Positive electrode composition, positive electrode composition slurry, positive electrode composition layer, positive electrode, and secondary battery

Abstract

This positive electrode composition for a secondary battery contains a layered rock salt-type lithium transition metal composite oxide as a positive electrode active material, a conductive additive, and a polyacrylonitrile-based polymer as a binder, wherein some or all of the conductive additive is solid particles, and the proportion of the conductive additive in the positive electrode composition is more than 0.1 mass% but not more than 1.9 mass%.

Description

Positive electrode composition, positive electrode composition slurry, positive electrode composition layer, positive electrode, and secondary battery

[0001] This disclosure relates to a positive electrode composition, a positive electrode composition slurry, a positive electrode composition layer, a positive electrode, and a secondary battery.

[0002] Polyvinylidene fluoride is known as a binder for battery electrodes. In recent years, the ecotoxicity and anthroptoxicity of organofluorine compounds have been pointed out, and regulations on the manufacture and use of organofluorine compounds have been strengthened worldwide, creating a demand for an alternative electrode binder to polyvinylidene fluoride. For example, Patent Documents 1 to 5 disclose polyacrylonitrile polymers as binders for battery electrodes.

[0003] Japanese Patent Publication No. 2007-194202, International Publication No. 2015 / 151518, International Publication No. 2018 / 235722, Japanese Patent Publication No. 2018-125126, Japanese Patent Publication No. 2023-125462

[0004] Secondary batteries in which the positive electrode active material is a layered rock salt type lithium transition metal composite oxide can be expected to have high energy density and excellent battery performance. This is because layered rock salt type lithium transition metal composite oxide has high capacity and high conductivity. However, the above secondary batteries have the following problems (1) to (3).

[0005] (1) Depending on the composition of the positive electrode composition, the slurry of the positive electrode composition may have poor fluidity and coating properties. (2) Depending on the composition of the positive electrode composition, the positive electrode composition layer may peel off from the current collector. (3) Repeated charging and discharging may cause the transition metal to leach from the layered rock salt type lithium transition metal composite oxide, resulting in a tendency for the battery life to be short.

[0006] This disclosure is made under the circumstances described above. The object of this disclosure is to provide a positive electrode composition for secondary batteries that has excellent coating properties, is difficult to peel off from the current collector, and is less prone to the leaching of transition metals from the positive electrode composition layer.

[0007] This disclosure includes the following aspects: <1> A positive electrode composition for a secondary battery, comprising: a layered rock salt type lithium transition metal composite oxide as a positive electrode active material; a conductive additive; and a polyacrylonitrile polymer as a binder, wherein part or all of the conductive additive is solid particles, and the proportion of the conductive additive in the positive electrode composition is greater than 0.1% by mass and less than or equal to 1.9% by mass. <2> The positive electrode composition according to <1>, wherein the layered rock salt type lithium transition metal composite oxide contains Ni. <3> The positive electrode composition according to <1> or <2>, wherein the average primary particle size of the layered rock salt type lithium transition metal composite oxide is 20 μm or less. <4> The positive electrode composition according to any one of <1> to <3>, wherein the proportion of the conductive additive in the positive electrode composition is 0.2% by mass or more. <5> The positive electrode composition according to any one of <1> to <4>, wherein the polyacrylonitrile polymer is a polymer containing at least one selected from the group consisting of unsaturated carboxylic acids, unsaturated alkyl carboxylic acid esters, and unsaturated carboxylic acid amides as a polymerization component. <6> A positive electrode composition slurry comprising the positive electrode composition according to any one of <1> to <5> and a solvent for dispersing and / or dissolving the positive electrode composition. <7> A positive electrode composition layer comprising the positive electrode composition according to any one of <1> to <5>. <8> A positive electrode comprising a current collector and the positive electrode composition layer according to <7> disposed on one or both sides of the current collector. <9> A secondary battery comprising the positive electrode according to <8>, a negative electrode, a separator, and an electrolyte.

[0008] According to this disclosure, a positive electrode composition for secondary batteries is provided that has excellent coating properties, is less likely to peel off from the current collector, and is less likely to leach transition metals from the positive electrode composition layer.

[0009] The embodiments of this disclosure are described below. These descriptions and embodiments are illustrative and do not limit the scope of the embodiments.

[0010] In this disclosure, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this disclosure, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples.

[0011] In this disclosure, "A and / or B" is synonymous with "at least one of A and B." In other words, "A and / or B" may be A alone, B alone, or a combination of A and B.

[0012] In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their objectives are achieved.

[0013] When referring to the amount of each component in a composition in this disclosure, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition. In this disclosure, each component may contain multiple types of particles. If there are multiple types of particles corresponding to each component in the composition, the particle size of each component refers to the value for a mixture of those multiple particles present in the composition, unless otherwise specified.

[0014] <Positive Electrode Composition> The positive electrode composition of this disclosure is a positive electrode composition for secondary batteries. The positive electrode composition of this disclosure contains a layered rock salt type lithium transition metal composite oxide as a positive electrode active material, a conductive additive, and a polyacrylonitrile polymer as a binder, wherein part or all of the conductive additive is solid particles, and the proportion of the conductive additive in the positive electrode composition is greater than 0.1% by mass and 1.9% by mass or less.

