Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
  • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
  • C08F220/04—Acids; Metal salts or ammonium salts thereof
  • C08F220/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• This disclosure relates to electrode binders, electrode slurries, LIB electrodes, and lithium-ion secondary batteries.
• LIBs lithium-ion secondary batteries
• the components of lithium-ion secondary batteries have a significant impact on battery characteristics.
• the electrodes which are components, contain binders that bind the electrodes to the current collectors, and the binder also plays a determining role in the performance of LIBs.
• electrodes that use silicon materials as the electrode active material undergo large volume changes during charging and discharging.
• the electrode itself is destroyed by repeated charging and discharging, resulting in a decrease in charge and discharge capacity and poor cycle characteristics.
• Various binders are being investigated to prevent destruction of the electrode itself.
• Patent Document 1 discloses a binder for LIB in which components containing monomer units derived from acrylic acid and monomer units derived from a specific compound are crosslinked with a specific crosslinking agent.
• Patent Document 2 discloses a binder for LIB anodes containing a (meth)acrylic copolymer containing (aminoalkyl-alkoxysilane)-(meth)acrylic acid units as repeating units.
• An object of the present disclosure is to provide at least one of an electrode binder that can improve the cycle characteristics of LIBs and an electrode slurry containing the same.
• electrode binders containing (meth)acrylic polymers have been studied with a focus on the weight-average molecular weight and creep displacement, and it has been found that the above-mentioned object can be achieved by controlling the weight-average molecular weight and creep displacement within specific ranges. That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows.
• R 1 and R 2 each independently represent a hydrogen atom or a methyl group
• M represents Na, K, or Li
• n and m represent the number of repetitions
• n/m is greater than 0 and not greater than 0.25.
• R3 represents a hydrogen atom or a methyl group
• R4 represents an alkylene group having 1 to 6 carbon atoms
• l represents the number of repetitions
• m/l is 0.8 or more and less than 4.0.
• the structural unit represented by formula (1) is more than 0 mol % and 8 mol % or less
• the structural unit represented by formula (2) is 48 mol % or more and 70 mol % or less
• the electrode binder according to the above [2] which contains the constitutional unit represented by formula (3) in a range of 23 mol % to 45 mol %.
• An electrode for LIB comprising the electrode binder described in any one of [1] to [7] above.
• the present disclosure provides at least one of an electrode binder that can improve the cycle characteristics of LIBs and an electrode slurry containing the same.
• the electrode binder of this embodiment contains a polymer having, as repeating units, a structural unit represented by formula (1) and a structural unit represented by formula (2) (hereinafter also referred to as “structural unit (1)” and “structural unit (2)", respectively.
• the electrode binder of this embodiment is an electrode binder containing a (meth)acrylic polymer.
• (meth)acrylic acid means at least one of acrylic acid and methacrylic acid
• (meth)acrylate means at least one of acrylate and methacrylate.
• R 1 and R 2 each independently represent a hydrogen atom or a methyl group
• M represents Na, K, or Li
• n and m represent the number of repetitions
• n/m is more than 0 and 0.25 or less, and more preferably 0.04 or more and 0.16 or less.
• the electrode binder of this embodiment contains a polymer having structural units (1) and (2), which not only improves the dispersibility of the electrode active material when made into an electrode slurry, but also improves the adhesive strength between the electrode active material and the current collector.
• the weight-average molecular weight (hereinafter also referred to as "Mw") of the electrode binder of this embodiment is 520,000 to 1,100,000, preferably 550,000 to 1,050,000, and more preferably 600,000 to 1,000,000. Electrodes containing an electrode binder with an Mw of less than 520,000 as a binder are prone to electrode destruction due to cohesive failure. On the other hand, electrode binders with an Mw of more than 1,100,000 are unable to wet the electrode active material and the fine irregularities on the current collector surface. Therefore, electrodes containing such electrode binders as a binder have low adhesive strength and are prone to electrode destruction due to adhesive failure.
• the creep displacement is determined by a nanoindentation test in accordance with ISO 14577-1.
• a specific example of the nanoindentation test is a nanoindentation test using a drift test method under the following conditions. Measurement temperature: 25°C Maximum load: 20 mN Maximum load holding time: 5000ms Time to reach maximum load: 10s Push-in speed: 2 mN/s
• h1 is the creep strain ( ⁇ m) when the maximum load is reached
• h2 is the maximum value of the creep strain ( ⁇ m) during the maximum load holding time.
