Binder composition for non-aqueous secondary battery electrodes, slurry composition for non-aqueous secondary battery positive electrodes, positive electrodes for non-aqueous secondary batteries, and non-aqueous secondary batteries

Abstract

Provided is a binder composition for nonaqueous secondary battery electrodes comprising a polymer A, wherein the polymer A contains 80.0 to 99.9 mass% of a nitrile group-containing monomeric unit, has a weight average molecular weight (Mw) of 700,000 to 2,000,000, and contains components having a molecular weight of less than 500,000 in a proportion of less than 30%.

Description

[Technical field]

[0001] The present invention relates to a binder composition for a non-aqueous secondary battery electrode, a slurry composition for a non-aqueous secondary battery positive electrode, a positive electrode for a non-aqueous secondary battery, and a non-aqueous secondary battery. [Background technology]

[0002] Non-aqueous secondary batteries such as lithium ion secondary batteries (hereinafter sometimes simply referred to as "secondary batteries") are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. For this reason, in recent years, improvements to battery components such as electrodes have been studied 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 usually includes a current collector and an electrode mixture layer formed on the current collector. The electrode mixture layer is formed, for example, by applying a slurry composition obtained by dispersing an electrode active material and a binder composition containing a binding agent in a dispersion medium onto the current collector and drying the 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 improvements in the performance of secondary batteries.

[0005] Specifically, for example, Patent Document 1 discloses a binder composition containing a polymer that contains 80% by weight or more and 99.9% by weight or less of repeating units derived from a monomer containing a nitrile group, and 0.1% by weight or more and 20% by weight or less of repeating units derived from an ethylenically unsaturated compound, and has a weight average molecular weight of 500,000 to 2,000,000 and a molecular weight distribution (Mw / Mn) of 3 to 13. According to Patent Document 1, by using a binder composition containing the above-mentioned polymer, an electrode that can provide excellent cycle characteristics for a secondary battery can be produced. For example, Patent Document 2 discloses a binder for lithium ion secondary battery electrodes, which includes a block copolymer that does not contain halogen atoms and does not contain unsaturated bonds in the main chain, a segment A that is compatible with an electrolyte solution containing ethylene carbonate and diethyl carbonate, and a segment B that is not compatible with the electrolyte solution, the segment A having polymerization units based on an acrylic acid alkyl ester having 1 to 5 carbon atoms in the alkyl group in the ester group, an methacrylic acid alkyl ester having 1 to 5 carbon atoms in the alkyl group in the ester group, and / or a monomer having a carboxylic acid group, and the segment B having polymerization units based on an α,β-unsaturated nitrile compound, a styrene-based monomer, an acrylic acid alkyl ester having 6 or more carbon atoms in the alkyl group in the ester group, and / or an methacrylic acid alkyl ester having 6 or more carbon atoms in the alkyl group in the ester group. The weight average molecular weight of the block copolymer described in Patent Document 2 is in the range of 1,000 to 500,000. According to Patent Document 2, by using a binder for lithium ion secondary battery electrodes containing the above-mentioned block copolymer, it is possible to provide an electrode for secondary batteries, which is used in lithium ion secondary batteries and the like and has improved high-temperature characteristics and long-term cycle characteristics. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5573966 [Patent Document 2] Patent No. 5696664 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in recent years, there has been a demand for further improvement in the performance of secondary batteries, and the conventional binder composition has room for improvement in terms of increasing the adhesion strength (hereinafter referred to as "peel strength") between an electrode mixture layer formed using the binder composition and a current collector while maintaining good cycle characteristics of the secondary battery.

[0008] Therefore, an object of the present invention is to provide a binder composition for a non-aqueous secondary battery electrode and a slurry composition for a non-aqueous secondary battery positive electrode, which are capable of forming an electrode mixture layer having excellent peel strength and enabling a secondary battery to exhibit good cycle characteristics. Another object of the present invention is to provide a positive electrode for a non-aqueous secondary battery, which has an excellent peel strength of a positive electrode mixture layer and is capable of causing the non-aqueous secondary battery to exhibit good cycle characteristics. Another object of the present invention is to provide a nonaqueous secondary battery that is excellent in battery characteristics such as cycle characteristics. [Means for solving the problem]

[0009] The present inventors have conducted extensive research with the aim of solving the above problems, and have found that the above problems can be advantageously solved by using a binder composition for a non-aqueous secondary battery electrode, which contains a polymer A having a predetermined composition and weight-average molecular weight, and which contains a component having a molecular weight within a predetermined range at a predetermined ratio, and have thus completed the present invention.

[0010] That is, the present invention has an object to advantageously solve the above-mentioned problems, and the binder composition for a non-aqueous secondary battery electrode of the present invention (hereinafter may be simply abbreviated as "binder composition") is a binder composition for a non-aqueous secondary battery electrode containing polymer A, characterized in that polymer A contains nitrile group-containing monomer units in a proportion of 80.0 mass % or more and 99.9 mass % or less, the weight average molecular weight (Mw) of polymer A is 700,000 or more and 2,000,000 or less, and the proportion of components in polymer A having a molecular weight of less than 500,000 is less than 30%. In this way, by using a binder composition containing polymer A which contains nitrile group-containing monomer units in a proportion of 80.0 mass% or more and 99.9 mass% or less, has a weight average molecular weight (Mw) of 700,000 or more and 2,000,000 or less, and has a proportion of components with a molecular weight of less than 500,000 of less than 30%, it is possible to form an electrode mixture layer with excellent peel strength, and to cause the secondary battery to exhibit good cycle characteristics. In the present invention, the phrase "containing a monomer unit" means that "a polymer obtained by using the monomer contains a structural unit derived from the monomer unit." In the present invention, the "content ratio of each monomer unit" is expressed as follows: 1 It can be measured using various magnetic resonance (NMR) methods such as H-NMR. In the present invention, the "weight average molecular weight" of the polymer can be measured by the method described in the Examples of this specification. In the present invention, the "proportion of components having a molecular weight of less than 500,000" can be determined by using a chromatogram obtained by gel permeation chromatography and calculating the ratio of the sum (X) of the peak areas of components having a molecular weight of less than 500,000 in the chromatogram to the total area (A) of the peaks in the chromatogram [=(X / A)×100%].

[0011] Here, in the binder composition for a non-aqueous secondary battery electrode of the present invention, the molecular weight distribution (Mw / Mn) of the polymer A is preferably less than 3.0. By using a binder composition containing a polymer A having a molecular weight distribution (Mw / Mn) of less than 3.0, an electrode mixture layer having superior peel strength can be formed, and the secondary battery can exhibit better cycle characteristics. In the present invention, the term "molecular weight distribution (Mw / Mn)" refers to the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn). In the present invention, the "molecular weight distribution" of a polymer can be measured by the method described in the examples of this specification.

[0012] In addition, in the binder composition for non-aqueous secondary battery electrodes of the present invention, the electrolyte swelling degree of the polymer A is preferably 120% by mass or more and 250% by mass or less. The electrolyte swelling degree is calculated by (W1 / W0)×100 using the mass W0 of a test piece prepared by drying a dispersion of the polymer A in N-methyl-2-pyrrolidone (hereinafter sometimes referred to as "NMP") at a temperature of 120° C. for 2 hours and the mass W1 of the test piece after immersing the test piece in an electrolyte at a temperature of 60° C. for 72 hours, and the electrolyte is a solution obtained by dissolving LiPF6 in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume mixing ratio: ethylene carbonate / ethyl methyl carbonate=3 / 7) at a concentration of 1.0 mol / L relative to the mixed solvent. By setting the degree of swelling in an electrolyte of the polymer A within the above range, an electrode mixture layer having improved peel strength can be formed, and an increase in the internal resistance of the secondary battery can be suppressed.

[0013] Furthermore, in the binder composition for non-aqueous secondary battery electrodes of the present invention, it is preferable that the polymer A further contains at least one of a carboxylic acid group-containing monomer unit and a (meth)acrylic acid ester monomer unit. If the polymer A contains at least one of a carboxylic acid group-containing monomer unit and a (meth)acrylic acid ester monomer unit, the peel strength of the electrode mixture layer can be further improved. In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0014] The present invention also aims to advantageously solve the above problems, and the slurry composition for a non-aqueous secondary battery positive electrode (hereinafter, sometimes simply abbreviated as "slurry composition") of the present invention is characterized by including a positive electrode active material, a conductive material, and any of the binder compositions for a non-aqueous secondary battery electrode described above. In this way, by using a slurry composition including a positive electrode active material, a conductive material, and any of the binder compositions described above, an electrode mixture layer having excellent peel strength can be formed, and good cycle characteristics can be exhibited in a non-aqueous secondary battery.

[0015] The present invention aims to advantageously solve the above problems, and the positive electrode for a non-aqueous secondary battery of the present invention is characterized in that it has a positive electrode mixture layer formed using the above-mentioned slurry composition for a positive electrode for a non-aqueous secondary battery. By using the above-mentioned slurry composition, it is possible to obtain a positive electrode for a non-aqueous secondary battery that has a positive electrode mixture layer with excellent peel strength and is capable of causing the secondary battery to exhibit good cycle characteristics.

