CN111490241A - A lithium-rich manganese-based cathode material coated in situ with lithium phosphate and preparation method thereof - Google Patents

Abstract

Lithium phosphate in-situ coated lithium-rich manganese-based positive electrode material and preparation method thereof, wherein the chemical formula of the material is x L i₂MnO₃·(1‑x)LiMO₂@Li₃PO₄Wherein x is more than or equal to 0.3 and less than or equal to 0.7, M is Ni or at least one of Ni, Co and Mn, and the mass fraction of lithium phosphate is 0.1-5%. The preparation method comprises the steps of adding a mixed solution of ammonia water and sodium carbonate and a mixed solution of nickel, cobalt and manganese into a reaction kettle in a concurrent flow manner, and carrying out coprecipitation reaction to obtain a precursor. Adding the precursor into a solution containing phosphate ions, stirring, precipitating, converting, filtering, washing and drying, and mixing with lithiumAnd mixing the sources, and calcining in an air atmosphere to obtain the lithium phosphate coated lithium-rich manganese-based positive electrode material. According to the invention, the lithium phosphate in-situ coating modification of the lithium-rich manganese-based anode material in the calcining process is realized by a precursor precipitation conversion method, the coating process is simplified, the cycle life and the rate capability of the lithium-rich manganese-based material are improved, and the lithium-rich manganese-based anode material has a prospect of large-scale production and application.

Description

A lithium-rich manganese-based cathode material coated in situ with lithium phosphate and preparation method thereof

technical field

The invention belongs to the technical field of positive electrode materials for lithium ion batteries, and in particular relates to a preparation method of a lithium-rich manganese-based positive electrode material precursor and a lithium phosphate-coated positive electrode material.

Background technique

In recent years, with the rapid development of mobile devices such as mobile phones and tablet computers and electric vehicles, people have put forward requirements for higher specific capacity, higher energy density, longer service life, and lower cost of lithium-ion batteries. Current commercial lithium-ion battery cathode materials such as LiCoO ₂ , LiFePO ₄ , LiMn ₂ O ₄ and LiNi _1-xy Co _x M _y O ₂ have limited specific capacity, which is a bottleneck restricting the further development of lithium-ion batteries. Li-rich manganese-based materials (xLi ₂ MnO ₃ ·(1-x)LiMO ₂ , M=Mn, Co, Ni, etc.) have a specific capacity of over 250 mAh g ⁻¹ and a theoretical energy density close to 1000 Wh/kg, and its main The low cost of the elemental component manganese has attracted the attention of many researchers and is considered to be the most promising cathode material for next-generation high specific energy lithium-ion batteries. However, Li-rich manganese-based materials suffer from low first-cycle Coulomb efficiency, severe capacity and voltage fading, and poor rate performance, which restrict their practical applications.

The main reasons for the problems of low Coulomb efficiency and voltage decay in the first cycle are the side reactions between the surface of the cathode material and the electrolyte and the dissolution of transition metal elements in the material during the charging and discharging process. In order to solve these problems, the coating strategy is often used. Improve material stability. For example, Chinese Patent No. CN 110364713 A discloses a preparation method of a composite conductive agent-coated single-crystal lithium-rich manganese-based positive electrode material. The method adopts liquid-phase ultrasound to disperse graphene, carbon nanotubes and conductive carbon black in a lithium-rich cathode material. The surface of the material is further sintered to obtain a single-crystal lithium-rich manganese-based positive electrode material coated with a composite conductive agent, and the good conductive network enables the material to have good electrochemical performance. Chinese Patent No. CN 110890541 A discloses a method for preparing a surface-modified lithium-rich manganese-based positive electrode material. The lithium-rich material is treated with coating liquids such as hydrogen phosphate, pyrophosphate and meta-aluminate. Ion conductor-coated material, this method enhances lithium ion diffusion and thus improves electrochemical performance.

