Non-aqueous secondary battery electrode binder composition, non-aqueous secondary battery electrode composition, non-aqueous secondary battery electrode, and non-aqueous secondary battery

Abstract

A non-aqueous secondary battery electrode binder composition according to the present invention includes a copolymer that is more than 20 mass% but less than 39.9 mass% a constituent unit (a) derived from an N-hydroxyalkyl(meth)acrylamide monomer, more than 60 mass% but less than 79.9 mass% a constituent unit (b) derived from a (meth)acrylamide monomer other than an N-hydroxyalkyl(meth)acrylamide monomer, and at least 0.1 mass% but no more than 5 mass% a constituent unit (c) derived from an acid group-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 negative electrode 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 a lithium battery binder comprising polyacrylic acid crosslinked with a crosslinking agent selected from specific compounds, wherein the viscosity of the crosslinked polyacrylic acid is within a specific range. Patent Document 2 also discloses a secondary battery binder containing a polymer compound, wherein the polymer compound contains acrylic repeating units, and the yellowness of a 3% by mass aqueous solution of the polymer compound is 14 or less. Patent Document 3 also discloses a non-aqueous secondary battery electrode binder composition comprising a water-soluble polymer containing N-hydroxyalkyl (meth)acrylamide monomer units in a proportion of 0.1% by mass to 20% by mass, and (meth)acrylamide monomer units other than the N-hydroxyalkyl (meth)acrylamide monomer units in a proportion of 40% by mass to 94.9% by mass, and a particulate polymer.

[0006] Japanese Patent Publication No. 2018-029069, Japanese Patent Publication No. 2021-136121, Japanese Patent No. 7020118

[0007] However, the technologies described in Patent Documents 1 and 2 do not necessarily provide sufficient cycle characteristics at high and low temperatures for secondary batteries manufactured using the binder. Furthermore, while the technology described in Patent Document 3 exhibits excellent cycle characteristics under high-temperature conditions for secondary batteries manufactured using the binder, sufficient studies have not been conducted on its cycle characteristics at low temperatures.

[0008] Therefore, the present invention aims to provide a binder composition for non-aqueous secondary battery electrodes that can form non-aqueous secondary batteries with excellent cycle characteristics even under high and low temperature conditions. Furthermore, the present invention aims to provide a non-aqueous secondary battery electrode composition and a non-aqueous secondary battery electrode that can form non-aqueous secondary batteries with excellent cycle characteristics even under high and low temperature conditions. Moreover, the present invention aims to provide a non-aqueous secondary battery with excellent cycle characteristics even under high and low temperature conditions.

[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, in predetermined proportions, structural units derived from N-hydroxyalkyl (meth)acrylamide monomers, structural units derived from (meth)acrylamide monomers other than N-hydroxyalkyl (meth)acrylamide monomers, and structural units derived from acid group-containing monomers.

[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 more than 20% by mass and less than 39.9% by mass of constituent units (a) derived from N-hydroxyalkyl (meth)acrylamide monomers, more than 60% by mass and less than 79.9% by mass of constituent units (b) derived from (meth)acrylamide monomers other than N-hydroxyalkyl (meth)acrylamide monomers, and 0.1% by mass or more and 5% by mass or less of constituent units (c) derived from acid group-containing monomers. [2] The binder composition for a non-aqueous secondary battery electrode according to [1], wherein the constituent unit (a) derived from N-hydroxyalkyl (meth)acrylamide is a constituent unit derived from N-hydroxyethylacrylamide. [3] 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 ６A binder composition for electrodes of a non-aqueous secondary battery according to [1] or [2], wherein the degree of swelling after immersion in (lithium hexafluoride phosphate) = 29 / 24 / 30 / 5 / 1 / 11 (wt)) at 60°C for 72 hours is 5.0% by mass or less. [4] A binder composition for electrodes of a non-aqueous secondary battery according to any one of [1] to [3], wherein at least a portion of the acid groups contained in the copolymer is neutralized with a basic compound. [5] A composition for electrodes of a non-aqueous secondary battery, comprising an electrode active material, a conductive material, and the binder composition for electrodes of a non-aqueous secondary battery according to any one of [1] to [4]. [6] A non-aqueous secondary battery electrode comprising an electrode composite layer formed using the non-aqueous secondary battery electrode composition according to [5]. [7] A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode according to [6] and an electrolyte.

[0011] According to the present invention, a binder composition for non-aqueous secondary battery electrodes can be provided that can form non-aqueous secondary batteries with excellent cycle characteristics even under high and low temperature conditions. Furthermore, according to the present invention, a binder composition for non-aqueous secondary battery electrodes and non-aqueous secondary battery electrodes can be provided that can form non-aqueous secondary batteries with excellent cycle characteristics even under high and low temperature conditions. Moreover, according to the present invention, a non-aqueous secondary battery with excellent cycle characteristics even under high and low temperature conditions can be provided.

