Cathode material, preparation method thereof, cathode sheet, secondary battery and electronic device

Abstract

The application discloses a positive electrode material, a preparation method thereof, a positive electrode sheet, a secondary battery and an electronic device. The positive electrode material comprises M1 elements, M2 elements and X elements; the M1 elements comprise one or more of vanadium elements, niobium elements or tantalum elements; the M2 elements comprise one or more of lanthanum elements, cerium elements, praseodymium elements, samarium elements, dysprosium elements, ytterbium elements, yttrium elements or lutetium elements; and the X elements comprise one or more of fluorine elements, chlorine elements, sulfur elements, nitrogen elements or boron elements. The application can improve high-temperature cycle performance and increase cycle life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a positive electrode material and a preparation method thereof, a positive electrode sheet, a secondary battery and an electronic device. BACKGROUND

[0002] In recent years, with the increasingly wide application range of secondary batteries, the application fields thereof are increasingly diversified, and therefore higher requirements are put forward for the performance thereof at unconventional temperatures. The secondary battery prepared by using lithium manganate as a positive electrode material has the advantages of high energy density and low cost. However, in a high-temperature environment, the lithium manganate positive electrode material is prone to dissolution, and is prone to structural and chemical changes in the process of cyclic charging and discharging, which leads to the deterioration of the high-temperature performance of the battery and the rapid capacity attenuation. Therefore, it is urgent to improve the high-temperature performance of the lithium manganate positive electrode battery. SUMMARY

[0003] The embodiments of the present application provide a positive electrode material and a preparation method thereof, a positive electrode sheet, a secondary battery and an electronic device, which can improve the high-temperature cycle performance of the lithium manganate battery.

[0004] In a first aspect, the embodiments of the present application provide a positive electrode material. The positive electrode material comprises M1 elements, M2 elements and X elements; the M1 elements comprise one or more of vanadium elements, niobium elements or tantalum elements, the ratio of the molar amount of the M1 elements to the molar amount of the positive electrode material is a; the M2 elements comprise one or more of lanthanum elements, cerium elements, praseodymium elements, samarium elements, dysprosium elements, ytterbium elements, yttrium elements or lutetium elements, the ratio of the molar amount of the M2 elements to the molar amount of the positive electrode material is b; the X elements comprise one or more of fluorine elements, chlorine elements, sulfur elements, nitrogen elements or boron elements, the ratio of the molar amount of the X elements to the molar amount of the positive electrode material is c; the above-mentioned positive electrode material is a near-spherical secondary particle, and it is assumed that a region from the outer surface of the secondary particle to a depth of 100 nm in the radial direction is a region I, and a region from the center of the sphere to a depth of 100 nm in the radial direction is a region II; in the region I, 0.02≤a≤0.05, 0.02≤b≤0.05, 0.001≤c≤0.04; in the region II, 0.001≤a≤0.02, 0.001≤b≤0.02.

[0005] Based on the positive electrode material of the embodiments of the present application, the inventors found that, on the basis of lithium manganate as a positive electrode active material, further doping M1 elements including vanadium elements, niobium elements or tantalum elements, M2 elements including lanthanum elements, cerium elements, praseodymium elements, samarium elements, dysprosium elements, ytterbium elements, yttrium elements or lutetium elements, and X elements including fluorine elements, chlorine elements, sulfur elements, nitrogen elements or boron elements, by adjusting the types and contents of the above-mentioned element doping to adjust the grain morphology of the positive electrode material, on the one hand, the (111) crystal plane with relatively low manganese ion dissolution rate can be highly exposed, thereby inhibiting the manganese dissolution phenomenon under high temperature environment, improving the high temperature cycle performance; on the other hand, the material structure can be stabilized, the Jiang-Taylor effect can be inhibited, and the configuration deformation in the long-term cycle process can be relieved, thereby increasing the positive electrode stability and improving the cycle life.

[0006] In some embodiments, in the I region, 0.025≤a≤0.045, 0.025≤b≤0.045, 0.005≤c≤0.03; and / or, in the II region, 0.005≤a≤0.01, 0.005≤b≤0.01. Based on the above-mentioned embodiments, by further adjusting the molar content of the elements in the I region and the II region of the positive electrode material within the above-mentioned range, the present application can further inhibit the manganese dissolution phenomenon under high temperature environment, improve the high temperature cycle performance, increase the positive electrode stability and improve the cycle life.

[0007] In some embodiments, the positive electrode material includes lithium elements, and the ratio of the molar amount of lithium elements to the molar amount of the positive electrode material is d, 1≤d≤1.08. Based on the above-mentioned embodiments, by further adjusting the molar concentration of the active material elements in the positive electrode material within a suitable range, the present application can better inhibit the manganese dissolution under high temperature environment, increase the positive electrode stability, further improve the high temperature cycle performance and improve the cycle life.

