Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
• • 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
• • 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
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
• • 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
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
• • 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

• the present invention relates to a binder composition for non-aqueous secondary battery electrodes, a slurry composition for non-aqueous secondary battery electrodes, electrodes for non-aqueous secondary batteries, and non-aqueous secondary batteries.
• Non-aqueous secondary batteries such as lithium-ion secondary batteries (hereinafter sometimes simply referred to as "secondary batteries") are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. For this reason, in recent years, improvements to battery components such as electrodes have been considered with the aim of further improving the performance of non-aqueous secondary batteries.
• An electrode used in a secondary battery typically comprises a current collector and an electrode mixture layer (positive electrode mixture layer or negative electrode mixture layer) formed on the current collector.
• This electrode mixture layer is formed, for example, by applying a slurry composition containing an electrode active material and a binder composition containing a binding agent onto the current collector and then drying the applied slurry composition.
• Patent Document 1 proposes a binder composition that contains an aromatic vinyl monomer unit, a conjugated diene monomer unit, and a hydrophilic monomer unit, and contains a polymer having a loss tangent tan ⁇ and a loss modulus G" within a predetermined range, as a binder composition capable of forming an electrode having excellent peel strength after exposure to high temperatures and a secondary battery having low internal resistance.
• Patent Document 2 proposes a binder composition that contains an ethylenically unsaturated carboxylic acid monomer unit, an aromatic vinyl monomer unit, and an aliphatic conjugated diene monomer unit, and has a degree of swelling in tetrahydrofuran and a tetrahydrofuran insoluble content within a predetermined numerical range, and a ratio of the viscosity at pH 8.0 to the viscosity at pH 3.0 when the solid content concentration is 30 mass% within a predetermined numerical range, as a binder composition for a non-aqueous secondary battery negative electrode capable of forming a negative electrode mixture layer having excellent peel resistance.
• the conventional binder compositions described above have room for improvement in terms of further reducing the internal resistance of secondary batteries and improving their high-temperature storage characteristics.
• an object of the present invention is to provide a binder composition for non-aqueous secondary battery electrodes and a slurry composition for non-aqueous secondary battery electrodes that are capable of forming a non-aqueous secondary battery having excellent high-temperature storage characteristics and low internal resistance.
• Another object of the present invention is to provide an electrode for a non-aqueous secondary battery, which is capable of forming a non-aqueous secondary battery having excellent high-temperature storage characteristics and low internal resistance. It is a further object of the present invention to provide a nonaqueous secondary battery which has excellent high-temperature storage characteristics and low internal resistance.
• the present inventors have conducted extensive research with the aim of solving the above problems.
• the present inventors have newly discovered that by using a binder composition for non-aqueous secondary battery electrodes that contains a particulate polymer including a polymer containing aromatic vinyl monomer units and conjugated diene monomer units, and water, and that has a loss tangent tan ⁇ value and gel content within a specified range, a non-aqueous secondary battery that has excellent high-temperature storage characteristics and low internal resistance can be obtained, and have completed the present invention.
• the present invention aims to solve the above problems, and [1] the binder composition for non-aqueous secondary battery electrodes of the present invention (hereinafter, sometimes simply abbreviated as "binder composition”) is a binder composition for non-aqueous secondary battery electrodes containing a particulate polymer and water, the particulate polymer contains a polymer containing an aromatic vinyl monomer unit and a conjugated diene monomer unit, the value of loss tangent tan ⁇ is 0.001 or more and less than 0.40, and the gel content is more than 75 mass% and 99.9 mass% or less.
• binder composition is a binder composition for non-aqueous secondary battery electrodes containing a particulate polymer and water, the particulate polymer contains a polymer containing an aromatic vinyl monomer unit and a conjugated diene monomer unit, the value of loss tangent tan ⁇ is 0.001 or more and less than 0.40, and the gel content is more than 75 mass% and 99.9
• a non-aqueous secondary battery having excellent high-temperature storage characteristics and low internal resistance can be obtained.
• the "monomer unit” of a polymer means “a repeating unit derived from the monomer contained in a polymer obtained by using the monomer.”
• the "loss tangent tan ⁇ " and “gel content” of the binder composition for a non-aqueous secondary battery electrode can be measured according to the method described in the Examples of this specification.
• the ratio (Da/Db) of the volume average particle diameter Da of the particulate polymer measured by a laser diffraction scattering method at a solid content concentration of 0.1% by mass to the average particle diameter Db of the particulate polymer measured by a dynamic light scattering method at a solid content concentration of 0.005% by mass is preferably 1.4 to 2.0. If the ratio (Da/Db) of the volume average particle diameter Da to the average particle diameter Db is equal to or greater than the lower limit, the high-temperature storage characteristics of the obtained non-aqueous secondary battery can be further improved.
• the cycle characteristics of the obtained non-aqueous secondary battery can be improved.
• the solid content concentration of the binder composition for a non-aqueous secondary battery electrode when measuring the "volume average particle diameter Da" and the "average particle diameter Db" can be adjusted by adding or removing water.
• the "volume average particle diameter Da" and the "average particle diameter Db" of the particulate polymer can be measured according to the method described in the examples of this specification.
• the binder composition for non-aqueous secondary battery electrodes described in [1] or [2] above preferably has a loss tangent tan ⁇ value of 0.15 or more. If the loss tangent tan ⁇ value is 0.15 or more, the high-temperature storage characteristics of the resulting non-aqueous secondary battery can be further improved and the internal resistance can be further reduced.
• the particulate polymer preferably contains a polymer A containing an aromatic vinyl monomer unit and a conjugated diene monomer unit, and a polymer B containing an aromatic vinyl monomer unit and a conjugated diene monomer unit and different from the polymer A. If the particulate polymer contains two or more types of polymers, the high-temperature storage characteristics of the obtained non-aqueous secondary battery can be further improved and the internal resistance can be further reduced.
• the term "polymer A and polymer B are different" means that they are different in at least one of their composition and properties.
• the particulate polymer preferably has a swelling degree in an electrolyte of 300% by mass or less. If the particulate polymer has a swelling degree in an electrolyte of 300% by mass or less, the output characteristics and cycle characteristics of the resulting non-aqueous secondary battery can be improved.
• the "electrolyte swelling degree" of the particulate polymer can be measured according to the method described in the Examples of this specification.
• the present invention also aims to solve the above problems, and [6] the slurry composition for non-aqueous secondary battery electrodes of the present invention (hereinafter sometimes simply abbreviated as "slurry composition") is characterized in that it contains an electrode active material and the binder composition for non-aqueous secondary battery electrodes described in any one of [1] to [5] above.
• slurry composition for non-aqueous secondary battery electrodes containing the binder composition for non-aqueous secondary battery electrodes described above, a non-aqueous secondary battery having excellent high-temperature storage characteristics and low internal resistance can be obtained.
