Binder composition for lithium-ion secondary battery electrode slurry, and uses thereof

Abstract

Provided is a binder composition for a lithium-ion secondary battery electrode slurry, the binder composition containing a water-soluble polymer and a particulate polymer, wherein the particulate polymer has a number average particle diameter between 25 nm and 500 nm inclusive and a viscosity between 500 mPa·s and 50,000 mPa·s inclusive. Also provided are a slurry for a lithium-ion secondary battery electrode, an electrode for a lithium-ion secondary battery, and a lithium-ion secondary battery obtained using said binder composition. Further provided are methods for manufacturing a slurry for a lithium-ion secondary battery electrode, an electrode for a lithium-ion secondary battery, and a lithium-ion secondary battery using said binder composition.

Description

Binder composition for lithium-ion secondary battery electrode slurry and its use

[0001] The present invention relates to a binder composition for a lithium ion secondary battery electrode slurry and its use. Specifically, the present invention relates to a binder composition for a lithium ion secondary battery electrode slurry, a slurry for a lithium ion secondary battery electrode, an electrode for a lithium ion secondary battery, a lithium ion secondary battery, and a method for producing the same.

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

[0003] The electrode may be a composite comprising a foil current collector and an electrode mixture layer thereon. Such an electrode mixture layer is typically formed by preparing a slurry containing an electrode active material, applying it to a current collector, and curing it. For example, the use of a non-carbon-based negative electrode active material, such as a silicon-based negative electrode active material (i.e., a silicon-containing negative electrode active material), which has a high theoretical capacitance, as part or all of the negative electrode active material has been considered.

[0004] However, non-carbon-based negative electrode active materials have disadvantages, such as a larger volume change during charging and discharging than carbon-based active materials, which can lead to a deterioration in the cycle characteristics and other properties of electrodes containing such materials. Furthermore, electrode mixture layers containing non-carbon-based negative electrode active materials can also have the disadvantage of being prone to so-called powder shedding when cutting raw sheets. To mitigate these various disadvantages, attempts have been made to combine multiple types of binders and add them as components of the electrode mixture layer (e.g., Patent Documents 1 and 2).

[0005] International Publication No. 2015 / 064464 (corresponding to U.S. Patent Application Publication No. 2016 / 0260973) International Publication No. 2004 / 004031 (corresponding to U.S. Patent Application Publication No. 2005 / 0244711)

[0006] When a combination of multiple binders is used as a component of the electrode mixture layer, each binder must be prepared, weighed, and added to the mixture system during slurry preparation, which complicates the process of forming the electrode mixture layer.

[0007] In order to simplify the process, it is conceivable to prepare a binder composition by premixing multiple types of binders and add the binder composition in a one-part state to the mixed system. However, according to the investigations of the present inventors, multiple types of binders for suppressing the disadvantages caused by the deposition change of the non-carbon-based negative electrode active material as described above easily cause problems such as aggregation when premixed to prepare a binder composition.

[0008] Therefore, an object of the present invention is to provide a binder composition for lithium ion secondary battery electrode slurry that can be prepared as a pre-formed material in a one-component state without aggregation, and that can suppress disadvantages such as a decrease in cycle characteristics and powder falling.

[0009] Another object of the present invention is to provide a method for easily producing a slurry for a lithium ion secondary battery electrode, an electrode for a lithium ion secondary battery, and a lithium ion secondary battery, which can suppress disadvantages such as a decrease in cycle characteristics and powder falling.

[0010] It is a further object of the present invention to provide a slurry for a lithium ion secondary battery electrode that can facilitate the production of an electrode for a lithium ion secondary battery and can suppress disadvantages such as a decrease in cycle characteristics and powder falling, an electrode for a lithium ion secondary battery that can be easily produced and can suppress disadvantages such as a decrease in cycle characteristics and powder falling, and a lithium ion secondary battery that can be easily produced and can suppress disadvantages such as a decrease in cycle characteristics.

[0011] The present inventors have conducted research to achieve the above-mentioned object. As a result, the present inventors have found that the above-mentioned problems can be solved by adopting a binder composition containing a water-soluble polymer and a particulate polymer, having specific physical properties, and containing a specific particulate polymer, and have completed the present invention. That is, the present invention provides the following.

[0012] (1) A binder composition for lithium ion secondary battery electrode slurry, comprising a water-soluble polymer and a particulate polymer, wherein the particulate polymer has a number average particle diameter of 25 nm or more and 500 nm or less, and a viscosity of 500 mPa·s or more and 50,000 mPa·s or less. (2) The binder composition for lithium ion secondary battery electrode slurry according to (1), having a solids concentration of 2 to 30 mass%. (3) The binder composition for lithium ion secondary battery electrode slurry according to (1) or (2), wherein the proportion of the particulate polymer is 0.01 mass% or more and 40 mass% or less, relative to a total of 100 mass% of the water-soluble polymer and the particulate polymer. (4) The binder composition for lithium ion secondary battery electrode slurry according to any one of (1) to (3), wherein, in a tensile strength test of a dried film of the binder composition for lithium ion secondary battery electrode slurry, the binder composition has a tensile modulus of 10 MPa to 8,000 MPa, a breaking strength of 10 MPa to 1,000 MPa, and a breaking elongation of 1% to 500%. (5) The binder composition for lithium ion secondary battery electrode slurry according to any one of (1) to (4), wherein the particulate polymer contains an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit. (6) The binder composition for lithium ion secondary battery electrode slurry according to (5), wherein the particulate polymer further contains an acid group-containing monomer unit. (7) The binder composition for lithium ion secondary battery electrode slurry according to any one of (1) to (4), wherein the particulate polymer is an unsaturated carboxylic acid alkyl ester polymer. (8) The binder composition for a lithium ion secondary battery electrode slurry according to (7), wherein the particulate polymer further contains an acid group-containing monomer unit. (9) A method for producing a slurry composition for a lithium ion secondary battery electrode, comprising mixing the binder composition for a lithium ion secondary battery electrode slurry according to any one of (1) to (8) with an electrode active material. (10) The method for producing a slurry composition for a lithium ion secondary battery electrode according to (9), wherein the electrode active material contains a silicon-based negative electrode active material.(11) A method for producing a lithium ion secondary battery electrode including an electrode mixture layer, the method comprising: obtaining a slurry composition for a lithium ion secondary battery electrode by the method for producing a slurry composition for a lithium ion secondary battery electrode according to (9) or (10); and curing the slurry composition for a lithium ion secondary battery electrode to form the electrode mixture layer. (12) A method for producing a lithium ion secondary battery, the method comprising: obtaining a lithium ion secondary battery electrode by the method for producing a lithium ion secondary battery electrode according to (11); and producing the lithium ion secondary battery using the lithium ion secondary battery electrode. (13) A slurry composition for a lithium ion secondary battery electrode, obtained by mixing the binder composition for a lithium ion secondary battery electrode slurry according to any one of (1) to (8) with an electrode active material. (14) The slurry composition for a lithium ion secondary battery electrode according to (13), wherein the electrode active material includes a silicon-based negative electrode active material. (15) An electrode for a lithium ion secondary battery, comprising an electrode mixture layer that is a cured product of the slurry composition for a lithium ion secondary battery electrode according to (13) or (14). (16) A lithium ion secondary battery, comprising the electrode for a lithium ion secondary battery according to (15).

[0013] According to the present invention, there is provided a binder composition for lithium ion secondary battery electrode slurry, which can be prepared as a pre-formed material in a one-component state without aggregation, and which can suppress disadvantages such as a decrease in cycle characteristics and powder falling.

[0014] Furthermore, according to the present invention, there are provided a slurry for a lithium ion secondary battery electrode, an electrode for a lithium ion secondary battery, and a manufacturing method for easily manufacturing a lithium ion secondary battery, which can suppress disadvantages such as a decrease in cycle characteristics and powder falling.

[0015] Furthermore, according to the present invention, there are provided a slurry for lithium ion secondary battery electrodes that can facilitate the production of electrodes for lithium ion secondary batteries and can suppress disadvantages such as a decrease in cycle characteristics and powder falling, an electrode for lithium ion secondary batteries that can be easily produced and can suppress disadvantages such as a decrease in cycle characteristics and powder falling, and a lithium ion secondary battery that can be easily produced and can suppress disadvantages such as a decrease in cycle characteristics.

[0016] The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and can be implemented with any modifications within the scope of the claims of the present invention and their equivalents.

[0017] In the following description, the term "solvent" is interpreted in a broad sense and also includes the meaning of a dispersion medium. That is, "solvent" includes not only a medium in a solution (i.e., a mixture of a liquid medium substance and a solute substance dissolved therein), but also a medium in a dispersion (i.e., a mixture of a liquid medium substance and a dispersion substance dispersed therein as solid particles or emulsion particles), and a medium in a mixture containing both a solute and a dispersion substance.

[0018] In the following description, a polymerized unit having a structure formed by polymerization of a certain monomer may be expressed using the name of the monomer. For example, a unit having a structure formed by polymerization of acrylic acid may be referred to as an "acrylic acid unit," a unit having a structure formed by polymerization of acrylamide may be referred to as an "acrylamide unit," and a unit having a structure formed by polymerization of acrylonitrile may be referred to as an "acrylonitrile unit." However, in the present invention, the structures of the molecule and its constituent elements are not limited by the production method.