[0008] In some embodiments, the positive electrode material in the above-mentioned I region 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-mentioned embodiments, by further adjusting the molar concentration of the doping elements in the positive electrode material within a suitable range, the present application can better play a synergistic effect, better inhibit the manganese dissolution under high temperature environment, increase the positive electrode stability, further improve the high temperature cycle performance and improve the cycle life.

[0009] In some embodiments, the above-mentioned X element is selected from fluorine elements and / or boron elements. Based on the above-mentioned embodiments, by selecting the above-mentioned elements as doping elements, the present application can more effectively reduce the manganese dissolution under high temperature environment, enhance the material structure stability, thereby further improving the high temperature cycle performance and improving the cycle life.

[0010] In some embodiments, the specific surface area of the positive electrode material is I m2 / g, 0.3≤I≤1.0; and / or, the lattice parameter of the positive electrode material is 2 8.2100≤J≤8.2400; and / or, the Dv50 of the positive electrode material is K μm, 5≤K≤20. Based on the above embodiments, by controlling the specific surface area within the above range, the high-temperature performance of the material can be further improved; by controlling the lattice parameter within the above range, the cycle performance of the material can be further improved; by controlling the Dv50 within the above range, the volume energy density of the material can be improved; by synergistically regulating the above parameters, they can be synergistic with each other, further improving the high-temperature cycle performance and increasing the cycle life. 8.2100≤J≤8.2400; and / or, the Dv50 of the positive electrode material is K μm, 5≤K≤20. Based on the above embodiments, by controlling the specific surface area within the above range, the high-temperature performance of the material can be further improved; by controlling the lattice parameter within the above range, the cycle performance of the material can be further improved; by controlling the Dv50 within the above range, the volume energy density of the material can be improved; by synergistically regulating the above parameters, they can be synergistic with each other, further improving the high-temperature cycle performance and increasing the cycle life.

[0011] In a second aspect, the embodiments of the present application provide a preparation method of a positive electrode material, comprising the following steps: (1) preparing a precursor containing M1 elements and M2 elements; (2) mixing the precursor containing M1 elements and M2 elements, a lithium source and a manganese source to obtain a precursor A; (3) placing the precursor A in an oxygen-containing atmosphere to perform first sintering to obtain a first sintering product as a precursor B; or, placing the precursor A in an oxygen-containing atmosphere to perform first sintering to obtain a first sintering product, and then mixing the first sintering product with a precursor containing X elements to obtain the precursor B; (4) placing the precursor B in an oxygen-containing atmosphere to perform second sintering to obtain the positive electrode material.

[0012] In the step (3), the temperature of the first sintering is 450-650℃, and the time is 4-8h; in the step (4), the temperature of the second sintering is 700-900℃, and the time is 8-12h. The lithium source is lithium carbonate and / or lithium hydroxide, and the manganese source is manganese dioxide and / or trimanganese tetroxide. Based on the above embodiments, by the above preparation steps, the defects of the positive electrode material crystal in the generation process can be reduced, and the element distribution inside the positive electrode material can also be controlled to form a core-shell structure material with different doping element concentrations in the I region and the II region, further improving the high-temperature cycle performance and increasing the cycle life.

[0013] In a third aspect, the embodiments of the present application provide a positive electrode tab, comprising a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector; the positive electrode material layer comprises the above positive electrode material or the positive electrode material prepared by the above method.

[0014] In some embodiments, the positive electrode material layer further comprises a ternary lithium material and / or lithium manganese iron phosphate and / or lithium iron phosphate. Based on the above embodiments, by mixing and doping the positive electrode material described in the present application with the ternary lithium material and the lithium manganese iron phosphate and lithium iron phosphate material, the ternary material, the lithium manganese iron phosphate material and the lithium iron phosphate material can achieve a high lithium ion diffusion rate, reduce the contact between the lithium manganese material and the electrolyte, reduce the interface side reaction, inhibit the structural degradation of the lithium manganese material, and protect the lithium manganese material, thereby improving the high-temperature cycle performance and prolonging the cycle life. At the same time, the mixed and doped use can also make the spinel lithium manganese material have a more stable structure, improve the diffusion impedance of the positive electrode sheet at different SOCs, and improve the low-temperature performance and safety performance.

[0015] In some embodiments, based on the total mass of the metal elements other than lithium in the positive electrode material layer, the mass percentage of the M1 element is P%, and the mass percentage of the M2 element is Q%, 0.1≤P≤0.5, 0.1≤Q≤0.5. Based on the above embodiments, by adjusting the ratio of the lithium manganese material to the ternary lithium material and the lithium manganese iron phosphate material in the positive electrode material within a suitable range, the present application can better play a synergistic effect, further improve the high-temperature cycle performance and prolong the cycle life, and improve the low-temperature performance and safety performance.