[0016] Furthermore, the present invention aims to advantageously solve the above problems, and the nonaqueous secondary battery of the present invention is a nonaqueous secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that the positive electrode is the above-mentioned positive electrode for a nonaqueous secondary battery. In this way, by using the above-mentioned positive electrode for a nonaqueous secondary battery, a secondary battery excellent in battery characteristics such as cycle characteristics can be obtained. Effect of the Invention

[0017] According to the present invention, it is possible to provide a binder composition for a non-aqueous secondary battery electrode and a slurry composition for a non-aqueous secondary battery positive electrode, which are capable of forming an electrode mixture layer having excellent peel strength and enabling a secondary battery to exhibit good cycle characteristics. Furthermore, according to the present invention, it is possible to provide a positive electrode for a non-aqueous secondary battery, which has an excellent peel strength of a positive electrode mixture layer and is capable of causing the non-aqueous secondary battery to exhibit good cycle characteristics. According to the present invention, a nonaqueous secondary battery having excellent battery characteristics such as cycle characteristics can be provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described in detail. Here, the binder composition for a non-aqueous secondary battery electrode of the present invention can be used when preparing a slurry composition for a non-aqueous secondary battery electrode. The binder composition for a non-aqueous secondary battery electrode of the present invention can be particularly suitably used when preparing a slurry composition for a non-aqueous secondary battery positive electrode of the present invention. Furthermore, the slurry composition for a non-aqueous secondary battery positive electrode of the present invention can be used when producing a positive electrode for a non-aqueous secondary battery such as a lithium ion secondary battery. The nonaqueous secondary battery of the present invention includes a positive electrode for a nonaqueous secondary battery formed using the slurry composition for a nonaqueous secondary battery positive electrode of the present invention.

[0019] (Binder composition for non-aqueous secondary battery electrodes) The binder composition for a non-aqueous secondary battery electrode of the present invention contains polymer A, and optionally further contains a solvent and other components that can be incorporated into an electrode of a secondary battery.

[0020] Here, in the binder composition of the present invention, polymer A is characterized in that (i) it contains nitrile group-containing monomer units in a proportion of 80.0 mass% or more and 99.9 mass% or less, (ii) it has a weight average molecular weight (Mw) of 700,000 or more and 2,000,000 or less, and (iii) the proportion of components having a molecular weight of less than 500,000 is less than 30%.

[0021] Furthermore, by using the binder composition of the present invention, it is possible to form an electrode mixture layer having excellent peel strength, and to enable the secondary battery to exhibit good cycle characteristics.

[0022] <Polymer A> Polymer A is a component that prevents components contained in an electrode mixture layer from being detached from the electrode mixture layer (i.e., functions as a binder) in an electrode produced by forming an electrode mixture layer on a current collector using a slurry composition prepared from the binder composition.

[0023] [Composition of Polymer A] The polymer A must contain the nitrile group-containing monomer as a repeating unit in the above-mentioned predetermined ratio. Furthermore, the polymer A preferably further contains at least one of a carboxylic acid group-containing monomer and a (meth)acrylic acid ester monomer unit as a repeating unit, and may further contain other monomer units other than those mentioned above.

[0024] -Nitrile group-containing monomer unit- The nitrile group-containing monomer unit is a repeating unit derived from a nitrile group-containing monomer. Since the polymer A contains the nitrile group-containing monomer unit, the peel strength of the electrode mixture layer formed using the binder composition can be excellent.

[0025] The nitrile group-containing monomer capable of forming the nitrile group-containing monomer unit may be an α,β-ethylenically unsaturated nitrile monomer. 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, and examples thereof include acrylonitrile; α-halogenoacrylonitrile such as α-chloroacrylonitrile and α-bromoacrylonitrile; α-alkylacrylonitrile such as methacrylonitrile and α-ethylacrylonitrile; and the like. Among these, from the viewpoint of forming a positive electrode mixture layer having excellent peel strength, acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is more preferred. The nitrile group-containing monomer may be used alone or in combination of two or more kinds in any ratio.

[0026] The content of the nitrile group-containing monomer unit in the polymer A must be 80.0% by mass or more, preferably 82.0% by mass or more, more preferably 85.0% by mass or more, and must be 99.9% by mass or less, preferably 95.0% by mass or less, based on the total repeating units contained in the polymer A being 100.0% by mass. By setting the content of the nitrile group-containing monomer unit in the polymer A to the above lower limit or more, the increase in the internal resistance of the secondary battery due to excessive swelling of the polymer A in the electrolyte can be suppressed, and the cycle characteristics and high-temperature storage characteristics of the secondary battery can be maintained well. On the other hand, by setting the content of the nitrile group-containing monomer unit in the polymer A to the above upper limit or less, the flexibility of the polymer A can be ensured, and the pressing property when preparing an electrode can be improved, thereby increasing the electrode density.

[0027] -Carboxylic acid group-containing monomer unit- The carboxylic acid group-containing monomer unit is a repeating unit derived from a carboxylic acid group-containing monomer. When the polymer A contains the carboxylic acid group-containing monomer unit, the peel strength of the electrode mixture layer formed using the binder composition can be improved.

[0028] Examples of the carboxylic acid group-containing monomer capable of forming the carboxylic acid group-containing monomer unit include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their derivatives. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid. Examples of the 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. The 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 maleate. Examples of the acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride. Furthermore, as the carboxylic acid group-containing monomer, an acid anhydride which generates a carboxylic acid group upon hydrolysis can also be used. 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. Among these, as the carboxylic acid group-containing monomer, acrylic acid, methacrylic acid, and itaconic acid are preferable, and methacrylic acid is more preferable. The carboxylic acid group-containing monomer may be used alone or in combination of two or more kinds in any ratio.

[0029] The content of the carboxylic acid group-containing monomer units in polymer A is preferably 0.1% by mass or more, more preferably 1.0% by mass or more, and preferably 10.0% by mass or less, more preferably 5.0% by mass or less, based on 100.0% by mass of all repeating units contained in polymer A. By setting the content of the carboxylic acid group-containing monomer units in polymer A within the above range, the peel strength of the electrode mixture layer can be favorably improved.

[0030] -(Meth)acrylic acid ester monomer unit- The (meth)acrylic acid ester monomer unit is a repeating unit derived from a (meth)acrylic acid ester monomer. When the polymer A contains the (meth)acrylic acid ester monomer unit, the peel strength of the electrode mixture layer formed using the binder composition can be further improved, and flexibility can be imparted to the electrode mixture layer.

[0031] Examples of (meth)acrylic acid ester monomers that can form the (meth)acrylic acid ester monomer unit include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, butyl acrylates such as n-butyl acrylate and t-butyl acrylate, octyl acrylates such as pentyl acrylate, hexyl acrylate, heptyl acrylate, and 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, cyclohexyl cycloacrylate, Examples of the methacrylic acid esters include acrylic acid esters such as β-hydroxyethyl acrylate; butyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, and t-butyl methacrylate; octyl methacrylates such as pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, and 2-ethylhexyl methacrylate; and alkyl methacrylates such as nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate. In particular, from the viewpoint of improving the output characteristics and cycle characteristics of a secondary battery, the (meth)acrylic acid ester monomer preferably has an alkyl group bonded to a non-carbonyl oxygen atom having 8 or less carbon atoms, and more preferably has 4 or less carbon atoms. The (meth)acrylic acid ester monomer may be used alone or in combination of two or more kinds in any ratio.

[0032] The content of the (meth)acrylic acid ester monomer units in polymer A is preferably 1.0 mass% or more, more preferably 4.0 mass% or more, and preferably 20.0 mass% or less, more preferably 10.0 mass% or less, based on 100.0 mass% of all repeating units contained in polymer A. By setting the content of the (meth)acrylic acid ester monomer units in polymer A within the above range, the peel strength of the electrode mixture layer can be further improved.

[0033] -Other monomer units- The other monomer units are repeating units derived from monomers other than the above-mentioned nitrile group-containing monomer, carboxylic acid group-containing monomer, and (meth)acrylic acid ester monomer. Here, the other monomer units that the polymer A may contain are not particularly limited, and examples thereof include aromatic vinyl monomer units, crosslinkable monomer units, and (meth)acrylamide monomer units. In this specification, the term "(meth)acrylamide" means acrylamide and / or methacrylamide. The other monomers may be used alone or in combination of two or more kinds in any ratio.

[0034] -Aromatic vinyl monomer unit- Examples of aromatic vinyl monomers capable of forming aromatic vinyl monomer units include styrene, α-methylstyrene, vinyltoluene, and divinylbenzene. The aromatic vinyl monomer may be used alone or in combination of two or more kinds in any ratio.

