Binder composition for nonaqueous secondary battery electrode, composition for nonaqueous secondary battery electrode, nonaqueous secondary battery electrode, and nonaqueous secondary battery

Abstract

A binder composition for a nonaqueous secondary battery electrode, including a copolymer, wherein the copolymer includes: 30-95 mass% a structural unit (a) derived from a (meth)acrylamide monomer; 1-60 mass% a structural unit (b) derived from a (meth)acrylic acid ester monomer; and 0.1-5 mass% a structural unit (c) derived from an acid-radical-containing monomer.

Description

Binder composition for non-aqueous secondary battery electrodes, composition for non-aqueous secondary battery electrodes, non-aqueous secondary battery electrodes and non-aqueous secondary battery

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

[0002] Non-aqueous secondary batteries (non-aqueous electrolyte secondary batteries), such as lithium-ion secondary batteries, are small, lightweight, have high energy density, and can be repeatedly charged and discharged, making them suitable for a wide range of applications. In recent years, with the advancement of high performance and miniaturization in various portable electronic and communication devices, there has been a growing demand for secondary batteries that are small, lightweight, have higher capacity, and exhibit further improvements in various battery characteristics such as cycle characteristics and discharge rate characteristics. To further enhance the performance of non-aqueous secondary batteries, improvements to various battery components such as electrodes are being considered.

[0003] Here, the electrodes of a non-aqueous secondary battery typically comprise a current collector and an electrode composite layer formed on the current collector. This electrode composite layer is prepared, for example, using a slurry composition obtained by dispersing a binder composition containing a binder and an electrode active material, etc., in a solvent.

[0004] Fluorine-based resins, such as polyvinylidene fluoride (PVDF) resin, are primarily used as binders for the electrodes of lithium-ion secondary batteries. However, fluorine-based resins decompose at high temperatures, and the released fluorine reacts violently with lithium, which has been pointed out as a safety concern. Furthermore, when using PVDF resin as a binder, organic solvents such as NMP are generally used as solvents for slurrying. However, from the perspectives of environmental considerations, worker safety, and cost, there is a demand for water-based binders that can be slurryed with aqueous solvents.

[0005] As an aqueous binder other than PVDF, for example, Patent Document 1 discloses the use of carboxymethylcellulose and styrene-butadiene rubber as binders. Furthermore, Patent Document 2 discloses a binder for a lithium-ion secondary battery negative electrode, which includes an emulsion in which particles containing a dispersant (A) and a dispersed phase (B) are dispersed in an aqueous dispersion medium, wherein the dispersant (A) is a polyvinyl alcohol-based resin having specific structural units, and the dispersed phase (B) is a polymer having structural units derived from a nitrile monomer. Furthermore, Patent Document 3 discloses a binder composition for non-aqueous secondary battery electrodes comprising polymer X, wherein polymer X contains 3% by mass or more and 20% by mass or less of acidic group-containing monomer units, 5% by mass or more and less than 50% by mass of repeating units derived from unsaturated monomer A, the solubility of the unsaturated monomer A in water is 1 g / 100 mL or more and 15 g / 100 mL or less, and the glass transition temperature of the unsaturated monomer A is 40°C or lower.

[0006] Japanese Patent Publication No. 4-342966, Japanese Patent Publication No. 2014-209469, International Publication No. 2024 / 070249

[0007] However, in the technology described in Patent Document 1, although the binder has good electrolyte resistance, the stability of the electrode active material in the slurry is low, and the electrode active material tends to settle. Low slurry stability makes it difficult to uniformly coat the slurry onto the current collector, for example, which leads to a decrease in battery characteristics such as cycle characteristics. Furthermore, the binder for lithium-ion secondary battery negative electrodes described in Patent Document 2 has good electrolyte resistance and, in addition, excellent stability of the electrode active material in the slurry. However, this binder has poor adhesion to the current collector, and secondary batteries made using this binder have poor cycle characteristics. Furthermore, the binder composition for non-aqueous secondary battery electrodes described in Patent Document 3 has high flexibility and excellent adhesion to the current collector, but there is room for improvement in terms of improving the cycle characteristics of non-aqueous secondary batteries made using this binder composition.

[0008] Therefore, the present invention aims to provide a binder composition for non-aqueous secondary battery electrodes that can form an electrode composition with excellent stability and a non-aqueous secondary battery with excellent cycle characteristics. Furthermore, the present invention aims to provide a non-aqueous secondary battery electrode that is both stable and capable of forming a non-aqueous secondary battery with excellent cycle characteristics, and a non-aqueous secondary battery with excellent cycle characteristics.

[0009] As a result of diligent research, the present inventors have found that the above problem can be solved by using a binder composition containing a copolymer that contains constituent units derived from (meth)acrylamide monomers, constituent units derived from (meth)acrylic acid ester monomers, and constituent units derived from acid group-containing monomers in predetermined proportions.

[0010] In other words, the present invention relates to the following: [1] A binder composition for a non-aqueous secondary battery electrode comprising a copolymer, wherein the copolymer comprises 30% by mass or more and 95% by mass or less of a constituent unit (a) derived from a (meth)acrylamide monomer, 1% by mass or more and 60% by mass or less of a constituent unit (b) derived from a (meth)acrylic acid ester monomer, and 0.1% by mass or more and 5% by mass or less of a constituent unit (c) derived from an acid group-containing monomer. [2] The binder composition for a non-aqueous secondary battery electrode according to [1], comprising 50% by mass or more and 95% by mass or less of the constituent unit (a) derived from the (meth)acrylamide monomer. [3] The binder composition for a non-aqueous secondary battery electrode according to [1] or [2], comprising 0.1% by mass or more and less than 3% by mass of the constituent unit (c) derived from the acid group-containing monomer. [4] A binder composition for non-aqueous secondary battery electrodes according to any one of [1] to [3], comprising a constituent unit (b) derived from the (meth)acrylic acid ester monomer, comprising a constituent unit (b) derived from at least one monomer selected from the group consisting of alkyl (meth)acrylic acid esters having an alkyl group having 1 to 3 carbon atoms, alkoxyalkyl (meth)acrylic acid esters having an alkoxyalkyl group having 1 to 3 carbon atoms, and hydroxyalkyl (meth)acrylic acid esters having a hydroxyalkyl group having 1 to 3 carbon atoms. [5] A binder composition for non-aqueous secondary battery electrodes according to any one of [1] to [4], wherein at least a portion of the acid groups contained in the copolymer are neutralized with a basic compound. [6] A film formed from the copolymer is subjected to a carbonate-based mixed solvent (EC (ethylene carbonate) / DMC (dimethyl carbonate) / MEC (ethyl methyl carbonate) / FEC (4-fluoroethylene carbonate) / VC (vinylene carbonate) / LiPF ６[1] to [5] The non-aqueous secondary battery electrode binder composition, wherein the swelling rate after immersion in (lithium hexafluoride phosphate) = 29 / 24 / 30 / 5 / 1 / 11 (wt)) at 60°C for 72 hours is 5% by mass or less. [7] A non-aqueous secondary battery electrode composition comprising an electrode active material, a conductive material, and the non-aqueous secondary battery electrode binder composition according to any one of items [1] to [6]. [8] A non-aqueous secondary battery electrode comprising a negative electrode composite layer formed using the non-aqueous secondary battery electrode composition according to [7]. [9] A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode according to [8] and an electrolyte.

[0011] According to the present invention, an electrode composition with excellent stability and a binder composition for non-aqueous secondary battery electrodes capable of forming a non-aqueous secondary battery with excellent cycle characteristics can be obtained. Furthermore, according to the present invention, a non-aqueous secondary battery electrode capable of forming a non-aqueous secondary battery with excellent stability and excellent cycle characteristics can be obtained. Moreover, according to the present invention, a non-aqueous secondary battery electrode capable of forming a non-aqueous secondary battery with excellent cycle characteristics can be obtained, and a non-aqueous secondary battery with excellent cycle characteristics can be obtained.

[0012] Embodiments of the present invention will be described below. It should be understood that the present invention is not limited to the embodiments described below, but also includes various modifications that do not alter the essence of the invention.

[0013] In this specification, numerical ranges described as "X to Y" are interpreted as including the numerical value X as the lower limit and the numerical value Y as the upper limit.

[0014] In this specification, "(meth)acrylic acid" means either or both methacrylic acid and acrylic acid. "(meth)acrylate" means either or both methacrylate and acrylate. "(meth)acrylamide" means either or both methacrylamide and acrylamide.