[0016] In a fourth aspect, the embodiments of the present application provide a secondary battery comprising the positive electrode sheet described above.

[0017] In a fifth aspect, the embodiments of the present application provide an electronic device comprising the secondary battery described above. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0019] The embodiments of the present application provide a secondary battery comprising a positive electrode, a non-aqueous electrolyte, a negative electrode and a separator.

[0020] Positive electrode

[0021] <Positive electrode material>

[0022] One embodiment of the present application provides a lithium manganate doped positive electrode material. The positive electrode material comprises M1 elements, M2 elements and X elements; the M1 elements comprise one or more of vanadium elements, niobium elements or tantalum elements, the ratio of the molar amount of the M1 elements to the molar amount of the positive electrode material is a; the M2 elements comprise one or more of lanthanum elements, cerium elements, praseodymium elements, samarium elements, dysprosium elements, ytterbium elements, yttrium elements or lutetium elements, the ratio of the molar amount of the M2 elements to the molar amount of the positive electrode material is b; the X elements comprise one or more of fluorine elements, chlorine elements, sulfur elements, nitrogen elements or boron elements, the ratio of the molar amount of the X elements to the molar amount of the positive electrode material is c. The positive electrode material is a near-spherical secondary particle, and a region from the outer surface of the secondary particle to a depth of 100 nm in the radial direction is region I, and a region from the center of the sphere to a depth of 100 nm in the radial direction is region II; in the above-mentioned region I, 0.02≤a≤0.05, 0.02≤b≤0.05, 0.001≤c≤0.04. Preferably, in region I, 0.025≤a≤0.045, 0.025≤b≤0.045, 0.005≤c≤0.03. For example, the value of a in region I can be 0.02, 0.028, 0.037, 0.041, 0.046, 0.05 or a value within a range formed by 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 a value within a range formed by 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 a value within a range formed by any two of these values. In the above-mentioned region II, 0.001≤a≤0.02, 0.001≤b≤0.02. Preferably, in region II, 0.005≤a≤0.01, 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 a value within a range formed by any 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 a value within a range formed by any two of these values. For example, the positive electrode 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 The positive electrode material based on the embodiments of the present application further dopes the doping element M1 including vanadium element, niobium element or tantalum element, the doping element M2 including lanthanum element, cerium element, praseodymium element, samarium element, dysprosium element, ytterbium element, yttrium element or lutetium element, and the doping element X including fluorine element, chlorine element, sulfur element, nitrogen element or boron element on the basis of the positive electrode active material of lithium manganate, inhibits manganese dissolution under high temperature environment, thereby increasing positive electrode stability, improving high temperature cycle performance and increasing cycle life.

[0023] In some embodiments, the positive electrode material includes lithium element, and the ratio of the molar amount of lithium element to the molar amount of the positive electrode material is d, 1≤d≤1.08. For example, the value of the ratio d of the molar amount of lithium element to the molar amount of the positive electrode material can be 1, 1.01, 1.04, 1.06, 1.07, 1.08 or a value within a range consisting of any two of these values. Based on the above embodiments, the present application further regulates the molar concentration of active material elements in the positive electrode material in a suitable range, better inhibits manganese dissolution under high temperature environment, increases positive electrode stability, further improves high temperature cycle performance and increases cycle life.

[0024] In some embodiments, the positive electrode material in the I region 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 the I region of the positive electrode material, the value of a+b+c can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or a value within a range consisting of any two of these values. For example, in the I region of the positive electrode material, the value of c / d can be 0.001, 0.005, 0.01, 0.02, 0.03 or a value within a range consisting of any two of these values. Based on the above embodiments, the present application further regulates the molar concentration of doping elements in the positive electrode material in a suitable range, so that it can better play a synergistic role, better inhibit manganese dissolution under high temperature environment, increase positive electrode stability, further improve high temperature cycle performance and increase cycle life.

[0025] In some embodiments, the X element is selected from fluorine element and / or boron element. For example, the X element is fluorine element and boron element. Based on the above embodiments, the present application further improves high temperature cycle performance and increases cycle life by selecting the above as the doping element.

[0026] In some embodiments, the specific surface area of the positive electrode material is I m 2 / g, 0.3≤I≤1.0. For example, the specific surface area I of the positive electrode material can be 0.3, 0.4, 0.6, 0.7, 0.9, 1.0, or a value within a range between any two of these values. The cell parameter of the positive electrode material is 8.2100≤J≤8.2400. For example, the value of the cell parameter of the positive electrode material can be 8.2100, 8.2189, 8.2204, 8.2235, 8.2311, 8.2379, 8.2400, or a value within a range between any two of these values. The Dv50 of the positive electrode material is K μm, 5≤K≤20. For example, the value of K can be 5, 8, 11, 14, 19, 20, or a value within a range between any two of these values. Based on the above embodiments, by controlling the sphericity, specific surface area, cell parameter, and Dv50 of the positive electrode material within the above ranges, the application can further improve the high-temperature cycle performance and increase the cycle life.

[0027] <Method for preparing a positive electrode material>

[0028] One embodiment of the application provides a method for preparing a positive electrode material, comprising the following steps:

[0029] (1) preparing a precursor containing M1 elements and M2 elements;

[0030] (2) mixing the precursor containing M1 elements and M2 elements, a lithium source, and a manganese source to obtain a precursor A;

[0031] (3) placing the precursor A in an oxygen-containing atmosphere to perform first sintering to obtain a first sintering product as a precursor B; or placing the precursor A in an oxygen-containing atmosphere to perform first sintering to obtain a first sintering product, and then mixing the first sintering product with a precursor containing X elements to obtain the precursor B;

[0032] (4) placing the precursor B in an oxygen-containing atmosphere to perform second sintering to obtain the positive electrode material;

[0033] In step (3), the temperature of the first sintering is 450-650°C, and the time is 4-8 h. In step (4), the temperature of the second sintering is 700-900°C, and the time is 8-12 h. The lithium source is lithium carbonate and / or lithium hydroxide, and the manganese source is manganese dioxide and / or trimanganese tetraoxide. Based on the above embodiments, the positive electrode material prepared by the preparation method of the embodiments of the application can further improve the high-temperature cycle performance and increase the cycle life.

[0034] In the application, the oxygen-containing atmosphere can be an air atmosphere or an oxygen atmosphere.

[0035] <Positive electrode sheet>

[0036] One embodiment of the present application provides a positive electrode tab, comprising a positive electrode current collector and a positive electrode material layer on at least one surface of the positive electrode current collector; the positive electrode material layer comprises the positive electrode material described above or the positive electrode material prepared by the method described above.

[0037] In some embodiments, the positive electrode material layer further comprises a ternary lithium material and a lithium iron manganese phosphate. For example, the ternary lithium material can be selected from NCM111, NCM523, NCM622, NCM811, NCA or NCMA. Based on the above embodiments, by mixing and doping the positive electrode material described in the present application with the ternary lithium material and the lithium iron manganese phosphate material, the energy storage device assembled by the mixed positive electrode material tab has good high-temperature cycle performance and cycle life, and the low-temperature performance and safety performance are also improved.

[0038] In some embodiments, based on the total mass of the metal elements other than lithium in the positive electrode material layer, the mass percentage of M1 element is P%, and the mass percentage of M2 element is Q%, 0.1≤P≤0.5, 0.1≤Q≤0.5. For example, the value of P can be 0.1, 0.2, 0.3, 0.4, 0.5 or a value within a range formed by any two of these values. The value of Q can be 0.1, 0.2, 0.3, 0.4, 0.5 or a value within a range formed by any two of these values. Based on the above embodiments, by adjusting the ratio of the lithium manganate material to the ternary lithium material and the lithium iron manganese phosphate material in the positive electrode material within a suitable range, the present application can better play a synergistic effect, further improve the high-temperature cycle performance and cycle life, and improve the low-temperature performance and safety performance.

[0039] In some embodiments, the positive electrode material layer further comprises a positive electrode conductive material; the type of positive electrode conductive material is not limited and any known conductive material can be used. Examples of the positive electrode conductive material can include, but are not limited to, carbon black such as acetylene black, Super-P, amorphous carbon such as needle coke, and the like; carbon nanotubes; graphene, and the like. The above positive electrode conductive materials can be used alone or in any combination.

[0040] In some embodiments, the positive electrode material layer includes a positive electrode binder; the kind of positive electrode binder is not particularly limited, and in the case of a coating method, it is only necessary to be a material that is soluble or dispersible in a liquid medium used at the time of electrode production. Examples of the positive electrode binder can include, but are not limited to, one or more of the following: polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, and the like resin-based polymers; butadiene-styrene rubber, nitrile rubber, fluorine rubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, and the like rubber-like polymers; styrene-butadiene-styrene block copolymer or its hydrogenated product, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer or its hydrogenated product, and the like thermoplastic elastomer-like polymers; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene-α-olefin copolymer, and the like soft resin-like polymers; polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene-ethylene copolymer, and the like fluorine-based polymers; and ion-conducting polymer compositions having alkali metal ions, and the like. The above-mentioned positive electrode binder can be used alone or in any combination.

[0041] The kind of solvent used to form the positive electrode slurry is not limited, and it is only necessary to be a solvent capable of dissolving or dispersing the positive electrode active material, the conductive material, the positive electrode binder, and a thickening agent used as necessary. Examples of the solvent used to form the positive electrode slurry can include any one of an aqueous solvent and an organic solvent. Examples of the aqueous medium can include, but are not limited to, a mixed medium of alcohol and water or water, and the like. Examples of the organic medium 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.

[0042] The thickening agent is generally used to adjust the viscosity of the slurry. In the case of using an aqueous medium, the slurry can be formed using a thickening agent and a butadiene-styrene rubber emulsion. The kind of thickening agent is not particularly limited, and examples thereof can include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphated starch, casein, and salts thereof, and the like. The above-mentioned thickening agent can be used alone or in any combination.

[0043] The kind of the positive electrode current collector is not particularly limited, and it can be any material known to be suitable for use as a positive electrode current collector. Examples of the positive electrode current collector can include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and the like; and materials such as carbon cloth, carbon paper, and the like. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum.

[0044] In order to reduce the electronic contact resistance of the positive electrode current collector and the positive electrode material layer, the surface of the positive electrode current collector can include a conductive aid or a conductive coating. Examples of the conductive aid can include, but are not limited to, carbon and noble metals such as gold, platinum, silver, and the like. Examples of the conductive coating can include a mixture layer containing inorganic oxides, a conductive agent, and a binder.

[0045] Non-aqueous electrolyte

[0046] The non-aqueous electrolyte used in the electrochemical device of the embodiments of the present application includes a lithium salt and a non-aqueous solvent.

[0047] The kind of the lithium salt of the present application is not particularly limited as long as the purpose of the present application can be achieved, for example, the lithium salt can include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis-trifluoromethanesulfonimide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), or lithium difluoro(oxalato)borate (LiDFOB). The mass percentage content of the lithium salt can be 8% to 15% based on the mass of the electrolyte, for example, the mass percentage content of the lithium salt can be 8%, 9%, 10%, 11%, 12.5%, 13%, 15%, or a range formed by any two of the above values.

[0048] The non-aqueous solvent is not particularly limited in the present application, and can include, for example, but is not limited to, at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, or another organic solvent. The carbonate compound can include, for example, but is not limited to, at least one of a chain carbonate compound or a cyclic carbonate compound. The chain carbonate compound can include, for example, but is 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 compound can include, for example, but is not limited to, at least one of vinylene carbonate, propylene carbonate, butylene carbonate, or ethylene ethylene carbonate. The carboxylic acid ester compound can include, for example, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or hexanolactone. The ether compound can include, for example, but is not limited to, at least one of dimethyl ether of ethylene glycol, 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 other organic solvent can include, for example, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0049] Negative electrode

[0050] 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 including a negative electrode active material. In some embodiments, the chargeable 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.

[0051] The negative electrode active material can include at least one of natural graphite, artificial graphite, meso-carbon microbe (MCMB), silicon, silicon-carbon composite, SiO x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate Li4Ti5O 12 12 (spinel structure), Li-Al alloy, or metallic lithium, etc. Optionally, the negative electrode active material can further include an amorphous carbon material, which can be soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbonizate, or calcined coke, etc.

[0052] The negative electrode material layer of the present application further includes a negative electrode binder. The negative electrode binder can improve the binding of the negative electrode active material particles to each other and the binding of the negative electrode active material to the current collector. The type of the negative electrode binder is not particularly limited as long as it is a material stable to an electrolyte or a solvent used in the electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of the resin binder include, but are not limited to, a fluorine resin, a polyacrylonitrile (PAN), a polyimide resin, an acrylic resin, a polyolefin resin, and the like. When a water-based solvent is used to prepare a negative electrode mixture slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or a salt thereof, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, and the like.

[0053] The negative electrode material layer of the present application further includes a conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent as long as it can achieve the object of the present application. For example, the negative electrode conductive agent can be at least one of acetylene black, ketjen black, a carbon nanotube, a carbon fiber, a carbon dot, or graphene, and the like, and the carbon nanotube can include, but is not limited to, at least one of a single-walled carbon nanotube or a multi-walled carbon nanotube.

[0054] The present application does not particularly limit the negative electrode current collector as long as it can achieve the object of the present application. For example, the negative electrode current collector can include a copper foil, an aluminum foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a polymer substrate coated with a conductive metal, and the like. Among them, the conductive metal includes, but is not limited to, copper, nickel, or titanium, and the material of the polymer substrate includes, but is not limited to, at least one of polyethylene, polypropylene, an ethylene-propylene copolymer, polyethylene terephthalate, polyethylene naphthalate, or poly-p-phenylene terephthalamide. In the present application, the thickness of the negative electrode current collector and the negative electrode material layer is not particularly limited as long as it can achieve the object of the present 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 the present application, the negative electrode mixture layer can be disposed on one surface in the thickness direction of the negative electrode current collector, or on both 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 a partial area of the negative electrode current collector, and the present application does not particularly limit it as long as it can achieve the object of the present application.

[0055] The present application does not particularly limit the compaction density of the negative electrode tab as long as it can achieve the object of the present application. For example, the compaction density of the negative electrode tab can be 1.0 g / cm 3 to 1.85 g / cm 3 The present application does not particularly limit the cold-pressing pressure of the negative electrode tab as long as it can achieve the object of the present application. For example, the cold-pressing pressure of the negative electrode tab can be 3 tons to 30 tons.

[0056] Optionally, the negative electrode sheet can further include a conductive layer between the negative current collector and the negative material layer. The composition of the conductive layer is not particularly limited in the present application and can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in the present application and can be at least one of the conductive agent and the binder described above. The mass ratio of the conductive agent and the binder in the conductive layer is not particularly limited in the present application and can be selected by a person skilled in the art according to actual needs, as long as the purpose of the present application can be achieved. The thickness of the conductive layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the thickness of the conductive layer is 1 μm to 10 μm.

[0057] Separator

[0058] The present application usually provides a separator between the positive electrode and the negative electrode. The separator is used to separate the positive electrode sheet and the negative electrode sheet, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass freely, and does not affect the electrochemical charging and discharging process.

[0059] The separator is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid; and the type of the separator can include at least one of woven film, non-woven film, microporous film, composite film, calendered film or spunlaced film.

[0060] In the present application, the separator can include a base material and a surface treatment layer. The base material can be a nonwoven fabric or a composite film having a porous structure, and the material of the base material can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. Optionally, a surface treatment layer is provided on at least one surface of the base material, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited in the present application, and for example, can include at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is not particularly limited in the present application, and for example, can be at least one of the aforementioned binders. The polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0061] In the present application, the separator has a pore diameter of 0.01 μm to 1 μm and a thickness of 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 range, insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the secondary battery can be ensured.

[0062] The present application also provides an electronic device including the secondary battery of the present application. The electronic device includes, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0063] Embodiment

[0064] The following will be described in more detail with examples and comparative examples of lithium ion batteries. The preparation method described in the present application is only an example, and any other suitable preparation method is within the scope of the present application. In addition, unless otherwise specified, "parts" and "%" are mass-based.

[0065] Example 1-1

[0066] <Preparation of lithium ion battery>

[0067] (1) Preparation of positive electrode:

[0068] <Preparation of positive electrode active material>

[0069] (1) A manganese sulfate solution and a solution containing vanadium elements and lanthanum elements were added to a reaction kettle, wherein the molar ratio of vanadium elements to manganese elements was 0.01 to 0.025, and the molar ratio of lanthanum elements to manganese elements was 0.01 to 0.025; the reaction kettle was kept at a certain stirring rate to carry out precipitation reaction and oxidation reaction, and when the particle size Dmin of the coprecipitate was measured to be ≥200 nm, precursor I was obtained; the manganese sulfate solution and the solution containing vanadium elements and lanthanum elements were continuously added to the precursor I, the molar ratio of vanadium elements to manganese elements was 0.0005 to 0.01, and the molar ratio of lanthanum elements to manganese elements was 0.0005 to 0.01, the reaction kettle was continuously kept at a certain stirring rate to carry out precipitation reaction and oxidation reaction, and when the particle size Dmin of the coprecipitate was measured to be ≥300 nm, precursor II was obtained; the suspension of the precipitate of precursor II was transferred to an aging kettle for aging; the suspension of the aged precursor II was dewatered, washed, and then dewatered by a plate and frame filter press or a centrifuge, and then dried to obtain a precursor III containing vanadium elements and lanthanum elements.

[0070] (2) The precursor III containing vanadium elements and lanthanum elements, lithium hydroxide and manganese dioxide were mixed to obtain a precursor A;

[0071] (3) The precursor A was placed in an oxygen-containing atmosphere to carry out first sintering to obtain a first sintering product, and then the first sintering product was mixed with a precursor containing fluorine elements to obtain a precursor B;

[0072] (4) The precursor B was placed in an oxygen-containing atmosphere to carry out second sintering to obtain a positive electrode active material Li 1.055 Mn 1.86 V 0.04 La 0.045 O 3.97 F 0.03 ;

[0073] In step (3), the temperature of the first sintering is 500°C, and the time is 5h; in step (4), the temperature of the second sintering is 800°C, and the time is 10h.

[0074] Preparation of the positive electrode sheet

[0075] The positive electrode active material, conductive agent, conductive carbon black, and polyvinylidene fluoride (PVDF) prepared in the above steps were mixed in a mass ratio of 95:2:3, N-methyl pyrrolidone (NMP) was added, and the mixture was stirred uniformly in a vacuum stirrer to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 9 μm, dried to obtain a positive electrode sheet with a single-coated positive electrode mixture layer. The above steps were repeated on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet with a double-coated positive electrode mixture layer. After cold pressing, sheet cutting, and slitting, the positive electrode sheet with a specification of 74 mm x 867 mm was dried.

[0076] (2) Preparation of the non-aqueous electrolyte: In a dry argon glove box, diethyl carbonate was used as a base solvent, lithium hexafluorophosphate (LiPF6) was dissolved in the base solvent, and vinylene carbonate was added as an additive to obtain an electrolyte. The mass percentage of LiPF6 was 12.5% and the mass percentage of vinylene carbonate was 2% based on the total mass of the electrolyte, and the remainder was diethyl carbonate.

[0077] (3) Preparation of the negative electrode: Artificial graphite was used as the negative electrode active material, and 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, and then deionized water was added as a solvent and stirred uniformly to prepare a negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry was uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, dried to obtain a negative electrode sheet with a single-coated negative electrode mixture layer. The above steps were repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet with a double-coated negative electrode mixture layer. After cold pressing, sheet cutting, and slitting, the negative electrode sheet with a specification of 76.6 mm x 875 mm was dried.

[0078] (4) Preparation of the separator: A porous polyethylene film with a thickness of 15 μm was used as the separator.

[0079] (5) Preparation of the lithium ion battery: The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, and the tabs were welded to obtain a bare cell. The bare cell was placed in a packaging bag, electrolyte was injected, and the bag was sealed. After processes such as formation, degassing, edge cutting, and capacity testing, the lithium ion battery was obtained.

[0080] <Testing method>

[0081] (1) High temperature cycle performance test

[0082] The lithium ion battery was placed in a 60°C constant temperature test box and rested for 30 minutes to allow the lithium ion battery to reach a constant temperature. It was charged to the delithiation amount P potential at 0.5C constant current, charged to a current of 0.05C at constant voltage, rested for 5 minutes, and discharged to 3.0V at 0.5C constant current. The initial discharge capacity C0was recorded. The same step was repeated for 100 cycles, and the discharge capacity C1after 100 cycles was recorded. The cycle capacity retention rate of the lithium ion battery was calculated.

[0083] High temperature cycle capacity retention rate = C1 / C0x 100%.

[0084] (2) Low temperature discharge performance test:

[0085] The lithium ion battery was placed in a high and low temperature box, the temperature was adjusted to 25°C, and it was rested for 30 minutes to allow the lithium ion battery to reach a constant temperature. The lithium ion battery that reached a constant temperature was discharged to 3.0V at a current of 0.5C, then charged to 4.5V at a current of 0.5C, and then charged to a current of 0.05C at a constant voltage of 4.5V. Similarly, at a temperature of 25°C, it was discharged to 3.0V at a current of 0.5C, and the discharge capacity was recorded as the initial discharge capacity. At a temperature of 25°C, it was charged to 4.5V at a constant current of 0.5C, and then charged to a current of 0.05C at a constant voltage of 4.5V. Then, the lithium ion battery was placed in a 0°C temperature environment and rested for 30 minutes to allow the temperature of the lithium ion battery to match the temperature of the external environment. It was discharged to 3.0V at a current of 0.5C at 0°C, and the discharge capacity was recorded as the low temperature discharge capacity.

[0086] Low temperature discharge capacity retention rate = (low temperature discharge capacity / initial discharge capacity) x 100%.

[0087] (3) Thermal safety performance test:

[0088] The lithium ion battery was placed in a 25°C constant temperature environment and rested for 30 minutes to allow the lithium ion battery to reach a constant temperature. It was charged to the delithiation amount P potential at 0.5C constant current, and then charged to a current of 0.05C at constant voltage. The lithium ion battery was transferred to a thermal box and heated to 130°C at a rate of 5°C / min, and kept at a constant temperature for 60 minutes. If the cell did not catch fire or explode, it was considered to pass the test. Twenty lithium ion battery samples were tested in parallel, and the pass rate of the thermal safety test was calculated.

[0089] Thermal safety pass rate = number of samples that passed the test / total number of samples x %.

[0090] (4) Positive electrode material element molar concentration depth distribution test

[0091] The cross section of the material particle is subjected to energy dispersive X-ray spectroscopy (EDS) analysis, the geometric center of the cross section is defined as the spherical center of the near-spherical secondary particle, the molar amount of each element in the I region and the II region of the positive electrode material and the molar amount of the positive electrode material are respectively tested, the ratio of the molar amount of each element in the different regions to the molar amount of the positive electrode material is calculated, and the values of a, b, c and d are obtained.

[0092] The lithium ion batteries of the following examples or comparative examples differ from Example 1-1 only in that the types of M1 elements, M2 elements and X elements and the ratios of the molar amounts of the elements in the I region and the II region to the molar amount of the positive electrode material are adjusted according to Table 1. The molar amounts of M1 elements, M2 elements and X elements in the positive electrode material are adjusted by changing the amount of raw materials added during preparation, and then the ratios of the molar amounts of the elements to the molar amount of the positive electrode material are calculated. The performance test results of the lithium ion batteries of each example and comparative example are shown in Table 1 below.

[0093] Table 1

[0094]

[0095]

[0096] In the above table, the molar ratio of the mixed niobium element and the tantalum element in Example 1-4 is 1:1; I-a is the ratio of the molar amount of M1 element in the I region of the positive electrode material to the molar amount of the positive electrode material, I-b is the ratio of the molar amount of M2 element in the I region of the positive electrode material to the molar amount of the positive electrode material, I-c is the ratio of the molar amount of X element in the I region of the positive electrode material to the molar amount of the positive electrode material, and II-a and II-b are the same; I-(a+b+c) is the sum of a, b and c in the I region of the positive electrode material; and d is the ratio of the value of c in the I region of the positive electrode material to the value of d in the positive electrode material.

[0097] As can be seen from Table 1, when the ratio of the molar amount of each element to the molar amount of the positive electrode material in the I region of the positive electrode material satisfies 0.02≤a≤0.05, 0.02≤b≤0.05 and 0.001≤c≤0.04, and the ratio of the molar amount of each element to the molar amount of the positive electrode material in the II region of the positive electrode material satisfies 0.001≤a≤0.02 and 0.001≤b≤0.02, the high-temperature cycle performance can be improved and the high-temperature cycle capacity retention rate can be increased. In particular, when the ratio of the molar amount of lithium element in the positive electrode material to the molar amount of the positive electrode material d satisfies 1≤d≤1.08, the high-temperature cycle performance can be further improved and the high-temperature cycle capacity retention rate can be increased. In particular, when the positive electrode material in the I region satisfies at least one of 0.05≤a+b+c≤0.1 and 0.001≤c / d≤0.03, the high-temperature cycle performance can be further improved and the high-temperature cycle capacity retention rate can be increased.

[0098] The lithium ion batteries of Examples 2-1 to 2-19 differ from Example 1-47 only in that the specific surface area, the cell parameter and the Dv50 of the positive electrode material crystal grains are as shown in Table 2.

[0099] Table 2

[0100]

[0101] As can be seen from Table 2, when the value of I in the specific surface area I (m 2 / g) of the positive electrode material crystal grains satisfies 0.3≤I≤1.0, the high-temperature performance of the material can be further improved, and the high-temperature cycle capacity retention rate is increased. In particular, when the value of J in the cell parameter J (A) of the positive electrode material crystal grains satisfies 8.2100≤J≤8.2400, the high-temperature performance of the material can be further improved, and the high-temperature cycle capacity retention rate is increased. In particular, when the value of K in the Dv50 parameter K (μm) of the positive electrode material crystal grains satisfies 5≤K≤20, the high-temperature performance of the material can be further improved, and the high-temperature cycle capacity retention rate is increased.

[0102] The lithium ion batteries of Examples 3-1 to 3-12 differ from Example 2-18 only in that the values of P and Q are adjusted according to Table 2. The values of P and Q are adjusted by adjusting the addition ratio of each material in the positive electrode material.

[0103] Table 3

[0104]

[0105] As can be seen from Table 3, when the lithium ion battery prepared in the embodiments of the present application further includes a ternary lithium material, a lithium manganese iron phosphate material or a lithium iron phosphate material, the value of P in the mass percentage content P% of the M1 element satisfies 0.1≤P≤0.5, and the value of Q in the mass percentage content Q% of the M2 element satisfies 0.1≤Q≤0.5, the high-temperature cycle performance can be improved, the high-temperature cycle capacity retention rate is increased, the low-temperature performance and safety performance are improved, and the low-temperature discharge capacity retention rate and the thermal safety pass rate are increased.

[0106] The above only describes preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present 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 Im. 2 / g, 0.3≤I≤1.0; and / or, The cell parameters of the cathode material are: 8.2100≤J≤8.2400; and / or, The Dv50 of the positive electrode material is Kμm, and 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) Prepare precursors containing M1 and M2 elements; (2) Mix the precursor containing elements M1 and M2 with lithium and manganese sources to obtain precursor A; (3) Precursor A is placed in an oxygen-containing atmosphere for a first sintering to obtain a first sintering product as precursor B; or, precursor A is placed in an oxygen-containing atmosphere for a first sintering to obtain a first sintering product, and then the first sintering product is mixed 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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