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 for a non-aqueous secondary battery electrode, the composition capable of forming an electrode that is for a non-aqueous secondary battery and has excellent peel strength. This binder composition for a non-aqueous secondary battery electrode contains a binder in particle form and water. When the binder composition for a non-aqueous secondary battery electrode has been brought to a pH of 8.0 and formed into a binder film, the average free volume radius of pores in the binder film is 0.30 nm to 0.50 nm according to positron annihilation lifetime spectroscopy.

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 for a secondary battery such as a lithium-ion secondary battery typically includes a current collector and an electrode mixture layer formed on the current collector. The electrode mixture layer is formed, for example, by applying a slurry composition, which is obtained by dispersing an electrode active material and a binder composition containing a binding agent in a dispersion medium, 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 in forming the electrode mixture layer in order to achieve further performance improvements in secondary batteries. Patent Documents 1 to 4 describe the use of a particulate polymer containing monomer units such as aromatic vinyl monomer units, aliphatic conjugated diene monomer units, and carboxyl group-containing monomer units as the binder contained in the binder composition.

[0005] Japanese Patent No. 6645430 Japanese Patent No. 6627763 Japanese Patent No. 5701519 International Publication No. 2010 / 114119

[0006] Here, when an electrode is produced by forming an electrode mixture layer from a slurry composition containing a binder composition, it is required to ensure high adhesion between the electrode mixture layer and a current collector (i.e., peel strength of the electrode). However, the conventional binder compositions described above have room for further improvement in terms of increasing the peel strength of the electrode.

[0007] Therefore, an object of the present invention is to provide a binder composition for a non-aqueous secondary battery electrode capable of forming a non-aqueous secondary battery electrode having excellent peel strength, a slurry composition for a non-aqueous secondary battery electrode containing the binder composition, a non-aqueous secondary battery electrode having excellent peel strength, and a non-aqueous secondary battery including the non-aqueous secondary battery electrode.

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems. Here, the present inventors have focused on pores in a binder film formed using a binder composition. The present inventors have found that an electrode with excellent peel strength can be formed by using a binder composition that contains a particulate binder and water and has pores in the binder film with a mean free volume radius within a predetermined range as measured by positron annihilation lifetime spectroscopy, and have completed the present invention.

[0009] That is, an object of the present invention is to advantageously solve the above-mentioned problems, and according to the present invention, there are provided binder compositions for non-aqueous secondary battery electrodes as set forth in the following [1] to [7], a slurry composition for non-aqueous secondary battery electrodes as set forth in the following [8], an electrode for non-aqueous secondary batteries as set forth in the following [9], and a non-aqueous secondary battery as set forth in the following

[10] .

[0010] [1] A binder composition for a non-aqueous secondary battery electrode, comprising a particulate binder and water, wherein the binder film formed from the binder composition for a non-aqueous secondary battery electrode, adjusted to a pH of 8.0, is measured by positron annihilation lifetime spectroscopy, and the mean free volume radius of the pores in the binder film is 0.30 nm or more and 0.50 nm or less. A binder composition containing a particulate binder and water, and having a mean free volume radius of the pores in the binder film formed after adjusting the pH to a predetermined value within the above range, can provide an electrode with excellent peel strength. In the present invention, the "binder film" can be prepared using the method described in the Examples of this specification. In the present invention, the "mean free volume radius" of the pores in the binder film can be measured using the method described in the Examples of this specification.

[0011] [2] Solid concentration 30% by mass, pH 8.0, shear rate 0.01 s －１ The binder composition for a non-aqueous secondary battery electrode according to [1] above, having a viscosity of 800 mPa·s or more under the conditions. A binder composition having a viscosity of at least the above value under specified conditions can further improve the peel strength of the electrode. In the present invention, the "viscosity" of the binder composition can be measured using the method described in the examples of this specification.

[0012] [3] The binder composition for a non-aqueous secondary battery electrode according to [1] or [2] above, wherein the ratio (Da / Db) of the average particle diameter Da of the particulate binder measured by dynamic light scattering to the average particle diameter Db of the particulate binder measured by laser diffraction scattering is 1.05 or more. A Da / Db ratio of at least this value further improves the peel strength of the electrode and enhances the storage characteristics of the secondary battery. In the present invention, the "average particle diameter Da" of the particulate binder refers to the "cumulant average particle diameter obtained by cumulant analysis of the particle size distribution (volume basis) measured by dynamic light scattering," which can be measured using the method described in the Examples of this specification. In the present invention, the "average particle diameter Db" of the particulate binder refers to the particle diameter (D50) at which the cumulative volume calculated from the smallest diameter in the particle size distribution (volume basis) measured by laser diffraction scattering is 50%. This can be measured using the method described in the Examples of this specification.

[0013] [4] The binder composition for a non-aqueous secondary battery electrode according to any one of [1] to [3] above, wherein the particulate binder has an average particle diameter Db of 500 nm or less as measured by a laser diffraction scattering method. When the average particle diameter Db of the particulate binder is the above value or less, the peel strength of the electrode can be further improved.

[0014] [5] The binder composition for a non-aqueous secondary battery electrode according to any one of [1] to [4] above, wherein the particulate binder comprises a polymer (A) containing at least one of an aliphatic conjugated diene monomer unit and a (meth)acrylic acid ester monomer unit. When the particulate binder comprises a polymer (A) containing an aliphatic conjugated diene monomer unit and / or a (meth)acrylic acid ester monomer unit, the peel strength of the electrode can be further improved. 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 term "(meth)acrylic acid" refers to acrylic acid and / or methacrylic acid.

[0015] [6] The binder composition for a non-aqueous secondary battery electrode according to [5], wherein the particulate binder contains a polymer (B) containing 80% by mass or more of an acidic functional group-containing monomer unit in a surface layer portion, and has particles containing the polymer (A) inside the surface layer portion. When the particulate binder has particles containing the polymer (A) inside the surface layer portion containing the polymer (B), the peel strength of the electrode can be further improved and the cycle characteristics of the secondary battery can be enhanced. In the present invention, the "content ratio (mass%)" of each monomer unit (each repeating unit) contained in the polymer is expressed as follows: １ H-NMR and １３ It can be measured using a nuclear magnetic resonance (NMR) method such as C-NMR.

[0016] [7] The binder composition for a non-aqueous secondary battery electrode according to any one of [1] to [6] above, having a pH of 6.0 or more and 10.0 or less. When the pH of the binder composition is within the above range, the tackiness of the binder composition can be improved and the peel strength of the electrode can be further improved. In the present invention, the "pH" of the binder composition refers to the pH measured at 25°C.

[0017] [8] 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 [1] to [7] above. The slurry composition comprising the electrode active material and any one of the binder compositions described above can provide the electrode with excellent peel strength.

[0018] [9] An electrode for a non-aqueous secondary battery, comprising an electrode mixture layer formed using the slurry composition for a non-aqueous secondary battery electrode according to [8] above. The electrode comprising an electrode mixture layer obtained using a slurry composition containing an electrode active material and any of the binder compositions described above has excellent peel strength.

[0019]

[10] A non-aqueous secondary battery having 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 electrode for a non-aqueous secondary battery described in [9]. A secondary battery including the above-described electrode has excellent storage characteristics and cycle characteristics.

[0020] The present invention provides a binder composition for a non-aqueous secondary battery electrode capable of forming a non-aqueous secondary battery electrode having excellent peel strength, a slurry composition for a non-aqueous secondary battery electrode containing the binder composition, a non-aqueous secondary battery electrode having excellent peel strength, and a non-aqueous secondary battery including the non-aqueous secondary battery electrode.

[0021] Hereinafter, embodiments of the present invention will be described in detail. Here, the binder composition for a non-aqueous secondary battery electrode of the present invention can be used to prepare the slurry composition for a non-aqueous secondary battery electrode of the present invention. The slurry composition for a non-aqueous secondary battery electrode of the present invention can be used to form 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 electrode of the present invention is characterized by comprising an electrode mixture layer formed from the slurry composition for a non-aqueous secondary battery electrode of the present invention. Furthermore, the non-aqueous secondary battery of the present invention is characterized by comprising a non-aqueous secondary battery electrode prepared using the slurry composition for a non-aqueous secondary battery electrode of the present invention.

[0022] (Binder composition for non-aqueous secondary battery electrodes) The binder composition of the present invention contains a particulate binder and water as a dispersion medium, and optionally further contains components other than the particulate binder and the dispersion medium (other components). Here, the binder composition of the present invention is characterized in that the mean free volume radius of pores in a binder film formed after adjusting the pH to a predetermined value is 0.30 nm or more and 0.50 nm or less.

[0023] The binder composition of the present invention contains a particulate binder and water, and the mean free volume radius of the pores in the binder film formed after adjusting the pH to a predetermined value is within the above-mentioned range, so that the use of this binder composition can provide an electrode with excellent peel strength. Although the reason why the above-mentioned effects are obtained by using the binder composition of the present invention is not clear, it is presumed to be as follows.

[0024] In order to improve the peel strength of an electrode, the present inventors focused on the pores (voids between particulate binders) present in a binder film formed from a binder composition. Here, the particulate binder in the slurry composition applied to a current collector may migrate toward the surface of the slurry composition on the side opposite the current collector due to thermal convection or the like when drying the slurry composition. It is believed that when the pores in the binder film are large, the above-mentioned migration of the particulate binder can be suppressed, thereby enabling the particulate binder to be uniformly distributed in the resulting electrode mixture layer. On the other hand, when the pores in the binder film are small, it is believed that the particulate binder can be distributed at high density in the resulting electrode mixture layer. Furthermore, the binder composition of the present invention allows the particulate binder to be distributed at high density and uniformly in the resulting electrode mixture layer by setting the mean free volume radius of the pores in the binder film to 0.30 nm or more and 0.50 nm or less. Therefore, by forming an electrode mixture layer on a current collector using a slurry composition containing the binder composition of the present invention, it is possible to firmly adhere the electrode active material to the current collector while favorably adhering the electrode active material to itself (i.e., it is possible to improve the peel strength of the electrode). For the above reasons, it is believed that the use of the binder composition of the present invention allows the electrode to exhibit excellent peel strength.