[0015] In this specification, "derivative" means a compound obtained by substituting one or more hydrogen atoms in the original compound with groups other than hydrogen atoms (substituents).

[0016] In this specification, in a copolymer produced by copolymerizing two or more kinds of monomers, the proportion of a structural unit formed by polymerizing a certain monomer in the copolymer usually coincides with the ratio (charging ratio) of the mass of the certain monomer to the mass of all the monomers used for the polymerization of the copolymer, unless otherwise specified. The proportion of each structural unit constituting the copolymer can also be measured by performing NMR measurement on the copolymer.

[0017] In this specification, the "non-aqueous secondary battery" means including a non-aqueous electrolyte secondary battery and an all-solid-state secondary battery. The "non-aqueous electrolyte" means an electrolyte substantially free of water. The "electrolyte substantially free of water" means that the concentration of water in the electrolyte is preferably 200 ppm (mass basis) or less, more preferably 100 ppm or less. The "all-solid-state secondary battery" means a secondary battery using a solid electrolyte such as an inorganic solid electrolyte or a solid polymer electrolyte without using a liquid as the electrolyte.

[0018] <<Binder Composition for Non-Aqueous Secondary Battery Electrodes>> The binder composition for non-aqueous secondary battery electrodes according to this embodiment (hereinafter also referred to as "binder composition") contains a copolymer containing 30% by mass or more and 95% by mass or less of a structural unit (a) derived from a (meth)acrylamide monomer, 1% by mass or more and 60% by mass or less of a structural unit (b) derived from a (meth)acrylate monomer, and 0.1% by mass or more and 5% by mass or less of a structural unit (c) derived from an acid group-containing monomer.

[0019] <Copolymer> The copolymer that constitutes the binder composition of the present embodiment contains 30% by mass or more and 95% by mass or less of a structural unit (a) derived from a (meth)acrylamide monomer, 1% by mass or more and 60% by mass or less of a structural unit (b) derived from a (meth)acrylate monomer, and 0.1% by mass or more and 5% by mass or less of a structural unit (c) derived from an monomer containing an acid group-containing monomer. By containing the copolymer in the binder composition of the present embodiment, a non-aqueous secondary battery electrode composition excellent in stability and a non-aqueous secondary battery excellent in cycle characteristics (hereinafter, also simply referred to as "secondary battery") can be formed. The reason for obtaining such an effect is not clear, but when the copolymer contains the structural unit (a) derived from the (meth)acrylamide monomer within the above range, strong intermolecular forces derived from the amide group act, and the cohesiveness of the copolymer increases. Therefore, it is presumed that the copolymer easily covers the surface of the electrode active material and exhibits excellent binding properties. In addition, it is considered that when the intermolecular force acts, it becomes difficult for the solvent to penetrate between the copolymers, the swelling property with respect to the electrolytic solution decreases, and the cycle characteristics of the secondary battery can be improved. Furthermore, by containing the structural unit (b) derived from the (meth)acrylate monomer within the above range, the flexibility of the copolymer can be increased without reducing the intermolecular force, and it is considered that the adhesion to the current collector is improved. Also, by setting the content of the structural unit (c) derived from the acid group-containing monomer within the above range, it is considered that excellent stability is exhibited when used as an electrode composition. Hereinafter, the structural units constituting the copolymer will be described.

[0020] (Constituent units (a) derived from (meth)acrylamide monomer) The copolymer contains constituent units (a) derived from (meth)acrylamide monomer. The copolymer contains constituent units (a) derived from (meth)acrylamide monomer, which improves the cohesiveness of the copolymer. As a result, the copolymer can easily coat the surface of the electrode active material well, improving the adhesion between the electrode composite layer and the current collector in electrodes made using the binder composition of this embodiment, and improving the cycle characteristics of secondary batteries equipped with such electrodes. In addition, the copolymer contains constituent units (a) derived from (meth)acrylamide monomer, which improves the dispersibility of electrode active materials and the like in electrode compositions made using the binder composition of this embodiment.

[0021] The (meth)acrylamide monomer that can form the constituent unit (a) derived from the (meth)acrylamide monomer is not particularly limited as long as it is a monomer having a (meth)acrylamide group. Specifically, examples of the (meth)acrylamide monomer include monoalkyl (meth)acrylamides such as (meth)acrylamide, N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-propyl (meth)acrylamide, and N-isopropyl (meth)acrylamide; dialkyl (meth)acrylamides such as N,N-dimethyl (meth)acrylamide and N,N-diethyl (meth)acrylamide; N-(hydroxyalkyl) (meth)acrylamides such as N-(2-hydroxymethyl) (meth)acrylamide, N-(2-hydroxyethyl) (meth)acrylamide, N-(2-hydroxypropyl) (meth)acrylamide, and N-(2-hydroxybutyl) (meth)acrylamide; diacetone (meth)acrylamide; acryloylmorpholine; and the like. These may be used individually or in combination of two or more. Among these, from the viewpoint of improving the cohesiveness of the copolymer and the stability of the electrode composition made using the binder composition of this embodiment, as well as the dispersibility of electrode active materials, it is preferable that the constituent unit (a) includes a constituent unit derived from at least one monomer selected from the group consisting of (meth)acrylamide, N-(2-hydroxyethyl)(meth)acrylamide, and diacetone(meth)acrylamide, and it is even more preferable that it includes a constituent unit derived from acrylamide.

[0022] The copolymer contains 30% by mass or more and 95% by mass or less of the constituent unit (a) derived from the (meth)acrylamide monomer, relative to the total monomer units contained in the copolymer. A content of 30% by mass or more of the constituent unit (a) derived from the (meth)acrylamide monomer improves the cohesiveness of the copolymer, making it easier for the copolymer to coat the surface of the electrode active material well. This improves the peel strength of electrodes made using the binder composition of this embodiment, and improves the cycle characteristics of secondary batteries equipped with such electrodes. In addition, by containing 30% by mass or more of the constituent unit (a), the dispersibility and stability of the electrode active material in the electrode composition made using the binder composition of this embodiment are improved, and the battery characteristics, such as the cycle characteristics of the resulting secondary battery, are improved. The content of the constituent unit (a) is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 75% by mass or more. Furthermore, if the content of the constituent unit (a) is 95% by mass or less, the cohesiveness of the copolymer is improved, and a secondary battery exhibiting good cycle characteristics can be obtained. In addition, the flexibility of the copolymer can be ensured, and electrode cracking of electrodes made using the binder composition of this embodiment and detachment due to expansion and contraction of the electrode active material during charging and discharging can be effectively prevented. The content of the constituent unit (a) is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0023] (Constituent units (b) derived from (meth)acrylic acid ester monomers) The copolymer has constituent units (b) derived from (meth)acrylic acid ester monomers. The copolymer having constituent units (b) derived from (meth)acrylic acid ester monomers improves the flexibility of the resulting copolymer. This improves the adhesion between electrode active materials and between the electrode composite layer and the current collector in electrodes made using the binder composition of this embodiment, thereby improving the cycle characteristics of secondary batteries made using said electrodes.

[0024] Examples of (meth)acrylic acid ester monomers that can form structural units derived from the (meth)acrylic acid ester monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (meth)acrylate (Meth)alkyl esters such as cyclohexyl acrylate, n-decyl methacrylate, isodecyl methacrylate, n-dodecyl methacrylate, n-lauryl methacrylate, n-octadecyl methacrylate, isodecyl methacrylate; 2-methoxymethyl methacrylate, 2-methoxyethyl methacrylate, 2-ethoxymethyl methacrylate, 2-ethoxyethyl methacrylate, 2-propoxyethyl methacrylate, (meth) Examples include alkoxyalkyl esters of (meth)acrylates such as 2-butoxyethyl acrylic acid, 2-methoxypropyl (meth)acrylate, 2-ethoxypropyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, and 4-ethoxybutyl (meth)acrylate; hydroxyalkyl esters of (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; (meth)acrylate esters having alicyclic hydrocarbon groups such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate; and (meth)acrylate esters having aromatic hydrocarbon groups such as phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, and benzyl (meth)acrylate. These may be used individually, or two or more may be used in combination.

