Binder composition for secondary battery electrodes, conductive material paste composition for secondary battery electrodes, slurry composition for secondary battery electrodes, electrode for secondary batteries, and secondary battery

Abstract

This binder composition for secondary battery electrodes contains a copolymer including a nitrile group-containing monomer unit and a linear alkylene structural unit having 4 or more carbon atoms. The copolymer has a weight average molecular weight of 5,000-500,000. The chlorine content in the binder composition is more than 0 but not more than 2,000 ppm with respect to the copolymer.

Description

Binder composition for secondary battery electrodes, conductive paste composition for secondary battery electrodes, slurry composition for secondary battery electrodes, secondary battery electrodes and secondary batteries

[0001] The present invention relates to a binder composition for secondary battery electrodes, a conductive paste composition for secondary battery electrodes, a slurry composition for secondary battery electrodes, an electrode for a secondary battery, and a secondary battery.

[0002] Secondary batteries such as lithium-ion secondary batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications. Therefore, in recent years, improvements to battery components such as electrodes have been investigated in order to further improve the performance of secondary batteries.

[0003] Here, an electrode used in a secondary battery such as a lithium-ion secondary battery typically includes a current collector and an electrode mixture layer (positive electrode mixture layer or negative electrode mixture layer) formed on the current collector. The electrode mixture layer is formed, for example, by applying a slurry composition containing an electrode active material and a binder composition containing a binding agent onto the current collector and then drying the applied slurry composition.

[0004] Therefore, in recent years, attempts have been made to improve the binder composition used in forming the electrode mixture layer in order to achieve further improvement in the performance of secondary batteries. Specifically, Patent Documents 1 to 3 disclose that the chlorine content in a binder composition containing a vinylidene fluoride polymer is set to 1000 ppm or less.

[0005] JP 2019-200894 A JP 2019-200895 A International Publication No. 2019 / 239781

[0006] Here, secondary batteries are required to have excellent cycle characteristics, but secondary batteries formed using the above-mentioned conventional binder compositions have room for further improvement in terms of cycle characteristics.

[0007] Therefore, an object of the present invention is to provide a binder composition for a secondary battery electrode, a conductive material paste composition for a secondary battery electrode, and a slurry composition for a secondary battery electrode, which can improve the cycle characteristics of the resulting secondary battery. Another object of the present invention is to provide an electrode for a secondary battery that can sufficiently improve the cycle characteristics of the secondary battery, and a secondary battery having excellent cycle characteristics.

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems. They have discovered that, when using a binder composition for secondary battery electrodes containing a copolymer including a linear alkylene structural unit having 4 or more carbon atoms and a nitrile group-containing monomer unit, the cycle characteristics of the resulting secondary battery can be improved by adjusting the weight-average molecular weight of the copolymer to 5,000 or more and 500,000 or less, and adjusting the chlorine content in the binder composition to more than 0 ppm and 2,000 ppm or less, based on the copolymer. Based on these findings, the present inventors have completed the present invention.

[0009]

[0010] The present invention aims to advantageously solve the above-mentioned problems, and provides a binder composition for a secondary battery electrode, comprising a copolymer including a linear alkylene structural unit having 4 or more carbon atoms and a nitrile group-containing monomer unit, wherein the copolymer has a weight-average molecular weight of 5,000 or more and 500,000 or less, and the binder composition has a chlorine content of more than 0 ppm and 2,000 ppm or less relative to the copolymer.

[0011] Thus, when a secondary battery is formed using a binder composition containing a copolymer including a linear alkylene structural unit having 4 or more carbon atoms and a nitrile group-containing monomer unit and having a weight-average molecular weight of 5,000 or more and 500,000 or less, and having a chlorine content of more than 0 ppm and 2,000 ppm or less relative to the copolymer, the cycle characteristics of the resulting secondary battery can be improved. In this specification, the term "monomer unit" of a polymer means "a repeating unit derived from the monomer contained in a polymer obtained using the monomer." The weight-average molecular weight of the polymer and the chlorine content of the binder composition can be measured according to the method described in the examples of this specification.

[0010] [2] Here, in the binder composition for secondary battery electrodes of the above [1], the copolymer preferably contains more than 0% by mass and not more than 50% by mass of hydrophilic group-containing monomer units. If the copolymer contains more than 0% by mass and not more than 50% by mass of hydrophilic group-containing monomer units, the cycle characteristics of the obtained secondary battery can be further improved. In this specification, the "proportion of each repeating unit (structural unit and monomer unit) in the copolymer" can be determined from the amount charged when synthesizing the copolymer, and can also be determined from the amount of the copolymer. １ It can also be measured using nuclear magnetic resonance (NMR) techniques such as H-NMR.

[0011] [3] The binder composition for a secondary battery electrode according to [1] or [2] above may further contain an organic solvent.

[0012] [4] The present invention also aims to advantageously solve the above-mentioned problems, and provides a conductive material paste composition for secondary battery electrodes, characterized in that it contains the binder composition for secondary battery electrodes of any one of [1] to [3] above and a conductive material. A secondary battery manufactured using a slurry composition for secondary battery electrodes prepared by adding an electrode active material and the like to such a conductive material paste composition for secondary battery electrodes has excellent cycle characteristics.

[0013] [5] Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and provides a slurry composition for a secondary battery electrode of the present invention, which is characterized by comprising an electrode active material, a conductive material, a solvent, and the binder composition for a secondary battery electrode of any one of [1] to [3] above. In this way, a secondary battery having excellent cycle characteristics can be manufactured by using a slurry composition for a secondary battery electrode that includes the binder composition for a secondary battery electrode that includes the above-mentioned copolymer.

[0014] [6] The present invention also aims to advantageously solve the above-mentioned problems, and provides a secondary battery electrode of the present invention, characterized in that it includes an electrode mixture layer formed using the slurry composition for a secondary battery electrode described in [5] above. In this way, by using the above-mentioned slurry composition for a secondary battery electrode, it is possible to satisfactorily form an electrode mixture layer and sufficiently improve the cycle characteristics of a secondary battery using the secondary battery electrode.

[0015] [7] Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and the secondary battery of the present invention is characterized by including the secondary battery electrode described in the above [6]. In this way, by using the above-mentioned secondary battery electrode, it is possible to sufficiently improve the cycle characteristics.

[0016] According to the present invention, it is possible to provide a binder composition for a secondary battery electrode, a conductive paste composition for a secondary battery electrode, and a slurry composition for a secondary battery electrode, which can improve the cycle characteristics of the resulting secondary battery. Furthermore, according to the present invention, it is possible to provide an electrode for a secondary battery that can sufficiently improve the cycle characteristics of the secondary battery, and a secondary battery having excellent cycle characteristics.

[0017] Hereinafter, embodiments of the present invention will be described in detail. Here, the binder composition for secondary battery electrodes of the present invention can be used when preparing a slurry composition for secondary battery electrodes. Furthermore, it is preferable that the binder composition for secondary battery electrodes of the present invention is mixed with a conductive material to form a conductive material paste composition for secondary battery electrodes containing the binder composition for secondary battery electrodes and the conductive material, and then the conductive material paste composition is used to prepare the slurry composition for secondary battery electrodes. Furthermore, the slurry composition for secondary battery electrodes prepared using the binder composition for secondary battery electrodes of the present invention can be used when forming electrodes for secondary batteries such as lithium-ion secondary batteries. Furthermore, the secondary battery of the present invention is characterized by using a secondary battery electrode formed using the slurry composition for secondary battery electrodes of the present invention. The binder composition for secondary battery electrodes, the conductive material paste composition for secondary battery electrodes, and the slurry composition for secondary battery electrodes of the present invention can be particularly suitably used when forming a positive electrode for a secondary battery.

[0018] (Binder Composition for Secondary Battery Electrode) The binder composition for a secondary battery electrode of the present invention is a binder composition for a secondary battery electrode containing a copolymer (hereinafter also referred to as "copolymer (A)") containing a linear alkylene structural unit having 4 or more carbon atoms and a nitrile group-containing monomer unit, wherein the copolymer has a weight average molecular weight of 5,000 or more and 500,000 or less, and the chlorine content in the binder composition is more than 0 ppm and 2,000 ppm or less with respect to the copolymer.

