Conductive material paste for non-aqueous electrolyte secondary battery, slurry composition for negative electrode of non-aqueous electrolyte secondary battery, negative electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

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

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

[0001] The present invention relates to a conductive material paste for a non-aqueous electrolyte secondary battery, a slurry composition for a 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.

[0002]

[0003] Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries are small, lightweight, have high energy density, and are capable of repeated charge and discharge, and are therefore used in a wide range of applications. An electrode for a nonaqueous electrolyte secondary battery includes, for example, a current collector and an electrode mixture layer formed on the current collector by drying a slurry composition for a nonaqueous electrolyte secondary battery electrode.

[0003] In recent years, fibrous conductive carbon such as carbon nanotubes (hereinafter sometimes abbreviated as "CNTs") has been used as a conductive material in forming an electrode mixture layer. Here, when forming an electrode mixture layer using fibrous conductive carbon, in order to obtain an electrode mixture layer in which the fibrous conductive carbon is well dispersed, a technique has been proposed in which the fibrous conductive carbon and a dispersant are premixed to form a conductive material paste for a non-aqueous electrolyte secondary battery electrode, and the obtained conductive material paste is combined with an electrode active material to prepare a slurry composition for a non-aqueous electrolyte secondary battery electrode (see, for example, Patent Documents 1 and 2).

[0004] International Publication No. 2020 / 196115 International Publication No. 2020 / 208880

[0005] However, the above-mentioned conventional techniques have room for further improvement in terms of suppressing the rate of increase in resistance during a high-temperature storage test in a nonaqueous electrolyte secondary battery. Specifically, there has been a need to provide a conductive material paste for a nonaqueous electrolyte secondary battery that can provide a nonaqueous electrolyte secondary battery in which the rate of increase in resistance during a high-temperature storage test is suppressed, while enabling the provision of a slurry composition for a negative electrode of a nonaqueous electrolyte secondary battery that maintains paste dispersibility and slurry viscosity stability.

[0006] Therefore, an object of the present invention is to provide a conductive material paste for a nonaqueous electrolyte secondary battery, which can provide a slurry composition for a nonaqueous electrolyte secondary battery negative electrode that maintains paste dispersibility and slurry viscosity stability, while providing a nonaqueous electrolyte secondary battery with a suppressed rate of resistance increase during a high-temperature storage test. Another object of the present invention is to provide a slurry composition for a nonaqueous electrolyte secondary battery negative electrode that maintains slurry viscosity stability, while providing a nonaqueous electrolyte secondary battery with a suppressed rate of resistance increase during a high-temperature storage test. Another object of the present invention is to provide a negative electrode for a nonaqueous electrolyte secondary battery, which can provide a nonaqueous electrolyte secondary battery with a suppressed rate of resistance increase during a high-temperature storage test. Another object of the present invention is to provide a nonaqueous electrolyte secondary battery with a suppressed rate of resistance increase during a high-temperature storage test.

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems, and have found that by using a conductive material paste for a non-aqueous electrolyte secondary battery containing carbon nanotubes, a dispersant that is a copolymer containing unsaturated carboxylic acid monomer units and (meth)acrylamide group-containing monomer units, a dispersant that is a thiazoline compound, and water as a dispersion medium, it is possible to provide a slurry composition for a 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 increase in resistance during a high-temperature storage test is suppressed, thereby completing the present invention.

[0008]

[0010] The present invention has an object to advantageously solve the above-mentioned problems, and provides a conductive material paste for non-aqueous electrolyte secondary batteries, the conductive material paste comprising 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.

[0011] Thus, by using a conductive material 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 negative electrode of a non-aqueous electrolyte secondary battery that maintains the paste dispersibility and slurry viscosity stability of the paste, a negative electrode for a non-aqueous electrolyte secondary battery that can provide a non-aqueous electrolyte secondary battery with a suppressed rate of increase in resistance during a high-temperature storage test, and a non-aqueous electrolyte secondary battery with a suppressed rate of increase in resistance during a high-temperature storage test.

[0009] Here, the copolymer serving as the dispersant (B) preferably further contains an aromatic sulfonic acid monomer unit.

[0010] In addition, in the copolymer that is the dispersant (B), when the total amount of monomer units is taken as 100 parts by mass, the content of the unsaturated carboxylic acid monomer units is preferably 5 parts by mass or more and 80 parts by mass or less.

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

[0012] At least a part of the unsaturated carboxylic acid monomer units contained in the copolymer serving as the dispersant (B) is preferably in the form of a neutralized salt such as an alkali metal salt or an ammonium salt.

[0013] The thiazoline or its derivative as the dispersant (C) is preferably an isothiazolinone or its derivative.

[0014] The conductive paste for a non-aqueous electrolyte secondary battery of the present invention preferably further contains carbon black.

[0015] It is also preferable that the conductive material paste further contains a particulate polymer, and 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 polymer constituent units.

[0016] It is also preferable that the pH of the conductive paste is 6 or more and 9 or less.

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

[0018] The negative electrode for a non-aqueous electrolyte secondary battery of the present invention includes a negative electrode mixture layer formed using the above-described slurry composition.

[0019] The nonaqueous electrolyte secondary battery of the present invention includes the above-described negative electrode.

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

[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 for producing a slurry composition for a non-aqueous electrolyte secondary battery negative electrode. Also, the negative electrode for a non-aqueous electrolyte secondary battery of the present invention comprises a negative electrode mixture layer formed using the slurry composition for a non-aqueous electrolyte secondary battery negative electrode of the present invention. Also, the non-aqueous electrolyte secondary battery of the present invention comprises 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 material paste for non-aqueous electrolyte secondary batteries of the present invention (hereinafter sometimes simply referred to as "conductive material paste") is a composition comprising carbon nanotubes (A), dispersants (B), and dispersants (C) dispersed and / or dissolved 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. Use of such a conductive material paste makes it possible to provide a slurry composition for a non-aqueous electrolyte secondary battery negative electrode that maintains the paste dispersibility and slurry viscosity stability of the paste, while also making it possible to fabricate a slurry composition for a non-aqueous electrolyte secondary battery negative electrode that can provide a non-aqueous electrolyte secondary battery with a suppressed rate of increase in resistance during a high-temperature storage test, a non-aqueous electrolyte secondary battery negative electrode that can provide a non-aqueous electrolyte secondary battery with a suppressed rate of increase in resistance during a high-temperature storage test, and a non-aqueous electrolyte secondary battery with a suppressed rate of increase in resistance during a high-temperature storage test.

[0023] <Carbon nanotubes (A)> The carbon nanotubes (A) are not particularly limited as long as they are carbon nanotubes (CNTs) that achieve the object of the present invention. Carbon nanotubes include single-walled (SW) carbon nanotubes and multi-walled (MW) carbon nanotubes, depending on the type of layer. The carbon nanotubes (A) may be single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination thereof, but single-walled carbon nanotubes are preferred from the viewpoint of being able to form a longer-distance conductive path in 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, and even more preferably 2 nm or more, and may be 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, and even more preferably 5 μm or more, and may be 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 equal to or greater than the above lower limits, CNT aggregation can be sufficiently suppressed, ensuring sufficient dispersibility of the CNTs as a conductive material. Furthermore, if the average diameter and average length are equal to or less than the above upper limits, a good conductive path can be formed in the electrode mixture 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, respectively, of 100 randomly selected CNTs using a TEM.