• the electrode active material preferably contains a silicon-based negative electrode active material.
• the present invention aims to solve the above problems, and [8] the non-aqueous secondary battery electrode of the present invention (hereinafter sometimes simply abbreviated as "electrode”) is an electrode for a non-aqueous secondary battery comprising a current collector and an electrode mixture layer located on the current collector, characterized in that the electrode mixture layer is a layer formed from the slurry composition for a non-aqueous secondary battery electrode described in [6] or [7] above.
• electrode is an electrode for a non-aqueous secondary battery comprising a current collector and an electrode mixture layer located on the current collector, characterized in that the electrode mixture layer is a layer formed from the slurry composition for a non-aqueous secondary battery electrode described in [6] or [7] above.
• the present invention aims to solve the above problems, and provides a non-aqueous secondary battery according to [9] the present invention, which comprises a positive electrode, a negative electrode, a separator, and an electrolyte, and is characterized in that at least one of the positive electrode and the negative electrode is the non-aqueous secondary battery electrode described in [8] above.
• a non-aqueous secondary battery electrode described above for at least one of the positive electrode and the negative electrode, a non-aqueous secondary battery having excellent high-temperature storage characteristics and low internal resistance can be obtained.
• a binder composition for a non-aqueous secondary battery electrode and a slurry composition for a non-aqueous secondary battery electrode which are capable of forming a non-aqueous secondary battery having excellent high-temperature storage characteristics and low internal resistance. Furthermore, according to the present invention, it is possible to provide an electrode for a non-aqueous secondary battery, which makes it possible to form a non-aqueous secondary battery having excellent high-temperature storage characteristics and low internal resistance. Furthermore, according to the present invention, a nonaqueous secondary battery having excellent high-temperature storage characteristics and low internal resistance can be provided.
• the binder composition for non-aqueous secondary battery electrodes of the present invention can be used when preparing a slurry composition for non-aqueous secondary battery electrodes.
• the slurry composition for non-aqueous secondary battery electrodes prepared using the binder composition for non-aqueous secondary battery electrodes of the present invention can be used when forming electrodes (electrodes for non-aqueous secondary batteries) for non-aqueous secondary batteries such as lithium ion secondary batteries.
• the non-aqueous secondary battery of the present invention is characterized by using an electrode for non-aqueous secondary batteries formed using the slurry composition for non-aqueous secondary battery electrodes of the present invention.
• the binder composition for a non-aqueous secondary battery electrode and the slurry composition for a non-aqueous secondary battery electrode of the present invention can be particularly suitably used when forming a negative electrode for a non-aqueous secondary battery.
• the binder composition for a non-aqueous secondary battery electrode of the present invention contains a particulate polymer and water as a dispersion medium, and optionally contains other components that can be incorporated into an electrode of a secondary battery.
• the particulate polymer contains a polymer containing an aromatic vinyl monomer unit and a conjugated diene monomer unit.
• the binder composition for a non-aqueous secondary battery electrode of the present invention has a loss tangent tan ⁇ value of 0.001 or more and less than 0.40, and a gel content of more than 75 mass% and 99.9 mass% or less.
• the particulate polymer contains a polymer containing aromatic vinyl monomer units and conjugated diene monomer units, and the loss tangent tan ⁇ value and gel content of the binder composition are within the above ranges, so that the internal resistance of a secondary battery equipped with an electrode formed using the binder composition can be reduced while allowing the secondary battery to exhibit excellent high-temperature storage characteristics.
• the particulate polymer is a component that can function as a binder that holds components such as an electrode active material so as not to be detached from an electrode mixture layer in an electrode having an electrode mixture layer formed using a slurry composition containing a binder composition.
• the particulate polymer is required to contain a polymer containing an aromatic vinyl monomer unit and a conjugated diene monomer unit, and may optionally further contain other polymers (for example, a polymer that does not contain an aromatic vinyl monomer unit and a conjugated diene monomer unit, and a polymer that contains only one of an aromatic vinyl monomer unit and a conjugated diene monomer unit).
• the particulate polymer may contain only one type of polymer containing an aromatic vinyl monomer unit and a conjugated diene monomer unit, or may contain two or more types.
• the polymer contained in the particulate polymer is usually a water-insoluble polymer, and when 0.5 g of the polymer is dissolved in 100 g of water at a temperature of 25° C., the insoluble content may be 90 mass % or more.
• the polymer contains aromatic vinyl monomer units and conjugated diene monomer units, and may optionally contain other monomer units.
• Aromatic vinyl monomer unit examples include aromatic monovinyl compounds such as styrene, styrenesulfonic acid and its salts, ⁇ -methylstyrene, p-t-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. Among these, styrene and its derivatives are preferred, and styrene is more preferred. These can be used alone or in combination of two or more.
• the proportion of aromatic vinyl monomer units contained in the polymer is preferably 1% by mass or more, more preferably 3% by mass or more, and is preferably 60% by mass or less, and more preferably 50% by mass or less, when the amount of all monomer units in the polymer is 100% by mass.
• conjugated diene monomers capable of forming conjugated diene monomer units include aliphatic conjugated diene compounds having 4 or more carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among these, 1,3-butadiene and isoprene are preferred, and 1,3-butadiene is more preferred. These can be used alone or in combination of two or more. By forming the conjugated diene monomer units of the polymer using 1,3-butadiene, the dispersion stability and thermal stability of the resulting polymer can be improved.
• the proportion of conjugated diene monomer units contained in the polymer is preferably 25% by mass or more, more preferably 30% by mass or more, and is preferably 99% by mass or less, more preferably 95% by mass or less, when the amount of all monomer units in the polymer is 100% by mass.
• the other monomer units that can be contained in the polymer are not particularly limited, and examples thereof include an acidic group-containing monomer unit and an amide group-containing monomer unit.
• acidic group-containing monomers that can form acidic group-containing monomer units include carboxylic acid group-containing monomers, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers.
• Examples of the carboxylic acid group-containing monomer include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their derivatives.
• Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid.
• Examples of the monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, ⁇ -acetoxyacrylic acid, ⁇ -trans-aryloxyacrylic acid, and ⁇ -chloro- ⁇ -E-methoxyacrylic acid.
• the dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid.
• dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters such as nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate.
• acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride.
• carboxylic acid group-containing monomer an acid anhydride which generates a carboxylic acid group upon hydrolysis can also be used.
• sulfonic acid group-containing monomer examples include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and 2-acrylamide-2-methylpropanesulfonic acid.
• (meth)allyl means allyl and/or methallyl.
• examples of the phosphate group-containing monomer include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate.
• (meth)acryloyl means acryloyl and/or methacryloyl.
• acidic group-containing monomers can be used alone or in combination of two or more.