[0019] In the following description, the term "(meth)acrylic" includes "acrylic", "methacrylic", and combinations thereof. For example, "(meth)acrylic acid" includes "acrylic acid", "methacrylic acid", and mixtures thereof. Similarly, the term "(meth)allyl" includes "allyl", "methallyl", and combinations thereof.

[0020] (Binder composition for lithium ion secondary battery electrode slurry) The binder composition of the present invention contains a water-soluble polymer and a particulate polymer. The binder composition of the present invention is a binder composition for lithium ion secondary battery electrode slurry. That is, the binder composition of the present invention can be useful when preparing a slurry for a lithium ion secondary battery electrode. The inventors have found that the binder composition of the present invention can be prepared without causing problems such as aggregation. When preparing a slurry composition using the binder composition of the present invention, since the binder composition of the present invention contains both a water-soluble polymer and a particulate polymer, these can be added to a mixed system all at once. As a result, the physical properties are adjusted by both the water-soluble polymer and the particulate polymer, making it possible to easily prepare a slurry composition with excellent properties.

[0021] (Water-soluble polymer) The water-soluble polymer is a polymer that is water-soluble. The term "water-soluble" for a polymer means that when a specific sample containing a polymer and water is passed through a 250-mesh screen, the mass of the solid content of the residue that does not pass through the screen and remains on the screen does not exceed 50% by mass of the solid content of the added polymer. Here, the specific sample is a mixture obtained by adding 1 part by mass of polymer (equivalent to the solid content) per 100 parts by mass of ion-exchanged water and stirring, and adjusting the mixture to at least one of the following conditions: a temperature in the range of 20°C to 70°C and a pH in the range of 3 to 12 (pH adjustment is performed using an aqueous NaOH solution and / or an aqueous HCl solution).

[0022] The water-soluble polymer can function as a dispersant for the electrode active material. The water-soluble polymer can particularly improve the dispersibility of silicon-based negative electrode active materials that tend to aggregate in solvents such as water. In addition, the water-soluble polymer has binding power. Therefore, in an electrode prepared using the binder composition of the present invention, the water-soluble polymer can also function as a binder that can hold components contained in the electrode mixture layer so that they do not detach from the electrode mixture layer.

[0023] The water-soluble polymer is preferably a water-soluble polymer having one or more of a carboxyl group, a nitrile group, and an amide group. Water-soluble polymers having these groups can function as thickeners in slurry compositions containing the binder composition of the present invention. In the electrode mixture layer obtained using such a slurry composition, the water-soluble polymer maintains the physical properties of the electrode mixture layer in an appropriate state, thereby improving characteristics such as cycle characteristics and resistance. Water-soluble polymers having these groups can also impart physical properties to a slurry composition containing a non-carbon-based negative electrode active material, such as a silicon-based negative electrode active material, so that the electrode mixture layer can be applied evenly and without clumping.

[0024] Examples of water-soluble polymers include natural products such as carboxymethyl cellulose, carboxymethyl starch, alginic acid, polyaspartic acid, salts thereof, and mixtures thereof; and synthetic products such as polycarboxylic acids, acrylamide-acrylic acid copolymers, acrylamide-acrylonitrile-acrylic acid copolymers, acrylamide-acrylic acid-2-acrylamido-2-methylpropanesulfonic acid copolymers, acrylamide-acrylic acid-methacrylic acid copolymers, acrylic acid-acrylonitrile-2-hydroxyethyl acrylate copolymers, and other copolymers with acrylic acid and methacrylic acid, salts thereof, and mixtures thereof. Furthermore, the above synthetic water-soluble polymers may be crosslinked structures using crosslinking agents such as dimethacrylic compounds, divinylbenzene, and diallyl compounds. By using these substances as water-soluble polymers, effects such as high capacity and excellent cycle characteristics can be obtained.

[0025] The water-soluble polymer is particularly preferably a polymer having at least one of a nitrile group and an amide group, since such a water-soluble polymer can improve the workability when applying the slurry composition onto a current collector or the like.

[0026] The water-soluble polymer containing a carboxyl group used in the present invention may be in the form of a salt in which the carboxyl group is accompanied by a counter ion. Examples of the counter ion include metal ions such as sodium ions and lithium ions. In particular, lithium ions are preferred because they can achieve high capacity and excellent cycle characteristics.

[0027] Among the above-mentioned water-soluble polymers, it is particularly preferable that the water-soluble polymer is an acrylamide-acrylic acid copolymer, an acrylamide-acrylonitrile-acrylic acid copolymer, or a mixture thereof. The acrylamide-acrylic acid copolymer is a copolymer containing acrylamide units and acrylic acid units in its molecular structure, and the acrylamide-acrylonitrile-acrylic acid copolymer is a copolymer containing acrylamide units and acrylic acid units in its molecular structure. These copolymers can be produced by copolymerizing a monomer composition containing acrylamide, acrylonitrile, or a mixture thereof (hereinafter referred to as copolymerizable monomer (B)) with acrylic acid. The charging ratio of the monomers in the monomer composition is usually the same as the ratio of the corresponding polymerized units present in the resulting polymer.

[0028] In the monomer composition used to prepare the acrylamide-acrylic acid copolymer or acrylamide-acrylonitrile-acrylic acid copolymer, the proportion of acrylic acid and copolymerizable monomer (B) relative to the total of 100% by mass can be appropriately adjusted so as to obtain the desired water-soluble polymer. Specifically, the proportion of acrylic acid is preferably 20.0% by mass or more and preferably 79.5% by mass or less. The proportion of copolymerizable monomer (B) is preferably 20.0% by mass or more and preferably 79.5% by mass or less. In addition to acrylic acid and copolymerizable monomer (B), such a monomer composition may further contain an optional monomer copolymerizable therewith. Examples of optional monomers include compounds copolymerizable with acrylic acid and copolymerizable monomer (B), specifically one or more compounds selected from the group consisting of polyfunctional compounds, ethylenically unsaturated sulfonic acids and salts thereof, and ethylenically unsaturated phosphoric acids and salts thereof.

[0029] The production of the water-soluble polymer can be achieved by mixing the monomer composition described above with, if necessary, additives such as a polymerization initiator and components such as a solvent, and polymerizing the mixture by a known method.

[0030] (Particulate polymer) The particulate polymer is a water-insoluble polymer, and is a polymer having a particulate shape in the binder composition and the slurry composition prepared using the binder composition. The "particulate polymer" is a polymer that is dispersible in an aqueous medium such as water, and exists in a particulate form in the aqueous medium. Usually, when 0.5 g of the particulate polymer is dissolved in 100 g of water at 25 ° C, the insoluble content of the particulate polymer is 90 mass % or more.

[0031] In the slurry composition, the particulate polymer can function as a binder. In particular, the present inventors have found that in the case of a slurry composition containing a non-carbon-based negative electrode active material, such as a silicon-based active material, as the electrode active material, adding a particulate polymer to the slurry composition tends to particularly deteriorate the cycle characteristics. On the other hand, if a particulate polymer is not used, the negative electrode composite layer tends to become brittle, resulting in the problem of so-called powder shedding when cutting the negative electrode raw material to produce the negative electrode. However, by adding only a small amount of particulate polymer within a predetermined range and adding it in combination with a predetermined water-soluble polymer, it is possible to reduce powder shedding compared to when no particulate polymer is added, and it is possible to improve the cycle characteristics and reduce resistance compared to when a large amount of particulate polymer is added.

[0032] Examples of the polymer constituting the particulate polymer include a particulate polymer containing an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit (hereinafter sometimes abbreviated as "particulate polymer (C1)"), and an unsaturated carboxylic acid alkyl ester polymer (hereinafter sometimes abbreviated as "particulate polymer (C2)"). Among these, the particulate polymer (C1) is particularly preferred from the viewpoint of reducing resistance and maintaining cycle characteristics.

[0033] (Particulate polymer (C1): polymer containing aliphatic conjugated diene monomer units and aromatic vinyl monomer units) In the particulate polymer (C1), the aliphatic conjugated diene monomer units are units having a structure obtained by polymerization of an aliphatic conjugated diene monomer, and the aromatic vinyl monomer units are units having a structure obtained by polymerization of an aromatic vinyl monomer. Examples of the aliphatic conjugated diene monomer include 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 2-ethyl-1,3-butadiene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, and substituted and side-chain conjugated hexadienes. Of these, 1,3-butadiene and isoprene are preferred, and 1,3-butadiene is more preferred. The aliphatic conjugated diene monomer may be used alone or in combination of two or more kinds in any ratio.

[0034] In the particulate polymer (C1), the content of the aliphatic conjugated diene monomer unit is preferably 20% by mass or more, more preferably 30% by mass or more, and preferably 75% by mass or less, more preferably 60% by mass or less, and particularly preferably 50% by mass or less. When the content of the aliphatic conjugated diene monomer unit is 20% by mass or more, the flexibility of the electrode can be increased, and when it is 70% by mass or less, the adhesion between the electrode mixture layer and the current collector can be improved, and the electrolyte resistance of the electrode obtained using the slurry composition of the present invention can be improved. In particular, when the slurry composition of the present invention is applied to a negative electrode containing a silicon-based negative electrode active material, these effects can be obtained well.

[0035] Examples of aromatic vinyl monomers include styrene, α-methylstyrene, vinyltoluene, divinylbenzene, and sodium p-styrenesulfonate, of which styrene and sodium p-styrenesulfonate are preferred, and styrene is more preferred. One type of aromatic vinyl monomer may be used alone, or two or more types may be used in combination at any ratio.