However, the current coating process still has defects. The preparation of lithium-rich manganese-based materials is divided into two steps: precursor synthesis and high-temperature calcination. The properties of the precursors are stable and easy to store, while the sintered lithium-rich manganese-based materials are more sensitive to environmental humidity and atmosphere conditions. Ordinary post-preparation-based coating strategies usually require Li-rich manganese-based materials to be treated in aqueous solutions, and their surface structures are easily destroyed, such as lithium ion loss, hydrogen ion intercalation, and phase transitions in the surface structure. The secondary calcination increases the crystallinity of the material, and this secondary high-temperature heating process generates energy consumption and additionally increases the complexity of the process. In order to avoid the coating treatment after the synthesis of Li-rich manganese-based materials, it is a necessary and challenging task to develop the in-situ uniform coating technology of precursors, which is important for simplifying the process flow, enhancing the controllability of the preparation and reducing the production cost. significance.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the technical problems of low coulombic efficiency in the first cycle, serious capacity and voltage attenuation, and poor rate performance of lithium-rich manganese-based materials, and propose a strategy for coating lithium-rich manganese-based cathode materials with lithium phosphate, and A simple precursor precipitation conversion in-situ coating technology was adopted to achieve efficient, uniform and stable coating during the synthesis of Li-rich manganese-based materials, and to improve the first-cycle Coulomb efficiency, cycle performance and rate performance of the material. The method of the invention has remarkable modification effect, low cost, simple operation, and is suitable for large-scale production.

Technical scheme of the present invention:

Lithium-rich manganese-based cathode material coated in situ by lithium phosphate, the chemical formula is xLi ₂ MnO ₃ ·(1-x)LiMO ₂ @Li ₃ PO ₄ , where 0.3≤x≤0.7, M is Ni, or Ni and Co and at least one of Mn, the mass fraction of lithium phosphate is 0.1%-5%, and the thickness of the coating layer is less than 30nm.

The preparation method of the lithium-rich manganese-based positive electrode material covered by the above-mentioned lithium phosphate in-situ comprises the following steps:

Step 1: One or more of nickel soluble salt, cobalt soluble salt and manganese soluble salt are prepared according to the above chemical formula, the metal ion concentration is 1-5mol/L salt solution A, and sodium carbonate 0.5-2mol/L is prepared Mixed solution B with ammonia water of 0.05-5mol/L to prepare soluble phosphate solution C with a concentration of 0.01-0.5mol/L;

Step 2: add deionized water to the reaction kettle, add solutions A and B to the reaction kettle in parallel, mechanically stir the reaction, control the temperature of the reaction solution to be constant, and control the pH to be constant by adjusting the flow rate of liquid B; Filtration, washing, and vacuum drying to obtain a lithium-rich manganese-based material precursor, TMCO ₃ , where TM is a transition metal;

Step ₃ : Disperse the obtained precursor TMCO in solution C, stir and react at room temperature, filter, wash, and vacuum dry to obtain a precursor coated with nickel phosphate;

Step 4: The nickel phosphate-coated precursor obtained in step 3 and the lithium source are mixed uniformly according to the metered excess of 0-10% lithium (preferably excess 5%), and calcined in an air atmosphere according to the set heating procedure to obtain lithium phosphate In situ coated Li-rich manganese-based cathode material.

Further, in step 1, the soluble metal salt is one or more of sulfate, nitrate and chloride salt, and the total metal concentration is 1-5mol/L, preferably 2mol/L, and the sodium carbonate concentration is 0.5-5mol/L, preferably 2mol/L, ammonia concentration is 0.05-5mol/L, preferably 0.5mol/L, soluble phosphate is lithium, sodium, potassium, ammonium phosphate, hydrogen phosphate and dihydrogen phosphate One or more of , the concentration is 0.01-0.5mol/L, preferably 0.1mol/L.

Further, in step 2, the metal salt solution A is injected into the reactor at a constant speed of 1-2mL/min, and the solution B is injected into the reactor at a rate of 0.5-2.5mL/min, and the pH of the reactor is controlled to be 7.3-8.3, preferably 7.8, and mechanical stirring. The speed is 300-900rpm/min, preferably 800rpm/min, the reaction temperature of the reactor is 40-70°C, preferably 55°C, and the reaction time is 10-40h.

