Coated lithium-rich manganese-based positive electrode material, preparation method thereof and lithium battery

Abstract

This invention provides a coated lithium-rich manganese-based cathode material, its preparation method, and a lithium battery, belonging to the field of cathode material technology. The invention involves adding a solid fluorinated additive and then sintering it. The fluorinated additive decomposes to generate fluorides and / or hydrogen fluoride and / or fluorine gas. The hydrogen fluoride or fluorine gas reacts with residual lithium on the surface of the lithium-rich manganese-based material to form a lithium fluoride coating layer. Simultaneously, the hydrogen fluoride also causes lithium ions to precipitate from the primary particles of the lithium-rich manganese-based material, thereby forming a spinel structure on the surface layer of the lithium-rich manganese-based material. The fluoride and / or lithium fluoride coating layer can isolate the electrolyte, protect the lithium-rich manganese-based material from electrolyte corrosion, suppress interfacial side reactions, and improve cycle stability. The spinel structure possesses chemical and electrochemical stability and can provide 3D Li + The transmission channel is beneficial for improving rate performance, etc.; at the same time, the preparation method is low in cost, high in safety, and simpler to operate.

Description

Technical Field

[0001] This invention belongs to the field of cathode material technology, specifically relating to a coated lithium-rich manganese-based cathode material, its preparation method, and a lithium battery. Background Technology

[0002] Layered lithium-rich manganese-based cathode materials, possessing high specific energy and capacity while being environmentally friendly, are considered the most promising cathode materials for rechargeable lithium batteries. However, during charge and discharge, active oxygen in Li2MnO3 participates in electrochemical reactions, causing the active oxygen in the structure to be converted into O2 and released. This reduces the binding energy between transition metal ions and oxygen, increases cation mixing, and leads to an irreversible phase transition in the material. Consequently, lithium-rich manganese-based cathode materials suffer from problems such as low initial coulombic efficiency, poor rate performance, and severe voltage decay.

[0003] Existing technologies include methods for preparing a coating layer on the surface of lithium-rich manganese-based cathode materials by pyrolysis of fluorine-containing gases. However, this method is costly, has poor safety, and the performance of the coated cathode material still needs further improvement. Summary of the Invention

[0004] The purpose of this invention is to provide a coated lithium-rich manganese-based cathode material, its preparation method, and a lithium battery thereof. The preparation method provided by this invention is low-cost, highly safe, and easy to operate, and the lithium battery assembled from the prepared cathode material exhibits better electrochemical performance.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a coated lithium-rich manganese-based cathode material, comprising the following steps: (1) The lithium-rich manganese-based material is mixed with a solid fluorine-containing additive to obtain a mixture; (2) The mixture obtained in step (1) is sintered to obtain a coated lithium-rich manganese-based cathode material.

[0006] Preferably, the chemical formula of the lithium-rich manganese-based material in step (1) is Li a [Ni x Co y Mn 1-x-y O 2+b , where 1.1≤a≤1.5, 0<x<0.5, 0≤y≤0.3, 0≤b≤0.6.

[0007] Preferably, the median particle size of the lithium-rich manganese-based material in step (1) is 2~15μm.

[0008] Preferably, the solid fluorinated additive in step (1) includes one or more of ammonium fluoride, potassium fluoride, polyvinylidene fluoride, polytetrafluoroethylene, and lithium fluorosilicate.

[0009] Preferably, the median particle size of the solid fluorine-containing additive in step (1) is 10 nm to 100 μm.

[0010] Preferably, in step (1), the mass ratio of the solid fluorine-containing additive to the lithium-rich manganese-based material is (0.01~5):100.

[0011] Preferably, the mixing in step (1) is ball milling; the ball milling includes a first ball milling, a second ball milling, and a third ball milling performed sequentially; the rotation speed of the first ball milling is 50~100 rpm, and the first ball milling time is 20~300 min; the rotation speed of the second ball milling is 100~300 rpm, and the second ball milling time is 20~300 min; the rotation speed of the third ball milling is 400~5000 rpm, and the third ball milling time is 20~600 min.

