Ternary cathode materials coated with manganese iron phosphate, preparation methods and applications

Abstract

This invention discloses a ternary cathode material coated with ferromanganese phosphate, its preparation method, and its application. The preparation method includes: pre-coating, where a carbon conductive mesh and a phosphorus source containing phosphate are coated onto the ternary cathode material to obtain a pre-coated ternary cathode material; and synthesis of the ferromanganese phosphate coating layer, where ferromanganese phosphate is synthesized using the phosphate groups in the phosphorus source of the pre-coated ternary cathode material as reaction sites to obtain the ferromanganese phosphate-coated ternary cathode material. This application pre-coats the ternary cathode material, resulting in a coating layer with a conductive mesh and rich in phosphate groups. The conductive mesh acts to fix the phosphorus source, and the phosphate groups serve as reaction sites for the synthesis of lithium manganese phosphate, enabling more uniform lithium manganese phosphate coating. This allows some ferromanganese phosphate to embed into the conductive mesh, increasing the coating strength of the coating layer. This not only isolates the ternary cathode material from the electrolyte but also improves the conductivity of the cathode material and the battery capacity.

Description

Technical Field

[0001] This invention relates to the field of lithium battery materials technology, and more specifically, to ternary cathode materials coated with manganese iron phosphate, their preparation methods, and applications. Background Technology

[0002] With the rapid development of new energy vehicles, the lithium-ion battery industry has also been propelled to the forefront. The cathode material determines the performance of a lithium-ion battery and is also the component with the highest cost. Currently, the main cathode materials include lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium iron phosphate. While lithium nickel cobalt manganese oxide is an excellent cathode material, it suffers from poor electrolyte compatibility. Surface coating technology is the most commonly used and effective improvement method, which can enhance the stability of the cathode material's surface structure and improve the battery's cycle performance under high voltage.

[0003] Lithium manganese iron phosphate (LMP) has a similar crystal structure to lithium iron phosphate (LFP) and is characterized by safety, long lifespan, and low cost. Its discharge voltage is synergistic with that of ternary materials. By coating the surface of ternary materials with LMP, the advantages of both can be maximized, and the inherent defects of ternary materials can be mitigated. Existing coating methods mostly involve mechanical grinding, using mechanical action to coat LMP particles onto the surface of ternary materials. For example, CN107546379A discloses a method for preparing LMP-coated ternary materials through mechanical fusion, in which nano-sized LMP particles are coated onto the surface of micron-sized ternary material particles through mechanical fusion. However, mechanical methods suffer from weak bonding between the coating layer and the core, making it difficult to achieve a tight and uniform coating.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a ternary cathode material coated with manganese iron phosphate, its preparation method, and its application.

[0006] This invention is implemented as follows:

[0007] In a first aspect, the present invention provides a method for preparing a ternary cathode material coated with manganese iron phosphate, comprising:

[0008] Pre-coating involves coating a carbon conductive mesh and a phosphorus source containing phosphate onto a ternary cathode material to obtain a pre-coated ternary cathode material.

[0009] The synthesis of the manganese iron phosphate coating layer involves using phosphate ions in the phosphorus source of the pre-coated ternary cathode material as the reaction site to synthesize manganese iron phosphate, thus obtaining the ternary cathode material coated with manganese iron phosphate.

[0010] In other embodiments of this application, the pre-coating includes phosphorus source coating and carbon conductive mesh coating;

[0011] The carbon conductive mesh coating is achieved by coating the phosphorus source surface with a carbon conductive mesh using a vacuum phase deposition coating method.

[0012] Preferably, the gases used in the vapor deposition are methane and acetylene;

[0013] More preferably, the molar ratio of methane to acetylene is 1:1 to 5:1.

[0014] In other embodiments of this application, the temperature of the carbon conductive mesh coating step is 300-500°C, the time is 2-10 hours, and the pressure is -18-22 kPa.

[0015] In other embodiments of this application, the phosphorus source coating is obtained by ball milling a mixture of ternary cathode material, phosphorus source, and dispersant.