• the measurement sample can be an electrode binder in the form of a 50 ⁇ m thick cast film formed on copper foil.
• the measurement device can be a standard nanoindenter (e.g., ENT-5, manufactured by ELIONIX) and a measuring indenter (shape: Berkovich).
• the main causes of electrode failure are thought to be cohesive failure, which occurs when the electrode binder itself breaks down, and adhesive failure, which occurs at the interface between the electrode binder and the electrode active material or current collector. Cohesive failure occurs when the electrode binder itself breaks down, causing the electrode active material to peel off from the current collector. Adhesive failure occurs when the electrode binder peels off at the interface between the electrode active material and current collector and the electrode binder.
• the Mw and creep displacement of the electrode binder of this embodiment are both important components in preventing electrode destruction.
• the cycle characteristics are improved when the binder is made into a LIB.
• R3 represents a hydrogen atom or a methyl group
• R4 represents an alkylene group having 1 to 6 carbon atoms.
• l represents the number of repetitions
• m/l is 0.8 or more and less than 4.0, and preferably m/l is 1.06 or more and 3.1 or less.
• R4 include a methylene group, an ethylene group, a propylene group, and a butylene group, and an ethylene group is preferred.
• the electrode binder of this embodiment has improved binding properties to the electrode active material and the current collector, thereby further suppressing the occurrence of adhesive failure.
• the glass transition temperature (Tg) is lowered, improving flexibility in low-temperature environments, which reduces the cohesive force of the electrode binder itself and further suppresses the occurrence of cohesive failure.
• the electrode binder of this embodiment may contain structural unit (1) in an amount greater than 0 mol%, 0.1 mol% or greater, or 2 mol% or greater, or 8 mol% or less, or 5 mol% or less, based on 100 mol% of the electrode binder of this embodiment.
• the electrode binder of this embodiment preferably contains structural unit (1) in a range of greater than 0 mol% and 8 mol% or less, more preferably in a range of 0.1 mol% or greater and 5 mol% or less, and even more preferably in a range of 2 mol% or greater and 5 mol% or less.
• the electrode binder of this embodiment may contain 48 mol% or more, 50 mol% or more, or 55 mol% or more of structural unit (2) relative to 100 mol% of the electrode binder of this embodiment, and may contain 70 mol% or less, or 65 mol% or less.
• the electrode binder of this embodiment preferably contains structural unit (2) in the range of 48 mol% or more and 70 mol% or less, more preferably contains structural unit (2) in the range of 50 mol% or more and 65 mol% or less, and even more preferably contains structural unit (2) in the range of 55 mol% or more and 65 mol% or less.
• the electrode binder of this embodiment may contain 23 mol% or more, 25 mol% or more, or 30 mol% or more of structural unit (3), or 45 mol% or less, or 40 mol% or less, based on 100 mol% of the electrode binder of this embodiment.
• the electrode binder of this embodiment preferably contains structural unit (3) in the range of 23 mol% or more and 45 mol% or less, more preferably 25 mol% or more and 45 mol% or less, and even more preferably 30 mol% or more and 40 mol% or less of structural unit (3).
• the electrode binder of this embodiment may be composed of the above-mentioned polymer, in which case the total of the structural units (1) to (3) is 100 mol%.
• the electrode binder of this embodiment may contain components other than the structural units (1) to (3). Therefore, the total of the structural units (1) to (3) may be 100 mol% or less, and may be less than 100 mol%.
• the total of the structural units (1) to (3) is preferably greater than 71 mol%, more preferably greater than 85 mol%, and even more preferably greater than 93 mol%.
• the total of the structural units (1) to (3) is preferably greater than 71 mol% but less than 100 mol%, more preferably greater than 85 mol% but less than 100 mol%, and even more preferably greater than 93 mol% but less than 100 mol%.
• the electrode binder of this embodiment may also be composed of the above-mentioned polymer, in which case the total of the structural units (1) to (4) is 100 mol%.
• the electrode binder of this embodiment may also contain components other than the structural units (1) to (4). Therefore, the total of the structural units (1) to (4) may be 100 mol% or less, and may be less than 100 mol%.