[0012] Preferably, in step (2), the sintering temperature is 200~800℃, the sintering time is 60~480min, and the heating rate to the sintering temperature is 1~10℃ / min.

[0013] The present invention also provides a coated lithium-rich manganese-based cathode material prepared by the preparation method described in the above technical solution.

[0014] The present invention also provides a lithium battery, wherein the positive electrode active material of the lithium battery is the coated lithium-rich manganese-based positive electrode material described in the above technical solution.

[0015] This invention provides a method for preparing a coated lithium-rich manganese-based cathode material, comprising the following steps: (1) mixing a lithium-rich manganese-based material with a solid fluorinated additive to obtain a mixture; (2) sintering the mixture obtained in step (1) to obtain a coated lithium-rich manganese-based cathode material. In this invention, the lithium-rich manganese-based material is mixed with a solid fluorinated additive and then sintered. The fluorinated additive decomposes to generate fluorides and / or hydrogen fluoride and / or fluorine gas. The hydrogen fluoride or fluorine gas forms a lithium fluoride coating layer with residual lithium on the surface of the lithium-rich manganese-based material, thereby modifying the surface of the lithium-rich manganese-based material. Simultaneously, the hydrogen fluoride also causes the Li in the primary particles of the lithium-rich manganese-based material to be affected. + The precipitation process forms a spinel structure on the surface of the lithium-rich manganese-based material. The fluoride and / or lithium fluoride coating layer isolates the electrolyte, protecting the material from electrolyte corrosion, suppressing interfacial side reactions, and improving cycle stability. The spinel structure possesses chemical and electrochemical stability, providing 3D Li... +The transmission channel is beneficial for improving rate performance, etc. Meanwhile, the preparation method provided by this invention is low-cost, highly safe, and simpler to operate. The results of the embodiments show that the half-cell assembled from the coated lithium-rich manganese-based cathode material prepared by this invention has an initial coulombic efficiency of over 87%, a 1C discharge specific capacity of over 165 mAh / g, and a capacity retention rate of over 104% after 50 cycles. Attached Figure Description

[0016] Figure 1 The images show the Raman spectra of the cathode materials in Example 2 and Comparative Example 1. Detailed Implementation

[0017] This invention provides a method for preparing a coated lithium-rich manganese-based cathode material, comprising the following steps: (1) The lithium-rich manganese-based material is mixed with a solid fluorine-containing additive to obtain a mixture; (2) The mixture obtained in step (1) is sintered to obtain a coated lithium-rich manganese-based cathode material.

[0018] Unless otherwise specified, the present invention does not impose any special restrictions on the source of the raw materials, and commercially available products well known to those skilled in the art can be used.

[0019] This invention mixes lithium-rich manganese-based materials with solid fluorine-containing additives to obtain a mixture.

[0020] In this invention, the preferred chemical formula of the lithium-rich manganese-based material is Li. a [Ni x Co y Mn 1-x-y O 2+b , where 1.1≤a≤1.5, 0<x<0.5, 0≤y≤0.3, 0≤b≤0.6.

[0021] In an embodiment of the present invention, the lithium-rich manganese-based material is specifically Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 .

[0022] In this invention, the median particle size of the lithium-rich manganese-based material is preferably 2-15 μm. As one embodiment, the median particle size of the lithium-rich manganese-based material can specifically be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm.

[0023] In one embodiment, the lithium-rich manganese-based material is a secondary aggregate with a polycrystalline morphology of primary particles agglomerated into spherical or near-spherical shapes. This invention does not impose a specific limitation on the particle size of the primary particles, as long as the median particle size of the lithium-rich manganese-based material is within the required range.

[0024] In this invention, the solid fluorinated additive preferably includes one or more of ammonium fluoride, potassium fluoride (KHF2), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and lithium fluorosilicate.

[0025] In this invention, the molecular weight (Mw) of the polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) is preferably independently between 100 and 600,000. By controlling the molecular weight of PVDF and PTFE within this range, the present invention achieves a suitable molecular weight, which is more conducive to uniform coating.

