Conductive material dispersion, method for producing slurry for positive electrode of non-aqueous secondary battery, method for producing positive electrode for non-aqueous secondary battery, and method for producing non-aqueous secondary battery

Abstract

The present invention provides a technology that enables a secondary battery to exhibit excellent output characteristics and cycle characteristics. When manufacturing a secondary battery, a conductive material dispersion containing a conductive material, a dispersant, and a solvent is used. The conductive material has a specific surface area of ​​800m 2 / g and above and 1300m 2 / g or less of carbon nanotubes, the volume average particle size (D90) of the carbon nanotubes in the conductive material dispersion is 50 μm or less, and the dispersant is a hydrogenated acrylonitrile-butadiene copolymer having a weight average molecular weight of 200,000 or less.

Description

Technical Field

[0001] The present invention relates to a conductive material dispersion, a method for producing a slurry for a positive electrode of a non-aqueous secondary battery, a method for producing a positive electrode for a non-aqueous secondary battery, and a method for producing a non-aqueous secondary battery. Background Art

[0002] Non-aqueous secondary batteries (hereinafter referred to as "secondary batteries"), such as lithium-ion secondary batteries, are compact, lightweight, have high energy density, and can be repeatedly charged and discharged, making them widely used. Therefore, in recent years, research has been underway to improve battery components such as electrodes in order to further enhance the performance of these batteries.

[0003] Here, a positive electrode for a secondary battery generally includes a current collector and a positive electrode composite material layer formed on the current collector. The positive electrode composite material layer is formed using, for example, a secondary battery positive electrode slurry formed by dispersing a positive electrode active material, a conductive material, and a binder in a dispersion medium.

[0004] Furthermore, in recent years, attempts have been made to improve secondary battery positive electrode slurries in order to further improve the performance of secondary batteries.

[0005] For example, Patent Document 1 proposes a slurry for secondary battery electrodes comprising an electrode active material and a carbon nanotube dispersion. The carbon nanotube dispersion described in Patent Document 1 contains carbon nanotubes, a binder, and a dispersion medium. The binder comprises a polymer (A) containing predetermined structural units. The ratio of the binder to the total solids content of the carbon nanotube dispersion is below a predetermined value, and the viscosity change rate of the carbon nanotube dispersion before and after standing for one week is within a predetermined range.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: International Publication No. 2019 / 181869. Summary of the Invention

[0009] Problems to be solved by the invention

[0010] However, in a secondary battery produced using the conventional secondary battery positive electrode slurry described in Patent Document 1, there is room for further improvement in terms of further enhancing electrical characteristics such as output characteristics and cycle characteristics.

[0011] Therefore, an object of the present invention is to provide a method for producing a non-aqueous secondary battery positive electrode slurry capable of enabling a secondary battery to exhibit excellent output characteristics and cycle characteristics, and a conductive material dispersion that can be preferably used to produce the secondary battery positive electrode slurry.

[0012] Another object of the present invention is to provide a method for producing a positive electrode for a non-aqueous secondary battery that enables the secondary battery to exhibit excellent output characteristics and cycle characteristics.

[0013] Furthermore, an object of the present invention is to provide a method for producing a non-aqueous secondary battery having excellent output characteristics and cycle characteristics.

[0014] Solutions for solving problems

[0015] The present inventors have focused on improving the output characteristics of secondary batteries by using carbon nanotubes (hereinafter referred to as "CNTs") with a large specific surface area, such as single-walled carbon nanotubes, as conductive materials for secondary batteries. However, according to the present inventors' research, when CNTs with a large specific surface area are used to prepare secondary battery positive electrode slurry, the resulting secondary battery positive electrode slurry has reduced drag properties. In addition, because such positive electrode slurry is difficult to apply uniformly to the current collector, the surface roughness of the positive electrode composite material layer formed by applying the positive electrode slurry increases, resulting in reduced cycle characteristics of the secondary battery.

[0016] Therefore, the present inventors conducted further research and found that the above-mentioned problems can be solved by using a low-molecular-weight hydrogenated acrylonitrile-butadiene copolymer (H-NBR) in combination with CNTs having a large specific surface area. Based on these findings, the present invention was completed.

[0017] That is, the object of the present invention is to advantageously solve the above-mentioned problems. The conductive material dispersion of the present invention is characterized by comprising a conductive material, a dispersant, and a solvent, wherein the conductive material has a specific surface area of ​​800 m 2 / g and above and 1300m 2 / g or less of carbon nanotubes, the volume average particle size (D90) of the carbon nanotubes in the conductive material dispersion is 50 μm or less, the dispersant is a hydrogenated acrylonitrile-butadiene copolymer, and the weight average molecular weight of the hydrogenated acrylonitrile-butadiene copolymer is 200,000 or less. 2 / g and above and 1300m 2 A conductive material dispersion comprising CNTs having a weight average particle size (D90) of 50 μm or less and a hydrogenated acrylonitrile-butadiene copolymer having a weight average molecular weight of 200,000 or less as a dispersant, and a solvent can provide a secondary battery positive electrode slurry with excellent slurry stability and coating uniformity.

[0018] In addition, in this specification, "volume average particle size (D90) of CNTs in the conductive material dispersion" refers to the particle size of CNTs in the conductive material dispersion when the cumulative volume calculated from the small diameter side reaches 90% in the particle size distribution (volume basis) measured by laser diffraction method.

[0019] In the present invention, the "specific surface area," the "volume average particle size (D90) of CNTs in the conductive material dispersion," and the "weight average molecular weight" can be determined by the methods described in Examples of this specification.

[0020] In the conductive material dispersion of the present invention, the iodine value of the hydrogenated acrylonitrile-butadiene copolymer is preferably 25 mg / 100 mg or less. If the iodine value of the hydrogenated acrylonitrile-butadiene copolymer is 25 mg / 100 mg or less, the dispersibility of the conductive material in the conductive material dispersion can be improved. Furthermore, use of this conductive material dispersion can improve the slurry stability of a secondary battery positive electrode slurry and enhance the cycle characteristics of a secondary battery produced using this secondary battery positive electrode slurry.

[0021] In the present invention, the "iodine value" can be determined by the method described in Examples of the present specification.

[0022] In addition, the conductive material dispersion of the present invention preferably contains the dispersant in an amount of 50 parts by mass or more and 400 parts by mass or less relative to 100 parts by mass of the conductive material. If the dispersant content in the conductive material dispersion is within the above range, both the slurry stability and coating uniformity of the secondary battery positive electrode slurry can be further improved.

[0023] Furthermore, the present invention aims to advantageously solve the above-mentioned problems. The method for producing a non-aqueous secondary battery positive electrode slurry of the present invention is characterized in that the non-aqueous secondary battery positive electrode slurry is obtained by mixing a positive electrode active material, a binder, and any of the above-mentioned conductive material dispersions. In this way, by mixing the positive electrode active material, the binder, and the conductive material dispersion of the present invention, a secondary battery positive electrode slurry with excellent slurry stability and coating uniformity can be efficiently produced.

[0024] In addition, in the method for producing a non-aqueous secondary battery positive electrode slurry of the present invention, it is preferred that the content of the conductive material in the non-aqueous secondary battery positive electrode slurry is less than 0.1 parts by mass relative to 100 parts by mass of the positive electrode active material. If the content of the conductive material in the secondary battery positive electrode slurry is less than 0.1 parts by mass relative to 100 parts by mass of the positive electrode active material, the slurry stability and coating uniformity of the resulting secondary battery positive electrode slurry can be further improved.

[0025] Furthermore, in the method for manufacturing a non-aqueous secondary battery positive electrode slurry of the present invention, the content of the binder in the non-aqueous secondary battery positive electrode slurry is preferably 0.1 parts by mass or more and 6 parts by mass or less relative to 100 parts by mass of the positive electrode active material. If the content of the binder in the secondary battery positive electrode slurry is within the above range, the adhesion between the positive electrode composite material layer and the current collector can be improved in the positive electrode produced using the secondary battery positive electrode slurry, and the resistance of the secondary battery can be suppressed to a low level.