[0036] In the particulate polymer (C1), the content of the aromatic vinyl monomer unit is preferably 20% by mass or more, more preferably 35% by mass or more, particularly preferably 40% by mass or more, preferably 75% by mass or less, more preferably 70% by mass or less, particularly preferably 66% by mass or less. When the content of the aromatic vinyl monomer unit is 20% by mass or more, the electrolyte resistance of the electrode obtained using the slurry composition of the present invention can be improved, and when it is 75% by mass or less, the strength of the electrode mixture layer and the adhesion to the current collector can be improved. In particular, when applied to a negative electrode containing a silicon-based negative electrode active material, such effects can be obtained well.

[0037] The particulate polymer (C1) particularly preferably contains 1,3-butadiene units as aliphatic conjugated diene monomer units and styrene units as aromatic vinyl monomer units (i.e., is a styrene-butadiene copolymer).More preferably, it is so-called styrene-butadiene rubber (SBR).

[0038] The particulate polymer (C1) may further contain an acid group-containing monomer unit. Examples of acid group-containing monomers that can form the acid group-containing monomer unit include monomers having a carboxylic acid group, monomers having a sulfo group, and monomers having a phosphoric acid group. The monomers having a carboxylic acid group are often ethylenically unsaturated carboxylic acid monomers. Examples of monomers having a carboxylic acid group include monocarboxylic acids and dicarboxylic acids. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of monomers having a sulfo group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and p-styrenesulfonic acid. Examples of monomers having a phosphate group include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-2-(meth)acryloyloxyethyl phosphate. Monomer units based on these monomers may be in the form of a salt in the particulate polymer. When the particulate polymer is a polymer containing monomer units having an acid group, some or all of the acid groups in the monomer units having an acid group may be in the form of anions. Examples of counter ions constituting the salt include alkali metal salts such as lithium salts, sodium salts, and potassium salts, and alkaline earth metal salts such as magnesium salts and calcium salts. One type of acid group-containing monomer may be used alone, or two or more types may be used in combination at any ratio.

[0039] The proportion of the acid group-containing monomer unit in the particulate polymer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less.

[0040] In addition, the particulate polymer (C1) may contain any repeating unit other than those described above, as long as the effects of the present invention are not significantly impaired. Examples of monomers corresponding to the any repeating units include vinyl cyanide monomers, unsaturated carboxylic acid alkyl ester monomers, and unsaturated carboxylic acid amide monomers. These may be used alone or in combination of two or more at any ratio.

[0041] The content ratio of the monomer corresponding to any repeating unit in the particulate polymer (C1) is not particularly limited, but the upper limit is preferably 10 mass% or less, more preferably 8 mass% or less, and particularly preferably 5 mass% or less in total, while the lower limit is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, and particularly preferably 1.5 mass% or more.

[0042] Examples of vinyl cyanide monomers include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-ethylacrylonitrile. Among these, acrylonitrile and methacrylonitrile are preferred. These may be used alone or in combination of two or more in any ratio.

[0043] Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate. Of these, methyl methacrylate is preferred. These may be used alone or in combination of two or more in any ratio.

[0044] Examples of unsaturated carboxylic acid amide monomers include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, and N,N-dimethyl acrylamide. Of these, acrylamide and methacrylamide are preferred. These may be used alone or in combination of two or more in any ratio.

[0045] Other examples of the optional repeating units that the particulate polymer (C1) may contain include units obtained by polymerization of monomers used in ordinary emulsion polymerization, such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, etc. These may be used alone or in combination of two or more at any ratio.

[0046] The particulate polymer (C1) can be produced, for example, by polymerizing a monomer composition containing the above-mentioned monomers in an aqueous solvent. Here, the content ratio of each monomer in the monomer composition can usually be the same as the content ratio of the repeating unit in the desired particulate polymer (C1).

[0047] The aqueous solvent is not particularly limited as long as it is capable of dispersing the particulate polymer (C1) in a particulate state, and is usually selected from aqueous solvents having a boiling point at normal pressure of usually 80°C or higher, preferably 100°C or higher, and usually 350°C or lower, preferably 300°C or lower.

[0048] Specifically, examples of aqueous solvents include water; ketones such as diacetone alcohol and γ-butyrolactone; alcohols such as ethyl alcohol, isopropyl alcohol, and normal propyl alcohol; glycol ethers such as propylene glycol monomethyl ether, methyl cellosolve, ethyl cellosolve, ethylene glycol tertiary butyl ether, butyl cellosolve, 3-methoxy-3-methyl-1-butanol, ethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and dipropylene glycol monomethyl ether; and ethers such as 1,3-dioxolane, 1,4-dioxolane, and tetrahydrofuran. Among these, water is particularly preferred from the viewpoints that it is not flammable and that a dispersion of particles of the particulate polymer (C1) can be easily obtained. Water may be used as the main solvent, and an aqueous solvent other than water may be mixed therewith, as long as the dispersion state of the particles of the particulate polymer (C1) can be ensured.

[0049] The polymerization method is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization can be used. As the polymerization method, any method such as ionic polymerization, radical polymerization, or living radical polymerization can be used. From the viewpoint of production efficiency, emulsion polymerization is particularly preferred. Emulsion polymerization offers advantages in terms of production efficiency, such as the ease of obtaining a high molecular weight product, and the fact that the polymer is obtained in a state dispersed in water as is, eliminating the need for redispersion treatment and allowing the polymer to be directly used in the production of the binder composition and slurry composition of the present invention. Emulsion polymerization can be carried out according to conventional methods.

[0050] The emulsifier, dispersant, polymerization initiator, polymerization aid, etc. used in the polymerization can be those generally used, and the amounts used are also generally used amounts. In addition, seed polymerization may be performed using seed particles. In addition, the polymerization conditions can be arbitrarily selected depending on the polymerization method, the type of polymerization initiator, etc.

[0051] Here, the aqueous dispersion of particles of the particulate polymer (C1) obtained by the above-mentioned polymerization method may be adjusted to a pH of usually 5 or more and usually 10 or less, preferably 9 or less, using a basic aqueous solution. Examples of substances contained in the basic aqueous solution include hydroxides of alkali metals (e.g., Li, Na, K, Rb, Cs), ammonia, inorganic ammonium compounds (e.g., NH ４ Examples of suitable organic amine compounds include alkali metal hydroxides (e.g., ethanolamine, diethylamine, etc.) and organic amine compounds (e.g., ethanolamine, diethylamine, etc.). Among these, pH adjustment using an alkali metal hydroxide is preferred because it improves the adhesion between the current collector and the electrode mixture layer, particularly the negative electrode mixture layer.

[0052] (Particulate polymer (C2): unsaturated carboxylic acid alkyl ester polymer) The particulate polymer (C2) is a polymer having unsaturated carboxylic acid alkyl ester monomer units, i.e., structural units obtained by polymerization of unsaturated carboxylic acid alkyl ester monomers. In the particulate polymer (C2), the content of the unsaturated carboxylic acid alkyl ester monomer units is preferably 50% by mass or more, more preferably 80% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less.

[0053] The particulate polymer (C2) may contain an acid group-containing monomer unit in addition to the unsaturated carboxylic acid alkyl ester monomer unit. Examples of the acid group-containing monomer capable of forming the acid group-containing monomer unit and the preferred range of the content thereof are the same as those in the particulate polymer (C1).

[0054] The particulate polymer (C2) may contain units obtained by polymerization of any monomer other than those mentioned above. Examples of such optional monomers include vinyl cyanide monomers, unsaturated carboxylic acid amide monomers, and (meth)acrylic acid glycidyl ether units. Examples of the unsaturated carboxylic acid alkyl ester monomers, vinyl cyanide monomers, and unsaturated carboxylic acid amide monomers include the same monomers as those mentioned as optional components of the monomers constituting the particulate polymer (C1). The particulate polymer (C2) can be produced by polymerizing the above-mentioned monomers by a polymerization method such as emulsion polymerization.

[0055] (Properties of the particulate polymer) The particulate polymer is water-insoluble and maintains its particulate shape in the binder composition and slurry composition of the present invention. When an electrode mixture layer such as a negative electrode mixture layer is formed from the slurry composition of the present invention, the particulate shape of the particulate polymer is at least partially maintained and exhibits the function of binding the active material.

[0056] The particulate polymer in the binder composition of the present invention has a number-average particle diameter within a specific range. Specifically, the number-average particle diameter is 25 nm or more, preferably 60 nm or more, more preferably 70 nm or more, and particularly preferably 90 nm or more, while being 500 nm or less, preferably 400 nm or less, and more preferably 200 nm or less. In particular, the number-average particle diameter can be preferably 30 to 165 nm, more preferably 31 to 163 nm. Having a number-average particle diameter within this range can improve the strength and flexibility of the resulting electrode, and these effects can be effectively achieved, particularly when applied to a negative electrode containing a silicon-based negative electrode active material. Furthermore, the present inventors have discovered that having a number-average particle diameter within this range can achieve the effect of maintaining the above-mentioned properties while allowing the binder composition to be prepared as a pre-prepared material by mixing it with a water-soluble polymer without aggregation. The number-average particle diameter can be easily measured using transmission electron microscopy, for example.

