water, distilled water, ion-exchanged water, and tap water.

[0104] The upper and lower limits of the content of water with respect to 100% by mass of the aqueous binder solution for lithium ion batteries are 99.9, 99, 95, 90, 85, 80% by mass, etc. are exemplified. In one embodiment, the above content is preferably 80 to 99.9% by mass.

[0105] The upper and lower limits of the mass ratio [(A) component / water] of the component (A) contained in the aqueous binder solution for lithium ion batteries and water are 0.25, 0.24, 0.22, 0.20, 0.18, 0.15, 0.12, 0.10, 0.09, 0.07, 0.05, etc. are exemplified. In one embodiment, the above mass ratio is preferably 0.05 to 0.25.

[0106] The upper and lower limits of the mass ratio [(B) component / water] of the component (B) contained in the aqueous binder solution for lithium ion batteries and water are 0.06, 0.05, 0.02, 0.01, 0.009, 0.007, 0.005, 0.003, 0.001, 0.0009, 0.0007, 0.0005, 0.0003, 0.0001, etc. are exemplified. In one embodiment, the above mass ratio is preferably 0.0001 to 0.06.

[0107] <Dispersion (emulsion)> In one embodiment, the aqueous binder solution for the lithium-ion battery contains a dispersion (emulsion).

[0108] The dispersion (emulsion) includes styrene-butadiene copolymer latex, polystyrene polymer latex, polybutadiene polymer latex, acrylonitrile-butadiene copolymer latex, polyurethane polymer latex, polymethyl methacrylate polymer latex, methyl methacrylate-butadiene copolymer latex, polyacrylate polymer latex, vinyl chloride polymer latex, vinyl acetate polymer emulsion, vinyl acetate-ethylene copolymer emulsion, polyethylene emulsion, carboxy-modified styrene-butadiene copolymer resin emulsion, acrylic resin emulsion, polyethylene, polypropylene, polyethylene terephthalate, polyamide (PA), polyimide (PI), polyamideimide (PAI), aromatic polyamide, alginic acid and its salts, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), etc.

[0109] The upper and lower limits of the content of the dispersion (emulsion) with respect to 100% by mass of component (A) are exemplified by 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 19, 17, 15, 13, 10, 9, 7, 5, 4, 2, 1, 0% by mass, etc. In one embodiment, from the viewpoints of electrode flexibility and discharge capacity retention rate, the above content is preferably 0 to 100% by mass.

[0110] <Thickener> In one embodiment, the aqueous binder solution for the lithium-ion battery contains a thickener.

[0111] The thickeners include cellulose polymers such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, and their ammonium salts and alkali metal salts; (modified) poly(meth)acrylic acid and their ammonium salts and alkali metal salts; polyvinyl alcohols such as (modified) polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, copolymers of maleic anhydride or maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified polyacrylic acid, oxidized starch, phosphate starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydrides, etc.

[0112] The upper and lower limits of the content of the thickener with respect to 100% by mass of component (A) are exemplified by 50, 45, 40, 35, 30, 25, 20, 19, 17, 15, 13, 10, 9, 7, 5, 4, 2, 1, 0% by mass, etc. In one embodiment, the above content is preferably 0 to 50% by mass.

[0113] <Additive> The aqueous binder solution for lithium-ion batteries may contain, as an additive, something that does not fall under any of component (A), component (B), water, the dispersion (emulsion), and the thickener.

[0114] Examples of the additive include dispersants, leveling agents, antioxidants, etc.

[0115] Examples of the dispersant include anionic dispersants, cationic dispersants, nonionic dispersants, polymeric dispersants, etc.

[0116] Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, metal surfactants, etc. By using the surfactant, splashing generated during coating can be prevented, and the smoothness of the layer (coating layer) of the above slurry can be improved.

[0117] Examples of the antioxidant include phenolic compounds, hydroquinone compounds, organic phosphorus compounds, sulfur compounds, phenylenediamine compounds, polymer-type phenolic compounds, etc. The polymer-type phenolic compound is a polymer having a phenolic structure in the molecule. The weight average molecular weight of the polymer-type phenolic compound is preferably from 200 to 1000, more preferably from 600 to 700.

[0118] Examples of the content of the additive include less than 5% by mass, less than 4% by mass, less than 2% by mass, less than 1% by mass, less than 0.9% by mass, less than 0.5% by mass, less than 0.4% by mass, less than 0.2% by mass, less than 0.1% by mass, less than 0.09% by mass, less than 0.05% by mass, less than 0.04% by mass, less than 0.02% by mass, less than 0.01% by mass, 0% by mass, etc. with respect to 100% by mass of the component (A) or the component (B).

[0119] Examples of the content of the additive with respect to 100% by mass of the above aqueous solution include less than 5% by mass, less than 4% by mass, less than 2% by mass, less than 1% by mass, less than 0.9% by mass, less than 0.5% by mass, less than 0.4% by mass, less than 0.2% by mass, less than 0.1% by mass, less than 0.09% by mass, less than 0.05% by mass, less than 0.04% by mass, less than 0.02% by mass, less than 0.01% by mass, 0% by mass, etc.

