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

Abstract

To provide a new secondary battery binder capable of suitably contributing to production of a battery and / or battery characteristics, or a slurry containing the secondary battery binder.SOLUTION: A secondary battery binder comprising a water-based polymer, wherein the water-based polymer has a moisture absorptivity (25 °C, 60 RH%) of 5% or more and 20% or less.SELECTED DRAWING: None

Description

[Technical Field]

[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. [Background technology]

[0002] Slurries containing binders are used in the manufacturing process of secondary batteries, particularly in the manufacturing process of electrodes. In recent years, due to concerns about the impact on the environment, interest has been 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-49061 Summary of the Invention [Problem to be solved by the invention]

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

[0005] The present disclosure includes the following aspects: [Section 1] Contains water-based polymers, The secondary battery binder, wherein the moisture absorption rate (25°C, 60RH%) of the aqueous polymer is 5% or more and 20% or less. [Section 2] Item 2. The secondary battery binder according to Item 1, wherein the aqueous polymer is a vinyl polymer having an acidic functional group-containing repeating unit. [Section 3] The water-based polymer is formula: -[CH2-C(R 1 )(C(=O)R 2 )]- [In the formula, R 1 is a hydrogen atom or CH3, R 2 NH2, OM (M is a hydrogen atom or a counter cation), O(CH2) n OH, NH(CH2) n OH (wherein each n is independently 1 or more and 6 or less). A repeating unit (1) represented by the formula: formula: -[CH2-CH(OH)]- Repeating unit (2) Item 3. The secondary battery binder according to item 1 or 2, comprising a repeating unit selected from [Section 4] In the water-based 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 repeating units containing an acidic functional group is 0.8 mol% or more, Item 4. The secondary battery binder according to Item 3, wherein the amount of nonionic repeating units is 40 mol % or more. [Section 5] Item 5. The secondary battery binder according to any one of items 1 to 4, which contains SBR. [Section 6] A slurry for a secondary battery, Item 6. A slurry comprising the secondary battery binder according to any one of items 1 to 5 and water. [Section 7] Item 7. The slurry according to item 6, further comprising an electrode active material. [Section 8] Item 8. A method for producing a secondary battery, comprising applying the slurry according to Item 6 or 7. [Section 9] Item 6. An electrode comprising the secondary battery binder according to any one of Items 1 to 5 or a component derived from the secondary battery binder. [Section 10] Item 6. An electrode comprising a heated and dried slurry according to Item 6 or 7. [Section 11] Item 11. A secondary battery comprising the electrode according to item 9 or 10. [Effects of the Invention]

[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 the resistance of the battery after charge-discharge cycling. DETAILED DESCRIPTION OF THE INVENTION

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

[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 in particular, is water-soluble.

[0012] [Characteristics of water-based polymers] The properties of water-based polymers are shown below.

[0013] (water soluble) 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, 15% by mass or less, preferably 5% by mass or less, and more preferably 1% by mass or less, based on the aqueous polymer.

[0014] (molecular weight, etc.) The weight average molecular weight (Mw) of the aqueous polymer measured by GPC-triple detector may be 100,000 or more, 300,000 or more, 500,000 or more, or 750,000 or more, preferably 100,000 or more, more preferably 300,000 or more, and may be 1,000,000 or less, 500,000 or less, 250,000 or less, or 100,000 or less, preferably 1,000,000 or less, more preferably 700,000 or less. This value is determined by the method described in the Examples. When the Mw of the aqueous polymer measured by GPC-triple detector is within the above range (particularly 500,000 or more), the viscosity stability of the aqueous solution can be improved, which can be preferable from the viewpoint of productivity in battery production.

