Binder composition for non-aqueous secondary battery negative electrode, slurry composition for non-aqueous secondary battery negative electrode, negative electrode for non-aqueous secondary battery, and non-aqueous secondary battery

Abstract

A purpose of the present invention is to provide a binder composition for a non-aqueous secondary battery negative electrode, the binder composition allowing for preparing a slurry composition having suppressed foaming characteristics and forming a negative electrode mixture layer having excellent peeling resistance. The present invention relates to a binder composition for a non-aqueous secondary battery negative electrode, the binder composition including a particulate binding material and water. The particulate binding material includes a polymer containing an ethylenic unsaturated carboxylic acid monomer unit, an aromatic vinyl monomer unit, and an aliphatic conjugated diene monomer unit. When a film of the particulate binding material is formed, and when the degree of swelling with respect to an insoluble content of tetrahydrofuran is 300-1500 mass% (inclusive), the insoluble content of tetrahydrofuran is 85-99 mass% (inclusive), and the solid content concentration of the binder composition is 30 mass%, the film has a ratio of the viscosity at a pH of 8.0 to the viscosity at a pH of 3.0 of 1.5-200 (inclusive).

Description

Binder composition for non-aqueous secondary battery negative electrode, slurry composition for non-aqueous secondary battery negative electrode, non-aqueous secondary battery negative electrode, and non-aqueous secondary battery

[0001] The present invention relates to a binder composition for a non-aqueous secondary battery negative electrode, a slurry composition for a non-aqueous secondary battery negative electrode, a non-aqueous secondary battery negative electrode, and a non-aqueous secondary battery.

[0002] Non-aqueous secondary batteries such as lithium ion secondary batteries (hereinafter sometimes simply referred to as "secondary batteries") are small, lightweight, have high energy density, and are capable of repeated charge and discharge, and are therefore used in a wide range of applications. Therefore, in recent years, improvements to battery components such as electrodes have been investigated with the aim of further improving the performance of non-aqueous secondary batteries.

[0003] An electrode used in a secondary battery typically includes a current collector and an electrode mixture layer (positive electrode mixture layer or negative electrode mixture layer) formed on the current collector. The electrode mixture layer is formed, for example, by applying a slurry composition containing an electrode active material and a binder composition containing a binding agent onto the current collector and then drying the applied slurry composition.

[0004] In recent years, efforts have been made to improve the binder compositions used in forming electrode mixture layers in order to further improve the performance of secondary batteries. For example, Patent Document 1 proposes a composition for an electric storage device comprising a polymer and a liquid solvent, with the aim of producing an electric storage device electrode that exhibits excellent flexibility and adhesion (adhesion ability, abrasion resistance, powder shedding resistance, etc.) and good charge / discharge durability (cycling characteristics). The polymer contains, in desired proportions, repeating units derived from a conjugated diene, repeating units derived from an unsaturated carboxylic acid, and at least one repeating unit selected from the group consisting of repeating units derived from an unsaturated carboxylic acid ester having a hydroxyl group or an ether group, repeating units derived from (meth)acrylamide, and repeating units derived from an α,β-unsaturated nitrile compound. Patent Document 1 also discloses that the polymer may be dispersed in a liquid solvent to form a latex, and that water may be used as the liquid solvent. Patent Document 1 also discloses a slurry for an electric storage device electrode containing the composition and an active material. Furthermore, Patent Document 1 discloses an electricity storage device electrode including a current collector and an active material layer formed by applying the slurry to the current collector and drying it, and an electricity storage device including the electrode.

[0005] Japanese Patent Application Laid-Open No. 2020-9651

[0006] In order to obtain good electrical characteristics of a nonaqueous secondary battery, it is desirable that the negative electrode mixture layer have a uniform porous structure with few defects such as pinholes, etc. In order to suppress the occurrence of pinholes, it is desirable that the slurry composition used to form the negative electrode mixture layer has little foaming.

[0007] Furthermore, since the negative electrode active material in the negative electrode composite layer repeatedly expands and contracts with charge and discharge, in order to maintain the performance of the nonaqueous secondary battery, it is desirable that the negative electrode composite layer formed on the current collector does not easily peel off from the current collector due to charge and discharge of the nonaqueous secondary battery.

[0008] However, a slurry composition using a conventional binder composition is prone to foaming, and there is a risk of pinholes occurring in the negative electrode mixture layer formed using the slurry composition. Furthermore, a negative electrode mixture layer formed from a slurry composition using the conventional binder composition has insufficient peel resistance from the current collector, leaving room for improvement.

[0009] Therefore, an object of the present invention is to provide a binder composition for a non-aqueous secondary battery negative electrode that can prepare a slurry composition with reduced foaming and form a negative electrode mixture layer with excellent peeling resistance. Another object of the present invention is to provide a slurry composition for a non-aqueous secondary battery negative electrode that includes the binder composition for a non-aqueous secondary battery negative electrode. Another object of the present invention is to provide a non-aqueous secondary battery negative electrode that includes a negative electrode mixture layer formed from the slurry composition for a non-aqueous secondary battery negative electrode. Another object of the present invention is to provide a non-aqueous secondary battery that includes the non-aqueous secondary battery negative electrode.

[0010] The present inventors have conducted extensive research to solve the above-mentioned problems, and have newly discovered that the above-mentioned problems can be solved by a binder composition for a non-aqueous secondary battery negative electrode, which comprises a particulate binder and water, wherein the particulate binder contains a specific monomer unit, and when a film of the particulate binder is formed, the film has a degree of swelling in tetrahydrofuran and an amount of insoluble matter within desired numerical ranges, and when the solid content concentration of the binder composition is 30 mass %, the ratio of the viscosity at pH 8.0 to the viscosity at pH 3.0 is within a desired numerical range, thereby completing the present invention.

[0011] The present invention aims to solve the above-mentioned problems. The present invention provides a binder composition for a non-aqueous secondary battery anode, comprising a particulate binder and water, wherein the particulate binder comprises a polymer containing ethylenically unsaturated carboxylic acid monomer units, aromatic vinyl monomer units, and aliphatic conjugated diene monomer units. When a film of the particulate binder is formed, the film has an insoluble portion swelling degree in tetrahydrofuran of 300% by mass to 1500% by mass, an insoluble portion in tetrahydrofuran of 85% by mass to 99% by mass, and a solids concentration of the binder composition of 30% by mass, the ratio of the viscosity at pH 8.0 to the viscosity at pH 3.0 is 1.5 to 200. This binder composition for a non-aqueous secondary battery anode can be used to prepare a slurry composition with reduced foaming and to form a negative electrode mixture layer with excellent peel resistance. In this specification, the term "monomer unit" of a polymer means "a repeating unit derived from the monomer contained in a polymer obtained using the monomer." The swelling degree, the insoluble content, the viscosity at pH 3.0, and the viscosity at pH 8.0 are calculated according to the method described in the Examples of this specification.

[0012] In the binder composition for a non-aqueous secondary battery negative electrode of the present invention, the proportion of the ethylenically unsaturated carboxylic acid monomer unit in the polymer is preferably 2% by mass or more and 35% by mass or less. If the proportion of the ethylenically unsaturated carboxylic acid monomer unit is equal to or more than the above lower limit, a negative electrode mixture layer having better peel resistance can be obtained. On the other hand, if the proportion of the ethylenically unsaturated carboxylic acid monomer unit is equal to or less than the above upper limit, a slurry composition with more suppressed foaming can be obtained. In this specification, the proportions of various monomer units in the polymer are defined as follows: １ It can be measured using H-NMR.

[0013] In the binder composition for a non-aqueous secondary battery negative electrode of the present invention, the polymer preferably further contains an ethylenically unsaturated amide monomer unit. When the polymer further contains an ethylenically unsaturated amide monomer unit, a negative electrode having excellent flexibility can be obtained.