[0035] -Cross-linking monomer unit- The crosslinkable monomer unit is a monomer unit derived from a monomer having a crosslinkable group. By including the crosslinkable monomer unit, the crosslink density of the polymer A can be increased with a small amount of the crosslinkable monomer unit, and the swelling property in the electrolyte can be reduced, so that the life characteristics of the obtained secondary battery can be improved. As the crosslinkable monomer capable of forming the crosslinkable monomer unit, a compound containing a thermally crosslinkable crosslinkable group in a monofunctional monomer having one olefinic double bond is preferred, for example, a monomer containing at least one selected from the group consisting of an epoxy group, an oxetanyl group, and an oxazoline group. Among these, a monomer containing an epoxy group is more preferred in terms of ease of adjusting crosslinking and crosslink density. Examples of the monomer containing an epoxy group include a monomer containing a carbon-carbon double bond and an epoxy group, and a monomer containing a halogen atom and an epoxy group. Examples of the monomer containing a carbon-carbon double bond and an epoxy group include glycidyl esters of unsaturated carboxylic acids such as vinyl glycidyl ether, allyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, etc. These may be used alone or in combination of two or more kinds in any ratio.

[0036] -(Meth)acrylamide monomer unit- Examples of the (meth)acrylamide monomer capable of forming a (meth)acrylamide monomer unit include acrylamide, methacrylamide, diethylacrylamide, and dimethylmethacrylamide. The (meth)acrylamide monomer may be used alone or in combination of two or more kinds in any ratio.

[0037] The content of the other monomer units in polymer A can be, for example, 0.1% by mass or more and 20.0% by mass or less, or may be 0% by mass, where the total repeating units contained in polymer A is taken as 100.0% by mass.

[0038] [Weight average molecular weight (Mw)] The weight average molecular weight (Mw) of the polymer A must be 700,000 or more, preferably 1,000,000 or more, must be 2,000,000 or less, preferably 1,800,000 or less, and more preferably 1,500,000 or less. By setting the weight average molecular weight (Mw) of the polymer A to the above lower limit or more, when the binder composition is used to prepare a slurry composition, the solid content contained in the slurry composition can be suppressed from settling, and an electrode mixture layer having excellent peel strength can be formed. On the other hand, by setting the weight average molecular weight (Mw) of the polymer A to the above upper limit or less, the slurry composition obtained by using the binder composition does not thicken excessively, and therefore the thickness of the electrode mixture layer can be made uniform, and an electrode mixture layer having excellent peel strength can be formed. The weight average molecular weight of polymer A can be adjusted, for example, by changing the method for preparing polymer A (eg, the amount of polymerization initiator).

[0039] [Ratio of components with molecular weight less than 500,000] In addition, the proportion of components having a molecular weight of less than 500,000 in the polymer A must be less than 30%, preferably less than 27%, and more preferably less than 25%. By making the proportion of components having a molecular weight of less than 500,000 in the polymer A less than 30%, the amount of low molecular weight components in the binder composition is reduced, so that the adhesion between the electrode mixture layer and the current collector interface can be increased, and as a result, the peel strength of the electrode mixture layer can be made excellent. In addition, it is presumed that the amount of low molecular weight components that inhibit the movement of the electrode active material is limited, which suppresses the increase in the viscosity of the electrolyte, and therefore the high-temperature storage characteristics of the secondary battery can be made excellent. In addition, the polymer A preferably has a ratio of components with a molecular weight of less than 400,000 of less than 25%, and more preferably has a ratio of components with a molecular weight of less than 300,000 of less than 20%. This reduces the amount of low molecular weight components in the binder composition, thereby improving the adhesion between the electrode mixture layer and the current collector interface, and as a result, the peel strength of the electrode mixture layer can be improved. In addition, the high-temperature storage characteristics of the secondary battery can be improved. The proportion of components having a molecular weight of less than 500,000 can be adjusted, for example, by changing the preparation method of polymer A. Specifically, when preparing polymer A, living radical polymerization described below can be used to obtain polymer A having a low proportion of components having a molecular weight of less than 500,000.

[0040] [Molecular weight distribution (Mw / Mn)] Furthermore, the molecular weight distribution (Mw / Mn) of the polymer A is preferably less than 3.0, more preferably less than 2.7, even more preferably less than 2.5, and particularly preferably less than 2.0. By making the molecular weight distribution (Mw / Mn) of the polymer A less than 3.0, the amount of low molecular weight components in the binder composition is reduced, so that the adhesion between the electrode mixture layer and the current collector interface can be improved, and as a result, the peel strength of the electrode mixture layer can be improved. In addition, it is presumed that the amount of low molecular weight components that inhibit the movement of the electrode active material is more limited, so that the increase in the viscosity of the electrolyte can be more suppressed, and the high temperature storage characteristics of the secondary battery can be improved. The lower limit of the molecular weight distribution (Mw / Mn) of the polymer A is not particularly limited, but is usually more than 1. The molecular weight distribution (Mw / Mn) of the polymer A can be adjusted, for example, by changing the preparation method of the polymer A. Specifically, when preparing the polymer A, living radical polymerization described later can be used to obtain a polymer A having a small molecular weight distribution (Mw / Mn).

[0041] [Electrolyte swelling rate] Here, the electrolyte swelling degree of the polymer A is preferably 120% by mass or more, more preferably 150% by mass or more, and preferably 250% by mass or less, more preferably 200% by mass or less. By setting the electrolyte swelling degree to the above lower limit or more, the polymer A becomes easily dissolved in NMP. Therefore, the slurry stability of the slurry composition prepared using the binder composition is improved, so that an electrode mixture layer with further improved peel strength can be formed. On the other hand, by setting the electrolyte swelling degree of the polymer A to the above upper limit or less, the polymer A becomes difficult to swell in the electrolyte. Therefore, in a secondary battery prepared using the binder composition, it is possible to suppress the occurrence of electrode swelling due to the swelling of the polymer A, and as a result, it is possible to suppress an increase in the internal resistance of the secondary battery. The degree of swelling of the polymer A in an electrolyte solution can be adjusted, for example, by changing the types and / or ratio of monomers used in preparing the polymer A.

[0042] [Method for preparing polymer A] The method for preparing the polymer A is not particularly limited. For example, the polymer A can be obtained by polymerizing a monomer composition containing the above-mentioned monomers. Here, in the present invention, the content ratio of each monomer unit in the monomer composition can be determined based on the content ratio of each monomer unit in polymer A. The polymerization method is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. may be used. As the polymerization reaction, any reaction such as ionic polymerization, radical polymerization, living radical polymerization, etc. may be used. As the emulsifier, dispersant, polymerization initiator, chain transfer agent, etc. that can be used in polymerization, those that are generally used may be used.

[0043] Here, as an example, a method for preparing the above-mentioned polymer A by a living radical polymerization reaction will be described, although the method for preparing the polymer A is not limited to the following example.

[0044] -Preparation of polymer A by living radical polymerization- In preparing the polymer A by living radical polymerization, it is preferable to use a RAFT compound or an organic tellurium compound as a polymerization initiator when polymerizing a monomer composition containing the above-mentioned monomer. In this case, an azo-based polymerization initiator may be used in combination with the organic tellurium compound. By using an azo-based polymerization initiator in combination, the living radical polymerization reaction can be promoted. And, according to the living radical polymerization, the molecular weight of the polymer A can be easily controlled, so that the polymer A, which needs to have a molecular weight of less than 500,000 of less than 30%, can be efficiently produced.

[0045] -RAFT Compounds- As a RAFT compound (reversible addition-fragmentation chain transfer: RAFT type radical polymerization compound) used in living radical polymerization, for example, those described in International Publication No. 2011 / 040288 can be used. The RAFT compound is represented by the following general formula (I).

[0046] [ka]

[0047] In formula (I), R 1 , R 2 is at least one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, and a phenyl group; R 3 is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a phenyl group, or C(=O)OR 4 group, C(=O)R 4 At least one selected from the group consisting of a halogen group, a cyano group, and a nitro group; 4 is a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and Z is SR 5 , OR 5 , at least one selected from the group consisting of an alkyl group having 1 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, and a phenyl group; 5is an alkyl group having 1 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, or a phenyl group.

[0048] -organotellurium compounds- As the organotellurium compound used in the living radical polymerization, for example, those described in JP-A-2018-172591, JP-A-2017-170250, and JP-A-2015-080189 can be used.

