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

Abstract

To provide a binder aqueous solution for a lithium ion battery electrode, a slurry for a lithium ion battery electrode, a lithium ion battery electrode, and a lithium ion battery.SOLUTION: A binder aqueous solution for a lithium ion battery electrode includes a water-soluble polymer (A) which is a polymer of a monomer group containing 5 to 80 mol% of a hydroxyl group-containing vinyl ether (a) with respect to 100 mol% of the monomer group. In one embodiment, the monomer group includes 20 to 95 mol% of a (meth) acrylamide group-containing compound (b).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 electrode, a lithium ion battery electrode, and a lithium ion battery. [Background technology]

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

[0003] Both the positive and negative electrodes of a lithium-ion battery are manufactured by dispersing an electrode active material and a binder resin in a solvent to form a slurry, which is applied to both sides of a current collector (e.g., a metal foil), drying and removing the solvent to form an electrode layer, and then compression molding this using a roll press or the like.

[0004] In recent years, various electrode active materials have been proposed for lithium ion battery electrodes in order to increase the battery capacity. However, some electrode active materials tend to expand and contract with charging and discharging. Therefore, lithium ion battery electrodes that tend to expand and contract with charging and discharging undergo volume changes from the beginning of repeated charging and discharging (springback property), and tend to deteriorate the electrical properties such as cycle characteristics of lithium ion batteries using them.

[0005] In this field, therefore, studies have been made to solve the above problems by using binder resins, and it has been proposed, for example, that good charge-discharge characteristics can be obtained by using polyacrylamide as a binder for water-soluble resins (Patent Documents 1 and 2). It has also been proposed to suppress the expansion and contraction that accompanies the charge and discharge of active materials by adding a crosslinking agent to the particulate resin, which is the binder resin (Patent Document 3). The crosslinking agent usually causes a crosslinking reaction during the drying process after the slurry composition is applied to the current collector, forming crosslinks between particles of the particulate resin, etc. [Prior art documents] [Patent documents]

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

[0007] However, the polyacrylamides of Patent Documents 1 and 2 cannot be made to have a high molecular weight to the extent that the binder resin is insoluble in water, from the viewpoint of ensuring solubility in water, and as a result, there is a problem that the resistance to springback caused by the expansion of the active material is insufficient.

[0008] In some cases, the combined use of the crosslinking agent described in Patent Document 3 may not be effective even if a large amount is added. In such cases, if a large amount of crosslinking agent is added to exert the effect of the crosslinking agent, for example, resistance to springback, the adhesion of the electrode active material layer to the current collector may be reduced, and desired effects such as high-temperature cycle characteristics may not be obtained, so there is room for further improvement.

[0009] When the neutralization rate of a polymer containing an unsaturated organic acid is low, the initial coulombic efficiency and capacity retention rate may decrease. Also, when the neutralization rate of a polymer containing an acrylic ester and an unsaturated organic acid exceeds 95%, the amount of unneutralized unsaturated organic acid increases due to hydrolysis of the acrylic ester. As a result, the initial coulombic efficiency and capacity retention rate decrease.

[0010] Therefore, an object of the present invention is to provide a good aqueous binder solution for lithium ion battery electrodes which imparts good initial coulombic efficiency, capacity retention and springback resistance to a lithium ion battery, and which imparts good curl prevention properties, electrode flexibility and electrode adhesion to an electrode, and which imparts good storage stability to a slurry. [Means for solving the problem]

[0011] As a result of extensive investigations, the present inventors have found that the above problems can be solved by a water-soluble polymer containing a specific unsaturated monomer as a constituent component.

[0012] The present disclosure provides the following: (Item 1) The aqueous binder solution for lithium ion battery electrodes comprises a water-soluble polymer (A) which is a polymer of a monomer group containing 5 to 80 mol % of a hydroxyl group-containing vinyl ether (a) relative to 100 mol % of the monomer group. (Item 2) The aqueous binder solution for a lithium ion battery electrode according to the above items, wherein the monomer group contains 20 to 95 mol % of the (meth)acrylamide group-containing compound (b). (Item 3) Item 10. The aqueous binder solution for a lithium ion battery electrode according to any one of the preceding items, wherein the monomer group contains 0.01 to 50 mol % of an unsaturated organic acid or an inorganic salt thereof (c). (Item 4) A slurry for a lithium ion battery electrode, comprising the aqueous binder solution for a lithium ion battery electrode according to any one of the above items and an electrode active material (B). (Item 5) A lithium ion battery electrode obtained by applying the lithium ion battery electrode slurry described in the above item to a current collector, drying and curing the slurry. (Item 6) A lithium ion battery comprising the lithium ion battery electrode described in the above item.

[0013] In the present disclosure, one or more of the above-described features may be provided in further combinations in addition to the combinations explicitly stated. Effect of the Invention

[0014] By using the aqueous binder solution for lithium ion battery electrodes of the present disclosure, a slurry having good storage stability can be produced, an electrode that is not curled, has high adhesion, and is flexible can be produced, and a lithium ion battery having good initial coulombic efficiency, capacity retention rate, and springback resistance can be produced. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] 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.

[0016] [Aqueous binder solution for lithium-ion battery electrodes: also called aqueous solution] The present disclosure provides an aqueous binder solution for a lithium ion battery electrode, comprising a water-soluble polymer (A) which is a polymer of a monomer group containing 5 to 80 mol % of a hydroxyl group-containing vinyl ether (a) relative to 100 mol % of the monomer group.

[0017] <Water-soluble polymer (A): Also referred to as component (A)> In this 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] <Hydroxyl-containing vinyl ether (a): also referred to as component (a)> In the present disclosure, the hydroxyl group-containing vinyl ether is H2C=CH-OROH (In the formula, R OH means a group having a hydroxyl group.) The compound represented by the formula:

[0019] In one embodiment, the hydroxyl group-containing vinyl ether is represented by the general formula (1): H2C=CH-R-OH (In the formula, R represents a substituted or unsubstituted oxyalkylene group having 1 to 5 carbon atoms, General formula (2): [ka] (In the formula, q is an integer of 1 to 3, and n is an integer of 1 or more. Furthermore, n is preferably an integer of 1 to 10.) A polyoxyalkylene group represented by the formula: [ka] or a combination thereof.) It is expressed as:

[0020] Examples of the alkylene group include a straight-chain alkylene group, a branched alkylene group, and a cycloalkylene group.

[0021] A straight chain alkylene group is -(CH2) n - (n is an integer of 1 or more). Examples of the linear alkylene group include a methylene group, an ethylene group, a propylene group, an n-butylene group, and an n-pentylene group.

[0022] A branched alkylene group is a straight-chain alkylene group in which at least one hydrogen atom is replaced by an alkyl group. Examples of the branched alkylene group include a methylmethylene group, an ethylmethylene group, a propylmethylene group, a butylmethylene group, a methylethylene group, an ethylethylene group, a propylethylene group, a methylpropylene group, a 2-ethylpropylene group, a dimethylpropylene group, and a methylbutylene group.

[0023] Examples of the cycloalkylene group include a monocyclic cycloalkylene group, a bridged ring cycloalkylene group, and a condensed ring cycloalkylene group.

[0024] In the present disclosure, a monocyclic ring refers to a ring structure formed by a carbon covalent bond and having no internal bridge structure. A fused ring refers to a ring structure in which two or more monocyclic rings share two atoms (i.e., each ring shares only one side (fused) with each other). A bridged ring refers to a ring structure in which two or more monocyclic rings share three or more atoms.

[0025] The monocyclic cycloalkylene group is exemplified by a cyclopentylene group.

[0026] Examples of the substituent on the oxyalkylene group include a hydroxy group, an amino group, an acetyl group, and a sulfonic acid group.

[0027] Examples of the hydroxyl group-containing vinyl ether include hydroxyalkyl vinyl ether and polyalkylene glycol monovinyl ether.

[0028] Examples of the hydroxyalkyl vinyl ether include hydroxy linear alkyl vinyl ether, hydroxy branched alkyl vinyl ether, and hydroxycycloalkyl vinyl ether.

[0029] Examples of hydroxy linear alkyl vinyl ethers include 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, and 5-hydroxypentyl vinyl ether.

[0030] Examples of hydroxy branched alkyl vinyl ethers include 2-hydroxypropyl vinyl ether, 2-hydroxy-2-methylpropyl vinyl ether, and 4-hydroxy-2-methylbutyl vinyl ether.

[0031] Examples of hydroxycycloalkyl vinyl ethers include 4-hydroxycyclopentyl vinyl ether.