[0025] The aspect ratio (length / diameter) of a CNT is usually greater than 5, and preferably greater than or equal to 10. Here, in the present invention, the "aspect ratio" of a CNT can be determined by measuring the major axis and minor axis of 100 randomly selected CNTs using a transmission electron microscope.

[0026] <<Method for Producing Carbon Nanotubes>> CNTs having the above-described properties can be prepared using known methods such as arc discharge, laser ablation, and super growth, without any particular limitations.

[0027] <<Carbon Nanotube (A) Content>> The content of the carbon nanotubes (A) relative to the total solid content of the conductive material paste may be, for example, 20% by mass or more, preferably 30% by mass or more, and more preferably 40% by mass or more. This content may also be, for example, 90% by mass or less, preferably 85% by mass or less, and more preferably 80% by mass or less. When the content of the carbon nanotubes (A) is equal to or greater than the above-mentioned lower limit, the electrical contact of the carbon nanotubes (A) in the electrode mixture layer can be better ensured, the internal resistance of the resulting secondary battery can be reduced, and better output characteristics can be exhibited. Furthermore, the capacity of the secondary battery can be more stably preserved. On the other hand, when the content of the carbon nanotubes (A) is equal to or less than the above-mentioned upper limit, the content of the dispersant (B) can be increased, thereby enhancing the effects of the dispersant (B) in improving the paste dispersibility of the resulting conductive material paste and the slurry viscosity stability of the resulting slurry composition.

[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, from the viewpoint of further improving the dispersibility of carbon nanotubes, the copolymer serving as the dispersant (B) may preferably further contain aromatic sulfonic acid monomer units. In the present invention, the term "water-soluble polymer" refers to a polymer that has an insoluble content of less than 1.0 mass % when 0.5 g of the polymer is dissolved in 100 g of water at a temperature of 25°C. Furthermore, the term "containing a monomer unit" in a polymer means that "a polymer obtained using the monomer contains a repeating unit derived from the monomer." Furthermore, in the present invention, the content ratio of the monomer unit in the polymer is: １ H-NMR and １３ It can be measured using a nuclear magnetic resonance (NMR) method such as C-NMR.

[0029] <<Unsaturated Carboxylic Acid Monomer Units>> Examples of the unsaturated carboxylic acid monomer units constituting the copolymer that is the dispersant (B) include ethylenically unsaturated carboxylic acid monomer units. Ethylenically unsaturated carboxylic acid monomers that can form ethylenically unsaturated carboxylic acid monomer units typically have no 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 derivatives thereof, ethylenically unsaturated dicarboxylic acids and acid anhydrides thereof, and derivatives thereof. The ethylenically unsaturated carboxylic acid monomers may be used alone 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, methylmaleic anhydride, and dimethylmaleic anhydride. Examples of derivatives of ethylenically unsaturated dicarboxylic acids include methylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, and fluoromaleic acid.

[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, as the ethylenically unsaturated carboxylic acid monomer, an ethylenically unsaturated monocarboxylic acid and an ethylenically unsaturated dicarboxylic acid are preferred, acrylic acid, methacrylic acid and itaconic acid are more preferred, and acrylic acid and methacrylic acid are even more preferred.Furthermore, from the viewpoint of suppressing excessive swelling of the obtained 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 moiety is an alkali metal salt or 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 serving as dispersant (B), when the total monomer units are taken as 100 parts by mass, the content of the unsaturated carboxylic acid monomer units is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 25 parts by mass or more, and is 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. When the content ratio of the unsaturated carboxylic acid monomer units in the copolymer serving as dispersant (B) is equal to or greater than the above-mentioned lower limit, the paste dispersibility of the resulting conductive material paste can be improved. On the other hand, when the content ratio of the unsaturated carboxylic acid monomer units in the copolymer serving as dispersant (B) is equal to or less than the above-mentioned upper limit, the suppression of the resistance increase rate during a high-temperature storage test of the resulting nonaqueous electrolyte secondary battery can be improved.

[0034] <<(Meth)acrylamide Group-Containing Monomer Unit>> The (meth)acrylamide monomer capable of forming the (meth)acrylamide group-containing monomer unit is acrylamide, methacrylamide, or a combination thereof.

[0035] In the copolymer serving as dispersant (B), when the total monomer units are taken as 100 parts by mass, the content of the (meth)acrylamide group-containing monomer units is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 25 parts by mass or more, and 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 serving as dispersant (B), when the total content of the unsaturated carboxylic acid monomer units is taken as 100 parts by mass, the content of the (meth)acrylamide group-containing monomer units is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 35 parts by mass or more, and 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. When the content ratio of the (meth)acrylamide group-containing monomer units is equal to or greater than the above lower limit, the cycle characteristics of the resulting nonaqueous electrolyte secondary battery can be improved. On the other hand, when the content of the (meth)acrylamide monomer unit is equal to or less than the upper limit, the viscosity stability of the resulting slurry composition can be improved.

[0036] <<Aromatic Sulfonic Acid Monomer Unit>> An "aromatic sulfonic acid monomer" capable of forming an aromatic sulfonic acid monomer unit refers to 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 divinyl benzene sulfonic acid.

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

[0038] In the copolymer serving as dispersant (B), when the total monomer units are taken as 100 parts by mass, the content of the aromatic sulfonic acid monomer units is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, and is 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. When the content of the aromatic sulfonic acid monomer units in the copolymer serving as dispersant (B) is equal to or greater than the above-mentioned lower limit, the paste dispersibility of the resulting conductive material paste can be improved. On the other hand, when the content of the aromatic sulfonic acid monomer units in the copolymer serving as dispersant (B) is equal to or less than the above-mentioned upper limit, the resistance increase rate suppression and cycle characteristics during a high-temperature storage test of the resulting nonaqueous electrolyte secondary battery can be improved.

[0039] <<Other Monomer Units>> The monomers that can form the other monomer units constituting the copolymer that is the dispersant (B) are not particularly limited as long as they are monomers that can be copolymerized with the monomer having a carbon-carbon unsaturated bond, and examples thereof include monomers having a carbon-carbon unsaturated bond other than the above-mentioned unsaturated carboxylic acid monomers, (meth)acrylamide group-containing monomers, and aromatic sulfonic acid monomers. Examples of such monomers having a carbon-carbon unsaturated bond 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 above-mentioned monomers copolymerizable with the monomer having a carbon-carbon unsaturated bond may be used alone, or two or more may be used in combination at any ratio.

[0040] <<Weight Average Molecular Weight>> The weight average molecular weight of the copolymer serving as dispersant (B) is preferably 4,000 or more, more preferably 8,000 or more, and even more preferably 10,000 or more, and is 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 dispersant (B) is equal to or greater than the above 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 serving as dispersant (B) is equal to or less than the above upper limit, the solids concentration of the conductive material paste can be increased. In the present 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 dispersant (B) is not particularly limited. Dispersant (B) is prepared, for example, by polymerizing a monomer composition containing one or more monomers in an aqueous solvent. The content of each monomer in the monomer composition can be determined based on the content of the desired monomer unit in the polymer. The polymerization method is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization can be used. The polymerization reaction can be any reaction such as ionic polymerization, radical polymerization, living radical polymerization, various types of condensation polymerization, or addition polymerization. During the polymerization, known emulsifiers and polymerization initiators can be used as needed.