[0015] The positive electrode composition of this disclosure exhibits excellent coating properties in slurry form. The positive electrode composition layer formed using the positive electrode composition of this disclosure is less likely to peel off from the current collector. The positive electrode composition layer formed using the positive electrode composition of this disclosure is less likely to leach transition metals when the secondary battery is repeatedly charged and discharged.

[0016] If all of the conductive additives in the positive electrode composition are non-solid particles (e.g., hollow particles, porous particles), the positive electrode composition slurry will have poor fluidity, making it difficult to coat the positive electrode composition layer. This is likely due to the low density or large specific surface area of ​​the non-solid particles. The positive electrode composition of this disclosure imparts fluidity and coatability to the slurry by having some or all of the conductive additives be solid particles.

[0017] If the binder of the cathode composition is a polymer other than a polyacrylonitrile polymer (for example, polyvinylidene fluoride), the cathode composition slurry may gel depending on the type of layered rock salt type lithium transition metal composite oxide. The cathode composition of this disclosure, by using a polyacrylonitrile polymer as the binder, imparts fluidity and coating properties to the slurry regardless of the type of layered rock salt type lithium transition metal composite oxide.

[0018] If the proportion of conductive additive in the positive electrode composition exceeds 1.9% by mass, the positive electrode composition layer may peel off from the current collector. By having a proportion of conductive additive in the positive electrode composition of this disclosure of 1.9% by mass or less, the positive electrode composition layer is less likely to peel off from the current collector. If the proportion of conductive additive in the positive electrode composition is 0.1% by mass or less, the charge and discharge capacity of the secondary battery will be insufficient. By having a proportion of conductive additive exceeding 0.1% by mass in the positive electrode composition of this disclosure, a practical positive electrode and secondary battery can be manufactured.

[0019] If the binder of the positive electrode composition is a polymer other than a polyacrylonitrile polymer (for example, polyvinylidene fluoride), transition metals may leach out from the positive electrode composition layer when the secondary battery is repeatedly charged and discharged. The positive electrode composition of this disclosure, because it uses a polyacrylonitrile polymer as the binder, is less prone to the leaching of transition metals from the positive electrode composition layer when the secondary battery is repeatedly charged and discharged.

[0020] Hereinafter, each component of the positive electrode composition will be described in detail.

[0021] [Layered rock salt-type lithium transition metal composite oxide] A layered rock salt-type lithium transition metal composite oxide is a lithium transition metal composite oxide having a layered rock salt-type crystal structure. The crystal structure of the lithium transition metal composite oxide can be identified by X-ray diffraction.

[0022] The layered rock salt-type lithium transition metal composite oxide contains lithium (Li), a transition metal, and oxygen (O). Examples of the transition metal include cobalt (Co), nickel (Ni), manganese (Mn), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), niobium (Nb), molybdenum (Mo), tantalum (Ta), and tungsten (W).

[0023] The layered rock salt-type lithium transition metal composite oxide may contain other elements in addition to lithium, the transition metal, and oxygen. Examples of other elements include nitrogen (N), fluorine (F), sodium (Na), magnesium (Mg), aluminum (Al), and silicon (Si). The presence of other elements may improve the stability of the crystal structure.

[0024] Specific examples of the layered rock salt-type lithium transition metal composite oxide include lithium cobaltate, lithium nickelate, lithium nickel cobalt oxide, lithium nickel manganese oxide, lithium cobalt manganese oxide, and lithium nickel cobalt manganese oxide.

[0025] Although a positive electrode composition slurry containing a Ni-containing layered rock salt-type lithium transition metal composite oxide is generally prone to gelation, according to the positive electrode composition of the present disclosure, fluidity and coatability can be imparted to the slurry even when the Ni-containing layered rock salt-type lithium transition metal composite oxide is used.

[0026] The average primary particle size of the layered rock salt type lithium transition metal composite oxide contained in the positive electrode composition is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 15 μm or less, from the viewpoint of lowering the volume resistivity of the positive electrode composition layer and increasing the charge / discharge capacity of the secondary battery. The average primary particle size of the layered rock salt type lithium transition metal composite oxide contained in the positive electrode composition is preferably 2 μm or more, more preferably 5 μm or more, and even more preferably 8 μm or more, from the viewpoint of the fluidity and coating properties of the positive electrode composition slurry.

[0027] The average primary particle size of layered rock salt type lithium transition metal composite oxide is determined by measuring the major axis of 100 randomly selected primary particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is either a layered rock salt type lithium transition metal composite oxide or a cathode composition, which are materials used to manufacture cathode compositions.

[0028] The proportion of layered rock salt type lithium transition metal composite oxide in the cathode composition is preferably 90% to 98% by mass, more preferably 92% to 98% by mass, and even more preferably 95% to 98% by mass.

[0029] The cathode composition of this disclosure may contain other cathode active materials other than layered rock salt type lithium transition metal composite oxide. Examples of other cathode active materials include olivine type lithium transition metal composite oxide and spinel type lithium transition metal composite oxide. The proportion of layered rock salt type lithium transition metal composite oxide in the total cathode active material is preferably 95% to 100% by mass, more preferably 98% to 100% by mass, and even more preferably 100% by mass.

[0030] [Conductive additives] Examples of conductive additives include particulate carbon materials such as graphite powder and acetylene black; fibrous carbon materials such as carbon nanofibers and vapor-grown carbon fibers (VGCF); and metal particles such as copper, iron, and nickel.