[0014] In the binder composition for a non-aqueous secondary battery negative electrode of the present invention, the proportion of the ethylenically unsaturated amide monomer unit in the polymer is preferably 1% by mass or more and 18% by mass or less. When the proportion of the ethylenically unsaturated amide monomer unit is within the above range, a negative electrode having excellent flexibility can be obtained.

[0015] The present invention also aims to solve the above-mentioned problems, and provides a slurry composition for a non-aqueous secondary battery negative electrode, comprising a negative electrode active material and the binder composition for a non-aqueous secondary battery negative electrode. Such a slurry composition for a non-aqueous secondary battery negative electrode can form a negative electrode mixture layer that is suppressed in foaming and has excellent peeling resistance.

[0016] The present invention also aims to solve the above-mentioned problems, and provides a negative electrode for a non-aqueous secondary battery, comprising a current collector and a negative electrode mixture layer located on the current collector, the negative electrode mixture layer being a layer formed from the above-mentioned slurry composition for a non-aqueous secondary battery. With such a negative electrode for a non-aqueous secondary battery, the generation of pinholes in the negative electrode mixture layer is suppressed, and the negative electrode mixture layer has excellent peel resistance.

[0017] Another object of the present invention is to solve the above-mentioned problems, and to provide a nonaqueous secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the above-mentioned negative electrode for a nonaqueous secondary battery. Such a nonaqueous secondary battery can maintain its performance for a long period of time even after repeated charge and discharge.

[0018] According to the present invention, it is possible to provide a binder composition for a non-aqueous secondary battery negative electrode, which is capable of preparing a slurry composition with reduced foaming and forming a negative electrode mixture layer with excellent peeling resistance. Furthermore, according to the present invention, it is possible to provide a slurry composition for a non-aqueous secondary battery negative electrode, which includes the binder composition for a non-aqueous secondary battery negative electrode. Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery negative electrode, which includes a negative electrode mixture layer formed from the slurry composition for a non-aqueous secondary battery negative electrode. Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery, which includes the non-aqueous secondary battery negative electrode.

[0019] Hereinafter, embodiments of the present invention will be described in detail. Hereinafter, the binder composition for a non-aqueous secondary battery negative electrode of the present invention (hereinafter sometimes simply abbreviated as "binder composition") can be used to prepare a slurry composition for a non-aqueous secondary battery negative electrode (hereinafter sometimes simply abbreviated as "slurry composition"). Furthermore, the slurry composition for a non-aqueous secondary battery negative electrode of the present invention can be used when producing a negative electrode for a non-aqueous secondary battery such as a lithium ion secondary battery (hereinafter sometimes simply abbreviated as "negative electrode"). Furthermore, the non-aqueous secondary battery negative electrode of the present invention can be used in a non-aqueous secondary battery.

[0020] (Binder Composition for Non-Aqueous Secondary Battery Negative Electrode) The binder composition for a non-aqueous secondary battery negative electrode of the present invention contains a particulate binder and water.

[0021] <Particulate Binder> The particulate binder serves to hold components such as the negative electrode active material so that they do not detach from the negative electrode mixture layer formed using a slurry composition containing a binder composition.

[0022] The particulate binder includes a polymer containing an ethylenically unsaturated carboxylic acid monomer unit, an aromatic vinyl monomer unit, and an aliphatic conjugated diene monomer unit. When the polymer is a particulate binder containing an ethylenically unsaturated carboxylic acid monomer unit, a negative electrode composite layer with excellent peel resistance can be formed. When the polymer is a particulate binder containing an aromatic vinyl monomer unit, a negative electrode with excellent cycle characteristics and excellent adhesion between the negative electrode composite layer and the current collector (hereinafter, sometimes simply referred to as "adhesion") can be obtained. When the polymer is a particulate binder containing an aliphatic conjugated diene monomer unit, a negative electrode with excellent flexibility can be obtained. It is preferable that the polymer further contains an ethylenically unsaturated amide monomer unit. When the polymer further contains an ethylenically unsaturated amide monomer unit, a negative electrode with even greater flexibility can be obtained.

[0023] [Ethylenically unsaturated carboxylic acid monomer unit] An ethylenically unsaturated carboxylic acid monomer capable of forming an ethylenically unsaturated carboxylic acid monomer unit usually does not have any hydroxyl groups (—OH) other than the hydroxyl group in the carboxyl group. Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acids and derivatives thereof, ethylenically unsaturated dicarboxylic acids and acid anhydrides thereof, and derivatives thereof. The ethylenically unsaturated carboxylic acid monomer may be used alone or in combination of two or more types in any ratio.

[0024] Examples of ethylenically unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of derivatives of ethylenically unsaturated monocarboxylic acids include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and β-diaminoacrylic acid. Examples of ethylenically unsaturated dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of acid anhydrides of ethylenically unsaturated dicarboxylic acids include maleic anhydride, diacrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride. Examples of derivatives of ethylenically unsaturated dicarboxylic acids include methylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, and fluoromaleic acid.

[0025] The ethylenically unsaturated carboxylic acid monomer is preferably a monofunctional ethylenically unsaturated carboxylic acid monomer having one ethylenically unsaturated bond (C=C) in the molecule. From the viewpoint of polymerizability, the ethylenically unsaturated carboxylic acid monomer is preferably an ethylenically unsaturated monocarboxylic acid or an ethylenically unsaturated dicarboxylic acid, more preferably acrylic acid, methacrylic acid, or itaconic acid, and even more preferably acrylic acid or methacrylic acid.

[0026] The proportion of the ethylenically unsaturated carboxylic acid monomer units in the polymer is preferably 2% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, even more preferably 11% by mass or more, particularly preferably 13% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, even more preferably 23% by mass or less, and particularly preferably 21% by mass or less, when the amount of all monomer units in the polymer is 100% by mass. If the proportion of the ethylenically unsaturated carboxylic acid monomer units is above the lower limit, a negative electrode mixture layer with better peel resistance can be formed. On the other hand, if the proportion of the ethylenically unsaturated carboxylic acid monomer units is below the upper limit, a slurry composition with more suppressed foaming can be obtained.

[0027] [Aromatic vinyl monomer unit] Examples of aromatic vinyl monomers that can form aromatic vinyl monomer units include aromatic monovinyl compounds such as styrene, styrene sulfonic acid and its salts, α-methylstyrene, p-t-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. Among these, styrene and its derivatives are preferred. These can be used alone or in combination of two or more, but it is preferable to use one type alone.

[0028] The proportion of aromatic vinyl monomer units in the polymer is preferably 12% by mass or more, more preferably 20% by mass or more, and even more preferably 21% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 40% by mass or less, when the amount of all monomer units in the polymer is 100% by mass. If the proportion of aromatic vinyl monomer units is above the above lower limit, a negative electrode with better adhesion and better cycle characteristics can be obtained. On the other hand, if the proportion of aromatic vinyl monomer units is below the above upper limit, a negative electrode with excellent flexibility can be obtained.

[0029] [Aliphatic Conjugated Diene Monomer Unit] Examples of aliphatic conjugated diene monomers capable of forming aliphatic conjugated diene monomer units include aliphatic conjugated diene compounds having 4 or more carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among these, 1,3-butadiene and isoprene are preferred, and 1,3-butadiene is more preferred. These can be used alone or in combination of two or more, but it is preferable to use one type alone. By using 1,3-butadiene to form aliphatic conjugated diene monomer units of a polymer, the dispersion stability and thermal stability of the resulting polymer can be improved.

[0030] The proportion of the aliphatic conjugated diene monomer units in the polymer is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, and is preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 59% by mass or less, and particularly preferably 55% by mass or less, when the amount of all monomer units in the polymer is 100% by mass. If the proportion of the aliphatic conjugated diene monomer units is equal to or greater than the above lower limit, a negative electrode having excellent flexibility can be obtained. On the other hand, if the proportion of the aliphatic conjugated diene monomer units is equal to or less than the above upper limit, a negative electrode having excellent adhesion and excellent cycle characteristics can be obtained.