[0042] <<Content of Dispersant (B)>> The content ratio of the solid content of the dispersant (B) relative to the total solid content of the conductive material paste may be, for example, 5% by mass or more, preferably 10% by mass or more, and more preferably 15% by mass or more. This content ratio may also be, for example, 70% by mass or less, preferably 50% by mass or less, and more preferably 40% by mass or less. When the content ratio of the dispersant (B) is equal to or greater than the above-mentioned lower limit, the paste dispersibility of the resulting conductive material paste and the slurry viscosity stability of the resulting slurry composition can be improved. On the other hand, when the content ratio of the dispersant (B) is equal to or less than the above-mentioned upper limit, the content ratio of the carbon nanotubes (A) can be increased, which can better ensure electrical contact of the carbon nanotubes (A) in the electrode mixture layer and reduce the internal resistance of the resulting secondary battery, thereby enhancing the effect of exhibiting better output characteristics.

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

[0044] Thiazoline compounds include thiazolines substituted with one or more substituents, and thiazoline fused rings formed by condensing a thiazoline with another ring (which may be further substituted with one or more substituents).

[0045] Examples of the substituent include, but are not limited to, an optionally substituted hydrocarbon group, oxo, a halogen atom (e.g., chlorine atom, fluorine atom, bromine atom, iodine atom, etc.), a hydroxyl group, a cyano group, an amino group, a carboxyl group, an optionally substituted hydrocarbon-oxy group, an optionally substituted hydrocarbon-thio group, etc. Examples of the hydrocarbon group (the same applies to the "hydrocarbon" in hydrocarbon-oxy group and hydrocarbon-thio group) include, but are not limited to, an alkyl group having 1 to 10 carbon atoms (e.g., a methyl group, an ethyl group, a propyl group, etc.), an alkenyl group having 2 to 6 carbon atoms (e.g., a vinyl group, an allyl group, etc.), an alkynyl group having 2 to 6 carbon atoms (e.g., an ethynyl group, a propynyl group, etc.), a cycloalkyl group having 3 to 10 carbon atoms (e.g., a cyclopentyl group, a cyclohexyl group, etc.), an aryl group having 6 to 14 carbon atoms (e.g., a phenyl group, etc.), etc. Examples of substituents that may be substituted on the optionally substituted hydrocarbon group, the optionally substituted hydrocarbon-oxy group, and the optionally substituted hydrocarbon-thio group include, but are not limited to, those described above.

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

[0047] The thiazoline compound is preferably an isothiazolinone compound from the viewpoint of improving the paste dispersibility of the resulting conductive material paste and the cycle characteristics and the resistance increase rate suppression during a high-temperature storage test of the resulting nonaqueous electrolyte secondary battery. The isothiazolinone compound has, for example, a structure represented by the following formula (1): (In formula (1), Y is a hydrogen atom or an optionally substituted hydrocarbon group, and X １ and X ２ are each independently a hydrogen atom, a halogen atom, or an optionally substituted alkyl group having 1 to 6 carbon atoms, or X １ and X ２ together form an aromatic ring. １ and X ２ do not cooperate to form an aromatic ring, X １ and X ２ may be the same or different.)

[0048] In formula (1), examples of the hydrocarbon group represented by Y include alkyl groups having 1 to 10 carbon atoms (e.g., methyl), alkenyl groups having 2 to 6 carbon atoms (e.g., vinyl, allyl), alkynyl groups having 2 to 6 carbon atoms (e.g., ethynyl, propynyl), cycloalkyl groups having 3 to 10 carbon atoms (e.g., cyclopentyl, cyclohexyl), and aryl groups having 6 to 14 carbon atoms (e.g., phenyl). Some or all of the hydrogen atoms in the hydrocarbon group represented by Y may be substituted with a substituent. Examples of such substituents include hydroxyl, halogen atoms (e.g., chlorine, fluorine, bromine, iodine), cyano, amino, carboxyl, alkoxy groups having 1 to 4 carbon atoms (e.g., methoxy, ethoxy), aryloxy groups having 6 to 10 carbon atoms (e.g., phenoxy), alkylthio groups having 1 to 4 carbon atoms (e.g., methylthio, ethylthio), and arylthio groups having 6 to 10 carbon atoms (e.g., phenylthio). When the hydrocarbon group of Y has a plurality of 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), X １ and X ２ Examples of the halogen atom in formula (1) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. １ and X ２ Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, and a pentyl group. These alkyl groups may have some or all of their hydrogen atoms substituted with a substituent. Examples of such a substituent include the same as those described above as the substituent in the hydrocarbon group of Y. In formula (1), X １ and X ２ Examples of the aromatic ring formed by X together include a benzene ring. １ and X２ The compound of formula (1) in which X cooperate to form an aromatic ring is called an "aromatic ring-isothiazoline compound." １ and X ２ The compound of formula (1) in which do not cooperate to form an aromatic ring is called a "non-aromatic ring-isothiazoline compound."

[0051] Here, in formula (1), X １ and X ２ are each preferably a hydrogen atom or together form an aromatic ring, and from the viewpoint of further dispersing the carbon nanotubes (A) in the conductive paste and further suppressing the deposition of lithium metal at the negative electrode in the case of a lithium ion secondary battery, X １ and X ２ More preferably, these together form an aromatic ring, that is, the isothiazolinone compound is preferably an aromatic ring-isothiazoline compound.

[0052] [Benzisothiazoline Compounds] As the aromatic ring-isothiazoline compounds, X １ and X ２ A benzoisothiazoline compound having a structure represented by the following formula (2), in which a benzene ring is formed as an aromatic ring, is preferred.

[0053] (In formula (2), Y is the same as in formula (1), and X ３ ~X ６ are each independently any one of a hydrogen atom, a halogen atom, a hydroxyl group, a cyano group, an amino group, a carboxyl group, an alkyl group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 4 carbon atoms. ３ ~X ６ may be the same or different.)

[0054] In formula (2), X ３ ~X ６ The halogen atom in formula (1) is X １ and X ２In formula (2), examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group. In formula (2), examples of the alkoxy group having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, and the like.

[0055] In formula (2), Y and X ３ ~X ６ is preferably a hydrogen atom.

