Binder for secondary battery electrode and use thereof

Abstract

A binder for a secondary battery electrode, the binder including a carboxyl group-containing non-crosslinked polymer or a salt thereof, wherein the carboxyl group-containing non-crosslinked polymer or the salt thereof includes a structural unit derived from an ethylenically unsaturated carboxylic acid monomer (a1), and a structural unit derived from an ethylenically unsaturated monomer (b) having a cationic group and / or a cation generating group, the amount of the structural unit derived from the monomer (a1) is 30 mass% or more based on the mass of the carboxyl group-containing non-crosslinked polymer or the salt thereof, and the amount of the structural unit derived from the monomer (b) is 2 mass% to 50 mass% inclusive based on the mass of the carboxyl group-containing non-crosslinked polymer or the salt thereof.

Description

Binders for secondary battery electrodes and their applications

[0001] This invention relates to a binder for secondary battery electrodes and its use.

[0002] Various energy storage devices, such as nickel-metal hydride batteries, lithium-ion batteries, and electric double-layer capacitors, have been put into practical use as secondary batteries. The electrodes used in these secondary batteries are manufactured by coating and drying a composition for forming an electrode mixture layer containing an active material and a binder onto a current collector. For example, in lithium-ion batteries, an aqueous binder containing styrene-butadiene rubber (SBR) latex and carboxymethylcellulose (CMC) is used as the binder for the negative electrode mixture layer composition. On the other hand, organic solvent-based binders such as polyvinylidene fluoride (PVDF) in an N-methyl-2-pyrrolidone (NMP) solution are widely used as the binder for the positive electrode mixture layer composition.

[0003] In recent years, as the applications of various secondary batteries have expanded, there has been a growing demand for improvements in energy density, reliability, and durability. For example, to increase the electrical capacity of lithium-ion secondary batteries, there has been an increase in specifications using silicon-based active materials as the negative electrode active material. However, silicon-based active materials are known to undergo large volume changes during charging and discharging, and repeated use can lead to peeling or detachment of the electrode mixture layer, resulting in a decrease in battery capacity and deterioration of cycle characteristics (durability).

[0004] To suppress such defects, studies are underway to improve durability by firmly bonding the active materials together with a binder (binding properties), reducing the size of the active materials to alleviate stress associated with swelling and shrinkage, and modifying the additives in the electrolyte.

[0005] In this context, acrylic acid polymers have been reported to be effective as binders that possess good cycle characteristics and are effective in improving the durability of the negative electrode mixture layer using silicon-based active materials.

[0006] Patent Document 1 discloses a binder containing a copolymer of acrylic acid or a salt of an acrylic acid derivative and acrylonitrile or an acrylonitrile derivative, which is said to be able to follow the expansion and contraction of silicon-based active materials and thus improve cycle characteristics.

[0007] Japanese Patent Publication No. 2015-115109

[0008] The binder for secondary battery electrodes disclosed in Patent Document 1 can impart good cycle characteristics. However, when a composition for secondary battery electrode composite layer (electrode slurry) was manufactured using this binder, it was found that the composition exhibited dilatancy in the same shear rate range as during coating (i.e., normally, the shear viscosity decreases as the shear rate increases, but in the same shear rate range as during coating, the decrease in shear viscosity was suppressed), which made process control such as film formation and coating difficult.

[0009] The present invention aims to provide a binder for secondary battery electrodes that is excellent in coating properties (dilatancy resistance) of the composite layer composition and the cycle characteristics of the secondary battery, a composite layer composition for secondary battery electrodes containing the binder, and a secondary battery electrode and a secondary battery formed using the composition.

[0010] The present inventors have found that the above problem can be solved by using a carboxyl group-containing non-crosslinked polymer or a salt thereof that contains a predetermined amount of structural units derived from an ethylenically unsaturated monomer having a cationic group and / or a cation-generating group.

[0011] The present invention includes the following embodiments: [1] A binder for secondary battery electrodes comprising a carboxyl group-containing non-crosslinked polymer or a salt thereof, wherein the carboxyl group-containing non-crosslinked polymer or a salt thereof comprises: a structural unit derived from an ethylenically unsaturated carboxylic acid monomer (a1) and a structural unit derived from an ethylenically unsaturated monomer (b) having a cationic group and / or a cation-generating group, wherein the amount of structural units derived from monomer (a1) is 30% by mass or more based on the mass of the carboxyl group-containing non-crosslinked polymer or a salt thereof, and the amount of structural units derived from monomer (b) is 2% by mass or more and 50% by mass or less based on the mass of the carboxyl group-containing non-crosslinked polymer or a salt thereof. [2] The binder for secondary battery electrodes according to [1], further comprising a structural unit derived from an amide group-containing ethylenically unsaturated monomer (c) of the carboxyl group-containing non-crosslinked polymer or a salt thereof. [3] The binder for secondary battery electrodes according to [2], wherein the amount of structural units derived from monomer (c) is 1% by mass or more and 50% by mass or less, based on the mass of the carboxyl group-containing non-crosslinked polymer or salt thereof. [4] The binder for secondary battery electrodes according to any one of [1] to [3], wherein monomer (b) has a quaternary ammonium group and / or a tertiary amino group. [5] The binder for secondary battery electrodes according to any one of [1] to [4], wherein the degree of neutralization of the carboxyl group-containing non-crosslinked polymer or salt thereof is 30 mol% or more and 95 mol% or less. [6] The binder for secondary battery electrodes according to any one of [1] to [5], wherein the binder for secondary battery electrodes further comprises a carboxyl group-containing crosslinked polymer or salt thereof. [7] The binder for secondary battery electrodes according to [6], wherein the carboxyl group-containing crosslinked polymer or salt thereof contains structural units derived from an ethylenically unsaturated carboxylic acid monomer (a2), and the amount of structural units derived from the monomer (a2) is 50% by mass or more based on the mass of the carboxyl group-containing crosslinked polymer or salt thereof.[8] A binder for secondary battery electrodes according to [6] or [7], wherein the amount of the carboxyl group-containing crosslinked polymer or salt thereof is 10% by mass or more and 80% by mass or less, based on the total mass of the carboxyl group-containing non-crosslinked polymer or salt thereof and the carboxyl group-containing crosslinked polymer or salt thereof. [9] A composition for a secondary battery electrode mixture layer, comprising the binder for secondary battery electrodes according to any one of [1] to [8], an electrode active material, and water.

[10] A secondary battery electrode, comprising a current collector and a mixture layer formed from the composition for a secondary battery electrode mixture layer according to [9], disposed on the surface of the current collector.

[11] A secondary battery, comprising the secondary battery electrode according to

[10] .

[0012] The present invention provides a binder for secondary battery electrodes that is excellent in coating properties (dilatancy resistance) of the composite layer composition and the cycle characteristics of the secondary battery, a composite layer composition for secondary battery electrodes containing the binder, and a secondary battery electrode and a secondary battery formed using the composition.

[0013] The embodiments of the present invention will be described in detail below, but the present invention is not limited to these, and various modifications are possible without departing from its essence.

[0014] <Definition> In this specification, the term "includes" means that in addition to the elements explicitly stated to be included, other elements may also be included.

[0015] In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0016] In this specification, "(meth)acrylate" means acrylate and / or methacrylate.

[0017] In this specification, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0018] In this specification, "ethylenically unsaturated monomer having a cationic group and / or a cation-generating group" means an ethylenically unsaturated monomer in which the cationic group and / or cation-generating group are bonded via covalent bonds.

[0019] In this specification, "cation-generating group" means a functional group that changes into a cationic group in water.

[0020] In this specification, "degree of neutralization" means the proportion of acidic groups (e.g., carboxyl groups) among the multiple acidic groups contained in the non-crosslinked polymer or crosslinked polymer described later that have been neutralized.

[0021] <Binder for secondary battery electrodes> One embodiment of the present invention relates to a binder for secondary battery electrodes comprising a carboxyl group-containing non-crosslinked polymer or a salt thereof, wherein the carboxyl group-containing non-crosslinked polymer or a salt thereof comprises structural units derived from an ethylenically unsaturated carboxylic acid monomer (a1) and structural units derived from an ethylenically unsaturated monomer (b) having a cationic group and / or a cation-generating group, wherein the amount of structural units derived from monomer (a1) is 30% by mass or more based on the mass of the carboxyl group-containing non-crosslinked polymer or a salt thereof, and the amount of structural units derived from monomer (b) is 2% by mass or more and 50% by mass or less based on the mass of the carboxyl group-containing non-crosslinked polymer or a salt thereof.