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

[0015] In this specification, in a copolymer produced by copolymerizing two or more kinds of monomers, the proportion of the constitutional unit formed by polymerizing a certain monomer in the copolymer usually coincides with the ratio (charge 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. In addition, by subjecting the copolymer to NMR measurement, the content of each constitutional unit constituting the copolymer can also be measured.

[0016] In this specification, “(meth)acrylic acid” means one or both of methacrylic acid and acrylic acid. Also, “(meth)acrylate” means one or both of methacrylate and acrylate. Also, “(meth)acrylamide” means one or both of methacrylamide and acrylamide.

[0017] In this specification, “non-aqueous secondary battery” means including a non-aqueous electrolyte secondary battery and an all-solid-state secondary battery. Note that “non-aqueous electrolyte” means an electrolyte substantially free of water. Note that “an 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. Also, “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 an electrolyte.

[0018] <<Binder composition for non-aqueous secondary battery electrode>> The binder composition for non-aqueous secondary battery electrode according to one embodiment of the present invention (hereinafter also referred to as “binder composition”) is a binder composition for non-aqueous secondary battery electrode containing a copolymer, wherein the copolymer contains a constitutional unit (a) derived from an N-hydroxyalkyl (meth)acrylamide monomer in an amount of more than 20% by mass and less than 39.9% by mass, a constitutional unit (b) derived from a (meth)acrylamide monomer other than N-hydroxyalkyl (meth)acrylamide in an amount of more than 60% by mass and less than 79.9% by mass, and a constitutional unit (c) derived from an acid group-containing monomer in an amount of 0.1% by mass or more and 5% by mass or less. [[ID=io]]

[0019] <Copolymer> The copolymer constituting the binder composition of this embodiment contains more than 20% by mass and less than 39.9% by mass of constituent units (a) derived from N-hydroxyalkyl (meth)acrylamide monomers, more than 60% by mass and less than 79.9% by mass of constituent units (b) derived from (meth)acrylamide monomers other than N-hydroxyalkyl (meth)acrylamide, and 0.1% by mass or more and 5% by mass of constituent units (c) derived from acid group-containing monomers. By containing the copolymer in the binder composition of this embodiment, a non-aqueous secondary battery (hereinafter also simply referred to as "secondary battery") that exhibits excellent cycle characteristics even under high and low temperature conditions can be formed. The reason for obtaining such effects is not clear, but by containing constituent units (a) derived from N-hydroxyalkyl (meth)acrylamide monomers within the above range, the flexibility of the copolymer is improved, cracking during electrode fabrication is less likely to occur, and furthermore, detachment due to expansion and contraction of the electrode active material during charging and discharging can be effectively suppressed, thereby improving the cycle characteristics when used as a secondary battery. In addition, by including a constituent unit (b) derived from (meth)acrylamide monomers other than N-hydroxyalkyl(meth)acrylamide within the above range, strong intermolecular forces derived from the amide group are exerted, improving the cohesiveness of the copolymer. As a result, when mixed with the electrode active material, the copolymer easily coats the surface of the electrode active material, and it is believed that electrodes formed using a binder composition containing this copolymer can exhibit excellent adhesion. Furthermore, by including a constituent unit (c) derived from an acid group-containing monomer within the above range, the flexibility of the copolymer and the stability of the electrode composition can be ensured without reducing the intermolecular forces. Thus, electrodes made using a binder composition containing this copolymer exhibit excellent flexibility and adhesion, resulting in high peel strength, and it is presumed that secondary batteries exhibiting excellent cycle characteristics even under high and low temperature conditions can be obtained. The constituent units of the copolymer will be described below.

[0020] (Constituent unit (a) derived from N-hydroxyalkyl (meth)acrylamide monomer) The copolymer constituting the binder composition of this embodiment contains a constituent unit (a) derived from N-hydroxyalkyl (meth)acrylamide monomer. The copolymer contains a constituent unit (a) derived from N-hydroxyalkyl (meth)acrylamide monomer, which improves the flexibility of the copolymer. As a result, the flexibility of electrodes made using the binder composition of this embodiment is improved, which effectively suppresses cracking during electrode fabrication and detachment due to expansion and contraction of the electrode active material during charging and discharging, thereby improving the cycle characteristics of secondary batteries made using these electrodes.

[0021] The N-hydroxyalkyl(meth)acrylamide monomer that can form the constituent unit (a) derived from the N-hydroxyalkyl(meth)acrylamide monomer is not particularly limited as long as it is a (meth)acrylamide having a hydroxyalkyl group. The alkyl group in the hydroxyalkyl group may be linear or branched. Furthermore, the alkyl group in the hydroxyalkyl group preferably has 2 to 4 carbon atoms, and more preferably 2 to 3 carbon atoms.