[0057] (Components, Physical Properties, etc. of Binder Composition) The binder composition of the present invention has a viscosity within a specific range. Specifically, the viscosity of the binder composition is 500 mPa·s or more, preferably 1000 mPa·s or more, and more preferably 2500 mPa·s or more, and is 50000 mPa·s or less, preferably 20000 mPa·s or less, and more preferably 17000 mPa·s or less. In particular, the viscosity of the binder composition can be preferably 1500 to 40000 mPa·s, and more preferably 4700 to 40000 mPa·s. The inventors have found that when the viscosity of the binder composition is within the above range, it is possible to prepare the binder composition as a pre-prepared material by mixing it with a water-soluble polymer without causing aggregation.

[0058] Furthermore, by having a viscosity equal to or greater than the lower limit, the binder composition can be provided with good thickening properties and can improve the dispersibility of the slurry composition prepared using the binder composition. By having a viscosity equal to or less than the upper limit, it is possible to suppress powder falling during the electrode production process and improve the ease of transportation when electrodes are continuously produced on a production line.

[0059] In the present application, the viscosity of the binder composition and the slurry composition can be measured in accordance with JIS K7117-1:1999 using a Brookfield viscometer (DV2T, manufactured by Eiko Seiki Co., Ltd.) at a temperature of 25±1°C, pH 8.0, and a rotation speed of 60 rpm (rotor: RV-3, 4, 5, 6, 7; selected appropriately according to the viscosity in accordance with the provisions of JIS K7117-1:1999).

[0060] The proportions of the water-soluble polymer and the particulate polymer in the binder composition of the present invention can be appropriately adjusted so that the physical properties of the binder composition and the physical properties of the slurry composition and electrode produced using the binder composition fall within the desired ranges.

[0061] Specifically, the proportion of the water-soluble polymer relative to the total of 100% by mass of the water-soluble polymer and the particulate polymer is preferably 60% by mass or more, more preferably 90% by mass or more, even more preferably 92% by mass or more, and is preferably 99.99% by mass or less, more preferably 99.9% by mass or less. When the proportion of the water-soluble polymer is equal to or greater than the lower limit, the slurry composition prepared using the binder composition can be imparted with good thickening properties, and the dispersibility of the slurry composition can be improved. When the proportion of the water-soluble polymer is equal to or less than the upper limit, powder falling during the electrode production process can be suppressed.

[0062] The proportion of the particulate polymer relative to 100% by mass of the total of the water-soluble polymer and the particulate polymer is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and is preferably 40% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less. In particular, the proportion of the particulate polymer is preferably 0.1 to 40% by mass. When the proportion of the particulate polymer is equal to or greater than the lower limit, powder falling during the electrode production process can be suppressed. When the proportion of the particulate polymer is equal to or less than the upper limit, aggregation of the particulate polymer in the binder composition can be suppressed, and the elastic modulus can be set within a desired range, thereby improving the cycle characteristics of the resulting battery.

[0063] The binder composition may contain a solvent in addition to the above-mentioned components. The solvent may be water or a mixture of water and a solvent other than water. The solvent functions as a solvent or a dispersion medium in the binder composition. In the binder composition of the present invention, the water-soluble polymer may be dissolved in water, and the particulate polymer may be dispersed in water.

[0064] Examples of solvents that can be used in combination with water include cyclic aliphatic hydrocarbon compounds such as cyclopentane and cyclohexane; aromatic hydrocarbon compounds such as toluene and xylene; ketone compounds such as ethyl methyl ketone and cyclohexanone; ester compounds such as ethyl acetate, butyl acetate, γ-butyrolactone and ε-caprolactone; nitrile compounds such as acetonitrile and propionitrile; ether compounds such as tetrahydrofuran and ethylene glycol diethyl ether; alcohol compounds such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; amide compounds such as N-methylpyrrolidone (NMP) and N,N-dimethylformamide; etc. These may be used alone or in combination of two or more at any ratio.

[0065] The amount of solvent in the binder composition of the present invention is preferably set so that the solids concentration of the binder composition falls within a desired range. In this application, the solids of the composition refer to substances that remain after the composition has been dried.

[0066] The solids concentration of the binder composition is preferably 2% by mass or more, more preferably 4% by mass or more, and is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. In particular, the solids concentration of the binder composition is 2 to 12% by mass. By having the solids content of the binder composition in this range, aggregation of the binder composition can be suppressed, and a slurry composition with good properties can be prepared using such a binder composition.

[0067] The binder composition of the present invention may consist solely of the above components, but may also contain optional components such as a conductive agent, a reinforcing material, a leveling agent, and an electrolyte additive in addition to the above components. These components are not particularly limited as long as they do not affect the battery reaction, and known components, such as those described in WO 2012 / 115096, can be used. These components may be used alone or in combination of two or more in any ratio.

[0068] The binder composition of the present invention may be a composition containing a low concentration of aggregates. Specifically, when a binder composition is passed through a 325 mesh sieve, the material remaining on the sieve surface is weighed as aggregates, and the amount of aggregates (mass %) relative to the total solid content of the binder composition is determined from the weighing results, it is preferable that the amount of aggregates is low. The proportion of the amount of aggregates is preferably 5 mass % or less, more preferably 3 mass % or less, even more preferably 0.5 mass % or less, and ideally zero mass %. A low amount of aggregates makes it possible to prepare a slurry composition and an electrode with good properties. Specifically, the dispersion of the water-soluble polymer and particulate polymer in the slurry composition and the electrode is improved, resulting in effects such as reduced powder shedding and improved cycle characteristics.

[0069] The binder composition of the present invention preferably has a film obtained by drying the binder composition, which has specific physical properties. Specifically, these physical properties can be evaluated for a dried film of the binder composition having a thickness of 500 μm. More specifically, the binder composition is applied to a petri dish and air-dried to obtain a flat, bubble-free film having a thickness of approximately 500 μm. This can be used as a dried film for measuring physical properties, and the physical properties can be evaluated. Even more specifically, a film of this thickness can be punched into a dumbbell shape (total length 60±2 mm, end width 20±0.2 mm, central length 30±2.0 mm, the central portion having tapered portions at both ends in the length direction and a parallel portion therebetween, the central parallel portion having a length of 15±2.0 mm and a width of 10±1.0 mm), and the resulting sample can be dried in a vacuum at 140°C for 10 hours, and the physical properties can be evaluated for the resulting sample.

[0070] Indicators of the physical properties of such test specimens include tensile modulus, breaking strength, and breaking elongation. These physical properties can be adjusted to desired values ​​by appropriately adjusting the types and proportions of the water-soluble polymer and particulate polymer that constitute the binder composition.

[0071] The tensile modulus is preferably 10 MPa or more, more preferably 30 MPa or more, and even more preferably 300 MPa or more, while being preferably 8000 MPa or less, more preferably 7000 MPa or less, and even more preferably 3000 MPa or less. In particular, the tensile modulus can be preferably 100 to 400 MPa, more preferably 210 to 400 MPa. When the tensile modulus of the dried film is within this range, deterioration of the resulting electrode due to expansion and contraction can be suppressed, and the cycle characteristics of the resulting battery can be improved. In particular, when applied to a negative electrode containing a silicon-based negative electrode active material, such effects can be effectively obtained.

[0072] The breaking strength is preferably 10 MPa or more, more preferably 40 MPa or more, and even more preferably 60 MPa or more, while preferably 1000 MPa or less, more preferably 700 MPa or less, and even more preferably 300 MPa or less. In particular, the breaking strength can be preferably 10 to 12 MPa, more preferably 80 to 120 MPa. When the breaking strength of the dried film is within this range, deterioration of the resulting electrode due to expansion and contraction can be suppressed, and the cycle characteristics of the resulting battery can be improved. In addition, powder falling off of the electrode can be effectively suppressed. In particular, when applied to a negative electrode containing a silicon-based negative electrode active material, these effects can be effectively obtained.

[0073] The breaking elongation is preferably 1% or more, more preferably 3% or more, and even more preferably 5% or more, while being preferably 500% or less, more preferably 100% or less, and even more preferably 30% or less. In particular, the breaking elongation can be preferably 4 to 50%, more preferably 10 to 20%. When the breaking strength of the dried film is equal to or greater than the lower limit, the brittleness of the resulting electrode can be reduced and powder shedding can be effectively suppressed. When the breaking strength of the dried film is equal to or less than the upper limit, the elastic modulus of the resulting electrode can be maintained at a satisfactory high value, resulting in improved cycle characteristics of the resulting battery.

[0074] (Slurry Composition for Lithium Ion Secondary Battery Electrode and Manufacturing Method Thereof) The slurry composition for lithium ion secondary battery electrode of the present invention is prepared by mixing the binder composition of the present invention and an electrode active material.

[0075] The electrode active material may be selected from known active materials used as active materials for lithium ion secondary battery electrodes. In particular, the electrode active material preferably contains a non-carbon-based negative electrode active material as part or all of the material.

[0076] Examples of non-carbon-based negative electrode active materials include metal-based negative electrode active materials.

[0077] A metal-based negative electrode active material is an active material containing a metal, typically containing an element capable of intercalating lithium, preferably having a theoretical electrical capacity per unit mass of 500 mAh / g or more when lithium is intercalated. In this case, the upper limit of the theoretical electrical capacity is not particularly limited, but can be, for example, 4000 mAh / g. Examples of metal-based negative electrode active materials include lithium metal, elemental metals capable of forming lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.), and alloys thereof, as well as oxides, sulfides, nitrides, silicides, carbides, phosphides, etc., thereof.

