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 an aqueous polymer, wherein the aqueous polymer has a moisture absorptivity (at 40 °C, 75 RH%) of 11 mass% or more.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, A secondary battery binder, wherein the water-based polymer has a moisture absorption rate (40°C, 75RH%) of 11% or more. [Section 2] Item 2. The secondary battery binder according to item 1, wherein the moisture absorption rate (40° C., 75 RH%) is 12% or more and 38% or less. [Section 3] 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. [Section 4] 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) 4. The secondary battery binder according to any one of items 1 to 3, comprising a repeating unit selected from the following: [Section 5] 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 5. The secondary battery binder according to item 4, wherein the amount of nonionic repeating units is 40 mol % or more. [Section 6] Item 6. The secondary battery binder according to any one of items 1 to 5, which contains SBR. [Section 7] Item 7. A slurry comprising the secondary battery binder according to any one of Items 1 to 6 and water. [Section 8] Item 8. The slurry according to item 7, comprising an electrode active material. [Section 9] Item 9. A method for producing a secondary battery, comprising applying the slurry according to Item 7 or 8. [Section 10] Item 7. An electrode for a secondary battery, comprising the secondary battery binder according to any one of Items 1 to 6 or a component derived from the secondary battery binder. [Section 11] Item 7. An electrode comprising a heated and dried slurry according to item 7 or 8. [Section 12] Item 12. A secondary battery comprising the electrode according to item 10 or 11. [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 battery expansion after charge-discharge cycles. 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, relative to the aqueous polymer.

[0014] (molecular weight, etc.) 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, 700,000 or more, or 1,500,000 or more, preferably 100,000 or more, more preferably 300,000 or more, and may be 2,000,000 or less, 1,000,000 or less, 800,000 or less, or 500,000 or less, preferably 2,000,000 or less, more preferably 1,000,000 or less. This value is determined by the method described in the examples. When the Mw of the aqueous polymer determined by GPC-RI is within the above range (particularly 300,000 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] (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 5.0 or more, 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 10 or less, 9.5 or less, 9.0 or less, 8.5 or less, 8.0 or less, 7.5 or less, or 7.0 or less, preferably 9.5 or less, more preferably 9.0 or less. This value is determined by the method described in the Examples, and ion-exchanged water is usually used as the water. When the pH is at least the lower limit (particularly 7.0 or higher (neutral to alkaline)), the flexibility of the polymer component including the aqueous polymer increases, 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. When the pH is equal to or higher than the lower limit (particularly pH 5.0 or higher, for example 5.5 or higher), the solubility in water increases, and viscosity stability can be improved. When the pH is equal to or lower than the upper limit (particularly, pH 7.5 or lower, for example, pH 7.4 or lower), the hydrogen bonding interaction of the acidic groups becomes stronger, and the viscosity stability can be improved.

[0016] (salt) The salinity (SAL) of the aqueous solution obtained when a water-based polymer is dissolved in water at a concentration of 2% by mass may be 1.0 ppt or more, 1.5 ppt or more, 2.0 ppt or more, or 2.5 ppt or more, preferably 1.2 ppt or more, more preferably 1.5 ppt or more, and may be 5.0 ppt or less, 4.0 ppt or less, 3.5 ppt or less, 3.0 ppt or less, 2.5 ppt or less, or 2.0 ppt or less, preferably 4.0 ppt or less, more preferably 3.0 ppt or less. This value is determined by the method described in the Examples, and ion-exchanged water is usually used as the water. When the salt content of the 2 mass % aqueous solution is within the above range (for example, 1.0 ppt or more, particularly 1.5 ppt to 5.0 ppt), the interaction between ions strengthens the bonds between polymers, thereby suppressing expansion of the active material.

[0017] (specific resistance) The resistivity of the aqueous solution obtained when a water-based polymer is dissolved in water at a concentration of 2% by mass may be 100 Ω·cm or more, 200 Ω·cm or more, 300 Ω·cm or more, 400 Ω·cm or more, or 500 Ω·cm or more, preferably 150 Ω·cm or more, more preferably 250 Ω·cm or more, and may be 1500 Ω·cm or less, 1000 Ω·cm or less, 600 Ω·cm or less, or 500 Ω·cm or less, preferably 500 Ω·cm or less, more preferably 400 Ω·cm or less. This value is determined by the method described in the Examples, and ion-exchanged water is usually used as the water.