[0022] Examples of the N-hydroxyalkyl(meth)acrylamide monomers include N-(2-hydroxyethyl)(meth)acrylamide, N-(2-hydroxypropyl)(meth)acrylamide, N-(1-hydroxypropyl)(meth)acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide, N-(3-hydroxybutyl)(meth)acrylamide, and N-(4-hydroxybutyl)(meth)acrylamide. These may be used individually or in combination of two or more.

[0023] In this embodiment, the constituent unit (a) derived from the N-hydroxyalkyl(meth)acrylamide monomer preferably includes a constituent unit derived from at least one monomer selected from the group consisting of N-(2-hydroxyethyl)acrylamide, N-(2-hydroxyethyl)methacrylamide, N-(2-hydroxypropyl)acrylamide, N-(2-hydroxypropyl)methacrylamide, and N-(3-hydroxypropyl)acrylamide; more preferably includes a constituent unit derived from at least one monomer selected from the group consisting of N-(2-hydroxyethyl)acrylamide, N-(2-hydroxyethyl)methacrylamide, and N-(2-hydroxypropyl)methacrylamide; and even more preferably includes a constituent unit derived from N-(2-hydroxyethyl)acrylamide. Including the above monomer-derived constituent unit (a) improves the flexibility of the copolymer, thereby further enhancing the flexibility of the resulting electrode.

[0024] The content of constituent unit (a) derived from N-hydroxyalkyl(meth)acrylamide monomer in the copolymer is greater than 20% by mass and less than 39.9% by mass relative to the total monomer units contained in the copolymer. When the content of constituent unit (a) is greater than 20% by mass, the copolymer exhibits excellent flexibility, improving the flexibility of electrodes made using the binder composition of this embodiment. This effectively suppresses cracking during electrode fabrication and detachment due to expansion and contraction of the electrode active material during charging and discharging, improving the cycle characteristics of secondary batteries equipped with such electrodes. The content of constituent unit (a) is preferably 22% by mass or more, more preferably 25% by mass or more, even more preferably 28% by mass or more, and particularly preferably 30% by mass or more. Furthermore, when the content of constituent unit (a) is less than 39.9% by mass, sufficient intermolecular forces derived from constituent unit (b) derived from (meth)acrylamide monomer can be secured, so the copolymer exhibits 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. The content of the constituent unit (a) is preferably 38% by mass or less, more preferably 36% by mass or less, even more preferably 35% by mass or less, and particularly preferably 34% by mass or less.

[0025] (Constituent units (b) derived from (meth)acrylamide monomers other than N-hydroxyalkyl(meth)acrylamide) The copolymer has constituent units (b) derived from (meth)acrylamide monomers other than N-hydroxyalkyl(meth)acrylamide monomers. The copolymer contains constituent units (b) derived from (meth)acrylamide monomers other than N-hydroxyalkyl(meth)acrylamide monomers, which improves the cohesiveness of the copolymer due to hydrogen bonding between amide groups. As a result, 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 is improved, and the cycle characteristics of secondary batteries made using said electrodes can be improved. In addition, when the binder composition of this embodiment is mixed with the electrode active material, the dispersibility of the electrode active material is increased, and the battery characteristics of the resulting secondary battery are improved.

[0026] The (meth)acrylamide monomer capable of forming the constituent unit (b) derived from the (meth)acrylamide monomer is not particularly limited as long as it is a monomer having a (meth)acrylamide group other than the N-hydroxyalkyl(meth)acrylamide monomer. 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; diacetone(methacrylamide); and acryloylmorpholine. These may be used individually or in combination of two or more. Among these, from the viewpoint of improving the cohesiveness of the copolymer, it is preferable that the constituent unit (b) includes a constituent unit derived from at least one monomer selected from the group consisting of acrylamide, methacrylamide, N-methylacrylamide, and N,N-dimethylacrylamide, more preferably a constituent unit derived from at least one monomer selected from the group consisting of acrylamide and methacrylamide, and particularly preferably a constituent unit derived from acrylamide.

[0027] The copolymer contains the constituent unit (b) derived from the (meth)acrylamide monomer in an amount greater than 60% by mass and less than 79.9% by mass relative to the total monomer units contained in the copolymer. A content of more than 60% by mass of the constituent unit (b) derived from the (meth)acrylamide monomer improves the cohesiveness of the copolymer due to inter-amide hydrogen bonding, thereby improving the coating properties of the copolymer on the electrode active material surface. This results in an electrode exhibiting excellent peel strength, improving the cycle characteristics of a secondary battery equipped with such an electrode. Furthermore, the copolymer's content of more than 60% by mass of the constituent unit (b) enhances the dispersibility of the electrode active material when the binder composition of this embodiment is mixed with the electrode active material, improving the battery characteristics, such as the cycle characteristics, of the resulting secondary battery. The content of the constituent unit (b) is preferably 62% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 68% by mass or more. Additionally, a content of less than 79.9% by mass of the constituent unit (b) ensures the flexibility of the copolymer. The content of the constituent unit (b) is preferably 78% by mass or less, more preferably 76% by mass or less, and even more preferably 74% by mass or less.

