Aqueous binder solution for lithium ion battery electrodes, slurry for lithium ion battery negative electrodes, negative electrodes for lithium ion batteries, and lithium ion batteries

Abstract

To provide a binder aqueous solution for a lithium ion battery electrode, a slurry for a lithium ion battery negative electrode, a negative electrode for a lithium ion battery, and a lithium ion battery.SOLUTION: A binder aqueous solution for a lithium ion battery is provided according to a disclosure hereof. The binder aqueous solution comprises: an acidic group-containing water-soluble polymer (A), which is a polymer of a group of monomers including 30 to 90 mol% of a (meth)acryl amide group-containing compound (a), 3 to 20 mol% of an unsaturated organic acid (b), and 5 to 40 mol% of alkali metal or alkali earth metal salt (c) of unsaturated organic acid to 100 mol% of a group of monomers; and an amino group-containing water-soluble polymer (B) of which the 1-mass% aqueous solution is pH9 or higher.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to an aqueous binder solution for a lithium ion battery electrode, a slurry for a lithium ion battery negative electrode, 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, for the purpose of further improving the performance of lithium ion batteries, improvements in battery components such as electrodes have been studied.

[0003] Both the positive and negative electrodes 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, in lithium ion battery electrodes, various electrode active materials have been proposed 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 (springback property) from the initial stage of repeated charge and discharge, and it is likely to deteriorate the 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 crosslinking 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 crosslinking agent usually causes a crosslinking reaction in the drying process after applying the slurry composition to the current collector, and forms crosslinks between particles of the particulate resin and the like. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-118908 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-106488 [Patent Document 3] International Publication No. 2015 / 098507 Summary of the Invention [Problem to be solved by the invention]

[0007] However, crosslinking with a crosslinking agent can reduce the flexibility of the binder resin, resulting in poor adhesion to the electrode. Furthermore, prior art binders lack sufficient dispersion stability. Furthermore, binders are required to provide good initial coulombic efficiency for lithium-ion batteries.

[0008] Therefore, an object of the present invention is to provide an aqueous binder solution for lithium ion batteries that imparts good initial coulombic efficiency to the lithium ion battery, good electrode adhesion to the electrode, and good dispersion stability to the slurry. [Means for solving the problem]

[0009] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved.

[0010] The present disclosure provides the following: (Item 1) With respect to 100 mol% of the monomer group, 30 to 90 mol % of a (meth)acrylamide group-containing compound (a), 3 to 20 mol % of an unsaturated organic acid (b), and It is a polymer of a monomer group containing 5 to 40 mol % of an alkali metal or alkaline earth metal salt of an unsaturated organic acid (c). A water-soluble polymer (A) containing an acidic group, and An amino group-containing water-soluble polymer (B) having a pH of 9 or more in a 1 mass% aqueous solution A binder aqueous solution for a lithium-ion battery, comprising (Item 2) The binder aqueous solution for a lithium-ion battery according to the above item, wherein the molar ratio (acidic group / amino group) of the acidic group of the acidic group-containing water-soluble polymer (A) to the amino group of the amino group-containing water-soluble polymer (B) is 1 to 15. (Item 3) The binder aqueous solution for a lithium-ion battery according to any one of the above items, wherein the molecular weight of the amino group-containing water-soluble polymer (B) is 1,600 to 50,000. (Item 4) The binder aqueous solution for a lithium-ion battery according to any one of the above items, wherein the residue ratio when the amino group-containing water-soluble polymer (B) is impregnated in dimethyl carbonate at 25 ° C for 24 hours is 20 mass% or more. (Item 5) The binder aqueous solution for a lithium-ion battery according to any one of the above items, wherein the amino group-containing water-soluble polymer (B) is polyallylamine. (Item 6) A slurry for a lithium-ion battery negative electrode, comprising the binder aqueous solution for a lithium-ion battery according to any one of the above items, and A negative electrode active material (C). (Item 7) A negative electrode for a lithium-ion battery obtained by applying and drying the slurry for a lithium-ion battery negative electrode according to the above item on a metal foil. (Item 8) A lithium-ion battery, comprising 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 can be provided in combination in addition to the explicitly described combinations.

Advantages of the Invention

[0012] The binder aqueous solution for a lithium-ion battery according to this embodiment can impart excellent dispersion stability to the slurry for a lithium-ion battery negative electrode. Further, the slurry for a lithium-ion battery negative electrode according to this embodiment has excellent dispersion stability. Furthermore, the negative electrode according to this embodiment has excellent adhesion. And the battery according to this embodiment has excellent initial Coulombic efficiency.

Mode for Carrying Out the Invention

[0013] Throughout the present disclosure, the ranges of numerical values such as physical property values and contents can be set as appropriate (for example, selected from the upper and lower limit values described in each of the following items). Specifically, for the numerical value α, when A4, A3, A2, A1 (where A4 > A3 > A2 > A1) etc. are exemplified as the upper and lower limits of the numerical value α, the range of the numerical value α is 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. are exemplified.

[0014] [Binder Aqueous Solution for Lithium-Ion Battery Electrode] The present disclosure is based on 100 mol% of the monomer group, (a) a (meth)acrylamide group-containing compound in an amount of 30 to 90 mol%, an unsaturated organic acid (b) in an amount of 3 to 20 mol%, and an alkali metal or alkaline earth metal salt (c) of an unsaturated organic acid in an amount of 5 to 40 mol%, and is a polymer of a monomer group, an acidic group-containing water-soluble polymer (A), and an amino group-containing water-soluble polymer (B) having a pH of 9 or more in a 1 mass% aqueous solution is provided as a binder aqueous solution for a lithium-ion battery.

[0015] <Acidic group-containing water-soluble polymer: also referred to as component (A)> In the present disclosure, the "acidic group" is a group having a hydrogen atom that can be ionized as a hydrogen ion, and means a group in which no hydrogen atom is ionized at all. Examples of the acidic group include a carboxyl group (-CO2H), a sulfonic acid group (-SO3H), a phosphoric acid group (-PO3H), etc.

[0016] On the one hand, an "acid group" is a group having a hydrogen atom that can be ionized as a hydrogen ion, and means a group in which one or more hydrogen atoms are ionized. The acid group is -CO2 - , -SO3 - , -PO3 - etc. are exemplified.

[0017] 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% by mass (less than 2.5 mg).

[0018] 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, the viscosity required for coating on the current collector cannot be imparted to the slurry.

[0019] 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% by mass, 0% by mass, etc.

[0020] 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".

[0021] <Compound (a) containing a (meth)acrylamide group: also referred to as component (a)> 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.

[0022] In one embodiment, the (meth)acrylamide group-containing compound has the following structural formula [Chemical formula] (wherein, R 1 is a hydrogen atom or a methyl group, and 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 that forms a ring structure, and 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 includes a morpholyl group, etc.).) is represented by

[0023] Examples of the alkyl group include a linear alkyl group, a branched alkyl group, a cycloalkyl group, etc.

[0024] The linear alkyl group is represented by the general formula -C n H 2n+1 (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, an n-decylmethyl group, etc.

[0025] The branched alkyl group is a group in which at least one hydrogen atom 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, a trimethylhexyl group, etc.

[0026] Examples of the cycloalkyl group include a monocyclic cycloalkyl group, a bridged ring cycloalkyl group, and a condensed ring cycloalkyl group.

[0027] In this disclosure, a monocyclic ring refers to a ring structure formed by a covalent carbon bond and having no internal bridges. A fused ring refers to a ring structure in which two or more monocyclic rings share two atoms (i.e., each ring shares (fused) only one edge with another). A bridged ring refers to a ring structure in which two or more monocyclic rings share three or more atoms.

[0028] 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.

[0029] Examples of the bridged ring cycloalkyl group include a tricyclodecyl group, an adamantyl group, and a norbornyl group.

[0030] The fused ring cycloalkyl group is exemplified by a bicyclodecyl group.

[0031] Examples of the (meth)acrylamide group-containing compound (a) include (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 salts include dimethylaminopropyl(meth)acrylamide methyl chloride quaternary salt, dimethylaminoethyl(meth)acrylate benzyl chloride quaternary salt, etc. Among these, the use of (meth)acrylamide, particularly acrylamide, not only reduces water absorption while maintaining water solubility, but also reduces irreversible capacity, and enables the production of a binder that has high interaction with electrode active materials, high slurry dispersibility, and high binding strength between electrode active materials within an electrode.