[0056] [Specific Examples of Thiazoline Compounds] Examples of thiazoline compounds include thiazoline, alkyl thiazolines (e.g., methyl thiazoline, ethyl thiazoline, octyl thiazoline), cycloalkyl thiazolines (e.g., cyclohexyl thiazoline), halogenated thiazolines (e.g., chlorothiazoline, dichlorothiazoline), alkyl halogenated thiazolines (e.g., methyl chlorothiazoline, ethyl chlorothiazoline, octyl chlorothiazoline, methyl dichlorothiazoline, ethyl dichlorothiazoline, octyl dichlorothiazoline), cycloalkyl halogenated thiazolines (e.g., cyclohexyl thiazoline), cyclohexylchlorothiazolinone, cyclohexyldichlorothiazolinone), thiazolinone, alkylthiazolinone (e.g., methylthiazolinone, ethylthiazolinone, octylthiazolinone), cycloalkylthiazolinone (e.g., cyclohexylthiazolinone), halogenated thiazolinone (e.g., chlorothiazolinone, dichlorothiazolinone), alkyl halogenated thiazolinone (e.g., methylchlorothiazolinone, ethylchlorothiazolinone, octylchlorothiazolinone, methyldichlorothiazolinone, ethyldichlorothiazolinone, octyldichlorothiazolinone, chlorothiazolinone), cycloalkyl halogenated thiazolinones (e.g., cyclohexylchlorothiazolinone, cyclohexyldichlorothiazolinone), benzothiazoline, alkyl benzothiazoline (e.g., methylbenzothiazoline, ethylbenzothiazoline, octylbenzothiazoline), cycloalkyl benzothiazoline (e.g., cyclohexylbenzothiazoline), halogenated benzothiazoline (e.g., chlorobenzothiazoline, dichlorobenzothiazoline), alkyl halogenated benzothiazoline (e.g., methylchlorobenzothiazoline, ethylchlorobenzothiazoline), chlorobenzothiazoline, octylchlorobenzothiazoline, methyldichlorobenzothiazoline, ethyldichlorobenzothiazoline, octyldichlorobenzothiazoline), cycloalkyl halogenated benzothiazolines (e.g., cyclohexylchlorobenzothiazoline, cyclohexyldichlorobenzothiazoline), benzothiazolinone, alkylbenzothiazolinone (e.g., methylbenzothiazolinone, ethylbenzothiazolinone, octylbenzothiazolinone), cycloalkylbenzothiazolinone (e.g., cyclohexylbenzothiazolinone),Examples of the halogenated benzothiazolinone include halogenated benzothiazolinones (e.g., chlorobenzothiazolinone, dichlorobenzothiazolinone), alkyl halogenated benzothiazolinones (e.g., methylchlorobenzothiazolinone, ethylchlorobenzothiazolinone, octylchlorobenzothiazolinone, methyldichlorobenzothiazolinone, ethyldichlorobenzothiazolinone, octyldichlorobenzothiazolinone), and cycloalkyl halogenated benzothiazolinones (e.g., cyclohexylchlorobenzothiazolinone, cyclohexyldichlorobenzothiazolinone). These may be used alone or in combination of two or more.

[0057] Among these, examples of the isothiazoline compounds represented by formula (1) include 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), cyclohexyldichlorothiazolinone, methylthiazolinone (e.g., 2-methyl-4-isothiazolin-3-one), ... Examples of the isothiazoline compounds include non-aromatic ring isothiazoline compounds such as thiazolinone (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-benzisothiazolin-3-one (BIT)) and methylbenzothiazolinone (e.g., N-methyl-1,2-benzisothiazolin-3-one). These compounds may be used alone or in combination of two or more.

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

[0059] <<Content of Dispersant (C)>> The content ratio of the solid content of the dispersant (C) relative to the total solid content of the conductive material paste may be, for example, 0.1 mass% or more, preferably 0.2 mass% or more, and more preferably 0.5 mass% or more. This content ratio may also be, for example, 20 mass% or less, preferably 10 mass% or less, and more preferably 5 mass% or less. When the content ratio of the dispersant (C) is equal to or greater than the above-mentioned lower limit, the paste dispersibility of the resulting conductive material 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 nonaqueous electrolyte secondary battery can be improved. On the other hand, when the content ratio of the dispersant (C) is equal to or greater than the above-mentioned lower limit, the content ratios of the carbon nanotubes (A) and the dispersant (B) can be increased, which can, for example, reduce the internal resistance of the resulting secondary battery and enhance the effect of exhibiting better output characteristics.

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

[0061] <Dispersion Medium Other Than Water> Examples of dispersion media other than water include organic solvents. Examples of organic solvents include, but are not limited to, 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. These organic solvents may be used alone or in combination.

[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 crystallites gather to form a turbostratic structure, and specific examples include 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 can densely pack the conductive adhesive layer, reduce electron transfer resistance, and further reduce the internal resistance of the electrochemical element.

[0063] The carbon black used in the present invention preferably contains a hetero element other than the carbon element, which is the main component. Specific examples of the hetero element include silicon, nitrogen, and boron. Boron is particularly preferred because it can reduce the electron transfer resistance and the internal resistance of the electrochemical device.

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

[0065] Here, the specific surface area of ​​the carbon black used in the present invention is 25 m from the viewpoint of maintaining good conductivity. ２ / g or more and 300m ２ / g or less, preferably 30m ２ / g or more and 200m ２ / g or less, more preferably 40m ２ / g or more and 150m ２ / g or less. If the specific surface area is too large, the viscosity becomes high, making it difficult to produce a slurry suitable for high-speed coating. Conversely, if the specific surface area is too small, the conductivity decreases. In addition, the dispersibility of the slurry deteriorates.

[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 having a volume average particle diameter within the above range is used, the spherical graphite and carbon black are packed at a high density in the conductive adhesive layer. The volume average particle diameter is measured and calculated using a laser diffraction particle size distribution analyzer (e.g., SALD-3100; manufactured by Shimadzu Corporation).

[0067] <<Particulate Polymer (Binder)>> The conductive material paste may further include a particulate polymer (particulate binder) as a binder. The particulate polymer includes, as polymer constituent units, at least an unsaturated carboxylic acid monomer unit, an aromatic vinyl monomer unit, and a diene-based monomer unit.

[0068] [Unsaturated Carboxylic Acid Monomer Unit] Examples of the unsaturated carboxylic acid monomer unit constituting the particulate polymer as a binder include those exemplified as the unsaturated carboxylic acid monomer unit constituting the dispersant (B).

[0069] In the particulate polymer used as a binder, when the total monomer units are taken as 100 parts by mass, the content of the 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, and 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 ratio of the unsaturated carboxylic acid monomer units in the particulate polymer used as a binder is equal to or greater than the above-mentioned lower limit, the stability of the slurry viscosity over time can be improved. On the other hand, if the content ratio of the unsaturated carboxylic acid monomer units in the particulate polymer used as a binder is equal to or less than the above-mentioned upper limit, the solids 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, p-t-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. The aromatic vinyl monomers may be used alone or in combination of two or more at any ratio. Among these, styrene is preferred.

[0071] In the particulate polymer used as a binder, when the total monomer units is 100 parts by mass, the content of the aromatic vinyl monomer units is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, and even more preferably 30 parts by mass or more, and is 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 ratio of the aromatic vinyl monomer units in the particulate polymer used as a binder is equal to or greater than the above-mentioned lower limit, stability during preparation of the negative electrode slurry can be improved, making it possible to prevent the slurry viscosity from increasing. On the other hand, if the content ratio of the aromatic vinyl monomer units in the particulate polymer used as a binder is equal to or less than the above-mentioned upper limit, the swelling degree with respect to the electrolyte solution used in the secondary battery can be within a suitable range.

[0072] [Diene Monomer Unit] 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-hexadienechloroprene, and cyanobutadiene. The above-mentioned conjugated diene monomers may be used alone or in combination of two or more in any ratio. Among these, 1,3-butadiene and isoprene are preferred, and 1,3-butadiene is more preferred, in terms of ease of availability.

[0073] In the particulate polymer as a binder, when the total monomer units are taken as 100 parts by mass, the content of the diene monomer units is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, and even more preferably 30 parts by mass or more, and is 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 ratio of the diene monomer units in the particulate polymer as a binder is equal to or greater than the above-mentioned lower limit, the binding strength of the electrode can be increased. On the other hand, if the content ratio of the diene monomer units in the particulate polymer as a binder is equal to or less than the above-mentioned upper limit, mechanical stability can be maintained during the preparation of the negative electrode slurry.