[0031] The average primary particle size of the conductive additive is preferably 1.0 nm to 800 nm, more preferably 1.2 nm to 600 nm, and even more preferably 1.5 nm to 400 nm, from the viewpoints of fluidity and coating properties of the positive electrode composition slurry, adhesion of the positive electrode composition layer to the current collector, and electronic conductivity of the positive electrode composition layer.

[0032] The average primary particle size of the conductive additive is determined by measuring the short diameter of 100 randomly selected primary particles during observation using a scanning electron microscope (SEM) or transmission electron microscope (TEM), and then averaging the short diameters of these 100 particles. The sample used for observation is either the conductive additive or the positive electrode composition, which is a material used to manufacture the positive electrode composition.

[0033] From the viewpoint of preventing the positive electrode composition layer from peeling off from the current collector, the proportion of the conductive additive in the positive electrode composition of this disclosure is 1.9% by mass or less, preferably 1.8% by mass or less, more preferably 1.7% by mass or less, and even more preferably 1.6% by mass or less. From the viewpoint of manufacturing a practical positive electrode and secondary battery, the proportion of the conductive additive in the positive electrode composition of this disclosure is greater than 0.1% by mass, preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.8% by mass or more.

[0034] Some or all of the conductive additive contained in the positive electrode composition of this disclosure are solid particles. Solid particles are particles that do not have voids inside. The fact that the particles are solid can be confirmed by observing the particles with a transmission electron microscope (TEM).

[0035] The proportion of solid particles in the total conductive additive is preferably 90% to 100% by mass, more preferably 95% to 100% by mass, and even more preferably 100% by mass, from the viewpoint of the fluidity and coating properties of the positive electrode composition slurry.

[0036] As a conductive additive constituting the positive electrode composition of this disclosure, particulate carbon material is preferred, and acetylene black is more preferred, from the viewpoint of fluidity and coating properties of the positive electrode composition slurry, adhesion of the positive electrode composition layer to the current collector, and electronic conductivity of the positive electrode composition layer. The mass percentage of acetylene black in the positive electrode composition of this disclosure is preferably 1.9% by mass or less, more preferably 1.8% by mass or less, even more preferably 1.7% by mass or less, and even more preferably 1.6% by mass or less. The proportion of acetylene black in the positive electrode composition of this disclosure is preferably more than 0.1% by mass, more preferably 0.2% by mass or more, even more preferably 0.5% by mass or more, and even more preferably 0.8% by mass or more.

[0037] The average primary particle size of the acetylene black is preferably 10 nm to 70 nm, more preferably 15 nm to 60 nm, and even more preferably 20 nm to 50 nm, from the viewpoints of fluidity and coating properties of the positive electrode composition slurry, adhesion of the positive electrode composition layer to the current collector, and electronic conductivity of the positive electrode composition layer.

[0038] [Polyacrylonitrile-based polymers] Polyacrylonitrile-based polymers are polymers that contain acrylonitrile and / or methacrylonitrile as polymerization components. It is preferable that polyacrylonitrile-based polymers contain acrylonitrile as polymerization components.

[0039] From the viewpoint of the solubility of the polyacrylonitrile polymer in the solvent constituting the cathode composition slurry, the total proportion of acrylonitrile and methacrylonitrile in the total polymerization components of the polyacrylonitrile polymer is preferably 50.0 mol% to 99.9 mol%, more preferably 70.0 mol% to 99.5 mol%, and even more preferably 80.0 mol% to 99.0 mol%.

[0040] From the viewpoint of solubility in the solvent constituting the positive electrode composition slurry, the polyacrylonitrile polymer is preferably a polymer that contains at least one selected from the group consisting of unsaturated carboxylic acids, unsaturated alkyl carboxylic acid esters, and unsaturated carboxylic acid amides as a polymerization component. From the above viewpoint, the polyacrylonitrile polymer is preferably a polymer that contains an unsaturated carboxylic acid and / or an unsaturated alkyl carboxylic acid ester as a polymerization component.

[0041] The unsaturated carboxylic acid, unsaturated alkyl carboxylic acid ester, and unsaturated carboxylic acid amide, which are polymerization components of polyacrylonitrile polymers, are preferably monomers having 10 or fewer carbon atoms, more preferably monomers having 7 or fewer carbon atoms, and even more preferably monomers having 5 or fewer carbon atoms. The unsaturated carboxylic acid, unsaturated alkyl carboxylic acid ester, and unsaturated carboxylic acid amide may be monomers having 2 or more carbon atoms, or monomers having 3 or more carbon atoms.

[0042] Examples of unsaturated carboxylic acids include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, and isocrotonic acid; and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid, mesaconic acid, glutaconic acid, and itaconic acid. The unsaturated carboxylic acid may be one type or two or more types. From the viewpoint of the solubility of the polyacrylonitrile polymer in the solvent constituting the positive electrode composition slurry, at least one of acrylic acid, methacrylic acid, and itaconic acid is preferred, at least one of methacrylic acid and itaconic acid is more preferred, and itaconic acid is even more preferred.