[0032] The upper and lower limits of the content of the (meth)acrylamide group-containing compound relative to 100 mol% of the monomer group are exemplified by 90, 89.95, 85, 80, 75, 70, 65, 60, 59.95, 55, 50, 45, 40, 35, 30 mol%, etc. In one embodiment, the above content is preferably 30 to 90 mol%.

[0033] The upper and lower limits of the content of the (meth)acrylamide group-containing compound relative to 100 mass% of the monomer group are exemplified by 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20 mass%, etc. In one embodiment, the above content is preferably 20 to 90 mass%.

[0034] <Unsaturated organic acid (b): Also referred to as component (b)> In the present disclosure, the unsaturated organic acid means a compound having an acidic group and a polymerizable unsaturated bond. The unsaturated organic acid may be used alone or in combination of two or more.

[0035] The acidic group of the unsaturated organic acid (b) corresponds to the acidic group of the component (A). The acidic group contained in the structural unit derived from the component (b) in the component (A), that is, the acidic group of the component (A), interacts with the amino group of the amino group-containing water-soluble polymer (B).

[0036] Examples of the unsaturated organic acid include unsaturated carboxylic acids, unsaturated sulfonic acids, unsaturated phosphoric acids, etc.

[0037] Examples of the unsaturated carboxylic acid include (meth)acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, etc.

[0038] 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.

[0039] 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-hydroxypropanephosphoric acid, and the like.

[0040] In the present disclosure, a compound that falls under both (meth)acrylamide group-containing compounds and unsaturated organic acids is regarded as an unsaturated organic acid.

[0041] Examples of the upper and lower limits of the content of unsaturated organic acid (b) with respect to 100 mol% of the monomer group include 20, 19, 17, 15, 14, 12, 11, 10, 9, 7, 5, 4, 3 mol%, etc. In one embodiment, from the viewpoint of suppressing insolubilization, gelation, reduction in slurry dispersibility, reduction in electrode adhesion, and reduction in irreversible capacity, the above content is more preferably 3 to 20 mol%.

[0042] Examples of the upper and lower limits of the content of unsaturated organic acid (b) with respect to 100 mass% of the monomer group include 30, 29, 27, 25, 23, 20, 19, 17, 15, 13, 10, 9, 7, 5, 3, 2 mass%, etc. In one embodiment, the above content is preferably 2 to 30 mass%.

[0043] The upper and lower limits of the number of moles derived from component (b) per 1 g of component (A) are 1.8, 1.7, 1.5, 1.49, 1.4, 1.3, 1.28, 1.2, 1, 0.9, 0.7, 0.69, 0.5, 0.41, 0.4, 0.38, 0.3 mmol / g, etc. In one embodiment, the number of moles is preferably 0.3 to 1.8 mmol / g.

[0044] <Alkali metal or alkaline earth metal salt of unsaturated organic acid (c): Also referred to as component (c)> The alkali metal or alkaline earth metal salts of unsaturated organic acids may be used alone or in combination of two or more.

[0045] Examples of unsaturated organic acids include those mentioned above.

[0046] Examples of the alkali metal include lithium, sodium, and potassium.

[0047] Examples of alkaline earth metals include magnesium and calcium.

[0048] The upper and lower limits of the content of the alkali metal or alkaline earth metal salt of the unsaturated organic acid relative to 100 mol% of the monomer group are, for example, 40, 35, 30, 25, 20, 15, 10, 5, 0 mol%, etc. In one embodiment, from the viewpoint of improving water solubility and slurry dispersibility and suppressing a decrease in electrode adhesion and a deterioration in water absorption, the content is preferably 5 to 40 mol%.

[0049] The upper and lower limits of the content of the alkali metal or alkaline earth metal salt of the unsaturated organic acid relative to 100% by mass of the monomer group are 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5% by mass, etc. In one embodiment, the content is preferably 5 to 70% by mass.

[0050] <Hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms> The hydroxyalkyl (meth)acrylate having a hydroxyalkyl group with 2 to 4 carbon atoms may be used alone or in combination of two or more thereof.

[0051] 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.

[0052] Examples of the hydroxyalkyl (meth)acrylate 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.

[0053] Examples of the upper and lower limits of the content of the hydroxyalkyl (meth)acrylate having a hydroxyalkyl group with 2 to 4 carbon atoms with respect 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%.

[0054] The upper and lower limits of the content of the hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms relative to 100% by mass of the monomer group are, for example, 40, 35, 30, 25, 20, 15, 10, 5, 0% by mass, etc. In one embodiment, the content is preferably 0 to 40% by mass.

[0055] <α,β-unsaturated nitrile> The α,β-unsaturated nitriles may be used alone or in combination of two or more thereof. The α,β-unsaturated nitriles are preferably used for the purpose of imparting flexibility to the electrode.

[0056] 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 preferred, and acrylonitrile is particularly preferred.

[0057] The upper and lower limits of the content of the α,β-unsaturated nitrile relative to 100 mol% of the monomer group are, for example, 40, 35, 30, 25, 20, 15, 10, 5, 0 mol%, etc. In one embodiment, the content is preferably 0 to 40 mol%.

[0058] The upper and lower limits of the content of the α,β-unsaturated nitrile relative to 100% by mass of the monomer group are, for example, 30, 25, 20, 15, 10, 5, 0% by mass, etc. In one embodiment, the content is preferably 0 to 30% by mass.

[0059] <Relative ratio of monomer components> The upper and lower limits of the molar ratio of component (b) to component (a) contained in the monomer group [substance amount of component (b) / substance amount of component (a)] are exemplified as 0.67, 0.65, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.05, 0.03, etc. In one embodiment, the molar ratio is preferably 0.03 to 0.67.

[0060] The upper and lower limits of the molar ratio of component (c) to component (a) contained in the monomer group [(amount of substance of component (c)) / (amount of substance of component (a))] are exemplified by 1.33, 1.3, 1.2, 1.1, 1, 0.9, 0.7, 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.07, 0.05, etc. In one embodiment, the above molar ratio is preferably 0.05 to 1.33.

[0061] The upper and lower limits of the molar ratio of component (c) to component (b) contained in the monomer group [(amount of substance of component (c)) / (amount of substance of component (b))] are exemplified by 13.3, 13, 11, 10, 9, 7, 5, 4, 3, 2, 1, 0.9, 0.7, 0.5, 0.4, 0.3, 0.25, etc. In one embodiment, the above molar ratio is preferably 0.25 to 13.3.

[0062] The upper and lower limits of the mass ratio of component (b) to component (a) contained in the monomer group [(mass of component (b)) / (mass of component (a))] are exemplified by 1.5, 1, 0.9, 0.5, 0.2, 0.1, 0.09, 0.05, 0.04, 0.02, etc. In one embodiment, the above mass ratio is preferably 0.02 to 1.5.

[0063] The upper and lower limits of the mass ratio of component (c) to component (a) contained in the monomer group [(mass of component (c)) / (mass of component (a))] are exemplified by 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.5, 0.2, 0.1, 0.09, 0.05, etc. In one embodiment, the above mass ratio is preferably 0.05 to 3.5.

[0064] The upper and lower limits of the mass ratio of component (c) to component (b) contained in the monomer group [(mass of component (c)) / (mass of component (b))] are exemplified by 35, 30, 25, 20, 15, 10, 5, 2, 1.5, 1, 0.9, 0.5, 0.2, 0.16, etc. In one embodiment, the above mass ratio is preferably 0.16 to 35.

[0065] <The monomer not falling under any of the above: Also referred to as other components> In the above monomer group, monomers other than components (a) to (c), hydroxyalkyl (meth)acrylates having a hydroxyalkyl group with 2 to 4 carbon atoms, 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 components may be used alone or in combination of two or more.

[0066] Examples of the other components include hydroxyl group-free unsaturated carboxylic acid esters, conjugated dienes, aromatic vinyl compounds, and the like.

[0067] 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, and hydroxyl group-free substituted (meth)acrylic acid esters.

[0068] 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, and the like.