[0022] The binder according to this embodiment contains a carboxyl group-containing non-crosslinked polymer or a salt thereof that contains a predetermined amount of structural units derived from an ethylenically unsaturated monomer (b) having a cationic group and / or a cation-generating group, thereby providing excellent coating properties (dilatancy resistance) for the composite layer composition (electrode slurry) and excellent cycle characteristics for the secondary battery.

[0023] The reason for the excellent dilatancy resistance and cycling characteristics is presumed to be that the structural units derived from monomer (b) improve the dispersibility of the electrode active material contained in the composite layer composition; however, the present invention is not limited in any way by the aforementioned presumed reason.

[0024] [Carboxyl group-containing non-crosslinked polymer or salt thereof (non-crosslinked polymer)] The binder according to this embodiment contains a carboxyl group-containing non-crosslinked polymer or a salt thereof. Hereinafter, unless otherwise specified, "non-crosslinked polymer" means both the carboxyl group-containing non-crosslinked polymer and its salt.

[0025] The non-crosslinked polymer contains structural units derived from an ethylenically unsaturated carboxylic acid monomer (a1) (hereinafter also referred to as "structural unit (a1)") and structural units derived from an ethylenically unsaturated monomer (b) having a cationic group and / or a cation-generating group (hereinafter also referred to as "structural unit (b)"). The non-crosslinked polymer may further contain structural units derived from an amide-containing ethylenically unsaturated monomer (c) (hereinafter also referred to as "structural unit (c)"). The non-crosslinked polymer may further contain structural units derived from other monomers copolymerizable with monomer (a1), (b), or (c).

[0026] The following describes the structural units of non-crosslinked polymers.

[0027] (Structural unit (a1) derived from ethylenically unsaturated carboxylic acid monomer (a1)) The non-crosslinked polymer in this embodiment includes structural unit (a1). Note that structural unit (a1) only needs to have a structure corresponding to monomer (a1) when ultimately incorporated into the non-crosslinked polymer; it is not necessarily required to use monomer (a1) when incorporating it into the non-crosslinked polymer. That is, for example, if a derivative or precursor of monomer (a1) is incorporated into the non-crosslinked polymer, and subsequently, a structural unit derived from the derivative or precursor is converted into structural unit (a1), the non-crosslinked polymer is interpreted as including structural unit (a1) derived from monomer (a1). This interpretation also applies to other structural units described later.

[0028] Non-crosslinked polymers containing structural unit (a1) can improve the adhesion of binders to current collectors. Furthermore, non-crosslinked polymers containing structural unit (a1) have excellent lithium ion desolvation effects and ionic conductivity, allowing for the formation of electrodes with low resistance and excellent high-rate characteristics. In addition, non-crosslinked polymers containing structural unit (a1) are water-swellable, which can improve the dispersion stability of electrode active materials and the like.

[0029] The monomer (a1) is a compound having an ethylenically unsaturated bond and a carboxyl group, and is preferably a compound having a (meth)acryloyl group and a carboxyl group. The carboxyl group may be in H-form (COOH) or may be in salt form.

[0030] Examples of the monomer (a1) include (meth)acrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, (meth)acrylamido alkylcarboxylic acids (e.g., (meth)acrylamidohexanoic acid and (meth)acrylamidododecanoic acid), monohydroxyethyl succinate (meth)acrylate, ω-carboxy-caprolactone mono(meth)acrylate, β-carboxyethyl (meth)acrylate, and salts thereof.

[0031] Although not particularly limited, the monomer (a1) is preferably (meth)acrylic acid or a salt thereof.

[0032] The monomer (a1) may be used alone, or two or more monomers may be used in combination.

[0033] The amount of the structural unit (a1) is 30% by mass or more, preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, based on the mass of the non-crosslinked polymer. When the amount of the structural unit (a1) is 30% by mass or more, the adhesiveness of the binder to a current collector can be further improved.

[0034] The upper limit of the amount of the structural unit (a1) is not particularly limited, and may be, for example, 98% by mass, 96% by mass, 94% by mass, or 92% by mass based on the mass of the non-crosslinked polymer.

[0035] A numerical range may be defined by arbitrarily combining the above lower limit and upper limit of the amount of the structural unit (a1). For example, the amount of the structural unit (a1) may be 30 to 98% by mass, 50 to 96% by mass, 70 to 94% by mass, or 90 to 92% by mass.

[0036] The amount of the structural unit (a1) can be adjusted, for example, by changing the amount of the monomer (a1) used in synthesizing the non-crosslinked polymer.

[0037] The amount of structural unit (a1) can be determined by measuring the non-crosslinked polymer using solid-state nuclear magnetic resonance (NMR). More specifically, it can be measured by the method described in the examples below.

[0038] (Structural unit (b)) derived from an ethylenically unsaturated monomer (b) having a cationic group and / or a cation-generating group. The non-crosslinked polymer in this embodiment includes structural unit (b).

[0039] It is presumed that non-crosslinked polymers containing structural unit (b) can improve the dispersibility of electrode active materials contained in the composite layer composition.

[0040] Monomer (b) is a compound having an ethylenically unsaturated bond and a cationic group and / or a cation-generating group, preferably a compound having a (meth)acryloyl group and a cationic group and / or a cation-generating group, and more preferably a compound having a (meth)acryloyl group and a cationic group.

[0041] Examples of cationic groups of monomer (b) include ammonium groups (e.g., secondary to quaternary ammonium groups), imidazolium groups, pyrrolidinium groups, pyridinium groups, piperidinium groups, and phosphonium groups. While not particularly limited, the cationic group is preferably an ammonium group, and more preferably a quaternary ammonium group.

[0042] Examples of cation-generating groups of monomer (b) include amino groups (e.g., secondary or tertiary amino groups), imidazole groups, pyrrolidine groups, pyridine groups, piperidine groups, and phosphine groups. While not particularly limited, the cation-generating group is preferably an amino group, and more preferably a tertiary amino group.

[0043] Examples of monomer (b) include trialkyl(meth)acryloyloxyalkylammonium halide and dialkylaminoalkyl (meth)acrylate.

[0044] While not particularly limited, monomer (b) is preferably trimethylacryloyloxyethylammonium chloride (DAC) or dimethylaminoethyl acrylate (DA), and more preferably DAC.

[0045] The monomer (b) may be a single type or a combination of two or more types.

[0046] The amount of structural unit (b) is 2% by mass or more, preferably 3% by mass or more, more preferably 4% by mass or more, even more preferably 5% by mass or more, and particularly preferably 6% by mass or more, based on the mass of the non-crosslinked polymer. By having an amount of structural unit (b) of 2% by mass or more, dilatancy resistance and cyclic properties can be further improved.

[0047] The amount of structural unit (b) is 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and particularly preferably 10% by mass or less, based on the mass of the non-crosslinked polymer. By having an amount of structural unit (b) of 50% by mass or less, dilatancy resistance and cyclic properties can be further improved.

[0048] The numerical range for the amount of structural unit (b) may be determined by arbitrarily combining the above lower and upper limits. For example, the amount of structural unit (b) may be 2 to 50 mass%, 3 to 40 mass%, 4 to 30 mass%, 5 to 20 mass%, or 6 to 10 mass%.

[0049] The amount of structural unit (b) can be adjusted, for example, by changing the amount of monomer (b) used in the synthesis of the non-crosslinked polymer.

[0050] The amount of structural unit (b) can be determined by measuring the non-crosslinked polymer using solid-state NMR. More specifically, it can be measured by the method described in the examples below.

[0051] The total amount of structural units (a1) and (b) is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on the mass of the non-crosslinked polymer.

[0052] There is no particular upper limit to the total amount of structural units (a1) and (b), but it may be, for example, 100% by mass, 90% by mass, or 80% by mass, based on the mass of the non-crosslinked polymer.

