Conductive paste for non-aqueous electrolyte secondary batteries, slurry composition for negative electrodes of non-aqueous electrolyte secondary batteries, negative electrode for non-aqueous electrolyte secondary batteries, and non-aqueous electrolyte secondary batteries

Abstract

The purpose of the present invention is to provide a conductive material paste for a non-aqueous electrolyte secondary battery, the paste enabling the provision of: a slurry composition for a negative electrode of a non-aqueous electrolyte secondary battery in which the dispersibility of a paste is maintained and the viscosity stability of the slurry is maintained; and a non-aqueous electrolyte secondary battery in which a resistance increase rate in a high temperature storage test is suppressed. This conductive material paste for a non-aqueous electrolyte secondary battery is characterized by containing carbon nanotubes (A), a dispersing agent (B), a dispersing agent (C) and water, with the dispersing agent (B) being a copolymer containing at least unsaturated carboxylic acid monomer units and (meth)acrylamide group-containing monomer units, and the dispersing agent (C) being a thiazoline or a derivative thereof.

Description

[Technical Field]

[0001] The present invention relates to a conductive paste for non-aqueous electrolyte secondary batteries, a slurry composition for the negative electrode of a non-aqueous electrolyte secondary battery, a negative electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion secondary batteries, are small, lightweight, have high energy density, and can be repeatedly charged and discharged, making them suitable for a wide range of applications. Here, the electrode for a non-aqueous electrolyte secondary battery comprises, for example, a current collector and an electrode composite layer formed by drying a slurry composition for non-aqueous electrolyte secondary battery electrodes on the current collector.

[0003] In recent years, fibrous conductive carbon, such as carbon nanotubes (hereinafter sometimes abbreviated as "CNT"), has been used as a conductive material in the formation of electrode composite layers. In forming electrode composite layers using fibrous conductive carbon, a technique has been proposed in which fibrous conductive carbon and a dispersant are pre-mixed to form a conductive paste for non-aqueous electrolyte secondary battery electrodes, and the resulting conductive paste is combined with an electrode active material to prepare a slurry composition for non-aqueous electrolyte secondary battery electrodes (see, for example, Patent Documents 1-2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2020 / 196115 [Patent Document 2] International Publication No. 2020 / 208880 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, the above-mentioned conventional technology still had room for improvement in suppressing the rate of resistance increase during high-temperature storage tests in non-aqueous electrolyte secondary batteries. Specifically, there was a need to provide a conductive paste for non-aqueous electrolyte secondary batteries that could provide a slurry composition for the negative electrode of a non-aqueous electrolyte secondary battery that maintains paste dispersibility and slurry viscosity stability, while also providing a non-aqueous electrolyte secondary battery in which the rate of resistance increase during high-temperature storage tests was suppressed.

[0006] Therefore, the present invention aims to provide a conductive paste for non-aqueous electrolyte secondary batteries that enables the provision of a slurry composition for the negative electrode of a non-aqueous electrolyte secondary battery that maintains paste dispersibility and slurry viscosity stability, while also enabling the provision of a non-aqueous electrolyte secondary battery in which the rate of resistance increase during high-temperature storage tests is suppressed. Furthermore, the present invention aims to provide a slurry composition for the negative electrode of a non-aqueous electrolyte secondary battery that enables the provision of a slurry composition for the negative electrode of a non-aqueous electrolyte secondary battery in which slurry viscosity stability is maintained, while also providing a non-aqueous electrolyte secondary battery in which the rate of resistance increase during high-temperature storage tests is suppressed. Furthermore, the present invention aims to provide a negative electrode for a non-aqueous electrolyte secondary battery that can provide a non-aqueous electrolyte secondary battery in which the rate of resistance increase during high-temperature storage tests is suppressed. Furthermore, the present invention aims to provide a non-aqueous electrolyte secondary battery in which the rate of resistance increase during high-temperature storage tests is suppressed. [Means for solving the problem]

[0007] The inventors diligently conducted research with the aim of solving the above problems. As a result, the inventors discovered that by using a conductive material paste for non-aqueous electrolyte secondary batteries containing carbon nanotubes, a dispersant which is a copolymer containing unsaturated carboxylic acid monomer units and (meth)acrylamide group-containing monomer units, a dispersant which is a thiazoline compound, and water as a dispersion medium, it is possible to provide a slurry composition for the anode of a non-aqueous electrolyte secondary battery that maintains paste dispersibility and slurry viscosity stability, while also providing a non-aqueous electrolyte secondary battery in which the rate of resistance increase during high-temperature storage tests is suppressed, thus completing the present invention.

[0008] In other words, the present invention aims to advantageously solve the above problems, and the conductive paste for non-aqueous electrolyte secondary batteries of the present invention contains carbon nanotubes (A), a dispersant (B), a dispersant (C), and water, wherein the dispersant (B) is a copolymer containing at least unsaturated carboxylic acid monomer units and (meth)acrylamide group-containing monomer units, and the dispersant (C) is thiazoline or a derivative thereof. Thus, by using a conductive paste for non-aqueous electrolyte secondary batteries containing carbon nanotubes (A), a dispersant (B), and a dispersant (C), it is possible to provide a slurry composition for a non-aqueous electrolyte secondary battery anode that maintains slurry viscosity stability while maintaining the paste dispersibility of the paste, a non-aqueous electrolyte secondary battery anode that can provide a non-aqueous electrolyte secondary battery in which the resistance increase rate during high-temperature storage tests is suppressed, and a non-aqueous electrolyte secondary battery in which the resistance increase rate during high-temperature storage tests is suppressed.

[0009] Here, the copolymer, which is the dispersant (B), preferably further contains aromatic sulfonic acid monomer units.

[0010] Furthermore, in the copolymer which is the dispersant (B), it is preferable that the content of unsaturated carboxylic acid monomer units is 5 parts by mass or more and 80 parts by mass or less, when the total monomer units are 100 parts by mass.

[0011] In addition, in the copolymer which is the dispersant (B), when the content of the unsaturated carboxylic acid monomer unit is 100 parts by mass, the content of the (meth)acrylamide group-containing monomer unit is preferably 25 parts by mass or more and 400 parts by mass or less.

[0012] In addition, at least a part of the unsaturated carboxylic acid monomer unit contained in the copolymer which is the dispersant (B) is preferably in the form of a neutral salt which is an alkali metal salt or an ammonium salt.

[0013] In addition, the thiazoline or its derivative which is the dispersant (C) is preferably an isothiazoline or its derivative.

[0014] In addition, the conductive material paste for non-aqueous electrolyte secondary battery of the present invention preferably further contains carbon black.

[0015] In addition, the conductive material paste further contains a particulate polymer, and it is preferable that the particulate polymer contains at least an unsaturated carboxylic acid monomer unit, an aromatic vinyl monomer unit, and a diene-based monomer unit as constituent units of the polymer.

[0016] In addition, it is preferable that the pH of the conductive material paste is 6 or more and 9 or less.

[0017] In addition, the slurry composition for the negative electrode of the non-aqueous electrolyte secondary battery of the present invention is characterized by containing a conductive material paste for non-aqueous electrolyte secondary battery and at least a silicon-based active material.

[0018] In addition, the negative electrode of the non-aqueous electrolyte secondary battery of the present invention includes a negative electrode composite material layer formed using the above-described slurry composition.

[0019] In addition, the non-aqueous electrolyte secondary battery of the present invention includes the above-described negative electrode.

Effects of the Invention

[0020] According to the present invention, it is possible to provide a conductive material paste for a non-aqueous electrolyte secondary battery that can maintain the paste dispersibility and slurry viscosity stability, and can provide a non-aqueous electrolyte secondary battery with a suppressed resistance increase rate during a high-temperature storage test. Also, according to the present invention, it is possible to provide a slurry composition for a non-aqueous electrolyte secondary battery negative electrode that can maintain the slurry viscosity stability, and can provide a non-aqueous electrolyte secondary battery with a suppressed resistance increase rate during a high-temperature storage test. And, according to the present invention, it is possible to provide a negative electrode for a non-aqueous electrolyte secondary battery that can provide a non-aqueous electrolyte secondary battery with a suppressed resistance increase rate during a high-temperature storage test. Furthermore, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery with a suppressed resistance increase rate during a high-temperature storage test.

Mode for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present invention will be described in detail. Here, the conductive material paste for a non-aqueous electrolyte secondary battery of the present invention is used as a material when manufacturing a slurry composition for a non-aqueous electrolyte secondary battery negative electrode. Further, the negative electrode for a non-aqueous electrolyte secondary battery of the present invention includes a negative electrode composite material layer formed using the slurry composition for a non-aqueous electrolyte secondary battery negative electrode of the present invention. Further, the non-aqueous electrolyte secondary battery of the present invention includes the negative electrode for a non-aqueous electrolyte secondary battery of the present invention.

[0022] (Conductive Material Paste for Non-Aqueous Electrolyte Secondary Battery) The conductive paste for non-aqueous electrolyte secondary batteries of the present invention (hereinafter sometimes simply referred to as "conductive paste") is a composition obtained by dispersing and / or dissolving carbon nanotubes (A), a dispersant (B), and a dispersant (C) in water as a dispersion medium. Here, the dispersant (B) is a copolymer containing at least unsaturated carboxylic acid monomer units and (meth)acrylamide group-containing monomer units. The dispersant (C) is thiazoline or a derivative thereof. By using such a conductive paste, it is possible to provide a slurry composition for a non-aqueous electrolyte secondary battery anode that maintains the paste dispersibility of the paste while maintaining slurry viscosity stability, and to provide a non-aqueous electrolyte secondary battery with a suppressed resistance increase rate during high-temperature storage tests.