[0069] 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, and the like.

[0070] Examples of the hydroxyl group-free alicyclic (meth)acrylic acid ester include cyclohexyl (meth)acrylate, and the like.

[0071] 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 40 mol% (for example, less than 30, 20, 19, 15, 10, 5, 1 mol%, 0 mol%).

[0072] 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 40% by mass or less (for example, less than 30, 20, 19, 15, 10, 5, 1% by mass, 0% by mass).

[0073] Examples of the conjugated diene include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadiene, substituted and side-chain conjugated hexadiene, and the like.

[0074] From the viewpoint of the cycle characteristics of the lithium-ion battery, the content of the conjugated diene with respect to 100 mol% of the above monomer group is preferably less than 10 mol%, and more preferably 0 mol%.

[0075] 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 content is preferably 0 to 30% by mass.

[0076] Examples of the aromatic vinyl compound include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, and the like.

[0077] From the viewpoint of the cycle characteristics of the lithium-ion battery, the content of the aromatic vinyl compound with respect to 100 mol% of the above monomer group is preferably less than 10 mol%, and more preferably 0 mol%.

[0078] Examples of the upper and lower limits of the content of the aromatic vinyl compound relative to 100% by mass of the monomer group include 30, 20, 10, 5, 1, 0% by mass, etc. In one embodiment, the content is preferably 0 to 30% by mass.

[0079] Examples of the ratio of components other than the hydroxyl group-free unsaturated carboxylic acid ester, the conjugated diene, and the aromatic vinyl compound in the monomer group are less than 10 mol%, less than 5 mol%, less than 2 mol%, less than 1 mol%, less than 0.1 mol%, less than 0.01 mol%, 0 mol%, etc. relative to 100 mol% of the monomer group. Further, examples relative to 100% by mass of the 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 0.3% by mass, less than 0.1% by mass, less than 0.05% by mass, less than 0.01% by mass, 0% by mass, etc.

[0080] <Method for producing component (A)> (A) component can be synthesized by various known polymerization methods, preferably radical polymerization methods. Specifically, a radical polymerization initiator and, if necessary, a chain transfer agent are added to a monomer mixture containing the above components, and a 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.

[0081] Various known radical polymerization initiators are 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, relative to 100% by mass of the monomer group that gives the (A) component.

[0082] Before the radical polymerization reaction and / or when solubilizing the obtained component (A) in water, etc., 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. In that case, the pH is preferably 2 to 11. Also, for the same purpose, it is also possible to use ethylenediaminetetraacetic acid (EDTA) or its salts, etc., which are metal ion sequestering agents.

[0083] <Physical properties of component (A)> The upper and lower limits of the glass transition temperature of component (A) are exemplified by 160, 155, 150, 145, 140, 135, 130, 125, 120, 115, 110, 105, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 0 °C, etc. In one embodiment, 0 °C or higher is preferred, and 30 °C or higher is more preferred from the viewpoints of mechanical strength and heat resistance.

[0084] The glass transition temperature of component (A) can be adjusted by the monomer combination. In component (A), its glass transition temperature can be determined based on the following Fox's equation from the glass transition temperature (Tg) (absolute temperature: K) of the homopolymers of the monomers 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 to W n are the mass fractions of the respective monomers, and Tg1 to Tg n are the glass transition temperatures (K) of the homopolymers of the respective monomers]

[0085] For example, the glass transition temperature is 165°C for a homopolymer of acrylamide, 106°C for a homopolymer of acrylic acid, -15°C for a homopolymer of hydroxyethyl acrylate, and 105°C for a homopolymer of acrylonitrile. The monomer composition constituting component (A) can be determined so as to obtain a component with a desired glass transition temperature. The glass transition temperature of a homopolymer of a monomer can be measured, for example, by heating from -100°C to 300°C (heating rate: 10°C / min) using a DSC (differential scanning calorimeter), DTA (differential thermal analyzer), TMA (thermomechanical analyzer), or the like. Values listed in literature can also be used. Examples of literature include "Chemical Handbook, Basics II, Compiled by the Chemical Society of Japan (Revised 5th Edition)," p. 325.

[0086] The weight average molecular weight (Mw) of component (A) is not particularly limited, but examples of the upper and lower limits include 7 million, 6.5 million, 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, 250,000, 200,000, 150,000, and 100,000. In one embodiment, from the viewpoint of dispersion stability of the slurry, the Mw is preferably 100,000 to 7 million, and more preferably 350,000 to 6 million.

[0087] The number average molecular weight (Mn) of component (A) is not particularly limited, but examples of upper and lower limits include 6,000,000, 5,500,000, 5,000,000, 4,500,000, 4,000,000, 3,500,000, 3,000,000, 2,000,000, 1,500,000, 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, and 10,000. In one embodiment, the number average molecular weight (Mn) of component (A) is preferably 10,000 or greater.

[0088] The weight average molecular weight and number average molecular weight can be determined as values calculated as polyacrylic acid by, for example, gel permeation chromatography (GPC) in an appropriate solvent.

[0089] Examples of the upper and lower limits of the molecular weight distribution (Mw / Mn) of component (A) include 15, 14, 13, 11, 10, 9, 7.5, 5, 4, 3, 2.9, 2.5, 2, 1.5, 1.1, etc. In one embodiment, the molecular weight distribution (Mw / Mn) of component (A) is preferably from 1.1 to 15.

[0090] The B-type viscosity of an aqueous solution containing 13% by mass of component (A) is not particularly limited, and examples of the upper and lower limits thereof include 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 B-type viscosity is preferably from 100 to 100,000 mPa·s.

[0091] The B-type viscosity is measured by a B-type viscometer such as "B-type viscometer model BM" manufactured by Toki Sangyo Co., Ltd.

[0092] Examples of the upper and lower limits of the content of component (A) with respect to 100% by mass of the binder aqueous solution for lithium ion batteries include 20, 19, 15, 14, 12, 10, 9, 7, 6, 5% by mass, etc. In one embodiment, the content is preferably from 5 to 20% by mass.

[0093] An amino group-containing water-soluble polymer (B) having a pH of 9 or more in a 1% by mass aqueous solution (also referred to as component (B)) Component (B) may be used alone or in combination of two or more.

[0094] Examples of the upper and lower limits of the pH of a 1% by mass aqueous solution of the amino group-containing water-soluble polymer (B) include 14, 13.5, 13, 12.5, 12, 11.5, 11.4, 11.3, 11, 10.8, 10.5, 10, 9.5, 9, etc. In one embodiment, the pH is preferably 9 or more. The pH of a 1% by mass aqueous solution of the amino group-containing water-soluble polymer (B) is measured, for example, as follows. Dilute the aqueous solution of the amino group-containing water-soluble polymer (B) with ion-exchanged water so that it becomes 1% by mass, and measure it at 25 °C using a suitable glass electrode pH meter (for example, product name "Handy pH Meter D-52", manufactured by Horiba, Ltd.).

[0095] (B) The amino group of the component is -NR aa R ab (R aa 、R ab are each independently a hydrogen atom or an alkyl group. Note that -NR aa R ab is not the -NR aa R ab that constitutes the amide group (-CONR aa R ab ). In one embodiment, the amino group of the (B) component is preferably -NH2.

[0096] Examples of the amino group-containing water-soluble polymer include polyallylamine, polyethyleneimine; polyethyleneimine derivatives such as poly-N-hydroxylethyleneimine, carboxymethylated polyethyleneimine sodium salt; polypropyleneimine; polypropyleneimine derivatives such as poly-N-2-dihydroxypropylpropyleneimine; aminoethylated acrylic polymers obtained by aminoethylating acrylic polymers; cationized celluloses obtained by modifying cellulose derivatives (hydroxyethyl cellulose, carboxymethyl cellulose, etc.) with cationizing agents having substituted or unsubstituted amino groups. In one embodiment, the amino group-containing water-soluble polymer (B) is preferably polyallylamine.