[0053] The numerical range may be determined by arbitrarily combining the above lower and upper limits for the total amount of structural units (a1) and (b). For example, the total amount of structural units (a1) and (b) may be 50 to 100% by mass, 60 to 90% by mass, or 70 to 80% by mass.

[0054] (Structural unit (c) derived from an amide group-containing ethylenically unsaturated monomer (c)) The non-crosslinked polymer in this embodiment may further contain structural unit (c).

[0055] Non-crosslinked polymers containing structural unit (c) can improve the binding properties of binders.

[0056] Monomer (c) is a compound having an ethylenically unsaturated bond and an amide group, preferably a compound having a (meth)acryloyl group and an amide group. A compound having an ethylenically unsaturated bond, an amide group, and a carboxyl group is interpreted as corresponding to monomer (a1) rather than monomer (c).

[0057] Examples of monomer (c) include (meth)acrylamide and its derivatives.

[0058] Examples of derivatives of (meth)acrylamide include N-alkyl(meth)acrylamide and N,N-dialkyl(meth)acrylamide.

[0059] Examples of N-alkyl(meth)acrylamides include N-isopropyl(meth)acrylamide, N-t-butyl(meth)acrylamide, N-n-butoxymethyl(meth)acrylamide, and N-isobutoxymethyl(meth)acrylamide.

[0060] Examples of N,N-dialkyl(meth)acrylamides include N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide.

[0061] While not particularly limited, monomer (c) is preferably (meth)acrylamide.

[0062] The monomer (c) may be a single type or a combination of two or more types.

[0063] The amount of structural unit (c) is preferably 1% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and particularly preferably 30% by mass or more, based on the mass of the non-crosslinked polymer. By having an amount of structural unit (c) of 1% by mass or more, dilatancy resistance and cyclic properties can be further improved.

[0064] The amount of structural unit (c) is preferably 50% by mass or less, more preferably 48% by mass or less, even more preferably 46% by mass or less, and particularly preferably 44% by mass or less, based on the mass of the non-crosslinked polymer. By having an amount of structural unit (c) of 50% by mass or less, dilatancy resistance and cyclic properties can be further improved.

[0065] The numerical range for the amount of structural unit (c) may be determined by arbitrarily combining the above lower and upper limits. For example, the amount of structural unit (c) may be 1 to 50 mass%, 10 to 48 mass%, 20 to 46 mass%, or 30 to 44 mass%.

[0066] The amount of structural unit (c) can be adjusted, for example, by changing the amount of monomer (c) used in the synthesis of the non-crosslinked polymer.

[0067] The amount of structural unit (c) can be determined by measuring the non-crosslinked polymer using solid-state NMR. More specifically, it can be measured by the method described in the examples below.

[0068] The total amount of structural units (a1), (b), and (c) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, based on the mass of the non-crosslinked polymer.

[0069] The upper limit of the total amount of structural units (a1), (b), and (c) is not particularly limited, but may be, for example, 100% by mass, 98% by mass, 96% by mass, or 94% by mass, based on the mass of the non-crosslinked polymer.

[0070] The numerical range may be determined by arbitrarily combining the above lower and upper limits for the total amount of structural units (a1), (b), and (c). For example, the total amount of structural units (a1), (b), and (c) may be 60 to 100% by mass, 70 to 98% by mass, 80 to 96% by mass, or 90 to 94% by mass.

[0071] (Salt of non-crosslinked polymer) In this embodiment, the carboxyl group of the non-crosslinked polymer may be H-type (COOH), salt-type, or a combination thereof (i.e., partly H-type and the rest salt-type).

[0072] Examples of carboxyl group salts include alkali metal salts (e.g., lithium salts, sodium salts, and potassium salts), alkaline earth metal salts (e.g., magnesium salts, calcium salts, and barium salts), other metal salts (e.g., aluminum salts), ammonium salts, and organic amine salts.

[0073] While not particularly limited, the salt form of the carboxyl group is preferably an alkali metal salt, more preferably a lithium salt, sodium salt, or potassium salt, and even more preferably a lithium salt.

[0074] The salt form of the carboxyl group can be changed, for example, by selecting the type of neutralizing agent (e.g., a base) used to adjust the degree of neutralization of the non-crosslinked polymer, as described later.

[0075] (Degree of neutralization of non-crosslinked polymer) In this embodiment, the degree of neutralization of the non-crosslinked polymer is preferably 30 mol% or more, more preferably 40 mol% or more, even more preferably 45 mol% or more, and particularly preferably 50 mol% or more. By having a degree of neutralization of 30 mol% or more of the non-crosslinked polymer, the dilatancy resistance and cyclic properties can be further improved.

[0076] In this embodiment, the degree of neutralization of the non-crosslinked polymer is preferably 95 mol% or less, more preferably 85 mol% or less, even more preferably 75 mol% or less, and particularly preferably 70 mol% or less. By having a degree of neutralization of the non-crosslinked polymer of 95 mol% or less, the dilatancy resistance and cyclic properties can be further improved.

[0077] The numerical range for the degree of neutralization of the non-crosslinked polymer may be determined by arbitrarily combining the above lower and upper limits. For example, the degree of neutralization of the non-crosslinked polymer may be set to 30-95 mol%, 40-85 mol%, 45-75 mol%, or 50-70 mol%.

[0078] The degree of neutralization of non-crosslinked polymers can be adjusted, for example, by changing the amount of neutralizing agent (e.g., a base) reacted with the non-crosslinked polymer.

[0079] The degree of neutralization of a non-crosslinked polymer can be determined by neutralization titration. Specifically, it can be measured by the following method.

[0080] Method for Measuring Degree of Neutralization 1. Prepare 40.0 g of a 3% aqueous solution of the non-crosslinked polymer. Add 10.0 g of cation exchange resin (Organo, AMBERLITE IR120B H) to the aqueous solution and treat the carboxyl group salt to obtain a precipitate of the non-crosslinked polymer with a degree of neutralization of 0 mol%. 2. Collect the precipitate obtained in 1. by filtration and dry it under reduced pressure at 80°C for 3 hours to remove volatile components to obtain a solid of the non-crosslinked polymer with a degree of neutralization of 0 mol%. 3. Disperse 0.4 g of the solid of the non-crosslinked polymer obtained in 2. in 39.6 g of ion-exchanged water and perform a neutralization titration using a 1% sodium hydroxide aqueous solution to create a titration curve. The pH of the aqueous solution is measured using a pH meter (HORIBA, Model: D-51, 25°C). 4. The pH of the reaction system and the pH of the solution are measured in 3. The amount of sodium hydroxide contained in the non-crosslinked polymer is determined from the intersection point with the titration curve obtained. The degree of neutralization is calculated from the ratio of the amount of sodium hydroxide contained in the non-crosslinked polymer to the amount of sodium hydroxide required from the start point to the end point of the neutralization titration, i.e., from 0 mol% to 100 mol% neutralization. Calculation formula: Degree of neutralization of non-crosslinked polymer (%) = [(Amount of sodium hydroxide contained in non-crosslinked polymer) / (Amount of sodium hydroxide required to go from 0 mol% to 100 mol% neutralization)] × 100

[0081] (Molecular weight of non-crosslinked polymer) The weight-average molecular weight of the non-crosslinked polymer in this embodiment is preferably 100,000 to 3,000,000, more preferably 300,000 to 2,500,000, even more preferably 500,000 to 2,000,000, and particularly preferably 550,000 to 1,500,000.

[0082] By having the weight-average molecular weight of the non-crosslinked polymer within the above range, the dilatancy resistance and cyclic properties can be further improved.

[0083] The weight-average molecular weight of a non-crosslinked polymer can be adjusted, for example, by changing the amount of polymerization initiator used in the synthesis of the non-crosslinked polymer.