[0018] (surface tension) The surface tension of an aqueous solution obtained when a water-based polymer is dissolved in water at a concentration of 2% by mass may be 10 mN / m or more, 30 mN / m or more, 50 mN / m or more, or 60 mN / m or more, preferably 50 mN / m or more, more preferably 65 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, and ion-exchanged water is usually used as the water. When the surface tension is within the above range (particularly 65 mN / m or more and 80 mN / m or less), the slurry has high uniformity when applied to the electrode, and an increase in resistance can be suppressed.

[0019] (Moisture absorption rate (40℃, 75%RH)) The moisture absorption rate of the aqueous polymer (40°C, 75% RH) is 11% or more, preferably 12% or more, and more preferably 15% or more. It may also be 40% or less, 35% or less, 30% or less, 25% or less, 20% or less, or 15% or less, and is preferably 40% or less, and more preferably 38% or less. This value is determined by the method described in the Examples. A polymer having a moisture absorption rate equal to or greater than the above-mentioned lower limit (11% or greater, particularly 15% or greater, and in one embodiment, 12% to 38% inclusive) has a similarly high interactivity with an active material (for example, an active material having a hydroxyl group, which has a structure similar to that of water), and this interaction allows it to exhibit high compliance with the expansion and contraction of the active material, thereby suppressing expansion.

[0020] [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.

[0021] The water-based polymer may be a random polymer or a block polymer, for example a random polymer.

[0022] (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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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 2NH2, 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:

[0028] In the repeating unit (1), R 1 is preferably a hydrogen atom.

[0029] In the repeating unit (1), R 2 In the formula, 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.

[0030] 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.

[0031] 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 2may 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.

[0032] 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).

[0033] The aqueous polymer preferably contains a repeating unit derived from (meth)acrylic acid (particularly a sodium salt or lithium salt).

[0034] (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.

[0035] [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 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.

[0036] 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, or 60 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 70 mol% or less.

[0037] 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 10 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 85 mol% or less.

[0038] 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, preferably 1 mol% or more, more preferably 20 mol% or more, and 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, preferably 60 mol% or less.

[0039] 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 85 mol% or less.

[0040] 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 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.

[0041] The amount of 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 10 mol% or more, more preferably 20 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 70 mol% or less.

[0042] The amount of 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 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 90 mol% or less, more preferably 85 mol% or less. The aqueous polymer may not contain repeating unit (2).

[0043] A repeating unit derived from (meth)acrylamide (R 2 The amount of NH2) in the aqueous polymer may be 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 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.

[0044] A repeating unit derived from (meth)acrylic acid or a salt thereof (R 2The amount of OM) in the aqueous polymer may be 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 10 mol% or more, more preferably 20 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 70 mol% or less.

[0045] [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.

[0046] 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.

[0047] 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 1.0% by mass, based on 100% by mass of the monomers that serve as raw materials for the aqueous polymer of the present disclosure.

[0048] The polymerization conditions can be appropriately set in accordance with the structure of the target compound.

[0049] [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.

[0050] [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).

[0051] 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.

[0052] <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.

[0053] [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 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.

[0054] [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).

[0055] [Secondary battery binder] The slurry contains a secondary battery binder, the types of which are described above.

[0056] [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.

[0057] [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.

[0058] (Negative electrode active material) The negative electrode active material is not particularly limited, and any negative electrode active material commonly used in the art may be used.

[0059] 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.

[0060] As the negative electrode active material, materials that can occlude and release 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 simple substances, alloys, compounds, solid solutions, or composite active materials containing silicon-containing materials, tin-containing materials, or 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 part of Si is replaced by 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. 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 12 etc., and titanium niobium composite compounds, etc. These materials can be used alone or in combination of two or more. Among these, silicon or silicon oxide is preferred, and for example, it may be a simple silicon or silicon oxide.

[0061] As the negative electrode active material, it is more preferable to use a composite obtained by mixing a 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 crystalline carbon include those described above.

[0062] 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.

[0063] (Positive electrode active material) The cathode active material is not particularly limited, and cathode active materials used in this technical field may be used.

[0064] The cathode 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 PO4 (where 0 < w < 1), LiFePO4, and the like.

[0065] [Amount of active material]<00003​​​​​​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.

[0067] [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 preferably 0.3 mass% or more, based on the slurry solids content (total amount of binder, active material, and conductive additive), and may be 10 mass% or less, 5.0 mass% or less, 3.0 mass% or less, or 1.0 mass% or less, and preferably 3.0 mass% or less, and more preferably 1.0 mass% or less.