• the total of the structural units (1) to (4) is preferably greater than 71.1 mol%, more preferably greater than 85 mol%, and even more preferably greater than 93 mol%.
• the total of the structural units (1) to (4) is preferably greater than 71.1 mol% and less than 100 mol%, more preferably greater than 85 mol% and less than 100 mol%, and even more preferably greater than 93 mol% and less than 100 mol%.
• the cross-linkable monomer is not particularly limited as long as it has a structure that allows at least two of the structural units (1) to (4) to be chemically bonded by cross-linking.
• the crosslinkable monomer may be, for example, a monomer having an ethylenically unsaturated bond.
• the monomer having an ethylenically unsaturated bond include one or more selected from the group consisting of (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 2-(dimethylamino)ethyl (meth)acrylate, and pentaerythritol tetra(meth)acrylate.
• the crosslinkable monomer may also be a (meth)acrylic acid derivative having an alkoxysilyl group, which is obtained by modifying (meth)acrylic acid with a silane coupling agent, for example.
• the electrode binder of the present embodiment can be produced, for example, by a polymerization step of polymerizing a composition in which at least a monomer having the structural unit (1) and a monomer having the structural unit (2) are dissolved in an aqueous medium at a temperature of 50°C or higher and 100°C or lower in the presence of a radical polymerization initiator.
• the monomer having the structural unit (1) may be, for example, at least one of acrylic acid and methacrylic acid, with acrylic acid being preferred.
• the monomer having structural unit (2) may be, for example, one or more selected from the group consisting of sodium acrylate, sodium methacrylate, potassium acrylate, potassium methacrylate, lithium acrylate, and lithium methacrylate, with sodium acrylate being preferred.
• the monomer of structural unit (2) may be a monomer of structural unit (1) modified with an alkali metal compound.
• Preferred water-soluble organic solvents include one or more selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol, 2-butanol, t-butanol, dimethylformamide, acetone, and 1,4-dioxane, as well as at least one of ethanol and 2-propanol (isopropanol), and even ethanol.
• the composition to be subjected to the polymerization step may have a silane coupling agent dissolved therein.
• the silane coupling agent reacts with a monomer having the structural unit (1) to form a monomer having the structural unit (4).
• Examples of the silane coupling agent include one or more selected from the group consisting of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, N-2(aminoethyl)3-aminopropyltrimethoxysilane, N-2(aminoethyl)3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyl
• the radical polymerization initiator may be one or more selected from the group consisting of persulfates such as potassium persulfate, azo compounds such as azobisisobutyronitrile, and peroxide compounds such as benzoyl peroxide, with potassium persulfate being preferred.
• persulfates such as potassium persulfate
• azo compounds such as azobisisobutyronitrile
• peroxide compounds such as benzoyl peroxide
• the electrode slurry of the present embodiment may be a slurry containing the electrode binder of the present embodiment, or may further be a slurry containing the electrode binder of the present embodiment, an electrode active material, and an aqueous medium, and is preferably a slurry containing the electrode binder of the present embodiment, an electrode active material, a conductive assistant, and an aqueous medium.
• the content of the electrode binder in the electrode slurry is preferably 1% by mass or more and 12% by mass or less, or 2% by mass or more and 8% by mass or less, expressed as the content of the electrode binder relative to the total mass of the electrode binder, electrode active material, and conductive additive in the electrode slurry (hereinafter also referred to as the "solids content").
• the electrode active material content in the electrode slurry is sufficient to ensure battery capacity. Furthermore, the adhesive strength between the electrode active material and the current collector is improved. This makes it less likely for the electrode active material to peel off from the current collector, further improving cycle characteristics.
• the electrode active material contained in the electrode slurry of this embodiment may be either a positive electrode active material or a negative electrode active material, but is preferably a negative electrode active material, and more preferably a negative electrode active material containing a silicon material. Negative electrode active materials containing a silicon material undergo large volume changes during charge and discharge, so the electrode binder of this embodiment is particularly effective in improving cycle characteristics.
• Si alloys are metals composed of Si and elements other than Si. Elements other than Si contained in Si alloys include elements from groups 2 to 15 of the periodic table.
• the carbon material can be, for example, one or more selected from the group consisting of graphite, natural graphite, and artificial graphite.