[0026] Furthermore, the present invention aims to advantageously solve the above-mentioned problems. The method for manufacturing a positive electrode for a non-aqueous secondary battery of the present invention is characterized by comprising forming a positive electrode composite material layer using the non-aqueous secondary battery positive electrode slurry obtained by the above-mentioned method. By forming the positive electrode composite material layer using the non-aqueous secondary battery positive electrode slurry obtained by the above-mentioned method, a positive electrode for a secondary battery can be manufactured that enables the secondary battery to exhibit excellent output characteristics and cycle characteristics.

[0027] Furthermore, the present invention aims to advantageously solve the above-mentioned problems. The method for manufacturing a non-aqueous secondary battery of the present invention is characterized by using a non-aqueous secondary battery positive electrode obtained by the above-mentioned method for manufacturing a non-aqueous secondary battery positive electrode. Thus, by using the non-aqueous secondary battery positive electrode obtained by the above-mentioned method, a secondary battery with excellent output and cycle characteristics can be manufactured.

[0028] Effects of the Invention

[0029] According to the present invention, there can be provided a method for producing a secondary battery positive electrode slurry capable of enabling a secondary battery to exhibit excellent output characteristics and cycle characteristics, and a conductive material dispersion liquid that can be preferably used to produce the secondary battery positive electrode slurry.

[0030] Furthermore, according to the present invention, it is possible to provide a method for producing a positive electrode for a secondary battery that enables the secondary battery to exhibit excellent output characteristics and cycle characteristics.

[0031] Furthermore, according to the present invention, a method for manufacturing a secondary battery having excellent output characteristics and cycle characteristics can be provided. DETAILED DESCRIPTION

[0032] Hereinafter, embodiments of the present invention will be described in detail.

[0033] Here, the conductive material dispersion of the present invention can be used when preparing a slurry for a secondary battery positive electrode. In addition, the method for manufacturing a slurry for a secondary battery positive electrode of the present invention is manufactured using the conductive material dispersion of the present invention. Furthermore, in the method for manufacturing a secondary battery positive electrode of the present invention, a slurry for a secondary battery positive electrode obtained by the method for manufacturing a slurry for a secondary battery positive electrode of the present invention is used. Moreover, in the method for manufacturing a secondary battery of the present invention, a positive electrode obtained by the method for manufacturing a secondary battery positive electrode of the present invention is used.

[0034] (Conductive material dispersion)

[0035] The conductive material dispersion of the present invention must contain a conductive material, a dispersant, and a solvent. Furthermore, in addition to the aforementioned components, the conductive material dispersion of the present invention may also contain additives. In this specification, the term "conductive material dispersion" generally does not include the positive electrode active material.

[0036] Furthermore, since the conductive material dispersion of the present invention comprises the conductive material, dispersant, and solvent described in detail below, the conductive material dispersion of the present invention can be used to prepare a secondary battery positive electrode slurry having excellent slurry stability and coating uniformity. Furthermore, the use of this secondary battery positive electrode slurry can produce a positive electrode that enables the secondary battery to exhibit excellent output and cycle characteristics.

[0037] Conductive materials

[0038] The conductive material is used to ensure electrical contact between the positive electrode active materials in the positive electrode composite material layer. Furthermore, as the conductive material used in the conductive material dispersion of the present invention, single-walled CNTs and / or multi-walled CNTs can be used, preferably single-walled to five-walled CNTs, and more preferably single-walled CNTs. Furthermore, CNTs can be surface-treated with strong acids such as nitric acid and sulfuric acid.

[0039] [Specific surface area of ​​CNT]

[0040] Furthermore, the specific surface area of ​​CNTs needs to be 800 m 2 / g or more, preferably 850m 2 / g or above, needs to be 1300m 2 / g or less, preferably 1250m 2 If the specific surface area of ​​CNTs is within the above range, the dispersibility of the conductive material can be ensured, and a good conductive path can be formed in the positive electrode composite material layer, thereby further improving the coating uniformity of the secondary battery positive electrode slurry and the output characteristics of the secondary battery.

[0041] [Volume Average Particle Size (D90) of CNTs in Conductive Material Dispersion]

[0042] Moreover, the volume average particle size (D90) of the CNT in the conductive material dispersion needs to be 50 μm or less, preferably 45 μm or less, more preferably 40 μm or less, and further preferably 30 μm or less. If the volume average particle size (D90) of the CNT in the conductive material dispersion is 50 μm or less, the dispersibility of the conductive material (CNT) in the conductive material dispersion can be further improved. Therefore, if the conductive material dispersion is used, the slurry stability of the secondary battery positive electrode slurry can be further improved, and the cycle characteristics of the secondary battery made using the secondary battery positive electrode slurry can be further improved.

[0043] The volume average particle size (D90) of the CNTs in the conductive material dispersion can be appropriately adjusted by changing the mixing conditions when preparing the conductive material dispersion.

[0044] Here, in the present invention, the method for producing CNTs used as the conductive material is not particularly limited, and CNTs can be produced using known CNT production methods such as arc discharge, laser ablation, and chemical vapor deposition (CVD).

[0045] Dispersants

[0046] A dispersant is used to disperse the conductive material contained in the conductive material dispersion. In the present invention, a hydrogenated acrylonitrile-butadiene copolymer is used as the dispersant for the conductive material dispersion. A hydrogenated acrylonitrile-butadiene copolymer is a hydride formed by hydrogenating some or all of the carbon-carbon unsaturated bonds in the main chain and side chains of the conjugated diene monomer of the acrylonitrile-butadiene copolymer.

[0047] Since the conductive material dispersion of the present invention uses hydrogenated acrylonitrile-butadiene copolymer as a dispersant, the surface roughness of the positive electrode composite material layer can be reduced and the cycle characteristics of the secondary battery can be improved by using the conductive material dispersion.

[0048] [Properties of hydrogenated acrylonitrile-butadiene copolymer]

[0049] [Weight average molecular weight]

[0050] Furthermore, the weight average molecular weight of the hydrogenated acrylonitrile-butadiene copolymer used in the present invention needs to be 200,000 or less, preferably 100,000 or less, more preferably 80,000 or less, and even more preferably 60,000 or less. Thus, by using a low molecular weight hydrogenated acrylonitrile-butadiene copolymer having a weight average molecular weight of 200,000 or less, the secondary battery positive electrode slurry can exhibit both excellent slurry stability and coating uniformity.

[0051] The weight average molecular weight of the hydrogenated acrylonitrile-butadiene copolymer can be appropriately adjusted by, for example, changing the composition of the hydrogenated acrylonitrile-butadiene copolymer or the hydrogenation conditions.

[0052] [Iodine value]

[0053] In addition, the iodine value of the hydrogenated acrylonitrile-butadiene copolymer used in the present invention is preferably 25 mg / 100 mg or less, more preferably 23 mg / 100 mg or less, and even more preferably 20 mg / 100 mg or less. If the iodine value of the hydrogenated acrylonitrile-butadiene copolymer is 25 mg / 100 mg or less, the dispersibility of the conductive material in the conductive material dispersion can be improved. In addition, if this conductive material dispersion is used, the slurry stability of the secondary battery positive electrode slurry can be improved, and the cycle characteristics of the secondary battery produced using the secondary battery positive electrode slurry can be improved.

[0054] Here, the iodine value of the hydrogenated acrylonitrile-butadiene copolymer can be, for example, 3 mg / 100 mg or more. The iodine value of the hydrogenated acrylonitrile-butadiene copolymer can be adjusted by changing the hydrogenation reaction conditions when preparing the hydrogenated acrylonitrile-butadiene copolymer.