[0043] Examples of unsaturated alkyl carboxylates include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, and isobutyl acrylate; alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, and isobutyl methacrylate; alkyl crotonic acid esters such as methyl crotonic acid, ethyl crotonic acid, n-propyl crotonic acid, isopropyl crotonic acid, n-butyl crotonic acid, t-butyl crotonic acid, and isobutyl crotonic acid; amino group-containing methacrylate esters such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; methoxypolyethylene glycol acrylate, ethoxypolyethylene Examples include acrylic acid esters containing alkoxyl groups such as glycol acrylate, ethoxydiethylene glycol acrylate, methoxydipropylene glycol acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, 2-butoxyethyl acrylate, and 2-phenoxyethyl acrylate; methacrylic acid esters containing alkoxyl groups such as methoxypolyethylene glycol methacrylate, ethoxypolyethylene glycol methacrylate, methoxydiethylene glycol methacrylate, methoxydipropylene glycol methacrylate, 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, 2-butoxyethyl methacrylate, and 2-phenoxyethyl methacrylate; and alkyl acrylates and alkyl methacrylates having phosphoric acid residues, sulfonic acid residues, boric acid residues, etc. in the alkyl group. The unsaturated carboxylate alkyl ester may be one or two or more. From the viewpoint of the solubility of the polyacrylonitrile polymer in the solvent constituting the positive electrode composition slurry, at least one of methyl acrylate and methyl methacrylate is preferred.

[0044] Examples of unsaturated carboxylic acid amides include acrylamide, methacrylamide, itaconic acid diamide, methylolacrylamide, and butoxymethylolacrylamide. There may be one or more unsaturated carboxylic acid amides. From the viewpoint of the solubility of the polyacrylonitrile polymer in the solvent constituting the positive electrode composition slurry, at least one of acrylamide, methacrylamide, and itaconic acid diamide is preferred, and at least one of acrylamide and methacrylamide is more preferred.

[0045] From the viewpoint of the solubility of the polyacrylonitrile polymer in the solvent constituting the cathode composition slurry, the total proportion of unsaturated carboxylic acids, unsaturated alkyl carboxylic acid esters, and unsaturated carboxylic acid amides in the total polymerization components is preferably 0.1 mol% to 50 mol%, more preferably 0.5 mol% to 30 mol%, and even more preferably 1 mol% to 20 mol%.

[0046] Polyacrylonitrile polymers may contain other monomers as polymerization components besides those mentioned above. Examples of other monomers include olefins (e.g., 1-olefins having 2 to 4 carbon atoms (ethylene, propylene, 1-butene, etc.)), vinyl compounds (e.g., vinyl acetate, vinyl chloride, vinyl sulfonic acid, maleic anhydride, N-vinylpyrrolidone, etc.), aromatic vinyl compounds (styrene, etc.), and heterocyclic vinyl compounds (vinylpyridine, vinylimidazole, etc.). The other monomers may be one type or two or more types.

[0047] The total proportion of other monomers in the total polymerization components of the polyacrylonitrile polymer may be 0 mol% to 5.0 mol%, 0 mol% to 1.0 mol%, or 0 mol% to 0.1 mol%.

[0048] The types and composition of the constituent units (i.e., polymerization components) of polyacrylonitrile polymers can be determined by nuclear magnetic resonance (NMR) spectroscopy.

[0049] From the viewpoint of the mechanical strength of the positive electrode composition layer, the weight-average molecular weight of the polyacrylonitrile polymer is preferably 10,000 or more, more preferably 50,000 or more, even more preferably 100,000 or more, and still more preferably 200,000 or more. From the viewpoint of the fluidity and coating properties of the positive electrode composition slurry, the weight-average molecular weight of the polyacrylonitrile polymer is preferably 5 million or less, more preferably 3 million or less, even more preferably 1 million or less, and still more preferably 500,000 or less.

[0050] The weight-average molecular weight of polyacrylonitrile polymers is measured by gel permeation chromatography (GPC). The mobile phase is dimethylformamide, the eluent is 50 mM lithium bromide / 10 mM phosphate-dimethylformamide, and the standard sample is polystyrene.

[0051] Polyacrylonitrile polymers can be produced, for example, by free radical polymerization. Free radical polymerization can be any of the following methods: solution polymerization, dispersion polymerization, bulk polymerization, suspension polymerization, or emulsion polymerization. From the viewpoint of polymer productivity, solution polymerization or suspension polymerization is preferred.

[0052] The cathode composition of this disclosure may contain other polymers (e.g., styrene-butadiene copolymers) as a binder, in addition to polyacrylonitrile polymers. The proportion of polyacrylonitrile polymers in the total binder is preferably 95% to 100% by mass, more preferably 98% to 100% by mass, and even more preferably 100% by mass.

[0053] The proportion of polyacrylonitrile polymer in the positive electrode composition of this disclosure is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more, from the viewpoint of preventing the positive electrode composition layer from peeling off from the current collector. The proportion of polyacrylonitrile polymer in the positive electrode composition of this disclosure is preferably 5.0% by mass or less, more preferably 4.0% by mass or less, and even more preferably 3.0% by mass or less, from the viewpoint of increasing the energy density of the battery.

[0054] The cathode compositions of this disclosure preferably contain substantially no fluorine-containing polymers. Examples of fluorine-containing polymers include polyvinylidene fluoride resins and fluorine-based rubbers. Examples of polyvinylidene fluoride resins include homopolymers of vinylidene fluoride (i.e., polyvinylidene fluoride); copolymers of vinylidene fluoride with halogen-containing monomers such as hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and trichloroethylene; copolymers of vinylidene fluoride with monomers other than halogen-containing monomers; copolymers of vinylidene fluoride with halogen-containing monomers and monomers other than halogen-containing monomers; and mixtures thereof.