[0016] Preferably, the mass ratio of the ternary cathode material, phosphorus source, and dispersant is (5-15):1:(6-20);

[0017] Preferably, the phosphorus source is at least one of ammonium polyphosphate, ammonium orthophosphate, diammonium hydrogen phosphate, or ammonium dihydrogen phosphate;

[0018] Preferably, the dispersant is one or both of ethanol and water;

[0019] Preferably, in the ball milling step, the ball milling speed is 200-500 r / min, the ball-to-material ratio is (10-50):1, and the ball milling time is 3-10 h;

[0020] More preferably, the ball milling is performed in a planetary ball mill;

[0021] Preferably, after the ball milling step, the material is dried at 60–100°C for 0.5–3 hours.

[0022] In other embodiments of this application, the pre-coating is performed by coating the ternary cathode material with a mixture of phosphorus source and carbon source;

[0023] Preferably, the ternary cathode material is placed in a spray coating device for spray coating, and then sintered.

[0024] Preferably, the coating solution used in the spray coating step is a mixed solution of organic matter and phosphoric acid and / or phosphate;

[0025] Preferably, the mass ratio of the organic matter to phosphoric acid and / or phosphate is 1:1 to 3;

[0026] Preferably, the mixed solution accounts for 1% to 15% of the mass of the ternary cathode material;

[0027] Preferably, the phosphate is at least one selected from ammonium dihydrogen phosphate, ammonium phosphate, and diammonium hydrogen phosphate;

[0028] Preferably, the organic compound is at least one of sucrose, glucose, and starch;

[0029] Preferably, the spraying time for the spray coating is 0.5 to 3 hours;

[0030] Preferably, the sintering is carried out at 300–600°C in an air atmosphere for 2–10 hours.

[0031] In other embodiments of this application, the synthesis of manganese ferric phosphate involves dispersing a pre-coated ternary cathode material in a solution containing divalent manganese ions and iron ions to obtain a ternary cathode material coated with manganese ferric phosphate.

[0032] Preferably, in the solution containing divalent manganese ions and iron ions, the concentration of manganese ions is 0.1–1 mol / L and the concentration of iron ions is 0.1–1 mol / L.

[0033] Preferably, the reaction time is 0.5 to 3 hours;

[0034] Preferably, the ternary cathode material is lithium nickel cobalt manganese oxide.

[0035] Secondly, the present invention provides a ternary cathode material coated with manganese iron phosphate, obtained according to any one of the foregoing embodiments.

[0036] Thirdly, the present invention provides a method for preparing a ternary cathode material coated with lithium manganese iron phosphate, wherein the ternary cathode material coated with lithium manganese iron phosphate as described in any of the foregoing embodiments is mixed and ground with a lithium source and a dispersant, dried and sintered to obtain a ternary cathode material coated with lithium manganese iron phosphate.

[0037] In other embodiments of this application, the drying is spray drying, wherein the inlet air temperature of the spray drying is 200-250°C and the outlet air temperature is 100-120°C;

[0038] Preferably, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium oxalate, and lithium acetate;

[0039] Preferably, the mixing and grinding time is 1 hour to 5 hours;

[0040] Preferably, the sintering is carried out under a protective atmosphere at 300–800°C for 2–10 hours;

[0041] More preferably, the protective atmosphere is a reducing atmosphere or argon.

[0042] Fourthly, the present invention provides an application of the manganese iron phosphate described in any of the foregoing embodiments in battery cathode materials.

[0043] The present invention has the following beneficial effects:

[0044] 1. Pre-coating ternary cathode material can obtain a coating layer with conductive mesh and rich in phosphate, which can be used as a phosphorus source for subsequent synthesis of lithium manganese iron phosphate. The conductive mesh plays the role of fixing the phosphorus source.

[0045] 2. Phosphate ions serve as the reaction site for the synthesis of lithium manganese iron phosphate, enabling more uniform coating of lithium manganese iron phosphate. The internal conductive network and the lithium manganese iron phosphate coating layer work together to isolate the ternary cathode material from the electrolyte and improve the conductivity of the cathode material and the battery capacity.

