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

Abstract

The purpose of the present invention is to provide a binder composition which is for a non-aqueous secondary battery electrode and which makes it possible to form an electrode that is for a non-aqueous secondary battery, that effectively suppresses a failure of the non-aqueous secondary battery, and that exhibits excellent flexibility. The present invention provides a binder composition which is for a non-aqueous secondary battery electrode and which comprises a particulate polymer and water, wherein: the particulate polymer includes a polymer which contains an aromatic vinyl monomer unit and a conjugated diene monomer unit; and a binder film formed using the binder composition for a non-aqueous secondary battery electrode has a maximum indentation load of not less than 100 nN and an elastic recovery amount of 120-200 nm when a surface of the binder film is pressed to a depth of 300 nm using an indenter in a nanoindentation test.

Description

Binder composition for non-aqueous secondary battery electrodes, slurry composition for non-aqueous secondary battery electrodes, electrodes for non-aqueous secondary batteries, and non-aqueous secondary batteries

[0001] The present invention relates to a binder composition for a non-aqueous secondary battery electrode, a slurry composition for a non-aqueous secondary battery electrode, an electrode for a non-aqueous secondary battery, 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] Therefore, in recent years, attempts have been made to improve the binder composition used to form the electrode mixture layer in order to achieve further improvement in the performance of secondary batteries. Specifically, for example, Patent Document 1 proposes a binder composition for a non-aqueous secondary battery negative electrode capable of forming a negative electrode mixture layer with excellent peel resistance, the binder composition comprising a polymer containing ethylenically unsaturated carboxylic acid monomer units, aromatic vinyl monomer units, and aliphatic conjugated diene monomer units, the degree of swelling in tetrahydrofuran and the amount of tetrahydrofuran insoluble matter falling within predetermined numerical ranges, and the ratio of the viscosity at pH 8.0 to the viscosity at pH 3.0 when the solids concentration is 30 mass% falling within predetermined numerical ranges.

[0005] International Publication No. 2023 / 008100

[0006] However, the conventional binder compositions described above have room for improvement in terms of suppressing defects in secondary batteries, such as the deposition of metals such as lithium on electrodes.

[0007] Furthermore, the conventional binder compositions described above also have room for improvement in terms of improving the flexibility of the electrodes.

[0008] Therefore, an object of the present invention is to provide a binder composition for non-aqueous secondary battery electrodes that can effectively suppress defects in non-aqueous secondary batteries and form electrodes for non-aqueous secondary batteries that have excellent flexibility. Another object of the present invention is to provide a slurry composition for non-aqueous secondary battery electrodes that can effectively suppress defects in non-aqueous secondary batteries and form electrodes for non-aqueous secondary batteries that have excellent flexibility. Another object of the present invention is to provide an electrode for non-aqueous secondary batteries that effectively suppresses defects in non-aqueous secondary batteries and has excellent flexibility. Another object of the present invention is to provide a non-aqueous secondary battery that effectively suppresses defects and has excellent flexibility.

[0009] 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 electrode, the binder composition comprising water and a particulate polymer including a polymer containing aromatic vinyl monomer units and conjugated diene monomer units, wherein a binder film formed using the binder composition for a non-aqueous secondary battery electrode has a predetermined maximum indentation load and a predetermined elastic recovery amount when subjected to a nanoindentation test, and have completed the present invention.

[0010] That is, the present invention aims to solve the above-mentioned problems. [1] The present invention provides a binder composition for a non-aqueous secondary battery electrode (hereinafter, sometimes simply referred to as the "binder composition") comprising a particulate polymer and water, wherein the particulate polymer comprises a polymer containing aromatic vinyl monomer units and conjugated diene monomer units. A binder film formed using the binder composition for a non-aqueous secondary battery electrode exhibits a maximum indentation load of 100 nN or more and an elastic recovery of 120 nm to 200 nm when the surface of the binder film is indented to a depth of 300 nm with an indenter in a nanoindentation test. The binder composition described above effectively suppresses defects in non-aqueous secondary batteries and enables the formation of non-aqueous secondary battery electrodes with excellent flexibility. In the present invention, the term "monomer unit" of a polymer refers to a repeating unit derived from the monomer contained in a polymer obtained using the monomer. In the present invention, the "maximum indentation load" and "elastic recovery amount" of the binder film can be measured according to the method described in the examples.

[0011] [2] In the binder composition for a non-aqueous secondary battery electrode according to [1] above, the ratio (Da / Db) of the volume average particle diameter Da of the particulate polymer measured by a laser diffraction scattering method at a solids concentration of 0.1% by mass to the average particle diameter Db of the particulate polymer measured by a dynamic light scattering method at a solids concentration of 0.005% by mass is preferably 1.4 or more and 2.0 or less. When the ratio (Da / Db) of the volume average particle diameter Da to the average particle diameter Db is equal to or greater than the lower limit, the resulting electrode can exhibit good peel strength. On the other hand, when the ratio (Da / Db) of the volume average particle diameter Da to the average particle diameter Db is equal to or less than the upper limit, the cycle characteristics of the resulting non-aqueous secondary battery can be improved. In the present invention, the solids concentration of the binder composition when measuring the "volume average particle diameter Da" and "average particle diameter Db" can be adjusted by adding or removing water. In the present invention, the "volume average particle diameter Da" and the "average particle diameter Db" of the particulate polymer can be measured according to the method described in the Examples.

[0012] [3] In the binder composition for a non-aqueous secondary battery electrode according to [1] or [2] above, the particulate polymer preferably contains a polymer A containing aromatic vinyl monomer units and conjugated diene monomer units, and a polymer B containing aromatic vinyl monomer units and conjugated diene monomer units and different from polymer A. If the particulate polymer contains two or more types of polymers, defects in the resulting non-aqueous secondary battery can be more effectively suppressed and the flexibility of the resulting electrode can be improved. In the present invention, polymer A and polymer B being "different" means that they are different in at least one of their composition and properties.

[0013] [4] In the binder composition for a non-aqueous secondary battery electrode according to any one of [1] to [3] above, the particulate polymer preferably has an electrolyte swelling degree of 300% by mass or less. When the particulate polymer has an electrolyte swelling degree of 300% by mass or less, the output characteristics and cycle characteristics of the resulting non-aqueous secondary battery can be improved. In the present invention, the "electrolyte swelling degree" of the particulate polymer can be measured according to the method described in the Examples.

[0014] [5] In the binder composition for a non-aqueous secondary battery electrode according to any one of [1] to [4] above, the polymer contained in the particulate polymer preferably further contains an amide group-containing monomer unit. If the polymer contained in the particulate polymer further contains an amide group-containing monomer unit, the cycle characteristics of the resulting non-aqueous secondary battery can be improved.

[0015] Another object of the present invention is to solve the above-mentioned problems, and [6] the present invention is a slurry composition for a non-aqueous secondary battery electrode (hereinafter sometimes simply abbreviated as "slurry composition") comprising an electrode active material and the binder composition for a non-aqueous secondary battery electrode of any one of [1] to [5] above. The above-mentioned slurry composition can effectively suppress defects in non-aqueous secondary batteries and form a non-aqueous secondary battery electrode with excellent flexibility.

[0016] [7] In the slurry composition for a non-aqueous secondary battery electrode according to [6] above, the electrode active material preferably contains a silicon-based negative electrode active material. Use of an electrode active material containing a silicon-based negative electrode active material can improve the output characteristics and capacity of the resulting non-aqueous secondary battery.

[0017] Another object of the present invention is to solve the above-mentioned problems, and [8] the present invention provides a non-aqueous secondary battery electrode (hereinafter sometimes simply referred to as "electrode") comprising a current collector and an electrode mixture layer located on the current collector, wherein the electrode mixture layer is a layer formed from the slurry composition for a non-aqueous secondary battery electrode according to [6] or [7] above. Such an electrode effectively suppresses defects in non-aqueous secondary batteries and has excellent flexibility.

[0018] Another object of the present invention is to solve the above-mentioned problems and provides [9] a non-aqueous secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte solution, wherein at least one of the positive electrode and the negative electrode is the electrode for a non-aqueous secondary battery according to claim 8. Such a secondary battery effectively suppresses defects and has excellent flexibility.

[0019] According to the present invention, a binder composition for non-aqueous secondary battery electrodes can be provided, which effectively suppresses defects in non-aqueous secondary batteries and allows the formation of electrodes for non-aqueous secondary batteries that have excellent flexibility. Furthermore, according to the present invention, a slurry composition for non-aqueous secondary battery electrodes can be provided, which effectively suppresses defects in non-aqueous secondary batteries and allows the formation of electrodes for non-aqueous secondary batteries that have excellent flexibility. Furthermore, according to the present invention, a non-aqueous secondary battery electrode can be provided, which effectively suppresses defects in non-aqueous secondary batteries and has excellent flexibility. Furthermore, according to the present invention, a non-aqueous secondary battery in which defects are effectively suppressed and has excellent flexibility can be provided.