[0078] Among metal-based negative electrode active materials, silicon-containing active materials (silicon-based negative electrode active materials) are preferred. The use of silicon-based negative electrode active materials has the advantage of enabling the lithium-ion secondary battery to have a high capacity. On the other hand, the use of silicon-based negative electrode active materials can have disadvantages, such as a larger volume change during charge and discharge than carbon-based active materials, making it easier for the characteristics of electrodes containing such materials to deteriorate, such as the cycle characteristics. Here, the use of silicon-based negative electrode active materials in combination with the binder composition of the present invention can provide the above-mentioned advantages while reducing such disadvantages, making them particularly preferred.

[0079] Examples of silicon-based negative electrode active materials include silicon (Si), silicon-containing alloys, SiO , SiOx, and composites of Si-containing materials and conductive carbon, which are obtained by coating or compounding Si-containing materials with conductive carbon. Thus, in addition to particles made of silicon and particles made of silicon and oxygen, particles containing silicon and carbon are also included in metal-based active materials. In particular, silicon-containing alloys (Si alloys) are preferred because they have high capacity and can achieve good cycle characteristics.

[0080] Examples of alloys containing silicon include alloy compositions containing silicon, aluminum, and transition metals such as iron, and further containing rare earth elements such as tin and yttrium.Specifically, examples of alloys containing silicon include a mixture of: (A) an amorphous phase containing silicon; and (B) a nanocrystalline phase containing tin, indium, and yttrium, a lanthanide element, an actinide element, or a combination thereof.More specifically, examples of alloys containing silicon include alloys represented by the following general formula (3): Si ａ Al ｂ T ｃ Sn ｄ In ｅ M ｆ Li ｇ ... (3) [wherein T is a transition metal, M is yttrium, a lanthanide element, an actinide element, or a combination thereof, the sum of a + b + c + d + e + f is equal to 1, and 0.35 ≦ a ≦ 0.70, 0.01 ≦ b ≦ 0.45, 0.05 ≦ c ≦ 0.25, 0.01 ≦ d ≦ 0.15, e ≦ 0.15, 0.02 ≦ f ≦ 0.15, and 0 < g ≦ {4.4 × (a + d + e) ​​+ b}}. Such alloys can be prepared, for example, by the method described in JP 2013-65569 A, specifically, by the melt spinning method.

[0081] SiOx is SiO and SiO ２ and Si, where x is usually 0.01 or more and less than 2. SiOx can be formed, for example, by utilizing the disproportionation reaction of silicon monoxide (SiO). Specifically, SiOx can be prepared by heat-treating SiO, optionally in the presence of a polymer such as polyvinyl alcohol, to produce silicon and silicon dioxide. The heat treatment can be carried out in an atmosphere containing organic gas and / or steam at a temperature of 900°C or higher, preferably 1000°C or higher, after pulverizing and mixing SiO and, optionally, a polymer.

[0082] Examples of composites of Si-containing materials and conductive carbon include compounds obtained by heat-treating a pulverized mixture of SiO, a polymer such as polyvinyl alcohol, and optionally a carbon material in an atmosphere containing an organic gas and / or steam. Also, known methods can be used, such as a method of coating the surface of SiO particles by chemical vapor deposition using an organic gas, or a method of forming composite particles (granulation) from SiO particles and graphite or artificial graphite by a mechanochemical method.

[0083] The proportion of the non-carbon-based negative electrode active material in the entire electrode active material is preferably 5% by mass or more, and more preferably 10% by mass or more. On the other hand, the upper limit of the proportion of the non-carbon-based negative electrode active material in the electrode active material is not particularly limited, but is preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 55% by mass or less. The remaining components in the electrode active material may be carbon-based active materials. By setting the proportion of the non-carbon-based negative electrode active material to the above lower limit or more, a high electrical capacity can be obtained. On the other hand, by setting the proportion of the non-carbon-based negative electrode active material to the above upper limit or less, good cycle characteristics can be obtained.

[0084] Examples of carbon-based negative electrode active materials that can be used in combination with non-carbon-based negative electrode active materials include those similar to those listed in Patent Document 1.

[0085] In the slurry composition of the present invention, the ratio of the binder component (i.e., the component that functions as a binder in the binder composition; the sum of the water-soluble polymer and the particulate polymer) to 100 parts by mass of the electrode active material is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 3 parts by mass or more, and preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less. By setting the blending amount of the binder component within the above range, the viscosity of the slurry composition can be made appropriate, thereby improving the workability when applying the slurry composition to a current collector, etc. Furthermore, by blending the binder component at a ratio of 0.5 parts by mass or more per 100 parts by mass of the electrode active material, good cycle characteristics can be obtained. Furthermore, by blending the binder component at a ratio of 10 parts by mass or less per 100 parts by mass of the electrode active material, the resistance of the resulting electrode can be reduced.

[0086] The slurry composition of the present invention may contain a solvent in addition to the binder composition of the present invention and the electrode active material. The solvent may be water or a mixture of water and a solvent other than water. Specific examples of the solvent may include the same solvents as those listed as examples of the solvent for the binder composition.

[0087] The slurry composition of the present invention may consist solely of the above components, but may also contain optional components in addition to the above components, specific examples of which include the same components as those listed as examples of the solvent for the binder composition.

[0088] The method for producing the slurry composition of the present invention is not particularly limited, but a preferred production method of the present invention involves mixing the binder composition of the present invention, an electrode active material, and, if necessary, optional components such as a solvent. This production method eliminates the need to weigh and add multiple types of binders separately, thereby simplifying the production process. In producing the slurry composition, in addition to the binder composition of the present invention, other components that can function as binders may be added. However, from the perspective of simplifying the production process, it is preferable to add only the binder composition of the present invention as a one-liquid preparation.

[0089] (Electrode for lithium ion secondary battery and manufacturing method thereof) The electrode for lithium ion secondary battery of the present invention comprises an electrode mixture layer that is a cured product of the slurry composition of the present invention. The electrode for lithium ion secondary battery of the present invention usually further comprises a current collector. The electrode for lithium ion secondary battery of the present invention can be easily manufactured by comprising an electrode mixture layer obtained from the slurry composition of the present invention, and further, when used in a battery, it can achieve effects such as improved cycle characteristics and reduced resistance, and in addition, it can achieve reduced powder falling when processed into a shape that can be housed in the exterior of the battery.

[0090] The secondary battery electrode of the present invention can be produced, for example, by a production method including the steps of obtaining a slurry composition for a lithium ion secondary battery electrode by the method for producing a slurry composition for a lithium ion secondary battery electrode of the present invention, and curing the slurry composition for a lithium ion secondary battery electrode to form the electrode mixture layer. The step of forming the electrode mixture layer can further include the steps of applying the slurry composition of the present invention onto a current collector (application step), drying the slurry composition applied onto the current collector to form an electrode mixture layer on the current collector (drying step), and optionally further heating the electrode mixture layer (heating step).

[0091] (Coating Step) The method for applying the slurry composition onto the current collector is not particularly limited, and known methods can be used. Specifically, examples of the coating method include a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. In this case, the slurry composition may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector after application and before drying can be appropriately set depending on the thickness of the electrode mixture layer obtained by drying.

[0092] Here, the current collector to which the slurry composition is applied is made of a material that is electrically conductive and electrochemically durable. Specifically, the current collector may be made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like. Among these, copper foil is particularly preferred as the current collector used for the negative electrode. The above-mentioned materials may be used alone or in combination of two or more in any ratio.

[0093] (Drying step) The method for drying the slurry composition on the current collector is not particularly limited and any known method can be used, for example, drying with warm air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams, etc. By drying the slurry composition on the current collector in this manner, an electrode mixture layer can be formed on the current collector, and a secondary battery electrode including the current collector and the electrode mixture layer can be obtained.

[0094] After the drying step, the electrode mixture layer may be subjected to a pressure treatment using a mold press, a roll press, etc. Pressure treatment can improve the adhesion between the electrode mixture layer and the current collector.

[0095] (Lithium-ion secondary battery and manufacturing method thereof) The lithium-ion secondary battery of the present invention includes the lithium-ion secondary battery electrode of the present invention. Specifically, the lithium-ion secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolyte, and a separator, and the negative electrode includes the lithium-ion secondary battery electrode of the present invention. The lithium-ion secondary battery of the present invention can be manufactured using the lithium-ion secondary battery electrode of the present invention. As a result, the battery can have high cycle characteristics and low resistance. Furthermore, the process of preparing the slurry composition is simple, and manufacturing problems such as powder falling off during cutting of the electrode are minimized, allowing for easy manufacturing. The secondary battery of the present invention can be suitably used in, for example, mobile phones such as smartphones, tablets, personal computers, electric vehicles, stationary emergency storage batteries, and the like.

[0096] (Positive Electrode) The positive electrode of the secondary battery may be a known positive electrode used as a positive electrode for a lithium ion secondary battery. Specifically, the positive electrode may be, for example, a positive electrode formed by forming a positive electrode composite layer on a current collector. The current collector may be made of a metal material such as aluminum. The positive electrode composite layer may be a layer containing a known positive electrode active material, a conductive material, and a binder, and the binder may be a known particulate polymer.

