Secondary battery binder, slurry, electrode, secondary battery manufacturing method, and secondary battery

Abstract

Provided is a novel secondary battery binder or slurry containing said secondary battery binder, the same being capable of suitably contributing to the manufacturing of a battery and / or to the battery characteristics due to the use of the secondary battery binder in which: an aqueous polymer is contained; the Na concentration of an aqueous solution obtained when the aqueous polymer is dissolved in water at a concentration of 2 mass% is 0.05-0.25 mass%; the electrolyte absorption rate of the aqueous polymer (at 25°C) is 8.0% or less; the composition of the electrolyte is such that the ratio of ethylene carbonate to dimethyl carbonate is 1:1 v / v%; and the pH of the aqueous solution obtained when the aqueous polymer is dissolved in water at a concentration of 2 mass% is, at 25°C, 6.5-8.5.

Description

Secondary battery binder, slurry, electrode, method for manufacturing secondary battery, and secondary battery

[0001] The present disclosure relates to a secondary battery binder, a slurry, an electrode, a method for manufacturing a secondary battery, and a secondary battery.

[0002] In the manufacturing process of secondary batteries, particularly in the manufacturing process of electrodes, a slurry containing a binder is used. In recent years, due to concerns about the impact on the environment, interest has been increasing in shifting from slurries using organic solvents to aqueous slurries using water as the solvent. Patent Document 1 discloses the use of an aqueous slurry containing a latex-based binder.

[0003] JP 2012-49061 A

[0004] The types and properties of the binder are not sufficiently considered in Patent Document 1. An object of the present disclosure is to provide a novel secondary battery binder that can favorably contribute to battery production and / or battery properties, or a slurry containing the secondary battery binder.

[0005] The present disclosure includes the following aspects: [Item 1] A secondary battery binder comprising an aqueous polymer, wherein the aqueous solution obtained when the aqueous polymer is dissolved in water at a concentration of 2 mass% has a Na concentration of 0.05 mass% or more and 0.25 mass% or less, the aqueous polymer has an electrolyte absorption rate (25°C) of 8.0% or less, the electrolyte solution has a composition in which the ethylene carbonate / dimethyl carbonate ratio is 1 / 1 v / v%, and the aqueous solution obtained when the aqueous polymer is dissolved in water at a concentration of 2 mass% has a pH of 6.5 or more and 8.5 or less at 25°C. [Item 2] The secondary battery binder according to Item 1, wherein the electrolyte absorption rate (25°C) is 2% or more and 6.5% or less. [Item 3] The secondary battery binder according to Item 1 or 2, wherein the aqueous polymer is a vinyl polymer having an acidic functional group-containing repeating unit. [Item 4] The aqueous polymer is a polymer represented by the formula: -[CH ２ -C(R １ ) (C(=O)R ２ )] - [wherein, R 1 is a hydrogen atom or CH ３ and R 2 is NH ２, OM (M is a hydrogen atom or a counter cation), O(CH ２ ) ｎ OH, NH(CH ２ ) ｎ OH (wherein n is independently 1 or more and 6 or less).] and a repeating unit (1) represented by the formula: -[CH ２ The secondary battery binder according to any one of Items 1 to 3, comprising a repeating unit selected from the repeating unit (2) represented by the formula: -CH(OH)]-. [Item 5] The secondary battery binder according to Item 4, wherein in the aqueous polymer, the amount of the repeating unit selected from the repeating unit (1) and the repeating unit (2) is 40 mol % or more, the amount of the acidic functional group-containing repeating unit is 0.8 mol % or more, and the amount of the nonionic repeating unit is 40 mol % or more. [Item 6] The secondary battery binder according to any one of Items 1 to 5, comprising SBR. [Item 7] A slurry comprising the secondary battery binder according to any one of Items 1 to 6 and water. [Item 8] The slurry according to Item 7, further comprising an electrode active material. [Item 9] A method for producing a secondary battery, comprising a step of applying the slurry according to Item 7 or 8. [Item 10] An electrode comprising the secondary battery binder according to any one of Items 1 to 6 or a component derived from the secondary battery binder. [Item 11] An electrode comprising a heat-dried product of the slurry according to Item 7 or 8. [Item 12] A secondary battery comprising the electrode according to Item 10 or 11.

[0006] The secondary battery binder according to the present disclosure or a slurry containing the secondary battery binder has one or more properties suitable for batteries or the manufacture of batteries. In particular, the use of the secondary battery binder according to the present disclosure or a slurry containing the secondary battery binder can suitably suppress battery expansion after charge-discharge cycles.

[0007] <Definitions of Terms, etc.> In this specification, regardless of whether "each independently" or a similar expression is explicitly stated, unless otherwise stated, when a term (symbol) that may appear multiple times in a chemical structure is defined, the definition applies independently to each occurrence.

[0008] In this specification, "(meth)acrylic" means "acrylic or methacrylic", and "(meth)allyl" means "allyl or methallyl".

[0009] In this specification, when multiple lower limit values ​​and multiple upper limit values ​​are separately described, any lower limit value and any upper limit value can be selected, and a numerical range that is a combination of the lower limit value and the upper limit value can be selected.

[0010] <Secondary Battery Binder> The secondary battery binder in the present disclosure is used to enhance the binding strength between particles inside an electrode in a secondary battery and the binding strength between an active material layer and a current collector.

[0011] [Water-based polymer] The secondary battery binder in the present disclosure includes a water-based polymer. The water-based polymer in the present disclosure is a polymer that can be dispersed in water by itself, and is particularly water-soluble.

[0012] [Characteristics of Water-Based Polymer] The characteristics of the water-based polymer are shown below.

[0013] (Water Solubility) When 2.0 g of the aqueous polymer is dissolved in 100 g of water at 25°C, the insoluble content may be 20% by mass or less, or 15% by mass or less, preferably 5% by mass or less, and more preferably 1% by mass or less, relative to the aqueous polymer.

[0014] (molecular weight, etc.)

[0015] The Mw (weight average molecular weight) of the aqueous polymer measured by GPC-RI may be 100,000 or more, 300,000 or more, 500,000 or more, 750,000 or more, or 1,500,000 or more, preferably 100,000 or more, more preferably 500,000 or more, and may be 3,000,000 or less, 1,000,000 or less, 500,000 or less, or 250,000 or less, preferably 1,000,000 or less, more preferably 800,000 or less. This value is determined by the method described in the examples.

[0016] (pH) The pH (25°C) of the aqueous solution obtained when the aqueous polymer is dissolved in water at a concentration of 2% by mass is 6.5 or more and 8.5 or less, and may be 7.0 or more, 7.5 or more, or 8.0 or less, 7.5 or less, or 7.0 or less. This value is determined by the method described in the Examples. Ion-exchanged water is usually used as the water. When the pH is equal to or greater than the lower limit (particularly 7.0 or more (neutral to alkaline)), the flexibility of the polymer component containing the aqueous polymer is increased and the polymer component can exhibit high compliance with the expansion and contraction of the active material. Similarly, when the pH is equal to or greater than the lower limit, the dispersibility of the slurry can be improved. When the pH is within the above range (particularly 6.5 or more and 7.5 or less), the viscosity stability of the aqueous polymer solution is improved, which is preferable from the viewpoint of productivity in battery production.

[0017] (Viscosity) The viscosity (25°C) of the aqueous solution obtained when a water-based polymer is dissolved in water at a concentration of 2% by mass may be 1 mPa·s or more, 5 mPa·s or more, 10 mPa·s or more, 25 mPa·s or more, or 50 mPa·s or more, preferably 5 mPa·s or more, more preferably 25 mPa·s or more, and may be 2000 mPa·s or less, 1000 mPa·s or less, 500 mPa·s or less, 100 mPa·s or less, 50 mPa·s or less, or 25 mPa·s or less, preferably 300 mPa·s or less, more preferably 100 mPa·s or less. This value is determined by the method described in the Examples. Ion-exchanged water is usually used as the water. By setting the viscosity within the above range (for example, 5 mPa·s or more and 200 mPa·s or less), the dispersibility of the active material and binder in the slurry is improved, a binder film is well formed on the active material, and expansion of the electrode (particularly the initial expansion rate) when made into a battery can be suppressed. Similarly, by setting the viscosity within the above range, the dispersibility of the slurry can be improved.