[0025] <Particulate Binder> In an electrode mixture layer formed using a slurry composition containing a binder composition, the particulate binder holds components such as the electrode active material contained in the electrode mixture layer so that they do not detach from the electrode mixture layer. The particulate binder is a water-insoluble particle made of a polymer. In the present invention, the term "water-insoluble" means that when 0.5 g of the particles are dissolved in 100 g of water at a temperature of 25°C, the insoluble content is 90 mass% or more.

[0026] <<Structure of Particulate Binder>> The structure of the particulate binder is not particularly limited as long as the mean free volume radius of the pores in the binder film can be within the above-mentioned range. From the viewpoint of further improving the peel strength of the electrode, it is preferable that the particulate binder contains a polymer (A) containing at least one of an aliphatic conjugated diene monomer unit and a (meth)acrylic acid ester monomer unit.

[0027] The structure of the particulate binder containing polymer (A) is not particularly limited, and examples thereof include the following: (i) particles consisting of a single polymer (A); (ii) core-shell particles consisting of a core (center) and a shell (outer shell), either of the core or shell being made of polymer (A); (iii) a structure having particles consisting of a single polymer (A) inside a surface layer containing polymer (B); and (iv) a structure having core-shell particles consisting of a core and a shell inside a surface layer containing polymer (B), either of the core or shell being made of polymer (A). Among these, from the viewpoint of further improving the peel strength of the electrode, the structures (iii) and (iv) above are preferred, and the structure (iv) above is more preferred.

[0028] When the particulate binder has the structure (iv) above, from the viewpoint of further improving the peel strength of the electrode, it is preferable that the core portion is made of the polymer (A) and the shell portion is made of a polymer (C) different from the polymer (A).

[0029] When the particulate binder has a surface layer portion (for example, when the particulate binder has the structure (iii) or (iv) above), the proportion of the surface layer portion in the particulate binder is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and particularly preferably 4% by mass or less. If the proportion of the surface layer portion in the particulate binder is within the above range, the peel strength of the electrode can be further improved and the storage characteristics of the secondary battery can be enhanced.

[0030] Furthermore, when the particulate binder has core-shell particles (for example, when the particulate binder has the structure (iv) above), the proportion of the core portion in the particulate binder is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 85% by mass or more, and is preferably 98% by mass or less, more preferably 96% by mass or less, and even more preferably 94% by mass or less. If the proportion of the core portion in the particulate binder is within the above range, the peel strength of the electrode can be further improved.

[0031] Furthermore, when the particulate binder has core-shell particles (for example, when the particulate binder has the structure (iv) above), the proportion of the shell portion in the particulate binder is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, and is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. If the proportion of the shell portion in the particulate binder is within the above range, the peel strength of the electrode can be further improved.

[0032] The polymer (A), the polymer (B) and the polymer (C) will be described in detail below.

[0033] [Polymer (A)] The polymer (A) contains at least one of an aliphatic conjugated diene monomer unit and a (meth)acrylic acid ester monomer unit, and optionally further contains an acidic functional group-containing monomer unit and an aromatic vinyl monomer unit. The polymer (A) may contain monomer units other than the aliphatic conjugated diene monomer unit, the (meth)acrylic acid ester monomer unit, the acidic functional group-containing monomer unit, and the aromatic vinyl monomer unit (hereinafter referred to as "other monomer units").

[0034] —Aliphatic Conjugated Diene Monomer Unit— Examples of aliphatic conjugated diene monomers that can form aliphatic conjugated diene monomer units include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), and 2,3-dimethyl-1,3-butadiene. These can be used alone or in combination of two or more. Among these, 1,3-butadiene is preferred.

[0035] When the polymer (A) contains aliphatic conjugated diene monomer units, the proportion of the aliphatic conjugated diene monomer units in the polymer (A), relative to the total mass of all repeating units (monomer units) in the polymer (A), is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 76% by mass or more, particularly preferably 78% by mass or more, and is preferably 90% by mass or less, and more preferably 85% by mass or less. If the proportion of the aliphatic conjugated diene monomer units in the polymer (A) is within the above-mentioned range, the peel strength of the electrode can be further improved and the cycle characteristics of the secondary battery can be enhanced.

[0036] —(Meth)acrylic acid ester monomer unit— Examples of (meth)acrylic acid ester monomers that can form (meth)acrylic acid ester monomer units include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, and 2-ethylhexyl acrylate; Examples of suitable methacrylic acid esters include alkyl methacrylates such as n-butyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, and 2-ethylhexyl methacrylate; hydroxyl group-containing acrylic acid esters such as 2-hydroxymethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxybutyl acrylate; and hydroxyl group-containing methacrylic acid esters such as 2-hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and 2-hydroxybutyl methacrylate. These may be used alone or in combination of two or more. Among these, alkyl (meth)acrylates are preferred, and n-butyl acrylate and methyl methacrylate are more preferred.

[0037] When the polymer (A) contains (meth)acrylic acid ester monomer units, the proportion of the (meth)acrylic acid ester monomer units in the polymer (A) is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, and is preferably 98% by mass or less, and more preferably 96% by mass or less, based on 100% by mass of all repeating units (monomer units) in the polymer (A). If the proportion of the (meth)acrylic acid ester monomer units in the polymer (A) is within the above-mentioned range, the peel strength of the electrode can be further improved.

[0038] The total proportion of the aliphatic conjugated diene monomer units and the (meth)acrylic acid ester monomer units in the polymer (A) is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 75% by mass or more, and is preferably 97% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less, based on 100% by mass of all repeating units (monomer units) in the polymer (A). If the total proportion of the aliphatic conjugated diene monomer units and the (meth)acrylic acid ester monomer units in the polymer (A) is within the above-mentioned range, the peel strength of the electrode can be further improved and the cycle characteristics of the secondary battery can be enhanced.

[0039] -Acidic functional group-containing monomer unit- Examples of acidic functional group-containing monomers that can form acidic functional group-containing monomer units include carboxyl group-containing monomers, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers. The acidic functional group of the acidic functional group-containing monomer unit may form a salt with an alkali metal, ammonia, or the like.

[0040] Examples of carboxyl group-containing monomers that can form carboxyl group-containing monomer units include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their derivatives. 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 butyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleates. Examples of dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, and citraconic anhydride. Furthermore, acid anhydrides that generate carboxyl groups upon hydrolysis can also be used as carboxyl group-containing monomers. Furthermore, examples of carboxyl group-containing monomers that can be used include ethylenically unsaturated polycarboxylic acids such as butenetricarboxylic acid, and partial esters of ethylenically unsaturated polycarboxylic acids such as monobutyl fumarate and mono-2-hydroxypropyl maleate.

[0041] Examples of sulfonic acid group-containing monomers capable of forming sulfonic acid group-containing monomer units include styrene sulfonic acid, vinyl sulfonic acid (ethylene sulfonic acid), methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, and 3-allyloxy-2-hydroxypropane sulfonic acid. In the present invention, "(meth)allyl" means allyl and / or methallyl.

[0042] Examples of the phosphate group-containing monomer capable of forming the phosphate group-containing monomer unit include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate. In the present invention, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0043] The above-mentioned monomers may be used singly or in combination of two or more. The acidic functional group-containing monomer capable of forming the acidic functional group-containing monomer unit is preferably a carboxyl group-containing monomer, more preferably acrylic acid or methacrylic acid, and even more preferably methacrylic acid.

[0044] When polymer (A) contains an acidic functional group-containing monomer unit, the proportion of the acidic functional group-containing monomer unit in polymer (A) is preferably 0.5% by mass or more, more preferably 1% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2.5% by mass or less, based on 100% by mass of all repeating units (monomer units) in polymer (A). If the proportion of the acidic functional group-containing monomer unit in polymer (A) is within the above range, the peel strength of the electrode can be further improved.

[0045] —Aromatic vinyl monomer unit— Examples of aromatic vinyl monomers that can form aromatic vinyl monomer units include aromatic monovinyl compounds such as styrene, α-methylstyrene, p-t-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. These can be used alone or in combination of two or more. Among these, styrene is preferred.

[0046] When polymer (A) contains aromatic vinyl monomer units, the proportion of aromatic vinyl monomer units in polymer (A) is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, and is preferably 35% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, and particularly preferably 22% by mass or less, based on 100% by mass of all repeating units (monomer units) in polymer (A). If the proportion of aromatic vinyl monomer units in polymer (A) is within the above range, the peel strength of the electrode can be further improved and the cycle characteristics of the secondary battery can be enhanced.

[0047] Other Monomer Units The other monomer units contained in the polymer (A) are not particularly limited. Examples of the other monomer units include a nitrile group-containing monomer unit and a crosslinkable monomer unit.

[0048] Examples of nitrile group-containing monomers capable of forming nitrile group-containing monomer units include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. These can be used alone or in combination of two or more. Among these, acrylonitrile is preferred.

[0049] When the polymer (A) contains a nitrile group-containing monomer unit, the proportion of the nitrile group-containing monomer unit in the polymer (A) is preferably 0.5% by mass or more, and more preferably 1% by mass or more, and is preferably 40% by mass or less, and more preferably 30% by mass or less, based on 100% by mass of all repeating units (monomer units) in the polymer (A).

