Positive electrode material and preparation method therefor, positive electrode sheet, secondary battery and electronic device

Abstract

Disclosed in the present application are a positive electrode material and a preparation method therefor, a positive electrode sheet, a secondary battery and an electronic device. The positive electrode material comprises an M1 element, an M2 element and an X element, wherein the M1 element comprises one or more of vanadium, niobium or tantalum; the M2 element comprises one or more of lanthanum, cerium, praseodymium, samarium, dysprosium, ytterbium, yttrium or lutetium; and the X element comprises one or more of fluorine, chlorine, sulfur, nitrogen or boron. The present application can improve the high-temperature cycle performance and prolong the cycle life.

Description

Positive electrode materials and their preparation methods, positive electrode sheets, secondary batteries and electronic devices Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a positive electrode material and its preparation method, a positive electrode sheet, a secondary battery, and an electronic device. Background Technology

[0002] In recent years, with the increasingly wide range of applications and diversification of fields, higher demands have been placed on the performance of rechargeable batteries under unconventional temperatures. Lithium manganese oxide (LMO) batteries, using LMO as the cathode material, offer advantages such as high energy density and low cost. However, at high temperatures, LMO cathode materials are prone to dissolution and structural and chemical changes during cyclic charging and discharging, leading to deterioration in high-temperature performance and rapid capacity decay. Therefore, there is an urgent need to improve the high-temperature performance of LMO cathode batteries. Summary of the Invention

[0003] This application provides a positive electrode material and its preparation method, a positive electrode sheet, a secondary battery, and an electronic device, which can improve the high-temperature cycle performance of lithium manganese oxide batteries.

[0004] In a first aspect, embodiments of this application provide a cathode material. The cathode material includes elements M1, M2, and X; element M1 includes one or more of vanadium, niobium, or tantalum, and the molar ratio of element M1 to the molar ratio of the cathode material is a; element M2 includes one or more of lanthanum, cerium, praseodymium, samarium, dysprosium, ytterbium, yttrium, or lutetium, and the molar ratio of element M2 to the molar ratio of the cathode material is b. Element X includes one or more of fluorine, chlorine, sulfur, nitrogen, or boron, and the molar ratio of element X to the molar ratio of the cathode material is c. The cathode material is a nearly spherical secondary particle. The region from the outer surface of the secondary particle to a depth of 100 nm is designated as region I, and the region from the center of the particle to a depth of 100 nm is designated as region II. In region I, 0.02 ≤ a ≤ 0.05, 0.02 ≤ b ≤ 0.05, and 0.001 ≤ c ≤ 0.04. In region II, 0.001 ≤ a ≤ 0.02 and 0.001 ≤ b ≤ 0.02.

[0005] Based on the cathode material of this application embodiment, the inventors discovered that, on the basis of lithium manganese oxide as the cathode active material, further doping with M1 elements including vanadium, niobium or tantalum, M2 elements including lanthanum, cerium, praseodymium, samarium, dysprosium, ytterbium, yttrium or lutetium, and X elements including fluorine, chlorine, sulfur, nitrogen or boron, and adjusting the type and content of the above-mentioned doping to regulate the grain morphology of the cathode material, on the one hand, can make the (111) crystal plane with relatively low manganese ion solubility in the grain highly exposed, thereby suppressing the manganese dissolution phenomenon under high temperature environment and improving high temperature cycle performance; on the other hand, it can stabilize the material structure, suppress the Ginger-Taylor effect, alleviate the configuration deformation during long-term cycling, thereby increasing the cathode stability and improving cycle life.

[0006] In some embodiments, in region I, 0.025 ≤ a ≤ 0.045, 0.025 ≤ b ≤ 0.045, and 0.005 ≤ c ≤ 0.03; and / or, in region II, 0.005 ≤ a ≤ 0.01 and 0.005 ≤ b ≤ 0.01. Based on the above embodiments, this application, by further controlling the elemental molar content in regions I and II of the cathode material within the above ranges, can further suppress manganese dissolution under high-temperature conditions, improve high-temperature cycle performance, increase cathode stability, and improve cycle life.

[0007] In some embodiments, the cathode material includes lithium, and the molar ratio of lithium to the molar ratio of the cathode material is d, where 1 ≤ d ≤ 1.08. Based on the above embodiments, this application further controls the molar concentration of active material elements in the cathode material within a suitable range, which can better suppress manganese dissolution under high-temperature conditions, increase cathode stability, further improve high-temperature cycle performance, and increase cycle life.

[0008] In some embodiments, the cathode material in region I above satisfies at least one of the following conditions: (1) 0.05 ≤ a + b + c ≤ 0.1; (2) 0.001 ≤ c / d ≤ 0.03. Based on the above embodiments, this application further regulates the molar concentration of doped elements in the cathode material within a suitable range, enabling it to better exert a synergistic effect, better suppress manganese dissolution under high temperature conditions, increase cathode stability, further improve high temperature cycle performance, and increase cycle life.