[0015] The Mz / Mw (breadth of molecular weight distribution) of the aqueous polymer as determined by GPC-triple detector may be 1.5 or more, 2.0 or more, 2.5 or more, or 3.0 or more, preferably 1.5 or more, more preferably 1.8 or more, and may be 5.0 or less, 4.0 or less, 3.0 or less, or 2.0 or less, preferably 3.0 or less, more preferably 2.8 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 a water-based polymer is dissolved in water at a concentration of 2% by mass may be 5.5 or more, 6.0 or more, 6.5 or more, 6.8 or more, 7.0 or more, 7.5 or more, 8.0 or more, or 8.5 or more, preferably 5.5 or more, more preferably 6.5 or more, and may be 9.0 or less, 8.5 or less, 8.0 or less, 7.5 or less, or 7.0 or less, preferably 8.5 or less, more preferably 7.5 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 higher than the lower limit (particularly 7.0 or higher (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 higher than the lower limit, the dispersibility of the slurry can be improved. By keeping the pH within the above range (particularly 5.0 or more and 7.5 or less), the viscosity stability of the aqueous polymer solution is good, which is preferable from the viewpoint of productivity in battery production. When the pH is equal to or lower than the upper limit (for example, pH 7.5 or lower), the hydrogen bonding interaction of the acidic groups becomes stronger, and the viscosity stability can be improved.

[0017] (APHA) The APHA of the aqueous solution obtained when a water-based polymer is dissolved in water at a concentration of 2% by mass may be 0 or more, 5 or more, or 10 or more, and may be 50 or less, 25 or less, 5 or less, or 1 or less, preferably 10 or less, and more preferably 8 or less. This value is determined by the method described in the Examples. Ion-exchanged water is usually used as the water.

[0018] (Turbidity) The turbidity of the aqueous solution obtained when a water-based polymer is dissolved in water at a concentration of 2% by mass may be 0.1 or more, 0.3 or more, or 0.5 or more, preferably 0.1 or more, more preferably 0.2 or more, and may be 25 or less, 5.0 or less, 2.5 or less, 1.0 or less, 0.5 or less, or 0.3 or less, preferably 1.0 or less, more preferably 0.5 or less. This value is determined by the method described in the Examples. Ion-exchanged water is usually used as the water. (surface tension) The surface tension of the aqueous solution obtained when a water-based polymer is dissolved in water at a concentration of 2% by mass may be 50 mN / m or more, or 60 mN / m or more, preferably 65 mN / m or more, more preferably 70 mN / m or more, and may be 100 mN / m or less, 80 mN / m or less, or 70 mN / m or less, preferably 90 mN / m or less, more preferably 80 mN / m or less. This value is determined by the method described in the Examples. Ion-exchanged water is usually used as the water. When the surface tension is within the above range (particularly 70 mN / m or more, 70 to 80 mN / m), the slurry has high uniformity when applied to the electrode, making it possible to suppress an increase in resistance.

[0019] (Moisture absorption rate (25℃, 60%RH)) The moisture absorption rate of the water-based polymer (at 25°C and 60% RH) is 5% or more and 20% or less. By keeping the moisture absorption rate within the above range, the direct current resistance (DCR) after cycling can be suitably suppressed. It is preferably 6.5% or more, more preferably 7.5% or more, and preferably 17% or less, more preferably 12.5% ​​or less. This value is determined by the method described in the Examples. Water-based polymers with a moisture absorption rate of 5.0% or higher have a relatively large number of polar functional groups that interact with water, which increases conductivity and is thought to result in suppressing an increase in the battery's DC resistance. Furthermore, water-based polymers with a moisture absorption rate of 20.0% or lower do not retain traces of moisture from the electrode manufacturing process, which is thought to suppress side reactions such as decomposition of the electrolyte and thus suppress an increase in the battery's DC resistance.

[0020] (glass transition temperature) The glass transition temperature of the aqueous polymer may be 30° C. or higher, 50° C. or higher, 60° C. or higher, 70° C. or higher, or 80° C. or higher, preferably 50° C. or higher, more preferably 60° C. or higher, and may be 120° C. or lower, 100° C. or lower, 80° C. or lower, 60° C. or lower, or 40° C. or lower, preferably 100° C. or lower, more preferably 90° C. or lower. This value is determined by the method described in the Examples. A glass transition temperature within the above range (particularly 50° C. or higher and 100° C. or lower) is preferable from the viewpoint of suppressing resistance. When the glass transition temperature is equal to or higher than the lower limit (for example, 50°C or higher), it is believed that the strength of the polymer as a binder is improved, the degree of coverage of the active material by the binder film is increased, and the generation of a high-resistance film due to decomposition of the electrolyte upon contact with the electrolyte can be suppressed, thereby suppressing an increase in resistance. When the glass transition temperature is equal to or lower than the upper limit (for example, 100° C. or lower), the flexibility of the polymer increases, allowing it to follow the expansion and contraction of the active material, and it is thought that an increase in resistance due to cracks on the electrode surface can be suppressed.