[0025] In this embodiment, it is preferable that the constituent unit (b) derived from the (meth)acrylic acid ester monomer includes a constituent unit (b1) derived from at least one monomer selected from the group consisting of alkyl (meth)acrylic acid esters having an alkyl group having 1 to 3 carbon atoms, alkoxyalkyl (meth)acrylic acid esters having an alkoxyalkyl group having 1 to 3 carbon atoms, and hydroxyalkyl (meth)acrylic acid esters having a hydroxyalkyl group having 1 to 3 carbon atoms. By including the constituent unit (b1) in the copolymer, the cycle characteristics of the secondary battery obtained using the binder composition of this embodiment can be further improved. The reason for obtaining this effect is not clear, but since the side chains of the monomers that form the constituent unit (b1) all have a short number of carbon atoms (1 to 3), the intermolecular forces derived from the constituent unit (a) derived from the (meth)acrylamide monomer tend to become stronger, and the cohesiveness of the copolymer tends to improve further. As a result, the coating properties of the copolymer over the electrode active material are further improved, and it is presumed that the adhesion of the electrode made from the binder composition of this embodiment is further improved. From the viewpoint of further enhancing the aforementioned effects, it is more preferable that the number of carbon atoms in the alkyl group of the (meth)acrylate alkyl ester, the alkoxyalkyl group of the (meth)acrylate alkoxyalkyl ester, and the hydroxyalkyl group of the (meth)acrylate hydroxyalkyl ester is 1 to 2. The constituent unit (b) derived from the (meth)acrylate monomer is more preferably derived from a constituent unit from at least one monomer selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, and 2-methoxymethyl (meth)acrylate, and even more preferably derived from a constituent unit from methyl acrylate.

[0026] The content of the constituent unit (b) derived from the (meth)acrylic acid ester monomer in the copolymer is 1% by mass or more and 60% by mass or less relative to the total monomer units contained in the copolymer. A content of 1% by mass or more of the constituent unit (b) allows the copolymer to exhibit good flexibility. This improves the adhesion between electrode active materials and between the electrode composite layer and the current collector in electrodes made using the binder composition of this embodiment, thereby improving the cycle characteristics of secondary batteries made using these electrodes. The content of the constituent unit (b) is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. Furthermore, if the content of the constituent unit (b) is 60% by mass or less, sufficient intermolecular forces derived from the constituent unit (a) derived from the (meth)acrylamide monomer can be secured, allowing the copolymer to exhibit high cohesiveness. This improves the adhesion between electrode active materials and between the current collector and the electrode composite layer in electrodes made using the binder composition of this embodiment, thereby improving the cycle characteristics of secondary batteries made using these electrodes. The content of the constituent unit (b) is preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less.

[0027] (Constituent units (c) derived from acid group-containing monomers) The copolymer has constituent units (c) derived from acid group-containing monomers. The copolymer contains constituent units (c) derived from acid group-containing monomers, which increases the solubility of the resulting copolymer in water. As a result, the dispersion stability and storage stability of the electrode composition made using the binder composition of this embodiment are achieved, and the cycle characteristics of the secondary battery made using the electrode composition can be improved.

[0028] Examples of acid group-containing monomers that can form the constituent unit (c) derived from the acid group-containing monomer include, for example, monomers having a -COOH group (carboxylic acid group) and -SO ３ Monomer having an H group (sulfonic acid group), -PO ３ H ２Examples include monomers having a group, monomers having a -PO(OH)(OR) group (where R represents a hydrocarbon group), etc. These may be used individually or in combination of two or more. If a monomer falls under the category of an acid group-containing monomer and also falls under the category of the (meth)acrylamide monomer and the (meth)acrylic acid ester monomer, it shall be considered an acid group-containing monomer.

[0029] Examples of monomers having the carboxylic acid group include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, their derivatives, and combinations thereof. Specific examples of monocarboxylic acids include (meth)acrylic acid and crotonic acid. Specific examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Examples of derivatives of dicarboxylic acids include methyl allyl maleate such as methyl maleic acid, dimethyl maleic acid, phenyl maleic acid, chloro maleic acid, dichloro maleic acid, and fluoromaleic acid; maleic acid esters such as diphenyl maleic acid, nonyl maleic acid, decyl maleic acid, dodecyl maleic acid, octadecyl maleic acid, and fluoroalkyl maleic acid; and the like.

[0030] Examples of monomers having the sulfonic acid group include, for example, monomers in which one of the conjugated double bonds of a diene compound such as isoprene and butadiene is sulfonated; vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfoethyl methacrylate, sulfopropyl methacrylate, sulfobutyl methacrylate, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and 3-alyloxy-2-hydroxypropanesulfonic acid (HAPS).

[0031] The aforementioned - PO ３ H ２Examples of monomers having a group and / or a -PO(OH)(OR) group (where R represents a hydrocarbon group) include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate.

[0032] Among these, it is preferable that the constituent unit (c) derived from the acid group-containing monomer includes a constituent unit derived from a monomer having a carboxylic acid group, more preferably includes a constituent unit derived from at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid, and even more preferably includes a constituent unit derived from acrylic acid.

[0033] The content of the constituent unit (c) derived from the acid group-containing monomer is 0.1% by mass or more and 5% by mass or less relative to the total monomer units constituting the copolymer. A content of 0.1% by mass or more of the acid group-containing monomer (c) results in improved dispersion stability and storage stability of the electrode composition produced using the binder composition of this embodiment, and improved cycle characteristics of the secondary battery produced using the electrode composition. The content of the constituent unit (c) is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 2.0% by mass or more. Furthermore, a content of 5% by mass or less of the constituent unit (c) results in improved dispersion stability and storage stability of the electrode composition produced using the binder composition of this embodiment, and improved cycle characteristics of the secondary battery produced using the electrode composition. The content of the constituent unit (c) is preferably less than 3.0% by mass, more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less.

[0034] In this embodiment, the total content of the constituent unit (a) derived from the (meth)acrylamide monomer, the constituent unit (b) derived from the (meth)acrylic acid ester monomer, and the constituent unit (c) derived from the acid group-containing monomer is preferably 40% by mass or more relative to the total monomer units contained in the copolymer. If the total content of the constituent units (a) to (c) is within the above range, the cohesiveness of the copolymer is improved. This improves the adhesion between the electrode composite layer and the current collector in the electrode made using the binder composition of this embodiment. In addition, the stability of the electrode composition made using the binder composition containing the copolymer is improved. As a result, the cycle characteristics of the secondary battery made using the electrode can be improved. The total content of the constituent units (a) to (c) is more preferably 50% by mass or more, and even more preferably 60% by mass or more. Furthermore, the upper limit of the total content of the constituent units (a) to (c) may be 100% by mass, 90% by mass, 80% by mass, or 70% by mass.

[0035] (Constituent units (d) derived from other monomers) The copolymer may further contain constituent units (d) other than the constituent units (a) derived from the (meth)acrylamide monomer, the constituent units (b) derived from the (meth)acrylic acid ester monomer, and the constituent units (c) derived from the acid group-containing monomer (hereinafter, "other constituent units (d)").

[0036] Examples of monomers that can constitute the other constituent unit (d) include vinyl ester monomers such as vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl laurylate, vinyl decanoate, vinyl stearate, vinyl hexanoate, vinyl octanoate, and vinyl palmitate; vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether, and butyl vinyl ether; α,β-ethylenically unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile; and heterocyclic vinyl monomers such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole. These can be one type or a combination of two or more types in any ratio.

[0037] If the copolymer contains the other constituent unit (d), its content may be 68.9% by mass or less, 40% by mass or less, 30% by mass or less, or 20% by mass or less, relative to the total monomer units constituting the copolymer. Furthermore, the lower limit of the content of the constituent unit (d) may be 0% by mass. That is, the content of the other constituent unit (d) may be 0% by mass or more and 68.9% by mass or less.

[0038] In this embodiment, it is preferable that at least a portion of the acid groups contained in the copolymer are neutralized with a basic compound. By neutralizing at least a portion of the acid groups contained in the copolymer with the basic compound, the solubility of the copolymer in water can be improved. This increases the uniformity of the mixing when the binder composition of this embodiment is mixed with the electrode active material, and improves the peel strength of the electrode formed using the binder composition.

[0039] The basic compound is not limited to any compound that can neutralize an acid group-containing monomer capable of forming a constituent unit (c) derived from the acid group-containing monomer, and examples include inorganic bases and organic bases. The basic compound can be used alone or in combination of two or more.

[0040] Examples of the inorganic bases include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; alkali metal salts of silica such as sodium orthosilicate, sodium metasilicate, and sodium sesquisilicate; alkali metal salts of phosphoric acid such as trisodium phosphate; alkali metal salts of carbonic acid such as disodium carbonate, sodium bicarbonate, and dipotassium carbonate; alkali metal salts of boric acid such as sodium borate; and ammonia.

