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 an olivine-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 comprises solid particles, the proportion of the conductive additive in the positive electrode composition is 4.8 mass% or less, and the proportion of the polyacrylonitrile-based polymer in the positive electrode composition is 0.7 mass% or more.

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 an olivine-type lithium transition metal composite oxide offer safety during overcharging and over-discharging, as well as a long battery life. This is because olivine-type lithium transition metal composite oxides have excellent thermal stability and cycle characteristics. However, since olivine-type lithium transition metal composite oxides are used with relatively small particle sizes to improve electronic conductivity, secondary batteries in which the positive electrode active material is an olivine-type lithium transition metal composite oxide have the following challenges (1) to (2).

[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.

[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 and is less likely to peel off from the current collector.

[0007] This disclosure includes the following aspects: <1> A positive electrode composition for a secondary battery, comprising: an olivine-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, the proportion of the conductive additive in the positive electrode composition is 4.8% by mass or less, and the proportion of the polyacrylonitrile-based polymer in the positive electrode composition is 0.7% by mass or more. <2> The positive electrode composition according to <1>, wherein the olivine-type lithium transition metal composite oxide contains Fe and / or Mn. <3> The positive electrode composition according to <1> or <2>, wherein the average primary particle size of the olivine-type lithium transition metal composite oxide is 10 μm or less. <4> The positive electrode composition according to any one of <1> to <3>, wherein the proportion of the polyacrylonitrile-based polymer in the positive electrode composition is 3.5% by mass or less. <5> The positive electrode composition according to any one of <1> to <4>, wherein the proportion of the conductive additive in the positive electrode composition is 0.1% by mass or more. <6> The positive electrode composition according to any one of <1> to <5>, 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. <7> A positive electrode composition slurry comprising the positive electrode composition according to any one of <1> to <6> and a solvent for dispersing and / or dissolving the positive electrode composition. <8> A positive electrode composition layer comprising the positive electrode composition according to any one of <1> to <6>. <9> A positive electrode comprising a current collector and the positive electrode composition layer according to <8> disposed on one or both sides of the current collector. <10> A secondary battery comprising the positive electrode according to <9>, a negative electrode, a separator, and an electrolyte.

[0008] This disclosure provides a positive electrode composition for secondary batteries that has excellent coating properties and is less likely to peel off from the current collector.

[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 an olivine-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, the proportion of the conductive additive in the positive electrode composition is 4.8% by mass or less, and the proportion of the polyacrylonitrile polymer in the positive electrode composition is 0.7% by mass or more.

[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.

[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 proportion of conductive additive in the positive electrode composition exceeds 4.8% 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 4.8% by mass or less, the positive electrode composition layer is less likely to peel off from the current collector.

[0018] If the binder of the positive electrode composition is a polymer other than a polyacrylonitrile-based polymer (for example, polyvinylidene fluoride), the positive electrode composition layer may peel off from the current collector. The positive electrode composition of this disclosure uses a polyacrylonitrile-based polymer as the binder, which has excellent adhesion to metal materials, making it less likely for the positive electrode composition layer to peel off from the current collector.

[0019] If the proportion of polyacrylonitrile polymer in the positive electrode composition is less than 0.7% 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 0.7% by mass or more, the positive electrode composition layer is less likely to peel off from the current collector.

[0020] The components of the positive electrode composition are described in detail below.

[0021] [Olivine-type lithium transition metal composite oxides] Olivine-type lithium transition metal composite oxides are lithium transition metal composite oxides that have an olivine-type crystal structure. The crystal structure of lithium transition metal composite oxides can be determined by X-ray diffraction.

[0022] Olivine-type lithium transition metal composite oxides generally contain lithium (Li), a transition metal, and an oxygen (O)-containing polyanion. Examples of transition metals include iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), and titanium (Ti). Examples of oxygen-containing polyanions include phosphates (PO ４ ３－ ), silicate (SiO ４ ４－ Examples include:

[0023] Olivine-type lithium transition metal composite oxides may contain elements other than lithium, transition metals, oxygen, phosphorus, and silicon. Examples of these other elements include magnesium (Mg), aluminum (Al), and zinc (Zn). The presence of these other elements may improve the stability of the crystal structure.