[0120] When the pH is 5 or more, the dispersibility of the conductive carbon assistant becomes good, and as a result, an excellent discharge capacity retention rate is exhibited. Therefore, the pH of the binder aqueous solution for lithium ion batteries is set to 5 or more. Examples of the upper and lower limits of the pH of the binder aqueous solution for lithium ion batteries include 9, 8.9, 8.5, 8, 7.9, 7.7, 7.5, 7.3, 7.1, 7, 6.9, 6.7, 6.5, 6.3, 6, 5.9, 5.6, 5.5, 5.4, 5.2, 5.1, 5, etc.

[0121] The pH can be measured at 25 °C using a glass electrode pH meter (for example, product name "pH meter D-52" manufactured by Horiba, Ltd.).

[0122] The aqueous binder solution for lithium-ion batteries can be used as an aqueous binder solution for lithium-ion battery electrodes, an aqueous binder solution for lithium-ion battery negative electrodes, a conductive carbon assistant dispersant for lithium-ion batteries, etc.

[0123] [Negative electrode slurry for lithium-ion batteries: Also referred to as slurry] This disclosure is a polymer of a monomer group containing 15 to 99.9 mol% of an unsaturated carboxylic acid or its inorganic salt with respect to 100 mol% of the monomer group, a water-soluble polymer (A) having a glass transition temperature of 110°C or lower, a hydrolyzed partial condensate (B) of an amino group-containing trialkoxysilane, a negative electrode active material (C), and a conductive carbon assistant (D) having a zeta potential of 0 mV or more at pH 5 to 7, to provide a negative electrode slurry for lithium-ion batteries.

[0124] Examples of the above-mentioned water-soluble polymer (A) and the hydrolyzed partial condensate (B) of the amino group-containing trialkoxysilane are as described above.

[0125] In this disclosure, "slurry" means a suspension of a liquid and solid particles.

[0126] Examples of the upper and lower limits of the content of component (A) with respect to 100% by mass of the above slurry are 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.9, 0.7, 0.5, 0.3, 0.1% by mass, etc. In one embodiment, the content with respect to 100% by mass of the above slurry is preferably 0.1 to 10% by mass.

[0127] Examples of the upper and lower limits of the content of component (B) with respect to 100% by mass of the above slurry are 5, 4, 3, 2, 1, 0.9, 0.7, 0.5, 0.3, 0.1, 0.09, 0.07, 0.05, 0.03, 0.01% by mass, etc. In one embodiment, the content is preferably 0.01 to 5% by mass.

[0128] ​Examples of the upper and lower limits of the water content with respect to 100% by mass of the above slurry include 70, 65, 60, 55, 50, 45, 40, 35, 30% by mass, etc. In one embodiment, the above content is preferably 30 to 70% by mass.

[0129] <Negative electrode active material (C): Also referred to as component (C)> The negative electrode active material may be used alone or in combination of two or more.

[0130] The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium, and an appropriate material can be selected as appropriate according to the type of the target lithium ion battery. It may be used alone or in combination of two or more. Examples of the negative 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.

[0131] The above carbon materials include graphite which is highly crystalline carbon (also referred to as graphite, examples include natural graphite, artificial graphite, etc.), low crystalline carbon (soft carbon, hard carbon), carbon black (Ketjen black, acetylene black, channel black, lamp black, oil furnace black, thermal black, etc.), fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon fibril, mesocarbon microbeads (MCMB), pitch-based carbon fiber, etc.

[0132] The above silicon materials include silicon, silicon oxide, silicon alloy, in addition to SiC, SiO x C y (0 < x ≤ 3, 0 < y ≤ 5), Si3N4, Si2N2O, SiO xSilicon oxide composites represented by (0 < x ≤ 2) (such as materials described in JP-A-2004-185810 and JP-A-2005-259697), silicon materials described in JP-A-2004-185810, etc. are exemplified. Further, the silicon materials described in Patent No. 5390336 and Patent No. 5903761 may also be used.

[0133] The above silicon oxide has a composition formula SiO x Silicon oxide represented by (0 < x < 2, preferably 0.1 ≤ x ≤ 1) is preferred.

[0134] The above 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. These transition metal silicon alloys are preferred because they have high electron conductivity and high strength. The silicon alloy is more preferably a silicon-nickel alloy or a silicon-titanium alloy, and particularly preferably 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 100 mol% of the metal elements in the above alloy. Note that the silicon material may be any of single crystal, polycrystal, and amorphous.

[0135] Further, when a silicon material is used as the negative electrode active material, a negative electrode active material other than the silicon material may be used in combination. Such negative electrode active materials include the above carbon materials; conductive polymers such as polyacene; A X B Y O Z (A is an alkali metal or a transition metal, B is at least one selected from transition metals such as cobalt, nickel, aluminum, tin, and manganese, O represents an oxygen atom, and X, Y, and Z are numbers in the ranges of 0.05 < X < 1.10, 0.85 < Y < 4.00, and 1.5 < Z < 5.00, respectively.) Composite metal oxides represented by, and other metal oxides, etc. are exemplified. When a silicon material is used as the negative electrode active material, it is preferable to use a carbon material in combination because the volume change accompanying the absorption and release of lithium is small.