[0023] <Carbon nanotube (A)> The carbon nanotube (A) is not particularly limited as long as it is a carbon nanotube (CNT) that achieves the objectives of the present invention. Depending on the type of layer structure, examples of carbon nanotubes include single-walled (SW) carbon nanotubes and multi-walled (MW) carbon nanotubes. The carbon nanotube (A) may be a single-walled carbon nanotube, a multi-walled carbon nanotube, or a combination thereof, but a single-walled carbon nanotube is preferred from the viewpoint of being able to form longer conductive paths within the negative electrode mixture layer.

[0024] The average diameter of the CNTs may be preferably 0.5 nm or more, more preferably 1 nm or more, even more preferably 2 nm or more, preferably 50 nm or less, more preferably 40 nm or less, and even more preferably 20 nm or less. The average length of the CNTs may be preferably 1 μm or more, more preferably 3 μm or more, even more preferably 5 μm or more, preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. If the average diameter and average length are above the lower limit, the aggregation of CNTs can be sufficiently suppressed, and the dispersibility of CNTs as a conductive material can be sufficiently ensured. Furthermore, if the average diameter and average length are below the upper limit, good conductive paths can be formed in the electrode composite layer, further improving the output characteristics of the secondary battery. The "average diameter" and "average length" can be determined by measuring the diameter (outer diameter) and length of 100 randomly selected CNTs using a TEM, respectively.

[0025] The aspect ratio (length / diameter) of CNTs is usually greater than 5, and preferably 10 or more. In this invention, the "aspect ratio" of CNTs can be determined by measuring the major and minor axes of 100 randomly selected CNTs using a transmission electron microscope.

[0026] <<Manufacturing method for carbon nanotubes>> CNTs having the properties described above can be prepared using known methods such as arc discharge, laser ablation, and supergrowth, without any particular limitations.

[0027] <<Carbon nanotube (A) content ratio>> The content of carbon nanotubes (A) relative to the total solid content of the conductive paste may be, for example, 20% by mass or more, preferably 30% by mass or more, and more preferably 40% by mass or more. Alternatively, this content may be, for example, 90% by mass or less, preferably 85% by mass or less, and more preferably 80% by mass or less. If the content of carbon nanotubes (A) is above the lower limit, better electrical contact of the carbon nanotubes (A) in the electrode composite layer can be ensured, reducing the internal resistance of the resulting secondary battery and enabling it to exhibit better output characteristics. Furthermore, the capacity of the secondary battery can be stored more stably. On the other hand, if the content of carbon nanotubes (A) is below the upper limit, the content of the dispersant (B) can be increased, and the effect of the dispersant (B) on improving the paste dispersibility of the resulting conductive paste and the slurry viscosity stability of the resulting slurry composition can be enhanced.

[0028] <Dispersant (B)> The dispersant (B) is a water-soluble copolymer containing at least unsaturated carboxylic acid monomer units and (meth)acrylamide group-containing monomer units. Furthermore, the copolymer that is the dispersant (B) may preferably further contain aromatic sulfonic acid monomer units from the viewpoint of further improving the dispersibility of carbon nanotubes. In this invention, "water-soluble polymer" refers to a polymer in which, 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 1.0% by mass. Furthermore, the statement that a polymer "contains monomer units" means that "the polymer obtained using those monomers contains repeating units derived from those monomers." Furthermore, in the present invention, the content ratio of monomer units in the polymer is, 1 H-NMR and 13 It can be measured using nuclear magnetic resonance (NMR) methods such as 13C-NMR.

[0029] <<Unsaturated carboxylic acid monomer units>> Examples of unsaturated carboxylic acid monomer units that constitute the copolymer acting as a dispersant (B) include ethylenically unsaturated carboxylic acid monomer units. Ethyleneally unsaturated carboxylic acid monomers that can form ethylenically unsaturated carboxylic acid monomer units typically do not have hydroxyl groups (-OH) other than the hydroxyl group in the carboxyl group. Examples of ethylenically unsaturated carboxylic acid monomers include ethylenically unsaturated monocarboxylic acids and their derivatives, ethylenically unsaturated dicarboxylic acids and their acid anhydrides, and their derivatives. The ethylenically unsaturated carboxylic acid monomer may be used individually or in combination of two or more types in any ratio.

[0030] Examples of ethylenically unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of derivatives of ethylenically unsaturated monocarboxylic acids include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and β-diaminoacrylic acid. Examples of ethylenically unsaturated dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of acid anhydrides of ethylenically unsaturated dicarboxylic acids include maleic anhydride, diacrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Examples of derivatives of ethylenically unsaturated dicarboxylic acids include methyl maleic acid, phenyl maleic acid, chloro maleic acid, dichloro maleic acid, and fluoro maleic acid.

[0031] Here, as the ethylenically unsaturated carboxylic acid monomer, a monofunctional ethylenically unsaturated carboxylic acid monomer having one ethylenically unsaturated bond (C=C) in the molecule is preferred. Furthermore, from the viewpoint of polymerizability, ethylenically unsaturated monocarboxylic acids and ethylenically unsaturated dicarboxylic acids are preferred as the ethylenically unsaturated carboxylic acid monomer, acrylic acid, methacrylic acid, and itaconic acid are more preferred, and acrylic acid and methacrylic acid are even more preferred. Moreover, from the viewpoint of suppressing excessive swelling of the resulting copolymer in the electrolyte, acrylic acid is even more preferred as the ethylenically unsaturated carboxylic acid monomer.

[0032] At least a portion of the unsaturated carboxylic acid monomer units may be in the form of a neutralized salt in which the carboxyl group portion is an alkali metal salt or an ammonium salt. Examples of alkali metal salts include lithium salts, sodium salts, potassium salts, rubidium salts, and cesium salts, with lithium salts being preferred.

[0033] In the copolymer that serves as the dispersant (B), when the total monomer units are 100 parts by mass, the content of unsaturated carboxylic acid monomer units is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 25 parts by mass or more, preferably 80 parts by mass or less, more preferably 70 parts by mass or less, and even more preferably 60 parts by mass or less. If the content of unsaturated carboxylic acid monomer units in the copolymer that serves as the dispersant (B) is above the lower limit, the paste dispersibility of the resulting conductive paste can be improved. On the other hand, if the content of unsaturated carboxylic acid monomer units in the copolymer that serves as the dispersant (B) is below the upper limit, the ability to suppress the rate of resistance increase during high-temperature storage tests of the resulting non-aqueous electrolyte secondary battery can be improved.

[0034] <<(meth)acrylamide group-containing monomer unit>> (Meth)acrylamide monomers that can form (meth)acrylamide group-containing monomer units are acrylamide, methacrylamide, or a combination thereof.

[0035] In the copolymer that is the dispersant (B), when the total monomer units are 100 parts by mass, the content of (meth)acrylamide group-containing monomer units is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 25 parts by mass or more, preferably 50 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 85 parts by mass or less. In the copolymer that is the dispersant (B), when the content of unsaturated carboxylic acid monomer units is 100 parts by mass, the content of (meth)acrylamide group-containing monomer units is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 35 parts by mass or more, preferably 400 parts by mass or less, more preferably 300 parts by mass or less, and even more preferably 200 parts by mass or less. If the content of (meth)acrylamide group-containing monomer units is above the lower limit, the cycle characteristics of the resulting non-aqueous electrolyte secondary battery can be improved. On the other hand, if the content of (meth)acrylamide monomer units is below the upper limit, the viscosity stability of the resulting slurry composition can be improved.

[0036] <<Aromatic sulfonic acid monomer units>> An "aromatic sulfonic acid monomer" that can form an aromatic sulfonic acid monomer unit is a compound having an aromatic ring, an ethylenically unsaturated bond, and a sulfonic acid group. Examples of aromatic sulfonic acid monomers include styrene sulfonic acid, naphthyl vinyl sulfonic acid, and divinylbenzene sulfonic acid.

[0037] At least a portion of the aromatic sulfonic acid monomer units may be in the form of a neutralized salt, which is an alkali metal salt or an ammonium salt. Examples of alkali metal salts include lithium salts, sodium salts, potassium salts, rubidium salts, and cesium salts, with sodium salts and lithium salts being preferred.

[0038] In the copolymer that serves as the dispersant (B), when the total monomer units are 100 parts by mass, the content of aromatic sulfonic acid monomer units is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less. If the content ratio of aromatic sulfonic acid monomer units in the copolymer that serves as the dispersant (B) is above the lower limit, the paste dispersibility of the resulting conductive paste can be improved. On the other hand, if the content ratio of aromatic sulfonic acid monomer units in the copolymer that serves as the dispersant (B) is below the upper limit, the resistance increase rate suppression and cycle characteristics of the resulting non-aqueous electrolyte secondary battery during high-temperature storage tests can be improved.

[0039] <<Other monomeric units>> Other monomer units that can form the monomer units constituting the copolymer, which is the dispersant (B), are not particularly limited as long as they are monomers copolymerizable with monomers having unsaturated carbon-carbon bonds. Examples include monomers having unsaturated carbon-carbon bonds other than the unsaturated carboxylic acid monomers, (meth)acrylamide group-containing monomers, and aromatic sulfonic acid monomers mentioned above. Examples of such monomers having unsaturated carbon-carbon bonds include cyano group-containing vinyl monomers, amino group-containing vinyl monomers, pyridyl group-containing vinyl monomers, and alkoxyl group-containing vinyl monomers. Note that the monomers copolymerizable with the monomers having unsaturated carbon-carbon bonds mentioned above may be used individually or in combination of two or more types in any ratio.