[0031] [Ethylenically unsaturated amide monomer unit] Examples of the ethylenically unsaturated amide monomer that can form the ethylenically unsaturated amide monomer unit include those obtained by amidating the above-mentioned ethylenically unsaturated carboxylic acid monomer (ethylenically unsaturated amide monomer). For example, examples of those obtained by amidating an ethylenically unsaturated monocarboxylic acid (ethylenically unsaturated monoamide monomer) include acrylamide, methacrylamide, crotonamide, etc. Among these, acrylamide and methacrylamide are preferred, and acrylamide is particularly preferred.

[0032] The proportion of the ethylenically unsaturated amide monomer units in the polymer is preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 3% by mass or more, particularly preferably 4.7% by mass or more, and is preferably 18% by mass or less, more preferably 13% by mass or less, even more preferably 10% by mass or less, and particularly preferably 8% by mass or less, when the amount of all monomer units in the polymer is taken as 100% by mass. When the proportion of the ethylenically unsaturated amide monomer units is within the above numerical range, a negative electrode having superior flexibility can be obtained.

[0033] [Other Monomer Units] The polymer may contain other monomer units as long as the objectives of the present invention are not impaired. Monomers that can form the other monomer units are not particularly limited, and examples thereof include nitrile group-containing monomers such as acrylonitrile and methacrylonitrile; and ethylenically unsaturated carboxylic acid ester monomers obtained by esterifying the above-mentioned ethylenically unsaturated carboxylic acid monomers. Here, the ethylenically unsaturated carboxylic acid ester monomers also include ethylenically unsaturated carboxylic acid ester monomers containing a hydroxyalkyl group, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate. In this specification, "(meth)acrylate" refers to acrylate and / or methacrylate.

[0034] [Properties of Particulate Binder] When the binder composition of the present invention is used to form a film of the particulate binder, the swelling degree of the insoluble portion of this film in tetrahydrofuran (THF) (hereinafter sometimes simply referred to as "swelling degree") is 300% by mass or more and 1500% by mass or less, and the insoluble portion of this film in tetrahydrofuran (hereinafter sometimes simply referred to as "insoluble portion") is 85% by mass or more and 99% by mass or less. The swelling degree and insoluble portion may depend on the crosslinking point density and number of crosslinks of the polymer contained in the particulate binder. That is, as the crosslinking point density and number of crosslinks increase, the polymer network structure becomes finer, the swelling degree decreases, and the insoluble portion increases. On the other hand, as the crosslinking point density and number of crosslinks decrease, the polymer network structure becomes coarser, the swelling degree increases, and the insoluble portion decreases. Therefore, a particulate binder having a swelling degree and an insoluble content within the above ranges has a polymer with a good network structure, and as a result, the binder composition of the present invention containing this particulate binder can prepare a slurry composition with reduced foaming and form a negative electrode mixture layer with excellent peel resistance. Furthermore, if the swelling degree and insoluble content of the particulate binder are within the above ranges, a negative electrode with excellent adhesion can be obtained. Note that the swelling degree and insoluble content can be adjusted by the amounts of molecular weight modifier and monomer used, as well as the polymerization conditions, when preparing the particulate binder.

[0035] The swelling degree is preferably 350% by mass or more, more preferably 400% by mass or more, and even more preferably 500% by mass or more, and is preferably 1400% by mass or less, more preferably 1200% by mass or less, and even more preferably 1000% by mass or less. If the swelling degree is above the lower limit, a negative electrode having superior adhesion can be obtained. On the other hand, if the swelling degree is below the upper limit, a negative electrode mixture layer having superior peel resistance can be formed.

[0036] The insoluble content is preferably 86% by mass or more, more preferably 87% by mass or more, and even more preferably 88% by mass or more, and is preferably 96% by mass or less, more preferably 94% by mass or less, and even more preferably 92% by mass or less. If the insoluble content is equal to or greater than the lower limit, a slurry composition with more suppressed foaming can be obtained. On the other hand, if the insoluble content is equal to or less than the upper limit, a negative electrode with better adhesion can be obtained.

[0037] The volume average particle diameter (D50) of the particulate binder is preferably 30 nm or more, more preferably 50 nm or more, even more preferably 100 nm or more, and preferably 1000 nm or less, more preferably 700 nm or less, and even more preferably 500 nm or less. If the volume average particle diameter (D50) of the particulate binder is within the above range, a negative electrode with superior adhesion can be obtained. In this specification, the "volume average particle diameter (D50)" refers to the particle diameter at which the cumulative volume calculated from the small diameter side becomes 50% in the particle size distribution (volume basis) measured by laser diffraction.

[0038] [Method for preparing particulate binder] The polymer contained in the particulate binder can be polymerized according to a known polymerization method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. Among these, emulsion polymerization is preferred because it is easy to adjust the swelling degree and the amount of insoluble matter. As the polymerization reaction, addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used.

[0039] During the polymerization reaction, it is preferable that the polymerization system contains a molecular weight modifier (chain transfer agent) because this allows the degree of swelling and the amount of insoluble matter to be adjusted within preferred ranges. Examples of molecular weight modifiers include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan; xanthogen compounds such as dimethyl xanthogen disulfide and diisopropyl xanthogen disulfide; terpinolene; thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram monosulfide; phenolic compounds such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, and carbon tetrabromide; thio compounds such as thioglycolic acid, thiomalic acid, and 2-ethylhexyl thioglycolate; diphenylethylene; and α-methylstyrene dimer. Among these, t-dodecyl mercaptan is preferred. The molecular weight modifiers described above may be used singly or in combination of two or more kinds in any ratio.

[0040] The amount of the molecular weight modifier used is preferably 0.03 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.3 parts by mass or more, and is preferably 2.0 parts by mass or less, more preferably 1.8 parts by mass or less, even more preferably 1.0 part by mass or less, and particularly preferably 0.8 parts by mass or less, relative to 100 parts by mass of the amount of the monomer used. If the amount of the molecular weight modifier used is within the above range, the swelling degree and the insoluble content can be easily adjusted to the preferred range.

[0041] In the polymerization reaction, in addition to the molecular weight modifier, commonly used additives such as an emulsifier, a dispersant, a polymerization initiator, a polymerization aid, etc. The amounts of these additives used may be the amounts commonly used.

[0042] The maximum temperature during the polymerization reaction is preferably above 80° C., more preferably at least 85° C., and is preferably below 100° C., more preferably at most 95° C. If the maximum temperature is within the above range, the swelling degree and the insoluble content can be adjusted to preferred ranges.

[0043] In the polymerization reaction, the duration of the temperature exceeding 80°C is preferably 1 hour or more, more preferably 2 hours or more, and even more preferably 3 hours or more, and preferably 7 hours or less, more preferably 6 hours or less, and even more preferably 5 hours or less. The temperature may be 85°C or more, less than 100°C, or 95°C or less. When the duration of the temperature is within the above range, the swelling degree and the insoluble content can be adjusted to preferred ranges.

[0044] <Solvent> The binder composition of the present invention must contain water as a solvent, but may also contain a small amount of an organic solvent.

[0045] <Other Components> The binder composition of the present invention may contain components other than the above components (other components) within the scope of the present invention. Examples of other components include antioxidants, antifoaming agents, dispersants, etc. One type of other component may be used alone, or two or more types may be used in combination at any ratio.

[0046] <Method for preparing binder composition> The binder composition of the present invention is not particularly limited, and can be prepared by mixing a particulate binder with other components that are optionally used in the presence of water. When the binder composition is prepared using a dispersion of a particulate binder, the liquid contained in the dispersion may be used as it is as a medium for the binder composition.