[0136] The oxide containing the lithium atom is a ternary lithium nickel cobalt manganese oxide, a lithium-manganese composite oxide (such as LiMn2O4), a lithium-nickel composite oxide (such as LiNiO2), a lithium-cobalt composite oxide (such as LiCoO2), a lithium-iron composite oxide (such as LiFeO2), a lithium-nickel-manganese composite oxide (LiNi 0.5 Mn 0.5 O2, etc.), a lithium-nickel-cobalt composite oxide (LiNi 0.8 Co 0.2 O2, etc.), a lithium-transition metal phosphate compound (such as LiFePO4), and a lithium-transition metal sulfate compound (Li x Fe2(SO4)3), a lithium-titanium composite oxide (lithium titanate: Li4Ti5O 12 ), etc. Lithium-transition metal composite oxides, and other conventionally known negative electrode active materials, etc. are exemplified.

[0137] From the viewpoint that the effects of the present invention are significantly exhibited, a carbon material and / or a material alloying with lithium are preferably contained in the negative electrode active material in an amount of 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0138] In one embodiment, a negative electrode active material (C) containing 1% by mass or more (2, 5, 10, 25, 50, 75, 90% by mass or more, 100% by mass) of silicon and / or silicon oxide covered with a carbon layer is preferable.

[0139] The shape of the negative electrode active material is not particularly limited and may be any shape such as particulate or thin film, etc., but particulate is preferred. The average particle diameter of the negative electrode active material is not particularly limited, and examples of its upper and lower limits include 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 4, 3, 2.9, 2, 1, 0.5, 0.1 μm, etc. In one embodiment, from the viewpoint of forming a uniform and thin coating film, more specifically, if it is 0.1 μm or more, the handleability is good, and if it is 50 μm or less, the electrode coating is easy. Therefore, the average particle diameter of the negative electrode active material is preferably 0.1 to 50 μm, more preferably 0.1 to 45 μm, still more preferably 1 to 10 μm, and particularly preferably 5 μm.

[0140] The upper and lower limits of the content of the component (A) with respect to 100% by mass of the negative electrode active material (C) in the above slurry are exemplified by 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1.5, 1, 0.5% by mass, etc. In one embodiment, the above content is preferably 0.5 to 15% by mass.

[0141] <Conductive carbon assistant (D) with a zeta potential of 0 mV or more at pH 5 to 7: also referred to as component (D)> The conductive carbon assistant (D) with a zeta potential of 0 mV or more at pH 5 to 7 may be used alone or in combination of two or more.

[0142] Examples of the conductive carbon assistant with a zeta potential of 0 mV or more at pH 5 to 7 include fibrous carbon, graphite particles, carbon black, etc. Examples of fibrous carbon include vapor-grown carbon fiber (VGCF), carbon nanotube (CNT), carbon nanofiber (CNF), etc. Examples of carbon black include acetylene black, ketjen black, furnace black, etc. In one embodiment, the conductive carbon assistant with a zeta potential of 0 mV or more at pH 5 to 7 is preferably carbon black.

[0143] (D) component may be a conductive carbon auxiliary agent with a zeta potential of 0 mV or more at pH 5 to 7. The shape of (D) component is not particularly limited. The dispersibility of the conductive carbon auxiliary agent can be determined by the magnitude of the absolute value of the zeta potential. The zeta potential is an index indicating the degree of the surface charge amount of particles. The greater the absolute value of the zeta potential of particle A, the stronger the repulsive force between particle A and particle A, and the easier it is to disperse. Conversely, the smaller the absolute value of the zeta potential of particle A, the easier it is for particle A to aggregate. A conductive carbon auxiliary agent with a zeta potential of 0 mV or more, particularly 0 to 30 mV, at pH 5 to 7 has low initial dispersibility and dispersion stability. However, the negative electrode slurry for a lithium ion battery containing (A) component, (B) component, and a conductive carbon auxiliary agent with a zeta potential of 0 mV or more at pH 5 to 7 exhibits high initial dispersibility and dispersion stability.

[0144] The zeta potential of the conductive carbon auxiliary agent at pH 5 to 7 can be measured at 25 °C (for example, at pH 6.1) using a zeta potential - particle size measurement system (product name "ELSZ - 1000Z" manufactured by Otsuka Electronics Co., Ltd.). The solution containing the conductive carbon auxiliary agent can be produced by using water as the solvent, adding the conductive carbon auxiliary agent, and stirring. Also, the pH of this solution can be adjusted by adding hydrochloric acid or sodium hydroxide.