[0040] <<Weight average molecular weight>> The weight-average molecular weight of the copolymer, which is the dispersant (B), is preferably 4,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, preferably 2,000,000 or less, more preferably 1,000,000 or less, and even more preferably 800,000 or less. If the weight-average molecular weight of the dispersant (B) is above the lower limit, the dispersibility of the conductive material paste can be improved. On the other hand, if the weight-average molecular weight of the copolymer, which is the dispersant (B), is below the upper limit, the solid content concentration of the conductive material paste can be increased. In this invention, the "weight-average molecular weight" of the polymer can be measured using the method described in the examples.

[0041] <<Method for producing dispersant (B)>> The method for producing the dispersant (B) is not particularly limited. The dispersant (B) can be prepared, for example, by polymerizing a monomer composition containing one or more monomers in an aqueous solvent. The content ratio of each monomer in the monomer composition can be determined according to the content ratio of the desired monomer units in the polymer. Furthermore, there are no particular restrictions on the polymerization method; any method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization can be used. In addition, any polymerization reaction such as ionic polymerization, radical polymerization, living radical polymerization, various condensation polymerizations, or addition polymerization can be used. During polymerization, known emulsifiers and polymerization initiators can be used as needed.

[0042] <<Percentage of Dispersant (B)>> The content ratio of the dispersant (B) solids relative to the total solids of the conductive paste may be, for example, 5% by mass or more, preferably 10% by mass or more, and more preferably 15% by mass or more. Alternatively, this content ratio may be, for example, 70% by mass or less, preferably 50% by mass or less, and more preferably 40% by mass or less. If the content ratio of the dispersant (B) is above the lower limit, the paste dispersibility of the resulting conductive paste and the slurry viscosity stability of the resulting slurry composition can be improved. On the other hand, if the content ratio of the dispersant (B) is below the upper limit, the content ratio of carbon nanotubes (A) can be increased, which can better ensure electrical contact of the carbon nanotubes (A) in the electrode composite layer, reduce the internal resistance of the resulting secondary battery, and enhance the effect of exhibiting better output characteristics.

[0043] <Dispersant (C)> Dispersant (C) is a thiazoline or a derivative thereof. In other words, dispersant (C) is a compound having a thiazoline skeleton. In this specification, "thiazoline" (including variant terms and parts of compound names) refers to both thiazolines and isothiazolines in which the nitrogen atom and sulfur atom are not adjacent. Thiazolines or their derivatives may also be referred to as "thiazoline compounds."

[0044] Examples of thiazoline compounds include thiazolines substituted with one or more substituents, and thiazoline condensed rings formed by the condensation of thiazoline with another ring (which may be further substituted with one or more substituents).

[0045] Examples of substituents include, but are not limited to, optionally substituted hydrocarbon groups, oxo groups, halogen atoms (e.g., chlorine atom, fluorine atom, bromine atom, iodine atom, etc.), hydroxyl groups, cyano groups, amino groups, carboxyl groups, optionally substituted hydrocarbon-oxy groups, and optionally substituted hydrocarbon-thio groups. Examples of hydrocarbon groups (including the "hydrocarbons" in hydrocarbon-oxy groups and hydrocarbon-thio groups) include, but are not limited to, C1-C10 alkyl groups (e.g., methyl group, ethyl group, propyl group, etc.), C2-C6 alkenyl groups (e.g., vinyl group, allyl group, etc.), C2-C6 alkynyl groups (e.g., ethynyl group, propynyl group, etc.), C3-C10 cycloalkyl groups (e.g., cyclopentyl group, cyclohexyl group, etc.), and C6-C14 aryl groups (e.g., phenyl group, etc.). Examples of substituents that may substitute for optionally substituted hydrocarbon groups, optionally substituted hydrocarbon-oxy groups, and optionally substituted hydrocarbon-thio groups include, but are not limited to, those mentioned above.

[0046] Rings that may condense with thiazoline include, but are not limited to, hydrocarbon rings (aliphatic hydrocarbon rings, aromatic hydrocarbon rings) and heterocycles (non-aromatic heterocycles, aromatic heterocycles). Examples of aliphatic hydrocarbon rings include, but are not limited to, cycloalkane rings (e.g., cyclopropane ring, cyclobutane ring, cyclopentane ring, cyclohexane ring) and cycloolefin rings (e.g., cyclopropene ring, cyclobutene ring, cyclopentene ring, cyclohexene ring). Examples of aromatic hydrocarbon rings include, but are not limited to, benzene rings and naphthalene rings. Examples of non-aromatic heterocycles include, but are not limited to, pyrrolidine rings, tetrahydrofuran rings, tetrahydrothiophene rings, pyrroline rings, pyrrole rings, dihydrofuran rings, dihydrothiophene rings, piperidine rings, piperazine rings, tetrahydropyran rings, morpholine rings, thiane rings, thiomorpholine rings, pyran rings, oxazine rings, thiopyran rings, and thiaidine rings. Examples of aromatic heterocycles include, but are not limited to, furan rings, oxazole rings, isoxazole rings, thiophene rings, thiazole rings, isothiazole rings, pyridine rings, pyridazine rings, pyrimidine rings, pyrazine rings, and triazine rings.

[0047] The thiazoline compound is preferably an isothiazoline compound, from the viewpoint of improving the paste dispersibility of the resulting conductive paste, as well as the cycle characteristics and resistance increase suppression during high-temperature storage tests of the resulting non-aqueous electrolyte secondary battery. An isothiazoline compound has, for example, the structure shown in formula (1) below. [ka] (In formula (1), Y is a hydrogen atom or an optionally substituted hydrocarbon group, and X1 and X2 are each independently a hydrogen atom, a halogen atom, or an optionally substituted C1-C6 alkyl group, or X1 and X2 together form an aromatic ring. If X1 and X2 do not together form an aromatic ring, X1 and X2 may be the same or different.)

[0048] In formula (1), examples of the hydrocarbon group Y include alkyl groups having 1 to 10 carbon atoms (such as a methyl group), alkenyl groups having 2 to 6 carbon atoms (such as a vinyl group or an allyl group), alkynyl groups having 2 to 6 carbon atoms (such as an ethynyl group or a propynyl group), cycloalkyl groups having 3 to 10 carbon atoms (such as a cyclopentyl group or a cyclohexyl group), and aryl groups having 6 to 14 carbon atoms (such as a phenyl group). Furthermore, the hydrocarbon group Y may have some or all of its hydrogen atoms substituted by substituents. Examples of such substituents include hydroxyl groups, halogen atoms (e.g., chlorine, fluorine, bromine, iodine, etc.), cyano groups, amino groups, carboxyl groups, alkoxy groups having 1 to 4 carbon atoms (e.g., methoxy, ethoxy, etc.), aryloxy groups having 6 to 10 carbon atoms (e.g., phenoxy, etc.), alkylthio groups having 1 to 4 carbon atoms (e.g., methylthio, ethylthio, etc.), and arylthio groups having 6 to 10 carbon atoms (e.g., phenylthio, etc.). If the hydrocarbon group Y has multiple substituents, the substituents may be the same or different.

[0049] In formula (1), Y is preferably a methyl group or a hydrogen atom, and more preferably a hydrogen atom.

[0050] In formula (1), examples of halogen atoms in X1 and X2 include fluorine, chlorine, bromine, and iodine atoms. In formula (1), examples of C1-C6 alkyl groups of X1 and X2 include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, and pentyl groups. These alkyl groups may have some or all of their hydrogen atoms substituted by substituents. Examples of such substituents are the same as those described above for substituents on the hydrocarbon group of Y. In formula (1), an aromatic ring formed jointly by X1 and X2 could be a benzene ring, etc. Hereinafter, compounds of formula (1) in which X1 and X2 jointly form an aromatic ring will be referred to as "aromatic ring-isothiazoline compounds," and compounds of formula (1) in which X1 and X2 do not jointly form an aromatic ring will be referred to as "non-aromatic ring-isothiazoline compounds."

[0051] In formula (1), it is preferable that X1 and X2 are either hydrogen atoms or form an aromatic ring together. Furthermore, from the viewpoint of further dispersing carbon nanotubes (A) in the conductive paste and further suppressing the deposition of lithium metal at the negative electrode in the case of lithium-ion secondary batteries, it is even more preferable that X1 and X2 form an aromatic ring together. In other words, it is preferable that the isothiazoline compound is an aromatic ring-isothiazoline compound.

[0052] [Benzisothiazoline compounds] Furthermore, as aromatic ring-isothiazoline compounds, benzoisothiazoline compounds having the structure shown in formula (2) below, in which X1 and X2 form benzene rings as aromatic rings, are preferred.

[0053] [ka] (In formula (2), Y is the same as in formula (1), and X3 to X6 are each independently one of the following: a hydrogen atom, a halogen atom, a hydroxyl group, a cyano group, an amino group, a carboxyl group, a C1-C4 alkyl group, or a C1-C4 alkoxy group. Note that X3 to X6 may be the same or different.)

[0054] In equation (2), the halogen atoms X3 to X6 are the same as those X1 and X2 in equation (1). In formula (2), examples of alkyl groups having 1 to 4 carbon atoms include methyl, ethyl, propyl, butyl, isobutyl, sec-butyl, and tert-butyl groups. In formula (2), examples of alkoxy groups having 1 to 4 carbon atoms include methoxy groups and ethoxy groups.

[0055] In equation (2), it is preferable that Y and X3 to X6 are hydrogen atoms.