[0050] The crosslinkable monomer capable of forming the crosslinkable monomer unit is a monomer having two or more polymerizable double bonds (e.g., olefinic double bonds) per molecule. Examples of the crosslinkable monomer include polyfunctional (meth)acrylates such as allyl (meth)acrylate, ethylene di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and trimethylolpropane-tri(meth)acrylate; polyfunctional allyl / vinyl ethers such as dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, and tetraallyloxyethane; divinylbenzene; vinyl glycidyl ether; allyl glycidyl ether; N-methylolacrylamide; and acrylamide. These may be used alone or in combination of two or more. Among these, N-methylolacrylamide and allyl glycidyl ether are preferred.

[0051] When the polymer (A) contains a crosslinkable monomer unit, the proportion of the crosslinkable monomer unit in the polymer (A) is preferably 1% by mass or more, more preferably 2% by mass or more, and is preferably 10% by mass or less, more preferably 5% by mass or less, based on 100% by mass of all repeating units (monomer units) in the polymer (A).

[0052] [Polymer (B)] The polymer (B) contains an acidic functional group-containing monomer unit, and may optionally further contain a monomer unit other than the acidic functional group-containing monomer unit.

[0053] Examples of the acidic functional group-containing monomer unit contained in polymer (B) include those described above in the section on "polymer (A)." Among them, a carboxyl group-containing monomer unit is preferred, and a methacrylic acid unit is more preferred.

[0054] When all repeating units (monomer units) in polymer (B) are taken as 100 mass%, polymer (B) preferably contains 80 mass% or more, more preferably 90 mass% or more, even more preferably 95 mass% or more, and particularly preferably 100 mass% of acidic functional group-containing monomer units (i.e., polymer (B) particularly preferably contains only acidic functional group-containing monomer units). When the proportion of acidic functional group-containing monomer units in polymer (B) is equal to or greater than the above lower limit, the peel strength of the electrode can be further improved and the storage characteristics of the secondary battery can be enhanced.

[0055] [Polymer (C)] The polymer (C) is a polymer different from the polymer (A) and polymer (B) described above. From the viewpoint of improving the cycle characteristics of the secondary battery, the polymer (C) preferably contains an aromatic vinyl monomer unit. The polymer (C) may optionally further contain a monomer unit other than the aromatic vinyl monomer unit. Examples of the monomer unit other than the aromatic vinyl monomer unit contained in the polymer (C) include the (meth)acrylic acid ester monomer unit described above in the section on "Polymer (A)."

[0056] Examples of the aromatic vinyl monomer units contained in the polymer (C) include those mentioned above in the section on "polymer (A)." Among these, styrene units are preferred.

[0057] When all repeating units (monomer units) in polymer (C) are taken as 100% by mass, polymer (C) preferably contains aromatic vinyl monomer units in a proportion of 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass (i.e., polymer (C) particularly preferably contains only aromatic vinyl monomer units). When the proportion of aromatic vinyl monomer units in polymer (C) is equal to or greater than the above-mentioned lower limit, the cycle characteristics of the secondary battery can be improved.

[0058] <<Properties of Particulate Binder>> [Average particle diameter Da measured by dynamic light scattering] The average particle diameter Da of the particulate binder is preferably 50 nm or more, more preferably 100 nm or more, even more preferably 200 nm or more, preferably 800 nm or less, more preferably 600 nm or less, even more preferably 400 nm or less, and particularly preferably 250 nm or less. Note that the value of the average particle diameter Da measured by dynamic light scattering is a value that relatively strongly reflects the spatial spread of the molecular chains in the surface layer of the particulate binder. In other words, when the particulate binder has, for example, core-shell particles inside the surface layer, it is presumed that the value of the average particle diameter Da of the particulate binder depends on the particle diameter of the entire structure (core part, shell part, and surface layer) of the particulate binder. Therefore, the average particle diameter Da of the particulate binder can be adjusted, for example, by changing the type and amount of the monomer used to form the particulate binder, the polymerization method and conditions, and the structure of the particulate binder.

[0059] [Average Particle Diameter Db Measured by Laser Diffraction Scattering Method] The average particle diameter Db of the particulate binder is preferably 50 nm or more, more preferably 75 nm or more, even more preferably 100 nm or more, particularly preferably 125 nm or more, and preferably 500 nm or less, more preferably 400 nm or less, even more preferably 300 nm or less, and particularly preferably 200 nm or less. If the average particle diameter Db of the particulate binder is equal to or greater than the lower limit, the injectability of the electrolyte solution into the secondary battery can be improved and the internal resistance of the secondary battery can be reduced. On the other hand, if the average particle diameter Db of the particulate binder is equal to or less than the upper limit, the surface area of ​​the particulate binder increases, increasing the contact area between the particulate binder and the electrode active material, thereby further improving the peel strength of the electrode. Note that the average particle diameter Db measured by laser diffraction scattering method is not significantly affected by the spatial spread of the molecular chains in the surface layer of the particulate binder. That is, when a particulate binder has core-shell particles inside a surface layer portion, for example, the average particle diameter Db of the particulate binder is presumably largely dependent on the particle diameters of the core portion and the shell portion, although it is also somewhat affected by the surface layer portion. Therefore, the average particle diameter Db of the particulate binder can be adjusted, for example, by changing the type and amount of the monomer used to form the particles inside the surface layer portion of the particulate binder, as well as the polymerization conditions.

[0060] [Da / Db] Here, the ratio (Da / Db) of the average particle diameter Da of the particulate binder to the average particle diameter Db of the particulate binder is preferably 1.05 or more, more preferably 1.20 or more, even more preferably 1.40 or more, preferably 3.00 or less, more preferably 2.50 or less, even more preferably 2.00 or less, and particularly preferably 1.75 or less. If Da / Db is equal to or greater than the above lower limit, migration of the particulate binder is suppressed when an electrode mixture layer is formed on a current collector using a slurry composition containing the binder composition, and the particulate binder is present in a well-dispersed state in the electrode mixture layer, thereby further improving the peel strength of the electrode. In addition, the storage characteristics of the secondary battery can be improved. On the other hand, if Da / Db is equal to or less than the above upper limit, the distribution density of the particulate binder in the electrode mixture layer is increased, thereby further improving the peel strength of the electrode.

[0061] <Dispersion medium> The dispersion medium of the binder composition of the present invention is not particularly limited as long as it contains water. For example, the binder composition of the present invention may contain only water as the dispersion medium, or the dispersion medium may be a mixture of water and an organic solvent (e.g., esters, ketones, alcohols). The binder composition of the present invention may contain one type of organic solvent, or may contain two or more types of organic solvents.

[0062] From the viewpoint of further improving the peel strength of the electrode, the proportion of water in the dispersion medium contained in the binder composition of the present invention is preferably 70% by mass or more and 100% by mass or less, more preferably 80% by mass or more and 100% by mass or less, even more preferably 90% by mass or more and 100% by mass or less, and particularly preferably 95% by mass or more and 100% by mass or less, where the mass of the entire dispersion medium is 100% by mass.

[0063] <Other Components> In addition to the particulate binder and dispersion medium described above, the binder composition of the present invention may contain other components, such as an acidic water-soluble polymer, an antioxidant, a preservative, etc. The other components may be used alone or in combination of two or more at any ratio.

[0064] <<Acidic Water-Soluble Polymer>> The acidic water-soluble polymer that can be contained in the binder composition is, for example, produced as a by-product by polymerization from a monomer that is a raw material for the particulate binder when the particulate binder is produced by polymerization. Such an acidic water-soluble polymer is, for example, a polymer that contains an acidic functional group-containing monomer unit and may optionally further contain a monomer unit other than the acidic functional group-containing monomer unit. Examples of acidic functional group-containing monomers that can form the acidic functional group-containing monomer units contained in the acidic water-soluble polymer include those described above in the section "Particulate Binder."

[0065] The weight-average molecular weight of such an acidic water-soluble polymer is preferably 500 or more, more preferably 700 or more, and even more preferably 1,000 or more, and is preferably 20,000 or less, more preferably 15,000 or less, more preferably 8,000 or less, even more preferably 3,500 or less, and particularly preferably 2,000 or less. When the weight-average molecular weight of the acidic water-soluble polymer is equal to or greater than the above-mentioned lower limit, the peel strength of the electrode can be further improved. Furthermore, when the weight-average molecular weight of the acidic water-soluble polymer is equal to or less than the above-mentioned upper limit, the viscosity of the binder composition can be prevented from increasing excessively, thereby improving the tackiness of the binder composition.

[0066] The acidic water-soluble polymer may be in the form of a salt (a salt of the acidic water-soluble polymer). That is, in the present invention, the "acidic water-soluble polymer" also includes the salt of the acidic water-soluble polymer. In addition, in the present invention, a polymer being "water-soluble" means that when 0.5 g of the polymer is dissolved in 100 g of water at a temperature of 25°C, the insoluble content is less than 10 mass%.

[0067] <Properties> <<Mean free volume radius of pores in binder film>> The binder composition of the present invention requires that the mean free volume radius of the pores in the binder film be 0.30 nm or more and 0.50 nm or less. The mean free volume radius of the pores in the binder film is preferably 0.31 nm or more, more preferably 0.32 nm or more, even more preferably 0.33 nm or more, preferably 0.45 nm or less, more preferably 0.40 nm or less, and even more preferably 0.34 nm or less. If the mean free volume radius of the pores in the binder film is 0.30 nm or more, migration of the particulate binder can be suppressed when an electrode mixture layer is formed on a current collector using a slurry composition containing the binder composition, thereby improving the peel strength of the electrode. On the other hand, if the mean free volume radius of the pores in the binder film is 0.50 nm or less, the distribution density of the particulate binder in the electrode mixture layer formed using a slurry composition containing the binder composition can be sufficiently high, thereby improving the peel strength of the electrode.