• carboxylic acid group-containing monomers are preferred, with acrylic acid, methacrylic acid, itaconic acid, maleic acid and fumaric acid being preferred, and acrylic acid, methacrylic acid and itaconic acid being more preferred.
• the proportion of acidic group-containing monomer units contained in the polymer is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, when the amount of all monomer units in the polymer is 100% by mass.
• amide group-containing monomers capable of forming amide group-containing monomer units include (meth)acrylamide, N-methylol(meth)acrylamide, dimethyl(meth)acrylamide, diethyl(meth)acrylamide, N-methoxymethyl(meth)acrylamide, and dimethylaminopropyl(meth)acrylamide.
• (meth)acrylamide is preferred, and acrylamide is more preferred. These can be used alone or in combination of two or more.
• (meth)acrylic means acrylic and/or methacrylic.
• the proportion of amide group-containing monomer units contained in the polymer is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, when the amount of all monomer units in the polymer is taken as 100% by mass.
• the glass transition point of the polymer is preferably ⁇ 100° C. or higher, more preferably ⁇ 90° C. or higher, and is preferably 30° C. or lower, and more preferably 10° C. or lower.
• the glass transition point of the polymer can be measured according to the method described in the Examples of this specification.
• the particulate polymer contained in the binder composition has a volume average particle diameter Da of preferably 50 nm or more, more preferably 100 nm or more, and preferably 200 nm or less, and more preferably 150 nm or less, when measured by a laser diffraction scattering method with the solid content concentration of the binder composition set to 0.1 mass %.
• the particulate polymer contained in the binder composition preferably has an average particle diameter Db of 150 nm or more, more preferably 200 nm or more, and more preferably 300 nm or less, and more preferably 250 nm or less, when measured by dynamic light scattering with the solid content concentration of the binder composition set to 0.005% by mass.
• the ratio (Da/Db) of the volume average particle diameter Da measured by the laser diffraction scattering method to the average particle diameter Db measured by the dynamic light scattering method is preferably 1.4 or more, more preferably 1.5 or more, even more preferably 1.6 or more, preferably 2.0 or less, more preferably 1.9 or less, and even more preferably 1.8 or less. If Da/Db is equal to or greater than the lower limit, the particulate polymer can cover the surface of the electrode active material well, and the high-temperature storage characteristics of the secondary battery can be further improved. If Da/Db is equal to or less than the upper limit, good binding strength is exhibited in the electrode mixture layer, and the cycle characteristics of the secondary battery can be further improved.
• the particulate polymer preferably has an electrolyte swelling degree of 110% by mass or more, more preferably 120% by mass or more, and preferably 300% by mass or less, more preferably 150% by mass or less, and even more preferably 140% by mass or less. If the electrolyte swelling degree of the particulate polymer is within the above range, the cell characteristics of the secondary battery can be improved.
• the volume average particle diameter Da, average particle diameter Db, and electrolyte swelling degree of the particulate polymer can be adjusted, for example, by changing the preparation conditions of the particulate polymer, the structure of the particulate polymer, and the composition of the polymer that constitutes the particulate polymer.
• the particulate polymer contained in the binder composition is not particularly limited, but preferably contains a polymer A containing an aromatic vinyl monomer unit and a conjugated diene monomer unit, and a polymer B containing an aromatic vinyl monomer unit and a conjugated diene monomer unit and different from the polymer A.
• the particulate polymer preferably contains particles containing the polymer A and particles containing the polymer B.
• the particles containing the polymer A and the particles containing the polymer B usually exist as separate particles in the binder composition without being composited.
• --Particles containing polymer A-- Polymer A contains aromatic vinyl monomer units and conjugated diene monomer units, and may optionally contain other monomer units.
• aromatic vinyl monomer units, conjugated diene monomer units, and other monomer units of polymer A are the same as those described above for the polymer contained in the particulate polymer, so a description thereof will be omitted here.
• polymer A preferably contains aromatic vinyl monomer units, conjugated diene monomer units, carboxylic acid group-containing monomer units, and amide group-containing monomer units, and more preferably contains styrene units, butadiene units, acrylic acid units, methacrylic acid units, and acrylamide units.
• the proportion of each monomer unit contained in polymer A is preferably as follows. That is, the proportion of aromatic vinyl monomer units in polymer A is preferably 40% by mass or more, more preferably 45% by mass or more, and is preferably 55% by mass or less, more preferably 50% by mass or less.
• the proportion of conjugated diene monomer units in polymer A is preferably 25% by mass or more, more preferably 30% by mass or more, and is preferably 40% by mass or less, more preferably 35% by mass or less.
• the proportion of carboxylic acid group-containing monomer units in polymer A is preferably 5% by mass or more, more preferably 10% by mass or more, and is preferably 20% by mass or less, more preferably 15% by mass or less.
• the proportion of amide group-containing monomer units in polymer A is preferably 1% by mass or more, more preferably 3% by mass or more, and is preferably 10% by mass or less, more preferably 7% by mass or less.
• the polymer A preferably has a higher glass transition point than the polymer B, and the glass transition point of the polymer A is preferably ⁇ 10° C. or higher, more preferably 0° C. or higher, and is preferably 30° C. or lower, and more preferably 10° C. or lower.
• the glass transition point of the polymer A can be measured by the method described in the Examples of this specification.
• the particles containing polymer A preferably have a volume average particle diameter Da of 100 nm or more, more preferably 130 nm or more, and more preferably 200 nm or less, and more preferably 150 nm or less, when measured by a laser diffraction scattering method in an aqueous dispersion having a solid content concentration of 0.1% by mass.
• the volume average particle diameter Da of the particles containing polymer A can be measured by the method described in the examples of this specification.
• the particles containing polymer A preferably have an average particle size Db of 200 nm or more, more preferably 220 nm or more, and more preferably 300 nm or less, and more preferably 250 nm or less, when measured by dynamic light scattering in an aqueous dispersion having a solid content concentration of 0.005% by mass.
• the average particle diameter Db of the particles containing polymer A can be measured by the method described in the Examples of this specification.
• the particle containing polymer A has a swelling degree in an electrolyte of preferably 110% by mass or more, more preferably 130% by mass or more, and preferably 150% by mass or less, and more preferably 140% by mass or less.
• the degree of swelling of the particles containing polymer A in an electrolyte solution can be measured by the method described in the examples of this specification.
• the particles containing polymer A preferably have a gel content of 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, and preferably 99.9% by mass or less, and more preferably 99% by mass or less. If the gel content is within the above range, the internal resistance of the secondary battery can be reduced. In the present invention, the gel content of the particles containing polymer A can be measured by the method described in the Examples of this specification.
• the particles containing polymer A preferably have a storage modulus of 2.00 MPa or more, more preferably 2.40 MPa or more, and even more preferably 2.60 MPa or more, and preferably 3.00 MPa or less, and more preferably 2.90 MPa or less. If the storage modulus of the particles containing polymer A is within the above range, the internal resistance of the secondary battery can be further reduced. In the present invention, the storage modulus of the particles containing polymer A can be measured by the method described in the Examples of this specification.