[0018] (Conductivity) The conductivity of the aqueous solution obtained when the aqueous polymer is dissolved in water at a concentration of 2% by mass may be 0.5 mS / cm or more, 1.5 mS / cm or more, 2.5 mS / cm or more, 3.0 mS / cm or more, 3.5 mS / cm or more, or 4.5 mS / cm or more, preferably 2.0 mS / cm or more, more preferably 2.5 mS / cm or more, and may be 10 mS / cm or less, 7.5 mS / cm or less, or 5.0 mS / cm or less, preferably 7.5 mS / cm or less, more preferably 4.0 mS / cm or less. This value is determined by the method described in the Examples. Ion-exchanged water is usually used as the water. When the conductivity is relatively low (for example, 3.3 mS / cm or less, particularly 3.0 mS / cm or less), foaming during stirring of the aqueous solution is suitably suppressed. Furthermore, it is believed that by ensuring that the conductivity is within the above range, the concentration of the ionic component does not become too high, suppressing the surfactant properties of the ionic component and preventing foaming. When the conductivity is relatively high (particularly 3.3 mS / cm or higher), the viscosity stability of the aqueous solution is favorable. This is believed to be because, when the conductivity is high, the concentration of polar functional groups derived from the structure of the aqueous polymer increases, strengthening the ionic interactions and stabilizing the viscosity of the aqueous solution.

[0019] (Na Concentration) The Na concentration of the aqueous solution obtained when the aqueous polymer is dissolved in water at a concentration of 2% by mass is 0.05% by mass or more and 0.25% by mass or less. When the Na concentration is within the above range, expansion of the electrode after charge / discharge cycles can be suppressed. When the Na concentration is equal to or greater than the above lower limit, uneven distribution of the aqueous polymer in the slurry can be suppressed, and uneven distribution of the binder when made into a battery can also be suppressed, which is thought to make it easier to suppress expansion of the active material. A preferred lower limit is 0.10% by mass or more. Furthermore, when the Na concentration is equal to or less than the above upper limit, adhesion to the active material is improved, which is thought to suppress expansion. In addition, it is thought that the uniformity of the slurry is improved and an increase in battery resistance can also be suppressed. This value is determined by the method described in the Examples. Ion-exchanged water is usually used as the water.

[0020] (Electrolyte Absorption Rate (25°C)) The electrolyte absorption rate (25°C) of the aqueous polymer is 8.0% or less. The composition of the electrolyte solution is an ethylene carbonate / dimethyl carbonate ratio of 1 / 1 v / v%. When the electrolyte absorption rate is within the above range, the DC resistance of the battery after charge / discharge cycles is favorably suppressed. From the same viewpoint, it is preferably 6.5% or less, more preferably 2% to 6.5%. An aqueous polymer having an electrolyte absorption rate (25°C) equal to or less than the above upper limit tends to have relatively high rigidity and high binder film strength. As a result, it is thought that the binder film is less likely to break or peel when the active material swells and shrinks due to charge / discharge of the battery, the coverage of the active material can be maintained high, the formation of a high-resistance film due to decomposition of the electrolyte solution due to contact with the electrolyte can be suppressed, and an increase in the DC resistance of the battery can be suppressed. This value is determined by the method described in the examples.

[0021] [Structure of aqueous polymer, etc.] The aqueous polymer can be obtained by polymerizing one or more types of monomers. The aqueous polymer may be a vinyl polymer. The vinyl polymer is a polymer obtained by polymerizing a vinyl monomer. Here, the vinyl monomer may be a compound having a polymerizable carbon-carbon double bond (ethylenically unsaturated double bond) (>C=C<), and may be a monomer containing a vinyl group, a vinylene group, a vinylidene group, an acryloyl group, a methacryloyl group, or a derivative group thereof. The aqueous polymer may be a (meth)acrylic polymer containing a repeating unit derived from a monomer having an acryloyl group or a methacryloyl group.

[0022] The water-based polymer may be a random polymer or a block polymer, for example a random polymer.

[0023] (Hydrophilic Repeating Unit) The aqueous polymer has a hydrophilic repeating unit. The hydrophilic repeating unit contains a hydrophilic group. Examples of the hydrophilic group include anionic groups such as a carboxy group, a sulfonic acid group, a phosphate group, and a nitrate group, cationic groups such as an amino group, a hydroxy group, a polyoxyethylene group (e.g., having a repeating number of 2 or more, 5 or more, or 10 or more), and nonionic hydrophilic groups such as an amide group. The anionic group and the cationic group may be in a free acid / base state, or a part or all of them may be in the form of a salt. The hydrophilic repeating unit may not contain a sulfonic acid group-containing repeating unit, and the aqueous polymer may not contain a sulfonic acid group-containing repeating unit.

[0024] In this specification, when an anionic group or a cationic group or a structure containing such a group (for example, a repeating unit containing an acidic functional group) is mentioned, it is intended to encompass not only the anionic group and the cationic group but also salts thereof, unless explicitly stated otherwise.

[0025] Examples of counter cations of anionic groups include metal ions, preferably light metal ions, more preferably lithium ions, sodium ions, or potassium ions, and particularly lithium ions or sodium ions. The counter cations may be monovalent to trivalent, monovalent to divalent, or monovalent, preferably monovalent. Examples of counter anions of cationic groups include inorganic acid ions such as phosphate ions, nitrate ions, and sulfate ions, and halide ions. The aqueous polymer may be anionic, or may not have a cationic group.

[0026] The aqueous polymer in the present disclosure preferably has a repeating unit having an acidic functional group as a hydrophilic repeating unit. The acidic functional group may be an anionic group such as a carboxy group, a sulfonic acid group, a phosphate group, or a nitrate group, preferably a carboxy group or a sulfonic acid group, and more preferably a carboxy group. These groups may exist in the form of a salt, and in this case, the above-mentioned metal ions are suitable as counter cations. Examples of repeating units having an acidic functional group include repeating units derived from (meth)acrylic acid, maleic acid, vinylsulfonic acid, or (meth)allylsulfonic acid.

[0027] The aqueous polymer of the present disclosure may have a nonionic hydrophilic repeating unit, such as a repeating unit derived from (meth)acrylamide, hydroxyalkyl (meth)acrylate, hydroxyalkyl (meth)acrylamide, polyoxyalkylene (meth)acrylate, polyoxyalkylene (meth)acrylamide, or vinyl alcohol.

[0028] Examples of suitable hydrophilic repeating units include those of the formula: —[CH ２ -C(R １ ) (C(=O)R ２ )] - [wherein, R 1 is a hydrogen atom or CH ３ and R 2 is NH ２ , OM (M is a hydrogen atom or a counter cation), O(CH ２ ) ｎ OH, NH(CH ２ ) ｎ OH (wherein n is independently 1 or more and 6 or less).] and a repeating unit (1) represented by the formula: -[CH ２ -CH(OH)]- (2)

[0029] In the repeating unit (1), R 1 is preferably a hydrogen atom.

[0030] In the repeating unit (1), R ２ In the formula (I), M may be a metal cation, preferably a light metal cation, more preferably a lithium ion, a sodium ion, or a potassium ion, and particularly may be a lithium ion or a sodium ion. M may be monovalent to trivalent, monovalent to divalent, or monovalent, and is preferably monovalent.

[0031] In the repeating unit (1), R ２ In the formula, n may be 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less, preferably 3 or less, and especially 2 or less.

[0032] The repeating unit (1) is R 2 It is preferable that the repeating unit (1) contains at least one of an NH group, an OH group, an ONa group, and an OLi group. 2 is only NH2 group, R 2 is only OH group, R 2 is an ONa group, or R 2 The repeating unit (1) may be an OLi group only. 2 may contain ONa groups and OH groups, and R 2 may contain an OLi group and an OH group, may contain an NH group and an OH group, may contain an NH group, an OH group and an ONa group, may contain an NH group, an OH group, an ONa group and an OLi group, or R 2 may include those having OH groups, OLi groups, and NH2 groups.