[0068] The mean free volume radius of the pores in the binder film can be adjusted, for example, by changing the type and amount of monomer used in preparing the particulate binder, as well as the polymerization method and conditions. Specifically, when preparing a particulate binder using a procedure including multistage polymerization, increasing the amount of acidic functional group-containing monomer added in the final stage of the multistage polymerization increases the mean free volume radius of the pores in the binder film, and decreasing the amount decreases the mean free volume radius. Furthermore, by adding the acidic functional group-containing monomer continuously in the final stage of the multistage polymerization, the mean free volume radius of the pores in the binder film increases, and by adding it all at once, the mean free volume radius decreases.

[0069] <<Shear rate 0.01 s －１ The binder composition of the present invention has a solids concentration of 30% by mass, a pH of 8.0, and a shear rate of 0.01 s －１The viscosity (η1) under these conditions is preferably 800 mPa·s or more, more preferably 2,000 mPa·s or more, even more preferably 3,000 mPa·s or more, and particularly preferably 10,000 mPa·s or more, and is preferably 2,000,000 mPa·s or less, more preferably 1,500,000 mPa·s or less, and even more preferably 1,000,000 mPa·s or less. If η1 is equal to or greater than the above lower limit, migration of the particulate binder can be suppressed when forming an electrode mixture layer on a current collector using a slurry composition containing the binder composition, and the particulate binder can be present in a well-dispersed state in the electrode mixture layer. Therefore, the peel strength of the electrode can be further improved. On the other hand, if η1 is equal to or less than the above upper limit, the viscosity of the binder composition can be prevented from increasing excessively, thereby improving the tackiness of the binder composition. The value of η1 can be adjusted by, for example, changing the type and amount of the monomer used to form the particulate binder, the polymerization method and conditions, and the structure of the particulate binder.

[0070] <<Shear rate 1000 s －１ The binder composition of the present invention has a solid content of 30% by mass, a pH of 8.0, and a shear rate of 1000 s －１The viscosity (η2) under these conditions is preferably 10 mPa·s or more, more preferably 20 mPa·s or more, even more preferably 50 mPa·s or more, even more preferably 85 mPa·s or more, particularly preferably 100 mPa·s or more, and preferably 250 mPa·s or less, more preferably 200 mPa·s or less, and even more preferably 150 mPa·s or less. If η2 is equal to or greater than the above lower limit, migration of the particulate binder can be suppressed when forming an electrode mixture layer on a current collector using a slurry composition containing the binder composition, and the particulate binder can be present in a well-dispersed state in the electrode mixture layer. Therefore, the peel strength of the electrode can be further improved. On the other hand, if η2 is equal to or less than the above upper limit, the viscosity of the binder composition can be prevented from increasing excessively, thereby improving the tackiness of the binder composition. The value of η2 can be adjusted by, for example, changing the type and amount of the monomer used to form the particulate binder, the polymerization method and conditions, and the structure of the particulate binder.

[0071] <<η1 / η2>> The ratio of η1 to η2 (η1 / η2) is preferably 25 or more, more preferably 50 or more, even more preferably 100 or more, still more preferably 1,000 or more, particularly preferably 5,000 or more, and is preferably 10,000 or less, more preferably 9,000 or less, and even more preferably 8,300 or less. If η1 / η2 is equal to or greater than the lower limit, the peel strength of the electrode can be further improved. Furthermore, if η1 / η2 is equal to or greater than the upper limit, the storage characteristics of the secondary battery can be improved.

[0072] <<pH>> The pH of the binder composition (pH of the dispersion medium) is preferably 6.0 or higher, more preferably 7.0 or higher, and preferably 10.0 or lower, more preferably 9.0 or lower, and even more preferably 8.0 or lower. When the pH of the binder composition is equal to or higher than the above lower limit, the peel strength of the electrode can be further improved. On the other hand, when the pH of the binder composition is equal to or lower than the above upper limit, the viscosity of the binder composition is prevented from increasing excessively, thereby improving the tackiness of the binder composition. The pH can be adjusted, for example, by adding an alkali species to the binder composition. Examples of alkali species include lithium hydroxide, sodium hydroxide, potassium hydroxide, and aqueous ammonia. Ammonia water is preferred because it is less likely to cause aggregates due to addition shock during alkali neutralization.

[0073] <Preparation of binder composition for non-aqueous secondary battery electrode> The binder composition of the present invention can be prepared by polymerizing, in an emulsion, monomers that are the basis of the structural units contained in the particulate binder. Examples of such a preparation method include a batch emulsion polymerization method, an emulsion (Em) prop method, and a seed polymerization method.

[0074] The batch emulsion polymerization method may be carried out, for example, by the following procedure: Monomers that form the monomer units contained in the particulate binder are mixed with water, an emulsifier, and a polymerization initiator. The mixture (emulsion) is heated to carry out a polymerization reaction. When a predetermined polymerization conversion rate is reached, the mixture is cooled to stop the reaction, thereby obtaining a mixture containing the particulate binder. Unreacted monomers are removed from the mixture. The pH of the mixture is adjusted to fall within the preferred pH range of the dispersion medium described above, and optionally, other components described above are added to obtain an aqueous dispersion as a binder composition. Heating during the polymerization reaction may be carried out, for example, at 40°C or higher, 45°C or higher, 50°C or higher, 55°C or higher, or 60°C or higher, 90°C or lower, 85°C or lower, 80°C or lower, 75°C or lower, or 70°C or lower. Unreacted monomers may be removed from the mixture by, for example, heated vacuum distillation or by blowing in steam.

[0075] The Em Prop method may be performed, for example, by the following procedure: A monomer for forming a core portion (the monomer for forming the polymer (A) described above) is mixed with water, an emulsifier, a polymerization initiator, and optionally a chain transfer agent. The mixture (emulsion) is heated to carry out a polymerization reaction until a predetermined polymerization conversion rate is reached, thereby obtaining a mixture containing a seed particle polymer as the core portion. Next, a monomer for forming a shell portion (the monomer for forming the polymer (C) described above), and optionally an emulsifier and water, are added to the mixture to continue polymerization. Next, a monomer for forming a surface layer portion (the monomer for forming the polymer (B) described above), and optionally an emulsifier and water, are continuously added to the mixture to continue polymerization. When a predetermined polymerization conversion rate is reached, the mixture is cooled to stop the reaction, thereby obtaining a mixture containing a particulate binder. Unreacted monomer is removed from the mixture. The pH of the mixture is adjusted to fall within the preferred pH range of the dispersion medium described above, and optionally, other components described above are added to obtain an aqueous dispersion as a binder composition containing core-shell particles and a particulate binder having a surface layer portion.

[0076] In the seed polymerization method, for example, a seed particle polymer consisting of a polymer containing one or more of the monomer units contained in polymer (A) is mixed with a monomer for forming polymer (A) (excluding that used to form the seed particle polymer), water, an emulsifier, a polymerization initiator, and optionally a chain transfer agent, and a polymerization reaction or the like is carried out in the same manner as above to obtain a mixture containing a seed particle polymer as a core portion. Next, a monomer for forming a shell portion (a monomer for forming polymer (C) described above), and optionally an emulsifier and water, are added to the mixture to continue polymerization. Next, a monomer for forming a surface layer portion (a monomer for forming polymer (B) described above), and optionally an emulsifier and water, are continuously added to the mixture to continue polymerization. When a predetermined polymerization conversion rate is reached, the mixture is cooled to stop the reaction, and a mixture containing a particulate binder is obtained. Unreacted monomer is removed from the mixture. The pH of the mixture is adjusted to fall within the preferred pH range of the dispersion medium described above, and optionally, other components described above are added to obtain an aqueous dispersion as a binder composition containing core-shell particles and a particulate binder having a surface layer portion.

[0077] When the particulate binder has particles composed of a single polymer (A) inside a surface layer containing polymer (B), the binder composition may be prepared, for example, by the following procedure, including two-stage polymerization. First, a monomer for forming polymer (A) is mixed with water, an emulsifier, a chain transfer agent, and a polymerization initiator. The mixture is heated to carry out a polymerization reaction until a predetermined polymerization conversion rate is reached, thereby forming particles composed of polymer (A). Next, a monomer for forming polymer (B), and optionally an emulsifier and water, are continuously added to the reaction solution to continue polymerization. When a predetermined polymerization conversion rate is reached, the mixture is cooled to terminate the reaction, thereby obtaining a mixture containing the particulate binder. Unreacted monomer is removed from the mixture. The pH of the mixture is adjusted to be within the preferred pH range of the dispersion medium described above, and optionally, other components described above are added.

[0078] When the particulate binder has core-shell particles composed of a core portion made of polymer (A) and a shell portion made of polymer (C) inside a surface layer portion containing polymer (B), the binder composition may be prepared, for example, by the following procedure including three-stage polymerization. First, in the first-stage polymerization, a monomer for forming polymer (A) is mixed with water, an emulsifier, a chain transfer agent, and a polymerization initiator. The mixture is heated and a polymerization reaction is carried out until a predetermined polymerization conversion rate is reached, thereby forming particles made of polymer (A). Next, in the second-stage polymerization, a monomer for forming polymer (C), and optionally an emulsifier and water, are added to the reaction solution to continue the polymerization. When the predetermined polymerization conversion rate is reached, the reaction is stopped by cooling to obtain an aqueous polymer dispersion containing core-shell particles composed of a core portion made of polymer (A) and a shell portion made of polymer (C), and water. Next, in the third-stage polymerization, a monomer for forming polymer (B), and optionally an emulsifier and water, are continuously added to the reaction solution to continue the polymerization. After each polymerization stage, unreacted monomers may be removed from the reaction solution. Optionally, the pH of the reaction solution after the reaction is adjusted to fall within the preferred pH range of the dispersion medium described above, and optionally, other components described above may be added.