[0019] The copolymer (A), an essential component of the binder composition for secondary battery electrodes of the present invention, contains a linear alkylene structural unit having 4 or more carbon atoms, thereby enabling good dispersion of a conductive material when used to prepare a slurry composition for secondary battery electrodes. Furthermore, the copolymer (A) contains a nitrile group-containing monomer unit, which is presumably responsible for the excellent flexibility and peel strength of the electrode mixture layer formed using the binder composition for secondary battery electrodes, thereby improving the cycle characteristics of the secondary battery. As a result, a secondary battery formed using the binder composition for secondary battery electrodes of the present invention exhibits low internal resistance and excellent cycle characteristics. Furthermore, the copolymer (A) has a weight-average molecular weight within the above-mentioned range, and the chlorine content of the binder composition is within a specified range relative to the copolymer (A), thereby improving the cycle characteristics of the resulting secondary battery.

[0020] <Copolymer (A)> The copolymer (A) can disperse a conductive material well in a slurry composition for a secondary battery electrode prepared using the binder composition. Furthermore, in an electrode produced by forming an electrode mixture layer on a current collector using the slurry composition for a secondary battery electrode prepared using the binder composition, the copolymer (A) holds components contained in the electrode mixture layer so as not to be detached from the electrode mixture layer (i.e., functions as a binder).

[0021] Here, the copolymer (A) is required to contain, as repeating units, a linear alkylene structural unit having 4 or more carbon atoms and a nitrile group-containing monomer unit, and may optionally further contain repeating units other than the linear alkylene structural unit having 4 or more carbon atoms and the nitrile group-containing monomer unit (hereinafter, sometimes referred to as "other repeating units").

[0022] [Straight-chain alkylene structural unit having 4 or more carbon atoms] The straight-chain alkylene structural unit having 4 or more carbon atoms is represented by the general formula: -C ｎ H ２ｎ - [where n is an integer of 4 or more]. Since the copolymer (A) has a linear alkylene structural unit having 4 or more carbon atoms, when used to prepare a slurry composition for a secondary battery electrode containing a conductive material, the copolymer (A) can improve the dispersibility of the conductive material and can also suppress aggregation of the conductive material in the slurry composition, thereby increasing the dispersion stability of the slurry composition.

[0023] Here, the method for introducing linear alkylene structural units having 4 or more carbon atoms into copolymer (A) is not particularly limited, and examples thereof include the following methods (1) and (2): (1) a method of preparing a copolymer from a monomer composition containing a conjugated diene monomer and hydrogenating the copolymer to convert the conjugated diene monomer units into linear alkylene structural units having 4 or more carbon atoms; and (2) a method of preparing a copolymer from a monomer composition containing a 1-olefin monomer. Among these, method (1) is preferred because it allows for easy production of copolymer (A).

[0024] Examples of conjugated diene monomers 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. Of these, 1,3-butadiene is preferred. That is, the linear alkylene structural unit having 4 or more carbon atoms is preferably a structural unit (conjugated diene hydride unit) obtained by hydrogenating a conjugated diene monomer unit, and more preferably a structural unit (1,3-butadiene hydride unit) obtained by hydrogenating a 1,3-butadiene unit. Selective hydrogenation of the conjugated diene monomer unit can be carried out using known methods such as oil phase hydrogenation and aqueous phase hydrogenation. Examples of 1-olefin monomers include ethylene, propylene, 1-butene, and 1-hexene. These conjugated diene monomers and 1-olefin monomers can be used alone or in combination of two or more.

[0025] The content of linear alkylene structural units having 4 or more carbon atoms in copolymer (A) is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, particularly preferably 50% by mass or more, and preferably 80% by mass or less, and more preferably 70% by mass or less, when the total repeating units in copolymer (A) (the sum of structural units and monomer units) is taken as 100% by mass. By setting the content of alkylene structural units to the above-mentioned lower limit or more, it is possible to further improve the dispersibility of the conductive material in the slurry composition and sufficiently increase the dispersion stability of the slurry composition. Furthermore, by setting the content of alkylene structural units to the above-mentioned upper limit or less, it is possible to suppress a decrease in the solubility of copolymer (A) in solvents such as N-methylpyrrolidone (NMP), and it is possible to fully exhibit the effect of dispersing the conductive material in copolymer (A). As a result, it is presumed that internal resistance can be reduced and cycle characteristics can be improved.

[0026] In addition, when the linear alkylene structural unit having 4 or more carbon atoms is a structural unit (conjugated diene hydrogenated unit) obtained by hydrogenating a conjugated diene monomer unit, it is preferable that the total content of the conjugated diene monomer unit and the linear alkylene structural unit having 4 or more carbon atoms in the copolymer (A) satisfies the above range.

[0027] [Nitrile Group-Containing Monomer Unit] The nitrile group-containing monomer unit is a repeating unit derived from a nitrile group-containing monomer. Since the copolymer (A) contains the nitrile group-containing monomer unit, it can exhibit excellent flexibility and binding strength. Therefore, an electrode mixture layer formed using a slurry composition for a secondary battery electrode containing the binder composition for a secondary battery electrode of the present invention can exhibit excellent peel strength and flexibility.

[0028] Here, examples of nitrile group-containing monomers capable of forming nitrile group-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, but examples include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile; and the like. Among these, from the viewpoint of increasing the binding strength of the copolymer (A) and improving the cycle characteristics of the resulting secondary battery, acrylonitrile and methacrylonitrile are preferred as nitrile group-containing monomers, with acrylonitrile being more preferred. These can be used alone or in combination of two or more.

[0029] The content of the nitrile group-containing monomer units in the copolymer (A), when the total repeating units in the copolymer (A) is taken as 100% by mass, is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, particularly preferably 30% by mass or more, and is preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. By setting the content of the nitrile group-containing monomer units in the copolymer (A) to be equal to or greater than the above-mentioned lower limit, the binding strength of the copolymer (A) can be improved, and the cycle characteristics of a secondary battery formed using the binder composition can be further improved. Furthermore, by setting the content of the nitrile group-containing monomer units in the copolymer (A) to be equal to or less than the above-mentioned upper limit, the dispersibility of the slurry composition can be further improved.

[0030] [Other Repeating Units] The repeating units other than the alkylene structural units and nitrile group-containing monomer units described above are not particularly limited, and examples thereof include repeating units derived from known monomers copolymerizable with the above-described monomers, such as hydrophilic group-containing monomer units and (meth)acrylic acid ester monomer units. Other repeating units also include aromatic vinyl monomer units derived from aromatic vinyl monomers such as styrene, α-methylstyrene, butoxystyrene, and vinylnaphthalene. These monomers can be used alone or in combination of two or more. In the present invention, "(meth)acrylic" refers to acrylic and / or methacrylic.

[0031] Furthermore, examples of the hydrophilic group-containing monomer capable of forming the hydrophilic group-containing monomer unit include polymerizable monomers having a hydrophilic group.Specific examples of the hydrophilic group-containing monomer include a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, a monomer having a phosphoric acid group, and a monomer having a hydroxyl group.

[0032] Examples of monomers having a carboxylic acid group include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their derivatives. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and β-diaminoacrylic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid esters such as methylallyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleates. Examples of dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Furthermore, examples of monomers having a carboxylic acid group include acid anhydrides that generate a carboxyl group upon hydrolysis. Other examples include monoesters and diesters of α,β-ethylenically unsaturated polycarboxylic acids, such as monoethyl maleate, 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.

[0033] Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, styrene sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, etc. In the present invention, "(meth)allyl" means allyl and / or methallyl.

