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

Abstract

To provide a novel secondary battery binder that can suitably contribute to the production of a battery and / or battery characteristics, or a slurry containing the secondary battery binder. [Solution means] including an aqueous polymer, A secondary battery binder having a conductivity of 3.3 mS / cm or less in an aqueous solution obtained when the aqueous polymer is dissolved in water at a concentration of 2% by mass.

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 Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, the types and properties of the binder have not been sufficiently studied. An object of the present disclosure is to provide a novel binder or a slurry containing the binder that can suitably contribute to the manufacturing of batteries and / or battery characteristics.

Means for Solving the Problems

[0005] The present disclosure includes the following aspects: [Item 1] Including an aqueous polymer, A secondary battery binder having a conductivity of 3.3 mS / cm or less in an aqueous solution obtained when the aqueous polymer is dissolved in water at a concentration of 2% by mass. [Item 2] The secondary battery binder according to Item 1, having a conductivity of 0.5 mS / cm or more. [Item 3] The secondary battery binder according to claim 1 or 2, wherein the aqueous polymer is a vinyl polymer having an acidic functional group-containing repeating unit. [Claim 4] The aqueous polymer is Formula: -[CH2-C(R 1 )(C(=O)R 2 )]- [In the formula, R 1 is a hydrogen atom or CH3, and R 2 is NH2, OM (M is a hydrogen atom or a counter cation), O(CH2) n OH, NH(CH2) n OH (n is each independently 1 or more and 6 or less).] The repeating unit (1) represented by, and Formula: -[CH2-CH(OH)]- The repeating unit (2) represented by The secondary battery binder according to any one of claims 1 to 3, comprising a repeating unit selected from [Claim 5] In the aqueous polymer, The amount of the repeating unit selected from the repeating unit (1) and the repeating unit (2) is 40 mol% or more, The amount of the acidic functional group-containing repeating unit is 0.8 mol% or more, The amount of the nonionic repeating unit is 40 mol% or more. The secondary battery binder according to claim 4. [Claim 6] The secondary battery binder according to any one of claims 1 to 5, comprising SBR. [Claim 7] A slurry comprising the secondary battery binder according to any one of claims 1 to 6 and water. [Claim 8] The slurry according to claim 7, further comprising an electrode active material. [Claim 9] A method for manufacturing a secondary battery, comprising a step of coating the slurry according to claim 7 or 8. [Claim 10] An electrode comprising the secondary battery binder according to any one of Items 1 to 6 or a component derived from the secondary battery binder. [Item 11] An electrode comprising a heat-dried product of the slurry according to Item 7 or 8. [Item 12] A secondary battery comprising the electrode according to Item 10 or 11. [Advantages of the Invention]

[0006] The secondary battery binder or slurry containing the secondary battery binder in the present disclosure has one or more properties suitable for a battery or its manufacture. In particular, by using the secondary battery binder in the present disclosure, foaming during slurry production can be suitably suppressed. [Modes for Carrying Out the Invention]

[0007] [Definition of Terms, etc.] In the present specification, regardless of whether the expression "each independently" or a similar expression is explicitly described, unless there is a description to the contrary, when a term (symbol) that can appear multiple times in a chemical structure is defined, the definition is applied independently for each occurrence.

[0008] In the present specification, "(meth)acryl" means "acryl or methacryl", and "(meth)allyl" means "allyl or methallyl".

[0009] In the present specification, when a plurality of lower limit values and a plurality of upper limit values are separately described, any lower limit value and upper limit value can be selected, and a numerical range of the 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, for example, to enhance the binding property between particles inside the electrode in a secondary battery and the binding property between the active material layer and the current collector.

[0011] [Water-Soluble Polymer] The secondary battery binder in the present disclosure contains an aqueous polymer. The aqueous polymer in the present disclosure is a polymer that can be dispersed in water alone and is particularly water-soluble.

[0012] [Properties of Aqueous Polymer, etc.] The properties of the aqueous polymer are shown below.

[0013] (Water Solubility) When 2 g of the aqueous polymer is dissolved in 100 g of water at 25°C, the insoluble matter may be 20% by mass or less, or 15% by mass or less with respect to the aqueous polymer, preferably 5% by mass or less, more preferably 1% by mass or less.

[0014] (Molecular Weight, etc.)

[0015] The Mw (weight average molecular weight) of the aqueous polymer by GPC-RI may be 100,000 or more, 300,000 or more, 500,000 or more, 750,000 or more, or 1,500,000 or more, preferably 150,000 or more, more preferably 180,000 or more, and may also be 3,000,000 or less, 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 550,000 or less. This value is determined by the method described in the examples.

[0016] The Mw / Mn (breadth of molecular weight distribution) of the aqueous polymer by GPC-RI may be 4.0 or more, 5.0 or more, 7.5 or more, 10 or more, or 12.5 or more, preferably 4.0 or more, and may also be 25 or less, 15 or less, 10 or less, 7.0 or less, or 5 or less, preferably 7.0 or less, more preferably 5.0 or less. This value is determined by the method described in the examples. When the Mw / Mn by GPC-RI is within the above range (especially 4.0 or more and 15 or less), suppression of expansion after charge-discharge cycles is suitable.