[0097] <Physical properties of component (B)> Examples of upper and lower limits of the molecular weight of the amino group-containing water-soluble polymer (B) include 50,000, 45,000, 40,000, 35,000, 30,000, 25,000, 20,000, 15,000, 10,000, 9,000, 7,500, 5,000, 2,500, and 1,600. In one embodiment, the molecular weight of the amino group-containing water-soluble polymer (B) is preferably 1,600 to 50,000, from the viewpoints of providing a sufficient viscosity for the aqueous binder solution and preventing insolubilization in water when interacting with the acid group-containing water-soluble polymer (A).

[0098] In this disclosure, when simply referring to "molecular weight," it means either formula weight or number average molecular weight. When the structure of a compound can be unequivocally expressed by a specific chemical formula (i.e., the molecular weight distribution is 1), the molecular weight refers to the formula weight. On the other hand, when the structure of a compound cannot be unequivocally expressed by a specific chemical formula (i.e., the molecular weight distribution is greater than 1), the molecular weight refers to the number average molecular weight.

[0099] The molecular weight of the component (B) can be determined, for example, by gel permeation chromatography (GPC) in an appropriate solvent, as a polyethylene oxide equivalent value.

[0100] The upper and lower limits of the residue rate when the amino group-containing water-soluble polymer (B) is impregnated in dimethyl carbonate at 25° C. for 24 hours are exemplified as 100, 99, 98, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20 mass%, etc. In one embodiment, the residue rate when the amino group-containing water-soluble polymer (B) is impregnated in dimethyl carbonate at 25° C. for 24 hours is preferably 20 mass% or more, more preferably 50 mass% or more.

[0101] The residue rate after immersion in dimethyl carbonate at 25° C. for 24 hours is measured, for example, as follows. (1) The aqueous solution of the amino group-containing water-soluble polymer (B) is dried for 12 hours at 130°C in a circulating air dryer (manufactured by ADVANTEC, product name "DRS420DA") to obtain a solid or liquid sample of the amino group-containing water-soluble polymer (B). (2) Weigh 1 g of the obtained test piece into a petri dish, add 50 g of dimethyl carbonate, and let it stand at 25 °C for 24 hours. (3) After that, except for the supernatant amino group-containing water-soluble polymer (B), the residue is dried in a 130 °C circulating air dryer (product name "DRS420DA" manufactured by ADVANTEC) for 1 hour and its mass is measured. (4) Calculate the residue ratio when impregnated in dimethyl carbonate at 25 °C for 24 hours using the following formula. Residue ratio when impregnated in dimethyl carbonate at 25 °C for 24 hours = {(mass after impregnation in dimethyl carbonate and drying) / (mass before impregnation in dimethyl carbonate)} × 100 (%)

[0102] Examples of the upper and lower limits of the amine value of the amino group-containing water-soluble polymer (B) include 24, 23.5, 23.2, 23, 22, 20, 19, 18, 17.5, 17, 15, 13, 11, 10 mmol / g, etc. The above amine value is preferably 10 to 24 mmol / g.

[0103] The amine value is calculated as follows. (1) When the constituent monomers of the amino group-containing water-soluble polymer (B) are known Monomer A (molecular weight M A ) is used at A mol%, and monomer B (molecular weight M B ) is used at B mol%, it is calculated by the following formula. Amine value = 1000 / [〔M A × (A / 100)〕 + 〔M B × (B / 100)〕]

[0104] (2) When the constituent monomers of the amino group-containing water-soluble polymer (B) are unknown The value in mgKOH / g obtained according to the potentiometric titration method described in JIS K7237 (1995) is converted to mmol / g and determined as the amount per 1 g of the solid content of the amino group-containing water-soluble polymer (B).

[0105] Due to the water solubility of component (B), it can interact with component (A), which is also water-soluble.

[0106] Examples of the upper and lower limits of the content of component (B) with respect to 100% by mass of the binder aqueous solution for a lithium ion battery include 3, 2.9, 2.7, 2.5, 2.3, 2, 1.9, 1.7, 1.5, 1.3, 1, 0.9, 0.7, 0.5, 0.3, 0.1, 0.09, 0.07, 0.05% by mass, etc. In one embodiment, the above content is preferably 0.05 to 3% by mass.

[0107] Examples of the upper and lower limits of the mass ratio of component (A) to component (B) contained in the binder aqueous solution for a lithium ion battery include 400, 375, 350, 325, 300, 275, 250, 225, 200, 199, 195, 190, 180, 175, 150, 125, 100, 99, 95, 90, 85, 80, 75, 70, 66, 65, 60, 55, 50, 49, 45, 40, 35, 33, 32, 30, 25, 10, 5, 2, 1.6, etc. In one embodiment, the above mass ratio is preferably 1.6 to 400.

[0108] Examples of the upper and lower limits of the molar ratio (acidic group / amino group) of the acidic group of the water-soluble polymer (A) containing an acidic group to the amino group of the water-soluble polymer (B) containing an amino group include 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, etc. In one embodiment, the above molar ratio is preferably 1 to 15.

[0109] <Water> Examples of water include ultrapure water, pure water, distilled water, ion-exchanged water, and tap water, etc.

[0110] Examples of the upper and lower limits of the water content with respect to 100% by mass of the binder aqueous solution for a lithium ion battery include 95, 90, 85, 80% by mass, etc. In one embodiment, the water content with respect to 100% by mass of the binder aqueous solution for a lithium ion battery is preferably 80 to 95% by mass.

[0111] The upper and lower limits of the mass ratio of component (A) to water [component (A) / water] contained in the aqueous binder solution for lithium ion batteries are, for example, 0.25, 0.2, 0.15, 0.1, 0.05, etc. In one embodiment, the mass ratio is preferably 0.05 to 0.25.

[0112] The upper and lower limits of the mass ratio of component (B) to water [component (B) / water] contained in the aqueous binder solution for lithium ion batteries are, for example, 0.038, 0.03, 0.02, 0.01, 0.009, 0.005, 0.003, 0.001, 0.0009, 0.0007, 0.0005, etc. In one embodiment, the mass ratio is preferably 0.0005 to 0.038.

[0113] <Dispersion (emulsion)> In one embodiment, the aqueous binder solution for a lithium ion battery includes a dispersion (emulsion).

[0114] Dispersions (emulsions) include 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 latex, polymethyl methacrylate-but ... Examples include diene copolymer resin emulsion, acrylic resin emulsion, polyethylene, polypropylene, polyethylene terephthalate, polyamide (PA), polyimide (PI), polyamideimide (PAI), aromatic polyamide, alginic acid and its salts, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), and the like.

[0115] (A) component, the upper and lower limits of the content of the dispersion (emulsion) with respect to 100% by mass of the component, 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, from the viewpoints of springback resistance and discharge capacity retention rate, the above content is preferably 0 to 50% by mass.

[0116] <Polyvinylpyrrolidone> In one embodiment, the aqueous binder solution for the lithium ion battery contains polyvinylpyrrolidone.

[0117] (A) component, the upper and lower limits of the content of polyvinylpyrrolidone with respect to 100% by mass of the component, are exemplified by 10, 9, 7, 5, 4, 2, 1, 0% by mass, etc. In one embodiment, from the viewpoint of suppressing the rheological change of the slurry, the above content is preferably 0 to 10% by mass.

[0118] <Additive> The aqueous binder solution for the lithium ion battery may contain, as an additive, something that does not fall under any of the (A) component, (B) component, water, and dispersion (emulsion).

[0119] Examples of the additive include a dispersant, a leveling agent, an antioxidant, a thickener, etc.

[0120] 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 the (A) component or (B) component.

[0121] In addition, 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.

[0122] Examples of the dispersant include anionic dispersants, cationic dispersants, nonionic dispersants, polymer dispersants, etc.

[0123] Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants. By using a surfactant, repulsion generated during coating can be prevented, and the smoothness of the layer (coating layer) of the above slurry can be improved.

[0124] Examples of the antioxidant include phenol compounds, hydroquinone compounds, organic phosphorus compounds, sulfur compounds, phenylenediamine compounds, polymer-type phenol compounds, etc. The polymer-type phenol compound is a polymer having a phenol structure in the molecule. The weight average molecular weight of the polymer-type phenol compound is preferably 200 to 1000, more preferably 600 to 700.

[0125] Examples of the thickener 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 their ammonium salts and alkali metal salts; polyvinyl alcohols such as (modified) polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, and copolymers of maleic anhydride or maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, modified polyacrylic acid, oxidized starch, phosphate starch, casein, various modified starches, hydrogenated acrylonitrile-butadiene copolymers, etc.

