Classifications

• • 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 an aqueous composition for a positive electrode of a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery.
• Secondary batteries are batteries that can be repeatedly charged and discharged.
• secondary batteries In recent years, with growing interest in environmental issues, the use of secondary batteries is increasing not only in electronic devices such as mobile phones and laptops, but also in fields such as automobiles and aircraft.
• research is being actively conducted.
• lithium-ion batteries which are lightweight, small, and have a high energy density, have attracted attention from various industries and are being actively developed.
• Lithium ion batteries are mainly composed of a positive electrode, an electrolyte, a negative electrode, and a separator.
• the electrodes (positive electrode, negative electrode) are made by applying an electrode composition onto a current collector.
• the positive electrode composition used to form the positive electrode mainly contains a positive electrode active material (hereinafter sometimes simply referred to as "active material"), a conductive assistant, a binder, and a solvent.
• active material positive electrode active material
• a conductive assistant a conductive assistant
• binder a binder
• solvent N-methyl-2-pyrrolidone
• PVDF is (i) chemically and electrically stable
• NMP is a solvent that is stable over time and dissolves PVDF
• NCM nickel-cobalt-manganese
• aqueous positive electrode compositions and thickeners and binders that can be used in positive electrode compositions.
• examples have been disclosed in which celluloses, polycarboxylic acid compounds, and the like are used as the water-soluble polymer (see Patent Documents 1 and 2 below).
• Patent Documents 1 and 2 give examples of water-soluble polymers such as celluloses such as carboxymethyl cellulose (CMC), polyacrylic acid compounds, and compounds with a vinylpyrrolidone structure, and in practice, cellulose compounds are used.
• CMC carboxymethyl cellulose
• these compounds are not necessarily sufficient, and there is room for improvement.
• the present invention aims to provide an aqueous composition for use in a positive electrode of a lithium ion secondary battery, which is an aqueous composition and has excellent stability over time, as well as a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery that use the aqueous composition.
• ⁇ 2> Further comprising a water-soluble polymer (B) containing a structural unit having a carboxyl group (excluding those corresponding to the water-soluble polymer (A)); The aqueous composition for a positive electrode of a lithium ion secondary battery according to ⁇ 1>.
• the weight average molecular weight of the water-soluble polymer (A) is 50,000 or more and 5,000,000 or less.
• ⁇ 4> Further comprising a conductive assistant, ⁇ 1> The aqueous composition for a positive electrode of a lithium ion secondary battery according to any one of ⁇ 1> to ⁇ 3>.
• the content of the conductive assistant in the composition is 3.5% by mass or more and 10.0% by mass or less with respect to the total amount of non-volatile components in the composition;
• ⁇ 6> Further comprising a particulate polymer ⁇ 5>
• the particulate polymer contains a (meth)acrylic acid ester monomer.
• the conductive assistant When elements present on the surface of the conductive assistant are measured by X-ray photoelectron spectroscopy and the abundance ratio (mass%) of oxygen atoms and the abundance ratio (mass%) of carbon atoms are calculated based on peak areas, the abundance ratio of oxygen atoms on the surface of the conductive assistant is 0.30 mass% or more and 2.00 mass% or less, and the ratio (O/C) of the abundance ratio (mass%) of oxygen atoms to the abundance ratio (mass%) of carbon atoms is 0.0020 or more and 0.0250 or less, the particulate polymer contains a constituent unit derived from an ethylenically unsaturated carboxylic acid (salt), the content ratio of the structural units derived from the ethylenically unsaturated carboxylic acid (salt) is 0.10 mass% or more and 15.00 mass% or less in total with respect to the total amount of the particulate polymer; ⁇ 5>
• the particulate polymer contains a constituent unit derived from an ethylenically unsaturated carboxylic acid (salt), the content ratio of the structural units derived from the ethylenically unsaturated carboxylic acid (salt) is 0.10 mass% or more and 15.00 mass% or less in total with respect to the total amount of the particulate polymer;
• the aqueous composition for a positive electrode of a lithium ion secondary battery according to ⁇ 6> or ⁇ 7>.
• the particulate polymer contains a monobasic acid (salt) and/or a dibasic acid (salt), ⁇ 6> to ⁇ 9>, wherein the aqueous composition for a positive electrode of a lithium ion secondary battery is as described in any one of ⁇ 6> to ⁇ 9>.
• the value (O ⁇ COOH) obtained by multiplying the abundance ratio (mass%) of oxygen atoms on the surface of the conductive assistant by the content ratio (mass%) of the total amount of structural units derived from the ethylenically unsaturated carboxylic acid (salt) contained in the particulate polymer is 0.030 to 10.00;
• the ratio (O/bound COOH) of the abundance ratio (mass%) of oxygen atoms on the surface of the conductive assistant and the content ratio (bound COOH) of the monomer derived from the ethylenically unsaturated carboxylic acid (salt) bound to the particulate polymer relative to the total amount of the monomer derived from the ethylenically unsaturated carboxylic acid (salt) contained in the particulate polymer is 0.0050 to 0.1000;
• the particulate polymer contains a crosslinkable monomer. ⁇ 6> to ⁇ 12>.
• ⁇ 14> Further comprising a preservative ⁇ 14> The aqueous composition for a positive electrode of a lithium ion secondary battery according to any one of ⁇ 1> to ⁇ 13>.
• the active material is a lithium phosphate compound.
• a positive electrode for a lithium ion secondary battery comprising the aqueous composition for a positive electrode for a lithium ion secondary battery according to any one of ⁇ 1> to ⁇ 15>.
• a lithium ion secondary battery comprising the positive electrode for lithium ion secondary batteries according to ⁇ 16>.
• the present invention provides an aqueous composition for lithium ion secondary battery positive electrodes that is an aqueous composition and has excellent stability, as well as a lithium ion secondary battery positive electrode and a lithium ion secondary battery that use the aqueous composition.
• (meth)acrylic means “acrylic” and its corresponding “methacrylic.”
• to means that the numerical values on both ends are included as the upper limit and the lower limit.
• the aqueous composition for a positive electrode of a lithium ion secondary battery according to the first embodiment includes an active material and a water-soluble polymer (A) (hereinafter sometimes simply referred to as "water-soluble polymer (A)") containing a constituent unit corresponding to a monomer having a sulfonic acid group, and the total amount of the constituent units corresponding to the monomer having a sulfonic acid group in the water-soluble polymer (A) is 25 mass % or more and 100 mass % or less with respect to the total amount of the water-soluble polymer (A).
• the aqueous composition for a positive electrode of a lithium ion secondary battery according to the first embodiment may be referred to as the "aqueous composition for a positive electrode”.
• the "water-soluble polymer” in the first embodiment is intended to include a water-soluble copolymer, and has the same meaning as the “water-soluble (co)polymer” in the second to fourth embodiments described below.
• the "sulfonic acid group” in the first embodiment includes a sulfonate salt group, and has the same meaning as the “sulfonic acid (salt) group” in the second to fourth embodiments described later.
• the "structural unit corresponding to a monomer” in the first embodiment may also be referred to as a "structural unit derived from a monomer".
• the "water-soluble polymer (A) containing a structural unit corresponding to a monomer having a sulfonic acid group” in the first embodiment is synonymous with the "water-soluble (co)polymer (A) containing a structural unit derived from a monomer having a sulfonic acid (salt) group” in the second embodiment described later and the "water-soluble (co)polymer containing a structural unit derived from a monomer having a sulfonic acid (salt) group” in the third and fourth embodiments described later.
• the "water-soluble polymer (B) containing a structural unit having a carboxyl group (excluding those corresponding to the water-soluble polymer (A))" in the first embodiment is synonymous with the "water-soluble (co)polymer (B) containing a structural unit having a carboxyl group (excluding those corresponding to the water-soluble (co)polymer (A))” in the second embodiment described later.
• the "particulate polymer” in the first embodiment includes a particulate copolymer, and has the same meaning as the "particulate (co)polymer” in the second to fourth embodiments described later.
• the aqueous composition for positive electrodes of the first embodiment contains a water-soluble resin that contains a specific amount of sulfonic acid groups, which improves the stability of viscosity and hysteresis over time.
• a water-soluble resin that contains a specific amount of sulfonic acid groups, which improves the stability of viscosity and hysteresis over time.
• the aqueous composition for positive electrodes of the first embodiment is a slurry composition for a positive electrode of a lithium ion secondary battery, and contains an aqueous solvent as a dispersion medium in addition to an active material and a water-soluble polymer (A).
• the aqueous composition for positive electrodes of the first embodiment may further contain a binder, a conductive assistant, a preservative, etc.
• the active material used in the aqueous composition for a positive electrode of the first embodiment is a material that can be used as a positive electrode active material.
• the positive electrode active material is an electrode active material used in a positive electrode, and is a material that transfers electrons in the positive electrode of a lithium ion secondary battery.
• the active material of the first embodiment is not particularly limited, and examples thereof include lithium-containing composite metal oxides having a layered structure, lithium-containing composite metal oxides having a spinel structure, and lithium-containing composite metal oxides having an olivine structure.
• lithium-containing composite metal oxides having a layered structure examples include lithium-containing cobalt oxide (LiCoO 2 ), lithium-containing nickel oxide (LiNiO 2 ), lithium composite oxides of Co—Ni—Mn, lithium composite oxides of Ni—Mn—Al, and lithium composite oxides of Ni—Co—Al.
• lithium-containing composite metal oxides having a spinel structure examples include lithium manganate ( LiMn2O4 ) and Li[Mn3 /2M1 /2 ] O4 (where M is Cr, Fe, Co, Ni, Cu, etc.) in which part of the Mn in lithium manganate is replaced with another transition metal.
• lithium-containing composite metal oxides having an olivine structure examples include olivine - type lithium phosphate compounds represented by LiXMPO4 (wherein M represents at least one element selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, and Mo, and X represents a number satisfying 0 ⁇ X ⁇ 2).
• M represents at least one element selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, and Mo
• X represents a number satisfying 0 ⁇ X ⁇ 2
• Other examples include transition metal oxides, transition metal sulfides, and lithium-containing composite metal oxides of lithium and a transition metal.
• active materials there is no particular limitation, but from the viewpoints of long life, safety, and easy availability of the positive electrode for a lithium ion secondary battery, olivine-type lithium phosphate compounds are preferred, specifically LiFePO 4 (lithium iron phosphate), LiMnPO 4 (lithium manganese phosphate), LiMn (1-y) Fe y PO 4 (lithium manganese iron phosphate) (y represents a number satisfying 0 ⁇ y ⁇ 1) are preferred, and LiFePO 4 is more preferred.
• These active materials may be carbon-coated to enhance electronic conductivity.
• the particle diameter of the active material is expressed by the volumetric D50 particle diameter, and is not particularly limited, but in order to easily obtain an appropriate viscosity of the aqueous composition for the positive electrode and to improve the Li ion conductivity, it is preferably 0.6 ⁇ m or more and 8.0 ⁇ m or less, more preferably 0.65 ⁇ m or more and 7.0 ⁇ m or less, even more preferably 0.7 ⁇ m or more and 6.0 ⁇ m or less, and particularly preferably 0.75 ⁇ m or more and less than 5.0 ⁇ m.
• a laser light diffraction scattering type particle size analyzer (Microtrack MT3300EXII, manufactured by Microtrack Bell Co., Ltd.) was used to measure the 50% cumulative diameter d50 calculated from the particle size distribution measurement value of the positive electrode active material, and this was used as the average particle diameter.
• the content of the active material in the aqueous composition for the positive electrode is preferably 70% by mass or more and 99.5% by mass or less, more preferably 80% by mass or more and 97% by mass or less, and particularly preferably 85% by mass or more and 95% by mass or less, based on the total amount of non-volatile components in the composition, in order to obtain high capacity and high load characteristics in a lithium ion secondary battery using a positive electrode obtained using the aqueous composition for the positive electrode of the first embodiment.
• non-volatile components in the composition refers to the non-volatile components excluding volatile components such as water in the aqueous composition for the positive electrode, and refers to the components remaining after drying when the aqueous composition for the positive electrode is dried at 130°C under normal pressure for 1 hour.
• the aqueous composition for a positive electrode according to the first embodiment includes a water-soluble polymer (A) including a structural unit corresponding to a monomer having a sulfonic acid group.