[0020] Hereinafter, embodiments of the present invention will be described in detail. The binder composition for a non-aqueous secondary battery electrode of the present invention can be used when preparing a slurry composition for a non-aqueous secondary battery electrode. The slurry composition for a non-aqueous secondary battery electrode prepared using the binder composition for a non-aqueous secondary battery electrode of the present invention can be used when forming an electrode (a non-aqueous secondary battery electrode) for a non-aqueous secondary battery such as a lithium ion secondary battery. Furthermore, the non-aqueous secondary battery of the present invention is characterized by using a non-aqueous secondary battery electrode formed using the slurry composition for a non-aqueous secondary battery electrode of the present invention. The binder composition for a non-aqueous secondary battery electrode and the slurry composition for a non-aqueous secondary battery electrode of the present invention can be particularly suitably used when forming a negative electrode for a non-aqueous secondary battery.

[0021] (Binder Composition for Non-Aqueous Secondary Battery Electrodes) The binder composition for non-aqueous secondary battery electrodes of the present invention comprises a particulate polymer and water as a dispersion medium, and optionally further comprises other components that can be incorporated into secondary battery electrodes. Furthermore, in the binder composition of the present invention, the particulate polymer comprises a polymer containing aromatic vinyl monomer units and conjugated diene monomer units. Furthermore, in the binder composition of the present invention, a binder film formed using the binder composition exhibits a maximum indentation load (hereinafter sometimes simply referred to as "maximum indentation load") of 100 nN or more and an elastic recovery (hereinafter sometimes simply referred to as "elastic recovery maximum indentation load") of 120 nm or more and 200 nm or less when a nanoindentation test is performed in which an indenter is pressed into the surface of the binder film to a depth of 300 nm.

[0022] The binder composition described above effectively suppresses defects in non-aqueous secondary batteries and enables the formation of electrodes for non-aqueous secondary batteries with excellent flexibility. The reasons for this are presumed to be as follows. First, when manufacturing an electrode, the electrode (comprising a current collector and an electrode mixture layer) can be pressed. By setting the maximum pressing load at or above the lower limit, the electrode active materials in the electrode mixture layer after pressing are maintained at a constant distance, thereby effectively suppressing an increase in the resistance of the electrode. This is presumed to effectively suppress defects in non-aqueous secondary batteries. Furthermore, when the binder composition of the present invention is used to form a negative electrode mixture layer of a lithium-ion secondary battery, it is presumed to effectively suppress an increase in the resistance of the resulting negative electrode and effectively suppress the precipitation of metallic lithium (lithium dendrites, etc.) in the negative electrode. Furthermore, by setting the elastic recovery amount to or below the upper limit, the binder can effectively stretch when a force is applied, such as when the electrode is bent, and therefore it is presumed to form an electrode for non-aqueous secondary batteries with excellent flexibility.

[0023] Furthermore, the binder composition of the present invention can improve the injectability of the obtained electrode mixture layer, presumably because, by setting the elastic recovery to be equal to or greater than the lower limit, the binder in the electrode mixture layer can appropriately increase the distance between the electrode active materials in the pressed electrode.

[0024] The binder composition of the present invention generally does not contain an electrode active material, which will be described later.

[0025] <Particulate Polymer> The particulate polymer is a component that can function as a binder to prevent components such as an electrode active material from detaching from an electrode mixture layer formed using a slurry composition containing a binder composition. The particulate polymer must contain a polymer containing aromatic vinyl monomer units and conjugated diene monomer units, and may optionally further contain other polymers (e.g., a polymer that does not contain aromatic vinyl monomer units and conjugated diene monomer units, and a polymer that contains only one of aromatic vinyl monomer units and conjugated diene monomer units). The particulate polymer may contain only one type of polymer containing aromatic vinyl monomer units and conjugated diene monomer units, or may contain two or more types. The polymer contained in the particulate polymer is usually a water-insoluble polymer, and when 0.5 g of the polymer is dissolved in 100 g of water at 25 ° C, the insoluble content may be 90 mass % or more.

[0026] [Polymer] The polymer contains aromatic vinyl monomer units and conjugated diene monomer units, and may optionally contain other monomer units.

[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, and styrene is more preferred. These can be used alone or in combination of two or more.

[0028] The proportion of aromatic vinyl monomer units contained in the polymer is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and preferably 60% by mass or less, when the amount of all monomer units in the polymer is 100% by mass. It is more preferably 55% by mass or less, and even more preferably 50% by mass or less. If the proportion of aromatic vinyl monomer units contained in the polymer is equal to or greater than the lower limit, the cycle characteristics of the resulting secondary battery can be improved. On the other hand, if the proportion of aromatic vinyl monomer units contained in the polymer is equal to or less than the upper limit, the flexibility of the resulting electrode can be improved. In the present invention, the content ratios of various monomer units in the polymer are as follows: １ It can be measured using nuclear magnetic resonance (NMR) such as H-NMR.

[0029] - Conjugated diene monomer unit - Examples of conjugated diene monomers that can form 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.

[0030] The proportion of the conjugated diene monomer units contained in the polymer is preferably 30% by mass or more, more preferably 35% by mass or more, and even more preferably 40% by mass or more, and preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% 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 conjugated diene monomer units contained in the polymer is equal to or greater than the above-mentioned lower limit, the flexibility of the resulting electrode can be improved. Furthermore, the resulting electrode can exhibit good peel strength. On the other hand, when the proportion of the conjugated diene monomer units contained in the polymer is equal to or less than the above-mentioned upper limit, swelling of the electrode can be effectively suppressed, and the cycle characteristics of the resulting secondary battery can be improved.

[0031] Other Monomer Units The other monomer units that can be contained in the polymer are not particularly limited, and examples thereof include an acidic group-containing monomer unit and an amide group-containing monomer unit.

[0032] Here, it is preferable that the polymer further contains an acidic group-containing monomer unit. If the polymer further contains an acidic group-containing monomer unit, swelling of the electrode can be effectively suppressed and the cycle characteristics of the resulting secondary battery can be improved. When the particulate polymer contains polymer A and polymer B described below, the acidic group-containing monomer unit may be contained in polymer A, polymer B, or both polymer A and polymer B, but it is preferable that both polymer A and polymer B contain the acidic group-containing monomer unit.

[0033] Examples of the acidic group-containing monomer capable of forming the acidic group-containing monomer unit include a carboxylic acid group-containing monomer, a sulfonic acid group-containing monomer, and a phosphoric acid group-containing monomer.

[0034] Examples of carboxylic acid group-containing monomers include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and derivatives thereof. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, and α-chloro-β-E-methoxyacrylic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters such as nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleates. Examples of dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride. Furthermore, as the carboxylic acid group-containing monomer, an acid anhydride that generates a carboxylic acid group upon hydrolysis can also be used.

[0035] Examples of sulfonic acid group-containing monomers include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, etc. In the present invention, "(meth)allyl" means allyl and / or methallyl.

[0036] Furthermore, examples of the phosphate group-containing monomer include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, ethyl-(meth)acryloyloxyethyl phosphate, etc. In the present invention, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0037] These acidic group-containing monomers can be used alone or in combination of two or more. Among these acidic group-containing monomers, carboxylic acid group-containing monomers are preferred, with acrylic acid, methacrylic acid, itaconic acid, maleic acid, and fumaric acid being preferred, and acrylic acid, methacrylic acid, and itaconic acid being more preferred.

[0038] The proportion of the acidic group-containing monomer units contained in the polymer is preferably 5% by mass or more, more preferably 8% by mass or more, and is preferably 15% by mass or less, more preferably 14% by mass or less, and even more preferably 13% by mass or less, when the amount of all monomer units in the polymer is 100% by mass.

[0039] Furthermore, it is preferable that the polymer further contains an amide group-containing monomer unit. If the polymer further contains an amide group-containing monomer unit, the cycle characteristics of the obtained nonaqueous secondary battery can be improved. Note that, when the particulate polymer contains polymer A and polymer B described below, the amide group-containing monomer unit may be contained in polymer A, polymer B, or both polymer A and polymer B, but it is preferable that polymer A contains the amide group-containing monomer unit.

[0040] Examples of amide group-containing monomers capable of forming amide group-containing monomer units include (meth)acrylamide, N-methylol(meth)acrylamide, dimethyl(meth)acrylamide, diethyl(meth)acrylamide, N-methoxymethyl(meth)acrylamide, and dimethylaminopropyl(meth)acrylamide. Among these, (meth)acrylamide is preferred, and acrylamide is more preferred. These may be used alone or in combination of two or more. In the present invention, "(meth)acryl" means acrylic and / or methacrylic.

