A method for preparing a high-nickel positive electrode material with a double-layer coated nanolayer

Abstract

The application discloses a method for preparing a high-nickel positive electrode material with a double-layer coated nanolayer, which comprises the following steps: first, preparing a high-nickel positive electrode material; then, coating lithium iron phosphate on the high-nickel positive electrode material; bridging glucose acid based on the coating layer of lithium iron phosphate; and then, coating lithium manganate; and finally, combining the lithium iron phosphate layer and the lithium manganate layer through the glucose acid. The method improves the binding force of the double-layer coating, improves the structural stability of the high-nickel positive electrode material, avoids peeling of the coating layer, and improves the charge-discharge cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of high-nickel cathode material preparation, and particularly relates to a method for preparing a high-nickel cathode material with a double-layered nanolayer coating. Background Technology

[0002] Lithium-ion batteries are widely used in electronics, automobiles, aerospace, and other fields due to their high energy density and good cycle performance. As people's requirements for the environmental friendliness, range, and lifespan of lithium-ion batteries increase, battery design and optimization become increasingly important. As the core of a lithium-ion battery, the quality of the cathode material directly determines the battery's performance. Multi-element cathode materials have become important active cathode materials for current power lithium-ion batteries, with commercially available examples such as NCM523, NCM622, and NCM811. However, with increasing nickel content, the amount of inactive residual lithium on the surface of multi-element materials gradually increases, severely affecting their capacity, rate capability, and other performance characteristics. During high-voltage charge and discharge, problems such as intraparticle cracking and material pulverization easily occur, causing a rapid decrease in cycle performance. Research has found that single-crystalling of multi-element material particles can significantly improve their cycle life and safety performance.

[0003] Currently, most published literature and patents both domestically and internationally employ single-layer or double-layer coatings using alumina, titanium dioxide, zinc oxide, or aluminum phosphate, or lithium cobalt oxide, lithium manganese oxide, or lithium iron phosphate. Double-layer coatings offer superior performance in all aspects compared to single-layer coatings. However, after prolonged use, it has been found that the double layers are prone to detachment, leading to poor cycle stability.

[0004] Therefore, there is an urgent need for a method to prepare high-nickel cathode materials that can achieve double-layer coating and improve the connection performance between the double coating layers. Summary of the Invention

[0005] Objective of the invention: The technical problem to be solved by the present invention is to provide a method for preparing a high-nickel cathode material with double-layer coating using lithium iron phosphate and lithium manganese oxide electrode materials, wherein the bonding force between the lithium iron phosphate and lithium manganese oxide layers is strong and the prepared high-nickel cathode material has high stability.

[0006] Technical solution: The present invention provides a method for preparing a high-nickel cathode material with a double-layer coated nanolayer, comprising the following steps:

[0007] (1) The lithium source and the precursor were uniformly mixed by molar ratio (0.95-1.05):1 and calcined to obtain a high-nickel cathode material;

[0008] (2) The high-nickel cathode material prepared above is mixed with lithium iron phosphate in a solvent and ball-milled to obtain coated cathode material I; wherein, the amount of lithium iron phosphate added is 1-20% of the mass of the high-nickel cathode material;

[0009] (3) The coated positive electrode material I and gluconic acid are mixed in a solvent and reacted for 1-2 hours to obtain the cross-linked gluconic acid coated positive electrode material I; wherein the molar ratio of gluconic acid to lithium iron phosphate is 1:0.5-2.

[0010] (4) The cross-linked gluconic acid coated cathode material I and lithium manganese oxide are mixed in a solvent and ball-milled to obtain coated cathode material II; wherein the amount of lithium manganese oxide added is 1-20% of the mass of the high nickel cathode material;

[0011] (5) The above-prepared coated cathode material II is dried under vacuum to obtain a high-nickel cathode material with a double-layer coated nanolayer.