[0028] (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.

[0029] 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 N-hydroxyalkyl(meth)acrylamide monomer and other (meth)acrylamide monomers, it shall be considered an acid group-containing monomer.

[0030] 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.

[0031] 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).

[0032] 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.

[0033] 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.

[0034] The content of the constituent unit (c) derived from the acid group-containing monomer in the copolymer 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 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. A content of 0.5% by mass or more is preferred, 0.8% by mass or more is more preferred, 1.2% by mass or more is even more preferred, and 1.5% by mass or more is particularly preferred. 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 4.5% by mass or less, more preferably less than 3% by mass, even more preferably 2.7% by mass or less, and particularly preferably 2.5% by mass or less.

[0035] In this embodiment, the total content of the constituent unit (a) derived from the N-hydroxyalkyl(meth)acrylamide monomer, the structural unit (b) derived from the (meth)acrylamide monomer, and the constituent unit (c) derived from the acid group-containing monomer is greater than 80.1% by mass and may be 90% 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 resulting copolymer will exhibit flexibility and cohesiveness, and the electrode made using the binder composition containing the copolymer will exhibit good flexibility and adhesion. As a result, the cycle characteristics of the secondary battery equipped with the electrode will be improved. The total content of the constituent units (a) to (c) may be 93% by mass or more, or 97% by mass or more. Furthermore, the upper limit of the total content of the constituent units (a) to (c) may be 100% by mass, 99.8% by mass, 99.5% by mass, or 99% by mass. In other words, the total content of the constituent units (a) to (c) may be greater than 80.1% by mass and less than or equal to 100% by mass.

[0036] (Other constituent units (d)) The binder composition of this embodiment may further contain constituent units (a) derived from the N-hydroxyalkyl (meth)acrylamide monomer, constituent units (b) derived from (meth)acrylamide monomers other than the N-hydroxyalkyl (meth)acrylamide monomer, and constituent units (d) other than the constituent units (c) derived from the acid group-containing monomer (hereinafter, "other constituent units (d)").

[0037] Examples of monomers that can constitute the other constituent unit (d) include (meth)acrylic acid ester monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, methoxymethyl (meth)acrylate, and cyclopentyl (meth)acrylate; vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl lauryl acid, vinyl decanoate, vinyl stearate, vinyl hexanoate, vinyl octanoate, and vinyl palmitate; and 2-hydroxy(meth)acrylate Examples include hydroxyl group-containing monomers such as roxyethyl ethyl phosphate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; 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; heterocyclic vinyl monomers such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole; and glycidyl group-containing monomers such as glycidyl (meth)acrylate and allyl glycidyl ether. These may be used individually or in any combination of two or more in any ratio.

[0038] If the binder composition of this embodiment contains the other constituent unit (d), its content may be less than 19.9% ​​by mass, 10% by mass or less, 7% by mass or less, or 3% 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, 0.2% by mass or 0.5% by mass. In other words, the content of the constituent unit (d) may be 0% by mass or more and less than 19.9% ​​by mass.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] (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 2.0% by mass or less.

[0045] The weight-average molecular weight (Mw) of the copolymer is preferably 500,000 to 4,000,000, more preferably 600,000 to 3,500,000, and even more preferably 700,000 to 3,000,000. When the weight-average molecular weight of the copolymer is within the above range, the adhesion between the electrode active materials and between the electrode composite layer and the current collector in the electrode formed using the binder composition of this embodiment is 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 from Resonaq, or the Asahipak series GF-HQ can be used. As eluents, neutral salt solutions such as aqueous sodium chloride solution, aqueous sodium nitrate solution, aqueous sodium hydrogen hydrochloride solution, aqueous sodium sulfate solution, and phosphate buffer 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. Polystyrene or pullulan can be used as the standard substance for GPC measurement.

[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, thereby improving the cycle characteristics of the secondary battery formed using electrodes made using the binder composition of this embodiment. The swelling rate is more preferably 4.8% by mass or less, even more preferably 4.5% by mass or less, even more preferably 4.2% by mass or less, and particularly preferably 3.8% by mass or less. The lower limit of the swelling rate is not particularly limited, but for example, it is 0% by mass. That is, the swelling rate 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 film (dried coating) with a thickness of 150 μm, and then drying this dry film in a carbonate-based mixed solvent (for example, (EC (ethylene carbonate) / DMC (dimethyl carbonate) / MEC (ethyl methyl carbonate) / FEC (4-fluoroethylene carbonate) / VC (vinyl 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 coating before immersion) / (Mass of film before immersion) × 100