[0056] [Specific examples of thiazoline compounds] Examples of thiazoline compounds include thiazolines, alkylthiazolines (e.g., methylthiazoline, ethylthiazoline, octylthiazoline), cycloalkylthiazolines (e.g., cyclohexylthiazoline), halogenated thiazolines (e.g., chlorothiazoline, dichlorothiazoline), alkylhalinated thiazolines (e.g., methylchlorothiazoline, ethylchlorothiazoline, octylchlorothiazoline, methyldichlorothiazoline, ethyldichlorothiazoline, octyldichlorothiazoline), and cycloalkylhalinated thiazolines (e.g., cyclohexyl (e.g., dichlorothiazolinone, cyclohexyldichlorothiazolinone), thiazolinone, alkylthiazolinone (e.g., methylthiazolinone, ethylthiazolinone, octylthiazolinone), cycloalkylthiazolinone (e.g., cyclohexylthiazolinone), halogenated thiazolinone (e.g., chlorothiazolinone, dichlorothiazolinone), alkylhalinated thiazolinone (e.g., methylchlorothiazolinone, ethylchlorothiazolinone, octylchlorothiazolinone, methyldichlorothiazolinone, ethyldichlorothiazolinone, octyldichlorothiazolinone) Cycloalkylhalogenated thiazolinones (e.g., cyclohexylchlorothiazolinone, cyclohexyldichlorothiazolinone), benzothiazolines, alkylbenzothiazolines (e.g., methylbenzothiazoline, ethylbenzothiazoline, octylbenzothiazoline), cycloalkylbenzothiazolines (e.g., cyclohexylbenzothiazoline), halogenated benzothiazolines (e.g., chlorobenzothiazoline, dichlorobenzothiazoline), alkylhalogenated benzothiazolines (e.g., methylchlorobenzothiazoline, ethylchlorobenzothiazoline, octylchlorobenzothiazoline, octylbenzothiazoline, octylchlorobenzothiazoline, octyl (Cutylchlorobenzothiazoline, methyldichlorobenzothiazoline, ethyldichlorobenzothiazoline, octyldichlorobenzothiazoline), cycloalkylhalogenated benzothiazolines (e.g., cyclohexylchlorobenzothiazoline, cyclohexyldichlorobenzothiazoline), benzothiazolinone, alkylbenzothiazolinone (e.g., methylbenzothiazolinone, ethylbenzothiazolinone, octylbenzothiazolinone), cycloalkylbenzothiazolinone (e.g., cyclohexylbenzothiazolinone), halogenated benzothiazolinone (e.g.,Examples include chlorobenzothiazolinones (e.g., dichlorobenzothiazolinone), alkylhalogenated benzothiazolinones (e.g., methylchlorobenzothiazolinone, ethylchlorobenzothiazolinone, octylchlorobenzothiazolinone, methyldichlorobenzothiazolinone, ethyldichlorobenzothiazolinone, octyldichlorobenzothiazolinone), and cycloalkylhalogenated benzothiazolinones (e.g., cyclohexylchlorobenzothiazolinone, cyclohexyldichlorobenzothiazolinone). These may be used individually or in combination of two or more.

[0057] Among these, isothiazoline compounds represented by formula (1) include, for example, methylchlorothiazolinone (e.g., 5-chloro-2-methyl-4-isothiazolin-3-one), methylthiazolinone (e.g., 2-methyl-4-isothiazolin-3-one (MIT)), octylthiazolinone (e.g., 2-n-octyl-4-isothiazolin-3-one), octyldichlorothiazolinone (e.g., 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one), ethylthiazolinone (e.g., 2-ethyl-4-isothiazolin-3-one), and cyclohexyldichlorothiazolinone. Examples include non-aromatic ring-isothiazoline compounds such as linone (e.g., 4,5-dichloro-2-cyclohexyl-4-isothiazolin-3-one), ethylchlorothiazolinone (e.g., 5-chloro-2-ethyl-4-isothiazolin-3-one), and octylchlorothiazolinone (e.g., 5-chloro-2-t-octyl-4-isothiazolin-3-one); and aromatic ring-isothiazoline compounds such as benzothiazolinone (e.g., 1,2-benzoisothiazolin-3-one (BIT)) and methylbenzothiazolinone (e.g., N-methyl-1,2-benzoisothiazolin-3-one). These may be used individually or in combination of two or more.

[0058] Among these, 2-methyl-4-isothiazolin-3-one (MIT) and 1,2-benzoisothiazolin-3-one (BIT) are preferred, and 1,2-benzoisothiazolin-3-one (BIT) is particularly preferred from the viewpoint of further dispersing conductive carbon in the conductive paste and further suppressing the deposition of lithium metal at the negative electrode of the secondary battery.

[0059] <<Percentage of dispersant (C) content>> The content ratio of the dispersant (C) solids relative to the total solids of the conductive paste may be, for example, 0.1% by mass or more, preferably 0.2% by mass or more, and more preferably 0.5% by mass or more. Alternatively, this content ratio may be, for example, 20% by mass or less, preferably 10% by mass or less, and more preferably 5% by mass or less. If the content ratio of the dispersant (C) is above the above lower limit, the paste dispersibility of the resulting conductive paste, the slurry viscosity stability of the resulting slurry composition, and the cycle characteristics and resistance increase rate suppression during high-temperature storage tests of the resulting non-aqueous electrolyte secondary battery can be improved. On the other hand, if the content ratio of the dispersant (C) is above the above lower limit, the content ratios of carbon nanotubes (A) and dispersant (B) can be increased, for example, reducing the internal resistance of the resulting secondary battery and enhancing the effect of exhibiting better output characteristics.

[0060] <Other ingredients> Other components that the conductive paste may contain are not limited to water, but include dispersion media other than water, carbon black as a conductive material other than carbon nanotubes (A), and components other than the electrode active material described later in the section on "Slurry Composition for Negative Electrode of Non-Aqueous Electrolyte Secondary Battery". These other components may be used individually or in combination of two or more.

[0061] <Dispersion media other than water> Examples of dispersion media other than water include organic solvents. Organic solvents are not particularly limited and include, for example, alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, and amyl alcohol; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; ethers such as diethyl ether, dioxane, and tetrahydrofuran; amide organic solvents such as N,N-dimethylformamide and N-methyl-2-pyrrolidone (NMP); and aromatic hydrocarbons such as toluene, xylene, chlorobenzene, orthodichlorobenzene, and paradichlorobenzene. Organic solvents can be used individually or in combination of two or more.

[0062] <<Carbon Black>> The conductive paste of the present invention may further contain carbon black to improve conductivity and reduce resistance. The carbon black used in the present invention is an aggregate in which several layers of graphite carbon microcrystals are gathered to form a random layered structure, and specifically includes acetylene black, Ketjen black, furnace black, channel black, and thermal lamp black. Among carbon blacks, acetylene black, furnace black, and Ketjen black are particularly preferred because they allow for high-density filling of the conductive adhesive layer, reducing electron transfer resistance and further reducing the internal resistance of the electrochemical element.

[0063] The carbon black used in the present invention preferably contains heteroatoms other than the main component, carbon. Specifically, examples of such heteroatoms include silicon, nitrogen, and boron, with boron being particularly preferred because it can reduce electron transfer resistance and thus reduce the internal resistance of the electrochemical element.

[0064] The heteroatom content in the carbon black used in this invention is preferably in the range of 0.01 to 20% by weight, more preferably in the range of 0.05 to 10% by weight, and particularly preferably in the range of 0.1 to 5% by weight. When the heteroatom content in the carbon black is within this range, the electron transfer resistance is reduced, and the internal resistance of the electrochemical element is reduced.

[0065] Here, the specific surface area of ​​the carbon black used in this invention is set at 25 m² from the viewpoint of maintaining good conductivity. 2 / g or more and 300m 2 Less than or equal to / g, preferably 30m 2 / g or more and 200m 2 / g or less, more preferably 40m 2 / g or more and 150m 2 The specific surface area should be less than / g. If the specific surface area is too large, the viscosity will be high, making it difficult to produce a slurry suitable for high-speed coating. Conversely, if the specific surface area is too small, the conductivity will decrease, and the dispersibility of the slurry will deteriorate.

[0066] The volume-average particle diameter of the carbon black used in the present invention is preferably 0.01 μm or more and less than 1.0 μm, more preferably 0.05 μm or more and less than 0.8 μm, and particularly preferably 0.1 μm or more and less than 0.5 μm. In the present invention, when carbon black with a volume-average particle diameter within the above range is used, the spheroidal graphite and carbon black in the conductive adhesive layer are densely packed. The volume-average particle diameter is the volume-average particle diameter calculated by measuring with a laser diffraction particle size distribution analyzer (e.g., SALD-3100; manufactured by Shimadzu Corporation).

[0067] <<Particulate Polymer (Binding Agent)>> The conductive paste may further contain particulate polymer (particulate binder) as a binder. The particulate polymer contains at least unsaturated carboxylic acid monomer units, aromatic vinyl monomer units, and diene monomer units as polymer constituent units.

[0068] [Unsaturated carboxylic acid monomer unit] An example of unsaturated carboxylic acid monomer units that constitute particulate polymers as binders is the unsaturated carboxylic acid monomer units that constitute dispersant (B).

[0069] In particulate polymers used as binders, when the total monomer units are 100 parts by mass, the content of unsaturated carboxylic acid monomer units is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, even more preferably 8 parts by mass or more, preferably 20 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 30 parts by mass or less. If the content of unsaturated carboxylic acid monomer units in the particulate polymer used as a binder is above the lower limit, the stability of the slurry viscosity over time can be improved. On the other hand, if the content of unsaturated carboxylic acid monomer units in the particulate polymer used as a binder is below the upper limit, the solid content concentration of the slurry can be increased.

[0070] [Aromatic vinyl monomer unit] Examples of aromatic vinyl monomers that can form aromatic vinyl monomer units include styrene, α-methylstyrene, pt-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. The aromatic vinyl monomer may be used individually or in combination of two or more types in any ratio. Among these, styrene is preferred.