• the particles containing polymer A preferably have a loss modulus of 1.00 MPa or more, more preferably 1.20 MPa or more, and preferably 1.60 MPa or less, more preferably 1.50 MPa or less, and even more preferably 1.45 MPa or less. If the loss modulus of the particles containing polymer A is within the above range, the internal resistance of the secondary battery can be further reduced. In the present invention, the loss modulus of the particles containing polymer A can be measured by the method described in the Examples of this specification.
• the particles containing polymer A preferably have a larger loss tangent tan ⁇ value than the particles containing polymer B, and the loss tangent tan ⁇ value of the particles containing polymer A is preferably 0.40 or more, more preferably 0.45 or more, preferably 0.75 or less, more preferably 0.60 or less, and even more preferably 0.55 or less.
• the loss tangent tan ⁇ value of the particles containing polymer A is within the above range, the internal resistance of the secondary battery can be further reduced.
• the loss tangent tan ⁇ of the particles containing polymer A can be measured by the method described in the examples of this specification.
• the volume average particle diameter Da and average particle diameter Db of the particles containing polymer A can be adjusted, for example, by changing the preparation conditions of the particles containing polymer A.
• the glass transition temperature, electrolyte swelling degree, gel content, storage modulus, loss modulus, and loss tangent tan ⁇ of the particles containing polymer A can be adjusted, for example, by changing the preparation conditions of the particles containing polymer A, the structure of the particles containing polymer A, and the composition of polymer A.
• --Particles containing polymer B-- Polymer B contains aromatic vinyl monomer units and conjugated diene monomer units, and may optionally contain other monomer units.
• aromatic vinyl monomer units, conjugated diene monomer units, and other monomer units of polymer B are the same as those described above for the polymer contained in the particulate polymer, so a description thereof will be omitted here.
• polymer B preferably contains aromatic vinyl monomer units, conjugated diene monomer units, and carboxylic acid group-containing monomer units, and more preferably contains styrene units, butadiene units, and methacrylic acid units.
• the proportion of each monomer unit contained in polymer B is preferably as follows. That is, the proportion of aromatic vinyl monomer units in polymer B is preferably 10% by mass or more, more preferably 20% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less.
• the proportion of conjugated diene monomer units in polymer B is preferably 50% by mass or more, more preferably 70% by mass or more, and is preferably 90% by mass or less, more preferably 75% by mass or less.
• the proportion of carboxylic acid group-containing monomer units in polymer B is preferably 1 mass % or more, more preferably 2 mass % or more, and is preferably 5 mass % or less, more preferably 4 mass % or less.
• the glass transition point of the polymer B is preferably ⁇ 70° C. or higher, more preferably ⁇ 60° C. or higher, and is preferably ⁇ 30° C. or lower, and more preferably ⁇ 50° C. or lower.
• the glass transition point of the polymer B can be measured by the method described in the Examples of this specification.
• the particles containing polymer B preferably have a volume average particle diameter Da of 90 nm or more, more preferably 100 nm or more, and more preferably 130 nm or less, and more preferably 120 nm or less, when measured by a laser diffraction scattering method in an aqueous dispersion having a solid content concentration of 0.1% by mass.
• the volume average particle diameter Da of the particles containing polymer B can be measured by the method described in the examples of this specification.
• the particles containing polymer B preferably have an average particle size Db of 180 nm or more, more preferably 200 nm or more, and more preferably 230 nm or less, and more preferably 220 nm or less, when measured by dynamic light scattering in an aqueous dispersion having a solid content concentration of 0.005% by mass.
• the average particle diameter Db of the particles containing polymer B can be measured by the method described in the Examples of this specification.
• the particle containing polymer B has a swelling degree in an electrolyte of preferably 110% by mass or more, more preferably 120% by mass or more, and preferably 150% by mass or less, and more preferably 140% by mass or less.
• the degree of swelling of the particles containing polymer B in an electrolyte solution can be measured by the method described in the Examples of this specification.
• the particles containing polymer B preferably have a gel content of 70% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more, and preferably 99% by mass or less, and more preferably 95% by mass or less. If the gel content is within the above range, the internal resistance of the secondary battery can be reduced. In the present invention, the gel content of the particles containing polymer B can be measured by the method described in the Examples of this specification.
• the particles containing polymer B preferably have a storage modulus of 0.40 MPa or more, more preferably 0.45 MPa or more, and even more preferably 0.55 MPa or more, and preferably 0.70 MPa or less, and more preferably 0.60 MPa or less. If the storage modulus of the particles containing polymer B is within the above range, the internal resistance of the secondary battery can be further reduced. In the present invention, the storage modulus of the particles containing polymer B can be measured by the method described in the Examples of this specification.
• the particles containing polymer B preferably have a loss modulus of 0.01 MPa or more, more preferably 0.05 MPa or more, and preferably 0.07 MPa or less, and more preferably 0.06 MPa or less. If the loss modulus of the particles containing polymer B is within the above range, the internal resistance of the secondary battery can be further reduced. In the present invention, the loss modulus of the particles containing polymer B can be measured by the method described in the Examples of this specification.
• the particles containing polymer B preferably have a loss tangent tan ⁇ of 0.05 or more, more preferably 0.10 or more, and preferably 0.30 or less, more preferably 0.20 or less, and even more preferably 0.13 or less. If the loss tangent tan ⁇ of the particles containing polymer B is within the above range, the internal resistance of the secondary battery can be further reduced. In the present invention, the loss tangent tan ⁇ of the particles containing polymer B can be measured by the method described in the examples of this specification.
• the volume average particle diameter Da and the average particle diameter Db of the particles containing polymer B can be adjusted, for example, by changing the preparation conditions of the particles containing polymer B.
• the glass transition temperature, electrolyte swelling degree, gel content, storage modulus, loss modulus, and loss tangent tan ⁇ of the particles containing polymer B can be adjusted, for example, by changing the preparation conditions of the particles containing polymer B, the structure of the particles containing polymer B, and the composition of polymer B.
• the ratio of the particles containing polymer B to the total of the particles containing polymer A and the particles containing polymer B is preferably 1% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, preferably 50% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. If the ratio of the particles containing polymer B is equal to or more than the lower limit, the peel strength of the obtained electrode can be increased. Furthermore, if the ratio of the particles containing polymer B is equal to or less than the upper limit, the internal resistance of the secondary battery can be further reduced.
• the particulate polymer including the above-mentioned polymer can be polymerized according to a known polymerization method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, or an emulsion polymerization method.
• the polymerization reaction can be addition polymerization such as ionic polymerization, radical polymerization, or living radical polymerization.