[0041] The proportion of the amide group-containing monomer units contained in the polymer is preferably 1% by mass or more, more preferably 2% by mass or more, and preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass or less, when the amount of all monomer units in the polymer is taken as 100% by mass. If the proportion of the amide group-containing monomer units contained in the polymer is within the above range, the cycle characteristics of the resulting nonaqueous secondary battery can be effectively improved.

[0042] Here, it is preferable that the polymer further contains an acidic group-containing monomer unit and an amide group-containing monomer unit, which can further improve the cycle characteristics of the resulting non-aqueous secondary battery.

[0043] The total proportion of the acidic group-containing monomer units and the amide group-containing monomer units contained in the polymer is preferably 6% by mass or more, more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 24% by mass or less, and even more preferably 20% by mass or less, when the amount of all monomer units in the polymer is taken as 100% by mass. If the total proportion of the acidic group-containing monomer units and the amide group-containing monomer units contained in the polymer is within the above range, the cycle characteristics of the resulting nonaqueous secondary battery can be effectively improved.

[0044] The glass transition point of the polymer is preferably −100° C. or higher, more preferably −90° C. or higher, and is preferably 30° C. or lower, and more preferably 10° C. or lower. If the glass transition point of the polymer is within the above range, the resulting electrode can exhibit good peel strength. In the present invention, the glass transition point of the polymer can be measured according to the method described in the Examples of this specification.

[0045] [Properties of Particulate Polymer] The particulate polymer contained in the binder composition has a volume average particle diameter Da of preferably 50 nm or more, more preferably 100 nm or more, and preferably 200 nm or less, and more preferably 150 nm or less, when measured by a laser diffraction scattering method with the solid content concentration of the binder composition set to 0.1 mass %.

[0046] Furthermore, the particulate polymer contained in the binder composition preferably has an average particle diameter Db of 150 nm or more, more preferably 200 nm or more, and is preferably 300 nm or less, and more preferably 250 nm or less, when measured by dynamic light scattering at a solids concentration of the binder composition of 0.005 mass %.

[0047] The ratio (Da / Db) of the volume average particle diameter Da measured by laser diffraction scattering to the average particle diameter Db measured by dynamic light scattering is preferably 1.4 or more, more preferably 1.5 or more, even more preferably 1.6 or more, and preferably 2.0 or less, more preferably 1.9 or less, and even more preferably 1.8 or less. If Da / Db is equal to or greater than the lower limit, the particulate polymer can adequately cover the surface of the electrode active material, thereby enabling the resulting electrode to exhibit good peel strength. On the other hand, if Da / Db is equal to or less than the upper limit, good binding strength is exerted in the electrode mixture layer, effectively suppressing swelling of the electrode and improving the cycle characteristics of the resulting secondary battery.

[0048] Furthermore, the particulate polymer preferably has an electrolyte swelling degree of 110% by mass or more, more preferably 120% by mass or more, and preferably 300% by mass or less, more preferably 150% by mass or less, and even more preferably 140% by mass or less. If the electrolyte swelling degree of the particulate polymer is 300% by mass or less, the output characteristics and cycle characteristics of the resulting secondary battery can be improved. Furthermore, if the electrolyte swelling degree of the particulate polymer is within the above range, the cell characteristics of the secondary battery can be effectively improved.

[0049] The volume average particle diameter Da, the average particle diameter Db, and the swelling degree in an electrolyte solution of the particulate polymer can be adjusted, for example, by changing the preparation conditions of the particulate polymer, the structure of the particulate polymer, and the composition of the polymer constituting the particulate polymer.

[0050] [One embodiment of particulate polymer] The particulate polymer contained in the binder composition is not particularly limited, but preferably contains a polymer A containing aromatic vinyl monomer units and conjugated diene monomer units, and a polymer B containing aromatic vinyl monomer units and conjugated diene monomer units and different from polymer A. Specifically, the particulate polymer preferably contains particles containing polymer A and particles containing polymer B. Note that the particles containing polymer A and the particles containing polymer B usually exist as separate particles in the binder composition without being composited.

[0051] -Particles Containing Polymer A- Polymer A contains aromatic vinyl monomer units and conjugated diene monomer units, and may optionally contain other monomer units.

[0052] Here, the aromatic vinyl monomer units, conjugated diene monomer units, and other monomer units of polymer A may be the same as those described above with respect to the polymer contained in the particulate polymer, and therefore, description thereof will be omitted here.

[0053] Among these, polymer A preferably contains an aromatic vinyl monomer unit, a conjugated diene monomer unit, a carboxylic acid group-containing monomer unit, and an amide group-containing monomer unit, and more preferably contains a styrene unit, a butadiene unit, an acrylic acid unit, a methacrylic acid unit, and an acrylamide unit.

[0054] When the amount of all monomer units in polymer A is taken as 100% by mass, the proportion of each monomer unit contained in polymer A is preferably as follows. That is, the proportion of aromatic vinyl monomer units in polymer A is preferably 40% by mass or more, more preferably 45% by mass or more, and preferably 55% by mass or less, and more preferably 50% by mass or less. The proportion of conjugated diene monomer units in polymer A is preferably 25% by mass or more, more preferably 30% by mass or more, and preferably 40% by mass or less, and more preferably 35% by mass or less. Furthermore, the proportion of carboxylic acid group-containing monomer units in polymer A is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 20% by mass or less, and more preferably 15% by mass or less. The proportion of amide group-containing monomer units in polymer A is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 10% by mass or less, and more preferably 7% by mass or less. The total proportion of the carboxylic acid group-containing monomer units and the amide group-containing monomer units in polymer A is preferably 6% by mass or more, more preferably 13% by mass or more, and is preferably 30% by mass or less, more preferably 22% by mass or less.

[0055] Furthermore, polymer A preferably has a higher glass transition point than polymer B, and the glass transition point of polymer A is preferably -10°C or higher, more preferably 0°C or higher, and preferably 30°C or lower, more preferably 10°C or lower. When the glass transition point of polymer A is within the above range, the resulting electrode can exhibit good peel strength. In the present invention, the glass transition point of polymer A can be measured using the method described in the examples of this specification.

[0056] Furthermore, the particles containing polymer A preferably have a volume average particle diameter Da of 100 nm or more, more preferably 130 nm or more, and preferably 200 nm or less, more preferably 150 nm or less, when measured by a laser diffraction scattering method in an aqueous dispersion having a solid content of 0.1% by mass. In the present invention, the volume average particle diameter Da of the particles containing polymer A can be measured using the method described in the examples of this specification.

[0057] Furthermore, the particles containing polymer A preferably have an average particle diameter Db of 200 nm or more, more preferably 220 nm or more, and preferably 300 nm or less, more preferably 250 nm or less, when measured by dynamic light scattering in an aqueous dispersion having a solid content of 0.005% by mass. In the present invention, the average particle diameter Db of the particles containing polymer A can be measured using the method described in the examples of this specification.

[0058] Furthermore, the particles containing polymer A preferably have an electrolyte swelling degree of 110% by mass or more, more preferably 130% by mass or more, and preferably 150% by mass or less, and more preferably 140% by mass or less. If the electrolyte swelling degree of the particles containing polymer A is within the above range, the cell characteristics of the secondary battery can be improved. In the present invention, the electrolyte swelling degree of the particles containing polymer A can be measured using the method described in the examples of this specification.

[0059] The particles containing polymer A preferably have a maximum indentation load of 100 nN or more, more preferably 200 nN or more, even more preferably 300 nN or more, preferably 1000 nN or less, and more preferably 800 nN or less. If the maximum indentation load of the particles containing polymer A is above the lower limit, defects in secondary batteries can be more effectively suppressed. On the other hand, if the maximum indentation load of the particles containing polymer A is below the upper limit, the electrode active material constituting the electrode mixture layer can be prevented from falling off from the electrode mixture layer when pressing or the like during electrode production (hereinafter, sometimes referred to as "powder falling"), thereby improving the electrode's resistance to powder falling. In addition, in the present invention, the maximum indentation load of the particles containing polymer A can be measured using the method described in the examples of this specification.

[0060] Furthermore, the particles containing polymer A preferably have an elastic recovery of 120 nm or more, more preferably 140 nm or more, even more preferably 200 nm or more, and preferably 250 nm or less, more preferably 230 nm or less, and even more preferably 225 nm or less. If the elastic recovery of the particles containing polymer A is equal to or greater than the above lower limit, the injectability of the electrode mixture layer can be improved. On the other hand, if the elastic recovery of the particles containing polymer A is equal to or less than the above upper limit, the flexibility of the resulting electrode can be improved. In the present invention, the elastic recovery of the particles containing polymer A can be measured using the method described in the examples of this specification.

[0061] The volume average particle diameter Da and average particle diameter Db of the particles containing polymer A can be adjusted, for example, by changing the preparation conditions of the particles containing polymer A. The glass transition point, electrolyte swelling degree, maximum indentation load, and elastic recovery amount of the particles containing polymer A can be adjusted, for example, by changing the preparation conditions of the particles containing polymer A (such as the amount and timing of addition of a molecular weight modifier, a polymerization initiator, etc.), the structure of the particles containing polymer A, and the composition of polymer A.