Further, in step 3, the reaction time of the precursor TMCO ₃ in the soluble phosphate solution C is 1min-24h, preferably 40min.

Further, in step 4, the charging ratio of the lithium source is 100% to 110% of the stoichiometric ratio, preferably 105% of the stoichiometric ratio. The lithium source is one or both of LiOH and Li ₂ CO ₃ , preferably Li ₂ CO ₃ .

Further, the calcination procedure described in step 4 is to first keep the temperature at 500-550°C for 4-6h, preferably at 500°C for 5h, and then raise the temperature to 750-900°C for 10-25h, preferably 800°C for 20h. .

Advantages and effects of the present invention:

1. Different from the coating after material synthesis, the present invention performs coating treatment on the precursor of the lithium-rich manganese-based material, so that the lithium-rich manganese-based material coated with lithium phosphate can be generated in the subsequent step of calcination, avoiding the traditional liquid phase. In the coating process, the more sensitive lithium-rich materials are washed with water and the process of secondary calcination simplifies the process flow.

2. The coating process of the precursor is based on the precipitation conversion reaction of the insoluble salt, which can convert the surface of the carbonate precursor into a coating layer in situ. The solid-liquid reaction ensures the uniformity of the coating, which is easy to operate and conducive to enlargement. Production.

3. Lithium phosphate has a stable crystal structure and has a certain lithium ion conductivity. The coating layer will not hinder the transmission of lithium ions while reducing surface side reactions, thereby improving the first circle Coulomb efficiency and capacity retention of the material. rate and rate capability.

4. The prepared lithium-rich manganese-based cathode material in situ coated with lithium phosphate has a micro-scale spherical morphology, high tap density, and is convenient for processing and application.

Description of drawings

FIG. 1 is a schematic diagram of the preparation process of the lithium-rich manganese-based cathode material coated with lithium phosphate provided by the present invention.

FIG. 2 is an SEM image of the carbonate precursor coated with nickel phosphate of Example 3 and the carbonate precursor of Comparative Example.

3 is a TEM image of the lithium-rich manganese-based material coated with lithium phosphate in Example 3 and the lithium-rich manganese-based material of Comparative Example.

4 is an XRD pattern of the lithium-rich manganese-based material coated with lithium phosphate in Example 3 and the lithium-rich manganese-based material of the comparative example.

FIG. 5 is a graph showing the cycle performance of the coin-type half cells of Example 3 and Comparative Example 1. FIG.

FIG. 6 is a graph showing the rate performance of the coin-type half cells of Example 3 and Comparative Example 1. FIG.

Detailed ways

In order to further understand the present invention, the present invention is further described below with reference to the accompanying drawings, but the protection scope of the present invention is not limited thereby.

Example 1

The value of x is 0.3, and the target chemical formula is 0.3Li ₂ MnO ₃ ·0.7LiNiO ₂ @Li ₃ PO _4. The preparation process is shown in Figure 1, and the specific parameters are as follows. Weigh 0.9mol MnCl ₂ and 2.1 mol NiCl ₂ solids, respectively, and prepare a metal salt solution A with a volume of 1.5 L; Weigh 3 mol Na ₂ CO ₃ , measure 65 mL of concentrated ammonia water (ammonia mass fraction 27%), put carbonic acid Sodium and ammonia water are prepared into lye B with a volume of 1.5L; 0.07mol K ₂ HPO ₄ solid is weighed and prepared into a coating solution C with a volume of 1L.

1L deionized water was added to the reaction kettle as the bottom liquid, the reaction temperature was 70 ° C, the stirring speed was 900 rpm/min, and the salt solution A and the lye B were simultaneously added to the reaction kettle through the peristaltic pump, and the salt solution A flow rate was 1.5 mL/min, the flow rate of lye B is 1.3-1.8mL/min, and the pH is controlled to 7.8 with lye. The reaction was stopped for 14 h, the reaction solution was filtered, the solid was washed with deionized water, and the carbonate precursor was obtained after vacuum drying at 80°C.