[0084] The weight-average molecular weight of non-crosslinked polymers can be measured by gel permeation chromatography (GPC). Specifically, 0.1 g of an aqueous solution of the non-crosslinked polymer (0.02 g as solid content of the non-crosslinked polymer) is taken, diluted with 40 g of a 0.1 M sodium nitrate aqueous solution to prepare a measurement sample, and the weight-average molecular weight in terms of polyethylene oxide can be determined by performing aqueous GPC measurement under the following conditions: (GPC measurement conditions) Polyethylene oxide solvent: 0.1 M Sodium nitrate aqueous solution temperature: 40°C Detector: RI Flow rate: 0.5 mL / min

[0085] [Method for producing non-crosslinked polymers] The method for producing non-crosslinked polymers in this embodiment is not particularly limited and can be produced using known methods. Examples of known methods include solution polymerization, precipitation polymerization, suspension polymerization, and emulsion polymerization.

[0086] Examples of methods for producing non-crosslinked polymers include polymerizing the monomers (a1) and (b) mentioned above, as well as any other raw materials such as monomer (c) as needed, in the presence of a polymerization initiator.

[0087] The type of polymerization initiator is not particularly limited, and known initiators can be used. Examples of known initiators include azo compounds, organic peroxides, and inorganic peroxides.

[0088] The conditions for the polymerization reaction can be adjusted as appropriate depending on the desired non-crosslinked polymer.

[0089] If necessary, the degree of neutralization of the non-crosslinked polymer may be adjusted by reacting it with a neutralizing agent.

[0090] Examples of neutralizing agents include alkali metal hydroxides (e.g., lithium hydroxide, sodium hydroxide, and potassium hydroxide) and alkaline earth metal hydroxides (e.g., magnesium hydroxide, calcium hydroxide, and barium hydroxide).

[0091] As a method for producing a non-crosslinked polymer, for example, the method described in Japanese Patent Application Publication No. 2024-38023 may be used.

[0092] [Carboxyl group-containing crosslinked polymer or salt thereof (crosslinked polymer)] The binder according to this embodiment preferably further comprises a carboxyl group-containing crosslinked polymer or a salt thereof. Hereinafter, unless otherwise specified, "crosslinked polymer" means both the carboxyl group-containing crosslinked polymer and its salt.

[0093] Methods for producing crosslinked polymers include, for example, copolymerizing crosslinkable monomers, utilizing chain transfer to polymer chains during radical polymerization, and adding a crosslinking agent to a polymer having reactive functional groups. From the viewpoint of ease of operation and ease of controlling the degree of crosslinking, copolymerizing crosslinkable monomers is preferred. Therefore, the following description will focus on crosslinked polymers obtained by copolymerization, but the crosslinked polymers are not limited to those obtained by the above method.

[0094] The crosslinked polymer preferably contains structural units derived from an ethylenically unsaturated carboxylic acid monomer (a2) (hereinafter also referred to as "structural unit (a2)"). The crosslinked polymer may further contain structural units derived from an ethylenically unsaturated monomer (d) copolymerizable with monomer (a2) (hereinafter also referred to as "structural unit (d)"). The crosslinked polymer may further contain structural units derived from a crosslinkable monomer (e) (hereinafter also referred to as "structural unit (e)").

[0095] The following describes the structural units of crosslinked polymers.

[0096] (Structural unit (a2) derived from ethylenically unsaturated carboxylic acid monomer (a2)) In this embodiment, the crosslinked polymer preferably contains structural unit (a2). In this embodiment, structural unit (a2) only needs to have a structure corresponding to monomer (a2) when it is finally incorporated into the crosslinked polymer, and it is not necessarily required to use monomer (a2) when incorporating it into the crosslinked polymer. That is, for example, even if a derivative or precursor of monomer (a2) is incorporated into the crosslinked polymer, and then a structural unit derived from the derivative or precursor is converted into structural unit (a2), the crosslinked polymer is interpreted as containing structural unit (a2) derived from monomer (a2). This interpretation also applies to other structural units described later.

[0097] Crosslinked polymers containing structural unit (a2) can improve the adhesion of binders to current collectors. Furthermore, crosslinked polymers containing structural unit (a2) have excellent lithium ion desolvation effects and ionic conductivity, allowing for the formation of electrodes with low resistance and excellent high-rate characteristics. In addition, because crosslinked polymers containing structural unit (a2) are water-swellable, they can improve the dispersion stability of electrode active materials and the like.

[0098] Since the details of monomer (a2) (e.g., structure and specific examples) are the same as those of monomer (a1), the description of monomer (a1) is quoted here, and the description of monomer (a2) is omitted.

[0099] The monomer (a2) may be a single type or a combination of two or more types.

[0100] The amount of structural unit (a2) 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 80% by mass or more, based on the mass of the crosslinked polymer. By having an amount of structural unit (a2) of 50% by mass or more, dilatancy resistance and cyclic properties can be further improved.

[0101] The upper limit of the amount of structural units (a2) is not particularly limited, but may be, for example, 100% by mass, 95% by mass, 90% by mass, or 85% by mass, based on the mass of the crosslinked polymer.

[0102] The numerical range for the amount of structural unit (a2) may be determined by arbitrarily combining the above lower and upper limits. For example, the amount of structural unit (a2) may be 50 to 100% by mass, 60 to 95% by mass, 70 to 90% by mass, or 80 to 85% by mass.

[0103] The amount of structural units (a2) can be adjusted, for example, by changing the amount of monomers (a2) used in the synthesis of the crosslinked polymer.

[0104] (Structural unit (d) derived from ethylenically unsaturated monomer (d)) The crosslinked polymer in this embodiment may further contain structural unit (d).

[0105] Examples of monomer (d) include ethylenically unsaturated monomers having anionic groups other than carboxyl groups (e.g., sulfonic acid groups and phosphate groups), and nonionic ethylenically unsaturated monomers.

[0106] While not particularly limited, monomer (d) is preferably a nonionic ethylenically unsaturated monomer. A crosslinked polymer containing structural unit (d) derived from a nonionic ethylenically unsaturated monomer can form an electrode with excellent flexibility.

[0107] The nonionic ethylenically unsaturated monomer is preferably (meth)acrylamide and its derivatives. Details of (meth)acrylamide and its derivatives (for example, specific examples) are as described in relation to monomer (c), so the description of monomer (c) is referenced here, and the description of (meth)acrylamide and its derivatives is omitted.

[0108] The nonionic ethylenically unsaturated monomer is preferably a (meth)acrylic acid ester. Examples of (meth)acrylic acid esters include the following compounds: alkyl (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; cycloalkyl (meth)acrylic acid esters such as cyclohexyl (meth)acrylate and methylcyclohexyl (meth)acrylate; alkoxyalkyl (meth)acrylic acid esters such as 2-methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; and hydroxyalkyl (meth)acrylic acid esters such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate.

[0109] The monomer (d) may be a single type or a combination of two or more types.

[0110] The lower limit of the amount of structural unit (d) is not particularly limited, but may be 0% by mass, 10% by mass, 20% by mass, or 30% by mass, based on the mass of the crosslinked polymer.

[0111] The amount of structural unit (d) is preferably 65% ​​by mass or less, more preferably 60% by mass or less, even more preferably 55% by mass or less, and particularly preferably 50% by mass or less, based on the mass of the crosslinked polymer.

[0112] The numerical range for the amount of structural unit (d) may be determined by arbitrarily combining the above lower and upper limits. For example, the amount of structural unit (d) may be 0 to 65 mass%, 10 to 60 mass%, 20 to 55 mass%, or 30 to 50 mass%.

[0113] The amount of structural unit (d) can be adjusted, for example, by changing the amount of monomer (d) used in the synthesis of the crosslinked polymer.

[0114] The total amount of structural units (a2) and (d) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, based on the mass of the crosslinked polymer.

[0115] The upper limit of the total amount of structural units (a2) and (d) is not particularly limited, but may be, for example, 100% by mass, 98% by mass, 96% by mass, or 94% by mass, based on the mass of the crosslinked polymer.

[0116] The numerical range may be determined by arbitrarily combining the above lower and upper limits for the total amount of structural units (a2) and (d). For example, the total amount of structural units (a2) and (d) may be 60 to 100% by mass, 70 to 98% by mass, 80 to 96% by mass, or 90 to 94% by mass.

[0117] (Structural unit derived from crosslinkable monomer (e) (structural unit (e))) The crosslinked polymer in this embodiment preferably contains structural unit (e).

[0118] Monomer (e) can form a cross-linked structure.