[0032] Examples of polyalkylene glycol monovinyl ethers include polymethylene glycol monovinyl ether, polyethylene glycol monovinyl ether, and polypropylene glycol monovinyl ether.

[0033] Examples of polymethylene glycol monovinyl ethers include dimethylene glycol monovinyl ether, trimethylene glycol monovinyl ether, tetramethylene glycol monovinyl ether, pentamethylene glycol monovinyl ether, hexamethylene glycol monovinyl ether, heptamethylene glycol monovinyl ether, octamethylene glycol monovinyl ether, nonamethylene glycol monovinyl ether, and decamethylene glycol monovinyl ether.

[0034] Examples of polyethylene glycol monovinyl ethers include diethylene glycol monovinyl ether, triethylene glycol monovinyl ether, tetraethylene glycol monovinyl ether, pentaethylene glycol monovinyl ether, hexaethylene glycol monovinyl ether, heptaethylene glycol monovinyl ether, octaethylene glycol monovinyl ether, nonaethylene glycol monovinyl ether, and decaethylene glycol monovinyl ether.

[0035] Examples of polypropylene glycol monovinyl ethers include dipropylene glycol monovinyl ether, tripropylene glycol monovinyl ether, tetrapropylene glycol monovinyl ether, pentapropylene glycol monovinyl ether, hexapropylene glycol monovinyl ether, heptapropylene glycol monovinyl ether, octapropylene glycol monovinyl ether, nonapropylene glycol monovinyl ether, and decapropylene glycol monovinyl ether.

[0036] The upper and lower limits of the content of the hydroxyl group-containing vinyl ether relative to 100 mol% of the monomer group are, for example, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 9, 5 mol%, etc. In one embodiment, the content of the hydroxyl group-containing vinyl ether relative to 100 mol% of the monomer group is 5 to 80 mol%.

[0037] The upper and lower limits of the content of the hydroxyl group-containing vinyl ether relative to 100% by mass of the monomer group are, for example, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5% by mass, etc. In one embodiment, the content of the hydroxyl group-containing vinyl ether relative to 100% by mass of the monomer group is 5 to 85% by mass.

[0038] <(Meth)acrylamide group-containing compound (b): also referred to as component (b)> In the present disclosure, the term "(meth)acrylamide group-containing compound" refers to a compound having a (meth)acrylamide group. As the (meth)acrylamide group-containing compound, various known compounds can be used without particular limitation, and they may be used alone or in combination of two or more kinds.

[0039] 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". In addition, "(meth)acryloyl" means "at least one selected from the group consisting of acryloyl and methacryloyl".

[0040] In one embodiment, the (meth)acrylamide group-containing compound has the following structural formula: [ka] (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 and R 3are each independently a hydrogen atom, a substituted or unsubstituted alkyl group, or an acetyl group; 2 and R 3 are groups that together form a ring structure, and R 4 and R 5 each independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, a hydroxyl 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), and an acetyl group. Examples of the substituent of the substituted alkyl group include a hydroxy group, an amino group, and an acetyl group. 2 and R 3 Examples of the group that combines with each other to form a ring structure include a morpholyl group. It is expressed by:

[0041] Examples of the alkyl group include a straight-chain alkyl group, a branched alkyl group, and a cycloalkyl group.

[0042] A straight chain alkyl group is -C n H 2n+1 (n is an integer of 1 or more). Examples of the straight-chain alkyl group include a methyl group, an ethyl group, a propyl group, a n-butyl group, a n-pentyl group, a n-hexyl group, a n-heptyl group, a n-octyl group, a n-nonyl group, and a n-decamethyl group.

[0043] A branched alkyl group is a group in which at least one hydrogen atom of a linear alkyl group is replaced with an alkyl group. Examples of branched alkyl groups 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.

[0044] Examples of the cycloalkyl group include a monocyclic cycloalkyl group, a bridged ring cycloalkyl group, and a condensed ring cycloalkyl group.

[0045] 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.

[0046] Examples of the bridged ring cycloalkyl group include a tricyclodecyl group, an adamantyl group, and a norbornyl group.

[0047] The condensed ring cycloalkyl group is exemplified by a bicyclodecyl group.

[0048] The number of carbon atoms in the alkyl group is not particularly limited, but examples of the upper and lower limits include 40, 35, 30, 29, 25, 20, 15, 12, 10, 9, 8, 7, 6, 5, 4, 3, 2, and 1.

[0049] Examples of the (meth)acrylamide group-containing compound 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, and examples of the salts include dimethylaminopropyl(meth)acrylamide methyl chloride quaternary salt, dimethylaminoethyl(meth)acrylate benzyl chloride quaternary salt, etc. Among these, when (meth)acrylamide, particularly acrylamide, is used, it is possible to prepare a binder that is highly water-soluble, has a high interaction with the electrode active material, and has high dispersibility in the slurry and high binding ability between the electrode active materials inside the electrode.

[0050] The upper and lower limits of the content of the (meth)acrylamide group-containing compound relative to 100 mol% of the monomer group are, for example, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20 mol%, etc. In one embodiment, the content is preferably in the range of 20 to 95 mol%.

[0051] The upper and lower limits of the content of the (meth)acrylamide group-containing compound relative to 100% by mass of the monomer group are 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10% by mass, etc. In one embodiment, the content of the (meth)acrylamide group-containing compound relative to 100% by mass of the monomer group is preferably 10 to 95% by mass.

[0052] <Unsaturated organic acid or its inorganic salt (c): Also referred to as component (c)> As the component (c), various known substances can be used without particular limitation, and they may be used alone or in combination of two or more kinds.

[0053] Examples of the unsaturated organic acid include unsaturated carboxylic acids, unsaturated sulfonic acids, and unsaturated phosphoric acids.

[0054] Examples of the unsaturated carboxylic acid include (meth)acrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid.

[0055] Examples of unsaturated sulfonic acids include α,β-ethylenically unsaturated sulfonic acids such as vinyl sulfonic acid, styrene sulfonic acid, and (meth)allyl sulfonic acid; (meth)acrylamide t-butyl sulfonic acid, 2-(meth)acrylamide-2-methylpropane sulfonic acid, 2-(meth)acrylamide-2-hydroxypropane sulfonic acid, 3-sulfopropane (meth)acrylic acid ester, and bis-(3-sulfopropyl)itaconic acid ester.

[0056] 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, and 3-(meth)acryloxy-2-hydroxypropane phosphoric acid.

[0057] In the present disclosure, a compound that corresponds to both a (meth)acrylamide group-containing compound and an unsaturated organic acid is considered to be an unsaturated organic acid.

[0058] In the present disclosure, the inorganic salt of an unsaturated organic acid refers to a salt in which the cationic moiety is a metal cation. Examples of the inorganic salt include an alkali metal salt and an alkaline earth metal salt.

[0059] Examples of the alkali metal include lithium, sodium, and potassium.

[0060] Examples of alkaline earth metals include magnesium and calcium.

[0061] The upper and lower limits of the content of the unsaturated organic acid or the inorganic salt thereof relative to 100 mol% of the monomer group are exemplified as 50, 45, 40, 35, 30, 25, 20, 15, 10, 9, 5, 4, 1, 0.9, 0.5, 0.3, 0.1, 0.09, 0.05, 0.03, 0.01 mol%, etc. In one embodiment, the content of the unsaturated organic acid or the inorganic salt thereof relative to 100 mol% of the monomer group is preferably 0.01 to 50 mol%.

[0062] The upper and lower limits of the content of the unsaturated organic acid or the inorganic salt thereof relative to 100% by mass of the monomer group are exemplified as 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 9, 5, 4, 1, 0.9, 0.5, 0.3, 0.1, 0.09, 0.05, 0.03, 0.01% by mass, etc. In one embodiment, the content of the unsaturated organic acid or the inorganic salt thereof relative to 100% by mass of the monomer group is preferably 0.01 to 75% by mass.

[0063] The upper and lower limits of the content of the unsaturated carboxylic acid or the inorganic salt thereof relative to 100 mol% of the monomer group are, for example, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 1, 0 mol%, etc. In one embodiment, the content of the unsaturated carboxylic acid or the inorganic salt thereof relative to 100 mol% of the monomer group is preferably 0 to 50 mol%.

[0064] The upper and lower limits of the content of the unsaturated carboxylic acid or the inorganic salt thereof relative to 100% by mass of the monomer group are, for example, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 1, 0% by mass, etc. In one embodiment, the content of the unsaturated carboxylic acid or the inorganic salt thereof relative to 100% by mass of the monomer group is preferably 0 to 60% by mass.