[0021] [Water-based polymer structure, etc.] The aqueous polymer can be obtained by polymerizing one or more types of monomers. The aqueous polymer can be a vinyl polymer. The vinyl polymer is a polymer obtained by polymerizing a vinyl monomer. The vinyl monomer can be any compound having a polymerizable carbon-carbon double bond (ethylenically unsaturated double bond) (>C=C<), and can 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 can 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 carboxyl group, a sulfonic acid group, a phosphate group, and a nitrate group; cationic groups such as an amino group; a hydroxyl 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 may be partially or completely in the form of a salt.

[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 of 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, for example, a carboxy group or a sulfonic acid group, particularly 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, examples of which include (meth)acrylamide, hydroxyalkyl (meth)acrylate, hydroxyalkyl (meth)acrylamide, polyoxyalkylene (meth)acrylate, polyoxyalkylene (meth)acrylamide, and vinyl alcohol.

[0028] Examples of suitable hydrophilic repeating units include: formula: -[CH2-C(R 1 )(C(=O)R 2 )]- [In the formula, R 1 is a hydrogen atom or CH3, R 2 NH2, OM (M is a hydrogen atom or a counter cation), O(CH2) n OH, NH(CH2) n OH (wherein each n is independently 1 or more and 6 or less). A repeating unit (1) represented by the formula: formula: -[CH2-CH(OH)]- Repeating unit (2) Examples of repeating units include those selected from the following:

[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 preferably 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 2In 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 only ONa group, or R 2 The repeating unit (1) may be only an OLi group. 2 may contain ONa groups and OH groups, and R 2 may contain OLi groups and OH groups, may contain NH2 groups and OH groups, may contain NH2 groups, OH groups and ONa groups, may contain NH2 groups, OH groups, ONa groups and OLi groups, or R 2 may include those with 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) and then saponifying it, or by reacting it with a polymer having a vinyl alcohol-based repeating unit (for example, 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 water-based polymers] 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 80 mol% or more, more preferably 90 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 0.8 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 60 mol% or less, more preferably 50 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 40 mol% or more, more preferably 60 mol% or more, and may be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 99 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 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, preferably 100 mol% or less, more preferably 90 mol% or less.

[0041] The total amount of repeating units (1) and repeating units (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 50 mol% or more, more preferably 60 mol% or more, and may be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 100 mol% or less, more preferably 90 mol% or less.

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

[0043] The amount of 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, or 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 50 mol% or less, more preferably 10 mol% or less. The aqueous polymer may not contain repeating unit (2).

[0044] A repeating unit derived from (meth)acrylamide (R 2The amount of NH2) 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 30 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, preferably 99 mol% or less, more preferably 80 mol% or less.

[0045] A repeating unit derived from (meth)acrylic acid or a salt thereof (R 2 The amount of 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 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 60 mol% or less, more preferably 40 mol% or less.

[0046] [Method of manufacturing water-based polymers] The aqueous polymer can be produced by any known method for producing copolymers. Preferably, it 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 resulting mixture is stirred while undergoing a polymerization reaction at a reaction temperature of approximately 50 to 100°C (e.g., 60 to 70°C). 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 3°C to 10°C above the reaction temperature (e.g., 4°C to 8°C). 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 WO2017 / 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 reducing agents such as sodium hydrogen sulfite; and azo-based initiators such as 2,2'-azobis-2-amidinopropane dihydrochloride (NC-32) (V-50) and 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044). The amount of radical polymerization initiator used is preferably about 0.05 to 2% by mass, more preferably about 0.1 to 1.5% by mass, based on 100% by mass of the monomers that serve as raw materials 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 aqueous 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 aqueous polymer alone.

[0051] [Other binder components] The secondary battery binder of the present disclosure may contain other binder components in addition to the aqueous polymer. Examples of other 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 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 is 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, 40% by mass or more, 60% by mass or more, 80% by mass or more, or 100% by mass or more, preferably 30% by mass or more, and may be 200% by mass or less, 100% by mass or less, 80% by mass or less, 60% by mass or less, 50% by mass or less, or 40% by mass or less, preferably 160% by mass or less, more preferably 150% by mass or less, based on 100% by mass of the slurry solids (total amount of binder, active material, and conductive additive).