[0049] Specific examples of the organic tellurium compound include 3-methyltellanyl-1-propene, 3-methyltellanyl-2-methyl-1-propene, 3-methyltellanyl-2-phenyl-1-propene, 3-methyltellanyl-3-methyl-1-propene, 3-methyltellanyl-3-phenyl-1-propene, 3-methyltellanyl-3-cyclohexyl-1-propene, 3-methyltellanyl-3-cyano-1-propene, 3-ethyltellanyl-1-propene, 3-methyltellanyl-3-cyclohexyl-1-propene, 3-methyltellanyl-3-cyano-1-propene, 3-ethyltellanyl-1-propene, 3-methyltellanyl-3-methyl ... tellanyl-3-dimethylaminocarbonyl-1-propene, 3-[(n-propyl)tellanyl]-1-propene, 3-isopropyltellanyl-1-propene, 3-(n-butyl)tellanylpropene, 3-[(n-hexyl)tellanyl]-1-propene, 3-phenyltellanyl-1-propene, 3-[(p-methylphenyl)tellanyl]-1-propene, 3-cyclohexyltellanyl-1-propene, 3-[(2-pyridyl)tellanyl]-1-propene, 3-methyltellanyl Rutellanyl-2-butene, 3-methyltellanyl-1-cyclopentene, 3-methyltellanyl-1-cyclohexene, 3-methyltellanyl-1-cyclooctene, 3-ethyltellanyl-1-cyclohexene, 3-methyltellanyl-1-cyclohexene, 3-[(n-propyl)tellanyl]-1-cyclohexene, 3-[(n-butyl)tellanyl]-1-cyclohexene, 2-(methyltellanylmethyl)methylacrylate, 2-(methyltellanylmethyl)acrylate ethyl acrylate, 2-(methyltellanylmethyl)n-butyl acrylate, 2-(ethyltellanylmethyl)methyl acrylate, 2-[(n-butyl)tellanylmethyl]methyl acrylate, 2-(cyclohexyltellanylmethyl)methyl acrylate, 1,4-bis(methyltellanyl)-2-butene, 1,4-bis(ethyltellanyl)-2-butene, 1,4-bis[(n-butyl)tellanyl]-2-butene, 1,4-bis(cyclohexyltellanyl)-2-butene, 1,4-bis(phenyltellanyl)-2-butene, (methyltellanylmethyl)benzene, (methyltellanylmethyl)naphthalene, ethyl-2-methyl-2-methyltellanyl-propionate, ethyl-2-methyl-2-n-butyltellanyl-propionate, (2-trimethylsiloxyethyl)-2-methyl-2-methyltellanyl-propionate, (2-hydroxyethyl)-2-methyl-2-methyltellanyl-propionate, (3-trimethylsilylpropargyl)-2-methyl-2-methyltellanyl-propionate, 2-methyltellanyl-isobutyrate, 2-(methyltellanyl)ethyl isobutyrate, and the like. These organotellurium compounds can be used alone or in combination of two or more at any ratio.

[0050] [Azo polymerization initiator] In addition, as the azo polymerization initiator, any azo polymerization initiator used in normal radical polymerization can be used without any particular limitation. Specific examples thereof include 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 1,1'-azobis(1-cyclohexanecarbonitrile), dimethyl-2,2'-azobisisobutyrate, 4,4'-azobis(4-cyanovaleric acid), 1,1'-azobis(1-acetoxy-1-phenylethane), 2,2'-azobis(2-methylbutyla), and the like. amide), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylamidinopropane) dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2'-azobis(2,4,4-trimethylpentane), 2-cyano-2-propylazoformamide, 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis(N-cyclohexyl-2-methylpropionamide), and the like. These azo-based polymerization initiators can be used alone or in combination of two or more kinds in any desired ratio.

[0051] Here, the amount of the polymerization initiator used is not particularly limited, but is usually preferably 0.01 mol or more, more preferably 0.05 mol or more, and preferably 1 mol or less, more preferably 0.5 mol or less, relative to 100 parts by mass of the monomer used in the polymerization.

[0052] In the case where an azo-based polymerization initiator is used in combination, the amount of the azo-based polymerization initiator used is not particularly limited, but is usually preferably 1 mol or more, more preferably 2 mol or more, and preferably 10 mol or less, more preferably 5 mol or less, relative to 1 mol of the organotellurium compound.

[0053] In the polymerization reaction, a solvent may or may not be used. When a solvent is used, the solvent to be used is not particularly limited, and examples thereof include the organic solvents described below that may be optionally contained in the binder composition.

[0054] The polymerization temperature is not particularly limited, but is usually 0° C. to 100° C., and preferably 20 to 80° C. The polymerization time is not particularly limited, but is usually 1 minute to 96 hours.

[0055] <Solvent> The solvent that the binder composition may optionally contain may be an aqueous solvent or an organic solvent used in preparing the above-mentioned polymer A. 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 polar organic solvents such as N,N-dimethylformamide and N-methyl-2-pyrrolidone (NMP); aromatic hydrocarbons such as toluene, xylene, chlorobenzene, orthodichlorobenzene, and paradichlorobenzene; and sulfur-containing compounds such as dimethyl sulfoxide. The solvent may be used alone or in combination of two or more kinds.

[0056] <Other ingredients> In addition to the above components, the binder composition of the present invention may contain components such as a reinforcing material, a leveling agent, a viscosity modifier, and an electrolyte additive. These are not particularly limited as long as they do not affect the battery reaction, and known components, such as those described in International Publication No. 2012 / 115096, can be used. In addition, these components may be used alone or in combination of two or more types in any ratio.

[0057] Furthermore, the amount of low molecular weight components (e.g., surfactants, preservatives, antifoaming agents, etc.) contained in the binder composition is preferably 0.01% by mass or less, and more preferably 0.005% by mass or less, based on 100% by mass of the total mass of the binder composition. By making the amount of low molecular weight components contained in the binder composition 0.01% by mass or less, the adhesion between the electrode mixture layer and the current collector interface can be further increased, and as a result, the peel strength of the electrode mixture layer can be further improved.

[0058] <Preparation of Binder Composition> The binder composition of the present invention can be prepared by mixing the above-described polymer A, a solvent, and other components by a known method.

[0059] (Slurry Composition for Non-aqueous Secondary Battery Cathode) The slurry composition for a non-aqueous secondary battery cathode of the present invention contains a cathode active material, a conductive material, and the above-described binder composition, and optionally further contains a polymer B and other components. Since the slurry composition of the present invention contains the above-described binder composition, the cathode composite layer formed using the slurry composition of the present invention has excellent peel strength and can exhibit good cycle characteristics in a secondary battery. Hereinafter, as an example, the case where the slurry composition of the present invention is a slurry composition for a lithium-ion secondary battery cathode will be described, but the present invention is not limited to the following example.

[0060] <Cathode Active Material> The cathode active material is a substance that transfers electrons at the cathode of a secondary battery. As the cathode active material for a lithium-ion secondary battery, a substance that can occlude and release lithium is usually used.

[0061] Specifically, the cathode active material for a lithium-ion secondary battery is not particularly limited, and includes lithium-containing cobalt oxide (LiCoO2), lithium manganate (LiMn2O4), lithium-containing nickel oxide (LiNiO2), lithium-containing composite oxide of Co-Ni-Mn (Li(CoMnNi)O2), lithium-containing composite oxide of Ni-Mn-Al, lithium-containing composite oxide of Ni-Co-Al, olivine-type lithium iron phosphate (LiFePO4), olivine-type lithium manganese phosphate (LiMnPO4), Li2MnO3-LiNiO2-based solid solution, Li 1+x Mn 2-x O4 (0 <X <2) represented by a lithium-excess spinel compound, Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56]O2, LiNi 0.5 Mn 1.5 Examples of the positive electrode active material include known positive electrode active materials such as O4. The positive electrode active material may be used alone or in combination of two or more kinds in any ratio.

[0062] From the viewpoint of increasing the capacity of lithium-ion secondary batteries, lithium-containing composite oxides having a high Ni content, so-called high-nickel lithium-containing composite oxides (for example, lithium-containing composite oxides of Co-Ni-Mn, lithium-containing composite oxides of Ni-Mn-Al, lithium-containing composite oxides of Ni-Co-Al, Li2MnO3-LiNiO2 solid solutions, Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 ]O2, LiNi 0.5 Mn 1.5 It is preferable to use O4).

[0063] However, when a high-nickel lithium-containing composite oxide is used as the positive electrode active material, the slurry composition tends to gel due to the high basicity of the slurry composition. In contrast, according to the present invention, the slurry composition is prepared using a binder composition containing polymer A, so that when a high-nickel lithium-containing composite oxide is used as the positive electrode active material, the high-nickel lithium-containing composite oxide is coated with polymer A. Therefore, the basicity of the slurry composition can be suppressed from increasing, and the gelation of the slurry composition can be prevented. Therefore, if the slurry composition of the present invention is used, a positive electrode composite layer having excellent peel strength can be efficiently formed even when a high-nickel lithium-containing composite oxide is used as the positive electrode active material.

[0064] Here, the content of the positive electrode active material in the slurry composition is preferably 94% by mass or more and 99% by mass or less, when the total solid content in the slurry composition is 100% by mass. By setting the content of the positive electrode active material in the slurry composition within the above range, the capacity of the secondary battery can be improved satisfactorily.

[0065] <Conductive material> The conductive material is for ensuring electrical contact between the positive electrode active materials, and is not particularly limited, and any known conductive material can be used.

[0066] From the viewpoint of improving the electrical conductivity, the slurry composition of the present invention preferably contains carbon nanotubes (hereinafter abbreviated as "CNTs"), which are fibrous carbon materials, as the conductive material. Here, the CNTs include single-walled or multi-walled carbon nanotubes. The specific surface area of ​​the CNTs is 50 m 2 / g or more, and 2 / g or more is more preferable, and 100m 2 / g or more is more preferable, and 2 / g or less, and 2 / g or less is more preferable, and 2 / g or less is more preferable. If the specific surface area of ​​the CNT is within the above range, good dispersibility of the CNT in the slurry composition can be ensured, and the viscosity of the slurry composition can be stabilized. In the present invention, the "specific surface area" refers to the nitrogen adsorption specific surface area measured by the BET method. Furthermore, as a conductive material other than CNT, it may further contain conductive carbon materials such as carbon black (e.g., acetylene black, Ketjen Black (registered trademark), furnace black, etc.), carbon nanohorns, milled carbon fibers obtained by crushing polymer fibers after firing, single-layer or multi-layer graphene, carbon nonwoven fabric sheets obtained by firing nonwoven fabric made of polymer fibers, and fibers or foils of various metals. From the viewpoint of further improving the conductivity, the slurry composition of the present invention preferably contains both CNT and carbon black as conductive materials, and more preferably contains both CNT and acetylene black. The conductive material may be used alone or in any combination of two or more kinds at any ratio. When both CNT and carbon black are used as the conductive material, the blending ratio of CNT to carbon black (CNT:carbon black) is preferably 1:5 to 5:1, and more preferably 1:1 to 2:1, by mass.