[0062] —Particles Containing Polymer B— Polymer B contains aromatic vinyl monomer units and conjugated diene monomer units, and may optionally contain other monomer units.

[0063] Here, the aromatic vinyl monomer units, conjugated diene monomer units, and other monomer units of polymer B may be the same as those described above with respect to the polymer contained in the particulate polymer, and therefore, description thereof will be omitted here.

[0064] Among these, polymer B preferably contains aromatic vinyl monomer units, conjugated diene monomer units and carboxylic acid group-containing monomer units, and more preferably contains styrene units, butadiene units and methacrylic acid units.

[0065] When the amount of all monomer units in polymer B is taken as 100% by mass, the proportion of each monomer unit contained in polymer B is preferably as follows. That is, the proportion of aromatic vinyl monomer units in polymer B is preferably 10% by mass or more, more preferably 20% by mass or more, and preferably 40% by mass or less, and more preferably 30% by mass or less. Furthermore, the proportion of conjugated diene monomer units in polymer B is preferably 50% by mass or more, more preferably 70% by mass or more, and preferably 90% by mass or less, and more preferably 75% by mass or less. Furthermore, the proportion of carboxylic acid group-containing monomer units in polymer B is preferably 1% by mass or more, more preferably 2% by mass or more, and preferably 5% by mass or less, and more preferably 4% by mass or less.

[0066] Furthermore, the glass transition point of polymer B is preferably −70° C. or higher, more preferably −60° C. or higher, and preferably −30° C. or lower, more preferably −50° C. or lower. When the glass transition point of polymer B is within the above range, the resulting electrode can exhibit good peel strength. In the present invention, the glass transition point of polymer B can be measured using the method described in the examples of this specification.

[0067] Furthermore, the particles containing polymer B preferably have a volume average particle diameter Da of 90 nm or more, more preferably 100 nm or more, and preferably 130 nm or less, and more preferably 120 nm or less, when measured by a laser diffraction scattering method in an aqueous dispersion having a solid content of 0.1% by mass. In the present invention, the volume average particle diameter Da of the particles containing polymer B can be measured using the method described in the examples of this specification.

[0068] The particles containing polymer B preferably have an average particle diameter Db of 180 nm or more, more preferably 200 nm or more, and preferably 230 nm or less, and more preferably 220 nm or less, when measured by dynamic light scattering in an aqueous dispersion having a solid content of 0.005% by mass. In the present invention, the average particle diameter Db of the particles containing polymer B can be measured using the method described in the examples of this specification.

[0069] Furthermore, the particles containing polymer B preferably have an electrolyte swelling degree of 110% by mass or more, more preferably 120% by mass or more, and preferably 150% by mass or less, and more preferably 140% by mass or less. If the electrolyte swelling degree of the particles containing polymer B is within the above range, the cell characteristics of the secondary battery can be improved. In the present invention, the electrolyte swelling degree of the particles containing polymer B can be measured using the method described in the examples of this specification.

[0070] The particles containing polymer B preferably have a maximum indentation load of 5 nN or more, more preferably 10 nN or more, even more preferably 20 nN or more, and preferably 50 nN or less, and more preferably 40 nN or less. If the maximum indentation load of the particles containing polymer B is equal to or greater than the above lower limit, defects in secondary batteries can be more effectively suppressed. On the other hand, if the maximum indentation load of the particles containing polymer B is equal to or less than the above upper limit, the resistance to powder shedding of the electrode can be improved. In the present invention, the maximum indentation load of the particles containing polymer B can be measured using the method described in the examples of this specification.

[0071] Furthermore, the particles containing polymer B preferably have an elastic recovery of 50 nm or more, more preferably 100 nm or more, even more preferably 120 nm or more, and preferably 200 nm or less, and more preferably 150 nm or less. If the elastic recovery of the particles containing polymer B is equal to or greater than the above lower limit, the injectability of the electrode mixture layer can be improved. On the other hand, if the elastic recovery of the particles containing polymer B is equal to or less than the above upper limit, the flexibility of the resulting electrode can be improved. In the present invention, the elastic recovery of the particles containing polymer B can be measured using the method described in the Examples of this specification.

[0072] The volume average particle diameter Da and average particle diameter Db of the particles containing polymer B can be adjusted, for example, by changing the preparation conditions of the particles containing polymer B. The glass transition point, electrolyte swelling degree, maximum indentation load, and elastic recovery amount of the particles containing polymer B can be adjusted, for example, by changing the preparation conditions of the particles containing polymer B (such as the amount and timing of addition of a molecular weight modifier, a polymerization initiator, etc.), the structure of the particles containing polymer B, and the composition of polymer B.

[0073] -Mixing Ratio- The ratio of the particles containing polymer B to the total of the particles containing polymer A and the particles containing polymer B (= {particles containing polymer B / (particles containing polymer A+particles containing polymer B)} × 100%) is preferably 1 mass % or more, more preferably 10 mass % or more, even more preferably 20 mass % or more, and preferably 50 mass % or less, more preferably 35 mass % or less, and even more preferably 30 mass % or less. When the ratio of the particles containing polymer B is equal to or greater than the above lower limit, the peel strength of the obtained electrode can be increased. On the other hand, when the ratio of the particles containing polymer B is equal to or less than the above upper limit, the internal resistance of the secondary battery can be effectively reduced.

[0074] [Method for Preparing Particulate Polymer] The particulate polymer including the above-mentioned polymer can be polymerized according to a known polymerization method, for example, a solution polymerization method, a suspension polymerization method, a bulk polymerization method, an emulsion polymerization method, etc. As the polymerization reaction, addition polymerization such as ionic polymerization, radical polymerization, living radical polymerization, etc. can be used.

[0075] During the polymerization reaction, a molecular weight modifier (chain transfer agent) may be used to adjust the maximum indentation load and elastic recovery within a preferred range. Commonly used additives such as emulsifiers, dispersants, polymerization initiators, and polymerization aids may also be used. The amounts and timing of addition of these additives can be adjusted appropriately depending on the properties of the resulting polymer.

[0076] <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.

[0077] <Properties of Binder Composition> The binder composition must have a maximum indentation load of 100 nN or more, preferably 130 nN or more, more preferably 200 nN or more, preferably 800 nN or less, more preferably 700 nN or less, and even more preferably 500 nN or less. If the maximum indentation load of the binder composition is equal to or greater than the lower limit, defects in secondary batteries can be more effectively suppressed. On the other hand, if the maximum indentation load of the binder composition is equal to or less than the upper limit, the resistance to powder shedding of the electrode can be improved.

[0078] The binder composition must have an elastic recovery of 120 nm or more and 200 nm or less, preferably 150 nm or more, preferably 195 nm or less, and more preferably 190 nm or less. If the elastic recovery of the binder composition is equal to or greater than the lower limit, the injectability of the electrode mixture layer can be improved. On the other hand, if the elastic recovery of the binder composition is equal to or less than the upper limit, the flexibility of the resulting electrode can be improved.

[0079] The maximum indentation load and elastic recovery of the binder composition can be adjusted by, for example, changing the composition of the particulate polymer and preparation conditions (such as the amounts of molecular weight modifier and polymerization initiator used).

[0080] <Method for preparing binder composition> The binder composition of the present invention is not particularly limited, and can be prepared by mixing the particulate polymer and other components, etc., which are optionally used, in the presence of water. When the binder composition is prepared using an aqueous dispersion of the particulate polymer, the water contained in the dispersion may be used as a dispersion medium for the binder composition as it is.

[0081] (Slurry Composition for Non-Aqueous Secondary Battery Electrode) The slurry composition for a non-aqueous secondary battery electrode of the present invention is a composition used for forming an electrode mixture layer, and contains an electrode active material and the above-described binder composition for a non-aqueous secondary battery electrode of the present invention, and optionally further contains other components. That is, the slurry composition for a non-aqueous secondary battery electrode of the present invention usually contains an electrode active material, the above-described particulate polymer, and water as a dispersion medium, and optionally further contains other components. Furthermore, since the slurry composition of the present invention contains the above-described binder composition, it is possible to effectively suppress defects in secondary batteries and form electrodes with excellent flexibility. Note that, below, as an example, a case where the slurry composition for a non-aqueous secondary battery electrode is a slurry composition for a lithium-ion secondary battery negative electrode will be described, but the present invention is not limited to the following example.

[0082] <Electrode active material> An electrode active material is a material that transfers electrons at an electrode of a secondary battery. A material that can absorb and release lithium is usually used as the negative electrode active material for a lithium ion secondary battery. Specific examples of the negative electrode active material for a lithium ion secondary battery include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials that are a combination of these.