[0047] <Properties of Binder Composition> When the binder composition of the present invention has a solids concentration of 30% by mass, the ratio of the viscosity at pH 8.0 to the viscosity at pH 3.0 (viscosity ratio α) is 1.5 or more and 200 or less. The viscosity ratio α may depend on the proportion of ethylenically unsaturated carboxylic acid monomer units in the polymer contained in the particulate binder. Furthermore, when the polymer contains ethylenically unsaturated amide monomer units, the viscosity ratio α also depends on the proportion of ethylenically unsaturated amide monomer units. That is, as the proportions of ethylenically unsaturated carboxylic acid monomer units and optional ethylenically unsaturated amide monomer units in the polymer increase, the proportions of carboxyl groups and optional amide groups in the polymer increase, and the viscosity ratio α increases. On the other hand, as the proportions of ethylenically unsaturated carboxylic acid monomer units and optional ethylenically unsaturated amide monomer units in the polymer decrease, the proportions of carboxyl groups and optional amide groups in the polymer decrease, and the viscosity ratio α decreases. Therefore, a particulate binder having a viscosity ratio α within the above range has a good ratio of carboxyl groups and any amide groups, and as a result, the binder composition of the present invention containing this particulate binder can prepare a slurry composition with suppressed foaming and can form a negative electrode composite layer with excellent peel-off resistance.

[0048] The viscosity ratio α is preferably 3 or more, more preferably 5 or more, and even more preferably 7 or more, and is preferably 150 or less, more preferably 100 or less, and even more preferably 20 or less. When the viscosity ratio α is equal to or greater than the lower limit, a negative electrode composite layer having superior peel resistance can be obtained. On the other hand, when the viscosity ratio α is equal to or less than the upper limit, a slurry composition having more suppressed foaming can be obtained. When the viscosity ratio α is within the above range, a negative electrode having excellent flexibility can be obtained.

[0049] The viscosity ratio α is not particularly limited as long as it is within the above range, but when the solid content concentration of the binder composition is 30 mass %, the viscosity at pH 3.0 is, for example, 10 mPa s or more, and may be 15 mPa s or more, while the viscosity at pH 3.0 is, for example, 50 mPa s or less, and may be 30 mPa s or less.

[0050] The viscosity ratio α is not particularly limited as long as it is within the above range, but when the solid content concentration of the binder composition is 30 mass %, the viscosity at pH 8.0 is, for example, 25 mPa·s or more, or may be 50 mPa·s or more, or 100 mPa·s or more, or may be 200 mPa·s or more, while the viscosity at pH 8.0 is, for example, 4500 mPa·s or less, or may be 3000 mPa·s or less, or may be 2000 mPa·s or less, or 1000 mPa·s or less, or may be 500 mPa·s or less.

[0051] In one embodiment, when the binder composition has a solids concentration of 20% by mass, the ratio of the viscosity at pH 9.0 to the viscosity at pH 4.0 (viscosity ratio β) is preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.5 or more, even more preferably 1.2 or more, particularly preferably 1.3 or more, preferably less than 10, more preferably less than 5, even more preferably less than 3, even more preferably 1.8 or less, and particularly preferably 1.6 or less. If the viscosity ratio β is equal to or greater than the lower limit, a negative electrode composite layer with superior peel resistance can be formed. On the other hand, if the viscosity ratio β is equal to or less than the upper limit, a slurry composition with more suppressed foaming can be obtained. Furthermore, if the viscosity ratio β is within the above range, a negative electrode with excellent flexibility can be obtained. In this specification, the viscosity at pH 4.0 and the viscosity at pH 9.0 are calculated according to the method described in the examples of this specification.

[0052] Although not particularly limited, the viscosity at pH 4.0 when the solid content concentration of the binder composition is 20 mass % is, for example, 15 mPa s or more, and may be 20 mPa s or more, while the viscosity at pH 4.0 is, for example, 40 mPa s or less, and may be 30 mPa s or less.

[0053] Although not particularly limited, the viscosity at pH 9.0 when the solid content concentration of the binder composition is 20 mass % is, for example, 16 mPa·s or more, or may be 21 mPa·s or more, or 25 mPa·s or more, while the viscosity at pH 9.0 is, for example, 80 mPa·s or less, or may be 50 mPa·s or less, or 40 mPa·s or less, or may be 35 mPa·s or less.

[0054] The viscosity at the various pH values ​​described above can be adjusted by the amounts of the ethylenically unsaturated carboxylic acid monomer and the optional ethylenically unsaturated amide monomer used when preparing the polymer contained in the particulate binder.

[0055] (Slurry Composition for Non-Aqueous Secondary Battery Negative Electrode) The slurry composition for a non-aqueous secondary battery negative electrode of the present invention is a composition used for forming a negative electrode composite layer of a negative electrode, and includes the binder composition for a non-aqueous secondary battery negative electrode described above, and further includes a negative electrode active material. That is, the slurry composition of the present invention includes a particulate binder, a negative electrode active material, and water, and may further include any other components. Furthermore, since the slurry composition of the present invention includes the binder composition of the present invention, it is possible to form a negative electrode composite layer that is suppressed in foaming and has excellent peeling resistance.

[0056] <Binder composition> The binder composition of the present invention containing a predetermined particulate binder and water is used as the binder composition. The amount of the binder composition in the slurry composition is not particularly limited. The amount of the binder composition is, in terms of solid content, for example, 0.5 parts by mass or more, or 0.7 parts by mass or more, or for example, 15 parts by mass or less, or 5 parts by mass or less, relative to 100 parts by mass of the total solid content of the slurry composition.

[0057] <Negative electrode active material> The negative electrode active material is not particularly limited, and known negative electrode active materials used in secondary batteries can be used. For example, negative electrode active materials that can be used in the negative electrode composite layer of a lithium ion secondary battery, which is an example of a secondary battery, are not particularly limited, and include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials that are combinations of these.

[0058] Carbon-based negative electrode active materials refer to active materials with a carbon backbone that can insert (also referred to as "doping") lithium. Specific examples of carbon-based negative electrode active materials include carbonaceous materials such as coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, pyrolytic vapor-grown carbon fibers, phenolic resin baked bodies, polyacrylonitrile-based carbon fibers, pseudoisotropic carbon, furfuryl alcohol resin baked bodies (PFA), and hard carbon, as well as graphitic materials such as natural graphite and artificial graphite. Metal-based negative electrode active materials refer to active materials that contain metals, and typically contain an element capable of inserting lithium in their structure, and have a theoretical electrical capacity per unit mass of 500 mAh / g or more when lithium is inserted. Examples of metal-based 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 oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. of these. Further examples include oxides such as lithium titanate. From the viewpoint of improving the capacity of the secondary battery, it is preferable to include at least a metal-based negative electrode active material, and it is more preferable to include a negative electrode active material containing Si. These negative electrode active materials exhibit particularly large expansion and contraction during charge and discharge, but the binder of the present invention can effectively suppress peeling of the negative electrode composite layer containing these negative electrode active materials. The above-mentioned negative electrode active materials may be used alone or in combination of two or more.

[0059] <Other Components> Other components that can be incorporated into the slurry composition are not particularly limited, and include thickeners, conductive materials, and the same components as those that can be incorporated into the binder composition of the present invention. Examples of thickeners include carboxymethyl cellulose and lithium salts of acrylic acid / acrylamide / hydroxyethylacrylamide copolymers. Note that, one type of other component may be used alone, or two or more types may be used in combination at any ratio.

[0060] <Preparation of Slurry Composition> The method for preparing the slurry composition is not particularly limited. For example, the binder composition, the negative electrode active material, and other components used as needed can be mixed in the presence of water to prepare the slurry composition. The medium used in preparing the slurry composition also includes the medium contained in the binder composition. The mixing method is not particularly limited, and mixing can be performed using a commonly used stirrer, disperser, etc.