[0034] Examples of the monomer having a phosphate group include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, ethyl-(meth)acryloyloxyethyl phosphate, etc. In the present invention, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0035] Examples of the monomer 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 compounds of the general formula: CH ２ =CR １ -COO-(C ｑ H ２ｑ O) ｐ -H (wherein p is an integer of 2 to 9, q is an integer of 2 to 4, R １represents hydrogen or a methyl group) and (meth)acrylic acid esters; mono(meth)acrylic acid esters 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; alkyl ethers such as (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, and (meth)allyl-6-hydroxyhexyl ether; mono(meth)allyl ethers of ethylene glycol; polyoxyalkylene glycol mono(meth)allyl ethers such as diethylene glycol mono(meth)allyl ether and dipropylene glycol mono(meth)allyl ether; mono(meth)allyl ethers of halogen- and hydroxy-substituted (poly)alkylene glycols such as glycerin mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether and (meth)allyl-2-hydroxy-3-chloropropyl ether; mono(meth)allyl ethers of polyhydric phenols such as eugenol and isoeugenol and halogen-substituted products thereof; (meth)allyl thioethers of alkylene glycols such as (meth)allyl-2-hydroxyethyl thioether and (meth)allyl-2-hydroxypropyl thioether; and the like.

[0036] The content of the hydrophilic group-containing monomer unit in the copolymer (A) is preferably greater than 0% by mass, more preferably 0.5% by mass or greater, even more preferably 2.0% by mass or greater, particularly preferably 5.0% by mass or greater, and preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 20% by mass or less. When the copolymer (A) contains the hydrophilic group-containing monomer unit, if the content is equal to or greater than the above-mentioned lower limit, the dispersibility of the conductive material can be further improved when the binder composition is blended with the conductive material. Furthermore, if the content of the hydrophilic group-containing monomer unit is equal to or less than the above-mentioned upper limit, the internal resistance of the resulting secondary battery can be further reduced and the cycle characteristics can be further improved.

[0037] Examples of (meth)acrylic acid ester monomers that can form (meth)acrylic acid ester monomer units that the copolymer (A) can contain as other repeating units include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate. alkyl acrylate esters such as acrylate; alkyl methacrylate esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate; and the like.

[0038] The content of the (meth)acrylic acid ester monomer in the copolymer (A) is not particularly limited, but is preferably 5.0 mass% or less, and more preferably 1.0 mass% or less. Of course, the copolymer (A) may not contain any (meth)acrylic acid ester monomer.

[0039] [Weight-Average Molecular Weight] From the viewpoint of improving the cycle characteristics of the resulting secondary battery, the weight-average molecular weight of the copolymer (A) must be 5,000 or more and 500,000 or less, preferably 10,000 or more, more preferably 20,000 or more, and preferably 300,000 or less, more preferably 250,000 or less, more preferably 150,000 or less, even more preferably 130,000 or less, particularly preferably 100,000 or less, and even particularly preferably 50,000 or less. If the weight-average molecular weight of the copolymer (A) is equal to or greater than the above-mentioned lower limit, the internal resistance of the resulting secondary battery can be further reduced. Furthermore, if the weight-average molecular weight of the copolymer (A) is equal to or less than the above-mentioned upper limit, it is presumed that the dispersibility of the conductive material can be further improved, thereby improving the cycle characteristics of the resulting secondary battery. The weight-average molecular weight of the copolymer (A) can be controlled depending on the polymerization conditions, for example, by adjusting the amount of chain transfer agent.

[0040] [Iodine Value] The iodine value of the copolymer (A) is preferably 3 mg / 100 mg or more, more preferably 8 mg / 100 mg or more, preferably 60 mg / 100 mg or less, more preferably 30 mg / 100 mg or less, and even more preferably 10 mg / 100 mg or less. If the iodine value of the copolymer (A) is within the above range, the copolymer (A) is stable in chemical structure against high potentials and can maintain its electrode structure even during long-term cycles, thereby providing a secondary battery with excellent cycle characteristics. The iodine value can be determined in accordance with JIS K6235;2006.

[0041] [Method for Preparing Copolymer (A)] The method for preparing the above-mentioned copolymer (A) is not particularly limited. For example, the copolymer (A) can be prepared by polymerizing a monomer composition containing the above-mentioned monomers in an aqueous solvent, optionally in the presence of a chain transfer agent, to obtain a copolymer, and then subjecting the obtained aqueous dispersion of the copolymer to a hydrogenation (hydrogenation) reaction.

[0042] Here, the content ratio of each monomer in the monomer composition used to prepare the copolymer (A) can be determined in accordance with the content ratio of each repeating unit in the copolymer (A). The polymerization method is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization can be used. Furthermore, the polymerization reaction can be any reaction such as ionic polymerization, radical polymerization, or living radical polymerization. Furthermore, the method for hydrogenating the polymer is not particularly limited, and a general method using a chlorine-containing catalyst such as palladium chloride (see, for example, JP 2013-8485 A) can be used.

[0043] Then, by adding a silver salt such as silver nitrate to the aqueous dispersion of copolymer (A) obtained through various reaction steps and filtering the mixture, it is possible to remove at least a portion of the chlorine contained in the residues of the additives and catalysts used in the various reaction steps from copolymer (A). In this case, the amount of chlorine to be removed can be adjusted depending on the amount of silver salt added, and the amount of chlorine contained in or associated with copolymer (A) can be controlled, thereby controlling the chlorine content relative to copolymer (A) in the binder composition.

[0044] If necessary, a silver salt such as silver nitrate, silver acetate, or silver perchlorate may be added to the aqueous dispersion of copolymer (A), and then an alkaline aqueous solution such as potassium hydroxide or sodium hydroxide may be added to adjust the pH of the aqueous dispersion of copolymer (A) to alkaline (for example, a pH range of 8.0 or more and 10.0 or less).

[0045] <Solvent> The binder composition for a secondary battery electrode may also contain an organic solvent. Examples of the organic solvent include 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-based polar organic solvents such as N,N-dimethylformamide and N-methylpyrrolidone (NMP); and aromatic hydrocarbons such as toluene, xylene, chlorobenzene, orthodichlorobenzene, and paradichlorobenzene. These solvents may be used alone or in combination. Among these, NMP is preferred as the solvent.

[0046] <Other Components> In addition to the above components, the binder composition for a secondary battery electrode of the present invention may contain components such as a reinforcing material, a leveling agent, a viscosity modifier, and an electrolyte additive. These components are not particularly limited as long as they do not affect the battery reaction, and known components, such as those described in WO 2012 / 115096, can be used. Furthermore, these components may be used alone or in combination of two or more types in any ratio.

[0047] <Chlorine Content in Binder Composition> The chlorine content in the binder composition, based on the mass of the copolymer, must be more than 0 ppm and not more than 2,000 ppm. It may be 1 ppm or more, or may be 5 ppm or more. It is preferably 1,400 ppm or less, more preferably less than 1,000 ppm, even more preferably 750 ppm or less, even more preferably 500 ppm or less, even more preferably 250 ppm or less, even more preferably 100 ppm or less, particularly preferably 50 ppm or less, and even particularly preferably 20 ppm or less. If the chlorine content in the binder composition is not more than the above upper limit, the cycle characteristics of the resulting secondary battery can be improved. Here, the chlorine that can be contained in the binder composition and that is subject to the numerical range in this section is not particularly limited, and can be, for example, chlorine derived from the production process of the copolymer (A). It can also be, for example, chlorine that has been mixed into the binder composition from the containers and piping used in preparing the binder composition. Furthermore, the chlorine may be contained by adding a chlorine-containing compound during the preparation of the binder composition. For example, the chlorine derived from the production process of the copolymer (A) may be a chlorine salt (e.g., CaCl ) that can be used as an additive such as a coagulant during the synthesis of the copolymer (A). ２ , MgCl ２, and NaCl, etc.), and chlorine derived from chlorine-containing metal catalysts that can be used in other processes such as hydrogenation and low-molecular-weight conversion. Generally, the binder composition can be in a solution state in which the polymer is dissolved or dispersed in a polymerization solvent, or in a solid state in which the binder composition is a dried polymer. For either binder composition state, the amount of chlorine must be measured in a state in which the chlorine present is uniformly dispersed throughout the sample to be measured. When the sample is in a solution state, a uniform chlorine distribution can be achieved by stirring, etc. On the other hand, when the sample is in a solid state, in order to prevent variations in measurement values ​​due to uneven distribution of chlorine, the sample can be dissolved in a solvent (e.g., NMP) to obtain a sample solution, which can then be stirred to obtain a uniform chlorine distribution to prepare a measurement sample. For measurement samples obtained by either method, treatments such as adding a solvent to adjust the viscosity may be performed as necessary when measuring the amount of chlorine. Furthermore, for example, when a binder composition in a solution state contains a chlorine-containing solvent such as chlorobenzene, pretreatment may be performed to remove chlorine derived from the solvent. The method of such pretreatment is not particularly limited, but it is necessary that the method does not remove chlorine attached to or accompanying the target copolymer. Such pretreatment includes a treatment of heating at a temperature that vaporizes the chlorine-containing solvent but does not vaporize the copolymer.