[0026] In this invention, the median particle size of the solid fluorinated additive is preferably 10 nm to 100 μm. As one embodiment, the median particle size of the solid fluorinated additive can specifically be 10 nm, 50 nm, 80 nm, 100 nm, 120 nm, 200 nm, 250 nm, 300 nm, 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 50 μm, 80 μm, or 100 μm.

[0027] When the median particle size of the solid fluorinated additive is not within the required range, the present invention preferably pulverizes the solid fluorinated additive.

[0028] This invention does not impose any special limitations on the pulverization operation; any technical solution well-known to those skilled in the art can be used to ensure that the particle size of the pulverized solid fluorine-containing additive is within the required range. As one embodiment, the pulverization may specifically be one or more of grinding, air jet milling, ball milling, or sand milling.

[0029] In this invention, the preferred mass ratio of the solid fluorinated additive to the lithium-rich manganese-based material is (0.01~5):100. As one embodiment, the mass ratio of the solid fluorinated additive to the lithium-rich manganese-based material can specifically be 0.01:100, 0.05:100, 0.1:100, 0.5:100, 1:100, 2:100, 3:100, 4:100, or 5:100. By controlling the mass ratio of the solid fluorinated additive to the lithium-rich manganese-based material within the above range, this invention can further improve the electrochemical performance of the battery assembled from the cathode material.

[0030] In this invention, the mixing is preferably ball milling; the ball milling is preferably carried out at room temperature; the ball milling preferably includes a first ball milling, a second ball milling, and a third ball milling performed sequentially.

[0031] In this invention, the rotation speed of the first ball mill is preferably 50-100 rpm; the milling time is preferably 20-300 min; the rotation speed of the second ball mill is preferably 100-300 rpm; the milling time is preferably 20-300 min; the rotation speed of the third ball mill is preferably 400-5000 rpm; and the milling time is preferably 20-600 min. In one embodiment, the rotational speed of the first ball mill can be specifically 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, or 100 rpm; the milling time can be specifically 20 min, 50 min, 100 min, 150 min, 200 min, 250 min, or 300 min; the rotational speed of the second ball mill can be specifically 100 rpm, 150 rpm, 200 rpm, 250 rpm, or 300 rpm; the milling time can be specifically 20 min, 50 min, 100 min, 150 min, 200 min, 250 min, or 300 min; the rotational speed of the third ball mill can be specifically 400 rpm, 800 rpm, 1000 rpm, 2000 rpm, 3000 rpm, 4000 rpm, or 5000 rpm; the milling time can be specifically 20 min, 50 min, 100 min, 300 min, 500 min, or 600 min. By controlling the ball milling parameters within the above-mentioned range, the present invention enables the raw materials to be mixed more evenly.

[0032] After obtaining the mixture, the present invention sinters the mixture to obtain a coated lithium-rich manganese-based cathode material.

[0033] In this invention, the sintering is preferably carried out under an inert atmosphere or an air atmosphere; the inert atmosphere is preferably a nitrogen atmosphere or an argon atmosphere. In this invention, sintering under an inert atmosphere can protect the solid fluorine-containing additives, allowing them to stably react with the surface of the lithium-rich manganese-based material as intended, thus ensuring the effective utilization of fluorine.

[0034] In this invention, the sintering temperature is preferably 200~800℃; the sintering time is preferably 60~480min; and the heating rate to the sintering temperature is preferably 1~10℃ / min. As one embodiment, the sintering temperature can specifically be 200℃, 300℃, 400℃, 500℃, 600℃, 700℃, or 800℃; the sintering time can specifically be 60min, 80min, 100min, 150min, 200min, 250min, 300min, 350min, 400min, 450min, or 480min; and the heating rate to the sintering temperature can specifically be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min. By controlling the sintering parameters within the above-mentioned range, this invention can further improve the electrochemical performance of lithium batteries assembled from cathode materials.

[0035] After sintering, the present invention preferably cools the sintered product to obtain a coated lithium-rich manganese-based cathode material.