[0074] [Other monomer units] The diene monomer that can form other monomer units that constitute particulate polymer is not particularly limited as long as it is a monomer that can be copolymerized with diene monomer, and for example, can be mentioned the above-mentioned unsaturated carboxylic acid monomer, the monomer that has carbon-carbon unsaturated bond other than aromatic vinyl monomer unit.As the monomer that has such carbon-carbon unsaturated bond, can be mentioned the vinyl monomer that contains cyano group, the vinyl monomer that contains amino group, the vinyl monomer that contains pyridyl group, the vinyl monomer that contains alkoxyl group etc.It should be noted that the above-mentioned diene monomer that can be copolymerized with diene monomer can be used alone, or can be used in combination of two or more kinds in any ratio.

[0075] <Properties of Conductive Material Paste> The pH of the conductive material paste is preferably 6 or more, more preferably 6.5 or more, and preferably 9 or less, and more preferably 8 or less. If the pH of the conductive material paste is equal to or greater than the above-mentioned lower limit, the viscosity stability of the negative electrode slurry can be increased. On the other hand, if the pH of the conductive material paste is equal to or less than the above-mentioned upper limit, the binding strength as a negative electrode can be increased.

[0076] <Method for producing conductive material paste> The conductive material paste of the present invention can be produced by mixing the above-mentioned carbon nanotubes (A), dispersant (B), dispersant (C), water, and other components used as needed in the above-mentioned blending amounts.

[0077] The above-mentioned mixing is preferably carried out through a step of preparing a premix containing carbon nanotubes (A), a dispersant (C), and water, and a step of adding the dispersant (B) to the premix. 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 premix, the dispersant (C) is first adsorbed onto the surface of the carbon nanotubes (A), and then the dispersant (B) can be favorably adsorbed via the dispersant (C). This makes it possible to provide a slurry composition for a nonaqueous electrolyte secondary battery negative electrode that maintains the paste dispersibility of the conductive material paste and the slurry viscosity stability, while suppressing the rate of increase in resistance during a high-temperature storage test.

[0078] The mixing of the various components is not particularly limited and can be carried out using a known mixing device, such as a disper, a homomixer, a planetary mixer, a kneader, a ball mill, or a bead mill.

[0079] (Slurry Composition for Negative Electrode of Non-Aqueous Electrolyte Secondary Battery) The slurry composition for negative electrode of non-aqueous electrolyte secondary battery of the present invention (hereinafter sometimes simply referred to as "slurry composition") contains the above-mentioned conductive material paste and at least a negative electrode active material (e.g., a silicon-based active material, etc.), and may contain a thickener, a binder, carbon black, a negative electrode active material (e.g., a silicon-based active material, etc.), and other optional components as needed. In this way, the slurry composition containing the above-mentioned conductive material paste maintains slurry viscosity stability, and an electrode including an electrode mixture layer formed from this slurry composition can suppress the rate of increase in resistance during a high-temperature storage test for a non-aqueous electrolyte secondary battery.

[0080] <Negative Electrode Active Material> <<Silicon-Based Active Material>> Examples of silicon-based active materials include silicon (Si), silicon-containing alloys, SiO, SiO ｘ and a composite of a Si-containing material and conductive carbon, which is obtained by coating or compounding a Si-containing material with conductive carbon.

[0081] The particle size of the silicon-based active material is not particularly limited and can be the same as that of a conventionally used electrode active material. The amount of the silicon-based active material in the slurry composition is also not particularly limited and can be within the range of conventionally used silicon-based active materials. 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 limited to, carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials that are combinations of these.

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

[0084] Examples of carbonaceous materials include graphitizable carbon and non-graphitizable carbon, which has a structure similar to an amorphous structure, such as glassy carbon. Examples of graphitizable carbon include carbon materials made from tar pitch obtained from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber, and pyrolytic vapor-grown carbon fiber. Examples of non-graphitizable carbon include phenolic resin calcined bodies, polyacrylonitrile-based carbon fibers, pseudoisotropic carbon, furfuryl alcohol resin calcined bodies (PFA), and hard carbon. Examples of graphitizable materials include natural graphite and artificial graphite. Examples of artificial graphite include artificial graphite obtained by heat-treating carbon containing easily graphitized carbon mainly at 2800°C or higher, graphitized MCMB obtained by heat-treating MCMB at 2000°C or higher, and graphitized mesophase pitch-based carbon fiber obtained by heat-treating mesophase pitch-based carbon fiber at 2000°C or higher.

[0085] The metal-based negative electrode active material is an active material containing a metal, and usually refers to an active material that contains an element capable of inserting lithium in its structure and has a theoretical electrical capacity per unit mass of 500 mAh / g or more when lithium is inserted. Examples of the metal-based active material 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.), alloys thereof, and oxides, sulfides, nitrides, carbides, phosphides, etc. thereof.

[0086] 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. The amount of the negative electrode active materials in the slurry composition is also not particularly limited and can be within the range of conventionally used negative electrode active materials. The negative electrode active materials can be used alone or in combination of two or more.

[0087] <<Amount of Negative Electrode Active Material and Silicon-Based Active Material>> The content 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, and more preferably 95% by mass or more. It may also be, for example, 99% by mass or less, preferably 98.5% by mass or less, and more preferably 98% by mass or less. When the content of the negative electrode active material is equal to or greater than the lower limit, the capacity of the resulting secondary battery can be increased. Furthermore, when the content of the negative electrode active material is equal to or less than the upper limit, the cycle characteristics of the resulting secondary battery can be improved. The content of the carbon nanotubes (A) relative to the negative electrode active material may be, for example, 0.01% by mass or more, preferably 0.05% by mass or more, and more preferably 0.1% by mass or more. It may also be, for example, 5% by mass or less, preferably 2% by mass or less, and more preferably 1% by mass or less. The content of the 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 be, for example, 40% by mass or less, preferably 35% by mass or less, more preferably 30% by mass or less. If the content of the silicon-based active material is equal to or greater than the above lower limit, the capacity of the resulting secondary battery can be further increased. Furthermore, if the content of the silicon-based active material is equal to or less than the above upper limit, the cycle characteristics of the resulting secondary battery can be further improved. The content of the carbon nanotubes (A) relative 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 be, for example, 5% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less.

[0088] <Thickener> The thickener is not particularly limited, but examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, polyvinyl alcohol, polymethacrylic acid, polyacrylic acid, and a terpolymer of acrylamide / acrylic acid / N-hydroxyethyl acrylamide. These can be used alone or in combination of two or more. Furthermore, these can be used in either an unneutralized state or a neutralized state. Among these, a terpolymer of acrylamide / acrylic acid / N-hydroxyethyl acrylamide is preferred.

[0089] Here, the thickener preferably has a weight-average molecular weight of 500,000 or more, more preferably 800,000 or more, and preferably 10,000,000 or less, 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] In the slurry composition of the present invention, the blending amount of the thickener is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more, and 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. When the blending amount of the thickener is 0.2 parts by mass or more, the cycle characteristics of the electrochemical device can be further improved, and when it is 5.0 parts by mass or less, the capacity of the electrochemical device can be improved.

[0091] <Binder> The above-described particulate polymer (particulate binder) can be used as the binder. In the slurry composition of the present invention, the blending amount of the above-described binder is preferably 0.1 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of the electrode active material. When the blending amount of the binder per 100 parts by mass of the electrode active material is within the above-described range, the peel strength of the electrode can be increased and the cycle characteristics of the electrochemical element can be further improved.