[0061] (Negative electrode for non-aqueous secondary battery) The negative electrode for a non-aqueous secondary battery of the present invention includes a current collector and a negative electrode mixture layer located on the current collector, the negative electrode mixture layer being a layer formed using the above-mentioned slurry composition for a non-aqueous secondary battery negative electrode. Since the negative electrode of the present invention has the negative electrode mixture layer formed using the slurry composition of the present invention, the generation of pinholes in the negative electrode mixture layer is suppressed and the negative electrode mixture layer has excellent peel resistance.

[0062] <Negative electrode mixture layer> The negative electrode mixture layer is made of a dried product of the slurry composition of the present invention, and typically contains a negative electrode active material and a component derived from a particulate binder, and may optionally further contain other components. Note that the components contained in the negative electrode mixture layer are those contained in the slurry composition of the present invention, and the preferred abundance ratio of each component is the same as the preferred abundance ratio of each component in the slurry composition. Furthermore, the binder is present in particulate form in the binder composition and the slurry composition, but in the negative electrode mixture layer formed using the slurry composition, it may be in particulate form or any other shape.

[0063] <Current Collector> A material that is electrically conductive and electrochemically durable is used as the current collector of the negative electrode. Specifically, the current collector may be made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like. Copper foil is particularly preferred as the current collector of the negative electrode. Note that these materials may be used alone or in combination of two or more in any ratio.

[0064] <Method for Manufacturing Negative Electrode> Here, the negative electrode composite layer of the negative electrode of the present invention can be formed using, for example, the following methods. 1) A method in which the slurry composition of the present invention is applied to the surface of a current collector and then dried; 2) A method in which the current collector is immersed in the slurry composition of the present invention and then dried; and 3) A method in which the slurry composition of the present invention is applied to a release substrate and dried to produce a negative electrode composite layer, and the obtained negative electrode composite layer is transferred to the surface of the current collector. Among these, method 1) is particularly preferred because it makes it easy to control the layer thickness of the negative electrode composite layer. Method 1) specifically includes a step of applying the slurry composition to the current collector (application step) and a step of drying the slurry composition applied to the current collector to form a negative electrode composite layer on the current collector (drying step).

[0065] [Coating Step] The method for applying the slurry composition to 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 or both sides of the current collector. 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 negative electrode composite layer obtained by drying.

[0066] [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, a drying method using warm air, hot air, or low-humidity air, a vacuum drying method, or a drying method using irradiation with infrared rays, electron beams, etc. By drying the slurry composition on the current collector in this manner, a negative electrode composite layer can be formed on the current collector, and a negative electrode including the current collector and the negative electrode composite layer located on the current collector can be obtained.

[0067] After the drying step, the negative electrode mixture layer may be subjected to a pressure treatment using a mold press, a roll press, or the like. The pressure treatment improves the adhesion between the negative electrode mixture layer and the current collector and further increases the density of the resulting negative electrode mixture layer. In addition, when the negative electrode mixture layer contains a curable polymer, it is preferable to cure the polymer after the formation of the negative electrode mixture layer.

[0068] (Nonaqueous secondary battery) The nonaqueous secondary battery of the present invention comprises a positive electrode, a negative electrode, an electrolyte, and a separator, and the negative electrode is the above-described negative electrode for a nonaqueous secondary battery. Because the secondary battery of the present invention comprises the negative electrode of the present invention, the performance of the secondary battery can be maintained over a long period of time even after repeated charging and discharging. Note that, as an example, the following description will be given of a case where the secondary battery is a lithium ion secondary battery, but the present invention is not limited to the following example. As the negative electrode has been described above, a description thereof will be omitted below.

[0069] <Positive Electrode> The positive electrode included in the secondary battery of the present invention is not particularly limited, and a known positive electrode used in secondary batteries can be used. Specifically, the positive electrode can be a positive electrode obtained by forming a positive electrode mixture layer on a current collector using a known manufacturing method.

[0070] The positive electrode active material to be blended into the positive electrode composite layer is not particularly limited, and known positive electrode active materials used in secondary batteries can be used. Examples of the positive electrode active material to be blended into the positive electrode composite layer include compounds containing transition metals, such as transition metal oxides, transition metal sulfides, and composite metal oxides of lithium and transition metals. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo. Specifically, the positive electrode active material is not particularly limited, and examples thereof include lithium-containing cobalt oxide (LiCoO ２ ), lithium manganese oxide (LiMn ２ O ４ ), lithium-containing nickel oxide (LiNiO ２ ), LiNi 5 / 10 Co 2 / 10 Mn 3 / 10 Lithium-containing composite oxides of Co-Ni-Mn, such as O2 (NMC532), lithium-containing composite oxides of Ni-Mn-Al, lithium-containing composite oxides of Ni-Co-Al, olivine-type lithium iron phosphate (LiFePO ４ ), olivine-type lithium manganese phosphate (LiMnPO ４ ), Li １＋ｘ Mn ２－ｘ O ４(0<X<2) Lithium-excess spinel compound represented by Li[Ni ０．１７ Li ０．２ Co ０．０７ Mn ０．５６ ]O ２ , LiNi ０．５ Mn １．５ O ４ The above-mentioned positive electrode active materials may be used singly or in combination of two or more.

[0071] The positive electrode current collector may be made of the material described for the negative electrode current collector. Aluminum foil is particularly preferred as the positive electrode current collector. The material used for the positive electrode current collector may be one type alone or two or more types in any combination.

[0072] <Electrolyte> As the electrolyte, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte of a lithium ion secondary battery, for example, a lithium salt is used. As the lithium salt, for example, LiPF ６ , LiAsF ６ , LiBF ４ , LiSbF ６ , LiAlCl ４ , LiClO ４ , C.F. ３ SO ３ Li, C ４ F ９ SO ３ Li, CF ３ COOLi, (CF ３ CO) ２ NLi, (CF ３ SO ２ ) ２ NLi, (C ２ F ５ SO ２ Among them, LiPF is preferred because it is easily soluble in solvents and shows a high degree of dissociation. ６ , LiClO ４ , C.F. ３ SO ３Li is preferred. Note that one type of electrolyte may be used alone, or two or more types may be used in combination at any ratio. Generally, the use of a supporting electrolyte with a higher degree of dissociation tends to result in higher lithium ion conductivity, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0073] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. Suitable examples include carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. Mixtures of these solvents may also be used. Among these, carbonates are preferred due to their high dielectric constant and wide stable potential range. Generally, the lower the viscosity of the solvent used, the higher the lithium ion conductivity, so the lithium ion conductivity can be adjusted by the type of solvent. The concentration of the electrolyte in the electrolyte can be adjusted as appropriate. Known additives can also be added to the electrolyte.

[0074] <Separator> The separator is not particularly limited, and for example, those described in JP 2012-204303 A can be used. Among these, a microporous film made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it allows the thickness of the entire separator to be thin, thereby increasing the proportion of electrode active material in the secondary battery and increasing the capacity per volume.

[0075] <Method for Manufacturing Secondary Battery> The secondary battery of the present invention can be manufactured, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the resulting assembly as needed according to the battery shape, placing it in a battery container, injecting an electrolyte into the battery container, and sealing it. The secondary battery of the present invention uses the negative electrode of the present invention. The secondary battery of the present invention may be provided with an overcurrent protection element such as a fuse or a PTC element, an expanded metal, a lead plate, or the like, as needed, to prevent internal pressure buildup, overcharging and overdischarging, and the like. 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.

[0076] The present invention will be described in detail 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, in a polymer produced by polymerizing multiple types of monomers, the proportion of a monomer unit formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of that certain monomer to all monomers used in the polymerization of the polymer, unless otherwise specified.

[0077] In the examples and comparative examples, various evaluations and measurements were carried out as follows.