[0048] (Conductive material paste composition for secondary battery electrode) The conductive material paste composition of the present invention contains the above-mentioned binder composition for secondary battery electrode and a conductive material. By using such a conductive material paste composition, the cycle characteristics of the obtained secondary battery can be improved. As the conductive material that can be contained in the conductive material paste, those described below in the section (Slurry composition for secondary battery electrode) can be used. In addition, optionally, the conductive material paste composition can contain the solvent and other components listed above in (Binder composition for secondary battery electrode).

[0049] The conductive material paste composition may contain, in terms of solid content, preferably 10 parts by mass or more, more preferably 15 parts by mass or more, preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 30 parts by mass or less of the binder composition per 100 parts by mass of the conductive material. When the blending amount of the binder composition in the conductive material paste is within the above-mentioned range, the dispersion stability of the conductive material paste can be improved.

[0050] The conductive material paste can be produced by mixing the above-described binder composition for a secondary battery electrode, a conductive material, and a solvent and other components as needed. When the binder composition contains a solvent, the solvent can be used as a dispersion medium. The mixing of the various components is not particularly limited, and can be carried out using a known mixing device. Examples of such mixing devices include a disperser, a homomixer, a planetary mixer, a kneader, a ball mill, a bead mill, and a homogenizer. The solid content concentration of the conductive material paste is not particularly limited, but is, for example, 1% by mass or more, preferably 2% by mass or more, more preferably 3% by mass or more, and 30% by mass or less, preferably 25% by mass or less, and more preferably 20% by mass or less.

[0051] (Slurry Composition for Secondary Battery Electrode) The slurry composition for a secondary battery electrode of the present invention contains an electrode active material, a conductive material, a solvent, and the above-mentioned binder composition, and optionally further contains other polymers and other components. That is, the slurry composition for a secondary battery electrode of the present invention contains an electrode active material, a conductive material, the above-mentioned copolymer (A), and a solvent, and optionally further contains other polymers and other components. And, since the slurry composition for a secondary battery electrode of the present invention contains the above-mentioned binder composition, a secondary battery with excellent cycle characteristics can be formed. Note that, below, as an example, a case will be described in which the slurry composition for a secondary battery electrode is a slurry composition for a lithium ion secondary battery positive electrode, but the present invention is not limited to the following example.

[0052] <Electrode Active Material> An electrode active material is a material that transfers electrons at an electrode of a secondary battery. As a positive electrode active material for a lithium ion secondary battery, a material that can absorb and release lithium is usually used.

[0053] Specifically, the positive electrode active material for a lithium ion secondary battery is not particularly limited, and may be a lithium-containing cobalt oxide (LiCoO ２ ), lithium manganese oxide (LiMn ２ O ４ ), lithium-containing nickel oxide (LiNiO ２ ), Co—Ni—Mn lithium-containing composite oxide (Li(Co Mn Ni)O ２ ), lithium-containing composite oxide of Ni-Mn-Al, lithium-containing composite oxide of Ni-Co-Al, olivine-type lithium iron phosphate (LiFePO ４ ), olivine-type lithium manganese phosphate (LiMnPO ４ ), Li ２ MnO ３ -LiNiO ２ system solid solution, Li １＋ｘ Mn ２－ｘ O ４ (0<X<2) Lithium-excess spinel compound represented by Li[Ni ０．１７ Li ０．２ Co ０．０７ Mn ０．５６ ]O ２ , LiNi ０．５ Mn １．５ O ４ The amount of the positive electrode active material and the particle size thereof are not particularly limited, and may be the same as those of conventionally used positive electrode active materials.

[0054] <Conductive Material> The conductive material is used to ensure electrical contact between electrode active materials. Examples of the conductive material include carbon black (e.g., acetylene black, Ketjen Black (registered trademark), furnace black, etc.), single-walled or multi-walled carbon nanotubes (multi-walled carbon nanotubes include cup-stacked types), carbon nanohorns, vapor-grown carbon fibers, milled carbon fibers obtained by calcining and then crushing polymer fibers, single-walled or multi-walled graphene, and conductive carbon materials such as carbon nonwoven fabric sheets obtained by calcining nonwoven fabrics made of polymer fibers; and fibers or foils of various metals. These materials can be used alone or in combination of two or more.

[0055] Among the above, conductive carbon materials are preferred because of their excellent chemical stability. Furthermore, carbon nanotubes are preferred as the conductive material from the viewpoint of reducing the resistance of the electrode mixture layer formed using the slurry composition to obtain a secondary battery with excellent output characteristics.

[0056] Here, the BET specific surface area of ​​the conductive material is preferably 100 m ２ / g or more, more preferably 150m ２ / g or more, and usually 2500m ２ / g or less. When the BET specific surface area of ​​the conductive material is equal to or greater than the above lower limit, a good conductive path is formed in the electrode mixture layer, and the output characteristics of the secondary battery can be further improved. Furthermore, when the BET specific surface area of ​​the conductive material is equal to or less than the above upper limit, aggregation of the conductive material can be suppressed, and the dispersibility of the conductive material can be ensured. "In the present invention, the term 'BET specific surface area' refers to the nitrogen adsorption specific surface area measured using the BET method."

[0057] Generally, conductive materials with a large BET specific surface area and fibrous conductive materials such as carbon nanotubes tend to aggregate easily and are difficult to disperse. However, the slurry composition for a secondary battery electrode of the present invention uses a binder composition containing the copolymer (A) described above, and therefore can disperse even conductive materials with a large BET specific surface area well and stably.

[0058] The content of the conductive material in the slurry composition for secondary battery electrodes is preferably 0.01 parts by mass or more and 20 parts by mass or less, based on 100 parts by mass of the positive electrode active material. If the amount of conductive material is too small, it may be difficult to ensure sufficient electrical contact between the electrode active materials. On the other hand, if the amount of conductive material is too large, the viscosity stability of the slurry composition may decrease, and the density of the electrode mixture layer may decrease, making it difficult to achieve a sufficiently high capacity secondary battery.

[0059] <Binder Composition> As the binder composition, a binder composition for a secondary battery electrode containing the above-mentioned copolymer (A) is used. Note that, from the viewpoint of dispersion stability, the content of the copolymer (A) in the slurry composition may be preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of the conductive material.

[0060] <Other Polymers> The other polymers usually function as a binder together with the copolymer (A). Examples of the other polymers that can function as a binder together with the copolymer (A) include, but are not limited to, fluorine-containing polymers such as polyvinylidene fluoride, polyacrylonitrile, and polymethyl methacrylate.

[0061] Here, the content of the other polymer in the slurry composition for a secondary battery electrode may be, for example, 5 parts by mass or more and 50 parts by mass or less, where the total content of the copolymer (A) and the other polymer is 100 parts by mass. When the content of the polymer (A) is equal to or more than the lower limit, the conductive material can be dispersed well. Furthermore, when the content of the polymer (A) is equal to or less than the upper limit, the adhesiveness of the resulting electrode can be improved.

[0062] The proportion of the other polymers in the binder (total of the copolymer (A) and the other polymers) is preferably 30% by mass or more, more preferably 40% by mass or more, and is preferably 95% by mass or less, and more preferably 90% by mass or less. If the proportion of the other polymers in the binder is high, the effect of the copolymer (A) in dispersing the conductive material may not be sufficiently obtained, and there is a risk that a slurry composition in which the conductive material is well dispersed may not be obtained.