[0071] In particulate polymers used as binders, when the total monomer units are 100 parts by mass, the content of aromatic vinyl monomer units is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, even more preferably 30 parts by mass or more, preferably 90 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less. If the content of aromatic vinyl monomer units in the particulate polymer used as a binder is above the lower limit, the stability during negative electrode slurry preparation can be improved, making it less likely for the slurry viscosity to increase. On the other hand, if the content of aromatic vinyl monomer units in the particulate polymer used as a binder is below the upper limit, the degree of swelling in relation to the electrolyte used in secondary batteries can be kept within a suitable range.

[0072] [Diene monomer units] Examples of diene monomers that can form diene monomer units include aliphatic conjugated diene monomers. Examples of aliphatic conjugated diene monomers include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene chloroprene, and cyanobutadiene. The above-mentioned conjugated diene monomers may be used individually or in combination of two or more in any ratio. Among these, 1,3-butadiene and isoprene are preferred due to their easy availability, and 1,3-butadiene is more preferred.

[0073] In particulate polymers used as binders, when the total monomer units are 100 parts by mass, the content of diene monomer units is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, even more preferably 30 parts by mass or more, preferably 80 parts by mass or less, more preferably 85 parts by mass or less, and even more preferably 70 parts by mass or less. If the content of diene monomer units in the particulate polymer used as a binder is above the lower limit, the bonding strength of the electrode can be increased. On the other hand, if the content of diene monomer units in the particulate polymer used as a binder is below the upper limit, the mechanical stability during the preparation of the negative electrode slurry can be maintained.

[0074] [Other monomeric units] Other monomer units that can form particulate polymers are not particularly limited as diene monomers, as long as they are copolymerizable with diene monomers. Examples include monomers having unsaturated carbon-carbon bonds other than the unsaturated carboxylic acid monomers and aromatic vinyl monomer units mentioned above. Examples of such monomers having unsaturated carbon-carbon bonds include cyano group-containing vinyl monomers, amino group-containing vinyl monomers, pyridyl group-containing vinyl monomers, and alkoxyl group-containing vinyl monomers. Note that the monomers copolymerizable with diene monomers mentioned above may be used individually or in combination of two or more types in any ratio.

[0075] <Properties of conductive paste> The pH of the conductive paste is preferably 6 or higher, more preferably 6.5 or higher, preferably 9 or lower, and most preferably 8 or lower. If the pH of the conductive paste is above the lower limit, the viscosity stability of the negative electrode slurry can be increased. On the other hand, if the pH of the conductive paste is below the upper limit, the bonding strength as a negative electrode can be increased.

[0076] <Method for manufacturing conductive paste> The conductive paste of the present invention can be manufactured by mixing the carbon nanotubes (A), dispersant (B), dispersant (C), water, and other components as needed, in the proportions described above.

[0077] Furthermore, the above-described mixing is preferably carried out through the steps of preparing a premixture containing carbon nanotubes (A), a dispersant (C), and water, and adding a dispersant (B) to the premixture. It is presumed that by first mixing the carbon nanotubes (A) and the dispersant (C) in the presence of water, and then adding the dispersant (B) to the resulting premixture, the dispersant (C) is first adsorbed onto the surface of the carbon nanotubes (A), and then the dispersant (B) is further adsorbed well via the dispersant (C). This makes it possible to provide a slurry composition for a negative electrode of a non-aqueous electrolyte secondary battery that maintains the paste dispersibility of the conductive material paste and maintains slurry viscosity stability, while suppressing the rate of resistance increase during high-temperature storage tests.

[0078] The mixing of various components is not particularly limited and can be carried out using known mixing equipment. Examples of such mixing equipment include dispersers, homomixers, planetary mixers, kneaders, ball mills, and bead mills.

[0079] (Slurry composition for non-aqueous electrolyte secondary battery negative electrode) The slurry composition for the negative electrode of a non-aqueous electrolyte secondary battery of the present invention (hereinafter sometimes simply referred to as "slurry composition") comprises the conductive material paste described above and at least a negative electrode active material (e.g., silicon-based active material, etc.), and may optionally contain a thickener, binder, carbon black, negative electrode active material (e.g., silicon-based active material, etc.), and other optional components. Thus, the slurry composition containing the conductive paste described above maintains slurry viscosity stability, and an electrode comprising an electrode composite layer formed from the slurry composition can suppress the rate of resistance increase during high-temperature storage tests for non-aqueous electrolyte secondary batteries.

[0080] <Negative electrode active material> <<Silicon-based active material>> Examples of the silicon-based active material include silicon (Si), an alloy containing silicon, SiO, SiO x , a composite of a Si-containing material and conductive carbon obtained by coating or compounding the Si-containing material with conductive carbon, and the like.

[0081] Note that the particle size of the silicon-based active material is not particularly limited and can be the same as that of the electrode active materials conventionally used. Also, the amount of the silicon-based active material in the slurry composition is not particularly limited and can be within the range conventionally used. And the silicon-based active material can be used alone or in combination of two or more.

[0082] <<Other negative electrode active materials>> Examples of other negative electrode active materials include, but are not particularly limited to, carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials obtained by combining these.

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

[0084] Examples of the carbonaceous material include graphitizable carbon and non-graphitizable carbon having a structure close to an amorphous structure typified by glassy carbon. Here, examples of the graphitizable carbon include carbon materials obtained from tar pitch obtained from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, pyrolytic vapor-grown carbon fibers, and the like. Examples of the non-graphitizable carbon include phenolic resin fired bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin fired bodies (PFA), hard carbon, and the like. Furthermore, examples of graphite materials include natural graphite and artificial graphite. Examples of artificial graphite include artificial graphite obtained by heat-treating carbon containing easily graphitizable carbon at temperatures above 2800°C, graphitized MCMB obtained by heat-treating MCMB at temperatures above 2000°C, and graphitized mesophase pitch carbon fibers obtained by heat-treating mesophase pitch carbon fibers at temperatures above 2000°C.

[0085] Furthermore, a metallic anode active material is an active material containing a metal, which typically contains an element in its structure that allows for lithium insertion, and has a theoretical electrical capacity of 500 mAh / g or more per unit mass when lithium is inserted. Examples of metallic active materials include lithium metal, elemental metals that can form lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Sn, Sr, Zn, Ti, etc.) and their alloys, as well as their oxides, sulfides, nitrides, carbides, and phosphides.

[0086] Furthermore, the particle size of the other negative electrode active materials is not particularly limited and can be the same as that of conventionally used electrode active materials. Furthermore, the amount of negative electrode active material in the slurry composition is not particularly limited and can be within the range of conventionally used materials. Furthermore, the negative electrode active material can be used alone or in combination of two or more types.

[0087] <<Amount of negative electrode active material and silicon-based active material>> The content ratio of the negative electrode active material relative to the total solid content of the slurry composition may be, for example, 90% by mass or more, preferably 92% by mass or more, more preferably 95% by mass or more, and may also be, for example, 99% by mass or less, preferably 98.5% by mass or less, more preferably 98% by mass or less. If the content ratio of the negative electrode active material is above the lower limit, the capacity of the resulting secondary battery can be increased. Furthermore, if the content ratio of the negative electrode active material is below the upper limit, the cycle characteristics of the resulting secondary battery can be improved. The content ratio of carbon nanotubes (A) to the negative electrode active material may be, for example, 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and may also be, for example, 5% by mass or less, preferably 2% by mass or less, more preferably 1% by mass or less. The content ratio of silicon-based active material relative to the total solid content of the slurry composition may be, for example, 3% by mass or more, preferably 5% by mass or more, more preferably 8% by mass or more, and may also be, for example, 40% by mass or less, preferably 35% by mass or less, and more preferably 30% by mass or less. If the content ratio of silicon-based active material is above the lower limit, the capacity of the resulting secondary battery can be further increased. Furthermore, if the content ratio of silicon-based active material is below the upper limit, the cycle characteristics of the resulting secondary battery can be further improved. The content ratio of carbon nanotubes (A) to the silicon-based active material may be, for example, 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and may also be, for example, 5% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less.

[0088] <Thickening agent> The thickening agent is not particularly limited, but examples include carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, polyvinyl alcohol, polymethacrylic acid, polyacrylic acid, and ternary copolymers of acrylamide / acrylic acid / N-hydroxyethylacrylamide. These can be used individually or in combination of two or more. Furthermore, they can be used in either an unneutralized or neutralized state. Among these, the ternary copolymer of acrylamide / acrylic acid / N-hydroxyethylacrylamide is preferred.

[0089] Here, the weight-average molecular weight of the thickener is preferably 500,000 or more, more preferably 800,000 or more, preferably 10,000,000 or less, and more preferably 8,000,000 or less. If the weight-average molecular weight of the thickener is 500,000 or more, the peel strength of the electrode can be increased, and if it is 10,000,000 or less, the cycle characteristics of the electrochemical element can be further improved.

[0090] Furthermore, in the slurry composition of the present invention, the amount of the thickening agent described above is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more, preferably 5.0 parts by mass or less, and more preferably 4.0 parts by mass or less, per 100 parts by mass of the negative electrode active material. If the amount of the thickening agent per 100 parts by mass of the negative electrode active material is 0.2 parts by mass or more, the cycle characteristics of the electrochemical element can be further improved, and if it is 5.0 parts by mass or less, the capacity of the electrochemical element can be improved.

[0091] <Binding agent> As a binder, the particulate polymer (particulate binder) described above can be used. In the slurry composition of the present invention, the amount of the binder described above is preferably 0.1 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of electrode active material. If the amount of binder per 100 parts by mass of electrode active material is within the above range, the peel strength of the electrode can be increased while further improving the cycle characteristics of the electrochemical element.