• a molecular weight regulator chain transfer agent
• chain transfer agent chain transfer agent
• commonly used additives such as emulsifiers, dispersants, polymerization initiators, and polymerization aids may also be used. The amounts of these additives used may be the amounts commonly used.
• the binder composition of the present invention may contain components other than the above components (other components) within the scope of the present invention.
• the other components include an antioxidant, a defoamer, a dispersant, etc.
• the other components may be used alone or in combination of two or more kinds in any ratio.
• the binder composition must have a gel content of more than 75% by mass and not more than 99.9% by mass, preferably not less than 85% by mass, more preferably not less than 95% by mass, and preferably not more than 99% by mass. If the gel content is within the above range, the elution of the particulate polymer into the electrolyte solution is suppressed, and the internal resistance of the secondary battery can be reduced.
• the binder composition has a storage modulus of preferably 0.20 MPa or more, more preferably 0.50 MPa or more, and even more preferably 1.00 MPa or more, and preferably 3.00 MPa or less, and more preferably 2.50 MPa or less. If the storage modulus of the binder composition is within the above range, the internal resistance of the secondary battery can be further reduced. In the present invention, the storage modulus of the binder composition can be measured by the method described in the examples of this specification.
• the loss modulus of the binder composition is preferably 0.01 MPa or more, more preferably 0.10 MPa or more, and even more preferably 0.30 MPa or more, and is preferably 1.50 MPa or less, and more preferably 1.00 MPa or less. If the loss modulus of the binder composition is within the above range, the internal resistance of the secondary battery can be further reduced. In the present invention, the loss modulus of the binder composition can be measured by the method described in the examples of this specification.
• the binder composition must have a loss tangent tan ⁇ value of 0.001 or more and less than 0.40, preferably 0.10 or more, more preferably 0.24 or more, preferably 0.37 or less, more preferably 0.31 or less, and even more preferably 0.26 or less. If the loss tangent tan ⁇ value of the binder composition is equal to or greater than the lower limit, the particulate polymer can be appropriately spread on the surface of the electrode active material, and the high-temperature storage characteristics can be improved while suppressing an increase in the internal resistance of the secondary battery.
• the particulate polymer can be excessively coated on the surface of the electrode active material, suppressing an increase in the internal resistance of the secondary battery, and the high elasticity can accommodate the expansion and contraction of the electrode active material during charging and discharging, thereby improving the cycle characteristics.
• the gel content, storage modulus, loss modulus and loss tangent tan ⁇ of the binder composition can be adjusted, for example, by changing the composition and preparation conditions of the particulate polymer.
• the binder composition of the present invention is not particularly limited, and can be prepared by mixing the particulate polymer and other components that are optionally used in the presence of water.
• the binder composition is prepared using an aqueous dispersion of the particulate polymer, the water contained in the dispersion may be used as a dispersion medium for the binder composition as it is.
• the slurry composition for a non-aqueous secondary battery electrode of the present invention is a composition used for forming an electrode mixture layer, and contains an electrode active material and the binder composition for a non-aqueous secondary battery electrode of the present invention described above, and optionally further contains other components. That is, the slurry composition for a non-aqueous secondary battery electrode of the present invention usually contains an electrode active material, the particulate polymer described above, and water as a dispersion medium, and optionally further contains other components.
• the slurry composition of the present invention contains the binder composition described above, it is possible to prepare an electrode for a non-aqueous secondary battery that can form a non-aqueous secondary battery having excellent high-temperature storage characteristics and low internal resistance.
• the nonaqueous secondary battery electrode slurry composition is a lithium ion secondary battery negative electrode slurry composition
• the present invention is not limited to the following example.
• An electrode active material is a material that transfers electrons at an electrode of a secondary battery.
• a negative electrode active material for a lithium ion secondary battery a material that can absorb and release lithium is usually used.
• examples of negative electrode active materials for lithium ion secondary batteries include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials that are combinations of these.
• carbon-based negative electrode active material refers to an active material with carbon as the main skeleton that can insert (also called “dope") lithium.
• examples of carbon-based negative electrode active materials include carbonaceous materials and graphite materials.
• Examples of the carbonaceous material include graphitic carbon and non-graphitic carbon having a structure close to an amorphous structure, such as glassy carbon.
• graphitizable carbon include carbon materials made from tar pitch obtained from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber, and pyrolytic vapor-grown carbon fiber.
• non-graphitizable carbon include phenol resin baked body, polyacrylonitrile carbon fiber, pseudoisotropic carbon, furfuryl alcohol resin baked body (PFA), and hard carbon.
• examples of the graphite material include natural graphite and artificial graphite.
• examples of the artificial graphite include artificial graphite obtained by heat-treating carbon containing graphitizable carbon mainly at 2800°C or higher, graphitized MCMB obtained by heat-treating MCMB at 2000°C or higher, and graphitized mesophase pitch-based carbon fiber obtained by heat-treating mesophase pitch-based carbon fiber at 2000°C or higher.
• Metal-based negative electrode active materials are active materials that contain metals, and usually contain an element capable of inserting lithium in its structure, and have a theoretical electric capacity of 500 mAh/g or more per unit mass when lithium is inserted.
• metal-based active materials include lithium metal, elemental metals capable of forming lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.), and alloys thereof, as well as oxides, sulfides, nitrides, silicides, carbides, and phosphides thereof.
• silicon-containing active materials silicon-based negative electrode active materials
• silicon-based negative electrode active materials are preferred as metal-based negative electrode active materials.
• silicon-based negative electrode active materials examples include silicon (Si), alloys containing silicon, SiO, SiO x , composites of Si-containing materials and conductive carbon obtained by coating or compounding Si-containing materials with conductive carbon, etc. Note that these silicon-based negative electrode active materials may be used alone or in combination of two or more.
• the binder composition As the binder composition, the above-mentioned binder composition of the present invention can be used.
• the content of the above-mentioned predetermined particulate polymer in the slurry composition can be, for example, 0.5 parts by mass or more and 15 parts by mass or less in terms of solid content per 100 parts by mass of the electrode active material.
• Other components that can be added to the slurry composition are not particularly limited, and include the same components as those that can be added to the binder composition of the present invention.
• the slurry composition may further contain a conductive material such as carbon black. These components may be used alone or in combination of two or more in any ratio.
• the above-mentioned slurry composition can be prepared by mixing the above-mentioned components by a known mixing method, for example, using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or a Filmix.
• a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or a Filmix.
• the electrode of the present invention comprises an electrode mixture layer formed using the above-mentioned slurry composition of the present invention, and usually has a current collector and an electrode mixture layer formed on the current collector.
• the electrode mixture layer is usually a layer formed by drying the slurry composition of the present invention, and contains at least an electrode active material and a polymer derived from the above-mentioned particulate polymer, and optionally contains other components.