[0017] (pH) When an aqueous solution is obtained by dissolving an aqueous polymer at a concentration of 2% by mass in water, the pH (25 °C) of the aqueous solution may be 5.0 or higher, 5.5 or higher, 6.0 or higher, 6.5 or higher, 6.8 or higher, 7.0 or higher, 7.5 or higher, 8.0 or higher, 8.5 or higher, or 9.0 or higher, preferably 5.5 or higher, more preferably 6.5 or higher. Further, it may be 10 or lower, 9.5 or lower, 9.0 or lower, 8.5 or lower, 8.0 or lower, 7.5 or lower, or 7.0 or lower, preferably 8.5 or lower, more preferably 7.0 or lower. This value is determined by the method described in the examples. Usually, ion-exchanged water is used as the water. When the pH is at least the above lower limit value (especially 7.0 or higher (neutral to alkaline)), the flexibility of the polymer component containing the aqueous polymer increases, and high followability can be exhibited even with respect to the expansion and contraction of the active material. When the pH is at least the above lower limit value, the dispersibility of the slurry can be improved. When the pH is within the above range (especially 5.0 or higher and 7.5 or lower), the viscosity stability of the aqueous polymer solution becomes good, which is preferable from the viewpoint of battery production productivity. When the pH is at most the upper limit value (especially pH 7.5 or lower), the hydrogen-bonding interaction of the acidic group becomes stronger, and the viscosity stability can be improved.

[0018] (Viscosity) When an aqueous solution is obtained by dissolving an aqueous polymer at a concentration of 2% by mass in water, the viscosity (25 °C) of the aqueous solution may be 1 mPa·s or higher, 5 mPa·s or higher, 10 mPa·s or higher, 25 mPa·s or higher, or 50 mPa·s or higher, preferably 3.0 mPa·s or higher, more preferably 15.0 mPa·s or higher. Further, it may be 2000 mPa·s or lower, 1000 mPa·s or lower, 500 mPa·s or lower, 100 mPa·s or lower, 50 mPa·s or lower, or 25 mPa·s or lower, preferably 50 mPa·s or lower, more preferably 30 mPa·s or lower. This value is determined by the method described in the examples. Usually, ion-exchanged water is used as the water. By setting the viscosity within the above range (for example, 3 mPa·s or more and 200 mPa·s or less), the dispersibility of the active material and the binder in the slurry can be increased, a good film of the binder can be formed on the active material, and the expansion of the electrode (especially the initial expansion rate) when made into a battery can be suppressed. Similarly, by setting the viscosity within the above range, the dispersibility of the slurry can be improved.

[0019] (Conductivity) The conductivity of the aqueous solution obtained when an aqueous polymer is dissolved in water at a concentration of 2% by mass is 3.3 mS / cm or less. When the conductivity is within the above range, foaming during kneading of the active material and the like can be suppressed. The conductivity is preferably 3.0 mS / cm or less. Also, it is preferably 0.5 mS / cm or more, and more preferably 2.0 mS / cm or more. It is considered that when the conductivity is within the above range, the concentration of the ionic component does not become too high, the surfactant properties of the ionic component are suppressed, and foaming can be suppressed. This value is determined by the method described in the examples. Usually, ion-exchanged water is used as the water.

[0020] (Specific resistance) The specific resistance of the aqueous solution obtained when an aqueous 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, 600 Ω·cm or more, 800 Ω·cm or more, or 1000 Ω·cm or more, preferably 300 Ω·cm or more, more preferably 350 Ω·cm or more, and may also be 2000 Ω·cm or less, 1500 Ω·cm or less, 1000 Ω·cm or less, 800 Ω·cm or less, or 600 Ω·cm or less, preferably 1500 Ω·cm or less, more preferably 800 Ω·cm or less. This value is determined by the method described in the examples. Usually, ion-exchanged water is used as the water.

[0021] (Turbidity) When the aqueous polymer solution is obtained by dissolving the aqueous polymer in water at a concentration of 2% by mass, the turbidity of the aqueous solution may be 0.1 or more, 0.3 or more, 1.0 or more, 5.0 or more, or 10 or more, preferably 0.3 or more, and may be 50 or less, 25 or less, 5.0 or less, 2.5 or less, or 1.0 or less, preferably 1.0 or less, more preferably 0.5 or less. This value is determined by the method described in the examples. Usually, ion-exchanged water is used as the water.

[0022] [Structure, etc. of aqueous polymer] The aqueous polymer is obtained by polymerizing one or more monomers. The aqueous polymer may be a vinyl polymer. The vinyl polymer is a polymer obtained by polymerizing a vinyl monomer. Here, the vinyl monomer may be a compound having a polymerizable carbon-carbon double bond (ethylenically unsaturated double bond) (>C=C<), and may be a monomer containing a vinyl group, vinylene group, vinylidene group, acryloyl group, methacryloyl group, or a derivative group thereof. The aqueous polymer may particularly be a (meth)acrylic polymer containing a repeating unit derived from a monomer having an acryloyl group or a methacryloyl group.

[0023] The aqueous polymer may be a random polymer or a block polymer, for example, a random polymer.

[0024] [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 carboxy group, sulfonic acid group, phosphoric acid group, and nitric acid group, cationic groups such as amino group, hydroxy group, polyoxyethylene group (for example, the repeating number is 2 or more, 5 or more, or 10 or more), and nonionic hydrophilic groups such as amide group. The anionic group and the cationic group may be in the state of free acid / base, or a part or all of them may be in the form of salt.

[0025] In this specification, when referring to an anionic group, a cationic group, or a structure containing such a group (for example, a repeating unit containing an acidic functional group), unless otherwise explicitly stated, it is intended to include not only the anionic group and the cationic group but also their salts.

[0026] Examples of the counter cation of the anionic group include metal ions, preferably light metal ions, more preferably lithium ions, sodium ions, or potassium ions, particularly lithium ions or sodium ions. The counter cation may be monovalent to trivalent, monovalent to divalent, or monovalent, preferably monovalent. Examples of the counter anion of the cationic group include inorganic acid ions such as phosphate ions, nitrate ions, and sulfate ions, halide ions, etc. The aqueous polymer may be anionic and may not have a cationic group.