[0036] The present invention does not impose any special limitations on the cooling operation; any technical solution known to those skilled in the art can be used to cool to room temperature.

[0037] As one implementation method, the cooling is natural cooling.

[0038] This invention mixes lithium-rich manganese-based materials with solid fluorine-containing additives and then sintersects them. During the sintering process, the fluorine-containing additives decompose to form a fluoride coating layer, which can physically block the cathode material and electrolyte, preventing high-valence metal cations and active species on the material surface from reacting with the electrolyte, and also inhibiting the corrosion of HF in the electrolyte. The decomposition of the fluorine-containing additives generates HF, causing the Li in the structure to... + The precipitation process forms a spinel phase on the cathode surface. The spinel phase is an ideal surface modification structure with chemical and electrochemical stability. It can prevent oxygen release and side reactions with the electrolyte, and can also inhibit local structural transformations starting from the surface and electrolyte decomposition. The fluorine-containing additives decompose to generate HF, which can reduce residual lithium on the substrate surface and improve the air stability and cycle stability of the material. At the same time, the generated LiF can physically block the cathode material and electrolyte. The coating layer can also confine the active oxygen species generated during charging inside the material, prevent oxygen escape, and thus alleviate the problems of low first-cycle coulombic efficiency, poor rate performance and cycle stability of lithium-rich manganese-based materials. The preparation method provided by this invention is simple, easy to operate, and suitable for mass production.

[0039] The present invention also provides a coated lithium-rich manganese-based cathode material prepared by the preparation method described in the above technical solution.

[0040] The present invention also provides a lithium battery, wherein the positive electrode active material of the lithium battery is the coated lithium-rich manganese-based positive electrode material described in the above technical solution.

[0041] This invention does not impose any special limitations on other types of materials and preparation methods for the lithium battery; any types of materials and preparation methods for lithium batteries that are well known to those skilled in the art can be used.

[0042] Because the cathode material prepared according to this invention is used as the active material, the lithium battery has excellent electrochemical performance.

[0043] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0044] Example 1 A method for preparing a coated lithium-rich manganese-based cathode material is as follows: (1) 500g of lithium-rich manganese-based material (Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 The median particle size of the material was 5 μm, and 0.25 g of lithium fluorosilicate (median particle size of 500 nm, mass ratio of lithium fluorosilicate to lithium-rich manganese-based material of 0.05:100) was first ball-milled at 60 rpm for 100 min at room temperature, then ball-milled at 200 rpm for 150 min, and then ball-milled at 800 rpm for 200 min to obtain a mixture. (2) The mixture obtained in step (1) is placed in a sagger and heated to 400°C for 300 min at a rate of 3°C / min in air atmosphere. It is then naturally cooled to room temperature to obtain a coated lithium-rich manganese-based cathode material.

[0045] Example 2 A method for preparing a coated lithium-rich manganese-based cathode material is as follows: (1) 500g of lithium-rich manganese-based material (Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 The median particle size of the material was 5 μm, and 0.5 g of lithium fluorosilicate (median particle size of 500 nm, mass ratio of lithium fluorosilicate to lithium-rich manganese-based material of 0.1:100) was first ball-milled at 60 rpm for 100 min at room temperature, then ball-milled at 200 rpm for 150 min, and then ball-milled at 800 rpm for 200 min to obtain a mixture. (2) The mixture obtained in step (1) is placed in a sagger and heated to 400°C for 300 min at a rate of 3°C / min in air atmosphere. It is then naturally cooled to room temperature to obtain a coated lithium-rich manganese-based cathode material.

[0046] Example 3 A method for preparing a coated lithium-rich manganese-based cathode material is as follows: (1) 500g of lithium-rich manganese-based material (Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 The median particle size of the material was 5 μm, and 0.75 g of lithium fluorosilicate (median particle size of 500 nm, mass ratio of lithium fluorosilicate to lithium-rich manganese-based material of 0.15:100) was first ball-milled at 60 rpm for 100 min at room temperature, then ball-milled at 200 rpm for 150 min, and then ball-milled at 800 rpm for 200 min to obtain a mixture. (2) The mixture obtained in step (1) is placed in a crucible and heated to 400°C for 300 min at a rate of 3°C / min under a nitrogen atmosphere. It is then naturally cooled to room temperature to obtain a coated lithium-rich manganese-based cathode material.