[0079] Here, from the viewpoint of easily keeping the average free volume radius of the pores of the binder film within the above-mentioned predetermined range, it is preferable to continuously add the acidic functional group-containing monomer used to form the polymer (B).

[0080] In addition, from the viewpoint of easily setting the average free volume radius of the pores of the binder film within the above-mentioned predetermined range, the polymerization temperature when forming the polymer (B) is preferably 75°C or higher and 90°C or lower.

[0081] Examples of emulsifiers used in preparing the binder composition include alkyldiphenyletherdisulfonic acid, dodecylbenzenesulfonic acid, lauryl sulfate, or salts thereof (e.g., potassium salts, sodium salts). Among these, alkyldiphenyletherdisulfonic acid salts are preferred. One type of emulsifier may be used alone, or two or more types may be used in combination at any ratio. The amount of emulsifier added is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, relative to 100 parts by mass of the total amount of monomers of the polymer constituting the particulate binder.

[0082] The polymerization initiator is not particularly limited, and examples thereof include known polymerization initiators such as potassium persulfate, sodium persulfate, n-butyllithium, and ammonium persulfate. One type of polymerization initiator may be used alone, or two or more types may be used in combination at any ratio. The amount of the polymerization initiator added is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, relative to 100 parts by mass of the total amount of the monomers of the polymer constituting the particulate binder.

[0083] Furthermore, the chain transfer agent is not particularly limited, and examples thereof include known chain transfer agents such as α-methylstyrene dimer, tert-dodecyl mercaptan, and 3-mercapto-1,2-propanediol. The amount of the chain transfer agent added is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, relative to 100 parts by mass of the total amount of the polymer monomers constituting the particulate binder.

[0084] (Slurry Composition for Non-Aqueous Secondary Battery Electrode) The slurry composition of the present invention is a composition used to form an electrode mixture layer of an electrode, and contains an electrode active material and the binder composition of the present invention described above, and optionally further contains components other than the above components (hereinafter referred to as "other components"). That is, the slurry composition of the present invention usually contains an electrode active material, the particulate binder described above, and a dispersion medium containing water, and optionally further contains other components. Furthermore, since the slurry composition of the present invention contains the binder composition described above, it is possible to ensure that the electrode exhibits excellent peel strength. Note that, as an example, the following description will be given of 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, but the present invention is not limited to the following example.

[0085] <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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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. Among these, silicon-containing active materials (silicon-based negative electrode active materials) are preferred as metal-based negative electrode active materials. This is because the use of silicon-based negative electrode active materials can increase the capacity of lithium-ion secondary batteries.

[0090] Examples of silicon-based negative electrode active materials include silicon (Si), silicon-containing alloys, SiO, and SiO ｘand 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.

[0091] <Binder composition> The binder composition of the present invention contains the above-mentioned specific particulate binder and a dispersion medium containing water, and optionally further contains other components. The content of the above-mentioned specific particulate binder in the slurry composition can be 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.

[0092] <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.

[0093] <Preparation of Slurry Composition for Non-Aqueous Secondary Battery Electrode> The method for preparing the slurry composition is not particularly limited. For example, the binder composition, the electrode active material, and other components used as needed can be mixed in the presence of an aqueous phase (aqueous medium) contained in the binder composition to prepare the slurry composition. The mixing method is not particularly limited, and mixing can be performed using a commonly used stirrer or disperser.

[0094] (Electrode for Non-Aqueous Secondary Battery) The electrode for a non-aqueous secondary battery of the present invention includes an electrode mixture layer formed using the above-described slurry composition for a non-aqueous secondary battery electrode. Therefore, the electrode mixture layer is composed of a dried product of the above-described slurry composition, and typically contains an electrode active material and components derived from a particulate binder, and optionally further contains other components. The components contained in the electrode mixture layer are those contained in the above-described slurry composition for a non-aqueous secondary battery electrode, and the preferred abundance ratio of each component is the same as the preferred abundance ratio of each component in the slurry composition. Furthermore, although the particulate binder is present in particulate form in the slurry composition, it may be in particulate form or any other shape in the electrode mixture layer formed using the slurry composition. Furthermore, the non-aqueous secondary battery electrode of the present invention has an electrode mixture layer formed using the above-described slurry composition for a non-aqueous secondary battery electrode, and therefore has excellent peel strength.

[0095] <Method of Forming an Electrode> The electrode mixture layer of the electrode of the present invention can be formed, for example, using the following methods: 1) A method of applying the slurry composition of the present invention to the surface of a current collector and then drying it; 2) A method of immersing a current collector in the slurry composition of the present invention and then drying it; and 3) A method of applying the slurry composition of the present invention to a release substrate and drying it to produce an electrode mixture layer, and then transferring the resulting electrode mixture layer to the surface of a current collector. Among these, method 1) is particularly preferred because it makes it easy to control the layer thickness of the electrode mixture layer. Method 1) specifically includes a step of applying the slurry composition to a current collector (application step) and a step of drying the slurry composition applied to the current collector to form an electrode mixture layer on the current collector (drying step).

[0096] <<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. In this case, the slurry composition may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector after application and before drying can be appropriately set depending on the thickness of the electrode mixture layer obtained by drying.

[0097] Here, the current collector to which the slurry composition is applied is made of a material that is electrically conductive and electrochemically durable. Specifically, the current collector may be made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. Note that one of the above materials may be used alone, or two or more may be used in combination in any ratio.

[0098] <<Drying Step>> The method for drying the slurry composition on the current collector is not particularly limited and any known method can be used, for example, a drying method using warm air, hot air, or low-humidity air, a vacuum drying method, or a drying method using irradiation with infrared rays or electron beams, etc. By drying the slurry composition on the current collector in this manner, an electrode mixture layer can be formed on the current collector, and an electrode including the current collector and the electrode mixture layer can be obtained.

[0099] After the drying step, the electrode mixture layer may be subjected to a pressure treatment using a mold press, a roll press, or the like. The pressure treatment improves the adhesion between the electrode mixture layer and the current collector and further increases the density of the resulting electrode mixture layer. In addition, when the electrode mixture layer contains a curable polymer, it is preferable to cure the polymer after the electrode mixture layer is formed.

[0100] (Nonaqueous secondary battery) The nonaqueous secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolyte, and a separator, and uses the above-described nonaqueous secondary battery electrode of the present invention as at least one of the positive electrode and the negative electrode. Note that, as an example, the following description will be given of a case where the secondary battery is a lithium ion secondary battery, but the present invention is not limited to the following example.

[0101] <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.

[0102] <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. ３ SO ３ Li, C ４ F ９ SO ３ Li, CF ３ COOLi, (CF ３ CO) ２ NLi, (CF ３ SO ２ ) ２ NLi, (C ２ F ５ SO ２ Among them, LiPF is the most popular because it is easily soluble in solvents and shows a high degree of dissociation. ６ , LiClO ４ , C.F. ３ SO３ 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.

[0103] 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 suitable. esters such as γ-butyrolactone and methyl formate are also suitable. Ethers such as 1,2-dimethoxyethane and tetrahydrofuran are also suitable. Sulfur-containing compounds such as sulfolane and dimethyl sulfoxide are also suitable. Mixtures of these solvents may also be used. Among these, carbonates are preferred due to their high dielectric constant and wide stable potential range. Generally, the lower the viscosity of the solvent used, the higher the lithium ion conductivity. Therefore, the lithium ion conductivity can be adjusted by the type of solvent. The concentration of the electrolyte in the electrolyte can be adjusted as appropriate. Known additives may also be added to the electrolyte.

[0104] <Separator> The separator is not particularly limited, and for example, the separator 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.

[0105] <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. In the non-aqueous secondary battery of the present invention, the above-described non-aqueous secondary battery electrode is used as at least one of the positive electrode and negative electrode, preferably the negative electrode. The non-aqueous secondary battery of the present invention may be provided with an overcurrent prevention element such as a fuse or a PTC element, an expanded metal, a lead plate, or the like, as necessary to prevent internal pressure buildup, overcharging and overdischarging, and the like within the secondary battery. 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.

[0106] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, the terms "%" and "parts" used to represent amounts are based on mass unless otherwise specified. In addition, 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 corresponds to the ratio (feed ratio) of that certain monomer to all the monomers used in the polymerization of the polymer, unless otherwise specified. In the examples and comparative examples, the average free volume radius of the pores of the binder film, the viscosity (η1 and η2) of the binder composition, the average particle diameters Da and Db of the particulate binder, the peel strength of the electrode, and the storage characteristics and cycle characteristics of the lithium-ion secondary battery were evaluated using the following methods.