[0027] The aqueous polymer in the present disclosure preferably has a repeating unit having an acidic functional group as a hydrophilic repeating unit. The acidic functional group may be an anionic group such as a carboxy group, a sulfonic acid group, a phosphoric acid group, a nitric acid group, etc., preferably a carboxy group or a sulfonic acid group, more preferably a carboxy group. These groups may exist in the form of salts, and in that case, the above-mentioned metal ions are suitable examples of the counter cation. Examples of the repeating unit having an acidic functional group include repeating units derived from (meth)acrylic acid, maleic acid, vinyl sulfonic acid, or (meth)allyl sulfonic acid, etc.

[0028] The aqueous polymer in the present disclosure may have a nonionic hydrophilic repeating unit. Examples of the nonionic hydrophilic repeating unit include (meth)acrylamide, hydroxyalkyl (meth)acrylate, hydroxyalkyl (meth)acrylamide, polyoxyalkylene (meth)acrylate, polyoxyalkylene (meth)acrylamide, vinyl alcohol, etc.

[0029] Examples of suitable hydrophilic repeating units include Formula: -[CH2-C(R 1 )(C(=O)R 2 )]- [wherein R 1 is a hydrogen atom or CH3, R 2 is NH2, OM (M is a hydrogen atom or a counter cation), O(CH2) n OH, NH(CH2) n OH (n is, independently of each other, 1 or more and 6 or less).] The repeating unit (1) represented by and -[CH2-CH(OH)]- The repeating unit (2) represented by include repeating units selected from

[0030] In the repeating unit (1), R 1 is preferably a hydrogen atom.

[0031] In the repeating unit (1), M in R 2 may be a metal cation, preferably an alkali metal cation, more preferably a lithium ion, a sodium ion, or a potassium ion, particularly preferably a lithium ion or a sodium ion. M may be monovalent to trivalent, monovalent to divalent, or monovalent, preferably monovalent.

[0032] In the repeating unit (1), n in R 2 may be 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less, preferably 3 or less, particularly preferably 2 or less.

[0033] The repeating unit (1) preferably contains at least one of those in which R 2 is an NH2 group, an OH group, an ONa group, and an OLi group. The repeating unit (1) is such that R 2 is only an NH2 group, R 2 is only an OH group, R 2 is only an ONa group, or R 2It may be only an OLi group. The repeating unit (1) is R 2 may include those having an ONa group and those having an OH group, or R 2 may include those having an OLi group and those having an OH group, or those having an NH2 group and those having an OH group, or those having an NH2 group, those having an OH group, and those having an ONa group, or those having an NH2 group, those having an OH group, those having an ONa group, and those having an OLi group, or R 2 may include those having an OH group, those having an OLi group, and those having an NH2 group.

[0034] The repeating unit (2) can be introduced, for example, by a method of saponifying after polymerizing a vinyl ester (such as vinyl acetate, vinyl propionate, etc., particularly vinyl acetate), a method of reacting a polymer having a vinyl alcohol-based repeating unit (such as polyvinyl alcohol), etc.

[0035] The aqueous polymer preferably contains a repeating unit derived from (meth)acrylic acid (particularly a sodium salt or a lithium salt).

[0036] (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 (for example, 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.

[0037] [Composition, etc. of aqueous polymer] The amount of the hydrophilic repeating unit 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 90 mol% or more, more preferably 95 mol% or more, and may also be 100 mol% or less, 90 mol% or less, 80 mol% or less, or 70 mol% or less.

[0038] The amount of the acid-functional repeating unit 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 in the aqueous polymer, preferably 0.8 mol% or more, more preferably 15 mol% or more, and may be 90 mol% or less, 80 mol% or less, or 70 mol% or less, preferably 40 mol% or less, more preferably 30 mol% or less.

[0039] The amount of the nonionic hydrophilic repeating unit may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more in the aqueous polymer, preferably 60 mol% or more, more preferably 70 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 80 mol% or less.

[0040] The amount of the non-hydrophilic repeating unit 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 in the aqueous polymer, 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 50 mol% or less, more preferably 10 mol% or less. The aqueous polymer may not contain a non-hydrophilic repeating unit.

[0041] The amount of the nonionic repeating unit may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more in the aqueous polymer, preferably 60 mol% or more, more preferably 70 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 80 mol% or less.

[0042] The total amount of repeating unit (1) and repeating unit (2) may be 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more in the aqueous polymer, preferably 50 mol% or more, more preferably 60 mol% or more, and may also 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 (1) may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more in the aqueous polymer, preferably 40 mol% or more, more preferably 60 mol% or more, and may also 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.

[0044] The amount of repeating unit (2) may be 20 mol% or more or 40 mol% or more in the aqueous polymer, and may also be 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).

[0045] (The amount of the repeating unit derived from (meth)acrylamide (where R in formula (1) 2 is NH2) may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more in the aqueous polymer, preferably 30 mol% or more, more preferably 50 mol% or more, and may also 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 80 mol% or less.

[0046] (The repeating unit derived from (meth)acrylic acid or its salt (where R in formula (1) 2The amount of [[OM]] may be 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, or 90 mol% or more in the aqueous polymer, 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 40 mol% or less, more preferably 30 mol% or less.