[0055] A positive electrode composition being substantially free of fluorine-containing polymers means that the mass ratio of fluorine-containing polymers to the total mass of the positive electrode composition is 0.1% by mass or less. The lower the mass ratio of fluorine-containing polymers to the total mass of the positive electrode composition, the better, and 0% by mass is particularly preferable. In other words, it is particularly preferable that the positive electrode composition does not contain fluorine-containing polymers.

[0056] <Positive Electrode Composition Slurry> The positive electrode composition slurry of the present disclosure comprises the positive electrode composition of the present disclosure and a solvent for dispersing and / or dissolving the components constituting the positive electrode composition. The solvent is preferably a solvent for dissolving polyacrylonitrile polymers.

[0057] Examples of solvents include amides such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol; and water. From the viewpoint of solubility of polyacrylonitrile polymers, amides are preferred as the solvent, and N-methyl-2-pyrrolidone is more preferred. One solvent or two or more solvents may be used.

[0058] From the viewpoint of the coating properties of the cathode composition slurry and the productivity of the cathode composition layer, the solvent content is preferably 10% to 90% by mass, more preferably 15% to 75% by mass, and even more preferably 20% to 60% by mass.

[0059] The positive electrode composition slurry may contain other components besides the positive electrode composition and solvent of this disclosure. Examples of other components include surfactants, dispersants, wetting agents, defoamers, pH adjusters, viscosity modifiers, and fluidizers. These additives may remain in the positive electrode composition layer as long as they are electrochemically stable within the operating range of the secondary battery and do not inhibit the reactions within the battery.

[0060] Cathode composition slurry can be manufactured by mixing the cathode composition with a solvent using various types of mixers. Examples of mixers include ball mills, sand mills, ultrasonic dispersers, homogenizers, and planetary mixers.

[0061] <Positive Electrode Composition Layer> The positive electrode composition layer of this disclosure is a layer containing the positive electrode composition of this disclosure and is a positive electrode active material layer.

[0062] The positive electrode composition layer of this disclosure contains a layered rock salt type lithium transition metal composite oxide as a positive electrode active material, a conductive additive, and a polyacrylonitrile-based polymer as a binder, wherein part or all of the conductive additive is solid particles. Preferably, the proportion of the conductive additive in the positive electrode composition layer of this disclosure is greater than 0.1% by mass and 1.9% by mass or less.

[0063] The layered rock salt type lithium transition metal composite oxide, conductive additive, polyacrylonitrile polymer, and other materials constituting the cathode composition layer of this disclosure are synonymous with the layered rock salt type lithium transition metal composite oxide, conductive additive, polyacrylonitrile polymer, and other materials constituting the cathode composition of this disclosure, and the embodiments and preferred forms are the same. The embodiments and preferred forms relating to the composition of the cathode composition layer of this disclosure are the same as the embodiments and preferred forms relating to the composition of the cathode composition of this disclosure.

[0064] The positive electrode composition layer of the present disclosure can be manufactured by coating one or both sides of a substrate (e.g., a current collector) with the positive electrode composition slurry of the present disclosure. If the positive electrode composition slurry contains any of the following: surfactants, dispersants, wetting agents, defoaming agents, pH adjusters, viscosity adjusters, or fluidizing agents, these components may remain in the positive electrode composition layer.

[0065] <Positive electrode> The positive electrode of the present disclosure comprises a current collector and a positive electrode composition layer of the present disclosure disposed on one or both sides of the current collector.

[0066] Examples of current collectors for the positive electrode include aluminum foil, titanium foil, and stainless steel foil with a thickness of 5 μm to 20 μm.

[0067] The positive electrode of this disclosure can be manufactured by applying the positive electrode composition slurry of this disclosure to one or both sides of a current collector, drying, and pressing. Examples of means for applying the positive electrode composition slurry to the current collector include a roll coater, gravure coater, reverse roll coater, Meyer bar, and die coater. Examples of drying means include blowing hot air, hot air, or low-humidity air; and irradiation with far-infrared or infrared rays. Examples of pressing means include a roll press and a die press.

[0068] The thickness of the positive electrode composition layer may be 0.005 to 5 mm, or 0.01 to 2 mm. The thickness of the positive electrode composition layer is the value obtained by subtracting the thickness of the current collector from the thickness of the positive electrode. The thickness of the current collector and the positive electrode are determined by measuring 10 points with a contact-type film thickness gauge and averaging the results.

[0069] <Secondary Battery> The secondary battery of this disclosure comprises a positive electrode, a negative electrode, a separator, and an electrolyte.

[0070] The positive electrode of the secondary battery of this disclosure operates by doping and dedoping of lithium ions. The negative electrode of the secondary battery of this disclosure may be an negative electrode that operates by doping and dedoping of lithium ions, or an negative electrode that operates by dissolution and deposition of metallic lithium. Doping means absorption, support, adsorption or insertion, and refers to the phenomenon in which lithium ions are incorporated into the active material of the electrode.

[0071] The secondary battery of this disclosure may be a non-aqueous secondary battery or an aqueous secondary battery.

[0072] An example of an embodiment of the secondary battery of this disclosure is a non-aqueous secondary battery in which both the positive and negative electrodes operate by doping and dedoping with lithium ions.