[0145] Examples of the upper and lower limits of the content of (D) component with respect to 100% by mass of the above slurry include 6, 5, 4, 3, 2, 1.9, 1.7, 1.5, 1.3, 1.1, 1, 0.9, 0.7, 0.5, 0.3, 0.1, 0.09, 0.07, 0.05, 0.03, 0.01, 0.009, 0.007, 0.005, 0.003, 0.001, 0.0009, 0.0007, 0.0005, 0.0003, 0.0001% by mass, etc. In one embodiment, the above content is preferably 0.0001 to 6% by mass.

[0146] <Conductive auxiliary agent other than (D) component> In one embodiment, a conductive auxiliary agent other than component (D) may be included in the slurry. Examples of the conductive auxiliary agent other than component (D) include carbon black having a zeta potential of less than 0 mV at pH 5 to 7, fine powder composed of Cu, Ni, Al, Si or an alloy thereof having an average particle size of 10 μm or less, and the like. The content of the conductive auxiliary agent other than component (D) is not particularly limited, but is preferably 0 to 10 parts by mass, more preferably 0.001 to 6 parts by mass, based on 100 parts by mass of the negative electrode active material.

[0147] <Slurry viscosity adjustment solvent> The slurry viscosity adjustment solvent is not particularly limited, and may include a non-aqueous medium having a standard boiling point of 80 to 350°C. The slurry viscosity adjustment solvent may be used alone or in combination of two or more. Examples of the slurry viscosity adjustment solvent include amide solvents such as N-methylpyrrolidone, dimethylformamide, and N,N-dimethylacetamide; hydrocarbon solvents such as toluene, xylene, n-dodecane, and tetralin; alcohol solvents such as methanol, ethanol, 2-propanol, isopropyl alcohol, 2-ethyl-1-hexanol, 1-nonanol, and lauryl alcohol; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, phorone, acetophenone, and isophorone; ether solvents such as dioxane and tetrahydrofuran (THF); ester solvents such as benzyl acetate, isopentyl butyrate, methyl lactate, ethyl lactate, and butyl lactate; amine solvents such as o-toluidine, m-toluidine, and p-toluidine; lactones such as γ-butyrolactone and δ-butyrolactone; sulfoxide-sulfone solvents such as dimethyl sulfoxide and sulfolane; water and the like. Among these, N-methylpyrrolidone is preferred from the viewpoint of coating workability. The content of the non-aqueous medium is not particularly limited, but is preferably 0 to 10% by mass based on 100% by mass of the slurry.

[0148] The slurry may contain, as an additive, something that does not fall under any of component (A), component (B), component (C), component (D), water, the conductive auxiliary agent other than component (D), and the slurry viscosity adjustment solvent, as long as the effects of the present invention are not inhibited. Examples of the additive include those described above.

[0149] The content of the additive is less than 5% by mass, less than 4% by mass, less than 2% by mass, less than 1% by mass, less than 0.9% by mass, less than 0.5% by mass, less than 0.4% by mass, less than 0.2% by mass, less than 0.1% by mass, less than 0.09% by mass, less than 0.05% by mass, less than 0.04% by mass, less than 0.02% by mass, less than 0.01% by mass, 0% by mass, etc., with respect to 100% by mass of any one of the components (A) to (D).

[0150] Regarding the dispersion (emulsion), it may be contained in a larger amount than the content of the above-mentioned additive. The upper and lower limits of the content of the dispersion (emulsion) with respect to 100% by mass of the negative electrode slurry for lithium-ion batteries are exemplified by 20, 19, 17, 15, 13, 10, 9, 7, 5, 4, 2, 1, 0% by mass, etc. In one embodiment, from the viewpoints of electrode flexibility and discharge capacity retention rate, the addition amount of the above-mentioned dispersion (emulsion) with respect to 100% by mass of the above-mentioned aqueous solution or the negative electrode slurry for lithium-ion batteries is preferably less than 5% by mass.

[0151] The upper and lower limits of the pH of the above-mentioned slurry are exemplified by 9, 8.9, 8.5, 8, 7.9, 7.7, 7.5, 7.3, 7.1, 7, 6.9, 6.7, 6.5, 6.3, 6, 5.9, 5.6, 5.5, 5.4, 5.2, 5.1, 5, etc.

[0152] The above-mentioned slurry is produced by mixing the components (A), (B), (C), (D), and water, and, if necessary, a conductive auxiliary agent other than the component (D), a slurry viscosity-adjusting solvent, and an additive.

[0153] Examples of the mixing means of the slurry include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, a Hobart mixer, etc.

[0154] [Negative electrode for lithium-ion battery] The present disclosure provides a negative electrode for a lithium-ion battery, which is obtained by applying the negative electrode slurry for a lithium-ion battery to a current collector and drying and curing the applied slurry. The negative electrode for a lithium-ion battery has a cured product of the negative electrode slurry for a lithium-ion battery on the surface of the current collector.