[0009] In some embodiments, element X is selected from fluorine and / or boron. Based on the above embodiments, by selecting the above elements as doping elements, this application can more effectively reduce manganese leaching under high-temperature environments, enhance the structural stability of the material, and thus further improve high-temperature cycling performance and increase cycle life.

[0010]

[0011] Based on the above embodiments, this application can further improve the high-temperature performance of the material by controlling the specific surface area within the above range; further improve the cycling performance of the material by controlling the cell parameters within the above range; improve the volumetric energy density of the material by controlling Dv50 within the above range; and improve the high-temperature cycling performance and increase the cycle life by coordinating and regulating the above parameters.

[0012] In a second aspect, this application provides a method for preparing a cathode material, comprising the following steps: (1) preparing a precursor containing elements M1 and M2; (2) mixing the precursor containing elements M1 and M2 with a lithium source and a manganese source to obtain precursor A; (3) placing precursor A in an oxygen-containing atmosphere for a first sintering to obtain a first sintered product as precursor B; or, placing precursor A in an oxygen-containing atmosphere for a first sintering to obtain a first sintered product, and then mixing the first sintered product with a precursor containing element X to obtain precursor B; (4) placing precursor B in an oxygen-containing atmosphere for a second sintering to obtain a cathode material.

[0013] In step (3), the first sintering temperature is 450℃ to 650℃, and the time is 4h to 8h; in step (4), the second sintering temperature is 700℃ to 900℃, and the time is 8h to 12h. The lithium source is lithium carbonate and / or lithium hydroxide, and the manganese source is manganese dioxide and / or manganese tetroxide. Based on the above embodiments, this application can reduce defects in the cathode material crystal during the formation process through the above preparation steps, and can also control the element distribution inside the cathode material to form a core-shell structure material with different doping element concentrations in region I and region II, further improving high-temperature cycle performance and increasing cycle life.

[0014] Thirdly, embodiments of this application provide a positive electrode sheet, including a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector; the positive electrode material layer includes the aforementioned positive electrode material or a positive electrode material prepared by the aforementioned method.

[0015] In some embodiments, the aforementioned cathode material layer further includes ternary lithium material and / or lithium manganese iron phosphate and / or lithium iron phosphate. Based on the above embodiments, by using the cathode material described in this application in combination with ternary lithium material and lithium manganese iron phosphate or lithium iron phosphate, the ternary material, lithium manganese iron phosphate, and lithium iron phosphate can achieve a high lithium-ion diffusion rate, reduce the contact between lithium manganese oxide material and electrolyte, reduce interfacial side reactions, inhibit the structural degradation of lithium manganese oxide, and protect the lithium manganese oxide material, thereby improving high-temperature cycle performance and increasing cycle life; at the same time, the combination can also make the spinel lithium manganese oxide material have a more stable structure, improve the diffusion impedance of the cathode sheet under different SOCs, and improve low-temperature performance and safety performance.

[0016] In some embodiments, based on the total mass of metal elements other than lithium in the aforementioned cathode material layer, the mass percentage of element M1 is P%, the mass percentage of element M2 is Q%, and 0.1≤P≤0.5, 0.1≤Q≤0.5. Based on the above embodiments, this application, by adjusting the ratio of lithium manganese oxide material to ternary lithium material and lithium manganese iron phosphate material in the cathode material within a suitable range, enables them to better exert a synergistic effect, further improve high-temperature cycle performance, increase cycle life, and simultaneously improve low-temperature performance and safety performance.

[0017] Fourthly, embodiments of this application provide a secondary battery, including the aforementioned positive electrode sheet.

[0018] Fifthly, embodiments of this application provide an electronic device including the aforementioned secondary battery. Embodiments of the present invention

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] This application provides a secondary battery, including a positive electrode, a non-aqueous electrolyte, a negative electrode, and a separator.