[0067] The content of the conductive material in the slurry composition is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, and preferably 5.0% by mass or less, and more preferably 3.0% by mass or less, when the total solid content in the slurry composition is 100% by mass. By setting the content of the conductive material to the above lower limit or more, it is possible to sufficiently ensure electrical contact between the positive electrode active materials. On the other hand, by setting the content of the conductive material to the above upper limit or less, it is possible to stabilize the viscosity of the slurry composition and improve the density of the positive electrode mixture layer, thereby sufficiently increasing the capacity of the secondary battery.

[0068] <Binder composition> As the binder composition used in the slurry composition of the present invention, a binder composition containing the above-mentioned polymer A is used.

[0069] The content of the binder composition in the slurry composition is preferably such that the amount of polymer A is 0.1% by mass or more, more preferably 1.0% by mass or more, and preferably 3.0% by mass or less, when the total solid content in the slurry composition is taken as 100% by mass. If the binder composition is contained in the slurry composition in an amount such that the amount of polymer A falls within the above range, the peel strength of the positive electrode mixture layer can be further improved.

[0070] <Polymer B> Furthermore, the polymer B that may be optionally contained in the slurry composition of the present invention is a component contained as a binder. Here, the binder is not particularly limited as long as it is a polymer other than the above-mentioned polymer A, and known binders such as vinyl acetate polymers, conjugated diene polymers, and acrylic polymers can be mentioned.

[0071] Here, the vinyl acetate polymer includes vinyl acetate homopolymer, ethylene-vinyl acetate copolymer, or a partially hydrolyzed polymer thereof, and the conjugated diene polymer refers to a polymer containing a conjugated diene monomer unit. Specific examples of the conjugated diene polymer include, but are not limited to, copolymers containing aromatic vinyl monomer units and aliphatic conjugated diene monomer units, such as styrene-butadiene copolymer (SBR), butadiene rubber (BR), acrylic rubber (NBR) (copolymers containing acrylonitrile units and butadiene units), styrene acrylic rubber (SNBR) (copolymers containing aromatic vinyl monomer units, nitrile group-containing monomer units, ethylenically unsaturated acid monomer units, and linear alkylene structural units having 4 or more carbon atoms), and hydrogenated products thereof. Among these, acrylic rubber and styrene acrylic rubber are preferred. The acrylic polymer refers to a polymer containing a (meth)acrylic acid ester monomer unit. The content of Polymer B relative to 100 parts by mass of Polymer A can be, for example, 0 parts by mass or more and 40 parts by mass or less.

[0072] The aromatic vinyl monomer unit contained in the conjugated diene polymer may be the aromatic vinyl monomer unit listed in the section on polymer A. The aliphatic conjugated diene monomer capable of forming the aliphatic conjugated diene monomer unit contained in the conjugated diene polymer is not particularly limited, and may be 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, etc. Among them, the aliphatic conjugated diene monomer is preferably 1,3-butadiene and isoprene, and more preferably isoprene. The aliphatic conjugated diene monomer may be used alone or in combination of two or more kinds at any ratio.

[0073] The content of polymer B in the slurry composition is preferably 0.5% by mass or less, and more preferably 0.3% by mass or less, when the total solid content in the slurry composition is taken as 100% by mass. If polymer B is contained in the slurry composition so that the amount of polymer B in the slurry composition is within the above range, the peel strength of the positive electrode mixture layer can be further improved while suppressing a decrease in the stability of the slurry composition containing the binder composition.

[0074] [Method for preparing polymer B] The method for preparing polymer B is not particularly limited, and polymer B can be prepared, for example, by the same method as that described in the above section "Method for preparing polymer A."

[0075] <Other ingredients> Other components that can be blended in the slurry composition of the present invention are not particularly limited, and include the same components as those that can be blended in the binder composition of the present invention. In addition, the other components may be used alone or in combination of two or more kinds in any ratio.

[0076] <Preparation of Slurry Composition for Non-Aqueous Secondary Battery Positive Electrode> The slurry composition for a non-aqueous secondary battery positive electrode of the present invention can be prepared by dissolving or dispersing each of the above components in an organic solvent. Specifically, the slurry composition can be prepared by mixing each of the above components with a solvent using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or a film mix. In addition, examples of solvents that can be used in the preparation of the slurry composition include the same solvents that can be contained in the binder composition of the present invention. In addition, the solvent contained in the binder composition may be used as the solvent used in the preparation of the slurry composition.

[0077] (Positive electrode for non-aqueous secondary batteries) The positive electrode for a non-aqueous secondary battery of the present invention includes, for example, a current collector and a positive electrode mixture layer formed on the current collector, and the positive electrode mixture layer is formed using the slurry composition for a non-aqueous secondary battery positive electrode of the present invention. That is, the positive electrode mixture layer contains at least a positive electrode active material, a conductive material, and a polymer A. In addition, the positive electrode mixture layer may optionally contain a polymer B and other components described above. Note that each component contained in the positive electrode mixture layer is contained in the above-mentioned slurry composition, and the preferred ratio of each component is the same as the preferred ratio of each component in the slurry composition. The positive electrode for a nonaqueous secondary battery of the present invention is produced using a slurry composition containing the binder composition of the present invention. Therefore, by using the positive electrode for a nonaqueous secondary battery of the present invention, it is possible to make the secondary battery exhibit excellent battery characteristics such as excellent cycle characteristics.

[0078] <Method of manufacturing positive electrode for non-aqueous secondary battery> Here, the positive electrode for a secondary battery of the present invention can be manufactured, for example, through a step of applying the above-mentioned slurry composition onto a current collector (application step) and a step of drying the slurry composition applied onto the current collector to form a positive electrode composite layer on the current collector (drying step).

[0079] [Coating process] The method of applying the slurry composition on the current collector is not particularly limited, and any known method can be used. Specifically, the application method can be a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like. 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 according to the thickness of the positive electrode mixture layer obtained by drying.

[0080] Here, a material having electrical conductivity and electrochemical durability is used as the current collector to which the slurry composition is applied. Specifically, a current collector made of aluminum or an aluminum alloy can be used as the current collector. In this case, aluminum and an aluminum alloy may be used in combination, or different types of aluminum alloys may be used in combination. Aluminum and aluminum alloys are excellent current collector materials because they are heat resistant and electrochemically stable.

[0081] [Drying process] The method for drying the slurry composition on the current collector is not particularly limited and may be a known method, such as 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, a positive electrode mixture layer can be formed on the current collector, and a positive electrode for a secondary battery including the current collector and the positive electrode mixture layer can be obtained.

[0082] After the drying step, the positive electrode mixture layer may be subjected to a pressure treatment using a mold press, a roll press, etc. The pressure treatment can improve the adhesion between the positive electrode mixture layer and the current collector.

[0083] (Non-aqueous secondary battery) The nonaqueous secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte, and uses the positive electrode for a nonaqueous secondary battery of the present invention as the positive electrode. Since the nonaqueous secondary battery of the present invention includes the positive electrode for a nonaqueous secondary battery of the present invention, the secondary battery can exhibit excellent battery characteristics such as cycle characteristics. In the following, a case where the nonaqueous 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.

[0084] <Negative electrode> As the negative electrode, a known negative electrode can be used. Specifically, as the negative electrode, for example, a negative electrode made of a thin plate of metallic lithium or a negative electrode formed by forming a negative electrode mixture layer on a current collector can be used. The current collector may be made of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, or platinum. The negative electrode mixture layer may be a layer containing a negative electrode active material and a binder. The binder is not particularly limited, and any known material may be used.

[0085] <Electrolyte> As the electrolyte, an organic electrolyte in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte, for example, a lithium salt is used. As the lithium salt, for example, LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, (C2F5SO2)NLi, etc. are listed. Among them, LiPF6, LiClO4, and CF3SO3Li are preferred, and LiPF6 is particularly preferred, since they are easily dissolved in the solvent and show a high degree of dissociation. Note that one type of electrolyte may be used alone, or two or more types may be used in combination at any ratio. Usually, the lithium ion conductivity tends to be higher 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.

[0086] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte, but 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); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; and the like are preferably used. A mixture of these solvents may also be used. Among them, it is preferable to use carbonates because they have a high dielectric constant and a wide stable potential range, and it is more preferable to use a mixture of ethylene carbonate and ethyl methyl carbonate. Usually, the lower the viscosity of the solvent used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted by the type of solvent. The concentration of the electrolyte in the electrolytic solution can be appropriately adjusted, and is preferably 0.5 to 15 mass%, more preferably 2 to 13 mass%, and even more preferably 5 to 10 mass%. The electrolytic solution may contain known additives, such as fluoroethylene carbonate and ethyl methyl sulfone.