[0073] The secondary battery of this disclosure has a structure in which a battery element in which a positive electrode and a negative electrode face each other via a separator is sealed together with an electrolyte in an outer casing.

[0074] One example of a negative electrode embodiment is a configuration in which an active material layer containing a negative electrode active material and a binder is arranged on one or both sides of a current collector. Another example of a negative electrode embodiment is a configuration in which an active material layer containing a negative electrode active material, a conductive additive, and a binder is arranged on one or both sides of a current collector. Examples of negative electrode active materials include materials that can electrochemically absorb lithium ions. Examples of such materials include carbon materials; alloys of silicon, tin, aluminum, etc. with lithium; and Wood's alloys. Examples of conductive additives include carbon materials such as acetylene black, Ketjen black, graphite powder, and ultrafine carbon fibers. Examples of binders include styrene-butadiene copolymers. Examples of current collectors include copper foil, nickel foil, and stainless steel foil with a thickness of 5 μm to 20 μm. A metallic lithium foil may be used as the negative electrode instead of the above negative electrode.

[0075] Examples of separators include polyolefin microporous membranes, composite membranes in which a heat-resistant resin layer is arranged on one or both sides of a polyolefin microporous membrane, composite membranes in which an inorganic particle layer is arranged on one or both sides of a polyolefin microporous membrane, and cellulose nonwoven fabrics.

[0076] Examples of electrolytes for non-aqueous secondary batteries include solutions in which lithium salts are dissolved in a non-aqueous solvent. LiPF4 is one such example of a lithium salt. ６ LiBF ４ LiClO ４Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; linear carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and their fluorine-substituted derivatives; and cyclic esters such as γ-butyrolactone and γ-valerolactone. Non-aqueous solvents may be used individually or in mixtures of two or more. As the electrolyte for a non-aqueous secondary battery, a solution is preferred in which a cyclic carbonate and a linear carbonate are mixed in a mass ratio (cyclic carbonate:linear carbonate) of 20:80 to 40:60, and a lithium salt is dissolved in it at a concentration of 0.5 mol / L to 1.5 mol / L. For non-aqueous secondary batteries, electrolytes with a lithium salt concentration exceeding 1.5 mol / L can be used, and concentrated electrolytes with a lithium salt concentration of 2 mol / L or higher can also be used.

[0077] Examples of electrolytes for aqueous secondary batteries include solutions in which lithium salts are dissolved in water. Examples of lithium salts include LiCl and Li ２ SO ４ These are some examples.

[0078] Examples of exterior materials include aluminum laminate film packs and metal cans. While batteries can take various shapes such as rectangular, cylindrical, and coin-shaped, the secondary battery of this disclosure may take any of these shapes.

[0079] The secondary battery of this disclosure can be manufactured by first producing a laminate in which a separator is placed between the positive electrode and the negative electrode, then housing this laminate in an outer casing, injecting an electrolyte therein, and sealing the outer casing.

[0080] When manufacturing a laminate with a separator placed between the positive electrode and the negative electrode, the method of placing the separator between the positive electrode and the negative electrode may be a method in which the positive electrode, separator, and negative electrode are stacked in that order in at least one layer each (the so-called stack method), or a method in which the positive electrode, separator, negative electrode, and separator are stacked in that order and wound in the length direction.

[0081] The cathode composition, cathode composition slurry, cathode composition layer, cathode, and secondary battery of this disclosure will be described in more detail below with reference to examples. The materials, amounts used, proportions, processing procedures, etc., shown in the following examples can be modified as appropriate without departing from the spirit of this disclosure. Therefore, the scope of the cathode composition, cathode composition slurry, cathode composition layer, cathode, and secondary battery of this disclosure should not be interpreted as being limited by the specific examples shown below.

[0082] In the following descriptions, synthesis, processing, and manufacturing were carried out at room temperature (25°C ± 3°C) unless otherwise specified.

[0083] <Measurement Methods and Evaluation Methods> The measurement and evaluation methods applied to the examples and comparative examples are as follows.

[0084] [Average Primary Particle Size of Cathode Active Material] Layered rock salt type lithium transition metal composite oxide used in the manufacture of the cathode composition was observed using a scanning electron microscope (SEM) to determine the average primary particle size. The major axis of 100 randomly selected primary particles on the SEM image was measured, and the average of the major axes of these 100 particles was taken as the average primary particle size (μm).

[0085] [Thickness of the positive electrode composition layer] The thickness of the current collector and the positive electrode were measured at 10 points using a contact-type thickness gauge, and the average of these measurements was used to determine the thickness of the positive electrode composition layer (μm). The thickness of the current collector was subtracted from the thickness of the positive electrode to determine the thickness of the positive electrode composition layer (μm).

[0086] [Volume Resistivity of the Positive Electrode Composition Layer] The positive electrode was used as the sample. The thickness of the current collector, the volume resistivity (known value), and the thickness of the positive electrode composition layer were input into the RM2610 electrode resistance measurement system (HIOKI E.E. CORPORATION), and the potential distribution of the positive electrode was measured using the system. The potential distribution was analyzed using the system to separate the resistance at the interface between the current collector and the positive electrode composition layer, and the volume resistivity (Ω・cm) of the positive electrode composition layer was determined.