[0063] <Other Components> Other components that can be blended into the slurry composition are not particularly limited and include the same components as those that can be blended into the binder composition of the present invention. In addition, the other components may be used alone or in combination of two or more in any ratio.

[0064] <Preparation of Slurry Composition> The above-mentioned slurry composition can be prepared by dissolving or dispersing each of the above components in a solvent such as an organic solvent. Specifically, the slurry composition can be prepared by mixing each of the above components with the solvent using a mixer such as a ball mill, sand mill, bead mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, or Filmix. Note that the solvent used to prepare the slurry composition may be the solvent contained in the binder composition.

[0065] Here, the order in which the components are mixed in the solvent is not particularly limited and can be any order. Specifically, when preparing the slurry composition, the components can be mixed in any of the following orders (1) to (5): (1) Mix all the components together; (2) Mix a binder composition for a secondary battery electrode containing the copolymer (A) with another polymer to obtain a binder composition, and then add an electrode active material and a conductive material to the obtained binder composition simultaneously or separately and mix them together; (3) Mix a binder composition for a secondary battery electrode containing the copolymer (A) with a conductive material to obtain a conductive material paste composition for a secondary battery electrode, and then add another polymer and an electrode active material to the conductive material paste composition simultaneously or separately and mix them together; (4) Mix a conductive material and an electrode active material, and then add a binder composition for a secondary battery electrode containing the copolymer (A) and another polymer to the obtained mixture simultaneously or separately and mix them together. (5) After mixing the conductive material, the electrode active material, and other polymers, the binder composition for secondary battery electrodes containing the copolymer (A) is added to the resulting mixture and mixed.

[0066] Among the above, it is preferable to mix the above components in the order of (3) above. If the binder composition for a secondary battery electrode and the conductive material are mixed in advance to obtain a conductive material paste composition for a secondary battery electrode containing the conductive material and the above-mentioned binder composition (i.e., containing the conductive material and the above-mentioned copolymer (A)), the copolymer (A) can be favorably adsorbed onto the surface of the conductive material, and the conductive material can be further favorably dispersed. Here, the mixing ratio of the components when preparing the conductive material paste composition for a secondary battery electrode or the conductive material dispersion may be set to a ratio that allows the desired slurry composition to be obtained.

[0067] (Secondary Battery Electrode) The secondary battery electrode of the present invention comprises a current collector and an electrode mixture layer formed on the current collector, the electrode mixture layer being formed using the above-mentioned slurry composition for a secondary battery electrode. That is, the electrode mixture layer contains at least an electrode active material, a conductive material, and a copolymer (A). The components contained in the electrode mixture layer are the same as those contained in the above-mentioned slurry composition for a secondary battery electrode, and the preferred abundance ratios of the components are the same as the preferred abundance ratios of the components in the slurry composition. Furthermore, since the secondary battery electrode of the present invention comprises an electrode mixture layer formed using the slurry composition for a secondary battery electrode of the present invention, a secondary battery with excellent cycle characteristics can be obtained.

[0068] <Method for manufacturing electrode> The electrode for a secondary battery of the present invention is manufactured, for example, through a step of applying the above-described slurry composition onto a current collector (application step) and a step of drying the slurry composition applied onto the current collector to form an electrode mixture layer on the current collector (drying step).

[0069] [Coating Step] The method for applying the slurry composition to the current collector is not particularly limited, and known methods can be used. Specifically, examples of the coating 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.

[0070] Here, the current collector to which the slurry composition is applied is made of a material that is electrically conductive and electrochemically durable. Specifically, the current collector may be made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. Note that one of the above materials may be used alone, or two or more may be used in combination in any ratio.

[0071] [Drying Step] The method for drying the slurry composition on the current collector is not particularly limited and any known method can be used, for example, drying with warm air, hot air, or low-humidity air, vacuum drying, or 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 secondary battery electrode including the current collector and the electrode mixture layer can be obtained.

[0072] After the drying step, the electrode mixture layer may be subjected to pressure treatment using a mold press or a roll press. Pressure treatment can improve the adhesion between the electrode mixture layer and the current collector. Furthermore, when the electrode mixture layer contains a curable polymer, it is preferable to cure the polymer after the electrode mixture layer is formed. Since the conductive material and the like are well dispersed in the slurry composition for secondary battery electrodes of the present invention, the electrode mixture layer formed using the slurry composition has a sufficiently high density, and the internal structure is less likely to be destroyed even when pressure treatment is performed. Therefore, by using the slurry composition for secondary battery electrodes of the present invention, the battery characteristics of the secondary battery can be sufficiently improved even when pressure treatment or the like is performed during electrode production.

[0073] (Secondary Battery) The secondary battery of the present invention comprises a positive electrode, a negative electrode, an electrolyte, and a separator, and uses the secondary battery electrode of the present invention as at least one of the positive electrode and the negative electrode. Since the secondary battery of the present invention comprises the secondary battery electrode of the present invention, it has excellent battery characteristics such as output characteristics. It is preferable that the secondary battery of the present invention uses the secondary battery electrode of the present invention as the positive electrode. In the following, a case where the secondary battery is a lithium-ion secondary battery will be described as an example, but the present invention is not limited to the following example.

[0074] <Electrode> Here, the electrode other than the above-described secondary battery electrode that can be used in the secondary battery of the present invention is not particularly limited, and a known electrode used in the manufacture of secondary batteries can be used. Specifically, as the electrode other than the above-described secondary battery electrode, an electrode obtained by forming an electrode mixture layer on a current collector using a known manufacturing method can be used.

[0075] <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 of a lithium ion secondary battery, 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.

[0076] 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 ethyl methyl carbonate (EMC) are preferably used. esters such as γ-butyrolactone and methyl formate are also suitable. Ethers such as 1,2-dimethoxyethane and tetrahydrofuran are also suitable. Sulfur-containing compounds such as sulfolane and dimethyl sulfoxide are also suitable. Mixtures of these solvents may also be used. Among these, carbonates are preferred because they have a high dielectric constant and a wide stable potential range. A mixture of ethylene carbonate and diethyl carbonate is even more preferred.

[0077] <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 secondary battery and increasing the capacity per volume.

[0078] <Method for Manufacturing Secondary Battery> The secondary battery of the present invention can be manufactured, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the resulting assembly as needed 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, a fuse, an overcurrent protection element such as a PTC element, an expanded metal, a lead plate, or the like may be provided as needed. The shape of the secondary battery may be, for example, any of a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, and the like.

[0079] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. Furthermore, in a polymer produced by polymerizing multiple types of monomers, the proportion of a monomer unit formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of that certain monomer to all monomers used in the polymerization of the polymer, unless otherwise specified. In the examples and comparative examples, various measurements and evaluations were carried out as follows.

[0080] <Weight-average molecular weight of copolymer (A)> The weight-average molecular weight (Mw) of copolymer (A) was measured by gel permeation chromatography (GPC) using a 10 mM LiBr-DMF solution under the following measurement conditions: Separation column: Shodex KD-806M (manufactured by Showa Denko K.K.) Detector: Differential refractometer detector RID-10A (manufactured by Shimadzu Corporation) Eluent flow rate: 0.3 mL / min Column temperature: 40°C Standard polymer: TSK standard polystyrene (manufactured by Tosoh Corporation)

[0081] <Iodine Value of Copolymer (A)> 100 g of the aqueous dispersion of copolymer (A) prepared in all Examples and Comparative Examples 1 to 4 was coagulated with 1 L of methanol and then vacuum-dried for 12 hours at a temperature of 60° C. The iodine value of the obtained dried polymer was measured in accordance with JIS K6235 (2006).

[0082] <Chlorine Content of Binder Composition> The binder compositions prepared as homogeneous solutions in the Examples and Comparative Examples were subjected to combustion-coulometric titration using a chlorine analyzer (TOX-2100H, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) to quantify the amount of chlorine contained, thereby obtaining the amount of chlorine (ppm by mass) based on the mass of the copolymer contained in the binder composition.