[0041] Examples of the organic bases include alkylamines such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and triethylamine; alkanolamines such as aminoethanol, methylaminoethanol, dimethylaminoethanol, ethylaminoethanol, diethylaminoethanol, diethanolamine, and triethanolamine; and amines having a nonionic group such as methoxypoly(oxyethylene / oxypropylene)-2-propylamine.

[0042] Among these, from the viewpoint of reducing the electrolyte swelling rate, the basic compound preferably contains a compound comprising at least one metal element selected from the group consisting of lithium, sodium, and potassium, and more preferably contains a compound comprising at least one metal element from lithium and sodium.

[0043] (Characteristics of the copolymer) The copolymer is not particularly limited, but is usually water-soluble. In this specification, "water-soluble" means that when 1 g (solid content) of the copolymer is dissolved in 100 g of water at a temperature of 25°C, the amount of insoluble content is 10.0% by mass or less.

[0044] The weight-average molecular weight (Mw) of the copolymer is preferably 500,000 to 5,000,000, more preferably 750,000 to 3,000,000, and even more preferably 1,000,000 to 2,000,000. When the weight-average molecular weight of the copolymer is within the above range, the adhesion of the electrode composite layer formed using the electrode composition containing the binder composition can be further improved. The weight-average molecular weight can be measured using an aqueous GPC measuring device. In the aqueous GPC measuring device, polymer-based packing materials such as polyhydroxymethacrylate and polyvinyl alcohol, which are common, can be used as column packing materials. As columns, for example, the Shodex OHpak series SB-806 HQ or SB-806M HQ, or the Asahipak series GF-HQ from Resonaq Corporation can be used. As the eluent, a neutral salt solution such as sodium chloride aqueous solution, sodium nitrate aqueous solution, sodium hydrogen hydrochloride aqueous solution, sodium sulfate aqueous solution, or phosphate buffer solution can be used. The concentration of these eluents is preferably, for example, about 0.1 to 0.3 mol / L. As the GPC measuring device, for example, the Shimadzu / L20 system can be used. As the standard substance for GPC measurement, polystyrene or pullulan can be used.

[0045] The weight-average molecular weight (Mw) of the copolymer can be controlled by the type and amount of monomers and polymerization initiators used as raw materials, as well as the time and temperature of the polymerization reaction during copolymer production.

[0046] The copolymer constituting the binder composition of this embodiment is used to bond the film formed by the copolymer to a carbonate-based mixed solvent (EC (ethylene carbonate) / DMC (dimethyl carbonate) / MEC (ethyl methyl carbonate) / FEC (4-fluoroethylene carbonate) / VC (vinylene carbonate) / LiPF ６It is preferable that the swelling rate after immersion in (lithium hexafluoride phosphate) = 29 / 24 / 30 / 5 / 1 / 11 (wt)) at 60°C for 72 hours is 5% by mass or less. When the swelling rate is 5% by mass or less, the peeling of the electrode active material from the current collector due to the swelling of the copolymer can be suppressed to a high degree, and the cycle characteristics of the resulting secondary battery are further improved. The swelling rate is more preferably 4% by mass or less, even more preferably 3% by mass or less, and particularly preferably 2% by mass or less. The lower limit of the swelling rate may be 0% by mass or 1% by mass, as this minimizes the reaction of the copolymer with the electrolyte and allows the electrode structure to be kept stable, thereby suppressing deterioration of battery performance even with long-term use. In other words, the degree of swelling may be 0% by mass or more and 5% by mass or less.

[0047] The aforementioned swelling rate is obtained by drying the copolymer at room temperature for 72 hours and at 150°C for 30 minutes to produce a dry polymer film (dry coating) with a thickness of 150 μm, and then drying this dry polymer film in a carbonate-based mixed solvent (for example, EC (ethylene carbonate) / DEC (diethylene carbonate) / MEC (ethyl methyl carbonate) / FEC (4-fluoroethylene carbonate) / VC (vinylene carbonate) / LiPF ６ The swelling rate (%) can be calculated by immersing the film in (lithium hexafluoride phosphate) = 29 / 24 / 30 / 5 / 1 / 11 (wt)) at 60°C for 72 hours, measuring the mass of the film after immersion, and using the following formula: Swelling rate (%) = (Mass of film after immersion - Mass of film before immersion) / (Mass of film before immersion) × 100

[0048] The copolymer preferably has a viscosity of 3,000 mPa·s or more when prepared as a 5% by mass aqueous solution. A viscosity of 3,000 mPa·s or more allows for adjustment of the viscosity and fluidity of the electrode composition containing the binder composition of this embodiment, thereby improving production efficiency. A viscosity of 5,000 mPa·s or more is more preferable, and 7,000 mPa·s or more is even more preferable. Furthermore, from the viewpoint of increasing the solid content concentration of the electrode composition and improving electrode productivity without excessively increasing the viscosity of the electrode composition, the viscosity is preferably 20,000 mPa·s or less, more preferably 150,000 mPa·s or less, and even more preferably 10,000 mPa·s or less. That is, the viscosity may be between 3,000 mPa·s and 20,000 mPa·s. The viscosity can be measured, for example, by a B-type viscometer.

[0049] Furthermore, in the binder composition of this embodiment, the content of the copolymer is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, when the nonvolatile content of the binder composition is set to 100% by mass. When the content of the copolymer is within the above range, the peel strength of the electrode made using the binder composition is improved, thereby improving the cycle characteristics of the secondary battery. The content of the copolymer may be 100% by mass or less, 90% by mass or less, or 80% by mass or less, when the nonvolatile content of the binder composition is set to 100% by mass. In other words, the content of the copolymer may be 40% by mass or more and 100% by mass or less.

[0050] (Method for producing copolymers) The method for producing the copolymers constituting the binder composition of this embodiment is not particularly limited and can be produced by known methods. For example, the copolymers can be produced by mixing the (meth)acrylamide monomer, the (meth)acrylic acid ester monomer, the acid group-containing monomer, and other monomers that may be optionally added as needed, in a solvent such as water to obtain a monomer mixture, adding a polymerization initiator to the monomer mixture, and carrying out a polymerization reaction.

[0051] The polymerization initiator added to the polymerization reaction is not particularly limited, and known polymerization initiators can be used. Examples of the polymerization initiators include 2,2'-azobis-(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis-2-methylpropionate methyl, 2,2'-azobisisobutyrate dimethyl, 2,2'-azobis-2-methylvaleronitrile, 1,1'-azobis-1-cycloheptanenitrile, 1,1'-azobis-1-phenylethane, phenylazotriphenylmethane, and peroxo Examples include potassium disulfate, sodium peroxodisulfate, ammonium peroxodisulfate, benzoyl peroxide, acetyl peroxide, tert-butyl peroxide, propionyl peroxide, lauroyl peroxide, tert-butyl peracetate, tert-butyl perbenzoate, tert-butyl hydroperoxide, tert-butyl peroxypivalate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and t-butylperoxy-2-ethylhexanoate. The amount of polymerization initiator added can be adjusted as appropriate.

[0052] The temperature during the polymerization reaction is not particularly limited, but is preferably 0°C or higher, more preferably 20°C or higher, particularly preferably 40°C or higher, and also preferably 150°C or lower, more preferably 125°C or lower, particularly preferably 100°C or lower. The specific polymerization temperature is set appropriately depending on the type of monomer used, the type of polymerization initiator, etc.

[0053] Furthermore, before adding a polymerization initiator to the monomer mixture, the pH of the monomer mixture may be adjusted as needed. Preferably, the pH of the monomer mixture is adjusted to a range of 3.5 to 6.5. By adjusting the pH of the monomer mixture to this range, the acidic component of the acid group-containing monomer is neutralized, making it easier to react more uniformly with other monomers. This improves the battery characteristics, such as the cycle characteristics, of the secondary battery produced using the resulting binder composition. Methods for adjusting the pH of the monomer mixture include, for example, adjusting it using a basic compound or an acid. Examples of basic compounds include those listed in the <Basic Compounds> section below. Specific examples of acids include inorganic acids such as phosphoric acid, hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as acetic acid and citric acid. These may be used individually or in combination of two or more.

[0054] Furthermore, a basic compound may be added after the polymerization reaction of the monomer mixture, if necessary. Adding a basic compound can increase the solubility in water of the copolymer obtained by the polymerization reaction. When adding the basic compound, the amount added is preferably in the range of 0.5 to 1.5 moles, and more preferably in the range of 0.9 to 1.1 moles, based on 1 mole of acidic groups contained in the acidic group-containing monomer.