[0068] [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.

[0069] [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 content (total amount of binder, active material, and conductive aid).

[0070] [Other ingredients] The slurries of the present disclosure may also contain other ingredients, such as conventional additives.

[0071] [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, or 0.5 mass% or less, and is preferably 3.0 mass% or less, and more preferably 1.0 mass% or less.

[0072] [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.

[0073] <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 contain a heated and dried slurry, and the binder may be decomposed or reacted by the heating and drying to be converted into components derived from the binder.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] <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 producing 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.

[0079] 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.

[0080] 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.

[0081] Other configurations of the secondary battery may also be the same as those of known secondary batteries.

[0082] 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]

[0083] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to these examples.

[0084] The abbreviations have the following meanings: AN: Acrylonitrile AA: acrylic acid AAm: acrylamide 2-HEA: 2-hydroxyethyl acrylate MAS: methallylsulfonic acid VA: vinyl alcohol CMC: Carboxymethyl cellulose SBR: Styrene butadiene rubber

[0085] <Preparation of polymer> The polymer was prepared according to the procedure described below.

[0086] Example 1 22.3 g (0.31 mol) of acrylic acid, 30.2 g (0.57 mol) of acrylonitrile, 8.5 g (0.12 mol) of acrylamide, 0.405 g of potassium persulfate, and 50 g of ion-exchanged water were added to a sealable vial having an internal volume of 500 ml and mixed to prepare an aqueous monomer solution. Separately, 500.0 g of ion-exchanged water was charged into a 1 L reactor equipped with a stirrer, thermometer, N2 gas inlet, 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 internal temperature was maintained at 80 °C for 1 hour. The internal temperature was then cooled to below 40 °C, and 69.5 g (0.31 mol) of a 5 mol / L lithium hydroxide aqueous solution was added to adjust the pH to 7.0, yielding an aqueous solution containing a water-based polymer. The repeating unit composition of the water-based polymer was AN / AA(H / Li) / AAm = 57 / 31 / 12 (molar ratio).

[0087] Example 2 A sealable vial having an internal volume of 500 ml was charged with 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, and the resulting mixture was mixed to prepare an aqueous monomer solution, which was then 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 over 3 hours using the dropping funnel while stirring. After the 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 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 3 Into 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 added and 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 using the dropping funnel over 3 hours while stirring. After the addition, the temperature was maintained at 80 °C 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 a water-based polymer. The repeating unit composition of the water-based polymer was 2-HEA / AA (H / Na) = 48 / 52 (molar ratio).

[0089] Example 4 A monomer aqueous solution was prepared by adding 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 to a sealable vial having an internal volume of 500 ml and mixing them. Separately, a 1 L reactor equipped with a stirrer, thermometer, N2 gas inlet tube, 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 raised to 75 °C. The prepared monomer aqueous solution was then added dropwise to the reactor using the dropping funnel over 3 hours while stirring. After the 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 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 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).

[0090] Example 5 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 having an internal volume of 500 ml and mixed 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 monomer aqueous solution was added dropwise to the reactor with stirring over 4 hours using the dropping funnel, while maintaining the same temperature. After the dropwise addition, the internal temperature was maintained at 65°C 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 content was filtered off. The solid content was 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) = 82 / 18 (molar ratio).

[0091] Example 6 103.6 g (1.20 mol) of methyl acrylate and 156.0 g (1.81 mol) of vinyl acetate were added to a beaker having an internal volume of 500 ml and mixed 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 monomer aqueous solution was added dropwise to the reactor with stirring over 4 hours using the dropping funnel, while maintaining the same temperature. After the dropwise addition, the internal temperature was maintained at 65°C 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 content was filtered off. The solid content was 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).

[0092] 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 with stirring, 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. After the dropwise addition, the internal temperature was maintained at 62°C for 0.5 hours, followed by stirring at 67°C for 1 hour. 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).

[0093] Comparative Example 2 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 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.

[0095] [Molecular weight, etc.] The polymers obtained in the above examples and comparative examples were measured for Mw (weight average molecular weight) in terms of standard polyethylene glycol / polyethylene oxide using GPC-RI under the following detailed conditions. [GPC-RI] GPC equipment: HLC-8320GPC (Tosoh Corporation) Column: TSK GMPW XL (Tosoh Corporation) Carrier: 0.1M sodium nitrate Column temperature: 40℃ Flow rate: 1.0mL / min Injection volume: 200μL Concentration: 0.5mg / 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, 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.