[0055] [Structural unit]

[0056] The hydrogenated acrylonitrile-butadiene copolymer used in the present invention comprises a nitrile group-containing monomer unit and a linear alkylene structural unit having 4 or more carbon atoms, and optionally further comprises other monomer units in addition to the nitrile group-containing monomer unit and the linear alkylene structural unit having 4 or more carbon atoms.

[0057] -Nitrile-containing monomer unit-

[0058] In the present invention, the nitrile group-containing monomer unit refers to a repeating unit derived from a nitrile group-containing monomer.

[0059] Here, examples of nitrile-containing monomers capable of forming nitrile-containing monomer units include α,β-ethylenically unsaturated nitrile monomers. Specifically, the α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group. Examples include acrylonitrile; α-halogenated acrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkyl acrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. Of these, acrylonitrile is preferred. These monomers can be used alone or in combination of two or more.

[0060] Moreover, when all repeating units (the total of monomer units and structural units) of the hydrogenated acrylonitrile-butadiene copolymer are taken as 100% by mass, the content ratio of the nitrile-containing monomer units in the hydrogenated acrylonitrile-butadiene copolymer is preferably 20% by mass or more, more preferably 23% by mass or more, further preferably 25% by mass or more, preferably 50% by mass or less, and more preferably 45% by mass or less. If the content ratio of the nitrile-containing monomer units in the hydrogenated acrylonitrile-butadiene copolymer is above the above lower limit, the cycle characteristics can be improved in the positive electrode for a secondary battery made using the conductive material dispersion of the present invention. In addition, if the content ratio of the nitrile-containing monomer units in the hydrogenated acrylonitrile-butadiene copolymer is below the above upper limit, the flexibility of the electrode can be further improved.

[0061] -Linear alkylene structural unit having 4 or more carbon atoms-

[0062] In the present invention, the linear alkylene structural unit having 4 or more carbon atoms refers to a unit having the general formula: -C n H 2n - (wherein n is an integer of 4 or greater) is a repeating unit consisting of an alkylene structure represented by

[0063] Here, the method for introducing an alkylene structural unit having 4 or more carbon atoms is not particularly limited, and examples thereof include the following methods (1) and (2):

[0064] (1) a method of preparing a polymer from a monomer composition comprising a conjugated diene monomer, and converting the conjugated diene monomer unit into an alkylene structural unit by hydrogenating the polymer;

[0065] (2) A method for producing a polymer from a monomer composition containing a 1-olefin monomer having 4 or more carbon atoms.

[0066] Among these, method (1) is preferred because it is easy to produce a polymer.

[0067] Examples of the conjugated diene monomer include conjugated diene compounds having 4 or more carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among these, 1,3-butadiene is preferred. Specifically, the linear alkylene structural unit having 4 or more carbon atoms is preferably a structural unit obtained by hydrogenating a conjugated diene monomer unit (a conjugated diene hydride unit), and more preferably a structural unit obtained by hydrogenating a 1,3-butadiene monomer unit (a 1,3-butadiene hydride unit).

[0068] In addition, the selective hydrogenation of the conjugated diene monomer units can be performed by a known method such as an oil layer hydrogenation method or an aqueous layer hydrogenation method.

[0069] Examples of the 1-olefin monomer having 4 or more carbon atoms include 1-butene and 1-hexene.

[0070] These can be used alone or in combination of two or more.

[0071] Furthermore, when all repeating units (the sum of monomer units and structural units) in the hydrogenated acrylonitrile-butadiene copolymer are taken as 100% by mass, the content of linear alkylene structural units having 4 or more carbon atoms in the hydrogenated acrylonitrile-butadiene copolymer is preferably 20% by mass or more, more preferably 23% by mass or more, even more preferably 25% by mass or more, preferably 70% by mass or less, more preferably 50% by mass or less, even more preferably 45% by mass or less, and particularly preferably 40% by mass or less. If the content of linear alkylene structural units having 4 or more carbon atoms in the hydrogenated acrylonitrile-butadiene copolymer is greater than the above lower limit, a positive electrode having further improved output characteristics can be produced by using a secondary battery positive electrode slurry containing a conductive material dispersion. Furthermore, when the content ratio of the linear alkylene structural units having 4 or more carbon atoms in the hydrogenated acrylonitrile-butadiene copolymer is below the above upper limit, the solubility of the hydrogenated acrylonitrile-butadiene copolymer in solvents such as N-methyl-2-methylpyrrolidone (NMP) can be ensured, thereby enabling the conductive material to be well dispersed in the conductive material dispersion.

[0072] Furthermore, examples of other monomer units include aromatic vinyl monomer units and hydrophilic group-containing monomer units.

[0073] -Aromatic vinyl monomer unit-

[0074] In the present invention, an aromatic vinyl monomer unit is a repeating unit derived from a monomer containing an aromatic vinyl group. Examples of aromatic vinyl monomers that can form aromatic vinyl monomer units include styrene, α-methylstyrene, vinyltoluene, and divinylbenzene. Styrene is preferred. These monomers can be used alone or in combination of two or more.

[0075] Moreover, when all repeating units (the total of monomer units and structural units) in the hydrogenated acrylonitrile-butadiene copolymer are taken as 100% by mass, the content ratio of the aromatic vinyl monomer unit in the hydrogenated acrylonitrile-butadiene copolymer is preferably 20% by mass or more, more preferably 30% by mass or more, preferably 60% by mass or less, and more preferably 50% by mass or less. If the content ratio of the aromatic vinyl monomer unit in the hydrogenated acrylonitrile-butadiene copolymer is within the above range, the dispersibility of the conductive material in the conductive material dispersion is further improved. Therefore, if the conductive material dispersion is used, the slurry stability of the secondary battery positive electrode slurry can be further improved. In addition, if the secondary battery positive electrode slurry is used, the cycle characteristics of the secondary battery can be further improved.

[0076] -Hydrophilic group-containing monomer units-

[0077] In the present invention, a hydrophilic group-containing monomer unit refers to a repeating unit derived from a hydrophilic group-containing monomer. Examples of the hydrophilic group-containing monomer that can form the hydrophilic group-containing monomer unit include polymerizable monomers having a hydrophilic group. Specifically, examples of the hydrophilic group-containing monomer include monomers having an acidic group-containing monomer unit, a hydroxyl group-containing monomer unit, and salts thereof. Examples of the acidic group-containing monomer unit include carboxylic acid groups, sulfonic acid groups, and phosphoric acid groups.

[0078] Examples of the monomer having a carboxylic acid group include monocarboxylic acids and derivatives thereof, dicarboxylic acids and anhydrides thereof, and derivatives thereof.

[0079] Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid.

[0080] Examples of the monocarboxylic acid derivative include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and β-diaminoacrylic acid.

[0081] Examples of the dicarboxylic acid include maleic acid, fumaric acid, and itaconic acid.

[0082] Examples of the anhydride of dicarboxylic acid include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride.

[0083] Examples of the dicarboxylic acid derivatives include maleic acid esters such as methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, methylallyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate.

[0084] Furthermore, as the monomer having a carboxylic acid group, an acid anhydride that generates a carboxyl group by hydrolysis can also be used.

[0085] In addition, monoesters and diesters of α,β-ethylenically unsaturated polycarboxylic acids such as maleic acid monoesters, diethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, monoethyl itaconate, diethyl itaconate, monobutyl itaconate, and dibutyl itaconate may also be mentioned.

[0086] Examples of the monomer having a sulfonic acid group include vinylsulfonic acid, methylvinylsulfonic acid, (meth)acrylic acidsulfonic acid, styrenesulfonic acid, 2-sulfonic ethyl (meth)acrylate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid.

[0087] In the present invention, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid.

[0088] Examples of the monomer having a phosphoric acid group include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate.