[0097] (Electrolyte) The electrolyte may be an electrolyte solution in which an electrolyte is dissolved in a solvent. Here, an organic solvent capable of dissolving the electrolyte may be used as the solvent. Specifically, the solvent may be an alkyl carbonate solvent such as ethylene carbonate, propylene carbonate, or γ-butyrolactone to which a viscosity adjusting solvent such as 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl acetate, dimethoxyethane, dioxolane, methyl propionate, or methyl formate has been added. The electrolyte may be a lithium salt. For example, the lithium salt described in JP 2012-204303 A may be used. Among these lithium salts, LiPF 6 is preferred as the electrolyte because it is easily soluble in organic solvents and exhibits a high degree of dissociation. ６ , LiClO ４ , C.F. ３ SO ３ Li is preferred. The electrolyte solution may be a gel electrolyte containing a polymer and the above-mentioned electrolyte solution, or may be a true polymer electrolyte.

[0098] (Separator) As the separator, for example, one described in JP 2012-204303 A can be used. Among them, a microporous film made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it allows the entire separator to have a thin film thickness, thereby increasing the ratio of electrode active material in the secondary battery and increasing the capacity per volume. Alternatively, a separator having a porous film formed by binding non-conductive particles with a known particulate polymer may be used.

[0099] (Method for Manufacturing Secondary Battery) In the method for manufacturing a secondary battery of the present invention, for example, a positive electrode and a negative electrode are stacked with a separator interposed therebetween, and the stack is rolled or folded as necessary according to the battery shape, placed in a battery container, and an electrolyte is poured into the battery container and sealed. To prevent internal pressure rise and overcharging / discharging of the lithium ion secondary battery, a fuse, an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary. The shape of the secondary battery may be, for example, a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, or the like.

[0100] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. Furthermore, the operations described below were carried out under conditions of room temperature and normal pressure unless otherwise specified.

[0101] (Measurement method and evaluation method) (Number average particle diameter) The binder composition was appropriately diluted (about 1000 times) and air-dried to prepare a sample. The sample was observed by transmission electron microscopy (TEM), and 10 particulate polymers in the observed image were randomly selected and their major diameters were measured. The arithmetic mean of the 10 measurements was taken as the number average particle diameter of the particulate polymer.

[0102] (Amount of Aggregates) The binder composition was left to stand for 7 days after preparation, then passed through a 325 mesh sieve, and the material remaining on the sieve surface was weighed as aggregates. From the weighing results, the amount of aggregates (mass%) relative to the total amount of solids in the binder composition was determined and evaluated according to the following criteria: A: 0.5 mass% or less B: More than 0.5 mass% and 3 mass% or less C: More than 3 mass% and 5 mass% or less D: More than 5 mass%

[0103] (Viscosity) The viscosity of the water-soluble polymer aqueous solution, binder composition and slurry composition was measured in accordance with JIS K7117-1:1999 using a B-type viscometer (DV2T, manufactured by Eiko Seiki Co., Ltd.) at a temperature of 25±1°C, pH 8.0 and a rotation speed of 60 rpm (rotor: RV-3, 4, 5, 6, 7; appropriately selected in accordance with the provisions of JIS K7117-1:1999 in accordance with the viscosity).

[0104] (Tensile Test of Dried Film) The binder composition was applied to a petri dish without air bubbles, and after visually confirming the absence of air bubbles, it was air-dried to obtain a film with a thickness of approximately 500 μm (a thickness within a range of 500 μm ± 25 μm). This was used as a dried film for measuring physical properties. The dried film was punched into a dumbbell shape (total length 60 ± 2 mm, end width 20 ± 0.2 mm, central length 30 ± 2.0 mm, the central portion having tapered portions at both ends and a parallel portion therebetween, the central parallel portion having a length of 15 ± 2.0 mm and a width of 10 ± 1.0 mm), and then vacuum dried at 140 °C for 10 hours to prepare a flat, bubble-free sample piece. This test piece was subjected to a tensile test using a tensile tester in a dry environment to obtain a stress-strain curve. The test conditions were a chuck distance of 10 mm, a sample width of 10 mm, and a tensile speed of 50 mm / min. The gradient of the stress-strain curve from 0.05% to 0.50% strain (the gradient of the line connecting the 0.05% point and the 0.50% point) was calculated to obtain the tensile modulus (MPa). The stress at which the test piece broke was determined as the breaking strength (MPa), and the strain at which it broke was determined as the breaking elongation (%). The breaking elongation (%) was calculated by dividing the displacement (mm) by the chuck distance of 10 mm.

[0105] (Powder Shedding Test) The negative electrode was cut into a 6 cm x 10 cm rectangle to prepare a sample. The mass (Y0) of the sample was measured. Then, eight locations on the sample were punched using a φ16 mm circular punching machine. To avoid burrs and deformed portions on the edge of the sample, the punching locations were set to an area approximately 2-3 mm inward from the edge of the sample. Both the punched circular sample and the sample with a circular hole were airbrushed, and the total mass (Y1) of these was measured. The powder shedding ratio (ratio of the mass after punching to the mass before punching) was calculated using the following formula and evaluated according to the following criteria. A higher value indicates less cracking and peeling at the edge of the negative electrode due to powder shedding. Powder shedding ratio = (Y1 / Y0) x 100 (%) A: 99.98% or more B: 99.97% or more but less than 99.98% C: 99.96% or more but less than 99.97% D: Less than 99.96%

[0106] (Cycle Characteristics of Lithium-Ion Secondary Battery) The lithium-ion secondary battery was left standing at 25°C for 5 hours after injection of the electrolyte. Next, it was charged to a cell voltage of 3.65 V using a constant current method at 25°C and 0.2 C, and then aged for 12 hours at 60°C. Then, it was discharged to a cell voltage of 2.75 V using a constant current method at 25°C and 0.2 C. Thereafter, it was subjected to CC-CV charging (upper limit cell voltage 4.20 V, cutoff current 0.02 C) using a constant current method at 25°C and 0.2 C, and CC discharging to 2.75 V using a constant current method at 25°C and 0.2 C. Thereafter, it was subjected to 100 cycles of charge and discharge at a charge voltage of 4.20 V, a discharge voltage of 2.75 V, and a charge / discharge rate of 0.5 C in a 25°C environment. At this time, the capacity at the first cycle, i.e., the initial discharge capacity X1, and the discharge capacity at the 50th cycle X2 were measured, and the capacity change rate expressed as ΔC' = (X2 / X1) × 100 (%) was calculated and evaluated according to the following criteria. The larger the value of this capacity change rate ΔC', the better the cycle characteristics. A: ΔC' is 84% ​​or more B: ΔC' is 82% or more but less than 84% C: ΔC' is 80% or more but less than 82% D: ΔC' is less than 80%

[0107] (Example 1) (1-1. Particulate Polymer) A monomer composition, 0.3 parts of t-dodecyl mercaptan as a molecular weight modifier, 2 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water as a solvent, and 1 part of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer, and after thorough stirring, the mixture was heated to 55°C to initiate polymerization. Here, the monomer composition used included 60 parts of styrene as the aromatic vinyl monomer, 34 parts of 1,3-butadiene as the aliphatic conjugated diene monomer, 5 parts of itaconic acid as the ethylenically unsaturated carboxylic acid monomer, and 1 part of 2-hydroxyethyl acrylate as the hydroxyl group-containing monomer.

[0108] When the monomer consumption reached 95.0%, the mixture was cooled to stop the reaction. A 5% aqueous solution of sodium hydroxide was added to the aqueous dispersion containing the polymer obtained in this way to adjust the pH to 8. An appropriate amount of ion-exchanged water was then added, and unreacted monomers were removed by heating and vacuum distillation. The mixture was then cooled to 30°C or below to obtain an aqueous dispersion of a particulate polymer.

[0109] (1-2. Aqueous Solution of Water-Soluble Polymer) (1-2-1. Addition of Monomer Composition) 720 g of ion-exchanged water was placed in a 1 L flask equipped with a septum and heated to a temperature of 40°C, and the atmosphere in the flask was purged with nitrogen gas at a flow rate of 100 mL / min. Next, 10 g of ion-exchanged water and the monomer composition were mixed and injected into the flask with a syringe. Here, 11.4 g (30.0%) of acrylic acid and 26.6 g (70.0%) of acrylamide were used as the monomer composition.

[0110] (1-2-2. Polymerization Reaction) After (1-2-1), the temperature was maintained at 40°C, and 8.0 g of a 2.5% aqueous solution of potassium persulfate as a polymerization initiator was added to the flask via syringe. Furthermore, 15 minutes later, 40 g of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator was added via syringe. After 4 hours, 4.0 g of a 2.5% aqueous solution of potassium persulfate as a polymerization initiator was added to the flask, followed by 20 g of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator. The temperature was raised from 40°C to 60°C, and the polymerization reaction was allowed to proceed. After 3 hours, the flask was opened to the air to terminate the polymerization reaction. An appropriate amount of ion-exchanged water was added, and the product was deodorized at 80°C to remove residual monomers. The pH of the product was then adjusted to 8 using a 10% aqueous solution of lithium hydroxide, yielding an aqueous solution of a water-soluble polymer. A portion of the resulting aqueous solution of the water-soluble polymer was diluted to a concentration of 1% by mass, and the viscosity was measured.