[0119] Examples of monomer (e) include polyfunctional polymerizable monomers having two or more polymerizable unsaturated groups (e.g., (meth)acryloyl groups and alkenyl groups), and monomers having self-crosslinkable crosslinkable functional groups (e.g., hydrolyzable silyl groups).

[0120] While not particularly limited, monomer (e) is preferably a polyfunctional polymerizable monomer having two or more alkenyl groups, and more preferably a polyfunctional polymerizable monomer having two or more allyl ether groups, from the viewpoint of forming a uniform crosslinked structure.

[0121] Examples of polyfunctional polymerizable monomers having a (meth)acryloyl group include the following compounds: di(meth)acrylates of dihydric alcohols such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate; tri(meth)acrylates of polyhydric alcohols of trihydric or higher valencies such as trimethylolpropane tri(meth)acrylate, trimethylolpropane ethylene oxide modified tri(meth)acrylate, glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate; poly(meth)acrylates such as tetra(meth)acrylate; and bisamides such as methylenebisacrylamide and hydroxyethylenebisacrylamide.

[0122] Examples of polyfunctional polymerizable monomers having an alkenyl group include the following compounds: polyfunctional allyl ether compounds such as trimethylolpropanediallyl ether, trimethylolpropanetrialyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, tetraallyloxyethane, and polyallyl saccharose; polyfunctional allyl compounds such as diallyl phthalate; and polyfunctional vinyl compounds such as divinylbenzene.

[0123] Examples of polyfunctional polymerizable monomers having (meth)acryloyl and alkenyl groups include the following compounds: allyl (meth)acrylate, isopropenyl (meth)acrylate, butenyl (meth)acrylate, pentenyl (meth)acrylate, and 2-(2-vinyloxyethoxy)ethyl (meth)acrylate.

[0124] Examples of monomers having self-crosslinkable functional groups include hydrolyzable silyl group-containing vinyl monomers, N-methylol(meth)acrylamide, and N-methoxyalkyl(meth)acrylate.

[0125] Examples of hydrolyzable silyl group-containing vinyl monomers include the following compounds: vinyl silanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane, and vinyldimethylmethoxysilane; silyl group-containing acrylic acid esters such as trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate, and methyldimethoxysilylpropyl acrylate; silyl group-containing methacrylic acid esters such as trimethoxysilylpropyl methacrylate, triethoxysilylpropyl methacrylate, methyldimethoxysilylpropyl methacrylate, and dimethylmethoxysilylpropyl methacrylate; silyl group-containing vinyl ethers such as trimethoxysilylpropyl vinyl ether; and silyl group-containing vinyl esters such as vinyl trimethoxysilylundecanoate.

[0126] The monomer (e) may be a single type or a combination of two or more types.

[0127] The amount of structural unit (e) is preferably 0.05 to 5% by mass, more preferably 0.1 to 4% by mass, even more preferably 0.2 to 3% by mass, and particularly preferably 0.3 to 2% by mass, based on the mass of the crosslinked polymer.

[0128] The amount of structural unit (e) can be adjusted, for example, by changing the amount of monomer (e) used in the synthesis of the crosslinked polymer.

[0129] The total amount of structural units (a2), (d), and (e) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, based on the mass of the crosslinked polymer.

[0130] The upper limit of the total amount of structural units (a2), (d), and (e) is not particularly limited, but may be, for example, 100% by mass, 98% by mass, 96% by mass, or 94% by mass, based on the mass of the crosslinked polymer.

[0131] The numerical range may be determined by arbitrarily combining the above lower and upper limits for the total amount of structural units (a2), (d), and (e). For example, the total amount of structural units (a2) and (d) may be 60 to 100% by mass, 70 to 98% by mass, 80 to 96% by mass, or 90 to 94% by mass.

[0132] (Salt of the crosslinked polymer) In this embodiment, the carboxyl group of the crosslinked polymer may be H-type (COOH), salt-type, or a combination thereof (i.e., partly H-type and the rest salt-type).

[0133] Examples of carboxyl group salts include alkali metal salts (e.g., lithium salts, sodium salts, and potassium salts), alkaline earth metal salts (e.g., magnesium salts, calcium salts, and barium salts), other metal salts (e.g., aluminum salts), ammonium salts, and organic amine salts.

[0134] While not particularly limited, the salt form of the carboxyl group is preferably an alkali metal salt, more preferably a lithium salt, sodium salt, or potassium salt, and even more preferably a lithium salt.

[0135] The salt form of the carboxyl group can be changed, for example, by selecting the type of neutralizing agent (e.g., a base) used to adjust the degree of neutralization of the cross-linked polymer, as described later.

[0136] (Degree of neutralization of the crosslinked polymer) In this embodiment, the degree of neutralization of the crosslinked polymer is preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, particularly preferably 80 mol% or more, and most preferably 90 mol% or more. A degree of neutralization of 50 mol% or more of the crosslinked polymer increases its water swelling properties and improves its dispersion stability.

[0137] The upper limit of the degree of neutralization of the crosslinked polymer in this embodiment is not particularly limited, but may be, for example, 100 mol%, 98 mol%, 96 mol%, 94 mol%, or 92 mol%.

[0138] The numerical range for the degree of neutralization of the crosslinked polymer may be determined by arbitrarily combining the above lower and upper limits. For example, the degree of neutralization of the crosslinked polymer may be set to 50-100 mol%, 60-98 mol%, 70-96 mol%, 80-94 mol%, or 90-92 mol%.

[0139] The degree of neutralization of the crosslinked polymer can be adjusted, for example, by changing the amount of neutralizing agent (e.g., a base) reacted with the crosslinked polymer.

[0140] The degree of neutralization of a crosslinked polymer can be determined by measuring the crosslinked polymer using infrared spectroscopy (IR). More specifically, it can be measured by the method described in the examples below.

[0141] (Water-swelled particle size of the crosslinked polymer) In this embodiment, the water-swelled particle size of the crosslinked polymer is preferably 0.1 to 6.0 μm, more preferably 0.3 to 5.0 μm, even more preferably 0.7 to 4.0 μm, and particularly preferably 1.0 to 3.0 μm.

[0142] By ensuring that the water-swollen particle size of the crosslinked polymer is within the above range, the binding properties of the binder can be improved.

[0143] The water-swollen particle size of the crosslinked polymer can be adjusted, for example, by changing the degree of crosslinking of the crosslinked polymer.

[0144] The water-swollen particle size of the crosslinked polymer can be measured using a laser diffraction / scattering particle size analyzer. More specifically, it can be measured by the method described in the examples below. The method described in International Publication No. 2017 / 073589 may also be referenced.

[0145] [Method for producing the crosslinked polymer] The method for producing the crosslinked polymer in this embodiment is not particularly limited and can be produced using known methods. Examples of methods for producing the crosslinked polymer include the methods described in International Publication No. 2017 / 073589 and Japanese Patent Application Publication No. 2024-75732.

[0146] [Amount of non-crosslinked polymer] The amount of non-crosslinked polymer is preferably 20 to 90% by mass, more preferably 40 to 80% by mass, and even more preferably 60 to 70% by mass, based on the total mass of the non-crosslinked polymer and the crosslinked polymer.

[0147] The amount of non-crosslinked polymer is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, even more preferably 30 to 70% by mass, and particularly preferably 40 to 60% by mass, based on the mass of the binder (solids).

[0148] [Amount of crosslinked polymer] The amount of crosslinked polymer is preferably 10 to 80% by mass, more preferably 20 to 60% by mass, and even more preferably 30 to 40% by mass, based on the total mass of the non-crosslinked polymer and the crosslinked polymer.

[0149] The amount of crosslinked polymer is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, even more preferably 15 to 40% by mass, and particularly preferably 20 to 30% by mass, based on the mass of the binder (solids).

[0150] [Optional Components] The binder according to this embodiment may contain further optional components. Examples of optional components include styrene-butadiene rubber (SBR), carboxymethylcellulose or its salts (CMC), and polyvinylidene fluoride (PVDF).

[0151] While not particularly limited, from the viewpoint of improving binding properties, the binder according to this embodiment preferably further contains SBR.

[0152] The amount of SBR is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, even more preferably 15 to 40% by mass, and particularly preferably 20 to 30% by mass, based on the mass of the binder (solid content).