• the polymer derived from the above-mentioned particulate polymer may be in a particulate form (i.e., the particulate polymer may be included in the electrode mixture layer as it is), or may be in any other form.
• the electrode of the present invention is made using the slurry composition of the present invention, and therefore the secondary battery can exhibit excellent high-temperature storage characteristics while reducing the internal resistance of the secondary battery.
• the electrode of the present invention can be produced, for example, through (1) a step of applying a slurry composition onto a current collector (application step), (2) a step of drying the slurry composition applied onto the current collector to form a dried slurry (drying step), and (3) a step of pressing the dried slurry on the current collector (pressing step).
• the method of applying the slurry composition onto the current collector is not particularly limited, and any known method can be used.
• the application method can be a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like.
• the slurry composition can be applied to only one side of the current collector, or can be applied to both sides.
• the thickness of the slurry film on the current collector after application and before drying can be appropriately set according to the thickness of the electrode mixture layer to be obtained.
• the method for drying the slurry composition on the current collector is not particularly limited and may be a known method, for example, a drying method using warm air, hot air, or low-humidity air, a vacuum drying method, or a drying method using infrared rays, electron beams, etc.
• a drying method using warm air, hot air, or low-humidity air for example, a drying method using warm air, hot air, or low-humidity air, a vacuum drying method, or a drying method using infrared rays, electron beams, etc.
• the method for pressing the dried slurry on the current collector is not particularly limited, and can be performed using a known pressing device. Among them, pressing with a press roll (roll pressing) is preferred from the viewpoint of pressing the dried slurry quickly and efficiently.
• pressing with a press roll roll pressing
• the density of the electrode mixture layer can be increased and the adhesion between the electrode mixture layer and the current collector can be improved.
• the nonaqueous secondary battery of the present invention includes the electrode for a nonaqueous secondary battery of the present invention. More specifically, the nonaqueous secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolyte, and a separator, and uses the electrode for a nonaqueous secondary battery of the present invention as at least one of the positive electrode and the negative electrode, preferably the negative electrode. Since the nonaqueous secondary battery of the present invention includes the electrode for a nonaqueous secondary battery of the present invention, it has excellent high-temperature storage characteristics and low internal resistance. In addition, the following will be described as an example in which the secondary battery is a lithium ion secondary battery, but the present invention is not limited to the following example.
• the electrode for a secondary battery of the present invention is used as at least one of the positive electrode and the negative electrode. That is, the positive electrode of the lithium ion secondary battery may be the electrode of the present invention and the negative electrode may be another known negative electrode, the negative electrode of the lithium ion secondary battery may be the electrode of the present invention and the positive electrode may be another known positive electrode, or both the positive electrode and the negative electrode of the lithium ion secondary battery may be the electrodes of the present invention.
• a known electrode other than the secondary battery electrode of the present invention an electrode formed by forming an electrode mixture layer on a current collector using a known manufacturing method can be used.
• an organic electrolyte in which a supporting electrolyte is dissolved in an organic solvent is usually used.
• a lithium salt is used as the supporting electrolyte.
• the lithium salt for example, LiPF6 , LiAsF6 , LiBF4 , LiSbF6, LiAlCl4 , LiClO4 , CF3SO3Li , C4F9SO3Li , CF3COOLi , ( CF3CO) 2NLi , ( CF3SO2 ) 2NLi , ( C2F5SO2 )NLi, etc. are listed.
• LiPF6 , LiClO4 , and CF3SO3Li are preferred because they are easily dissolved in a solvent and show a high degree of dissociation .
• the electrolyte may be used alone or in combination of two or more.
• the lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.
• the organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte, but for example, in a lithium ion secondary battery, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC); esters such as ⁇ -butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; and the like are preferably used. A mixture of these solvents may also be used. Among them, carbonates are preferred because they have a high dielectric constant and a wide stable potential range. The concentration of the electrolyte in the electrolytic solution can be appropriately adjusted. Known additives may also be added to the electrolytic solution.
• DMC dimethyl carbonate
• EC ethylene carbonate
• the separator is not particularly limited, and for example, the separators described in JP 2012-204303 A can be used. Among these, a microporous film made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred, since it can reduce the thickness of the entire separator, thereby increasing the ratio of the electrode active material in the secondary battery and increasing the capacity per volume.
• a polyolefin resin polyethylene, polypropylene, polybutene, polyvinyl chloride
• the non-aqueous secondary battery of the present invention can be manufactured, for example, by stacking a positive electrode and a negative electrode with a separator therebetween, wrapping or folding the stack according to the shape of the battery as necessary, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the container. At least one of the positive electrode and the negative electrode is the electrode for the non-aqueous secondary battery of the present invention.
• a fuse an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary.
• the shape of the secondary battery may be, for example, a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, or any other type.
• the amounts of "%" and “parts” are by mass unless otherwise specified.
• the ratio of monomer units formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of that certain monomer to all monomers used in the polymerization of the polymer, unless otherwise specified.
• various evaluations and measurements were carried out as follows.
• the particle size distribution (volume basis) of the measurement sample was measured using a particle size distribution measurement device (manufactured by Shimadzu Corporation, product name "SALD-2300") using a laser diffraction scattering method as the measurement principle, in accordance with JIS Z8825, and the particle diameter (D50) at which the cumulative volume calculated from the small diameter side in the measured particle size distribution became 50% was defined as the average particle diameter Da.
• the measurement samples used were an aqueous dispersion of a polymer adjusted to a solid content concentration of 0.1% by mass, and a binder composition adjusted to a solid content concentration of 0.1% by mass.
• ⁇ Average particle diameter Db measured by dynamic light scattering method The particle size distribution of the measurement sample was measured using a particle size distribution measuring device (manufactured by Otsuka Electronics Co., Ltd., model "FPAR-1000") using the dynamic light scattering method as the measurement principle, and the particle diameter (D50) at which the cumulative frequency of the light scattering intensity calculated from the small diameter side in the measured particle size distribution was 50% was taken as the average particle diameter Db.
• FPAR-1000 particle size distribution measuring device
• the measurement conditions for the dynamic light scattering method were as follows. Dispersion medium: water Measurement temperature: 25°C Measured concentration (solid content): 0.005% by mass Scattering angle: 160° Light source laser wavelength: 632.8 nm ⁇ Glass transition temperature> A water dispersion of the polymer to be measured was dried to prepare a measurement sample.
• DSC differential scanning calorimetry
• the glass transition point was determined from the intersection between the baseline immediately before the endothermic peak of the DSC curve where the differential signal (DDSC) is 0.05 mW/min/mg or more appears, and the tangent of the DSC curve at the inflection point that first appears after the endothermic peak.
• DDSC differential signal
• a measurement sample aqueous dispersion of a polymer or a binder composition
• the solid content was 1.5 g.