[0107] <Mean Free Volume Radius> Aqueous ammonia was added as needed to the negative electrode binder compositions prepared in the Examples and Comparative Examples, and the pH of the binder composition was adjusted to 8.0. The pH-adjusted binder composition (solid content concentration 30%) was applied to a polyester release film (manufactured by PANAC Corporation, product name "PET125SG1") using a table coater at a coating speed of 50 mm / sec, and dried in a drying oven at 80°C for 20 minutes. The binder film was further dried under vacuum at 100°C for 10 hours to form a binder film (thickness: 50 nm) on the release film. The binder film was peeled from the release film and attached to a 15 mm x 15 mm square Si wafer. After vacuum degassing at room temperature, positron annihilation lifetime measurements were performed under the following conditions. Measurement device: Fuji IMBAC Co., Ltd., product name "Small Positron Beam Generator PALS-200A" Positron source: ２２ Na-based positron beam gamma ray detector: BaF ２ Scintillator + high-speed electron multiplier tube (manufactured by Anton Paar) Instrument constant: 245-257 ps, 24.55 ps / ch Beam intensity: 5 keV Measurement atmosphere: vacuum Total counts: approximately 5,000,000 counts Three-component analysis was performed on the positron annihilation lifetime curve obtained by the above measurement using the nonlinear least squares method, and τ1, τ2, and τ3 were assigned in descending order of annihilation lifetime. The mean free volume radius was then calculated from the longest mean annihilation lifetime τ3. <Viscosity> The solids concentration of the negative electrode binder compositions prepared in the Examples and Comparative Examples was adjusted to 30% by adding water or removing moisture through concentration. Aqueous ammonia was added to the binder composition with the adjusted solids concentration as needed to adjust the pH of the binder composition to 8.0. The viscosity of the binder composition after adjusting the solids concentration and pH obtained above at each shear rate was measured using a rotational rheometer (manufactured by Anton Paar, model "MCR302"), and the viscosity was measured at a shear rate of 0.01 s. －１ The viscosity at the shear rate of 1000 s is η1 (mPa s). －１The viscosity at this time was defined as η2 (mPa s). The measurement conditions were as follows. Jig used: CP50-1 (φ50 mm parallel plate) Measurement temperature: 25°C <Average particle diameter Da> Using a particle size distribution measurement device (manufactured by Otsuka Electronics Co., Ltd., model "nanoSAQLA") that uses dynamic light scattering as its measurement principle, the particle size distribution (volume basis) of the negative electrode binder compositions prepared in the examples and comparative examples was measured, and the cumulant average particle diameter obtained by cumulant analysis was defined as the average particle diameter Da. The measurement conditions for the dynamic light scattering method were as follows. Dispersion medium: ion-exchanged water Measurement temperature: 25±1°C Measurement concentration (solid content concentration): 0.5% Scattering angle: 168.8° Light source laser wavelength: 660 nm <Average particle diameter Db> Using a particle size distribution measurement device (manufactured by Beckman Coulter, Inc., product name "LS13 320 XR") based on the laser diffraction scattering method, the particle size distribution (volume basis) of the negative electrode binder compositions prepared in the Examples and Comparative Examples was measured, and the particle diameter (D50) at which the cumulative volume calculated from the smallest diameter side reached 50% in the measured particle size distribution was defined as the average particle diameter Db. <Peel strength> The negative electrodes (negative electrodes A and B) prepared in the Examples and Comparative Examples were cut into rectangular shapes measuring 100 mm in length and 10 mm in width to prepare test specimens. The test specimen was placed with the surface of the negative electrode composite layer facing down, and cellophane tape was attached to the surface of the negative electrode composite layer. The cellophane tape used was that specified in JIS Z1522. The cellophane tape was fixed to a test table. Then, one end of the current collector was pulled vertically upward at a pulling rate of 50 mm / min, and the stress when peeled was measured. This measurement was performed three times, and the average value was calculated. This average value was used as the peel strength and evaluated according to the following criteria: A: Peel strength of 10 N / m or more; B: Peel strength of 8 N / m or more but less than 10 N / m; C: Peel strength of 6 N / m or more but less than 8 N / m; D: Peel strength of less than 6 N / m. <Storage Characteristics> After injecting the electrolyte, the lithium ion secondary batteries A prepared in the Examples and Comparative Examples were left at 25°C for 5 hours. Next, they were charged at 25°C and a constant current of 0.2 C to a cell voltage of 3.65 V, and then aged at 60°C for 12 hours. Then, they were discharged at 25°C and a constant current of 0.2 C to a cell voltage of 3.00 V.Thereafter, constant current (CC)-constant voltage (CV) charging (upper limit cell voltage 4.20V) was performed using a 0.2C constant current method, and CC discharge was performed to 3.00V using a 0.2C constant current method. This 0.2C charge-discharge cycle was repeated three times. Thereafter, one cycle of charge-discharge operation was performed at a temperature of 25°C, a cell voltage of 4.20-3.00V, and a charge-discharge rate of 1.0C, and the discharge capacity at this time was designated as the initial capacity X1. Thereafter, a temperature of 25°C, a 0.2C constant current method was used, and constant current (CC)-constant voltage (CV) charging (upper limit cell voltage 4.20V) was performed to fully charge the battery, and the battery was stored for 30 days at a temperature of 60°C. After storage, one cycle of charge-discharge operation was performed at a temperature of 25°C, a cell voltage of 4.20-3.00V, and a charge-discharge rate of 1.0C, and the discharge capacity at this time was designated as the post-storage capacity X2. Using the discharge capacities X1 and X2, the capacity change rate, ΔC = (X2 / X1) × 100 (%), was calculated and evaluated according to the following criteria. A larger value of the capacity change rate ΔC indicates better storage characteristics. A: ΔC is 96% or more. B: ΔC is 90% or more but less than 96%. C: ΔC is less than 90%. <Cycle Characteristics> After injecting the electrolyte, the lithium ion secondary batteries B prepared in the Examples and Comparative Examples were left to stand at 25°C for 5 hours. Next, they were charged at 25°C and a constant current of 0.2 C to a cell voltage of 3.65 V, and then aged at 60°C for 12 hours. Then, they were discharged at 25°C and a constant current of 0.2 C to a cell voltage of 3.00 V. Subsequently, constant current (CC)-constant voltage (CV) charging (upper limit cell voltage 4.20 V) was performed using a 0.2 C constant current method, followed by CC discharge to 3.00 V using a 0.2 C constant current method. This 0.2 C charge-discharge cycle was repeated three times. Subsequently, 100 cycles of charge-discharge were performed at a cell voltage of 4.20-3.00 V and a charge-discharge rate of 1.0 C in an environment of 25°C. The discharge capacity of the first cycle was defined as X3, and the discharge capacity of the 100th cycle as X4. Using the discharge capacities X3 and X4, the capacity change rate, ΔC' = (X3 / X4) × 100 (%), was calculated and evaluated according to the following criteria. The larger the value of this capacity change rate ΔC', the better the cycle characteristics. A: ΔC' is 91% or more; B: ΔC' is 86% or more but less than 91%; C: ΔC' is less than 86%.