[0048] The copolymer preferably has a viscosity of 800 mPa·s or more when prepared as a 5% by mass aqueous solution. A viscosity of 800 mPa·s or more allows for the development of dispersion stability and storage stability in the electrode composition prepared using the binder composition of this embodiment. A viscosity of 1500 mPa·s or more is more preferable, and 3000 mPa·s or more is even more preferable. Furthermore, from the viewpoint of manufacturability, the viscosity of the copolymer when prepared as a 5% aqueous solution is preferably 40000 mPa·s or less, more preferably 30000 mPa·s or less, and even more preferably 20000 mPa·s or less. That is, the viscosity of the copolymer when prepared as a 5% by mass aqueous solution may be between 800 mPa·s and 40000 mPa·s. The viscosity can be measured using a B-type viscometer.

[0049] Furthermore, in the binder composition of this embodiment, the content of the copolymer is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 97% by mass or more, when the non-volatile 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, and the cycle characteristics of the secondary battery are improved. The content of the copolymer may be 100% by mass or less, 99% by mass or less, or 98% by mass or less, when the non-volatile content of the binder composition is set to 100% by mass.

[0050] (Method for producing the copolymer) The method for producing the copolymer constituting the binder composition of this embodiment is not particularly limited and can be produced by known methods. For example, the copolymer can be produced by mixing the N-hydroxyalkyl(meth)acrylamide monomer, (meth)acrylamide monomers other than the N-hydroxyalkyl(meth)acrylamide monomer, the acid group-containing monomer, and other monomers that may be 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 solid 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 solid 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 of the other polymers is preferably 50% by mass or less, more preferably 30% by mass or less, and particularly preferably 10% 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 of the other polymers may be 0% by mass. That is, the content of the other polymers may be 0% by mass or more and 50% by mass or less.

[0061] <Additives> The binder composition of this embodiment may further contain various additives as needed, such as surfactants, antioxidants, light stabilizers, plasticizers, and organic or inorganic fillers, to the extent that they do not impair the effects of the present invention.

[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] Furthermore, if the binder composition of this embodiment contains the additive, its content is preferably 3% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1% by mass or less, based on 100% by mass of the nonvolatile content of the binder composition of this embodiment. The lower limit of the content of the additive may also be 0% by mass. In other words, the content of the additive may be 0% by mass or more and 3% by mass or less.

[0064] <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.

[0065] <<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.

[0066] (Electrode Active Material) As the electrode active material, various selections can be made according to the type of electrode to be manufactured and then blended. That is, the composition for non-aqueous secondary battery electrodes of this embodiment includes a composition for non-aqueous secondary battery positive electrodes and a composition for non-aqueous secondary battery negative electrodes. Specifically, by using the 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 the negative electrode active material described later as the electrode active material, a composition for non-aqueous secondary battery negative electrodes can be obtained.

[0067] When the composition for non-aqueous secondary battery electrodes of this embodiment is used to manufacture the 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. 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.

[0068] When the composition for non-aqueous secondary battery electrodes of this embodiment is used to manufacture the 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. For example, lithium cobalt oxide (LiCoO <00ooo09>), lithium nickel oxide (LiNiO ２ ), lithium manganate (LiMnO ２ ), and their composite oxides (LiCoxNiyMnzO ２ , x + y + z = 1), lithium manganese spinel (LiMn ２ O ４ ), lithium vanadium compounds, V ２O ５ , V ６ O １３ , VO ２ MnO ２ , 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.

[0069] (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.

[0070] (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.

[0071] Examples of the preservatives mentioned above include those similar to those described in the binder composition.

[0072] 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.

[0073] (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.

[0074] ≪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.

[0075] The material and shape of the current collector are not particularly limited; for example, copper, nickel, titanium, stainless steel, etc., can be used in the form of foil, perforated foil, mesh, or other strip-like material. Porous materials, such as porous metal (foamed metal) or carbon paper, can also be used.

[0076] 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.

[0077] Furthermore, the integration of electrode compositions molded into sheet-like, pellet-like, or other shapes with current collectors can be carried out by known methods such as rolling, pressing, or a combination thereof. The electrode density after integration is, for example, 1.0 to 1.8 g / cm³. ３ Preferably, 1.1 to 1.7 g / cm³ ３ That is the case.

[0078] The electrode composite layer formed on the current collector and the electrode composite layer integrated with the current collector are preferably subjected to heat treatment. 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.

[0079] ≪Non-aqueous secondary battery≫ The non-aqueous secondary battery of this embodiment includes the electrode of this embodiment. When used in a wet electrolyte secondary battery, for example, the secondary battery of this embodiment can be constructed by arranging the positive electrode and the electrode of this embodiment opposite each other with a separator in between, and injecting an electrolyte.

[0080] 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.