[0033] The repeating unit (2) can be introduced, for example, by polymerizing a vinyl ester (vinyl acetate, vinyl propionate, etc., particularly vinyl acetate) followed by saponification, or by reacting a polymer having a vinyl alcohol-based repeating unit (e.g., polyvinyl alcohol).

[0034] The aqueous polymer preferably contains a repeating unit derived from (meth)acrylic acid (particularly a sodium salt or lithium salt).

[0035] (Non-hydrophilic repeating unit) The aqueous polymer may have a non-hydrophilic repeating unit. The non-hydrophilic repeating unit does not have a hydrophilic group (e.g., an ionic group). Examples of the non-hydrophilic repeating unit include repeating units derived from (meth)acrylonitrile, (meth)acrylic acid alkyl ester, vinyl chloride, etc.

[0036] [Composition of aqueous polymer, etc.] The amount of hydrophilic repeating units in the aqueous polymer may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more, preferably 20 mol% or more, more preferably 40 mol% or more, and may be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less.

[0037] The amount of the acidic functional group-containing repeating unit in the aqueous polymer may be 0.8 mol% or more, 3 mol% or more, 5 mol% or more, 10 mol% or more, 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more, preferably 5 mol% or more, more preferably 10 mol% or more, and may be 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 60 mol% or less.

[0038] The amount of nonionic hydrophilic repeating units in the aqueous polymer may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more, preferably 20 mol% or more, more preferably 40 mol% or more, and may be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 80 mol% or less.

[0039] The amount of non-hydrophilic repeating units in the aqueous polymer may be 0 mol% or more, 1 mol% or more, 3 mol% or more, 5 mol% or more, 20 mol% or more, 40 mol% or more, or 50 mol% or more, or may be 70 mol% or less, 50 mol% or less, 40 mol% or less, 30 mol% or less, 20 mol% or less, 10 mol% or less, 5 mol% or less, or 3 mol% or less, and the aqueous polymer may not contain non-hydrophilic repeating units.

[0040] The amount of nonionic repeating units in the aqueous polymer may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more, preferably 20 mol% or more, more preferably 40 mol% or more, and may be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 80 mol% or less.

[0041] The total amount of the repeating unit (1) and the repeating unit (2) in the aqueous polymer may be 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more, preferably 40 mol% or more, more preferably 50 mol% or more, and may be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less.

[0042] The amount of the repeating unit (1) in the aqueous polymer may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more, preferably 40 mol% or more, more preferably 50 mol% or more, and may be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less.

[0043] The amount of the repeating unit (2) in the aqueous polymer may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more, preferably 20 mol% or more, more preferably 40 mol% or more, and may be 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 70 mol% or less. The aqueous polymer may not contain the repeating unit (2).

[0044] A repeating unit derived from (meth)acrylamide (R ２ NH ２The amount of the hydroxybenzoate (H2O3) in the aqueous polymer may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more, preferably 20 mol% or more, more preferably 30 mol% or more, and may be 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 70 mol% or less.

[0045] A repeating unit derived from (meth)acrylic acid or a salt thereof (R ２ The amount of the OM) in the aqueous polymer may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more, preferably 10 mol% or more, more preferably 20 mol% or more, and may be 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 70 mol% or less.

[0046] [Method for Producing Aqueous Polymers] The method for producing the aqueous polymer is not particularly limited, and can be produced using known copolymer production methods. Preferably, the polymer can be synthesized by aqueous radical polymerization. Specifically, a radical polymerization initiator and, if necessary, a chain transfer agent are added to a monomer mixture, and the polymerization reaction is carried out at a reaction temperature of approximately 50 to 100°C (e.g., 60 to 70°C) while stirring. The reaction time is not particularly limited, and may be approximately 1 to 10 hours. After the reaction time has elapsed, the mixture may be further aged for 15 minutes to 2 hours (e.g., 30 minutes to 1.5 hours) at a temperature of +3°C to +10°C (e.g., +4°C to +8°C) above the reaction temperature. Aging can reduce the amount of unreacted monomer. When the aqueous polymer contains vinyl alcohol units, the saponification conditions may be set with reference to, for example, the method for producing a copolymer of vinyl alcohol and an alkali metal neutralized product of an ethylenically unsaturated carboxylic acid, as described in WO 2017 / 168947.

[0047] The monomer concentration at the start of polymerization may be 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, or 25% by mass or more, and may be 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less, and in one aspect, is 10% by mass or more and 11% by mass or less, 15% by mass or more and 17% by mass or less, or 11% by mass or more and 13% by mass or less.

[0048] Various known initiators can be used without particular limitation. Examples of radical polymerization initiators include persulfates such as potassium persulfate and ammonium persulfate; redox-based polymerization initiators that combine such persulfates with a reducing agent such as sodium hydrogen sulfite; and azo-based initiators such as 2,2'-azobis-2-amidinopropane dihydrochloride (V-50, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 2,2'-azobis(2,4-dimethylvaleronitrile) (V-65, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The amount of radical polymerization initiator used is preferably about 0.05 to 2% by mass, and more preferably about 0.1 to 1.5% by mass, relative to 100% by mass of the monomer group that serves as the raw material for the aqueous polymer of the present disclosure.

[0049] The polymerization conditions can be appropriately set in accordance with the structure of the target compound.

[0050] [Amount of Water-Based Polymer] The amount of the water-based polymer in the secondary battery binder may be 25% by mass or more, 50% by mass or more, 75% by mass or more, 95% by mass or more, or 99% by mass or more, preferably 50% by mass or more, more preferably 75% by mass or more, and may be 99% by mass or less, 90% by mass or less, 80% by mass or less, or 70% by mass or less. The secondary battery binder may be the water-based polymer alone.

[0051] [Other Binder Components] The secondary battery binder according to the present disclosure may contain other binder components in addition to the aqueous polymer. Examples of the other binder components include known binder resins, such as styrene-butadiene rubber (SBR), styrene-ethylene-butylene-styrene copolymer (SEBS), polyimide (PI), polyamide, and ethylene-vinyl acetate copolymer (EVA).

[0052] The amount of other binder components in the secondary battery binder may be 0% by mass or more, 0.5% by mass or more, 5% by mass or more, 10% by mass or more, or 25% by mass or more, and may be 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, or 5% by mass or less, for example, 3% by mass or less.

[0053] <Slurry> The slurry of the present disclosure contains the secondary battery binder and water, and may further contain an electrode active material. The slurry may also contain battery particles such as a conductive additive and other liquid media, and is typically an electrode slurry containing an electrode active material. The slurry may be a positive electrode slurry containing a positive electrode active material or a negative electrode slurry containing a negative electrode active material.

[0054] [Liquid Medium] The slurry contains a liquid medium (aqueous medium) containing water. The liquid medium is preferably water alone from the viewpoint of environmental concerns, but may also contain an organic solvent, such as alcohol (ethanol, methanol, isopropyl alcohol, etc.). The amount of the organic solvent in the liquid medium may be 30% by mass or less, 20% by mass or less, 10% by mass or less, 5% by mass or less, or 3% by mass or less, and preferably 10% by mass or less.

[0055] [Amount of Liquid Medium] The amount of the liquid medium is adjusted according to the desired slurry solids concentration. The amount of the liquid medium may be 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, or 60% by mass or more, preferably 30% by mass or more, more preferably 50% by mass or more, relative to 100% by mass of the slurry solids (the total amount of the secondary battery binder, active material, and conductive additive). The amount of the liquid medium may be 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, or 40% by mass or less, preferably 70% by mass or less, more preferably 60% by mass or less.

[0056] [Secondary Battery Binder] The slurry contains a secondary battery binder, the types of which are as described above.