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

[0057] [Amount of secondary battery binder] The amount of secondary battery binder in the slurry solids (total amount of 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 may be 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 3.0% by mass or less, more preferably 1.0% by mass or less. A content equal to or greater than the above lower limit is preferred from the viewpoint of achieving a good binder effect. A content equal to or less than the above upper limit is preferred 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 is not particularly limited, and negative electrode active materials used in this technical field may be used.

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

[0061] As the negative electrode active material, materials capable of storing and releasing a large amount of lithium ions, such as silicon (Si), tin (Sn), titanium (Ti), etc., may be used. These materials can be used in the form of a single substance, an alloy, a compound, a solid solution, or a composite active material containing a silicon-containing material, a tin-containing material, or a titanium-containing material. Examples of silicon-containing materials include Si, Si / C, SiOx (0.05 < x < 1.95), or an alloy, compound, or solid solution 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 substitutes a part of Si can be used. 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 lithium titanates such as Li2TiO3, Li4Ti5O <​​​​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 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 both of them may be used. Examples of the crystalline carbon include those described above.

[0063] The method for manufacturing the negative electrode active material is not particularly limited. When manufacturing an active material composite in which the first negative electrode active material and the second negative electrode active material are mixed, a method in which both are uniformly dispersed may be adopted. For example, a method of mixing the first negative electrode active material and the second negative electrode active material with a ball mill can be mentioned.

[0064] (Positive electrode active material) The positive electrode active material is not particularly limited, and a positive electrode active material used in this technical field may be used.

[0065] The positive electrode active material may be a lithium-containing composite oxide. Examples of the lithium-containing composite oxide include, for example, LiMnO2, LiFeO2, LiCoO2, LiMn2O4, Li2FeSiO4, 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 (where 0 ≤ x < 1, 0 ≤ y < 1, 0 ≤ z < 1, and 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 ​​​ [Amount of active material] The amount of active material in the slurry solids (total amount of binder, active material, and conductive aid) 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 99% by mass or less, 95% by mass or less, 90% by mass or less, or 85% by mass or less.

[0067] [Conductive additive] As the conductive aid, conductive aids used in the present 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 the 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, based on the slurry solids content (total amount of binder, active material, and conductive additive).

[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 at least one substituent selected from the group consisting of a hydroxy group, an amino group, and an imino group, and a carboxy group, or humic acid. Examples of organic acids containing a hydroxy group and a carboxy 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 carboxy 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 carboxy 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 dispersing agent] The amount of the dispersion aid may be 0.1 mass% or more, 0.5 mass% or more, 1.0 mass% or more, 1.5 mass% or more, or 3.0 mass% or more, and is preferably 0.3 mass% or more, and may be 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, based on the slurry solids (total amount of binder, active material, and conductive aid).

[0071] [Other ingredients] The slurries of the present disclosure may also contain other ingredients, such as conventional additives.

[0072] [Amount of other ingredients] The amount of other components (individual amount or total amount) of the slurry solids (total amount of binder, active material, and conductive aid) 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, 1.0 mass% or less, 0.5 mass% or less, and is preferably 3.0 mass% or less, and more preferably 1.0 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 optionally, a conductive additive, a dispersing aid, etc. are mixed to form a slurry. The timing of adding the liquid medium is not particularly limited. The secondary battery 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 secondary battery binder of the present disclosure, and optionally, a conductive additive, 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. 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 binder may be decomposed or reacted by heat drying and converted into a component derived from the 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 (e.g., 0.05 MPa or lower, 0.03 MPa or lower, 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 substance 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 substances (e.g., stainless steel). The current collector may also be made of Fe plated with Cu. From the viewpoints of high electrical conductivity, stability in the electrolyte, and oxidation resistance, Cu, Ni, stainless steel, etc. are preferred as materials 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, stability in the electrolyte, and 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-like substrate, a three-dimensional substrate, etc. Using 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 aforementioned secondary battery electrode of the present disclosure. The secondary battery of the present disclosure may be any battery that includes the secondary battery electrode of the present disclosure as either one or both of the positive electrode and the negative electrode. The method for manufacturing the secondary battery of the present disclosure uses the secondary battery electrode of the present disclosure (i.e., the secondary battery binder of the present disclosure) and is produced 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. [Example]