[0081] Examples of the electrolyte include LiClO ４ LiPF ６ LiAsF ６ LiBF ４ LiSO ３ CF ３ A 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.

[0082] 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, the 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.

[0083] The structure of a secondary battery using the non-aqueous secondary battery electrode binder composition of 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 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. The non-aqueous secondary battery electrode binder composition of this embodiment can also be applied to electrochemical devices in general that use the insertion and removal of lithium ions as a charge and discharge mechanism, such as hybrid capacitors and solid lithium secondary batteries.

[0084] The binder composition for non-aqueous secondary battery electrodes, the electrode composition, the electrode, and the secondary battery having the electrode of the present invention have been described above. However, the present invention is not limited to the configuration of the embodiments 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 the present invention may each have additional configurations in addition to the configuration of the embodiments described above, or may be replaced with any configuration that performs a similar function.

[0085] 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.

[0086] <Monomers> HEAA: N-(2-hydroxyethyl)acrylamide HPMA: N-(2-hydroxypropyl)methacrylamide AM: Acrylamide DAAM: Diacetone acrylamide AA: Acrylic acid MA: Methyl acrylate VP: N-vinylpyrrolidone

[0087] (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. Dissolved oxygen in the deionized water was then removed by nitrogen blower. A mixture of 25 parts by mass of N-(2-hydroxyethyl)acrylamide, 71 parts by mass of acrylamide, 4 parts by mass of acrylic acid, 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 binder composition (7.7% by mass in terms of non-volatile content, pH 5.3, viscosity 31000 mPa·s).

[0088] (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 (ARE-310 manufactured by Thinky Corporation) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm. The binder composition obtained in (1) above (non-volatile content 7.7% 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 (7.7% by mass of nonvolatile content) was diluted with distilled water to adjust the nonvolatile content concentration to 5.0% by mass. 16.8 parts by mass of this binder composition (0.84 parts by mass in terms of nonvolatile content) was added to the mixture obtained above and mixed until the mixture was homogeneous. Then, the mixture was stirred for 2 minutes in a rotating / revolving mixer (Thinky ARE-310) 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 mixture, the viscosity was measured with 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 mixture was stirred for 30 seconds in a rotating / revolving mixer (Thinky ARE-310) at a rotation speed of 1000 rpm and a revolving speed of 2000 rpm to prepare the negative electrode composition.

[0089] (3) The coating amount (surface density) of the mixture layer after drying of the 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 a negative electrode mixture layer density of 1.55 g / cm³ was measured using a roll press (Small desktop roll press SA-602 manufactured by Tester Industries Co., Ltd.) ３ The mixture was pressed to a thickness of 66.7 μm. It was then vacuum-dried at 110°C for 10 hours to obtain the negative electrode (surface density 8.8 g / cm²). ２ The density of the negative electrode mixture layer is 1.5 g / cm³. ３ A composite layer thickness of 68.6 μm was obtained. The initial charging capacity per unit area of ​​this electrode was 4.95 mAh / cm². ２ Therefore, the negative electrode (surface density 8.8 gm / cm³) ２ The density of the negative electrode mixture layer is 1.5 g / cm³. ３ The combined layer thickness is 68.6 μm, and the initial charge capacity per unit area is 4.95 mAh / cm². ２ ) was obtained.

[0090] (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 rotating / revolving mixer (Thinky ARE-310) at a rotation speed of 1000 rpm and a revolving speed of 2000 rpm. To this mixture, 27.0 parts by mass (2.16 parts by mass in terms 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 obtained above 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 stirring generated heat, 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. Next, 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, prepared to a non-volatile content concentration of 8% by mass, was added to the mixture and mixed until the whole was homogeneous. Then, 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, and then cooled to room temperature with ice water. Next, 5 parts by mass of anhydrous N-methylpyrrolidone were added and mixed until the mixture was homogenized. Then, to adjust the viscosity of the slurry, the viscosity was measured using a B-type viscometer, and an appropriate amount of anhydrous N-methylpyrrolidone was added to the mixture so that the viscosity was in the range of 2000 to 4000 Pa·s at a rate of 30 rpm. Finally, the mixture was stirred for 30 seconds in a rotation / revolution mixer (Thinky ARE-310) at a rotation rate of 1000 rpm and a revolution rate of 2000 rpm to prepare the cathode composition.

[0091] (5) The amount of composite coating (surface density) after the preparation and drying of the positive electrode is 25.0 mg / cm². ２The 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 a roll press machine (Small desktop roll press SA-602 manufactured by Tester Industries Co., Ltd.) was used to press the positive electrode mixture layer to a density of 3.4 g / cm³. ３ The mixture was pressed to a thickness of 73.3 μm, and then vacuum-dried at 110°C for 10 hours to obtain the positive electrode. The initial charge capacity per unit area of ​​this electrode was 4.49 mAh / cm². ２ That is the case.