[0047] [Method for producing aqueous polymer] The method for producing the aqueous polymer is not particularly limited, and it can be produced using a known method for producing a copolymer. Preferably, it can be synthesized by an aqueous solution radical polymerization method. Specifically, a radical polymerization initiator and, if necessary, a chain transfer agent are added to a monomer mixture, and the polymerization reaction may be carried out at a reaction temperature of about 50 to 100 °C (for example, 60 to 70 °C) while stirring. The reaction time is not particularly limited and may be about 1 to 10 hours. After the reaction time has elapsed, it may be further aged at a temperature of +3 °C to +10 °C (for example, +4 °C to +8 °C) for 15 minutes to 2 hours (for example, 30 minutes to 1.5 hours). Aging can reduce the amount of unreacted monomer. When the aqueous polymer has a vinyl alcohol unit, for example, the saponification conditions may be set with reference to the method for producing a copolymer of vinyl alcohol and an alkali metal neutralized product of an ethylenically unsaturated carboxylic acid described in WO2017 / 168947.

[0048] The monomer concentration at the start of polymerization may be 5 mass% or more, 10 mass% or more, 15 mass% or more, 20 mass% or more, or 25 mass% or more, and may also be 30 mass% or less, 25 mass% or less, 20 mass% or less, 15 mass% or less, or 10 mass% or less. In one embodiment, it is 10 mass% or more and 11 mass% or less, 15 mass% or more and 17 mass% or less, or 11 mass% or more and 13 mass% or less.

[0049] As the initiator, various known ones can be used without particular limitation. Examples of radical polymerization initiators include persulfates such as potassium persulfate and ammonium persulfate; redox polymerization initiators obtained by combining such persulfates with reducing agents such as sodium bisulfite; azo 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 the 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 monomer group that is the raw material of the aqueous polymer in the present disclosure.

[0050] Each polymerization condition and the like can be appropriately set according to the structure of the target compound.

[0051] [Amount of aqueous polymer] The amount of the aqueous polymer 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 in the secondary battery binder, preferably 50% by mass or more, more preferably 75% by mass or more, and may also 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.

[0052] [Other binder components] The secondary battery binder in the present disclosure may contain other binder components in addition to the aqueous polymer. Examples of other components include known binder resins and the like, such as styrene-butadiene rubber (SBR), styrene-ethylene-butylene-styrene copolymer (SEBS), polyimide (PI), polyamide, ethylene-vinyl acetate copolymer (EVA), and the like.

[0053] The amount of other binder components 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 in the secondary battery binder, and may also 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.

[0054] <Slurry> The slurry of the present disclosure contains the aforementioned secondary battery binder and water, and may further contain an electrode active material. The slurry may contain battery particles such as a conductive assistant 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.

[0055] [Liquid medium] The slurry contains a liquid medium (aqueous medium) containing water. The liquid medium is preferably water alone from the perspective of concerns about environmental impact, but may contain an organic solvent such as alcohol (ethanol, methanol, isopropyl alcohol, etc.). The amount of the organic solvent 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 in the liquid medium, and is preferably 10% by mass or less.

[0056] [Amount of liquid medium] 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 with respect to 100% by mass of the slurry solid content (total amount of the secondary battery binder, active material, and conductive assistant), preferably 30% by mass or more, and may also 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.

[0057] [Secondary battery binder] The slurry contains a secondary battery binder. The types of the secondary battery binder are as described above.

[0058] [Amount of secondary battery binder] The amount of the secondary battery binder 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 in the slurry solid content (total amount of the secondary battery binder, active material, and conductive assistant), 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. Being not less than the above lower limit is preferable from the viewpoint of achieving good effects of the secondary battery binder. Being not more than the above upper limit is preferable from the viewpoint of making the battery have a high capacity.

[0059] 〔Active material〕 The active material is an electrode active material, and examples thereof include a negative electrode active material and a positive electrode active material. When the active material is, for example, a negative electrode active material, it can include, for example, a carbon material, and can also include at least one of silicon and silicon oxide. Specific materials of the negative electrode active material and the positive electrode active material are exemplified below.

[0060] (Negative electrode active material) The negative electrode active material is not particularly limited, and a negative electrode active material used in this technical field may be used.

[0061] As the negative electrode active material, a carbon material such as crystalline carbon or amorphous carbon may be used. Examples of crystalline carbon may be amorphous, plate-like, flaky, spherical, or fibrous, and include graphite such as natural graphite or artificial graphite. Examples of amorphous carbon include soft carbon (easily graphitizable carbon) or hard carbon (difficultly graphitizable carbon), mesophase pitch carbide, fired coke, and the like.

[0062] As the negative electrode active material, materials capable of storing and releasing a large amount of lithium ions such as silicon (Si), tin (Sn), and titanium (Ti) may be used. These materials can be used in the form of a simple substance, alloy, compound, solid solution, or composite active material containing a silicon-containing material, tin-containing material, or titanium-containing material. Examples of the silicon-containing material 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 for a part of Si. The silicon-containing material may be a silicon oxide. Examples of the tin-containing material include Ni2Sn4, Mg2Sn, SnOx (0 < x < 2), SnO2, SnSiO3, LiSnO, etc. Examples of the titanium-containing material include lithium titanates such as Li2TiO3, Li4Ti5O 12 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 preferable, and for example, it may be a simple substance of Si or silicon oxide.

[0063] 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 the crystalline carbon include those described above.

[0064] 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.

[0065] (Positive electrode active material) The cathode active material is not particularly limited, and a cathode active material used in this technical field may be used.

[0066] The cathode active material may be a lithium-containing composite oxide. Examples of the lithium-containing composite oxide include 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.

[0067] [Amount of active material] The amount of the active material 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 in the slurry solid content (total amount of the secondary battery binder, active material, and conductive assistant), preferably 55% by mass or more, more preferably 75% by mass or more, and also 99% by mass or less, 95% by mass or less, 90% by mass or less, or 85% by mass or less.

[0068] [Conductive assistant] As the conductive aid, those 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 the carbon powder include commonly used ones such as acetylene black (AB), ketjen black (KB), graphite, carbon fiber, carbon tube, graphene, amorphous carbon, hard carbon, soft carbon, glassy carbon, carbon nanofiber, carbon nanotube and other carbon materials. These may be used alone or in combination of two or more.