[0126] The upper and lower limits of the B-type viscosity of an aqueous binder solution for a lithium-ion battery containing 1.5% by mass in total of component (A) and component (B) are exemplified by 100,000, 90,000, 80,000, 70,000, 60,000, 50,000, 40,000, 30,000, 25,000, 22,000, 20,000, 19,000, 16,000, 15,000, 10,000, 9,500, 9,300, 9,000, 8,000, 7,000, 6,900, 6,500, 6,000, 5,700, 5,500, 5,000, 4,500, 4,000, 3,000, 2,000, 1,000, 900, 800, 700, 500 mPa·s, etc. In one embodiment, from the viewpoint of improving slurry dispersion stability and electrode adhesion, the above B-type viscosity is preferably 500 to 100,000 mPa·s, more preferably 800 to 80,000 mPa·s, and even more preferably 1,000 to 50,000 mPa·s.

[0127] The upper and lower limits of the pH of the aqueous binder solution for a lithium-ion battery are exemplified by 9, 8.9, 8.5, 8, 7.9, 7.5, 7, 6.9, 6.5, 6, 5.9, 5.6, 5.5, 5.4, 5.2, 5.1, 5, 4, etc. In one embodiment, from the viewpoint of solution stability, the pH of the aqueous binder solution for a lithium-ion battery is preferably pH 4 to 9, and more preferably pH 4 to 7.

[0128] The pH is measured at 25°C using a glass electrode pH meter (for example, product name "pH meter D-52" manufactured by Horiba, Ltd.).

[0129] The aqueous binder solution for a lithium-ion battery can be used as an aqueous binder solution for a lithium-ion battery electrode, an aqueous binder solution for a lithium-ion battery negative electrode, or a thickener for a lithium-ion battery.

[0130] [Slurry for lithium-ion battery negative electrode: Also referred to as slurry] The present disclosure provides a slurry for a lithium-ion battery negative electrode containing the above aqueous binder solution for a lithium-ion battery electrode and a negative electrode active material (C).

[0131] In the present disclosure, "slurry" means a suspension of a liquid and solid particles.

[0132] Examples of the upper and lower limits of the content of component (A) with respect to 100% by mass of the above slurry include 99.9, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 4, 2, 1, 0.9, 0.5, 0.2, 0.1% by mass, etc. In one embodiment, the above content is preferably 0.1 to 99.9% by mass.

[0133] Examples of the upper and lower limits of the content of component (B) with respect to 100% by mass of the above slurry include 1, 0.9, 0.7, 0.5, 0.3, 0.2, 0.1, 0.09, 0.07, 0.05, 0.03, 0.01, 0.009, 0.007, 0.005, 0.003, 0.002, 0.001% by mass, etc. In one embodiment, the above content is preferably 0.001 to 1% by mass.

[0134] 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.

[0135] <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.

[0136] 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 depending on the type of the target lithium ion battery. Examples of the negative electrode active material include carbon materials, as well as materials that alloy with lithium such as silicon materials, oxides containing lithium atoms, lead compounds, tin compounds, arsenic compounds, antimony compounds, and aluminum compounds.

[0137] Examples of the carbon material include highly crystalline carbon such as graphite (also known as black lead, and examples thereof include natural graphite and artificial graphite), low-crystalline carbon (soft carbon and hard carbon), carbon black (such as ketjen black, acetylene black, channel black, lamp black, oil furnace black, and thermal black), fullerene, carbon nanotubes, carbon nanofibers, carbon nanohorns, carbon fibrils, mesocarbon microbeads (MCMB), and pitch-based carbon fibers.

[0138] The above silicon materials include silicon, silicon oxide, silicon alloys, as well as SiC and SiO x C y (0 <x≦3、0<y≦5)、Si3N4、Si2N2O、SiO x (0 <x≦2)で表記されるシリコンオキサイド複合体(例えば特開2004-185810号公報や特開2005-259697号公報に記載されている材料等)、特開2004-185810号公報に記載されたシリコン材料等が例示される。また、特許第5390336号、特許第5903761号に記載されたシリコン材料を用いても良い。

[0139] The silicon oxide has the composition formula SiO x (0 <x<2、好ましくは0.1≦x≦1)で表されるシリコンオキサイドが好ましい。

[0140] The silicon alloy is preferably an alloy of silicon and at least one transition metal selected from the group consisting of titanium, zirconium, nickel, copper, iron, and molybdenum. Silicon alloys of these transition metals are preferred because they have high electronic conductivity and high strength. The silicon alloy is more preferably a silicon-nickel alloy or a silicon-titanium alloy, and particularly preferably a silicon-titanium alloy. The silicon content in the silicon alloy is preferably 10 mol % or more, more preferably 20 to 70 mol %, relative to 100 mol % of the metal elements in the silicon alloy. The silicon material may be single crystalline, polycrystalline, or amorphous.

[0141] In addition, 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, manganese, etc., 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, since the volume change accompanying the occlusion and release of lithium is small, it is preferable to use a carbon material in combination.

[0142] The oxides containing the above lithium atoms include lithium nickel cobalt manganese oxide, lithium-manganese composite oxide (such as LiMn2O4), lithium-nickel composite oxide (such as LiNiO2), lithium-cobalt composite oxide (such as LiCoO2), lithium-iron composite oxide (such as LiFeO2), lithium-nickel-manganese composite oxide (LiNi 0.5 Mn 0.5 O2, etc.), lithium-nickel-cobalt composite oxide (LiNi 0.8 Co 0.2 O2, etc.), lithium-transition metal phosphate compound (such as LiFePO4), and lithium-transition metal sulfate compound (Li x Fe2(SO4)3), 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.

[0143] From the viewpoint that the effects of the present invention are significantly exhibited, a carbon material and / or a material that alloyizes with lithium is preferably contained in the negative electrode active material at 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.

[0144] In one embodiment, a negative electrode active material preferably contains 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.

[0145] The shape of the negative electrode active material is not particularly limited and may be any shape such as particulate or thin film shape, but particulate shape is preferred. The average particle size 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 size of the negative electrode active material is preferably 0.1 to 50 μm, more preferably 0.1 to 45 μm, further preferably 1 to 10 μm, and particularly preferably 5 μm.

[0146] In the present disclosure, "particle size" means the maximum distance among the distances between any two points on the contour line of the particle (the same applies hereinafter). Also, in the present disclosure, "average particle size" is, unless otherwise specified, a value calculated as the average value of the particle sizes of the particles observed in several to several tens of fields of view using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) (the same applies hereinafter).

[0147] Examples of 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 include 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.

[0148] <Conductive aid> In one embodiment, the slurry may contain a conductive additive. Examples of the conductive additive include fibrous carbon such as vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and carbon nanofibers (CNF); graphite particles; carbon black such as acetylene black, ketjen black, and furnace black; and fine powders of Cu, Ni, Al, Si, or alloys thereof having an average particle size of 10 μm or less. The content of the conductive additive is not particularly limited, but is preferably 0 to 10% by mass, and more preferably 0.5 to 6% by mass, of the negative electrode active material components.

[0149] <Slurry viscosity adjusting solvent> The slurry viscosity adjusting solvent is not particularly limited, but may include a non-aqueous medium having a normal boiling point of 80 to 350° C. The slurry viscosity adjusting solvent may be used alone or in combination of two or more kinds. Examples of slurry viscosity adjusting solvents 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; and water. Among these, N-methylpyrrolidone is preferred for its ease of application. The content of the non-aqueous medium is not particularly limited, but is preferably 0 to 10% by mass relative to 100% by mass of the slurry.

[0150] The slurry may contain additives other than those of component (A), component (B), component (C), water, a conductive additive, or a slurry viscosity adjusting solvent, as long as the additives do not impair the effects of the present invention. Examples of additives include those listed above.

[0151] 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 (C).

[0152] 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 slurry for the negative electrode of the lithium-ion battery 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 springback resistance and discharge capacity retention rate, the addition amount of the dispersion (emulsion) with respect to 100% by mass of the above aqueous solution or the slurry for the negative electrode of the lithium-ion battery is preferably less than 5% by mass.