[0155] As the current collector, various known ones can be used without particular limitation. The material of the current collector is not particularly limited, and examples include metal materials such as copper, iron, aluminum, nickel, stainless steel, nickel-plated steel, and carbon materials such as carbon cloth and carbon paper. The form of the current collector is also not particularly limited. In the case of a metal material, examples include a metal foil, a metal cylinder, a metal coil, and a metal plate, and in the case of a carbon material, examples include a carbon plate, a carbon thin film, and a carbon cylinder. Among them, when using a negative electrode active material as the negative electrode, a copper foil is preferable as the current collector because it is currently used in industrialized products.

[0156] The coating means is not particularly limited, and examples include conventionally known coating devices such as a comma coater, a gravure coater, a microgravure coater, a die coater, and a bar coater.

[0157] The drying means is also not particularly limited. The temperature is preferably 60 to 200°C, more preferably 60 to 180°C. The atmosphere may be dry air or an inert atmosphere.

[0158] The thickness of the negative electrode (cured product) is not particularly limited, but is preferably 5 to 300 μm, more preferably 10 to 250 μm. By setting the thickness within the above range, it is easier to obtain a sufficient function of lithium absorption and release with respect to a high-density current value.

[0159] [Lithium-ion battery] The present disclosure provides a lithium-ion battery including the negative electrode for a lithium-ion battery. The battery also includes an electrolyte solution and a packaging material, which are not particularly limited.

[0160] Examples of the electrolyte solution include a non-aqueous electrolyte solution in which a supporting electrolyte is dissolved in a non-aqueous solvent. Further, the non-aqueous electrolyte solution may include a film-forming agent.

[0161] The non-aqueous solvent can be any of various known ones without particular limitation, and it may be used alone or in combination of two or more. Examples of the non-aqueous solvent include chain carbonate solvents such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; cyclic carbonate solvents such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain ether solvents such as 1,2-dimethoxyethane; cyclic ether solvents such as tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, and 1,3-dioxolane; chain ester solvents such as methyl formate, methyl acetate, and methyl propionate; cyclic ester solvents such as γ-butyrolactone and γ-valerolactone; and acetonitrile. Among these, a combination of a mixed solvent containing cyclic carbonate and chain carbonate is preferable.

[0162] As the supporting electrolyte, a lithium salt is used. The lithium salt can be any of various known ones without particular limitation, and it may be used alone or in combination of two or more. Examples of the supporting electrolyte include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. Among them, LiPF6, LiClO4, and CF3SO3Li, which are easily soluble in the solvent and exhibit a high degree of dissociation, are preferable. Since the higher the degree of dissociation of the supporting electrolyte used, the higher the lithium ion conductivity, the lithium ion conductivity can be adjusted by the type of the supporting electrolyte.

[0163] The film-forming agent can be any of various known ones without particular limitation, and it may be used alone or in combination of two or more. Examples of the film-forming agent include carbonate compounds such as vinylene carbonate, vinyl ethylene carbonate, vinyl ethyl carbonate, methyl phenyl carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; alkene sulfides such as ethylene sulfide and propylene sulfide; sultone compounds such as 1,3-propane sultone and 1,4-butane sultone; and acid anhydrides such as maleic anhydride and succinic anhydride. The content of the film-forming agent in the electrolyte solution is not particularly limited, but is preferably 10% by mass or less, 8% by mass or less, 5% by mass or less, and 2% by mass or less in this order. By setting the content to 10% by mass or less, it becomes easier to obtain advantages of the film-forming agent such as suppression of the initial irreversible capacity and improvement of low-temperature characteristics and rate characteristics.

[0164] The form of the above lithium-ion battery is not particularly limited. Examples of the form of the lithium-ion battery include a cylinder type in which a sheet electrode and a separator are spiral, a cylinder type of 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 the batteries of these forms in an arbitrary exterior case, they can be used in an arbitrary shape such as a coin type, a cylindrical type, or a square type.

[0165] The manufacturing method of the above lithium-ion battery is not particularly limited, and it may be assembled by an appropriate procedure according to the structure of the battery. Examples of the manufacturing method of the lithium-ion battery include the method described in JP-A-2013-089437. A battery can be manufactured by placing a negative electrode on an exterior case, providing an electrolytic solution and a separator thereon, and further placing a positive electrode so as to face the negative electrode, and fixing it with a gasket and a sealing plate.

Examples

[0166] Hereinafter, the present invention will be specifically described through Examples and Comparative Examples. However, the descriptions in the above-mentioned preferred embodiments and the following examples are provided for illustrative purposes only and not for the purpose of limiting the present invention. Therefore, the scope of the present invention is not limited to the embodiments or examples specifically described in this specification, but is limited only by the scope of the claims. Also, in each of the examples and comparative examples, unless otherwise specified, numerical values such as parts and % are based on mass.