• the sample was dried for 24 hours in an environment of 22 to 25 ° C., and further dried for 1 hour at 110 ° C. to obtain a film.
• the film was cut into 2.5 mm squares, and about 0.3 g was precisely weighed.
• the mass of the film piece obtained by cutting was designated as W0.
• the film piece was immersed in 80 mL of tetrahydrofuran (THF) at 25 ° C. for 24 hours.
• THF tetrahydrofuran
• the film piece was pulled out of THF and vacuum-dried at 105 ° C. for 3 hours, and the mass W1 of the film piece was measured.
• the gel content (amount insoluble in THF) was calculated according to the following formula.
• Electrolyte swelling rate (mass%) (W1/W0) ⁇ 100 ⁇ Storage modulus, loss modulus and loss tangent tan ⁇ >
• a measurement sample (aqueous dispersion of a polymer or a binder composition) was weighed out on a Teflon petri dish so that the thickness after drying would be 50 ⁇ m, and then vacuum dried at room temperature for 12 hours to obtain a polymer film.
• the storage modulus and loss modulus of the polymer film prepared above were measured at 20° C.
• the cellophane tape was fixed to a test stand. Then, one end of the current collector was pulled vertically upward at a pulling speed of 150 mm/min to measure the stress when peeled off. This measurement was performed three times, and the average value was calculated as the peel strength, which was evaluated according to the following criteria. The higher the peel strength, the greater the binding strength of the negative electrode composite layer to the current collector, i.e., the greater the adhesion strength.
• C Peel strength is less than 7 N/m ⁇ Cycle characteristics of secondary battery> The cycle characteristics were evaluated using the secondary batteries produced in the examples and comparative examples.
• the secondary battery was first left at rest for 6 hours at a temperature of 25°C. Then, in an environment at a temperature of 25°C, it was charged for 100 minutes by a constant current method of 0.1C. Then, in an environment at a temperature of 60°C, it was subjected to aging treatment for 12 hours. Then, in an environment at a temperature of 25°C, it was charged to a cell voltage of 4.20V by a constant current method of 0.5C, and discharged to a cell voltage of 2.75V, and the initial capacity C0 was measured. This charge and discharge was further repeated, and the capacity C1 after 100 cycles was measured. Then, the capacity retention rate C2 was calculated according to the following calculation formula.
• Capacity maintenance rate C2 (C1/C0) x 100
• the cycle characteristics were evaluated according to the following criteria: A larger capacity retention C2 value indicates better cycle characteristics.
• the IV resistance was measured using the secondary batteries produced in the examples and comparative examples. Specifically, first, the battery was conditioned by charging at a charge rate of 0.1C until the voltage reached 4.2V at a temperature of 25°C, pausing for 10 minutes, and then discharging CV at a discharge rate of 0.1C to 3.0V three times.
• the battery was charged to 3.75V at 1C (C is a value expressed as rated capacity (mA)/1 hour (h)) in a -10°C atmosphere, and then charged for 15 seconds and discharged for 15 seconds at 0.5C, 1.0C, 1.5C, and 2.0C with 3.75V as the center, and the battery voltage after 15 seconds on the charging side in each case was plotted against the current value, and the slope was determined as the IV resistance (charging IV resistance).
• the obtained IV resistance value ( ⁇ ) was evaluated according to the following criteria. The smaller the IV resistance value, the lower the internal resistance of the secondary battery and the better the low-temperature characteristics.
• IV resistance is 15 ⁇ or less
• High temperature storage characteristics of secondary batteries> The secondary battery thus prepared was charged to a cell voltage of 4.2 V by a constant current method of 0.5 C in an atmosphere of 25° C., and then discharged to 3.0 V to measure the initial discharge capacity C0. The secondary battery was then charged to a cell voltage of 4.2 V by a constant current method of 0.5 C in an atmosphere of 25° C. Then, the secondary battery was stored (high-temperature storage) in an atmosphere of 60° C. for 3 weeks.
• the capacity retention rate (%) (remaining capacity C1/initial discharge capacity C0) ⁇ 100 was calculated and evaluated according to the following criteria: A higher capacity retention rate indicates that the secondary battery has better high-temperature storage characteristics. A: Capacity retention rate is 90% or more. B: Capacity retention rate is 80% or more and less than 90%. C: Capacity retention rate is less than 80%.
• Example 1 Preparation of Binder Composition> [Preparation of particles containing polymer A] Into a 5 MPa pressure vessel A equipped with a stirrer, 2.1 parts of styrene as an aromatic vinyl monomer, 3.3 parts of 1,3-butadiene as a conjugated diene monomer, 0.1 parts of methacrylic acid as a carboxylic acid group-containing monomer, 0.23 parts of dodecyl diphenyl ether disulfonic acid sodium salt as an emulsifier, 15 parts of ion-exchanged water, and 0.02 parts of potassium persulfate as a polymerization initiator were placed to obtain a mixture A. The obtained mixture A was thoroughly stirred, and then heated to 57° C.
• the temperature of the content of the pressure-resistant vessel A after obtaining the seed particles was raised to 75° C., and the mixture B was added to the pressure-resistant vessel A over a period of 5 hours.
• the addition of 0.48 parts of potassium persulfate as a polymerization initiator to the heat-resistant vessel A was started to initiate polymerization. That is, the overall monomer composition was 48.7 parts of styrene, 32.3 parts of 1,3-butadiene, 14.2 parts of acrylic acid, 4.7 parts of acrylamide, and 0.1 part of methacrylic acid.
• the polymerization was continued until the polymerization conversion reached 96%.
• 3 parts of methacrylic acid as a carboxylic acid group-containing monomer and 37 parts of ion-exchanged water were continuously added to the same pressure vessel under stirring for forming the shell portion to continue polymerization.
• This aqueous dispersion was heated to 70°C, and when the polymerization conversion rate reached 97%, it was cooled to stop the reaction, and a polymer as a shell portion was formed on the outer surface of the core portion, to obtain a mixture containing polymer particles having a core-shell structure. Thereafter, the unreacted monomer was removed by heating and reduced pressure distillation.
• the obtained mixed solution was defoamed under reduced pressure to obtain a slurry composition for negative electrodes with good fluidity.
• a slurry composition for negative electrodes with good fluidity was obtained.
• the above-mentioned negative electrode slurry composition was applied to a copper foil (current collector) having a thickness of 16 ⁇ m with a comma coater so that the coating amount was 10 mg/cm 2.
• the copper foil coated with the negative electrode slurry composition was transported at a speed of 0.5 m/min in an oven at a temperature of 75° C. for 2 minutes and then in an oven at a temperature of 120° C. for 2 minutes, thereby drying the negative electrode slurry composition on the copper foil and obtaining a negative electrode raw material.
• the negative electrode raw material was rolled with a roll press to obtain a negative electrode having a negative electrode composite layer thickness of 80 ⁇ m.