[0055] After the polymerization reaction, purification may be performed as needed. Purification methods include reprecipitation of the produced copolymer in a poor solvent, filtration, and subsequent drying under reduced pressure; evaporation of unreacted monomers and solvent; and GPC preparative separation. These methods may be carried out in combination.

[0056] The solution containing the copolymer obtained by the polymerization reaction can be used as is as the binder composition of this embodiment.

[0057] <Solvent> The binder composition of this embodiment may contain a solvent. Examples of the solvent include aqueous solvents and non-aqueous solvents. Examples of non-aqueous solvents include aromatic solvents such as benzene, toluene, and xylene; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone; aliphatic alcohol solvents such as isopropyl alcohol and n-butanol; alkylene glycol monoalkyl ether solvents such as ethylene glycol monomethyl ether and diethylene glycol monomethyl ether; ether solvents such as diethyl ether, dibutyl ether, tetrahydrofuran, and ethylene glycol dimethyl ether; and other organic solvents. These may be used individually or in combination of two or more in any ratio.

[0058] When the binder composition of this embodiment contains a solvent, the amount of solvent is preferably such that the non-volatile content concentration of the binder composition is within the range of 50% by mass or less, and more preferably within the range of 10% by mass or less. When the non-volatile content concentration of the binder composition of this embodiment is within the above range, the workability when manufacturing the non-aqueous secondary battery electrode composition described later is improved.

[0059] <Other Polymers> The binder composition of this embodiment may contain polymers other than the copolymer (hereinafter referred to as "other polymers"), to the extent that the objectives of this disclosure are not hindered. Examples of other polymers include polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and polyacrylonitrile (PAN).

[0060] If the binder composition of this embodiment contains the other polymers, the content ratio is preferably 60% by mass or less, more preferably 55% by mass or less, and particularly preferably 50% by mass or less, based on 100% by mass of the nonvolatile content of the binder composition of this embodiment. Furthermore, the lower limit of the content ratio of the other resins may be 0% by mass. That is, the content ratio of the other resins may be 0% by mass or more and 60% by mass or less.

[0061] <Additives> The binder composition of this embodiment may further contain various additives as needed, such as preservatives, surfactants, antioxidants, light stabilizers, plasticizers, and organic or inorganic fillers, to the extent that they do not impair the effects of the present invention. When the binder composition of this embodiment contains the above-mentioned additives, the content ratio is preferably 30% by mass or less, more preferably 10% by mass or less, and even more preferably 3% by mass or less, based on 100% by mass of the non-volatile content of the binder composition of this embodiment. Furthermore, the lower limit of the content ratio of the above-mentioned additives may be 0% by mass.

[0062] Any known preservative can be used. Specifically, examples of preservatives include organic sulfur compounds, organic nitrogen sulfur compounds, organic halogen compounds, haloallyl sulfone compounds, iodopropagyl compounds, N-haloalkylthio compounds, nitrile compounds, pyridine compounds, 8-oxyquinoline compounds, benzothiazole compounds, isothiazoline compounds, dithiol compounds, pyridine oxide compounds, nitropropane compounds, organotin compounds, phenol compounds, quaternary ammonium salt compounds, triazine compounds, thiazine compounds, anilide compounds, adamantane compounds, dithiocarbamate compounds, brominated indanone compounds, benzyl bromacetate compounds, inorganic salt compounds, alcohols such as ethanol and isopropyl alcohol, and benzalkonium chloride. These may be used alone or in combination of two or more. In addition, commercially available preservatives can be used. Examples of commercially available products include Actiside MBS and Actiside MV4 (manufactured by So Japan Co., Ltd.).

[0063] <Method for preparing a binder composition for non-aqueous secondary battery electrodes> The binder composition of this embodiment can be prepared by mixing the copolymer with, if necessary, other polymers or additives. Alternatively, the copolymer may be diluted with a solvent before being used as the binder composition of this embodiment.

[0064] ≪Composition for Non-Aqueous Secondary Battery Electrodes≫ The composition for non-aqueous secondary battery electrodes of this embodiment contains an electrode active material, a conductive material, and the binder composition for non-aqueous secondary battery electrodes of this embodiment.

[0065] (Electrode active material) As the electrode active material, various materials can be selected and blended according to the type of electrode to be manufactured. That is, the composition for non-aqueous secondary battery electrodes of the present embodiment includes a composition for non-aqueous secondary battery positive electrodes and a composition for non-aqueous secondary battery negative electrodes. Specifically, by using a positive electrode active material described later as the electrode active material, a composition for non-aqueous secondary battery positive electrodes can be obtained. Similarly, by using a negative electrode active material described later as the electrode active material, a composition for non-aqueous secondary battery negative electrodes can be obtained.

[0066] When the composition for non-aqueous secondary battery electrodes of the present embodiment is used to manufacture a negative electrode of a lithium-ion secondary battery, as the electrode active material (negative electrode active material), a metal compound, metal oxide, metal sulfide, or conductive polymer material capable of doping or intercalating lithium ions can be used, and there is no particular limitation. Specifically, examples of the negative electrode active material include carbon materials such as graphite, natural graphite, and artificial graphite, silicon-based materials such as silicon, silicon oxide, and silicon-containing alloys, tin-based materials, polyacene-based conductive polymers, and composite metal oxides such as lithium titanate.

[0067] When the composition for non-aqueous secondary battery electrodes of the present embodiment is used to manufacture a positive electrode of a lithium-ion secondary battery, as the electrode active material (positive electrode active material), a metal compound, metal oxide, metal sulfide, or conductive polymer material capable of doping or intercalating lithium ions can be used, and there is no particular limitation. Specific examples of the positive electrode active material include, for example, lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), lithium manganate (LiMnO ２ ), and composite oxides thereof (LiCoxNiyMnzO ２ , x + y + z = 1), lithium manganese spinel (LiMn ２ O ４ ), lithium vanadium compounds, V ２ O ５ , V ６ O １３ , VO ２ , MnO２ , TiO ２ MoV ２ O ８ TiS ２ , V ２ S ５ , VS ２ MoS ２ MoS ３ , Cr ３ O ８ , Cr ２ O ５ Olivine type LiMPO ４ Conductive polymers such as (M: Co, Ni, Mn, Fe), polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene, as well as porous carbon, can be used individually or in combination.

[0068] (Conductive materials) Examples of conductive materials include acetylene black, Ketjen black, carbon black, vapor-grown carbon fibers, and conductive carbon such as carbon nanotubes. Carbon powder such as graphite, and fibers and foils of various metals may also be used. These may be used individually or in combination of two or more types.

[0069] (Other Components) The electrode composition of this embodiment may contain components other than the electrode active material, the conductive material, and the binder composition for non-aqueous secondary battery electrodes of this embodiment. Examples of other components that the electrode composition of this embodiment may contain include viscosity modifiers, preservatives, and pH adjusters.

[0070] Examples of the preservatives mentioned above include those similar to those described in the binder composition.

[0071] Examples of viscosity modifiers include poly(meth)acrylic acid; cellulosic polymers such as carboxymethylcellulose, methylcellulose, ethylcellulose, and hydroxypropylcellulose; ammonium salts or alkali metal salts of the cellulose compounds or poly(meth)acrylic acid; modified polyvinyl alcohol, polyethylene oxide; polyvinylpyrrolidone, polycarboxylic acid, starch oxide, starch phosphate, casein, various modified starches, chitin, and chitosan derivatives.

[0072] (Method for producing a composition for non-aqueous secondary battery electrodes) The electrode composition of this embodiment is obtained by mixing and dispersing the electrode active material, the conductive material, and the binder composition for non-aqueous secondary battery electrodes of this embodiment. There are no particular restrictions on the order of addition during mixing. Furthermore, a non-aqueous solvent may be added as appropriate to adjust the viscosity of the obtained electrode composition of this embodiment and to improve dispersion stability. Dispersion can be carried out using a dispersion device such as a stirrer, a rotary-orbit mixer, a ball mill, a super sand mill, or a pressurized kneader.

[0073] ≪Non-aqueous secondary battery electrode≫ The non-aqueous secondary battery electrode of this embodiment comprises an electrode composite layer formed using a non-aqueous secondary battery electrode composition. Specifically, for example, it can be obtained by applying the non-aqueous secondary battery electrode composition of this embodiment to a current collector to form an electrode composite layer as a thin film. Alternatively, the non-aqueous secondary battery electrode composition may be molded into a sheet, pellet, or other shape and integrated with a current collector to obtain the electrode. The non-aqueous secondary battery electrode of the present invention encompasses both a non-aqueous secondary battery negative electrode and a non-aqueous secondary battery positive electrode. Specifically, a non-aqueous secondary battery negative electrode can be formed by using the non-aqueous secondary battery negative electrode composition. Similarly, a non-aqueous secondary battery positive electrode can be formed by using the non-aqueous secondary battery positive electrode composition.