[0069] [Amount of conductive aid] The amount of the conductive aid may be 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 3.0% by mass or more, or 5.0% by mass or more in the slurry solid content (total amount of the secondary battery binder, the active material and the conductive aid), preferably 0.3% by mass or more, and may be 10% by mass or less, 5.0% by mass or less, 3.0% by mass or less, 1.0% by mass or less, preferably 3.0% by mass or less, more preferably 1.0% by mass or less.

[0070] [Dispersing aid] The slurry of the present disclosure may further contain a dispersing aid. As the dispersing aid, 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 is preferable. Examples of the organic acid having 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 the organic acid having 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 the organic acid having an imino group and a carboxy group include proline, 3-hydroxyproline, 4-hydroxyproline, and pipecolic acid. Among these, from the viewpoint of availability, glucuronic acid, humic acid, glycine, polyglycine, aspartic acid, or glutamic acid is preferable.

[0071] [Amount of dispersing aid] The amount of the dispersing aid may be 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 1.5% by mass or more, or 3.0% by mass or more in the slurry solid content (total amount of the secondary battery binder, the active material, and the conductive aid), preferably 0.3% by mass or more, and may be 5.0% by mass or less, 3.0% by mass or less, 1.0% by mass or less, preferably 3.0% by mass or less, more preferably 1.0% by mass or less.

[0072] [Other components] The slurry of the present disclosure may contain other components, such as conventional additives and the like.

[0073] [Amount of other components] The amount of other components (each amount or total amount) may be 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 3.0% by mass or more, or 5.0% by mass or more in the slurry solid content (total amount of the secondary battery binder, active material, and conductive assistant), preferably 0.3% by mass or more, and may be 10% 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.

[0074] 〔Method for manufacturing slurry〕 The method for manufacturing the slurry of the present disclosure is not particularly limited and is manufactured by mixing components. For example, a secondary battery binder, a liquid medium, an active material, and further, if necessary, a conductive assistant, a dispersion assistant, 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 the like may be mixed to form a slurry. Alternatively, the active material, the secondary battery binder of the present disclosure, and further, if necessary, a conductive assistant, a dispersion assistant, etc. may be mixed in a solid state, and then the liquid medium may be added to form a paste-like slurry.

[0075] <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 the active material in the present disclosure described above. That is, the electrode of the present disclosure can be produced, for example, by coating the slurry of the present disclosure described above on a current collector and drying it. Therefore, the electrode may include a heat-dried product of the slurry. The secondary battery binder may be decomposed or reacted by heat drying and converted into a component derived from the secondary battery binder.

[0076] 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 may also be 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. The heat drying may be performed under reduced pressure (for example, 0.05 MPa or lower, 0.03 MPa or lower, or 0.01 MPa or lower). The time for heat drying 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 also 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.

[0077] When the electrode of the present disclosure is a negative electrode, as the material constituting the current collector, for example, conductive substances such as C, Cu, Ni, Fe, V, Nb, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, Al, etc., alloys containing two or more of these conductive substances (for example, stainless steel) can be used. Further, the current collector may be one in which Cu is plated on Fe. From the viewpoints of high electrical conductivity, excellent stability and oxidation resistance in the electrolytic solution, Cu, Ni, stainless steel, etc. are preferable as the material of the current collector of the negative electrode, and Cu or Ni is more preferable from the viewpoint of material cost.

[0078] When the electrode of the present disclosure is a positive electrode, as the material constituting the current collector, for example, conductive substances such as C, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, Al, etc., alloys containing two or more of these conductive substances (for example, stainless steel) can be used. From the viewpoints of high electrical conductivity, excellent stability and oxidation resistance in the electrolytic solution, C, Al, stainless steel, etc. are preferable as the material of the current collector of the positive electrode, and Al is more preferable from the viewpoint of material cost.

[0079] The shape of the current collector is not particularly limited, and for example, a foil-shaped substrate, a three-dimensional substrate, etc. can be used. In addition, when using a three-dimensional substrate (foamed metal, mesh, woven fabric, non-woven fabric, expand, etc.), the high-rate charge and discharge characteristics are also likely to be good.

[0080] <Battery> The secondary battery of the present disclosure includes the electrode for secondary battery of the present disclosure described above. The secondary battery of the present disclosure may be provided with the electrode for secondary battery of the present disclosure as either one or both of the positive electrode and the negative electrode. The secondary battery of the present disclosure is manufactured by using the electrode for secondary battery of the present disclosure (that is, by using the binder in the present disclosure) and by a method used in this technical field.

[0081] The secondary battery of the present disclosure is preferably a non-aqueous electrolyte secondary battery, and particularly preferably a lithium-ion secondary battery. Since a lithium-ion secondary battery needs to contain lithium ions, a lithium salt is preferably used as the electrolyte. Examples of this lithium salt include lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium trifluoromethanesulfonimide, and the like. The electrolyte can be used alone as one kind or in combination of two or more kinds.

[0082] As the electrolytic solution, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, etc. can be used. The electrolytic solution can be used alone as one kind or in combination of two or more kinds. In particular, propylene carbonate alone, a mixture of ethylene carbonate and diethyl carbonate, or γ-butyrolactone alone is preferable. Note that the mixing ratio of the above-mentioned mixture of ethylene carbonate and diethyl carbonate can be arbitrarily adjusted within the range where one component is 10 to 90% by volume.

[0083] Regarding the configurations of other secondary batteries, the configurations of known secondary batteries can be adopted.

[0084] Although the embodiments have been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims.