[0167] Example 1-1 <Production of water-soluble polymer (A)> Into a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, 1228 g of ion-exchanged water, 189.8 g (2.10 mol) of 80% acrylic acid, and 0.33 g (0.0021 mol) of sodium methallylsulfonate were added. After removing the oxygen in the reaction system through nitrogen gas, the temperature was raised to 50°C. Then, 1.4 g of 2,2'-azobis-2-amidinopropane dihydrochloride (product name "NC-32" manufactured by Nippon Shokubai Co., Ltd.) and 15 g of ion-exchanged water were added, and the temperature was raised to 80°C and reacted for 3 hours. Thereafter, 140.3 g (1.68 mol) of a 48% aqueous sodium hydroxide solution was added as a neutralizing agent and stirred to obtain an aqueous solution containing a water-soluble polymer (A) with a neutralization rate of 80%.

[0168] <Production of hydrolyzed partial condensate (B) of amino group-containing trialkoxysilane> Into a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, 100 g of ion-exchanged water, 100 g of methanol, 1.23 g of nitric acid, and 200 g of 3-aminopropyltrimethoxysilane (product name "KBM-903" manufactured by Shin-Etsu Chemical Co., Ltd.) were added and reacted at 25°C for 0.5 hour to obtain a homogeneous aqueous solution containing a hydrolyzed partial condensate (B) of amino group-containing trialkoxysilane with a condensation degree of 1.4 and a weight average molecular weight of 160.

[0169] <Production of an aqueous binder solution for lithium-ion batteries> Into a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, 10 parts by mass of a hydrolyzed partial condensate (B) of an amino group-containing trialkoxysilane was added to 90 parts by mass of a water-soluble polymer (A), and the mixture was stirred for 30 minutes to obtain an aqueous binder solution for a lithium-ion battery. The B-type viscosity of this aqueous solution at 25°C was 12,810 mPa·s, and the pH was 7.1.

[0170] Examples 1 other than Example 1-1 were the same as Example 1-1 except that in the above Example 1-1, the monomer composition, the amount of the neutralizing agent, and the amount of the hydrolyzed partial condensate (B) of the amino group-containing trialkoxysilane were changed to those shown in Table 1, and an aqueous binder solution for a lithium-ion battery containing a water-soluble polymer (A) and a hydrolyzed partial condensate (B) of an amino group-containing trialkoxysilane was obtained.

[0171] Comparative Example 1-1 Into a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, 1228 g of ion-exchanged water, 189.8 g (2.10 mol) of 80% acrylic acid, and 0.33 g (0.0021 mol) of sodium methallylsulfonate were placed. After removing oxygen in the reaction system through nitrogen gas, the temperature was raised to 50°C. Then, 1.4 g of 2,2'-azobis-2-amidinopropane dihydrochloride (product name "NC-32" manufactured by Nippon Chemical Co., Ltd.) and 15 g of ion-exchanged water were added, and the temperature was raised to 80°C and the reaction was carried out for 3 hours. Thereafter, 140.3 g (1.68 mol) of a 48% aqueous sodium hydroxide solution was added as a neutralizing agent and stirred to obtain an aqueous solution containing a water-soluble polymer. The B-type viscosity of this aqueous solution at 25°C was 12,520 mPa·s, and the pH was 6.1.

[0172] Comparative Examples 1 other than the above Comparative Example 1-1 were the same as Example 1-1 except that the monomer composition, the amount of the neutralizing agent, and the amount of the hydrolyzed partial condensate (B) of the amino group-containing trialkoxysilane were changed to those shown in Table 1, and an aqueous binder solution for a lithium-ion battery was obtained.

Table 1

[0173] Glass transition temperature The value calculated based on Fox's equation.

[0174] Weight average molecular weight The weight average molecular weight was determined as the value in terms of polyacrylic acid measured by gel permeation chromatography (GPC) under a 0.2 M phosphate buffer / acetonitrile solution (90 / 10, pH 8.0). The GPC apparatus used was HLC-8220 (manufactured by Tosoh Corporation), and the column used was SB-806M-HQ (manufactured by SHODEX).

[0175] pH The pH of each binder aqueous solution was measured at 25 °C using a glass electrode pH meter (product name "Handy pH Meter D-52", manufactured by Horiba, Ltd.).

[0176] B-type viscosity The viscosity of each binder aqueous solution was measured at 25 °C using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., product name "B-type viscometer TVB-10M") under the following conditions. When the viscosity is less than 1,000 to 10,000 mPa·s: Use No. 3 rotor, rotation speed 12 rpm. When the viscosity is 10,000 mPa·s or more: Use No. 3 rotor, rotation speed 6 rpm.

[0177] Manufacture of conductive carbon assistant paste Example 2-1 Using a commercially available rotation and revolution mixer (product name: "Awatori Ren Taro", manufactured by Shinchi Co., Ltd.), 40 parts by mass of a binder aqueous solution for a lithium ion battery containing the water-soluble polymer (A) obtained in Example 1-1 and the hydrolyzed partial condensate (B) of an amino group-containing trialkoxysilane in terms of solid content was placed in a container dedicated to the mixer, and 60 parts by mass of carbon black (manufactured by Imerys C.C. Japan Co., Ltd., "Super C65") having a zeta potential of 16 mV at pH 6.1 was added thereto. Ion-exchanged water was added thereto so that the solid content concentration became 13.5%, and the container was set in the above rotation and revolution mixer. Next, it was kneaded at 2000 rpm for 10 minutes to obtain a conductive carbon auxiliary agent paste.