[0057] [Amount of secondary battery binder] The amount of secondary battery binder in the slurry solids (total amount of secondary battery binder, active material, and conductive additive) may be 0.1% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 1.5% by mass or more, 3.0% by mass or more, or 5.0% by mass or more, preferably 0.3% by mass or more, and 10% by mass or less, 7.5% by mass or less, 5.0% by mass or less, 3.0% by mass or less, 1.0% by mass or less, 0.5% by mass or less, preferably 5.0% by mass or less, more preferably 4.0% by mass or less. Being equal to or greater than the above lower limit is preferable from the viewpoint of exhibiting the effect of the binder well. Being equal to or less than the above upper limit is preferable from the viewpoint of achieving a high capacity battery.

[0058] [Active Material] The active material is an electrode active material, and may be a negative electrode active material or a positive electrode active material. When the active material is a negative electrode active material, it may contain, for example, a carbon material, and may also contain, for example, at least one of silicon and silicon oxide. Specific examples of the negative electrode active material and the positive electrode active material are shown below.

[0059] (Negative Electrode Active Material) The negative electrode active material may be any negative electrode active material used in the art.

[0060] Carbon materials such as crystalline carbon and amorphous carbon may be used as the negative electrode active material. Examples of crystalline carbon include graphite, such as natural graphite or artificial graphite, which may be amorphous, plate-like, flake-like, spherical, or fibrous. Examples of amorphous carbon include soft carbon (easily graphitizable carbon) or hard carbon (non-graphitizable carbon), mesophase pitch carbide, and calcined coke.

[0061] Materials capable of absorbing and releasing large amounts of lithium ions, such as silicon (Si), tin (Sn), and titanium (Ti), may be used as the negative electrode active material. These materials may be used in the form of simple substances, alloys, compounds, solid solutions, or composite active materials containing silicon-containing materials, tin-containing materials, and titanium-containing materials. Examples of silicon-containing materials include Si, Si / C, SiOx (0.05<x<1.95), or alloys, compounds, or solid solutions in which at least one element selected from the group consisting of B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, W, Zn, C, N, and Sn is substituted for a portion of the Si. The silicon-containing material may be a silicon oxide. Examples of tin-containing materials include Ni2Sn4, Mg2Sn, SnOx (0<x<2), SnO2, SnSiO3, LiSnO, etc. Examples of titanium-containing materials include Li2TiO3 and Li4Ti5O 12 Examples of the material include lithium titanates such as those mentioned above, and titanium-niobium composite compounds. These materials can be used singly or in combination of two or more. Among these, silicon or silicon oxide is preferred, and may be, for example, simple silicon or silicon oxide.

[0062] As the negative electrode active material, it is more preferable to use a composite obtained by mixing silicon or silicon oxide as the first negative electrode active material and a carbon material as the second negative electrode active material. As the carbon material, any carbon material generally used in secondary batteries, particularly non-aqueous electrolyte secondary batteries, can be used, and crystalline carbon, amorphous carbon, or a combination of these may be used. Examples of crystalline carbon include those described above.

[0063] The method for producing the negative electrode active material is not particularly limited. When producing an active material composite by mixing the first negative electrode active material and the second negative electrode active material, a method in which both materials are uniformly dispersed may be employed, such as a method in which the first negative electrode active material and the second negative electrode active material are mixed in a ball mill.

[0064] (Positive Electrode Active Material) The positive electrode active material is not particularly limited, and any positive electrode active material used in the art may be used.

[0065] The positive electrode active material may be a lithium-containing composite oxide. Examples of the lithium-containing composite oxide include LiMnO, LiFeO, LiCoO, LiMnO, LiFeSiO, and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi x Co y M z O2 (wherein 0≦x<1, 0≦y<1, 0≦z<1, x+y+z=1, and M is at least one element selected from the group consisting of Mn, V, Mg, Mo, Nb, Fe, Cu, and Al), LiMn （１－ｗ） Fe ｗ PO4 (where 0<w<1), LiFePO4, etc.

[0066] [Amount of active material] The amount of the active material in the slurry solids (total amount of secondary battery binder, active material, and conductive additive) may be 35% by mass or more, 45% by mass or more, 55% by mass or more, 65% by mass or more, 75% by mass or more, or 95% by mass or more, preferably 55% by mass or more, more preferably 75% by mass or more, and may be 99% by mass or less, 95% by mass or less, 90% by mass or less, or 85% by mass or less.

[0067] [Conductive Aid] As the conductive aid, a conductive aid used in this technical field can be used. The conductive aid is not particularly limited as long as it has conductivity, but carbon powder is preferred. Examples of carbon powder include commonly used carbon materials such as acetylene black (AB), ketjen black (KB), graphite, carbon fiber, carbon tube, graphene, amorphous carbon, hard carbon, soft carbon, glassy carbon, carbon nanofiber, and carbon nanotube. These may be used alone or in combination of two or more.

[0068] [Amount of conductive additive] The amount of conductive additive in the slurry solids (total amount of secondary battery binder, active material, and conductive additive) may be 0.1 mass% or more, 0.5 mass% or more, 1.0 mass% or more, 3.0 mass% or more, or 5.0 mass% or more, and is preferably 0.3 mass% or more, and may be 10 mass% or less, 5.0 mass% or less, 3.0 mass% or less, or 1.0 mass% or less, and is preferably 3.0 mass% or less, and more preferably 1.0 mass% or less.

[0069] [Dispersing Aid] The slurry of the present disclosure may further contain a dispersing aid. Examples of the dispersing aid include an organic acid containing a carboxyl group and at least one substituent selected from the group consisting of a hydroxyl group, an amino group, and an imino group, or humic acid. Examples of organic acids containing a hydroxyl group and a carboxyl group include lactic acid, tartaric acid, citric acid, malic acid, glycolic acid, tartronic acid, glucuronic acid, and humic acid. Examples of organic acids containing an amino group and a carboxyl group include glycine, alanine, phenylalanine, 4-aminobutyric acid, leucine, isoleucine, lysine, glutamic acid, aspartic acid, glutamine, asparagine, histidine, tryptophan, cysteine, and polymers thereof. Examples of organic acids containing an imino group and a carboxyl group include proline, 3-hydroxyproline, 4-hydroxyproline, and pipecolic acid. Among these, glucuronic acid, humic acid, glycine, polyglycine, aspartic acid, and glutamic acid are preferred from the viewpoint of availability.

[0070] [Amount of Dispersion Aid] The amount of the dispersion aid may be 0.1 parts by mass or more, 0.5 parts by mass or more, 1.0 parts by mass or more, 1.5 parts by mass or more, or 3.0 parts by mass or more, and is preferably 0.3 parts by mass or more, and may be 5.0 parts by mass or less, 3.0 parts by mass or less, or 1.0 part by mass or less, and is preferably 3.0 parts by mass or less, and more preferably 1.0 part by mass or less, relative to 100 parts by mass of the slurry solids (total amount of the secondary battery binder, active material, and conductive aid).

[0071] Other Components The slurry of the present disclosure may contain other components, such as conventional additives.

[0072] [Amount of Other Components] The amount of other components (individual amount or total amount) may be 0.1 parts by mass or more, 0.5 parts by mass or more, 1.0 parts by mass or more, 3.0 parts by mass or more, or 5.0 parts by mass or more, and preferably 0.3 parts by mass or more, relative to 100 parts by mass of the slurry solids content (total amount of secondary battery binder, active material, and conductive additive), and may be 10 parts by mass or less, 5.0 parts by mass or less, 3.0 parts by mass or less, 1.0 part by mass or less, 0.5 parts by mass or less, and preferably 3.0 parts by mass or less, and more preferably 1.0 part by mass or less.

[0073] [Method for Producing Slurry] The method for producing the slurry of the present disclosure is not particularly limited, and the slurry is produced by mixing the components. For example, a binder, a liquid medium, an active material, and, if necessary, a conductive aid, a dispersing aid, etc. are mixed to form a slurry. The timing of adding the liquid medium is not particularly limited. The binder of the present disclosure may be dispersed or dissolved in the liquid medium in advance, and then the active material and other components may be mixed to form a slurry. Alternatively, the active material, the binder of the present disclosure, and, if necessary, a conductive aid, a dispersing aid, etc. may be mixed in a solid state, and then the liquid medium may be added to form a paste-like slurry.