[0021] positive electrode

[0022] <Cathode Materials>

[0023] One embodiment of this application provides a lithium manganese oxide-doped cathode material. The cathode material includes elements M1, M2, and X; element M1 includes one or more of vanadium, niobium, or tantalum, with the molar ratio of M1 to the cathode material being a; element M2 includes one or more of lanthanum, cerium, praseodymium, samarium, dysprosium, ytterbium, yttrium, or lutetium, with the molar ratio of M2 to the cathode material being b; element X includes one or more of fluorine, chlorine, sulfur, nitrogen, or boron, with the molar ratio of X to the cathode material being c. The cathode material is a nearly spherical secondary particle. Region I is defined as the region radially from the outer surface of the secondary particle to a depth of 100 nm, and Region II is defined as the region radially from the center of the particle to a depth of 100 nm. In Region I, 0.02 ≤ a ≤ 0.05, 0.02 ≤ b ≤ 0.05, and 0.001 ≤ c ≤ 0.04. Preferably, in region I, 0.025 ≤ a ≤ 0.045, 0.025 ≤ b ≤ 0.045, and 0.005 ≤ c ≤ 0.03. For example, in region I, the value of a can be 0.02, 0.028, 0.037, 0.041, 0.046, 0.05, or any two of these values; for example, the value of b in region I can be 0.02, 0.025, 0.031, 0.042, 0.047, 0.05, or any two of these values; for example, the value of c in region I can be 0.001, 0.005, 0.02, 0.03, 0.04, or any two of these values. In region II, 0.001 ≤ a ≤ 0.02 and 0.001 ≤ b ≤ 0.02. Preferably, in region II, 0.005 ≤ a ≤ 0.01, and 0.005 ≤ b ≤ 0.01. For example, the value of a in region II can be 0.001, 0.009, 0.012, 0.017, 0.019, 0.02, or any value within the range of two of these values; for example, the value of b in region II can be 0.001, 0.004, 0.008, 0.011, 0.016, 0.02, or any value within the range of two of these values. For example, the cathode material can be Li. 1.05 Mn 1.88 Nb 0.03 Ce 0.04 O 3.98 F 0.02 Li 1.055 Mn 1.86 V 0.04 La 0.045 O 3.97 B 0.03 Or Li 1.06 Mn 1.855 Ta 0.045 Ce0.04 O 3.985 N 0.015 Based on the cathode material of this application embodiment, using lithium manganese oxide as the cathode active material, it is further doped with dopant element M1, including vanadium, niobium or tantalum, dopant element M2, including lanthanum, cerium, praseodymium, samarium, dysprosium, ytterbium, yttrium or lutetium, and dopant element X, including fluorine, chlorine, sulfur, nitrogen or boron, to suppress manganese dissolution under high temperature conditions, thereby increasing cathode stability, improving high temperature cycle performance, and increasing cycle life.

[0024] In some embodiments, the cathode material includes lithium, and the molar ratio of lithium to the cathode material is d, where 1 ≤ d ≤ 1.08. For example, the value of d, the molar ratio of lithium to the cathode material, can be 1, 1.01, 1.04, 1.06, 1.07, 1.08, or any value within a range of two of these values. Based on the above embodiments, this application further controls the molar concentration of active material elements in the cathode material within a suitable range to better suppress manganese dissolution under high-temperature conditions, increase cathode stability, further improve high-temperature cycle performance, and increase cycle life.

[0025] In some embodiments, the cathode material in region I satisfies at least one of the following conditions: (1) 0.05 ≤ a + b + c ≤ 0.1; (2) 0.001 ≤ c / d ≤ 0.03. For example, in region I of the cathode material, the value of a + b + c can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value within the range of any two of these values. For example, in region I of the cathode material, the value of c / d can be 0.001, 0.005, 0.01, 0.02, 0.03, or any value within the range of any two of these values. Based on the above embodiments, this application further regulates the molar concentration of doped elements in the cathode material within a suitable range, enabling it to better exert a synergistic effect, better suppress manganese dissolution under high-temperature conditions, increase cathode stability, further improve high-temperature cycle performance, and increase cycle life.

[0026] In some embodiments, element X is selected from fluorine and / or boron. For example, element X is fluorine and boron. Based on the above embodiments, this application further improves high-temperature cycling performance and increases cycle life by selecting the above as doping elements.

[0027] In some embodiments, the specific surface area of ​​the cathode material is I m 2 / g, 0.3≤I≤1.0. For example, the specific surface area I of the cathode material can be 0.3, 0.4, 0.6, 0.7, 0.9, 1.0, or any value within the range of any two of these values. The cell parameter of the cathode material is J Å, 8.2100≤J≤8.2400. For example, the value of the cell parameter of the cathode material can be 8.2100, 8.2189, 8.2204, 8.2235, 8.2311, 8.2379, 8.2400, or any value within the range of any two of these values. The Dv50 of the cathode material is K μm, 5≤K≤20. For example, the value of K can be 5, 8, 11, 14, 19, 20, or any value within the range of any two of these values. Based on the above embodiments, this application can further improve high-temperature cycling performance and increase cycle life by controlling the sphericity, specific surface area, cell parameters and Dv50 of the cathode material in a coordinated manner within the above range.

[0028] <Preparation Methods of Cathode Materials>

[0029] One embodiment of this application provides a method for preparing a cathode material, comprising the following steps:

[0030] (1) Preparation of precursors containing elements M1 and M2;

[0031] (2) Mix the precursor containing elements M1 and M2, the lithium source and the manganese source to obtain precursor A;

[0032] (3) Place precursor A in an oxygen-containing atmosphere for the first sintering to obtain the first sintered product as precursor B; or, place precursor A in an oxygen-containing atmosphere for the first sintering to obtain the first sintered product, and then mix the first sintered product with a precursor containing element X to obtain precursor B.