[0065] The upper and lower limits of the content of the unsaturated sulfonic acid or an inorganic salt thereof relative to 100 mol% of the monomer group are, for example, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 1, 0 mol%, etc. In one embodiment, the content of the unsaturated sulfonic acid or an inorganic salt thereof relative to 100 mol% of the monomer group is preferably 0 to 50 mol%.

[0066] The upper and lower limits of the content of the unsaturated sulfonic acid or an inorganic salt thereof relative to 100% by mass of the monomer group are exemplified as 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 1, 0% by mass, etc. In one embodiment, the content of the unsaturated sulfonic acid or an inorganic salt thereof relative to 100% by mass of the monomer group is preferably 0 to 75% by mass.

[0067] The upper and lower limits of the content of the unsaturated phosphoric acid or inorganic salt thereof relative to 100 mol% of the monomer group are, for example, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 1, 0 mol%, etc. In one embodiment, the content of the unsaturated phosphoric acid or inorganic salt thereof relative to 100 mol% of the monomer group is preferably 0 to 50 mol%.

[0068] The upper and lower limits of the content of the unsaturated phosphoric acid or an inorganic salt thereof relative to 100% by mass of the monomer group are exemplified as 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 1, 0% by mass, etc. In one embodiment, the content of the unsaturated phosphoric acid or an inorganic salt thereof relative to 100% by mass of the monomer group is preferably 0 to 75% by mass.

[0069] <Relative ratio of the amounts of components (a) to (c) in the monomer group> The upper and lower limits of the molar ratio of the (a) component to the (b) component contained in the monomer group [amount of substance of the (a) component / amount of substance of the (b) component] are, for example, 4, 3, 2, 1, 0.9, 0.7, 0.5, 0.3, 0.1, 0.09, 0.07, 0.05, etc. In one embodiment, the molar ratio of the (a) component to the (b) component contained in the monomer group [amount of substance of the (a) component / amount of substance of the (b) component] is preferably 0.05 to 4.

[0070] The upper and lower limits of the molar ratio of the (a) component to the (c) component contained in the monomer group [amount of substance of the (a) component / amount of substance of the (c) component] are 8000, 7500, 5000, 2500, 1000, 750, 500, 250, 100, 90, 75, 50, 25, 10, 9, 7, 5, 3, 1, 0.9, 0.7, 0.5, 0.3, 0.1, etc. In one embodiment, the molar ratio of the (a) component to the (c) component contained in the monomer group [amount of substance of the (a) component / amount of substance of the (c) component] is preferably 0.1 to 8000.

[0071] The upper and lower limits of the molar ratio of the (b) component to the (c) component contained in the monomer group [amount of substance of the (b) component / amount of substance of the (c) component] are 9500, 9000, 8000, 7500, 5000, 2500, 1000, 750, 500, 250, 100, 90, 75, 50, 25, 10, 9, 7, 5, 3, 1, 0.9, 0.7, 0.5, 0.4, etc. In one embodiment, the molar ratio of the (b) component to the (c) component contained in the monomer group [amount of substance of the (b) component / amount of substance of the (c) component] is preferably 0.4 to 9500.

[0072] The upper and lower limits of the mass ratio of the (a) component to the (b) component contained in the monomer group [mass of the (a) component / mass of the (b) component] are 8.5, 8, 7.5, 5, 3, 1, 0.9, 0.5, 0.3, 0.1, 0.09, 0.06, etc. In one embodiment, the mass ratio of the (a) component to the (b) component contained in the monomer group [mass of the (a) component / mass of the (b) component] is preferably 0.06 to 8.5.

[0073] The upper and lower limits of the mass ratio of the (a) component to the (c) component contained in the monomer group [mass of the (a) component / mass of the (c) component] are 8500, 8000, 7500, 5000, 2500, 1000, 750, 500, 250, 100, 90, 75, 50, 25, 10, 9, 7, 5, 3, 1, 0.9, 0.7, 0.5, 0.3, 0.1, 0.09, 0.06, etc. In one embodiment, the mass ratio of the (a) component to the (c) component contained in the monomer group [mass of the (a) component / mass of the (c) component] is preferably 0.06 to 8500.

[0074] The upper and lower limits of the mass ratio of the (b) component to the (c) component contained in the monomer group [mass of the (b) component / mass of the (c) component] are 8000, 7500, 5000, 2500, 1000, 750, 500, 250, 100, 90, 75, 50, 25, 10, 9, 7, 5, 3, 1, 0.9, 0.7, 0.5, 0.3, 0.13, etc. In one embodiment, the mass ratio of the (b) component to the (c) component contained in the monomer group [mass of the (b) component / mass of the (c) component] is preferably 0.13 to 8000.

[0075] <Monomers other than those mentioned above: Also called other components> In the above monomer group, a monomer (other component) other than any of the components (a) to (c) can be used as long as it does not impair the desired effects of the present invention. As the other component, various known ones may be used alone or two or more kinds may be used in combination.

[0076] Examples of other components include non-hydroxyl group-containing unsaturated carboxylic acid esters, conjugated dienes, aromatic vinyl compounds, and the like.

[0077] The hydroxyl-free unsaturated carboxylic acid ester is preferably a hydroxyl-free (meth)acrylic acid ester. Examples of the hydroxyl-free (meth)acrylic acid ester include a hydroxyl-free linear (meth)acrylic acid ester, a hydroxyl-free branched (meth)acrylic acid ester, a hydroxyl-free alicyclic (meth)acrylic acid ester, and a hydroxyl-free substituted (meth)acrylic acid ester.

[0078] Examples of non-hydroxyl group-containing linear (meth)acrylate esters 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, and decyl (meth)acrylate.

[0079] Examples of non-hydroxyl group-containing branched (meth)acrylic acid esters include i-propyl (meth)acrylate, i-butyl (meth)acrylate, i-amyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0080] Examples of the non-hydroxyl group-containing alicyclic (meth)acrylic acid ester include cyclohexyl (meth)acrylate.

[0081] Examples of non-hydroxyl group-containing substituted (meth)acrylic esters include glycidyl (meth)acrylate, allyl (meth)acrylate, and ethylene di(meth)acrylate.

[0082] The non-hydroxyl group-containing unsaturated carboxylic acid ester is preferably used for the purpose of imparting flexibility to the electrode. From the above viewpoint, the content of the non-hydroxyl group-containing unsaturated carboxylic acid ester relative to 100 mol % of the monomer group is preferably less than 40 mol % (e.g., 30, 20, 19, 15, 10, 5, less than 1 mol %, or 0 mol %).

[0083] The content of the non-hydroxyl group-containing unsaturated carboxylic acid ester relative to 100% by mass of the above monomer group is preferably 90% by mass or less (for example, less than 80, 70, 60, 50, 40, 30, 20, 19, 15, 10, 5, 1 mass%, or 0 mass%).

[0084] Examples of conjugated dienes include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadiene, and substituted and side-chain conjugated hexadienes.

[0085] The content of the conjugated diene relative to 100 mol % of the monomer group is preferably less than 10 mol %, more preferably 0 mol %, from the viewpoint of the cycle characteristics of a lithium ion battery.

[0086] The upper and lower limits of the content of the conjugated diene relative to 100% by mass of the monomer group are, for example, 30, 20, 10, 5, 1, 0% by mass, etc. In one embodiment, the content is preferably 0 to 30% by mass.

[0087] Examples of aromatic vinyl compounds include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, and divinylbenzene.

[0088] The content of the aromatic vinyl compound relative 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.

[0089] The upper and lower limits of the content of the aromatic vinyl compound relative to 100% by mass of the monomer group are, for example, 30, 20, 10, 5, 1, 0% by mass, etc. In one embodiment, the content is preferably 0 to 30% by mass.

[0090] The proportion of other components other than the hydroxyl group-free unsaturated carboxylic acid ester, the conjugated diene, and the aromatic vinyl compound in the monomer group is, relative to 100 mol% of the monomer group, exemplified by 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. Furthermore, relative to 100 mass% of the monomer group, exemplified by less than 10 mass%, less than 9 mass%, less than 7 mass%, less than 5 mass%, less than 4 mass%, less than 2 mass%, less than 1 mass%, less than 0.9 mass%, less than 0.5 mass%, less than 0.3 mass%, less than 0.1 mass%, less than 0.05 mass%, less than 0.01 mass%, 0 mass%, etc.