[0012] This invention employs two cathode materials, lithium iron phosphate and lithium manganese oxide, to double-coat a high-nickel cathode material. During the coating process, gluconic acid is used to link the two materials. The hydroxyl and carboxyl groups on gluconic acid can chelate with the cations in lithium iron phosphate and lithium manganese oxide, thereby binding the two layers together. Through the bridging effect of gluconic acid, the prepared coating layers of lithium iron phosphate and lithium manganese oxide are tightly bonded, improving the bonding force between layers and thus enhancing the structural stability of the prepared high-nickel cathode material.

[0013] In addition, olivine-type lithium iron phosphate has strong PO bonds, a robust structure, and good thermal stability, while spinel-type LMO exhibits rapid three-dimensional (3D) LiFe. + It possesses diffusion channels and excellent ionic conductivity, along with some advantages shared with LFP and LMO, such as being free of precious elements. A two-step ball milling method allows a dual-nanocomposite coating to be formed on the high-nickel cathode material, directly preventing contact between the high-nickel cathode material and the electrolyte and suppressing side reactions. Furthermore, the coating effectively inhibits internal structural losses caused by the H2-H3 phase transition in the high-nickel material, which helps reduce charge transfer and improve the diffusion coefficient.

[0014] Furthermore, in step (1) of this preparation method, the lithium source includes at least one of lithium carbonate, lithium hydroxide, or lithium nitrate; the precursor is Ni. x Co y D 1-x-y (OH)2, wherein 0.80≤x≤0.95, 0.05≤y≤0.20, 0≤1-xy≤0.20, and D is one or more of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, and rare earth elements.

[0015] Furthermore, in step (1) of the preparation method, the calcination is pre-calcined at 400-500℃ for 2-6 hours, followed by calcination at 600-900℃ under an O2 atmosphere for 15-30 hours; wherein the flow rate of the O2 is 50-150 mL / min, and the heating rate is 3-6℃ / min.

[0016] Furthermore, in steps (2) to (4) of the preparation method, the solvent is deionized water or ethanol.

[0017] Furthermore, in steps (2) and (4) of the preparation method, the ball milling time is 1-3 hours.

[0018] Furthermore, in step (5) of the preparation method, the vacuum drying is performed at 60-90℃ for 10-20 hours.

[0019] Furthermore, in step (5) of the preparation method, the thickness of the coating layer of the high-nickel cathode material with double-layer nanolayer coating is 0.1-50 nm, and the particle size of the high-nickel cathode material is 2-20 μm. Preferably, the thickness of the coating layer can be 5-15 nm, and the particle size of the high-nickel cathode material can be 5-10 μm.

[0020] Preferably, in steps (2) and (4) of the preparation method, the amount of lithium iron phosphate added is 5-15% of the mass of the high-nickel cathode material; the amount of lithium manganese oxide added is 5-15% of the mass of the high-nickel cathode material.

[0021] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are: the high-nickel cathode material is coated in situ with nano-LFP and LMO, and the resulting coating layer can directly prevent the cathode material from contacting the electrolyte and suppress the occurrence of side reactions; moreover, the bonding force between the two layers is strong, which improves the structural stability of the high-nickel cathode material, prevents the coating layer from falling off, and improves the charge-discharge cycle performance. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope image of the high-nickel cathode material prepared in Example 3 of the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0024] It should be noted that all raw materials used in this invention are commercially available. Among them, the nickel precursor Ni for the high-nickel cathode material... x Co y D 1-x-y(OH)2, wherein 0.80≤x≤0.95, 0.05≤y≤0.20, 0≤1-xy≤0.20, and D is one or more of alkali metal elements, alkaline earth metal elements, group 13 elements, group 14 elements, transition metal elements and rare earth elements, which can be purchased from companies such as Zhongwei Co., Ltd., Huayou Cobalt, and GEM Co., Ltd., and is a well-known technology in this field.

[0025] The double-layer coated nanolayer high-nickel cathode material prepared in this invention has a coating layer thickness of 0.1-50 nm and a high-nickel cathode material particle size of 2-20 μm. Preferably, the coating layer thickness is 5-15 nm and the high-nickel cathode material particle size is 5-10 μm.