[0092] <Other Optional Components> Examples of other optional components that can be contained in the slurry composition include a reinforcing material, an antioxidant, and an electrolyte additive that has a function of suppressing decomposition of the electrolyte. These optional components can be used alone or in combination of two or more.

[0093] <Method for Preparing Slurry Composition> When the above-mentioned components are mixed to obtain a slurry composition, the mixing method is not particularly limited, and for example, a known mixing device can be used.

[0094] (Negative Electrode for Non-Aqueous Electrolyte Secondary Battery) 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") includes a negative electrode mixture layer obtained by forming the negative electrode mixture layer using the above-described slurry composition of the present invention. More specifically, the negative electrode of the present invention typically has a structure in which a negative electrode mixture layer made of a dried product of the slurry composition of the present invention is provided on a current collector. Therefore, the negative electrode mixture layer contains carbon nanotubes (A), dispersant (B), and dispersant (C), and may also contain a thickener, binder, carbon black, a negative electrode active material (e.g., a silicon-based active material), and other optional components as needed. The preferred abundance ratio of each component in the electrode mixture layer is the same as the preferred abundance ratio of each component in the slurry composition. The negative electrode of the present invention includes a negative electrode mixture layer formed using the above-described slurry composition of the present invention, and therefore 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 that can be used include those made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum. These materials can be used alone or in combination of two or more. Furthermore, a current collector made of copper (e.g., copper foil) is preferred as the negative electrode current collector.

[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 above-described slurry composition of the present invention to at least one surface of a current collector and drying the composition to form an electrode mixture layer. More specifically, the manufacturing method includes a step of applying the slurry composition to at least one surface of a current collector (application step), and a step of drying the slurry composition applied to at least one surface of the current collector to form an electrode mixture layer on the current collector (drying step).

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

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

[0099] After the drying step, the electrode mixture layer may be subjected to pressure treatment using a mold press, a roll press, etc. Pressure treatment can improve the peel strength of the negative electrode.

[0100] (Non-aqueous electrolyte secondary battery) The non-aqueous electrolyte secondary battery of the present invention includes the above-described negative electrode of the present invention. Furthermore, since the non-aqueous electrolyte secondary battery of the present invention includes the negative electrode of the present invention, it has excellent suppression of the rate of resistance increase 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] Hereinafter, the configuration of a lithium ion secondary battery will be described as an example of the nonaqueous electrolyte secondary battery of the present invention. This lithium ion secondary battery includes the negative electrode of the present invention, a positive electrode, an electrolyte, and a separator.

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

[0103] <Electrolyte> As the electrolyte, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte, for example, a lithium salt is used. As the lithium salt, for example, LiPF ６ , LiAsF ６ , LiBF ４ , LiSbF ６ , LiAlCl ４ , LiClO ４ , C.F. ３ SO ３ Li, C ４ F ９ SO ３ Li, CF ３ COOLi, (CF ３ CO) ２ NLi, (CF ３ SO ２ ) ２ NLi, (C ２ F ５ SO ２ Among them, LiPF is particularly preferred because it is easily soluble in solvents and shows a high degree of dissociation. ６ , LiClO ４ , C.F. ３ SO ３ Li is preferred, and LiPF ６ is particularly preferred. Note that one type of electrolyte may be used alone, or two or more types may be used in combination 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. For example, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (EMC) are preferably used. Ethers such as 1,2-dimethoxyethane and tetrahydrofuran are also suitable. Sulfur-containing compounds such as sulfolane and dimethyl sulfoxide are also suitable. Mixtures of these solvents may also be used. Among these, carbonates are preferred because of their high dielectric constant and wide stable potential range. A mixture of ethylene carbonate and ethyl methyl carbonate is even more preferred. The concentration of the electrolyte in the electrolyte 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. The electrolyte may also contain known additives such as fluoroethylene carbonate (FEC), vinylene carbonate (VC), and ethyl methyl sulfone.

[0105] <Separator> The separator is not particularly limited, and for example, those described in JP 2012-204303 A can be used. Among these, a microporous film made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it allows the thickness of the entire separator to be thin, thereby increasing the proportion of electrode active material in the lithium ion secondary battery and increasing the capacity per volume.

[0106] <Method for Manufacturing Nonaqueous Electrolyte Secondary Battery> A nonaqueous electrolyte secondary battery according to the present invention can be manufactured, for example, by stacking the negative electrode of the present invention and a positive electrode with a separator interposed therebetween, rolling or folding the resulting assembly as necessary according to the battery shape, placing it in a battery container, injecting an electrolyte into the battery container, and sealing it. To prevent internal pressure rise, overcharge / discharge, and the like in the secondary battery, a fuse, an overcurrent protection element such as a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary. The shape of the nonaqueous electrolyte secondary battery may be, for example, a coin type, a button type, a sheet type, a cylindrical type, a prismatic type, a flat type, or the like.

[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, the terms "%" and "parts" used to represent amounts are based on mass unless otherwise specified. In addition, in a polymer produced by copolymerizing multiple types of monomers, the proportion of a monomer unit formed by polymerizing a certain monomer in the polymer usually corresponds to the ratio (feed ratio) of the certain monomer to all the monomers used in the polymerization of the polymer, unless otherwise specified. In the examples and comparative examples, the weight-average molecular weight of the water-soluble polymer (corresponding to the dispersant (B)), the dispersion stability of the conductive material 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 a high-temperature storage test of the lithium-ion secondary battery were evaluated using the following methods.

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

[0109] <Dispersion Stability> The viscosity η1 of the conductive paste immediately after preparation was measured using a Brookfield viscometer at a temperature of 25°C and a spindle rotation speed of 60 rpm, 60 seconds after the start of spindle rotation. After measuring η1, 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 taken as the paste viscosity ratio, and was evaluated according to the following criteria. The closer the paste viscosity ratio value is to 1.0, the more the viscosity increase of the conductive paste is suppressed and the more excellent the dispersion stability is. A: Paste viscosity ratio is less than 1.15 B: Paste viscosity ratio is 1.15 or more but less than 1.6 C: Paste viscosity ratio is 1.6 or more but less than 2.0 D: Paste viscosity ratio is 2.0 or more

[0110] <Viscosity Stability> The viscosity η3 of the slurry composition immediately after preparation was measured using a Brookfield viscometer at a temperature of 25°C and a spindle rotation speed of 60 rpm, 60 seconds after the start of spindle rotation. After measuring η3, the slurry composition 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 taken as the slurry viscosity ratio, and was 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 and the more excellent the viscosity stability is. A: Slurry viscosity ratio is less than 1.2 B: Slurry viscosity ratio is 1.2 or more but less than 1.4 C: Slurry viscosity ratio is 1.4 or more but less than 1.5 D: Slurry viscosity ratio is 1.5 or more