[0033] (4) Precursor B is placed in an oxygen-containing atmosphere for a second sintering to obtain the cathode material;

[0034] In step (3), the first sintering temperature is 450°C to 650°C, and the time is 4 hours to 8 hours; in step (4), the second sintering temperature is 700°C to 900°C, and the time is 8 hours to 12 hours. The lithium source is lithium carbonate and / or lithium hydroxide, and the manganese source is manganese dioxide and / or manganese tetroxide. Based on the above embodiments, the cathode material prepared by the preparation method of this application can further improve high-temperature cycling performance and increase cycle life.

[0035] The oxygen-containing atmosphere in this application can be an air atmosphere or an oxygen atmosphere.

[0036] <Positive Electrode>

[0037] One embodiment of this application provides a positive electrode sheet, including a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector; the positive electrode material layer includes the above-described positive electrode material or a positive electrode material prepared by the above-described method.

[0038] In some embodiments, the cathode material layer further includes ternary lithium material and lithium manganese iron phosphate. For example, the ternary lithium material can be selected from NCM111, NCM523, NCM622, NCM811, NCA, or NCMA. Based on the above embodiments, by using the cathode material described in this application in combination with ternary lithium material and lithium manganese iron phosphate material, the energy storage device assembled from the mixed cathode material electrode sheet has good high-temperature cycle performance and cycle life, while also improving low-temperature performance and safety performance.

[0039] In some embodiments, based on the total mass of metal elements other than lithium in the cathode material layer, the mass percentage of element M1 is P%, and the mass percentage of element M2 is Q%, with 0.1 ≤ P ≤ 0.5 and 0.1 ≤ Q ≤ 0.5. For example, the value of P can be 0.1, 0.2, 0.3, 0.4, 0.5, or any value within the range of any two of these values. The value of Q can be 0.1, 0.2, 0.3, 0.4, 0.5, or any value within the range of any two of these values. Based on the above embodiments, this application, by adjusting the ratio of lithium manganese oxide material to ternary lithium material and lithium manganese iron phosphate material in the cathode material within a suitable range, enables them to better exert a synergistic effect, further improve high-temperature cycle performance, increase cycle life, and simultaneously improve low-temperature performance and safety performance.

[0040] In some embodiments, the positive electrode material layer further includes a positive electrode conductive material; there is no limitation on the type of positive electrode conductive material, and any known conductive material can be used. Examples of positive electrode conductive materials may include, but are not limited to, acetylene black, Super-P carbon black, amorphous carbon such as needle coke, carbon nanotubes, graphene, etc. The above-mentioned positive electrode conductive materials can be used alone or in any combination.

[0041] In some embodiments, the positive electrode material layer includes a positive electrode binder; there are no particular limitations on the type of positive electrode binder, and in the case of a coating method, any material that can be dissolved or dispersed in the liquid medium used during electrode manufacturing is acceptable. Examples of positive electrode adhesives may include, but are not limited to, one or more of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; thermoplastic elastomer-like polymers such as styrene-butadiene-styrene block copolymers or their hydrides, ethylene-propylene-diene terpolymers, styrene-ethylene-butadiene-ethylene copolymers, and styrene-isoprene-styrene block copolymers or their hydrides; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions with alkali metal ion conductivity. The above-mentioned positive electrode adhesives may be used alone or in any combination.

[0042] There are no restrictions on the type of solvent used to form the positive electrode slurry, as long as it is capable of dissolving or dispersing the positive electrode active material, conductive material, positive electrode binder, and thickener used as needed. Examples of solvents used to form the positive electrode slurry can include any of aqueous and organic solvents. Examples of aqueous media can include, but are not limited to, mixtures of alcohol and water or water. Examples of organic media can include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran; amides such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

[0043] Thickeners are typically used to adjust the viscosity of slurries. In the case of aqueous media, thickeners and styrene-butadiene rubber latex can be used for slurry preparation. There are no particular limitations on the types of thickeners; examples include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts. The above-mentioned thickeners can be used alone or in any combination.

[0044] There are no particular limitations on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. Examples of positive electrode current collectors may include, but are not limited to, metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum.

[0045] To reduce the electronic contact resistance between the positive current collector and the positive electrode material layer, the surface of the positive current collector may include a conductive additive or a conductive coating. Examples of conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. Examples of conductive coatings may include a mixture layer containing inorganic oxides, conductive agents, and binders.

[0046] Non-aqueous electrolyte

[0047] The non-aqueous electrolyte used in the electrochemical device of this application includes lithium salts and non-aqueous solvents.