[0108] Example 1 Preparation of a Binder Composition for Negative Electrodes First-Stage Polymerization 20.0 parts of styrene as an aromatic vinyl monomer, 73.0 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 2.0 parts of alkyl diphenyl ether disulfonate as an emulsifier, 143.0 parts of ion-exchanged water, 0.1 parts of tert-dodecyl mercaptan as a chain transfer agent, and 0.3 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer, and after thorough stirring, the mixture was heated to 55°C to initiate polymerization and allowed to react for 10 hours. Second-Stage Polymerization 4.0 parts of styrene as an aromatic vinyl monomer were then added to the polymerization system, which was then heated to 65°C and allowed to react for an additional 6 hours. Third-Stage Polymerization The pressure vessel was then heated to 85°C, and 3.0 parts of methacrylic acid as an acidic functional group-containing monomer was continuously added to the polymerization system over 1 hour, followed by an additional 8 hours of reaction. Thereafter, unreacted monomers were removed by heating and vacuum distillation. As a result, an aqueous dispersion of particulate binder was obtained, having core-shell particles composed of a core portion made of polymer (A) formed in the first polymerization stage and a shell portion made of polymer (C) formed in the second polymerization stage, inside a surface layer portion containing polymer (B) formed in the third polymerization stage. [pH adjustment] The obtained aqueous dispersion of particulate binder was neutralized with ammonia water, and the pH was adjusted to 7.0 to obtain a binder composition for a negative electrode. Using this binder composition, the average free volume radius, η1, η2, Da, and Db were measured. The results are shown in Table 1. <Preparation of slurry composition for negative electrode> [Slurry composition A for negative electrode] Artificial graphite (tap density: 0.85 g / cm) was added as a negative electrode active material to a planetary mixer equipped with a disperser. ３A mixture was obtained by adding 100 parts of a 2% aqueous solution of carboxymethyl cellulose (manufactured by TIMCAL, product name "Super C65") as a conductive material, 1 part of carbon black (manufactured by TIMCAL, product name "Super C65") as a conductive material, and 1.2 parts of a 2% aqueous solution of carboxymethyl cellulose (manufactured by Daicel Corporation, product name "Daicel 2200") as a thickener, in terms of solid content. The resulting mixture was adjusted to a solid content of 60% with ion-exchanged water and then mixed at 25°C for 60 minutes. Next, the solid content was adjusted to 52% with ion-exchanged water, and then mixed for an additional 15 minutes at 25°C to obtain a mixed solution. 2.0 parts of the negative electrode binder composition prepared above, in terms of solid content, and ion-exchanged water were added to the resulting mixed solution, and the final solid content was adjusted to 48%. After further mixing for 10 minutes, the mixture was degassed under reduced pressure to obtain a negative electrode slurry composition A with good fluidity. [Negative electrode slurry composition B] A negative electrode slurry composition B was obtained in the same manner as the negative electrode slurry composition A, except that the amount of the negative electrode binder composition added was changed from 2.0 parts to 1.5 parts in terms of solid content equivalent. <Formation of negative electrode> [Negative electrode A] The negative electrode slurry composition A obtained above was coated on a 15 μm-thick copper foil current collector using a comma coater at a speed of 1.2 m / min until the coating weight after drying was 10.5 mg / cm ２ The copper foil was dried by conveying it at a speed of 1.2 m / min through an oven at 120°C for 1 minute and then through an oven at 130°C for 1 minute. The obtained negative electrode blank was rolled with a roll press to reduce the density of the negative electrode composite layer to 1.70 g / cm. ３ Negative electrode B (density of negative electrode mixture layer: 1.70 g / cm 3) was obtained in the same manner as for negative electrode A, except that negative electrode slurry composition B was used instead of negative electrode slurry composition A. ３ The peel strength of each of the negative electrodes A and B was evaluated. The results are shown in Table 1. <Formation of Positive Electrode> A LiCoO film with a median diameter of 12 μm was used as the positive electrode active material. ２100 parts of the above, 2 parts of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., product name "HS-100") as a conductive material, 2 parts of polyvinylidene fluoride (manufactured by Kureha Corporation, product name "#7208") as a binder, in terms of solid content, and N-methylpyrrolidone as a solvent were mixed to a total solids concentration of 70%. These were mixed using a planetary mixer to obtain a positive electrode slurry composition. The obtained positive electrode slurry composition was coated using a comma coater on a 20 μm thick aluminum foil current collector so that the basis weight after drying was 23 mg / cm ２ The aluminum foil was then coated with the coating and dried so that the density of the positive electrode composite layer became 4.0 g / cm. This drying was performed by conveying the aluminum foil at a speed of 0.5 m / min through an oven at 60°C for 2 minutes. Thereafter, the aluminum foil was heat-treated at 120°C for 2 minutes to obtain a positive electrode blank. The positive electrode blank was then rolled with a roll press to obtain a positive electrode composite layer having a density of 4.0 g / cm. ３ A positive electrode of 1000 W was obtained. <Preparation of Separator> A single-layer polypropylene separator (manufactured by Celgard, product name "Celgard 2500") was prepared as a separator made of a separator substrate. <Preparation of Lithium-Ion Secondary Battery> [Lithium-Ion Secondary Battery A] A laminate was obtained by interposing the pressed positive electrode and pressed negative electrode A prepared as described above and a separator (a 20 μm thick polypropylene microporous membrane) in a separator / positive electrode / separator / negative electrode configuration. Next, the electrode and separator laminate was wound around a core with a diameter of 20 mm to obtain a wound body including a positive electrode, a separator, and a negative electrode. Subsequently, the obtained wound body was compressed in one direction at a speed of 10 mm / sec until it reached a thickness of 4.5 mm, thereby obtaining a flattened body. The obtained flattened body was elliptical in plan view, and its major axis / minor axis ratio (major axis / minor axis) was 7.7. In addition, a non-aqueous electrolyte (LiPF with a concentration of 1.0 M) ６A solution (solvent): a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (mass ratio), further containing 2 volume% vinylene carbonate (VC) as an additive, was prepared. Next, the flat body was housed in an aluminum laminate case together with the nonaqueous electrolyte solution. After connecting the negative and positive electrode leads to the designated locations, the opening of the laminate case was thermally sealed to produce a laminated lithium-ion secondary battery A as a nonaqueous secondary battery. The resulting lithium-ion secondary battery A was a pouch-shaped battery measuring 35 mm wide, 48 mm high, and 5 mm thick, with a nominal capacity of 700 mAh. The storage characteristics of this lithium-ion secondary battery A were evaluated. The results are shown in Table 1. [Lithium-ion secondary battery B] A lithium-ion secondary battery B (pouch-shaped, 35 mm wide x 48 mm high x 5 mm thick; nominal capacity: 700 mAh) was fabricated in the same manner as the lithium-ion secondary battery A described above, except that negative electrode B was used instead of negative electrode A. The cycle characteristics of this lithium-ion secondary battery B were evaluated. The results are shown in Table 1.

[0109] Example 2 A negative electrode binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that, when preparing the negative electrode binder composition, the amount of styrene added in the first polymerization stage was changed from 20.0 parts to 16.0 parts, and the amount of styrene added in the second polymerization stage was changed from 4.0 parts to 8.0 parts. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0110] Example 3 A negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a negative electrode binder composition prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. <Preparation of Negative Electrode Binder Composition> [First-Stage Polymerization] A 5 MPa pressure vessel equipped with a stirrer was charged with 10.0 parts of n-butyl acrylate as a (meth)acrylic acid ester monomer, 13.5 parts of styrene as an aromatic vinyl monomer, 71.5 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 0.6 parts of alkyl diphenyl ether disulfonate as an emulsifier, 140.0 parts of ion-exchanged water, 0.1 parts of tert-dodecyl mercaptan as a chain transfer agent, and 0.1 parts of potassium persulfate as a polymerization initiator. After thorough stirring, the mixture was heated to 55°C to initiate polymerization and allowed to react for 10 hours. The pressure vessel was then heated to 65°C and allowed to react for another 6 hours. [Second-stage polymerization] The pressure vessel was then heated to 85°C, and 5.0 parts of methacrylic acid as an acidic functional group-containing monomer was continuously added to the polymerization system over 2 hours, followed by another 6-hour reaction. The unreacted monomer was then removed by heated, reduced-pressure distillation to obtain an aqueous dispersion of particulate binder. As a result, an aqueous dispersion of particulate binder was obtained, having particles made of the polymer (A) formed in the first-stage polymerization inside a surface layer containing the polymer (B) formed in the second-stage polymerization. [pH adjustment] The obtained aqueous dispersion of particulate binder was neutralized with ammonia water, and the pH was adjusted to 7.0 to obtain a binder composition for a negative electrode.

[0111] Example 4 A negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a negative electrode binder composition prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. <Preparation of Negative Electrode Binder Composition> [First-Stage Polymerization] A 5 MPa pressure vessel equipped with a stirrer was charged with 74.0 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 23.0 parts of acrylonitrile as a nitrile group-containing monomer, 2.0 parts of alkyl diphenyl ether disulfonate as an emulsifier, 143.0 parts of ion-exchanged water, 0.1 parts of tert-dodecyl mercaptan as a chain transfer agent, and 0.3 parts of potassium persulfate as a polymerization initiator. After thorough stirring, the mixture was heated to 55°C to initiate polymerization and allowed to react for 10 hours. The pressure vessel was then heated to 65°C, and the reaction was allowed to continue for an additional 6 hours. [Second-stage polymerization] The pressure vessel was then heated to 85°C, and 3.0 parts of methacrylic acid as an acidic functional group-containing monomer was continuously added to the polymerization system over 1 hour, followed by a further 8-hour reaction. The unreacted monomer was then removed by heated vacuum distillation to obtain an aqueous dispersion of particulate binder. As a result, an aqueous dispersion of particulate binder was obtained, containing particles of the polymer (A) formed in the first-stage polymerization inside a surface layer containing the polymer (B) formed in the second-stage polymerization. [pH adjustment] The obtained aqueous dispersion of particulate binder was neutralized with aqueous ammonia, and the pH was adjusted to 7.0 to obtain a binder composition for a negative electrode.

[0112] Example 5 A negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a negative electrode binder composition prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. <Preparation of negative electrode binder composition> [First-stage polymerization] In a 5 MPa pressure vessel equipped with a stirrer, 76.0 parts of n-butyl acrylate and 2.75 parts of methyl methacrylate as (meth)acrylic acid ester monomers, 1.0 parts of methacrylic acid as an acidic functional group-containing monomer, 1.0 parts of acrylonitrile as a nitrile group-containing monomer, 1.2 parts of N-methylolacrylamide and 1.0 parts of allyl glycidyl ether as crosslinkable monomers, 0.3 parts of alkyl diphenyl ether disulfonate as an emulsifier, 300.0 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator were added, and the mixture was thoroughly stirred, and then heated to 70 ° C. to initiate polymerization, and the mixture was allowed to react for 4 hours. [Second-stage polymerization] Next, 13.8 parts of styrene as an aromatic vinyl monomer and 0.25 parts of methyl methacrylate as a (meth)acrylic acid ester monomer were added to the polymerization system within 1 hour of addition time. After the addition was completed, the pressure vessel was heated to 80°C and the reaction was continued for another 2 hours. [Third-stage polymerization] The pressure vessel was then heated to 85°C, and 3.0 parts of methacrylic acid as an acidic functional group-containing monomer was continuously added to the polymerization system over 1 hour, followed by a further reaction for 6 hours. Unreacted monomers were then removed by heated vacuum distillation to obtain an aqueous dispersion of particulate binder. As a result, an aqueous dispersion of particulate binder was obtained, having core-shell particles composed of a core portion made of polymer (A) formed in the first-stage polymerization and a shell portion made of polymer (C) formed in the second-stage polymerization, inside a surface layer containing polymer (B) formed in the third-stage polymerization. [pH adjustment] The obtained aqueous dispersion of particulate binder was neutralized with ammonia water to adjust the pH to 8.0, thereby obtaining a binder composition for a negative electrode.

[0113] Example 6 A negative electrode binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that, during the preparation of the negative electrode binder composition, the amount of styrene added in the first polymerization stage was changed from 20.0 parts to 15.0 parts, the amount of 1,3-butadiene added in the first polymerization stage was changed from 73.0 parts to 51.0 parts, and the amount of methacrylic acid added in the third polymerization stage was changed from 3.0 parts to 30.0 parts. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0114] Comparative Example 1 A negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a negative electrode binder composition prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2. <Preparation of Negative Electrode Binder Composition> A 5 ​​MPa pressure vessel equipped with a stirrer was charged with 1.0 part of 2-hydroxyethyl acrylate as a (meth)acrylic acid ester monomer, 3.8 parts of itaconic acid as an acidic functional group-containing monomer, 62.0 parts of styrene as an aromatic vinyl monomer, 33.2 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 0.4 parts of alkyl diphenyl ether disulfonate as an emulsifier, 150.0 parts of ion-exchanged water, 0.1 parts of tert-dodecyl mercaptan as a chain transfer agent, and 1.0 part of potassium persulfate as a polymerization initiator. The mixture was thoroughly stirred and then heated to 55°C to initiate polymerization, and allowed to react for 10 hours. Thereafter, unreacted monomers were removed by heating and distillation under reduced pressure to obtain an aqueous dispersion of a particulate binder. [pH Adjustment] The obtained aqueous dispersion of a particulate binder was neutralized with ammonia water to adjust the pH to 8.0 to obtain a binder composition for a negative electrode.