[0024] As an example of a general formula for olivine-type lithium transition metal composite oxides, LiMPO ４ Examples include lithium transition metal phosphates (where M is one or more transition metals). The transition metal M is preferably one or more selected from the group consisting of Fe, Mn, Co, Ni, and Ti, with Fe and / or Mn being more preferred. A portion of the transition metal M may be substituted with Mg, Al, Zn, etc. This substitution may improve the stability of the crystal structure.

[0025] From the viewpoint of improving electronic conductivity, olivine-type lithium transition metal composite oxides are preferably in a form in which the particle surface is coated with carbon.

[0026] From the viewpoint of increasing the charge and discharge capacity of the secondary battery, the average primary particle size of the olivine-type lithium transition metal composite oxide contained in the positive electrode composition is preferably 10 μm or less, more preferably 9 μm or less, and even more preferably 8 μm or less. From the viewpoint of the fluidity and coating properties of the positive electrode composition slurry, the average primary particle size of the olivine-type lithium transition metal composite oxide contained in the positive electrode composition is preferably 1 μm or more.

[0027] The average primary particle size of the olivine-type lithium transition metal composite oxide is determined by measuring the major diameters of 100 randomly selected primary particles in observation with a scanning electron microscope (SEM), and averaging the major diameters of the 100 particles. The sample used for SEM observation is the olivine-type lithium transition metal composite oxide which is a material for producing a positive electrode composition, or the positive electrode composition.

[0028] The proportion of the olivine-type lithium transition metal composite oxide in the positive electrode composition is preferably 90% by mass to 98% by mass, more preferably 91% by mass to 98% by mass, and still more preferably 92% by mass to 98% by mass.

[0029] The positive electrode composition of the present disclosure may contain other positive electrode active materials other than the olivine-type lithium transition metal composite oxide. Examples of the other positive electrode active materials include layered rock salt-type lithium transition metal composite oxides and spinel-type lithium transition metal composite oxides. The proportion of the olivine-type lithium transition metal composite oxide in the entire positive electrode active material is preferably 95% by mass to 100% by mass, more preferably 98% by mass to 100% by mass, and still more preferably 100% by mass.

[0030] [Conductive Aid] Examples of the conductive aid 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 aid is preferably 1.0 nm to 800 nm, more preferably 1.2 nm to 600 nm, and still more preferably 1.5 nm to 400 nm, from the viewpoints of the fluidity and coatability of the positive electrode composition slurry, the adhesion of the positive electrode composition layer to a current collector, and the electronic conductivity of the positive electrode composition layer.

[0032] The average primary particle size of the conductive aid is determined by measuring the minor diameters of 100 randomly selected primary particles in observation with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and averaging the minor diameters of the 100 particles. The sample used for observation is the conductive aid which is a material for producing a positive electrode composition, or the positive electrode composition.

[0033] From the viewpoint of suppressing peeling of the positive electrode composition layer from the current collector, the proportion of the conductive auxiliary agent in the positive electrode composition of the present disclosure is 4.8% by mass or less. The proportion of the conductive auxiliary agent in the positive electrode composition of the present disclosure is more than 0% by mass. From the viewpoint of producing a practical positive electrode and a secondary battery, the proportion of the conductive auxiliary agent in the positive electrode composition of the present disclosure is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, still more preferably 0.8% by mass or more, and still more preferably 1.0% by mass or more.

[0034] Part or all of the conductive auxiliary agent contained in the positive electrode composition of the present disclosure is solid particles. A solid particle is a particle that has no internal voids. Whether a particle is a solid particle can be confirmed by observing the particle with a transmission electron microscope (TEM).

[0035] From the viewpoints of fluidity and coatability of the positive electrode composition slurry, the proportion of solid particles in the entire conductive auxiliary agent is preferably 90% by mass to 100% by mass, more preferably 95% by mass to 100% by mass, and still more preferably 100% by mass.