[0048] This application does not impose any particular limitation on the type of lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(fluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalateborate)borate (LiBOB), or lithium difluorooxalateborate (LiDFOB). Based on the mass of the electrolyte, the mass percentage content of the lithium salt may be from 8% to 15%, for example, the mass percentage content of the lithium salt may be 8%, 9%, 10%, 11%, 12.5%, 13%, 15%, or a range of any two of these values.

[0049] This application does not impose any particular limitation on the types of non-aqueous solvents mentioned above, as long as they can achieve the purpose of this application. For example, they may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The carbonate compounds mentioned above may include, but are not limited to, at least one of chain carbonate compounds or cyclic carbonate compounds. The chain carbonate compounds mentioned above may include, but are not limited to, at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate. The cyclic carbonate compounds mentioned above may include, but are not limited to, at least one of ethylene carbonate, propylene carbonate, butyl carbonate, or ethylene ethylene carbonate. The carboxylic acid ester compounds mentioned above may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of ethylene glycol dimethyl ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0050] negative electrode

[0051] The negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer containing a negative electrode active material. In some embodiments, the rechargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0052]

[0053] Optionally, the negative electrode active material may further include amorphous carbon materials, which may be soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, or calcined coke, etc.

[0054] The negative electrode material layer of this application also includes a negative electrode binder. The negative electrode binder can improve the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. When a negative electrode slurry is prepared using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol, etc.

[0055] The negative electrode material layer of this application also includes a conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent, as long as it can achieve the purpose of this application. For example, the negative electrode conductive agent can be at least one of acetylene black, Ketjen black, carbon nanotubes, carbon fibers, carbon dots, or graphene, etc., and the aforementioned carbon nanotubes can include, but are not limited to, at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0056] This application does not impose any particular limitation on the negative electrode current collector, as long as it achieves the purpose of this application. For example, the negative electrode current collector may comprise copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal. The conductive metal includes, but is not limited to, copper, nickel, or titanium, and the polymer substrate material includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene terephthalate, polyethylene terephthalate, or poly(p-phenylene terephthalate). In this application, there are no particular limitations on the thickness of the negative electrode current collector and the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode material layer is 30 μm to 160 μm. In this application, the negative electrode mixture layer may be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or only a part of it. This application has no particular restrictions, as long as the purpose of this application can be achieved.

[0057] This application does not impose any particular limitation on the compaction density of the negative electrode sheet, as long as it achieves the purpose of this application. For example, the compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 Up to 1.85 g / cm 3 This application does not impose any particular limitation on the cold pressing pressure of the negative electrode sheet, as long as the purpose of this application can be achieved. For example, the cold pressing pressure of the negative electrode sheet can be from 3 tons to 30 tons.

[0058] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and it can be at least one of the aforementioned conductive agents and binders. This application does not impose any particular limitation on the mass ratio of the conductive agent to the binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. This application does not impose any particular limitation on the thickness of the conductive layer, as long as the purpose of this application is achieved; for example, the thickness of the conductive layer is 1 μm to 10 μm.

[0059] diaphragm

[0060] This application typically includes a separator between the positive and negative electrodes. The separator is used to separate the positive and negative electrode plates, prevent internal short circuits in the secondary battery, allow electrolyte ions to pass freely, and does not affect the electrochemical charging and discharging process.

[0061] This application does not impose any particular limitation on the diaphragm, as long as it can achieve the purpose of this application. For example, the material of the diaphragm may include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid; the type of diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane or spun membrane.

[0062] In this application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. This application does not have any particular limitation on the aforementioned inorganic particles, and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not have any particular limitation on the aforementioned binders, and may include at least one of the aforementioned binders. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0063] In this application, the pore size of the separator is from 0.01 μm to 1 μm, and the thickness is from 5 μm to 50 μm. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above ranges, insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the secondary battery can be ensured.

[0064] This application also provides an electronic device that includes the secondary battery described in the embodiments of this application. Electronic devices include, but are not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0065] Example

[0066] The following examples, using lithium-ion batteries as an example, provide more specific illustrations of the implementation methods of the secondary battery of this application. The preparation methods described in this application are merely illustrative; any other suitable preparation methods are within the scope of this application. Furthermore, unless otherwise specified, "parts" and "%" refer to mass measurements.

[0067] Example 1-1

[0068] <Preparation of Lithium-ion Batteries>

[0069] (1) Preparation of the positive electrode:

[0070] <Preparation of Positive Electrode Active Materials>

[0071] (1) Add manganese sulfate solution and a solution containing vanadium and lanthanum to the reactor, wherein the molar ratio of vanadium to manganese is 0.01 to 0.025, and the molar ratio of lanthanum to manganese is 0.01 to 0.025; maintain a certain stirring rate in the reactor to carry out precipitation and oxidation reactions. When the particle size Dmin of the coprecipitate is measured to be ≥200 nm, precursor I is obtained; continue to add manganese sulfate solution and a solution containing vanadium and lanthanum to precursor I, wherein the molar ratio of vanadium to manganese is... The molar ratio of lanthanum to manganese is 0.0005 to 0.01. The reaction vessel is kept at a certain stirring rate to carry out precipitation and oxidation reactions. When the particle size Dmin of the coprecipitate is measured to be ≥300nm, precursor II is obtained. The suspension of precursor II is transferred to an aging vessel for aging. The aged precursor II suspension is dehydrated, washed, and dehydrated again through a plate and frame filter press or centrifuge, and then dried to obtain precursor III containing vanadium and lanthanum.