• the negative electrode active material preferably has an average particle size (D50) of 1 ⁇ m or more and 40 ⁇ m or less.
• the particle size (D50) of the Si compound contained in the negative electrode active material is preferably 0.01 ⁇ m or more and 5 ⁇ m or less, more preferably 0.01 ⁇ m or more and 1 ⁇ m or less, and even more preferably 0.05 ⁇ m or more and 0.6 ⁇ m or less.
• the particle size (D50) is the volume average particle size measured with a laser particle size distribution analyzer. Having the particle size of the Si compound within the above range further suppresses the decrease in the initial capacity and initial efficiency of the battery due to surface oxidation of the Si compound. Additionally, the decrease in cycle characteristics due to the expansion and destruction of the Si compound due to the insertion of lithium ions during charging is further suppressed.
• the capacity and cycle characteristics of the battery are further optimized when it is made into a battery.
• the positive electrode active material contained in the electrode slurry of this embodiment is more preferably a positive electrode active material having an average particle size (D50) of 5 ⁇ m or less.
• Positive electrode active material having an average particle size (D50) of 5 ⁇ m or less tends to peel off from the current collector foil during electrode formation, and the electrode binder of this embodiment is highly effective in improving peel strength.
• the positive electrode active material may have at least one of a spinel structure and an olivine structure.
• the positive electrode active material with a spinel structure is an oxide containing Li and Mn.
• Elements contained in addition to Li, Mn, and O include elements from groups 2 to 15 of the periodic table.
• the aqueous medium contained in the electrode slurry may be, for example, one or more selected from the group consisting of water, 2-propanol (isopropyl alcohol), N-methylpyrrolidone, and dimethylformamide, with water being preferred.
• the electrode slurry may be produced by a production method including a mixing step in which the electrode binder of this embodiment, the electrode active material, the aqueous medium, and, if necessary, the conductive additive are mixed.
• the mixing may be performed by any known mixing method, and may involve the use of one or more machines selected from the group consisting of an agitator, a mixer, a kneader, and a kneader.
• the slurry obtained in the above mixing process is used as the electrode slurry of this embodiment, and by applying it to a current collector and drying it, an electrode containing this is obtained.
• LIBs equipped with electrodes containing the electrode binder can also be used as secondary batteries in electric vehicles, hybrid vehicles, vending machines, electric carts, load leveling energy storage systems, household energy storage devices, distributed power storage systems (built into stationary electrical appliances), and emergency power supply systems.
• Mw weight average molecular weight
• the measurement sample was prepared by forming the electrode binder on a copper foil as
• Example 1 A reactor equipped with a stirrer, thermometer, cooling tube, nitrogen gas inlet tube, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise to the reactor with stirring over a period of 3 hours, and after completion of the addition, polymerization was carried out at the same temperature for 6 hours. In other words, the polymerization time was 9 hours.
• the mixture was cooled to 50°C and diluted with 175.9 g of water to obtain a polymer having structural units (1), (2), and (3) as repeating units, in which R1 was a hydrogen atom, R2 was a hydrogen atom, R3 was a hydrogen atom, R4 was an ethylene group, n/m was 0.05, and m/l was 1.65, and in which the content of structural unit (1) was 3.1 mol%, the content of structural unit (2) was 60.3 mol%, and the content of structural unit (3) was 36.6 mol%, and this polymer was used as the electrode binder of this example.
• the Mw of the electrode binder in this example was 820,000.
• Example 2 A reactor equipped with a stirrer, thermometer, cooling tube, nitrogen gas inlet tube, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 7.9 g of 3-aminopropyltriethoxysilane, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise to the reactor with stirring over a period of 3 hours, and after completion of the addition, polymerization was carried out at the same temperature for 6 hours. In other words, the polymerization time was 9 hours.
• the mixture was cooled to 50°C and diluted with 228.8 g of water to obtain a polymer having the structural units (1), (2), (3), and (4) as repeating units, in which R1 is a hydrogen atom, R2 is a hydrogen atom, R3 is a hydrogen atom, R4 is an ethylene group, R5 is a hydrogen atom, R6 is a propylene group, R7 is an ethoxy group, R8 is an ethyl group, L is -NH-, n/m is 0.002, m/l is 1.65, and p/m is 0.05, and in which the content of the structural unit (1) was 0.1 mol%, the content of the structural unit (2) was 60.3 mol%, the content of the structural unit (3) was 36.5 mol%, and the content of the structural unit (4) was 3.1 mol%, and this polymer was used as the electrode binder of this example.