[0153] The above slurry is produced by mixing the component (A), the component (B), the component (C), water, and, if necessary, a conductive auxiliary agent and a slurry viscosity adjusting solvent.

[0154] 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.

[0155] [Negative electrode of lithium-ion battery] The present disclosure provides a negative electrode for a lithium-ion battery obtained by applying the above slurry for the negative electrode of the lithium-ion battery to a current collector and drying and curing it. The above negative electrode for a lithium-ion battery has a cured product of the above slurry for the negative electrode of the lithium-ion battery on the surface of the current collector.

[0156] The current collector can be any of various known ones 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 metal materials, examples include metal foil, metal cylinder, metal coil, metal plate, etc., and in the case of carbon materials, examples include carbon plate, carbon thin film, carbon cylinder, etc. Among them, when the electrode active material is used as the negative electrode, a copper foil is preferable as the current collector because it is currently used in industrialized products.

[0157] The coating means is not particularly limited, and examples include conventionally known coating devices such as comma coater, gravure coater, micro gravure coater, die coater, bar coater, etc.

[0158] The drying means is also not particularly limited. The temperature is preferably 60 to 200 °C, more preferably 100 to 195 °C. The atmosphere may be dry air or an inert atmosphere.

[0159] 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 it within the above range, it is easier to obtain a sufficient function of lithium absorption and release for a high-density current value.

[0160] [Lithium Ion Battery] The present disclosure provides a lithium ion battery including the negative electrode for a lithium ion battery described above. In one embodiment, the battery includes an electrolyte solution, a separator, a positive electrode, etc. These are not particularly limited.

[0161] Examples of the electrolyte solution include non-aqueous electrolytes in which a supporting electrolyte is dissolved in a non-aqueous solvent. Further, the non-aqueous electrolyte may include a film-forming agent.

[0162] Non-aqueous solvents can be any of various known ones without particular limitation, and can be used alone or in combination of two or more. Examples of non-aqueous solvents include chain carbonate solvents such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; cyclic carbonate solvents such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain ether solvents such as 1,2-dimethoxyethane; cyclic ether solvents such as 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 preferred.

[0163] As the supporting electrolyte, a lithium salt is used. Various known lithium salts can be used without particular limitation, and can 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 show a high degree of dissociation, are preferred. Since the higher the degree of dissociation of the supporting electrolyte, the higher the lithium ion conductivity, the lithium ion conductivity can be adjusted by the type of the supporting electrolyte.

[0164] 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.

[0165] The separator is an article interposed between the positive electrode and the negative electrode and is used to prevent 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 used after being impregnated with the non-aqueous electrolyte solution. Materials for the separator include polyolefins such as polyethylene and polypropylene, and polyethersulfone, etc., and polyolefin is preferably used.

[0166] Various known positive electrodes can be used without particular limitation. The positive electrode is exemplified by those obtained by preparing a slurry by mixing a positive electrode active material, a conductive assistant, and a positive electrode binder with an organic solvent, and applying, drying, and pressing the prepared slurry onto a positive electrode current collector.

[0167] Examples of the positive electrode active material include inorganic positive electrode active materials and organic positive electrode active materials. 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 above transition metals include Fe, Co, Ni, Mn, Al, etc. Inorganic compounds used as the positive electrode active material include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiFePO4, LiNi 1 / 2 Mn 3 / 2 O4, LiCo1 / 3 Ni 1 / 3 Mn 1 / 3 O2, Li[Li 0.1 Al 0.1 Mn 1.8 O4, LiFeVO4 and other lithium-containing complex metal oxides; transition metal sulfides such as TiS2, TiS3, amorphous MoS2, etc.; Cu2V2O3, amorphous V2O-P2O5, MoO3, V2O5, V6O 13 and other transition metal oxides are exemplified. These compounds may be partially element-substituted. Examples of the organic cathode active material include conductive polymers such as polyacetylene and poly-p-phenylene. Iron-based oxides with 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 during reduction firing. Also, these compounds may be partially element-substituted. Among these, LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiFePO4, LiNi 1 / 2 Mn 3 / 2 O4, LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, Li[Li 0.1 Al 0.1 Mn 1.8 O4 is preferred.

[0168] Examples of the conductive aid include fibrous carbon such as vapor-grown carbon fiber (VGCF), carbon nanotube (CNT), carbon nanofiber (CNF), graphite particles, carbon black such as acetylene black, ketjen black, furnace black; fine powder composed of Cu, Ni, Al, Si or their alloys with an average particle size of 10 μm or less, etc.

[0169] The binder for the positive electrode 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 binder for the positive electrode include fluorine-based resins (such as polyvinylidene fluoride and polytetrafluoroethylene), polyolefins (such as polyethylene and polypropylene), polymers having unsaturated bonds (such as styrene-butadiene rubber, isoprene rubber, and butadiene rubber), and acrylic acid-based polymers (such as acrylic acid copolymers and methacrylic acid copolymers).

[0170] Examples of the positive electrode current collector include aluminum foil and stainless steel foil.

[0171] 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 the sheet electrode and the separator are spiral, a cylinder type of inside-out structure in which the pellet electrode and the separator are combined, and a coin type in which the pellet electrode and the 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.

[0172] 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

[0173] Hereinafter, the present invention will be specifically described through Examples and Comparative Examples. However, the description in the above preferred embodiments and the following examples are provided only for the purpose of illustration and not for the purpose of limiting the present invention. Therefore, the scope of the present invention is not limited to the embodiments and examples specifically described in this specification, but is limited only by the scope of the claims. Further, in each of the examples and comparative examples, unless otherwise specified, numerical values such as parts and % are based on mass.

[0174] <Acidic Group-Containing Water-Soluble Polymer (A)> Manufacturing Example 1 A reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet was charged with 1800 g of ion-exchanged water, 350 g (2.46 mol) of 50% aqueous acrylamide solution, 148 g (1.64 mol) of 80% aqueous acrylic acid solution, and 0.32 g (0.0021 mol) of sodium methallylsulfonate. After removing oxygen from the reaction system by passing nitrogen gas through the reactor, the temperature was raised to 55 °C. 2.64 g of 2,2'-azobis-2-amidinopropane dihydrochloride (manufactured by Nippoh Chemical Co., Ltd., product name "NC-32") and 20 g of ion-exchanged water were added, and the temperature was raised to 80 °C and the reaction was carried out for 3 hours. Subsequently, 103 g (1.23 mol) of 48% aqueous sodium hydroxide solution was added as a neutralizer and stirred. Ion-exchanged water was added to adjust the solids concentration to 13%, yielding an aqueous solution containing an acidic group-containing water-soluble polymer (A). The Brookfield viscosity of this solution at 25°C was 20,000 mPa·s.

[0175] In the production examples other than Production Example 1, aqueous solutions containing the acidic group-containing water-soluble polymer (A) were prepared in the same manner as in Production Example 1, except that the monomer composition was changed to that shown in Table 1.

[0176] Comparative Manufacturing Example 1 A reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet was charged with 1280 g of ion-exchanged water, 500 g (3.52 mol) of 50% acrylamide aqueous solution, and 0.28 g (0.0018 mol) of sodium methallylsulfonate. After removing oxygen from the reaction system by passing nitrogen gas through the reactor, the temperature was raised to 55°C. 2.3 g of 2,2'-azobis-2-amidinopropane dihydrochloride (product name "NC-32" manufactured by Nippoh Chemical Co., Ltd.) and 20 g of ion-exchanged water were then added, and the reaction was carried out at 80°C for 3 hours. Subsequently, ion-exchanged water was added to adjust the solids concentration to 13%, yielding a water-soluble polymer solution. The Brookfield viscosity of this solution at 25°C was 15,000 mPa·s.

[0177] In Comparative Production Examples 2 to 5, an aqueous solution containing a water-soluble polymer was prepared in the same manner as in Production Example 1, except that the monomer composition was changed to that shown in Table 1.