[0091] <Method of manufacturing component (A)> The component (A) can be synthesized by various known polymerization methods, preferably radical polymerization methods. Specifically, it is preferable to add a radical polymerization initiator and, if necessary, a chain transfer agent to a monomer mixture containing the above components, and carry out a polymerization reaction at a reaction temperature of 50 to 100° C. while stirring. The reaction time is not particularly limited, and is preferably 1 to 10 hours.

[0092] As the radical polymerization initiator, various known ones can be used without any particular limitation. Examples of the radical polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate; redox-based polymerization initiators combining the above-mentioned persulfates with a reducing agent such as sodium hydrogen sulfite; and azo-based initiators such as 2,2'-azobis-2-amidinopropane dihydrochloride. 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 the component (A).

[0093] For the purpose of improving production stability, before the radical polymerization reaction and / or when the obtained component (A) is dissolved in water, the pH of the reaction solution may be adjusted with a common neutralizing agent such as ammonia, organic amine, potassium hydroxide, sodium hydroxide, lithium hydroxide, etc. In this case, the pH is preferably 2 to 11. For the same purpose, it is also possible to use a metal ion-sequestering agent such as ethylenediaminetetraacetic acid (EDTA) or a salt thereof.

[0094] When the (A) component has an acid group, the neutralization rate can be adjusted appropriately according to the application (a neutralization rate of 100% indicates that the acid component contained in the (A) component is neutralized with the same number of moles of alkali. A neutralization rate of 50% indicates that the acid component contained in the (A) component is neutralized with half the number of moles of alkali). The neutralization rate when dispersing the electrode active material is not particularly limited. In one embodiment, the neutralization rate is preferably 95 to 100% after the formation of a coating layer or the like. From the viewpoint of preventing a decrease in the initial capacity, 95% or more is preferable, and from the viewpoint of preventing hydrolysis, 100% or less is preferable. Examples of neutralization salts include Li salts, Na salts, K salts, ammonium salts, Mg salts, Ca salts, Zn salts, and Al salts.

[0095] In one embodiment, the component (A) is preferably an inorganic salt. The inorganic salt of the component (A) refers to a salt in which the cationic moiety is a metal cation. Examples of the inorganic salt include those mentioned above.

[0096] <Physical properties of component (A)> Examples of upper and lower limits of the glass transition temperature of the component (A) are 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, and 0° C. In one embodiment, 0° C. or higher is preferable, and from the viewpoint of mechanical strength and heat resistance, 30° C. or higher is more preferable.

[0097] The glass transition temperature of component (A) can be adjusted by the combination of monomers. The glass transition temperature of component (A) can be calculated from the glass transition temperature (Tg) (absolute temperature: K) of the homopolymer of the monomers and their mass fractions based on the Fox formula shown below. 1 / Tg=(W1 / Tg1)+(W2 / Tg2)+(W3 / Tg3)+···+(W n / Tg n ) [Wherein, Tg is the glass transition temperature (K) of the polymer to be determined, W1 to W n is the mass fraction of each monomer, Tg1 to Tg n indicates the glass transition temperature (K) of the homopolymer of each monomer.

[0098] For example, the glass transition temperature is 165°C for homopolymer of acrylamide, 106°C for homopolymer of acrylic acid, -15°C for homopolymer of hydroxyethyl acrylate, and 105°C for homopolymer of acrylonitrile. The monomer composition constituting component (A) can be determined so as to obtain a component having a desired glass transition temperature. The glass transition temperature of the homopolymer of the monomer can be measured, for example, under conditions of 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 ​​described in literature can also be used. Examples of literature include "Chemical Handbook Basics II Edited by the Chemical Society of Japan (Revised 5th Edition)", p. 325, and the like.

[0099] The gel fraction of the cured product of component (A) is not particularly limited, but examples of upper and lower limits of the gel fraction of the cured product of component (A) are 99.9%, 95%, 90%, 85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, etc. In one embodiment, from the viewpoint of the effect of expressing springback resistance due to charge / discharge cycles, it is preferably 20% or more, and more preferably 25% or more.

[0100] The gel fraction of the cured product of component (A) is calculated using the following formula: Gel fraction (%) = {water insoluble residue (g) / mass of solid resin (g)} x 100 This is the value calculated by:

[0101] In one embodiment, the curing conditions for the cured product are, for example, 120° C. for 4 hours.

[0102] The gel fraction is measured, for example, as follows. An appropriate amount (for example, 10 g) of the aqueous binder solution for lithium ion battery electrodes containing component (A) is placed in an appropriate container (for example, an ointment can (manufactured by Sogo Rikagaku Glass Works, product name "Ointment Can Tinplate")) and dried under appropriate drying conditions (for example, in a circulating air dryer (manufactured by Advantec Toyo Co., Ltd., product name "Air-Blowing Constant Temperature Dryer DSR420DA") at 120°C for 4 hours), to obtain a solid resin after thermal crosslinking. The mass of the solid resin is accurately measured at 25°C using an appropriate mass meter (for example, manufactured by Sartorius Japan Co., Ltd., product name "Standard Balance CPA324S"). The measured solid resin is transferred to an appropriate container (e.g., a 300 mL beaker) containing an appropriate amount (e.g., 150 mL) of pure water, and immersed in the water under appropriate conditions (e.g., at 25°C for 3 hours) while stirring using an appropriate magnetic stirrer (e.g., Tokyo Rikakikai Co., Ltd., product name "Powerful Magnetic Stirrer RCX-1000D"), and then filtered under reduced pressure using an appropriate device (e.g., Kiriyama Funnel (manufactured by Kiriyama Seisakusho Co., Ltd., product name "Kiriyama Funnel SB-60") and a suction bell (manufactured by Kiriyama Seisakusho Co., Ltd., product name "Suction Bell VKB-200"), and filter paper (manufactured by Kiriyama Seisakusho Co., Ltd., "No. 50B")). Thereafter, the insoluble residue remaining on the filter paper is dried under appropriate conditions (e.g., 120°C for 3 hours) in an appropriate dryer (e.g., the above-mentioned air circulating dryer), and the mass of the insoluble residue is accurately measured at an appropriate temperature (e.g., 25°C) using an appropriate mass meter (e.g., the above-mentioned mass meter), and the gel fraction of the resin after thermal crosslinking of the water-soluble battery binder is calculated using the above formula.

[0103] The thermal crosslinking of the (A) component is believed to be due to the hydroxyl groups derived from the hydroxyl group-containing vinyl ether (a) and the amide groups derived from the (meth)acrylamide group-containing compound (b). The molar ratio of the hydroxyl groups to the amide groups (hydroxyl groups / amide groups) in the (A) component is not particularly limited, but it is preferable that the amide groups are in excess. The upper and lower limits of the molar ratio of the hydroxyl groups to the amide groups (hydroxyl groups / amide groups) are exemplified as 2.0, 1.5, 1.0, 0.9, 0.7, 0.5, 0.3, 0.1, 0.09, 0.07, 0.05, etc. In one embodiment, the hydroxyl groups / amide groups=0.05 to 2.0 is preferred, and 0.1 to 2.0 is more preferred. By satisfying the above, it is believed that the effect of expressing springback resistance accompanying charge / discharge cycles can be obtained without impairing the adhesion of the active material layer to the current collector, but the present invention is not intended to be limited thereto.

[0104] The weight average molecular weight (Mw) of the (A) component 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 the dispersion stability of the slurry, it is preferably 100,000 to 7 million, and more preferably 350,000 to 6 million.

[0105] The number average molecular weight (Mn) of the component (A) is not particularly limited, but examples of the upper and lower limits include 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, 300,000, 200,000, 100,000, 50,000, 10,000, etc. In one embodiment, the number average molecular weight (Mn) of the component (A) is preferably 10,000 or more.

[0106] The weight average molecular weight and number average molecular weight can be determined, for example, as a polyacrylic acid equivalent value measured in an appropriate solvent by gel permeation chromatography (GPC).

[0107] Examples of the upper and lower limits of the molecular weight distribution (Mw / Mn) of the component (A) are 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 the component (A) is preferably 1.1 to 15.

[0108] The B-type viscosity of an aqueous solution containing 13% by mass of component (A) is not particularly limited, but examples of the upper and lower limits include 100,000, 90,000, 80,000, 70,000, 60,000, 50,000, 45,000, 40,000, 30,000, 20,000, 10,000, 900, 700, 500, 300, 200, 1000, 900, 700, 500, 300, 200, 100 mPa s, etc. In one embodiment, the B-type viscosity is preferably in the range of 100 to 100,000 mPa s.