• the Mw of the electrode binder in this example was 740,000.
• Example 3 A reactor equipped with a stirrer, thermometer, cooling tube, nitrogen gas inlet tube, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 1.5 g of 3-aminopropyltriethoxysilane, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise to the reactor with stirring over a period of 3 hours, and after completion of the addition, polymerization was carried out at the same temperature for 6 hours. In other words, the polymerization time was 9 hours.
• the mixture was cooled to 50°C and diluted with 185.9 g of water to obtain a polymer having the structural units (1), (2), (3), and (4) as repeating units, in which R1 is a hydrogen atom, R2 is a hydrogen atom, R3 is a hydrogen atom, R4 is an ethylene group, R5 is a hydrogen atom, R6 is a propylene group, R7 is an ethoxy group, R8 is an ethyl group, L is -NH-, n/m is 0.04, m/l is 1.64, and p/m is 0.01, and in which the content of structural unit (1) was 2.6 mol%, the content of structural unit (2) was 60.2 mol%, the content of structural unit (3) was 36.6 mol%, and the content of structural unit (4) was 0.6 mol%, and this polymer was used as the electrode binder of this example.
• the Mw of the electrode binder in this example was 980,000.
• Example 4 A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet tube, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 1.0 g of 3-aminopropyltriethoxysilane, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise to the reactor with stirring over a period of 3 hours, and after completion of the addition, polymerization was carried out at the same temperature for 6 hours. In other words, the polymerization time was 9 hours.
• Example 5 A reactor equipped with a stirrer, thermometer, cooling tube, nitrogen gas inlet tube, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 0.5 g of 3-aminopropyltriethoxysilane, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise to the reactor with stirring over a period of 3 hours, and after completion of the addition, polymerization was carried out at the same temperature for 6 hours. In other words, the polymerization time was 9 hours.
• Example 6 A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet tube, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.3 g of sodium acrylate, 48.2 g of 2-hydroxyethyl acrylate, 0.5 g of 3-aminopropyltriethoxysilane, 0.5 g of 2-(dimethylamino)ethyl methacrylate, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise to the reactor with stirring over a period of 3 hours. After completion of the addition, the mixture was allowed to polymerize at the same temperature for 6 hours.
• the polymerization time was 9 hours.
• the mixture was cooled to 50°C and diluted with 178.6 g of water to obtain a polymer having the structural units (1), (2), (3), and (4) as repeating units, in which R 1 is a hydrogen atom, R 2 is a hydrogen atom, R 3 is a hydrogen atom, R 4 is an ethylene group, R 5 is a hydrogen atom, R 6 is a propylene group, R 7 is an ethoxy group, R 8 is an ethyl group, L is -NH-, n/m is 0.05, m/l is 1.65, and p/m is 0.003, and in which the content of the structural unit (1) was 3.0 mol%, the content of the structural unit (2) was 60.2 mol%, the content of the structural unit (3) was 36.4 mol%, and the content of the structural unit (4) was 0.2 mol%, and this polymer was used as the electrode binder of this example.
• Example 7 A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet tube, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.5 g of acrylic acid, 64.0 g of sodium acrylate, 47.9 g of 2-hydroxyethyl acrylate, 1.0 g of polyethylene glycol diacrylate, 0.4 g of potassium persulfate, and 300.0 g of water was added dropwise to the reactor with stirring over a period of 3 hours, and after completion of the addition, polymerization was carried out at the same temperature for 6 hours. In other words, the polymerization time was 9 hours.
• the mixture was cooled to 50°C and diluted with 206.2 g of water to obtain a polymer having structural units (1), structural units (2), and structural units (3) as repeating units, in which R1 was a hydrogen atom, R2 was a hydrogen atom, R3 was a hydrogen atom, R4 was an ethylene group, n/m was 0.05, and m/l was 1.65, and in which the content of structural unit (1) was 3.1 mol%, the content of structural unit (2) was 60.0 mol%, and the content of structural unit (3) was 36.3 mol%, and this polymer was used as the electrode binder of this example.