[0083] Here, the carbon-based negative electrode active material refers to an active material having carbon as the main skeleton into which lithium can be inserted (also referred to as "doped"). Examples of the carbon-based negative electrode active material include carbonaceous materials and graphite materials.

[0084] Examples of carbonaceous materials include graphitizable carbon and non-graphitizable carbon, which has a structure similar to an amorphous structure, such as glassy carbon. Examples of graphitizable carbon include carbon materials made from tar pitch obtained from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber, and pyrolytic vapor-grown carbon fiber. Examples of non-graphitizable carbon include phenolic resin calcined bodies, polyacrylonitrile-based carbon fibers, pseudoisotropic carbon, furfuryl alcohol resin calcined bodies (PFA), and hard carbon.

[0085] Furthermore, examples of graphite materials include natural graphite, artificial graphite, etc. Here, examples of artificial graphite include artificial graphite obtained by heat-treating carbon containing easily graphitized carbon mainly at 2800°C or higher, graphitized MCMB obtained by heat-treating MCMB at 2000°C or higher, and graphitized mesophase pitch-based carbon fiber obtained by heat-treating mesophase pitch-based carbon fiber at 2000°C or higher.

[0086] Furthermore, the term "metal-based negative electrode active material" refers to an active material containing a metal, typically containing an element capable of inserting lithium in its structure, and having 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 alloys thereof, as well as oxides, sulfides, nitrides, silicides, carbides, phosphides, etc., thereof. Among these, active materials containing silicon (silicon-based negative electrode active materials) are preferred as metal-based negative electrode active materials. By using a silicon-based negative electrode active material, the output characteristics and capacity of the resulting non-aqueous secondary battery can be improved.

[0087] Examples of silicon-based negative electrode active materials include silicon (Si), silicon-containing alloys, SiO, and SiO ｘ and a composite of a Si-containing material and conductive carbon, which is obtained by coating or compounding a Si-containing material with conductive carbon. These silicon-based negative electrode active materials may be used alone or in combination of two or more.

[0088] <Binder composition> The binder composition of the present invention described above can be used as the binder composition. The content of the predetermined particulate polymer in the slurry composition can be, for example, 0.5 parts by mass or more and 15 parts by mass or less in terms of solid content per 100 parts by mass of the electrode active material.

[0089] <Other Components> Other components that can be blended into the slurry composition are not particularly limited, and include the same components as the other components that can be blended into the binder composition of the present invention. The slurry composition may further contain a conductive material such as carbon black. These components may be used alone or in combination of two or more in any ratio.

[0090] <Preparation of Slurry Composition for Non-Aqueous Secondary Battery Electrode> The above-described slurry composition can be prepared by mixing the above-described components by a known mixing method, for example, using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or a Filmix.

[0091] (Electrode for non-aqueous secondary battery) The electrode of the present invention comprises an electrode mixture layer formed using the above-mentioned slurry composition of the present invention, and typically includes a current collector and an electrode mixture layer formed on the current collector. The electrode mixture layer is typically a layer formed by drying the slurry composition of the present invention, and contains at least an electrode active material and a polymer derived from the particulate polymer, and optionally contains other components. In the electrode mixture layer, the polymer derived from the particulate polymer may be in a particulate form (i.e., the particulate polymer may be contained in the electrode mixture layer as is), or may have any other form.

[0092] Furthermore, since the electrode of the present invention is produced using the slurry composition of the present invention, it effectively suppresses defects in secondary batteries and has excellent flexibility.

[0093] <Method for Forming Electrode> The electrode of the present invention can be produced, for example, through (1) a step of applying a slurry composition onto a current collector (application step), (2) a step of drying the slurry composition applied onto the current collector to form a dried slurry (drying step), and (3) a step of pressing the dried slurry on the current collector (pressing step).

[0094] <<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 application 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. During application, 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 to be obtained.

[0095] <<Drying Step>> The method for drying the slurry composition on the current collector is not particularly limited and any known method can be used, including drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with infrared rays, electron beams, etc. By drying the slurry composition on the current collector in this manner, a dried slurry is formed on the current collector.

[0096] <<Pressing Step>> The method for pressing the dried slurry on the current collector is not particularly limited, and can be performed using a known pressing device. Among them, pressing with a press roll (roll pressing) is preferred from the viewpoint of pressing the dried slurry quickly and efficiently. By undergoing the pressing step, the density of the electrode mixture layer can be increased and the adhesion between the electrode mixture layer and the current collector can be improved.

[0097] (Nonaqueous secondary battery) The nonaqueous secondary battery of the present invention includes the nonaqueous secondary battery electrode of the present invention. More specifically, the nonaqueous secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolyte, and a separator, and uses the nonaqueous secondary battery electrode of the present invention as at least one of the positive electrode and the negative electrode, preferably the negative electrode. Furthermore, since the nonaqueous secondary battery of the present invention includes the nonaqueous secondary battery electrode of the present invention, defects are effectively suppressed and the battery has excellent flexibility. In the following, a case where the secondary battery is a lithium ion secondary battery will be described as an example, but the present invention is not limited to the following example.

[0098] <Electrode> As described above, the secondary battery electrode of the present invention is used as at least one of the positive electrode and the negative electrode. That is, the positive electrode of the lithium ion secondary battery may be the electrode of the present invention and the negative electrode may be another known negative electrode, the negative electrode of the lithium ion secondary battery may be the electrode of the present invention and the positive electrode may be another known positive electrode, or both the positive electrode and the negative electrode of the lithium ion secondary battery may be the electrode of the present invention. Note that, as a known electrode other than the secondary battery electrode of the present invention, an electrode obtained by forming an electrode mixture layer on a current collector using a known manufacturing method can be used.

[0099] <Electrolyte> As the electrolyte, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. For example, in a lithium ion secondary battery, a lithium salt is used as the supporting electrolyte. For example, LiPF ６ , LiAsF ６ , LiBF ４ , LiSbF ６ , LiAlCl ４ , LiClO ４ , C.F. ３SO 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 ３ Li is preferred. Note that one type of electrolyte may be used alone, or two or more types may be used in combination. Generally, the lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0100] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. For example, in lithium ion secondary batteries, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC) are preferably used. Other suitable solvents include 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. The concentration of the electrolyte in the electrolyte can be adjusted as appropriate. Known additives may also be added to the electrolyte.

[0101] <Separator> The separator is not particularly limited, and for example, the separators 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.

[0102] <Method for Manufacturing Non-Aqueous Secondary Battery> The non-aqueous 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 stack as necessary according to the battery shape, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the container. At least one of the positive electrode and the negative electrode is an electrode for the non-aqueous secondary battery of the present invention. To prevent internal pressure increases, overcharge / discharge, and the like, 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.

[0103] 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, 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. In the examples and comparative examples, various evaluations and measurements were carried out as follows.

[0104] <Maximum Indentation Load and Elastic Recovery of Binder Film> A measurement sample (aqueous polymer dispersion or binder composition) was dropped into a Petri dish so that the solid content was 4.0 g. The sample was then dried for 24 hours in an environment of 22 to 25°C, and further dried at 140°C for 10 hours to obtain a binder film with a thickness of 500 μm. The obtained binder film was then subjected to a nanoindentation test using a microcompression tester (Shimadzu Corporation, "MCT-W500") at 23°C under measurement conditions of 0.001 Pa (absolute pressure) or less. A spherical indenter (tip radius: 10 μm) was brought into contact with the surface of the binder film, and the surface of the binder film was pressed into the thickness direction to a depth of 300 nm using the indenter, followed by unloading. A load-displacement curve was created by plotting the indentation depth on the horizontal axis and the indentation load on the vertical axis, with the point where the indenter contacted the surface of the binder film as the displacement 0. The load when the specimen was pressed to a maximum depth of 300 nm was recorded as the maximum indentation load. The difference between the maximum indentation depth (300 nm) and the depth at which the indentation load became 0 upon unloading was recorded as the amount of elastic recovery.

[0105] <Volume average particle diameter Da measured by laser diffraction scattering method> Using a particle size distribution analyzer (manufactured by Shimadzu Corporation, product name "SALD-2300") that uses laser diffraction scattering as its measurement principle, the particle size distribution (volume basis) of a measurement sample was measured in accordance with JIS Z8825, and the particle diameter (D50) at which the cumulative volume calculated from the smallest diameter side in the measured particle size distribution becomes 50% was defined as the average particle diameter Da. Note that, as the measurement samples, an aqueous dispersion of a polymer adjusted to a solids concentration of 0.1% by mass and a binder composition adjusted to a solids concentration of 0.1% by mass were used.