[0109] The Brookfield viscosity is measured using a Brookfield viscometer such as the "Brookfield Viscometer Model BM" manufactured by Toki Sangyo Co., Ltd.

[0110] Examples of the upper and lower limits of the pH of the aqueous binder solution for lithium ion battery electrodes are 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, and 5. In one embodiment, the pH of the aqueous binder solution for lithium ion battery electrodes is preferably pH 5 to 9 from the viewpoint of solution stability.

[0111] 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.).

[0112] The upper and lower limits of the content of the component (A) relative to 100% by mass of the aqueous binder solution for lithium ion battery electrodes are, for example, 25, 23, 21, 20, 19, 15, 14, 12, 10, 9, 7, 6, 5% by mass, etc. In one embodiment, the content of the component (A) relative to 100% by mass of the aqueous binder solution for lithium ion battery electrodes is preferably 5 to 25% by mass.

[0113] The upper and lower limits of the water content relative to 100% by mass of the aqueous binder solution for lithium ion battery electrodes are, for example, 95, 90, 85, 80% by mass, etc. In one embodiment, the water content relative to 100% by mass of the aqueous binder solution for lithium ion battery electrodes is preferably 80 to 95% by mass.

[0114] The upper and lower limits of the mass ratio of the component (A) to water contained in the aqueous binder solution for lithium ion battery electrodes are, for example, 0.25, 0.2, 0.15, 0.1, 0.05, etc. In one embodiment, the mass ratio of the component (A) to water contained in the aqueous binder solution for lithium ion battery electrodes is preferably 0.05 to 0.25.

[0115] <Additives> The aqueous binder solution for lithium ion battery electrodes may contain an additive that is neither classified as component (A) nor as water.

[0116] Examples of the additives include dispersants, leveling agents, antioxidants, thickeners, and dispersions (emulsions).

[0117] Examples of the content of the additive, relative to 100 mass% of the (A) component, include 5 mass% or less, less than 5 mass%, less than 4 mass%, less than 2 mass%, less than 1 mass%, less than 0.9 mass%, less than 0.5 mass%, less than 0.4 mass%, less than 0.2 mass%, less than 0.1 mass%, less than 0.09 mass%, less than 0.05 mass%, less than 0.04 mass%, less than 0.02 mass%, less than 0.01 mass%, 0 mass%, etc. In one embodiment, the content of the additive is preferably 5 mass% or less relative to 100 mass% of the (A) component, from the viewpoint that haze occurs in the binder when the content exceeds 5 mass%.

[0118] Examples of the content of the additive relative to 100% by mass of the above aqueous solution are 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, and 0% by mass.

[0119] Examples of the dispersant include anionic dispersants, cationic dispersants, nonionic dispersants, and polymer dispersants.

[0120] Examples of the leveling agent include surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants. By using a surfactant, it is possible to prevent repellency during coating and improve the smoothness of the slurry layer (coating layer).

[0121] Examples of the antioxidant include phenol compounds, hydroquinone compounds, organic phosphorus compounds, sulfur compounds, phenylenediamine compounds, and polymeric phenol compounds. The polymeric phenol compounds are polymers having a phenol structure in the molecule. The weight average molecular weight of the polymeric phenol compounds is preferably 200 to 1000, and more preferably 600 to 700.

[0122] Examples of thickeners include cellulose-based polymers such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose, and their ammonium salts and alkali metal salts; (modified) poly(meth)acrylic acid and their ammonium salts and alkali metal salts; (modified) polyvinyl alcohols such as copolymers of acrylic acid or acrylates and vinyl alcohol, and copolymers of maleic anhydride or maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, modified polyacrylic acid, oxidized starch, starch phosphate, casein, various modified starches, and hydrogenated acrylonitrile-butadiene copolymers.

[0123] 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, poly ... 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.

[0124] The dispersion (emulsion) may be contained in an amount greater than the amount of the additives described above. The upper and lower limits of the content of the dispersion (emulsion) relative to 100% by mass of the (A) component are, for example, 20, 19, 17, 15, 13, 10, 9, 7, 5, 4, 2, 1, and 0% by mass. In one embodiment, from the viewpoints of springback resistance and discharge capacity retention rate, the amount of the dispersion (emulsion) added relative to 100% by mass of the (A) component is preferably less than 5% by mass.

[0125] The aqueous binder solution for a lithium ion battery electrode can be used as an aqueous binder solution for a lithium ion battery negative electrode or an aqueous binder solution for a lithium ion battery positive electrode.

[0126] [Lithium-ion battery electrode slurry: also called slurry] The present disclosure provides a slurry for a lithium ion battery electrode, comprising the above-mentioned aqueous binder solution for a lithium ion battery electrode and an electrode active material (B).

[0127] In this disclosure, "slurry" means a suspension of liquid and solid particles.

[0128] The upper and lower limits of the content of the component (A) relative to 100 mass% of the slurry are 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 mass%, etc. In one embodiment, the content is preferably 0.1 to 99.9 mass%.

[0129] Examples of water include ultrapure water, pure water, distilled water, ion-exchanged water, and tap water.

[0130] The upper and lower limits of the water content relative to 100% by mass of the slurry are, for example, 70, 65, 60, 55, 50, 45, 40, 35, 30% by mass, etc. In one embodiment, the content is preferably 30 to 70% by mass.

[0131] <Electrode active material (B)> The electrode active material may be used alone or in combination of two or more thereof. Examples of the electrode active material include a negative electrode active material and a positive electrode active material.

[0132] The negative electrode active material is not particularly limited as long as it can reversibly absorb and release lithium, and an appropriate material can be selected depending on the type of the target lithium ion battery, and 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 aluminum compounds that are alloyed with lithium.

[0133] The above carbon materials include graphite which is highly crystalline carbon (also called 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.

[0134] In addition to silicon, silicon oxide, and silicon alloy, the above silicon materials include SiC, SiO x C y (0 < x ≤ 3, 0 < y ≤ 5), Si3N4, Si2N2O, SiO x Silicon oxide composites represented by (0 < x ≤ 2) (such as the 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.

[0135] The above silicon oxide has a composition formula SiO x Silicon oxide represented by (0 < x < 2, preferably 0.1 ≤ x ≤ 1) is preferred.

[0136] 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 - 70 mol% with respect to 100 mol% of the metal elements in the above silicon alloy. Note that the silicon material may be any of single crystal, polycrystal, and amorphous.

[0137] When a silicon material is used as the electrode active material, an electrode active material other than the silicon material may be used in combination. Such electrode active materials include the above-mentioned 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.) Examples include composite metal oxides represented by the formula and other metal oxides. When a silicon material is used as the electrode active material, it is preferable to use a carbon material in combination because the volume change accompanying the occlusion and release of lithium is small.

[0138] 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 compounds (such as LiFePO4), and lithium-transition metal sulfate compounds (Li x Fe2(SO4)3), lithium-titanium composite oxide (lithium titanate: Li4Ti5O 12 ), etc. lithium-transition metal composite oxides, and other conventionally known electrode active materials, etc. are exemplified.

[0139] From the viewpoint of significantly exerting the effects of the present invention, the carbon material and / or the material alloying with lithium are preferably contained in the 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.

[0140] In one embodiment, the electrode active material (B) is preferably a negative electrode active material containing 1 mass % or more (2, 5, 10, 25, 50, 75, 90 mass % or more, 100 mass %) of silicon and / or silicon oxide covered with a carbon layer.

[0141] Positive electrode active materials are broadly classified into active materials containing inorganic compounds and active materials containing organic compounds. Examples of inorganic compounds contained in positive electrode active materials include metal oxides. Examples of metal oxides include transition metal oxides, composite oxides of lithium and transition metals, transition metal sulfides, etc. Examples of the transition metals include Fe, Co, Ni, Mn, Al, etc. Inorganic compounds used in positive electrode active materials include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiFePO4, LiNi 1 / 2 Mn 3 / 2 O4, LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, LiCo 0.3 Ni 0.5 Mn 0.2 O2, LiCo 0.2 Ni 0.6 Mn 0.2 O2, LiCo 0.1 Ni 0.8 Mn 0.1 O2, LiCo 0.15 Ni 0.8 Al 0.05 O2, Li [Li 0.1 Al 0.1 Mn 1.8 ]O4, LiFeVO4 and other lithium-containing composite metal oxides; TiS2, TiS3, amorphous MoS2 and other transition metal sulfides; Cu2V2O3, amorphous V2O-P2O5, MoO3, V2O5, V6O 13Examples of the organic compound contained in the positive electrode 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 making a carbon source material present during reduction and firing. Also, these compounds may be partially substituted with elements. Among these, in terms of practicality, electrical properties, and long life, LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiFePO4, LiNi 1 / 2 Mn 3 / 2 O4, LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, LiCo 0.3 Ni 0.5 Mn 0.2 O2, LiCo 0.2 Ni 0.6 Mn 0.2 O2, LiCo 0.1 Ni 0.8 Mn 0.1 O2, LiCo 0.15 Ni 0.8 Al 0.05 O2, Li [Li 0.1 Al 0.1 Mn 1.8 ]O4 is preferred.