[0047] Example 4 A method for preparing a coated lithium-rich manganese-based cathode material is as follows: (1) 500g of lithium-rich manganese-based material (Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 The median particle size of the sample was 5 μm, and 0.1 g of potassium fluoride (KHF2, median particle size 10 μm, mass ratio of potassium fluoride to lithium-rich manganese-based material was 0.02:100) was first ball-milled at 60 rpm for 100 min at room temperature, then ball-milled at 200 rpm for 150 min, and then ball-milled at 800 rpm for 200 min to obtain a mixture. (2) The mixture obtained in step (1) is placed in a crucible and sintered at 500°C for 300 min at a rate of 3°C / min under a nitrogen atmosphere. It is then naturally cooled to room temperature to obtain a coated lithium-rich manganese-based cathode material.

[0048] Example 5 A method for preparing a coated lithium-rich manganese-based cathode material is as follows: (1) 500g of lithium-rich manganese-based material (Li 1.3 [Ni 0.35 Mn 0.65 O 2.3The median particle size of the polyvinylidene fluoride (Mw of 400,000 to 600,000 and median particle size of 15 μm) was first ball-milled at 60 rpm for 100 min at room temperature, then at 200 rpm for 150 min, and then at 800 rpm for 400 min to obtain a mixture. (2) The mixture obtained in step (1) is placed in a sagger and heated to 600°C for 300 min at a rate of 3°C / min in air atmosphere. It is then naturally cooled to room temperature to obtain a coated lithium-rich manganese-based cathode material.

[0049] Example 6 A method for preparing a coated lithium-rich manganese-based cathode material is as follows: (1) 500g of lithium-rich manganese-based material (Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 The median particle size of 5 μm and 0.25 g of polytetrafluoroethylene (median particle size of 500 nm) were first ball-milled at 60 rpm for 100 min at room temperature, then ball-milled at 200 rpm for 150 min, and then ball-milled at 800 rpm for 400 min to obtain a mixture. (2) The mixture obtained in step (1) is placed in a crucible and sintered at 500°C for 240 min at a rate of 3°C / min under a nitrogen atmosphere. It is then naturally cooled to room temperature to obtain a coated lithium-rich manganese-based cathode material.

[0050] Example 7 A method for preparing a coated lithium-rich manganese-based cathode material is as follows: (1) 500g of lithium-rich manganese-based material (Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 The median particle size of the sample was 5 μm and 0.25 g of ammonium fluoride (median particle size of 5 μm) were first ball-milled at 60 rpm for 100 min at room temperature, then ball-milled at 200 rpm for 150 min, and then ball-milled at 800 rpm for 400 min to obtain a mixture. (2) The mixture obtained in step (1) is placed in a crucible and sintered at 500°C for 240 min at a rate of 3°C / min under a nitrogen atmosphere. It is then naturally cooled to room temperature to obtain a coated lithium-rich manganese-based cathode material.

[0051] Comparative Example 1 Lithium-rich manganese-based cathode material Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 .

[0052] Comparative Example 2 500g of lithium-rich manganese-based material (Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 The material (with a median particle size of 5 μm) was first ball-milled at 60 rpm for 100 min at room temperature, then at 200 rpm for 150 min, and then at 800 rpm for 200 min. It was then placed in a crucible and sintered at 500 °C for 240 min at a rate of 3 °C / min under a nitrogen atmosphere. After natural cooling to room temperature, lithium-rich manganese-based cathode material was obtained.