[0106] <Average particle diameter Db measured by dynamic light scattering> The particle size distribution of the measurement sample was measured using a particle size distribution measurement device (manufactured by Otsuka Electronics Co., Ltd., model "FPAR-1000") that uses dynamic light scattering as its measurement principle, and the particle diameter (D50) at which the cumulative frequency of light scattering intensity calculated from the small diameter side in the measured particle size distribution becomes 50% was defined as the average particle diameter Db. The measurement samples used were an aqueous dispersion of a polymer adjusted to a solid content concentration of 0.005% by mass using ion-exchanged water and a binder composition adjusted to a solid content concentration of 0.005% using ion-exchanged water. The measurement conditions for the dynamic light scattering method were as follows: Dispersion medium: Water Measurement temperature: 25°C Measurement concentration (solid content): 0.005% by mass Scattering angle: 160° Light source laser wavelength: 632.8 nm

[0107] <Glass transition point> A measurement sample was prepared by drying an aqueous dispersion of the polymer to be measured. Next, a differential scanning calorimetry (DSC) measurement apparatus (manufactured by SII NanoTechnology Inc., product name "EXSTAR DSC6220") was used. 10 mg of the measurement sample was weighed into an aluminum pan. An empty aluminum pan was used as a reference. Measurements were performed in accordance with JIS K7121 under the following conditions: a temperature range of -100°C to 100°C, a heating rate of 10°C / min, and a differential scanning calorimetry (DSC) curve was obtained. During this heating process, the glass transition point was determined from the intersection of the baseline immediately before the endothermic peak of the DSC curve where the differential signal (DDSC) is 0.05 mW / min / mg or more appears, and the tangent to the DSC curve at the first inflection point that appears after the endothermic peak.

[0108] <Electrolyte Swelling Degree> First, a measurement sample (aqueous dispersion of polymer or binder composition) was dried in an environment with a humidity of 50% and a temperature of 23 to 25°C to form a film with a thickness of 1±0.3 mm, and then dried in a vacuum dryer at a temperature of 60°C for 10 hours to obtain a film. Next, this film was cut and approximately 1 g was precisely weighed. The mass of the obtained film piece was designated as W0. This film piece was then subjected to a 1.0 M LiPF 5 solution as an electrolyte solution in an environment with a temperature of 60°C. ６The film piece was immersed in a solution (a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (mass ratio), containing 2 mass% vinylene carbonate and 2 mass% fluoroethylene carbonate as additives) for 3 days to allow it to swell. The film piece was then removed, the electrolyte on the surface was wiped with a Kimwipe, and the mass was measured. The mass of the film piece after swelling was designated W1. The electrolyte swelling degree was calculated using the following formula: Electrolyte swelling degree (mass%) = (W1 / W0) × 100

[0109] <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 cracks there were, indicating better 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, but cracks were present when the metal rod diameter was 4.0 mm C: Cracks were present when the metal rod diameter was 5.0 mm

[0110] <Suppression of secondary battery malfunctions> The manufactured lithium ion secondary battery was fully charged to a depth of charge (SOC) of 100% at a constant current of 1 C in an environment at a temperature of -10°C. The fully charged secondary battery was disassembled to remove the negative electrode, and the surface condition of the negative electrode composite layer of the negative electrode was observed. The area of ​​lithium deposited on the surface of the negative electrode composite layer was then measured, and the lithium deposition rate on the negative electrode = (area of ​​deposited lithium / surface area of ​​negative electrode composite layer) x 100 (%) was calculated. Evaluation was then performed according to the following criteria. A lower lithium deposition rate indicates more effectively suppressed secondary battery malfunctions. A: Lithium deposition rate less than 10% B: Lithium deposition rate 10% or more but less than 20% C: Lithium deposition rate 20% or more

[0111] <Pouring Ability of Negative Electrode Composite Layer> The negative electrode composite layers prepared in the Examples and Comparative Examples were vacuum-dried at a gauge pressure of −0.09 MPa or less at 60° C. for 10 hours. Then, in a dry room (dew point of −50° C. or less), a 1.0 M LiPF solution was applied to the surface of the negative electrode composite layer of the test negative electrode. ６10 μL of a containing electrolyte solution (solvent: a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 3 / 7 (mass ratio), additive: 2 vol% vinylene carbonate (solvent ratio)) was dropped using a pipetter, and a φ10 mm transparent hemispherical plastic cover was placed on the dropped electrolyte solution (droplet). Next, the time required for the electrolyte solution to disappear from the negative electrode mixture layer (disappearance time) was measured visually, and the injectability of the negative electrode mixture layer was evaluated according to the following criteria. The shorter the disappearance time, the better the injectability. A: Disappearance time: 0 seconds or more and less than 60 seconds B: Disappearance time: 60 seconds or more and less than 120 seconds C: Disappearance time: 120 seconds or more and less than 180 seconds D: Disappearance time: 180 seconds or more

[0112] <Negative Electrode Powder Shedding Resistance> The negative electrodes prepared in the Examples and Comparative Examples were cut to 5 cm x 5 cm, and the weight W1 of the resulting test piece was measured using an electronic balance (to five decimal places). Next, using a 1 mm wide cross-cut jig (a jig conforming to JIS K5400) and a 9 mm wide cutter, the copper foil (current collector) side of the test piece was turned upside down, and the test piece was cut (slit) at 11 locations from the copper foil side in a direction parallel to the application direction (the direction in which the negative electrode composite layer slurry was applied when forming the negative electrode composite layer). Note that the blade of the cutter was folded and replaced before use. Then, both sides of the test piece were lightly brushed with a brush to remove any detached powder, and the weight W2 of the test piece was measured using an electronic balance (to five decimal places). The powder shedding rate = (W1 - W2) / W1 x 100 (%) was calculated from the obtained W1 and W2, and evaluated according to the following criteria. The smaller the powder shedding rate, the better the resistance to powder shedding. A: Powder shedding rate is less than 0.15% B: Powder shedding rate is 0.15% or more and less than 0.25% C: Powder shedding rate is 0.25% or more

[0113] <Peel Strength> The negative electrodes prepared in the Examples and Comparative Examples were cut directly into rectangular shapes measuring 100 mm in length and 10 mm in width to prepare test specimens. The obtained test specimens were placed with the surface of the negative electrode composite layer facing downward, and cellophane tape was applied to the surface of the negative electrode composite layer. Cellophane tape specified in JIS Z1522 was used as the cellophane tape. The cellophane tape was fixed to a test table. One end of the current collector was then pulled vertically upward at a pulling rate of 150 mm / min to measure the stress when peeled off. This measurement was performed three times, and the average value was calculated as the peel strength, which was evaluated according to the following criteria. A higher peel strength indicates a stronger adhesive force of the negative electrode composite layer to the current collector, i.e., a higher adhesion strength. A: Peel strength of 8 N / m or more B: Peel strength of 7 N / m or more but less than 8 N / m C: Peel strength of less than 7 N / m

[0114] <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 100 cycles was measured. The capacity retention C2 was calculated according to the following formula: C2 (%) = (C1 / C0) × 100. The cycle characteristics were evaluated according to the following criteria. Note that a higher capacity retention C2 indicates better cycle characteristics. A: Capacity retention rate C2 is 92% or more. B: Capacity retention rate C2 is 87% or more and less than 92%. C: Capacity retention rate C2 is less than 87%.

[0115] Example 1 Preparation of Binder Composition Production of Particles Comprising Polymer A 2.1 parts of styrene as an aromatic vinyl monomer, 3.3 parts of 1,3-butadiene as a conjugated diene monomer, 0.1 parts of methacrylic acid as a carboxylic acid group-containing monomer, 0.23 parts of dodecyl diphenyl ether disulfonic acid sodium salt as an emulsifier, 15 parts of ion-exchanged water, and 0.02 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel A equipped with a stirrer to obtain a mixture A. The obtained mixture A was thoroughly stirred and then heated to 57°C to initiate polymerization and reacted for 5 hours, and then heated to 70°C and reacted for an additional 4 hours to obtain seed particles. Separately, 46.6 parts of styrene as an aromatic vinyl monomer, 29.0 parts of 1,3-butadiene as a conjugated diene monomer, 14.2 parts of acrylic acid as a carboxylic acid group-containing monomer, 4.7 parts of acrylamide as an amide group-containing monomer, 0.5 parts of tert-dodecyl mercaptan as a molecular weight modifier, 0.20 parts of sodium lauryl sulfate as an emulsifier, and 44 parts of ion-exchanged water were added to a 5 MPa pressure vessel B equipped with a stirrer to obtain a mixture B. After obtaining the seed particles, the temperature of the contents of the pressure vessel A was raised 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 0.48 parts of potassium persulfate as a polymerization initiator to the heat-resistant vessel A. That is, the overall monomer composition was 48.7 parts of styrene, 32.3 parts of 1,3-butadiene, 14.2 parts of acrylic acid, 4.7 parts of acrylamide, and 0.1 parts of methacrylic acid. Five hours after the start of polymerization, the addition of the entire mixture containing these monomer compositions was completed, and then 0.5 parts of potassium persulfate was added as a polymerization initiator. The mixture was then heated to 90°C and reacted for 4 hours. When the polymerization conversion rate reached 97%, the mixture was cooled to stop the reaction. A 5% aqueous solution of sodium hydroxide was added to the mixture containing the polymer to adjust the pH to 8. Unreacted monomers were then removed by heating and distillation under reduced pressure. The mixture was then cooled to obtain an aqueous dispersion containing polymer A. Various measurements and evaluations were performed using the obtained aqueous dispersion. The results are shown in Table 1.