[0083] <Dispersibility of Conductive Material in Conductive Material Paste Composition> The conductive material paste compositions prepared in the examples and comparative examples were measured using a rheometer ("MCR302" manufactured by Anton Paar) at a temperature of 25°C and a shear rate of 2.5 s －１The viscosity was measured under the above conditions. Using this viscosity, the dispersibility of the conductive material dispersion was evaluated according to the following criteria. At the same solid content concentration (or a solid content concentration of a very similar value), the lower the viscosity of the conductive material paste composition, the better the dispersion of fibrous conductive materials such as CNTs. Furthermore, the better the dispersion of CNTs etc. in the conductive material paste composition, the better the dispersibility of CNTs etc. in the resulting slurry composition. A+: Viscosity less than 700 mPa·s A: Viscosity 700 mPa·s or more and less than 1000 mPa·s B+: Viscosity 1000 mPa·s or more and less than 2000 mPa·s B: Viscosity 2000 mPa·s or more and less than 3000 mPa·s C: Viscosity 3000 mPa·s or more and less than 10000 mPa·s D: Viscosity 10000 mPa·s or more

[0084] <Cycle Characteristics> After injecting the electrolyte, the lithium-ion secondary batteries prepared in the Examples and Comparative Examples were left at 25°C for 3 hours. Next, they were charged to a cell voltage of 3.65 V at 25°C using a constant current of 0.2 C, followed by aging at 60°C for 12 hours. They were then discharged to a cell voltage of 3.00 V using a constant current of 0.2 C at 25°C. They were then subjected to CC-CV charging (upper cell voltage 4.20 V) using a constant current of 0.2 C, followed by CC discharge to 3.00 V using a constant current of 0.2 C. This 0.2 C charge-discharge cycle was repeated three times. Subsequently, 200 cycles of charge-discharge were performed at a temperature of 45°C, with a cell voltage of 4.20-3.00 V, a charge rate of 1.0 C, and a discharge rate of 2.0 C. The discharge capacity at the first cycle was defined as X1, and the discharge capacity at the 200th cycle as X2. Using the discharge capacities X1 and X2, the capacity retention rate shown by ΔC = (X2 / X1) × 100 (%) was calculated and evaluated according to the following criteria. A larger value of this capacity retention rate ΔC indicates that the lithium ion secondary battery has better cycle characteristics. A+: Capacity retention rate is 92% or more A: Capacity retention rate is 89% or more and less than 92% B+: Capacity retention rate is 86% or more and less than 89% B: Capacity retention rate is 83% or more and less than 86% C: Capacity retention rate is 80% or more and less than 83% D: Capacity retention rate is less than 80%

[0085] <Internal Resistance> The lithium-ion secondary batteries fabricated in the Examples and Comparative Examples were allowed to stand at 25°C for 5 hours after electrolyte injection. Next, the batteries were charged to a cell voltage of 4.2V at a constant current of 0.2C and discharged to a cell voltage of 3.0V, a cycle of three cycles, and the initial capacity was measured. After charging to a depth of charge (SOC) of 50%, the batteries were charged for 20 seconds and discharged for 20 seconds at 0.5C, 1.0C, 1.5C, and 2.0C, centered around 50% SOC. The battery voltage after 20 seconds in each case (on the charge side and the discharge side) was plotted against the current value, and the slope was calculated as the IV resistance (Ω) (IV resistance during charging and IV resistance during discharging). The obtained IV resistance values ​​(Ω) were evaluated according to the following criteria. A smaller IV resistance value indicates a lower internal resistance. A+: IV resistance value is less than 2.15 Ω A: IV resistance value is 2.15 Ω or more and less than 2.2 Ω B+: IV resistance value is 2.2 Ω or more and less than 2.3 Ω B: IV resistance value is 2.3 Ω or more and less than 2.4 Ω C: IV resistance value is 2.4 Ω or more and less than 2.5 Ω D: IV resistance value is 2.5 Ω or more

[0086] Hereinafter, with Example 9 as the standard, other Examples and Comparative Examples will be described in order.

[0087] Example 9 Preparation of Copolymer (A) A reactor was charged with 200 parts of ion-exchanged water, 25 parts of a 10% aqueous solution of sodium dodecylbenzenesulfonate, 30 parts of acrylonitrile as a nitrile group-containing monomer unit, 10 parts of methacrylic acid as a hydrophilic group-containing monomer unit, and 2.50 parts of t-dodecyl mercaptan as a chain transfer agent, in that order. The internal gas was then purged with nitrogen three times, and 60 parts of 1,3-butadiene as a conjugated diene monomer was then charged. The reactor was then maintained at 10°C, and 0.03 parts of cumene hydroperoxide as a polymerization initiator, a reducing agent, and an appropriate amount of a chelating agent were charged. The polymerization reaction was continued with stirring, and when the polymerization conversion rate reached 80%, the polymerization reaction was terminated by adding 0.1 parts of a 10% aqueous solution of hydroquinone as a polymerization terminator. The residual monomer was then removed at a water temperature of 80°C, yielding an aqueous dispersion of a precursor of copolymer (A). The aqueous dispersion and a palladium catalyst (a solution obtained by mixing an equal weight of ion-exchanged water with a 1% by weight aqueous solution of palladium chloride) were added to an autoclave so that the palladium content relative to the solid content mass of the resulting aqueous dispersion of the precursor was 3,000 ppm. A hydrogenation reaction was carried out for 3 hours at a hydrogen pressure of 3 MPa and a temperature of 55°C, obtaining an aqueous dispersion of the target copolymer (A). The contents were then returned to room temperature, the system was immersed in a nitrogen atmosphere, and the mixture was concentrated using an evaporator to a solid content of 40% to obtain an aqueous dispersion of hydrogenated nitrile rubber as an aqueous dispersion of copolymer (A). Next, 0.95% by weight of silver nitrate was added to this aqueous dispersion based on the solid content of the aqueous dispersion, and the resulting precipitate was filtered and removed using a 200-mesh filter. Subsequently, the pH of the aqueous dispersion from which the precipitate had been removed was adjusted to 9.5 using a 2.5% aqueous KOH solution. To 100 parts of this aqueous dispersion, 200 parts of N-methylpyrrolidone (hereinafter also referred to as "NMP") was added, and all water and residual monomers were evaporated under reduced pressure. The N-methylpyrrolidone was then evaporated to obtain an 8 mass % NMP solution of copolymer (A) as a binder composition for secondary battery electrodes. The resulting binder composition was subjected to measurement of the chlorine content. Furthermore, the weight average molecular weight and iodine value of the resulting copolymer (A) were measured as described above.

[0088] <Preparation of conductive paste composition for secondary battery positive electrode> Carbon nanotubes (specific surface area: 280 m) were used as a conductive material. 2 4.0 parts of the hydroxybenzoate (1.0 part of the binder composition (equivalent to the solid content)) and 95.0 parts of NMP were stirred using a disper (3000 rpm, 10 minutes), and then mixed for 1 hour at a peripheral speed of 8 m / s using a bead mill using zirconia beads with a diameter of 1 mm to produce a conductive material paste composition for secondary battery positive electrodes (hereinafter also referred to as "conductive material paste") with a solid content concentration of 5.0 mass %. The conductive material dispersibility of the obtained conductive material paste was evaluated as described above.

[0089] <Preparation of slurry composition for secondary battery positive electrode and production of positive electrode> A ternary active material (LiNi) having a layered structure was used as the positive electrode active material. 0.6 Co 0.2 Mn 0.2 A positive electrode slurry was prepared by adding 98.0 parts of PO2 (average particle size: 10 μm), 1.0 part of polyvinylidene fluoride as a binder, 1.0 part of the conductive material paste (solid content equivalent), and NMP, and mixing with a planetary mixer (60 rpm, 30 minutes). The amount of NMP added was adjusted so that the viscosity of the resulting positive electrode slurry composition (measured with a single cylindrical 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.

[0090] <Preparation of Positive Electrode> An aluminum foil having a thickness of 20 μm was prepared as a current collector. The slurry composition for a positive electrode obtained as described above was coated on one side of the aluminum foil using a comma coater so that the coating weight after drying was 20 mg / cm. 2 The coating was dried at 90°C for 20 minutes and at 120°C for 20 minutes, and then heat-treated at 60°C for 10 hours to obtain a positive electrode blank. This positive electrode blank was rolled using a roll press to a density of 3.2 g / cm. 3 A sheet-like positive electrode was fabricated from the positive electrode mixture layer and aluminum foil. The sheet-like positive electrode was then cut into a piece having a width of 48.0 mm and a length of 47 cm to prepare a positive electrode for a lithium ion secondary battery.