[0111] (1-3. Binder composition) The aqueous dispersion of the particulate polymer obtained in (1-1) and the aqueous solution of the water-soluble polymer obtained in (1-2) were mixed using a disper to obtain a binder composition. The mixing ratios of the aqueous dispersion of the particulate polymer and the aqueous solution of the water-soluble polymer were 5% by mass and 95% by mass, respectively, in terms of solid content ratio to their total. The solid content concentration of the obtained binder composition was 5% by mass.

[0112] The obtained binder composition was evaluated for viscosity, number average particle size of the particulate polymer, amount of aggregates, and tensile properties of the dried film.

[0113] (1-4. Negative electrode slurry composition) 50 parts of SiOx (theoretical capacity: 2400 mAh / g, volume average particle diameter D50: 5 μm) as a silicon-based negative electrode active material, 50 parts of artificial graphite (theoretical capacity: 360 mAh / g, volume average particle diameter D50: 23 μm) as a carbon-based negative electrode active material, and the binder composition obtained in (1-2) were blended in a planetary mixer so that the solid content was 3.0 parts, and the mixture was kneaded with the planetary mixer at 40 rpm for 60 minutes to obtain a slurry.

[0114] Ion-exchanged water was added to the obtained slurry, and the mixture was mixed to a viscosity of 3500 to 4500 MPa·s, and further mixed for 10 minutes, followed by degassing under reduced pressure to obtain a negative electrode slurry composition.

[0115] (1-5. Negative Electrode) A copper foil having a thickness of 15 μm was prepared as a negative electrode current collector. The negative electrode slurry composition obtained in (1-4) was applied to one side of the copper foil using a comma coater. The coating amount after drying was 4.5 mg / cm. ２ The copper foil coated with the negative electrode slurry composition was transported at a speed of 0.3 m / min through an oven at 60°C for 2 minutes and then through an oven at 110°C for 2 minutes to dry the slurry composition on the copper foil, thereby obtaining a negative electrode blank.

[0116] The obtained negative electrode blank was pressed with a roll press to a composite layer density of 1.63 g / cm ３ ~1.67g / cm ３ The resultant negative electrode was pressed so that the powder distribution was within the range of 100 μm, and then placed in a vacuum environment at 120° C. for 10 hours to remove moisture. This resulted in a negative electrode including a current collector and a negative electrode mixture layer formed thereon. The resulting negative electrode was subjected to a powder shedding test.

[0117] (1-6. Positive electrode) A planetary mixer was charged with Li (Ni) as a positive electrode active material. ０．５ Co ０．２ Mn ０．３ ) O ２ A slurry composition for a positive electrode was prepared by adding and mixing 96 parts of cellulose acetate (average particle size: 10 μm), 2 parts of acetylene black (HS-100 manufactured by Denki Kagaku Kogyo K.K.) as a conductive aid, 2 parts of PVDF (polyvinylidene fluoride, KF-1100 manufactured by Kureha Chemical Industries, Ltd.), and an amount of 2-methylpyrrolidinone to give a total solids concentration of 67%.

[0118] An aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector. The positive electrode slurry composition was applied to one side of the aluminum foil using a comma coater. The coating amount after drying was 24 mg / cm. ２The aluminum foil coated with the positive electrode slurry composition was transported at a speed of 0.5 m / min through an oven at 60°C for 2 minutes and then through an oven at 120°C for 2 minutes, thereby drying the slurry composition on the aluminum foil and obtaining a positive electrode substrate.

[0119] The obtained positive electrode blank was pressed with a roll press machine to a density of 3.40 g / cm ３ ~3.50 g / cm ３ The mixture was pressed so that the density was distributed within a range of 1.0 μm, and then placed in a vacuum environment at 120° C. for 3 hours to remove moisture. This resulted in a positive electrode including a current collector and a positive electrode mixture layer formed thereon.

[0120] (1-7. Production of Lithium-Ion Secondary Battery) A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm; produced by a dry method; porosity 55%) was prepared and placed in a 5×5 cm ２ The negative electrode prepared in step (1-5) was cut into a rectangle of 4.0 × 3.0 cm to obtain a rectangular negative electrode. The positive electrode prepared in step (1-6) was cut into a rectangle of 3.8 × 2.8 cm to obtain a rectangular positive electrode. As the electrolyte, a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio) (containing 2 parts by volume of vinylene carbonate as an additive and 1.0 M LiPF ６ (including the above) was prepared. An aluminum packaging exterior was also prepared as the exterior of the battery. A rectangular positive electrode was placed inside the aluminum packaging exterior so that the surface on the current collector side was in contact with the aluminum packaging exterior. Next, a rectangular separator was placed on the surface on the positive electrode composite layer side of the rectangular positive electrode. Furthermore, a rectangular negative electrode was placed on the separator so that the surface on the negative electrode composite layer side was in contact with the separator. After that, an electrolyte was filled into the aluminum packaging exterior. Furthermore, the aluminum packaging exterior was closed by heat sealing at 150°C, and a laminate cell type lithium ion secondary battery was produced.

[0121] The cycle characteristics of the obtained lithium ion secondary battery were evaluated.

[0122] Example 2 A water-soluble polymer aqueous solution, a binder composition, a negative electrode, and a lithium-ion secondary battery were produced and evaluated using the same procedures as in Example 1, except for the following changes: In (1-2-1), the amount of ion-exchanged water added was changed. As a result, the solids concentration of the binder composition obtained in (1-3) was 7 mass%. In (1-2-1), the monomer composition was changed to 7.6 g (20.0%) of acrylic acid, 26.6 g (70.0%) of acrylamide, and 3.8 g (10%) of acrylonitrile.

[0123] Example 3 (3-1. Aqueous Solution of Water-Soluble Polymer) After step (1-2-1) of Example 1, the temperature was maintained at 40°C, and 9.6 g of a 2.5% aqueous solution of potassium persulfate as a polymerization initiator was added to the flask using a syringe. Furthermore, 15 minutes later, 48 g of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator was added using a syringe. After 4 hours, 4.8 g of a 2.5% aqueous solution of potassium persulfate as a polymerization initiator was added to the flask, and then 24 g of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator was added. The temperature was raised from 40°C to 60°C, and the polymerization reaction was allowed to proceed. After 3 hours, the flask was opened to the air to terminate the polymerization reaction, and an appropriate amount of ion-exchanged water was added. The product was deodorized at a temperature of 80°C to remove residual monomers. The pH of the product was then adjusted to 8 using a 10% aqueous solution of lithium hydroxide, thereby obtaining an aqueous solution of a water-soluble polymer. A portion of the obtained water-soluble polymer aqueous solution was taken and diluted to a concentration of 1% by mass, and the viscosity was measured. The viscosity value was lower than the result of a similar measurement for the water-soluble polymer aqueous solution obtained in Example 1.

[0124] (3-2. Binder Composition, Negative Electrode, and Lithium-Ion Secondary Battery) A binder composition, a negative electrode, and a lithium-ion secondary battery were produced and evaluated by the same procedures as in (1-1) and (1-3) of Example 1, except for the following changes: The water-soluble polymer obtained in (3-1) was used instead of the one obtained in (1-2-2).

[0125] Example 4 (4-1. Aqueous Solution of Water-Soluble Polymer) After step (1-2-1) of Example 1, the temperature was maintained at 40°C, and 5.6 g of a 2.5% aqueous solution of potassium persulfate as a polymerization initiator was added to the flask using a syringe. Furthermore, 15 minutes later, 28 g of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator was added using a syringe. After 4 hours, 2.8 g of a 2.5% aqueous solution of potassium persulfate as a polymerization initiator was added to the flask, and then 14 g of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator was added. The temperature was raised from 40°C to 60°C, and the polymerization reaction was allowed to proceed. After 3 hours, the flask was opened to the air to terminate the polymerization reaction, and an appropriate amount of ion-exchanged water was added. The product was deodorized at a temperature of 80°C to remove residual monomers. The pH of the product was then adjusted to 8 using a 10% aqueous solution of lithium hydroxide, thereby obtaining an aqueous solution of a water-soluble polymer. A portion of the obtained water-soluble polymer aqueous solution was taken and diluted to a concentration of 1% by mass, and the viscosity was measured. The viscosity value was higher than the result of a similar measurement of the water-soluble polymer aqueous solution obtained in Example 1.

[0126] (4-2. Binder Composition, Negative Electrode, and Lithium-Ion Secondary Battery) A binder composition, a negative electrode, and a lithium-ion secondary battery were produced and evaluated by the same procedures as in (1-1) and (1-3) of Example 1, except for the following changes: The water-soluble polymer obtained in (4-1) was used instead of the one obtained in (1-2-2).

[0127] Example 5 A binder composition, a negative electrode, and a lithium-ion secondary battery were produced and evaluated by the same procedures as in Example 4, except for the following changes: In (1-2-2), the amount of ion-exchanged water added was changed. As a result, the solids concentration of the binder composition obtained in (1-3) was 2 mass%.

[0128] Example 6 A binder composition, a negative electrode, and a lithium ion secondary battery were produced and evaluated by the same procedures as in Example 3, except for the following changes: In (1-2-2), the amount of ion-exchanged water added was changed. In (1-3), the mixing ratios of the aqueous dispersion of the particulate polymer and the aqueous solution of the water-soluble polymer were changed to 40% by mass and 60% by mass, respectively, in terms of solid content. As a result, the solid content concentration of the binder composition obtained in (1-3) was 12% by mass.