[0026] Example 1

[0027] The preparation method of the double-layer coated high-nickel cathode material in this embodiment includes the following steps:

[0028] (1) The lithium source LiOH·H2O and the precursor Ni 0.8 Co 0.1 Al 0.1 (OH)₂ was thoroughly mixed at a molar ratio of 1.03:1 and then ground in a planetary mill at 300 r / min for 2 h to obtain powder. The powder was placed in a tube furnace and pre-calcined at 450 °C for 5 h, and then calcined at 800 °C under an O₂ atmosphere for 12 h to obtain high-nickel NCA cathode material. The flow rate of O₂ was 100 mL / min and the heating rate was 5 °C / min.

[0029] (2) NCA cathode material and LFP are mixed in ethanol, stirred and sonicated for 1 hour, and then ball-milled at a rate of 200 r / min for 2 hours to obtain NCA@LFP; wherein, the amount of LFP added is 5% of the mass of high nickel cathode material;

[0030] (3) NCA@LFP and gluconic acid are mixed in ethanol and reacted for 1-2 hours to obtain cross-linked gluconic acid NCA@LFP; wherein the molar ratio of gluconic acid to lithium iron phosphate is 1:1.

[0031] (4) NCA@LFP and LMO crosslinked gluconic acid were mixed in ethanol, stirred and sonicated for 1 h, and then ball-milled at a rate of 100 r / min for 2 h to obtain NCA@LFP@LMO; wherein, the amount of lithium manganese oxide added was 5% of the mass of the high nickel cathode material.

[0032] (5) NCA@LFP@LMO was vacuum dried at 80℃ for 12 h to obtain the product NCA@LFP@LMO(A 10 F 0.5 M 0.5 ).

[0033] Example 2

[0034] (1) The lithium source LiOH·H2O and the precursor Ni 0.8 Co 0.1 Al 0.1 (OH)₂ was thoroughly mixed at a molar ratio of 1.03:1 and then ground in a planetary mill at 300 r / min for 2 h to obtain powder. The powder was placed in a tube furnace and pre-calcined at 450 °C for 5 h, and then calcined at 800 °C under an O₂ atmosphere for 12 h to obtain high-nickel NCA cathode material. The flow rate of O₂ was 100 mL / min and the heating rate was 5 °C / min.

[0035] (2) NCA cathode material and LFP are mixed in ethanol, stirred and sonicated for 1 hour, and then ball-milled at a rate of 200 r / min for 2 hours to obtain NCA@LFP; wherein, the amount of LFP added is 10% of the mass of high nickel cathode material;

[0036] (3) NCA@LFP and gluconic acid are mixed in ethanol and reacted for 1-2 hours to obtain cross-linked gluconic acid NCA@LFP; wherein the molar ratio of gluconic acid to lithium iron phosphate is 1:1.5.

[0037] (4) NCA@LFP and LMO crosslinked gluconic acid were mixed in ethanol, stirred and sonicated for 1 h, and then ball-milled at a rate of 100 r / mind for 2 h to obtain NCA@LFP@LMO; wherein, the amount of lithium manganese oxide added was 5% of the mass of the high nickel cathode material.

[0038] (5) NCA@LFP@LMO was vacuum dried at 80℃ for 12 h to obtain the product NCA@LFP@LMO(A 10 F1M 0.5 ).

[0039] Example 3

[0040] (1) The lithium source LiOH·H2O and the precursor Ni 0.8 Co 0.1 Al 0.1 (OH)₂ was thoroughly mixed at a molar ratio of 1.03:1 and then ground in a planetary mill at 300 r / min for 2 h to obtain powder. The powder was placed in a tube furnace and pre-calcined at 450 °C for 5 h, and then calcined at 800 °C under an O₂ atmosphere for 12 h to obtain high-nickel NCA cathode material. The flow rate of O₂ was 100 mL / min and the heating rate was 5 °C / min.

[0041] (2) NCA cathode material and LFP are mixed in ethanol, stirred and sonicated for 1 hour, and then ball-milled at a rate of 200 r / min for 2 hours to obtain NCA@LFP; wherein, the amount of LFP added is 5% of the mass of high nickel cathode material;

[0042] (3) NCA@LFP and gluconic acid are mixed in ethanol and reacted for 1-2 hours to obtain cross-linked gluconic acid NCA@LFP; wherein the molar ratio of gluconic acid to lithium iron phosphate is 1:0.5.

[0043] (4) NCA@LFP and LMO crosslinked gluconic acid were mixed in ethanol, stirred and sonicated for 1 h, and then ball-milled at a rate of 100 r / min for 2 h to obtain NCA@LFP@LMO; wherein, the amount of lithium manganese oxide added was 10% of the mass of the high nickel cathode material.

[0044] (5) NCA@LFP@LMO was vacuum dried at 80℃ for 12 h to obtain the product NCA@LFP@LMO(A 10 F 0.5 M1).

[0045] Structural characterization

[0046] The double-coated high-nickel cathode material prepared in this embodiment was analyzed by scanning electron microscopy, such as... Figure 1 As shown in the figure, the high-nickel cathode material prepared in this invention has a protective coating on its particle surface, which is distributed throughout.

[0047] Example 4

[0048] (1) The lithium source LiOH·H2O and the precursor Ni 0.8 Co 0.1 Al 0.1 (OH)₂ was thoroughly mixed at a molar ratio of 1.03:1 and then ground in a planetary mill at 300 r / min for 2 h to obtain powder. The powder was placed in a tube furnace and pre-calcined at 450 °C for 5 h, and then calcined at 800 °C under an O₂ atmosphere for 12 h to obtain high-nickel NCA cathode material. The flow rate of O₂ was 100 mL / min and the heating rate was 5 °C / min.

[0049] (2) NCA cathode material and LFP are mixed in ethanol, stirred and sonicated for 1 hour, and then ball-milled at a rate of 200 r / min for 2 hours to obtain NCA@LFP; wherein, the amount of LFP added is 10% of the mass of high nickel cathode material;

[0050] (3) NCA@LFP and gluconic acid are mixed in ethanol and reacted for 1-2 hours to obtain cross-linked gluconic acid NCA@LFP; wherein the molar ratio of gluconic acid to lithium iron phosphate is 1:2.

[0051] (4) NCA@LFP and LMO crosslinked gluconic acid were mixed in ethanol, stirred and sonicated for 1 h, and then ball-milled at a rate of 100 r / min for 2 h to obtain NCA@LFP@LMO; wherein, the amount of lithium manganese oxide added was 10% of the mass of the high nickel cathode material.

[0052] (5) NCA@LFP@LMO was vacuum dried at 80℃ for 12 h to obtain the product NCA@LFP@LMO(A 10 F1M1).

[0053] Example 5

[0054] (1) The lithium source LiOH·H2O and the precursor Ni 0.8 Co 0.1 Al 0.1 (OH)₂ was thoroughly mixed at a molar ratio of 0.95:1 and then ground in a planetary mill at 300 r / min for 2 h to obtain powder. The powder was then placed in a tube furnace and pre-calcined at 400 °C for 6 h, followed by calcination at 600 °C under an O₂ atmosphere for 30 h to obtain high-nickel NCA cathode material. The flow rate of O₂ was 50 mL / min, and the heating rate was 3 °C / min.

[0055] (2) NCA cathode material and LFP are mixed in ethanol, stirred and sonicated for 1 hour, and then ball-milled at a rate of 200 r / min for 1 hour to obtain NCA@LFP; wherein, the amount of LFP added is 1% of the mass of high nickel cathode material;

[0056] (3) NCA@LFP and gluconic acid are mixed in ethanol and reacted for 1-2 hours to obtain cross-linked gluconic acid NCA@LFP; wherein the molar ratio of gluconic acid to lithium iron phosphate is 1:0.5.

[0057] (4) NCA@LFP and LMO crosslinked gluconic acid were mixed in ethanol, stirred and sonicated for 1 h, and then ball-milled at a rate of 100 r / min for 1 h to obtain NCA@LFP@LMO; wherein, the amount of lithium manganese oxide added was 20% of the mass of the high nickel cathode material.

[0058] (5) NCA@LFP@LMO was vacuum dried at 60℃ for 20 h to obtain the product NCA@LFP@LMO(A 10 F 0.1 M2).

[0059] Example 6

[0060] (1) The lithium source LiOH·H2O and the precursor Ni 0.8 Co 0.1 Al 0.1(OH)₂ was thoroughly mixed at a molar ratio of 1.05:1 and then ground in a planetary mill at 300 r / min for 2 h to obtain powder. The powder was then placed in a tube furnace and pre-calcined at 500 °C for 2 h, followed by calcination at 900 °C under an O₂ atmosphere for 15 h to obtain high-nickel NCA cathode material. The flow rate of O₂ was 150 mL / min, and the heating rate was 6 °C / min.

[0061] (2) NCA cathode material and LFP are mixed in water, stirred and sonicated for 1 hour, and then ball-milled at a rate of 200 r / min for 3 hours to obtain NCA@LFP; wherein, the amount of LFP added is 20% of the mass of high nickel cathode material;

[0062] (3) NCA@LFP and gluconic acid are mixed in water and reacted for 1-2 hours to obtain cross-linked gluconic acid NCA@LFP; wherein the molar ratio of gluconic acid to lithium iron phosphate is 1:2.

[0063] (4) NCA@LFP and LMO of cross-linked gluconic acid were mixed in water, stirred and sonicated for 1 h, and then ball-milled at a rate of 100 r / min for 3 h to obtain NCA@LFP@LMO; wherein, the amount of lithium manganese oxide added was 1% of the mass of the high nickel cathode material.

[0064] (5) NCA@LFP@LMO was vacuum dried at 90℃ for 10 h to obtain the product NCA@LFP@LMO(A 10 F2M 0.1 ).

[0065] Comparative Example 1

[0066] Comparative Example 1 is a high-nickel cathode material without lithium iron phosphate and / or lithium manganese oxide coating. Its preparation method is the same as that in Examples 1-4, specifically including the following steps:

[0067] Lithium source LiOH·H2O and precursor Ni 0.8 Co 0.1 Al 0.1 (OH)2 was thoroughly mixed at a molar ratio of 1.03:1 and then ground in a planetary mill at 300 r / min for 2 h to obtain powder. The powder was placed in a tube furnace and pre-calcined at 450℃ for 5 h, and then calcined at 800℃ under an O2 atmosphere for 12 h to obtain high-nickel NCA cathode material. The flow rate of O2 was 100 mL / min and the heating rate was 5℃ / min.

[0068] Comparative Example 2

[0069] The basic steps of Comparative Example 2 are the same as those of Example 2, except that only lithium iron phosphate is used for coating, specifically including the following steps:

[0070] (1) The lithium source LiOH·H2O and the precursor Ni 0.8 Co 0.1 Al 0.1 (OH)₂ was thoroughly mixed at a molar ratio of 1.03:1 and then ground in a planetary mill at 300 r / min for 2 h to obtain powder. The powder was placed in a tube furnace and pre-calcined at 450 °C for 5 h, and then calcined at 800 °C under an O₂ atmosphere for 12 h to obtain high-nickel NCA cathode material. The flow rate of O₂ was 100 mL / min and the heating rate was 5 °C / min.

[0071] (2) NCA cathode material and LFP are mixed in ethanol, stirred and sonicated for 1 hour, and then ball-milled at a rate of 200 r / min for 2 hours to obtain NCA@LFP; wherein, the amount of LFP added is 10% of the mass of high nickel cathode material;

[0072] (3) NCA@LFP was vacuum dried at 80℃ for 12 h to obtain the product NCA@LFP(A 10 F1M0);

[0073] Comparative Example 3

[0074] The basic steps of Comparative Example 3 are the same as those of Example 3, except that only lithium iron phosphate is used for coating, specifically including the following steps:

[0075] (1) The lithium source LiOH·H2O and the precursor Ni 0.8 Co 0.1 Al 0.1 (OH)₂ was thoroughly mixed at a molar ratio of 1.03:1 and then ground in a planetary mill at 300 r / min for 2 h to obtain powder. The powder was placed in a tube furnace and pre-calcined at 450 °C for 5 h, and then calcined at 800 °C under an O₂ atmosphere for 12 h to obtain high-nickel NCA cathode material. The flow rate of O₂ was 100 mL / min and the heating rate was 5 °C / min.

[0076] (2) NCA and LMO were mixed in a solvent, stirred and sonicated for 1 hour, and then ball-milled at 200 r / min for 2 hours to obtain NCA@LMO; wherein, the amount of lithium manganese oxide added was 10% of the mass of the high-nickel cathode material;

[0077] (3) NCA@LMO was vacuum dried at 80℃ for 12 h to obtain the product NCA@LMO(A 10 F0M1).

[0078] Comparative Example 4

[0079] The basic steps are the same as in Example 3, except that gluconic acid is not used for bridging. The specific steps are as follows:

[0080] (1) The lithium source LiOH·H2O and the precursor Ni 0.8 Co 0.1 Al 0.1 (OH)₂ was thoroughly mixed at a molar ratio of 1.03:1 and then ground in a planetary mill at 300 r / min for 2 h to obtain powder. The powder was placed in a tube furnace and pre-calcined at 450 °C for 5 h, and then calcined at 800 °C under an O₂ atmosphere for 12 h to obtain high-nickel NCA cathode material. The flow rate of O₂ was 100 mL / min and the heating rate was 5 °C / min.

[0081] (2) NCA cathode material and LFP are mixed in ethanol, stirred and sonicated for 1 hour, and then ball-milled at a rate of 200 r / min for 2 hours to obtain NCA@LFP; wherein, the amount of LFP added is 5% of the mass of high nickel cathode material;

[0082] (3) NCA@LFP and LMO were mixed in ethanol, stirred and sonicated for 1 hour, and then ball-milled at a rate of 100 r / min for 2 hours to obtain NCA@LFP@LMO; wherein, the amount of lithium manganese oxide added was 10% of the mass of the high-nickel cathode material.

[0083] (4) NCA@LFP@LMO was vacuum dried at 80℃ for 12 h to obtain the product NCA@LFP@LMO(A 10 F 0.5 M1).

[0084] Performance testing

[0085] The positive electrode materials prepared in the above embodiments and comparative examples were used to prepare a positive electrode material layer. The prepared positive electrode material layer was then pressed with an electrolyte and a negative electrode sheet to obtain a battery. Ten batteries prepared in each embodiment and comparative example were taken and tested at 25°C on a Blue Battery testing device, with a test voltage range of 2.7-4.3V. The batteries were subjected to charge-discharge cycle tests at a discharge efficiency of 0.1C. After two weeks of cycles, a 50-cycle test was performed at 1C. Then, the test was stopped after two weeks of charge-discharge cycles at 0.1C. The average values ​​for each group were taken. The average first discharge specific capacity, average first discharge efficiency, and room temperature cycle retention rate of the batteries are shown in Table 1.

[0086] The specific preparation steps of the battery are as follows: the prepared positive electrode material is mixed with a conductive agent and a binder in a certain proportion to form a slurry, which is then coated onto aluminum foil. After vacuum drying and rolling, it is formed into a positive electrode sheet. A lithium metal sheet is used as the negative electrode. The electrolyte includes a 1.15M lithium hexafluorophosphate (LiPF6) solution, and the solvent is a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC), with a volume ratio of EC to DMC of 1:1. A coin cell is then assembled. The positive electrode materials prepared in the examples and comparative examples were subjected to DSC testing using TG-thermogravimetric analysis.

[0087] Table 1. Battery performance test results for the examples and comparative examples.

[0088]

[0089]

[0090] As shown in Table 1, the high-nickel cathode material, after being coated, exhibited significantly improved charge-discharge cycle performance at room temperature (2.7-4.3V) in the embodiments. This demonstrates that the double-layer coating of the present invention effectively improves the high-nickel structure. Compared to Comparative Example 4, the connection between the two layers is stronger, improving structural stability, increasing capacity, suppressing O2 release, preventing phase transition, improving cycle performance, and enhancing safety performance. The strongest exothermic peak in the embodiments is also much higher than that in the comparative example, indicating that double-layer coating is beneficial for improving the thermal stability of the material, thereby enhancing battery safety performance.

[0091] In addition to the above embodiments, the lithium source used in the preparation method of the present invention may include at least one of lithium carbonate, lithium hydroxide, or lithium nitrate; the precursor is Ni. x Co y D 1-x-y (OH)2, where 0.80≤x≤0.95, 0.05≤y≤0.20, 0≤1-xy≤0.20, and D is one or more of alkali metal elements, alkaline earth metal elements, group 13 elements, group 14 elements, transition metal elements, and rare earth elements. The specific raw materials used do not affect the final high-nickel cathode material.

Claims

1. A method for preparing a high-nickel cathode material with a double-layered nanolayer coating, characterized in that, Includes the following steps: (1) A high-nickel cathode material is prepared by uniformly mixing the lithium source and the precursor at a molar ratio of (0.95-1.05):1 and calcining. The lithium source includes at least one of lithium carbonate, lithium hydroxide, or lithium nitrate. The precursor is Ni. x Co y D 1-x-y (OH)2, wherein 0.80≤x≤0.95, 0.05≤y≤0.20, 0≤1-xy≤0.20, and D is one or more of alkali metal elements, alkaline earth metal elements, Group 13 elements, Group 14 elements, transition metal elements, and rare earth elements; calcination is performed by pre-calcination at 400-500℃ for 2-6 h, followed by calcination at 600-900℃ in an O2 atmosphere at a flow rate of 50-150 mL / min for 15-30 h, with a heating rate of 3-6℃ / min; (2) The high-nickel cathode material prepared above is mixed with lithium iron phosphate in a solvent and ball-milled to obtain coated cathode material I; wherein the amount of lithium iron phosphate added is 1-20% of the mass of the high-nickel cathode material; (3) The coated positive electrode material I and gluconic acid are mixed in a solvent and reacted for 1-2 hours to obtain the cross-linked gluconic acid coated positive electrode material I; wherein the molar ratio of gluconic acid to lithium iron phosphate is 1:0.5-2. (4) The cross-linked gluconic acid coated cathode material I and lithium manganese oxide are mixed in a solvent and ball-milled to obtain coated cathode material II; wherein the amount of lithium manganese oxide added is 1-20% of the mass of the high-nickel cathode material; (5) The above-prepared coated cathode material II is dried under vacuum to obtain a high-nickel cathode material with a double-layer coated nanolayer.

2. The method for preparing a high-nickel cathode material with a double-layered nanolayer according to claim 1, characterized in that, In steps (2) to (4), the solvent is deionized water or ethanol.

3. The method for preparing a high-nickel cathode material with a double-layered nanolayer according to claim 1, characterized in that, In steps (2) and (4), the ball milling time is 1-3 hours.

4. The method for preparing a high-nickel cathode material with a double-layered nanolayer according to claim 1, characterized in that, In step (5), vacuum drying is performed at 60-90℃ for 10-20 hours.

5. The method for preparing a high-nickel cathode material with a double-layered nanolayer according to claim 1, characterized in that, In step (5), the thickness of the coating layer of the high-nickel cathode material with double-layer nano-coated layer is 0.1-50 nm, and the particle size of the high-nickel cathode material is 2-20 μm.

6. The method for preparing a high-nickel cathode material with a double-layered nanolayer according to claim 5, characterized in that, The coating thickness is 5-15 nm, and the particle size of the high-nickel cathode material is 5-10 μm.

7. The method for preparing a high-nickel cathode material with a double-layered nanolayer according to claim 1, characterized in that, In steps (2) and (4), the amount of lithium iron phosphate added is 5-15% of the mass of the high-nickel cathode material; the amount of lithium manganese oxide added is 5-15% of the mass of the high-nickel cathode material.

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