[0036] As the conductive auxiliary agent constituting the positive electrode composition of the present disclosure, from the viewpoints of fluidity and coatability 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, a particulate carbon material is preferable, and acetylene black is more preferable. The mass proportion of acetylene black in the positive electrode composition of the present disclosure is preferably 4.8% by mass or less. The mass proportion of acetylene black in the positive electrode composition of the present disclosure is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, still more preferably 0.8% by mass or more, and still more preferably 1.0% by mass or more.

[0037] From the viewpoints of fluidity and coatability 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 average primary particle diameter of acetylene black is preferably 10 nm to 70 nm, more preferably 15 nm to 60 nm, and still more preferably 20 nm to 50 nm.

[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] 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 0.7% by mass or more, more preferably 0.8% 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 increasing the energy density of the battery, the proportion of polyacrylonitrile polymer in the positive electrode composition of this disclosure is preferably 3.5% by mass or less, more preferably 3.0% by mass or less, and even more preferably 2.5% by mass or less.

[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 an olivine-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 4.8% by mass or less. Preferably, the proportion of the conductive additive in the positive electrode composition layer of this disclosure is 0.7% by mass or more.

[0063] The olivine-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 olivine-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] <Rechargeable Battery> The rechargeable 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 include the following. Examples of non-aqueous solvents include: cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted products thereof; and cyclic esters such as γ-butyrolactone and γ-valerolactone. One non-aqueous solvent may be used alone, or two or more non-aqueous solvents may be used as a mixture. As an electrolyte solution for a non-aqueous secondary battery, a solution obtained by mixing a cyclic carbonate and a chain carbonate at a mass ratio (cyclic carbonate: chain carbonate) of 20:80 to 40:60 and dissolving a lithium salt in a range of 0.5 mol / L to 1.5 mol / L is suitable. As an electrolyte solution for a non-aqueous secondary battery, an electrolyte solution having a lithium salt concentration of more than 1.5 mol / L can also be used, and a concentrated electrolyte solution having a lithium salt concentration of 2 mol / L or more can also be used.

[0077] Examples of electrolyte solutions for aqueous secondary batteries include solutions obtained by dissolving a lithium salt in water. Examples of lithium salts include LiCl, Li ２ SO ４ and the like.

[0078] Examples of exterior materials include packs made of aluminum laminate film, metal cans, and the like. While battery shapes include prismatic, cylindrical, coin-shaped, and the like, the secondary battery of the present disclosure may have any shape.

[0079] The secondary battery of the present disclosure can be manufactured by: producing a laminate in which a separator is disposed between a positive electrode and a negative electrode; then housing the laminate in an exterior material; injecting an electrolyte solution thereinto; and sealing the exterior material.

[0080] When producing a laminate in which a separator is disposed between a positive electrode and a negative electrode, the method of disposing the separator between the positive electrode and the negative electrode may be a method (a so-called stacking method) in which at least one layer each of the positive electrode, the separator, and the negative electrode are stacked in this order, or may be a method in which the positive electrode, the separator, the negative electrode, and the separator are stacked in this 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] The average primary particle size was determined by observing olivine-type lithium transition metal composite oxides used in the manufacture of the cathode composition using a scanning electron microscope (SEM). 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] [Discharge Capacity] The test secondary battery was subjected to one charge-discharge cycle, and the discharge capacity (mAh / cm²) was determined. ２ ) was requested. ・LiFePO ４ Positive electrode: Charging was performed using 0.2C constant current charging followed by 3.5V constant voltage charging, and discharging was performed using 0.2C constant current discharge at a cutoff voltage of 2.0V. • LiMn ０．６ Fe ０．４ PO ４ Positive electrode: Charging was performed using 0.2C constant current charging followed by 4.5V constant voltage charging, and discharge was performed using 0.2C constant current discharge at a cutoff voltage of 2.5V.