[0087] <separator> As the separator, 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 can reduce the thickness of the entire separator, thereby increasing the ratio of the positive electrode active material in the secondary battery and increasing the capacity per volume.

[0088] The nonaqueous secondary battery can be produced, for example, by stacking the positive electrode for the nonaqueous secondary battery of the present invention and the negative electrode via a separator, wrapping or folding the stack according to the battery shape as necessary, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the container. In addition, the nonaqueous secondary battery of the present invention may be provided with an overcurrent protection element such as a fuse or a PTC element, an expanded metal, a lead plate, or the like, as necessary, in order to prevent the occurrence of an internal pressure rise of the secondary battery, overcharging and overdischarging, and the like. 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 square type, a flat type, and the like. EXAMPLES

[0089] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" expressing amounts are based on mass unless otherwise specified. In addition, in a polymer produced by copolymerizing multiple types of monomers, the ratio of monomer units 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, the weight average molecular weight (Mw), number average molecular weight (Mn), molecular weight distribution (Mw / Mn), proportion of molecular weights less than 500,000, and degree of swelling in electrolyte of polymer A, as well as the peel strength of the positive electrode mixture layer, output characteristics, cycle characteristics, and high-temperature storage characteristics of the secondary battery were measured and evaluated by the following methods.

[0090] <Weight average molecular weight (Mw), number average molecular weight (Mn) and molecular weight distribution (Mw / Mn)> A portion of the polymer A prepared in each of the examples and comparative examples was sampled, and the weight average molecular weight (Mw) and number average molecular weight (Mn) of the polymer A were measured using gel permeation chromatography (GPC), and the molecular weight distribution (Mw / Mn) was calculated. Specifically, polymer A was adjusted to a solid content of 0.2% and passed through a 0.2 μm filter. The resulting solution was subjected to gel permeation chromatography (Tosoh, HLC-8220) using one "TSK guard column α" and two "TSKgel columin α-M" columns connected in series, and dimethylformamide was used as a solvent at a flow rate of 1.0 mL / min to determine the weight average molecular weight (Mw) and number average molecular weight (Mn) of polymer A in terms of standard polystyrene. The molecular weight distribution (Mw / Mn) was then calculated.

[0091] <Proportion of components with molecular weight less than 500,000> A chromatograph of polymer A was obtained using a gel permeation chromatograph (HLC-8220, manufactured by Tosoh Corporation) and tetrahydrofuran as a developing solvent. From the obtained chromatogram, the total peak area (A) and the total peak area (X) of components having a molecular weight of less than 500,000 were calculated. The proportion of components having a molecular weight of less than 500,000 in polymer A was calculated using the following formula. Percentage of components with molecular weight less than 500,000 (%) = (X / A) x 100

[0092] <Electrolyte swelling rate> The NMP dispersion containing the polymer A prepared in the examples and comparative examples was formed into a film having a thickness of 2±0.5 mm, dried in a vacuum dryer at a temperature of 120° C. for 2 hours, and then cut and weighed to about 1 g. The obtained film piece was used as a test piece, and the mass of this film piece was W0. This film piece was immersed in an electrolyte solution [composition: LiPF6 solution with a concentration of 1.0 mol (solvent is a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume mixing ratio: ethylene carbonate / ethyl methyl carbonate = 3 / 7)) and 2 volume% vinylene carbonate (solvent ratio) was added as an additive] in an environment at a temperature of 60° C. for 72 hours (3 days) to swell. Thereafter, the film piece was pulled up, the electrolyte solution on the surface was lightly wiped off, and the mass was measured. The mass of the film piece after swelling was W1. The degree of swelling due to the electrolyte was calculated using the following formula. Electrolyte swelling rate (%) = (W1 / W0) x 100

[0093] <Peel strength of positive electrode mixture layer> The positive electrodes for lithium ion secondary batteries prepared in the examples and comparative examples were cut into a rectangle of 100 mm in length and 10 mm in width to prepare test pieces, and cellophane tape (compliant with JIS Z1522) was attached to the surface of the positive electrode composite layer with the surface having the positive electrode composite layer facing down, and one end of the current collector was pulled vertically and peeled off at a speed of 100 mm / min to measure the stress (the cellophane tape was fixed to the test table). The measurement was performed three times, and the average value was calculated as the peel strength, which was evaluated according to the following criteria. The larger the peel strength value, the stronger the adhesion between the positive electrode composite layer and the current collector, and the higher the peel strength of the positive electrode composite layer. A: Peel strength is 40N / m or more B: Peel strength is 30N / m or more and less than 40N / m C: Peel strength is 20N / m or more and less than 30N / m D: Peel strength is less than 20N / m

[0094] <Output characteristics of secondary batteries> The lithium ion secondary batteries prepared in the examples and comparative examples were left to stand at 25°C for 5 hours after injecting the electrolyte. Next, the batteries were charged to a cell voltage of 3.65V at a constant current of 0.2C at 25°C, and then aged at 60°C for 12 hours. Then, the batteries were discharged to a cell voltage of 3.00V at a constant current of 0.2C at 25°C. Then, CC-CV charging (upper cell voltage 4.20V) was performed at a constant current of 0.2C, and CC discharging was performed at a constant current of 0.2C to a cell voltage of 3.00V. This charging and discharging at 0.2C was repeated three times. Next, in an environment at a temperature of 25°C, constant current charging and discharging was performed at 0.2C between cell voltages of 4.20-3.00V, and the discharge capacity at this time was defined as C0. Thereafter, similarly, CC-CV charging was performed at a constant current of 0.2C, and CC discharging was performed at a constant current of 2.0C to 3.00V in an environment at a temperature of 25°C, and the discharge capacity at this time was defined as C1. Then, the ratio (%) of the discharge capacity (C1) at 2.0C to the discharge capacity (C0) at 0.2C, which is represented by (C1 / C0) x 100 (%), was calculated as the capacity retention rate, and was evaluated according to the following criteria. The larger the capacity retention rate, the smaller the decrease in discharge capacity at high current and the lower the internal resistance (i.e., the better the output characteristics). A: Capacity retention rate is 75% or more B: Capacity retention rate is 73% or more but less than 75% C: Capacity retention rate is 70% or more but less than 73% D: Capacity retention rate is less than 70%

[0095] <Cycle characteristics> Ten lithium ion secondary batteries prepared in the examples and comparative examples were repeatedly charged to 4.3 V by a constant current method of 0.2 C in an atmosphere at 60° C., and discharged to 3.0 V, and the electric capacity was measured. The average value of the 10 cells was taken as the measured value, and the charge / discharge capacity retention rate, which is expressed as the ratio (%) of the electric capacity at the end of 50 cycles to the electric capacity at the end of 5 cycles, was calculated and used as the evaluation standard for cycle characteristics. A higher value of the charge / discharge capacity retention rate indicates better cycle characteristics. A: Charge / discharge capacity retention rate is 80% or more B: Charge / discharge capacity retention rate is 70% or more but less than 80% C: Charge / discharge capacity retention is 50% or more but less than 70% D: Charge / discharge capacity retention is 30% or more but less than 50%

[0096] <High temperature storage characteristics> The lithium ion secondary battery produced in the examples and comparative examples was left at rest for 5 hours at a temperature of 25°C after injecting the electrolyte. Next, the battery was charged to a cell voltage of 3.65V at a constant current of 0.2C at a temperature of 25°C, and then aged for 12 hours at a temperature of 60°C. Then, the battery was discharged to a cell voltage of 3.00V at a constant current of 0.2C at a temperature of 25°C. Then, the battery was CC-CV charged (upper limit cell voltage 4.20V) at a constant current of 0.2C, and CC discharged to a cell voltage of 3.00V at a constant current of 0.2C. This charge and discharge at 0.2C was repeated three times. The third discharge capacity at 0.2C was taken as the initial capacity Cx. Then, the battery was CC-CV charged (upper limit cell voltage 4.20V) at a constant current of 0.2C. The lithium ion secondary battery was then stored for 4 weeks in an inert oven with a nitrogen atmosphere at 60°C in the treatment chamber. Thereafter, the cell was discharged at a constant current of 0.2 C until the cell voltage reached 3.00 V, and the discharge capacity at this time was taken as Cy. The high-temperature capacity retention rate, expressed as (Cy / Cx) x 100 (%), was calculated and evaluated according to the following criteria. A higher high-temperature capacity retention rate indicates less degradation of the lithium-ion battery during high-temperature storage (i.e., better high-temperature storage characteristics). A: High temperature capacity retention rate is 80% or more B: High temperature capacity retention rate is 75% or more and less than 80% C: High-temperature capacity retention is 70% or more and less than 75% D: High temperature capacity retention rate is less than 70%