[0078] <Evaluation of foaming of slurry composition> 100 g of each of the slurry compositions prepared in the examples and comparative examples was added to a container with an inner diameter of 6 cm, and the slurry composition was stirred at 2000 rpm for 5 minutes using a disperser equipped with a 3 cm diameter sawtooth disk turbine blade. Thereafter, the slurry composition was added to a pressurizing case, and the case internal pressure was adjusted to 0.1 MPa (gauge pressure) with nitrogen gas and maintained for 3 minutes. After removal, the number of bubbles with a diameter of 0.1 mm or more present on the entire liquid surface of the slurry composition was counted using a 20x magnifying glass. The fewer the number of bubbles, the more suppressed the foaming of the slurry composition. A: Number of bubbles is 1 or less B: Number of bubbles is 2 or more but less than 6 C: Number of bubbles is 6 or more but less than 10 D: Number of bubbles is 10 or more but less than 12 E: Number of bubbles is 12 or more

[0079] <Evaluation of Negative Electrode Peel Strength (Adhesion Between Negative Electrode Composite Layer and Copper Foil (Current Collector))> Each of the negative electrodes prepared in the Examples and Comparative Examples was cut into a rectangle measuring 1 cm wide x 8 cm long to obtain a test piece. The test piece was then fixed with the negative electrode composite layer surface facing up. Cellophane tape (compliant with JIS Z1522) was then attached to the entire surface of the negative electrode composite layer of the test piece, and the cellophane tape was peeled off from one end of the test piece in a 180° direction at a rate of 50 mm / min, and the stress at this time was measured. Similar measurements were performed five times, and the average value was taken as the peel strength. The peel strength was evaluated according to the following criteria. A higher peel strength indicates better adhesion between the negative electrode composite layer and the current collector. A: Peel strength is 3.5 N / m or more. B: Peel strength is 3.0 N / m or more and less than 3.5 N / m. C: Peel strength is 2.5 N / m or more and less than 3.0 N / m. D: Peel strength is 2.0 N / m or more and less than 2.5 N / m. E: Peel strength is less than 2.0 N / m.

[0080] <Evaluation of Flexibility of Negative Electrode> Each of the negative electrodes prepared in the examples and comparative examples was cut into a rectangle measuring 1 cm wide x 8 cm long to obtain a test piece. Next, a plurality of metal rods with different diameters were prepared, and the test piece was wrapped around each metal rod so that the copper foil of the test piece was on the metal rod side. The wrapped test piece was visually checked for cracks in the composite layer of the test piece. The smaller the diameter of the metal rod, the more excellent the flexibility. A: No cracks when the metal rod diameter was 4.0 mm B: No cracks when the metal rod diameter was 5.0 mm, cracks when 4.0 mm C: No cracks when the metal rod diameter was 6.0 mm, cracks when 5.0 mm D: No cracks when the metal rod diameter was 7.0 mm, cracks when 6.0 mm E: Cracks when the metal rod diameter was 7.0 mm

[0081] <Evaluation of Cycle Characteristics of Secondary Battery> The cycle characteristics were evaluated using the secondary batteries fabricated in the examples and comparative examples. Specifically, the secondary batteries were first left at 25°C for 6 hours. Then, they were charged for 100 minutes at 25°C using a constant current of 0.1 C. Then, they were aged for 12 hours at 60°C. Next, they were charged to a cell voltage of 4.20 V using a constant current of 0.5 C at 25°C, and then discharged to a cell voltage of 2.75 V. The initial capacity C0 was measured. This charge / discharge cycle was further repeated, and the capacity C1 after 50 cycles was measured. The capacity retention C2 was then calculated according to the following formula: C2 (%) = (C1 / C0) × 100. A larger value for the capacity retention C2 indicates better cycle characteristics. A: Capacity maintenance rate C2 is 90% or more. B: Capacity maintenance rate C2 is 85% or more and less than 90%. C: Capacity maintenance rate C2 is 80% or more and less than 85%. D: Capacity maintenance rate C2 is 75% or more and less than 80%. E: Capacity maintenance rate C2 is less than 75%.

[0082] <Evaluation of Peel Resistance of Negative Electrode Mixture Layer> Peel resistance was evaluated using the secondary batteries prepared in the examples and comparative examples. Specifically, first, the secondary batteries were subjected to an aging treatment in the same manner as in the evaluation of cycle characteristics described above. Next, in an environment of 25°C, the secondary batteries were charged to 4.2 V at 0.2 C and discharged to 3.0 V at 0.2 C. Next, the cells were disassembled, and the negative electrodes were removed. The removed negative electrodes were washed with diethyl carbonate, and the negative electrode surfaces were visually observed and evaluated according to the following criteria. The fewer cracks and peeling on the negative electrode surface, the better the secondary battery performance can be maintained over a long period of time even after repeated charge and discharge. A: No cracking or peeling was observed on the entire negative electrode surface, or the area where cracking and / or peeling was observed was less than 10% of the entire negative electrode surface. B: Cracking and / or peeling was observed in 10% or more and less than 15% of the entire negative electrode surface area. C: Cracking and / or peeling was observed in 15% or more and less than 25% of the entire negative electrode surface area. D: Cracking and / or peeling was observed in 25% or more and less than 30% of the entire negative electrode surface area. E: Cracking and / or peeling was observed in 30% or more of the entire negative electrode surface area.

[0083] <Calculation of Viscosity Ratio α> The binder compositions prepared in the Examples and Comparative Examples were used to calculate the viscosity (η ３ ) at pH 8.0 (η ８ Specifically, the solid content concentration of the binder composition was adjusted to 30%, the pH to 3.0, and the viscosity η was measured using a Brookfield viscometer under the conditions of a temperature of 25°C, a spindle rotation speed of 60 rpm, and a spindle rotation time of 60 seconds. ３ (unit: mPa s) was measured. Then, the viscosity η ８ The viscosity ratio α was then calculated according to the following formula: α = η ８ / η ３ The pH was adjusted by adding a 5% aqueous solution of sodium hydroxide dropwise using an electrode pH meter, and the solids concentration of the binder composition was adjusted by adding ion-exchanged water.

[0084] <Calculation of Viscosity Ratio β> The binder compositions prepared in the Examples and Comparative Examples were used to calculate the viscosity (η ４ ) at pH 9.0 (η ９ Specifically, the solid content concentration of the binder composition was set to 20%, and the viscosity η was measured using a B-type viscometer under the conditions of a temperature of 25° C., pH 4.0, a spindle rotation speed of 60 rpm, and a spindle rotation time of 60 seconds. ４ Then, the viscosity η was measured under the same conditions except that the pH was adjusted to 9.0. ９ The viscosity ratio β was then calculated according to the following formula: β = η ９ / η ４ The pH was adjusted by adding a 5% aqueous solution of sodium hydroxide dropwise using an electrode pH meter, and the solids concentration of the binder composition was adjusted by adding ion-exchanged water.