[0153] Although CMC also functions as a dispersant, it is presumed that the non-crosslinked polymer in this embodiment also has dispersing properties; therefore, the binder in this embodiment may or may not contain CMC.

[0154] If CMC is included, the amount of CMC may be, for example, 5-60% by mass, 10-50% by mass, 15-40% by mass, or 20-30% by mass, based on the mass of the binder (solid content).

[0155] <Composition for Secondary Battery Electrode Mixture Layer> One embodiment of the present invention relates to a composition for a secondary battery electrode mixture layer (electrode slurry) comprising the above-mentioned secondary battery electrode binder, an electrode active material, and water.

[0156] The secondary battery electrode mixture layer composition according to this embodiment may be a negative electrode mixture layer composition or a positive electrode mixture layer composition, but is preferably a negative electrode mixture layer composition.

[0157] [Binder] Details of the binder for secondary battery electrodes in this embodiment are as described in the section above titled <Binder for Secondary Battery Electrodes>.

[0158] The amount of non-crosslinked polymer contained in the binder is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, and even more preferably 1 to 3% by mass, based on the mass of the composite layer composition (solid content).

[0159] The amount of crosslinked polymer contained in the binder is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, and even more preferably 1 to 3% by mass, based on the mass of the composite layer composition (solid content).

[0160] The amount of binder is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, and even more preferably 1 to 6% by mass, based on the mass of the composite layer composition (solid content).

[0161] [Electrode Active Material] The type of electrode active material is not particularly limited, and known active materials can be used. The negative electrode active material and positive electrode active material are described below.

[0162] (Negative electrode active material) Examples of negative electrode active materials include carbon-based materials, lithium metals, lithium alloys, and metal oxides.

[0163] While not particularly limited, the negative electrode active material preferably contains a carbon-based material.

[0164] Examples of carbon-based materials include graphite (e.g., natural graphite and artificial graphite), hard carbon, and soft carbon.

[0165] The negative electrode active material more preferably contains silicon-based material in addition to carbon-based material. The inclusion of silicon-based material can increase the energy density.

[0166] Examples of silicon-based materials include silicon, silicon alloys, and silicon monoxide (SiO).

[0167] The amount of carbon-based material is preferably 65 to 95% by mass, more preferably 70 to 90% by mass, and even more preferably 75 to 85% by mass, based on the mass of the negative electrode active material.

[0168] The amount of silicon-based material is preferably 5 to 35% by mass, more preferably 10 to 30% by mass, and even more preferably 15 to 25% by mass, based on the mass of the negative electrode active material.

[0169] The negative electrode active material may be a single type or a combination of two or more types.

[0170] (Positive electrode active material) Examples of positive electrode active materials include lithium salts of transition metal oxides.

[0171] Examples of lithium salts of transition metal oxides include layered rock salt-type lithium-containing metal oxides and spinel-type lithium-containing metal oxides.

[0172] Examples of layered rock salt-type lithium-containing metal oxides include lithium cobalt oxide, lithium nickel oxide, and NCM{Li(Ni ｘ Co ｙ Mn ｚ ) O ２ [x+y+z=1]}, and NCA{Li(Ni ｘ Co ｙ Al ｚ ) O ２ [x + y + z = 1] is one example.

[0173] Examples of spinel-type lithium-containing metal oxides include lithium manganese oxide.

[0174] The positive electrode active material may be a single type or a combination of two or more types.

[0175] [Viscosity of the composition for the composite layer] The viscosity of the composition for the composite layer may be, as a B-type viscosity at 60 rpm, for example, 500 to 100,000 mPa·s, 1,000 to 50,000 mPa·s, 1,000 to 10,000 mPa·s, 1,000 to 8,000 mPa·s, 1,000 to 7,000 mPa·s, 1,000 to 6,000 mPa·s, 1,000 to 5,000 mPa·s, 1,000 to 4,000 mPa·s, or 1,000 to 3,000 mPa·s.

[0176] [Method for Manufacturing the Composition for the Composition Layer] The method for manufacturing the composition for the composition for the composition layer according to this embodiment is not particularly limited and can be manufactured using known methods. Examples of methods for manufacturing the composition for the composition for the composition layer include the methods described in International Publication No. 2017 / 073589 and Japanese Patent Application Publication No. 2024-75732.

[0177] <Secondary Battery Electrode> One embodiment of the present invention relates to a secondary battery electrode comprising a current collector and a composite layer formed from the above-described secondary battery electrode composite layer composition, disposed on the surface of the current collector.

[0178] The electrode according to this embodiment may be a negative electrode or a positive electrode, but is preferably a negative electrode.

[0179] Details of the composition for the secondary battery electrode mixture layer in this embodiment are as described in the section above, "Composition for the secondary battery electrode mixture layer."

[0180] The type of current collector is not particularly limited, and known current collectors can be used. Examples of current collectors include copper current collectors and aluminum current collectors.

[0181] The method for manufacturing the electrode according to this embodiment is not particularly limited and can be manufactured using known methods. Examples of electrode manufacturing methods include those described in International Publication No. 2017 / 073589 and Japanese Patent Application Publication No. 2024-75732.

[0182] <Secondary Battery> One embodiment of the present invention relates to a secondary battery including the secondary battery electrodes described above.

[0183] The secondary battery according to this embodiment is preferably a secondary battery for use in a vehicle.

[0184] The secondary battery according to this embodiment is preferably a non-aqueous electrolyte secondary battery, and more preferably a non-aqueous electrolyte lithium-ion secondary battery.

[0185] The secondary battery according to this embodiment preferably includes a negative electrode, a positive electrode, a separator, and an electrolyte.

[0186] The negative electrode of the secondary battery according to this embodiment may be the electrode according to the above-described embodiment. The positive electrode of the secondary battery according to this embodiment may be the electrode according to the above-described embodiment.

[0187] It is preferable that the negative electrode of the secondary battery according to this embodiment is the electrode according to the above-described embodiment.

[0188] The type of separator is not particularly limited, and known separators can be used. Examples of separators include separators made of polyolefins (e.g., polyethylene and polypropylene) and separators made of polytetrafluoroethylene.

[0189] The type of electrolyte is not particularly limited, and known electrolytes can be used. Examples of electrolytes include cyclic carbonates (e.g., propylene carbonate and ethylene carbonate) and linear carbonates (e.g., ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate).

[0190] The electrolyte can be one type only, or a combination of two or more types.

[0191] The present invention will be described in more detail below using examples and comparative examples, but the technical scope of the present invention is not limited thereto.

[0192] The various values in the examples may be used as the preferred lower limits or upper limits in the above-mentioned embodiments of the present invention. Further, any combination of two values of the same type in the examples may be used to form a preferred numerical range.

[0193] Hereinafter, unless otherwise explicitly stated, "parts" and "%" mean "parts by mass" and "mass%", respectively.

[0194] <Non-crosslinked polymer> [Measurement method] (Measurement of solid content concentration) Approximately 1.0 g of a sample is collected in a weighing bottle [B (g)] whose mass has been measured in advance, and the mass of the weighing bottle containing the sample [W ０ (g)] was accurately measured. The weighing bottle containing the sample was placed in a windless dryer, dried at 155°C for 45 minutes, and then its mass [W １ (g)] was measured. The solid content concentration was determined from the following formula. Solid content concentration (mass%) = [(W １ - B) / (W ０ - B)] × 100

[0195] (Measurement of the amount of each structural unit in the non-crosslinked polymer) The amount of each structural unit in the non-crosslinked polymer was measured by solid-state nuclear magnetic resonance (NMR). Specifically, the non-crosslinked polymer was spread on an aluminum cup and vacuum-dried at 70°C for 2 hours to obtain a dried solid. The dried solid was pulverized using a mortar, filled into a zirconia sleeve, and used as a measurement sample. Solid-state NMR measurement was performed under the following conditions to measure the amount (mass%) of each structural unit of the non-crosslinked polymer.