[0074] <Electrode> The electrode of the present disclosure is an electrode for a secondary battery, and includes the secondary battery binder (or a component derived from the secondary battery binder) and an active material according to the present disclosure. That is, the electrode of the present disclosure can be produced, for example, by applying the slurry of the present disclosure to a current collector and drying it. Therefore, the electrode may include a heat-dried product of the slurry. The secondary battery binder may be decomposed or reacted by heat drying and converted into a component derived from the secondary battery binder.

[0075] The temperature during heat drying may be 50°C or higher, 70°C or higher, 90°C or higher, 110°C or higher, or 130°C or higher, preferably 70°C or higher, and 300°C or lower, 250°C or lower, 200°C or lower, 175°C or lower, 150°C or lower, or 125°C or lower, preferably 150°C or lower. Heat drying may be carried out under reduced pressure (for example, 0.05 MPa or lower, 0.03 MPa or lower, or 0.01 MPa or lower). The heat drying time may be 1 hour or longer, 3 hours or longer, 6 hours or longer, 10 hours or longer, or 15 hours or longer, preferably 6 hours or longer, and may be 72 hours or shorter, 48 hours or shorter, 36 hours or shorter, 24 hours or shorter, or 18 hours or shorter, preferably 24 hours or shorter.

[0076] When the electrode of the present disclosure is a negative electrode, the material constituting the current collector may be, for example, a conductive material such as C, Cu, Ni, Fe, V, Nb, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, or Al, or an alloy containing two or more of these conductive materials (e.g., stainless steel). The current collector may also be made of Fe plated with Cu. From the viewpoints of high electrical conductivity, excellent stability in the electrolyte, and excellent oxidation resistance, Cu, Ni, stainless steel, etc. are preferred as the material for the negative electrode current collector, and Cu or Ni is more preferred from the viewpoint of material cost.

[0077] When the electrode of the present disclosure is a positive electrode, the material constituting the current collector may be, for example, a conductive substance such as C, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, or Al, or an alloy containing two or more of these conductive substances (for example, stainless steel). From the viewpoints of high electrical conductivity, excellent stability in the electrolyte, and excellent oxidation resistance, C, Al, stainless steel, etc. are preferred as the material for the positive electrode current collector, and Al is more preferred from the viewpoint of material cost.

[0078] The shape of the current collector is not particularly limited, and for example, a foil substrate, a three-dimensional substrate, etc. Use of a three-dimensional substrate (foam metal, mesh, woven fabric, nonwoven fabric, expanded fabric, etc.) tends to improve high-rate charge / discharge characteristics.

[0079] <Battery> The secondary battery of the present disclosure includes the secondary battery electrode of the present disclosure. The secondary battery of the present disclosure may include the secondary battery electrode of the present disclosure as either one or both of the positive electrode and the negative electrode. The secondary battery of the present disclosure is produced using the secondary battery electrode of the present disclosure (i.e., using the secondary battery binder of the present disclosure) by a method used in the technical field.

[0080] The secondary battery of the present disclosure is preferably a nonaqueous electrolyte secondary battery, and particularly preferably a lithium ion secondary battery. Because lithium ion secondary batteries must contain lithium ions, a lithium salt is preferred as the electrolyte. Examples of the lithium salt include lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and lithium trifluoromethanesulfonyl imide. The electrolyte may be used alone or in combination of two or more.

[0081] Examples of the electrolyte solution that can be used include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and γ-butyrolactone. The electrolyte solution can be used alone or in combination of two or more. Propylene carbonate alone, a mixture of ethylene carbonate and diethyl carbonate, or γ-butyrolactone alone are particularly preferred. The mixing ratio of the above-mentioned mixture of ethylene carbonate and diethyl carbonate can be adjusted as long as one of the components accounts for 10 to 90% by volume.

[0082] Other configurations of the secondary battery may also be the same as those of known secondary batteries.

[0083] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0084] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to these examples.

[0085] The abbreviations have the following meanings: AA: Acrylic acid AAm: Acrylamide 2-HEA: 2-hydroxyethyl acrylate SMAS: Sodium methallylsulfonate VA: Vinyl alcohol CMC: Carboxymethyl cellulose SBR: Styrene butadiene rubber

[0086] <Preparation of Polymer> The polymer was prepared according to the procedure described below.

[0087] Reference Example 1 A sealable vial having an internal volume of 500 ml was charged with 34.9 g (0.49 mol) of acrylamide, 0.2 g (0.001 mol) of sodium methallylsulfonate, 35.3 g (0.49 mol) of acrylic acid, 48.6 g (0.42 mol) of 2-hydroxyethyl acrylate, 1.36 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (product name "VA-044" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 210.0 g of ion-exchanged water, and the charged solution was mixed to prepare an aqueous monomer solution, which was then deoxygenated. Separately, a stirrer, a thermometer, and N ２A 2 L reaction vessel equipped with a gas inlet tube, a reflux condenser, and a dropping funnel was charged with 858.3 g of ion-exchanged water, and N ２ After deoxygenating the system by blowing in gas, the internal temperature was raised to 68°C. Subsequently, the deoxygenated aqueous monomer solution was added dropwise to the reaction vessel over 3 hours using a dropping funnel while stirring. After the dropwise addition, the internal temperature was maintained at 68°C for 2 hours. The mixture was further stirred at 73°C for 1 hour, cooled to 30°C, and 30.3 g of a 48% by mass aqueous NaOH solution was added until the pH reached 5.5, yielding an aqueous solution containing an aqueous polymer. The repeating unit composition of the aqueous polymer was AAm / AA(H / Na) / 2-HEA / SMAS = 35 / 35 / 29.9 / 0.1 (molar ratio).

[0088] Example 1 40.0 g (0.56 mol) of acrylic acid, 60.0 g (0.52 mol) of 2-hydroxyethyl acrylate, 0.367 g of ammonium persulfate, and 50.0 g of ion-exchanged water were added to a sealable vial with an internal volume of 500 ml and mixed to prepare an aqueous monomer solution, which was then deoxygenated. ２ A 1 L reaction vessel equipped with a gas inlet tube, a reflux condenser, and a dropping funnel was charged with 500.0 g of ion-exchanged water, and N ２ After deoxygenating the system by blowing in gas, the internal temperature was raised to 75°C. Subsequently, the prepared aqueous monomer solution was added dropwise to the reaction vessel over a period of 3 hours using a dropping funnel while stirring. After the dropwise addition, the temperature was maintained for 2 hours. The internal temperature was then raised to 80°C and maintained for 1 hour. The internal temperature was then cooled to 40°C, and 124.9 g (0.53 mol) of a 5 mol / L aqueous sodium hydroxide solution was added to adjust the pH to 6.5, yielding an aqueous solution containing an aqueous polymer. The repeating unit composition of the aqueous polymer was 2-HEA / AA (H / Na) = 48 / 52 (molar ratio).

[0089] Example 2 23.8 g (0.33 mol) of acrylic acid, 22.6 g (0.19 mol) of 2-hydroxyethyl acrylate, 68.9 g (0.97 mol) of acrylamide, 0.608 g of ammonium persulfate, and 225.0 g of ion-exchanged water were added to a sealable vial with an internal volume of 500 ml and mixed to prepare an aqueous monomer solution. ２A 1 L reaction vessel equipped with a gas inlet tube, a reflux condenser, and a dropping funnel was charged with 607.6 g of ion-exchanged water, and N ２ After deoxygenating the system by blowing in gas, the internal temperature was raised to 75°C. Subsequently, the prepared aqueous monomer solution was added dropwise to the reaction vessel over a period of 3 hours using a dropping funnel while stirring. After the dropwise addition, the reaction vessel was maintained at this temperature for 2 hours. The internal temperature was then raised to 80°C and maintained at this temperature for 1 hour. The internal temperature was cooled to 30°C, and 70.57 g (0.30 mol) of a 5 mol / L aqueous sodium hydroxide solution was added to adjust the pH to 6.5, yielding an aqueous solution containing an aqueous polymer. The repeating unit composition of the aqueous polymer was 2-HEA / AA(H / Na) / AAm = 13 / 22 / 65 (molar ratio).