Take 1 g of carbonate precursor, and disperse it in 30 mL of coating solution C, stir and react at room temperature for 60 min, and then filter, wash and dry by the aforementioned method to obtain a precursor coated with nickel phosphate. The nickel phosphate-coated precursor and Li ₂ CO ₃ were mixed with a mortar according to the ratio of Li:(Mn+Ni)=1.36:1, and the temperature was first kept at 500 °C for 6 h in a muffle furnace in an air atmosphere, and then heated to Incubate at 850°C for 15h, and grind after natural cooling to obtain a lithium-rich manganese-based material coated with lithium phosphate.

Example 2

The value of x is 0.5, and the target chemical formula is 0.5Li ₂ MnO ₃ ·0.5LiNi _0.5 Mn _0.5 O ₂ @Li ₃ PO _4. The preparation process is shown in Figure 1, and the specific parameters are as follows. Weigh 2.25mol Mn(NO ₃ ) ₂ and 0.75mol Ni(NO ₃ ) ₂ solids, respectively, and prepare a metal salt solution A with a volume of 1.5 L; Weigh 3 mol Na ₂ CO ₃ , measure 50 mL of concentrated ammonia (ammonia mass fraction 27%), sodium carbonate and ammonia water were prepared into alkaline solution B with a volume of 1.5 L; 0.01 mol of Na ₃ PO ₄ was weighed to prepare a coating liquid C with a volume of 1 L.

In the reaction kettle, add 1L deionized water as the bottom liquid, the reaction temperature is 45 ° C, the stirring speed is 700rpm/min, and the salt solution A and the lye B are simultaneously added to the reaction kettle through the peristaltic pump, and the salt solution A flow rate is 1.7 mL/min, the flow rate of lye B is 1.4-2.0mL/min, and the pH is controlled to 7.5 with lye. The reaction was stopped for 12 h, the reaction solution was filtered, the solid was washed with deionized water, and the carbonate precursor was obtained after vacuum drying at 80°C.

Take 1 g of carbonate precursor and disperse it in 30 mL of coating solution C, stir and react at room temperature for 20 min, and then filter, wash and dry by the aforementioned method to obtain a precursor coated with nickel phosphate. The nickel phosphate-coated precursor and Li ₂ CO ₃ were mixed with a mortar according to the ratio of Li:(Mn+Ni)=1.57:1, and kept at 550 °C for 5 h in an air atmosphere muffle furnace, and then heated to Incubate at 900°C for 25h, and grind after natural cooling to obtain a lithium-rich manganese-based material coated with lithium phosphate.

Example 3

The value of x is 0.5, and the target chemical formula is 0.5Li ₂ MnO ₃ ·0.5LiNi _1/3 Co _1/3 Mn _1/3 O ₂ @Li ₃ PO _4. The preparation process is shown in Figure 1, and the specific parameters are as follows . Weigh 2mol MnSO ₄ , 0.5mol CoSO ₄ and 0.5mol NiSO ₄ solids, respectively, and prepare them into a metal salt solution A with a volume of 1.5L; Weigh 3mol Na ₂ CO ₃ , measure 55 mL of concentrated ammonia (the mass fraction of ammonia is 27%) ), sodium carbonate and ammonia water are prepared into lye B with a volume of 1.5L; 0.1mol Na ₂ HPO ₄ solid is weighed and prepared into a coating liquid C with a volume of 1 L.

In the reaction kettle, add 1L of deionized water as the bottom liquid, the reaction temperature is 55 ° C, the stirring speed is 800rpm/min, and the salt solution A and the lye B are added to the reaction kettle simultaneously by the peristaltic pump, and the flow rate of the salt solution A is 1.5 mL/min, the flow rate of lye B is 1.3-1.7mL/min, and the pH is controlled to 7.8 with lye. The reaction was stopped for 16 h, the reaction solution was filtered, the solid was washed with deionized water, and the carbonate precursor was obtained after vacuum drying at 80°C.