[0074] The material and shape of the current collector are not particularly limited. For example, copper, copper alloys, nickel, aluminum, aluminum alloys, titanium, stainless steel, etc., can be used in the form of foil, perforated foil, mesh, or other strip-like materials. Porous materials, such as porous metal (foamed metal) or carbon paper, can also be used.

[0075] The method for applying the non-aqueous secondary battery electrode composition to the current collector is not particularly limited, but known methods include, for example, metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade coating, gravure coating, and screen printing. After application, it is preferable to perform rolling treatment using a flat plate press, calender roll, etc., as needed.

[0076] Furthermore, the integration of the electrode composition, which is molded into a sheet, pellet, or other shape, with the current collector can be carried out by known methods such as rolling, pressing, or a combination thereof. The electrode density after integration of the electrode composition and the current collector is, for example, 1.0 to 1.8 g / cm³. ３ Preferably, 1.1 to 1.7 g / cm³ ３ That is the case.

[0077] The electrode composition (electrode composite layer) formed on the current collector is preferably heat-treated. The heat treatment conditions are, for example, 80 to 150°C for 5 to 20 hours. This heat treatment removes the solvent, hardens the binder, and increases strength, thereby improving the adhesion between the electrode active materials and between the electrode active materials and the current collector. These heat treatments are preferably carried out in an inert atmosphere such as helium, argon, or nitrogen, or in a vacuum atmosphere, in order to prevent oxidation of the current collector during the treatment.

[0078] ≪Non-aqueous secondary battery≫ The non-aqueous secondary battery of this embodiment is equipped with the electrodes of the present invention described above. When the secondary battery of this embodiment is used, for example, in a wet electrolyte secondary battery, it can be constructed by arranging the electrodes of this embodiment opposite each other via a separator and injecting an electrolyte.

[0079] As the separator, for example, a nonwoven fabric, cloth, microporous film, or a combination thereof, mainly composed of polyolefins such as polyethylene and polypropylene can be used. However, if the positive and negative electrodes of the non-aqueous electrolyte secondary battery to be manufactured are not in direct contact, a separator does not need to be used.

[0080] The electrolyte can be, for example, LiClO ４ LiPF ６ LiAsF ６ LiBF ４ LiSO ３ CF ３A so-called organic electrolyte can be used, which is obtained by dissolving lithium salts such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidine-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, etc., in one or more non-aqueous solvents.

[0081] The structure of the secondary battery in this embodiment is not particularly limited, but it is common to have a structure in which the positive electrode, negative electrode, and a separator provided as needed are wound in a flat spiral shape to form a wound electrode plate group, or these are stacked as flat plates to form a stacked electrode plate group, and these electrode plate groups are sealed in an outer casing. A secondary battery using the non-aqueous secondary battery negative electrode binder composition of this embodiment can be used as, for example, a paper battery, a button battery, a coin battery, a stacked battery, a cylindrical battery, a prismatic battery, etc.

[0082] The binder composition for non-aqueous secondary battery electrodes of this embodiment is also applicable to electrochemical devices in general that use the insertion and deinsertion of lithium ions as a charge and discharge mechanism, such as hybrid capacitors and solid lithium secondary batteries.

[0083] The binder composition for non-aqueous secondary battery electrodes, the electrode composition, the electrode, and the secondary battery having the electrode of this embodiment have been described above. However, the present invention is not limited to the configuration of the embodiment described above. For example, the binder composition for non-aqueous secondary battery electrodes, the electrode composition, the electrode, and the secondary battery having the electrode of this embodiment may each have additional configurations in addition to the configuration of the embodiment described above, or may be replaced with any configuration that performs a similar function.

[0084] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples. The raw materials used in each example and comparative example are listed below.

[0085] Am: Acrylamide HEAA: N-(2-hydroxyethyl)acrylamide DAAM: Diacetone acrylamide N-MAM: N-hydroxymethylacrylamide MA: Methyl acrylate EA: Ethyl acrylate MTA: 2-methoxyethyl acrylate HEAA: 2-hydroxyethyl acrylate AA: Acrylic acid

[0086] <Example 1> (1) Preparation of Binder Composition 600.0 parts by mass of deionized water was charged into a 2.0 L reaction vessel equipped with a stirrer, thermometer, cooler and nitrogen blower, and heated to 75°C. After that, dissolved oxygen in the deionized water was removed by nitrogen blowing. A mixture of 3 parts by mass of acrylic acid, 40 parts by mass of methyl acrylate, 7 parts by mass of 2-methoxyethyl acrylate, 50 parts by mass of acrylamide, 0.40 parts by mass of ammonium persulfate and 60.0 parts by mass of deionized water was added dropwise over 3 hours to carry out the polymerization reaction. After the dropwise addition was completed, it was held at the same temperature for 3 hours and then cooled. An aqueous lithium hydroxide solution was added at a temperature of 40°C or lower to adjust the pH and dilute the mixture to obtain a binder composition (non-volatile content 5.7% by mass, pH 5.3).

[0087] (2) Preparation of the negative electrode composition 11.5 parts by mass of SiO negative electrode material (initial charge capacity 2062 mAh / g, initial discharge capacity 1631 mAh / g), 84.5 parts by mass of artificial graphite (initial charge capacity 371 mAh / g, initial discharge capacity 346 mAh / g), 0.97 parts by mass of acetylene black (AcB), and 0.03 parts by mass of carbon nanotubes (CNT) were weighed out and stirred for 30 seconds in a rotation / revolution mixer (Thinky ARE-310) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm. The binder composition obtained in (1) above (non-volatile content 5.7% by mass) was diluted with distilled water to obtain a binder composition adjusted to a non-volatile content concentration of 5.0% by mass. 43.2 parts by mass (2.16 parts by mass in terms of non-volatile content) of this binder composition was mixed with 2.8 parts by mass of distilled water and mixed until the mixture became a paste. Next, the mixture was stirred for 2 minutes in a rotation / revolution mixer (Thinky ARE-310) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm. Since the mixture generated heat during stirring, it was cooled to room temperature with ice water. The mixture was then stirred again for 2 minutes at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm, and then cooled to room temperature with ice water. Next, the binder composition obtained in (1) above (non-volatile content 5.7% by mass) was diluted with distilled water to adjust the non-volatile content concentration to 5.0% by mass. 16.8 parts by mass of this binder composition (0.84 parts by mass in terms of non-volatile content) was added and mixed until the mixture was homogeneous. Then, using a rotation / revolution mixer (Thinky ARE-310), the mixture was stirred for 2 minutes at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm, and cooled to room temperature with ice water. 1.3 parts by mass of distilled water was added and mixed until the mixture was homogeneous. Next, to adjust the viscosity of the slurry, the viscosity was measured using a B-type viscometer, and distilled water was added as needed to bring the viscosity to a range of 2000 to 4000 Pa·s at a speed of 30 rpm. Finally, the negative electrode composition was prepared by stirring for 30 seconds in a rotation / revolution mixer (Thinky ARE-310) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm.

[0088] (3) The coating amount (surface density) of the negative electrode composite layer after drying of the negative electrode negative electrode of the non-aqueous secondary battery is 8.8 mg / cm². ２The gap of the bar coater was adjusted so that the negative electrode composition obtained in (2) above was coated onto the copper foil, which is the current collector, using the bar coater. After that, it was dried for 8 minutes in a forced-air dryer set to 80°C. The dried electrode was cut into strips 40 mm wide, and the density of the negative electrode composite layer was measured using a roll press (Small Tabletop Roll Press SA-602 manufactured by Tester Industries Co., Ltd.) to 1.55 g / cm³. ３ The material was pressed to a thickness of 66.7 μm for the negative electrode composite layer. It was then vacuum dried at 110°C for 10 hours. As a result, the negative electrode (surface density 8.8 gm / cm²) ２ , negative electrode composite layer density 1.5g / cm ３ The negative electrode composite layer thickness is 68.6 μm, and the initial charge capacity per unit area is 4.95 mAh / cm². ２ ) was obtained.