[0046] 3. Manganese and iron ions react with phosphate ions in the conductive network to form ferric manganese phosphate, which allows some of the ferric manganese phosphate to embed into the conductive network, thereby increasing the coating strength of the coating layer.

[0047] 4. An overly dense coating layer can affect lithium-ion transport. After the phosphate ions in the phosphorus source dissolve, the coating layer on the surface of the ternary cathode material becomes loose, forming lithium-ion channels and accelerating lithium-ion transport. Attached Figure Description

[0048] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 SEM image of the sample prepared in Example 1;

[0050] Figure 2 This is a TEM image of the sample prepared in Example 1. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0052] This embodiment provides a method for preparing a ternary cathode material coated with manganese iron phosphate, including:

[0053] Pre-coating involves coating a carbon conductive mesh and a phosphorus source containing phosphate onto a ternary cathode material to obtain a pre-coated ternary cathode material.

[0054] The synthesis of the manganese iron phosphate coating layer involves using phosphate ions in the phosphorus source of the pre-coated ternary cathode material as the reaction site to synthesize manganese iron phosphate, thus obtaining the ternary cathode material coated with manganese iron phosphate.

[0055] In this embodiment, pre-coating the ternary cathode material yields a coating layer with a conductive mesh and rich in phosphate ions. Manganese and iron ions react with phosphate ions in the conductive mesh to generate ferromanganese phosphate, allowing some of the ferromanganese phosphate to embed within the conductive mesh, thus increasing the coating strength. Phosphate ions serve as reaction sites for subsequent ferromanganese phosphate synthesis, facilitating uniform lithium iron phosphate coating. Furthermore, the dissolution of phosphate ions loosens the coating layer on the surface of the ternary cathode material, forming lithium-ion channels and accelerating lithium-ion transport. This prevents an overly dense coating layer from hindering lithium-ion transport. The conductive mesh acts as a fixation point for the phosphorus source and, together with the lithium iron phosphate coating layer, isolates the ternary cathode material from the electrolyte while improving the conductivity of the cathode material and the battery capacity. In this embodiment, the carbon conductive mesh is created by adjusting the coating methods and parameters to ensure a uniform coverage of pores on the carbon conductive layer, similar to a "mesh." This allows phosphate ions in the phosphorus source to react with manganese and iron ions, and also serves as a channel for phosphate dissolution or the entry of iron and manganese ions.

[0056] In the pre-coating step, the phosphorus source and the carbon conductive mesh can be coated separately to form two relatively independent coating layers, or they can be coated in a mixed layer in which the carbon conductive layer forms a grid-like structure and the phosphorus source fills the gaps in the grid.

[0057] In other embodiments of this application, the pre-coating includes phosphorus source coating and carbon conductive mesh coating;

[0058] The carbon conductive mesh coating is achieved by coating the phosphorus source surface with a carbon conductive mesh using a vacuum phase deposition coating method.

[0059] In some preferred embodiments, the gases used for the vapor deposition are methane and acetylene;

[0060] In some preferred embodiments, the molar ratio of methane to acetylene is 1:1 to 5:1.

[0061] The phosphorus source and the carbon conductive mesh are coated separately. The phosphorus source is coated in the inner layer, and the carbon conductive mesh is placed on the outer layer, forming two relatively independent coating layers. The phosphorus source can be exposed to the outside through the mesh of the carbon conductive mesh, which facilitates the subsequent synthesis of manganese iron phosphate.

[0062] In this embodiment, the carbon conductive mesh is coated using vapor phase deposition, which allows for relatively uniform coating of the carbon conductive mesh.

[0063] In other embodiments of this application, the temperature of the carbon conductive mesh coating step is 300-500°C, the time is 2-10 hours, and the pressure is -18-22 kPa.