[0090] Reference Example 2 46.5 g (0.54 mol) of methyl acrylate and 211.8 g (2.46 mol) of vinyl acetate were added to a sealable vial bottle having an internal volume of 500 ml and mixed to prepare an aqueous monomer solution. ２ A 2-L reaction vessel equipped with a gas inlet tube, a reflux condenser, and a dropping funnel was charged with 768 g of ion-exchanged water and 12 g of anhydrous sodium sulfate, and N ２ Gas was blown into the system to deoxygenate it. Subsequently, 1 g of partially saponified polyvinyl alcohol (saponification degree 88%) and 1.2 g of lauryl peroxide were added, and the internal temperature was raised to 60°C. Subsequently, the prepared monomer aqueous solution was added dropwise to the reaction vessel over 4 hours using a dropping funnel while stirring. After the addition, the internal temperature was maintained at 65°C for 2 hours, and the precipitated solid was filtered. The same reaction vessel as above was charged with the obtained solid, 450 g of methanol, 420 g of ion-exchanged water, 140 g of sodium hydroxide, and 0.52 g of hydrazine, and the mixture was stirred at 35°C for 3 hours. Subsequently, the internal temperature was cooled to 30°C, acetic acid was added to adjust the pH to 7.5, and the solid was filtered. The solid was then washed with methanol and dried under reduced pressure at 60°C for 8 hours to obtain an aqueous polymer. The repeating unit composition of the aqueous polymer was VA / AA (H / Na) = 82 / 18 (molar ratio).

[0091] [Comparative Example 1] Stirrer, thermometer, N ２ A 2 L reaction vessel equipped with a gas inlet tube, a reflux condenser, and a dropping funnel was charged with 831.0 g of ion-exchanged water, and N２ After deoxygenating the system by blowing in gas, the internal temperature was raised to 68°C. A previously prepared mixture of 126.6 g (1.78 mol) of acrylamide, 2.9 g (0.02 mol) of sodium methallylsulfonate, 1.45 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (Fujifilm Wako Pure Chemical Industries, Ltd. product name "VA-044"), and 250.0 g of ion-exchanged water was added dropwise using a dropping funnel over 3 hours. After the dropwise addition, the mixture was maintained at the same temperature for 1.5 hours. Subsequently, 1.45 g of VA-044 and 20 g of ion-exchanged water were added, and the mixture was stirred at the same temperature for 1 hour, followed by stirring at 73°C for 1 hour, yielding an aqueous solution containing a water-based polymer. The repeating unit composition of the water-based polymer was AAm / SMAS = 99 / 1 (molar ratio).

[0092] [Comparative Example 2] Stirrer, thermometer, N ２ A 1 L reaction vessel equipped with a gas inlet tube, a reflux condenser, and a dropping funnel was charged with 485.3 g of ion-exchanged water and 100.0 g of terminal thiol-modified polyvinyl alcohol (degree of polymerization: 375, degree of saponification: 98.7 mol%). ２ After deoxygenating the system by blowing in gas, the internal temperature was raised to 95°C and cooled to room temperature. Subsequently, the pH was adjusted to 3.0 using 0.5N sulfuric acid. Next, the internal temperature was raised to 62°C, and with stirring, 9.9g (0.14mol) of acrylic acid, 1.70g of ammonium persulfate, and 75.2g of ion-exchanged water were added dropwise using a dropping funnel over 1.5 hours. After the dropwise addition, the internal temperature was maintained at 62°C for 0.5 hours, and then stirred at 67°C for 1 hour. The internal temperature was then cooled to 30°C, and 5.72g (0.69mol) of a 48% by mass aqueous sodium hydroxide solution was added to obtain an aqueous solution containing a water-based polymer. The repeating unit composition of the water-based polymer was VA / AA (H / Na) = 94 / 6 (molar ratio).

[0093] Comparative Example 3 A mixture of carboxymethyl cellulose and styrene-butadiene rubber (CMC / SBR=1 / 2 (solid weight ratio)) was used.

[0094] <Measurement of Polymer Properties> The properties of the aqueous polymers obtained in the above-mentioned Reference Examples, Examples, and Comparative Examples were measured using the following test methods.

[0095] [Molecular Weight, etc.] The weight-average molecular weight (Mw) of the aqueous polymers obtained in the above Reference Examples, Examples, and Comparative Examples was measured using GPC-RI in terms of standard polyethylene glycol / polyethylene oxide. Detailed conditions are as follows: [GPC-RI] GPC device: HLC-8320GPC (Tosoh Corporation) Column: TSK GMPW XL (Tosoh Corporation) Carrier: 0.1 M sodium nitrate Column temperature: 40°C Flow rate: 1.0 mL / min Injection volume: 200 μL Concentration: 0.5 mg / mL

[0096] [pH] A polymer aqueous solution was prepared by dissolving a water-based polymer in water to a solids concentration of 2% by mass. The aqueous solution was kept at 25°C, and then the pH was measured using a pH meter (manufactured by Horiba, Ltd., model "D-71", glass pH electrode: model "9681S-10D"). The pH was calculated by rounding the measured value to one decimal place.

[0097] [Viscosity] A polymer aqueous solution was prepared by dissolving a water-based polymer in water to a solids concentration of 2% by mass, and the solution was kept at 25°C. Then, the viscosity of the polymer aqueous solution was measured using a B-type viscometer (manufactured by BROOKFIELD, model "DV1MLVTJ0"). The spindle and rotation speed corresponding to the viscosity were used during measurement as follows: LV-2, 12 rpm: 200 mPa·s or more and 2500 mPa·s or less LV-1, 30 rpm: 20 mPa·s or more and less than 200 mPa·s

[0098] [Conductivity] A polymer aqueous solution was prepared by dissolving a water-based polymer in water to a solids concentration of 2% by mass, and the aqueous solution was kept at 25° C. After that, the conductivity was measured using a conductivity meter (manufactured by AS ONE, model “AS710”). The conductivity was calculated by rounding the measured value to one decimal place.

[0099] [Na Concentration] A water-based polymer was dissolved in water to a solids concentration of 2% by mass to prepare a polymer aqueous solution. 60% by mass nitric acid was added to the solution, and the solution was heated and dissolved to prepare a measurement solution. The mass of Na contained in the measurement solution was measured by analysis using an inductively coupled plasma optical emission spectrometer (manufactured by Thermo Fisher Scientific). The Na concentration of the 2% by mass aqueous polymer solution was calculated using the following formula: Na concentration = mass of Na in measurement solution / mass of aqueous polymer solution added × 100 [%]

[0100] [Electrolyte Solution Absorption Rate (25°C)] 20 g of a polymer aqueous solution prepared by dissolving a water-based polymer in water to a solids concentration of 2% by mass was added to a polypropylene tray (manufactured by AS ONE, model "DT-1") and dried at 60°C for 15 hours in a constant temperature incubator (manufactured by Yamato Scientific, model "DKM300"), and then further dried for 24 hours in a vacuum dryer (manufactured by AS ONE, model "AVO-310N") at 60°C and a reduced pressure of 0.1 MPa to produce a film. The film produced by the above method was cut into 40 mg pieces (approximately 2 cm square) in a dry oven with a dew point of -70°C, and the weight of the film before immersion in the electrolyte was measured. The cut film was then placed in a 50 mL screw cap vial, and 20 g of electrolyte (ethylene carbonate / dimethyl carbonate = 1 / 1 v / v%, Kishida Chemical Co., Ltd.) was added to immerse the film. The screw cap vial was then sealed and stored for 22 hours in a safety tester (manufactured by ESPEC, model "CSH112") set at 25°C. After storage, the film was removed from the electrolyte in the dry chamber, sandwiched between Kimwipes and wiped with a load of approximately 700 g for 2 seconds. The weight after immersion in the electrolyte was measured, and the electrolyte absorption rate was calculated using the following formula: Electrolyte absorption rate = (weight after immersion in electrolyte - weight before immersion in electrolyte) / weight before immersion in electrolyte x 100 [%]. <Characteristics of Battery / Slurry / Binder Solution> Batteries / slurries / binder solutions were prepared using the aqueous polymers obtained in the above Reference Examples / Examples / Comparative Examples, and their characteristics were measured. The test methods were as follows.