Examples

[0085] Hereinafter, the present disclosure will be described in detail with reference to examples, but the present disclosure is not limited to these examples.

[0086] The meanings of the abbreviations are as follows. AN: Acrylonitrile AA: Acrylic acid AAm: Acrylamide 2-HEA: 2-Hydroxyethyl acrylate MAS: Methallyl sulfonic acid VA: Vinyl alcohol

[0087] <Preparation of polymer> An aqueous polymer was prepared according to the procedure described below.

[0088] [Example 1] Into a sealable vial with an internal volume of 500 ml, 35.3 g (0.49 mol) of acrylamide, 0.2 g (0.001 mol) of sodium methallyl sulfonate, 35.3 g (0.49 mol) of acrylic acid, 48.6 g (0.42 mol) of 2-hydroxyethyl acrylate, 1.36 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (product name "VA-044" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 210.0 g of ion-exchanged water were added and mixed to prepare a monomer aqueous solution, which was then deoxygenated. Separately from the above, 858.3 g of ion-exchanged water was charged into a 2 L reaction vessel equipped with a stirrer, a thermometer, an N2 gas inlet tube, a reflux condenser and a dropping funnel. After deoxygenating the system by blowing N2 gas, the internal temperature was raised to 68 °C. Subsequently, the deoxygenated monomer aqueous solution was dropped into the reaction vessel with stirring through the dropping funnel over 3 hours. After dropping, the internal temperature was maintained at 68 °C for 2 hours. Further, it was stirred at 73 °C for 1 hour, cooled to 30 °C, and 30.3 g of a 48 mass% NaOH aqueous solution was added until the pH reached 5.5 to obtain an aqueous solution containing an aqueous polymer. The composition of the repeating unit of the aqueous polymer was AAm / AA(H / Na) / 2-HEA / MAS(H / Na) = 35 / 35 / 29.9 / 0.1 (molar ratio).

[0089] Example 2 In a sealable vial with an internal volume of 500 ml, 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 (product name "VA-044" manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.), and 250.0 g of ion-exchanged water were added and mixed to prepare a monomer aqueous solution, which was then deoxygenated. Separately from the above, 831.0 g of ion-exchanged water was charged into a 2 L reaction vessel equipped with a stirrer, a thermometer, an N2 gas inlet tube, a reflux condenser, and a dropping funnel. After blowing N2 gas to deoxygenate the system, the internal temperature was raised to 68°C. Subsequently, the prepared monomer aqueous solution was added dropwise to the reaction vessel through the dropping funnel over 3 hours while stirring. After the addition, it was held at the same temperature for 1.5 hours. Subsequently, 1.45 g of VA-044 and 20 g of ion-exchanged water were added, and the mixture was stirred at the same temperature for 1 hour. Further, it was stirred at 73°C for 1 hour to obtain an aqueous solution containing an aqueous polymer. The composition of the repeating unit of the aqueous polymer was AAm / MAS(H / Na) = 99 / 1 (molar ratio).

[0090] Example 3 In a sealable vial with an internal volume of 500 ml, 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 added and mixed to prepare a monomer aqueous solution. Separately from the above, 607.6 g of ion-exchanged water was charged into a 1-L reaction vessel equipped with a stirrer, a thermometer, an N2 gas inlet tube, a reflux condenser, and a dropping funnel. After blowing N2 gas to deoxygenate the system, the internal temperature was raised to 75°C. Subsequently, the prepared monomer aqueous solution was added dropwise to the reaction vessel with stirring over 3 hours using the dropping funnel. After the addition, it was held for 2 hours. Thereafter, the internal temperature was raised to 80°C and held for 1 hour. The internal temperature was cooled to 30°C, and 70.57 g (0.30 mol) of a 5 mol / L aqueous sodium hydroxide solution was added to adjust the pH to 6.5, obtaining an aqueous solution containing an aqueous polymer. The composition of the repeating unit of the aqueous polymer was 2-HEA / AA(H / Na) / AAm = 13 / 22 / 65 (molar ratio).

[0091] [Comparative 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 with an internal volume of 500 ml and mixed to prepare a monomer aqueous solution. Separately from the above, 500.0 g of ion-exchanged water was charged into a 1-L reaction vessel equipped with a stirrer, a thermometer, an N2 gas inlet tube, a reflux condenser, and a dropping funnel. After blowing N2 gas to deoxygenate the system, the internal temperature was raised to 75°C. Subsequently, the prepared monomer aqueous solution was added dropwise to the reaction vessel with stirring over 3 hours using the dropping funnel. After the addition, the internal temperature was held at 80°C for 1 hour. Thereafter, the internal temperature was cooled to 40°C or lower, and 69.5 g (0.31 mol) of a 5 mol / L aqueous lithium hydroxide solution was added to adjust the pH to 7.0, obtaining an aqueous solution containing an aqueous polymer. The composition of the repeating unit of the aqueous polymer was AN / AA(H / Li) / AAm = 57 / 31 / 12 (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 added to a beaker with an internal volume of 500 ml and mixed to prepare a monomer aqueous solution. Separately from the above, 768 g of ion-exchanged water and 12 g of anhydrous sodium sulfate were charged into a 2-L reaction vessel equipped with a stirrer, a thermometer, an N2 gas inlet tube, a reflux condenser, and a dropping funnel, 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 reaction vessel with stirring over 4 hours using the dropping funnel. After the addition, the internal temperature was maintained at 65 °C for 2 hours, and the precipitated solid content was filtered. Into the same reaction vessel as above, the obtained solid content, 450 g of methanol, 420 g of ion-exchanged water, 140 g of sodium hydroxide, and 0.52 g of hydrazine were charged, 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 after filtering off the solid content, 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 unit of the aqueous polymer was VA / AA(H / Na) = 60 / 40 (molar ratio).