[0064] Since the coating in this embodiment is a carbon conductive mesh rather than a carbon conductive layer, it is necessary to consider both the uniformity of the carbon layer coverage and the thickness of the carbon layer to form a "carbon conductive mesh" and a "non-carbon conductive layer". Therefore, it is necessary to adjust the deposition parameters to optimize the structure of the carbon conductive mesh.

[0065] In other embodiments of this application, the phosphorus source coating is obtained by ball milling a mixture of ternary cathode material, phosphorus source, and dispersant.

[0066] In some preferred embodiments, the mass ratio of the ternary cathode material, phosphorus source, and dispersant is (5-15):1:(6-20);

[0067] In some preferred embodiments, the phosphorus source is at least one of ammonium polyphosphate, ammonium orthophosphate, diammonium hydrogen phosphate, or ammonium dihydrogen phosphate;

[0068] In some preferred embodiments, the dispersant is one or both of ethanol and water;

[0069] In some preferred embodiments, during the ball milling step, the ball milling speed is 200-500 r / min, the ball-to-material ratio is (10-50):1, and the ball milling time is 3-10 h.

[0070] In some preferred embodiments, the ball milling is performed in a planetary ball mill;

[0071] In some preferred embodiments, the ball milling step is followed by drying at 60–100°C for 0.5–3 hours.

[0072] In this embodiment, the phosphorus source can be ammonium phosphate, such as ammonium polyphosphate. As a phosphorus source, ammonium polyphosphate will not only cause phosphate ions to dissolve, making the original coating layer on the surface of lithium nickel cobalt manganese oxide loose and forming lithium ion channels, but the decomposition of ammonium polyphosphate will also increase the number of lithium ion channels and accelerate the transport of lithium ions.

[0073] In other embodiments of this application, the pre-coating is performed by coating the ternary cathode material with a mixture of phosphorus source and carbon source;

[0074] In some preferred embodiments, the ternary cathode material is placed in a spray coating device for spray coating, and then sintered.

[0075] In some preferred embodiments, the coating solution used in the spray coating step is a mixed solution of organic matter and phosphoric acid and / or phosphate;

[0076] In some preferred embodiments, the mass ratio of the organic matter to phosphoric acid and / or phosphate is 1:1 to 3;

[0077] In some preferred embodiments, the mixed solution accounts for 1% to 15% of the mass of the ternary cathode material;

[0078] In some preferred embodiments, the phosphate is at least one of ammonium dihydrogen phosphate, ammonium phosphate, and diammonium hydrogen phosphate;

[0079] In some preferred embodiments, the organic compound is at least one of sucrose, glucose, and starch;

[0080] In some preferred embodiments, the spraying time for the spray coating is 0.5 to 3 hours;

[0081] Preferably, the sintering is carried out at 300–600°C in an air atmosphere for 2–10 hours.

[0082] In this embodiment, a mixture of phosphorus source and carbon source is used to coat the ternary cathode material to obtain a mixed layer of carbon conductive mesh and phosphorus source. The carbon conductive mesh structure in this embodiment is relatively three-dimensional, which allows the phosphorus source to be relatively firmly fixed in the network of carbon conductive mesh.

[0083] In other embodiments of this application, the synthesis of manganese ferric phosphate involves dispersing a pre-coated ternary cathode material in a solution containing divalent manganese ions and iron ions to obtain a ternary cathode material coated with manganese ferric phosphate.

[0084] In some preferred embodiments, the concentration of manganese ions in the solution containing divalent manganese ions and iron ions is 0.1–1 mol / L, and the concentration of iron ions is 0.1–1 mol / L.

[0085] In some preferred embodiments, the reaction time is 0.5 to 3 hours;

[0086] In some preferred embodiments, the ternary cathode material is lithium nickel cobalt manganese oxide.

[0087] In this embodiment, uniformly distributed phosphate ions are used as reaction sites for the synthesis of lithium manganese iron phosphate, which can achieve more uniform lithium manganese iron phosphate coating. The internal conductive mesh and the lithium manganese iron phosphate coating layer work together to isolate lithium nickel cobalt manganese oxide from the electrolyte and improve the conductivity of the cathode material and the battery capacity.