[0092] <Other optional ingredients> Other optional components that may be included in the slurry composition include, for example, reinforcing agents, antioxidants, and electrolyte additives that have the function of suppressing the decomposition of the electrolyte. These optional components can be used individually or in combination of two or more.

[0093] <Method for preparing slurry composition> There are no particular restrictions on the mixing method when obtaining a slurry composition by mixing the above-mentioned components; for example, known mixing equipment can be used.

[0094] (Non-aqueous electrolyte secondary battery negative electrode) The negative electrode for a non-aqueous electrolyte secondary battery of the present invention (hereinafter sometimes simply referred to as "the negative electrode of the present invention") comprises a negative electrode composite layer obtained by forming it using the slurry composition of the present invention as described above. More specifically, the negative electrode of the present invention usually has a structure in which a negative electrode composite layer made of the dried slurry composition of the present invention is provided on a current collector. Therefore, the negative electrode composite layer contains carbon nanotubes (A), a dispersant (B), and a dispersant (C), and may optionally contain a thickener, a binder, carbon black, a negative electrode active material (e.g., silicon-based active material), and other optional components. The preferred ratio of each component in the electrode composite layer is the same as the preferred ratio of each component in the slurry composition. Furthermore, since the negative electrode of the present invention comprises a negative electrode composite layer formed using the slurry composition of the present invention described above, it can exhibit excellent cycle characteristics in a non-aqueous electrolyte secondary battery.

[0095] <Current collector> The negative electrode current collector is made of a material that is electrically conductive and electrochemically durable. Examples of current collectors include those made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum. These materials can be used individually or in combination of two or more. For the negative electrode current collector, a copper current collector (such as copper foil) is preferred.

[0096] <Method for manufacturing a negative electrode> The method for manufacturing the negative electrode of the present invention is not particularly limited. For example, the negative electrode of the present invention can be manufactured by applying the slurry composition of the present invention described above to at least one surface of a current collector and drying it to form an electrode composite layer. More specifically, the manufacturing method includes the steps of applying the slurry composition to at least one surface of a current collector (coating step) and drying the slurry composition applied to at least one surface of the current collector to form an electrode composite layer on the current collector (drying step).

[0097] <<Coating process>> The method for applying the slurry composition onto the current collector is not particularly limited, and known methods can be used. Specifically, application methods include the doctor blade method, dip method, reverse roll method, direct roll method, gravure method, extrusion method, and brush application method. In this case, the slurry composition may be applied to only one side of the current collector or to both sides. The thickness of the slurry film on the current collector before drying after application can be appropriately set according to the thickness of the electrode composite layer obtained after drying.

[0098] <<Drying process>> The method for drying the slurry composition on the current collector is not particularly limited and known methods can be used, such as drying with hot air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams. By drying the slurry composition on the current collector in this way, an electrode composite layer is formed on the current collector, and a negative electrode comprising the current collector and the electrode composite layer can be obtained.

[0099] Furthermore, after the drying process, the electrode composite layer may be subjected to pressure treatment using a die press or roll press. Pressure treatment can improve the peel strength of the negative electrode.

[0100] (Nonaqueous electrolyte secondary battery) The non-aqueous electrolyte secondary battery of the present invention is equipped with the negative electrode of the present invention described above. Furthermore, because the non-aqueous electrolyte secondary battery of the present invention is equipped with the negative electrode of the present invention, it exhibits excellent resistance increase suppression during high-temperature storage tests and excellent cycle characteristics. Examples of the non-aqueous electrolyte secondary battery of the present invention include lithium-ion secondary batteries and sodium-ion secondary batteries.

[0101] Herein, the configuration of a lithium-ion secondary battery as an example of the non-aqueous electrolyte secondary battery of the present invention will be described. This lithium-ion secondary battery comprises the negative electrode, positive electrode, electrolyte, and separator of the present invention.

[0102] <Positive electrode> The positive electrode is not particularly limited and any known positive electrode for non-aqueous electrolyte secondary batteries (e.g., lithium-ion secondary batteries) can be used.

[0103] <Electrolyte> Typically, an organic electrolyte is used, which is obtained by dissolving a supporting electrolyte in an organic solvent. For example, lithium salts are used as supporting electrolytes. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. Among these, LiPF6, LiClO4, and CF3SO3Li are preferred, with LiPF6 being particularly preferred, because they are easily soluble in the solvent and exhibit a high degree of dissociation. Note that one type of electrolyte may be used alone, or two or more types may be used in any ratio. 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.

[0104] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte, but suitable examples include carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (EMC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. A mixture of these solvents may also be used. Among these, carbonates are preferred because they have a high dielectric constant and a wide stable potential range, and a mixture of ethylene carbonate and ethyl methyl carbonate is even more preferred. The concentration of the electrolyte in the electrolyte solution can be adjusted as appropriate. For example, it is preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and even more preferably 5 to 10% by mass. In addition, known additives such as fluoroethylene carbonate (FEC), vinylene carbonate (VC), and ethyl methyl sulfone may be added to the electrolyte solution.

[0105] <Separator> The separator is not particularly limited, and for example, those described in Japanese Patent Publication No. 2012-204303 can be used. Among these, a microporous membrane made of polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it allows for a thinner overall film thickness of the separator, thereby increasing the ratio of electrode active material in the lithium-ion secondary battery and thus increasing the capacity per unit volume.

[0106] <Manufacturing method of non-aqueous electrolyte secondary battery> A non-aqueous electrolyte secondary battery according to the present invention can be manufactured, for example, by stacking the negative electrode and positive electrode of the present invention via a separator, winding or folding them as needed according to the battery shape, placing them in a battery container, and then injecting the electrolyte into the battery container and sealing it. To prevent pressure rise inside the secondary battery, overcharge and discharge, etc., an overcurrent prevention element such as a fuse or PTC element, expanded metal, lead plates, etc. may be provided as needed. The shape of the non-aqueous electrolyte secondary battery may be any of the following: coin type, button type, sheet type, cylindrical type, rectangular type, flat type, etc. [Examples]

[0107] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" used to express quantities refer to mass unless otherwise specified. Furthermore, in polymers produced by copolymerizing multiple types of monomers, the proportion of a monomer unit formed by polymerizing a certain monomer in the polymer is, unless otherwise specified, usually equal to the ratio (starting ratio) of that particular monomer to the total monomers used in the polymerization of the polymer. In the examples and comparative examples, the weight-average molecular weight of the water-soluble polymer (corresponding to dispersant (B)), the dispersion stability of the conductive paste, the viscosity stability of the slurry composition, the water content of the negative electrode, the cycle characteristics of the lithium-ion secondary battery, and the resistance increase rate during high-temperature storage tests of the lithium-ion secondary battery were evaluated using the following methods.

[0108] <Weight average molecular weight> A water-soluble polymer (corresponding to dispersant (B)) was used as the polymer to be measured, and its weight-average molecular weight was measured by gel permeation chromatography (GPC) using the following procedure. First, the polymer to be measured was added to approximately 5 mL of eluent to a solid content concentration of approximately 0.5 g / L, and slowly dissolved at room temperature. After visually confirming the dissolution of the polymer, the sample for measurement was gently filtered through a 0.45 μm pore size filter. Then, the weight-average molecular weight as a value converted to a standard substance was calculated by creating a calibration curve using a standard substance. The measurement conditions were as follows. <<Measurement Conditions>> Column: Manufactured by Showa Denko Corporation, product name Shodex OHpak (SB-G, SB-807HQ, SB-806MHQ) Eluent: 0.1M Tris buffer (with 0.1M potassium chloride added) Flow rate: 0.5mL / min Sample concentration: 0.05 g / L (solid content concentration) Injection volume: 200μL Column temperature: 40℃ Detector: Differential refractive index detector RI (manufactured by Tosoh Corporation, product name "RI-8020") Standard material: Monodisperse pullulan (manufactured by Showa Denko Corporation)

[0109] <Dispersion stability> The viscosity η1 of the conductive paste immediately after preparation was measured using a B-type viscometer at a temperature of 25°C and a spindle rotation speed of 60 rpm, 60 seconds after the start of spindle rotation. The conductive paste was stored at 25°C for 10 days under static conditions, and the viscosity η2 after storage was measured in the same manner as for viscosity η1. The ratio of η2 to η1 (η2 / η1) was defined as the paste viscosity ratio and evaluated according to the following criteria. The closer the paste viscosity ratio is to 1.0, the more the viscosity increase of the conductive paste is suppressed, indicating superior dispersion stability. A: Paste viscosity ratio is less than 1.15 B: Paste viscosity ratio is 1.15 or higher and less than 1.6 C: Paste viscosity ratio is 1.6 or higher and less than 2.0 D: Paste viscosity ratio is 2.0 or higher

[0110] <Viscosity stability> The viscosity η3 of the slurry composition immediately after preparation was measured using a B-type viscometer at a temperature of 25°C and a spindle rotation speed of 60 rpm, 60 seconds after the start of spindle rotation. The slurry composition after η3 measurement was stored at 25°C for 3 days under static conditions, and the viscosity η4 after storage was measured in the same manner as for viscosity η3. The ratio of η4 to η3 (η4 / η3) was defined as the slurry viscosity ratio and evaluated according to the following criteria. The closer the slurry viscosity ratio value is to 1.0, the more the viscosity increase of the slurry composition is suppressed, indicating excellent viscosity stability. A: Slurry viscosity ratio is less than 1.2 B: Slurry viscosity ratio is 1.2 or higher and less than 1.4 C: Slurry viscosity ratio is 1.4 or higher and less than 1.5 D: Slurry viscosity ratio is 1.5 or higher