[0085] <Calculation of Swelling Degree and Insoluble Content in Tetrahydrofuran (THF)> Each of the binder compositions prepared in the Examples and Comparative Examples was dropped into a Petri dish so that the solid content was 1.5 g. Next, the binder composition was dried for 24 hours in an environment of 22 to 25°C, and further dried for 1 hour at 110°C to obtain a film of a particulate binder. Next, this film was cut into 2.5 mm square pieces, and approximately 0.3 g was precisely weighed. The mass of the film piece obtained by cutting was designated as W0. Next, the film piece was immersed in 80 mL of THF at 25°C for 24 hours. Next, the film piece was removed from THF, and the mass W1 of the film piece was measured. Next, this film piece was vacuum dried at 105°C for 3 hours, and the mass W2 of the film piece was measured. Then, the swelling degree (mass%) of the insoluble content in THF was calculated according to the following formula. Swelling degree (mass%) = (W1 / W2) x 100 The amount of insoluble matter in THF (mass%) was calculated according to the following formula: Insoluble matter (mass%) = (W2 / W0) x 100

[0086] Example 1 Preparation of a binder composition for a secondary battery negative electrode 2.18 parts of styrene as an aromatic vinyl monomer, 1.66 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 0.116 parts of methacrylic acid as an ethylenically unsaturated carboxylic acid group monomer, 0.23 parts of dodecyl diphenyl ether disulfonic acid sodium salt as an emulsifier, 15 parts of ion-exchanged water, and 0.017 parts of potassium persulfate as a polymerization initiator were added to a 5 MPa pressure vessel A equipped with a stirrer to obtain a mixture A. After thorough stirring, the mixture A was heated to 57°C to initiate polymerization and reacted for 5 hours. The temperature was then raised to 70°C, and the mixture was allowed to react for an additional 4 hours to obtain seed particles. Separately, into a 5 MPa pressure vessel B equipped with a stirrer, 20.704 parts of styrene as an aromatic vinyl monomer, 50.34 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 18 parts of acrylic acid as an ethylenically unsaturated carboxylic acid group monomer, 7 parts of acrylamide as an ethylenically unsaturated amide monomer unit, 0.5 parts of tert-dodecyl mercaptan as a molecular weight modifier, 0.20 parts of dodecyl diphenyl ether disulfonic acid sodium salt as an emulsifier, and 44 parts of ion-exchanged water were added to obtain a mixture B. After obtaining the seed particles, the temperature of the contents of the pressure vessel A was heated to 75°C, and mixture B was added to the pressure vessel A over 5 hours. At the same time, polymerization was initiated by starting the addition of 0.5 parts of potassium persulfate as a polymerization initiator to the pressure vessel A. The total monomer composition consisted of 22.884 parts of styrene, 52 parts of 1,3-butadiene, 18 parts of acrylic acid, 7 parts of acrylamide, and 0.116 parts of methacrylic acid. After the addition of the entire amount of Mixture B was completed, the mixture was further heated to 90°C and reacted for 4 hours. When the polymerization conversion rate reached 97%, the mixture was cooled to stop the reaction, and a mixture containing a polymer was obtained. Next, a 5% aqueous sodium hydroxide solution was added to this mixture, and the pH was adjusted to 8. Next, unreacted monomer was removed by heating and vacuum distillation. Next, the obtained residue was further cooled to obtain a binder composition for secondary battery negative electrodes containing the desired particulate polymer (particulate binder, volume average particle diameter (D50): 150 nm).The viscosity ratio α, viscosity ratio β, swelling degree in tetrahydrofuran (THF), and insoluble content were calculated using the obtained binder composition for a secondary battery negative electrode. The results are shown in Table 1.

[0087] <Preparation of Slurry Composition for Secondary Battery Negative Electrode> 90.2 parts of artificial graphite and 6.8 parts of SiOx as negative electrode active materials, and 2.0 parts (solid content equivalent) of a carboxymethyl cellulose sodium aqueous solution as thickener A were added to a planetary mixer equipped with a disperser. The mixture was further diluted with ion-exchanged water to a solid content of 61.5% and then mixed at room temperature for 40 minutes. Next, the mixture was gradually diluted with ion-exchanged water to solid contents of 56% and 51%, and 1.0 part (solid content equivalent) of the binder composition for secondary battery negative electrodes was added to obtain a mixed solution. The resulting mixed solution was defoamed under reduced pressure to obtain a slurry composition for secondary battery negative electrodes with good fluidity. The resulting slurry composition for secondary battery negative electrodes was evaluated for foaming. The results are shown in Table 1.

[0088] <Preparation of Secondary Battery Negative Electrode> The above-mentioned slurry composition for secondary battery negative electrode was applied to a copper foil (current collector) having a thickness of 16 μm using a comma coater so that the coating amount after drying was 10 mg / cm ２ The copper foil coated with the secondary battery negative electrode slurry composition was then transported at a speed of 0.5 m / min through an oven at 75°C for 2 minutes and then through an oven at 120°C for 2 minutes to dry the secondary battery negative electrode slurry composition on the copper foil, thereby obtaining a negative electrode blank with a negative electrode composite layer formed on the copper foil. The negative electrode blank was then rolled using a roll press to obtain a secondary battery negative electrode with a negative electrode composite layer thickness of 80 μm. The peel strength and flexibility of the obtained secondary battery negative electrode were evaluated. The results are shown in Table 1.

[0089] <Preparation of Secondary Battery Positive Electrode> 96 parts of lithium nickel manganese cobalt oxide as the positive electrode active material, 2 parts (solids content equivalent) of PVDF (polyvinylidene fluoride) as a binder for secondary battery positive electrodes, 2 parts of acetylene black as a conductive material, and 20 parts of N-methylpyrrolidone as a solvent were added to a planetary mixer and mixed to obtain a slurry composition for secondary battery positive electrodes. The obtained slurry composition for secondary battery positive electrodes was applied to a 16 μm-thick aluminum foil (current collector) using a comma coater so that the coating amount after drying was 24.5 mg / cm. ２ The aluminum foil coated with the slurry composition for a secondary battery positive electrode was then 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 to dry the slurry composition for a secondary battery positive electrode on the aluminum foil, thereby obtaining a positive electrode raw sheet having a positive electrode composite layer formed on the aluminum foil. The positive electrode raw sheet was then rolled using a roll press to obtain a positive electrode for a secondary battery having a positive electrode composite layer thickness of 70 μm.

[0090] <Preparation of secondary battery separator> A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm; manufactured by a dry method; porosity 55%) was cut into a 5 cm × 5 cm square to prepare a secondary battery separator. This secondary battery separator was used in the following secondary battery.

[0091] <Preparation of Secondary Battery> An aluminum packaging material was prepared as the battery packaging material. The positive electrode was cut into a 4 cm x 4 cm square and placed so that the surface on the aluminum foil (current collector) side was in contact with the aluminum packaging material. Next, the square separator was placed on the surface of the positive electrode composite layer of the positive electrode. Next, the negative electrode was cut into a 4.2 cm x 4.2 cm square and placed on the separator so that the surface on the negative electrode composite layer side faced the separator. Then, LiPF 5 with a concentration of 1.0 M was used as an electrolyte. ６A solution (containing a 3 / 7 mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) as the solvent and 2% by volume of vinylene carbonate and 2% by mass of fluoroethylene carbonate as additives) was filled into the battery. Furthermore, to seal the opening of the aluminum packaging, the exterior of the aluminum packaging was closed by heat sealing at a temperature of 150°C, thereby producing a laminate cell type secondary battery. The cycle characteristics and peel resistance of the mixture layer of the obtained secondary battery were evaluated. The results are shown in Table 1.

[0092] (Examples 2 to 7) In preparing the binder composition for a secondary battery negative electrode, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that the amount of molecular weight modifier used was changed to the amount shown in Table 1. The results are shown in Table 1.

[0093] (Examples 8 to 15) In preparing the binder composition for secondary battery negative electrodes, various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that the blending amounts of acrylic acid, 1,3-butadiene, styrene, and acrylamide in mixture B were changed so that the resulting particulate polymer had the composition shown in Table 1. The results are shown in Table 1.

[0094] (Example 16) In preparing a binder composition for a secondary battery negative electrode, the amounts of acrylic acid, 1,3-butadiene, styrene, and acrylamide in mixture B were changed so that the resulting particulate polymer had the composition shown in Table 1, and the amount of molecular weight modifier used was changed to the amount shown in Table 1. Except for this, various operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0095] (Example 17) In preparing a slurry composition for a secondary battery negative electrode, various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that thickener A (sodium carboxymethyl cellulose) was replaced with thickener B (lithium salt of acrylic acid / acrylamide / hydroxyethylacrylamide copolymer) obtained by the following polymerization method. The results are shown in Table 1.