[0142] In one embodiment, the electrode active material (B) is preferably a positive electrode active material containing iron phosphate and / or a metal oxide.

[0143] The shape of the electrode active material is not particularly limited, and may be any shape such as fine particles or thin film, but fine particles are preferred. The average particle size of the electrode active material is not particularly limited, but the upper and lower limits are 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 handling property is good, and if it is 50 μm or less, the application of the electrode is easy, so that the average particle size of the electrode active material is preferably 0.1 to 50 μm, more preferably 0.1 to 45 μm, even more preferably 1 to 10 μm, and particularly preferably 5 μm.

[0144] In this disclosure, the term "particle size" refers to the maximum distance between any two points on the contour of a particle (hereinafter the same). In addition, in this disclosure, the term "average particle size" refers to a value calculated as the average particle size of particles observed in several to several tens of fields of view using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) unless otherwise specified (hereinafter the same).

[0145] The upper and lower limits of the content of the component (A) relative to 100% by mass of the electrode active material (B) in the above slurry are 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 content of the component (A) relative to 100% by mass of the electrode active material (B) is preferably 0.5 to 15% by mass.

[0146] <Conductive assistant> In one embodiment, a conductive assistant may be included in the slurry. Examples of the conductive assistant include fibrous carbon such as vapor grown carbon fiber (VGCF), carbon nanotube (CNT), and carbon nanofiber (CNF), graphite particles, carbon black such as acetylene black, ketjen black, and furnace black, and fine powder of Cu, Ni, Al, Si, or alloys thereof having an average particle size of 10 μm or less. The content of the conductive assistant is not particularly limited, but is preferably 0 to 10 mass %, more preferably 0.5 to 6 mass %, based on the electrode active material components.

[0147] <Slurry viscosity adjusting solvent> The slurry viscosity adjusting solvent is not particularly limited, and 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 the slurry viscosity adjusting 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 and sulfone solvents such as dimethyl sulfoxide and sulfolane; and water. 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 relative to 100% by mass of the slurry.

[0148] The above-mentioned slurry may contain, as an additive, an additive other than the (A) component, the (B) component, water, a conductive assistant, or a slurry viscosity adjusting solvent, within a range that does not impair the effects of the present invention. Examples of the additive include those mentioned above.

[0149] The content of the additives is, for example, 0 to 5% by mass, less than 1% by mass, less than 0.1% by mass, less than 0.01% by mass, 0% by mass, etc., relative to 100% by mass of the component (A).

[0150] The content of the additive relative to 100% by mass of the component (B) is, for example, 0 to 5% by mass, less than 1% by mass, less than 0.1% by mass, less than 0.01% by mass, or 0% by mass.

[0151] The dispersion (emulsion) may be contained in a larger amount than the additives described above. The upper and lower limits of the content of the dispersion (emulsion) relative to 100% by mass of the slurry for lithium ion battery electrodes are 20, 19, 17, 15, 13, 10, 9, 7, 5, 4, 2, 1, and 0% by mass. In one embodiment, from the viewpoint of springback resistance and discharge capacity retention rate, the amount of the dispersion (emulsion) added relative to 100% by mass of the aqueous solution or the slurry for lithium ion battery electrodes is preferably less than 5% by mass.

[0152] The lithium ion battery electrode slurry can be used as a lithium ion battery negative electrode slurry or a lithium ion battery positive electrode slurry.

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

[0154] Examples of means for mixing the slurry include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, and a Hobart mixer.

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

[0156] The current collector may be any of various known current collectors without any particular limitation. The material of the current collector is not particularly limited, and examples thereof include metal materials such as copper, iron, aluminum, nickel, stainless steel, and nickel-plated steel, and carbon materials such as carbon cloth and carbon paper. The form of the current collector is also not particularly limited, and examples of metal materials include metal foil, metal cylinder, metal coil, and metal plate, and examples of carbon materials include carbon plate, carbon thin film, and carbon cylinder. Among them, when the electrode active material is used for the negative electrode, copper foil is preferred as the current collector because it is currently used in industrialized products.

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

[0158] The drying means is not particularly limited, and 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 electrode (cured product) is not particularly limited, but is preferably 5 to 300 μm, and more preferably 10 to 250 μm. By setting the thickness within the above range, it may become easier to obtain a sufficient Li absorption / release function for a high-density current value.

[0160] The lithium ion battery electrode can be used as a positive electrode or a negative electrode of a lithium ion battery.

[0161] [Lithium-ion battery] The present disclosure provides a lithium ion battery including the lithium ion battery electrode. The battery also includes, but is not limited to, an electrolyte and a packaging material.

[0162] (electrolyte) The electrolyte solution may be, for example, a non-aqueous electrolyte solution in which a supporting electrolyte is dissolved in a non-aqueous solvent, etc. The non-aqueous electrolyte solution may also contain a film-forming agent.

[0163] As the non-aqueous solvent, various known solvents can be used without any particular limitation, and 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 a cyclic carbonate and a chain carbonate is preferred.

[0164] The supporting electrolyte is a lithium salt. Various known lithium salts can be used without particular limitation, and 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, (C2F5SO2)NLi, etc. Among them, LiPF6, LiClO4, and CF3SO3Li, which are easily soluble in a solvent and show a high degree of dissociation, are preferred. The higher the degree of dissociation of the supporting electrolyte used, the higher the lithium ion conductivity, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0165] The coating agent may be any of various known agents without particular limitation, and may be used alone or in combination of two or more. Examples of the coating 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 coating 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 that order. By setting the content to 10% by mass or less, it becomes easier to obtain the advantages of the coating agent, such as suppression of initial irreversible capacity and improvement of low-temperature characteristics and rate characteristics.

[0166] The shape of the lithium ion battery is not particularly limited. Examples of the shape of the lithium ion battery include a cylinder type in which a sheet electrode and a separator are spirally wound, a cylinder type with 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. In addition, by housing a battery of these shapes in an arbitrary exterior case, it can be used in an arbitrary shape such as a coin type, a cylindrical type, or a square type.

[0167] The method for manufacturing the lithium ion battery is not particularly limited, and the battery may be assembled in an appropriate procedure according to the structure of the battery. The lithium ion battery may be manufactured, for example, by the method described in JP 2013-089437 A. The battery can be manufactured by placing a negative electrode on an exterior case, providing an electrolyte and a separator thereon, placing a positive electrode facing the negative electrode, and fixing them with a gasket and a sealing plate. EXAMPLES

[0168] The present invention will be specifically described below through examples and comparative examples. However, the above-mentioned description of the preferred embodiment and the following examples are provided for illustrative purposes only and are not provided 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 claims. In each example and comparative example, unless otherwise specified, numerical values ​​such as parts and % are based on mass.

[0169] 1. (A) Production of component Manufacturing Example 1 In a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, 1450g of ion-exchanged water, 137.3g (1.5580mol) of hydroxyethyl vinyl ether, 188.6g (1.3266mol) of 50% aqueous acrylamide solution, and 0.09g (0.0006mol) of sodium methallylsulfonate were placed, and oxygen in the reaction system was removed by passing nitrogen gas through it, after which the temperature was raised to 50°C. 2.3g of 2,2'-azobis-2-amidinopropane dihydrochloride (manufactured by Nippoh Chemical Co., Ltd., product name "NC-32") and 50g of ion-exchanged water were placed therein, and the temperature was raised to 80°C and the reaction was carried out for 3 hours, obtaining an aqueous solution containing a water-soluble polymer.