[0072] (2) Precursor III, which contains vanadium and lanthanum, lithium hydroxide and manganese dioxide are mixed to obtain precursor A;

[0073] (3) Precursor A is placed in an oxygen-containing atmosphere for the first sintering to obtain the first sintered product. Then the first sintered product is mixed with a fluorine-containing precursor to obtain precursor B.

[0074] (4) Precursor B is placed in an oxygen-containing atmosphere for a second sintering to obtain the positive electrode active material Li. 1.055 Mn 1.86 V 0.04 La 0.045 O 3.97 F 0.03 ;

[0075] In step (3), the temperature of the first sintering is 500℃ and the time is 5h; in step (4), the temperature of the second sintering is 800℃ and the time is 10h.

[0076] <Preparation of the positive electrode>

[0077] The positive electrode active material, conductive carbon black, and polyvinylidene fluoride (PVDF) prepared in the above steps were mixed at a mass ratio of 95:2:3. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated onto one surface of a 9 μm thick aluminum foil for the positive electrode current collector, and then dried to obtain a positive electrode sheet with a single-sided coating of the positive electrode agent layer. The above steps were repeated on the other surface of the aluminum foil for the positive electrode current collector to obtain a positive electrode sheet with a double-sided coating of the positive electrode agent layer. After cold pressing, cutting, slitting, and drying, a positive electrode sheet with a size of 74 mm × 867 mm was obtained.

[0078] (2) Preparation of non-aqueous electrolyte: In a dry argon atmosphere glove box, diethyl carbonate was used as the base solvent, and lithium hexafluorophosphate (LiPF6) was dissolved in the base solvent. Ethylene carbonate was added as an additive to obtain the electrolyte. The total mass of the electrolyte consisted of 12.5% ​​LiPF6, 2% vinylene carbonate, and the remainder was diethyl carbonate.

[0079] (3) Preparation of the negative electrode: Using artificial graphite as the negative electrode active material, the negative electrode active material, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carbon nanotubes (CNT), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95.8:2.4:0.5:0.5:0.8. Deionized water was then added as a solvent and stirred evenly to prepare a negative electrode slurry with a solid content of 45wt%. The negative electrode slurry was uniformly coated on one surface of a 6μm thick copper foil for the negative electrode current collector and dried to obtain a negative electrode sheet with a single-sided coating of the negative electrode mixture layer. The above steps were repeated on the other surface of the copper foil for the negative electrode current collector to obtain a negative electrode sheet with a double-sided coating of the negative electrode mixture layer. After cold pressing, cutting, slitting, and drying, a negative electrode sheet with a size of 76.6mm×875mm was obtained.

[0080] (4) Preparation of the diaphragm: A porous polyethylene film with a thickness of 15 μm was used as the diaphragm.

[0081] (5) Preparation of lithium-ion batteries: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The tabs are welded on, and the cells are wound to obtain bare cells. The bare cells are placed in packaging bags, electrolyte is injected, and the cells are sealed. After processes such as formation, degassing, edge trimming, and capacity testing, lithium-ion batteries are obtained.

[0082] <Testing Methods>

[0083] (1) High-temperature cycling performance test

[0084] The lithium-ion battery was placed in a 60°C constant temperature test chamber and allowed to stand for 30 minutes to reach a constant temperature. It was then charged at a constant current of 0.5C to the delithiation potential P, followed by constant voltage charging until the current reached 0.05C. After standing for 5 minutes, it was discharged at a constant current of 0.5C to 3.0V, and this was recorded as the initial discharge capacity C0. This process was repeated 100 times, and the discharge capacity C1 after 100 cycles was recorded. The cycle capacity retention rate of the lithium-ion battery was then calculated.

[0085] High-temperature cycling capacity retention rate = C1 / C0 × 100%.

[0086] (2) Low-temperature discharge performance test:

[0087] The lithium-ion battery was placed in a high-low temperature chamber, and the temperature was adjusted to 25°C. It was left to stand for 30 minutes to allow the battery to reach a constant temperature. The battery was then discharged at a constant current of 0.5C to 3.0V, followed by constant current charging at 0.5C to 4.5V, and then constant voltage charging at 4.5V until the current reached 0.05C. Again at 25°C, it was discharged at a constant current of 0.5C to 3.0V; the discharge capacity at this point was recorded as the initial discharge capacity. At 25°C, it was charged at a constant current of 0.5C to 4.5V, and then constant voltage charging at 4.5V until the current reached 0.05C. The battery was then placed at 0°C and left to stand for 30 minutes to allow its temperature to equalize with the ambient temperature. At 0°C, it was discharged at a constant current of 0.5C to 3.0V; the discharge capacity at this point was recorded as the low-temperature discharge capacity.