[0089] In addition, in the present invention, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0090] Examples of monomers having a hydroxyl group include: ethylenically unsaturated alcohols such as (meth)allyl alcohol, 3-butene-1-ol, and 5-hexene-1-ol; alkanol esters of ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, and di-2-hydroxypropyl itaconate; and monomers having the general formula: CH2=CR 1 -COO-(C q H 2q O) p -H (wherein p is an integer from 2 to 9, q is an integer from 2 to 4, and R 1Esters of polyalkylene glycol represented by (a) hydrogen or methyl) and (meth)acrylic acid; mono(meth)acrylates of dihydroxy esters of dicarboxylic acids such as 2-hydroxyethyl-2'-(meth)acryloyloxyphthalate and 2-hydroxyethyl-2'-(meth)acryloyloxysuccinate; vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; (meth)allyl-2-hydroxyethyl ether, (meth)allyl-2-hydroxypropyl ether, (meth)allyl-3-hydroxypropyl ether, (meth)allyl-2-hydroxybutyl ether, (meth)allyl-3-hydroxybutyl ether, (meth)allyl-4-hydroxybutyl ether, (meth)allyl-6-hydroxybutyl ether. Mono(meth)allyl ethers of alkylene glycols such as hydroxyhexyl ether; mono(meth)allyl ethers of polyoxyalkylene glycols such as diethylene glycol mono(meth)allyl ether and dipropylene glycol mono(meth)allyl ether; mono(meth)allyl ethers of halogen- and hydroxyl-substituted (poly)alkylene glycols such as glycerol mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether, and (meth)allyl-2-hydroxy-3-chloropropyl ether; mono(meth)allyl ethers of polyphenols such as eugenol and isoeugenol and their halogen-substituted products; (meth)allyl sulfides of alkylene glycols such as (meth)allyl-2-hydroxyethyl sulfide and (meth)allyl-2-hydroxypropyl sulfide. Among these, monomers having a carboxylic acid group are preferred, and methacrylic acid is more preferred. These can be used alone or in combination of two or more.

[0091] Moreover, when all repeating units (the total of monomer units and structural units) in the hydrogenated acrylonitrile-butadiene copolymer are taken as 100% by mass, the content ratio of the hydrophilic group-containing monomer units in the hydrogenated acrylonitrile-butadiene copolymer is preferably 0.1% by mass or more, more preferably 1% by mass or more, preferably 10% by mass or less, and more preferably 8% by mass or less. If the content ratio of the hydrophilic group-containing monomer units in the hydrogenated acrylonitrile-butadiene copolymer is above the above lower limit, the flexibility of the electrode can be improved in the secondary battery positive electrode prepared using the secondary battery positive electrode slurry comprising the conductive material dispersion of the present invention. In addition, if the content ratio of the hydrophilic group-containing monomer units in the hydrogenated acrylonitrile-butadiene copolymer is below the above upper limit, the battery resistance of the secondary battery can be reduced when the secondary battery positive electrode slurry comprising the conductive material dispersion of the present invention is used to prepare the secondary battery.

[0092] [Method for producing hydrogenated acrylonitrile-butadiene copolymer]

[0093] The method for producing the hydrogenated acrylonitrile-butadiene copolymer is not particularly limited. For example, the copolymer can be produced by polymerizing a monomer composition containing the above-mentioned monomers in the presence of a molecular weight modifier and a terminator, and then hydrogenating the obtained copolymer.

[0094] The polymerization method of the acrylonitrile-butadiene copolymer is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization can be used. In addition, any reaction such as ionic polymerization, free radical polymerization, and living radical polymerization can be used as the polymerization reaction.

[0095] In addition, the emulsifiers, dispersants, polymerization initiators, polymerization aids, molecular weight regulators, and terminators used in the polymerization can be commonly used emulsifiers, dispersants, polymerization initiators, polymerization aids, molecular weight regulators, and terminators, and their amounts can also be commonly used. In addition, the solution containing the hydrogenated acrylonitrile-butadiene copolymer obtained by polymerizing the above-mentioned monomer composition and the polymerization solvent can be directly used to prepare the conductive material dispersion. Furthermore, the method of the hydrogenation reaction is not particularly limited and can be carried out according to known methods.

[0096] [Content of dispersant]

[0097] Moreover, relative to 100 parts by mass of conductive material, the content of the dispersant (i.e., hydrogenated acrylonitrile-butadiene copolymer) in the conductive material dispersion is preferably more than 50 parts by mass, more preferably more than 100 parts by mass, preferably less than 400 parts by mass, more preferably less than 300 parts by mass. If the content of the dispersant in the conductive material dispersion is more than the above-mentioned lower limit, the slurry stability and coating uniformity of the secondary battery positive electrode slurry obtained using the conductive material dispersion can be made to be more excellent. In addition, if the content of the dispersant in the conductive material dispersion is below the above-mentioned upper limit, the resistance of the secondary battery made of the secondary battery positive electrode slurry including the conductive material dispersion can be suppressed to increase, so that the output characteristics of the secondary battery are excellent.

[0098] [Solvent]

[0099] The solvent contained in the conductive material dispersion is not particularly limited, and an organic solvent can be used, for example. As an organic solvent, there can be mentioned: cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; ketones such as acetone, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, methylcyclohexane, and ethylcyclohexane; chlorinated aliphatic hydrocarbons such as dichloromethane, chloroform, and carbon tetrachloride; esters such as ethyl acetate, butyl acetate, γ-butyrolactone, and ε-caprolactone; nitriles such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether; alcohols such as methanol, ethanol, isopropyl alcohol, ethylene glycol, and ethylene glycol monomethyl ether; amides such as N-methyl-2-methylpyrrolidone (NMP) and N,N-dimethylformamide. Among these, NMP is preferred. These can be used alone or in combination of two or more to form a mixed solvent.

[0100] <Additives>

[0101] Furthermore, additives that can be optionally contained in the conductive material dispersion of the present invention are not particularly limited, and examples thereof include surface tension modifiers, viscosity modifiers, reinforcing materials, etc. These additives may be used alone or in combination of two or more.

[0102] <Preparation of Conductive Material Dispersion>

[0103] The conductive material dispersion of the present invention can be prepared by mixing the aforementioned conductive material, dispersant, solvent, and any additives using known methods. Specifically, the conductive material dispersion can be prepared by mixing the aforementioned components using a mixer such as a disperser, ball mill, sand mill, bead mill, pigment disperser, attritor, ultrasonic disperser, homogenizer, planetary mixer, or Filmix. The solids concentration of the conductive material dispersion can be, for example, 0.5% to 25% by mass.

[0104] The obtained conductive material dispersion can be preferably used in the method for producing a slurry for a secondary battery positive electrode of the present invention, for example, as described below.

[0105] (Method for producing slurry for secondary battery positive electrode)

[0106] In the manufacturing method of the secondary battery positive electrode slurry of the present invention, the positive electrode active material, the binder, and the above-mentioned conductive material dispersion of the present invention are mixed to obtain the secondary battery positive electrode slurry. In addition, in the manufacturing method of the secondary battery positive electrode slurry of the present invention, in addition to mixing the above-mentioned components, other components may also be mixed. Moreover, according to the manufacturing method of the present invention, by using the conductive material dispersion of the present invention, it is possible to obtain a secondary battery positive electrode slurry with excellent slurry stability and coating uniformity. Below, the positive electrode active material, the binder and the other components are described in order.

[0107] <Positive electrode active material>

[0108] The positive electrode active material is a substance that transfers electrons in the positive electrode of the secondary battery. For example, when the secondary battery is a lithium ion secondary battery, a substance that can absorb and release lithium is generally used as the positive electrode active material.

[0109] In addition, below, a positive electrode active material in a case where the secondary battery is a lithium ion secondary battery will be described as an example, but the present invention is not limited to the following example.

