Aluminum, zinc-coated positive electrode material and preparation method and application thereof

Abstract

This invention provides an aluminum-zinc coated cathode material, its preparation method, and its application. The aluminum-zinc coated cathode material includes a core and a coating layer covering the core. Based on the aluminum-zinc coated cathode material, it includes 0.08-0.30 wt% zinc and 0.05-0.50 wt% aluminum. The aluminum-zinc coated cathode material provided by this invention, with the coating layer using specific amounts of zinc and aluminum, exhibits high electronic conductivity, effectively suppressing the migration of nickel ions to the lithium layer during cycling (cation mixing), maintaining the integrity of the material's main layered structure. This not only slows down structural degradation caused by phase transitions and oxygen release, reduces hydrofluoric acid corrosion and electrolyte decomposition side reactions, but also improves interfacial ion / electron transport kinetics, thereby significantly enhancing the material's cycle stability and electrochemical performance at high rates.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to an aluminum-zinc coated cathode material, its preparation method, and its application. Background Technology

[0002] Existing high-nickel ternary cathode materials (such as Ni) 0.8 Co 0.1 Mn 0.1 O2 has problems such as poor structural stability, easy cation mixing and phase transition during cycling, serious surface side reactions, and insufficient electrolyte compatibility, resulting in short cycle life, rapid rate performance degradation, and poor thermal stability. In addition, although existing surface coating technologies (such as Al2O3, ZrO2, etc.) can partially improve interface stability, they are difficult to balance high interface protection and high ion / electron conduction performance, which restricts their application in high-performance lithium-ion batteries. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the defects of poor cycle performance and poor electrical performance at high rates of existing cathode materials, thereby providing an aluminum-zinc coated cathode material, its preparation method and application.

[0004] Therefore, the present invention provides the following technical solution: The first aspect of this invention protects an aluminum-zinc coated cathode material, wherein the aluminum-zinc coated cathode material includes a core and a coating layer covering the core; The positive electrode material coated with aluminum and zinc includes 0.08-0.30 wt% zinc and 0.05-0.50 wt% aluminum.

[0005] As an example, the mass percentage of zinc in the aluminum-zinc coated cathode material can be 0.08wt%, 0.09wt%, 0.10wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.20wt%, 0.30wt%, or within any of the above values; the mass percentage of aluminum in the aluminum-zinc coated cathode material can be 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.10wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.20wt%, 0.30wt%, 0.40wt%, 0.50wt%, or within any of the above values.

[0006] In some alternative embodiments, the positive electrode material coated with aluminum and zinc includes 0.10-0.15 wt% zinc and 0.10-0.15 wt% aluminum by mass.

[0007] In this invention, the specific thickness can be adjusted according to the actual situation. Typically, without limitation, the thickness of the coating layer is 5-10 nm.

[0008] A second aspect of this invention protects a method for preparing the aforementioned aluminum-zinc coated cathode material, wherein the preparation method includes the following steps: S1, soluble zinc salt, soluble aluminum salt, chelating agent and solvent are mixed, filtered and calcined to obtain an aluminum-zinc mixture; S2, after mixing the cathode material precursor and lithium source, the first sintering is performed to obtain a sintered product; S3, after mixing the aluminum-zinc mixture with a calcined product, a second sintering is performed to obtain an aluminum-zinc coated cathode material.

[0009] In this invention, the cathode material precursor is a conventional high-nickel ternary cathode material precursor (LiNi) in the art. x Co y Mn z O2 (x≥0.6), typically non-limitingly, the cathode material precursor includes Ni. 0.8 Co 0.1 Mn 0.1 (OH)2 and / or Ni 0.9 Co 0.05 Mn 0.05 (OH)2.

[0010] In this invention, the lithium source is a conventional lithium source in the art, and typically, without limitation, the lithium source includes lithium carbonate and / or lithium hydroxide.

[0011] In this invention, the solvent is a conventional solvent in the art. Typically, without limitation, the solvent includes water and / or ethanol, and may be selected as ethanol and water in a volume ratio of 1:1.

[0012] In this invention, the filtration is a conventional operation in the art, and after filtration, the precipitate can be washed with a solvent.

[0013] In some alternative embodiments, the soluble zinc salt includes at least one of zinc acetate, zinc nitrate, zinc chloride, and zinc sulfate, and may be zinc acetate.

[0014] In some alternative embodiments, the soluble aluminum salt includes at least one of aluminum nitrate, aluminum chloride, aluminum sulfate, and aluminum acetate, and may be aluminum nitrate.

[0015] In some alternative embodiments, the chelating agent includes at least one selected from citric acid, ammonium citrate, ethylenediaminetetraacetic acid, and tartaric acid, with citric acid being an option.

[0016] In some optional embodiments, the molar ratio of zinc in the soluble zinc salt to aluminum in the soluble aluminum salt is (0.005-0.01):(0.01-0.05); as an example, the molar ratio of zinc in the soluble zinc salt to aluminum in the soluble aluminum salt can be 0.005:0.01, 0.006:0.02, 0.007:0.01, 0.007:0.02, 0.008:0.02, etc. 0.009:0.02, or any of the above values; alternatively, it could be (0.007-0.009):(0.01-0.02). For example, it could be 0.007:0.01, 0.007:0.02, 0.008:0.01, 0.008:0.02, 0.009:0.01, 0.009:0.02, or any of the above values.

[0017] In some alternative embodiments, the molar ratio of zinc to chelating agent in the soluble zinc salt is (0.005-0.01):1; as an example, the molar ratio of zinc to chelating agent in the soluble zinc salt can be 0.005:1, 0.006:1, 0.007:1, 0.008:1, 0.009:1, 0.01:1, or within any range of the above values.

[0018] In this invention, the amount of solvent used is conventional in the art, typically and non-limitingly, such that the zinc ion concentration in the system is 0.005-0.05 mol / L.

[0019] In some optional embodiments, the mass ratio of the aluminum-zinc mixture to the calcined product is (0.1-0.7):(99.0-99.9); as an example, the mass ratio of the aluminum-zinc mixture to the calcined product can be 0.1:99.9, 0.2:99.8, 0.3:99.7, 0.4:99.6, 0.5:99.5, 0.6:99.4, 0.7:99.3, or within any of the above values; alternatively, it can be (0.2-0.4):(99.6-99.8); as an example, it can be 0.2:99.8, 0.3:99.7, 0.4:99.6, or within any of the above values.

[0020] In some alternative embodiments, the calcination conditions include: heating to 400-500℃ at a rate of 2-5℃ / min and calcining for 1-5 hours; as an example, the heating rate can be 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min; the calcination temperature can be 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, or 500℃; and the calcination time can be 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours, or within any range of the above values.

[0021] In this invention, the calcination is carried out in an air atmosphere and / or an oxygen atmosphere.

[0022] In some alternative embodiments, the calcination conditions include: heating to 450-480°C at a rate of 2-5°C / min and calcining for 2-3 hours; as an example, the preferred calcination temperature is 450°C, 460°C, 470°C, 480°C, or within any range of the above values.

[0023] In some alternative embodiments, the first sintering includes a primary sintering and a secondary sintering.

[0024] Optionally, the conditions for the first sintering include: heating to 550-700℃ at a rate of 2-5℃ / min and calcining for 1-5 hours; as an example, the heating rate can be 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min; the sintering temperature can be 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃, or 700℃; and the sintering time can be 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours, or within any range of the above values.

[0025] Optionally, the conditions for the secondary sintering include: heating to 600-820℃ at a rate of 2-5℃ / min and calcining for 12-24h; as an example, the heating rate can be 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min; the sintering temperature can be 600℃, 650℃, 680℃, 730℃, 740℃, 750℃, 770℃, or 820℃; and the sintering time can be 12h, 14h, 16h, 18h, 20h, 22h, or 24h, or within any range of the above values.

[0026] In this invention, the first sintering is carried out in an air atmosphere and / or an oxygen atmosphere.

[0027] In this invention, in step S3, the mixing method is a conventional mixing method in the art, which can mix evenly. Typically, without limitation, ball milling is used for mixing. The ball milling conditions are adjusted according to the actual situation. Generally, the ball milling speed is controlled at 200-500 r / min and the time is 1-5 h.

[0028] In some optional embodiments, the conditions for the second sintering include: heating to 700-950℃ at a rate of 2-5℃ / min and calcining for 8-24 hours; as an example, the heating rate can be 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min; the sintering temperature can be 700℃, 750℃, 800℃, 850℃, 900℃, or 950℃; the sintering time can be 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, or 24h, or within any range of the above values; optionally, the conditions for the second sintering include: heating to 800-900℃ and calcining for 12-24 hours. For example, the temperature can be 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, or 900℃; the time can be 12h, 14h, 16h, 18h, 20h, 22h, or 24h, or within any range of the above values.

[0029] In this invention, the second sintering is carried out in an air atmosphere and / or an oxygen atmosphere.

[0030] A third aspect of this invention protects a secondary battery, wherein the secondary battery comprises the aforementioned aluminum-zinc coated positive electrode material or the aluminum-zinc coated positive electrode material prepared by the aforementioned preparation method.

[0031] The technical solution of this invention has the following advantages: 1. This invention provides an aluminum-zinc coated cathode material, wherein the aluminum-zinc coated cathode material comprises a core and a coating layer covering the core; based on the aluminum-zinc coated cathode material, it comprises 0.08-0.30 wt% zinc and 0.05-0.50 wt% aluminum. The aluminum-zinc coated cathode material provided by this invention, with the coating layer using specific amounts of zinc and aluminum, exhibits high electronic conductivity, effectively suppressing the migration of nickel ions to the lithium layer during cycling (cation mixing), maintaining the integrity of the material's main layered structure, not only mitigating structural degradation caused by phase transition and oxygen release, reducing hydrofluoric acid corrosion and electrolyte decomposition side reactions, but also improving interfacial ion / electron transport kinetics, thereby significantly enhancing the material's cycle stability and electrochemical performance at high rates.

[0032] 2. This invention provides a method for preparing an aluminum-zinc coated cathode material, wherein the preparation method includes the following steps: S1, mixing a soluble zinc salt, a soluble aluminum salt, a chelating agent, and a solvent, filtering, and calcining to obtain an aluminum-zinc mixture; S2, mixing a cathode material precursor and a lithium source and then performing a first sintering to obtain a sintered product; S3, mixing the aluminum-zinc mixture with the sintered product and then performing a second sintering to obtain an aluminum-zinc coated cathode material. The method for preparing aluminum-zinc coated cathode materials provided by this invention first synthesizes an aluminum-zinc mixture through liquid-phase mixing and calcination, so that aluminum elements are uniformly doped into the zinc oxide lattice to form a coating precursor with excellent conductivity and structural stability. Then, the aluminum-zinc mixture is thoroughly mixed with a calcined product and sintered at high temperature for a second time, so that the aluminum-zinc mixture forms a uniform, dense and firmly bonded nano-coating layer in situ on the surface of the cathode material. This effectively suppresses cation mixing, interfacial side reactions and structural decay during the cycling process of the cathode material, while improving the interfacial ion conduction and electron conduction capabilities, thereby significantly enhancing the cycling stability and electrical performance of the material at high rates. Detailed Implementation

[0033] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having” and any variations thereof in the text of this invention are intended to cover non-exclusive inclusion.

[0035] In the description of the embodiments of the present invention, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0036] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0037] The "range" disclosed in this invention is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This range can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. In this invention, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein; "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter can be, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0038] In the description of the embodiments of the present invention, the term "and / or" is merely a description of the relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0039] In the description of the embodiments of the present invention, the term "at least one" refers to one or more (including two).

[0040] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0041] The concentration of the NaOH solution is 1 mol / L; Ni 0.8 Co 0.1 Mn 0.1 (OH)2, purchased from GEM Co., Ltd.

[0042] Example 1 This embodiment provides a method for preparing an aluminum-zinc coated cathode material, the method comprising the following steps: S1. Weigh zinc acetate and aluminum nitrate according to a Zn:Al:C6H8O7 molar ratio of 0.008:0.02; weigh zinc acetate and citric acid according to a Zn:C6H8O7 molar ratio of 0.008:1; dissolve zinc acetate, aluminum nitrate and citric acid in a mixed solvent of ethanol and water with a volume ratio of 1:1 to make the zinc ion concentration 0.01mol / L; under stirring, add NaOH solution dropwise to adjust the pH to 11.0, continue stirring for 4h, filter, wash the precipitate, and calcine in air at a temperature of 5℃ / min to 450℃ for 2h to obtain aluminum-zinc mixture powder; S2, according to (Ni element) Ni was mixed with a molar ratio of Co and Mn (total) to Li of 1:1.05. 0.8 Co 0.1 Mn 0.1 (OH)2 and Li2CO3 were sintered in an oxygen atmosphere at a temperature of 5℃ / min to 600℃ for 5h; then sintered at a temperature of 3℃ / min to 810℃ for 15h to obtain a calcined product. S3, 0.3g of aluminum-zinc mixture powder is mixed with 99.7g of calcined product and ball-milled at a speed of 300r / min for 2h to obtain a mixture. Under an oxygen atmosphere, the mixture is heated to 800℃ at 5℃ / min and held for 15h. After cooling, aluminum and zinc coated cathode material is obtained.

[0043] Example 2 This embodiment provides a method for preparing an aluminum-zinc coated cathode material, the method comprising the following steps: S1, according to the method of Example 1; S2, according to the method of Example 1; S3, 0.5g of aluminum-zinc mixture powder is mixed with 99.5g of calcined product and ball-milled at a speed of 300r / min for 2h to obtain a mixture. Under an oxygen atmosphere, the mixture is heated to 800℃ at 5℃ / min and held for 15h. After cooling, aluminum and zinc coated cathode material is obtained.

[0044] Example 3 This embodiment provides a method for preparing an aluminum-zinc coated cathode material, the method comprising the following steps: S1, according to the method of Example 1; S2, according to the method of Example 1; S3, 0.7g of aluminum-zinc mixture powder is mixed with 99.3g of calcined product and ball-milled at a speed of 300r / min for 2h to obtain a mixture. Under an oxygen atmosphere, the mixture is heated to 800℃ at 5℃ / min and held for 15h. After cooling, aluminum and zinc coated cathode material is obtained.

[0045] Example 4 This embodiment provides a method for preparing an aluminum-zinc coated cathode material, the method comprising the following steps: S1. Weigh zinc nitrate and aluminum nitrate according to a Zn:Al:C6H8O7 molar ratio of 0.008:0.02; weigh zinc nitrate and tartaric acid according to a Zn:C6H8O7 molar ratio of 0.008:1; dissolve zinc nitrate, aluminum nitrate and tartaric acid in a mixed solvent of ethanol and water with a volume ratio of 1:1, so that the zinc ion concentration in the system is 0.01mol / L; under stirring, add NaOH solution dropwise to adjust the pH to 11.0, continue stirring for 4h, filter, wash the precipitate, and calcine in air at a temperature of 5℃ / min to 450℃ for 2h to obtain aluminum-zinc mixture powder; S2, according to the method of Example 1; S3, in accordance with the method of Example 1.

[0046] Example 5 This embodiment provides a method for preparing an aluminum-zinc coated cathode material, the method comprising the following steps: S1. Weigh zinc acetate and aluminum nitrate according to a Zn:Al:C6H8O7 molar ratio of 0.005:0.02; weigh zinc acetate and citric acid according to a Zn:C6H8O7 molar ratio of 0.005:1; dissolve zinc acetate, aluminum nitrate and citric acid in a mixed solvent of ethanol and water with a volume ratio of 1:1 to make the zinc ion concentration 0.01mol / L; under stirring, add NaOH solution dropwise to adjust the pH to 11.0, continue stirring for 4h, filter, wash the precipitate, and calcine in air at a temperature of 5℃ / min to 450℃ for 2h to obtain aluminum-zinc mixture powder; S2, according to the method of Example 1; S3, in accordance with the method of Example 1.

[0047] Example 6 This embodiment provides a method for preparing an aluminum-zinc coated cathode material, the method comprising the following steps: S1, following the method of Example 1, except that zinc acetate and aluminum nitrate are weighed according to a Zn:Al element ratio of 0.008:0.02; zinc acetate and citric acid are weighed according to a Zn:C6H8O7 molar ratio of 0.008:1; zinc acetate, aluminum nitrate and citric acid are dissolved in a mixed solvent of ethanol and water with a volume ratio of 1:1 to make the zinc ion concentration 0.01mol / L; under stirring, NaOH solution is added dropwise to adjust the pH to 11.0, stirring is continued for 4h, filtered, the precipitate is washed, and calcined in air at a temperature of 3℃ / min to 450℃ for 2h to obtain aluminum-zinc mixture powder; S2, according to the method of Example 1; S3, in accordance with the method of Example 1.

[0048] Example 7 This embodiment provides a method for preparing an aluminum-zinc coated cathode material, the method comprising the following steps: S1, according to the method of Example 1; S2, according to the method of Example 1; S3, 0.3g of aluminum-zinc mixture powder is mixed with 99.7g of calcined product and ball-milled at a speed of 300r / min for 2h to obtain a mixture. Under an oxygen atmosphere, the mixture is heated to 700℃ at 3℃ / min and held for 12h. After cooling, aluminum and zinc coated cathode material is obtained.

[0049] Comparative Example 1 This comparative example provides a method for preparing a cathode material, the method comprising the following steps: According to (Ni element) Ni was mixed with a molar ratio of Co and Mn (total) to Li of 1:1.05. 0.8 Co 0.1 Mn 0.1 (OH)2 and Li2CO3 were sintered in an oxygen atmosphere at a temperature of 5℃ / min to 600℃ for 5h; then sintered at a temperature of 3℃ / min to 810℃ for 15h to obtain the cathode material.

[0050] Comparative Example 2 This comparative example provides a method for preparing an aluminum-coated cathode material, the method comprising the following steps: S1, according to (Ni element) Ni was mixed with a molar ratio of Co and Mn (total) to Li of 1:1.05. 0.8 Co 0.1 Mn 0.1 (OH)2 and Li2CO3 were sintered in an oxygen atmosphere at a temperature of 5℃ / min to 600℃ for 5h; then sintered at a temperature of 3℃ / min to 810℃ for 15h to obtain a calcined product. S2, 0.3g of nano Al2O3 powder (purchased from Hubei Smail Nano New Materials Co., Ltd.) was mixed with 99.7g of calcined product and ball-milled at a speed of 300r / min for 2h to obtain a mixture. The mixture was heated to 800℃ at 5℃ / min and held for 15h under an oxygen atmosphere. After cooling, aluminum-coated cathode material was obtained.

[0051] Comparative Example 3 This comparative example provides a method for preparing an aluminum-zinc coated cathode material, the method comprising the following steps: S1. Weigh zinc acetate and aluminum nitrate according to a Zn:Al:C6H8O7 molar ratio of 0.03:0.02; weigh zinc acetate and citric acid according to a Zn:C6H8O7 molar ratio of 0.075:1; dissolve zinc acetate, aluminum nitrate and citric acid in a mixed solvent of ethanol and water with a volume ratio of 1:1 to make the zinc ion concentration 0.01mol / L; under stirring, add NaOH solution dropwise to adjust the pH to 11.0, continue stirring for 4h, filter, wash the precipitate, and calcine in air at a temperature of 5℃ / min to 450℃ for 2h to obtain aluminum-zinc mixture powder; S2, according to the method of Example 1; S3, in accordance with the method of Example 1.

[0052] Comparative Example 4 This comparative example provides a method for preparing a zirconium-coated cathode material, the method comprising the following steps: S1, according to (Ni element) Ni was mixed with a molar ratio of Co and Mn (total) to Li of 1:1.05. 0.8 Co 0.1 Mn 0.1 (OH)2 and Li2CO3 were sintered in an oxygen atmosphere at a temperature of 5℃ / min to 600℃ for 5h; then sintered at a temperature of 3℃ / min to 810℃ for 15h to obtain a calcined product. S2, 0.3g of nano ZrO2 powder (purchased from Hubei Smail Nanomaterials Co., Ltd.) was mixed with 99.7g of calcined product and ball-milled at a speed of 300r / min for 2h to obtain a mixture; under an oxygen atmosphere, the mixture was heated to 800℃ at a rate of 5℃ / min and held for 15h, and then cooled to obtain zirconium-coated cathode material.

[0053] Test case Weigh 5g of the material obtained from the comparative example and place it in a polytetrafluoroethylene digestion vessel. Add 10mL of mixed acid, which is 30wt% nitric acid and 34.5wt% hydrochloric acid with a volume ratio of 3:1. Microwave digestion is performed. After complete digestion, the mixture is cooled and brought to a final volume of 50mL. The mass percentage of zinc and aluminum in the aluminum- and zinc-coated cathode materials is determined using ICP-MS (inductively coupled plasma mass spectrometry). The test results are shown in Table 1; Table 1

[0054] Electrode fabrication and battery assembly The materials prepared in the examples and comparative examples, conductive carbon black, and PVDF were mixed at a mass ratio of 80:10:10 to obtain a positive electrode mixture. The positive electrode mixture was then mixed with N-methylpyrrolidone (NMP) to form a slurry, wherein the ratio of the positive electrode mixture to NMP was 2:1 (g / mL). This slurry was coated on aluminum foil, and the areal density was 1.5 mg / cm³. 2 After drying, a positive electrode sheet is made; the negative electrode material is a lithium sheet; the electrolyte is a 1 mol / L LiPF6 ethylene carbonate (EC) and dimethyl carbonate (DMC) solution, wherein the volume ratio of EC to DMC is 1:1; the positive electrode sheet, separator (polypropylene composite membrane), negative electrode sheet and electrolyte are assembled into a 2032 type coin cell in an Ar gas glove box with a water content and oxygen content of less than 5 ppm.

[0055] At 25°C, the voltage was initially charged to 4.3V at a constant current rate of 0.1C, and then discharged to 3.0V at a rate of 0.1C to obtain the initial charge / discharge capacity. The initial charge / discharge specific capacity was then calculated. The discharge capacity over 350 cycles was recorded, and the discharge specific capacity over 350 cycles was calculated. Initial coulombic efficiency = (initial discharge capacity / initial charge capacity) × 100%; The capacity retention rate test method is as follows: At 25°C, the battery is charged to 4.3V at a constant current of 0.1C and discharged to 3.0V at a constant current of 0.1C, and the charge-discharge cycle is repeated 350 times; the capacity retention rate at the 350th cycle = (0.1C discharge capacity at the 350th cycle / 0.1C discharge capacity at the 1st cycle) × 100%; Test method for rate performance: Under 25℃ conditions, the battery is charged at a constant current of 0.2C to 4.3V, discharged at a constant current of 0.2C to 3.0V, and repeated 5 times; charged at a constant current of 0.5C to 4.3V, discharged at a constant current of 0.5C to 3.0V, and repeated 5 times; charged at a constant current of 1C to 4.3V, discharged at a constant current of 1C to 3.0V, and repeated 5 times; charged at a constant current of 2C to 4.3V, discharged at a constant current of 2C to 3.0V, and repeated 5 times; charged at a constant current of 5C to 4.3V, discharged at a constant current of 5C to 3.0V, and repeated 5 times; finally, charged at a constant current of 0.2C to 4.3V, discharged at a constant current of 0.2C to 3.0V, and repeated 5 times; the nC rate discharge specific capacity is calculated. At least three parallel cells were tested for each sample group to ensure data reproducibility. The test results are shown in Tables 2 and 3; Table 2

[0056] Table 3

[0057] Comparing Example 1 and Comparative Example 1, Table 2 shows that Comparative Example 1 has a higher initial discharge specific capacity. Table 3 shows that Comparative Example 1 has a higher discharge specific capacity under a low rate current (0.2C). The inventors speculate that this is because lithium diffusion is sufficient, with sufficient extraction / insertion and low interfacial resistance, resulting in a higher discharge specific capacity. However, when the rate is increased, the structural stability decreases, the interfacial side reactions become severe, the discharge performance decreases, and it has no practical application value.

[0058] Comparing Example 1 with Comparative Examples 2 and 4, it can be seen that compared with the traditional Al2O3 and ZrO2 coating, the aluminum-zinc composite coating of the present invention has lower interfacial impedance, better electronic / ionic conductivity, and more stable structure.

[0059] Comparing Example 1 and Comparative Example 3, it can be seen that when the zinc content exceeds the range defined by the present invention, even if the aluminum content is still within the range defined by the present invention, the electrochemical performance of the obtained cathode material is lower than that of Example 1. The inventors speculate that excessive zinc will lead to uneven distribution of the coating layer, which will increase the interfacial impedance, hinder lithium ion transport, and may induce unnecessary interfacial side reactions or damage the structural integrity of the coating layer, thereby weakening the structural stability of the cathode material.

[0060] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An aluminum-zinc coated cathode material, characterized in that, The aluminum-zinc coated cathode material includes a core and a coating layer covering the core; The positive electrode material coated with aluminum and zinc includes 0.08-0.30 wt% zinc and 0.05-0.50 wt% aluminum.

2. The aluminum-zinc coated cathode material according to claim 1, characterized in that, The positive electrode material coated with aluminum and zinc includes 0.10-0.15 wt% zinc and 0.10-0.15 wt% aluminum.

3. A method for preparing the aluminum-zinc coated cathode material as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: S1, soluble zinc salt, soluble aluminum salt, chelating agent and solvent are mixed, filtered and calcined to obtain an aluminum-zinc mixture; S2, after mixing the cathode material precursor and lithium source, the first sintering is performed to obtain a sintered product; S3, after mixing the aluminum-zinc mixture with a calcined product, a second sintering is performed to obtain an aluminum-zinc coated cathode material.

4. The method for preparing the aluminum-zinc coated cathode material according to claim 3, characterized in that, The soluble zinc salt includes at least one of zinc acetate, zinc nitrate, zinc chloride, and zinc sulfate, and may be zinc acetate. And / or, the soluble aluminum salt includes at least one of aluminum nitrate, aluminum chloride, aluminum sulfate, and aluminum acetate, and may be aluminum nitrate; And / or, the chelating agent includes at least one of citric acid, ammonium citrate, ethylenediaminetetraacetic acid, and tartaric acid, with citric acid being the preferred choice.

5. The method for preparing the aluminum-zinc coated cathode material according to claim 3 or 4, characterized in that, The molar ratio of zinc in soluble zinc salts to aluminum in soluble aluminum salts is (0.005-0.01):(0.01-0.05). And / or, the molar ratio of zinc to chelating agent in the soluble zinc salt is (0.005-0.01):1; And / or, the mass ratio of the aluminum-zinc mixture to the calcined product is (0.1-0.7):(99.0-99.9).

6. The method for preparing the aluminum-zinc coated cathode material according to claim 5, characterized in that, The molar ratio of zinc in soluble zinc salts to aluminum in soluble aluminum salts is (0.007-0.009):(0.01-0.02); And / or, the mass ratio of the aluminum-zinc mixture to the calcined product is (0.2-0.4):(99.6-99.8).

7. The method for preparing the aluminum-zinc coated cathode material according to any one of claims 3-6, characterized in that, The calcination conditions include: heating to 400-500℃ at a rate of 2-5℃ / min and calcining for 1-5 hours; Optionally, the calcination conditions include: heating to 450-480℃ at a rate of 2-5℃ / min and calcining for 2-3 hours.

8. The method for preparing the aluminum-zinc coated cathode material according to any one of claims 3-7, characterized in that, The first sintering includes primary sintering and secondary sintering; Optionally, the conditions for the first sintering include: heating to 550-700℃ at a rate of 2-5℃ / min and calcining for 1-5 hours; Optionally, the conditions for the secondary sintering include: heating to 600-820℃ at a rate of 2-5℃ / min and calcining for 12-24 hours.

9. The method for preparing the aluminum-zinc coated cathode material according to any one of claims 3-8, characterized in that, The conditions for the second sintering include: heating to 700-950℃ at a rate of 2-5℃ / min and calcining for 8-24 hours; Optionally, the conditions for the second sintering include: heating to 800-900℃ and calcining for 12-24 hours.

10. A secondary battery, characterized in that, The secondary battery includes the aluminum-zinc coated cathode material as described in claim 1 or 2, or the aluminum-zinc coated cathode material prepared by the preparation method of the aluminum-zinc coated cathode material as described in any one of claims 3-9.

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