[0178] The above zeta potential was measured at 25 °C and pH 6.1 using a zeta potential and particle size measurement system (product name: "ELSZ-1000Z", manufactured by Otsuka Electronics Co., Ltd.).

[0179] In Examples 2 other than Example 2-1 and Comparative Example 2, conductive carbon auxiliary agent pastes were prepared in the same manner as in Example 2-1, except that the composition was changed to that shown in the following table in Example 2-1.

[0180] <Initial dispersion test of conductive carbon auxiliary agent paste> Using a commercially available laser diffraction / scattering particle size distribution measuring device (product name: "LA-960", manufactured by Horiba), the median diameters "D50" and "D90" of the conductive carbon auxiliary agent paste obtained in Example 2-1 were measured. The higher the measured values of "D50" and "D90", the worse the initial dispersibility of the conductive auxiliary agent and the more it is aggregated. The lower the values of "D50" and "D90", the better the initial dispersibility of the conductive auxiliary agent. The numerical value of the median diameter "D50" was evaluated according to the following evaluation criteria. A: 3.5 μm or less B: Larger than 3.5 μm The numerical value of "D90" was evaluated according to the following evaluation criteria. A: 7.0 μm or less B: Larger than 7.0 μm

[0181] <Dispersion Stability Test of Conductive Carbon Auxiliary Agent Paste> After allowing the conductive carbon auxiliary agent paste obtained in Example 2-1 to stand at room temperature for 24 hours, the median diameters “D50” and “D90” were measured. The greater the change in the measured values of “D50” and “D90”, the worse the dispersion stability of the conductive carbon auxiliary agent, indicating aggregation. The smaller the change in the values of “D50” and “D90”, the better the dispersion stability of the conductive carbon auxiliary agent. The change rates of “D50” and “D90” were calculated using the following formula and evaluated according to the following evaluation criteria. Change rate of “D50” (%) = [((D50 of the conductive carbon auxiliary agent paste after 24 hours) - (D50 of the conductive carbon auxiliary agent paste after the initial dispersion test)) / (D50 of the conductive carbon auxiliary agent paste after the initial dispersion test)] × 100 Change rate of “D90” (%) = [((D90 of the conductive carbon auxiliary agent paste after 24 hours) - (D90 of the conductive carbon auxiliary agent paste after the initial dispersion test)) / (D90 of the conductive carbon auxiliary agent paste after the initial dispersion test)] × 100 A: Less than ±40% B: ±40% or more

Table 2

[0182] Manufacture, Cell Fabrication, and Evaluation of Anode Slurry <Manufacture of Anode Slurry> Example 3-1 A slurry was prepared using a commercially available homodisper (Model 2.5, manufactured by Primix Corporation). As the container, a mayonnaise bottle was used. 5.0 parts by mass of the aqueous binder solution for lithium ion batteries containing the water-soluble polymer (A) and the hydrolyzed partial condensate (B) of the amino group-containing trialkoxysilane obtained in Example 1-1 in terms of solid content, 95 parts by mass of graphite with a D50 (median diameter) of 20 μm, 5 parts by mass of silicon monoxide particles with a D50 (median diameter) of 5 μm (“CC powder”, manufactured by Osaka Titanium Technologies Co., Ltd.), and 1 part by mass of a conductive carbon assistant (“Super C65”, manufactured by Imerys C.C. Japan Co., Ltd.) were mixed. Ion-exchanged water was added thereto so that the solid content concentration became 47%, and the container was set in the above homodisper. Then, it was kneaded at 2000 rpm for 30 minutes. Thereafter, defoaming was performed for 1 minute using a rotation-revolution mixer (“Avatori Rettaro”, manufactured by Shin-Kee Co., Ltd.) to obtain a slurry for the negative electrode.

[0183] In Examples 3 other than Example 3-1 and Comparative Example 3, slurries were prepared in the same manner as Example 3-1, except that the composition was changed to that shown in the following table in Example 3-1.

[0184] <Storage Stability Test of Slurry for Negative Electrode> The storage stability immediately after slurry preparation was visually evaluated according to the following criteria. A: The whole is a homogeneous paste-like state, there is no liquid separation, and no aggregates are observed. B: The whole is a substantially homogeneous paste-like state, slight liquid separation is observed, but no aggregates are observed. C: A small amount of aggregates and a lot of liquid separation are observed at the bottom of the container.

[0185] <Manufacture of Negative Electrode> On the surface of the current collector made of copper foil, the above slurry for lithium ion batteries was uniformly applied by the doctor blade method so that the film thickness after drying was 170 μm, dried at 80 °C for 30 minutes, and then heat-treated at 150 °C / vacuum for 120 minutes. Thereafter, the density of the film (negative electrode active material layer) was 1.5 g / cm 3The negative electrode was obtained by pressing with a roll press so as to achieve this.