[0092] (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.

[0093] (Examples 2-7) A negative electrode binder composition was obtained using the same procedure as in Example 1, except that the types and amounts of materials used were changed as shown in Table 1, and the amount of lithium hydroxide aqueous solution added was also changed to adjust the pH and non-volatile concentration as shown in Table 1. Furthermore, a negative electrode composition, a negative electrode, a positive electrode composition, a positive electrode, and a secondary battery were obtained using the same procedure as in Example 1, except that the negative electrode binder composition was used.

[0094] (Example 8) (1) Preparation of polymer-containing solution In Example 1 (1), the types of materials used and their amounts were changed as shown in Table 1 to obtain a polymer-containing solution (non-volatile content concentration 7.8% by mass, pH 5.9, viscosity 31000 mPa·s).

[0095] (2) Preparation of anode binder composition and anode composition 11.5 parts by mass of SiO anode 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 (ARE-310 manufactured by Thinky) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm. The polymer-containing solution obtained in (1) above (non-volatile content 7.7% by mass) was diluted with distilled water to obtain a polymer-containing solution with a non-volatile content concentration of 5.0%. 9.0 parts by mass (0.45 parts by mass in terms of non-volatile content) of this polymer-containing solution and 37.5 parts by mass (0.75 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.) adjusted to a non-volatile content concentration of 2.0% as a viscosity modifier were added and mixed until the mixture 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. Next, the polymer-containing solution obtained in (1) above (7.7% by mass of nonvolatile content) was diluted with distilled water to adjust the polymer-containing solution to a nonvolatile content concentration of 5.0% by mass. 6.0 parts by mass of this solution (0.3 parts by mass in terms of nonvolatile content) and 10.8 parts by mass of distilled water were added and mixed until the mixture was homogeneous. Then, 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, and cooled to room temperature with ice water. Next, 1.3 parts by mass of distilled water and 2.96 parts by mass (1.5 parts by mass in terms of non-volatile content) of styrene-butadiene copolymer (SBR) (DS407H, manufactured by DIC Corporation, non-volatile content concentration 50.8%) as other polymers were added and mixed until the mixture was homogenized. Then, the mixture was stirred for 30 seconds in a rotating / revolving mixer (ARE-310, manufactured by Thinky Corporation) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm.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 it within the range of 2000 to 4000 Pa·s at a rotation 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.

[0096] (3) Preparation of non-aqueous secondary batteries, etc. A negative electrode, a positive electrode composition, a positive electrode, and a secondary battery were obtained in the same manner as in Example 1, except that the negative electrode composition obtained in (2) above was used.

[0097] (Example 9) (1) Preparation of the negative electrode binder composition In the preparation of the negative electrode binder composition, the types and amounts of materials used were changed as shown in Table 1, and pH adjustment and dilution were performed using an aqueous ammonia solution instead of an aqueous lithium hydroxide solution, except that the procedure was the same as in Example 1 to obtain a negative electrode binder composition (non-volatile content 7.9% by mass, pH 5.7, viscosity 29000 mPa·s).

[0098] (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 (ARE-310 manufactured by Thinky Corporation) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm. 25.3 parts by mass (2.0 parts by mass in terms of non-volatile content) of the binder composition obtained in (1) above (non-volatile content 7.9% by mass) and 21.0 parts by mass (0.42 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.) adjusted to a non-volatile content concentration of 2.0% as a viscosity modifier were added and mixed until the mixture 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. Next, 29.0 parts by mass (0.58 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.), adjusted to a non-volatile content concentration of 2.0% as a viscosity modifier, was added to the mixture obtained above and mixed until the whole was homogeneous. Then, 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, and cooled to room temperature with ice water. Next, to adjust the viscosity of the slurry, the viscosity was measured with a B-type viscometer, and distilled water was added as needed to bring it to a range of 2000 to 4000 Pa·s at a rotation speed of 30 rpm. Finally, the negative electrode composition was prepared by stirring for 30 seconds 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.

[0099] (3) Preparation of non-aqueous secondary batteries, etc. A negative electrode, a positive electrode composition, a positive electrode, and a secondary battery were obtained in the same manner as in Example 1, except that the negative electrode composition obtained in (2) above was used.

[0100] (Example 10, Comparative Examples 1-4) A negative electrode binder composition was obtained using the same procedure as in Example 1, except that the types and amounts of materials used were changed as shown in Table 1, and the amount of lithium hydroxide aqueous solution added was also changed to adjust the pH and non-volatile concentration as shown in Table 1. Furthermore, a negative electrode composition, a negative electrode, a positive electrode composition, a positive electrode, and a secondary battery were obtained using the same procedure as in Example 1, except that the negative electrode binder composition was used.

[0101] The copolymers obtained in each of the above examples were water-soluble according to the definitions specified herein.