[0091] <Preparation of Negative Electrode> 33 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3.5 parts of itaconic acid as a carboxylic acid group-containing monomer, 63.5 parts of styrene as an aromatic vinyl monomer, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer, and after thorough stirring, the mixture was heated to 50 ° C to initiate polymerization. When the polymerization conversion rate reached 96%, the mixture was cooled to terminate the polymerization reaction, yielding a mixture containing a particulate binder (styrene-butadiene copolymer). A 5% aqueous sodium hydroxide solution was added to the mixture to adjust the pH to 8, and unreacted monomer was removed by heated vacuum distillation. The mixture was then cooled to 30 ° C or below to obtain an aqueous dispersion containing a binder for the negative electrode. 48.75 parts of artificial graphite and 48.75 parts of natural graphite as negative electrode active materials, and 1 part of carboxymethyl cellulose as a thickener (solid content equivalent) were added to a planetary mixer. The mixture was then diluted with ion-exchanged water to a solid content of 60%, and then kneaded for 60 minutes at a rotation speed of 45 rpm. Then, 1.5 parts of the aqueous dispersion containing the negative electrode binder obtained as described above (solid content equivalent) was added, and the mixture was kneaded for 40 minutes at a rotation speed of 40 rpm. Ion-exchanged water was then added to the mixture to a viscosity of 5000±500 mPa·s (measured with a Brookfield viscometer at 25°C and 60 rpm), thereby preparing a negative electrode slurry composition. The above negative electrode slurry composition was applied to the surface of a 15 μm-thick copper foil current collector using a comma coater, with a coating amount of 12.0±0.5 mg / cm2. Thereafter, the copper foil coated with the negative electrode slurry composition was transported at a speed of 400 mm / min through an oven at a temperature of 80°C for 2 minutes and then through an oven at a temperature of 110°C for 2 minutes to dry the slurry composition on the copper foil, thereby obtaining a negative electrode blank having a negative electrode composite layer formed on a current collector. This negative electrode blank was rolled using a roll press to obtain a negative electrode blank having a density of 1.6 g / cm 3 A sheet-shaped negative electrode was fabricated from the negative electrode mixture layer and aluminum foil. The sheet-shaped negative electrode was then cut into a piece having a width of 50.0 mm and a length of 52 cm to prepare a negative electrode for a lithium ion secondary battery.

[0092] <Preparation of Lithium-ion Secondary Battery> The positive electrode for lithium-ion secondary battery and the negative electrode for lithium-ion secondary battery were arranged so that the electrode composite layers faced each other, and a 15 μm thick separator (a microporous polyethylene film) was interposed between them. The resulting wound body was wound around a core having a diameter of 20 mm to obtain a wound body. The obtained wound body was then compressed in one direction at a speed of 10 mm / sec until the thickness reached 4.5 mm. The wound body after compression had an elliptical shape in a plan view, and the ratio of its major axis to its minor axis (major axis / minor axis) was 7.7. In addition, LiPF 5 with a concentration of 1.0 M was used as the electrolyte. ６ A solution (solvent: a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio), additive: containing 2 volume % vinylene carbonate (solvent ratio)) was prepared. The compressed wound body was then housed in an aluminum laminate case together with 3.2 g of electrolyte. A nickel lead wire was connected to a predetermined location on the negative electrode for the secondary battery, and an aluminum lead wire was connected to a predetermined location on the positive electrode for the secondary battery. The opening of the case was then thermally sealed to obtain a lithium ion secondary battery as an electrochemical element of the present invention. This lithium ion secondary battery was a pouch-shaped battery measuring 35 mm wide, 60 mm high, and 5 mm thick, and had a nominal capacity of 700 mAh. The cycle characteristics and internal resistance of the obtained secondary battery were measured as described above. The results are shown in Table 1.

[0093] (Example 1) In preparing <Preparation of Copolymer (A)>, the amounts of various monomers charged were changed so that the composition of the resulting copolymer (A) would be as shown in Table 1. In addition, the amount of t-dodecyl mercaptan used as a molecular weight modifier was changed to 0.5 parts. Furthermore, after silver nitrate was added to the aqueous dispersion and the precipitate was filtered through a 200-mesh filter, 200 parts of NMP was added without adjusting the pH using a 2.5% aqueous KOH solution. Other than these, the same operations, measurements, and evaluations as in Example 9 were carried out. The results are shown in Table 1.

[0094] (Examples 2 and 3) In the preparation of <Preparation of Copolymer (A)>, the amounts of various monomers charged were changed so that the composition of the resulting copolymer (A) would be as shown in Table 1. The amount of t-dodecyl mercaptan used as a molecular weight modifier was changed to 0.5 parts. Furthermore, the amount of silver nitrate added to the aqueous dispersion was changed to 0.60 mass% (Example 2) or 0.24 mass% (Example 3) based on the solid content of the aqueous dispersion. After filtering the precipitate through a 200-mesh filter, 200 parts of NMP was added without adjusting the pH using a 2.5% aqueous KOH solution. Other than these, the same operations, measurements, and evaluations as in Example 9 were performed. The results are shown in Table 1.

[0095] (Examples 4 and 5) In preparing <Preparation of Copolymer (A)>, the amounts of various monomers charged were changed so that the composition of the resulting copolymer (A) would be as shown in Table 1. In addition, the amount of t-dodecyl mercaptan used as a molecular weight modifier was changed to 0.07 parts (Example 4) and 0.65 parts (Example 5). Furthermore, silver nitrate was added to the aqueous dispersion, and the precipitate was filtered through a 200-mesh filter. 200 parts of NMP was then added without adjusting the pH using a 2.5% aqueous KOH solution. Except for these, the same operations, measurements, and evaluations as in Example 9 were carried out. The results are shown in Table 1.

[0096] (Example 6) In the preparation of <Preparation of Copolymer (A)>, the amounts of various monomers charged were changed so that the composition of the resulting copolymer (A) would be as shown in Table 1. Silver nitrate was added to the aqueous dispersion, and the precipitate was filtered through a 200-mesh filter. 200 parts of NMP was then added without adjusting the pH with a 2.5% aqueous KOH solution. Except for this, the same operations, measurements, and evaluations as in Example 9 were carried out. The results are shown in Table 1.

[0097] (Examples 7 and 8) In preparing <Preparation of Copolymer (A)>, the amounts of various monomers charged were changed so that the composition of the resulting copolymer (A) would be as shown in Table 1. The amount of t-dodecyl mercaptan used as a molecular weight modifier was changed to 0.5 parts. Furthermore, the amount of silver nitrate added to the aqueous dispersion was changed to 0.60 mass% (Example 7) or 0.24 mass% (Example 8) based on the solid content of the aqueous dispersion. After filtering the precipitate through a 200-mesh filter, 200 parts of NMP was added without adjusting the pH using a 2.5% KOH aqueous solution. Other than these, the same operations, measurements, and evaluations as in Example 9 were performed. The results are shown in Table 1.

[0098] (Examples 10 and 11) <Preparation of Copolymer (A)> In the preparation, the amounts of various monomers charged were changed so that the composition of the resulting copolymer (A) would be as shown in Table 1. Except for this, the same operations, measurements, and evaluations as in Example 9 were carried out. The results are shown in Table 1.

[0099] (Example 12) In preparing <Preparation of Copolymer (A)>, the amount of silver nitrate added to the aqueous dispersion was changed to 0.60 mass% based on the solid content of the aqueous dispersion. Except for this, the same operations, measurements, and evaluations as in Example 9 were carried out. The results are shown in Table 1.

[0100] (Example 13) In preparing <Preparation of Copolymer (A)>, the amount of silver nitrate added to the aqueous dispersion was changed to 0.24 mass% based on the solid content of the aqueous dispersion. Except for this, the same operations, measurements, and evaluations as in Example 9 were carried out. The results are shown in Table 1.