[0096] <Polymerization Method of Thickener B (Lithium Salt of Acrylic Acid / Acrylamide / Hydroxyethylacrylamide Copolymer)> 800 parts of ion-exchanged water was placed in a 1 L glass flask. Next, 40 parts of acrylamide, 35 parts of acrylic acid, and 25 parts of hydroxyethylacrylamide were mixed, and the mixture was poured into the flask. Next, the atmosphere in the flask was purged with nitrogen gas at 1000 mL / min. The contents of the flask were heated to 40°C, and then 25.0 parts of a 1.0% aqueous solution of ascorbic acid as a polymerization accelerator was added via syringe. 15 minutes later, 18.0 parts of a 2.0% aqueous solution of potassium persulfate as a polymerization initiator was added via syringe to the flask to initiate the polymerization reaction. 4 hours after the addition of the polymerization initiator, 4.4 parts of a 2.0% aqueous solution of potassium persulfate as a polymerization initiator was added to the flask, and then 11.1 parts of a 1.0% aqueous solution of ascorbic acid as a polymerization accelerator was added to the flask. The temperature was then raised to 60°C to allow the polymerization reaction to proceed. Two hours after the addition of the polymerization initiator, the flask was opened to the air to terminate the polymerization reaction. To the resulting polymer, an 8% aqueous solution of lithium hydroxide was added, and the mixture was stirred at 25° C. for 6 hours while adjusting the pH to 8.0 to obtain a lithium salt of an acrylic acid / acrylamide / hydroxyethylacrylamide copolymer as thickener B.

[0097] (Comparative Examples 1 and 2) In preparing a binder composition for a secondary battery negative electrode, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that the blending amounts of acrylic acid, 1,3-butadiene, styrene, and acrylamide in mixture B were changed so that the resulting particulate polymer had the composition shown in Table 1. The results are shown in Table 1.

[0098] (Comparative Example 3) In preparing a binder composition for a secondary battery negative electrode, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that all of the styrene in mixture A was replaced with 1,3-butadiene, and the amounts of acrylic acid, 1,3-butadiene, styrene, and acrylamide in mixture B were changed so that the resulting particulate polymer had the composition shown in Table 1. The results are shown in Table 1.

[0099] (Comparative Example 4) In preparing a binder composition for a secondary battery negative electrode, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that all of the 1,3-butadiene in mixture A was replaced with styrene, and the amounts of acrylic acid, 1,3-butadiene, styrene, and acrylamide in mixture B were changed so that the resulting particulate polymer had the composition shown in Table 1. The results are shown in Table 1.

[0100] (Comparative Examples 5 and 6) In the preparation of binder compositions for secondary battery negative electrodes, the amount of molecular weight modifier used was changed to the amount shown in Table 1, and the polymerization conditions for the particulate polymer were changed to the conditions shown in Table 1. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0101] Comparative Example 7 In preparing a binder composition for a secondary battery negative electrode, a 5 MPa pressure vessel equipped with a stirrer was charged with 300 parts of water, 0.5 parts of sodium dodecylbenzenesulfonate as an emulsifier, 0.5 parts of potassium persulfate as a polymerization initiator, 0.3 parts of α-methylstyrene dimer and 1.8 parts of dodecyl mercaptan as molecular weight modifiers, and 30 parts of 1,3-butadiene, 20 parts of methacrylic acid, 10 parts of 2-hydroxyethyl acrylate, 20 parts of glycerin monomethacrylate, 10 parts of acrylamide, and 10 parts of cyclohexyl acrylate as monomers, in that order, and the polymerization reaction was carried out at 50°C for 10 hours to obtain a mixture containing a polymer. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0102]

[0103] The abbreviations of the monomers in Table 1 refer to the following compounds: (1) AA: acrylic acid (2) MAA: methacrylic acid (3) BD: 1,3-butadiene (4) ST: styrene (5) AAm: acrylamide (6) HEA: 2-hydroxyethyl acrylate (7) GLM: glycerin monomethacrylate (8) CHNA: cyclohexyl acrylate

[0104] Table 1 shows that Examples 1 to 17 were able to provide a nonaqueous secondary battery negative electrode binder composition capable of preparing a slurry composition with suppressed foaming and forming a negative electrode composite layer with excellent peeling resistance. Table 1 shows that Comparative Example 1, in which the viscosity ratio α is less than the lower limit of the present invention, was unable to form a negative electrode composite layer with excellent peeling resistance, while Comparative Examples 2 and 7, in which the viscosity ratio α exceeds the upper limit of the present invention, were unable to prepare a slurry composition with suppressed foaming. Table 1 also shows that Comparative Examples 5 and 7, in which the swelling degree exceeds the upper limit of the present invention and the insoluble content is less than the lower limit of the present invention, were unable to form a negative electrode composite layer with excellent peeling resistance. Table 1 also shows that Comparative Example 6, in which the swelling degree is less than the lower limit of the present invention and the insoluble content exceeds the upper limit of the present invention, exhibits poor adhesion between the negative electrode composite layer and the current collector. Table 1 also shows that Comparative Examples 3 and 7, in which the polymer does not contain an aromatic vinyl-containing compound, exhibit poor negative electrode cycle characteristics, and Comparative Example 3 exhibits poor adhesion between the negative electrode composite layer and the current collector. It can be seen from Table 1 that in Comparative Example 4, in which the polymer did not contain an aliphatic conjugated diene, the flexibility of the negative electrode was poor.

[0105] According to the present invention, it is possible to provide a binder composition for a non-aqueous secondary battery negative electrode, which is capable of preparing a slurry composition with reduced foaming and forming a negative electrode mixture layer with excellent peeling resistance. Furthermore, according to the present invention, it is possible to provide a slurry composition for a non-aqueous secondary battery negative electrode, which includes the binder composition for a non-aqueous secondary battery negative electrode. Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery negative electrode, which includes a negative electrode mixture layer formed from the slurry composition for a non-aqueous secondary battery negative electrode. Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery, which includes the non-aqueous secondary battery negative electrode.

Claims

1. A binder composition for a non-aqueous secondary battery negative electrode, comprising a particulate binder and water, The particulate binder includes a polymer containing an ethylenically unsaturated carboxylic acid monomer unit, an aromatic vinyl monomer unit, and an aliphatic conjugated diene monomer unit, When a film of the particulate binder is formed, the film has a swelling degree in tetrahydrofuran of insoluble matter of 300% by mass or more and 1500% by mass or less, has an insoluble matter content in tetrahydrofuran of 85% by mass or more and 99% by mass or less, A binder composition for a non-aqueous secondary battery negative electrode, wherein when the solid content concentration of the binder composition is 30% by mass, the ratio of the viscosity at pH 8.0 to the viscosity at pH 3.0 is 1.5 or more and 200 or less.

2. The binder composition for a non-aqueous secondary battery negative electrode according to claim 1, wherein the proportion of the ethylenically unsaturated carboxylic acid monomer unit in the polymer is 2% by mass or more and 35% by mass or less.

3. The binder composition for a non-aqueous secondary battery negative electrode according to claim 1, wherein the polymer further contains an ethylenically unsaturated amide monomer unit.

4. The binder composition for a non-aqueous secondary battery negative electrode according to claim 3, wherein the proportion of the ethylenically unsaturated amide monomer unit in the polymer is 1% by mass or more and 18% by mass or less.

5. A slurry composition for a non-aqueous secondary battery negative electrode, comprising a negative electrode active material and the binder composition for a non-aqueous secondary battery negative electrode according to any one of claims 1 to 4.

6. A negative electrode for a non-aqueous secondary battery, comprising a current collector and a negative electrode composite material layer located on the current collector, The negative electrode for a non-aqueous secondary battery, wherein the negative electrode composite material layer is a layer formed by the slurry composition for a non-aqueous secondary battery negative electrode according to claim 5.

7. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolytic solution, wherein the negative electrode is the negative electrode for a non-aqueous secondary battery according to claim 6, the non-aqueous secondary battery.