• Example 8 A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet tube, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise to the reactor over a period of 3 hours with stirring. After the addition was completed, 0.5 g of 3-glycidoxypropyltrimethoxysilane was added and the mixture was polymerized at the same temperature for 6 hours. In other words, the polymerization time was 9 hours.
• Example 9 A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet tube, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.3 g of sodium acrylate, 48.2 g of 2-hydroxyethyl acrylate, 0.5 g of 2-(dimethylamino)ethyl methacrylate, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise to the reactor with stirring over a period of 3 hours.
• Example 10 A reactor equipped with a stirrer, thermometer, cooling tube, nitrogen gas inlet tube, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 7.9 g of 3-aminopropyltriethoxysilane, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise to the reactor with stirring over a period of 3 hours, and after completion of the addition, polymerization was carried out at the same temperature for 12 hours. In other words, the polymerization time was 15 hours.
• the mixture was cooled to 50°C and neutralized with an aqueous solution in which 33.3 g of sodium hydroxide was dissolved in 341.3 g of water to obtain a polymer having the structural unit (1) and the structural unit (2) as repeating units, in which R1 is a hydrogen atom, R2 is a hydrogen atom, and n/m is 0.67, and in which the content of the structural unit (1) was 39.8 mol% and the content of the structural unit (2) was 60.2 mol%, and this polymer was used as the electrode binder of this comparative example.
• the Mw of the electrode binder of this comparative example was 510,000.
• a mixture was obtained by weighing and mixing 7 mass % of the electrode binder of each of the Examples and Comparative Examples, 92.5 mass % of the negative electrode active material obtained by mixing SiOC negative electrode active material and graphite at a mass ratio of 20:80, and 0.5 mass % of the conductive additive (acetylene black). Water was then added to the mixture in an amount 1.05 times the mass of the mixture, and the mixture was mixed for 10 minutes using a rotation/revolution mixer to prepare an electrode slurry.
• the conductive additive acetylene black
• the prepared electrode slurry was applied to a copper foil having a thickness of 15 ⁇ m using an applicator so that the solid content was 3 mg/ cm2 , and then dried in a stationary dryer at 110°C for 0.5 hours. After drying, a circle having a diameter of 14 mm was punched out and heat-treated in vacuum at 110°C for 3 hours to obtain a negative electrode for LIB.
• a half-cell consisting of a coin cell using metallic lithium as the counter electrode was prepared as the evaluation battery.
• the evaluation half-cell was prepared by stacking the negative electrode, a 19 mm diameter polypropylene separator, a 19 mm diameter glass filter, a gasket, a 16 mm diameter x 0.6 mm thick metallic lithium, a SUS metal plate, a SUS washer, and a coin battery lid in this order in a CR2032 type (20 mm diameter, 3.2 mm thickness) coin battery case in a glove box, and then screwing on the lid.
• the negative electrode, separator, and glass filter were immersed in an electrolyte solution before stacking and wetted with the electrolyte solution.
• the electrolyte solution used was a 1:1 mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio, containing 1.2 mol/L LiPF 6 and 2 vol% fluoroethylene carbonate as the electrolyte.
• the prepared positive electrode slurry was applied to a 20 ⁇ m thick aluminum foil using an applicator so that the solid content was 15 mg/ cm2 , dried at 100°C for 5 minutes in a stationary dryer, and further dried at 100°C for 12 hours in a vacuum. After that, pressure was applied in the electrode thickness direction using a roll press (manufactured by Thank Metals Co., Ltd.) to process the electrode to a density of 1.8 g/cc, thereby obtaining a positive electrode for LIB.
• the peel strength was determined by a tensile test using a tensile tester (Tensilon RTG-1210, manufactured by A&D Co., Ltd.) as the measuring device, and the peel strength of the sample was measured using a 180° peel method under the following conditions. Measurement temperature: 25°C
• Tensile speed 100 mm/min
• One side of a 20 mm wide double-sided tape manufactured by Nichiban Co., Ltd., product name: Nicetack
• was attached to a 1.5 mm thick polycarbonate substrate was attached to a 1.5 mm thick polycarbonate substrate, and the non-adhesive side of a substrate tape (single-sided tape: manufactured by Nitto Denko Corporation, polyester adhesive tape No.

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