[0088] Secondly, the present invention provides a ternary cathode material coated with manganese iron phosphate, obtained according to any one of the foregoing embodiments.

[0089] Thirdly, the present invention provides a method for preparing a ternary cathode material coated with lithium manganese iron phosphate, wherein the ternary cathode material coated with lithium manganese iron phosphate as described in any of the foregoing embodiments is mixed and ground with a lithium source and a dispersant, dried and sintered to obtain a ternary cathode material coated with lithium manganese iron phosphate.

[0090] In other embodiments of this application, the drying is spray drying, wherein the inlet air temperature of the spray drying is 200-250°C and the outlet air temperature is 100-120°C;

[0091] In some preferred embodiments, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium oxalate, and lithium acetate;

[0092] In some preferred embodiments, the mixing and grinding time is 1 hour to 5 hours;

[0093] In some preferred embodiments, the sintering is carried out under a protective atmosphere at 300–800°C for 2–10 hours;

[0094] In some preferred embodiments, the protective atmosphere is a reducing atmosphere or argon.

[0095] Fourthly, the present invention provides an application of the manganese iron phosphate described in any of the foregoing embodiments in battery cathode materials.

[0096] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0097] Example 1:

[0098] Step 1: Take 50g of lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2) was added to a mixture of 5g ammonium polyphosphate and 55g dispersant, and the mixture was ball-milled in a planetary ball mill. The dispersant was ethanol, the milling speed was 300 r / min, the ball-to-material ratio was 15:1, and the milling time was 3 h. After ball milling, the mixture was dried at 60℃ for 2 h to obtain the ammonium polyphosphate-coated ternary cathode material.

[0099] Step 2: Subsequently, a conductive carbon mesh is coated onto the surface of the above-mentioned positive electrode material by vacuum phase deposition. The gas used is a mixture of methane and acetylene with a molar ratio of 2:1. The coating temperature is 400℃, the time is 2h, and the pressure is -20kpa.

[0100] Step 3: Under magnetic stirring, the pre-coated ternary cathode material was added to 500 ml of a solution containing divalent manganese and iron, with a manganese and iron ion concentration of 0.5 mol / L. The reaction was allowed to proceed for 2 hours to obtain a cathode material coated with manganese iron phosphate. The phosphorus, iron, and manganese content in the material was measured using ICP. After filtration, the mixture was ground with lithium hydroxide and ethanol at a stoichiometric ratio of Fe:Mn:Li = 0.8:0.2:1 for 3 hours, with a solid-liquid volume ratio of 1:1. The above mixture was then spray-dried to obtain a dry powder. The spray drying inlet air temperature was 200℃, and the outlet air temperature was 100℃. The dry powder was sintered at 700℃ for 8 hours under argon atmosphere. The sintered product was then pulverized to obtain a ternary cathode material coated with lithium manganese iron phosphate. The SEM and TEM characterization results are as follows: Figure 1 and Figure 2 As shown.

[0101] The obtained positive electrode material was mixed with acetylene black and polyvinylidene fluoride at a mass ratio of 9:0.2:0.3, with N-methylpyrrolidone as a dispersant. After uniform mixing, the mixture was coated onto aluminum foil, dried in a forced-air environment at 80°C for 5 hours, and then vacuum dried at 100°C for 12 hours. Using PP as the separator, 1M lithium hexafluorophosphate (EC / DMC / DEC, volume ratio 1:1:1) as the electrolyte, and lithium metal sheet as the negative electrode, a button cell was assembled with the positive electrode made of the above materials and subjected to constant current charge-discharge tests at a voltage of 2.0–4.3V.

[0102] Example 2:

[0103] This embodiment provides a battery, which differs from the battery preparation method provided in Embodiment 1 in that, in Embodiment 2, step 2 specifically includes: spraying a coating solution to pre-coat the ternary cathode material. 100g of the ternary cathode material is placed in a spray coating device for spray coating, with a spraying time of 0.5h. The coating solution is a mixed solution of 3g ammonium dihydrogen phosphate and 2g sucrose. The coated ternary cathode material is sintered at 400℃ in air atmosphere for 3h to obtain the pre-coated ternary cathode material.