[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 MAS: methallylsulfonic acid VA: vinyl alcohol

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

[0087] Example 1 A monomer aqueous solution was prepared by mixing 35.3 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 (Fujifilm Wako Pure Chemical Industries, Ltd. product name "VA-044"), and 210.0 g of ion-exchanged water in a sealable vial with an internal volume of 500 ml, and the mixture was deoxygenated. Separately, a 2 L reactor equipped with a stirrer, thermometer, N2 gas inlet, reflux condenser, and dropping funnel was charged with 858.3 g of ion-exchanged water. N2 gas was blown into the reactor to deoxygenate the system, and the internal temperature was raised to 68 °C. Subsequently, the deoxygenated monomer aqueous solution was added dropwise to the reactor using the dropping funnel over 3 hours while stirring. After the addition, the internal temperature was raised to 68 °C and stirring continued for 2 hours. The mixture was further stirred at 73 °C for 1 hour, cooled to 30 °C, and 30.3 g of 48 wt% NaOH aqueous solution was added until the pH reached 5.5, yielding an aqueous solution containing a water-based polymer. The repeating unit composition of the water-based polymer was AAm / AA(H / Na) / 2-HEA / MAS(H / Na) = 35 / 35 / 29.9 / 0.1 (molar ratio).

[0088] Example 2 A monomer aqueous solution was prepared by mixing 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 in a sealable vial with an internal volume of 500 ml, and the mixture was deoxygenated. Separately, a 2 L reactor equipped with a stirrer, thermometer, N2 gas inlet, reflux condenser, and dropping funnel was charged with 831.0 g of ion-exchanged water. N2 gas was blown in to deoxygenate the system, and the internal temperature was then raised to 68°C. Next, the prepared monomer aqueous solution was added dropwise to the reactor using the dropping funnel over 3 hours while maintaining the internal temperature at 68°C. After the addition, the temperature was maintained for 1.5 hours. Next, 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. The mixture was further stirred 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 / MAS(H / Na) = 99 / 1 (molar ratio).

[0089] Example 3 In a sealable vial having an internal volume of 500 ml, 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 mixed to prepare an aqueous monomer solution, which was then deoxygenated. Separately, 500.0 g of ion-exchanged water was charged into a 1 L reactor equipped with a stirrer, thermometer, N2 gas inlet tube, reflux condenser, and dropping funnel. N2 gas was blown into the system to deoxygenate it, and the internal temperature was raised to 75 °C. The prepared monomer aqueous solution was then added dropwise to the reactor over 3 hours using the dropping funnel while stirring. After the addition, the mixture was maintained for 2 hours, then heated to 80 °C and stirred 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 (pH 6.5), yielding an aqueous solution containing a water-based polymer. The repeating unit composition of the water-based polymer was 2-HEA / AA (H / Na) = 48 / 52 (molar ratio).

[0090] Example 4 23.8 g (0.33 mol) of acrylic acid, 22.6 g (0.19 mol) of 2-hydroxyethyl acrylate, 69.3 g (0.97 mol) of acrylamide, 0.608 g of ammonium persulfate, and 225.0 g of ion-exchanged water were mixed in a sealable vial having an internal volume of 500 ml to prepare an aqueous monomer solution. Separately, a 1 L reactor equipped with a stirrer, thermometer, N2 gas inlet, reflux condenser, and dropping funnel was charged with 607.6 g of ion-exchanged water. N2 gas was blown into the system to deoxygenate it, and the internal temperature was then raised to 75 °C. The prepared monomer aqueous solution was then added dropwise to the reactor over 3 hours using the dropping funnel while stirring. After the addition, the mixture was stirred for 2 hours while maintaining the internal temperature at 75 °C. The internal temperature was then raised to 80 °C and held for 1 hour. The internal temperature was then cooled to 30 °C, and 70.57 g (0.30 mol) of a 5 mol / L aqueous sodium hydroxide solution was added (pH 6.5), yielding an aqueous solution containing a water-based polymer. The repeating unit composition of the water-based polymer was 2-HEA / AA(H / Na) / AAm = 13 / 22 / 65 (molar ratio).