[0089] (4) Preparation of non-aqueous secondary electrode composition In a room with humidity adjusted to 30% or less, the cathode material LiMn ０．６ Co ０．２ Ni ０．２ O ２94.0 parts by mass of (initial charge capacity 191 mAh / g, initial discharge capacity 171 mAh / g) and 3.0 parts by mass of acetylene black were weighed out and stirred for 30 seconds in a rotation / revolution mixer (Thinky ARE-310) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm. 27.0 parts by mass (2.16 parts by mass of non-volatile content) of an anhydrous N-methylpyrrolidone solution of polyvinylidene fluoride adjusted to a non-volatile content concentration of 8.0% by mass, and 19.0 parts by mass of anhydrous N-methylpyrrolidone were added and mixed until the mixture became a paste. Next, the mixture was stirred for 2 minutes in a rotation / revolution mixer (Thinky ARE-310) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm. Since heat was generated by the stirring, it was cooled to room temperature with ice water. The mixture was stirred again for 2 minutes at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm, and then cooled to room temperature with ice water. 10.5 parts by mass (0.84 parts by mass in terms of non-volatile content) of an anhydrous N-methylpyrrolidone solution of polyvinylidene fluoride, which had been previously prepared to a non-volatile content concentration of 8% by mass, was added and mixed until homogeneous. Then, using a rotation / revolution mixer (Thinky ARE-310), the mixture was stirred for 2 minutes at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm, and then cooled to room temperature with ice water. 5 parts by mass of anhydrous N-methylpyrrolidone were added and mixed until homogeneous. Next, to adjust the viscosity of the slurry, the viscosity was measured using a B-type viscometer, and anhydrous N-methylpyrrolidone was added as needed to bring the viscosity to a range of 2000 to 4000 Pa·s at a rotation speed of 30 rpm. Finally, the cathode composition was prepared by stirring for 30 seconds in a rotation / revolution mixer (Thinky ARE-310) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm.

[0090] (5) The surface density of the cathode composite layer after the preparation and drying of the cathode is 25.0 mg / cm². ２ The gap of the bar coater was adjusted so that the positive electrode composition prepared in (4) above was coated onto the aluminum foil current collector using the bar coater. Next, it was dried for 10 minutes in a forced-air dryer set to 80°C. The dried electrode was cut into strips 40 mm wide, and the density of the positive electrode composite layer was measured using a roll press (Small Tabletop Roll Press SA-602 manufactured by Tester Industries Co., Ltd.) to 3.4 g / cm³. ３After pressing the material to a thickness of 73.3 μm for the positive electrode composite layer, it was vacuum-dried at 110°C for 10 hours. As a result, the positive electrode surface density was 25.0 gm / cm². ２ , positive electrode composite layer density 3.4g / cm ３ The positive electrode composite layer thickness is 73.3 μm, and the initial charge capacity per unit area is 4.49 mAh / cm². ２ ) was obtained.

[0091] (6) Fabrication of a non-aqueous secondary battery The negative electrode fabricated in (3) above was cut into a 24 mm x 24 mm square with a tab, and the positive electrode fabricated in (5) above was cut into a 22 mm x 22 mm square with a tab using a die cutter. Nickel tab leads were welded to the tab portion of the cut electrodes, and aluminum tab leads were welded to the tab portion of the negative electrode, and aluminum tab leads were welded to the tab portion of the positive electrode. Next, a separator (a 25 micron thick polyethylene microporous membrane) was cut into a 28 mm x 3.8 cm rectangle using a die cutter. The positive and negative electrodes were placed facing each other with the separator in between, wrapped in laminate film, and the tab portion was fixed by heat sealing. Then, the electrolyte (1.0 M LiPF4) was added. ６ A laminate-type secondary battery was fabricated by adding 300 μL of a mixed solution of ethylene carbonate / dimethyl carbonate / methyl ethyl carbonate (30 / 30 / 40 by volume ratio) plus 1% vinyl carbonate and 5% fluoroethylene carbonate, and then completely sealing it by vacuum lamination.

[0092] (Examples 2-12) Except for changing the types and amounts of materials used in the preparation of the negative electrode binder composition as shown in Tables 1 and 2, and adjusting the amount of neutralizing salt (basic compound) added as appropriate to adjust the non-volatile content concentration and pH as shown in Tables 1 and 2, the negative electrode binder composition was prepared in the same procedure as in Example 1. Furthermore, the negative electrode composition, negative electrode, positive electrode composition, positive electrode, and secondary battery were manufactured in the same manner as in Example 1, except that the negative electrode binder composition was used.

[0093] (Example 13) (1) Preparation of the negative electrode binder composition 600.0 parts by mass of deionized water was charged into a 2.0 L reaction vessel equipped with a stirrer, thermometer, cooler, and nitrogen blower, and heated to 75°C. Dissolved oxygen in the deionized water was then removed by nitrogen blowing. A mixture of 2.9 parts by mass of acrylic acid, 12.0 parts by mass of methyl acrylate, 0.1 parts by mass of ethyl acrylate, 85.0 parts by mass of acrylamide, 0.40 parts by mass of ammonium persulfate, and 60.0 parts by mass of deionized water was added dropwise over 3.0 hours to carry out the polymerization reaction. After the dropwise addition was completed, the mixture was held at the same temperature for 3 hours and then cooled. An aqueous lithium hydroxide solution was added at a temperature of 40°C or lower to adjust the pH and dilute the mixture to obtain a negative electrode binder composition (non-volatile content 5.3% by mass, pH 5.4).

[0094] (2) Preparation of the negative electrode composition 11.5 parts by mass of SiO negative electrode material (initial charge capacity 2062 mAh / g, initial discharge capacity 1631 mAh / g), 84.5 parts by mass of artificial graphite (initial charge capacity 371 mAh / g, initial discharge capacity 346 mAh / g), 0.97 parts by mass of acetylene black, and 0.03 parts by mass of carbon nanotubes were weighed out and stirred for 30 seconds in a rotation / revolution mixer (Thinky ARE-310) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm. The binder composition obtained above was diluted with distilled water to adjust the non-volatile content to 5.0% by mass. 28.8 parts by mass (1.44 parts by mass in terms of non-volatile content) of this binder composition were added. 36.0 parts by mass (0.72 parts by mass in terms of non-volatile content) of an aqueous solution of carboxymethylcellulose sodium salt (CMC, Sunrose MAC350HC, manufactured by Nippon Paper Industries Co., Ltd.), dissolved in distilled water and adjusted to a non-volatile content of 2.0%, were added, and the mixture was mixed until it became a paste. Next, the mixture was stirred for 2 minutes in a rotation / revolution mixer (ARE-310, manufactured by Thinky Corporation) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm. Since heat was generated by the stirring, it was cooled to room temperature with ice water. The mixture was stirred again for 2 minutes at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm, and then cooled to room temperature with ice water. First, an aqueous solution of the binder composition shown in Synthesis Example 1, prepared to a non-volatile content concentration of 5.0% by mass, was added in an amount of 11.2 parts by mass (0.56 parts by mass in terms of non-volatile content), and an aqueous solution of carboxymethylcellulose sodium salt (CMC, Sunrose MAC350HC, manufactured by Nippon Paper Industries, Ltd.), prepared to a concentration of 2.0%, was added in an amount of 14.0 parts by mass (0.28 parts by mass in terms of non-volatile content). The mixture was then mixed until homogeneous, and then stirred for 2 minutes in a rotation / revolution mixer (ARE-310, manufactured by Thinky Corporation) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm, and cooled to room temperature with ice water. After that, the mixture was mixed until homogeneous. Next, to adjust the viscosity of the slurry, the viscosity was measured using a B-type viscometer, and distilled water was added as needed to bring the viscosity to a range of 2000 to 4000 Pa·s at a rate of 30 rpm. Finally, the negative electrode composition was prepared by stirring for 30 seconds in a rotation / revolution mixer (Thinky ARE-310) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm.

[0095] (3) Preparation of a non-aqueous secondary battery Using the negative electrode composition obtained above, a negative electrode, a positive electrode composition, a positive electrode, and a secondary battery were obtained in the same procedure as in (3) to (6) in Example 1.

[0096] (Example 14) In preparing the negative electrode binder composition, the types and amounts of materials used were changed as shown in Table 2, and the amount of lithium hydroxide aqueous solution added was adjusted as appropriate to achieve the non-volatile content concentration and pH shown in Table 2. Otherwise, the negative electrode binder composition was prepared in the same procedure as in Example 13. Furthermore, a negative electrode composition, a negative electrode, a positive electrode composition, a positive electrode, and a secondary battery were obtained in the same manner as in Example 13, except that the negative electrode binder composition was used.