[0087] <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

[0088] Carbon-coated lithium iron phosphate powder (LiFePO ４ A cathode composition was prepared by mixing 93.0 parts by mass of (T2) (average primary particle size 8 μm, MSE Supplies LLC, USA), 4.8 parts by mass of acetylene black (solid particles, average primary particle size 36 nm, Denka Co., Ltd., Denka Black), and 2.2 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.

[0089] 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.

[0090] 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.

[0091] [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.

[0092] [Example 2] A battery was manufactured in the same manner as in Example 1, except that the carbon-coated lithium iron phosphate powder (average primary particle size 8 μm) was replaced with another carbon-coated lithium iron phosphate powder (average primary particle size 12 μm). The carbon-coated lithium iron phosphate powder used in Example 2 was obtained by classifying the carbon-coated lithium iron phosphate powder used in Example 1.

[0093] [Examples 3-4] 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.

[0094] [Comparative Example 2] 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.

[0095] [Examples 5-6] Batteries were manufactured in the same manner as in Example 1, except that the amount of polyacrylonitrile polymer used was changed as shown in Table 1.

[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 polyacrylonitrile polymer 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 the positive electrode and battery could not be manufactured.

[0097] [Comparative Example 4] In the same manner as in Example 1, however, the polyacrylonitrile polymer was replaced with polyvinylidene fluoride (weight-average molecular weight 630,000, Kureha Corporation, KF Polymer W#7200) and an attempt was made to manufacture a battery. However, after roll pressing the positive electrode composition layer, the positive electrode composition layer peeled off from the aluminum foil, and the positive electrode and battery could not be manufactured.

[0098] [Example 7] The same procedure as in Example 1, except that carbon-coated lithium iron phosphate powder is replaced with carbon-coated lithium iron manganese phosphate powder (LiMn ０．６ Fe ０．４ PO ４ The battery was manufactured using a modified material with an average primary particle size of 1 μm (MTI Corporation, USA, Lib-LMFPO).

[0099] [Comparative Example 5] In the same manner as in Example 1, however, carbon-coated lithium iron phosphate powder is replaced with carbon-coated lithium manganese iron phosphate powder (LiMn ０．６ Fe ０．４ PO ４ We attempted to manufacture batteries by changing the polymer to an average primary particle size of 1 μm (MTI Corporation, USA, Lib-LMFPO) and the polyacrylonitrile polymer to polyvinylidene fluoride (weight-average molecular weight 630,000, Kureha Corporation, KF Polymer W#7200). However, after roll pressing the positive electrode composition layer, the positive electrode composition layer peeled off from the aluminum foil, making it impossible to manufacture the positive electrode and battery.

[0100] The abbreviations in Table 1 have the following meanings: • LFP: Carbon-coated lithium iron phosphate (LiFePO) ４ ) ・LMFP: Carbon-coated manganese iron lithium phosphate (LiMn ０．６ Fe ０．４ PO ４ ) AB: Acetylene Black KB: Ketjen Black PAN: Polyacrylonitrile Polymer PVDF: Polyvinylidene Fluoride

[0101]

[0102]

[0103] 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.

[0104] The disclosure of Japanese application number 2025-040698, filed on 13 March 2025, is incorporated herein by reference in its entirety.

Claims

1. A positive electrode composition for a secondary battery, comprising: an olivine-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, the proportion of the conductive additive in the positive electrode composition is 4.8% by mass or less, and the proportion of the polyacrylonitrile-based polymer in the positive electrode composition is 0.7% by mass or more.

2. The positive electrode composition according to claim 1, wherein the olivine-type lithium transition metal composite oxide contains Fe and / or Mn.

3. The cathode composition according to claim 1, wherein the average primary particle size of the olivine-type lithium transition metal composite oxide is 10 μm or less.

4. The positive electrode composition according to claim 1, wherein the proportion of the polyacrylonitrile polymer in the positive electrode composition is 3.5% by mass or less.

5. The positive electrode composition according to claim 1, wherein the proportion of the conductive additive in the positive electrode composition is 0.1% by mass or more.

6. 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.

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

8. A positive electrode composition layer comprising the positive electrode composition according to any one of claims 1 to 6.

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

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

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