[0110] The positive electrode active material for lithium ion secondary batteries is not particularly limited, and examples thereof include lithium cobalt oxide (LiCoO2), lithium manganate (LiMn2O4), lithium nickel oxide (LiNiO2), Co-Ni-Mn lithium-containing composite oxide (Li(CoMnNi)O2), Ni-Mn-Al lithium-containing composite oxide, Ni-Co-Al lithium-containing composite oxide, olivine-type lithium iron phosphate (LiFePO4), olivine-type lithium manganese phosphate (LiMnPO4), Li2MnO3-LiNiO2 solid solution, Li 1+x Mn 2-x O4 (0 < X ​​< 2) represented by lithium-excess spinel compounds, Li [Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 ]O2、LiNi 0.5 Mn 1.5 O4 and other known positive electrode active materials.

[0111] Among the above, from the viewpoint of improving the battery capacity of lithium ion secondary batteries, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium-containing composite oxides of Co-Ni-Mn, Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 ]O2 or LiNi 0.5 Mn 1.5 O4, more preferably lithium cobalt oxide (LiCoO2), Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 ]O2、LiNi 0.5 Mn 1.5 O4 or LiNi 0.5 Co 0.2 Mn 0.3 O2. These can be used alone or in combination of two or more.

[0112] <Binder>

[0113] The binder is a substance that prevents the components contained in the positive electrode composite material layer from being separated from the positive electrode composite material layer in the positive electrode produced using the secondary battery slurry obtained by the manufacturing method of the present invention. The binder used in the manufacturing method of the secondary battery positive electrode slurry of the present invention is not particularly limited. From the perspective of further improving the stability of the secondary battery positive electrode slurry, a fluorine-based polymer is preferably used.

[0114] [Fluoropolymers]

[0115] As fluorine-based polymers, there are no particular limitations, and examples include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, perfluoroalkoxy fluororesins, tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-tetrafluoroethylene copolymers, ethylene-chlorotrifluoroethylene copolymers, and vinylidene fluoride-hexafluoropropylene copolymers (vinylidene fluoride-hexafluoropropylene copolymers). Among them, polyvinylidene fluoride (PVdF) is preferred as the fluorine-based polymer.

[0116] [Other ingredients]

[0117] As other components, any components such as reinforcing materials, leveling agents, viscosity modifiers, and electrolyte additives can be cited. These are not particularly limited as long as they do not affect the battery reaction. In addition, these components can be used alone or in combination of two or more in any ratio.

[0118] In the method for producing the secondary battery positive electrode slurry of the present invention, the method for mixing the above components is not particularly limited. For example, the mixing can be performed using the same mixer as used to prepare the above-mentioned conductive material dispersion.

[0119] <Content of Conductive Material in Secondary Battery Positive Electrode Slurry>

[0120] Furthermore, the content of the conductive material in the secondary battery positive electrode slurry obtained by the manufacturing method of the present invention is not particularly limited, but is preferably 0.1 parts by mass or less, and more preferably 0.08 parts by mass or less, relative to 100 parts by mass of the positive electrode active material. If the content of the conductive material in the secondary battery positive electrode slurry is 0.1 parts by mass or less, both slurry stability and coating uniformity of the secondary battery slurry can be sufficiently excellent.

[0121] <Content of Binder in Secondary Battery Positive Electrode Slurry>

[0122] Furthermore, the content of the binder in the secondary battery positive electrode slurry obtained by the manufacturing method of the present invention is not particularly limited. The content of the binder is preferably 0.1 parts by mass or more, preferably 6 parts by mass or less, and more preferably 1 part by mass or less, relative to 100 parts by mass of the positive electrode active material, calculated as solid content. If the content of the binder in the secondary battery positive electrode slurry is within the above range, in the positive electrode produced using the secondary battery positive electrode slurry, the adhesion between the positive electrode composite material layer and the current collector can be improved, and the resistance of the secondary battery can be suppressed to a sufficiently low level.

[0123] Furthermore, the slurry for secondary battery positive electrodes obtained by the production method of the present invention can be preferably used in the production method of a secondary battery positive electrode of the present invention described below, for example.

[0124] (Method for Manufacturing Positive Electrode for Secondary Battery)

[0125] The method for manufacturing a secondary battery electrode of the present invention includes forming a positive electrode composite material layer using a secondary battery positive electrode slurry obtained by the method for manufacturing a secondary battery positive electrode slurry of the present invention. Here, the positive electrode composite material layer can be formed, for example, by the following steps: applying the secondary battery positive electrode slurry obtained by the manufacturing method of the present invention to at least one side of a current collector (coating step); and drying the secondary battery positive electrode slurry formed on at least one side of the current collector to form a positive electrode composite material layer on at least one side of the current collector (drying step).

[0126] [Coating process]

[0127] As a method for applying the secondary battery positive electrode slurry to the current collector, there is no particular limitation, and known methods can be used. Specifically, as a coating method, a doctor blade method, an immersion method, a reverse roller method, a direct roller method, a gravure printing method, an extrusion method, a brush coating method, etc. can be used. The thickness of the slurry film on the current collector before drying after coating can be appropriately set according to the thickness of the positive electrode composite material layer obtained by drying.

[0128] Here, as the current collector for coating the secondary battery positive electrode slurry, a material having electrical conductivity and electrochemical durability can be used. Specifically, current collectors made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. can be used. Furthermore, the above materials can be used alone or in combination of two or more in any ratio.

[0129] [Drying process]

[0130] The method for drying the secondary battery positive electrode slurry on the current collector is not particularly limited, and known methods can be used, including, for example, drying using warm air, hot air, or low-humidity air; vacuum drying; and drying using irradiation with infrared rays, electron beams, or the like. By drying the secondary battery positive electrode slurry on the current collector in this manner, a positive electrode composite material layer can be formed on the current collector, resulting in a secondary battery positive electrode having the current collector and the positive electrode composite material layer.

[0131] In addition, after the drying step, the positive electrode material layer may be subjected to a press treatment using a die press or a roll press, etc. The press treatment can improve the adhesion between the positive electrode material layer and the current collector.

[0132] Moreover, the positive electrode obtained by the manufacturing method of the secondary battery positive electrode of the present invention has a current collector and a positive electrode composite material layer formed on the current collector, and the positive electrode composite material layer is formed using the secondary battery positive electrode slurry obtained by the manufacturing method of the present invention. That is, the positive electrode composite material layer contains at least a positive electrode active material, carbon nanotubes as a conductive material, and hydrogenated acrylonitrile-butadiene copolymer as a dispersant. In addition, the various components contained in the positive electrode composite layer are the various components contained in the secondary battery positive electrode slurry obtained by the manufacturing method of the present invention, and the preferred presence ratio of these various components is the same as the preferred presence ratio of the various components in the secondary battery positive electrode slurry.

[0133] Furthermore, the positive electrode composite material layer of the secondary battery positive electrode obtained by the manufacturing method of the present invention is formed using a secondary battery positive electrode slurry containing the conductive material dispersion of the present invention, so that the conductive material forms a good conductive network within the positive electrode composite material layer. Thus, by using this secondary battery positive electrode, the cycle characteristics of the secondary battery can be improved, the internal resistance can be reduced, and the output characteristics of the secondary battery can be improved.

[0134] (Method for Manufacturing Secondary Battery)

[0135] The method for manufacturing a secondary battery of the present invention uses a secondary battery positive electrode obtained by the manufacturing method of the present invention. Furthermore, according to the method for manufacturing a secondary battery of the present invention, a secondary battery having excellent output characteristics and cycle characteristics can be manufactured. In addition, the following description uses a case where the secondary battery is a lithium-ion secondary battery as an example, but the present invention is not limited to the following example.

[0136] <Negative electrode>

[0137] As the negative electrode of the secondary battery, a known negative electrode can be used. Specifically, for example, a negative electrode formed of a thin plate of metallic lithium or a negative electrode having a negative electrode composite material layer formed on a current collector can be used.

[0138] In addition, the current collector may be formed from a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, or platinum. Furthermore, the negative electrode composite material layer may be a layer comprising a negative electrode active material and a negative electrode binder. Furthermore, the negative electrode binder is not particularly limited, and any known material may be used.