[0091] Comparative Example 1 A 1 L reaction vessel equipped with a stirrer, thermometer, N2 gas inlet tube, reflux condenser, and dropping funnel was charged with 485.3 g of ion-exchanged water and 100.0 g of terminally thiol-modified polyvinyl alcohol (degree of polymerization: 375, degree of saponification: 98.7 mol%). N2 gas was blown in to deoxygenate the system, and the internal temperature was raised to 95°C and then cooled to room temperature. The pH was then adjusted to 3.0 with 0.5 N sulfuric acid. The internal temperature was then raised to 62°C, and 9.9 g (0.14 mol) of acrylic acid, 1.70 g of ammonium persulfate, and 75.2 g of ion-exchanged water were added dropwise via the dropping funnel over 1.5 hours with stirring. After the dropwise addition, the mixture was stirred for 0.5 hours while maintaining the internal temperature at 62°C, followed by an additional 1 hour of stirring at 67°C. The internal temperature was then cooled to 30°C, and 5.72 g (0.69 mol) of 48% by mass aqueous sodium hydroxide solution was added to obtain an aqueous solution containing a water-based polymer. The composition of the repeating units of the water-based polymer was VA / AA (H / Na) = 94 / 6 (molar ratio).

[0092] Comparative Example 2 103.6 g (1.20 mol) of methyl acrylate and 156.0 g (1.81 mol) of vinyl acetate were mixed in a beaker having an internal volume of 500 ml to prepare an aqueous monomer solution. Separately, a 2 L reactor equipped with a stirrer, thermometer, N2 gas inlet, reflux condenser, and dropping funnel was charged with 768 g of ion-exchanged water and 12 g of anhydrous sodium sulfate, and N2 gas was blown in to deoxygenate the system. 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 aqueous monomer solution was added dropwise to the reactor over 4 hours using the dropping funnel while stirring. After the addition, the internal temperature was raised to 65°C and stirring was continued for 2 hours, and the precipitated solid was filtered. The obtained solid, 450 g of methanol, 420 g of ion-exchanged water, 140 g of sodium hydroxide, and 0.52 g of hydrazine were charged to the same reactor as above, 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 matter was filtered, washed with methanol, and dried under reduced pressure at 60°C for 8 hours to obtain an aqueous polymer. The composition of the repeating units of the aqueous polymer was VA / AA (H / Na) = 60 / 40 (molar ratio).

[0093] <Measurement of polymer properties> The properties of the polymers obtained in the above Examples and Comparative Examples were measured. The test methods are as follows. In each test, an aqueous polymer solution was used in which an aqueous polymer was dissolved in ion-exchanged water.

[0094] [Molecular weight, etc.] The polymers obtained in the above Examples and Comparative Examples were measured for Mw (weight average molecular weight) and Mz / Mw (breadth of molecular weight distribution) in terms of standard polyethylene glycol / polyethylene oxide using a GPC triple detector. [GPC-Triple Detector] GPC light scattering device: CHR6000 (Malvern OMNISEC REVERAL) Column: COL9002 (Malvern OMNISEC REVERAL) Carrier: 0.1M sodium nitrate Column temperature: 35℃ Flow rate: 1.0mL / min Injection volume: 150μL Concentration: 2.0mg / mL

[0095] [pH] 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 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.

[0096] [APHA] A polymer aqueous solution was prepared by dissolving a water-based polymer in water to a solids concentration of 2% by mass. 30 ml of the solution was placed in a screw tube, and the Hazen color number of the measurement sample was measured using a Hazen meter Type: HM-IV (X Electronics Design Co., Ltd.) in an environment of 25°C.

[0097] [Turbidity] A polymer aqueous solution was prepared by dissolving a water-based polymer in water to a solids concentration of 2% by mass. The solution was added to an acrylic resin cell (manufactured by AS ONE, model "ST-MA"), and the absorbance at 660 nm was measured using an ultraviolet-visible-near-infrared spectrophotometer (manufactured by Hitachi High-Tech Science, model "UH4150"). Similarly, the absorbance at 660 nm of standard samples with turbidities of 1, 20, and 100 was measured, and a calibration curve was created. The turbidity of each polymer aqueous solution was calculated from the calibration curve of the absorbance of the polymer aqueous solution and the turbidity of the standard sample.