[0087] [Discharge Capacity] The test secondary battery was subjected to one charge-discharge cycle, and the discharge capacity (mAh / cm²) was determined. ２ The following was determined: Charging was performed using 0.2C constant current charging followed by 4.2V constant voltage charging, and discharging was performed using either 0.2C constant current discharge or 2C constant current discharge at a cutoff voltage of 2.5V.

[0088] [Amount of Cobalt (Co) Adhesion to the Negative Electrode] A test secondary battery underwent 14 charge-discharge cycles. Charging was performed using a constant current and constant voltage of 0.2C / 4.2V, and discharging was performed sequentially at a cutoff voltage of 2.5V, with three 0.2C discharges, one 0.5C discharge, and one discharge each from 1C to 10C, increasing by 1C each time. After charging and discharging, the coin cell was disassembled and the negative electrode was removed. The surface of the negative electrode was analyzed using an energy-dispersive X-ray fluorescence analyzer EDX-800HS (Shimadzu Corporation), and the intensity of the CoKα rays (cps / μA) was defined as the amount of Co adhesion.

[0089] <Battery Manufacturing> [Example 1] The following polyacrylonitrile polymer was synthesized. • Polymerization components: Acrylonitrile 97.1 mol%, Methyl acrylate 2.5 mol%, Itaconic acid 0.4 mol% • Weight-average molecular weight 300,000

[0090] Lithium cobalt oxide powder (LiCoO ２ A cathode composition was prepared by mixing 96.1 parts by mass of (Nippon Chemical Industries, Ltd., Cellseed) with an average primary particle size of 8.5 μm, 1.90 parts by mass of acetylene black (solid particles, average primary particle size of 36 nm, Denka Co., Ltd., Denka Black), and 2.0 parts by mass of a polyacrylonitrile polymer. An appropriate amount of N-methyl-2-pyrrolidone was added to the cathode composition and kneaded to prepare a cathode composition slurry. The cathode composition slurry was applied to one side of a 20 μm thick aluminum foil using a roll coater and dried, and then roll-pressed to obtain the cathode. The thickness of the cathode composition layer was 60 μm.

[0091] A negative electrode composition slurry was prepared by kneading 300 parts by mass of artificial graphite, 7.5 parts by mass of a water-soluble dispersion containing 40% by mass of a styrene-butadiene copolymer modified material, 3 parts by mass of carboxymethylcellulose as a thickening agent, and an appropriate amount of water. The negative electrode composition slurry was applied to one side of a 10 μm thick copper foil using a roll coater and dried, and then roll-pressed to obtain the negative electrode.

[0092] The positive electrode was punched out in a circular shape with a diameter of 12 mm. The negative electrode was punched out in a circular shape with a diameter of 14 mm. A polyethylene microporous membrane (thickness 8 μm, porosity 36%) was punched out in a circular shape with a diameter of 16 mm. The polyethylene microporous membrane was sandwiched between the positive and negative electrodes and placed in a coin cell with an inner diameter of 17 mm. The coin cell was injected with electrolyte and sealed to obtain a test secondary battery. The electrolyte contained 1 mol / L LiPF4. ６ - Ethylene carbonate / ethyl methyl carbonate (mass ratio 3:7) was used.

[0093] [Comparative Example 1] In the same manner as in Example 1, except that acetylene black was replaced with Ketjenblack (hollow particles, average primary particle size 34 nm, Lion Specialty Chemicals Co., Ltd., EC300J), an attempt was made to manufacture a battery. However, during the production of the positive electrode composition slurry, as the solvent was added, the state changed from a non-fluid wet powder state to a state in which the wet powder separated into a liquid state, and a fluid slurry could not be produced. Therefore, it was not possible to coat the aluminum foil with the positive electrode composition slurry, and the positive electrode and battery could not be manufactured.

[0094] [Examples 2 to 4] Batteries were manufactured in the same manner as in Example 1, except that the amount of acetylene black used was changed as shown in Table 1.

[0095] [Comparative Example 2] A battery was manufactured in the same manner as in Example 1, except that the amount of acetylene black used was changed as shown in Table 1. However, the amount of acetylene black used was too small, and it was not a practical secondary battery.

[0096] [Comparative Example 3] An attempt was made to manufacture a battery in the same manner as in Example 1, except that the amount of acetylene black used was changed as shown in Table 1. However, after roll pressing the positive electrode composition layer, the positive electrode composition layer peeled off from the aluminum foil, and it was not possible to manufacture the positive electrode and the battery.

[0097] [Comparative Example 4] A battery was manufactured in the same manner as in Example 1, except that the polyacrylonitrile polymer was replaced with polyvinylidene fluoride (weight-average molecular weight 630,000, Kureha Corporation, KF Polymer W#7200).

[0098] [Example 5] A battery was produced in the same manner as in Example 1, except that the lithium cobaltate powder (average primary particle diameter: 8.5 μm) was replaced with another lithium cobaltate powder (LiCoO ２ , average primary particle diameter: 18 μm, Nihon Kagaku Kogyo Co., Ltd., Cellseed).

[0099] [Example 6] A battery was produced in the same manner as in Example 1, except that the lithium cobaltate powder (average primary particle diameter: 8.5 μm) was replaced with another lithium cobaltate powder (LiCoO ２ , average primary particle diameter: 22 μm, Nihon Kagaku Kogyo Co., Ltd., Cellseed).