[0116] [Preparation of Particles Containing Polymer B] First, in the first-stage polymerization, 25.0 parts of styrene as an aromatic vinyl monomer, 72.0 parts of 1,3-butadiene as a conjugated diene monomer, 100.0 parts of ion-exchanged water, 0.7 parts of dodecylbenzenesulfonic acid as an emulsifier, 0.1 parts of α-methylstyrene dimer as a chain transfer agent (molecular weight modifier), and 0.3 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer and thoroughly stirred. The mixture was then heated to 60°C to initiate polymerization. The polymerization was continued until the polymerization conversion rate reached 96%. Next, in the second-stage polymerization, 3.0 parts of methacrylic acid as a carboxylic acid group-containing monomer and 37.0 parts of ion-exchanged water were continuously added to the same pressure vessel under stirring to form the shell portion, and the polymerization was continued. This aqueous dispersion was heated to 70°C, and when the polymerization conversion rate reached 97%, it was cooled to stop the reaction, and a polymer was formed as a shell portion on the outer surface of the core portion, yielding a mixture containing polymer particles having a core-shell structure. Subsequently, unreacted monomers were removed by heating and vacuum distillation. A 5% aqueous sodium hydroxide solution was added to the mixture containing the polymer particles, adjusting the pH to 7, yielding an aqueous dispersion containing polymer B. Various measurements and evaluations were performed using the obtained aqueous dispersion. The results are shown in Table 1.

[0117] [Preparation of binder composition] An aqueous dispersion of polymer A and an aqueous dispersion of polymer B were mixed so that the mass ratio of the solid contents was 9:1 (polymer A:polymer B) to obtain a binder composition (aqueous dispersion). Various measurements and evaluations were carried out using the obtained binder composition. The results are shown in Table 2.

[0118] <Preparation of Slurry Composition for Negative Electrode> 87.3 parts of artificial graphite as a carbon-based negative electrode active material and SiO as a silicon-based negative electrode active material were placed in a planetary mixer equipped with a disperser. Ｘ9.7 parts of carboxymethylcellulose sodium aqueous solution as a thickener (solid content equivalent) was added, and the solid content concentration was adjusted to 61.5% with ion-exchanged water, and mixed at room temperature for 40 minutes. After mixing, the solid content concentration was gradually adjusted to 56% and 51% with ion-exchanged water, and 1.0 part (solid content equivalent) of the binder composition obtained as above was added to obtain a mixed solution. The obtained mixed solution was degassed under reduced pressure to obtain a negative electrode slurry composition with good fluidity.

[0119] <Production of Negative Electrode> The above-described negative electrode slurry composition was applied to a copper foil (current collector) having a thickness of 16 μm using a comma coater in an amount of 10 mg / cm. ２ The copper foil coated with the negative electrode slurry composition was 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 negative electrode slurry composition on the copper foil, thereby obtaining a negative electrode blank. The negative electrode blank was rolled using a roll press to obtain a negative electrode having a negative electrode composite layer thickness of 80 μm. The obtained negative electrode was evaluated for flexibility, powder shedding resistance, pourability, and peel strength. The results are shown in Table 2.

[0120] <Production of Positive Electrode> 96 parts of lithium nickel manganese cobalt oxide as a positive electrode active material, 2 parts of PVDF (polyvinylidene fluoride) as a binder for a positive electrode composite layer in terms of solid content, 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 positive electrode slurry composition. The obtained positive electrode slurry composition 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 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 to dry the positive electrode slurry composition on the aluminum foil, thereby obtaining a positive electrode blank. The positive electrode blank was rolled using a roll press to obtain a positive electrode having a positive electrode composite layer thickness of 70 μm.

[0121] <Preparation of Separator> A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm; manufactured by a dry method; porosity 55%) was prepared. This separator was cut into a 5 cm × 5 cm square and used in the following secondary battery.

[0122] <Preparation of Secondary Battery> An aluminum packaging material was prepared as the battery packaging. The positive electrode was cut into a 4 cm x 4 cm square and placed so that the surface on the 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. Furthermore, 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 the electrolyte. ６ A solution (the solvent was a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (mass ratio), containing 2 mass% vinylene carbonate and 2 mass% fluoroethylene carbonate as additives) was filled into the battery. Furthermore, in order to seal the opening of the aluminum packaging, the aluminum packaging exterior was closed by heat sealing at 150°C, and a laminate cell-type lithium ion secondary battery was produced. The resulting secondary battery was evaluated for suppression of secondary battery defects and cycle characteristics. The results are shown in Table 2.

[0123] Examples 2 and 3 A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared in the same manner as in Example 1, except that, when preparing the binder composition, an aqueous dispersion of polymer A and an aqueous dispersion of polymer B were mixed so that the mass ratio of the solid contents (polymer A:polymer B) was 7:3 (Example 2) and 5:5 (Example 3), respectively, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0124] Examples 4 to 6 A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared in the same manner as in Example 1, except that the amount of tert-dodecyl mercaptan used as a molecular weight modifier during the preparation of particles containing polymer A was changed to 0.3 parts, and further, after the addition of the entire amount of the mixture containing the monomer composition was completed (i.e., 5 hours after the start of polymerization), the mixture was heated to 90°C and reacted for 4 hours without adding 0.5 parts of potassium persulfate, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0125] Example 7 A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were produced in the same manner as in Example 1, except that a binder composition prepared as follows was used, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0126] <Preparation of Binder Composition> First, in the first-stage polymerization, 55 parts of styrene as an aromatic vinyl monomer, 44 parts of 1,3-butadiene as a conjugated diene monomer, 100 parts of ion-exchanged water, 0.7 parts of dodecylbenzenesulfonic acid as an emulsifier, 0.3 parts of α-methylstyrene dimer as a chain transfer agent (molecular weight modifier), and 0.5 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer and thoroughly stirred. The mixture was then heated to 60°C to initiate polymerization. The polymerization was continued until the polymerization conversion rate reached 96%. Next, in the second-stage polymerization, 1 part of methacrylic acid as a carboxylic acid group-containing monomer and 37 parts of ion-exchanged water were continuously added to the same pressure vessel under stirring to continue the polymerization. This aqueous dispersion was heated to 70°C, and when the polymerization conversion rate reached 97%, the reaction was stopped by cooling, and a polymer was formed as a shell on the outer surface of the core, to obtain a mixture containing polymer particles having a core-shell structure. Thereafter, unreacted monomers were removed by heating and vacuum distillation. A 5% aqueous solution of sodium hydroxide was added to the mixture containing the polymer particles, and the pH was adjusted to 7, to obtain an aqueous dispersion (binder composition) containing a polymer (particulate polymer).

[0127] (Example 8) A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were produced in the same manner as in Example 1, except that a binder composition prepared as follows was used, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0128] <Preparation of Binder Composition> First, in the first-stage polymerization, 60 parts of styrene as an aromatic vinyl monomer, 34 parts of 1,3-butadiene as a conjugated diene monomer, 100 parts of ion-exchanged water, 0.7 parts of dodecylbenzenesulfonic acid as an emulsifier, 0.3 parts of α-methylstyrene dimer as a chain transfer agent (molecular weight modifier), and 0.5 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer and thoroughly stirred. The mixture was then heated to 60°C to initiate polymerization. The polymerization was continued until the polymerization conversion rate reached 96%. Next, in the second-stage polymerization, 6 parts of methacrylic acid as a carboxylic acid group-containing monomer and 37 parts of ion-exchanged water were continuously added to the same pressure vessel under stirring to continue the polymerization. This aqueous dispersion was heated to 70°C, and when the polymerization conversion rate reached 97%, the reaction was stopped by cooling, and a polymer was formed as a shell on the outer surface of the core, to obtain a mixture containing polymer particles having a core-shell structure. Thereafter, unreacted monomers were removed by heating and vacuum distillation. A 5% aqueous solution of sodium hydroxide was added to the mixture containing the polymer particles, and the pH was adjusted to 7, to obtain an aqueous dispersion (binder composition) containing a polymer (particulate polymer).