[0129] Example 7 A binder composition, a negative electrode, and a lithium ion secondary battery were produced and evaluated by the same procedures as in Example 1, except for the following changes. When preparing the particulate polymer (1-1), the ratio of the monomer composition to the solvent was changed, and the amount of emulsifier added was also changed, and polymerization was performed. After polymerization, the resulting aqueous dispersion was concentrated by heating to adjust the solids concentration. The resulting particulate polymer had the same composition of polymerization units as in Example (1-1), but had a smaller number-average particle diameter. After adjusting the solids concentration of the aqueous dispersion of the particulate polymer, the solids concentration in the binder composition was 5% by mass, the same as in Example 1.

[0130] (Example 8) (8-1. Aqueous Solution of Water-Soluble Polymer) A sodium salt of carboxymethyl cellulose ("MAC200HC" manufactured by Nippon Paper Industries Co., Ltd.) was dissolved in ion-exchanged water to a solids concentration of 2%, to obtain an aqueous solution (i). Separately, polyacrylic acid (manufactured by Aldrich, molecular weight 1,250,000) was dissolved in ion-exchanged water, and a 10% aqueous solution of lithium hydroxide was added to adjust the pH to 8, to prepare an aqueous solution (ii) with a solids concentration of 4%. Aqueous solutions (i) and (ii) were mixed so that the solids ratio was 50:50, to obtain an aqueous solution of a water-soluble polymer.

[0131] (8-2. Binder composition, negative electrode, and lithium ion secondary battery) A binder composition, a negative electrode, and a lithium ion secondary battery were produced and evaluated by the same procedures as in (1-1) and (1-3) of Example 1, except for the following changes: - As the water-soluble polymer, the one obtained in (8-1) was used instead of the one obtained in (1-2-2). The solid content concentration of the obtained binder composition was 3 mass%.

[0132] Example 9 A binder composition, a negative electrode, and a lithium ion secondary battery were produced and evaluated by the same procedures as in Example 1, except for the following changes: In (1-3), the mixing ratios of the aqueous dispersion of the particulate polymer and the aqueous solution of the water-soluble polymer were changed to 0.1% by mass and 99.9% by mass, respectively, in terms of solid content ratio relative to their total.

[0133] Comparative Example 1 A binder composition, a negative electrode, and a lithium ion secondary battery were produced and evaluated by the same procedures as in Example 1, except for the following changes. When preparing the particulate polymer (1-1), the ratio of the monomer composition to the solvent was changed, and the amount of emulsifier added was also changed, and polymerization was performed. After polymerization, the mixture was heated and concentrated to adjust the solids concentration of the aqueous dispersion. The resulting particulate polymer had the same composition of polymerization units as in Example (1-1), but had a smaller number-average particle diameter. After adjusting the solids concentration of the aqueous dispersion of the particulate polymer, the solids concentration in the binder composition was 5% by mass, the same as in Example 1.

[0134] (Comparative Example 2) (C2-1. Aqueous Solution of Water-Soluble Polymer) After step (1-2-1) of Example 1, the temperature was maintained at 40°C, and 4.0 g of a 2.5% aqueous solution of potassium persulfate as a polymerization initiator was added to the flask using a syringe. Furthermore, 15 minutes later, 20 g of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator was added using a syringe. After 4 hours, 2.0 g of a 2.5% aqueous solution of potassium persulfate as a polymerization initiator was added to the flask, and then 10 g of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator was added. The temperature was raised from 40°C to 60°C, and the polymerization reaction was allowed to proceed. After 3 hours, the flask was opened to the air to terminate the polymerization reaction, and an appropriate amount of ion-exchanged water was added. The product was deodorized at a temperature of 80°C to remove residual monomers. Thereafter, the pH of the product was adjusted to 8 using a 10% aqueous solution of lithium hydroxide, thereby obtaining an aqueous solution of a water-soluble polymer. A portion of the obtained water-soluble polymer aqueous solution was taken and diluted to a concentration of 1% by mass, and the viscosity was measured. The viscosity value was higher than the result of a similar measurement for the water-soluble polymer aqueous solution obtained in Example 4.

[0135] (C2-2. Binder Composition, Negative Electrode, and Lithium-Ion Secondary Battery) A binder composition, a negative electrode, and a lithium-ion secondary battery were produced and evaluated by the same procedures as in (1-1) and (1-3) of Example 1, except for the following changes: The water-soluble polymer obtained in (C2-1) was used instead of the one obtained in (1-2-2).

[0136] Comparative Example 3 A binder composition, a negative electrode, and a lithium ion secondary battery were produced and evaluated by the same procedures as in Example 1, except for the following changes: In (1-3), the mixing ratios of the aqueous dispersion of the particulate polymer and the aqueous solution of the water-soluble polymer were changed to 80% by mass and 20% by mass, respectively, in terms of solid content relative to their total. The solid content concentration of the obtained binder composition was 10% by mass.

[0137] The outline of the examples and comparative examples and the evaluation results are shown in Tables 1 and 2.

[0138]

[0139]

[0140] Water-soluble polymer composition: AA-AM: acrylic acid-acrylamide copolymer AA-AM(L): acrylic acid-acrylamide copolymer, lower viscosity than AA-AM AA-AM(H): acrylic acid-acrylamide copolymer, higher viscosity than AA-AM AA-AM(VH): acrylic acid-acrylamide copolymer, even higher viscosity than AA-AM(H) AN-AA-AM: acrylonitrile-acrylic acid-acrylamide copolymer CMC+PAA: mixture of carboxymethyl cellulose and polyacrylic acid Particulate polymer composition: SBR(1): prepared in Example 1(1-1) SBR(2): prepared in Example 7 SBR(3): prepared in Comparative Example 1 *1: viscosity in a state where aggregation has occurred

[0141] From the above results, it can be seen that in the examples that satisfy the requirements of the present invention, a binder composition that contains both a water-soluble polymer and a particulate polymer, that can facilitate the preparation of a slurry composition, that can suppress powder falling off of the resulting electrode, and that can improve the cycle characteristics of the resulting battery can be prepared in a state that does not cause aggregation.

Claims

1. A binder composition for lithium ion secondary battery electrode slurry, comprising a water-soluble polymer and a particulate polymer, wherein the particulate polymer has a number average particle diameter of 25 nm or more and 500 nm or less, and a viscosity of 500 mPa·s or more and 50,000 mPa·s or less.

2. The binder composition for lithium ion secondary battery electrode slurry according to claim 1, having a solids concentration of 2 to 30 mass %.

3. A binder composition for lithium ion secondary battery electrode slurry according to claim 1, wherein the proportion of the particulate polymer is 0.01 mass % or more and 40 mass % or less in a total of 100 mass % of the water-soluble polymer and the particulate polymer.

4. The binder composition for lithium ion secondary battery electrode slurry according to claim 1, wherein a tensile strength test of a dried film of the binder composition for lithium ion secondary battery electrode slurry shows a tensile modulus of 10 MPa or more and 8000 MPa or less, a breaking strength of 10 MPa or more and 1000 MPa or less, and an elongation at break of 1% or more and 500% or less.

5. The binder composition for a lithium ion secondary battery electrode slurry according to claim 1, wherein the particulate polymer contains aliphatic conjugated diene monomer units and aromatic vinyl monomer units.

6. The binder composition for a lithium ion secondary battery electrode slurry according to claim 5, wherein the particulate polymer further contains an acid group-containing monomer unit.

7. The binder composition for lithium ion secondary battery electrode slurry according to claim 1, wherein the particulate polymer is an unsaturated carboxylic acid alkyl ester polymer.

8. The binder composition for a lithium ion secondary battery electrode slurry according to claim 7, wherein the particulate polymer further contains an acid group-containing monomer unit.

9. A method for producing a slurry composition for a lithium ion secondary battery electrode, comprising mixing the binder composition for a lithium ion secondary battery electrode slurry according to any one of claims 1 to 8 with an electrode active material.

10. The method for producing a slurry composition for a lithium ion secondary battery electrode according to claim 9, wherein the electrode active material comprises a silicon-based negative electrode active material.

11. A method for producing an electrode for a lithium ion secondary battery including an electrode mixture layer, comprising: a step of obtaining a slurry composition for a lithium ion secondary battery electrode by the method for producing a slurry composition for a lithium ion secondary battery electrode according to claim 9; and a step of hardening the slurry composition for a lithium ion secondary battery electrode to form the electrode mixture layer.

12. A method for manufacturing a lithium ion secondary battery, comprising: a step of obtaining an electrode for a lithium ion secondary battery by the method for manufacturing an electrode for a lithium ion secondary battery according to claim 11; and a step of manufacturing the lithium ion secondary battery using the electrode for a lithium ion secondary battery.

13. A slurry composition for lithium ion secondary battery electrodes, comprising a mixture of the binder composition for lithium ion secondary battery electrode slurry according to any one of claims 1 to 8 and an electrode active material.

14. The slurry composition for a lithium ion secondary battery electrode according to claim 13, wherein the electrode active material comprises a silicon-based negative electrode active material.

15. An electrode for a lithium ion secondary battery, comprising an electrode mixture layer which is a cured product of the slurry composition for a lithium ion secondary battery electrode according to claim 13.

16. A lithium ion secondary battery comprising the electrode for a lithium ion secondary battery according to claim 15.

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