[0111] <Moisture content> The negative electrodes obtained in the examples and comparative examples were cut to a size of 10 cm wide x 10 cm long to prepare test specimens. These test specimens were left at a temperature of 25°C and a dew point of -60°C for 24 hours. Subsequently, the moisture content of the test specimens was measured using a coulometric titration moisture meter and the Karl Fischer method (JIS K-0068 (2001) moisture vaporization method, vaporization temperature 150°C), and evaluated according to the following criteria. A lower moisture content in the test specimen indicates superior moisture removal performance of the negative electrode. A: Moisture content is less than 500 ppm B: Moisture content between 500 ppm and less than 700 ppm C: Moisture content between 700 ppm and less than 1000 ppm D: Moisture content of 1000 ppm or more

[0112] <Cycle Characteristics> After the electrolyte was injected into the lithium-ion secondary battery, it was left to stand for 24 hours at 25°C. Next, the battery was charged to a cell voltage of 4.35V using a constant current method of 0.1C, and then discharged to a cell voltage of 2.75V. The initial capacity C0 was measured. Furthermore, the battery was repeatedly charged to a cell voltage of 4.35V using a constant current method of 1.0C at 25°C, and then discharged to a cell voltage of 2.75V using the same constant current method. The capacity C1 after 100 cycles was measured. The capacity retention rate (%) = C1 / C0 × 100 was then calculated and evaluated according to the following criteria. A higher capacity retention rate indicates superior cycle characteristics of the lithium-ion secondary battery. A: Capacity retention rate of 90% or more B: Capacity retention rate is 85% or more but less than 90% C: Capacity retention rate is 80% or more but less than 85% D: Capacity retention rate is less than 80%

[0113] <Resistance change rate during high-temperature storage test> After the electrolyte was injected into the lithium-ion secondary battery, it was left to stand for 24 hours at 25°C. Next, the battery was charged to a cell voltage of 4.35V using a constant current method at 0.1C, and then discharged to a cell voltage of 2.75V to measure its initial capacity. Subsequently, after charging to a depth of charge (SOC) of 50%, the battery was charged for 30 seconds and discharged for 30 seconds at 1.0C, centered around the 50% SOC. The IV resistance R1 was calculated by dividing the voltage change during the 30 seconds of charging by the current. The cells were again charged to 4.35V using a constant current method at 0.1C, and a high-temperature storage test was performed by storing them in a constant temperature chamber at 60°C for one week. After the test, the IV resistance was measured in the cells in the same manner to obtain the IV resistance R2. The resistance change rate was calculated using (R2 / R1) × 100 and evaluated according to the following criteria. The closer the resistance change rate is to 100%, the better the lithium-ion secondary battery's durability during high-temperature storage tests. A: Resistivity change rate is less than 110% B: Resistivity change rate is 110% or more but less than 120% C: Resistivity change rate is 120% or more but less than 140% D: Resistivity change rate is 140% or more

[0114] (Example 1) <Preparation of water-soluble polymers> 900 parts of deionized water were added to a 1.5 L glass flask equipped with a stirring blade, heated to 40°C, and the flask was purged with nitrogen gas at a flow rate of 100 mL / min. Next, 30 parts of acrylic acid as an unsaturated carboxylic acid monomer, 40 parts of acrylamide as a (meth)acrylamide group-containing monomer, and 30 parts of sodium styrenesulfonate as an aromatic sulfonic acid monomer were mixed and injected into the flask. After that, nitrogen bubbling was performed at a flow rate of 1.5 L / min for 60 minutes using a sintered metal nozzle to degas the mixture, and then 10 parts of a 5.0% aqueous solution of ascorbic acid as a polymerization accelerator were added by syringe. Five minutes after the addition of the polymerization accelerator, 10 parts of a 10% aqueous solution of ammonium persulfate as a polymerization initiator were added to the flask by syringe to start the polymerization reaction. Two hours after the addition of the polymerization initiator, the temperature was raised to 60°C and maintained for two hours to allow the polymerization reaction to proceed. Four hours after adding the polymerization initiator, the flask was opened to air to stop the polymerization reaction. An 8% aqueous solution of lithium hydroxide was added, and the pH was adjusted to 8.0 while maintaining the temperature at 25°C to obtain an aqueous solution of a water-soluble polymer (weight-average molecular weight: 106,000) to be used as a dispersant (B).

[0115] <Preparation of conductive paste> 100 parts of carbon nanotubes (A) (single-walled, 6.3 μm length, 1.8 nm diameter (outer diameter)), 1.0 part of 1,2-benzoisothiazolin-3-one as a dispersant (C), and an appropriate amount of deionized water as a dispersion medium (solvent) were stirred in a disperser (3000 rpm, 60 minutes), and then mixed for 30 minutes at a peripheral speed of 8 m / s using a bead mill with 1 mm diameter zirconia beads. To the resulting premixture, 100 parts (equivalent to solid content) of an aqueous solution of the water-soluble polymer obtained as a dispersant (B) as described above was added, and the mixture was further mixed in a bead mill for 30 minutes to produce a conductive paste (solid content concentration: 2.0%). The pH of this conductive paste was 8.0. The dispersion stability of this conductive paste was evaluated. The results are shown in Table 1.

[0116] <Preparation of particulate binder> The particulate binder (particulate polymer) used as a binder was prepared as follows. In a 5 MPa pressure vessel A equipped with a stirrer, 3.15 parts styrene, 1.66 parts 1,3-butadiene, 0.2 parts sodium lauryl sulfate as an emulsifier, 20 parts deionized water, and 0.03 parts potassium persulfate as a polymerization initiator were added and thoroughly stirred. The mixture was then heated to 60°C to initiate polymerization, and the reaction was carried out for 6 hours to obtain seed particles. After the above reaction, the mixture was heated to 75°C, and the addition of a mixture of 53.85 parts styrene, 31.34 parts 1,3-butadiene, 10.0 parts acrylic acid, 0.25 parts tert-dodecyl mercaptan as a chain transfer agent, and 0.35 parts sodium lauryl sulfate as an emulsifier was started from another container B into pressure vessel A. Simultaneously, the addition of 1 part potassium persulfate as a polymerization initiator to pressure vessel A was started to initiate the second stage of polymerization. Specifically, the monomer composition consisted of 57 parts styrene, 33 parts 1,3-butadiene, and 10 parts acrylic acid. Five and a half hours after the start of the second polymerization stage, the entire mixture containing these monomer compositions was added, and the reaction was then continued at 85°C for 6 hours. The reaction was stopped by cooling when the polymerization conversion rate reached 97%. A 5% aqueous sodium hydroxide solution was added to the mixture containing the polymer to adjust the pH to 8. Unreacted monomers were then removed by heated vacuum distillation. After further cooling, an aqueous dispersion of particulate binder (water-insoluble) was obtained.

[0117] <Preparation of slurry composition for negative electrode> In a planetary mixer with a disperser, artificial graphite (volume average particle size: 24.5 μm, specific surface area: 3.5 m²) is used as a carbon-based negative electrode active material. 2 90 parts ( / g) and SiO as a silicon-based negative electrode active material xTen parts of the material and 2.0 parts (equivalent to solid content) of an aqueous solution of carboxymethylcellulose sodium salt as a thickening agent were added, and the solid content was adjusted to 58% with deionized water. The mixture was then mixed at room temperature for 60 minutes. After mixing, the conductive paste obtained as described above was added to the planetary mixer so that the carbon nanotubes amounted to 0.1 parts (equivalent to solid content), and the mixture was mixed. Next, the solid content was adjusted to 50% with deionized water, and then 1.0 part (equivalent to solid content) of the aqueous dispersion of the binder obtained as described above was added to obtain a mixed solution. The obtained mixed solution was defoamed under reduced pressure to obtain a smooth anode slurry composition. The viscosity stability of this anode slurry composition was evaluated. The results are shown in Table 1.

[0118] <Manufacturing of negative electrodes> The negative electrode slurry composition obtained as described above was coated onto a 16 μm thick copper foil (current collector) using a comma coater, resulting in a dry film thickness of 105 μm and a coating amount of 10 mg / cm². 2 The mixture was applied in this manner. The copper foil coated with this negative electrode slurry composition was transported at a speed of 0.5 m / min in an oven at 100°C for 2 minutes, and then in an oven at 120°C for another 2 minutes to dry the negative electrode slurry composition on the copper foil and obtain a negative electrode base roll. This negative electrode base roll was rolled in a roll press to obtain a negative electrode with a negative electrode composite layer thickness of 80 μm. The moisture content of this negative electrode was evaluated. The results are shown in Table 1.

[0119] <Manufacturing of positive electrodes> A slurry composition for the positive electrode was obtained by mixing 95 parts of LiCoO2 having a spinel structure as the positive electrode active material, 3 parts of PVDF (polyvinylidene fluoride) in terms of solid content as the positive electrode binder, 2 parts of acetylene black as the conductive material, and 20 parts of N-methylpyrrolidone as the solvent in a planetary mixer. The obtained cathode slurry composition was coated onto a 20 μm thick aluminum foil (current collector) using a comma coater so that the film thickness after drying would be approximately 100 μm. The aluminum foil coated with this cathode slurry composition was transported at a speed of 0.5 m / min in an oven at 60°C for 2 minutes, and then in an oven at 120°C for another 2 minutes to dry the cathode slurry composition on the aluminum foil and obtain a cathode base roll. This cathode base roll was rolled in a roll press to obtain a cathode with a cathode composite layer thickness of 70 μm.

[0120] <Obtaining a separator> A single-layer polypropylene separator (65 mm wide, 500 mm long, 25 μm thick; manufactured by dry process; porosity 55%) was prepared. This separator was cut into 5 cm x 5 cm squares and used in the manufacture of the lithium-ion secondary battery described below.