[0100] [Example 7] A battery was produced in the same manner as in Example 1, except that the lithium cobaltate powder was replaced with lithium nickel cobalt manganese oxide powder (LiNi ０．６ Co ０．２ Mn ０．２ O ２ , average primary particle diameter: 10 μm, Toshima Seisakusho Co., Ltd.).

[0101] [Example 8] A battery was produced in the same manner as in Example 1, except that the lithium cobaltate powder was replaced with lithium nickel cobalt manganese oxide powder (LiNi ０．８ Co ０．１ Mn ０．１ O ２ , average primary particle diameter: 10 μm, Toshima Seisakusho Co., Ltd.).

[0102] [Example 9] A battery was produced in the same manner as in Example 1, except that the lithium cobaltate powder was replaced with lithium nickel cobalt manganese oxide powder (LiNi ０．９ Co ０．０５ Mn ０．０５ O ２ , average primary particle diameter: 12 μm, MTI Corporation, U.S.A.).

[0103] [Comparative Example 5] A battery was produced in the same manner as in Example 1, except that the lithium cobaltate powder was replaced with lithium nickel cobalt manganese oxide powder (LiNi ０．６ Co ０．２ Mn ０．２ O ２We attempted to manufacture a battery by changing the polymer (average primary particle size 10 μm, manufactured by Toyoshima Seisakusho Co., Ltd.) and the polyacrylonitrile polymer to polyvinylidene fluoride (weight-average molecular weight 630,000, manufactured by Kureha Corporation, KF Polymer W#7200). However, we were unable to produce a fluid cathode composition slurry. Consequently, we were unable to coat the cathode composition slurry onto the aluminum foil, and therefore were unable to manufacture the cathode and battery.

[0104] [Comparative Example 6] In the same manner as in Example 1, however, lithium cobaltate powder is replaced with lithium nickel cobalt manganese oxide powder (LiNi ０．８ Co ０．１ Mn ０．１ O ２ We attempted to manufacture a battery by changing the polymer (average primary particle size 10 μm, manufactured by Toyoshima Seisakusho Co., Ltd.) and the polyacrylonitrile polymer to polyvinylidene fluoride (weight-average molecular weight 630,000, manufactured by Kureha Corporation, KF Polymer W#7200). However, we were unable to produce a fluid cathode composition slurry. Consequently, we were unable to coat the cathode composition slurry onto the aluminum foil, and therefore were unable to manufacture the cathode and battery.

[0105] [Comparative Example 7] In the same manner as in Example 1, however, lithium cobaltate powder is replaced with lithium nickel cobalt manganese oxide powder (LiNi ０．９ Co ０．０５ Mn ０．０５ O ２ We attempted to manufacture a battery by changing the polymer to an average primary particle size of 12 μm (MTI Corporation, USA) and the polyacrylonitrile polymer to polyvinylidene fluoride (weight-average molecular weight 630,000, Kureha Corporation, KF Polymer W#7200). However, we were unable to produce a fluid cathode composition slurry. Consequently, we were unable to coat the cathode composition slurry onto the aluminum foil, and therefore could not manufacture the cathode or the battery.

[0106] The abbreviations in Table 1 have the following meanings: • LCO: Lithium cobalt oxide (LiCoO) ２ ) ・NCM622: Lithium nickel cobalt manganese oxide (LiNi ０．６ Co ０．２ Mn ０．２ O２ ) ・NCM811: Lithium nickel cobalt manganese oxide (LiNi ０．８ Co ０．１ Mn ０．１ O ２ ) ・NCM9.5.5: Lithium nickel cobalt manganese oxide (LiNi ０．９ Co ０．０５ Mn ０．０５ O ２ ) AB: Acetylene Black KB: Ketjen Black PAN: Polyacrylonitrile Polymer PVDF: Polyvinylidene Fluoride

[0107]

[0108]

[0109] All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

[0110] The disclosure of Japanese application number 2025-040697, filed on 13 March 2025, is incorporated herein by reference in its entirety.

Claims

1. A positive electrode composition for a secondary battery, comprising: a layered rock salt type lithium transition metal composite oxide as a positive electrode active material; a conductive additive; and a polyacrylonitrile polymer as a binder, wherein part or all of the conductive additive is in the form of solid particles, and the proportion of the conductive additive in the positive electrode composition is greater than 0.1% by mass and less than or equal to 1.9% by mass.

2. The cathode composition according to claim 1, wherein the layered rock salt type lithium transition metal composite oxide contains Ni.

3. The cathode composition according to claim 1, wherein the average primary particle size of the layered rock salt type lithium transition metal composite oxide is 20 μm or less.

4. The positive electrode composition according to claim 1, wherein the proportion of the conductive additive in the positive electrode composition is 0.2% by mass or more.

5. The positive electrode composition according to claim 1, wherein the polyacrylonitrile polymer is a polymer that contains at least one selected from the group consisting of unsaturated carboxylic acids, unsaturated alkyl carboxylic acid esters, and unsaturated carboxylic acid amides as a polymerization component.

6. A cathode composition slurry comprising a cathode composition according to any one of claims 1 to 5, and a solvent for dispersing and / or dissolving the cathode composition.

7. A positive electrode composition layer comprising the positive electrode composition according to any one of claims 1 to 5.

8. A positive electrode comprising a current collector and a positive electrode composition layer according to claim 7, disposed on one or both sides of the current collector.

9. A secondary battery comprising the positive electrode, negative electrode, separator, and electrolyte as described in claim 8.

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