[0098] 〔surface tension〕 Measurements were made at 25°C using an image processing solid-liquid interface analysis system (Kyowa Interface Science Co., Ltd., model "DropMaster 500") Specifically, a polymer aqueous solution prepared by dissolving a water-based polymer in water to a solids concentration of 2% by mass was collected in a syringe, and the maximum diameter (de) of the pendant drop hanging from the needle tip was automatically measured. From this value, the diameter (ds) at a position de above the bottom of the liquid was calculated, and the surface tension was calculated using the following formula. Surface tension = g ρ (de)² 1 / H [mN / m] (where g is the gravitational constant, ρ is the density of the aqueous solution of the polymer compound, and 1 / H is the correction term calculated from ds / de)

[0099] [Moisture absorption rate (25℃, 60%RH)] A polymer aqueous solution was prepared by dissolving a water-based polymer in water to a solids concentration of 2% by mass. 20 g of the solution was placed in 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"). This was followed by additional drying 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 prepared 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 before storage was measured. The cut film was then placed in a 50 mL screw tube bottle and stored with the lid open in a safety tester (manufactured by ESPEC, model "CSH-112") set at 25°C and 60% RH for 21 hours. After storage, the weight of the film was measured in a dry oven with a dew point of -70°C, and the moisture absorption rate was calculated using the following formula. Moisture absorption rate = (weight after storage - weight before storage) / weight before storage x 100[%]

[0100] [Glass transition temperature] A polymer aqueous solution was prepared by dissolving a water-based polymer in water to a solids concentration of 2% by mass. 20 g of this solution was placed in a polypropylene tray (manufactured by AS ONE, model "DT-1") and dried at 60°C for 8 hours in a constant temperature incubator (manufactured by Yamato Scientific, model "DKM300"), followed by additional drying 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. Using 5 mg of the film (approximately 2 mm square) prepared by the above method, measurements were carried out under the following conditions using a differential scanning calorimeter (manufactured by Hitachi High-Tech Science, model "DSC600"). Measurement conditions: The temperature was increased from -30°C to 150°C at a rate of 10°C / min, cooled to -30°C at 10°C / min, and then increased to 400°C. The glass transition temperature observed during the second temperature increase was used. Sample pan: SUS pan Measurement sample mass: 4 mg Calculation of glass transition temperature: The glass transition temperature was calculated by rounding off the decimal point of the temperature at the intersection of the tangent line at the start of the descent and the tangent line at the end of the descent on the chart during the second heating run measured with a differential scanning calorimeter.

[0101] <Characteristics of batteries / slurries / polymer aqueous solutions, etc.> Using the aqueous polymers obtained in the above Examples and Comparative Examples, a battery / slurry / aqueous polymer solution was prepared, and its properties were measured. The test methods were as follows.

[0102] [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 (solid content equivalent) were kneaded together. Water was then added to the mixture to achieve 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 with 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.). A heat treatment (reduced pressure, 100°C, 12 hours or more) was then performed to prepare a negative electrode. The thickness of the active material layer in the resulting negative electrode was 36 μm, and the capacity density of the negative electrode was 3.5 mAh / cm. 2 It was.

[0103] [Coin cell assembly] A coin cell (CR2032) was fabricated comprising the negative electrode prepared above and the following positive electrode, separator, and electrolyte. ·Positive electrode: LiNi 0.5 Co 0.2 Mn 0.3 O2 (manufactured by Hachisansha Co., Ltd.) Separator: Glass filter (Advantech Co., Ltd., product name GA-100) Electrolyte: A solution in which LiPF6 is dissolved at a concentration of 1 mol / L in a solvent made by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1, and 1 mass% of vinylene carbonate (VC) and 1 mass% of fluoroethylene carbonate (FEC), which are electrolyte additives, are added.

[0104] [Capacity retention rate measurement] Each coin cell prepared as described above was charged to 4.2 V at 30°C with a current equivalent to 0.1 C, discharged to 2.5 V at a current equivalent to 0.1 C, charged to 4.2 V at a current equivalent to 0.5 C, and discharged to 2.5 V at a current equivalent to 0.5 C for three cycles 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, discharged at a constant current for 12 seconds at a current equivalent to 0.2 C, then charged at a current equivalent to 0.1 C for 24 seconds, discharged at a constant current for 12 seconds at a current equivalent to 0.5 C, then charged at a current equivalent to 0.1 C for 1 minute, discharged at a constant current for 12 seconds at a current equivalent to 1 C, then charged at a current equivalent to 0.1 C for 2 minutes, discharged at a constant current for 12 seconds at a current equivalent to 2 C, and then discharged to 2.5 V at a current equivalent 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, and this cycle was repeated for 97 cycles (4th to 100th cycles). Thereafter, the same operation as that used to measure the initial discharge capacity was carried out to measure the discharge capacity after 100 cycles. Capacity retention rate after 100 cycles = [Discharge capacity after 100 cycles (mAh / g)] / [Initial discharge capacity after aging (mAh / g)] × 100 [%]