[0097] [Salt content (SAL)] 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 kept at 25°C, and then the salt content was measured using a conductivity meter (manufactured by AS ONE, model "AS710", electrode "2301-S") calibrated with a standard solution of 1413 μS / cm. The salt content was calculated by rounding the measured value to one decimal place.

[0098] [Specific resistance] 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 kept at 25°C and then the resistivity was measured using a conductivity meter (manufactured by AS ONE, model "AS710", electrode "2301-S"). The salt content was calculated by rounding the measured value to one decimal place.

[0099] 〔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") The maximum diameter (d e ) of the pendant drop hanging from the needle tip was automatically measured, and the diameter (d s ) at a position de above the bottom of the liquid was calculated from this value, 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 polymer solution, and 1 / H is the correction term calculated from ds / de)

[0100] [Moisture absorption rate (40℃, 75%RH)] A 20 g aqueous polymer 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"), 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 40°C and 75% 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 (40℃, 75%RH) = (Weight after storage - Weight before storage) / Weight before storage × 100[%]

[0101] <Characteristics of batteries / slurries / aqueous solutions, etc.> The polymers obtained in the above Examples and Comparative Examples were measured for the following properties. The test methods were as follows.

[0102] [Expansion rate after 100 cycles] The expansion rate of the electrode thickness 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 Co., Ltd.), 5.8 parts by mass of silicon monoxide (KSC-1265, manufactured by Shin-Etsu Chemical Co., Ltd.), and a polymer aqueous solution were kneaded together to a solid content of 0.9 parts by mass. Water was then added to the mixture to 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 additives for electrolytes, are added.

[0104] [Expansion 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 (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). The secondary battery was then disassembled in the dry oven, and the negative electrode was removed. After washing with dimethyl carbonate and drying under reduced pressure at 23°C for 1 hour, 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 rate after 100 cycles = (active material layer thickness after disassembly after 100 cycles) / (active material layer thickness at the time of battery fabrication) × 100 [%]

[0105] [Peel strength] The 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 Co., Ltd.), 5.8 parts by mass of silicon monoxide (KSC-1265, manufactured by Shin-Etsu Chemical Co., Ltd.), and a polymer aqueous solution were kneaded together to a solid content of 0.9 parts by mass. Water was then added to the mixture to 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. [Peel strength measurement] The peel strength (N / 15 mm) of each electrode obtained was measured when the active material layer was peeled from the current collector foil. 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 the electrode (the current collector foil side) was then attached to a stainless steel plate with double-sided tape. This was used as an 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 (Shimadzu Corporation, small benchtop tester EZ-SX) to measure the peel strength between the active material layer of the electrode and the current collector foil.

[0106] [Mandrel test: Cracked electrode (3 mm)] The mandrel test was carried out according to the following procedure. [Electrode preparation] An electrode was prepared 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 and a mandrel with a diameter of 3 mm, so that the active material layer was facing outward, and the number of electrodes with cracks or breaks on the electrode surface was recorded.

[0107] [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, and the solution was kept at 25°C, after which the viscosity before storage was measured using a Brookfield type viscometer (model DV1MLVTJ0, manufactured by Brookfield).The 2% by mass aqueous solution was then left to stand at 20°C for one week, adjusted to 25°C, and the viscosity after storage was measured using a Brookfield type viscometer (model DV1MLVTJ0, manufactured by Brookfield). The viscosity change rate was calculated using the following formula. Viscosity change rate: (viscosity after storage - viscosity before storage) / viscosity before storage x 100 [%] The spindle and rotation speed corresponding to the viscosity were used as follows: LV-2, 12 rpm: 250 to 2500 mPa·s LV-1, 30 rpm: 20 to 200 mPa·s

[0108] The test results are summarized in the table below. TIFF2026035046000001.tif66164 [Industrial Applicability]

[0109] 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 (40°C, 75RH%) of the aqueous polymer is 11% or more.

2. 2. The secondary battery binder according to claim 1, wherein the moisture absorption rate (at 40°C and 75 RH%) is 12% or more and 38% or less.

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

4. 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:

5. 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; 5. The secondary battery binder of claim 4, wherein the amount of nonionic repeating units is 40 mol % or more.

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

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

8. The slurry of claim 7 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. 3. An electrode comprising the secondary battery binder according to claim 1 or 2 or a component derived from said secondary battery binder.

11. An electrode comprising the heat-dried slurry according to claim 8.

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

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