[0101] [Capacity Retention Rate After 100 Cycles] The capacity retention rate after 100 cycles was determined according to the following procedure. [Electrode Preparation] As electrode active materials, 23.3 parts by mass of artificial graphite (G-49, manufactured by Jiangxi Zichen Technology), 5.8 parts by mass of silicon monoxide (KSC-1265, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.9 parts by mass of a polymer aqueous solution, calculated as solid content, were kneaded together. Water was then added to the mixture to give a solid content of 58% by mass, followed by kneading to prepare a negative electrode slurry. The resulting negative electrode slurry was applied to a rolled copper foil having a thickness of 18 μm, dried, and then the rolled copper foil and the coating were bonded together using a roll press (manufactured by Ohno Roll Co., Ltd.). The negative electrode was then prepared by heat treatment (reduced pressure, 100°C, 12 hours or more). The thickness of the active material layer in the obtained negative electrode was 36 μm, and the capacity density of the negative electrode was 3.5 mAh / cm ２ It was.

[0102] [Assembly of Coin Cell] A coin cell (CR2032) was fabricated comprising the negative electrode prepared above, the following positive electrode, separator, and electrolyte. Positive electrode: LiNi ０．５ Co ０．２ Mn ０．３ O ２ (Manufactured by Hachisansha Co., Ltd.) Separator: Glass filter (product name GA-100 manufactured by Advantec Co., Ltd.) Electrolyte: LiPF in a solvent made by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 ６ A solution obtained by dissolving the above at a concentration of 1 mol / L and adding 1 mass % of vinylene carbonate (VC) and 1 mass % of fluoroethylene carbonate (FEC), which are additives for electrolytes.

[0103] [Measurement of Capacity Retention Rate] Each coin cell prepared as described above was subjected to three cycles of charging at 30° C. to 4.2 V at a current corresponding to 0.1 C, discharging to 2.5 V at a current corresponding to 0.1 C, charging to 4.2 V at a current corresponding to 0.5 C, and discharging to 2.5 V at a current corresponding to 0.5 C, to perform battery aging. Subsequently, the coin cell was charged to 4.2 V at a current corresponding to 0.5 C, discharged to SOC 50 at a current corresponding to 0.5 C, discharged at a constant current for 12 seconds at a current corresponding to 0.2 C, charged for 24 seconds at a current corresponding to 0.1 C, discharged at a constant current for 12 seconds at a current corresponding to 0.5 C, charged for 1 minute at a current corresponding to 0.1 C, discharged at a constant current for 12 seconds at a current corresponding to 1 C, charged for 2 minutes at a current corresponding to 0.1 C, discharged at a constant current for 12 seconds at a current corresponding to 2 C, and then discharged to 2.5 V at a current corresponding to 0.2 C, and the initial discharge capacity was measured. Subsequently, the battery was charged to 4.2 V at a current equivalent to 1 C and discharged to 2.5 V at a current equivalent to 1 C for 97 cycles (4th to 100th cycles). The same procedure as used to measure the initial discharge capacity was then repeated to measure the discharge capacity after 100 cycles. Capacity retention after 100 cycles = [discharge capacity after 100 cycles (mAh / g)] / [initial discharge capacity after aging (mAh / g)] × 100 [%].

[0104] [Discharge Capacity After 100 Cycles] The discharge capacity after 100 cycles in the above test for [Capacity Maintenance Rate After 100 Cycles] was measured.

[0105] [Expansion rate after 100 cycles] The expansion rate after 100 cycles was determined according to the following procedure: [Fabrication of electrode] An electrode was fabricated in the same manner as described above in [Capacity retention rate after 100 cycles].

[0106] [Assembly of Coin Cell] In the same manner as described above in [Capacity Retention Rate After 100 Cycles], a coin cell (CR2032) was fabricated comprising a negative electrode, the following positive electrode, a separator, and an electrolyte solution.

[0107] [Measurement of Expansion Coefficient] Each coin cell prepared as described above was subjected to three cycles of charging at 30° C. to 4.2 V at a current corresponding to 0.1 C, discharging to 2.5 V at a current corresponding to 0.1 C, charging to 4.2 V at a current corresponding to 0.5 C, and discharging to 2.5 V at a current corresponding to 0.5 C, to perform battery aging. Subsequently, the coin cell was charged to 4.2 V at a current corresponding to 0.5 C, discharged to SOC 50 at a current corresponding to 0.5 C, discharged at a constant current of 0.2 C for 12 seconds, charged at a current corresponding to 0.1 C for 24 seconds, discharged at a constant current of 0.5 C for 12 seconds, charged at a current corresponding to 0.1 C for 1 minute, discharged at a constant current of 1 C for 12 seconds, charged at a current corresponding to 0.1 C for 2 minutes, discharged at a constant current of 2 C for 12 seconds, and then discharged at a current corresponding to 0.2 C to 2.5 V (initial discharge operation). Subsequently, the battery was charged to 4.2 V at a current equivalent to 1 C and discharged to 2.5 V at a current equivalent to 1 C for 97 cycles (4th to 100th cycles). The coin cell was then disassembled in the dry chamber, and the negative electrode was removed. The negative electrode was washed with dimethyl carbonate and dried under reduced pressure at 23°C for 1 hour, after which the electrode thickness was measured with a micrometer. The active material layer thickness was calculated by subtracting the copper foil thickness from the electrode thickness, and the expansion coefficient was calculated using the following formula: Expansion coefficient after 100 cycles = (active material layer thickness after disassembly after 100 cycles) / (active material layer thickness at the time of battery fabrication) × 100 [%]

[0108] [Direct Current Resistance (DCR) after 100 Cycles] [Electrode Fabrication] An electrode was fabricated in the same manner as described above in [Capacity Retention Rate after 100 Cycles]. [Coin Cell Assembly] A coin cell (CR2032) was fabricated in the same manner as described above in [Capacity Retention Rate after 100 Cycles], including a negative electrode, the following positive electrode, a separator, and an electrolyte.

[0109] [Measurement of DC Resistance After 100 Cycles] Each coin cell prepared as described above was subjected to three cycles of charging at 30°C to 4.2 V at a current corresponding to 0.1 C, discharging to 2.5 V at a current corresponding to 0.1 C, charging to 4.2 V at a current corresponding to 0.5 C, and discharging to 2.5 V at a current corresponding to 0.5 C, to age the battery. Subsequently, the battery was charged to 4.2 V at a current equivalent to 0.5 C, then discharged to SOC50 at a current equivalent to 0.5 C, and then subjected to a constant current discharge for 12 seconds at a current equivalent to 0.2 C. After that, the battery was charged for 24 seconds at a current equivalent to 0.1 C, and then subjected to a constant current discharge for 12 seconds at a current equivalent to 0.5 C. After that, the battery was charged for 1 minute at a current equivalent to 0.1 C, and then subjected to a constant current discharge for 12 seconds at a current equivalent to 1 C. After that, the battery was charged for 2 minutes at a current equivalent to 0.1 C, and then subjected to a constant current discharge for 12 seconds at a current equivalent to 2 C. The battery was then discharged to 2.5 V at a current equivalent to 0.2 C (initial discharge operation). Subsequently, the battery was charged to 4.2 V at a current equivalent to 1 C, and then subjected to a discharge operation to 2.5 V at a current equivalent to 1 C for 97 cycles (4th to 100th cycles). Thereafter, the same operation as the initial discharge operation was performed. The DC resistance of each coin cell was calculated from the discharge current and voltage values ​​at 10.0 seconds of C-rate, and was taken as the DC resistance after 100 cycles.