[0097] (Comparative Examples 1-3) The negative electrode binder compositions were prepared using the same procedure as in Example 1, except that the types and amounts of materials used were changed as shown in Table 2, and the lithium hydroxide aqueous solution was adjusted to have the non-volatile content concentration and pH shown in Table 2. The negative electrode compositions, negative electrodes, positive electrode compositions, positive electrodes, and secondary batteries were obtained in the same manner as in Example 1.

[0098] (Comparative Example 4) In preparing the negative electrode binder composition, the types and amounts of materials used were changed as shown in Table 2, and the lithium hydroxide aqueous solution was adjusted to have the non-volatile content concentration and pH shown in Table 1. Otherwise, the negative electrode binder composition was prepared in the same procedure as in Example 13. The negative electrode composition, negative electrode, positive electrode composition, positive electrode, and secondary battery were obtained in the same manner as in Example 13.

[0099] The copolymers obtained in each of the above examples were water-soluble according to the definitions specified herein.

[0100] <Weight-average molecular weight of copolymers> For aqueous GPC measurements, a Shimadzu / L20 system was used as the HPLC instrument, and Shodex OHpak SB-806MHQ columns (8.0 mm I.D. × 300 mm L × 2) were used. A 0.2 mol / L sodium nitrate aqueous solution was used as the eluent, and the sample was dissolved to a concentration of 0.5%. The sample was then filtered through a φ0.45 filter and measured. The weight-average molecular weight was determined using an RI detector while introducing 50 μL of the sample and flowing it at a flow rate of 0.70 mL / min. A calibration curve was created using STANDARD P-82 (Pullulan) manufactured by Resonaq Corporation as the standard substance. The results are shown in Tables 1 and 2.

[0101] <Swelling Rate of Copolymer> After applying the binder composition obtained above onto a PET film, it was left to dry at room temperature for 3 days to form a copolymer film (coating). After peeling it off, it was cut into 1.0 cm × 1.0 cm squares and then dried in an 80°C forced-air dryer for 1 hour, and then in a 110°C vacuum dryer for 10 hours. The thickness of the obtained film was 100 to 150 μm. After measuring the mass of this film, a carbonate-based mixed solvent (EC (ethylene carbonate) / DMC (dimethyl carbonate) / MEC (ethyl methyl carbonate) / FEC (4-fluoroethylene carbonate) / VC (vinylene carbonate) / LiPF) was used. ６ The film was immersed in lithium hexafluoride phosphate (29 / 24 / 30 / 5 / 1 / 11 wt) at 60°C for 72 hours, and then its mass was measured again. The swelling rate was calculated using the following formula. The results are shown in Tables 1 and 2. Swelling rate (%) = (film mass after immersion - film mass before immersion) / (film mass before immersion) × 100

[0102] <Viscosity of Binder Composition> The viscosity of the binder composition was measured using a B-type viscometer (Viscometer TV-10M, Toki Sangyo Co., Ltd.) at 25°C under the following conditions. The results are shown in Tables 1 and 2. (Measurement conditions) For viscosity less than 20,000 mPa·s: No. 4 rotor used, rotation speed 30 rpm. For viscosity of 20,000 mPa·s or more: No. 4 rotor used, rotation speed 12 rpm.

[0103] <Stability of Negative Electrode Compositions> The viscosity of each negative electrode composition was measured using a B-type viscometer, and then the compositions were left standing in an oven heated to 45°C for two days. After standing, the viscosity was measured again using a B-type viscometer, and the viscosity change rate was calculated using the following formula. The stability was then evaluated according to the following evaluation criteria. The results are shown in Tables 1 and 2. Viscosity change rate (%) = Viscosity of negative electrode composition after standing / Viscosity of negative electrode composition before standing × 100 (Evaluation criteria) ◎ (Good): Less than 110% ○ (Good): 110% or more and less than 120% △ (Insufficient): 120% or more and less than 130% × (Poor): 130% or more

[0104] <Peel Strength of the Negative Electrode> The negative electrode prepared as described above was left overnight in a constant temperature and humidity chamber at 25°C and 20% relative humidity. Then, it was cut into strips 25 mm wide and 100 mm long. Next, using double-sided tape (Nitto Denko No. 5015), the active material side was attached to a stainless steel plate to create a sample for peel strength testing. Approximately 10 mm of the copper foil edge was peeled off, and polyimide tape was attached there to serve as the attachment point for the peel tester. The peel strength test sample was mounted on a peel tester (Shimadzu Corporation Autograph AG-X Plus), and a 180°C peel test was performed in a 20% relative humidity environment for evaluation. The results are shown in Tables 1 and 2. (Evaluation Criteria) ◎ (Good): Peel strength of 6.0 N / m or more ○ (Good): Peel strength of 4.5 N / m or more and less than 6.0 N / m △ (Insufficient): Peel strength of 3.0 N / m or more and less than 4.6 N / m × (Poor): Peel strength of less than 3.0 N / m

[0105] <Cycle Characteristics of Secondary Batteries> The secondary batteries prepared in each example and comparative example were mounted on a charge / discharge device and left at 25°C for 3 hours. After that, one charge / discharge cycle was performed at 0.1C, and the initial charge / discharge efficiency was measured. Next, the charge / discharge cycle at 0.2C was repeated 50 times, and the discharge capacity retention rate after 50 cycles (relative to the first discharge capacity at 0.2C) was measured using the following formula. The results are shown in Tables 1 and 2. Discharge capacity retention rate (%) = 100 × Discharge capacity at 50th cycle (mAh / g) / Initial discharge capacity (mAh / g) (Evaluation Criteria) ◎ (Good): Discharge capacity retention rate of 95% or more 〇 (Good): Discharge capacity retention rate of 80% or more and less than 95% △ (Insufficient): Discharge capacity retention rate of 70% or more and less than 80% × (Poor): Discharge capacity retention rate of less than 70%

[0106]

[0107]

[0108] As shown in Tables 1-2, the binder compositions of Examples 1-14 exhibited superior stability of the negative electrode composition compared to the comparative example, and the negative electrodes of Examples 1-14 showed superior peel strength compared to the comparative example. The cycle characteristics of the secondary batteries equipped with these negative electrodes were all excellent, receiving a rating of ◎ (95% or higher).

Claims

1. A binder composition for non-aqueous secondary battery electrodes comprising a copolymer, wherein the copolymer comprises 30% to 95% by mass of constituent units (a) derived from (meth)acrylamide monomers, 1% to 60% by mass of constituent units (b) derived from (meth)acrylic acid ester monomers, and 0.1% to 5% by mass of constituent units (c) derived from acid group-containing monomers.

2. The binder composition for non-aqueous secondary battery electrodes according to claim 1, comprising 50% by mass or more and 95% by mass or less of the constituent unit (a) derived from the (meth)acrylamide monomer.

3. The binder composition for non-aqueous secondary battery electrodes according to claim 1, comprising 0.1% by mass or more and less than 3% by mass of the constituent unit (c) derived from the acid group-containing monomer.

4. The binder composition for non-aqueous secondary battery electrodes according to claim 1, wherein the constituent unit (b) derived from the (meth)acrylic acid ester monomer comprises a constituent unit derived from at least one monomer selected from the group consisting of alkyl (meth)acrylic acid esters having an alkyl group having 1 to 3 carbon atoms, alkoxyalkyl (meth)acrylic acid esters having an alkoxyalkyl group having 1 to 3 carbon atoms, and hydroxyalkyl (meth)acrylic acid esters having a hydroxyalkyl group having 1 to 3 carbon atoms.

5. The binder composition for non-aqueous secondary battery electrodes according to claim 1, wherein at least a portion of the acid groups contained in the copolymer are neutralized with a basic compound.

6. The film formed from the copolymer is subjected to a carbonate-based mixed solvent (EC (ethylene carbonate) / DMC (dimethyl carbonate) / MEC (ethyl methyl carbonate) / FEC (4-fluoroethylene carbonate) / VC (vinylene carbonate) / LiPF ６ The electrode binder composition for a non-aqueous secondary battery according to claim 1, wherein the swelling rate after immersion in (lithium hexafluoride phosphate) = 29 / 24 / 30 / 5 / 1 / 11 (wt)) at 60°C for 72 hours is 5% by mass or less.

7. A composition for a non-aqueous secondary battery electrode, comprising an electrode active material, a conductive material, and a binder composition for a non-aqueous secondary battery electrode according to any one of claims 1 to 6.

8. A non-aqueous secondary battery electrode comprising an electrode composite layer formed using the non-aqueous secondary battery electrode composition described in claim 7.

9. A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode described in claim 8 and an electrolyte.

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