[0139] Electrolyte

[0140] As the electrolyte, an organic electrolyte in which a supporting electrolyte is dissolved in an organic solvent can generally be used. As the supporting electrolyte of a lithium ion secondary battery, for example, a lithium salt can be used. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2Nli, (CF3SO2)2Nli, (C2F5SO2)NLi, etc. Among them, LiPF6, LiClO4, and CF3SO3Li are preferred because they are easily dissolved in solvents and show a high degree of dissociation, and LiPF6 is particularly preferred. In addition, one electrolyte can be used alone, or two or more electrolytes can be used in combination in any ratio. Generally, there is a tendency that the higher the degree of dissociation of the supporting electrolyte, the higher the lithium ion conductivity. Therefore, the lithium ion conductivity can be adjusted according to the type of supporting electrolyte.

[0141] As the organic solvent used in the electrolyte, there is no particular limitation 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 ethyl methyl carbonate (EMC) can be preferably used; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as cyclopentane and dimethyl sulfoxide. In addition, a mixture of these solvents can also be used. Among them, due to the high dielectric constant and wide stable potential region, carbonates are preferably used, and a mixture of ethylene carbonate and ethyl methyl carbonate is more preferably used.

[0142] <Spacer>

[0143] The separator is not particularly limited and may include known separators such as organic separators. Organic separators are porous members formed of organic materials, and examples thereof include microporous films or nonwoven fabrics made of polyolefin resins such as polyethylene and polypropylene, or aromatic polyamide resins.

[0144] Moreover, in the manufacturing method of the secondary battery of the present invention, after the process of manufacturing the positive electrode according to the manufacturing method of the positive electrode for the secondary battery of the present invention is implemented, the positive electrode and the negative electrode obtained are overlapped across a spacer, and are wound, folded, etc. according to the shape of the battery as needed, and placed in a battery container, and an electrolyte is injected into the battery container and sealed. In order to prevent the internal pressure rise of the secondary battery, the occurrence of overcharge and discharge, etc., anti-overcurrent elements such as fuses, PTC elements, porous metal mesh, guide plates, etc. can also be provided as needed. The shape of the secondary battery can be any one of a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, etc.

[0145] Example

[0146] Hereinafter, the present invention will be described based on Examples, but the present invention is not limited to these Examples. In the following description, "%" and "parts" showing amounts are based on mass unless otherwise specified.

[0147] The ratio of each monomer unit in the polymer is generally consistent with the ratio (feed ratio) of monomers capable of forming each monomer unit in the monomer composition used for polymerization of the polymer. In the Examples and Comparative Examples, various physical properties were measured or evaluated using the following methods.

[0148] <Iodine value>

[0149] The iodine value of the polymer was determined in accordance with JIS K6235;2006.

[0150] <Weight average molecular weight>

[0151] The weight average molecular weight of the polymer was determined by gel permeation chromatography (GPC). Specifically, a calibration curve was prepared using a polystyrene standard substance, and the weight average molecular weight as a standard substance conversion value was calculated. In addition, the distribution of the weight average molecular weight was rounded off to the nearest integer when the value was less than 10,000, and rounded off to the nearest integer when the value was more than 10,000, and the evaluation was performed. In addition, the measurement conditions and the measurement apparatus were as follows.

[0152] Column: TSKgelα-M×2 pieces (Φ7.8mmI.D.×30cm×2 pieces manufactured by Tosoh Corporation)

[0153] Eluent: dimethylformamide (50 mM lithium bromide, 10 mM phosphoric acid)

[0154] Flow rate: 0.5 mL / min

[0155] Sample concentration: about 0.5g / L (solid content concentration)

[0156] Injection volume: 200 μL

[0157] Column temperature: 40°C

[0158] Detector: RI detector (HLC-8320GPC RI detector manufactured by Tosoh Corporation)

[0159] Detector conditions: RI: Pol(+), Res(1.0s)

[0160] Molecular weight marker: Tosoh Corporation standard polystyrene kit PStQuick K

[0161] <Volume Average Particle Size (D90) of CNTs in Conductive Material Dispersion>

[0162] The prepared conductive material dispersion was diluted to an appropriate concentration and used as a measurement sample. Using a laser diffraction particle size analyzer (SALD-7100, manufactured by Shimadzu Corporation) with a solvent refractive index set to 1.47 (solvent: N-methyl-2-pyrrolidone), the CNT particle size distribution (volume basis) was measured to determine the volume average particle size (D90) of the CNTs in the conductive material dispersion.

[0163] The concentration of the measurement sample was set to a concentration at which the absorbance in the measurement device became 0.2 or less.

[0164] <Slurry stability>

[0165] The slurry stability of the positive electrode slurry was evaluated based on the viscosity change rate of the positive electrode slurry.

[0166] Specifically, the viscosity (η1) of the freshly prepared positive electrode slurry was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., "RB-80L") at a temperature of 25°C, a rotation speed of 60 rpm, and a rotation time of 60 seconds. The positive electrode slurry was then stored at 25°C for 5 days. The viscosity (η2) of the positive electrode slurry after storage was measured in the same manner as the viscosity (η1) described above. The viscosity change Δη was calculated using the obtained viscosities (η1) and (η2) according to the following formula.

[0167] Viscosity change Δη (%) = (|η1-η2| / η1) × 100

[0168] The slurry stability of the positive electrode slurry was then evaluated according to the following criteria: The smaller the viscosity change Δη, the better the slurry stability of the positive electrode slurry, and the better the dispersion state of the conductive material contained in the positive electrode slurry can be maintained.

[0169] A: Viscosity change Δη is less than 20%.

[0170] B: The viscosity change Δη is 20% or more and less than 50%.

[0171] C: Viscosity change Δη is 50% or more.

[0172] <Coating uniformity>

[0173] Cut the prepared pressed positive electrode into a 10 cm x 10 cm size. Then, visually inspect the cut surface of the positive electrode, and evaluate the coating uniformity based on the number of surface irregularities (aggregates). The fewer surface irregularities (aggregates) observed visually, the more uniformly the positive electrode slurry can be applied, and the better the coating uniformity.

[0174] A: No irregularities (aggregates) on the positive electrode surface were visually confirmed.

[0175] B: Fewer than 5 visually observed irregularities (aggregates) on the positive electrode surface.

[0176] C: Five or more visually confirmed irregularities (aggregates) on the positive electrode surface.

[0177] Output Characteristics

[0178] The prepared laminated lithium ion secondary battery was charged at 140 mA at 25°C until the voltage reached 4.2 V, then charged at 4.2 V until the charging current reached 14 mA. The battery was then discharged at 140 mA until the voltage reached 3 V, which was used as the initial capacity.

[0179] The laminated lithium-ion secondary battery whose initial capacity has been measured is charged at a constant current of 0.2C at 25°C until the battery voltage reaches 4.2V, and then charged at a constant voltage of 4.2V until the charging current reaches 0.02C. Next, it is discharged at a constant current of 2C until the battery voltage reaches 3.0V, which is taken as the 2C capacity. The value of [(2C capacity) / (initial capacity)]×100(%) is used as the output characteristic, and the output characteristics of the lithium-ion secondary battery are evaluated according to the following criteria. The higher the value of the output characteristic, the better the initial output characteristics of the lithium-ion secondary battery, that is, the smaller the internal resistance.

[0180] A: Output characteristics are 90% or more.

[0181] B: The output characteristic is 80% or more and less than 90%.

[0182] C: Output characteristic is less than 80%.

[0183] Cycle Characteristics

[0184] The prepared lithium-ion secondary battery was charged at a constant current of 1C until the battery voltage reached 4.2V, and then discharged at a constant current of 1C until the battery voltage reached 3V, 100 times at 45°C. The charge-discharge capacity retention ratio [=(B) / (A)×100(%)] was calculated from the 100th discharge capacity (discharge capacity "B") relative to the first discharge capacity (discharge capacity "A"), and the cycle characteristics of the lithium-ion secondary battery were evaluated according to the following criteria. The higher the charge-discharge capacity retention ratio, the better the cycle characteristics of the lithium-ion secondary battery.