Take 1 g of carbonate precursor and disperse it in 30 mL of coating solution C, stir and react at room temperature for 40 min, and then filter, wash and dry by the aforementioned method to obtain a precursor coated with nickel phosphate. The precursor coated with nickel phosphate and Li ₂ CO ₃ were mixed with a mortar according to the ratio of Li:(Mn+Co+Ni)=1.55:1. The temperature was raised to 800°C for 20 hours, and then ground after natural cooling to obtain a lithium-rich manganese-based material coated with lithium phosphate.

Example 4

The value of x is 0.7, and the target chemical formula is 0.7Li ₂ MnO ₃ ·0.3LiNi _0.375 Co _0.25 Mn _0.375 O ₂ @Li ₃ PO _4. The preparation process is shown in Figure 1, and the specific parameters are as follows. Weigh 2.44mol MnSO ₄ , 0.22 mol CoSO ₄ and 0.34 mol NiSO ₄ solids, respectively, and prepare a metal salt solution A with a volume of 1.5 L; weigh 3 mol Na ₂ CO ₃ , measure 35 mL of concentrated ammonia (the mass fraction of ammonia) 27%), sodium carbonate and ammonia water were prepared into alkaline solution B with a volume of 1.5 L; 0.2 mol of (NH ₄ ) ₂ HPO ₄ was weighed to prepare a coating liquid C with a volume of 1 L.

In the reaction kettle, add 1L of deionized water as the bottom liquid, the reaction temperature is 60 ° C, and the stirring speed is 800 rpm/min. Simultaneously, the salt solution A and the lye B are added to the reaction kettle in parallel by the peristaltic pump, and the flow rate of the salt solution A is 1.3 mL/min, the flow rate of lye B is 1.1-1.5mL/min, and the pH is controlled to 8.1 with lye. The reaction was stopped for 18 h, the reaction solution was filtered, the solid was washed with deionized water, and the carbonate precursor was obtained after vacuum drying at 80°C.

Take 1 g of carbonate precursor and disperse it in 30 mL of coating solution C, stir and react at room temperature for 180 min, and then filter, wash and dry by the aforementioned method to obtain a precursor coated with nickel phosphate. The nickel phosphate-coated precursor and LiOH were mixed with a mortar according to the ratio of Li:(Mn+Co+Ni)=1.78:1, and the temperature was first kept at 550°C for 6h in a muffle furnace in an air atmosphere, and then heated to 850°C. Incubate at ℃ for 20h, and grind after natural cooling to obtain a lithium-rich manganese-based material coated with lithium phosphate.

Comparative ratio

In order to demonstrate the beneficial effect of Li-rich manganese-based cathode materials coated in situ with lithium phosphate, an uncoated Li-rich manganese-based comparative material was constructed.

The value of x is 0.5, and the synthetic target chemical formula is 0.5Li ₂ MnO ₃ ·0.5LiNi _1/3 Co _1/3 Mn _1/3 O ₂ material. Weigh 2mol MnSO ₄ , 0.5mol CoSO ₄ and 0.5mol NiSO ₄ solids, respectively, and prepare them into a metal salt solution A with a volume of 1.5 L; Weigh 3mol Na ₂ CO ₃ , measure 55 mL of concentrated ammonia (the mass fraction of ammonia is 27 %), sodium carbonate and ammonia water were prepared into alkaline solution B with a volume of 1.5 L; 0.1 mol of Na ₂ HPO ₄ was weighed to prepare a coating liquid C with a volume of 1 L.

In the reaction kettle, add 1L of deionized water as the bottom liquid, the reaction temperature is 55 ° C, the stirring speed is 800rpm/min, and the salt solution A and the lye B are added to the reaction kettle simultaneously by the peristaltic pump, and the flow rate of the salt solution A is 1.5 mL/min, the flow rate of lye B is 1.3-1.7mL/min, and the pH is controlled to 7.8 with lye. The reaction was stopped for 16 h, the reaction solution was filtered, the solid was washed with deionized water, and the carbonate precursor was obtained after vacuum drying at 80°C.