[0093] <Measurement of Polymer Properties> The properties of the aqueous polymers obtained in the above Examples / Comparative Examples were measured. The test methods are as follows. Note that all the aqueous polymer solutions used in each test method were aqueous polymer solutions in which the aqueous polymer was dissolved in ion-exchanged water.

[0094] [Molecular Weight, etc.] Regarding the aqueous polymers obtained in the above Examples / Comparative Examples, Mw (weight-average molecular weight) and Mw / Mn (breadth of molecular weight distribution) were measured using GPC-RI in terms of standard polyethylene glycol / polyethylene oxide conversion. The details of the conditions are as follows. [GPC-RI] GPC apparatus: HLC-8320GPC (manufactured by Tosoh Corporation) Column: TSK GMPW XL (manufactured by Tosoh Corporation) Carrier: 0.1 M sodium nitrate Column temperature: 40 °C Flow rate: 1.0 mL / min Injection volume: 200 μL Concentration: 0.5 mg / mL

[0095] 〔pH〕 An aqueous polymer solution prepared by dissolving an aqueous polymer in water so that the solid content concentration is 2% by mass was kept at 25°C, and then the pH was measured using a pH meter (manufactured by Horiba, Ltd., model "D-71", glass pH electrode: model "9681S-10D"). The pH was calculated by rounding the second decimal place of the measured value.

[0096] 〔Viscosity〕 An aqueous polymer solution prepared by dissolving an aqueous polymer in water so that the solid content concentration is 2% by mass was kept at 25°C, and then the viscosity of the aqueous polymer solution was measured using a B-type viscometer (manufactured by BROOKFIELD, model "DV1MLVTJ0"). Note that the spindle and rotation speed corresponding to the viscosity were adopted during the measurement as follows. LV-2, 12 rpm: 250 - 2500 mPa·s LV-1, 30 rpm: 20 - 200 mPa·s

[0097] 〔Conductivity〕 An aqueous polymer solution prepared by dissolving an aqueous polymer in water so that the solid content concentration is 2% by mass was kept at 25°C, and then the conductivity was measured using a conductivity meter (manufactured by AS ONE, model "AS710"). The conductivity was calculated by rounding the second decimal place of the measured value.

[0098] 〔Specific Resistance〕 An aqueous polymer solution prepared by dissolving an aqueous polymer in water so that the solid content concentration is 2% by mass was kept at 25°C, and then the specific resistance was measured using a conductivity meter (manufactured by AS ONE, model "AS710", electrode "2301-S"). The salt content was calculated by rounding the first decimal place of the measured value.

[0099] 〔Turbidity〕 An aqueous polymer solution prepared by dissolving a water-based polymer in water to a solid content concentration of 2% by mass was added to a cell made of acrylic resin (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 absorbances at 660 nm of standard samples with turbidities of 1, 20, and 100 were measured respectively to obtain a calibration curve. The turbidity of the aqueous polymer solution was calculated from the calibration curve of the absorbance of the aqueous polymer solution and the turbidity of the standard samples.

[0100] <Properties of battery / slurry / binder solution, etc.> Using the water-based polymer obtained in the above Examples / Comparative Examples, a battery / slurry / binder solution was prepared and its properties were measured. The test methods are as follows.

[0101] [Capacity retention rate after 100 cycles] The capacity retention rate after 100 cycles was determined according to the following procedure. [Fabrication of electrode] 23.3 parts by mass of artificial graphite (manufactured by Jiangxi Zichen Technology, G-49), 5.8 parts by mass of silicon monoxide (manufactured by Shin-Etsu Chemical Co., Ltd., KSC-1265), and 0.9 parts by mass of the aqueous polymer solution in terms of solid content were kneaded. Further, water was added and kneaded so that the solid content concentration became 58% by mass to prepare a negative electrode slurry. The obtained negative electrode slurry was applied onto a rolled copper foil with a thickness of 18 μm and dried, and then the rolled copper foil and the coating film were adhesively bonded by a roll press machine (manufactured by Ohno Roll Co., Ltd.). Next, heat treatment (under reduced pressure, 100 °C, 12 hours or more) was performed to fabricate a negative electrode. The thickness of the active material layer in the obtained negative electrode was 36 μm, and the capacity density of the negative electrode was 3.5 mAh / cm 2 It was.

[0102] [Assembly of coin cell] A coin cell (CR2032) was fabricated with the negative electrode prepared above, the following positive electrode, a separator, and an electrolyte. · Positive electrode: LiNi 0.5 Co 0.2 Mn 0.3O2 (manufactured by Yamasaki Co., Ltd.) · Separator: Glass filter (product name GA-100, manufactured by Advantec Co., Ltd.) · Electrolyte: A solution prepared by dissolving LiPF6 at a concentration of 1 mol / L in a solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1, adding 1 mass% of vinylene carbonate (VC), which is an additive for the electrolyte, and 1 mass% of fluoroethylene carbonate (FEC).