[0186] <Manufacture of Positive Electrode> As the positive electrode active material, LiNi 0.5 Co 0.2 Mn 0.3 O2, acetylene black as a conductive assistant, and polyvinylidene fluoride (PVDF) as a binder were mixed in amounts of 88 parts by mass, 6 parts by mass, and 6 parts by mass, respectively. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to produce a positive electrode slurry for a lithium-ion battery. The positive electrode slurry for the lithium-ion battery was uniformly coated on the surface of a current collector made of aluminum foil by the doctor blade method so that the film thickness after drying would be 110 μm, dried at 150 °C for 30 minutes, and then heat-treated at 150 °C / vacuum for 120 minutes. Thereafter, the positive electrode was obtained by pressing with a roll press so as to achieve a density of 3.0 g / cm 3 for the film (positive electrode active material layer).

[0187] <Evaluation of Electrode Flexibility> The negative electrode was cut into a width of 10 mm and a length of 70 mm, and wound around a Teflon (registered trademark) rod with a diameter of 30 mmφ with the active material layer on the outside, and the state of the surface of the active material layer was observed and evaluated according to the following criteria. A: No cracks or peeling occurred in the active material layer adhered to the current collector. B: Cracks were observed in the active material layer adhered to the current collector, but no peeling was recognized. C: Cracks were observed in the active material layer adhered to the current collector, and peeling was recognized. Electrodes with high electrode flexibility are less likely to cause problems such as curling, cracking, and loss of active material in the electrode manufacturing process. On the other hand, electrodes with low electrode flexibility are highly likely to cause problems such as curling, cracking, and loss of active material in the electrode manufacturing process, and tend to be a factor in reducing the discharge capacity retention rate.

[0188] <Assembly of Lithium Half-Cell> In an argon-replaced glove box, the negative electrode and the positive electrode, which were punched and formed into a diameter of 16 mm, were placed inside the packing on the Al-made lower lid of a test cell (manufactured by Nippon Tomcell Co., Ltd.). Next, a separator (manufactured by CS TECH CO., LTD, trade name "Selion P2010") made of a polypropylene porous membrane punched into a diameter of 24 mm was placed. Further, after injecting 500 μL of electrolyte so that air did not enter, a commercially available metallic lithium foil punched and formed into a diameter of 16 mm was placed, and the outer body of the test cell was closed and sealed with screws to assemble a lithium half cell. The electrolyte used here is a solution in which LiPF6 is dissolved at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1 / 1 (mass ratio).

[0189] <Charge-discharge measurement> The lithium half cell was placed in a constant temperature bath at 25 °C, and charging was started at a constant current (0.1C). When the voltage reached 0.01V, charging was completed (cut-off). Next, discharging was started at a constant current (0.1C), and the charge-discharge was repeated 30 times with the time point when the voltage reached 1.0V as the end of discharge (cut-off). In addition, under the above measurement conditions, "1C" indicates the current value at which a cell having a certain capacitance is discharged at a constant current and the discharge ends in 1 hour. For example, "0.1C" means the current value at which the discharge ends in 10 hours, and "10C" means the current value at which the discharge is completed in 0.1 hours.

[0190] <Discharge capacity retention rate> The discharge capacity retention rate was determined from the following formula. Discharge capacity retention rate = {(Discharge capacity at the 30th cycle) / (Discharge capacity at the 1st cycle)} × 100 (%)

Table 3

Claims

1. A polymer of a monomer group containing 15 to 99.9 mol% of an unsaturated carboxylic acid or its inorganic salt, based on 100 mol% of the monomer group, a water-soluble polymer (A) having a glass transition temperature of less than 100°C, and a hydrolyzed partial condensate (B) of an amino group-containing trialkoxysilane, a binder aqueous solution for a lithium-ion battery having a pH of 5 or more.

2. The binder aqueous solution for a lithium-ion battery according to Claim 1, containing 15 to 60 mol% of a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms, based on 100 mol% of the monomer group.

3. The binder aqueous solution for a lithium-ion battery according to Claim 1 or 2, wherein the molar ratio (amino group / carboxyl group) of the amino group of the hydrolyzed partial condensate (B) of the amino group-containing trialkoxysilane to the carboxyl group of the water-soluble polymer (A) is 0.05 or more.

4. A negative electrode slurry for a lithium-ion battery, containing a polymer of a monomer group containing 15 to 99.9 mol% of an unsaturated carboxylic acid or its inorganic salt, based on 100 mol% of the monomer group, a water-soluble polymer (A) having a glass transition temperature of less than 100°C, a hydrolyzed partial condensate (B) of an amino group-containing trialkoxysilane, a negative electrode active material (C), and a conductive carbon assistant (D) having a zeta potential of 0 mV or more at pH 5 to 7.

5. A negative electrode for a lithium-ion battery obtained by applying the negative electrode slurry for a lithium-ion battery according to Claim 4 to a current collector and drying and curing it.

6. A lithium-ion battery including the negative electrode for a lithium-ion battery according to Claim 5. ​ ​

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