[0185] A: The charge and discharge capacity retention rate is 90% or more.

[0186] B: The charge and discharge capacity retention rate is 80% or more and less than 90%.

[0187] C: The charge and discharge capacity retention rate is less than 80%.

[0188] (Example 1)

[0189] Preparation of dispersant

[0190] Into a reactor were sequentially charged 180 parts of ion-exchanged water, 25 parts of a 10% aqueous solution of sodium dodecylbenzenesulfonate as an emulsifier, 40 parts of styrene as an aromatic vinyl monomer, 26 parts of acrylonitrile as a nitrile-containing monomer, 4 parts of methacrylic acid as a carboxylic acid-containing monomer, and 2 parts of tert-dodecylmercaptan as a molecular weight modifier. The atmosphere in the reactor was then replaced with nitrogen three times, and 30 parts of 1,3-butadiene as a conjugated diene monomer was added. Polymerization was initiated by adding 0.1 parts of cumene hydroperoxide as a polymerization initiator to the reactor maintained at 10°C, and the polymerization reaction proceeded while stirring. When the monomer-to-polymer conversion reached 85%, 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) was added as a terminator, and residual monomers were removed using a rotary evaporator at 60°C to obtain an aqueous dispersion of acrylonitrile-butadiene copolymer (A), which served as a precursor for the dispersant. The obtained aqueous dispersion of the acrylonitrile-butadiene copolymer (A) (total solid content: 48 g) was placed in a 1 L autoclave equipped with a stirrer, and nitrogen gas was flowed for 10 minutes to remove dissolved oxygen in the aqueous dispersion.

[0191] Then, 50 mg of palladium acetate, serving as a hydrogenation catalyst, was dissolved in 180 mL of water to which nitric acid had been added in an amount 4 times the molar amount of palladium (Pd). After the system was purged twice with hydrogen, the contents of the autoclave were heated to 50° C. while pressurized to 3 MPa with hydrogen, and a hydrogenation reaction was carried out for 6 hours to obtain a hydrogenated acrylonitrile-butadiene copolymer (A) serving as a dispersant. The resulting hydrogenated acrylonitrile-butadiene copolymer (A) had an iodine value of 15 mg / 100 mg.

[0192] <Preparation of NMP solution containing dispersant>

[0193] The aqueous dispersion of the hydrogenated acrylonitrile-butadiene copolymer (A) obtained as described above is mixed with NMP as a solvent to obtain a mixed solution. Subsequently, all water contained in the obtained mixed solution is evaporated under reduced pressure to obtain an NMP solution containing the hydrogenated acrylonitrile-butadiene copolymer (A). The obtained NMP solution containing the hydrogenated acrylonitrile-butadiene copolymer (A) is used as the NMP solution containing the dispersant.

[0194] <Preparation of Conductive Material Dispersion>

[0195] 0.06 parts of CNT (A) (specific surface area: 1200 m 2 / g), 0.12 parts (in terms of solid content) of the NMP solution containing the dispersant obtained above, and 99.1 parts of NMP as a solvent were stirred (3000 rpm for 10 minutes), and then mixed at a peripheral speed of 8 m / s for 2 hours using a bead mill using zirconia beads with a diameter of 1 mm to prepare a conductive material dispersion (A) having a solid content concentration of 0.9% by mass (0.3% by mass in terms of CNTs). The volume average particle size (D90) of the CNTs (A) in the conductive material dispersion (A) was 20 μm.

[0196] <Preparation of positive electrode slurry>

[0197] 100 parts of lithium cobalt oxide (LiCoO2, average particle size: 10 μm) as a positive electrode active material, 0.18 parts (0.06 parts in terms of CNT conversion) of the conductive material dispersion (A) obtained as described above, 1.0 parts of polyvinylidene fluoride (PVdF, manufactured by Wu Yu Co., Ltd., #7208) as a binder, and NMP as a solvent were stirred (60 rpm, 30 minutes) by a planetary mixer to prepare a positive electrode slurry. In addition, the amount of NMP added was adjusted so that the viscosity of the obtained positive electrode slurry (measured by a single cylinder rotational viscometer in accordance with JIS Z8803:1991. Temperature: 25°C, rotation speed: 60 rpm) was within the range of 4000 to 5000 mPa·s. The obtained positive electrode slurry was used to evaluate the slurry stability and coating uniformity. The results are shown in Table 1.

[0198] <Making the positive electrode>

[0199] A 20 μm thick aluminum foil was prepared as a current collector. The positive electrode slurry obtained above was applied to one side of the aluminum foil using a notch wheel coater so that the mass per unit area after drying was 10 mg / cm 2 The positive electrode raw material was rolled by a roller press to produce a material having a density of 3.2 g / cm 3 A sheet-shaped positive electrode was formed by a positive electrode composite material layer (on one side) and aluminum foil. The thickness of the sheet-shaped positive electrode was 30 μm. The sheet-shaped positive electrode was cut into pieces 4.6 cm wide and 50 cm long to prepare a positive electrode for a lithium-ion secondary battery.

[0200] <Production of the negative electrode>

[0201] A planetary mixer was used to stir 100 parts of spherical artificial graphite (volume average particle size: 12 μm) as a negative electrode active material, 1.5 parts of styrene butadiene polymer as a negative electrode binder, 1 part of carboxymethyl cellulose as a thickener, and an appropriate amount of water as a dispersion medium to prepare a negative electrode slurry.

[0202] Next, a copper foil with a thickness of 15 μm was prepared as a current collector. The negative electrode slurry obtained as described above was applied to one side of the copper foil so that the coating amount after drying was 7 mg / cm 2 The negative electrode raw material was rolled by a roller press to produce a negative electrode raw material with a density of 1.6 g / cm 3 The negative electrode sheet was formed by combining the negative electrode composite material layer (on one side) and copper foil. The negative electrode sheet was then cut into pieces with a width of 4.8 cm and a length of 52 cm to prepare a negative electrode for a lithium ion secondary battery.

[0203] <Manufacturing of lithium-ion secondary batteries>

[0204] The positive and negative electrodes obtained above were wound around a core with a diameter of 20 mm, with a separator (a 15 μm thick polypropylene microporous film) interposed therebetween, to form a wound body. The resulting wound body was then compressed in one direction at a speed of 10 mm / s to a thickness of 4.5 mm. The compressed wound body had an elliptical shape when viewed from above, with a major diameter to minor diameter ratio (major diameter / minor diameter) of 7.7.

[0205] In addition, an electrolyte solution [composition: 1.0M LiPF6 solution (the solvent is a mixed solution of 5% by mass of fluoroethylene carbonate added to a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 3 / 7 (mass ratio), and 2% by volume of vinylene carbonate is added as an additive] is prepared.

[0206] Afterwards, the compressed wound body was placed in an aluminum laminated housing together with 3.2g of non-aqueous electrolyte. Then, a nickel wire was connected to the specified position of the negative electrode, and an aluminum wire was connected to the specified position of the positive electrode. The opening of the laminated housing was then sealed with heat to obtain a lithium-ion secondary battery. The lithium-ion secondary battery was in the shape of a bag with a width of approximately 35mm, a height of approximately 50mm, and a thickness of approximately 5mm. The nominal capacity of the battery was 750mAh. The output characteristics and cycle characteristics of the obtained lithium-ion secondary battery were evaluated. The results are shown in Table 1.