[0110] [Peel Strength] Peel strength (peel strength) was determined according to the following procedure. [Electrode Preparation] As electrode active materials, 23.3 parts by mass of artificial graphite (G-49, manufactured by Jiangxi Zichen Technology), 5.8 parts by mass of silicon monoxide (KSC-1265, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.9 parts by mass of a polymer aqueous solution, calculated as solid content, were kneaded together. Furthermore, water was added to the mixture so that the solid content concentration was 58% by mass, and the mixture was kneaded to prepare a negative electrode slurry. The obtained negative electrode slurry was applied to a rolled copper foil having a thickness of 18 μm and dried. The rolled copper foil and the coating were then intimately bonded together using a roll press (manufactured by Ohno Roll Co., Ltd.), and then heat-treated (reduced pressure, 100°C, 12 hours or more) to prepare a negative electrode. The thickness of the active material layer in the obtained negative electrode was 36 μm, and the capacity density of the negative electrode was 3.5 mAh / cm ２[Peel Strength Measurement] For each of the obtained electrodes, the peel strength (N / 15 mm) when the active material layer was peeled from the current collector foil was measured. Specifically, the electrode was cut into a piece 80 mm wide x 15 mm long, adhesive tape was attached to the surface (the electrode active material layer side), and then the electrode (the current collector foil side) was attached to a stainless steel plate with double-sided tape to secure the electrode, which was used as an evaluation sample. Using this evaluation sample, a 90-degree peel test of the electrode from the stainless steel plate (a 90-degree peel test of adhesive tape from a negative electrode fixed to a stainless steel plate) was performed using a tensile tester (a small benchtop tester EZ-SX manufactured by Shimadzu Corporation), and the peel strength between the active material layer and the current collector foil in the electrode was measured.

[0111] [Mandrel Test] A mandrel test was performed according to the following procedure. [Electrode Fabrication] Electrodes were fabricated in the same manner as described above in [Peel Strength]. [Mandrel Test] In accordance with JIS K 5600-5-1, a bending test was performed on four electrodes, with the active material side of the electrode facing outward, using a mandrel with a diameter of 3 mm, so that the active material layer faced outward, and the number of electrodes with cracks or breaks on the electrode surface was recorded.

[0112] [Viscosity Change Rate After 1 Week at 20°C] A polymer aqueous solution was prepared by dissolving a water-based polymer in water to a solids concentration of 2% by mass. The aqueous solution was kept at 25°C, and the viscosity before storage was measured using a Brookfield type viscometer (manufactured by Brookfield, model "DV1MLVTJ0"). The 2% by mass polymer aqueous solution was then left to stand at 20°C for 1 week, and after keeping the temperature at 25°C, the viscosity after storage was measured using a Brookfield type viscometer (manufactured by Brookfield, model "DV1MLVTJ0"). The viscosity change rate was calculated using the following formula: Viscosity change rate = (viscosity after storage - viscosity before storage) / viscosity before storage × 100 [%]. Note that the spindle and rotation speed corresponding to the viscosity were used as follows. LV-2, 12 rpm: 200 mPa·s or more and 2500 mPa·s or less LV-1, 30 rpm: 20 mPa·s or more and less than 200 mPa·s

[0113] The test results are summarized in the table below.

[0114] The present disclosure is suitable for use as a power source for mobile communication devices, portable electronic devices, electric bicycles, electric motorcycles, electric vehicles, and the like.

[0115] Furthermore, the present disclosure also includes the following aspects: [Item 1] A secondary battery binder comprising an aqueous polymer, wherein the aqueous solution obtained when the aqueous polymer is dissolved in water at a concentration of 2% by mass has a Na concentration of 0.05% by mass or more and 0.25% by mass or less, and the aqueous polymer has an electrolyte absorption rate (25°C) of 8.0% or less. [Item 2] The secondary battery binder according to Item 1, wherein the electrolyte absorption rate (25°C) is 2% or more and 6.5% or less. [Item 3] The secondary battery binder according to Item 1 or 2, wherein the aqueous polymer is a vinyl polymer having an acidic functional group-containing repeating unit. [Item 4] The aqueous polymer is a compound represented by the formula: -[CH ２ -C(R １ ) (C(=O)R ２ )] - [wherein, R 1 is a hydrogen atom or CH ３ and R 2 is NH ２ , OM (M is a hydrogen atom or a counter cation), O(CH ２ ) ｎ OH, NH(CH ２ ) ｎ OH (wherein n is independently 1 or more and 6 or less).] and a repeating unit (1) represented by the formula: -[CH ２The secondary battery binder according to any one of Items 1 to 3, comprising a repeating unit selected from the repeating unit (2) represented by the formula: -CH(OH)]-. [Item 5] The secondary battery binder according to Item 4, wherein in the aqueous polymer, the amount of the repeating unit selected from the repeating unit (1) and the repeating unit (2) is 40 mol % or more, the amount of the acidic functional group-containing repeating unit is 0.8 mol % or more, and the amount of the nonionic repeating unit is 40 mol % or more. [Item 6] The secondary battery binder according to any one of Items 1 to 5, comprising SBR. [Item 7] A slurry comprising the secondary battery binder according to any one of Items 1 to 6 and water. [Item 8] The slurry according to Item 7, further comprising an electrode active material. [Item 9] A method for producing a secondary battery, comprising a step of applying the slurry according to Item 7 or 8. [Item 10] An electrode comprising the secondary battery binder according to any one of Items 1 to 6 or a component derived from the secondary battery binder. [Item 11] An electrode comprising a heat-dried product of the slurry according to Item 7 or 8. [Item 12] A secondary battery comprising the electrode according to Item 10 or 11.

Claims

1. A secondary battery binder comprising a water-based polymer, wherein the aqueous solution obtained when the water-based polymer is dissolved in water at a concentration of 2 mass% has a Na concentration of 0.05 mass% or more and 0.25 mass% or less, the aqueous solution has an electrolyte absorption rate (25°C) of 8.0% or less, the electrolyte has a composition in which the ratio of ethylene carbonate to dimethyl carbonate is 1 / 1 v / v%, and the aqueous solution obtained when the water-based polymer is dissolved in water at a concentration of 2 mass% has a pH at 25°C of 6.5 or more and 8.5 or less.

2. The secondary battery binder according to claim 1, wherein the electrolyte absorption rate (25°C) is 2% or more and 6.5% or less.

3. The secondary battery binder according to claim 1 or 2, wherein the aqueous polymer is a vinyl polymer having a repeating unit containing an acidic functional group.

4. The water-based polymer has the formula: -[CH ２ -C(R １ ) (C(=O)R ２ )] - [wherein, R 1 is a hydrogen atom or CH ３ and R 2 is NH ２ , OM (M is a hydrogen atom or a counter cation), O(CH ２ ) ｎ OH, NH(CH ２ ) ｎ OH (wherein n is independently 1 or more and 6 or less).] and a repeating unit (1) represented by the formula: -[CH ２ 3. The secondary battery binder according to claim 1, comprising a repeating unit selected from the repeating unit (2) represented by the formula:

5. The secondary battery binder according to claim 4, wherein in the aqueous polymer, the amount of the repeating unit selected from the repeating unit (1) and the repeating unit (2) is 40 mol % or more, the amount of the repeating unit containing an acidic functional group is 0.8 mol % or more, and the amount of the nonionic repeating unit is 40 mol % or more.

6. The secondary battery binder according to claim 1 or 2, which contains SBR.

7. A slurry comprising the secondary battery binder according to claim 1 or 2 and water.

8. The slurry of claim 7, further comprising an electrode active material.

9. A method for producing a secondary battery, comprising the step of applying the slurry according to claim 7.

10. An electrode comprising the secondary battery binder of claim 1 or 2 or a component derived from said secondary battery binder.

11. An electrode comprising the heat-dried slurry of claim 7.

12. A secondary battery comprising the electrode according to claim 10.

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