[0196] (Solid-state NMR measurement conditions) Apparatus: JNM-ECA400 (manufactured by JEOL Ltd.) Sample tube: zirconia sleeve Sample rotation speed: 15 kHz Measured nuclide: 13C Chemical shift reference: the high-field signal of adamantane was set to 29.5 ppm (external standard) Pulse sequence: CPMAS method

[0197] [Production of Non-Crosslinked Polymers] (Production Example 1: Non-Crosslinked Polymer Y-1) A reactor equipped with a stirring blade, thermometer, reflux condenser, and nitrogen inlet tube was used. Under a nitrogen atmosphere, 450.0 parts of deionized water, 50.0 parts of acrylic acid (hereinafter also referred to as "AA"), and 50.0 parts of trimethylacryloyloxyethylammonium chloride (hereinafter also referred to as "DAC") were added to the reactor and heated to 60°C. 1.20 parts of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name "V-50", hereinafter also referred to as "V-50"), which is an initiator, were added to this solution to start polymerization, and the reaction was carried out for 6 hours. After further reaction at 80°C for 2 hours, the polymerization reaction solution was cooled, and after the internal temperature had dropped to 45°C, lithium hydroxide monohydrate (hereinafter referred to as "LiOH・H") was added. ２ 17.5 parts of the powder of (also known as "O") were added and stirred at 45°C for 30 minutes to obtain an aqueous solution of non-crosslinked polymer Y-1 (lithium salt, degree of neutralization 60 mol%). The solid content concentration of the above aqueous solution was 21.4% by mass. Solid NMR measurement revealed that of the total structural units of Y-1, 55.0% by mass were derived from AA and 45.0% by mass were derived from DAC.

[0198] (Production Examples 2-15: Non-crosslinked polymers Y-2 to Y-15) The same procedure as in Production Example 1 was followed, except that the amount of each raw material used was as shown in Table 1, to obtain aqueous solutions of non-crosslinked polymers Y-2 to Y-15. The results are shown in Table 1.

[0199] (Comparative Production Examples 1 and 2: Non-crosslinked polymers Y-16 and Y-17) The same procedure as in Production Example 1 was followed, except that the amount of each raw material used was as shown in Table 1, to obtain aqueous solutions of non-crosslinked polymers Y-16 and Y-17. The results are shown in Table 1.

[0200]

[0201] The meanings of the abbreviations listed in Table 1 are as follows: AA: Acrylic acid; DAC: Trimethylacryloyloxyethylammonium chloride; DA: Dimethylaminoethyl acrylate; AAm: Acrylamide; V-50: 2,2'-Azobis(2-methylpropionamidine) dihydrochloride; LiOH; H ２ O: Lithium hydroxide monohydrate, NaOH: Sodium hydroxide, KOH: Potassium hydroxide

[0202] <Crosslinked Polymer> [Measurement Method] (Measurement of Water-Swelled Particle Size of Crosslinked Polymer) 0.25 g of crosslinked polymer powder and 49.75 g of deionized water were weighed into a 100 cc container and set in a rotation / revolution type agitator (Sinky Co., Ltd., Awatori Rentaro AR-250). Agitation treatment (rotation speed 2,000 rpm / revolution speed 800 rpm, 7 minutes), followed by defoaming treatment (rotation speed 2,200 rpm / revolution speed 60 rpm, 1 minute) was performed to prepare a hydrogel in which the crosslinked polymer was swollen in water. Next, the particle size distribution of the above hydrogel was measured using a laser diffraction / scattering particle size analyzer (Microtrac Bell Co., Ltd., Microtrac MT-3300EXII) with deionized water as the dispersion medium. When an appropriate amount of hydrogel was added to a system circulating an excess amount of dispersion medium over the hydrogel to obtain the appropriate scattered light intensity, the measured particle size distribution shape stabilized after a few minutes. Once stability was confirmed, the particle size distribution was measured, and the volume-based median diameter (D50), which is a representative value of the particle size, was obtained.

[0203] [Production of Crosslinked Polymers] (Production Example 16: Crosslinked Polymer R-1) A reactor equipped with a stirring blade, thermometer, reflux condenser, and nitrogen inlet tube was used. 567 parts of acetonitrile, 2.2 parts of deionized water, 100.0 parts of acrylic acid (hereinafter also referred to as "AA"), 0.9 parts of trimethylolpropanediallyl ether (manufactured by Osaka Soda Co., Ltd., trade name "Neoallyl T-20"), and triethylamine equivalent to 1.0 mol% of the above AA were charged into the reactor. After thoroughly purging the reactor with nitrogen, the internal temperature was raised to 55°C. After confirming that the internal temperature had stabilized at 55°C, 0.040 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name "V-65") were added as a polymerization initiator. When turbidity was observed in the reaction solution, this point was taken as the polymerization initiation point. The monomer concentration was calculated to be 15%. Cooling of the polymerization reaction solution was started 12 hours after the polymerization initiation point, and after the internal temperature dropped to 25°C, lithium hydroxide monohydrate (hereinafter referred to as "LiOH·H") was added. ２ 52.4 parts of the powder of (also known as "O") were added. After the addition, stirring was continued at room temperature for 12 hours to obtain a slurry-like polymerization reaction solution in which particles of crosslinked polymer R-1 (lithium salt, degree of neutralization 90 mol%) were dispersed in the medium.

[0204] The resulting polymerization reaction solution was centrifuged to settle the polymer particles, and the supernatant was removed. Then, the precipitate was redispersed in an equal mass of acetonitrile, and the washing operation, in which the polymer particles were settled by centrifugation and the supernatant was removed, was repeated twice. The precipitate was collected and dried under reduced pressure at 80°C for 3 hours to remove volatile components, thereby obtaining the crosslinked polymer R-1 powder. Since crosslinked polymer R-1 is hygroscopic, it was stored in a sealed container with water vapor barrier properties.

[0205] When the powder of cross-linked polymer R-1 was subjected to IR measurement, the degree of neutralization was determined from the intensity ratio of the peak originating from the C=O group of carboxylic acid and the peak originating from the C=O group of lithium carboxylic acid. This result was 90 mol%, which was equal to the value calculated from the initial charge. Furthermore, the water-swollen particle size of cross-linked polymer R-1 in an aqueous medium was 1.54 μm.

[0206] (Production Example 17: Crosslinked Polymer R-2) The same procedure as in Production Example 16 was followed, except that the amount of each raw material used was as shown in Table 2, to obtain the polymerization reaction solution for crosslinked polymer R-2. The results are shown in Table 2.

[0207]

[0208] The meanings of the abbreviations listed in Table 2 are as follows: AA: Acrylic acid; HEA: 2-Hydroxyethyl acrylate; T-20: Trimethylolpropanediallyl ether; TEA: Triethylamine; V-65: 2,2'-Azobis(2,4-Dimethylvaleronitrile); LiOH; H ２ O: Lithium hydroxide monohydrate

[0209] <Example 1> [Production of electrode mixture layer composition] Artificial graphite (manufactured by Showa Denko, trade name "SCMG-CF") and SiO (manufactured by Osaka Titanium Technologies, 5 μm) were used as active materials. An aqueous solution of non-crosslinked polymer Y-1 and styrene-butadiene rubber (SBR) were used as binders. Artificial graphite:SiO:Y-1:SBR were added to a planetary mixer (Primix, Hibismix 2P-03 type) with water as the diluent so that the solid content concentration of the electrode mixture layer composition was 50% by mass, in a mass ratio of artificial graphite:SiO:Y-1:SBR = 76.8:19.2:3.0:1.0 (solid content), and the mixture was mixed for 1 hour and 30 minutes to produce an electrode mixture layer composition in slurry form (electrode slurry).

[0210] [Evaluation of dilatancy resistance] Using a rheometer (Anton Paar, MCR301), the shear rate was measured from 0 to 200 (s). －１ The shear viscosity of the electrode slurry was measured while varying the shear rate (s). －１ (A) The shear viscosity at ) is given by the shear rate 13 (s －１ When the shear viscosity in (B) was calculated as (B) / (A), the viscosity ratio (X value) was determined to be 0.53, resulting in a "B" rating according to the following criteria. A lower X value indicates better resistance to dilatancy.