[0105] [Discharge capacity after 100 cycles] In the above test for [Capacity retention rate after 100 cycles], the discharge capacity after 100 cycles was measured.

[0106] [DC resistance (DCR) after 100 cycles] [Electrode preparation] An electrode was prepared in the same manner as described above in [Capacity retention rate after 100 cycles]. [Coin cell assembly] In the same manner as described above in [Capacity retention rate after 100 cycles], a coin cell (CR2032) was prepared that included a negative electrode and the following positive electrode, separator, and electrolyte.

[0107] [Measurement of DC resistance after 100 cycles] Each coin cell prepared as described above was charged to 4.2 V at 30°C with a current equivalent to 0.1 C, discharged to 2.5 V at a current equivalent to 0.1 C, charged to 4.2 V at a current equivalent to 0.5 C, and discharged to 2.5 V at a current equivalent to 0.5 C for three cycles 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, discharged at a constant current for 12 seconds at a current equivalent to 0.2 C, then charged at a current equivalent to 0.1 C for 24 seconds, discharged at a constant current for 12 seconds at a current equivalent to 0.5 C, then charged at a current equivalent to 0.1 C for 1 minute, discharged at a constant current for 12 seconds at a current equivalent to 1 C, then charged at a current equivalent to 0.1 C for 2 minutes, discharged at a constant current for 12 seconds at a current equivalent to 2 C, and 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 discharged to 2.5 V at a current equivalent to 1 C, and this cycle was repeated for 97 cycles (4th to 100th cycles). Thereafter, the same operation as the initial discharge operation was carried out. The DC resistance of the cell was calculated from the discharge current and voltage values ​​at 10.0 seconds for each C-rate, and was taken as the DC resistance after 100 cycles.

[0108] [Foaming] A polymer aqueous solution prepared by dissolving a water-based polymer in water to a solids concentration of 2% by mass was poured into a glass bottle (45 mm diameter, 110 mm height) to a height of 5.5 cm, and a 35 mm diameter disper (PRIMIX, model "Homo Disper 2.5") was added to a height of 3.5 cm, followed by stirring for 2 minutes at 2500 rpm in an environment of 23°C. After 15 minutes of stirring, the state of foaming was visually confirmed, and solutions with almost no bubbles (approximately 20 or fewer bubbles in the solution) were rated as ◯, and solutions with many bubbles visible throughout were rated as ×.

[0109] The test results are summarized in the table below. TIFF2026035048000001.tif93162 [Industrial Applicability]

[0110] 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.

Claims

1. Contains water-based polymers, The secondary battery binder, wherein the moisture absorption rate (at 25° C. and 60% RH) of the aqueous polymer is 5% or more and 20% or less.

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

3. The water-based polymer is formula: -[CH ２ -C(R １ )(C(=O)R ２ )]- [In the formula, 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 each n is independently 1 or more and 6 or less). A repeating unit (1) represented by the formula: formula: -[CH ２ -CH(OH)]- Repeating unit (2) represented by 3. The secondary battery binder according to claim 1, comprising a repeating unit selected from:

4. In the water-based 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 repeating units containing an acidic functional group is 0.8 mol% or more; 4. The secondary battery binder of claim 3, wherein the amount of nonionic repeating units is 40 mol % or more.

5. 3. The secondary battery binder of claim 1 or 2, comprising SBR.

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

7. The slurry of claim 6 further comprising an electrode active material.

8. A method for producing a secondary battery, comprising the step of applying the slurry according to claim 6 .

9. 3. An electrode comprising the secondary battery binder according to claim 1 or 2 or a component derived from said secondary battery binder.

10. An electrode comprising the heat-dried slurry according to claim 7.

11. A secondary battery comprising the electrode according to claim 9.

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