• water-soluble refers to a polymer that is dissolved in water at 25° C. for 0.5 g. When dissolved, the insoluble content is less than 3.0% by mass. In the case where the solubility of the water-soluble polymer in water varies depending on the pH of the water, the water-soluble polymer becomes water-soluble. If there is a pH range, the polymer can be considered water soluble.
• structural unit corresponding to a monomer having a sulfonic acid group means a structural unit in a polymer having a structure corresponding to a monomer having a sulfonic acid group.
• a structural unit corresponding to a monomer having a sulfonic acid group may be referred to as a "sulfonic acid group-containing unit.”
• the "sulfonic acid group” is a group represented by "-SO 3 -R", where R may be a hydrogen atom, an alkali metal (Na, K, Li, etc.), or an ammonium (NH 3 ) salt.
• R may be a hydrogen atom, an alkali metal (Na, K, Li, etc.), or an ammonium (NH 3 ) salt.
• Examples of the sulfonic acid group in the first embodiment are not particularly limited, but include, for example, -SO 3 H, -SO 3 Na, -SO 3 K, -SO 3 Li, and -SO 3 NH 3 .
• the monomer having a sulfonic acid group is not particularly limited, and examples thereof include monomers in which one of the conjugated double bonds of diene compounds such as isoprene and butadiene is sulfonated; vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfoethyl methacrylate, sulfopropyl methacrylate, sulfobutyl methacrylate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and the like, and examples of the salts thereof include lithium salts, sodium salts, potassium salts, and ammonium salts.
• reactive emulsifiers having so-called sulfonic acid groups such as alkylaryl sulfosuccinates (e.g., Sanyo Chemical Industries, Ltd.'s “ELEMINOL (trademark) JS-2” and “ELEMINOL (trademark) JS-5"; Kao Corporation's “LATEMUL (trademark) S-120", “LATEMUL (trademark) S-180A”, and “LATEMUL (trademark) S-180”); polyoxyethylene alkylpropenyl phenyl ether sulfates (e.g., Daiichi Kogyo Seiyaku Co., Ltd.'s "Aqualon (trademark) HS-10” and “LATEMUL (trademark) S-180”);
• the polyoxyethylene sulfate include ⁇ -[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]- ⁇ -polyoxyethylene sulfate (for example, ADEKA
• styrene sulfonic acid vinyl sulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid, and lithium salts, sodium salts, potassium salts, and ammonium salts thereof are preferred, and styrene sulfonic acid, and lithium salts, sodium salts, potassium salts, and ammonium salts thereof are more preferred.
• the water-soluble polymer (A) may contain, in addition to the sulfonic acid group-containing unit, a structural unit corresponding to another polymerizable monomer (hereinafter, sometimes referred to as "other monomer").
• the other monomer is not particularly limited, but may include a polymerizable compound that does not contain a sulfonic acid group and contains a hydrophilic group other than a sulfonic acid group.
• Examples of other monomers include monomers having a carboxyl group such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, 2-acryloyloxyethyl succinic acid, and vinyl benzoic acid; monomers having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate; 3-allyloxy-2-hydroxypropane phosphoric acid, dioctyl-2-methacryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, monomethyl-2-methacryloyloxyethyl phosphate, dimethyl-2-methacryloyloxyethyl phosphate, monoethyl and monomers having a phosphate group such as mono-n-butyl-2-methacryloyloxyethyl
• examples of other monomers to be combined with the monomer containing a sulfonic acid group in the first embodiment are preferably acrylic acid, itaconic acid, fumaric acid, methacrylic acid, 2-hydroxyethyl (meth)acrylate, (meth)acrylonitrile, (meth)acrylamide, and styrene, more preferably acrylic acid, methacrylic acid, 2-hydroxyethyl (meth)acrylate, and (meth)acrylamide, and even more preferably methacrylic acid and 2-hydroxyethyl (meth)acrylate, from the viewpoint of increasing the stability over time of the viscosity and hysteresis of the aqueous composition for the positive electrode without impairing the water solubility.
• the other monomer one type from the above examples may be used alone, or two or more types may be used in combination.
• the total amount of sulfonic acid group-containing units in the water-soluble polymer (A) in the first embodiment is 25% by mass or more and 100% by mass or less, based on the total amount of the water-soluble polymer (A), from the viewpoint of stability over time of viscosity and hysteresis.
• the lower limit of the total amount of sulfonic acid group-containing units in the water-soluble polymer (A) in the first embodiment is more preferably 27% by mass or more, and even more preferably 29% by mass or more.
• the content of the structural unit corresponding to the other monomer in the water-soluble polymer (A) is preferably 75% by mass or less, more preferably 73% by mass or less, and particularly preferably 71% by mass or less, based on the total amount of the water-soluble polymer (A).
• the content of the water-soluble polymer (A) in the aqueous composition for a positive electrode is preferably from 0.5 mass % to 5.0 mass %, more preferably from 0.7 mass % to 4.5 mass %, and particularly preferably from 1.0 mass % to 4.0 mass %, relative to the total amount of non-volatile components in the composition.
• the pH of the water-soluble polymer (A) in the first embodiment is preferably 4.0 to 11.0, more preferably 4.5 to 10.7, and particularly preferably 5.0 to 10.5.
• the "pH of the water-soluble polymer” refers to the pH after adjusting the water-soluble polymer aqueous solution to 5% by mass solids with water.
• the pH can be adjusted with, for example, sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydroxide, sodium hydrogen carbonate, disodium hydrogen phosphate, amines such as monoethanolamine, dimethylethanolamine, triethanolamine, and triethylamine, and is preferably sodium hydroxide, potassium hydroxide, or lithium hydroxide, and more preferably sodium hydroxide or lithium hydroxide. These can be used alone or in combination.
• the weight average molecular weight of the water-soluble polymer (A) in the first embodiment is, from the viewpoints of viscosity of the aqueous composition for a positive electrode and ease of handling, preferably from 50,000 to 5,000,000, more preferably from 100,000 to 3,000,000, even more preferably from 200,000 to 1,000,000, and particularly preferably from 500,000 to 1,000,000.
• the weight average molecular weight of the water-soluble polymer (A) can be measured by the method described in the examples below, and can be appropriately adjusted by known means.
• the viscosity of the aqueous composition for the positive electrode in the first embodiment is preferably 300 mPa ⁇ s or more and 20,000 mPa ⁇ s or less, more preferably 500 mPa ⁇ s or more and 10,000 mPa ⁇ s or less, even more preferably 1,000 mPa ⁇ s or more and 8,000 mPa ⁇ s or less, and particularly preferably 1,000 mPa ⁇ s or more and 6,000 mPa ⁇ s or less.
• the water-soluble polymer (A) in the first embodiment may contain a preservative.
• a preservative for example, the ones described below can be used alone or in combination.
• the water-soluble polymer (A) in the first embodiment is not particularly limited, but can be produced, for example, by polymerizing a monomer composition containing the above-mentioned monomers in an aqueous solvent.
• the ratio (mass basis) of each monomer in the monomer composition can usually be the same as the ratio of the constituent units in the water-soluble polymer.
• aqueous solvents include those described below.
• the polymerization method of the water-soluble polymer (A) in the first embodiment is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization can be used.
• the polymerization method of the water-soluble polymer in the first embodiment can be any method such as ionic polymerization, radical polymerization, and living radical polymerization.
• a polymerization initiator, a molecular weight regulator, a chelating agent, a pH regulator, and the like can be appropriately added to produce the polymer.
• polymerization initiator examples include organic peroxides such as lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, and 3,3,5-trimethylhexanoyl peroxide, azo compounds such as ⁇ , ⁇ '-azobisisobutyronitrile and 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and persulfate compounds such as ammonium persulfate, potassium persulfate, and sodium persulfate.
• organic peroxides such as lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, and 3,3,5-trimethylhexanoyl peroxide
• azo compounds such as ⁇ , ⁇ '-azobisisobutyronitrile
• the polymerization temperature and polymerization time can be arbitrarily selected depending on the polymerization method and the type of polymerization initiator, etc. Usually, the polymerization temperature is about 30° C. or higher, and the polymerization time is about 0.5 to 30 hours.
• the aqueous composition for a positive electrode of the first embodiment may further contain, in addition to the water-soluble polymer (A), a water-soluble polymer (B) (excluding those corresponding to the water-soluble polymer (A)) containing a structural unit having a carboxyl group (hereinafter, may be simply referred to as "water-soluble polymer (B)").
• a water-soluble polymer (B) excluding those corresponding to the water-soluble polymer (A)) containing a structural unit having a carboxyl group
• water-soluble polymer (B) As the water-soluble polymer (B), the “water-soluble (co)polymer (B)" described in the second embodiment described later can be used.
• the aqueous composition for a positive electrode according to the first embodiment may contain an aqueous solvent as a dispersion medium.
• the aqueous solvent is not particularly limited as long as it is a solvent that can be used in the aqueous composition for the positive electrode, but for example, an aqueous solvent having a boiling point of 80° C. or higher at normal pressure is preferable.
• the aqueous solvent is not particularly limited, but examples thereof include water; alcohols such as ethyl alcohol, isopropyl alcohol, and normal propyl alcohol; glycol ethers such as propylene glycol monomethyl ether, methyl cellosolve, ethyl cellosolve, ethylene glycol tertiary butyl ether, butyl cellosolve, 3-methoxy-3-methyl-1-butanol, ethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and dipropylene glycol monomethyl ether; ketones such as diacetone alcohol and ⁇ -butyrolactone; and ethers such as 1,3-dioxolane, 1,4-dioxolane, and tetrahydrofuran.
• water is preferable from the viewpoint of ease of handling and ease of application to the aqueous composition for the positive electrode.
• the aqueous solvent may be
• the content of the dispersion medium in the aqueous composition for positive electrodes is preferably 35% by mass or more and 65% by mass or less, more preferably 37% by mass or more and 64% by mass or less, and particularly preferably 39% by mass or more and 63% by mass or less, based on the total amount in the composition, from the viewpoints of the stability of the viscosity and hysteresis of the aqueous composition for positive electrodes over time, and of making the thickness uniform during line coating.
• the aqueous composition for a positive electrode of the first embodiment may contain a binder.
• a binder a known binder that can be dispersed in an aqueous solvent and used in the aqueous composition for a positive electrode may be appropriately selected and used.
• the binder is not particularly limited, and examples thereof include particulate polymers that are water-insoluble and dispersed in water.
• the particulate polymers may be used alone or in combination of two or more kinds. By adding the particulate polymer, flexibility is imparted to the positive electrode, and an improvement in yield is expected.
• the particulate polymer may be, for example, a polymer having a specific structural unit.
• the structural units of the particulate polymer are not particularly limited, but may include structural units derived from the following monomers: For example, (meth)acrylic acid ester monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, octadecyl (meth)acrylate, and tetradecyl meth)acrylate; aromatic vinyl monomers such as styrene and vinyl naphthalene; nitrile group-containing monomers such as acrylonitrile; aromatic divinyl monomers such as divinylbenzene; polyalkylene glycol mono
• the above-mentioned monomers having a carboxyl group, monomers having a phosphoric acid group, and monomers having a sulfonic acid group may be salts of the carboxyl group, phosphoric acid group, and sulfonic acid group, for example, lithium salts, sodium salts, potassium salts, and ammonium salts of the carboxyl group, phosphoric acid group, and sulfonic acid group.
• the other monomers one of the above-mentioned examples may be used alone, or two or more of them may be used in combination.
• the particulate polymer may further contain a crosslinkable monomer.
• the crosslinkable monomer is not particularly limited, and may be a crosslinkable group-containing structural unit among the structural units of the particulate polymer exemplified above, and may be, for example, a structural unit derived from the following monomers: For example, alkylene glycol di(meth)acrylate monomers such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 1,9-nonanediol di(meth)acrylate; trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythri
• the average particle size of the binder is not particularly limited, but from the viewpoint of the strength and flexibility of the positive electrode obtained by using the aqueous composition for a positive electrode, it is preferably 50 nm or more and 1000 nm or less, more preferably 80 nm or more and 700 nm or less, even more preferably 100 nm or more and 500 nm or less, and particularly preferably 130 nm or more and 400 nm or less.
• the average particle size of the binder can be measured by the method described in the examples below, and can be appropriately adjusted by known means.
• the content of the binder (particulate polymer) in the aqueous composition for the positive electrode is preferably 0.5% by mass or more and 10.0% by mass or less, more preferably 1.0% by mass or more and 9.0% by mass or less, and particularly preferably 1.5% by mass or more and 7.0% by mass or less, based on the total amount of non-volatile components in the composition.
• the pH of the binder (particulate polymer) dispersion in the first embodiment is preferably 4.0 to 11.0, more preferably 5.0 to 10.0, and particularly preferably 5.5 to 9.5, from the viewpoint of storage stability of the binder dispersion.
• the glass transition temperature of the particulate polymer in the first embodiment is preferably ⁇ 75° C. or higher, more preferably ⁇ 70° C. or higher, particularly preferably ⁇ 65° C. or higher, and is preferably 50° C. or lower, more preferably 40° C. or lower, even more preferably 35° C. or lower, particularly preferably 30° C. or lower, from the viewpoints of the flexibility and windability of the electrode, and the binding property between the electrode active material layer and the current collector.
• the glass transition temperature of the particulate polymer can be adjusted by combining various monomers.
• the glass transition temperature is obtained by measuring with a differential scanning calorimeter (DSC) in accordance with ASTM D3418-15.
• a DDSC curve is obtained by differentiating the DSC curve.
• the glass transition temperature obtained from the peak corresponding to the temperature range in which the slope of the DSC curve is maximum is the glass transition temperature in this specification.
• the binder (particulate polymer) dispersion in the first embodiment is not particularly limited, and can be prepared, for example, by emulsion polymerization or suspension polymerization using raw material monomers, or by dispersing a solution-polymerized copolymer in water and removing the solvent.
• Appropriate seed particles can be used when polymerizing the monomers, and the seed particles can also be obtained by normal emulsion polymerization.
• the binder (particulate polymer) dispersion can be produced by appropriately using a polymerization initiator, a reducing agent, a chain transfer agent, a chelating agent, a pH adjuster, an emulsifier, a preservative, an antifoaming agent, etc. in an aqueous medium.
• a polymerization initiator e.g., a polymerization initiator, a reducing agent, a chain transfer agent, a chelating agent, a pH adjuster, an emulsifier, a preservative, an antifoaming agent, etc.
• a aqueous dispersion medium can be used as the aqueous medium.
• the emulsifier is not particularly limited, but for example, anionic surfactants, nonionic surfactants, amphoteric surfactants, reactive surfactants, etc. can be used alone or in combination of two or more.
• Anionic surfactants include, but are not limited to, non-reactive alkyl sulfates, polyoxyethylene alkyl ether sulfate salts, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyl sulfosuccinates, alkyldiphenyl ether disulfonates, naphthalene sulfonate-formaldehyde condensates, polyoxyethylene polycyclic phenyl ether sulfate salts, polyoxyethylene distyrenated phenyl ether sulfate salts, fatty acid salts, alkyl phosphates, polyoxyethylene alkyl phenyl ether sulfate salts, etc.
• Nonionic surfactants include, but are not limited to, polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene distyrenated phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, alkyl alkanolamides, polyoxyethylene alkyl phenyl ethers, etc.
• amphoteric surfactants examples include betaines such as lauryl betaine and stearyl betaine, and amino acid surfactants such as lauryl- ⁇ -alanine, stearyl- ⁇ -alanine, and lauryl di(aminoethyl)glycine.
• the reactive surfactant is not particularly limited, but is preferably, for example, an ethylenically unsaturated monomer having a sulfonic acid group, a sulfonate group, or a sulfate ester group, or a salt thereof, and is preferably a compound having a sulfonic acid group or a group which is an ammonium salt or an alkali metal salt thereof (an ammonium sulfonate group, or an alkali metal sulfonate group).
• alkylaryl sulfosuccinates e.g., Sanyo Chemical Industries, Ltd.'s "ELEMINOL (trademark) JS-2” and “ELEMINOL (trademark) JS-5"; Kao Corporation's “LATEMUL (trademark) S-120", “LATEMUL (trademark) S-180A”, and “LATEMUL (trademark) S-180”); polyoxyethylene alkylpropenylphenyl ether sulfates (e.g., Daiichi Kogyo Seiyaku Co., Ltd.'s "AQUALON (trademark) HS-10” and “AQUALON (trademark) HS-1025”); ⁇ -[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]- ⁇ -polyoxyethylene sulfates (e.g., Asahi Denka Kogyo Co., Ltd.'s "ADEKA REASOAP (trademark) SE-1025N”);
• the amount of the emulsifier used is preferably 0.01% by mass or more and 5.0% by mass or less, more preferably 0.05% by mass or more and 3.0% by mass or less, even more preferably 0.1% by mass or more and 2.0% by mass or less, and most preferably 0.15% by mass or more and 1.0% by mass or less, based on 100% by mass of the total monomers.
• the emulsifier may be used alone or in combination of two or more kinds.
• the polymerization initiator is not particularly limited, and examples thereof include water-soluble polymerization initiators such as sodium persulfate, potassium persulfate, ammonium persulfate, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride; oil-soluble polymerization initiators such as benzoyl peroxide, lauryl peroxide, and t-butyl peroxybenzoate; and redox polymerization initiators in combination with reducing agents such as sodium sulfite, ascorbic acid or a salt thereof, erythorbic acid or a salt thereof, and Rongalit, which can be used alone or in combination.
• water-soluble polymerization initiators such as sodium persulfate, potassium persulfate, ammonium persulfate, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride
• oil-soluble polymerization initiators such as benzoyl peroxide, lauryl peroxide, and t-but
• chain transfer agent examples include mercaptan-based chain transfer agents such as n-butyl mercaptan, t-butyl mercaptan, t-dodecyl mercaptan, n-octyl mercaptan, and n-lauryl mercaptan; dimers of nucleus-substituted ⁇ -methylstyrene such as ⁇ -methylstyrene dimer; disulfides such as tetramethyl thiuradium disulfide and tetraethyl thiuradium disulfide; halogenated derivatives of hydrocarbons such as carbon tetrachloride and carbon tetrabromide; and 2-ethylhexyl thioglycolate.
• mercaptan-based chain transfer agents such as n-butyl mercaptan, t-butyl mercaptan, t-dodecyl mercapt
• sodium ethylenediaminetetraacetate, pentasodium diethylenetriaminepentaacetate, etc. can be used.
• pH adjusters include sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydroxide, sodium hydrogen carbonate, disodium hydrogen phosphate, and amines such as monoethanolamine, dimethylethanolamine, triethanolamine, and triethylamine.
• Sodium hydroxide, potassium hydroxide, and lithium hydroxide are preferred, and sodium hydroxide and lithium hydroxide are more preferred. These can be used alone or in combination.
• preservatives include isothiazoline compounds, phenols and their alkali metal salts, chlorinated quinones, nitro group-containing compounds, amines, amides, iodine-containing compounds, thiazoles, thiocyanates, etc., such as 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 1,2-benzisothiazolin-3-one, 2,2-dibromo-3-nitrilopropionamide, 2-n-octyl 4-isothiazolin-3-one, 2-bromo-2-nitropropane-1,3-diol, 2,2-dibromo-2-nitroethanol, etc.
• defoaming agent examples include mineral oil-based defoaming agents, polyether-based defoaming agents, silicone-based defoaming agents, and emulsion-based defoaming agents.
• mineral oil-based defoaming agents examples include mineral oil-based defoaming agents, polyether-based defoaming agents, silicone-based defoaming agents, and emulsion-based defoaming agents.
• NOPTAM 777F manufactured by San Nopco
• ADEKA CATE B-925 ADEKA CATE B-940
• ADEKA CATE B-556 manufactured by ADEKA Corporation
• the aqueous composition for a positive electrode of the first embodiment may contain a conductive assistant.
• the conductive assistant has a role of improving electrical contact between active materials.
• the aqueous composition for a positive electrode of the first embodiment can improve the discharge rate characteristics, etc. of a lithium ion secondary battery.
• the conductive assistant in the first embodiment is not particularly limited, but may be appropriately selected from known conductive assistants such as carbon black, furnace black, acetylene black, ketjen black, graphite, vapor-grown carbon fiber, carbon nanotubes, and other conductive carbons.
• One type of conductive assistant may be used alone, or two or more types may be used in any combination at any ratio.
• the content of the conductive additive in the aqueous composition for the positive electrode is preferably 3.5% by mass or more and 10.0% by mass or less, more preferably 3.6% by mass or more and 9.0% by mass or less, even more preferably 3.8% by mass or more and 8.0% by mass or less, and particularly preferably 4.1% by mass or more and 7.0% by mass or less, based on the total amount of non-volatile components in the composition.
• the positive electrode aqueous composition of the first embodiment includes a conductive assistant and a particulate polymer
• the abundance ratio of oxygen atoms on the surface of the conductive assistant may be 0.30 mass% or more and 2.00 mass% or less
• the ratio (O/C) of the abundance ratio (mass%) of atoms to the abundance ratio (mass%) of carbon atoms may be 0.0020 or more and 0.0250 or less
• the particulate polymer may include a structural unit derived from an ethylenically unsaturated carboxylic acid (salt), and the content ratio of the structural unit derived from an ethylenically unsaturated carboxylic acid (salt) may be 0.10 mass% or more and 15.00 mass% or less in total with
• the particulate polymer may contain a constituent unit derived from an ethylenically unsaturated carboxylic acid (salt), and the content ratio of the constituent unit derived from an ethylenically unsaturated carboxylic acid (salt) may be 0.10 mass% or more and 15.00 mass% or less in total with respect to the total amount of the particulate polymer.
• the particulate polymer may be a "particulate (co)polymer" described in the second or fourth embodiment described below.
• the particulate polymer may contain a monobasic acid (salt) and/or a dibasic acid (salt).
• a monobasic acid (salt) and dibasic acid (salt) As the monobasic acid (salt) and dibasic acid (salt), the "monobasic acid (salt)" and “dibasic acid (salt)” described in the fourth embodiment described later can be used.
• the aqueous composition for the positive electrode in the first embodiment may have a value (O x COOH) obtained by multiplying the proportion (mass%) of oxygen atoms present on the surface of the conductive assistant by the proportion (mass%) of the total amount of constituent units derived from ethylenically unsaturated carboxylic acid (salt) contained in the particulate polymer, which is 0.030 to 10.00.
• the conductive assistant and particulate polymer may be the "conductive assistant" described in the fourth embodiment described below.
• the positive electrode aqueous system composition of the first embodiment may have a ratio (O/bound COOH) of the content ratio (mass%) of the oxygen atoms on the surface of the conductive assistant and the content ratio (bound COOH) of the monomer derived from the ethylenically unsaturated carboxylic acid (salt) bound to the particulate polymer to the total amount of the monomer derived from the ethylenically unsaturated carboxylic acid (salt) contained in the particulate polymer of 0.0050 to 0.1000.
• the conductive assistant and particulate polymer may use the "conductive assistant" described in the fourth embodiment described below.
• the aqueous composition for a positive electrode of the first embodiment may contain a preservative.
• the preservative may be contained in the water-soluble polymer (A) as described above.
• the aqueous composition for a positive electrode of the first embodiment can further increase the stability over time of viscosity and hysteresis.
• the preservative is not particularly limited, but examples thereof include isothiazoline compounds, phenols and their alkali metal salts, chlorinated quinones, nitro group-containing compounds, amines, amides, iodine-containing compounds, thiazoles, and thiocyanates, and examples thereof include 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 1,2-benzisothiazolin-3-one, 2,2-dibromo-3-nitrilopropionamide, 2-n-octyl 4-isothiazolin-3-one, 2-bromo-2-nitropropane-1,3-diol, and 2,2-dibromo-2-nitroethanol.
• the content of the preservative in the aqueous composition for the positive electrode is preferably 0.00001% by mass or more and 1% by mass or less, more preferably 0.00002% by mass or more and 0.5% by mass or less, and particularly preferably 0.00004% by mass or more and 0.1% by mass or less, based on the total amount of non-volatile components in the composition, from the viewpoints of the stability of viscosity and hysteresis over time, and the adhesive strength of the electrode.
• the positive electrode for lithium ion secondary batteries of the first embodiment includes the aqueous composition for positive electrodes of the first embodiment.
• the positive electrode for lithium ion secondary batteries of the first embodiment can be manufactured using the aqueous composition for positive electrodes of the first embodiment.
• the manufacturing method for the positive electrode for lithium ion secondary batteries of the first embodiment is not particularly limited, but for example, the aqueous composition for positive electrodes of the first embodiment can be applied to a current collector for positive electrodes, heated, and dried to manufacture a positive electrode for lithium ion secondary batteries.
• the positive electrode current collector is not particularly limited, but for example, aluminum foil is used.
• the method of applying the aqueous composition for positive electrodes of the first embodiment to the positive electrode current collector is not particularly limited, and any coater head can be used, such as a reverse roll coater, a comma bar coater, a gravure coater, or an air knife coater.
• the method of drying the coating film of the aqueous composition for positive electrodes of the first embodiment is not particularly limited, and can be, for example, left to dry, blown dry, hot air dry, an infrared heater, or a far-infrared heater.
• the drying temperature of the coating film of the aqueous composition for positive electrodes of the first embodiment is not particularly limited, and can be, for example, 60°C to 150°C.
• the lithium ion secondary battery of the first embodiment includes the positive electrode for the lithium ion secondary battery of the first embodiment.
• Typical components of the lithium ion secondary battery of the first embodiment include a negative electrode, a negative electrode current collector, a positive electrode, a positive electrode current collector, a separator, and an electrolyte, and the lithium ion secondary battery of the first embodiment may be one in which at least the positive electrode, which is a main component thereof, is obtained using an aqueous composition for a positive electrode.
• the method for manufacturing the lithium ion secondary battery of the first embodiment is not particularly limited, but for example, a method of opposing the negative electrode and the positive electrode of the first embodiment via a separator, injecting an electrolyte solution, and sealing the battery can be mentioned.
• the negative electrode and the electrolyte solution are not particularly limited, and can be appropriately selected and used from those applicable to the lithium ion secondary battery.
• the electrolyte solution can be one in which an electrolyte such as LiClO 4 , LiBF 4 , or LiPF 6 is dissolved in an organic solvent.
• the organic solvent is not particularly limited, but for example, ethers, ketones, lactones, nitriles, amines, amides, carbonates, chlorinated hydrocarbons, etc.
• the aqueous composition for a lithium ion secondary battery positive electrode according to the first embodiment may further contain a water-soluble polymer (B) (excluding those corresponding to the water-soluble polymer (A)) containing a structural unit having a carboxyl group.
• the aqueous composition for a positive electrode of a lithium ion secondary battery according to the second embodiment includes an active material, a water-soluble (co)polymer (A) including a structural unit derived from a monomer having a sulfonic acid (salt) group, and a water-soluble (co)polymer (B) including a structural unit having a carboxyl group (excluding those corresponding to the water-soluble (co)polymer (A)), in which the content of the structural unit derived from the monomer having a sulfonic acid (salt) group is 25 mass % or more and 100 mass % or less with respect to the total solid content of the water-soluble (co)polymer (A).
• the following description of the water-soluble polymer (B) can be applied directly to the aqueous composition for a positive electrode of the first embodiment.
• the aqueous composition for a positive electrode of a lithium ion secondary battery of the second embodiment has the same configuration as those described in the other embodiments, except for the water-soluble (co)polymer (B) described below.
• the slurry composition described in JP 2014-165108 A is said to be able to achieve both high levels of cycle characteristics and adhesion.
• the inventors' investigations revealed that, depending on the combination of specific components in the slurry composition, the aggregation of the components in the slurry composition can cause viscosity changes over time, and when using the slurry to manufacture a positive electrode for a lithium-ion secondary battery, there are issues such as insufficient electrode adhesion.
• the aqueous composition for positive electrodes of the first and second embodiments described above which contains the water-soluble (co)polymer (B), has excellent viscosity stability over time and electrode adhesion, and it is possible to provide a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery using the composition.
• the aqueous composition for a positive electrode according to the second embodiment includes a water-soluble (co)polymer (B) containing a structural unit having a carboxyl group (however, the water-soluble (co)polymer (B) corresponds to the water-soluble (co)polymer (A).
• the water-soluble (co)polymer (B) of the second embodiment can function as a thickener for the aqueous composition for the positive electrode.
• the term "structural unit having a carboxyl group” includes a structural unit derived from a monomer having a carboxyl group, a structural unit derived from a (co)polymer having a carboxyl group, or an alkali metal salt thereof (e.g., Na, K). Therefore, the water-soluble (co)polymer (B) in the second embodiment is understood to be a water-soluble resin having at least one or both of a structural unit derived from a monomer having a carboxyl group and a structural unit derived from a (co)polymer having a carboxyl group.
• the structural unit having a carboxyl group is not particularly limited as long as the structural unit constituting the polymer has a carboxyl group, but examples thereof include glucose units having a carboxyl group in part of the glucose units constituting cellulose, (meth)acrylic acid units, and the like. From the viewpoint of increasing the viscosity and hysteresis stability over time of the aqueous composition for the positive electrode, glucose units having a carboxyl group in part of the glucose units constituting cellulose are preferred.
• the water-soluble (co)polymer (B) of the second embodiment may contain one type of the structural units listed above alone, or two or more types in any combination and ratio.
• water-soluble (co)polymer (B) examples include, but are not limited to, cellulose derivatives having a carboxyl group, poly(meth)acrylic acid, sodium poly(meth)acrylate, etc. Among these, carboxymethylcellulose and carboxymethylcellulose alkali metal salts (e.g., sodium salt), which are cellulose derivatives having a carboxyl group, are preferred.
• the water-soluble (co)polymer (B) can be used alone or in any combination and ratio of two or more kinds.
• water-soluble (co)polymers include, for example, the Sunrose MAC (registered trademark) series, Sunrose (registered trademark) F, A, and SLD series from Nippon Paper Industries Co., Ltd., and the Cellogen (registered trademark) series from Daiichi Kogyo Seiyaku Co., Ltd.
• the content ratio of the structural unit having a carboxyl group in the water-soluble (co)polymer (B) in the second embodiment is not particularly limited, but from the viewpoint of the stability of viscosity and hysteresis over time, it is preferably 25% by mass or more and 100% by mass or less relative to the total solid content of the water-soluble (co)polymer (B), and the lower limit is more preferably 27% by mass or more, and even more preferably 29% by mass or more.
• the content ratio of the structural unit having a carboxyl group in the water-soluble (co)polymer (B) in the second embodiment can be measured by absorbance measurement.
• the content ratio of the constituent unit derived from the other monomer is not particularly limited, but is preferably 75 mass% or less, more preferably 73 mass% or less, and particularly preferably 71 mass% or less, based on the total solid content of the water-soluble (co)polymer (B).
• the lower limit side is not particularly limited as long as it is more than 0 mass%.
• the content ratio of the water-soluble (co)polymer (B) in the water-soluble (co)polymer in the second embodiment is not particularly limited, but from the viewpoints of the viscosity and hysteresis stability over time of the aqueous composition for the positive electrode and the electrode adhesion, the content is preferably 5 mass % or more and 70 mass % or less, more preferably 10 mass % or more and 60 mass % or less, and particularly preferably 20 mass % or more and 50 mass % or less, relative to the total amount of non-volatile components of the water-soluble (co)polymer.
• the content of the water-soluble (co)polymer (B) in the aqueous composition for the positive electrode is not particularly limited, but from the viewpoints of the viscosity and hysteresis stability over time of the aqueous composition for the positive electrode and electrode adhesion, it is preferably from 0.3 mass% to 5.0 mass%, more preferably from 0.4 mass% to 1.5 mass%, and particularly preferably from 0.45 mass% to 1.0 mass%, based on the total amount of non-volatile components in the aqueous composition.
• the pH of the water-soluble (co)polymer (B) in the second embodiment is not particularly limited, but is preferably 4.0 to 11.0, more preferably 4.5 to 10.7, and particularly preferably 5.0 to 10.5.
• the "pH of the water-soluble (co)polymer (B)” refers to the pH after adjusting the water-soluble (co)polymer aqueous solution to 1 mass% solids with water.
• the pH can be adjusted with, for example, sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydroxide, sodium hydrogen carbonate, disodium hydrogen phosphate, amines such as monoethanolamine, dimethylethanolamine, triethanolamine, and triethylamine, and is preferably sodium hydroxide, potassium hydroxide, or lithium hydroxide, and more preferably sodium hydroxide or lithium hydroxide. These can be used alone or in combination.
• the weight average molecular weight (Mw) of the water-soluble (co)polymer (B) in the second embodiment is not particularly limited, but from the viewpoint of the viscosity stability of the aqueous composition for the positive electrode, it is preferably from 10,000 to 1,000,000, more preferably from 30,000 to 700,000, and particularly preferably from 50,000 to 500,000.
• the weight average molecular weight (Mw) of the water-soluble (co)polymer (B) can be measured using gel permeation chromatography (GPC).
• the viscosity of the water-soluble (co)polymer (B) is not particularly limited and can be appropriately set according to the desired performance. From the viewpoint of viscosity stability, the viscosity of the water-soluble (co)polymer (B) is preferably 10 mPa ⁇ s or more and 10,000 mPa ⁇ s or less, more preferably 50 mPa ⁇ s or more and 7,000 mPa ⁇ s or less, and even more preferably 100 mPa ⁇ s or more and 5,000 mPa ⁇ s or less. The viscosity can be measured by using a rheometer "MCR-102" manufactured by Anton Paar Co., Ltd., at 25°C using a 1% concentration aqueous solution of the water-soluble (co)polymer (B).
• the content ratio of the water-soluble (co)polymer (A) to the water-soluble (co)polymer (B) in the second embodiment is not particularly limited, but from the viewpoints of the viscosity and hysteresis stability over time of the aqueous composition for the positive electrode and electrode adhesion, it is preferably 1.0:9.0 to 9.0:1.0 in terms of solid content, more preferably 1.0:4.0 to 8.0:1.0, and even more preferably 1.0:1:0 to 7.0:1.0.
• the content ratio of the structural units derived from the ethylenically unsaturated carboxylic acid (salt) is not particularly limited, but is preferably 0.10% by mass or more and 15.00% by mass or less in total based on the total amount of the particulate (co)polymer.
• the content is preferably 0.20 mass % or more and 10.00 mass % or less, more preferably 0.50 mass % or more and 7.50 mass % or less, and further preferably 1.00 mass % or more and 4.
• the content of the structural unit derived from the ethylenically unsaturated carboxylic acid (salt) is within the above range, aggregation in the aqueous composition is suppressed, and the viscosity and Since the aqueous composition has excellent stability over time in terms of hysteresis, when the aqueous composition is applied to a current collector, it can be applied while maintaining a suitable degree of fluidity, and tends to be easy to handle. Furthermore, the adhesiveness to the electrode is also excellent.
• the content ratio of the structural unit derived from an ethylenically unsaturated carboxylic acid (salt) can be measured by subjecting the particulate (co)polymer to potentiometric titration.
• the aqueous composition for a positive electrode of a lithium ion secondary battery according to the first and second embodiments may further contain a particulate polymer.
• the aqueous composition for a positive electrode of a lithium ion secondary battery according to the third embodiment includes a particulate (co)polymer and a water-soluble (co)polymer including a constituent unit derived from a monomer having a sulfonic acid (salt) group, and the content of the constituent unit derived from the monomer having a sulfonic acid (salt) group is 25 mass % or more and 100 mass % or less with respect to the total amount of the water-soluble (co)polymer.
• the following description of the particulate (co)polymer can be applied directly to the aqueous composition for a positive electrode of the first and second embodiments.
• the aqueous composition for a positive electrode of a lithium ion secondary battery of the third embodiment has the same configuration as that of the other embodiments, except for the particulate (co)polymer described below.
• JP 2014-165108 A gives examples of water-soluble polymers such as celluloses such as carboxymethyl cellulose (CMC), polyacrylic acid compounds, and compounds with a vinylpyrrolidone structure, and in practice, cellulose compounds are used.
• CMC carboxymethyl cellulose
• these compounds are not necessarily sufficient in terms of the stability over time of the aqueous composition, and there is room for improvement.
• the coating film formed by applying the aqueous composition to a current collector and drying it may cause defects, so-called electrode cracks, and there is still room for improvement in this regard as well.
• the aqueous compositions for positive electrodes of the first and third embodiments described above which contain a particulate (co)polymer, have excellent stability of viscosity over time and can suppress the occurrence of cracks in the electrode, and it is possible to provide a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery using the composition.
• the content ratio of the constitutional unit derived from the monobasic acid (salt) monomer is not particularly limited, but from the viewpoint of the dispersion stability of the particles, it is preferable that the content ratio of the constitutional unit derived from the monobasic acid (salt) monomer is 100% or more and 150% or less of the total amount of the particulate (co)polymer. 0.1% by mass or more and 20.0% by mass or less is preferable, 0.1% by mass or more and 10.0% by mass or less is more preferable, and 0.2% by mass or more and 5.0% by mass or less is even more preferable.
• the content ratio of the constitutional unit derived from the monobasic acid (salt) monomer is particularly preferably 0.2% by mass or more and 2.0% by mass or less.
• the aqueous composition for use tends to be excellent in handleability because it suppresses aggregation in the aqueous composition and can be applied to a current collector while maintaining a suitable fluidity when applied thereto, and also has storage stability. They tend to be superior in terms of
• the content ratio of the constituent units derived from the dibasic acid (salt) monomer is not particularly limited, but from the viewpoint of the mechanical strength of the particles, it is preferably 0.1 mass% or more and 10.0 mass% or less, more preferably 0.5 mass% or more and 5.0 mass% or less, even more preferably 1.0 mass% or more and 4.5 mass% or less, and particularly preferably 1.5 mass% or more and 3.5 mass% or less, relative to the total amount of the particulate (co)polymer.
• the content ratio of the constituent units derived from the dibasic acid (salt) monomer is within the above range, aggregation in the aqueous composition is suppressed, and when applied to a current collector, it can be applied while maintaining appropriate fluidity, so that the handling property tends to be excellent and the storage stability also tends to be excellent.
• the aqueous compositions for a lithium ion secondary battery positive electrode according to the first to third embodiments may contain a conductive assistant and a particulate (co)polymer.
• an aqueous composition for a lithium ion secondary battery positive electrode according to a fourth embodiment includes a conductive assistant and a particulate (co)polymer, and when elements present on a surface of the conductive assistant are measured by X-ray photoelectron spectroscopy and the abundance ratio (mass%) of oxygen atoms and the abundance ratio (mass%) of carbon atoms are calculated based on peak areas, the abundance ratio of oxygen atoms on the surface of the conductive assistant is 0.30 mass% or more and 2.00 mass% or less and the ratio (O/C) of the abundance ratio (mass%) of oxygen atoms to the abundance ratio (mass%) of carbon atoms is 0.0020 or more and 0.0250 or less, the particulate (co)polymer includes structural units derived from an ethylenically
• the following descriptions regarding the conductive assistant and the particulate (co)polymer can be applied as they are to the aqueous compositions for positive electrodes of the first to third embodiments.
• the aqueous composition for positive electrodes of lithium ion secondary batteries of the third embodiment has the same configuration as those described in the other embodiments, except for the conductive assistant and the particulate (co)polymer described below.
• the conductive adhesive composition for electrochemical element electrodes described in International Publication No. 2013/018887 is said to contribute to improving the adhesion between the current collector and the electrode composition layer.
• the inventors have discovered through their research that when a specific conductive assistant is combined with a specific binder, the conductive assistant in the aqueous composition aggregates, which causes the viscosity of the aqueous composition to change over time.
• the coating film formed by applying the aqueous composition to a current collector and drying the composition may cause so-called electrode cracks, such as defects, and it has been found that there is still room for improvement in these respects.
• the aqueous compositions for positive electrodes according to the first to fourth embodiments described above which contain a conductive assistant and a particulate (co)polymer, have excellent stability of viscosity over time and can suppress the occurrence of cracks in the electrode, and it is possible to provide a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery using the composition.
• the aqueous composition for positive electrodes of the fourth embodiment may contain a conductive assistant and a particulate polymer, and the proportion of oxygen atoms present on the surface of the conductive assistant is within a predetermined numerical range, the ratio of the proportion of oxygen atoms present on the surface to the proportion of carbon atoms is within a predetermined numerical range, and the particulate (co)polymer contains a predetermined amount of a constituent unit derived from an ethylenically unsaturated carboxylic acid (salt), thereby suppressing the occurrence of aggregation of the conductive assistant in the aqueous composition for positive electrodes, and therefore the viscosity and hysteresis have excellent stability over time, and the coating film coated and dried with the aqueous composition for positive electrodes has improved flexibility.
• a lithium ion secondary battery positive electrode having a uniform thickness during line coating and excellent uniformity between products can be efficiently produced. Furthermore, the occurrence of cracks in the electrode of the lithium ion secondary battery positive electrode can be suppressed, which also contributes to improving the product yield.
• the conductive assistant in the fourth embodiment is not particularly limited, and may be appropriately selected from known conductive assistants such as furnace black, carbon black, acetylene black, ketjen black, graphite, vapor-grown carbon fiber, carbon nanotubes, and other conductive carbons.
• the conductive assistant may be used alone or in combination of two or more types in any ratio. Among these, from the viewpoint of cost merit, it is preferable that the conductive assistant contains furnace black, and it is particularly preferable that the conductive assistant contains furnace black as an essential component.
• the proportion of oxygen atoms present on the surface of the conductive assistant may be 0.30% by mass or more and 2.00% by mass or less, and the ratio (O/C) of the proportion of oxygen atoms (mass%) to the proportion of carbon atoms (mass%) may be 0.0020 or more and 0.0250 or less.
• the proportion of oxygen atoms present on the surface of the conductive assistant is preferably 0.40% by mass or more and 2.00% by mass or less, and more preferably 0.50% by mass or more and 2.00% by mass or less.
• the ratio (O/C) of the abundance ratio (mass%) of oxygen atoms to the abundance ratio (mass%) of carbon atoms is preferably 0.0030 or more and 0.0230 or less, more preferably 0.0040 or more and 0.0220 or less, and even more preferably 0.0050 or more and 0.0210 or less.
• the aggregation of the conductive assistant in the aqueous composition tends to be suppressed, and the aqueous composition tends to have excellent stability over time in viscosity and hysteresis.
• the abundance ratios of oxygen atoms and carbon atoms present on the surface of the conductive additive can be measured by X-ray photoelectron spectroscopy (XPS).
• XPS X-ray photoelectron spectroscopy
• the abundance ratio (mass%) of oxygen atoms can be determined based on the peak area of the O1s spectrum (525-545 eV) in XPS analysis
• the abundance ratio (mass%) of carbon atoms can be determined based on the peak area of the C1s spectrum (280-300 eV) in XPS analysis.
• O/C can be calculated from the abundance ratios of oxygen atoms and carbon atoms determined respectively.
• the aqueous composition for a positive electrode of the fourth embodiment may contain, as the particulate polymer, a constituent unit derived from an ethylenically unsaturated carboxylic acid (salt).
• a constituent unit derived from an ethylenically unsaturated carboxylic acid (salt) By containing the auxiliary and the particulate polymer, aggregation of the conductive auxiliary in the aqueous composition can be suppressed, and the aqueous composition has excellent stability over time of viscosity and hysteresis.
• the content of the constituent units derived from the ethylenically unsaturated carboxylic acid (salt) is, in total, 0.10% by mass or more and 15.00% by mass or less, preferably 0.20% by mass or more and 10.00% by mass or less, more preferably 0.50% by mass or more and 7.50% by mass or less, and even more preferably 1.00% by mass or more and 4.00% by mass or less, relative to the total amount of the particulate (co)polymer.
• the viscosity and hysteresis of the aqueous composition are excellent in stability over time, and when the aqueous composition is applied to a current collector, it can be applied while maintaining an appropriate fluidity, and therefore tends to be easy to handle.
• the value (O ⁇ COOH) obtained by multiplying the proportion (mass%) of oxygen atoms on the surface of the conductive assistant in the aqueous composition for the positive electrode in the fourth embodiment by the content (mass%) of the total amount of constituent units derived from ethylenically unsaturated carboxylic acid (salt) in the particulate (co)polymer is not particularly limited, but is preferably 0.030 to 10.00, more preferably 0.100 to 7.00, even more preferably 0.300 to 6.00, and particularly preferably 0.600 to 5.00.
• the value (O ⁇ COOH) obtained by multiplying the proportion (mass%) of oxygen atoms on the surface of the conductive assistant by the content (mass%) of the total amount of constituent units derived from ethylenically unsaturated carboxylic acid (salt) in the particulate (co)polymer is less than 0.030, the adhesion to the electrode is insufficient and the electrode cracks, and if it exceeds 10.00, aggregation occurs in the aqueous composition, and the viscosity and hysteresis of the aqueous composition change over time, becoming unstable.
• the ratio (O/bound COOH) of the proportion (mass %) of oxygen atoms on the surface of the conductive assistant to the content (bound COOH) of monomers derived from ethylenically unsaturated carboxylic acid (salt) bound to the particulate (co)polymer relative to the total amount of monomers derived from ethylenically unsaturated carboxylic acid (salt) contained in the particulate (co)polymer is not particularly limited, but is preferably 0.0050 to 0.1000, more preferably 0.0065 to 0.0900, and even more preferably 0.0080 to 0.0800.
• the content ratio (bound COOH) of the monomer derived from an ethylenically unsaturated carboxylic acid (salt) bound to the particulate (co)polymer is calculated as follows.
• the acid value of the surface of the particulate (co)polymer is determined by conductometric titration, and the acid value is converted into the content of the monomer derived from the ethylenically unsaturated carboxylic acid (salt) bound to the particulate (co)polymer, and calculated according to the following formula.
• Bonded COOH content (parts by mass) of monomer derived from ethylenically unsaturated carboxylic acid (salt) calculated from acid value/content (parts by mass) of monomer derived from ethylenically unsaturated carboxylic acid (salt) charged before polymerization ⁇ 100
• sample preparation method and titration conditions for conductometric titration are as follows: A particulate (co)polymer with a solid content of 2 g was diluted to 10% with distilled water and centrifuged with an ultracentrifuge (Optima L-90K manufactured by Beckman Coulter) to separate into a particle phase and an aqueous phase. Distilled water was added to the aqueous phase-removed sedimentation sample, and the sample was redispersed with a shaker. The aqueous phase removal and redispersion by centrifugation were repeated a total of three times.
• ultracentrifuge Optima L-90K manufactured by Beckman Coulter
• ion exchange resin (DIAION SK1B manufactured by Mitsubishi Chemical) was added to the particulate (co)polymer from which the aqueous phase had been removed, and the mixture was stirred for 5 minutes, and the ion exchange resin was removed by filtration. This operation was repeated until the pH value did not change. The solid content of the particulate (co)polymer from which the aqueous phase had been removed after ion exchange was measured. 15 g of the particulate (co)polymer from which the aqueous phase had been removed was weighed in a 100 ml beaker and diluted to 50 g with distilled water.
• the solution was set in an automatic titrator (Hiranuma Sangyo Co., Ltd.: COM-1750, electrode used: TPT-351) and subjected to conductometric titration with 0.1 N potassium hydroxide while stirring. The end point was detected by the V1 intersection detection method and the acid value was calculated.
• an automatic titrator Hiranuma Sangyo Co., Ltd.: COM-1750, electrode used: TPT-351
• the end point was detected by the V1 intersection detection method and the acid value was calculated.
• the particulate (co)polymer in the fourth embodiment is not particularly limited as long as it contains a structural unit derived from an ethylenically unsaturated carboxylic acid (salt), and the ethylenically unsaturated carboxylic acid (salt) may contain, for example, a monobasic acid (salt) and/or a dibasic acid (salt). One of these may be used alone, or two or more may be used in any ratio.
• the monobasic acid (salt) is not particularly limited, but examples include monomers having a carboxyl group such as (meth)acrylic acid, crotonic acid, vinylbenzoic acid, and cinnamic acid, monomers having a sulfonic acid group such as styrenesulfonic acid, methallylsulfonic acid, allylsulfonic acid, and vinylsulfonic acid, and salts thereof (e.g., sodium salts, potassium salts, and ammonium salts). Of these, it is preferable to include (meth)acrylic acid. Of these, one type may be used alone, or two or more types may be used in any ratio.
• Dibasic acids include, for example, itaconic acid, fumaric acid, maleic acid, citraconic acid, muconic acid, and salts thereof (e.g., sodium salt, potassium salt, and ammonium salt).
• a dibasic acid salt only one of the carboxyl groups in the monomer may be in the form of a salt, or both may be in the form of a salt.
• one type may be used alone, or two or more types may be used in any ratio.
• the content ratio of the constituent units derived from the monobasic acid (salt) is not particularly limited, but from the viewpoint of dispersion stability of the particles, it is preferably 0.01% by mass or more and 2.00% by mass or less, more preferably 0.10% by mass or more and 1.75% by mass or less, even more preferably 0.20% by mass or more and 1.50% by mass or less, and particularly preferably 0.20% by mass or more and 1.25% by mass or less, relative to the total amount of the particulate (co)polymer.
• the aqueous composition for positive electrodes of the fourth embodiment tends to suppress aggregation in the aqueous composition, and to have excellent stability over time of the viscosity and hysteresis of the aqueous composition, and to have excellent storage stability.
• the content ratio of the constituent units derived from the monobasic acid (salt) can be measured by pyrolysis gas chromatography (pyrolysis GC-MS).
• the content ratio of the constituent units derived from the dibasic acid (salt) is not particularly limited, but from the viewpoint of the mechanical strength of the particles, it is preferably 0.10 mass% or more and 5.00 mass% or less, more preferably 0.50 mass% or more and 4.50 mass% or less, even more preferably 1.00 mass% or more and 4.00 mass% or less, and particularly preferably 1.50 mass% or more and 3.50 mass% or less, relative to the total amount of the particulate (co)polymer.
• the content ratio of the constituent units derived from the dibasic acid (salt) is within the above range, aggregation in the aqueous composition is suppressed, and the aqueous composition tends to have excellent stability over time of viscosity and hysteresis and excellent storage stability.
• the aqueous composition tends to have excellent stability over time of viscosity and hysteresis and excellent storage stability.
• the content ratio of the constituent units derived from the dibasic acid (salt) can be measured by liquid chromatography.
• the present invention is not limited to the above-mentioned embodiments.
• the aqueous composition for positive electrodes of the embodiments may contain known additives in addition to the above-mentioned components.
• Preparation Examples 2 to 6 In each Preparation Example, polymerization was completed in the same manner as Preparation Example 1, except that the amount of sodium p-styrenesulfonate was changed as shown in Table 1. Thereafter, after cooling to room temperature, water and sodium hydroxide were added so as to obtain the solid content and pH shown in Table 1 (sodium hydroxide was added in an amount such that the pH would be as shown in Table 1 when the obtained aqueous water-soluble polymer solution was diluted to 5 mass %). Furthermore, 0.02 mass % of 2-methyl-4-isothiazolin-3-one was added to the obtained aqueous water-soluble polymer solution, thereby obtaining water-soluble polymers 2 to 6. The physical properties of the water-soluble polymers 2 to 6 were as shown in Table 1.
• the molecular weight of each water-soluble polymer was evaluated using GPC.
• the water-soluble polymer was diluted with ion-exchanged water to about 0.1% by mass, and passed through a 45 ⁇ m filter to obtain a measurement sample.
• the column temperature was 40° C.
• the eluent was a pH 9.0 buffer solution (manufactured by Kishida Chemical Co., Ltd., containing sodium tetraborate and boric acid)
• the eluent flow rate was 0.6 ml/min
• the columns were Asahipak GF-7M HQ and GF-210 HQ.
• Sodium polyacrylate was used for the calibration curve, and the obtained weight average molecular weight value was taken as the molecular weight.
• Preparation Example 7 Into the reactor, 130 parts by mass of ion-exchanged water and 0.05 parts by mass of an aqueous solution of sodium alkyl diphenyl ether sulfonate (DOW CHEMICAL, Dowfax 2A1) in terms of solid content were added, and the mixture was heated to 70 ° C. while stirring and purging with nitrogen. Next, 10 parts by mass of a 5% aqueous solution of sodium persulfate was added to the reactor.
• DOW CHEMICAL sodium alkyl diphenyl ether sulfonate
• a mixed liquid obtained by mixing 84 parts by mass of n-butyl acrylate, 15 parts by mass of 2-hydroxyethyl methacrylate, 1 part by mass of trimethylolpropane triacrylate, 0.15 parts by mass of an aqueous solution of sodium alkyl diphenyl ether sulfonate in terms of solid content, and 125 parts by mass of ion-exchanged water was emulsified with a homogenizer, and the emulsion obtained by emulsification was dropped over 2.5 hours while maintaining the temperature at 70 ° C. After completion of the dropwise addition, polymerization was continued at 70 ° C. for 2 hours, and then the temperature was raised to 80 ° C.
• the mixture was cooled to room temperature, and the pH and solid content were adjusted to 8.0 and 20% with a 5% aqueous sodium hydroxide solution and water, respectively, and 0.05% by mass of 1,2-benzoisothiazolin-3-one was added to the aqueous dispersion of the particulate polymer, followed by filtration through a mesh having an opening of 74 ⁇ m to obtain a particulate polymer 1.
• the physical properties of the particulate polymer 1 were as shown in Table 2.
• particulate polymer 3 was filtered through a mesh with an opening of 74 ⁇ m to obtain particulate polymer 3.
• the physical properties of particulate polymer 3 were as shown in Table 2.
• the particle sizes of the particulate polymers 1 and 2 were measured using a concentrated particle size analyzer "FPAR-1000" manufactured by Otsuka Electronics Co., Ltd., which uses dynamic light scattering as its measurement principle. The measurement was performed using a concentrated probe under conditions of 25°C and a light amount of 20,000 to 50,000, and the value of 50% of the cumulative particle size of the obtained scattering intensity distribution data was taken as the particle size. The results are shown in Table 2.
• aqueous composition for positive electrode ⁇ Preparation of aqueous composition for positive electrode>
• a planetary mixer with a disperser 1.5 parts by mass of water-soluble polymer 1 in terms of solid content and 5 parts by mass of acetylene black (manufactured by Denka Corporation, Denka Black Li-400; "Li-400” in the table below) as a conductive assistant were added and mixed by stirring for 10 minutes.
• 100 parts by mass of lithium iron phosphate manufactured by Puled Technology Industry Co., Ltd., P600A, particle size 1 ⁇ m; "Puled P600A” in the table below
• ion-exchanged water was added so that the solid content was as shown in Table 3, and the mixture was stirred and mixed for 10 minutes to obtain an aqueous composition for the positive electrode (aqueous composition 1).
• Example 2 to 6, 9 to 12, Comparative Examples 1 to 3 In each Example, water-based compositions 2 to 6 and 9 to 12 were obtained in the same manner as in Example 1, except that the substances such as the water-soluble polymer were changed as shown in Table 3.
• Example 7 Each substance such as the water-soluble polymer was changed as shown in Table 3, and 100 parts by mass of lithium iron phosphate was added and stirred and mixed for 30 minutes in the same manner as in Example 1. Next, ion-exchanged water was added so that the particulate polymer 1 became 3.5 parts by mass in terms of solid content and the solid content shown in Table 3 was obtained, and the mixture was stirred and mixed for 10 minutes to obtain an aqueous composition 7.
• Example 8 Aqueous composition 8 was obtained in the same manner as in Example 7, except that the substances such as the water-soluble polymer and the particulate polymer were changed as shown in Table 3.
• Examples 13 to 14 Aqueous compositions 13 and 14 were obtained in the same manner as in Example 7, except that the substances such as the water-soluble polymer and the particulate polymer were changed as shown in Table 3.
• Viscosity and hysteresis of aqueous composition for positive electrode The viscosity and hysteresis of the obtained aqueous composition were measured using a rheometer "MCR-102" manufactured by Anton Paar. The measurements were performed at 25°C and at shear rates ranging from 1 to 100 (1/s) using a cone plate "CP-50-1". The initial viscosity was taken as the value of 1 (1/s) when the shear rate was increasing. The hysteresis was calculated using a value of a shear rate of 4.2 ⁇ 0.2 (1/s) and was calculated as (viscosity on increase - viscosity on decrease) / viscosity on increase x 100 (%).
• the aqueous composition was placed in a container and left to stand at 25°C for one day while rotating with a mix rotor, and the viscosity and hysteresis of the aqueous composition were measured under the same conditions as described above.
• the viscosity change after one day was calculated as (initial viscosity - viscosity after one day)/initial viscosity x 100 (%).
• the hysteresis change after one day was calculated as (viscosity during rise - viscosity during fall)/viscosity during rise x 100 (%) using a shear rate of 4.2 ⁇ 0.2 (1/s).
• the aqueous composition was applied to one side of an aluminum foil having a thickness of 20 ⁇ m as a positive electrode current collector using a die coater, dried at 100° C. for 10 minutes, and compression molded using a roll press. At this time, the amount of non-volatile content of the aqueous composition for the positive electrode was 12 mg/cm 2 , and the density of the mixture layer after roll pressing was 2.2 g/cm 3 . At this time, the electrode adhesion was evaluated using the obtained electrode. The composition and the secondary battery positive electrode thus obtained were used to evaluate various physical properties as described below.
• the produced positive electrode for the secondary battery was punched out into a 30 mm ⁇ 30 mm square using a Thomson blade (mirror-finished blade), and the degree of peeling of the electrode layer after punching was evaluated according to the following criteria.
• No peeling 4 The shortest distance from the closest point in the in-plane center of the exposed current collecting foil to the periphery is within 1 mm 3: The shortest distance from the closest point in the in-plane center of the exposed current collecting foil to the periphery is more than 1 mm and within 5 mm 2: The shortest distance from the closest point in the in-plane center of the exposed current collecting foil to the periphery is more than 5 mm and within 10 mm 1: The shortest distance from the closest point in the in-plane center of the exposed current collecting foil to the periphery exceeds 10 mm
• Water-soluble polymer 8 Sodium hydroxide was added to a poly(2-acrylamide-2-methyl-1-propanesulfonic acid) solution (manufactured by Aldrich), and 0.02% by mass of 2-methyl-4-isothiazolin-3-one was added to the water-soluble polymer aqueous solution to adjust the pH to 7.0, which was used as water-soluble polymer 8. The molecular weight measured by the above-mentioned method was 760,000.
• Water-soluble polymer 9 Sunrose MAC-350HC (carboxymethyl cellulose, manufactured by Nippon Paper Industries Co., Ltd.) was used as water-soluble polymer 9.
• Water-soluble polymer 10 Water and sodium hydroxide were added to polyacrylic acid (manufactured by Aldrich, molecular weight 1.25 million) to adjust the pH to 8.6, and this was used as water-soluble polymer 10.
• Water-soluble polymer 11 PS-1 (sodium polystyrene sulfonate, manufactured by Tosoh Finechem Co., Ltd.) was used as the water-soluble polymer 11.
• the pH was 10.0, and the molecular weight measured by the above-mentioned method was 26,000.
• Water-soluble polymer 12 PS-5 (sodium polystyrene sulfonate, manufactured by Tosoh Finechem Co., Ltd.) was used as the water-soluble polymer 12.
• Water-soluble polymer 13 PS-50 (polystyrene sodium sulfonate, manufactured by Tosoh Finechem Co., Ltd.) was used as the water-soluble polymer 13.
• the pH was 10.0, and the molecular weight measured by the above-mentioned method was 370,000.
• the aqueous composition of Comparative Example 3 in which a water-soluble resin in which the total amount of sulfonic acid group-containing units in the water-soluble polymer (A) was less than 25 mass% for the active material lithium iron phosphate had a large viscosity change, especially after one day, and was poor in stability.
• the obtained monomer mixture was emulsified with a homogenizer to obtain a monomer emulsion.
• the obtained monomer emulsion was added dropwise, and the dropwise addition was completed in 2.5 hours while maintaining the internal temperature at 80°C, and polymerization was continued for 1 hour. Thereafter, the internal temperature was raised from 80° C. to 85° C. and maintained at that temperature for 3 hours to complete the polymerization.
• the mixture was cooled to room temperature, and the pH and solid content were adjusted to 8.0 and 20% with a 5% aqueous sodium hydroxide solution and water, respectively, and 0.05% by mass of 1,2-benzoisothiazolin-3-one was added to the aqueous dispersion of the particulate (co)polymer, followed by filtration through a mesh having an opening of 74 ⁇ m to obtain a particulate (co)polymer a1.
• the physical properties of the particulate (co)polymer a1 were as shown in Table 4.
• the acid amounts of the obtained particulate (co)polymer a1 were quantified by acid titration, and as a result, itaconic acid was 3% by mass and acrylic acid was 1.1% by mass relative to the total amount of the particulate (co)polymer a1.
• Preparation Examples a2 to a10 and a13 Particulate (co)polymers a2 to a10 and a13 were obtained in the same manner as in Preparation Example a1, except that the monomer composition was changed as shown in Table 1. The physical properties of the particulate (co)polymers a2 to a10 and a13 were as shown in Table 4.
• the pH of the particulate (co)polymer is the pH of an aqueous solution of the particulate (co)polymer when the solid content is 5% by mass.
• Table 4 represent the following compounds.
• St styrene 2-EHA: 2-ethylhexyl acrylate
• BA n-butyl acrylate
• MMA methyl methacrylate
• AA acrylic acid
• MAA methacrylic acid
• IA itaconic acid
• AN acrylonitrile
• HEMA 2-hydroxyethyl methacrylate
• 1,9-ND 1,9-nonanediol dimethacrylate
• TMPT-A trimethylolpropane triacrylate
• Examples a2 to a18, Comparative Examples a1 to a2 In each example, the types and compositions of the conductive assistant, particulate (co)polymer, and water-soluble (co)polymer were changed as shown in Tables 5 and 6, and aqueous compositions a2 to a18 and a22 to a23 were obtained in the same manner as in Example a1.
• the obtained aqueous composition for positive electrode was applied to one side of an aluminum foil having a thickness of 20 ⁇ m, which was a positive electrode current collector, using a die coater, and dried at 100° C. for 10 minutes, and then compression molded using a roll press machine. At this time, the amount of active material applied to the positive electrode was 12 mg/cm 2 , and the density of the electrode layer after roll pressing was 2.2 g/cm 3 . At this time, the electrode obtained was used to evaluate cracking of the electrode. The electrode thus obtained was used as a secondary battery positive electrode.
• the aqueous composition for positive electrode and the positive electrode for secondary battery obtained as described above were used to evaluate various physical properties as described below. The results are shown in Tables 5 and 6.
• Viscosity and hysteresis of aqueous composition for positive electrode The viscosity and hysteresis of the obtained aqueous composition were measured by the above-mentioned method. The absolute value of the hysteresis was evaluated according to the following criteria. A rating of C or higher was considered to be acceptable, and a rating of D was considered to be unacceptable. A: 0% or more, less than 20% B: 20% or more, less than 40% C: 40% or more, less than 60% D: 60% or more or immobilization due to aggregation
• the viscosity and hysteresis of the aqueous composition for the positive electrode were measured by the method described above.
• the absolute values of the rate of change in viscosity and hysteresis over time were evaluated according to the following criteria. A rating of C or higher was considered to be acceptable, and a rating of D was considered to be unacceptable. A: 0% or more, less than 20% B: 20% or more, less than 40% C: 40% or more, less than 60% D: 60% or more or immobilization due to aggregation
• Viscosity change rate of slurry after stirring (initial viscosity ⁇ viscosity after 1 day of stirring)/initial viscosity ⁇ 100(%)
• a rating of C or higher was considered to be acceptable, and D was considered to be unacceptable.
• the obtained particulate (co)polymer was left to stand in an oven at 130 ° C. for 1 hour and dried.
• the particulate (co)polymer film obtained by drying was cut out and used as a sample for measurement.
• the mass of the film at that time (Wa: unit g) was measured.
• the sample was placed in a 50 mL vial together with 20 g of a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio 1:2), and the mixed solvent was allowed to penetrate at 60 ° C. for 7 days, after which the sample was taken out and washed with the mixed solvent. Then, the sample was left to stand in an oven at 150 ° C.
• Electrolyte insoluble content (%) (Wc/Wa) x 100 A: 97% or more B: 90% or more but less than 97% C: 85% or more but less than 90% D: Less than 85%
• Active material Lithium iron phosphate (Pulead Technology Industry, product name "P600A", particle size 1 ⁇ m)
• Conductive assistant A surface oxygen atom content: 0.60 mass%, O/C: 0.0061
• Conductive assistant B surface oxygen atom content: 0.88 mass%, O/C: 0.0090
• Conductive assistant C surface oxygen atom content: 2.00 mass%, O/C: 0.0206
• Conductive assistant D surface oxygen atom content: 0.54 mass%, O/C: 0.0054
• Conductive assistant E surface oxygen atom content: 0.19 mass%, O/C: 0.0019
• Water-soluble (co)polymer p-NaSS: sodium polystyrene sulfonate (manufactured by Tosoh Finechem Co., Ltd., product name "PS-100", weight average molecular weight: 540,000, pH: 10.0)
• CMC Carboxymethyl cellulose
• Preparation Examples b2 and b3 In each preparation example, polymerization was completed in the same manner as in Preparation Example b1, except that the amounts of sodium p-styrenesulfonate and methacrylic acid were changed as shown in Table 7. Thereafter, after cooling to room temperature, water and sodium hydroxide were added so as to obtain the solid content and pH shown in Table 7 (sodium hydroxide was added in an amount such that the pH would be as shown in Table 7 when the obtained water-soluble polymer aqueous solution was diluted to 5% by mass).
• the molecular weight of each water-soluble (co)polymer (B) was evaluated using gel filtration chromatography (GFC).
• GFC gel filtration chromatography
• the water-soluble polymer was diluted with ion-exchanged water to about 0.1% by mass, and passed through a 45 ⁇ m filter to obtain a measurement sample.
• the column temperature was 40° C.
• the eluent was a 100 mmol sodium nitrate aqueous solution
• the eluent flow rate was 1.0 ml/min
• the column was Shodex OHpak SB-803 HQ+SB-805 HQ. Pullulan was used for the calibration curve, and the obtained weight average molecular weight value was taken as the molecular weight.
• a monomer solution obtained by mixing 73 parts by mass of 2-ethylhexyl acrylate, 8 parts by mass of methyl methacrylate, 17 parts by mass of styrene, and 0.25 parts by mass of 1,9-nonanediol dimethacrylate, 0.45 parts by mass of sodium dodecyl diphenyl ether sulfonate, and 55 parts by mass of ion-exchanged water were added.
• the obtained monomer mixture was emulsified with a homogenizer to obtain a monomer emulsion.
• the obtained monomer emulsion was dropped over 2.5 hours while maintaining the internal temperature at 80°C, and then polymerization was continued for another hour.
• a particulate (co)polymer b2 was obtained in the same manner as in Preparation Example b1, except that the monomer composition was changed as shown in Table 8.
• the physical properties of the particulate (co)polymer b2 are shown in Table 8.
• particle size The particle sizes of the particulate (co)polymers b1 and b2 were measured by the method described above.
• Example b1 A rotation/revolution type mixer (manufactured by Thinky Corporation) was charged with 3.5 parts by mass, calculated as solid content, of particulate (co)polymer b1, 1.5 parts by mass, calculated as solid content, of sodium polystyrene sulfonate (manufactured by Tosoh Finechem Co., Ltd., product name "PS-100") as a water-soluble (co)polymer (A), 0.5 parts by mass, calculated as solid content, of carboxymethylcellulose (manufactured by Nippon Paper Industries Co., Ltd., product name "Sunrose MAC (registered trademark) 350HC”) as a water-soluble (co)polymer (B), 100 parts by mass of lithium iron phosphate (manufactured by Pulead Technology Industry Co., Ltd., P600A, particle size 1 ⁇ m) as a positive electrode active material, and furnace black (manufactured
• Example b2 to b17 Comparative Examples b1 to b3
• the water-soluble (co)polymers (A) and (B), and the type and composition of the particulate (co)polymer were changed as shown in Tables 9 and 10, and the aqueous compositions b2 to b20 were obtained in the same manner as in Example b1.
• the obtained aqueous composition for the positive electrode was compression molded by the above-mentioned method, and the electrode adhesion was evaluated using the obtained electrode.
• the electrode thus obtained was used as a secondary battery positive electrode.
• the aqueous composition for positive electrode and the positive electrode for secondary battery obtained as described above were used to evaluate various physical properties as described below. The results are shown in Tables 9 and 10.
• Viscosity and hysteresis of aqueous composition for positive electrode The viscosity and hysteresis of the obtained aqueous composition were measured by the above-mentioned method. The absolute value of the hysteresis was evaluated according to the following criteria. A rating of C or higher was considered to be acceptable, and a rating of D was considered to be unacceptable. A: 0% or more, less than 20% B: 20% or more, less than 40% C: 40% or more, less than 60% D: 60% or more or immobilization due to aggregation
• the viscosity and hysteresis of the aqueous composition for the positive electrode were measured by the method described above.
• the absolute values of the rate of change in viscosity and hysteresis over time were evaluated according to the following criteria. A rating of C or higher was considered to be acceptable, and a rating of D was considered to be unacceptable. A: 0% or more, less than 20% B: 20% or more, less than 40% C: 40% or more, less than 60% D: 60% or more or immobilization due to aggregation
• Electrode Adhesion of Slurry After Stirring After stirring the slurry according to the method for the stability of the stirred slurry, the slurry was used to prepare a lithium ion secondary battery positive electrode. The surface of the obtained electrode was visually observed, and the degree of peeling of the electrode layer was judged according to the following criteria. A rating of C or higher was considered to be acceptable, and a rating of D was considered to be unacceptable. A: No peeling B: No defects within the coating surface, defects on the edge of the coating surface (less than 5 places) C: No defects within the coating surface, defects on the edge of the coating surface (5 or more places) D: Defects present on the coating surface
• Active material Lithium iron phosphate (Pulead Technology Industry Co., Ltd., product name "P600A", particle size 1 ⁇ m)
• Conductive additive Furnace black (Super P-Li, manufactured by Imerys)
• Water-soluble (co)polymer (A-1) aqueous solution of sodium polystyrene sulfonate (manufactured by Tosoh Finechem Co., Ltd., product name "PS-100", weight average molecular weight (Mw): 540,000, pH: 10.0)
• Water-soluble (co)polymer (A-3) aqueous solution of sodium polystyrene
• the aqueous composition for the positive electrode of a lithium ion secondary battery which contains an active material, a water-soluble (co)polymer (A) containing a constituent unit derived from a monomer having a sulfonic acid (salt) group, and a water-soluble (co)polymer (B) containing a constituent unit having a carboxyl group (excluding those corresponding to the water-soluble (co)polymer (A)), and in which the content ratio of the constituent unit derived from a monomer having a sulfonic acid (salt) group is 25 mass% or more and 100 mass% or less with respect to the total solid content of the water-soluble (co)polymer (A), has improved stability of the stirred slurry and electrode adhesion of the slurry at the initial stage and after stirring compared to Comparative Examples b1 to b3.
• Comparative Example b1 which does not contain the water-soluble (co)polymer (B), has inferior stability of the stirred slurry and electrode adhesion of the slurry after stirring. It can also be seen that Comparative Example b2, which does not contain the water-soluble (co)polymer (A), has inferior viscosity change and hysteresis after one day.
• Comparative Example b3 in which the content of the structural unit derived from a monomer having a sulfonic acid (salt) group is 25 mass% or less relative to the total solid content of the water-soluble (co)polymer (A), the viscosity change and hysteresis after one day, the stability of the stirred slurry, and the electrode adhesion of the slurry at the initial stage and after stirring are inferior.
• Preparation examples c3 to c4 In each preparation example, water-soluble (co)polymers C3 and C4 were obtained in the same manner as in Preparation Example C2, except that the amounts of sodium p-styrenesulfonate and methacrylic acid were changed as shown in Table 11. The physical properties of the water-soluble (co)polymers c3 and c4 are shown in Table 11.
• PNaSS sodium polystyrene sulfonate (manufactured by Tosoh Finechem Co., Ltd., product name "PS-100", weight average molecular weight: 540,000, pH: 10.0)
• NaSS sodium p-styrenesulfonate
• MAA methacrylic acid
• CMC carboxymethyl cellulose (manufactured by Nippon Paper Industries Co., Ltd., product name "Sunrose MAC (registered trademark) 350HC”)
• the pH of the water-soluble (co)polymers c1 to c4 is the pH of the aqueous solution of the water-soluble (co)polymer when the solid content is 5% by mass
• the pH of the water-soluble (co)polymer c5 is the pH of the aqueous solution of the water-soluble (co)polymer when the solid content is 1% by mass.
• the obtained monomer mixture was emulsified with a homogenizer to obtain a monomer emulsion.
• the obtained monomer emulsion was added dropwise, and the dropwise addition was completed in 2.5 hours while maintaining the internal temperature at 80°C, and polymerization was continued for 1 hour. Thereafter, the internal temperature was raised from 80° C. to 85° C. and maintained at that temperature for 3 hours to complete the polymerization. Thereafter, the mixture was cooled to room temperature, and adjusted to pH 8.0 and solid content 20% with 5% aqueous sodium hydroxide solution and water, and 0.05% by mass of 1,2-benzoisothiazolin-3-one was added to the aqueous dispersion of the particulate (co)polymer, followed by filtration through a mesh with an opening of 74 ⁇ m to obtain particulate (co)polymer c1.
• the physical properties of the particulate (co)polymer c1 are shown in Table 12.
• Preparation examples c7 to c11 Particulate (co)polymers c2 to c6 were obtained in the same manner as in Preparation Example c6, except that the monomer composition was changed as shown in Table 12. The physical properties of the particulate (co)polymers c2 to c6 are shown in Table 12. It was 12th street.
• the pH of the particulate (co)polymer is the pH of an aqueous dispersion of the particulate (co)polymer when the solid content is 20% by mass.
• Example c1 ⁇ Preparation of aqueous composition for positive electrode>
• a planetary mixer equipped with a disperser 2.35 parts by mass of particulate polymer c1 in terms of solid content, 0.75 parts by mass of water-soluble (co)polymer c1 in terms of solid content, 0.75 parts by mass of water-soluble (co)polymer c5 in terms of solid content, 100 parts by mass of lithium iron phosphate (P600A, manufactured by Pulea Technology Industry, particle size 1 ⁇ m) as a positive electrode active material, and 5 parts by mass of furnace black (Super P-Li, manufactured by Imerys) as a conductive assistant were added, and ion-exchanged water was further added so that the solid content would be as shown in Table 13, and the mixture was stirred and mixed for 30 minutes and degassed to obtain an aqueous composition c1 for a positive electrode.
• Li iron phosphate P600A, manufactured by Pulea Technology Industry, particle size 1 ⁇ m
• furnace black
• Examples c2 to c11, Comparative Examples c1 to c3 In each example, the types and compositions of the water-soluble (co)polymer and particulate (co)polymer were changed as shown in Table 13, and the same procedures as in Example c1 were carried out to obtain aqueous compositions c2 to c14.
• the resulting aqueous composition for the positive electrode was compression molded by the above-mentioned method, and the electrode was evaluated for cracking using the resulting electrode.
• the electrode thus obtained was used as a positive electrode for a secondary battery.
• the aqueous composition for positive electrode and the positive electrode for secondary battery obtained as described above were used to evaluate various physical properties as described below. The results are shown in Table 13.
• Viscosity and hysteresis of aqueous composition for positive electrode The viscosity and hysteresis of the obtained aqueous composition were measured by the above-mentioned method. The absolute value of the hysteresis was evaluated according to the following criteria. A rating of C or higher was considered to be acceptable, and a rating of D was considered to be unacceptable. A: 0% or more, less than 20% B: 20% or more, less than 40% C: 40% or more, less than 60% D: 60% or more or immobilization due to aggregation
• the viscosity and hysteresis of the aqueous composition for the positive electrode were measured by the method described above.
• the absolute values of the rate of change in viscosity and hysteresis over time were evaluated according to the following criteria. A rating of C or higher was considered to be acceptable, and D was considered to be unacceptable. A: 0% or more, less than 20% B: 20% or more, less than 40% C: 40% or more, less than 60% D: 60% or more or immobilization due to aggregation
• Electrolyte insoluble matter The electrolyte insoluble matter was measured by the above-mentioned method and was judged according to the above-mentioned criteria.
• Active material Lithium iron phosphate (Pulead Technology Industry, product name "P600A”, particle size 1 ⁇ m)
• Conductive additive Furnace black (Super P-Li, manufactured by Imerys)
• Examples c1 to c11 shown in Table 13 show that the aqueous composition for the positive electrode of a lithium ion secondary battery, which contains a particulate (co)polymer and a water-soluble (co)polymer containing a constituent unit derived from a monomer having a sulfonic acid (salt) group, and in which the content ratio of the constituent unit derived from the monomer having a sulfonic acid (salt) group is 25 mass% or more and 100 mass% or less with respect to the total amount of the water-soluble (co)polymer, suppresses electrode cracking compared to Comparative Examples c1 to c3.
• Comparative Example c2 which does not contain a water-soluble (co)polymer containing a constituent unit derived from a monomer having a sulfonic acid (salt) group
• Comparative Example c3 which contains a water-soluble (co)polymer in which the content ratio of the constituent unit derived from a monomer having a sulfonic acid (salt) group is less than 25 mass%, have inferior stability during slurry stirring.
• a conductive assistant and a particulate (co)polymer When elements present on the surface of the conductive assistant are measured by X-ray photoelectron spectroscopy and the abundance ratio (mass%) of oxygen atoms and the abundance ratio (mass%) of carbon atoms are calculated based on peak areas, the abundance ratio of oxygen atoms on the surface of the conductive assistant is 0.30 mass% or more and 2.00 mass% or less, and the ratio (O/C) of the abundance ratio (mass%) of oxygen atoms to the abundance ratio (mass%) of carbon atoms is 0.0020 or more and 0.0250 or less, the particulate (co)polymer contains a constituent unit derived from an ethylenically unsaturated carboxylic acid (salt), the content ratio of the structural units derived from the ethylenically unsaturated carboxylic acid (salt) is 0.1% by mass or more and 15.00% by mass or less in total with respect to the total amount of the particulate (
• ⁇ a2> the content ratio of the structural units derived from the ethylenically unsaturated carboxylic acid (salt) is 0.10 mass% or more and 5.00 mass% or less in total with respect to the total amount of the particulate (co)polymer;
• ⁇ a3> the structural unit derived from the ethylenically unsaturated carboxylic acid (salt) contains a monobasic acid (salt) and/or a dibasic acid (salt);
• the content ratio of the structural units derived from the monobasic acid (salt) is 0.01% by mass or more and 2.00% by mass or less in total relative to the total amount of the particulate (co)polymer, and/or the content ratio of the structural units derived from the dibasic acid (salt) is 0.10% by mass or more and 5.00% by mass or less in total relative to the total amount of the particulate (co)polymer;
• ⁇ a5> The value (O ⁇ COOH) obtained by multiplying the abundance ratio (mass%) of oxygen atoms on the surface of the conductive assistant by the content ratio (mass%) of the total amount of structural units derived from the ethylenically unsaturated carboxylic acid (salt) contained in the particulate (co)polymer is 0.030 to 10.00;
• the aqueous composition for a positive electrode of a lithium ion secondary battery according to any one of ⁇ a1> to ⁇ a4>.
• ⁇ a6> the ratio (O/bound COOH) of the abundance ratio (mass%) of oxygen atoms on the surface of the conductive assistant and the content ratio (bound COOH) of the monomer derived from the ethylenically unsaturated carboxylic acid (salt) bound to the particulate (co)polymer relative to the total amount of the monomer derived from the ethylenically unsaturated carboxylic acid (salt) contained in the particulate (co)polymer is 0.0050 to 0.1000;
• the aqueous composition for a positive electrode of a lithium ion secondary battery according to any one of ⁇ a1> to ⁇ a5>.
• the particulate (co)polymer further contains a constituent unit derived from a crosslinkable monomer.
• the abundance ratio of oxygen atoms on the surface of the conductive assistant is 0.5% by mass or more and 2.0% by mass or less;
• the content of the conductive assistant is 3.5% by mass or more and 10.0% by mass or less with respect to the total amount of non-volatile components in the aqueous composition;
• ⁇ a10> Further comprising a water-soluble (co)polymer,
• the water-soluble (co)polymer contains a structural unit derived from a monomer having a sulfonic acid (salt) group.
• ⁇ a12> the content of the structural unit derived from the monomer having a sulfonic acid (salt) group is 25% by mass or more and 100% by mass or less based on the total solid content of the water-soluble (co)polymer;
• ⁇ a13> Further comprising a preservative, The aqueous composition for a positive electrode of a lithium ion secondary battery according to any one of ⁇ a1> to ⁇ a12>.
• the active material includes a lithium phosphate compound.
• ⁇ a15> A positive electrode for a lithium ion secondary battery, comprising the aqueous composition for a positive electrode for a lithium ion secondary battery according to any one of ⁇ a1> to ⁇ a14>.
• ⁇ a16> A lithium ion secondary battery comprising the positive electrode for lithium ion secondary batteries according to ⁇ a15>.
• ⁇ b2> The pH of the water-soluble (co)polymer (A) is 4.0 or more and 11.0 or less.
• ⁇ b3> The pH of the water-soluble (co)polymer (B) is 4.0 or more and 11.0 or less.
• ⁇ b4> The content ratio of the water-soluble (co)polymer (A) to the water-soluble (co)polymer (B) is 1:9 to 9:1 in terms of solid content.
• ⁇ b5> Further comprising a conductive assistant, The aqueous composition for a positive electrode of a lithium ion secondary battery according to any one of ⁇ b1> to ⁇ b4>.
• the content of the conductive assistant is 3.5% by mass or more and 10.0% by mass or less with respect to the total amount of non-volatile components in the aqueous composition;
• ⁇ b7> Further comprising a particulate (co)polymer,
• the particulate (co)polymer contains a constituent unit derived from an ethylenically unsaturated carboxylic acid (salt), the content ratio of the structural units derived from the ethylenically unsaturated carboxylic acid (salt) is 0.10% by mass or more and 15.00% by mass or less in total with respect to the total amount of the particulate (co)polymer;
• ⁇ b9> Further comprising a preservative, The aqueous composition for a positive electrode of a lithium ion secondary battery according to any one of ⁇ b1> to ⁇ b8>.
• the active material includes a lithium phosphate compound.
• ⁇ b11> A positive electrode for a lithium ion secondary battery, comprising the aqueous composition for a positive electrode for a lithium ion secondary battery according to any one of ⁇ b1> to ⁇ b10>.
• ⁇ b12> A lithium ion secondary battery comprising the positive electrode for lithium ion secondary batteries according to ⁇ b11>.
• the particulate (co)polymer contains a constituent unit derived from a dibasic acid (salt) monomer, The aqueous composition for a positive electrode of a lithium ion secondary battery according to ⁇ c1>.
• the particulate (co)polymer contains a constituent unit derived from a crosslinkable monomer, The aqueous composition for a positive electrode of a lithium ion secondary battery according to ⁇ c1> or ⁇ c2>.
• the pH of the water-soluble (co)polymer is 4.0 or more and 11.0 or less.
• ⁇ c5> Further comprising a conductive assistant;
• ⁇ c6> The content of the conductive assistant is 3.5% by mass or more and 10.0% by mass or less with respect to the total amount of non-volatile components in the aqueous composition;
• ⁇ c7> Further comprising a preservative, The aqueous composition for a positive electrode of a lithium ion secondary battery according to any one of ⁇ c1> to ⁇ c6>.
• ⁇ c8> Further comprising an active material, The active material includes a lithium phosphate compound.
• ⁇ c9> A positive electrode for a lithium ion secondary battery, comprising the aqueous composition for a positive electrode for a lithium ion secondary battery according to any one of ⁇ c1> to ⁇ c8>.
• ⁇ c10> A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to ⁇ c9>.

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