[0115] (Comparative Example 2) When preparing the binder composition for a negative electrode, the amount of styrene added in the first polymerization stage was changed from 20.0 parts to 11.0 parts, the amount of 1,3-butadiene added in the first polymerization stage was changed from 73.0 parts to 33.0 parts, and the amount of methacrylic acid added in the third polymerization stage was changed from 3.0 parts to 52.0 parts. Except for this, a binder composition for a negative electrode, a slurry composition for a negative electrode, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1. Then, evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0116] Comparative Example 3 A negative electrode binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that, during the preparation of the negative electrode binder composition, the amount of 1,3-butadiene added in the first polymerization stage was changed from 73.0 parts to 75.0 parts, and the amount of methacrylic acid added in the third polymerization stage was changed from 3.0 parts to 1.0 part. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

[0117] Comparative Example 4 A negative electrode binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that, when preparing the negative electrode binder composition, the amount of 1,3-butadiene added in the first polymerization stage was changed from 73.0 parts to 74.0 parts, and the amount of methacrylic acid added in the third polymerization stage was changed from 3.0 parts to 2.0 parts. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

[0118] Comparative Example 5 A negative electrode binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that, during the preparation of the negative electrode binder composition, the addition method of 3.0 parts of methacrylic acid in the third polymerization stage was changed from continuous addition to lump addition. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

[0119] Comparative Example 6 A negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a negative electrode binder composition prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2. <Preparation of Negative Electrode Binder Composition> [Step of Preparing Block Copolymer Solution] 233.3 kg of cyclohexane, 54.2 mmol of N,N,N',N'-tetramethylethylenediamine (TMEDA), and 30.0 kg of styrene as an aromatic vinyl monomer were added to a pressure-resistant reactor. While stirring these at 40°C, 1806.5 mmol of n-butyllithium as a polymerization initiator was added, and polymerization was carried out for 1 hour while the temperature was raised to 50°C. The polymerization conversion of styrene was 100%. Subsequently, 70.0 kg of 1,3-butadiene as an aliphatic conjugated diene monomer was continuously added to the pressure-resistant reactor over 1 hour while controlling the temperature to maintain a temperature of 50 to 60°C. After the addition of 1,3-butadiene was completed, the polymerization reaction was continued for another 1 hour. The polymerization conversion of 1,3-butadiene was 100%. Next, 722.6 mmol of dichlorodimethylsilane as a coupling agent was added to the pressure-resistant reactor, and a coupling reaction was carried out for 2 hours to form a styrene-butadiene coupled block copolymer. Thereafter, 3612.9 mmol of methanol was added to the reaction solution and mixed thoroughly to deactivate the active terminals. Next, 100 parts of this reaction solution (containing 30.0 parts of the polymer component) were mixed with 0.05 parts of 4-[[4,6-bis(octylthio)-1,3,5-triazin-2-yl]amino]-2,6-di-tert-butylphenol as a hindered phenol-based antioxidant and 0.09 parts of 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane as a phosphite-based antioxidant. The resulting mixed solution was gradually added dropwise to warm water at 85 to 95°C to volatilize the solvent, thereby obtaining a precipitate. The precipitate was then pulverized and dried with hot air at 85°C to recover a dried product containing the block copolymer. The recovered dried product was then dissolved in cyclohexane to prepare a block copolymer solution having a block copolymer concentration of 5.0%.[Emulsification Step] Sodium alkylbenzene sulfonate was dissolved in ion-exchange water to prepare a 0.15% aqueous solution. Then, 1,000 g of the resulting block copolymer solution and 1,400 g of the resulting aqueous solution were placed in a tank and premixed by stirring. Subsequently, the premix was transferred from the tank to a high-pressure emulsifying disperser "LAB1000" (manufactured by SPXFLOW) using a metering pump and circulated (number of passes: 5) to obtain an emulsion by phase inversion of the premix. Next, cyclohexane in the resulting emulsion was distilled off under reduced pressure using a rotary evaporator. The distilled emulsion was then centrifuged at 7,000 rpm for 10 minutes in a centrifuge (manufactured by Hitachi Koki Co., Ltd., product name "Himac CR21N"), and the upper layer was removed for concentration. Finally, the upper layer was filtered through a 100-mesh wire mesh to obtain an aqueous dispersion (block copolymer latex) containing particulated block copolymers (core particles). [Grafting Step] The obtained block copolymer latex was diluted with distilled water to a ratio of 850 parts water to 100 parts block copolymer (solids equivalent). The diluted block copolymer latex was then placed in a nitrogen-substituted polymerization reactor equipped with a stirrer and heated to 30°C with stirring. In a separate vessel, 5.6 parts of methyl methacrylate as a (meth)acrylic acid ester monomer, 5.6 parts of methacrylic acid as an acidic functional group-containing monomer, and 100.8 parts of distilled water were mixed to prepare a diluted solution. This diluted solution was added over 30 minutes to a polymerization reactor heated to 30°C, resulting in 5.6 parts methyl methacrylate and 5.6 parts methacrylic acid per 100 parts block copolymer. In a separate vessel, a solution containing 7 parts distilled water and 0.01 parts ferrous sulfate (manufactured by Chubu Chelest Co., Ltd., trade name "Frost Fe") as a reducing agent was prepared. The obtained solution was added to a polymerization reaction vessel, and then 0.5 parts of 1,1,3,3-tetramethylbutyl hydroperoxide (manufactured by NOF Corporation, trade name "Perocta H") as an oxidizing agent was added. The mixture was reacted at 30°C for 1 hour and then at 70°C for a further 2 hours.The resulting aqueous dispersion of the particulate binder was neutralized with aqueous ammonia to adjust the pH to 7.0, thereby obtaining a binder composition for a negative electrode.

[0120] In Tables 1 and 2 shown below, "BA" represents n-butyl acrylate, "MMA" represents methyl methacrylate, "β-HEA" represents 2-hydroxyethyl acrylate, "MAA" represents methacrylic acid, "IA" represents itaconic acid, "ST" represents styrene, "BD" represents 1,3-butadiene, "AN" represents acrylonitrile, "NMA" represents N-methylolacrylamide, and "AGE" represents allyl glycidyl ether. In Tables 1 and 2, "Da / Db" is expressed as a value rounded to two decimal places, and "η1 / η2" is expressed as a value rounded to one decimal place.

[0121]

[0122]

[0123] Table 1 shows that electrodes with excellent peel strength were produced in Examples 1 to 6, which used binder compositions containing a particulate binder and water and in which the mean free volume radius of the pores in the binder film was within a predetermined range. On the other hand, Table 2 shows that the peel strength of the electrodes was reduced compared to Examples 1 to 6 in Comparative Examples 1 to 6, which used binder compositions in which the mean free volume radius of the pores in the binder film was outside the predetermined range.

[0124] The present invention provides a binder composition for a non-aqueous secondary battery electrode capable of forming a non-aqueous secondary battery electrode having excellent peel strength, a slurry composition for a non-aqueous secondary battery electrode containing the binder composition, a non-aqueous secondary battery electrode having excellent peel strength, and a non-aqueous secondary battery including the non-aqueous secondary battery electrode.

Claims

1. A binder composition for a non-aqueous secondary battery electrode, comprising a particulate binder and water, wherein the binder composition for a non-aqueous secondary battery electrode is adjusted to a pH of 8.0 and a binder film formed therefrom has an average free volume radius of pores of 0.30 nm or more and 0.50 nm or less, as measured by a positron annihilation lifetime spectroscopy.

2. Solid concentration 30% by mass, pH 8.0, shear rate 0.01 s －１ 2. The binder composition for a non-aqueous secondary battery electrode according to claim 1, wherein the viscosity under the above conditions is 800 mPa·s or more.

3. The binder composition for a non-aqueous secondary battery electrode according to claim 1, wherein the ratio (Da / Db) of the average particle diameter Da of the particulate binder measured by a dynamic light scattering method to the average particle diameter Db of the particulate binder measured by a laser diffraction scattering method is 1.05 or more.

4. The binder composition for a non-aqueous secondary battery electrode according to claim 1, wherein the particulate binder has an average particle diameter Db of 500 nm or less as measured by a laser diffraction scattering method.

5. The binder composition for a non-aqueous secondary battery electrode according to claim 1, wherein the particulate binder comprises a polymer (A) containing at least one of an aliphatic conjugated diene monomer unit and a (meth)acrylic acid ester monomer unit.

6. The binder composition for a non-aqueous secondary battery electrode according to claim 5, wherein the particulate binder contains a polymer (B) containing 80 mass% or more of an acidic functional group-containing monomer unit in a surface layer portion, and has particles containing the polymer (A) inside the surface layer portion.

7. The binder composition for a non-aqueous secondary battery electrode according to claim 1, having a pH of 6.0 or more and 10.0 or less.

8. 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 7.

9. A non-aqueous secondary battery electrode comprising an electrode mixture layer formed using the slurry composition for a non-aqueous secondary battery electrode according to claim 8.

10. 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 electrode for a non-aqueous secondary battery according to claim 9.

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