[0097] Example 1 <Preparation of Polymer A> 41.3 mg (0.25 mmol) of 2,2'-azobis(isobutyronitrile) as an azo-based polymerization initiator and 32.4 mg (0.13 mmol) of ethyl 2-(methyltellanyl)isobutyrate as an organic tellurium compound were weighed into a glass reactor, and a stirrer was placed in the glass reactor. Next, 300 g of dimethyl sulfoxide as an organic solvent, 95 parts (1.8 mol) of acrylonitrile as a nitrile group-containing monomer, and 1 part (11.6 mmol) of methacrylic acid as a carboxylic acid group-containing monomer were added, and the temperature was raised to 60°C, and the mixture was stirred at 60°C to carry out the first stage polymerization reaction. After the polymerization reaction started, the viscosity of the solution gradually increased. Then, the polymerization reaction was continued for 15 hours to obtain a block copolymer of polyacrylonitrile and methacrylic acid having a tellurium functional group at the end. Thereafter, the glass reactor was depressurized and the temperature was maintained at 60° C. for 24 hours to distill off unreacted acrylonitrile. Next, 4 parts (31.2 mmol) of n-butyl acrylate as a (meth)acrylic acid ester monomer was further added to the above glass reactor, and the mixture was stirred at a temperature of 60°C to carry out a second-stage polymerization reaction. The polymerization reaction was continued for 24 hours to obtain a dimethyl sulfoxide solution containing a block copolymer of polyacrylonitrile, methacrylic acid, and n-butyl acrylate as polymer A. The dimethyl sulfoxide solution containing the polymer A was coagulated with a large amount of ion-exchanged water, washed, and vacuum dried at 60° C. for 24 hours to obtain a block copolymer of polyacrylonitrile, methacrylic acid, and n-butyl acrylate as the polymer A. The yield of the obtained polymer A was 65 g (yield 65%). The weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the obtained polymer A and the proportion of components of the polymer A having a molecular weight of less than 500,000 are shown in Table 1.

[0098] <Preparation of Positive Electrode Slurry Composition> [Premixing process] For the disperser, one CNT was used as a conductive material (specific surface area measured according to the BET method: 150 m 20.06 parts in terms of solids of 100 parts by mass of 1000 g / g) and a hydrogenated acrylonitrile-butadiene rubber solution as polymer B (manufactured by Zeon Corporation, "BM720-H") were added, and further, NMP as an organic solvent was added so that the solids concentration was 4%, and the mixture was stirred and mixed at a temperature of 25±3°C and a rotation speed of 3000 rpm for 10 minutes to obtain a premixture.

[0099] [Main mixing process] The premix obtained in the above process was mixed with a lithium-containing composite oxide of Co-Ni-Mn (NCM622, LiNi 5 / 10 Co 2 / 10 Mn 3 / 10 97 parts of ethyl alcohol (O2), 0.5 parts (solids content equivalent) of acetylene black (manufactured by Denka Company, Limited, "Denka Black (registered trademark)") as a conductive material, and 1.5 parts (solids content equivalent) of Polymer A adjusted with NMP to a solids concentration of 6% were added and mixed by stirring at a temperature of 25±3°C and a rotation speed of 50 rpm to obtain a positive electrode slurry composition having a viscosity of 3,600 mPa s as measured using a B-type viscometer at 60 rpm (rotor M4) and 25±3°C.

[0100] <Preparation of positive electrode> The slurry composition for positive electrodes obtained as described above was applied to a 20 μm-thick aluminum foil current collector with a comma coater in an amount of 20±0.5 mg / cm. 2 The coating was applied so that the result was as follows. The positive electrode slurry composition on the aluminum foil was dried by transporting the aluminum foil at a speed of 300 mm / min through an oven at a temperature of 90° C. for 2 minutes and then through an oven at a temperature of 110° C. for 2 minutes, thereby obtaining a positive electrode raw sheet in which a positive electrode composite layer was formed on the current collector. Thereafter, the positive electrode composite layer side of the prepared positive electrode blank was roll-pressed under conditions of a temperature of 25±3°C and a linear pressure of 14 tonnes, so that the density of the positive electrode composite layer became 3.30 g / cm 3 The positive electrode thus obtained was subjected to the peel strength evaluation of the positive electrode mixture layer according to the above-mentioned method. The results are shown in Table 1.

[0101] <Preparation of binder composition for negative electrode> In a 5MPa pressure vessel equipped with a stirrer, 65 parts of styrene, 35 parts of 1,3-butadiene, 2 parts of itaconic acid, 1 part of 2-hydroxyethyl acrylate, 0.3 parts of t-dodecyl mercaptan as a molecular weight regulator, 5 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 1 part of potassium persulfate as a polymerization initiator were added, thoroughly stirred, and then heated to a temperature of 55°C to initiate polymerization. When the monomer consumption reached 95.0%, the reaction was stopped by cooling. A 5% aqueous solution of sodium hydroxide was added to the aqueous dispersion containing the polymer thus obtained, and the pH was adjusted to 8. Thereafter, unreacted monomers were removed by heating and reduced pressure distillation. Thereafter, the temperature was cooled to 30°C or less to obtain an aqueous dispersion containing a binder composition for a negative electrode.

[0102] <Preparation of Slurry Composition for Negative Electrode> Into a planetary mixer, 48.75 parts of artificial graphite (theoretical capacity: 360mAh / g) as a negative electrode active material, 48.75 parts of natural graphite (theoretical capacity: 360mAh / g), and 1 part of carboxymethylcellulose as a thickener in terms of solid content were added. Further, the mixture was diluted with ion-exchanged water so that the solid content concentration was 60%, and then kneaded for 60 minutes at a rotation speed of 45 rpm. Then, 1.5 parts of the negative electrode binder composition obtained above in terms of solid content were added, and kneaded for 40 minutes at a rotation speed of 40 rpm. Then, ion-exchanged water was added so that the viscosity was 3000±500mPa·s (measured with a B-type viscometer at 25°C and 60 rpm), to prepare a negative electrode slurry composition.

[0103] <Preparation of negative electrode> The negative electrode slurry composition was applied to the surface of a 15 μm-thick copper foil current collector with a comma coater in an amount of 11±0.5 mg / cm 2 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, thereby drying the negative electrode slurry composition on the copper foil and obtaining a negative electrode raw sheet having a negative electrode mixture layer formed on a current collector. Thereafter, the negative electrode composite layer side of the produced negative electrode blank was roll-pressed under conditions of a temperature of 25±3°C and a linear pressure of 11 t (tons) to obtain a negative electrode composite layer density of 1.60 g / cm 3 A negative electrode of 1000 nm was obtained.

[0104] <Preparation of separator for secondary battery> A single-layer polypropylene separator (manufactured by Celgard, "#2500") was used.

[0105] <Production of lithium-ion secondary battery> Using the above negative and positive electrodes and separators, a single-layer laminate cell (equivalent to an initial design discharge capacity of 40 mAh) was fabricated and placed in an aluminum package. Then, a 1.0 M LiPF6 solution (solvent: a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio), containing 2 volume% vinylene carbonate (solvent ratio) as an additive) was filled in as an electrolyte. Furthermore, in order to seal the opening of the aluminum package, the aluminum package was closed by heat sealing at a temperature of 150°C, and a lithium-ion secondary battery was produced. The output characteristics, cycle characteristics, and high-temperature storage characteristics of this lithium-ion secondary battery were evaluated as described above. The results are shown in Table 1.