[0104] Example 3:

[0105] This embodiment provides a battery whose preparation method differs from that of the battery provided in Embodiment 2. In Embodiment 3, the amounts of ternary cathode material, phosphorus source, and organic matter are adjusted to obtain a pre-coated ternary cathode material with the same carbon and phosphoric acid content as in Embodiment 1.

[0106] Example 4:

[0107] This embodiment provides a battery, which differs from the battery preparation method provided in Embodiment 1 in that, in Embodiment 4, the coating time in step 2 is 5 hours and the pressure is -20 kPa.

[0108] Example 5:

[0109] This embodiment provides a battery, which differs from the battery preparation method provided in Embodiment 1 in that, in Embodiment 5, the coating time in step 2 is 10 hours and the pressure is -20 kPa.

[0110] Example 6:

[0111] This embodiment provides a battery, which differs from the battery preparation method provided in Embodiment 1 in that, in Embodiment 6, step 1 involves lithium nickel cobalt manganese oxide (LiNiO2). 0.8 Co 0.1 Mn 0.1 The amount of O2 added is 25g.

[0112] Example 7:

[0113] This embodiment provides a battery, which differs from the battery preparation method provided in Embodiment 1 in that, in Embodiment 6, step 1 involves lithium nickel cobalt manganese oxide (LiNiO2). 0.8 Co 0.1 Mn 0.1 The amount of O2 added is 75g.

[0114] Example 8:

[0115] This embodiment provides a battery, which differs from the battery preparation method provided in Embodiment 2 in that, in Embodiment 8, the coating solution in step 1 is a mixed solution of 2g ammonium dihydrogen phosphate and 2g sucrose.

[0116] Example 9:

[0117] This embodiment provides a battery, which differs from the battery preparation method provided in Embodiment 2 in that, in Embodiment 9, the coating solution in step 1 is a mixed solution of 6g ammonium dihydrogen phosphate and 2g sucrose.

[0118] Comparative Example 1:

[0119] Comparative Example 1 provides a battery whose preparation method differs from that of the battery provided in Example 1 in that, in Comparative Example 1, ammonium polyphosphate is not added in step 1, and phosphorus source is added in step 3 according to the stoichiometric ratio of lithium manganese iron phosphate. After sintering, a ternary cathode material coated with lithium manganese iron phosphate is obtained.

[0120] Comparative Example 2

[0121] Compared with Example 1, Comparative Example 2 differs in that it does not include steps 1 and 2 of Example 1, i.e., it does not perform pre-coating treatment of the ternary cathode material. In step 3, a phosphorus source is added according to the stoichiometric ratio of lithium manganese iron phosphate, and after sintering, a ternary cathode material coated with lithium manganese iron phosphate is obtained.

[0122] Comparative Example 3

[0123] Compared to Example 1, Comparative Example 3 differs in that it does not include steps 1 and 2 of Example 1, i.e., it does not undergo pre-coating treatment of the ternary cathode material. In step 3, a phosphorus source in the stoichiometric ratio of lithium manganese iron phosphate and sucrose at a mass fraction of 3% of lithium manganese iron phosphate are added, and after sintering, a ternary cathode material coated with lithium manganese iron phosphate is obtained. The battery performance of Examples 1-9 and Comparative Examples 1-3 was tested, and the results are shown in Table 1.

[0124] Table 1 compares the performance of the products obtained from each embodiment and comparative example.

[0125]

[0126] As shown in the table above, compared with the battery prepared by directly coating lithium manganese iron phosphate cathode material, the battery prepared by the cathode material coated with lithium manganese iron phosphate provided in the embodiments of the present invention has better cycle performance and better cycle stability, indicating that the lithium manganese iron phosphate coating layer is tightly bonded to the ternary material.

[0127] