Aqueous composition for lithium-ion secondary battery positive electrode, positive electrode for lithium-ion secondary battery, and lithium-ion secondary battery

Abstract

An aqueous composition for the positive electrode of a lithium ion secondary battery, the aqueous composition containing a water-soluble polymer (A) comprising constituent units corresponding to a monomer having a sulfonic acid group, wherein the total amount of the constituent units corresponding to a monomer having a sulfonic acid group in the water-soluble polymer (A) is 25-100 mass% with respect to the whole water-soluble polymer (A).

Description

[Technical Field]

[0001] This invention relates to an aqueous composition for lithium-ion secondary battery positive electrodes, a lithium-ion secondary battery positive electrode, and a lithium-ion secondary battery. [Background technology]

[0002] Rechargeable batteries are batteries that can be repeatedly charged and discharged. Against the backdrop of growing environmental concerns in recent years, the use of rechargeable batteries is advancing not only in electronic devices such as mobile phones and laptops, but also in fields such as automobiles and aircraft. In response to this increasing demand for rechargeable batteries, research is also being actively conducted. In particular, lithium-ion batteries, which are lightweight, compact, and have high energy density, are attracting attention from various industries, and their development is thriving.

[0003] Lithium-ion batteries are mainly composed of a positive electrode, electrolyte, negative electrode, and separator. Among these, the electrodes (positive and negative electrodes) are made by coating an electrode composition onto a current collector. The positive electrode composition used to form the positive electrode mainly consists of a positive electrode active material (hereinafter sometimes simply referred to as "active material"), a conductive additive, a binder, and a solvent. Polyvinylidene fluoride (PVDF) is commonly used as the binder in positive electrode compositions, and N-methyl-2-pyrrolidone (NMP) is commonly used as the solvent. The main reasons for using these in positive electrode compositions are that (i) PVDF is chemically and electrically stable, and NMP is a solvent that dissolves PVDF and has long-term stability, and (ii) nickel-cobalt-manganese (NCM) series active materials, which are commonly used as positive electrode active materials, are said to be particularly prone to degradation in water if they have a high nickel content, and therefore require the use of an organic solvent.

[0004] In recent years, there has been growing interest in the handling characteristics of solvents from various perspectives. From this standpoint, NMP is difficult to handle, and the use of solvents with superior handling characteristics is desired. Furthermore, PVDF may be subject to PFAS (per-fluoropolymer) regulations. Therefore, there is a growing demand for electrode compositions that are not subject to PFAS regulations and do not use organic solvents, specifically water-based compositions.

[0005] Under these circumstances, various studies and developments are being conducted on aqueous cathode compositions and thickeners and binders that can be used in cathode compositions. As a composition for forming the cathode of a secondary battery, progress is being made in developing cathodes formed from an aqueous paste for cathodes containing a cathode active material, an aqueous dispersion elastomer, and a water-soluble polymer that acts as a thickener. Among these, examples using celluloses and polycarboxylic acid compounds as water-soluble polymers have been disclosed (see Patent Documents 1 and 2 below). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2005-63825 [Patent Document 2] Japanese Patent Publication No. 2006-134777 [Overview of the project] [Problems that the invention aims to solve]

[0007] Regarding thickeners included in aqueous pastes for cathodes, Patent Documents 1 and 2 exemplify water-soluble polymers such as celluloses including carboxymethylcellulose (CMC), polyacrylic acid compounds, and compounds having a vinylpyrrolidone structure, and in practice, cellulose compounds are used. However, these compounds are not always sufficient in terms of the long-term stability of aqueous formulations, and there is room for improvement.

[0008] To solve the above-mentioned problems, the present invention aims to provide an aqueous composition for lithium-ion secondary battery cathodes that is an aqueous composition and has excellent stability over time, as well as a lithium-ion secondary battery cathode using the same, and a lithium-ion secondary battery. [Means for solving the problem]

[0009] <1> Active material and, A water-soluble polymer (A) containing a constituent unit corresponding to a monomer having a sulfonic acid group, Includes, The total amount of constituent units corresponding to the monomer having the sulfonic acid group in the water-soluble polymer (A) is 25% by mass or more and 100% by mass or less relative to the total amount of the water-soluble polymer (A). Aqueous composition for the positive electrode of lithium-ion secondary batteries. <2> A water-soluble polymer (B) containing a carboxyl group-containing structural unit (excluding those corresponding to the water-soluble polymer (A)) further comprises: <1> Aqueous composition for lithium-ion secondary battery cathodes as described above. <3> The weight-average molecular weight of the water-soluble polymer (A) is between 50,000 and 5,000,000. <1> or <2> Aqueous composition for lithium-ion secondary battery cathodes as described above. <4> Further containing a conductive additive, <1> ~ <3> Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <5> The content of the conductive additive in the composition is 3.5% by mass or more and 10.0% by mass or less, relative to the total amount of nonvolatile components in the composition. <4> Aqueous composition for lithium-ion secondary battery cathodes as described above. <6> Further comprising particulate polymer, <1> ~ <5> Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <7> The particulate polymer contains a (meth)acrylic acid ester monomer. The aqueous composition for a positive electrode of a lithium-ion secondary battery according to <6>. <8> It further contains a conductive assistant and a particulate polymer. When the 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 the peak area, 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 structural unit derived from an ethylenically unsaturated carboxylic acid (salt). The content ratio of the structural unit derived from the ethylenically unsaturated carboxylic acid (salt) is 0.10 mass% or more and 15.00 mass% or less in total based on the total amount of the particulate polymer. The aqueous composition for a positive electrode of a lithium-ion secondary battery according to any one of <1> to <5>. <9> The particulate polymer contains a structural unit derived from an ethylenically unsaturated carboxylic acid (salt). The content ratio of the structural unit derived from the ethylenically unsaturated carboxylic acid (salt) is 0.10 mass% or more and 15.00 mass% or less in total based on 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>. <10> The particulate polymer contains a monobasic acid (salt) and / or a dibasic acid (salt). The aqueous composition for a positive electrode of a lithium-ion secondary battery according to any one of <6> to <9>. <11> 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 the structural units derived from the ethylenically unsaturated carboxylic acid (salt) that the particulate polymer has is 0.030 to 10.00. The aqueous composition for a positive electrode of a lithium ion secondary battery according to <8>. <12> The ratio (O / bound COOH) of the proportion (mass %) of oxygen atoms on the surface of the conductive aid to the content ratio (bound COOH) of the monomer derived from the ethylenically unsaturated carboxylic acid (salt) bound to the particulate polymer with respect 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 aqueous composition for a positive electrode of a lithium ion secondary battery according to <8> or <9>. <13> The particulate polymer contains a crosslinkable monomer. The aqueous composition for a positive electrode of a lithium ion secondary battery according to any one of <6> to <12>. <14> Further comprising a preservative. The aqueous composition for a positive electrode of a lithium ion secondary battery according to any one of <1> to <13>. <15> The active material is a lithium phosphate compound. The aqueous composition for a positive electrode of a lithium ion secondary battery according to any one of <1> to <14>. <16> A positive electrode for a lithium ion secondary battery comprising the aqueous composition for a positive electrode of a lithium ion secondary battery according to any one of <1> to <15>. <17> A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to <16>.

Advantages of the Invention

[0010] According to the present invention, an aqueous composition for a positive electrode of a lithium ion secondary battery, which is an aqueous composition and has excellent stability, a positive electrode for a lithium ion secondary battery using the same, and a lithium ion secondary battery can be provided.

Modes for Carrying Out the Invention

[0011] The embodiments of the present invention (hereinafter also referred to as "these embodiments") will be described in detail below. It should be noted that the present invention is not limited to these embodiments, and can be implemented with various modifications within the scope of its gist. In this specification, "(meth)acrylic" means "acrylic" and its corresponding "methacrylic." Furthermore, unless otherwise specified, "~" in this specification includes the values ​​at both ends as the upper and lower limits.

[0012] 《First Embodiment》 <Aqueous composition for lithium-ion secondary battery cathodes> The aqueous composition for the positive electrode of a lithium-ion secondary battery according to the first embodiment comprises an active material and a water-soluble polymer (A) (hereinafter sometimes simply referred to as "water-soluble polymer (A)") containing constituent units corresponding to monomers having sulfonic acid groups, wherein the total amount of constituent units corresponding to monomers having sulfonic acid groups in the water-soluble polymer (A) is 25% by mass or more and 100% by mass or less relative to the total amount of the water-soluble polymer (A). Hereinafter, the aqueous composition for the positive electrode of a lithium-ion secondary battery according to the first embodiment may be referred to as "aqueous composition for positive electrode".

[0013] In the first embodiment, "water-soluble polymer" includes water-soluble copolymers and is synonymous with "water-soluble (co)polymer" in the second to fourth embodiments described below. In the first embodiment, "sulfonic acid group" means a sulfonic acid base and is synonymous with "sulfonic acid (salt) group" in the second to fourth embodiments described below. In the first embodiment, the "constituent unit corresponding to the monomer" is sometimes referred to as the "constituent unit derived from the monomer." In the first embodiment, "water-soluble polymer (A) containing constituent units corresponding to monomers having sulfonic acid groups" is synonymous with "water-soluble (co)polymer (A) containing constituent units derived from monomers having sulfonic acid (salt) groups" in the second embodiment described later, and with "water-soluble (co)polymer containing constituent units derived from monomers having sulfonic acid (salt) groups" in the third and fourth embodiments described later. In the first embodiment, "water-soluble polymer (B) containing a carboxyl group component (excluding those corresponding to the water-soluble polymer (A))" is synonymous with "water-soluble (co)polymer (B) containing a carboxyl group component (excluding those corresponding to the water-soluble (co)polymer (A))" in the second embodiment described below. In the first embodiment, "particulate polymer" includes particulate copolymers and is synonymous with "particulate (co)polymer" in the second to fourth embodiments described below.

[0014] The aqueous cathode composition of the first embodiment includes a water-soluble resin containing a specific amount of sulfonic acid groups, thereby improving the time-dependent stability of viscosity and hysteresis. As a result, even when using the aqueous cathode composition after a certain period of time, for example, lithium-ion secondary battery cathodes with uniform thickness during line coating and excellent uniformity between products can be efficiently manufactured.

[0015] The aqueous positive electrode composition of the first embodiment is a slurry composition for the positive electrode of a lithium-ion secondary battery, and in addition to an active material and a water-soluble polymer (A), it contains an aqueous solvent as a dispersion medium. Furthermore, the aqueous positive electrode composition of the first embodiment may also contain a binder, a conductive additive, a preservative, and the like.

[0016] (active material) The active material used in the aqueous composition for the positive electrode of the first embodiment is a substance that can be used as a positive electrode active material. The positive electrode active material is an electrode active material used in the positive electrode, and is a substance that transfers electrons in the positive electrode of a lithium-ion secondary battery. The active material of the first embodiment is not particularly limited, but examples 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-type structure. Examples of lithium-containing composite metal oxides having a layered structure include lithium-containing cobalt oxide (LiCoO2), lithium-containing nickel oxide (LiNiO2), Co-Ni-Mn lithium composite oxide, Ni-Mn-Al lithium composite oxide, and Ni-Co-Al lithium composite oxide. Examples of lithium-containing composite metal oxides having a spinel structure include lithium manganese (LiMn2O4), or Li[Mn], which is obtained by substituting some of the Mn in lithium manganese with other transition metals. 3 / 2 M 1 / 2 Examples include ]O4 (where M is Cr, Fe, Co, Ni, Cu, etc.). Examples of lithium-containing composite metal oxides having an olivine-type structure include Li X Examples include olivine-type lithium phosphate compounds represented by MPO4 (wherein M represents at least one 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). Other examples include transition metal oxides, transition metal sulfides, and lithium-containing composite metal oxides of lithium and transition metals.

[0017] Among these active materials, although not particularly limited, olivine-type lithium phosphate compounds are preferred from the viewpoint of long lifespan, safety, and availability for lithium-ion secondary battery cathodes. Specifically, LiFePO4 (lithium iron phosphate), LiMnPO4 (lithium manganese phosphate), LiMn (1-y) Fe y PO4 (lithium iron manganese phosphate) (where y is a number satisfying 0 ≤ y ≤ 1) is preferred, and LiFePO4 is more preferred. These active materials may be carbon-coated to enhance electronic conductivity.

[0018] -Particle size- The particle size of the active material is expressed as the volume-based D50 particle size and is not particularly limited, but in order to easily obtain an appropriate viscosity for the cathode aqueous composition and to improve Li ion conductivity, it is preferably 0.6 μm to 8.0 μm, more preferably 0.65 μm to 7.0 μm, even more preferably 0.7 μm to 6.0 μm, and particularly preferably 0.75 μm to less than 5.0 μm. In the first embodiment, the 50% cumulative diameter d50 obtained from the measured particle size distribution of the cathode active material was measured using a laser light diffraction scattering particle size analyzer (Microtrac MT3300EXII, manufactured by Microtrac Bell Co., Ltd.), and this was taken as the average particle size.

[0019] The content of the active material in the cathode aqueous system composition is preferably 70% to 99.5% by mass, more preferably 80% to 97% by mass, and particularly preferably 85% to 95% by mass, relative to the total amount of nonvolatile components in the composition, in order to obtain high capacity and high load characteristics in a lithium-ion secondary battery using the cathode aqueous system composition obtained using the cathode aqueous system composition of the first embodiment. Here, "nonvolatile components in the composition" refers to the nonvolatile components excluding volatile components such as water in the cathode aqueous system composition, and means the components remaining after drying the cathode aqueous system composition at 130°C for 1 hour under normal pressure.

[0020] (Water-soluble polymer (A)) The cathode aqueous composition of the first embodiment includes a water-soluble polymer (A) containing constituent units corresponding to monomers having sulfonic acid groups. The water-soluble polymer (A) of the first embodiment can serve as a thickening agent for the composition. In the water-soluble resin of the first embodiment, "water-soluble" means that when 0.5 g of the polymer is dissolved in 100 g of water at 25°C, the insoluble content is less than 3.0% by mass. In cases where the solubility of the water-soluble polymer in water changes depending on the pH of the water, if there is a pH range in which the water-soluble polymer becomes water-soluble, the polymer can be considered water-soluble.

[0021] In the water-soluble resin of the first embodiment, "constituent unit corresponding to a monomer having a sulfonic acid group" means a constituent unit in the polymer having a structure corresponding to a monomer having a sulfonic acid group. Hereinafter, the constituent unit corresponding to a monomer having a sulfonic acid group may be referred to as a "sulfonic acid group-containing unit."

[0022] In the first embodiment, the "sulfonic acid group" is a group represented by "-SO3-R", where R may be a hydrogen atom, an alkali metal (Na, K, Li, etc.), or an ammonium (NH3) salt. Examples of sulfonic acid groups in the first embodiment are not limited to, but include -SO3H, -SO3Na, -SO3K, -SO3Li, -SO3NH3, etc. Monomers having a sulfonic acid group are not particularly limited, but examples 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-alyloxy-2-hydroxypropanesulfonic acid, etc., and examples of their salts include lithium salts, sodium salts, potassium salts, ammonium salts, etc. Furthermore, reactive emulsifiers having so-called sulfonic acid groups, for example, alkylallyl sulfosuccinates (e.g., "Eleminol (trademark) JS-2" and "Eleminol (trademark) JS-5" manufactured by Sanyo Chemical Industries; "Latemul (trademark) S-120", "Latemul (trademark) S-180A", and "Latemul (trademark) S-180" manufactured by Kao Corporation, etc.); polyoxyethylene alkylpropenylphenyl ether sulfates (e.g., "Aqualon (trademark) HS-10" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) Examples include "Aqualon (trademark) HS-1025"); α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfate (for example, "Adekaria Soap (trademark) SE-1025N" manufactured by Asahi Denka Kogyo Co., Ltd.); ammonium=α-sulfonato-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene (for example, "Aqualon (trademark) KH-10" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). From the viewpoint of improving the viscosity and hysteresis stability over time of the cathode aqueous composition, styrene sulfonic acid, vinyl sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and their lithium salts, sodium salts, potassium salts, and ammonium salts are preferred, and styrene sulfonic acid, and their lithium salts, sodium salts, potassium salts, and ammonium salts are more preferred.

[0023] The water-soluble polymer (A) in the first embodiment may contain, in addition to the sulfonic acid group-containing units, constituent units corresponding to other polymerizable monomers (hereinafter sometimes referred to as "other monomers"). Examples of other monomers are not particularly limited, but include polymerizable compounds that do not contain sulfonic acid groups and contain hydrophilic groups other than sulfonic acid groups. Other examples of monomers include monomers having carboxyl groups such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, 2-acryloyloxyethyl succinic acid, and vinylbenzoic acid; monomers having hydroxyl groups such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate; 3-alyroxy-2-hydroxypropane phosphate, dioctyl-2-methacryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, monomethyl-2-methacryloyloxyethyl phosphate, dimethyl-2-methacryloyloxyethyl phosphate, and monoethyl Examples include monomers having a phosphate group, such as -2-methacryloyloxyethyl phosphate, diethyl-2-methacryloyloxyethyl phosphate, monoisopropyl-2-methacryloyloxyethyl phosphate, diisopropyl-2-methacryloyloxyethyl phosphate, mono-n-butyl-2-methacryloyloxyethyl phosphate, di-n-butyl-2-methacryloyloxyethyl phosphate, monobutoxyethyl-2-methacryloyloxyethyl phosphate, dibutoxyethyl-2-methacryloyloxyethyl phosphate, mono(2-ethylhexyl)-2-methacryloyloxyethyl phosphate, and di(2-ethylhexyl)-2-methacryloyloxyethyl phosphate.Also, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate Monomers such as alkyl (meth)acrylates including n-tetradecyl (meth)acrylate and stearyl (meth)acrylate, polyalkylene glycol mono(meth)acrylate monomers including polyethylene glycol mono(meth)acrylate and polypropylene glycol mono(meth)acrylate; monomers such as styrene, 1,3-butadiene, (meth)acrylonitrile, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, and glycidyl (meth)acrylate can also be used as long as their water solubility is not impaired. While not particularly limited, examples of other monomers to be combined with the monomer containing a sulfonic acid group in the first embodiment include, from the viewpoint of not impairing water solubility and improving the viscosity and hysteresis stability over time of the cathode aqueous composition, 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. One of the other monomers exemplified above may be used alone, or two or more may be used in combination.

[0024] In the first embodiment, the total amount of sulfonic acid group-containing units in the water-soluble polymer (A) 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 viscosity and the time-dependent stability of 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 more preferably 29% by mass or more.

[0025] In the first embodiment, when the water-soluble polymer (A) contains constituent units corresponding to other monomers, the content of the constituent units corresponding to other monomers 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).

[0026] -Content- From the viewpoint of viscosity and hysteresis stability over time, the content of water-soluble polymer (A) in the cathode aqueous composition is preferably 0.5% to 5.0% by mass, more preferably 0.7% to 4.5% by mass, and particularly preferably 1.0% to 4.0% by mass, relative to the total amount of nonvolatile components in the composition.

[0027] -pH- In the first embodiment, the pH of the water-soluble polymer (A) is preferably 4.0 to 11.0, more preferably 4.5 to 10.7, and particularly preferably 5.0 to 10.5. Here, "pH of the water-soluble polymer" refers to the pH after adjusting the aqueous solution of the water-soluble polymer with water to a solid content of 5% by mass. The pH can be adjusted with, for example, sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydroxide, sodium bicarbonate, disodium hydrogen phosphate, amines such as monoethanolamine, dimethylethanolamine, triethanolamine, and triethylamine, and preferably sodium hydroxide, potassium hydroxide, and lithium hydroxide, and more preferably sodium hydroxide and lithium hydroxide. These can be used individually or in combination.

[0028] -Molecular weight- In the first embodiment, the weight-average molecular weight of the water-soluble polymer (A) is preferably 50,000 to 5,000,000, more preferably 100,000 to 3,000,000, even more preferably 200,000 to 1,000,000, and particularly preferably 500,000 to 1,000,000, from the viewpoint of viscosity and ease of handling of the cathode aqueous composition. 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 adjusted as appropriate by known means.

[0029] -Viscosity of the aqueous composition for the positive electrode- In the first embodiment, the viscosity of the aqueous composition for the positive electrode is preferably 300 mPa·s to 20,000 mPa·s, more preferably 500 mPa·s to 10,000 mPa·s, even more preferably 1,000 mPa·s to 8,000 mPa·s, and particularly preferably 1,000 mPa·s to 6,000 mPa·s, from the viewpoint of ease of handling.

[0030] The water-soluble polymer (A) in the first embodiment may contain a preservative. Examples of preservatives, such as those described later, can be used individually or in combination.

[0031] -Method for producing water-soluble polymer (A)- The water-soluble polymer (A) in the first embodiment is not particularly limited, but for example, it can be produced by polymerizing a monomer composition containing the monomers described above in an aqueous solvent. In this case, the ratio (by mass) of each monomer in the monomer composition can usually be the same as the ratio of constituent units in the water-soluble polymer. Examples of aqueous solvents are described later. Furthermore, the polymerization method for the water-soluble polymer (A) in the first embodiment is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization can be used. In addition, any method such as ionic polymerization, radical polymerization, or living radical polymerization can be used as the polymerization method for the water-soluble polymer in the first embodiment. In the method for synthesizing the water-soluble polymer (A) in the first embodiment, polymerization initiators, molecular weight modifiers, chelating agents, pH adjusters, etc., can be added as appropriate. Examples of polymerization initiators 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 α,α'-azobisisobutyronitrile and 2,2'-azobis(2-methylpropionamidine) dihydrochloride; and persulfate compounds such as ammonium persulfate, potassium persulfate, and sodium persulfate. A single polymerization initiator may be used alone, or two or more may be used in any ratio. The polymerization temperature and polymerization time can be arbitrarily selected depending on the polymerization method and the type of polymerization initiator. Typically, the polymerization temperature is approximately 30°C or higher, and the polymerization time is about 0.5 to 30 hours.

[0032] (Water-soluble polymer containing a carboxyl group (B)) The aqueous cathode composition of the first embodiment may further contain, in addition to the water-soluble polymer (A), a water-soluble polymer (B) containing a constituent unit having a carboxyl group (excluding those corresponding to the water-soluble polymer (A)) (hereinafter sometimes simply referred to as "water-soluble polymer (B)"). The "water-soluble (co)polymer (B)" described in the second embodiment below can be used as the water-soluble polymer (B).

[0033] (dispersion medium) The aqueous composition for the positive electrode of 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 it is preferably an aqueous solvent with a boiling point of 80°C or higher at atmospheric pressure. The aqueous solvent is not particularly limited, but examples include water; alcohols such as ethyl alcohol, isopropyl alcohol, and n-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 γ-butyrolactone; and ethers such as 1,3-dioxolane, 1,4-dioxolane, and tetrahydrofuran. Water is preferred as the aqueous solvent from the viewpoint of ease of handling and ease of application to the aqueous composition for the positive electrode. The aqueous solvent may be used alone or two or more in any ratio.

[0034] The content of the dispersion medium in the cathode aqueous system composition is preferably 35% to 65% by mass, more preferably 37% to 64% by mass, and particularly preferably 39% to 63% by mass, based on the total amount in the composition, from the viewpoint of the time-dependent stability of the viscosity and hysteresis of the cathode aqueous system composition and the homogeneity of the thickness during line coating.

[0035] (binder) The cathode aqueous composition of the first embodiment may contain a binder. As the binder, any known binder that can be dispersed in an aqueous solvent and used in the cathode aqueous composition can be appropriately selected and used. There are no particular limitations on the binder, but for example, a particulate polymer that is water-insoluble and dispersed in water can be used. One type of particulate polymer may be used alone, or two or more types may be used in combination. By adding a particulate polymer, flexibility is imparted to the cathode, and an improvement in yield can be expected.

[0036] Particulate polymers include, for example, polymers having predetermined structural units. While there are no particular limitations on the structural units of particulate polymers, examples include structural units derived from the following monomers: (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 vinylnaphthalene; and nitrile group-containing monomers such as acrylonitrile. Aromatic divinyl monomers such as divinylbenzene; polyalkylene glycol mono(meth)acrylate monomers such as polyethylene glycol mono(meth)acrylate and polypropylene glycol mono(meth)acrylate; alkylene glycols 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. Coll di(meth)acrylate monomers; polyol poly(meth)acrylate monomers such as trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tetra(meth)acrylate; allyl compound monomers such as diallyl fumarate, diaryl lutaconate, triallyl isocyanurate; vinyltrimethoxysilane, vinyltriethoxy Silane monomers such as sisilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltriethoxysilane; aliphatic conjugated diene monomers such as 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 2-chlor-1,3-butadiene;Monomers having carboxyl groups such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and 2-acryloyloxyethyl succinic acid; 3-alyroxy-2-hydroxypropane phosphate, dioctyl-2-methacryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, monomethyl-2-methacryloyloxyethyl phosphate, dimethyl-2-methacryloyloxyethyl phosphate, monoethyl-2-methacryloyloxyethyl phosphate, diethyl-2-methacryloyloxyethyl phosphate, monoisopropyl-2-methacryloyloxyethyl phosphate, diisopropyl-2-methacryloyloxyethyl phosphate, mono-n-butyl-2-methacryloyloxyethyl phosphate, di-n-butyl-2-methacryloyloxyethyl phosphate, monobutoxyethyl-2-methacryloyloxyethyl phosphate, dibutoxyethyl-2-methacryloyloxyethyl phosphate Examples include monomers having a phosphate group such as roxyethyl phosphate, mono(2-ethylhexyl)-2-methacryloyloxyethyl phosphate, and di(2-ethylhexyl)-2-methacryloyloxyethyl phosphate; unsaturated carboxylic acid amide monomers such as (meth)acrylamide and N,N-dimethyl(meth)acrylamide; unsaturated monomers containing hydroxyalkyl groups such as β-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate; unsaturated monomers having an epoxy group such as glycidyl (meth)acrylate; and monomers having a sulfonic acid group such as vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfoethyl methacrylate, sulfopropyl methacrylate, sulfobutyl methacrylate, 2-acrylamide-2-methylpropanesulfonic acid, and 3-alyloxy-2-hydroxypropanesulfonic acid. The monomers having a carboxyl group, a phosphate group, and a sulfonic acid group described above may also be salts of the carboxyl group, phosphate group, or sulfonic acid group. For example, lithium salts, sodium salts, potassium salts, or ammonium salts of the carboxyl group, phosphate group, or sulfonic acid group may be used. The other monomers may be used individually from the examples given above, or two or more may be used in combination.

[0037] The particulate polymer may further contain crosslinkable monomers. The inclusion of crosslinkable monomers in the particulate polymer prevents the compound layer from dissolving in the electrolyte, thus maintaining good battery characteristics. There are no particular limitations on the crosslinkable monomers, but they are any constituent units of the particulate polymers exemplified above that have a crosslinkable group, and examples include constituent units 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, 1,9-nonanediol di(meth)acrylate; trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tetra(meth) Examples include polyol poly(meth)acrylate monomers such as acrylates; allyl compound monomers such as diallyl fumarate, diaryl uitaconate, and triallyl isocyanurate; and silane monomers such as vinyltrimethoxysilane, vinyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltriethoxysilane. Other monomers may be used individually from the examples above, or two or more may be used in combination.

[0038] -Average particle size- The average particle size of the binder (particulate polymer) is not particularly limited, but from the viewpoint of strength and flexibility of the cathode obtained using the aqueous cathode composition, it is preferably 50 nm to 1000 nm, more preferably 80 nm to 700 nm, even more preferably 100 nm to 500 nm, and particularly preferably 130 nm to 400 nm. The average particle size of the binder can be measured by the method described in the examples below and can be adjusted as appropriate by known means.

[0039] From the viewpoint of strength and flexibility of the positive electrode obtained using the positive electrode aqueous composition, the binder (particulate polymer) content in the positive electrode aqueous composition 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, relative to the total amount of nonvolatile components in the composition.

[0040] -pH- In the first embodiment, the pH of the binder (particulate polymer) dispersion 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, preferably 50°C or lower, more preferably 40°C or lower, even more preferably 35°C or lower, and particularly preferably 30°C or lower, from the viewpoint of electrode flexibility and windability, and bonding 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 it with a differential scanning calorimeter (DSC) in accordance with ASTM D3418-15. A DDSC curve is obtained by differentiating the DSC curve. If the DDSC curve has multiple peaks, the glass transition temperature obtained from the peak corresponding to the temperature range where the slope of the DSC curve is maximum is the glass transition temperature as used herein.

[0041] -Method for producing binder dispersion- The binder (particulate polymer) dispersion in the first embodiment is not particularly limited, but can be prepared, for example, by emulsion polymerization or suspension polymerization using monomers as raw materials, or by dispersing a solution-polymerized copolymer in water and removing the solvent. Appropriate seed particles can be used when polymerization of monomers, and seed particles can also be obtained by conventional emulsion polymerization. Furthermore, known methods can be employed for polymerization, and the product can be manufactured in an aqueous medium using a polymerization initiator, reducing agent, chain transfer agent, chelating agent, pH adjuster, emulsifier, preservative, defoamer, etc. as appropriate. The above-mentioned aqueous dispersion medium can be used as the aqueous medium.

[0042] The emulsifier is not particularly limited, but for example, anionic surfactants, nonionic surfactants, amphoteric surfactants, and reactive surfactants can be used alone or in combination of two or more.

[0043] Anionic surfactants are not particularly limited, but examples include nonreactive alkyl sulfates, polyoxyethylene alkyl ether sulfates, alkylbenzene sulfons, alkylnaphthalene sulfons, alkyl sulfosuccinates, alkyldiphenyl ether disulfons, naphthalene sulfonic acid formalin condensates, polyoxyethylene polycyclic phenyl ether sulfates, polyoxyethylene distyrenated phenyl ether sulfates, fatty acid salts, alkyl phosphates, and polyoxyethylene alkylphenyl ether sulfates.

[0044] Nonionic surfactants are not particularly limited, but examples include 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, and polyoxyethylene alkylphenyl ethers.

[0045] While not particularly limited, amphoteric surfactants include betaines such as lauryl betaine and stearyl betaine, and amino acid-type surfactants such as lauryl-β-alanine, stearyl-β-alanine, and lauryl di(aminoethyl)glycine.

[0046] The reactive surfactant is not particularly limited, but for example, it is an ethylenically unsaturated monomer having a sulfonic acid group, a sulfonate group, or a sulfate ester group and salts thereof, and is preferably a compound having a sulfonic acid group or a group that is an ammonium salt or alkali metal salt thereof (ammonium sulfonate group or alkali metal sulfonate group). Specific examples include alkylallyl sulfosuccinates (for example, "Eleminol (trademark) JS-2" and "Eleminol (trademark) JS-5" manufactured by Sanyo Chemical Industries; "Latemul (trademark) S-120," "Latemul (trademark) S-180A," and "Latemul (trademark) S-180" manufactured by Kao Corporation); polyoxyethylene alkylpropenylphenyl ether sulfates (for example, "Aqualon (trademark) HS-10" and "Aqualon (trademark) HS-1025" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.); α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfates (for example, "Adekaria Soap (trademark) SE-1025N" manufactured by Asahi Denka Kogyo Co., Ltd.); ammonium = α Examples include -sulfonato-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene (for example, "Aqualon (trademark) KH-10" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxypolyoxyethylene (for example, "Adekarya Soap (trademark) NE-20", "Adekarya Soap (trademark) NE-30", "Adekarya Soap (trademark) NE-40" manufactured by Asahi Denka Kogyo Co., Ltd.), and polyoxyethylene alkylpropenylphenyl ether (for example, "Aqualon (trademark) RN-10", "Aqualon (trademark) RN-20", "Aqualon (trademark) RN-30", "Aqualon (trademark) RN-50" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). The amount of emulsifier used is preferably 0.01% to 5.0% by mass, more preferably 0.05% to 3.0% by mass, even more preferably 0.1% to 2.0% by mass, and most preferably 0.15% to 1.0% by mass, based on 100% by mass of the total monomer. The emulsifier may be used alone or in combination of two or more types.

[0047] While not particularly limited, the polymerization initiators can be used individually or in combination with 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 formed in combination with reducing agents such as sodium sulfite, ascorbic acid or its salts, erythorbic acid or its salts, and rongalit. As chain transfer agents, mercaptan-based chain transfer agents such as n-butyl mercaptan, t-butyl mercaptan, t-dodecyl mercaptan, n-octyl mercaptan, and n-lauryl mercaptan; nuclear-substituted α-methylstyrene dimers such as α-methylstyrene dimer; disulfides such as tetramethylthiuradium disulfide and tetraethylthiuradium disulfide; halogenated hydrocarbon derivatives such as carbon tetrachloride and carbon tetrabromide; and 2-ethylhexyl thioglycolate can be used individually or in combination. As chelating agents, sodium ethylenediaminetetraacetate, pentasodium diethylenetriaminepentaacetate, etc., can be used. Examples of pH adjusting agents include sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydroxide, sodium bicarbonate, disodium hydrogen phosphate, and amines such as monoethanolamine, dimethylethanolamine, triethanolamine, and triethylamine. Preferably, sodium hydroxide, potassium hydroxide, and lithium hydroxide are used, and more preferably, sodium hydroxide and lithium hydroxide. These can be used individually or in combination. Examples of preservatives include isothiazolinoline compounds, phenols and their alkali metal salts, quinone chlorides, nitro group-containing compounds, amines, amides, iodine-containing compounds, thiazoles, thiocyanates, etc. Examples include 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 1,2-benzoisothiazolin-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. These can be used alone or in combination. Examples of defoaming agents include mineral oil-based defoaming agents, polyether-based defoaming agents, silicone-based defoaming agents, and emulsion-based defoaming agents. For example, Noptum 777F (manufactured by Sunopco), Adekanate B-925, Adekanate B-940, and Adekanate B-556 (manufactured by ADEKA) can be used.

[0048] (Conductive additive) The aqueous positive electrode composition of the first embodiment may contain a conductive additive. The conductive additive plays a role in improving the electrical contact between the active materials. By including a conductive additive, the aqueous positive electrode composition of the first embodiment can improve the discharge rate characteristics of the lithium-ion secondary battery.

[0049] The conductive additive in the first embodiment is not particularly limited, but known conductive additives such as carbon black, furnace black, acetylene black, Ketjen black, graphite, vapor-grown carbon fibers, and conductive carbon such as carbon nanotubes can be appropriately selected and used. One type of conductive additive may be used alone, or two or more types may be used in any ratio.

[0050] The content of the conductive additive in the positive electrode aqueous system composition is preferably 3.5% to 10.0% by mass, more preferably 3.6% to 9.0% by mass, more preferably 3.8% to 8.0% by mass, and particularly preferably 4.1% to 7.0% by mass, relative to the total amount of nonvolatile components in the composition, from the viewpoint of improving the viscosity of the positive electrode aqueous system composition, hysteresis, and electrical contact between positive electrode active materials.

[0051] In the case where the cathode aqueous system composition of the first embodiment includes a conductive additive and a particulate polymer, for example, when the elements present on the surface of the conductive additive are measured by X-ray photoelectron spectroscopy and the proportion of oxygen atoms (mass%) and carbon atoms (mass%) are calculated based on the peak area, the proportion of oxygen atoms on the surface of the conductive additive may be 0.30% by mass or more and 2.00% by mass or less, and the ratio of the proportion of atoms (mass%) to the proportion of carbon atoms (mass%) (O / C) may be 0.0020 or more and 0.0250 or less. The particulate polymer may contain constituent units derived from ethylenically unsaturated carboxylic acids (salts), and the content of constituent units derived from ethylenically unsaturated carboxylic acids (salts) may be 0.10% by mass or more and 15.00% by mass or less in total with respect to the total amount of particulate polymer. In addition to the conductive additive and particulate polymer described above, the "conductive additive" and "particulate (co)polymer" described in the fourth embodiment described later may be used.

[0052] The aqueous system composition for the positive electrode in the first embodiment may include particulate polymers containing constituent units derived from ethylenically unsaturated carboxylic acids (salts), and the content ratio of constituent units derived from ethylenically unsaturated carboxylic acids (salts) may be 0.10% by mass or more and 15.00% by mass or less in total with respect to the total amount of particulate polymers. In addition to the particulate polymers described above, the "particulate (co)polymers" described in the second or fourth embodiment below may be used.

[0053] The cathode aqueous system composition of the first embodiment may contain a particulate polymer that includes a monobasic acid (salt) and / or a dibasic acid (salt). The monobasic acid (salt) and dibasic acid (salt) described in the fourth embodiment below can be used.

[0054] The aqueous system composition for the positive electrode in the first embodiment may have a value (O×COOH) of 0.030 to 10.00, which is the product of the proportion of oxygen atoms on the surface of the conductive additive (mass%) and the proportion of the total amount of constituent units derived from ethylenically unsaturated carboxylic acid (salt) in the particulate polymer (mass%). In addition to the conductive additive described above, the "conductive additive" described in the fourth embodiment below may be used as the conductive additive and particulate polymer.

[0055] The aqueous system composition for the positive electrode in the first embodiment may have a ratio (O / bonded COOH) of 0.0050 to 0.1000 between the proportion of oxygen atoms on the surface of the conductive additive (mass%) and the ratio of the content of monomers derived from ethylenically unsaturated carboxylic acid (salt) bound to the particulate polymer (bonded COOH) to the total amount of monomers derived from ethylenically unsaturated carboxylic acid (salt) contained in the particulate polymer. In addition to the conductive additive described above, the "conductive additive" described in the fourth embodiment below may be used as the conductive additive and particulate polymer.

[0056] (Preservative) The cathode aqueous system composition of the first embodiment may contain a preservative. The preservative may be contained in the water-soluble polymer (A) as described above. By including a preservative, the viscosity and hysteresis stability over time can be further improved in the cathode aqueous system composition of the first embodiment. While not particularly limited, examples of preservatives include isothiazolinoline compounds, phenols and their alkali metal salts, quinone chlorides, nitro group-containing compounds, amines, amides, iodine-containing compounds, thiazoles, thiocyanates, etc. For example, 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 1,2-benzoisothiazolin-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.

[0057] The amount of preservatives in the cathode aqueous composition is preferably 0.00001% to 1% by mass, more preferably 0.00002% to 0.5% by mass, and particularly preferably 0.00004% to 0.1% by mass, relative to the total amount of nonvolatile components in the composition, from the viewpoint of viscosity, hysteresis stability over time, and electrode bonding strength.

[0058] <Positive electrode for lithium-ion secondary batteries> The positive electrode for a lithium-ion secondary battery according to the first embodiment includes the aqueous composition for the positive electrode according to the first embodiment. In other words, the positive electrode for a lithium-ion secondary battery according to the first embodiment can be manufactured using the aqueous composition for the positive electrode according to the first embodiment. The method for manufacturing the positive electrode for a lithium-ion secondary battery according to the first embodiment is not particularly limited, but for example, the positive electrode for a lithium-ion secondary battery can be manufactured by applying the aqueous composition for the positive electrode according to the first embodiment to a current collector for a positive electrode, heating it, and drying it. The current collector for the positive electrode is not particularly limited, but for example, aluminum foil can be used.

[0059] The method for applying the aqueous composition for the positive electrode of the first embodiment to the positive electrode current collector is not particularly limited, but any coater head can be used, such as a reverse roll coater, comma bar coater, gravure coater, or air knife coater. The method for drying the coated film of the aqueous composition for the positive electrode of the first embodiment is not particularly limited, but for example, standing drying, forced-air drying, hot air drying, infrared heater, or far-infrared heater can be used. The drying temperature of the coated film of the aqueous composition for the positive electrode of the first embodiment is not particularly limited, but for example, it can be set to 60°C to 150°C.

[0060] <Lithium-ion rechargeable battery> The lithium-ion secondary battery of the first embodiment includes a 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. The lithium-ion secondary battery of the first embodiment only needs to have a positive electrode, which is at least one of its main components, obtained using an aqueous composition for the positive electrode.

[0061] The method for manufacturing the lithium-ion secondary battery of the first embodiment is not particularly limited, but examples include a method in which the negative electrode and the positive electrode of the first embodiment are placed facing each other via a separator, an electrolyte is injected, and then sealed. The negative electrode and electrolyte are not particularly limited, and those applicable to lithium-ion secondary batteries can be appropriately selected and used. For example, as the electrolyte, an electrolyte such as LiClO4, LiBF4, or LiPF6 dissolved in an organic solvent can be used. The organic solvent is not particularly limited, but examples include ethers, ketones, lactones, nitriles, amines, amides, carbonates, and chlorinated hydrocarbons. Typical examples include tetrahydrofuran, acetonitrile, butyronitrile, propylene carbonate, ethylene carbonate, and diethyl carbonate, and can be used as one type or a mixture of two or more types.

[0062] 《Second Embodiment》 As described above, the aqueous composition for the positive electrode of a lithium-ion secondary battery described in the first embodiment may further contain a water-soluble polymer (B) containing a carboxyl group (excluding those corresponding to the water-soluble polymer (A)). Furthermore, the aqueous composition for the positive electrode of a lithium-ion secondary battery according to the second embodiment comprises an active material, a water-soluble (co)polymer (A) containing constituent units derived from monomers having sulfonic acid (salt) groups, and a water-soluble (co)polymer (B) containing constituent units having carboxyl groups (excluding those corresponding to the water-soluble (co)polymer (A)), wherein the content ratio of the constituent units derived from monomers having sulfonic acid (salt) groups is 25% by mass or more and 100% by 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 directly applied to the aqueous cathode composition of the first embodiment. Furthermore, the aqueous cathode composition of the lithium-ion secondary battery of the second embodiment is the same as that of the other embodiments except for the water-soluble (co)polymer (B) described below.

[0063] For example, the slurry composition described in Japanese Patent Publication No. 2014-165108 is said to achieve a high level of both cycle characteristics and adhesion. On the other hand, the present inventors have investigated and found that depending on the combination of components in the slurry composition, viscosity changes over time occur due to aggregation of components in the slurry composition, and that when manufacturing lithium-ion secondary battery cathodes using such slurry, there are problems such as insufficient electrode adhesion. From these findings, it has been found that there is still room for improvement in conventional compositions for lithium-ion secondary battery cathodes in terms of viscosity stability over time and electrode adhesion.

[0064] From the above points, the aqueous compositions for positive electrodes of the first and second embodiments described above, which include a water-soluble (co)polymer (B), exhibit 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 said composition.

[0065] (Water-soluble (co)polymer (B)) The cathode aqueous composition of the second embodiment may contain a water-soluble (co)polymer (B) containing a carboxyl group-containing structural unit (excluding those corresponding to the water-soluble (co)polymer (A)). The water-soluble (co)polymer (B) of the second embodiment can serve as a thickening agent for the cathode aqueous composition.

[0066] In this specification, "carboxyl group-containing structural units" is a term that includes structural units derived from monomers containing carboxyl groups, structural units derived from (co)polymers containing carboxyl groups, or alkali metal salts 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 structural units derived from monomers containing carboxyl groups and structural units derived from (co)polymers containing carboxyl groups.

[0067] The constituent units having carboxyl groups are not particularly limited as long as the constituent units of the polymer have carboxyl groups, but examples include glucose units having carboxyl groups in some of the glucose units constituting cellulose, (meth)acrylic acid units, etc. From the viewpoint of improving the viscosity and hysteresis stability over time of the aqueous composition for the cathode, glucose units having carboxyl groups in some of the glucose units constituting cellulose are preferred. The water-soluble (co)polymer (B) of the second embodiment may contain one of the above-mentioned constituent units alone, or two or more in any combination and ratio.

[0068] Specific examples of water-soluble (co)polymer (B) include, but are not limited to, cellulose derivatives having carboxyl groups, poly(meth)acrylic acid, and sodium poly(meth)acrylate. Among these, carboxymethylcellulose and alkali metal salts of carboxymethylcellulose (e.g., sodium salts), which are cellulose derivatives having carboxyl groups, are preferred. Water-soluble (co)polymer (B) can be used individually or in any combination and ratio of two or more types.

[0069] Examples of commercially available water-soluble (co)polymers (B) include the Sunrose MAC® series, Sunrose® F, A, and SLD series from Nippon Paper Industries Ltd., and the Selogen® series from Daiichi Kogyo Seiyaku Co., Ltd.

[0070] The content of carboxyl group-containing structural units in the water-soluble (co)polymer (B) in the second embodiment is not particularly limited, but from the viewpoint of viscosity and the time-dependent stability of hysteresis, 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), with a lower limit of 27% by mass or more, and even more preferably 29% by mass or more. The content of carboxyl group-containing structural units in the water-soluble (co)polymer (B) in the second embodiment can be measured by absorbance measurement.

[0071] In the second embodiment, if the water-soluble (co)polymer (B) contains constituent units derived from other monomers, the content of constituent units derived from other monomers is not particularly limited, but is preferably 75% by mass or less, more preferably 73% by mass or less, and particularly preferably 71% by mass or less, relative to the total solid content of the water-soluble (co)polymer (B). The lower limit is not particularly limited, and may be greater than 0% by mass.

[0072] -Content- The content ratio of water-soluble (co)polymer (B) in the water-soluble (co)polymer in the second embodiment is not particularly limited, but from the viewpoint of viscosity and hysteresis stability over time of the cathode aqueous composition and electrode adhesion, it is preferably 5% by mass or more and 70% by mass or less, more preferably 10% by mass or more and 60% by mass or less, and particularly preferably 20% by mass or more and 50% by mass or less, based on the total amount of nonvolatile components of the water-soluble (co)polymer.

[0073] The content of the water-soluble (co)polymer (B) in the cathode aqueous composition is not particularly limited, but from the viewpoint of viscosity, hysteresis stability over time, and electrode adhesion of the cathode aqueous composition, it is preferably 0.3% to 5.0% by mass, more preferably 0.4% to 1.5% by mass, and particularly preferably 0.45% to 1.0% by mass, relative to the total amount of nonvolatile components in the aqueous composition.

[0074] -pH- 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. Here, "pH of water-soluble (co)polymer (B)" refers to the pH after adjusting the aqueous solution of the water-soluble (co)polymer with water to a solid content of 1% by mass. The pH can be adjusted with, for example, sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydroxide, sodium bicarbonate, 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 individually or in combination.

[0075] -Molecular weight- 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 viscosity stability of the cathode aqueous composition, it is preferably 10,000 to 1,000,000, more preferably 30,000 to 700,000, and particularly preferably 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).

[0076] -viscosity- The viscosity of the water-soluble (co)polymer (B) is not particularly limited and can be set appropriately 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 to 10,000 mPa·s, more preferably 50 mPa·s to 7,000 mPa·s, and even more preferably 100 mPa·s to 5,000 mPa·s. The viscosity can be measured using an Anton Paar MCR-102 rheometer with a 1% aqueous solution of the water-soluble (co)polymer (B) at 25°C.

[0077] In the second embodiment, the ratio of the content of water-soluble (co)polymer (A) to water-soluble (co)polymer (B) is not particularly limited, but from the viewpoint of viscosity, hysteresis stability over time, and electrode adhesion of the aqueous composition for the positive electrode, 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.

[0078] (Particulate (co)polymer) The content of the constituent units derived from ethylenically unsaturated carboxylic acids (salts) is not particularly limited, but is 0.10% by mass or more and 15.00% by mass or less in total, 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 particulate (co)polymer. By having the content of the constituent units derived from ethylenically unsaturated carboxylic acids (salts) within the above range, aggregation in the aqueous composition is suppressed, and the viscosity and hysteresis of the aqueous composition are excellent over time. Therefore, when applying the aqueous composition to a current collector, it can be applied while maintaining appropriate fluidity, and tends to be easy to handle. Furthermore, adhesion to the electrode also tends to improve. The content of the constituent units derived from ethylenically unsaturated carboxylic acids (salts) can be measured by potentiometric titration of the particulate (co)polymer.

[0079] 《Third Embodiment》 The aqueous compositions for lithium-ion secondary battery cathodes described in the first and second embodiments may further contain particulate polymers. Furthermore, the aqueous composition for the positive electrode of a lithium-ion secondary battery according to the third embodiment comprises a particulate (co)polymer and a water-soluble (co)polymer containing constituent units derived from a monomer having a sulfonic acid (salt) group, wherein the content ratio of the constituent units derived from the monomer having a sulfonic acid (salt) group is 25% by mass or more and 100% by mass or less with respect to the total amount of the water-soluble (co)polymer. The following description of particulate (co)polymers can be directly applied to the cathode aqueous compositions of the first and second embodiments. Furthermore, the lithium-ion secondary battery cathode aqueous composition of the third embodiment is the same as that of the other embodiments except for the particulate (co)polymer described below.

[0080] Regarding the thickeners included in the aqueous composition for positive electrodes, Japanese Patent Publication No. 2014-165108 exemplifies water-soluble polymers such as celluloses including carboxymethylcellulose (CMC), polyacrylic acid compounds, and compounds having a vinylpyrrolidone structure, and in practice, cellulose compounds are used. However, these compounds are not always sufficient in terms of the long-term stability of the aqueous composition, and there is room for improvement. Furthermore, when manufacturing lithium-ion secondary battery positive electrodes using these aqueous compositions, the coating film obtained by applying the aqueous composition to the current collector and drying may develop defects, or so-called electrode cracks, and there is still room for improvement in this regard as well.

[0081] From the above points, the aqueous compositions for positive electrodes of the first and third embodiments described above, which include particulate (co)polymers, exhibit excellent viscosity stability over time and can suppress the occurrence of electrode cracking, thereby providing a positive electrode for a lithium-ion secondary battery and a lithium-ion secondary battery using the said composition.

[0082] (Particulate (co)polymer) In the third embodiment, the content of constituent units derived from monobasic acid (salt) monomers is not particularly limited, but from the viewpoint of particle dispersion stability, it is preferably 0.1% to 20.0% by mass, more preferably 0.1% to 10.0% by mass, even more preferably 0.2% to 5.0% by mass, and particularly preferably 0.2% to 2.0% by mass, relative to the total amount of particulate (co)polymer. Because the content of constituent units derived from monobasic acid (salt) monomers is within the above range, the aqueous composition for the positive electrode of the third embodiment suppresses aggregation in the aqueous composition and can be applied to the current collector while maintaining appropriate fluidity, thus tending to have excellent handling properties and excellent storage stability.

[0083] In the third embodiment, the content of constituent units derived from dibasic acid (salt) monomers is not particularly limited, but from the viewpoint of the mechanical strength of the particles, it is preferably 0.1% by mass or more and 10.0% by mass or less, more preferably 0.5% by mass or more and 5.0% by mass or less, even more preferably 1.0% by mass or more and 4.5% by mass or less, and particularly preferably 1.5% by mass or more and 3.5% by mass or less, relative to the total amount of particulate (co)polymer. When the content of constituent units derived from dibasic acid (salt) monomers 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, thus tending to have excellent handling properties and excellent storage stability.

[0084] 《Fourth Embodiment》 The aqueous compositions for lithium-ion secondary battery positive electrodes described in the first to third embodiments may contain a conductive additive and a particulate (co)polymer. Furthermore, the aqueous composition for the positive electrode of a lithium-ion secondary battery according to the fourth embodiment comprises a conductive additive and a particulate (co)polymer, wherein when the elements present on the surface of the conductive additive are measured by X-ray photoelectron spectroscopy and the proportion of oxygen atoms (mass%) and carbon atoms (mass%) are calculated based on the peak area, the proportion of oxygen atoms on the surface of the conductive additive is 0.30 mass% or more and 2.00 mass% or less, and the ratio of the proportion of oxygen atoms (mass%) to the proportion of carbon atoms (mass%) (O / C) is 0.0020 or more and 0.0250 or less, and the particulate (co)polymer contains constituent units derived from ethylenically unsaturated carboxylic acid (salt), and the content of the constituent units derived from 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 (co)polymer, this is an aqueous composition for the positive electrode of a lithium-ion secondary battery. The following descriptions regarding conductive additives and particulate (co)polymers can be directly applied to the aqueous cathode compositions of the first to third embodiments. Furthermore, the aqueous cathode composition for lithium-ion secondary batteries of the third embodiment is the same as that described in the other embodiments, except for the conductive additives and particulate (co)polymers described below.

[0085] For example, 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. On the other hand, the inventors' investigations revealed that when a specific conductive additive is combined with a specific binder, the conductive additive in the aqueous composition aggregates, and as a result, the viscosity of the aqueous composition changes over time. Furthermore, when using these aqueous compositions to manufacture the positive electrode of a lithium-ion secondary battery, the coating film obtained by applying the aqueous composition to the current collector and drying it may develop defects or other so-called electrode cracks, and it was found that there is still room for improvement in these respects.

[0086] From the above, the aqueous compositions for positive electrodes of the first to fourth embodiments described above, which include a conductive additive and a particulate (co)polymer, exhibit excellent viscosity stability over time and can suppress the occurrence of electrode cracking. This makes it possible to provide a positive electrode for a lithium-ion secondary battery and a lithium-ion secondary battery using the composition.

[0087] The aqueous positive electrode composition of the fourth embodiment may contain a conductive additive and a particulate polymer, wherein the proportion of oxygen atoms present on the surface of the conductive additive is within a predetermined numerical range, the ratio of the proportion of oxygen atoms to the proportion of carbon atoms present on the surface is within a predetermined numerical range, and the particulate (co)polymer contains a predetermined amount of constituent units derived from ethylenically unsaturated carboxylic acid (salt). This suppresses aggregation of the conductive additive in the aqueous positive electrode composition, resulting in excellent time-dependent stability of viscosity and hysteresis, and the coating film applied and dried with the aqueous positive electrode composition exhibits improved flexibility. As a result, even when using the aqueous positive electrode composition after a certain period of time, for example, lithium-ion secondary battery positive electrodes with uniform thickness during line coating and excellent uniformity between products can be efficiently manufactured. Furthermore, the occurrence of electrode cracking in the lithium-ion secondary battery positive electrode can be suppressed, contributing to improved product yield.

[0088] (Conductive additive) The conductive additive in the fourth embodiment is not particularly limited, and known conductive additives such as furnace black, carbon black, acetylene black, Ketjen black, graphite, vapor-grown carbon fibers, and conductive carbon such as carbon nanotubes can be appropriately selected and used. One type of conductive additive may be used alone, or two or more types may be used in any ratio. Among these, from the viewpoint of cost benefits, it is preferable that the conductive additive contains furnace black, and it is particularly preferable that it contains furnace black as an essential component.

[0089] In the fourth embodiment, the proportion of oxygen atoms present on the surface of the conductive additive is 0.30% by mass or more and 2.00% by mass or less, and the ratio of the proportion of oxygen atoms (mass%) to the proportion of carbon atoms (mass%) (O / C) may be 0.0020 or more and 0.0250 or less. Preferably, the proportion of oxygen atoms present on the surface of the conductive additive is 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. If the proportion of oxygen atoms present on the surface of the conductive additive is less than 0.30% by mass, the dispersibility in aqueous solvents deteriorates, and if it is more than 2.00% by mass, the performance as a conductive additive deteriorates, resulting in a decrease in battery performance when a lithium-ion secondary battery cathode is manufactured. The ratio of the mass percentage of oxygen atoms to the mass percentage of carbon atoms (O / C) is preferably 0.0030 to 0.0230, more preferably 0.0040 to 0.0220, and even more preferably 0.0050 to 0.0210. When the mass percentage of oxygen atoms present on the surface of the conductive additive, and the ratio of the mass percentage of oxygen atoms to the mass percentage of carbon atoms (O / C) are within the above range, aggregation of the conductive additive in the aqueous composition tends to be suppressed, and the viscosity and hysteresis of the aqueous composition tend to be excellent over time.

[0090] In this specification, the relative abundance of oxygen and carbon atoms present on the surface of a conductive additive can be measured by X-ray photoelectron spectroscopy (XPS). For example, the relative abundance of oxygen atoms (mass%) can be determined based on the peak area of ​​the O1s spectrum (525-545 eV) in the XPS analysis, and the relative abundance of carbon atoms (mass%) can be determined based on the peak area of ​​the C1s spectrum (280-300 eV) in the XPS analysis. Then, the O / C ratio can be determined from the respective relative abundances of oxygen and carbon atoms.

[0091] (Particulate (co)polymer) The aqueous cathode composition of the fourth embodiment may contain constituent units derived from ethylenically unsaturated carboxylic acids (salts) as particulate polymers. By including the above-mentioned conductive additive and particulate polymer in the aqueous cathode composition, aggregation of the conductive additive in the aqueous composition can be suppressed, and the viscosity and hysteresis of the aqueous composition are excellent over time.

[0092] In the fourth embodiment, the content of constituent units derived from ethylenically unsaturated carboxylic acids (salts) is 0.10% by mass or more and 15.00% by mass or less in total, 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, based on the total amount of particulate (co)polymer. By having the content of constituent units derived from ethylenically unsaturated carboxylic acids (salts) within the above range, the viscosity and hysteresis of the aqueous composition are excellent over time stability, and when the aqueous composition is applied to a current collector, it can be applied while maintaining appropriate fluidity, thus tending to have excellent handling properties.

[0093] In the fourth embodiment, the value obtained by multiplying the proportion of oxygen atoms on the surface of the conductive additive in the cathode aqueous composition (mass%) by the proportion (mass%) of the total amount of constituent units derived from the ethylenically unsaturated carboxylic acid (salt) in the particulate (co)polymer (O×COOH) 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. If the value obtained by multiplying the proportion of oxygen atoms on the surface of the conductive additive (mass%) by the total amount of constituent units derived from the ethylenically unsaturated carboxylic acid (salt) in the particulate (co)polymer (O×COOH) is less than 0.030, adhesion to the electrode is insufficient and cracking of the electrode occurs, and if it is greater than 10.00, aggregation occurs in the aqueous composition, the viscosity and hysteresis of the aqueous composition change over time and become unstable.

[0094] In the fourth embodiment, the ratio (O / bonded COOH) of the proportion of oxygen atoms on the surface of the conductive additive (mass%) to the proportion of monomers derived from ethylenically unsaturated carboxylic acid (salt) bound to the particulate (co)polymer (bonded COOH) 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. When the ratio (O / bonded COOH) of the oxygen atom content (mass%) on the surface of the conductive additive to the content (bonded 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 within the above range, adhesion to the electrode is excellent, the occurrence of electrode cracking tends to be suppressed, and aggregation in the aqueous composition is suppressed, resulting in excellent temporal stability of viscosity and hysteresis of the aqueous composition.

[0095] In this specification, the ratio of monomers derived from ethylenically unsaturated carboxylic acids (salts) bound to the particulate (co)polymer (bonded COOH) to the total amount of monomers derived from ethylenically unsaturated carboxylic acids (salts) contained in the particulate (co)polymer is determined as follows.

[0096] The acid value of the surface of the particulate (co)polymer is determined by conductivity titration, and this acid value is converted to the content of monomers derived from ethylenically unsaturated carboxylic acids (salts) bonded to the particulate (co)polymer, and calculated using the following formula. Bonded COOH = Content (parts by mass) of monomers derived from ethylenically unsaturated carboxylic acid (salt) calculated from the acid value / Content (parts by mass) of monomers derived from ethylenically unsaturated carboxylic acid (salt) in the preparation before polymerization × 100

[0097] The sample preparation method and titration conditions for conductivity titration are as follows: A 2g solids-containing particulate (co)polymer was diluted to 10% with distilled water and centrifuged in an ultracentrifuge (Beckman Coulter: Optima L-90K) to separate the particulate phase from the aqueous phase. Distilled water was added to the aqueous phase-removed sedimentation sample and redispersed using a shaker. The process of removing the aqueous phase by centrifugation and redispersing was repeated a total of three times. 5g of ion exchange resin (Mitsubishi Chemical: DIAION SK1B) was added to the particulate (co)polymer from which the aqueous phase had been removed, and the mixture was stirred for 5 minutes. The ion exchange resin was then removed by filtration. This procedure was repeated until the pH no longer changed. The solids content of the particulate (co)polymer after ion exchange and removal of the aqueous phase was measured. 15g of the particulate (co)polymer from which the aqueous phase had been removed was weighed into a 100ml beaker and diluted to 50g with distilled water. The sample was placed in an automatic titrator (Hiranuma Sangyo Co., Ltd.: COM-1750, electrode used: TPT-351) and subjected to conductivity titration with 0.1 N potassium hydroxide while stirring. The endpoint was detected using the V1 intersection detection method, and the acid value was determined.

[0098] The particulate (co)polymer in the fourth embodiment is not particularly limited as long as it contains constituent units derived from an ethylenically unsaturated carboxylic acid (salt), and the ethylenically unsaturated carboxylic acid (salt) may include, 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.

[0099] 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 styrene sulfonic acid, metaallyl sulfonic acid, allyl sulfonic acid, and vinyl sulfonic acid; and salts thereof (e.g., sodium salts, potassium salts, and ammonium salts). Among these, (meth)acrylic acid is preferred. One of these may be used alone, or two or more may be used in any ratio.

[0100] Examples of dibasic acids (salts) include itaconic acid, fumaric acid, maleic acid, citraconic acid, muconic acid, and their salts (e.g., sodium salts, potassium salts, and ammonium salts). In the case of dibasic acid salts, only one of the carboxyl groups in the monomer may be in salt form, or both may be in salt form. Among these, it is preferable to include at least one selected from the group consisting of itaconic acid and itaconic acid salts (e.g., sodium salts, potassium salts, and ammonium salts), and more preferably itaconic acid or sodium itaconate. One of these may be used alone, or two or more may be used in any ratio.

[0101] The content of constituent units derived from monobasic acid (salt) is not particularly limited, but from the viewpoint of particle dispersion stability, it is preferably 0.01% to 2.00% by mass, more preferably 0.10% to 1.75% by mass, even more preferably 0.20% to 1.50% by mass, and particularly preferably 0.20% to 1.25% by mass, relative to the total amount of particulate (co)polymer. By having the content of constituent units derived from monobasic acid (salt) within the above range, the cathode aqueous composition of the fourth embodiment tends to suppress aggregation in the aqueous composition, exhibit excellent temporal stability of viscosity and hysteresis of the aqueous composition, and have excellent storage stability. Furthermore, it tends to have excellent handling properties because it can be applied to the current collector while maintaining appropriate fluidity. The content of constituent units derived from monobasic acid (salt) can be measured by pyrolysis gas chromatography (pyrolysis GC-MS).

[0102] The content of constituent units derived from dibasic acids (salts) is not particularly limited, but from the viewpoint of the mechanical strength of the particles, it is preferably 0.10% to 5.00% by mass, more preferably 0.50% to 4.50% by mass, even more preferably 1.00% to 4.00% by mass, and particularly preferably 1.50% to 3.50% by mass, relative to the total amount of particulate (co)polymer. When the content of constituent units derived from dibasic acids (salts) is within the above range, aggregation in the aqueous composition is suppressed, the viscosity and hysteresis of the aqueous composition are excellent over time, and the composition tends to have excellent storage stability. In addition, when applied to a current collector, it can be applied while maintaining appropriate fluidity, so it tends to have excellent handling properties. The content of constituent units derived from dibasic acids (salts) can be measured by liquid chromatography.

[0103] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above. For example, the cathode aqueous system composition of the embodiment may include known additives in addition to the components described above. [Examples]

[0104] The embodiments will be described in more detail below with reference to examples, but the embodiments are not limited in any way by these examples.

[0105] Examples 1- 8、12~ 14, Reference examples 1~3, Comparative Examples 1-3 <Example of preparation of water-soluble polymer (A)> [Preparation Example 1] 667 parts by mass of deionized water and 100 parts by mass of sodium p-styrenesulfonate were added to the reactor. The sodium p-styrenesulfonate was dissolved in the deionized water, and the reactor was purged with nitrogen and heated to 50°C, where it was maintained. 1.05 parts by mass of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50; polymerization initiator) was dissolved in 10.5 parts by mass of deionized water and added to the reactor. After adding the aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, the temperature was raised to 80°C and maintained at 80°C for 3 hours to complete the polymerization. After that, it was cooled to room temperature, and water was added to bring the solid content to 10% by mass. Furthermore, 0.02% by mass of 2-methyl-4-isothiazolin-3-one (preservative) was added to the obtained aqueous solution of the water-soluble polymer to obtain water-soluble polymer 1. The physical properties of the obtained water-soluble polymer 1 are shown in Table 1.

[0106] [Preparation Examples 2-6] In each preparation example, polymerization was completed in the same manner as in Preparation Example 1, except that the amount of sodium p-styrene sulfonate was changed as shown in Table 1. After cooling to room temperature, water and sodium hydroxide were added to achieve the solid content and pH shown in Table 1 (the amount of sodium hydroxide added was such that the pH shown in Table 1 is obtained when the resulting aqueous solution of the water-soluble polymer is diluted to 5% by mass). Furthermore, 0.02% by mass of 2-methyl-4-isothiazolin-3-one was added to the resulting aqueous solution of the water-soluble polymer to obtain water-soluble polymers 2 to 6. The physical properties of water-soluble polymers 2 to 6 were as shown in Table 1.

[0107] [Table 1] The abbreviations in Table 1 refer to the following compounds. NaSS: Sodium p-styrene sulfonate MAA: Methacrylic acid HEMA: 2-hydroxyethyl methacrylate

[0108] (molecular weight) The molecular weight of each water-soluble polymer was evaluated using GPC. The water-soluble polymer was diluted with deionized water to approximately 0.1% by mass and passed through a 45 μm filter to prepare the measurement sample. Measurements were performed under the following conditions: column temperature 40°C, eluent pH 9.0 buffer (Kishida Chemical Co., Ltd., containing sodium tetraborate and boric acid), eluent flow rate 0.6 ml / min, and column Asahipak GF-7M HQ and GF-210 HQ. Sodium polyacrylate was used as the calibration curve, and the obtained weight-average molecular weight was defined as the molecular weight.

[0109] <Examples of particulate polymer preparation> [Preparation Example 7] 130 parts by mass of deionized water and 0.05 parts by mass (in terms of solid content) of an aqueous solution of sodium alkyldiphenyl ethersulfonate (DOW CHEMICAL, Dowfax 2A1) were added to the reactor, and the temperature was raised to 70°C and maintained while stirring under nitrogen purging. Next, 10 parts by mass of a 5% aqueous solution of sodium persulfate was added to the reactor. To this, a mixture of 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 (in terms of solid content) of aqueous solution of sodium alkyldiphenyl ethersulfonate, and 125 parts by mass of deionized water was mixed and emulsified in a homogenizer. The resulting emulsion was added dropwise over 2.5 hours while maintaining the temperature at 70°C. After the dropwise addition was complete, polymerization was continued at 70°C for 2 hours, and then the temperature was raised to 80°C and maintained for 1 hour to complete the polymerization. The mixture was then cooled to room temperature, and the pH was adjusted to 8.0 and the solid content to 20% using a 5% sodium hydroxide aqueous solution and water. 0.05% by mass of 1,2-benzoisothiazolin-3-one was added to the aqueous dispersion of the particulate polymer, and the mixture was filtered through a 74 μm mesh to obtain particulate polymer 1. The physical properties of particulate polymer 1 are shown in Table 2.

[0110] [Preparation Example 8] Particulate polymer 2 was obtained in the same manner as in Preparation Example 7, except that the monomer composition was changed as shown in Table 1. The physical properties of particulate polymer 2 were as shown in Table 1.

[0111] [Preparation Example 9] In a reactor, 120 parts by mass of deionized water, 0.02 parts by mass of aqueous solution of alkyldiphenyl ethersulfonate (DOW CHEMICAL, Dowfax 2A1) on a solid content basis, and 1.7 parts by mass of itaconic acid were added. The mixture was then heated to 80°C while stirring under nitrogen purging and maintained at that temperature. Next, 4 parts by mass of 5% aqueous solution of sodium persulfate was added to the reactor. To this mixture, 68.6 parts by mass of 2-ethylhexyl acrylate, 20.5 parts by mass of styrene, 8 parts by mass of methyl methacrylate, 1 part of methacrylic acid, 0.2 parts by mass of 1,9-nonanediol dimethacrylate, 0.4 parts by mass of aqueous solution of alkyldiphenyl ethersulfonate on a solid content basis, and 38 parts by mass of deionized water were added. This mixture was emulsified in a homogenizer, and the resulting emulsion was added dropwise over 2.5 hours while maintaining the temperature at 80°C. After the dropwise addition was complete, polymerization was continued at 80°C for 1 hour, then the temperature was raised to 85°C and held for 2 hours to complete the polymerization. After that, it was cooled to room temperature, and the pH was adjusted to 8.0 and the solid content to 30% with a 10% sodium hydroxide aqueous solution and water. 0.05% by mass of 1,2-benzoisothiazolin-3-one was added to the aqueous dispersion of the particulate polymer, and the mixture was filtered through a 74 μm mesh to obtain particulate polymer 3. The physical properties of particulate polymer 3 are shown in Table 2.

[0112] (Particle size) The particle sizes of particulate polymers 1 and 2 were measured using the "FPAR-1000" concentrated particle size analyzer manufactured by Otsuka Electronics, which uses dynamic light scattering as its measurement principle. The measurement was performed using a concentrated probe, under conditions of 25°C and light intensity of 20,000 to 50,000, and the particle size was defined as the 50% cumulative particle size value of the obtained scattering intensity distribution data. The results are shown in Table 2.

[0113] [Table 2] The abbreviations in Table 2 refer to the following compounds. 2EHA:2-Ethylhexylacrylate BA: n-butyl acrylate ST: Styrene MMA: Methyl methacrylate IA: Itaconic acid MAA: Methacrylic acid HEMA: 2-hydroxyethyl methacrylate A-TMPT: Trimethylolpropane triacrylate 1,9-ND:1,9-nonanediol dimethacrylate

[0114] <Preparation of a cathode aqueous system composition> [Example 1] In a planetary mixer equipped with a disperser, 1.5 parts by mass of water-soluble polymer 1 (calculated on a solid content basis) and 5 parts by mass of acetylene black (Denka Co., Ltd., Denka Black Li-400; "Li-400" in the table below) as a conductive additive were added and stirred for 10 minutes. Next, 100 parts by mass of lithium iron phosphate (Pulead Technology Industry Co., Ltd., P600A, particle size 1 μm; "Pulead P600A" in the table below) were added as the positive electrode active material and stirred for 30 minutes. Furthermore, ion-exchanged water was added to obtain the solid content shown in Table 3, and stirred for 10 minutes to obtain the aqueous composition for the positive electrode (aqueous composition 1).

[0115] [Examples 2-6] 、1 2. Reference examples 1~3, Comparative Examples 1-3] In each example, aqueous compositions 2-6 and 9-12 were obtained in the same manner as in Example 1, except that the water-soluble polymers and other substances were changed as shown in Table 3.

[0116] [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 using the same procedure as in Example 1, and the mixture was stirred for 30 minutes. Next, 3.5 parts by mass of particulate polymer 1 (in terms of solid content) and ion-exchanged water were added to achieve the solid content shown in Table 3, and the mixture was stirred for 10 minutes to obtain aqueous composition 7.

[0117] [Example 8] Aqueous composition 8 was obtained in the same manner as in Example 7, except that the water-soluble polymers and particulate polymers were changed as shown in Table 3.

[0118] [Examples 13-14] Aqueous compositions 13 to 14 were obtained in the same manner as in Example 7, except that the water-soluble polymers and particulate polymers were changed as shown in Table 3.

[0119] (Viscosity and hysteresis of aqueous composition for positive electrode) The viscosity and hysteresis of the obtained aqueous compositions were measured using an Anton Paar MCR-102 rheometer. Measurements were performed at 25°C using a CP-50-1 cone plate and at shear rates ranging from 1 to 100 (1 / s). The initial viscosity was defined as the value at 1 (1 / s) as the shear rate increased. For hysteresis, the value at a shear rate of 4.2 ± 0.2 (1 / s) was used, and the calculation was (viscosity at increase - viscosity at decrease) / viscosity at increase × 100 (%).

[0120] (Changes in viscosity and hysteresis of the cathode aqueous composition over time) The aqueous composition was placed in a container and left at 25°C for 1 day while rotating with a mix rotor. The viscosity and hysteresis of the aqueous composition were measured under the same conditions as described above. The viscosity change after 1 day was calculated as (initial viscosity - viscosity after 1 day) / initial viscosity × 100 (%). The hysteresis change after 1 day was calculated using a shear rate of 4.2 ± 0.2 (1 / s) as the formula: (viscosity during increase - viscosity during decrease) / viscosity during increase × 100 (%).

[0121] (Fabrication of the positive electrode of a secondary battery) A water-based composition was applied to one side of a 20 μm thick aluminum foil, which would serve as the positive electrode current collector, using a die coater. After drying at 100°C for 10 minutes, it was compressed and molded using a roll press. At this time, the amount of non-volatile content of the water-based composition for the positive electrode applied was 12 mg / cm². 2 The density of the mixture layer after roll pressing was 2.2 g / cm³. 3This was done. At this time, the electrode adhesion was evaluated using the obtained electrodes. The compositions and secondary battery cathodes obtained as described above were used for various physical property evaluations described later.

[0122] (Cracks during electrode punching) The fabricated positive electrode of the secondary battery was punched out into a 30mm x 30mm square using a die-cutting die (mirror-finished die), and the degree of peeling of the electrode layer after punching was determined according to the following criteria. 5: No peeling 4. The shortest distance from the point closest to the center of the exposed current collector foil to its periphery is within 1 mm. 3: The shortest distance from the point closest to the center of the exposed current collector foil to its periphery is between 1 mm and 5 mm. 2: The shortest distance from the point closest to the center of the exposed current collector foil to its periphery is between 5mm and 10mm. 1: The shortest distance from the point closest to the center of the exposed current collector foil to its periphery exceeds 10 mm.

[0123] [Table 3]

[0124] Details of each component in Table 3 are shown below. • Super P Li: Carbon Black (manufactured by Imerys) Water-soluble polymer 7: PS-100 (sodium polystyrene sulfonate, manufactured by Tosoh Finechem Co., Ltd.) was used as water-soluble polymer 7. The pH was 10.0, and the molecular weight measured by the method described above was 540,000. • Water-soluble polymer 8: Sodium hydroxide was added to a poly(2-acrylamido-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 aqueous solution of the water-soluble polymer to adjust the pH to 7.0. This solution was used as water-soluble polymer 8. The molecular weight measured by the above method was 760,000. • Water-soluble polymer 9: Sunrose MAC-350HC (carboxymethylcellulose, 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 water-soluble polymer 11. The pH was 10.0, and the molecular weight measured by the method described above was 26,000. • Water-soluble polymer 12: PS-5 (sodium polystyrene sulfonate, manufactured by Tosoh Finechem Co., Ltd.) was used as water-soluble polymer 12. The pH was 10.0, and the molecular weight measured by the method described above was 93,500. Water-soluble polymer 13: PS-50 (sodium polystyrene sulfonate, manufactured by Tosoh Finechem Co., Ltd.) was used as water-soluble polymer 13. The pH was 10.0, and the molecular weight measured by the method described above was 370,000.

[0125] The results shown in Table 3 indicate that the aqueous compositions in the examples using the water-soluble resin of this embodiment with lithium iron phosphate as the active material all exhibited superior viscosity changes and hysteresis changes after one day compared to the aqueous composition of Comparative Example 1 using carboxymethylcellulose as a thickener. Furthermore, the aqueous composition of Comparative Example 2 using polyacrylic acid as a thickener was confirmed to have undergone phase separation after one day. In addition, the aqueous composition of Comparative Example 3, which used a water-soluble resin with a total amount of sulfonic acid groups in the water-soluble polymer (A) of less than 25% by mass with respect to lithium iron phosphate as the active material, showed particularly large viscosity changes after one day and exhibited poor stability.

[0126] Examples a1-a18, Comparative Examples a1-a2 <Examples of particulate (co)polymer preparation> [Preparation example a1] 0.015 parts by mass of sodium dodecyldiphenyl ethersulfonate, 3 parts by mass of itaconic acid, and 122 parts by mass of deionized water were added to a reactor, and the temperature was raised to 80°C and maintained while stirring. To this, 0.2 parts by mass of sodium persulfate was added. A monomer solution prepared by mixing 67.45 parts by mass of 2-ethylhexyl acrylate, 1 part by mass of acrylic acid, 20.5 parts by mass of styrene, 8.0 parts by mass of methyl methacrylate, and 0.05 parts by mass of 1,9-nonanediol dimethacrylate was added, along with 0.4 parts by mass of sodium dodecyldiphenyl ethersulfonate, 0.8 parts by mass of sodium persulfate, and 55 parts by mass of deionized water. The resulting monomer mixture was emulsified in a homogenizer to obtain a monomer emulsion. The obtained monomer emulsion was added dropwise, and after 2.5 hours while maintaining the internal temperature at 80°C, the dropwise addition was stopped, and polymerization was continued for 1 hour. Subsequently, the internal temperature was raised from 80°C to 85°C and maintained for 3 hours to complete the polymerization. The mixture was then cooled to room temperature, and the solution was adjusted to pH 8.0 and solid content 20% with a 5% sodium hydroxide aqueous solution and water. 0.05% by mass of 1,2-benzoisothiazolin-3-one was added to the aqueous dispersion of the particulate (co)polymer, and the mixture was filtered through a 74 μm mesh to obtain particulate (co)polymer a1. The physical properties of particulate (co)polymer a1 are shown in Table 4. Furthermore, the acid content of the obtained particulate (co)polymer a1 was quantified by acid titration, and it was found to be 3% by mass of itaconic acid and 1.1% by mass of acrylic acid relative to the total amount of particulate (co)polymer a1.

[0127] [Preparation Examples a2-a10 and a13] Particulate (co)polymers a2-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 particulate (co)polymers a2-a10 and a13 were as shown in Table 4.

[0128] (Particle size) The particle sizes of particulate (co)polymers a1-a10 and a13 were measured using the method described above. The results are shown in Table 4.

[0129] (pH) The pH of particulate (co)polymer is the pH of an aqueous solution of the particulate (co)polymer with a solid content of 5% by mass.

[0130] [Table 4] The abbreviations in Table 4 refer to the following compounds. St: Styrene 2-EHA:2-Ethylhexylacrylate 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

[0131] <Preparation of the aqueous composition for the positive electrode> [Example a1] In a planetary mixer equipped with a disperser, 4 parts by mass of particulate polymer a1 (based on solid content), 1.5 parts by mass of sodium polystyrene sulfonate (manufactured by Tosoh Finechem Co., Ltd., product name "PS-100") as a water-soluble (co)polymer (based on solid content), 100 parts by mass of lithium iron phosphate (manufactured by Pulea Technology Industry, P600A, particle size 1 μm) as a positive electrode active material, and 5 parts by mass of furnace black (manufactured by Imerys, Super P-Li) as a conductive additive were added. Then, deionized water was added to obtain the solid content shown in Tables 5 and 6, and the mixture was stirred and defoamed for 30 minutes to obtain the positive electrode aqueous system composition a1.

[0132] [Examples a2-a18, Comparative Examples a1-a2] In each example, except for the points where the types and compositions of the conductive aid, particulate (co)polymer, and water-soluble (co)polymer were changed as shown in Tables 5 and 6, aqueous compositions a2 to a18 and a22 to a23 were obtained in the same manner as in Example a1.

[0133] <Fabrication of the Positive Electrode for a Lithium-Ion Secondary Battery> The obtained aqueous composition for the positive electrode was applied to one side of an aluminum foil with a thickness of 20 μm, which was the positive electrode current collector, using a die coater, dried at 100 °C for 10 minutes, and then compression-molded using a roll press machine. At this time, the active material coating amount of the positive electrode was 12 mg / cm 2 , and the density of the electrode layer after roll pressing was 2.2 g / cm 3 was adjusted to be. At this time, the obtained electrode was used to evaluate the cracking of the electrode. The electrode thus obtained was used as the positive electrode of the secondary battery. Using the aqueous composition for the positive electrode and the positive electrode of the secondary battery obtained as described above, various physical property evaluations described later were performed. The results are shown in Tables 5 and 6.

[0134] (Viscosity and Hysteresis of the Aqueous Composition for the Positive Electrode) For the obtained aqueous composition, the viscosity and hysteresis were measured by the method described above. Based on the absolute value of the hysteresis, the following criteria were used for evaluation. An evaluation of C or higher was considered a pass, and D was considered a fail. A: 0% or more and less than 20% B: 20% or more and less than 40% C: 40% or more and less than 60% D: 60% or more or immobilization due to aggregation

[0135] (Time-Dependent Changes in the Viscosity and Hysteresis of the Aqueous Composition for the Positive Electrode) The time-dependent changes in the viscosity and hysteresis of the aqueous composition for the positive electrode were measured by the method described above. Based on the absolute value of the rate of change over time of the viscosity and hysteresis, the following criteria were used for evaluation. An evaluation of C or higher was considered a pass, and D was considered a fail. A: 0% or more and less than 20% B: 20% or more and less than 40% C: 40% or more and less than 60% D: 60% or more or immobilization due to aggregation

[0136] (Stability of stirred slurry) 30g of the prepared slurry was placed in a 50mL plastic bottle and stirred with a mixing rotor at 40rpm for 24 hours. After stirring, the viscosity of the slurry was measured with a rheometer, and the viscosity change rate was calculated using the following formula and judged according to the following criteria. Viscosity change rate of slurry after stirring = (Initial viscosity - Viscosity after 1 day of stirring) / Initial viscosity × 100 (%) The absolute value of the viscosity change rate of the stirred slurry was used for evaluation according to the following criteria. A rating of C or higher was considered a pass, and a rating of D was considered a fail. A: Less than 20% B: 20% or more, less than 40% C: 40% or more, less than 60% D: Immobilization by 60% or more or aggregation

[0137] (Electrode cracking) The obtained electrodes were punched out into 30mm x 30mm squares using a die-cutting die (mirror-finished die). The surface of the electrode layer after punching was visually inspected, and the degree of peeling was judged according to the following criteria. A rating of C or higher was considered a pass, and a rating of D was considered a fail. A: No peeling B: The shortest distance from the point closest to the center of the exposed current collector foil to its periphery is within 1 mm. C: The shortest distance from the point closest to the center of the exposed current collector foil to its periphery is greater than 1 mm and less than 5 mm. D: The shortest distance from the point closest to the center of the exposed current collector foil to its periphery exceeds 5 mm.

[0138] (Electrolyte insoluble matter) The obtained particulate (co)polymer was allowed to stand in an oven at 130°C for 1 hour to dry. The film of the dried particulate (co)polymer was cut off and used as a sample for measurement. The mass of the film (Wa: in g) was measured. Then, the sample was placed in a 50 mL vial 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 permeate the sample at 60°C for 7 days. After that, the sample was removed and washed with the mixed solvent. Then, the sample was allowed to stand in an oven at 150°C for 1 hour, and the mass of the sample (Wc: in g) was measured. The insoluble portion of the particulate (co)polymer in the electrolyte was calculated using the following formula and judged according to the following criteria. Electrolyte insoluble content (%)=(Wc / Wa)×100 A: Over 97% B: 90% or more, less than 97% C: 85% to less than 90% D: Less than 85%

[0139] [Table 5] [Table 6]

[0140] Details of each component in Tables 5 and 6 are shown below. • Active material: Lithium iron phosphate (manufactured by Pulead Technology Industry, product name "P600A", particle size 1 μm) • Conductive additives: Conductive additive A (Oxygen atom abundance on the surface: 0.60 mass%, O / C: 0.0061) Conductive additive B (Oxygen atom abundance on the surface: 0.88% by mass, O / C: 0.0090) Conductive additive C (Oxygen atom abundance on the surface: 2.00 mass%, O / C: 0.0206) Conductive additive D (Oxygen atom abundance on the surface: 0.54 mass%, O / C: 0.0054) Conductive additive E (Oxygen atom abundance on the surface: 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: Carboxymethylcellulose (manufactured by Nippon Paper Industries, product name "Sunrose MAC® 350HC")

[0141] From the results of Examples a1 to a18 shown in Tables 5 and 6, a conductive additive and a particulate (co)polymer are included, and when the elements present on the surface of the conductive additive are measured by X-ray photoelectron spectroscopy and the proportion of oxygen atoms (mass%) and carbon atoms (mass%) are calculated based on the peak area, the proportion of oxygen atoms on the surface of the conductive additive is 0.30 mass% or more and 2.00 mass% or less, and the ratio of the proportion of oxygen atoms (mass%) to the proportion of carbon atoms (mass%) is (O / In a lithium-ion secondary battery cathode aqueous composition in which C) is 0.0020 or more and 0.0250 or less, and the particulate (co)polymer contains constituent units derived from ethylenically unsaturated carboxylic acid (salt), and the content ratio of the constituent units derived from ethylenically unsaturated carboxylic acid (salt) is 0.10% by mass or more and 5.00% by mass or less in total with respect to the total amount of the particulate (co)polymer, it can be seen that the stability of the stirred slurry is improved and electrode cracking is suppressed compared to comparative examples a1 and a2.

[0142] Example b1 ~b2, b4~b16, reference example b1~b2, Comparative examples b1~b3》 <Example of preparation of water-soluble (co)polymer (A)> [Preparation example b1] 667 parts by mass of deionized water, 75 parts by mass of sodium p-styrenesulfonate, and 25 parts of methacrylic acid were added to the reactor. The sodium p-styrenesulfonate was dissolved in the deionized water, and the mixture was purged with nitrogen and heated to 50°C, where it was maintained. 1.05 parts by mass of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50; polymerization initiator) was dissolved in 10.5 parts by mass of deionized water and added to the reactor. After adding the aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, the temperature was raised to 80°C and maintained at 80°C for 3 hours to complete the polymerization. After that, it was cooled to room temperature, and water was added to bring the solid content to 10% by mass. Furthermore, 0.02% by mass of 2-methyl-4-isothiazolin-3-one (preservative) was added to the obtained aqueous solution of the water-soluble polymer to obtain water-soluble (co)polymer (A-4). The physical properties of the obtained water-soluble polymer (A-4) are shown in Table 7.

[0143] [Preparation examples b2, b3] In each preparation example, polymerization was completed in the same manner as in preparation example b1, except that the amounts of sodium p-styrene sulfonate and methacrylic acid were changed as shown in Table 7. After cooling to room temperature, water and sodium hydroxide were added to achieve the solid content and pH shown in Table 7 (the amount of sodium hydroxide added was such that the pH shown in Table 7 is obtained when the obtained aqueous solution of the water-soluble polymer is diluted to 5% by mass). Furthermore, 0.02% by mass of 2-methyl-4-isothiazolin-3-one was added to the obtained aqueous solution of the water-soluble polymer to obtain water-soluble (co)polymers (A-5) and (A-6). The physical properties of water-soluble (co)polymers (A-5) and (A-6) are shown in Table 7. [Table 7] The abbreviations in Table 7 refer to the following compounds. NaSS: Sodium p-styrene sulfonate MAA: Methacrylic acid

[0144] (Molecular weight of water-soluble (co)polymer (A)) The molecular weight of each water-soluble (co)polymer (A) was evaluated using the GPC method described above.

[0145] (Molecular weight of water-soluble (co)polymer (B)) The molecular weight of each water-soluble (co)polymer (B) was evaluated using gel filtration chromatography (GFC). The water-soluble polymer was diluted with deionized water to approximately 0.1% by mass and passed through a 45 μm filter to prepare the measurement sample. Measurement was performed under the following conditions: column temperature 40°C, 100 mmol sodium nitrate aqueous solution as the eluent, eluent flow rate 1.0 ml / min, and Shodex OHpak SB-803 HQ + SB-805 HQ column. Pullulan was used as the calibration curve, and the obtained weight-average molecular weight was defined as the molecular weight.

[0146] <Examples of binder preparation (particulate (co)polymer)> [Preparation example b1] To a reactor, 1.75 parts by mass of itaconic acid, 0.015 parts by mass of sodium dodecyldiphenyl ethersulfonate, and 120 parts by mass of deionized water were added, and the temperature was raised to 80°C and maintained while stirring. To this, 0.05 parts by mass of sodium persulfate was added. Next, a monomer solution prepared 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 was added, along with 0.45 parts by mass of sodium dodecyldiphenyl ethersulfonate and 55 parts by mass of deionized water. The resulting monomer mixture was emulsified in a homogenizer to obtain a monomer emulsion. The obtained monomer emulsion was added dropwise to the next reactor over 2.5 hours while maintaining the internal temperature at 80°C, and polymerization was then continued for a further 1 hour. Subsequently, 0.03 parts by mass of Perbutyl Z (manufactured by NOF Corporation), 0.03 parts by mass of anhydrous zinc bicarbonate sodium sulfate, and 19 g of deionized water were added, and the mixture was held for 30 minutes to complete the polymerization and obtain polymer particles. To 100 parts by mass of the solid content of the obtained polymer particles, 0.0005 parts by mass of methylisothiazoline was added as an additive, and then sodium hydroxide was added dropwise to adjust the pH to 8.0 and the solid content to 20% by mass to obtain particulate (co)polymer b1. The physical properties of particulate (co)polymer b1 are shown in Table 8.

[0147] [Adjustment example b2] 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 particulate (co)polymer b2 were as shown in Table 8.

[0148] (Particle size) The particle sizes of particulate (co)polymers b1 and b2 were measured by the method described above.

[0149] [Table 8] The abbreviations in Table 8 refer to the following compounds. St: Styrene 2-EHA:2-Ethylhexylacrylate MMA: Methyl methacrylate MAA: Methacrylic acid IA: Itaconic acid 1,9-ND:1,9-nonanediol dimethacrylate

[0150] <Preparation of the aqueous composition for the positive electrode> [Example b1] In a rotating / revolving mixer (manufactured by Thinky Co., Ltd.), 3.5 parts by mass of particulate (co)polymer b1 (based on solid content), 1.5 parts by mass 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 of carboxymethylcellulose (manufactured by Nippon Paper Industries Co., Ltd., product name "Sunrose MAC® 350HC") as a water-soluble (co)polymer (B), 100 parts by mass of lithium iron phosphate (manufactured by Pulea Technology Industry, P600A, particle size 1 μm) as a positive electrode active material, and 5 parts by mass of furnace black (manufactured by Imerys Co., Ltd., Super P-Li) as a conductive additive were added. Then, ion-exchanged water was added to obtain the solid content shown in Table 9, and the mixture was stirred and defoamed for 30 minutes to obtain the positive electrode aqueous system composition b1.

[0151] [Example b2] , b4~b16, reference examples b1~b2, Comparative examples b1~b3] In each example, aqueous compositions b2 to b20 were obtained in the same manner as in Example b1, except that the types and compositions of the water-soluble (co)polymers (A) and (B), and the particulate (co)polymers were changed as shown in Tables 9 and 10.

[0152] <Fabrication of positive electrodes for lithium-ion secondary batteries>

[0153] The obtained aqueous composition for the positive electrode was compressed and molded using the method described above, and the electrode adhesion was evaluated using the resulting electrode. The electrode thus obtained was used as the positive electrode of a secondary battery. The aqueous cathode composition and secondary battery cathode obtained as described above were used for various physical property evaluations described later. The results are shown in Tables 9 and 10.

[0154] (Viscosity and hysteresis of aqueous composition for positive electrode) The viscosity and hysteresis of the obtained aqueous compositions were measured using the method described above. The absolute value of the hysteresis was evaluated according to the following criteria. A rating of C or higher was considered a pass, and a rating of D was considered a fail. A: 0% or more, less than 20% B: 20% or more, less than 40% C: 40% or more, less than 60% D: Immobilization by 60% or more or aggregation

[0155] (Changes in viscosity and hysteresis of the cathode aqueous composition over time) The changes in viscosity and hysteresis over time of the cathode aqueous system composition were measured using 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. An evaluation of C or higher was considered a pass, and a D was considered a fail. A: 0% or more, less than 20% B: 20% or more, less than 40% C: 40% or more, less than 60% D: Immobilization by 60% or more or aggregation

[0156] (Stability of stirred slurry) The stability of the stirred slurry was measured using the method described above and judged according to the criteria described above.

[0157] (Initial electrode adhesion) The surface of the obtained electrodes was visually inspected, and the degree of peeling of the electrode layer was judged according to the following criteria. A rating of C or higher was considered a pass, and a rating of D was considered a fail. A: No peeling B: No defects within the surface of the coating, but there are defects at the edges of the coating (less than 5 locations). C: No defects within the surface of the coating, but defects at the edges of the coating (5 or more locations). D: There is a defect in the in-plane surface of the coating.

[0158] (Electrode adhesion of slurry after stirring) After stirring the slurry according to the method for stabilizing the stirred slurry, a lithium-ion secondary battery cathode was fabricated using the slurry. The surface of the obtained electrode was visually inspected, and the degree of electrode layer delamination was judged according to the following criteria. A rating of C or higher was considered a pass, and a rating of D was considered a fail. A: No peeling B: No defects within the surface of the coating, but there are defects at the edges of the coating (less than 5 locations). C: No defects within the surface of the coating, but defects at the edges of the coating (5 or more locations). D: There is a defect in the in-plane surface of the coating.

[0159] [Table 9] [Table 10]

[0160] Details of each component in Tables 9 and 10 are shown below. • Active material: Lithium iron phosphate (Pulead Technology Industry) (Manufactured by [company name], product name "P600A", particle size 1 μm) • Conductive additive: Furnace Black (manufactured by Imerys, Super P-Li) • Water-soluble (co)polymer (A-1): Sodium polystyrene sulfonate aqueous solution (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-2): Sodium polystyrene sulfonate aqueous solution (manufactured by Tosoh Finechem Co., Ltd., product name "PS-50", weight-average molecular weight (Mw): 500,000, pH: 10.0) • Water-soluble (co)polymer (A-3): Sodium polystyrene sulfonate aqueous solution (manufactured by Tosoh Finechem Co., Ltd., product name "PS-5", weight-average molecular weight (Mw): 75,000, pH: 10.0) • Water-soluble (co)polymer (A-7): Polystyrene sulfonic acid aqueous solution (manufactured by Sigma-Aldrich, poly(4-styrene sulfonic acid) solution, weight-average molecular weight (Mw): 75,000, pH: 3.0) • Water-soluble (co)polymer (B-1): Carboxymethylcellulose (manufactured by Nippon Paper Industries, product name "Sunrose MAC® 350HC", weight-average molecular weight (Mw): 340,000, pH: 7.0) • Water-soluble (co)polymer (B-2): Carboxymethylcellulose (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "Selogen WS-C", weight-average molecular weight (Mw): 90,000, pH: 7.0)

[0161] Examples b1~ shown in Tables 9 and 10 b2, b4~b16The results show that a lithium-ion secondary battery cathode aqueous composition comprising an active material, a water-soluble (co)polymer (A) containing constituent units derived from monomers having sulfonic acid (salt) groups, and a water-soluble (co)polymer (B) containing constituent units having carboxyl groups (excluding those corresponding to the water-soluble (co)polymer (A)), wherein the content ratio of the constituent units derived from monomers having sulfonic acid (salt) groups is 25% by mass or more and 100% by mass or less relative to the total solid content of the water-soluble (co)polymer (A), exhibits improved stability of the stirred slurry and improved electrode adhesion of the slurry both initially and after stirring, compared to comparative examples b1 to b3. In particular, comparative example b1, which does not contain water-soluble (co)polymer (B), shows inferior stability of the stirred slurry and inferior electrode adhesion of the slurry after stirring. Furthermore, comparative example b2, which does not contain water-soluble (co)polymer (A), shows inferior viscosity change and hysteresis after 1 day. Furthermore, in Comparative Example b3, in which the content of the constituent units derived from monomers having sulfonic acid (salt) groups is 25% by mass or less relative to the total solid content of the water-soluble (co)polymer (A), it can be seen that the viscosity change and hysteresis after 1 day, the stability of the stirred slurry, and the electrode adhesion of the slurry initially and after stirring are inferior.

[0162] Examples c1-c11, Comparative Examples c1-c3 <Examples of preparation of water-soluble (co)polymers> [Preparation example c1] As the water-soluble (co)polymer c1, an aqueous solution of sodium polystyrene sulfonate (manufactured by Tosoh Finechem Co., Ltd., product name "PS-100", weight-average molecular weight: 540,000, pH: 10.0) was used.

[0163] [Preparation example c2] 667 parts by mass of deionized water and 75 parts by mass of sodium p-styrenesulfonate were added to the reactor. The sodium p-styrenesulfonate was dissolved in the deionized water, and after nitrogen purging, 25 parts by mass of methacrylic acid was added, and the internal temperature was raised to 50°C and maintained there. 1.05 parts by mass of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50; polymerization initiator) was dissolved in 10.5 parts by mass of deionized water and added to the reactor. After adding the aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, the internal temperature was raised to 80°C and maintained at 80°C for 3 hours to complete the polymerization. After that, it was cooled to room temperature, and water was added to make the solid content 10% by mass. Furthermore, 0.02% by mass of 2-methyl-4-isothiazolin-3-one (preservative) was added to the obtained aqueous solution of the water-soluble (co)polymer to obtain water-soluble (co)polymer c2. The properties of the obtained water-soluble (co)polymer c2 are shown in Table 11.

[0164] [Preparation examples c3-c4] In each preparation example, water-soluble (co)polymers c3 and c4 were obtained by the same method as in preparation example c2, except that the amounts of sodium p-styrene sulfonate and methacrylic acid were changed as shown in Table 11. The physical properties of water-soluble (co)polymers c3 and c4 were as shown in Table 11.

[0165] [Preparation example c5] Carboxymethylcellulose (manufactured by Nippon Paper Industries, product name "Sunrose MAC® 350HC") was used as the water-soluble (co)polymer c5.

[0166] [Table 11] The abbreviations in Table 11 refer to the following compounds. 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-styrene sulfonate MAA: Methacrylic acid CMC: Carboxymethylcellulose (manufactured by Nippon Paper Industries, product name "Sunrose MAC® 350HC")

[0167] (molecular weight) The molecular weights of each water-soluble (co)polymer c1 to c4 were evaluated using the GPC method described above. Furthermore, the molecular weight of water-soluble (co)polymer c5 was evaluated using the GFC method described above.

[0168] (pH) The pH of 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 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.

[0169] <Examples of particulate (co)polymer preparation> [Preparation example c6] 0.015 parts by mass of sodium dodecyldiphenyl ethersulfonate, 3 parts by mass of itaconic acid, and 122 parts by mass of deionized water were added to a reactor, and the temperature was raised to 80°C and maintained while stirring. To this, 0.2 parts by mass of sodium persulfate was added. A monomer solution prepared by mixing 67.45 parts by mass of 2-ethylhexyl acrylate, 1 part by mass of acrylic acid, 20.5 parts by mass of styrene, 8 parts by mass of methyl methacrylate, and 0.05 parts by mass of 1,9-nonanediol dimethacrylate was added, along with 0.4 parts by mass of sodium dodecyldiphenyl ethersulfonate, 0.8 parts by mass of sodium persulfate, and 55 parts by mass of deionized water. The resulting monomer mixture was emulsified in a homogenizer to obtain a monomer emulsion. The obtained monomer emulsion was added dropwise, and after 2.5 hours while maintaining the internal temperature at 80°C, the addition was stopped, and polymerization was continued for 1 hour. Subsequently, the internal temperature was raised from 80°C to 85°C and maintained for 3 hours to complete the polymerization. After that, it was cooled to room temperature, adjusted to pH 8.0 and a solid content of 20% with 5% aqueous sodium hydroxide solution and water, 0.05% by mass of 1,2-benzisothiazolin-3-one was added to the aqueous dispersion of the particulate (co)polymer, and it was filtered through a mesh with an opening of 74 μm to obtain the particulate (co)polymer c1. The physical properties of the particulate (co)polymer c1 were as shown in Table 12.

[0170] [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 were as shown in Table 12.

[0171] (Particle diameter) The particle diameters of the particulate (co)polymers c1 to c6 were measured by the method described above. The results are shown in Table 12.

[0172] (pH) The pH of the particulate (co)polymer is the pH of the aqueous dispersion of the particulate (co)polymer when the solid content is 20% by mass.

[0173]

Table 12

[0174] <Preparation of Aqueous Composition for Positive Electrode> [Example c1] In a planetary mixer equipped with a disperser, 2.35 parts by mass of particulate polymer c1 (based on solid content), 0.75 parts by mass of water-soluble (co)polymer c1 (based on solid content), 0.75 parts by mass of water-soluble (co)polymer c5 (based on solid content), 100 parts by mass of lithium iron phosphate (Pulead Technology Industry, P600A, particle size 1 μm) as a positive electrode active material, and 5 parts by mass of furnace black (Imeris, Super P-Li) as a conductive additive were added. Then, deionized water was added to obtain the solid content shown in Table 13, and the mixture was stirred and defoamed for 30 minutes to obtain the positive electrode aqueous system composition c1.

[0175] [Examples c2-c11, Comparative Examples c1-c3] In each example, aqueous compositions c2 to c14 were obtained in the same manner as in Example c1, except that the types and compositions of the water-soluble (co)polymer and particulate (co)polymer were changed as shown in Table 13.

[0176] <Fabrication of positive electrodes for lithium-ion secondary batteries> The obtained aqueous composition for the positive electrode was compressed and molded using the method described above, and the electrode cracking was evaluated using the resulting electrode. The electrode obtained in this way was used as the positive electrode of a secondary battery. The aqueous cathode composition and secondary battery cathode obtained as described above were used for various physical property evaluations described later. The results are shown in Table 13.

[0177] (Viscosity and hysteresis of aqueous composition for positive electrode) The viscosity and hysteresis of the obtained aqueous compositions were measured using the method described above. The absolute value of the hysteresis was evaluated according to the following criteria. A rating of C or higher was considered a pass, and a rating of D was considered a fail. A: 0% or more, less than 20% B: 20% or more, less than 40% C: 40% or more, less than 60% D: Immobilization by 60% or more or aggregation

[0178] (Changes in viscosity and hysteresis of the cathode aqueous composition over time) The temporal changes in the viscosity and hysteresis of the aqueous composition for the positive electrode were measured by the method described above. Based on the absolute values of the rates of change over time of the viscosity and hysteresis, evaluation was performed according to the following criteria. An evaluation of C or higher was considered a pass, and D was considered a fail. A: 0% or more and less than 20% B: 20% or more and less than 40% C: 40% or more and less than 60% D: 60% or more or immobilization due to aggregation

[0179] (Stability of the stirred slurry) The stability of the stirred slurry was measured by the method described above and judged according to the above criteria.

[0180] (Electrode cracking) Electrode cracking was carried out by the method described above and judged according to the above criteria.

[0181] (Insoluble matter in the electrolyte) The insoluble matter in the electrolyte was carried out by the method described above and judged according to the above criteria.

[0182]

Table 13

[0183] The details of each component in Table 13 are shown below. · Active material: Lithium iron phosphate (manufactured by Pulead Technology Industry Co., Ltd., product name "P600A", particle size 1 μm) · Conductive aid: Furnace black (manufactured by Imerys, Super P-Li)

[0184] From the results of Examples c1 to c11 shown in Table 13, it can be seen that an aqueous composition for lithium-ion secondary battery positive electrode, comprising a particulate (co)polymer and a water-soluble (co)polymer containing constituent units derived from monomers having sulfonic acid (salt) groups, wherein the content of the constituent units derived from monomers having sulfonic acid (salt) groups is 25% by mass or more and 100% by mass or less relative to the total amount of the water-soluble (co)polymer, suppresses electrode cracking compared to Comparative Examples c1 to c3. Furthermore, it can be seen that Comparative Example c2, which does not contain a water-soluble (co)polymer containing constituent units derived from monomers having sulfonic acid (salt) groups, and Comparative Example c3, which contains a water-soluble (co)polymer with a content of constituent units derived from monomers having sulfonic acid (salt) groups of less than 25% by mass, exhibits inferior stability during slurry stirring.

[0185] The disclosures of Japanese Patent Application No. 2023-115758, filed on 14 July 2023, Japanese Patent Application No. 2024-053460, filed on 28 March 2024, Japanese Patent Application No. 2024-053275, filed on 28 March 2024, and Japanese Patent Application No. 2024-053283, filed on 28 March 2024, are incorporated herein by reference in their entirety. Furthermore, all documents, patent applications, and technical standards described in this specification are incorporated by reference to the same extent as if each individual document, patent application, and technical standard had been specifically and individually noted to be incorporated by reference.

[0186] Examples of means for solving the problems of the lithium-ion secondary battery cathode aqueous composition, lithium-ion secondary battery cathode, and lithium-ion secondary battery described in the second to fourth embodiments above are shown below.

[0187] <a1> It contains a conductive additive and a particulate (co)polymer, When the elements present on the surface of the conductive additive are measured by X-ray photoelectron spectroscopy and the proportion of oxygen atoms (mass%) and carbon atoms (mass%) are calculated based on the peak area, the proportion of oxygen atoms on the surface of the conductive additive is 0.30 mass% or more and 2.00 mass% or less, and the ratio of the proportion of oxygen atoms (mass%) to the proportion of carbon atoms (mass%) (O / C) is 0.0020 or more and 0.0250 or less. The particulate (co)polymer contains constituent units derived from ethylenically unsaturated carboxylic acid (salt), The content of the constituent 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, relative to the total amount of the particulate (co)polymer. Aqueous composition for the positive electrode of lithium-ion secondary batteries. <a2> The content of the constituent units derived from the ethylenically unsaturated carboxylic 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. <a1>Aqueous composition for lithium-ion secondary battery cathodes as described above. <a3> The constituent unit derived from the ethylenically unsaturated carboxylic acid (salt) includes a monobasic acid (salt) and / or a dibasic acid (salt). <a1>or <a2>Aqueous composition for lithium-ion secondary battery cathodes as described above. <a4> The content of constituent units derived from the monobasic acid (salt) is 0.01% by mass or more and 2.00% by mass or less in total with respect to the total amount of the particulate (co)polymer, and / or the content of constituent units derived from the dibasic acid (salt) is 0.10% by mass or more and 5.00% by mass or less in total with respect to the total amount of the particulate (co)polymer. <a3>Aqueous composition for lithium-ion secondary battery cathodes as described above. <a5> The product of the proportion of oxygen atoms on the surface of the conductive additive (mass%) and the proportion of the total amount of constituent units derived from the ethylenically unsaturated carboxylic acid (salt) in the particulate (co)polymer (O×COOH) is 0.030 to 10.00. <a1> ~ <a4>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <a6> The ratio (O / bonded COOH) of the amount of monomers derived from the ethylenically unsaturated carboxylic acid (salt) bonded to the particulate (co)polymer to the total amount of monomers derived from the ethylenically unsaturated carboxylic acid (salt) contained in the particulate (co)polymer is 0.0050 to 0.1000. <a1> ~ <a5>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <a7> The particulate (co)polymer further comprises structural units derived from a crosslinkable monomer. <a1> ~ <a6>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <a8> The proportion of oxygen atoms on the surface of the conductive additive is 0.5% by mass or more and 2.0% by mass or less. <a1> ~ <a7>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <a9> The content of the conductive additive is 3.5% by mass or more and 10.0% by mass or less, relative to the total amount of nonvolatile components in the aqueous composition. <a1> ~ <a8>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <a10> Further comprising a water-soluble (co)polymer, <a1> ~ <a9>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <a11> The water-soluble (co)polymer contains constituent units derived from monomers having a sulfonic acid (salt) group. <a10>Aqueous composition for lithium-ion secondary battery cathodes as described above. <a12> The content of the constituent units derived from the monomer having the sulfonic acid (salt) group is 25% by mass or more and 100% by mass or less with respect to the total amount of solids of the water-soluble (co)polymer. <a11>Aqueous composition for lithium-ion secondary battery cathodes as described above. <a13> Contains preservatives, <a1> ~ <a12>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <a14> It further contains active material, The active material includes a lithium phosphate compound. <a1> ~ <a13>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <a15> <a1> ~ <a14>A lithium-ion secondary battery positive electrode comprising the aqueous composition for lithium-ion secondary battery positive electrode described in any one of the following. <a16> <a15>A lithium-ion secondary battery, including the positive electrode for lithium-ion secondary batteries described above.

[0188] <b1> Active material and, A water-soluble (co)polymer (A) containing constituent units derived from monomers having a sulfonic acid (salt) group, A water-soluble (co)polymer (B) containing a carboxyl group-containing structural unit (excluding those corresponding to the water-soluble (co)polymer (A)), The content of the constituent units derived from the monomer having the sulfonic acid (salt) group is 25% by mass or more and 100% by mass or less, relative to the total solid content of the water-soluble (co)polymer (A). Aqueous composition for the positive electrode of lithium-ion secondary batteries. <b2> The pH of the aforementioned water-soluble (co)polymer (A) is 4.0 or higher and 11.0 or lower. <b1>Aqueous composition for lithium-ion secondary battery cathodes as described above. <b3> The pH of the aforementioned water-soluble (co)polymer (B) is 4.0 or higher and 11.0 or lower. <b2>or <b3>Aqueous composition for lithium-ion secondary battery cathodes as described above. <b4> The ratio of the content 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. <b1> ~ <b3>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <b5> Further containing a conductive additive, <b1> ~ <b4>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <b6> The content of the conductive additive is 3.5% by mass or more and 10.0% by mass or less, relative to the total amount of nonvolatile components in the aqueous composition. <b5>Aqueous composition for lithium-ion secondary battery cathodes as described above. <b7> Further comprising particulate (co)polymer, <b1> ~ <b6>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <b8> The particulate (co)polymer contains constituent units derived from ethylenically unsaturated carboxylic acid (salt), The content of the constituent 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, relative to the total amount of the particulate (co)polymer. <b7>Aqueous composition for lithium-ion secondary battery cathodes as described above. <b9> Contains preservatives, <b1> ~ <b8>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <b10> The active material includes a lithium phosphate compound. <b1> ~ <b9>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <b11> <b1> ~ <b10>A positive electrode for a lithium-ion secondary battery comprising an aqueous composition for lithium-ion secondary battery positive electrodes described in any one of the following. <b12> <b11>A lithium-ion secondary battery, including the positive electrode for lithium-ion secondary batteries described above.

[0189] <c1> Particulate (co)polymer and A water-soluble (co)polymer containing constituent units derived from monomers having a sulfonic acid (salt) group, Includes, The content of the constituent units derived from the monomer having the sulfonic acid (salt) group is 25% by mass or more and 100% by mass or less, relative to the total amount of the water-soluble (co)polymer. Aqueous composition for the positive electrode of lithium-ion secondary batteries. <c2> The particulate (co)polymer contains constituent units derived from dibasic acid (salt) monomers. <c1>Aqueous composition for lithium-ion secondary battery cathodes as described above. <c3> The particulate (co)polymer contains constituent units derived from a crosslinkable monomer. <c1>or <c2>Aqueous composition for lithium-ion secondary battery cathodes as described above. <c4> The pH of the aforementioned water-soluble (co)polymer is 4.0 or higher and 11.0 or lower. <c1> ~ <c3>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <c5> Further containing a conductive additive, <c1> ~ <c4>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <c6> The content of the conductive additive is 3.5% by mass or more and 10.0% by mass or less, relative to the total amount of nonvolatile components in the aqueous composition. <c5>Aqueous composition for lithium-ion secondary battery cathodes as described above. <c7> Contains preservatives, <c1> ~ <c6>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <c8> It further contains active material, The active material includes a lithium phosphate compound. <c1> ~ <c7>Aqueous composition for lithium-ion secondary battery positive electrode as described in any one of the following. <c9> <c1> ~ <c8>A positive electrode for a lithium-ion secondary battery comprising an aqueous composition for lithium-ion secondary battery positive electrodes described in any one of the following. <c10> <c9> A lithium-ion secondary battery, including the positive electrode for lithium-ion secondary batteries described above.< / c9> < / c10> < / c1> < / c9> < / c1> < / c1> < / c1> < / c1> < / b12> < / b1> < / b11> < / b1> < / b1> < / b1> < / b1> < / b1> < / a16> < / a1> < / a15> < / a1> < / a1> < / a1> < / a1> < / a1> < / a1> < / a1> < / a1>

Claims

1. Active material and, A water-soluble polymer (A) containing a constituent unit corresponding to a monomer having a sulfonic acid group, This is an aqueous composition for lithium-ion secondary battery positive electrodes, The total amount of constituent units corresponding to the monomer having the sulfonic acid group in the water-soluble polymer (A) is 25% by mass or more and 100% by mass or less of the total amount of the water-soluble polymer (A). The weight-average molecular weight of the water-soluble polymer (A) is 200,000 or more and 1,000,000 or less. The viscosity change of the composition after one day is less than 60%, and the hysteresis change after one day is less than 40%. Aqueous composition for the positive electrode of lithium-ion secondary batteries.

2. A water-soluble polymer (B) containing a constituent unit having a carboxyl group (excluding those corresponding to the water-soluble polymer (A)). ) further includes, The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 1.

3. Further containing a conductive additive, The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 1.

4. The content of the conductive additive in the composition is 3.5% by mass or more and 10.0% by mass or less, relative to the total amount of nonvolatile components in the composition. The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 3.

5. Further comprising particulate polymer, The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 1.

6. The particulate polymer contains (meth)acrylic acid ester monomers, The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 5.

7. It further contains a conductive additive and a particulate polymer, When the elements present on the surface of the conductive additive are measured by X-ray photoelectron spectroscopy and the proportion of oxygen atoms (mass%) and carbon atoms (mass%) are calculated based on the peak area, the proportion of oxygen atoms on the surface of the conductive additive is 0.30 mass% or more and 2.00 mass% or less, and the ratio of the proportion of oxygen atoms (mass%) to the proportion of carbon atoms (mass%) (O / C) is 0.0020 or more and 0.0250 or less. The particulate polymer contains constituent units derived from ethylenically unsaturated carboxylic acids (salts), The content of the constituent 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, relative to the total amount of the particulate polymer. The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 1.

8. The particulate polymer contains constituent units derived from ethylenically unsaturated carboxylic acids (salts), The content of the constituent 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, relative to the total amount of the particulate polymer. The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 5.

9. The particulate polymer comprises a monobasic acid (salt) and / or a dibasic acid (salt). The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 8.

10. The product of the proportion of oxygen atoms on the surface of the conductive additive (mass%) and the proportion of the total amount of constituent units derived from the ethylenically unsaturated carboxylic acid (salt) in the particulate polymer (O × COOH) is 0.030 to 10.

00. The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 7.

11. The ratio (O / bonded COOH) of the amount of monomers derived from the ethylenically unsaturated carboxylic acid (salt) bonded to the particulate polymer to the total amount of monomers derived from the ethylenically unsaturated carboxylic acid (salt) contained in the particulate polymer is 0.0050 to 0.1000. The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 7.

12. The particulate polymer contains a crosslinkable monomer. The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 5.

13. Contains preservatives, The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 1.

14. The active material is a lithium phosphate compound. The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 1.

15. The viscosity change of the composition after one day is, [(Initial viscosity - viscosity after 1 day) / Initial viscosity] x 100 (%) It is calculated as follows, and The hysteresis change of the above composition after one day was determined using a shear rate of 4.2 ± 0.2 (1 / s). [(Viscosity during increase - Viscosity during decrease) / Viscosity during increase] × 100 (%) It is calculated as follows: The aqueous composition for the positive electrode of a lithium-ion secondary battery according to claim 1.

16. A lithium-ion secondary battery positive electrode obtained by drying the aqueous composition for lithium-ion secondary battery positive electrode according to any one of claims 1 to 15.

17. A lithium-ion secondary battery comprising the positive electrode for a lithium-ion secondary battery described in Claim 16.

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