[0178] Comparative Production Example 6 Into a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, 700 g of ion-exchanged water, 12.7 g (0.14 mol) of an 80% aqueous acrylic acid solution, 233 g (1.27 mol) of 2-ethylhexyl acrylate, and 2.4 g of sodium polyoxyethylene alkyl ether sulfate as an emulsifier were placed. After removing oxygen in the reaction system through nitrogen gas, the temperature was raised to 80°C. 2.4 g of 2,2'-azobis-2-amidinopropane dihydrochloride (product name "NC-32" manufactured by Nippon Chemical Co., Ltd.) and 20 g of ion-exchanged water were added thereto, and the reaction was carried out at 80°C for 3 hours. Thereafter, ion-exchanged water was added so that the solid content concentration became 13% to obtain a polymer aqueous dispersion.

[0179] In Comparative Production Examples 7 and 8, a polymer aqueous dispersion was prepared in the same manner as in Comparative Production Example 6, except that the monomer composition was changed to that shown in Table 1.

[0180]

Table 1

[0181] B-type viscosity of component (A) The viscosity of each Production Example and Comparative Production Example was measured at 25° C. under the following conditions using a Brookfield viscometer (manufactured by Toki Sangyo Co., Ltd., product name: Brookfield viscometer model BM). For viscosity of 100,000 to 20,000 mPa·s: Use No. 4 rotor, rotation speed 6 rpm For viscosity less than 20,000 mPa·s: Use No. 3 rotor, rotation speed 6 rpm

[0182] Weight average molecular weight The weight-average molecular weight was determined as a polyacrylic acid equivalent value by gel permeation chromatography (GPC) in a 0.2 M phosphate buffer / acetonitrile solution (90 / 10, pH 8.0). The GPC equipment used was an HLC-8220 (Tosoh Corporation) and the column was an SB-806M-HQ (Shodex).

[0183] <Amino group-containing water-soluble polymer (B)> Polyallylamine ("PAA-15C" manufactured by Nittobo Medical Co., Ltd.) Polyallylamine ("PAA-05" manufactured by Nittobo Medical Co., Ltd.) Polyallylamine ("PAA-25" manufactured by Nittobo Medical Co., Ltd.) Polyethyleneimine (Nippon Shokubai Co., Ltd. "SP-200") Since all of the constituent monomers of the above component (B) were known, the amine value (the number of moles derived from amino group components per gram of component (B)) was calculated from the molecular weight and content of the monomers, as described in the specification.

[0184] Into a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, 100 g of a 15% aqueous solution of polyallylamine (manufactured by Nittobo Medical Co., Ltd., "PAA-15C") was placed, 25.8 g of concentrated hydrochloric acid was added and stirred, and ion-exchanged water was added so that the solid content concentration became 15% to obtain polyallylamine hydrochloride.

[0185]

Table 2

[0186] pH of 1% aqueous solution of amino group-containing water-soluble polymer (B) The pH of a 1% aqueous solution of each amino group-containing water-soluble polymer (B) was measured at 25 °C using a glass electrode pH meter (product name "Handy pH Meter D-52", manufactured by Horiba, Ltd.) after diluting the amino group-containing water-soluble polymer (B) aqueous solution with ion-exchanged water to 1%.

[0187] Residue ratio when component (B) is impregnated in dimethyl carbonate at 25 °C for 24 hours The amino group-containing water-soluble polymer (B) aqueous solution was dried for 12 hours using a 130 °C circulating air dryer (product name "DRS420DA" manufactured by ADVANTEC) to obtain a solid or liquid sample of the amino group-containing water-soluble polymer (B). About 1 g of the obtained test piece was weighed into a petri dish, 50 g of dimethyl carbonate was added, and it was allowed to stand at 25 °C for 24 hours. Then, after removing the supernatant amino group-containing water-soluble polymer (B), the residue was dried for 1 hour using a 130 °C circulating air dryer (product name "DRS420DA" manufactured by ADVANTEC) and the mass was measured. Residue ratio when impregnated in dimethyl carbonate at 25 °C for 24 hours = {(mass after impregnation in dimethyl carbonate and drying) / (mass before impregnation in dimethyl carbonate)} × 100 (%) Due to the high residue ratio of the amino group-containing water-soluble polymer (B) after impregnation with dimethyl carbonate, the amount of the amino group-containing water-soluble polymer (B) eluted into the electrolyte inside the lithium-ion battery after the lithium-ion battery is fabricated is reduced.

[0188] Production of Aqueous Binder Solution for Lithium-Ion Batteries Example 1-1 An aqueous binder solution for lithium-ion batteries was prepared using a commercially available homodisper (Primix Corporation, "Homodisper 2.5 type"). 15 g of an aqueous solution containing the acidic group-containing water-soluble polymer (A) obtained in Production Example 1 was placed in a mayonnaise bottle as a container, deionized water was added so that the solid content concentration became 1.5%, and the container was set on the above homodisper. Then, it was mixed and stirred at 3,000 rpm for 10 minutes. Thereafter, 0.347 g of a 15% polyallylamine aqueous solution ("PAA-15C" manufactured by Nittobo Medical Co., Ltd.) was added, further deionized water was added so that the solid content concentration became 1.5%, and it was mixed and stirred at 3,000 rpm for 30 minutes to obtain an aqueous binder solution for lithium-ion batteries. The B-type viscosity of this solution at 25°C was 16,000 mPa·s.

[0189] In Example 1 other than Example 1-1, an aqueous binder solution for lithium-ion batteries was prepared in the same manner as in Example 1-1, except that the types and amounts of the acidic group-containing water-soluble polymer (A) and the amino group-containing water-soluble polymer (B) were changed to those shown in the following table.

[0190] Comparative Example 1-1 An aqueous binder solution for lithium-ion batteries was prepared using a commercially available homodisper (Primix Corporation, "Homodisper 2.5 type"). 15 g of an aqueous solution containing the acidic group-containing water-soluble polymer (A) obtained in Production Example 1 was placed in a mayonnaise bottle as a container, deionized water was added so that the solid content concentration became 1.5%, and the container was set on the above homodisper. Then, it was mixed and stirred at 3,000 rpm for 10 minutes to obtain an aqueous binder solution for lithium-ion batteries. The B-type viscosity of this solution at 25°C was 130 mPa·s.

[0191] Comparative Example 1-2 An aqueous binder solution for a lithium-ion battery was prepared using a commercially available homodisper (Primix Corporation's "Homodisper 2.5 type"). 15 g of an aqueous solution containing the acidic group-containing water-soluble polymer (A) obtained in Production Example 1 was placed in a mayonnaise bottle as a container, deionized water was added so that the solid content concentration became 1.5%, and the container was set on the above homodisper. Next, it was mixed and stirred at 3,000 rpm for 10 minutes. Then, 0.347 g of a 15% aqueous polyallylamine hydrochloride solution was added, further deionized water was added so that the solid content concentration became 1.5%, and it was mixed and stirred at 3,000 rpm for 30 minutes to obtain an aqueous binder solution for a lithium-ion battery. The B-type viscosity of this solution at 25°C was 140 mPa·s.

[0192] In Comparative Example 1 other than Comparative Examples 1-1 and 1-2, an aqueous binder solution for a lithium-ion battery was prepared in the same manner as Comparative Example 1-2, except that the types and amounts of the acidic group-containing water-soluble polymer (A) and the amino group-containing water-soluble polymer (B) were changed to those shown in the following table.

[0193]

Table 3

[0194] B-type viscosity of the aqueous binder solution for a lithium-ion battery The viscosities of each Example and Comparative Example were measured at 25°C under the following conditions using a B-type viscometer (product name "B-type viscometer model BM" manufactured by Toki Sangyo Co., Ltd.). When the viscosity is 100,000 to 20,000 mPa·s: Use No. 4 rotor, rotation speed 6 rpm When the viscosity is less than 20,000 to 1,000 mPa·s: Use No. 4 rotor, rotation speed 12 rpm When the viscosity is less than 1,000 mPa·s: Use No. 3 rotor, rotation speed 60 rpm

[0195] Water absorption rate Ten grams of lithium-ion battery binder solution was dried at 130°C for 12 hours in a circulating air dryer (ADVANTEC, product name "DRS420DA"), and the resulting solid was placed in a polyethylene bag and crushed to approximately 5 mm x 5 mm with a wooden hammer. The crushed solid was placed in a vacuum dryer (ADVANTEC, product name "VO-320P"), evacuated to a gauge pressure of 76 cmHg or less at 130°C, and dried for 12 hours. Approximately 1 g of the resulting test piece was weighed into a petri dish and placed in a low-temperature, constant-temperature, constant-humidity chamber (ADVANTEC, product name "THE051FA") at 30°C and 90% humidity for 3 hours, after which the mass was measured. Water absorption rate = {(mass after leaving at 30°C and 90% humidity for 3 hours) / (mass immediately after drying)} x 100 - 100 (%) The low water absorption rate of lithium-ion battery binders reduces the amount of water remaining inside the lithium-ion battery after it is assembled. If water remains inside the battery cell, it will decompose due to an undesired electrochemical reaction inside the battery cell, and gas will be generated inside the battery cell when it is stored at high temperatures. If the binder resin has a low water absorption rate, less water will remain in the electrodes after drying, and less water will be mixed into the cell. As a result, gas generation can be suppressed.