[0170] Manufacturing Example 2 550g of ion-exchanged water was placed in a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, and oxygen in the reaction system was removed by passing nitrogen gas through the reaction apparatus, and the temperature was raised to 80°C. A mixed solution of 99.0g (1.1236mol) of hydroxyethyl vinyl ether, 870.8g (6.1241mol) of 50% aqueous acrylamide solution, 0.2g (0.0014mol) of sodium methallylsulfonate, and 100g of ion-exchanged water, and a mixed solution of 5.3g of 2,2'-azobis-2-amidinopropane dihydrochloride (manufactured by Nippoh Chemical Co., Ltd., product name "NC-32") and 170g of ion-exchanged water were simultaneously added dropwise to the reaction apparatus. The mixture was added dropwise over 3 hours while being kept at 80°C, to obtain an aqueous solution containing a water-soluble polymer.

[0171] Manufacturing Examples 3 and 4 An aqueous solution containing a water-soluble polymer was prepared in the same manner as in Production Example 1 above, except that the monomer composition in Production Example 1 was changed to that shown in Table 1.

[0172] Production Example 5 In a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, 1340g of ion-exchanged water, 68.8g (0.7806mol) of hydroxyethyl vinyl ether, 237.0g (1.6669mol) of 50% aqueous acrylamide solution, 55.2g (0.6123mol) of 80% acrylic acid, and 0.24g (0.0015mol) of sodium methallylsulfonate were placed, and oxygen in the reaction system was removed by passing nitrogen gas through it, after which the temperature was raised to 50°C. 2.3g of 2,2'-azobis-2-amidinopropane dihydrochloride (manufactured by Nippoh Chemical Co., Ltd., product name "NC-32") and 50g of ion-exchanged water were placed therein, and the temperature was raised to 80°C and the reaction was carried out for 3 hours. Thereafter, 51.0 g (0.6123 mol) of a 48% aqueous sodium hydroxide solution was added as a neutralizing agent and stirred, and ion-exchanged water was added so that the solid content concentration became 13%, to obtain an aqueous solution containing a water-soluble polymer.

[0173] Manufacturing Examples 6 and 7 An aqueous solution containing a water-soluble polymer was prepared in the same manner as in Production Example 5 above, except that the monomer composition in Production Example 5 was changed to that shown in Table 1.

[0174] Comparative Manufacturing Example 1 In a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, 1310 g of ion-exchanged water, 462.9 g (3.2549 mol) of 50% acrylamide aqueous solution, and 0.26 g (0.0016 mol) of sodium methallylsulfonate were placed, and oxygen in the reaction system was removed by passing nitrogen gas through it, after which the temperature was raised to 50° C. Then, 2.3 g of 2,2'-azobis-2-amidinopropane dihydrochloride (manufactured by Nippoh Chemical Co., Ltd., product name "NC-32") and 50 g of ion-exchanged water were placed, and the temperature was raised to 80° C. and the reaction was carried out for 3 hours, to obtain an aqueous solution containing a water-soluble polymer.

[0175] Comparative Manufacturing Example 2 An aqueous solution containing a water-soluble polymer was prepared in the same manner as in Comparative Production Example 1, except that the monomer composition in Comparative Production Example 1 was changed to that shown in Table 1.

[0176] Comparative Manufacturing Example 3 In a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, 1400g of ion-exchanged water, 200.9g (1.4129mol) of 50% acrylamide aqueous solution, 46.8g (0.5194mol) of 80% acrylic acid, 76.9g (0.6623mol) of 2-hydroxyethyl acrylate, and 0.41g (0.0026mol) of sodium methallylsulfonate were placed, and oxygen in the reaction system was removed by passing nitrogen gas through it, and the temperature was raised to 50°C. 2.2g of 2,2'-azobis-2-amidinopropane dihydrochloride (manufactured by Nippoh Chemical Co., Ltd., product name "NC-32") and 50g of ion-exchanged water were placed therein, and the temperature was raised to 80°C and the reaction was carried out for 3 hours. Thereafter, 34.6 g (0.4156 mol) of a 48% aqueous solution of sodium hydroxide was added as a neutralizing agent and stirred, and ion-exchanged water was added so that the solid concentration became 13%, to obtain an aqueous solution containing a water-soluble polymer.

[0177] Comparative Example 4 An aqueous solution containing a water-soluble polymer was prepared in the same manner as in Comparative Production Example 3, except that the monomer composition and the amount of neutralizing agent in Comparative Production Example 3 were changed to those shown in Table 1.

[0178] B type viscosity The viscosity of each aqueous binder solution 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 of less than 20,000 mPa s: use No. 3 rotor, rotation speed 6 rpm.

[0179] Weight average molecular weight The weight average molecular weight was determined as a polyacrylic acid equivalent value measured by gel permeation chromatography (GPC) in 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).

[0180] Gel fraction 10 g of the aqueous binder solution for lithium-ion battery electrodes containing component (A) was placed in an ointment can (manufactured by Sogo Rikagaku Glass Works, product name "Ointment Can Tinplate") and dried at 120°C for 4 hours in a circulating air dryer (manufactured by Advantec Toyo Co., Ltd., product name "Air-Blowing Constant Temperature Dryer DSR420DA") to obtain a solid resin after thermal crosslinking. The mass of the solid resin was accurately measured at 25°C using a mass meter (manufactured by Sartorius Japan, product name "Standard Balance CPA324S"). The measured solid resin was transferred to a container (300 mL beaker) containing 150 mL of pure water, and immersed in water at 25 ° C for 3 hours under stirring conditions using a magnetic stirrer (manufactured by Tokyo Rikakikai Co., Ltd., product name "Powerful Magnetic Stirrer RCX-1000D"), and then filtered under reduced pressure with filter paper (manufactured by Kiriyama Seisakusho Co., Ltd., "No. 50B") using a Kiriyama funnel (manufactured by Kiriyama Seisakusho Co., Ltd., product name "Kiriyama Funnel SB-60") and a suction bell (manufactured by Kiriyama Seisakusho Co., Ltd., product name "Suction Bell VKB-200") The insoluble residue remaining on the filter paper was then dried at 120 ° C for 3 hours in the above-mentioned air circulation dryer, and the mass of the insoluble residue was accurately measured with the above-mentioned mass meter at 25 ° C., and the gel fraction of the resin after thermal crosslinking of the water-soluble battery binder was calculated from the following formula. Gel fraction (%) = {insoluble residue (g) / mass of solid resin (g)} x 100

[0181] Curl Rating The curl was evaluated as follows: Two adjacent sides of a piece of aluminum foil cut to 50mm x 50mm were fixed to a glass plate with tape, and a binder solution was evenly applied to the surface of the aluminum foil to a thickness of 400μm using the doctor blade method, and then dried for 5 minutes in a 120℃ air circulating dryer (manufactured by ADVANTEC, product name "DRS420DA"). After removing from the dryer and leaving it to stand for 2 minutes, the height between the corner not fixed with tape and the glass surface was measured. The greater the height, the greater the curl. The curl of the binder film correlates with the curl when made into an electrode, and the greater the curl of the binder film, the greater the curl when made into an electrode, which may cause problems such as peeling during the electrode creation process. The height was evaluated as follows: A: Less than 10 mm B: 10mm or more and less than 20mm C:20mm or more

[0182] [Table 1] ·HEVE: Hydroxyethyl vinyl ether ·DEGV: Diethylene glycol monovinyl ether AM: Acrylamide (Mitsubishi Chemical Corporation "50% Acrylamide") ·DMAA: N,N-Dimethyl(meth)acrylamide ("DMAA" manufactured by KJ Chemicals Co., Ltd.) AA: Acrylic acid (Osaka Organic Chemical Industry Co., Ltd. "80% acrylic acid") AN: Acrylonitrile (Mitsubishi Chemical Corporation "Acrylonitrile") ·HEA: 2-hydroxyethyl acrylate ("HEA" manufactured by Osaka Organic Chemical Industry Ltd.) ·SMAS: Sodium methallyl sulfonate NaOH: Sodium hydroxide (Kanto Chemical Co., Ltd. "48% sodium hydroxide solution")

[0183] 2. Electrode slurry production and cell fabrication and evaluation Example 1-1: Evaluation of electrodes <Production of electrode slurry> Using a commercially available planetary centrifugal mixer (product name "Awatori Rentaro", manufactured by Thinky Corporation), 3 parts by mass of the aqueous solution obtained in Production Example 1 in terms of solid content, 91 parts of lithium cobalt oxide LCO (LiCoO2, manufactured by Nippon Chemical Industry Co., Ltd., product name "Cellseed C-5H") as an electrode active material, and 6 parts of acetylene black were mixed in a container dedicated to the mixer. Ion-exchanged water was added thereto so that the solid content concentration was 50%, and the container was set in the mixer. Next, the mixture was kneaded at 2000 rpm for 10 minutes, and then degassed for 1 minute to obtain a slurry for an electrode.