[0101] (Example 14) In preparing <Preparation of Copolymer (A)>, the amount of t-dodecyl mercaptan used as a molecular weight modifier was changed to 0.65 parts. Except for this, the same operations, measurements, and evaluations as in Example 9 were carried out. The results are shown in Table 1.

[0102] (Example 15) In preparing <Preparation of Copolymer (A)>, the amount of t-dodecyl mercaptan used as a molecular weight modifier was changed to 0.5 parts. Except for this, the same operations, measurements, and evaluations as in Example 9 were carried out. The results are shown in Table 1.

[0103] Example 16 <Preparation of Copolymer (A)> The amounts of various monomers charged were changed to obtain the composition of the resulting copolymer (A) shown in Table 2. The amount of t-dodecyl mercaptan used as a molecular weight modifier was changed to 0.5 parts. Furthermore, during the hydrogenation reaction, a palladium catalyst was added to the autoclave so that the palladium content relative to the solid content mass of the aqueous dispersion of the precursor was 2,500 ppm. Furthermore, the amount of silver nitrate added to the aqueous dispersion was changed to 0.79 mass% based on the solid content of the aqueous dispersion. After filtering the precipitate through a 200-mesh filter, 200 parts of NMP was added without adjusting the pH using a 2.5% KOH aqueous solution. Other than these, the same operations, measurements, and evaluations as in Example 9 were performed. The results are shown in Table 2.

[0104] (Example 17) In preparing <Preparation of Copolymer (A)>, a palladium catalyst was added to the autoclave during the hydrogenation reaction so that the palladium content relative to the mass of the solids contained in the aqueous dispersion of the precursor was 2500 ppm. Furthermore, the amount of silver nitrate added to the aqueous dispersion was changed to 0.79 mass% based on the mass of the solids of the aqueous dispersion. Except for this, the same operations, measurements, and evaluations as in Example 9 were performed. The results are shown in Table 2.

[0105] Example 18 <Preparation of Copolymer (A)> The amounts of various monomers charged were changed to obtain the composition of the resulting copolymer (A) shown in Table 2. The amount of t-dodecyl mercaptan used as a molecular weight modifier was changed to 0.5 parts. Furthermore, during the hydrogenation reaction, a palladium catalyst was added to the autoclave so that the palladium content relative to the solid content mass of the aqueous dispersion of the precursor was 2,500 ppm. Furthermore, the amount of silver nitrate added to the aqueous dispersion was changed to 0.43 mass% based on the solid content of the aqueous dispersion. After filtering the precipitate through a 200-mesh filter, 200 parts of NMP was added without adjusting the pH using a 2.5% KOH aqueous solution. Other than these, the same operations, measurements, and evaluations as in Example 9 were performed. The results are shown in Table 2.

[0106] (Comparative Example 1) In preparing <Preparation of Copolymer (A)>, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that no silver nitrate was added to the aqueous dispersion of copolymer (A) obtained by polymerization, and KCl was added so that the chlorine content was 1,000 ppm based on the solid content mass of the aqueous dispersion. The results are shown in Table 2.

[0107] (Comparative Example 2) In preparing <Preparation of Copolymer (A)>, various operations, measurements, and evaluations were carried out in the same manner as in Example 6, except that no silver nitrate was added to the aqueous dispersion of copolymer (A) obtained by polymerization, and KCl was added so that the chlorine content was 1,000 ppm based on the solid content mass of the aqueous dispersion. The results are shown in Table 2.

[0108] Comparative Example 3 In preparing <Preparation of Copolymer (A)>, 85 parts of ion-exchanged water and 0.2 parts of sodium dodecylbenzenesulfonate were placed in a reactor A equipped with a mechanical stirrer and a condenser under a nitrogen atmosphere, and the mixture was heated to 55°C with stirring. 0.3 parts of potassium persulfate was added as a 5.0% aqueous solution to the reactor A. Next, in a separate vessel B equipped with a mechanical stirrer under a nitrogen atmosphere, 94.0 parts of acrylonitrile as a nitrile group-containing monomer, 1.0 parts of acrylamide as a basic group-containing monomer, 2.0 parts of acrylic acid as an acidic group-containing monomer, and 3.0 parts of n-butyl acrylate as a (meth)acrylic acid ester monomer, as well as 0.6 parts of sodium dodecylbenzenesulfonate, 0.035 parts of tertiary dodecyl mercaptan, 0.4 parts of polyoxyethylene lauryl ether, and 80 parts of ion-exchanged water were added, and the mixture was emulsified with stirring to prepare a monomer mixture. This monomer mixture was then added to reactor A at a constant rate over 5 hours while being stirred and emulsified, and the reaction was continued until the polymerization conversion reached 95%, yielding an aqueous dispersion of polyacrylonitrile (PAN) copolymer primarily containing acrylonitrile units (94% by mass). Subsequently, KCl was added to the resulting aqueous dispersion of the PAN copolymer so that the chlorine content was 10 ppm relative to the solids mass, and then an appropriate amount of NMP was added to obtain a mixture. Subsequently, vacuum distillation was performed at 90°C to remove water and excess NMP from the mixture, yielding an NMP solution of the PAN copolymer (solids concentration: 8%). Measurements and evaluations similar to those in Example 9 were then performed. The results are shown in Table 2.

[0109] (Comparative Example 4) In preparing <Preparation of Copolymer (A)>, the amount of t-dodecyl mercaptan used as a molecular weight modifier was changed to 0.02 parts. Except for this, the same operations, measurements, and evaluations as in Example 9 were carried out. The results are shown in Table 2.

[0110] In Table 1 below, "NMP" represents N-methylpyrrolidone.

[0111]

[0112] Tables 1 and 2 show that when a binder composition for a secondary battery electrode containing a copolymer including a linear alkylene structural unit having 4 or more carbon atoms and a nitrile group-containing monomer unit is used, the cycle characteristics of the resulting secondary battery are improved by adjusting the weight-average molecular weight of the copolymer to 5,000 or more and 500,000 or less, and adjusting the chlorine content in the binder composition to more than 0 and 2,000 ppm or less relative to the copolymer. Table 2 also shows that the cycle characteristics of the resulting secondary batteries were inferior in Comparative Examples 1 and 2, in which the chlorine content in the binder composition exceeded the upper limit, Comparative Example 3, in which the polymer did not contain a linear alkylene structural unit having 4 or more carbon atoms, and Comparative Example 4, in which the weight-average molecular weight of the polymer exceeded the upper limit.

[0113] According to the present invention, it is possible to provide a binder composition for a secondary battery electrode, a conductive paste composition for a secondary battery electrode, and a slurry composition for a secondary battery electrode, which can improve the cycle characteristics of the resulting secondary battery. Furthermore, according to the present invention, it is possible to provide an electrode for a secondary battery that can sufficiently improve the cycle characteristics of the secondary battery, and a secondary battery having excellent cycle characteristics.

Claims

1. A binder composition for secondary battery electrodes, comprising a copolymer having a linear alkylene structural unit having 4 or more carbon atoms and a nitrile group-containing monomer unit, wherein the copolymer has a weight average molecular weight of 5,000 or more and 500,000 or less, and the chlorine content in the binder composition is more than 0 ppm and 2,000 ppm or less with respect to the copolymer.

2. The binder composition for secondary battery electrodes according to claim 1, wherein the copolymer contains hydrophilic group-containing monomer units in a content ratio of more than 0 mass % and not more than 50 mass %.

3. The binder composition for a secondary battery electrode according to claim 1 or 2, further comprising an organic solvent.

4. A conductive paste composition for secondary battery electrodes, comprising the binder composition for secondary battery electrodes according to any one of claims 1 to 3 and a conductive material.

5. A slurry composition for a secondary battery electrode, comprising an electrode active material, a conductive material, a solvent, and the binder composition for a secondary battery electrode according to any one of claims 1 to 3.

6. A secondary battery electrode comprising an electrode mixture layer formed using the slurry composition for a secondary battery electrode according to claim 5.

7. A secondary battery comprising the electrode for a secondary battery according to claim 6.

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