[0129] Example 9 A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared in the same manner as in Example 1, except that particles containing polymer A (aqueous dispersion of polymer A) prepared as follows were used, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0130] [Preparation of Particles Comprising Polymer A] 2.1 parts of styrene as an aromatic vinyl monomer, 3.3 parts of 1,3-butadiene as a conjugated diene monomer, 0.1 parts of methacrylic acid as a carboxylic acid group-containing monomer, 0.23 parts of dodecyl diphenyl ether disulfonic acid sodium salt as an emulsifier, 15 parts of ion-exchanged water, and 0.02 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel A equipped with a stirrer to obtain a mixture A. After thorough stirring, the obtained mixture A was heated to 57°C to initiate polymerization and reacted for 5 hours, and then heated to 70°C and reacted for an additional 4 hours to obtain seed particles. Separately, 43.2 parts of styrene as an aromatic vinyl monomer, 28.1 parts of 1,3-butadiene as a conjugated diene monomer, 14.2 parts of acrylic acid as a carboxylic acid group-containing monomer, 9.0 parts of acrylamide as an amide group-containing monomer, 0.5 parts of tert-dodecyl mercaptan as a molecular weight modifier, 0.20 parts of sodium lauryl sulfate as an emulsifier, and 44 parts of ion-exchanged water were added to a 5 MPa pressure vessel B equipped with a stirrer to obtain a mixture B. After obtaining the seed particles, the temperature of the contents of the pressure vessel A was raised 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 0.48 parts of potassium persulfate as a polymerization initiator to the heat-resistant vessel A. That is, the overall monomer composition was 45.3 parts of styrene, 31.4 parts of 1,3-butadiene, 14.2 parts of acrylic acid, 9.0 parts of acrylamide, and 0.1 parts of methacrylic acid. Five hours after the start of polymerization, the addition of the entire mixture containing these monomer compositions was completed, and then 0.5 parts of potassium persulfate was added as a polymerization initiator.The mixture was then heated to 90°C and reacted for 4 hours.When the polymerization conversion rate reached 97%, the mixture was cooled to stop the reaction.A 5% aqueous solution of sodium hydroxide was added to the mixture containing this polymer to adjust the pH to 8.Then, unreacted monomers were removed by heating and distillation under reduced pressure.The mixture was then cooled to obtain an aqueous dispersion containing polymer A.

[0131] Comparative Example 1 A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared in the same manner as in Example 1, except that the aqueous dispersion containing polymer A was used as the binder composition without using the aqueous dispersion containing polymer B, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0132] Comparative Example 2 A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared in the same manner as in Example 4, except that the aqueous dispersion containing polymer A was used as the binder composition without using the aqueous dispersion containing polymer B, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0133] Comparative Example 3 A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were produced in the same manner as in Example 1, except that a binder composition prepared as follows was used, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0134] <Preparation of Binder Composition> A reactor was charged with 150 parts of ion-exchanged water, 4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 65 parts of styrene as an aromatic vinyl monomer, 1.5 parts of acrylic acid and 3.5 parts of itaconic acid as carboxylic acid group-containing monomers, and 0.5 parts of t-dodecyl mercaptan as a molecular weight modifier, in this order. Next, the gas inside the reactor was replaced with nitrogen three times, and then 30 parts of 1,3-butadiene as a conjugated diene monomer was charged. The reactor was maintained at 60°C, and 0.5 parts of potassium persulfate as a polymerization initiator was charged to initiate the polymerization reaction, which was continued with stirring. When the polymerization conversion rate reached 96%, the reactor was cooled, and 0.1 parts of a hydroquinone aqueous solution (10% concentration) as a polymerization terminator was added to terminate the polymerization reaction. Subsequently, residual monomers were removed using a rotary evaporator at a water temperature of 60°C, yielding an aqueous dispersion of a polymer (particulate polymer). A 5% aqueous solution of sodium hydroxide was added to the mixture containing this particulate polymer to adjust the pH to 8, thereby preparing a binder composition.

[0135] Comparative Example 4 A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were produced in the same manner as in Example 1, except that a binder composition prepared as follows was used, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0136] <Preparation of Binder Composition> 1.93 parts of styrene as an aromatic vinyl monomer, 3.08 parts of 1,3-butadiene as a conjugated diene monomer, 0.15 parts of itaconic acid as a carboxylic acid group-containing monomer, 0.2 parts of sodium lauryl sulfate as an emulsifier, 20 parts of ion-exchanged water, and 0.03 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel A equipped with a stirrer, and after sufficient stirring, the mixture was heated to 60°C to initiate polymerization, and the mixture was allowed to react for 6 hours to obtain seed particles. After the above reaction, the mixture was heated to 75 ° C., and 27.54 parts of styrene as an aromatic vinyl monomer, 43.86 parts of 1,3-butadiene as a conjugated diene monomer, 2.07 parts of itaconic acid as a carboxylic acid group-containing monomer, 4.60 parts of acrylonitrile, 14.74 parts of methyl methacrylate, 1.11 parts of acrylamide, 0.27 parts of tert-dodecyl mercaptan as a molecular weight modifier, and 0.35 parts of sodium lauryl sulfate as an emulsifier were added from another container B to pressure-resistant container A. At the same time, the second-stage polymerization was initiated by starting the addition of 0.97 parts of potassium persulfate as a polymerization initiator to pressure-resistant container A. Furthermore, 4 hours after the start of the second-stage polymerization (after addition of 70% of the entire monomer composition), 0.92 parts of hydroxyethyl acrylate was added to pressure-resistant container A over 1.5 hours. Five and a half hours after the start of the second-stage polymerization, the addition of the entire mixture containing these monomer compositions was completed, and then the mixture was further heated to 85°C and reacted for 6 hours. When the polymerization conversion rate reached 97%, the reaction was stopped by cooling to obtain a mixture containing a particulate polymer. A 5% aqueous solution of sodium hydroxide was added to this mixture containing the particulate polymer to adjust the pH to 8. Thereafter, unreacted monomers were removed by heating and distillation under reduced pressure. Thereafter, the mixture was further cooled to obtain an aqueous dispersion (binder composition) containing the desired particulate polymer.

[0137]

[0138]

[0139] As is clear from Table 2, the binder compositions of Examples 1 to 9 can effectively suppress defects in non-aqueous secondary batteries and can form electrodes for non-aqueous secondary batteries that are excellent in flexibility.

[0140] According to the present invention, a binder composition for non-aqueous secondary battery electrodes can be provided, which effectively suppresses defects in non-aqueous secondary batteries and allows the formation of electrodes for non-aqueous secondary batteries that have excellent flexibility. Furthermore, according to the present invention, a slurry composition for non-aqueous secondary battery electrodes can be provided, which effectively suppresses defects in non-aqueous secondary batteries and allows the formation of electrodes for non-aqueous secondary batteries that have excellent flexibility. Furthermore, according to the present invention, a non-aqueous secondary battery electrode can be provided, which effectively suppresses defects in non-aqueous secondary batteries and has excellent flexibility. Furthermore, according to the present invention, a non-aqueous secondary battery in which defects are effectively suppressed and has excellent flexibility can be provided.

Claims

1. A binder composition for a non-aqueous secondary battery electrode, comprising a particulate polymer and water, wherein the particulate polymer comprises a polymer containing an aromatic vinyl monomer unit and a conjugated diene monomer unit, and a binder film formed using the binder composition for a non-aqueous secondary battery electrode has a maximum indentation load of 100 nN or more and an elastic recovery of 120 nm or more and 200 nm or less when a nanoindentation test is performed and the surface of the binder film is indented to a depth of 300 nm with an indenter.

2. The binder composition for non-aqueous secondary battery electrodes according to claim 1, wherein the ratio (Da / Db) of the volume average particle diameter Da of the particulate polymer measured by a laser diffraction scattering method at a solid content concentration of 0.1 mass % to the average particle diameter Db of the particulate polymer measured by a dynamic light scattering method at a solid content concentration of 0.005 mass % is 1.4 or more and 2.0 or less.

3. The binder composition for a non-aqueous secondary battery electrode according to claim 1, wherein the particulate polymer comprises: a polymer A containing an aromatic vinyl monomer unit and a conjugated diene monomer unit; and a polymer B containing an aromatic vinyl monomer unit and a conjugated diene monomer unit and different from the polymer A.

4. The binder composition for a non-aqueous secondary battery electrode according to claim 1, wherein the particulate polymer has a degree of swelling in an electrolyte of 300 mass % or less.

5. The binder composition for a non-aqueous secondary battery electrode according to claim 1, wherein the polymer contained in the particulate polymer further contains an amide group-containing monomer unit.

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

7. The non-aqueous secondary battery electrode slurry composition according to claim 6, wherein the electrode active material comprises a silicon-based negative electrode active material.

8. A non-aqueous secondary battery electrode comprising a current collector and an electrode mixture layer located on the current collector, wherein the electrode mixture layer is a layer formed from the slurry composition for a non-aqueous secondary battery electrode according to claim 6.

9. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein at least one of the positive electrode and the negative electrode is the non-aqueous secondary battery electrode according to claim 8.

Images