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

[0112] <Cycle Characteristics> After the electrolyte was poured into the lithium-ion secondary battery, the battery was left standing for 24 hours in an environment at 25°C. Subsequently, the battery was charged to a cell voltage of 4.35V by a constant current method of 0.1C and discharged to a cell voltage of 2.75V, and the initial capacity C0 was measured. Furthermore, the battery was repeatedly charged to a cell voltage of 4.35V by a constant current method of 1.0C in an environment at 25°C, and discharged to a cell voltage of 2.75V by the same constant current method as in the charge mode, and the capacity C1 after 100 cycles was measured. The capacity retention rate (%) = C1 / C0 x 100 was calculated and evaluated according to the following criteria. A higher capacity retention rate indicates better cycle characteristics of the lithium-ion secondary battery. A: Capacity retention rate is 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 injecting the electrolyte, the lithium-ion secondary battery was left standing for 24 hours at 25°C. Next, the battery was charged to a cell voltage of 4.35 V at a constant current of 0.1 C and discharged to a cell voltage of 2.75 V, and the initial capacity was measured. After charging to a depth of charge (SOC) of 50%, the battery was charged for 30 seconds and discharged for 30 seconds at 1.0 C, centered around 50% SOC. The IV resistance R1 was calculated by dividing the voltage change over the 30 seconds of charging by the current. The battery was again charged to a cell voltage of 4.35 V at a constant current of 0.1 C, and then stored in a thermostatic chamber at 60°C for one week. After the high-temperature storage test, the IV resistance of the cell was measured in the same manner to obtain the IV resistance R2. The resistance change rate was calculated by (R2 / R1) x 100 and evaluated according to the following criteria. The closer the resistance change rate is to 100%, the more excellent the durability of the lithium ion secondary battery during high-temperature storage tests. A: Resistance change rate is less than 110% B: Resistance change rate is 110% or more but less than 120% C: Resistance change rate is 120% or more but less than 140% D: Resistance change rate is 140% or more

[0114] Example 1 Preparation of Water-Soluble Polymer 900 parts of ion-exchanged water were placed in a 1.5-L glass flask equipped with a stirring blade and heated to 40°C. The flask was then 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 poured into the flask. After degassing by nitrogen bubbling for 60 minutes at a flow rate of 1.5 L / min using a sintered metal nozzle, 10 parts of a 5.0% aqueous solution of ascorbic acid as a polymerization accelerator were added via 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 via syringe to the flask to initiate the polymerization reaction. Two hours after the addition of the polymerization initiator, the temperature was raised to 60°C and maintained at this temperature for two hours to allow the polymerization reaction to proceed. Four hours after the addition of the polymerization initiator, the flask was opened to the air to terminate the polymerization reaction, and an 8% aqueous solution of lithium hydroxide was added thereto, followed by adjusting the pH 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) as dispersant (B).

[0115] <Preparation of Conductive Material Paste> 100 parts of CNT (single-walled, length 6.3 μm, diameter (outer diameter) 1.8 nm) as carbon nanotubes (A), 1.0 part of 1,2-benzisothiazolin-3-one as dispersant (C), and an appropriate amount of ion-exchanged water as 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 zirconia beads having a diameter of 1 mm. 100 parts (solids equivalent) of the aqueous solution of a water-soluble polymer as dispersant (B) obtained as described above were added to the resulting premix, and the mixture was further mixed in a bead mill for 30 minutes to produce a conductive material paste (solids concentration: 2.0%). The pH of this conductive material paste was 8.0. The dispersion stability of this conductive material paste was evaluated. The results are shown in Table 1.

[0116] <Preparation of Particulate Binder> A particulate binder (particulate polymer) as a binder was prepared as follows. 3.15 parts of styrene, 1.66 parts of 1,3-butadiene, 0.2 parts of sodium lauryl sulfate as an emulsifier, 20 parts of ion-exchanged water, and 0.03 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel A equipped with a stirrer, and after thorough stirring, the mixture was heated to 60°C to initiate polymerization. The reaction was continued for 6 hours to obtain seed particles. After the above reaction, the mixture was heated to 75°C, and from another vessel B containing 53.85 parts of styrene, 31.34 parts of 1,3-butadiene, 10.0 parts of acrylic acid, 0.25 parts of tert-dodecyl mercaptan as a chain transfer agent, and 0.35 parts of sodium lauryl sulfate as an emulsifier, the addition of this mixture to pressure vessel A was initiated. At the same time, the addition of 1 part of potassium persulfate as a polymerization initiator to pressure vessel A was initiated to initiate the second-stage polymerization. That is, the total monomer composition used was 57 parts of styrene, 33 parts of 1,3-butadiene, and 10 parts of acrylic acid. Five and a half hours after the start of the second-stage polymerization, the addition of the entire mixture containing these monomer compositions was completed, and the mixture was then heated to 85°C and reacted for 6 hours. When the polymerization conversion rate reached 97%, the mixture was cooled to stop the reaction. A 5% aqueous solution of sodium hydroxide was added to the mixture containing this polymer to adjust the pH to 8. Thereafter, unreacted monomers were removed by heating and distillation under reduced pressure. The mixture was then cooled to obtain an aqueous dispersion of a particulate binder (water-insoluble).

[0117] <Preparation of Slurry Composition for Negative Electrode> Artificial graphite (volume average particle diameter: 24.5 μm, specific surface area: 3.5 m) was added as a carbon-based negative electrode active material to a planetary mixer equipped with a disperser. ２ / g) 90 parts, and SiO as a silicon-based negative electrode active material ｘ10 parts of the conductive paste and 2.0 parts (solids equivalent) of an aqueous solution of carboxymethylcellulose sodium salt as a thickener were added, and the solids concentration was adjusted to 58% with ion-exchanged 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 were 0.1 parts (solids equivalent) and mixed. Next, the solids concentration was adjusted to 50% with ion-exchanged water, and 1.0 part (solids equivalent) of the aqueous dispersion of the binder obtained as described above was added to obtain a mixed solution. The resulting mixed solution was degassed under reduced pressure to obtain a negative electrode slurry composition with good fluidity. The viscosity stability of this negative electrode slurry composition was evaluated. The results are shown in Table 1.

[0118] <Production of Negative Electrode> The slurry composition for negative electrode obtained as described above was applied to a copper foil (current collector) having a thickness of 16 μm using a comma coater so that the film thickness after drying was 105 μm and the coating amount was 10 mg / cm. ２ The copper foil coated with the negative electrode slurry composition was transported at a speed of 0.5 m / min through an oven at 100°C for 2 minutes, and then through an oven at 120°C for 2 minutes to dry the negative electrode slurry composition on the copper foil, thereby obtaining a negative electrode blank. The negative electrode blank was rolled using a roll press to obtain a negative electrode having a negative electrode composite layer thickness of 80 μm. The moisture content of this negative electrode was evaluated. The results are shown in Table 1.

[0119] <Production of Positive Electrode> A planetary mixer was used to prepare a positive electrode active material, LiCoO ２95 parts of PVDF (polyvinylidene fluoride) as a positive electrode binder, 3 parts by solids equivalent, 2 parts of acetylene black as a conductive material, and 20 parts of N-methylpyrrolidone as a solvent were mixed to obtain a positive electrode slurry composition. The obtained positive electrode slurry composition was applied to 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 the positive electrode slurry composition was transported at a speed of 0.5 m / min through an oven at a temperature of 60 ° C. for 2 minutes, and then through an oven at a temperature of 120 ° C. for 2 minutes, thereby drying the positive electrode slurry composition on the aluminum foil and obtaining a positive electrode blank. This positive electrode blank was rolled using a roll press to obtain a positive electrode having a positive electrode composite layer thickness of 70 μm.