Take 1g of carbonate precursor and Li ₂ CO ₃ and mix them with a mortar according to the ratio of Li:(Mn+Co+Ni)=1.55:1, keep at 500℃ for 5h in an air atmosphere muffle furnace, and then heat up The temperature was kept at 800 °C for 20 h, and then ground after natural cooling to obtain a comparative lithium-rich manganese-based material.

test case

(1) Material characterization: The lithium-rich manganese-based material coated with lithium phosphate prepared in Example 3 was subjected to elemental analysis using ICP-AES, and it was found that the coating amount of Li ₃ PO ₄ was 0.61%. The lithium-rich manganese-based material coated with lithium phosphate prepared in Example 3 and the material of the comparative example were characterized by SEM. The results are shown in Figure 2, and both have good spherical morphology. The lithium-rich manganese-based material coated with lithium phosphate prepared in Example 3 and the material of the comparative example were characterized by TEM. As shown in Figure 3, there is a lithium phosphate coating layer of about 10 nm on the surface of the material of the example, while the comparative example The surface of the material is smooth. The lithium-rich manganese-based material coated with lithium phosphate prepared in Example 3 and the material of the comparative example were characterized by XRD, as shown in Figure 4, except for the superlattice peak at 20-30 degrees, both spectra were consistent with R- 3m space group structure, and no obvious impurity peak appears, indicating that the lithium-rich manganese-based material coated with lithium phosphate synthesized by the present invention is of high purity.

(2) Battery assembly: The lithium-rich manganese-based material coated with lithium phosphate prepared in Example 3 and the material of the comparative example were respectively mixed with Super P and PVDF according to a mass ratio of 8:1:1, pulped and coated, After vacuum drying, it was cut into 10mm diameter discs, and half-cells were assembled with metal lithium sheets as negative electrodes.

(3) Performance test: The above assembled half-cell was subjected to a cycle test at a rate of 0.5C (1C=250mAh g ^-1 ) in a voltage range of 2-4.8V. As shown in Figure 5, the phosphoric acid prepared in Example 3 The lithium-coated Li-rich manganese-based material has an initial discharge capacity of 234mAh g ^{-1 at 0.5C, a capacity of 189mAh g-1 after} 200 cycles, and a capacity retention rate of 80.7%. The initial discharge capacity of the comparative material at 0.5C is 237mAh g ^- 1- After ^1,200 cycles, the capacity is 173mAh g ^-1 , and the capacity retention rate is 72.9%, which indicates that the lithium phosphate-coated lithium-rich material prepared by the present invention has better capacity retention rate and cycle rate than the uncoated lithium-rich material performance. The rate test is shown in Figure 6. The discharge capacities of the lithium-rich manganese-based material coated with lithium phosphate prepared in Example 3 at 0.1C, 1C, 5C, and 10C are 274mAh g ^-1 , 210mAh g ^-1 , and 144mAh g, respectively. ^-1 and 108mAh g ^-1 , while the discharge capacities of the comparative materials were 271mAh g ^-1 , 189mAh g ^-1 , 118mAh g ^-1 and 70mAh g ^-1 , respectively, which indicated that the lithium phosphate-coated lithium-rich manganese prepared by the present invention The base material has better rate capability than the uncoated Li-rich material.

The above examples are only to illustrate the relevant principles and implementations, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made to the present invention without departing from the principles of the present invention shall be included in the present invention. within the scope of protection.