[0088] Low-temperature discharge capacity retention rate = (low-temperature discharge capacity / initial discharge capacity) × 100%.

[0089] (3) Thermal safety performance test:

[0090] The lithium-ion battery was placed in a constant temperature environment of 25℃ and allowed to stand for 30 minutes to reach the constant temperature. It was then charged at a constant current of 0.5C to the delithiation potential P, and then charged at a constant voltage until the current reached 0.05C. The lithium-ion battery was transferred to a hot chamber and heated to 130℃ at a rate of 5℃ / min, and held at that temperature for 60 minutes. The battery was considered to have passed if it did not catch fire or explode. Twenty lithium-ion battery samples were tested in parallel, and the pass rate of the thermal safety test was calculated.

[0091] Thermal safety pass rate = (Number of samples that passed the test / Total number of samples) × %.

[0092] (4) Depth distribution test of elemental molar concentration of cathode material

[0093] Energy-dispersive X-ray spectroscopy (EDS) analysis was performed on the cross-section of the material particles. The geometric center of the cross-section was defined as the center of the near-spherical secondary particle. The molar amounts of each element in region I and region II of the cathode material were measured in relation to the molar amount of the cathode material. The ratio of the molar amounts of each element in different regions to the molar amounts of the cathode material was calculated to obtain the corresponding values ​​of a, b, c, and d.

[0094] The lithium-ion batteries in the following embodiments or comparative examples differ from those in Examples 1-1 only in that the types of elements M1, M2, and X are adjusted according to Table 1, and the molar ratio of each element in region I and region II to the molar amount of the cathode material is also adjusted. The molar amounts of elements M1, M2, and X in the cathode material are adjusted by changing the amount of raw materials added during the preparation process, and the molar ratio of each element to the cathode material is then calculated. The performance test results of the lithium-ion batteries in each embodiment and comparative example are shown in Table 1 below.

[0095] [Revised according to Detailed Rules 26, August 21, 2025] Table 1

[0096] [Corrected according to Rule 26, August 21, 2025] [Deleted]

[0097] [Corrected according to Rule 26, August 21, 2025] [Deleted]

[0098] *In the table above, the molar ratio of niobium and tantalum in Examples 1-4 is 1:1; Ia is the ratio of the molar amount of element M1 in region I of the cathode material to the molar amount of the cathode material; Ib is the ratio of the molar amount of element M2 in region I of the cathode material to the molar amount of the cathode material; Ic is the ratio of the molar amount of element X in region I of the cathode material to the molar amount of the cathode material; II-a and II-b follow the same pattern; I-(a+b+c) is the sum of a, b, and c in region I of the cathode material; (Ic) / d is the ratio of the c value in region I of the cathode material to the d value in the cathode material.

[0099] As shown in Table 1, the lithium-ion battery prepared in the embodiments of this application can improve high-temperature cycling performance and increase high-temperature cycling capacity retention when the molar ratio of each element to the positive electrode material in region I of the positive electrode material satisfies 0.02≤a≤0.05, 0.02≤b≤0.05, and 0.001≤c≤0.04, and the molar ratio of each element to the positive electrode material in region II of the positive electrode material satisfies 0.001≤a≤0.02 and 0.001≤b≤0.02. Specifically, when the molar ratio d of lithium element to the positive electrode material is controlled to satisfy 1≤d≤1.08, high-temperature cycling performance and high-temperature cycling capacity retention can be further improved. In particular, when the positive electrode material in region I is controlled to satisfy at least one of 0.05≤a+b+c≤0.1 and 0.001≤c / d≤0.03, high-temperature cycling performance and high-temperature cycling capacity retention can be further improved.

[0100] The lithium-ion batteries in Examples 2-1 to 2-19 differ from those in Examples 1-47 only in that the specific surface area, cell parameters, and Dv50 of the cathode material grains are shown in Table 2.

[0101] Table 2

[0102]

[0103] As shown in Table 2, the lithium-ion battery prepared in the embodiments of this application, when the specific surface area I(m²) of the positive electrode material grains is adjusted... 2 When the value of I in the cathode material ( / g) satisfies 0.3≤I≤1.0, the high-temperature performance of the material can be further improved, and the high-temperature cycling capacity retention rate can be increased. Specifically, when the value of J in the cell parameter J Å of the cathode material grains satisfies 8.2100≤J≤8.2400, the high-temperature performance of the material can be further improved, and the high-temperature cycling capacity retention rate can be increased. Similarly, when the value of K in the Dv50 parameter K μm of the cathode material grains satisfies 5≤K≤20, the high-temperature performance of the material can be further improved, and the high-temperature cycling capacity retention rate can be increased.