[0211] (Criteria for determining dilatancy resistance) A: X value less than 0.50 B: X value 0.50 or more and less than 0.70 C: X value 0.70 or more and less than 0.90 D: X value 0.90 or more

[0212] [Negative electrode preparation] Using a variable applicator, the electrode slurry was applied onto a current collector (copper foil, thickness: 16.5 μm), and a composite layer was formed by drying in a forced-air dryer at 80°C for 15 minutes. Subsequently, the composite layer had a thickness of 50 ± 5 μm and a composite density of 1.60 ± 0.10 g / cm³. ３ After rolling to the desired shape, the negative electrode plate was punched out in a 3 cm square for battery evaluation.

[0213] [Preparation of the positive electrode] In N-methylpyrrolidone (NMP) solvent, LiNi is used as the positive electrode active material. ０．５ Co ０．２ Mn ０．３ O ２ A composition for the positive electrode composite layer was prepared by mixing 100 parts of (NCM) and 2 parts of acetylene black, and then mixing in 4 parts of polyvinylidene fluoride (PVDF) as a binder for the positive electrode. Next, the composition for the positive electrode composite layer was applied to a current collector (aluminum foil, thickness: 20 μm) using a variable applicator and dried to form a composite layer. Subsequently, the thickness of the composite layer was 125 ± 1 μm and the composite density was 3.0 ± 0.10 g / cm³. ３ After rolling to achieve the desired shape, the positive electrode plate was punched out in a 3 cm square for battery evaluation.

[0214] [Preparation of Electrolyte] A mixed solvent consisting of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio EC:DMC = 3:7) is to be mixed with vinylene carbonate (VC) at a concentration of 1% by mass and fluoroethylene carbonate (FEC) at a concentration of 2% by mass, and LiPF ６ A non-aqueous electrolyte was prepared by dissolving 1.2 mol / liter of [the substance].

[0215] [Fabrication of Secondary Battery] An electrode body was created by placing a positive electrode and a negative electrode, each fitted with lead terminals, opposite each other via a separator (polyethylene: film thickness 16 μm, porosity 47%). This body was then placed in an aluminum laminate battery casing, injected with electrolyte, and sealed to create a test battery. The design capacity of the test battery is 50 mAh. The battery's design capacity was determined based on a charging termination voltage of 4.2 V.

[0216] [Cycle Characteristics Evaluation] Under conditions of 2.5 to 4.2V in a 25°C environment, charge and discharge were repeated at a charge / discharge rate of 0.5C, and the capacity C after 100 cycles was evaluated. １００ The following was measured. The charge / discharge capacity retention rate (ΔC) was calculated using the following formula. Note that C ０ This is the capacity at cycle 0. ΔC (%) = [C １００ / C ０ ] × 100

[0217] ΔC was 83.0%, resulting in a "C" rating according to the following criteria. A higher ΔC value indicates superior cycle characteristics.

[0218] (Cycle characteristic assessment criteria) A: ΔC is 85.0% or higher B: ΔC is 84.0% or higher but less than 85.0% C: ΔC is 83.0% or higher but less than 84.0% D: ΔC is less than 83.0%

[0219] [Overall Assessment] Based on the evaluation of dilatancy resistance and cycle characteristics described above, an overall assessment was made according to Table 3. Since the evaluation of dilatancy resistance was "B" and the evaluation of cycle characteristics was "C", the overall assessment was "C". Note that an overall assessment of "A" to "C" is considered a passing grade.

[0220]

[0221] <Examples 2-22 and Comparative Examples 1 and 2> Manufacturing and evaluation were carried out in the same manner as in Example 1, except that the material composition was as shown in Table 4. The results are shown in Table 4.

[0222]

[0223] The meanings of the abbreviations listed in Table 4 are as follows: • SBR: Styrene-butadiene rubber • CMC: Carboxymethylcellulose sodium

[0224] <Results> In Examples 1 to 22, the electrode slurry containing the non-crosslinked polymer exhibited excellent dilatancy resistance, and the secondary battery exhibited excellent cycle characteristics. This is presumed to be because a predetermined amount of structural units (structural unit (b)) derived from the ethylenically unsaturated monomer (b) having cationic groups and / or cation-generating groups improved the dispersibility of the electrode active material.

[0225] As can be seen from the comparison of Examples 3 to 6, the dilatancy resistance and cycle characteristics could be further improved by adjusting the amount of structural unit (b). This is presumed to be because the presence of an appropriate amount of cationic groups and / or cation-generating groups of structural unit (b) suppressed the re-aggregation of the electrode active materials.

[0226] As can be seen from the comparison of Examples 7 to 9, the dilatancy resistance and cycling properties could be further improved by adjusting the amount of structural units (structural unit (c)) derived from the amide group-containing ethylenically unsaturated monomer (c). This is presumed to be because the presence of the amide group in structural unit (c) improved its adsorption to the electrode active material.

[0227] As can be seen from the comparison of Examples 5, 11, and 12, the dilatancy resistance and cyclic properties of the non-crosslinked polymer could be further improved by adjusting the degree of neutralization.

[0228] As can be seen from the comparison between Examples 5 and 19-21, the dilatancy resistance and cyclic properties could be further improved by adjusting the ratio of non-crosslinked polymers to crosslinked polymers.

[0229] On the other hand, in Comparative Examples 1 and 2, structural unit (b) was either absent or excessive, making it impossible to achieve both dilatancy resistance and cyclic properties, with particularly poor cyclic properties.

[0230] A secondary battery formed using the binder according to the above embodiment of the present invention is expected to be used, for example, as an in-vehicle secondary battery where high capacity is required, particularly as a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte lithium-ion secondary battery.

Claims

1. A binder for secondary battery electrodes comprising a carboxyl group-containing non-crosslinked polymer or a salt thereof, wherein the carboxyl group-containing non-crosslinked polymer or salt thereof comprises structural units derived from an ethylenically unsaturated carboxylic acid monomer (a1) and structural units derived from an ethylenically unsaturated monomer (b) having a cationic group and / or a cation-generating group, wherein the amount of structural units derived from monomer (a1) is 30% by mass or more based on the mass of the carboxyl group-containing non-crosslinked polymer or salt thereof, and the amount of structural units derived from monomer (b) is 2% by mass or more and 50% by mass or less based on the mass of the carboxyl group-containing non-crosslinked polymer or salt thereof.

2. The binder for secondary battery electrodes according to claim 1, wherein the carboxyl group-containing non-crosslinked polymer or salt thereof further comprises structural units derived from an amide group-containing ethylenically unsaturated monomer (c).

3. The binder for secondary battery electrodes according to claim 2, wherein the amount of structural units derived from the monomer (c) is 1% by mass or more and 50% by mass or less, based on the mass of the carboxyl group-containing non-crosslinked polymer or salt thereof.

4. The binder for secondary battery electrodes according to claim 1, wherein the monomer (b) has a quaternary ammonium group and / or a tertiary amino group.

5. The binder for secondary battery electrodes according to claim 1, wherein the degree of neutralization of the carboxyl group-containing non-crosslinked polymer or a salt thereof is 30 mol% or more and 95 mol% or less.

6. The binder for secondary battery electrodes according to any one of claims 1 to 5, wherein the binder for secondary battery electrodes further comprises a carboxyl group-containing crosslinked polymer or a salt thereof.

7. The binder for secondary battery electrodes according to claim 6, wherein the carboxyl group-containing crosslinked polymer or salt thereof contains structural units derived from an ethylenically unsaturated carboxylic acid monomer (a2), and the amount of structural units derived from the monomer (a2) is 50% by mass or more, based on the mass of the carboxyl group-containing crosslinked polymer or salt thereof.

8. The binder for secondary battery electrodes according to claim 6, wherein the amount of the carboxyl group-containing crosslinked polymer or salt thereof is 10% by mass or more and 80% by mass or less, based on the total mass of the carboxyl group-containing non-crosslinked polymer or salt thereof and the carboxyl group-containing crosslinked polymer or salt thereof.

9. A composition for a secondary battery electrode mixture layer, comprising the binder for secondary battery electrodes described in claim 8, an electrode active material, and water.

10. A secondary battery electrode comprising: a current collector; and a composite layer formed from the secondary battery electrode composite layer composition according to claim 9, disposed on the surface of the current collector.

11. A secondary battery comprising the secondary battery electrode described in claim 10.

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