[0207] (Example 2)

[0208] As the conductive material, CNT (B) (specific surface area: 910 m 2 / g) instead of CNT (A), the same procedures as in Example 1 were followed to prepare a conductive material dispersion (B). A positive electrode slurry, a positive electrode, a negative electrode, and a lithium-ion secondary battery were prepared in the same manner as in Example 1, except that the conductive material dispersion (B) was used instead of the conductive material dispersion (A). Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0209] (Example 3)

[0210] A positive electrode slurry, a positive electrode, a negative electrode, and a lithium-ion secondary battery were prepared in the same manner as in Example 1, except that the amount of the conductive material dispersion (A) was changed to 0.27 parts in terms of solid content (0.09 parts in terms of CNTs) when preparing the positive electrode slurry. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0211] (Example 4)

[0212] When preparing the dispersant, the amount of palladium acetate used as a hydrogenation catalyst was changed to 25 mg, and the iodine value of the hydrogenated acrylonitrile-butadiene copolymer used as the dispersant was adjusted to 22 mg / 100 mg. A positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0213] (Example 5)

[0214] When preparing the positive electrode slurry, the ratio (mass ratio) of the dispersant (hydrogenated acrylonitrile-butadiene copolymer) to the conductive material (CNT (A)) in the conductive material dispersion (A) was adjusted to 1:1. A positive electrode slurry, a positive electrode, a negative electrode, and a lithium-ion secondary battery were prepared in the same manner as in Example 1. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0215] (Example 6)

[0216] When preparing the conductive material dispersion, the circumferential speed when mixing the various components was changed to 6 m / s. A conductive material dispersion (C) was prepared in the same manner as in Example 1. The volume average particle size (D90) of the CNTs in the resulting conductive material dispersion (C) was 45 μm. Then, the conductive material dispersion (C) was used instead of the conductive material dispersion (A). A positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0217] (Example 7)

[0218] When preparing the dispersant, the amount of acrylonitrile as the nitrile-containing monomer was changed to 34 parts, the amount of methacrylic acid as the carboxylic acid-containing monomer was changed to 4 parts, the amount of 1,3-butadiene was changed to 62 parts, and styrene was not used. A positive electrode slurry, a positive electrode, a negative electrode, and a lithium-ion secondary battery were prepared in the same manner as in Example 1. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0219] (Example 8)

[0220] When preparing the positive electrode slurry, the positive electrode active material is changed to a ternary active material (LiNi 0.5 Co 0.2 Mn 0.3 A positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the above-mentioned conditions were met. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0221] (Comparative Example 1)

[0222] A positive electrode slurry, a positive electrode, a negative electrode, and a lithium-ion secondary battery were prepared in the same manner as in Example 1, except that hydrogenated acrylonitrile-butadiene copolymer was not used as a dispersant when preparing the positive electrode slurry. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0223] (Comparative Example 2)

[0224] When preparing the conductive material dispersion, CNT (C) (specific surface area: 390 m 2 A positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1, except that CNT (A) was replaced with 100% tantalum (g). Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0225] (Comparative Example 3)

[0226] When preparing the conductive material dispersion, the circumferential speed when mixing the various components was changed to 4 m / s. A conductive material dispersion (X) was prepared in the same manner as in Example 1. The volume average particle size (D90) of the CNTs in the resulting conductive material dispersion (X) was 70 μm. Then, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium-ion secondary battery were prepared in the same manner as in Example 1 except that the conductive material dispersion (X) was used instead of the conductive material dispersion (A). Then, various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0227] [Table 1]

[0228]

[0229] In Table 1,

[0230] "LCO" stands for lithium cobalt oxide (LiCoO2),

[0231] "NCM" means ternary active material (LiNi 0.5 Co 0.2 Mn 0.3 O2),

[0232] "CNT" stands for carbon nanotube,

[0233] "PVdF" stands for polyvinylidene fluoride,

[0234] "ST" stands for styrene,

[0235] "H-BD" represents 1,3-butadiene hydride unit,

[0236] "BD" stands for butadiene,

[0237] "AN" stands for acrylonitrile,

[0238] "MAA" stands for methacrylic acid.

[0239] As shown in Table 1, the specific surface area of ​​the conductive material is 800 m 2 / g and above and 1300m 2 / g or less CNTs, a hydrogenated acrylonitrile-butadiene copolymer with a weight-average molecular weight of 200,000 or less as a dispersant, and a conductive material dispersion of a solvent, wherein the volume average particle size (D90) of the conductive material (CNT) in the conductive material dispersion is 50 μm or less (Examples 1 to 8), a positive electrode slurry with excellent slurry stability and coating uniformity can be prepared, and the output characteristics and cycle characteristics of a lithium ion secondary battery having a positive electrode produced using the positive electrode slurry can be improved.

[0240] On the other hand, it was found that when the conductive material dispersion containing no dispersant was used (Comparative Example 1), the specific surface area of ​​the conductive material (CNT) in the conductive material dispersion was less than 800 m 2 / g (Comparative Example 2), and when the average volume particle size (D90) of the conductive material (CNT) in the conductive material dispersion exceeds 50 μm (Comparative Example 3), at least one of the slurry stability and coating uniformity of the obtained positive electrode slurry is poor, or one of the output characteristics and cycle characteristics of the obtained lithium ion secondary battery is poor.

[0241] Industrial applicability

[0242] According to the present invention, there can be provided a method for producing a secondary battery positive electrode slurry capable of enabling a secondary battery to exhibit excellent output characteristics and cycle characteristics, and a conductive material dispersion liquid that can be preferably used to produce the secondary battery positive electrode slurry.

[0243] Furthermore, according to the present invention, a method for producing a positive electrode for a secondary battery that can be used to produce a secondary battery having excellent output characteristics and cycle characteristics can be provided.

[0244] Furthermore, according to the present invention, a method for manufacturing a secondary battery having excellent output characteristics and cycle characteristics can be provided.

Claims

1. A conductive material dispersion comprising a conductive material, a dispersant and a solvent, The conductive material has a specific surface area of ​​800m 2 / g and above and 1300m 2 / g or less carbon nanotubes, The volume average particle size D90 of the carbon nanotubes in the conductive material dispersion is 50 μm or less, The dispersant is hydrogenated acrylonitrile-butadiene copolymer, The weight average molecular weight of the hydrogenated acrylonitrile-butadiene copolymer is less than 200,000, The volume average particle size D90 refers to the particle size of the carbon nanotubes in the conductive material dispersion when the cumulative volume calculated from the smaller diameter side reaches 90% in a volume-based particle size distribution measured by a laser diffraction method.

2. The conductive material dispersion according to claim 1, wherein The iodine value of the hydrogenated acrylonitrile-butadiene copolymer is 25 mg / 100 mg or less.

3. The conductive material dispersion according to claim 1 or 2, wherein The content of the dispersant in the conductive material dispersion is 50 parts by mass or more and 400 parts by mass or less relative to 100 parts by mass of the conductive material. 4 . A method for producing a slurry for a positive electrode of a non-aqueous secondary battery, comprising mixing a positive electrode active material, a binder, and the conductive material dispersion according to claim 1 to obtain the slurry for a positive electrode of a non-aqueous secondary battery.

5. The method for producing a slurry for a positive electrode of a non-aqueous secondary battery according to claim 4, wherein: The content of the conductive material in the non-aqueous secondary battery positive electrode slurry is less than 0.1 parts by mass relative to 100 parts by mass of the positive electrode active material.

6. The method for producing a slurry for a positive electrode of a non-aqueous secondary battery according to claim 4 or 5, wherein: The content of the binder in the non-aqueous secondary battery positive electrode slurry is 0.1 parts by mass or more and 6 parts by mass or less relative to 100 parts by mass of the positive electrode active material.

7. A method for producing a positive electrode for a non-aqueous secondary battery, comprising the steps of forming a positive electrode composite material layer using a slurry for a positive electrode for a non-aqueous secondary battery, The non-aqueous secondary battery positive electrode slurry is obtained by the method according to any one of claims 4 to 6. 8 . A method for producing a non-aqueous secondary battery, comprising using the positive electrode for a non-aqueous secondary battery obtained by the method according to claim 7 .

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