[0104] The lithium-ion batteries in Examples 3-1 to 3-12 differ from those in Examples 2-18 only in that the P and Q values ​​are adjusted according to Table 2. The P and Q values ​​are adjusted by changing the proportions of each material added to the cathode material.

[0105] Table 3

[0106]

[0107] As shown in Table 3, the lithium-ion battery prepared in the embodiments of this application, when the cathode material also includes ternary lithium material, lithium manganese iron phosphate or lithium iron phosphate material, and the value of P in the mass percentage content P% of element M1 satisfies 0.1≤P≤0.5, and the value of Q in the mass percentage content Q% of element M2 satisfies 0.1≤Q≤0.5, can improve high-temperature cycle performance, increase high-temperature cycle capacity retention rate, and simultaneously improve low-temperature performance and safety performance, thereby increasing low-temperature discharge capacity retention rate and thermal safety pass rate.

[0108] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode material, characterized in that, The cathode material includes elements M1, M2, and X; The M1 element includes one or more of vanadium, niobium, or tantalum, and the molar ratio of the M1 element to the molar ratio of the positive electrode material is a. The M2 element includes one or more of lanthanum, cerium, praseodymium, samarium, dysprosium, ytterbium, yttrium, or lutetium, and the molar amount of the M2 element is b to the molar amount of the cathode material. The X element includes one or more of fluorine, chlorine, sulfur, nitrogen, or boron, and the molar ratio of the X element to the molar ratio of the positive electrode material is c. The positive electrode material is a near-spherical secondary particle. The region from the outer surface of the secondary particle to a depth of 100 nm is designated as region I, and the region from the center of the particle to a depth of 100 nm is designated as region II. In region I, 0.02≤a≤0.05, 0.02≤b≤0.05, and 0.001≤c≤0.04; In region II, 0.001≤a≤0.02, 0.001≤b≤0.

02.

2. The cathode material according to claim 1, characterized in that, In region I, 0.025 ≤ a ≤ 0.045, 0.025 ≤ b ≤ 0.045, 0.005 ≤ c ≤ 0.03; and / or, In region II, 0.005≤a≤0.01 and 0.005≤b≤0.

01.

3. The cathode material according to claim 2, characterized in that, The cathode material includes lithium, and the molar ratio of the lithium to the molar ratio of the cathode material is d, where 1 ≤ d ≤ 1.

08.

4. The cathode material according to claim 3, characterized in that, The cathode material in region I satisfies at least one of the following conditions: (1) 0.05≤a+b+c≤0.1; (2) 0.001≤c / d≤0.

03.

5. The cathode material according to any one of claims 1 to 4, characterized in that, The element X is selected from fluorine and / or boron.

6. The cathode material according to any one of claims 1 to 4, characterized in that, The specific surface area of ​​the cathode material is I m 2 / g, 0.3≤I≤1.0; and / or, The cell parameters of the cathode material are J Å, 8.2100≤J≤8.2400; and / or, The Dv50 of the positive electrode material is K μm, where 5 ≤ K ≤ 20.

7. The method for preparing the cathode material according to any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Preparation of precursors containing elements M1 and M2; (2) The precursor containing elements M1 and M2, lithium source and manganese source are mixed to obtain precursor A; (3) Place precursor A in an oxygen-containing atmosphere for the first sintering to obtain the first sintered product as precursor B; or, place precursor A in an oxygen-containing atmosphere for the first sintering to obtain the first sintered product, and then mix the first sintered product with a precursor containing element X to obtain precursor B. (4) Precursor B is placed in an oxygen-containing atmosphere for a second sintering to obtain the cathode material; In step (3), the temperature of the first sintering is 450°C to 650°C and the time is 4h to 8h; in step (4), the temperature of the second sintering is 700°C to 900°C and the time is 8h to 12h.

8. A positive electrode sheet, characterized in that, It includes a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector; The cathode material layer comprises the cathode material according to any one of claims 1 to 6 or the cathode material prepared by the preparation method according to claim 7.

9. The positive electrode sheet according to claim 8, characterized in that, The cathode material layer also includes ternary lithium material and / or lithium manganese iron phosphate.

10. The positive electrode sheet according to claim 9, characterized in that, Based on the total mass of the metal elements other than lithium in the cathode material layer, the mass percentage of element M1 is P%, the mass percentage of element M2 is Q%, 0.1≤P≤0.5, and 0.1≤Q≤0.

5.

11. A secondary battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 8 to 10.

12. An electronic device, characterized in that, Includes the secondary battery as described in claim 11.

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