[0103] [Measurement of capacity retention rate] For each coin cell prepared as described above, at 30 °C, it was charged to 4.2 V with a current corresponding to 0.1C, discharged to 2.5 V with a current corresponding to 0.1C, charged to 4.2 V with a current corresponding to 0.5C, and discharged to 2.5 V with a current corresponding to 0.5C. This operation was repeated 3 cycles to age the battery. Subsequently, after charging to 4.2 V with a current corresponding to 0.5C, discharging to SOC50 with a current corresponding to 0.5C, performing a constant current discharge for 12 seconds with a current corresponding to 0.2C, charging for 24 seconds with a current corresponding to 0.1C, performing a constant current discharge for 12 seconds with a current corresponding to 0.5C, charging for 1 minute with a current corresponding to 0.1C, performing a constant current discharge for 12 seconds with a current corresponding to 1C, charging for 2 minutes with a current corresponding to 0.1C, performing a constant current discharge for 12 seconds with a current corresponding to 2C, and then discharging to 2.5 V with a current corresponding to 0.2C, the initial discharge capacity was measured. Subsequently, the operation of charging to 4.2 V with a current corresponding to 1C and discharging to 2.5 V with a current corresponding to 1C was performed for 97 cycles (cycles 4 to 100). Thereafter, the same operation as when measuring the initial discharge capacity was performed, and the discharge capacity after 100 cycles was measured. The capacity retention rate was calculated using the following formula. Capacity retention rate after 100 cycles = [Discharge capacity after 100 cycles (mAh / g)] / [Initial discharge capacity after aging (mAh / g)] × 100 [%]

[0104] [Discharge capacity after 100 cycles] The discharge capacity after 100 cycles was measured in the test of the above [capacity retention rate after 100 cycles].

[0105] [DC resistance (DCR) after 100 cycles] [Fabrication of electrodes] Electrodes were fabricated in the same manner as described in the above [capacity retention rate after 100 cycles]. [Assembly of coin cells] A coin cell (CR2032) equipped with a negative electrode, the following positive electrode, a separator, and an electrolyte was fabricated in the same manner as described in the above [capacity retention rate after 100 cycles].

[0106] [Measurement of DC resistance after 100 cycles] For each coin cell fabricated as described above, at 30 °C, it was charged to 4.2 V with a current corresponding to 0.1C, discharged to 2.5 V with a current corresponding to 0.1C, charged to 4.2 V with a current corresponding to 0.5C, and discharged to 2.5 V with a current corresponding to 0.5C. This operation was repeated 3 cycles to age the battery. Subsequently, after charging to 4.2 V with a current corresponding to 0.5C, it was discharged to SOC50 with a current corresponding to 0.5C, discharged at a constant current for 12 seconds with a current corresponding to 0.2C, charged for 24 seconds with a current corresponding to 0.1C, discharged at a constant current for 12 seconds with a current corresponding to 0.5C, charged for 1 minute with a current corresponding to 0.1C, discharged at a constant current for 12 seconds with a current corresponding to 1C, charged for 2 minutes with a current corresponding to 0.1C, discharged at a constant current for 12 seconds with a current corresponding to 2C, and then discharged to 2.5 V with a current corresponding to 0.2C (initial discharge operation). Subsequently, it was charged to 4.2 V with a current corresponding to 1C and discharged to 2.5 V with a current corresponding to 1C for 97 cycles (cycles 4 to 100). Thereafter, the same operation as the initial discharge operation was performed. The DC resistance of the cell was calculated from the values of the discharge current and voltage at 10.0 seconds of the C-rate of each coin cell and taken as the DC resistance after 100 cycles.

[0107] [Foaming (amount of foam after 15 minutes)] An aqueous polymer solution in which an aqueous polymer is dissolved in water so that the solid content concentration is 2% by mass is added to a glass bottle (diameter 45 mm, height 110 mm) up to a height of 5.5 cm, and a disperser with a diameter of 35 mm (manufactured by PRIMIX, model "Homodisper 2.5 type") is attached up to a position at a height of 3.5 cm, and stirred at 2500 rpm for 2 minutes in an environment at 23°C. The state of foaming 15 minutes after stirring was visually confirmed, and an aqueous solution with almost no visible bubbles (criterion: about 20 or fewer bubbles in the aqueous solution) was marked as 〇, and an aqueous solution with many bubbles visible throughout was marked as ×.

[0108] The test results are summarized in the following table. TIFF0007708944000001.tif91164

Industrial Applicability

[0109] The present disclosure is suitably used for power sources of mobile communication devices, portable electronic devices, electric bicycles, electric motorcycles, electric vehicles, and the like.

Claims

**Claim 1** Comprising an aqueous polymer, A secondary battery binder, wherein the conductivity of an aqueous solution obtained when the aqueous polymer is dissolved in water at a concentration of 2% by mass is 3.3 mS / cm or less at 25°C. **Claim 2** The secondary battery binder according to claim 1, wherein the conductivity is 0.5 mS / cm or more. **Claim 3** The secondary battery binder according to claim 1 or 2, wherein the aqueous polymer is a vinyl polymer having an acidic functional group-containing repeating unit. **Claim 4** The aqueous 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 (n is, independently of each other, 1 or more and 6 or less).] The repeating unit (1) represented by, and Formula: - [CH ２ - CH(OH)]- The repeating unit (2) represented by The secondary battery binder according to claim 1 or 2, comprising a repeating unit selected from. **Claim 5** In the aqueous polymer, The amount of the repeating unit selected from the repeating unit (1) and the repeating unit (2) is 40 mol% or more, The amount of the acidic functional group-containing repeating unit is 0.8 mol% or more, The secondary battery binder according to claim 4, wherein the amount of the nonionic repeating unit is 40 mol% or more. **Claim 6** The secondary battery binder according to claim 1 or 2, comprising SBR. **Claim 7** A slurry comprising the secondary battery binder according to claim 1 or 2 and water. **Claim 8** The slurry according to claim 7, further comprising an electrode active material. **Claim 9** A method for manufacturing a secondary battery, comprising a step of coating the slurry according to claim 7. **Claim 10** An electrode comprising the secondary battery binder according to claim 1 or 2 or a component derived from the secondary battery binder. **Claim 11** An electrode comprising a heat-dried product of the slurry according to claim 8. **Claim 12** A secondary battery comprising the electrode according to claim 10.

Images