[0196] Slurry production, cell fabrication and evaluation Example 2-1 <Production of slurry for lithium-ion battery negative electrodes> A slurry was prepared using a commercially available Homo Disper (Homo Disper 2.5 type manufactured by Primix Corporation). Two parts by mass (solids content) of the aqueous binder solution for lithium ion batteries obtained in Example 1-1 and 98 parts by mass of artificial graphite (G1-A# manufactured by Jiangxi Zishen Technology Co., Ltd.) with a D50 (median diameter) of 20 μm were mixed in a mayonnaise jar. Ion-exchanged water was added to dilute the slurry to a viscosity of 3,000±100 mPa·s. In this example, the solids concentration was 41%. The container was placed in the Homo Disper. The mixture was then kneaded at 3,000 rpm for 20 minutes. The mixture was then degassed for 1 minute using a planetary mixer (Thinky Corporation's Awatori Rentaro) to obtain a slurry for lithium ion battery negative electrodes.

[0197] For Examples and Comparative Examples other than Example 2-1, slurries were prepared in the same manner as Example 2-1, except that the composition was changed to that shown in the following table in Example 2-1.

[0198]

Table 4

[0199] <Assembly of Lithium Half Cell> The above slurry was uniformly applied onto the surface of a current collector (20 μm) made of copper foil by the doctor blade method so that the film thickness after drying would be 170 μm. After drying at 150 °C for 30 minutes, heat treatment was performed at 150 °C / vacuum for 120 minutes to obtain an electrode. Then, the film (electrode active material layer) was pressed by a roll press so that the density would be 1.5 g / cm 3 to obtain a negative electrode. In an argon-substituted glove box, a negative electrode electrode punched and formed into a diameter of 16 mm was placed inside a packing on an Al-made lower lid of a test cell (manufactured by Nippon Tomcell Co., Ltd.). Next, a separator (manufactured by CS TECH CO., LTD, "Selion P2010") made of a polypropylene porous membrane punched into a diameter of 24 mm was placed. Further, after injecting 500 μL of an electrolytic solution so that air would not enter, a commercially available metal 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 a screw to assemble a lithium half cell. The electrolytic solution 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).

[0200] <Charge and 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 discharging was completed (cut-off) when the voltage reached 1.0V. Charge and discharge tests were performed.

[0201] Note that in the above measurement conditions, "1C" indicates the current value at which a cell with a certain capacitance is discharged at a constant current and the discharge ends in 1 hour. For example, "0.1C" refers to the current value at which the discharge ends in 10 hours, and "10C" refers to the current value at which the discharge is completed in 0.1 hours.

[0202] <Slurry dispersion stability test> 6 g of the above slurry was placed in a reinforced hard screw-cap test tube (manufactured by Nippon Electric Glass Co., Ltd.), and centrifuged at 1,000 rpm for 3 minutes using a small benchtop centrifuge (Kokusan Co., Ltd. "H-11n"). The solid content of the slurry before centrifugation, the supernatant of the slurry after centrifugation, and the solid content of each slurry were measured. The solid content was obtained by putting 1 g of the slurry into an ointment can (manufactured by Sogo Rika Glass Co., Ltd., product name "Ointment can made of tinplate"), drying it at 130°C for 1 hour in a circulating air dryer (manufactured by Advantec Toyo Co., Ltd., product name "Forced air constant temperature dryer DSR420DA"), and obtaining the solid matter of the slurry. The solid content was calculated from the following formula. Solid content (%) = {mass of solid matter after drying (g) / mass of slurry before drying (g)} × 100 The dispersion stability of the slurry was calculated from the following formula and evaluated according to the following evaluation criteria. Slurry dispersion stability (%) = {mass of solid matter after drying (g) / mass of slurry before drying (g)} × 100 A: 90% or more B: 80% or more and less than 90% C: 50% or more and less than 80% D: Less than 50%

[0203] <Electrode adhesion evaluation> The electrode adhesion was evaluated as follows. A test piece with a width of 2 cm and a length of 10 cm was cut out from the electrode. After pressing and attaching a double-sided adhesive tape with a width of 20 mm ("Nice Tack (registered trademark)", manufactured by Nichiban Co., Ltd.) to the surface of the active material layer of the test piece, it was pasted on paper with the current collector surface facing up. Using a tensile testing machine ("Tensilon RTM-100" manufactured by A&D Company, Ltd.) under the condition of 25°C, the stress when the current collector was peeled off from one end of the test piece in the 180° direction at a speed of 30 mm / min was measured. The measurement was carried out 5 times, converted to the value per 20 mm width, and the average value was calculated as the peel strength. The greater 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, indicating that it is difficult for the active material layer or the active materials to peel off from the current collector. Based on the peel strength values, the evaluation was carried out as follows. A: The peel strength was greater than 5 N / m. B: The peel strength was greater than 3 N / m and less than or equal to 5 N / m. C: The peel strength was 0.5 - 3 N / m. D: The peel strength was less than 0.5 N / m.

[0204] <Measurement of the initial Coulomb efficiency> Based on the values of the initial charge capacity (mAh) and the initial discharge capacity (mAh) during the charge-discharge cycle test at room temperature (25°C), the initial Coulomb efficiency was obtained by the following formula. Initial Coulomb efficiency = {(Initial discharge capacity) / (Initial charge capacity)} × 100

Claims

1. Based on 100 mol% of the monomer group, 30 to 90 mol% of a (meth)acrylamide group-containing compound (a), 3 to 20 mol% of an unsaturated organic acid (b), and a polymer of a monomer group containing 5 to 40 mol% of an alkali metal or alkaline earth metal salt (c) of an unsaturated organic acid, an acidic group-containing water-soluble polymer (A), and an amino group-containing water-soluble polymer (B) having a pH of 9 or more in a 1 mass% aqueous solution are included, and the mass ratio (the acidic group-containing water-soluble polymer (A) / the amino group-containing water-soluble polymer (B)) is 97 / 3 to 99.5 / 0.5, an aqueous binder solution for a lithium-ion battery.

2. The aqueous binder solution for a lithium-ion battery according to Claim 1, wherein the molar ratio (acidic group / amino group) of the acidic group contained in the acidic group-containing water-soluble polymer (A) to the amino group contained in the amino group-containing water-soluble polymer (B) is 1 to 15.

3. The aqueous binder solution for a lithium-ion battery according to Claim 1 or 2, wherein the molecular weight of the amino group-containing water-soluble polymer (B) is 1,600 to 50,000.

4. The aqueous binder solution for a lithium-ion battery according to any one of Claims 1 to 3, wherein the residue ratio when the amino group-containing water-soluble polymer (B) is impregnated in dimethyl carbonate at 25 °C for 24 hours is 20 mass% or more.

5. The aqueous binder solution for a lithium-ion battery according to any one of Claims 1 to 4, wherein the amino group-containing water-soluble polymer (B) is polyallylamine.

6. An aqueous slurry for a lithium-ion battery negative electrode, comprising the aqueous binder solution for a lithium-ion battery according to any one of Claims 1 to 5, and a negative electrode active material (C).

7. A negative electrode for a lithium-ion battery, obtained by applying and drying the aqueous slurry for a lithium-ion battery negative electrode according to Claim 6 on a metal foil.

8. A lithium-ion battery, comprising the negative electrode for a lithium-ion battery according to Claim 7.

Images