[0053] Comparative Example 3 500g of lithium-rich manganese-based material (Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 The median particle size (5 μm) was heated to 400 °C at a rate of 3 °C / min under a nitrogen atmosphere and held for 1 h. Then the nitrogen atmosphere was turned off and a mixture of fluorine and nitrogen gas (fluorine gas accounted for 5% of the mass of the mixture) was introduced at a rate of 10 L / min and held for 2 h. Then the mixture was turned off and nitrogen gas was introduced and held for 1 h. The mixture was then naturally cooled to room temperature to obtain a lithium-rich manganese-based cathode material.

[0054] Performance testing The positive electrode materials from Examples 1-7 and Comparative Examples 1-3 were mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 92:4:4. N-methylpyrrolidone was added to obtain a mixed slurry with a solid content of 50%. The mixed slurry was coated on aluminum foil (coating thickness of 200 nm), and after vacuum drying, it was cut into circular substrates. Then, it was assembled into CR2025 button half-cells in an argon-filled glove box and tested in a Xinwei battery tester with a test voltage of 2.3~4.52V.

[0055] The specific capacity, initial coulombic efficiency, specific capacity at 1C discharge, and capacity retention after 50 cycles of the CR2025 button half-cells assembled with the cathode materials in Examples 1-7 and Comparative Examples 1-3 are shown in Table 1.

[0056] Table 1. Electrochemical performance of CR2025 button half-cells assembled with the cathode materials in Examples 1-7 and Comparative Examples 1-3.

[0057] As can be seen from Table 1, the half-cell assembled with the cathode material prepared in this invention has better electrochemical performance.

[0058] The Raman spectra of the cathode materials in Example 2 and Comparative Example 1 are as follows: Figure 1 As shown. From Figure 1As can be seen from the data, compared with Comparative Example 1, Example 2 has a lower resolution of ~590cm. -1 The layered structure peaks on both sides show significant broadening, because the peak on the right side is located at ~630 cm⁻¹. -1 The spinel structure peaks on the left and right sides confirm that a spinel structure was formed on the surface of the cathode material prepared in Example 2.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a coated lithium-rich manganese-based cathode material, comprising the following steps: (1) The lithium-rich manganese-based material is mixed with a solid fluorine-containing additive to obtain a mixture; (2) The mixture obtained in step (1) is sintered to obtain a coated lithium-rich manganese-based cathode material.

2. The preparation method according to claim 1, characterized in that, The chemical formula of the lithium-rich manganese-based material in step (1) is Li a [Ni x Co y Mn 1-x-y O 2+b , where 1.1≤a≤1.5, 0<x<0.5, 0≤y≤0.3, 0≤b≤0.

6.

3. The preparation method according to claim 1, characterized in that, The median particle size of the lithium-rich manganese-based material in step (1) is 2~15μm.

4. The preparation method according to claim 1, characterized in that, The solid fluorinated additive in step (1) includes one or more of ammonium fluoride, potassium fluoride, polyvinylidene fluoride, polytetrafluoroethylene, and lithium fluorosilicate.

5. The preparation method according to claim 1, characterized in that, The median particle size of the solid fluorine-containing additive in step (1) is 10 nm to 100 μm.

6. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of the solid fluorine-containing additive to the lithium-rich manganese-based material is (0.01~5):

100.

7. The preparation method according to claim 1, characterized in that, The mixing in step (1) is ball milling; the ball milling includes a first ball milling, a second ball milling and a third ball milling performed sequentially; the rotation speed of the first ball milling is 50~100 rpm, and the first ball milling time is 20~300 min; the rotation speed of the second ball milling is 100~300 rpm, and the second ball milling time is 20~300 min; the rotation speed of the third ball milling is 400~5000 rpm, and the third ball milling time is 20~600 min.

8. The preparation method according to claim 1, characterized in that, In step (2), the sintering temperature is 200~800℃, the sintering time is 60~480min, and the heating rate to the sintering temperature is 1~10℃ / min.

9. The coated lithium-rich manganese-based cathode material prepared by the preparation method according to any one of claims 1 to 8.

10. A lithium battery, characterized in that, The positive electrode active material of the lithium battery is the coated lithium-rich manganese-based positive electrode material as described in claim 9.

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