[0102] <Evaluation> <Weight-average molecular weight of copolymer> 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. 50 μL of the sample was added and the weight-average molecular weight was determined using an RI detector while flowing at a flow rate of 0.70 mL / min. A calibration curve was created using Resonaq STANDARD P-82 (Pullulan) as the standard substance. The results are shown in Table 1.

[0103] <Swelling Rate of Copolymer> The binder composition obtained above (in Example 8, a polymer-containing solution) was applied to a PET film and left to dry at room temperature for 3 days to form a copolymer film (coating). After peeling, 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 coating, 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. ６The film was immersed in lithium hexafluoride phosphate (29 / 24 / 30 / 5 / 1 / 11 wt) at 60°C for 72 hours, and the mass of the film was measured again. The swelling rate was calculated using the following formula. The results are shown in Table 1. Swelling rate (%) = (film mass after immersion - film mass before immersion) / (film mass before immersion) × 100

[0104] <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: (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

[0105] <Electrode Flexibility Evaluation> The negative electrode obtained above was wrapped around a SUS cylindrical rod with a diameter of 8 cm, and the presence or absence of cracks in the negative electrode composite layer was visually evaluated. (Evaluation Criteria) ○: No cracks occurred ×: Cracks occurred

[0106] <Peel Strength of the Negative Electrode> The negative electrode obtained above 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-degree peel test was performed in a 20% relative humidity environment for evaluation. The results are shown in Table 1. (Evaluation Criteria) ◎ (Good): Peel strength of 7.0 N / m or more 〇 (Good): Peel strength of 5.0 N / m or more and less than 7.0 N / m △ (Insufficient): Peel strength of 3.0 N / m or more and less than 5.0 N / m × (Poor): Peel strength of less than 3.0 N / m

[0107] <Cycle Characteristics of Secondary Batteries> (High-Temperature Cycle Characteristics) Secondary batteries prepared in each example and comparative example were mounted on a charge / discharge device, left at 25°C for 3 hours, and then charged and discharged once at 0.1C to measure the initial charge / discharge efficiency. Next, the charge / discharge cycle was repeated 100 times at 45°C and 0.5C, and the discharge capacity retention rate after 100 cycles (100 times) relative to the first discharge capacity (initial discharge capacity) was calculated using the following formula, and the high-temperature cycle characteristics were evaluated based on the evaluation criteria below. Discharge capacity retention rate (%) = 100 × Discharge capacity after 100 cycles (mAh / g) / Initial discharge capacity (mAh / g) (Evaluation Criteria) ◎ (Good): Discharge capacity retention rate of 90% or more 〇 (Good): Discharge capacity retention rate of 85% or more and less than 90% △ (Insufficient): Discharge capacity retention rate of 70% or more and less than 85% × (Poor): Discharge capacity retention rate of less than 70%

[0108] (Low-Temperature Cycle Characteristics) 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 was repeated 100 times at 0°C and 0.5C. The discharge capacity retention rate after 100 cycles (100 cycles) relative to the first discharge capacity (initial discharge capacity) was calculated using the same formula as the measurement method for high-temperature cycle characteristics, and the low-temperature cycle characteristics were evaluated. The evaluation criteria were the same as the evaluation criteria for high-temperature cycle characteristics.

[0109]

[0110] As shown in Table 1, the negative electrodes produced using the binder compositions of Examples 1 to 10 exhibited excellent electrode flexibility and peel strength (adhesion), and the high-temperature and low-temperature cycle characteristics of secondary batteries equipped with these negative electrodes were all excellent, rated at or above ○.

Claims

1. A binder composition for non-aqueous secondary battery electrodes comprising a copolymer, wherein the copolymer comprises more than 20% by mass and less than 39.9% by mass of constituent units (a) derived from N-hydroxyalkyl (meth)acrylamide monomers, more than 60% by mass and less than 79.9% by mass of constituent units (b) derived from (meth)acrylamide monomers other than N-hydroxyalkyl (meth)acrylamide monomers, and 0.1% by mass or more and 5% by mass or less of constituent units (c) derived from acid group-containing monomers.

2. The binder composition for non-aqueous secondary battery electrodes according to claim 1, wherein the constituent unit (a) derived from the N-hydroxyalkyl (meth)acrylamide monomer contains a constituent unit derived from N-hydroxyethylacrylamide.

3. 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 A binder composition for electrodes of a non-aqueous secondary battery according to claim 1, wherein the degree of swelling after immersion in (lithium hexafluoride phosphate) = 29 / 24 / 30 / 5 / 1 / 11 (wt)) at 60°C for 72 hours is 5.0% by mass or less.

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

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

6. A non-aqueous secondary battery electrode comprising an electrode composite layer formed using the non-aqueous secondary battery electrode composition described in claim 5.

7. A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode described in claim 6 and an electrolyte.

Images