• the peel strength of the obtained negative electrode was evaluated, and the results are shown in Table 1.
• a planetary mixer was charged with 96 parts of lithium nickel manganese cobalt oxide as a positive electrode active material, 2 parts of PVDF (polyvinylidene fluoride) as a binder for a positive electrode mixture layer in terms of solid content, 2 parts of acetylene black as a conductive material, and 20 parts of N-methylpyrrolidone as a solvent, and mixed to obtain a slurry composition for a positive electrode.
• PVDF polyvinylidene fluoride
• the obtained positive electrode slurry composition was applied to an aluminum foil (current collector) having a thickness of 16 ⁇ m using a comma coater so that the coating amount after drying was 24.5 mg/cm 2.
• the aluminum foil coated with the positive electrode slurry composition was conveyed at a speed of 0.5 m/min through an oven at a temperature of 60° C. for 2 minutes and then through an oven at a temperature of 120° C. for 2 minutes, thereby drying the positive electrode slurry composition on the aluminum foil and obtaining a positive electrode raw material.
• the positive electrode raw material was rolled with a roll press to obtain a positive electrode having a positive electrode composite layer having a thickness of 70 ⁇ m.
• a single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 ⁇ m; produced by a dry method; porosity 55%) was prepared. This separator was cut into a 5 cm ⁇ 5 cm square and used in the following secondary battery.
• Example 2 Except for the fact that, when preparing the binder composition, the aqueous dispersion of polymer A and the aqueous dispersion of polymer B were mixed so that the mass ratio of the solid contents (polymer A:polymer B) was 7:3 (Example 2) and 5:5 (Example 3), respectively, the binder composition, the negative electrode slurry composition, the negative electrode, the positive electrode, the separator, and the secondary battery were prepared in the same manner as in Example 1, and measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
• Examples 4 to 6 A binder composition, a slurry composition for negative electrode, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared in the same manner as in Examples 1 to 3, except that the amount of tert-dodecyl mercaptan used as a molecular weight modifier during preparation of the particles containing polymer A was changed to 0.3 parts, and further, after the entire addition of the mixture containing the monomer composition was completed (i.e., 5 hours after the start of polymerization), the mixture was heated to 90° C. without adding 0.5 parts of potassium persulfate and reacted for 4 hours, and measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
• Example 7 In the preparation of particles containing polymer A, the amount of tert-dodecyl mercaptan used as a molecular weight modifier was changed to 1.0 part, and the amount of potassium persulfate used as a polymerization initiator added simultaneously with mixture B was changed from 0.48 parts to 0.98 parts, and further, in the preparation of particles containing polymer B, the amount of ⁇ -methylstyrene dimer used as a chain transfer agent (molecular weight modifier) was changed to 0.5 parts, and the amount of potassium persulfate used as a polymerization initiator was changed to 0.5 parts.
• a binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared in the same manner as in Example 1, and measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
• Example 8 Except for using the binder composition prepared as follows, a binder composition, a slurry composition for negative electrode, a negative electrode, a positive electrode, a separator, and a secondary battery were produced in the same manner as in Example 1, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.
• Binder Composition First, in the first stage polymerization, 4 parts of styrene as an aromatic vinyl monomer for forming a core portion, 91 parts of 1,3-butadiene as a conjugated diene monomer, 100 parts of ion-exchanged water, 0.7 parts of dodecylbenzenesulfonic acid as an emulsifier, 0.1 parts of ⁇ -methylstyrene dimer as a chain transfer agent (molecular weight regulator), and 0.3 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer and thoroughly stirred. Thereafter, the mixture was heated to 60° C. to initiate polymerization.
• aqueous dispersion was heated to 70°C, and when the polymerization conversion rate reached 97%, it was cooled to stop the reaction, and a polymer was formed as the shell portion on the outer surface of the core portion, to obtain a mixture containing polymer particles having a core-shell structure. Thereafter, unreacted monomers were removed by heating and reduced pressure distillation. A 5% aqueous sodium hydroxide solution was added to the mixture containing the polymer particles, and the pH was adjusted to 7 to obtain an aqueous dispersion (binder composition) containing a polymer (particulate polymer).
• Comparative Example 3 Except for using the binder composition prepared as follows, a binder composition, a slurry composition for negative electrode, a negative electrode, a positive electrode, a separator, and a secondary battery were produced in the same manner as in Example 1, and measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
• Binder Composition Into the reactor, 150 parts of ion-exchanged water, 4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 65 parts of styrene as an aromatic vinyl monomer, 1.5 parts of acrylic acid and 3.5 parts of itaconic acid as carboxylic acid group-containing monomers, and 0.5 parts of t-dodecyl mercaptan as a molecular weight regulator were charged in this order. Next, the gas inside the reactor was replaced with nitrogen three times, and then 30 parts of 1,3-butadiene as a conjugated diene monomer was charged.
• Comparative Example 4 Except for using the binder composition prepared as follows, a binder composition, a slurry composition for negative electrode, a negative electrode, a positive electrode, a separator, and a secondary battery were produced in the same manner as in Example 1, and measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
• Binder Composition Into a 5 MPa pressure vessel A equipped with a stirrer, 1.93 parts of styrene as an aromatic vinyl monomer, 3.08 parts of 1,3-butadiene as a conjugated diene monomer, 0.15 parts of itaconic acid as a carboxylic acid group-containing monomer, 0.2 parts of sodium lauryl sulfate as an emulsifier, 20 parts of ion-exchanged water, and 0.03 parts of potassium persulfate as a polymerization initiator were placed, thoroughly stirred, and then heated to 60° C. to initiate polymerization. The mixture was allowed to react for 6 hours to obtain seed particles.
• a binder composition, a slurry composition for negative electrode, an aqueous electrode, a positive electrode, a separator, and a secondary battery were produced in the same manner as in Example 1, and measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
• a binder composition for a non-aqueous secondary battery electrode and a slurry composition for a non-aqueous secondary battery electrode which are capable of forming a non-aqueous secondary battery having excellent high-temperature storage characteristics and low internal resistance. Furthermore, according to the present invention, it is possible to provide an electrode for a non-aqueous secondary battery, which makes it possible to form a non-aqueous secondary battery having excellent high-temperature storage characteristics and low internal resistance. Furthermore, according to the present invention, a nonaqueous secondary battery having excellent high-temperature storage characteristics and low internal resistance can be provided.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Inorganic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Battery Electrode And Active Subsutance (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=94395045

Family Applications (1)

Country Status (2)

Citations (4)

• 2024
  • 2024-07-30 JP JP2025537455A patent/JPWO2025028541A1/ja active Pending
  • 2024-07-30 WO PCT/JP2024/027223 patent/WO2025028541A1/ja active Pending

Patent Citations (4)

Also Published As

Similar Documents

Legal Events