[0121] <Manufacturing of secondary batteries> An aluminum packaging material was prepared as the battery casing. The positive electrode was cut into a 4cm x 4cm square and placed so that the surface on the current collector side was in contact with the aluminum packaging material. Next, the square separator was placed on the surface of the positive electrode composite layer. Furthermore, the negative electrode was cut into a 4.2cm x 4.2cm square and placed on the separator so that the surface on the negative electrode composite layer side faced the separator. Subsequently, a 1.0M LiPF6 solution (solvent being a mixed solvent of ethylene carbonate / diethyl carbonate = 1 / 2 (volume ratio)) was filled as the electrolyte, and fluoroethylene carbonate and vinylene carbonate (each containing 2 vol% (solvent ratio)) were added as additives. Finally, the opening of the aluminum packaging material was sealed by heat sealing at 150°C, and the aluminum packaging material was closed to manufacture a laminate cell type lithium-ion secondary battery. The cycle characteristics and resistance increase rate during high-temperature storage tests were evaluated for this lithium-ion secondary battery. The results are shown in Table 1.

[0122] (Example 2) In preparing the water-soluble polymer, an aqueous solution of the water-soluble polymer (weight-average molecular weight: 214,000) was obtained using 20 parts of acrylic acid as an unsaturated carboxylic acid monomer and 80 parts of acrylamide as a (meth)acrylamide group-containing monomer, in the same manner as in Example 1. Various manufacturing, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0123] (Example 3) In preparing the conductive paste, various manufacturing, measurements, and evaluations were performed in the same manner as in Example 1, except that carbon nanotubes (A) were CNTs (multilayer, length 3.9 μm, diameter (outer diameter) 14 nm). The results are shown in Table 1.

[0124] (Example 4) Except for adding 50 parts (equivalent to the amount of solids) of an aqueous solution of a water-soluble polymer as a dispersant (B) to the conductive paste, various manufacturing, measurements, and evaluations were carried out in the same manner as in Example 3. The results are shown in Table 1.

[0125] (Examples 5, 6, 8) In preparing the water-soluble polymer, aqueous solutions of the water-soluble polymer (weight-average molecular weight: 87,000 in Example 5, 87,000 in Example 6, and 25,000 in Example 8) were obtained using acrylic acid as an unsaturated carboxylic acid monomer, acrylamide as a (meth)acrylamide group-containing monomer, and sodium styrene sulfonate as an aromatic sulfonic acid monomer, in a blending ratio of 60 parts:20 parts:20 parts in Example 5, 72 parts:24 parts:4 parts in Example 6, and 15 parts:55 parts:30 parts in Example 8. The manufacturing, measurement, and evaluation were carried out in the same manner as in Example 1, except that the monomers used were acrylic acid as an unsaturated carboxylic acid monomer, acrylamide as a (meth)acrylamide group-containing monomer, and sodium styrene sulfonate as an aromatic sulfonic acid monomer.

[0126] (Example 7) Except for preparing the binder in the same manner as in Example 1, where the monomers styrene:butadiene:acrylic acid were blended in parts of 61 parts:37 parts:2 parts to obtain a particulate binder (particulate polymer) as a binder, various manufacturing, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0127] (Example 9) The conductive paste was prepared in the same manner as in Example 1, except that 2-methylthiazoline was used as the dispersant (C). Various manufacturing, measurements, and evaluations were performed. The results are shown in Table 1.

[0128] (Comparative Example 1) Except for using 0.8 parts of triaminotriazine as a dispersant (C) in the preparation of the conductive paste, various manufacturing, measurement, and evaluation procedures were carried out in the same manner as in Example 2. The results are shown in Table 1.

[0129] (Comparative Example 2) Except for the absence of a dispersant (C) in the preparation of the conductive paste, various manufacturing, measurement, and evaluation procedures were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0130] (Comparative Example 3) In preparing the water-soluble polymer, various manufacturing, measurements, and evaluations were carried out in the same manner as in Example 1, except that an aqueous solution of the water-soluble polymer (weight-average molecular weight: 143,000) was obtained using 21 parts vinylnaphthalene and 79 parts allyl sulfonic acid as monomers. The results are shown in Table 1.

[0131] (Comparative Example 4) In preparing the water-soluble polymer, various manufacturing, measurement, and evaluation procedures were carried out in the same manner as in Example 1, except that an aqueous solution of the water-soluble polymer (weight-average molecular weight: 250,000) was obtained using only acrylic acid as the monomer. The results are shown in Table 1.

[0132] (Comparative Example 5) In preparing the water-soluble polymer, only acrylamide was used as the monomer, and an aqueous solution of the water-soluble polymer (weight-average molecular weight: 227,000) was obtained without adding an aqueous lithium hydroxide solution. Except for this, the preparation, measurement, and evaluation of the conductive material paste were carried out in the same manner as in Example 1. However, since a slurry composition for the negative electrode could not be prepared, subsequent manufacturing, measurement, and evaluation could not be performed. The results are shown in Table 1.

[0133] (Comparative Example 6) In preparing the water-soluble polymer, an aqueous solution of the water-soluble polymer (weight-average molecular weight: 159,000) was obtained using 40 parts of acrylic acid and 60 parts of styrene sulfonic acid as monomers. Except for these parts, the manufacturing, measurement, and evaluation procedures were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0134] (Comparative Example 7) The conductive paste was prepared in the same manner as in Example 1, except that an aqueous solution of a water-soluble polymer was not added as a dispersant (B). Various manufacturing, measurements, and evaluations were performed. The results are shown in Table 1.

[0135] (Comparative Example 8) Except that, when preparing the conductive paste, an aqueous solution of the water-soluble polymer as a dispersant (B) was not added, and instead, when preparing the slurry composition for the negative electrode, an aqueous solution of the water-soluble polymer produced in Example 1 was added as a thickening agent, various manufacturing, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0136] [Table 1-1]

[0137] [Table 1-2]

[0138] The abbreviations used in the table are as follows: AA: Acrylic acid Aamid: Acrylamide SSNa: Sodium styrene sulfonate St: Styrene BD: Butadiene CMC: Carboxymethylcellulose sodium salt

[0139] Table 1 shows that by using the conductive pastes of Examples 1 to 9, it is possible to provide a slurry composition for the anode of a non-aqueous electrolyte secondary battery that maintains paste dispersibility and slurry viscosity stability, while also providing a non-aqueous electrolyte secondary battery in which the resistance increase rate during high-temperature storage tests is suppressed. [Industrial applicability]

[0140] According to the present invention, it is possible to provide a conductive paste for a non-aqueous electrolyte secondary battery that enables the provision of a slurry composition for the negative electrode of a non-aqueous electrolyte secondary battery that maintains paste dispersibility and slurry viscosity stability, while also providing a non-aqueous electrolyte secondary battery in which the rate of resistance increase during high-temperature storage tests is suppressed. Furthermore, according to the present invention, it is possible to provide a slurry composition for a non-aqueous electrolyte secondary battery anode that maintains slurry viscosity stability while also providing a non-aqueous electrolyte secondary battery in which the rate of resistance increase during high-temperature storage tests is suppressed. Furthermore, according to the present invention, it is possible to provide a negative electrode for a non-aqueous electrolyte secondary battery that can provide a non-aqueous electrolyte secondary battery in which the rate of resistance increase during high-temperature storage tests is suppressed. Furthermore, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery in which the rate of resistance increase during high-temperature storage tests is suppressed.

Claims

1. A conductive paste for non-aqueous electrolyte secondary batteries, comprising carbon nanotubes (A), a dispersant (B), a dispersant (C), and water, wherein the dispersant (B) is a copolymer comprising at least an unsaturated carboxylic acid monomer unit and a (meth)acrylamide group-containing monomer unit, and the dispersant (C) is thiazoline or a derivative thereof.

2. The conductive paste for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that the copolymer, which is the dispersant (B), further contains aromatic sulfonic acid monomer units.

3. The conductive paste for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that, in the copolymer which is the dispersant (B), when the total monomer units are 100 parts by mass, the content of the unsaturated carboxylic acid monomer units is 5 parts by mass or more and 80 parts by mass or less.

4. The conductive paste for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that, in the copolymer which is the dispersant (B), when the content of the unsaturated carboxylic acid monomer unit is 100 parts by mass, the content of the (meth)acrylamide group-containing monomer unit is 25 parts by mass or more and 400 parts by mass or less.

5. The conductive paste for non-aqueous electrolyte secondary battery according to claim 1, characterized in that at least a portion of the unsaturated carboxylic acid monomer units contained in the copolymer which is the dispersant (B) is in the form of a neutralized salt which is an alkali metal salt or an ammonium salt.

6. The conductive paste for non-aqueous electrolyte secondary battery according to claim 1, characterized in that the dispersant (C) is thiazoline or a derivative thereof is isothiazoline or a derivative thereof.

7. A conductive paste for a non-aqueous electrolyte secondary battery according to claim 1, further comprising carbon black.

8. The conductive paste for a non-aqueous electrolyte secondary battery according to claim 1, wherein the conductive paste further comprises a particulate polymer, and the particulate polymer comprises at least an unsaturated carboxylic acid monomer unit, an aromatic vinyl monomer unit, and a diene monomer unit as constituent units of the polymer.

9. The conductive paste for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that the pH of the conductive paste is 6 or more and 9 or less.

10. A slurry composition for a negative electrode of a non-aqueous electrolyte secondary battery, characterized by comprising a conductive paste for non-aqueous electrolyte secondary batteries according to any one of claims 1 to 9, and at least a silicon-based active material.

11. A negative electrode for a non-aqueous electrolyte secondary battery, comprising a negative electrode composite layer formed using the slurry composition described in claim 10.

12. A non-aqueous electrolyte secondary battery comprising the negative electrode described in claim 11.

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