Claims (10)

1. a lithium-rich manganese-based positive electrode material covered by lithium phosphate in-situ, is characterized in that, the chemical formula of the lithium-rich manganese-based positive electrode material covered by described lithium phosphate is as shown in formula (I): xLi ₂ MnO ₃ ·(1-x)LiMO ₂ @Li ₃ PO ₄ (I); Wherein 0.3≤x≤0.7, M is selected from Ni, or at least one element of Ni, Co and Mn. 2 . The lithium-rich manganese-based cathode material in-situ coated with lithium phosphate according to claim 1 , wherein the mass fraction of lithium phosphate is 0.1%-5%, and the thickness of the coating layer is less than 30 nm. 3 . 3. the preparation method of the lithium-rich manganese-based positive electrode material of lithium phosphate in-situ coating according to claim 1, is characterized in that, comprises the following steps: Step 1: prepare one or more of nickel soluble salt, cobalt soluble salt and manganese soluble salt according to the metering ratio in the above chemical formula to prepare salt solution A with metal ion concentration of 1-5mol/L, prepare 0.5-2mol of sodium carbonate /L and ammonia water 0.05-5mol/L mixed solution B, prepare soluble phosphate solution C with a concentration of 0.01-0.5mol/L; Step 2: add deionized water to the reaction kettle, add solutions A and B to the reaction kettle in parallel, mechanically stir the reaction, control the temperature of the reaction solution to be constant, and control the pH to be constant by adjusting the flow rate of liquid B; Filtration, washing, and vacuum drying to obtain a lithium-rich manganese-based material precursor, TMCO ₃ , where TM is a transition metal; Step ₃ : Disperse the obtained precursor TMCO in solution C, stir and react at room temperature, filter, wash, and vacuum dry to obtain a precursor coated with nickel phosphate; Step 4: Mix the nickel phosphate-coated precursor obtained in step 3 and the lithium source uniformly, and calcine in an air atmosphere according to a set heating procedure to obtain a lithium-rich manganese-based cathode material coated with lithium phosphate in-situ. 4. the preparation method of the lithium-rich manganese-based positive electrode material coated by lithium phosphate in-situ according to claim 3, is characterized in that, in step 1, described soluble metal salt is sulfate, nitrate, chloride salt One or more of, the total metal concentration is 1-5mol/L, the sodium carbonate concentration is 0.5-5mol/L, the ammonia concentration is 0.05-5mol/L, and the soluble phosphate is lithium, sodium, potassium, ammonium phosphoric acid One or more of salt, hydrogen phosphate and dihydrogen phosphate, the concentration is 0.01-0.5mol/L, preferably 0.1mol/L. 5. the preparation method of the lithium-rich manganese-based positive electrode material of lithium phosphate in-situ coating according to claim 3, is characterized in that, in step 2, metal salt solution A is injected into reactor with 1-2mL/min uniform speed, solution B Inject the reaction kettle at a rate of 0.5-2.5mL/min to control the pH of the solution, the pH is controlled to be 7.3-8.3, and the mechanical stirring speed is 300-900rpm/min. 6 . The method for preparing a lithium-rich manganese-based positive electrode material coated in situ with lithium phosphate according to claim 3 , wherein in step 2, the reaction temperature of the reaction kettle is 40-70° C., and the reaction time is 10-40h. 7 . 7. the preparation method of the lithium-rich manganese-based positive electrode material of lithium phosphate in-situ coating according to claim 3, is characterized in that, in step 3, precursor TMCO ₃ The reaction time in soluble phosphate is 1min-24h, preferably 40min. 8. The preparation method of the lithium-rich manganese-based positive electrode material covered by lithium phosphate in-situ according to claim 3, wherein the charging ratio of the lithium source in step 4 is 100% to 110% of the stoichiometric ratio; _The source is one or both of _LiOH and Li2CO3. 9. The preparation method of the lithium-rich manganese-based positive electrode material coated with lithium phosphate in-situ according to claim 3, wherein the calcination procedure described in step 4 is that under the air atmosphere, the temperature is first kept at 500-550°C for 4- 6h, then heated to 750-900°C for 10-25h sintering, and then naturally cooled to room temperature to obtain a lithium-rich manganese-based cathode material in-situ coated with lithium phosphate. 10 . The method for preparing a lithium-rich manganese-based cathode material in-situ coated with lithium phosphate according to claim 9 , wherein the sintering temperature is 800° C. for 20 hours. 11 .

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