[0106] Example 2 A slurry composition for a positive electrode, a positive electrode, a binder composition for a negative electrode, a slurry composition for a negative electrode, a negative electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1, except that 4 parts of styrene were used as an aromatic vinyl monomer instead of n-butyl acrylate as a (meth)acrylic acid ester monomer during the preparation of polymer A. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0107] Example 3 A positive electrode slurry composition, a positive electrode, a negative electrode binder composition, a negative electrode slurry composition, a negative electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1, except that 4 parts of 2-ethylhexyl acrylate was used instead of n-butyl acrylate as the (meth)acrylic acid ester monomer during the preparation of polymer A. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0108] Example 4 In preparing polymer A, 1 part of acrylic acid was used instead of methacrylic acid as a carboxylic acid group-containing monomer, and 4 parts of acrylamide as a (meth)acrylamide monomer was used instead of n-butyl acrylate as a (meth)acrylic acid ester monomer, in the same manner as in Example 1. A positive electrode slurry composition, a positive electrode, a negative electrode binder composition, a negative electrode slurry composition, a negative electrode, and a lithium ion secondary battery were produced. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0109] Example 5 In preparing polymer A, the amount of acrylonitrile as a nitrile group-containing monomer was changed to 82 parts, and the amount of n-butyl acrylate as a (meth)acrylic acid ester monomer was changed to 17 parts, but the same procedure as in Example 1 was followed to prepare a positive electrode slurry composition, a positive electrode, a negative electrode binder composition, a negative electrode slurry composition, a negative electrode, and a lithium ion secondary battery. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0110] Example 6 A slurry composition for a positive electrode, a positive electrode, a binder composition for a negative electrode, a slurry composition for a negative electrode, a negative electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1, except that the reaction temperature was 40° C. and the reaction time was 15 hours during the preparation of polymer A. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0111] Example 7 A slurry composition for a positive electrode, a positive electrode, a binder composition for a negative electrode, a slurry composition for a negative electrode, a negative electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1, except that the reaction temperature was 65° C. and the reaction time was 20 hours during the preparation of polymer A. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0112] Example 8 In preparing polymer A, the amount of acrylonitrile as a nitrile group monomer was changed to 80 parts, and the amount of 2-ethylhexyl acrylate as a (meth)acrylic acid ester monomer was changed to 19 parts, but the same procedure as in Example 3 was followed to prepare a positive electrode slurry composition, a positive electrode, a negative electrode binder composition, a negative electrode slurry composition, a negative electrode, and a lithium ion secondary battery. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0113] Example 9 In preparing the polymer A, methacrylic acid was not used as a carboxylic acid group-containing monomer, and the amount of n-butyl acrylate as a (meth)acrylic acid ester monomer was changed to 5 parts, in the same manner as in Example 1. A positive electrode slurry composition, a positive electrode, a negative electrode binder composition, a negative electrode slurry composition, a negative electrode, and a lithium ion secondary battery were produced. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0114] Comparative Example 1 A positive electrode slurry composition, a positive electrode, a negative electrode binder composition, a negative electrode slurry composition, a negative electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1, except that polymer A prepared as follows was used. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 2. <Preparation of Polymer A> In a pressure vessel equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen gas inlet tube, 400 parts of ion-exchanged water were charged, and while gently rotating the stirrer, the pressure was reduced (-600 mmHg) and normalized with nitrogen gas three times. Then, using a dissolved oxygen meter, it was confirmed that the oxygen concentration in the gas phase of the reaction vessel was 1% or less and that the dissolved oxygen in the water was 1 ppm or less. After that, 0.2 parts of partially saponified polyvinyl alcohol (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., "Gosenol GH-20" (saponification degree 86.5 mol% to 89.0 mol%)) was gradually added as a dispersant and dispersed well, and then the temperature was gradually raised to 60°C while stirring was continued and maintained for 30 minutes to dissolve the partially saponified polyvinyl alcohol. Next, under the condition of a nitrogen gas flow rate of 0.5 ml / min, 85 parts of acrylonitrile as a nitrile group-containing monomer, 5 parts of methacrylic acid as a carboxylic acid group-containing monomer, and 0.2 parts of t-dodecyl mercaptan as a molecular weight regulator were charged, stirred and mixed, and kept at 60±2°C. A solution in which 0.4 parts of 1,1-azobis(1-acetoxy-1-phenylethane) (manufactured by Otsuka Chemical Co., Ltd., "OTAZO-15"; abbreviated as OT Azo-15) which is an oil-soluble polymerization initiator was dissolved in 10 parts of acrylonitrile which is a nitrile group-containing monomer was added thereto, and the reaction was started. After the reaction was allowed to proceed for 3 hours at 60±2°C, the reaction was continued for another 2 hours at 70±2°C, and the reaction was allowed to proceed for another 2 hours at 80±2°C. The mixture was then cooled to 40°C or less to obtain polymer particles. The obtained polymer particles were collected on a 200 mesh filter cloth, washed three times with 100 parts of ion-exchanged water, and then dried under reduced pressure at 70° C. for 12 hours for isolation and purification, thereby obtaining Polymer A.

[0115] Comparative Example 2 In preparing polymer A, the amount of acrylonitrile group as a nitrile group-containing monomer was changed to 60 parts, methacrylic acid as a carboxylic acid group-containing monomer was not used, and the amount of n-butyl acrylate as a (meth)acrylic acid ester monomer was changed to 40 parts. In the same manner as in Example 1, except that, a positive electrode slurry composition, a positive electrode, a negative electrode binder composition, a negative electrode slurry composition, a negative electrode, and a lithium ion secondary battery were produced. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0116] Comparative Example 3 In preparing polymer A, the amount of acrylonitrile as a nitrile group-containing monomer was changed to 80 parts, and the amount of n-butyl acrylate as a (meth)acrylic acid ester monomer was changed to 20 parts, except that the same procedure as in Comparative Example 2 was followed to prepare a positive electrode slurry composition, a positive electrode, a negative electrode binder composition, a negative electrode slurry composition, a negative electrode, and a lithium ion secondary battery. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0117] Comparative Example 4 In preparing polymer A, the amount of acrylonitrile as a nitrile group-containing monomer was changed to 85 parts, and 10 parts of methacrylic acid and 5 parts of acrylic acid were used as carboxylic acid group-containing monomers. The same procedure as in Example 1 was followed to prepare a positive electrode slurry composition, a positive electrode, a negative electrode binder composition, a negative electrode slurry composition, a negative electrode, and a lithium ion secondary battery. Various measurements and evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

[0118] In addition, in Table 1 shown below, "AN" indicates acrylonitrile, "MAA" stands for methacrylic acid; "AA" represents acrylic acid, "BA" indicates n-butyl acrylate; "2-EHA" indicates 2-ethylhexyl acrylate, "ST" stands for styrene. "Aam" indicates acrylamide, "CNT" stands for carbon nanotube. "AceB" stands for acetylene black. "NCM" refers to a lithium-containing composite oxide of Co-Ni-Mn as the positive electrode active material.

[0119] [Table 1]

[0120] [Table 2]

[0121] From Table 1, it can be seen that in Examples 1 to 9, which use a binder composition containing polymer A having a content of nitrile group-containing monomer units of 80.0 mass% or more and 99.9 mass% or less, a weight average molecular weight (Mw) of 700,000 or more and 2,000,000 or less, and a proportion of components having a molecular weight of less than 500,000 being less than 30%, the peel strength of the positive electrode mixture layer can be increased, and the output characteristics, cycle characteristics, and high-temperature storage characteristics of the secondary battery can be improved. Furthermore, Table 2 shows that in Comparative Example 1, in which the proportion of components in polymer A having a molecular weight of less than 500,000 exceeds 30%, and in Comparative Example 4, in which the proportion of components in polymer A having a molecular weight of less than 500,000 is 30%, the cycle characteristics and high-temperature storage characteristics of the secondary battery can be improved, but the peel strength of the positive electrode composite layer and the output characteristics of the secondary battery cannot be improved. Furthermore, Table 2 shows that in Comparative Example 2, in which the proportion of nitrile group-containing monomer units contained in Polymer A is less than 80 mass%, the peel strength of the electrode mixture layer can be increased, but the output characteristics, cycle characteristics, and high-temperature storage characteristics of the secondary battery cannot be improved. Furthermore, Table 2 shows that in Comparative Example 3, in which the weight-average molecular weight of polymer A is less than 700,000, the cycle characteristics of the secondary battery can be improved, but the peel strength of the positive electrode composite layer cannot be increased, and the output characteristics and high-temperature storage characteristics of the secondary battery cannot be improved. [Industrial Applicability]

[0122] According to the present invention, it is possible to provide a binder composition for a non-aqueous secondary battery electrode and a slurry composition for a non-aqueous secondary battery positive electrode, which are capable of forming an electrode mixture layer having excellent peel strength and enabling a non-aqueous secondary battery to exhibit good cycle characteristics. Furthermore, according to the present invention, it is possible to provide a positive electrode for a non-aqueous secondary battery, which has an excellent peel strength of a positive electrode mixture layer and is capable of causing the non-aqueous secondary battery to exhibit good cycle characteristics. Furthermore, according to the present invention, a nonaqueous secondary battery having excellent battery characteristics such as cycle characteristics can be provided.

Claims

1. A binder composition for a non-aqueous secondary battery positive electrode, comprising polymer A, The polymer A contains nitrile group-containing monomer units in a ratio of 80.0% by mass or more and 99.9% by mass or less, and further contains at least one of a carboxylic acid group-containing monomer unit and a (meth)acrylic acid ester monomer unit, The content ratio of other monomer units in the polymer A is 0 mass%; The weight average molecular weight (Mw) of the polymer A is 700,000 or more and 2,000,000 or less, A binder composition for a non-aqueous secondary battery positive electrode, wherein the proportion of components in the polymer A having a molecular weight of less than 500,000 is less than 27%.

2. The binder composition for a non-aqueous secondary battery positive electrode according to claim 1 , wherein the molecular weight distribution (Mw / Mn) of the polymer A is less than 3.

0.

3. The degree of swelling of the polymer A in an electrolyte solution is 120% by mass or more and 250% by mass or less, The degree of swelling in an electrolyte solution is calculated by (W1 / W0)×100, using a mass W0 of a test piece prepared by drying an N-methyl-2-pyrrolidone dispersion of the polymer A at a temperature of 120° C. for 2 hours and a mass W1 of the test piece after immersing the test piece in an electrolyte solution at a temperature of 60° C. for 72 hours, The electrolyte was a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio: ethylene carbonate / ethyl methyl carbonate=3 / 7) and LiPF ６ The binder composition for a positive electrode of a nonaqueous secondary battery according to claim 1 or 2, which is a solution obtained by dissolving the above in a concentration of 1.0 mol / L in the mixed solvent.

4. A slurry composition for a non-aqueous secondary battery positive electrode, comprising a positive electrode active material, a conductive material, and the binder composition for a non-aqueous secondary battery positive electrode according to any one of claims 1 to 3.

5. A positive electrode for a non-aqueous secondary battery comprising a positive electrode mixture layer formed using the slurry composition for a non-aqueous secondary battery positive electrode according to claim 4.

6. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, The positive electrode is the positive electrode for a nonaqueous secondary battery according to claim 5 .

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