[0184] <Electrode manufacturing> The above-mentioned lithium-ion battery electrode slurry was uniformly applied to the surface of an aluminum foil current collector by a doctor blade method so that the film thickness after drying would be 100 μm, and then the coating was dried at 60° C. for 30 minutes and then heat-treated at 150° C. / vacuum for 120 minutes. After that, the density of the film (electrode active material layer) was 3.0 g / cm 3 The electrode was obtained by pressing the electrode sheet with a roll press machine so that the electrode sheet had a thickness of 100 mm.

[0185] <Assembling lithium half-cells> In an argon-substituted glove box, the above electrode was punched out to a diameter of 16 mm and placed inside the packing on the Al bottom cover of a test cell (manufactured by Nippon Tomcell Co., Ltd.). Next, a separator made of a polypropylene porous film punched out to a diameter of 24 mm (manufactured by CS TECH CO., LTD, product name "Selion P2010") was placed, and 500 μL of electrolyte was poured in to prevent air from entering, and then a commercially available metallic lithium foil punched out to a diameter of 16 mm was placed on the separator. The exterior body of the test cell was closed and sealed with screws to assemble a lithium half cell. The electrolyte used here was a solution in which LiPF6 was dissolved at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1 / 1 (mass ratio).

[0186] Examples 1-2 to 1-8, Comparative Examples 1-1 to 1-5 A lithium half-cell was obtained in the same manner as in Example 1-1 above, except that the composition was changed to that shown in Table 2.

[0187] Example 2-1: Evaluation of electrodes <Production of electrode slurry> Using a commercially available planetary centrifugal mixer (product name "Awatori Rentaro", manufactured by Thinky Corporation), 5 parts by mass of the aqueous solution obtained in Production Example 1, 20 parts by mass of silicon monoxide particles having a D50 of 5 μm ("CC Powder", manufactured by Osaka Titanium Technologies Co., Ltd.), and 80 parts by mass of natural graphite (manufactured by Ito Graphite Industries Co., Ltd., product name "Z-5F") were mixed in a dedicated container for the mixer. Ion-exchanged water was added thereto so that the solid concentration was 40%, and the container was set in the mixer. Next, the mixture was kneaded at 2000 rpm for 10 minutes, and then degassed for 1 minute to obtain a slurry for electrodes.

[0188] <Electrode manufacturing> The above-mentioned lithium-ion battery electrode slurry was uniformly applied to the surface of a copper foil current collector by a doctor blade method so that the film thickness after drying would be 80 μm, and then the coating was dried at 150° C. for 30 minutes and then heat-treated at 150° C. / vacuum for 120 minutes. After that, the density of the film (electrode active material layer) was 1.5 g / cm 3 The electrode was obtained by pressing the electrode sheet with a roll press machine so that the electrode sheet had a thickness of 100 mm.

[0189] <Assembling lithium half-cells> A lithium half-cell was produced in the same manner as in Example 1-1.

[0190] Comparative Example 2-1 A lithium half-cell was obtained in the same manner as in Example 2-1 above, except that the composition was changed to that shown in Table 2.

[0191] <Storage stability test of electrode slurry> The viscosity of the electrode slurry (unit: mPa s) was measured using a Brookfield viscometer, and then it was stored in an oven heated to 40°C for three days. After storage, the viscosity was measured again using the Brookfield viscometer, and the change in viscosity was calculated using the following formula and evaluated according to the following criteria. Viscosity change (%) = (viscosity of electrode slurry after storage) / (viscosity of electrode slurry before storage) × 100 A: Less than 110% B: 110% or more but less than 120% C: 120% or more but less than 130% D: 130% or more

[0192] <Electrode flexibility evaluation> The electrode was cut to a width of 10 mm and a length of 70 mm, and wrapped around a 30 mm diameter Teflon rod with the active material layer facing outward. The surface condition of the active material layer was observed and evaluated according to the following criteria. A: The active material layer bonded to the current collector had no cracks or peeling whatsoever. B: Cracks are observed in the active material layer bonded to the current collector, but no peeling is observed. C: Cracks and peeling were observed in the active material layer bonded to the current collector.

[0193] <Electrode Adhesion Evaluation> The electrode adhesion was evaluated as follows. A test piece measuring 2 cm wide x 10 cm long was cut out from the electrode and fixed with the coating surface facing up. Next, a 15 mm wide adhesive tape ("Cellotape (registered trademark)" manufactured by Nichiban Co., Ltd.) (specified in JIS Z1522) was applied to the surface of the active material layer of the test piece while pressing it, and then the stress was measured when the adhesive tape was peeled off from one end of the test piece in the 180° direction at a speed of 30 mm / min using a tensile tester ("Tensilon RTM-100" manufactured by A&D Co., Ltd.) under conditions of 25°C. The measurement was performed five times, converted into a value per 15 mm width, and the average value was calculated as the peel strength. The higher the peel strength, the higher the adhesion strength between the current collector and the active material layer or the binding strength between the active materials, indicating that the active material layer or the active materials are less likely to peel off from the current collector. The peel strength was evaluated as follows. A: The peel strength was greater than 5 N / m. B: Peel strength was 1 to 5 N / m. C: The peel strength was less than 1 N / m.

[0194] <Charge / discharge measurement> The lithium half-cell was placed in a thermostatic chamber at 25° C., and charging was started at a constant current (0.1 C), and charging was completed (cut off) when the voltage reached 5.0 V. Next, discharging was started at a constant current (0.1 C), and charging and discharging was repeated 30 times, with discharging completed (cut off) when the voltage reached 3.0 V. In the above measurement conditions, "1C" refers to the current value at which a cell with a certain capacity is discharged at a constant current and the discharge is completed in 1 hour. For example, "0.1C" refers to the current value at which the discharge is completed in 10 hours, and "10C" refers to the current value at which the discharge is completed in 0.1 hour.

[0195] Example 2-1, Comparative Example 2-1 <Charge / discharge measurement> The lithium half-cell was placed in a thermostatic chamber at 25° C., and charging was started at a constant current (0.1 C), and charging was completed (cut off) when the voltage reached 0.01 V. Next, discharging was started at a constant current (0.1 C), and charging and discharging was repeated 30 times, with discharging completed (cut off) when the voltage reached 1.0 V.

[0196] <Initial Coulombic Efficiency Measurement> The initial coulombic efficiency was calculated from the initial charge capacity (mAh) and initial discharge capacity (mAh) when a charge / discharge cycle test was performed at room temperature (25° C.) using the following formula. Initial coulombic efficiency = {(initial discharge capacity) / (initial charge capacity)} x 100

[0197] <Springback rate measurement> After 30 charge-discharge cycle tests at room temperature (25°C), the lithium half-cell was disassembled and the thickness of the electrodes was measured. The springback rate of the electrodes was calculated using the following formula. Springback rate = {(electrode thickness after 30 cycles - current collector thickness) / (electrode thickness before charge / discharge - current collector thickness)} x 100 - 100 (%)

[0198] <Discharge capacity maintenance rate> The discharge capacity retention rate was calculated according to the following formula. Discharge capacity retention rate = {(discharge capacity at 30th cycle) / (discharge capacity at 1st cycle)} x 100 (%)

[0199] [Table 2] · LCO: Lithium cobalt oxide (LiCoO2) NMC: Lithium nickel manganese cobalt oxide (Li[Ni 1 / 3 Mn 1 / 3 Co 1 / 3 ]O2)

Claims

1. The aqueous binder solution for a lithium ion battery electrode comprises a fluorine atom-free water-soluble polymer (A) which is a polymer of a monomer group containing, relative to 100 mol %, 5 to 80 mol % of a hydroxyl group-containing vinyl ether (a) and 20 to 95 mol % of a (meth)acrylamide group-containing compound (b).

2. 2. The aqueous binder solution for lithium ion battery electrodes according to claim 1, wherein the monomer group contains 0.01 to 50 mol % of an unsaturated organic acid or an inorganic salt thereof (c).

3. A slurry for a lithium ion battery electrode, comprising the aqueous binder solution for a lithium ion battery electrode according to claim 1 or 2 and an electrode active material (B).

4. A lithium ion battery electrode obtained by applying the lithium ion battery electrode slurry according to claim 3 to a current collector, followed by drying and curing.

5. A lithium ion battery comprising the lithium ion battery electrode of claim 4.

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