[0120] <Obtaining a Separator> A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm; manufactured by a dry method; porosity 55%) was prepared. This separator was cut into a 5 cm × 5 cm square and used in the manufacture of the following lithium-ion secondary battery.

[0121] <Manufacture of Secondary Battery> An aluminum packaging material was prepared as the battery packaging. The positive electrode was cut into a 4 cm x 4 cm square and placed so that the surface on the current collector side was in contact with the aluminum packaging material. Next, the square separator was placed on the surface of the positive electrode composite layer of the positive electrode. Furthermore, the negative electrode was cut into a 4.2 cm x 4.2 cm square and placed on the separator so that the surface on the negative electrode composite layer side faced the separator. Then, 1.0 M LiPF 6 was used as the electrolyte. ６ The solution (solvent was a mixed solvent of ethylene carbonate / diethyl carbonate = 1 / 2 (volume ratio)) and additives containing fluoroethylene carbonate and vinylene carbonate (each containing 2 volume % (solvent ratio)) were filled. Furthermore, in order to seal the opening of the aluminum packaging, the aluminum packaging exterior was closed by heat sealing at 150°C, thereby producing a laminate cell type lithium ion secondary battery. The cycle characteristics and the rate of increase in resistance during a high-temperature storage test were evaluated for this lithium ion secondary battery. The results are shown in Table 1.

[0122] (Example 2) In preparing the water-soluble polymer, 20 parts of acrylic acid as the unsaturated carboxylic acid monomer and 80 parts of acrylamide as the (meth)acrylamide group-containing monomer were used as monomers to obtain an aqueous solution of the water-soluble polymer (weight average molecular weight: 214,000). Except for this, various productions, 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 material paste, various production, measurement, and evaluation were carried out in the same manner as in Example 1, except that CNTs (multi-layered, length 3.9 μm, diameter (outer diameter) 14 nm) were used as the carbon nanotubes (A) to obtain the conductive material paste. The results are shown in Table 1.

[0124] (Example 4) In preparing the conductive material paste, various production, measurements and evaluations were carried out in the same manner as in Example 3, except that 50 parts (solid content equivalent) of an aqueous solution of a water-soluble polymer was added as the dispersant (B). The results are shown in Table 1.

[0125] (Examples 5, 6, 8) When preparing the water-soluble polymer, the monomers were acrylic acid as the unsaturated carboxylic acid monomer, acrylamide as the (meth)acrylamide group-containing monomer, and sodium styrenesulfonate as the 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, to obtain an aqueous solution 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). Except for this, various productions, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0126] (Example 7) In preparing the binder, the blending ratio of styrene:butadiene:acrylic acid as monomers was set to 61 parts:37 parts:2 parts to obtain a particulate binder (particulate polymer) as the binder. Except for this, various production, measurement, and evaluation were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0127] (Example 9) In preparing the conductive paste, various production, measurements and evaluations were carried out in the same manner as in Example 1, except that 2-methylthiazoline was used as the dispersant (C). The results are shown in Table 1.

[0128] Comparative Example 1 Except for using 0.8 parts of triaminotriazine as the dispersant (C) in preparing the conductive paste, various production, measurements, and evaluations were carried out in the same manner as in Example 2. The results are shown in Table 1.

[0129] Comparative Example 2 Except for not adding the dispersant (C) when preparing the conductive paste, various production, measurements and evaluations 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, 21 parts of vinylnaphthalene and 79 parts of allylsulfonic acid were used as monomers to obtain an aqueous solution of a water-soluble polymer (weight average molecular weight: 143,000). Except for this, various productions, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

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

[0132] Comparative Example 5: In preparing the water-soluble polymer, acrylamide alone 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. The preparation, measurement, and evaluation of a conductive paste were carried out in the same manner as in Example 1, except that a negative electrode slurry composition could not be prepared, and therefore the subsequent production, measurement, and evaluation could not be carried out. The results are shown in Table 1.

[0133] (Comparative Example 6) In preparing the water-soluble polymer, 40 parts of acrylic acid and 60 parts of styrene sulfonic acid were used as monomers to obtain an aqueous solution of a water-soluble polymer (weight average molecular weight: 159,000). Except for this, various production, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0134] (Comparative Example 7) In preparing the conductive paste, various production, measurements and evaluations were carried out in the same manner as in Example 1, except that the aqueous solution of the water-soluble polymer as the dispersant (B) was not added. The results are shown in Table 1.

[0135] (Comparative Example 8) In preparing the conductive material paste, the aqueous solution of the water-soluble polymer as the dispersant (B) was not added, and instead, in preparing the negative electrode slurry composition, the aqueous solution of the water-soluble polymer produced in Example 1 was added as the aqueous solution of the thickener, and various productions, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0136]

[0137]

[0138] The abbreviations in the table are as follows: AA: acrylic acid, Aamid: acrylamide, SSNa: sodium styrene sulfonate, St: styrene, BD: butadiene, CMC: sodium carboxymethyl cellulose salt.

[0139] Table 1 shows that by using the conductive material pastes of Examples 1 to 9, it is possible to provide a slurry composition for a negative electrode of a nonaqueous electrolyte secondary battery that maintains paste dispersibility and slurry viscosity stability, and also provides a nonaqueous electrolyte secondary battery in which the rate of increase in resistance during a high-temperature storage test is suppressed.

[0140] According to the present invention, it is possible to provide a conductive material paste for a nonaqueous electrolyte secondary battery, which can provide a nonaqueous electrolyte secondary battery negative electrode with a suppressed rate of resistance increase during a high-temperature storage test while maintaining paste dispersibility and slurry viscosity stability. Furthermore, according to the present invention, it is possible to provide a slurry composition for a nonaqueous electrolyte secondary battery negative electrode with a suppressed rate of resistance increase during a high-temperature storage test while maintaining slurry viscosity stability. Furthermore, according to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery negative electrode with a suppressed rate of resistance increase during a high-temperature storage test.

Claims

1. A conductive material paste for a non-aqueous electrolyte secondary battery, comprising carbon nanotubes (A), a dispersant (B), a dispersant (C), and water, wherein the dispersant (B) is a copolymer containing 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 material paste for a non-aqueous electrolyte secondary battery according to Claim 1, wherein the copolymer which is the dispersant (B) further contains an aromatic sulfonic acid monomer unit.

3. The conductive material paste for a non-aqueous electrolyte secondary battery according to Claim 1, wherein 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 unit is 5 parts by mass or more and 80 parts by mass or less.

4. The conductive material paste for a non-aqueous electrolyte secondary battery according to Claim 1, wherein 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 material paste for a non-aqueous electrolyte secondary battery according to Claim 1, wherein at least a part 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 material paste for a non-aqueous electrolyte secondary battery according to Claim 1, wherein the thiazoline or a derivative thereof which is the dispersant (C) is isothiazoline or a derivative thereof.

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

8. The conductive material paste for a non-aqueous electrolyte secondary battery according to Claim 1, further comprising a particulate polymer, wherein 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.

9. The conductive material paste for a non-aqueous electrolyte secondary battery according to Claim 1, wherein the pH of the conductive material paste is 6 or more and 9 or less.

10. A slurry composition for a negative electrode of a non-aqueous electrolyte secondary battery, comprising the conductive material paste for a non-aqueous electrolyte secondary battery 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 material layer formed using the slurry composition according to claim 10.

12. A non-aqueous electrolyte secondary battery, comprising the negative electrode according to claim 11.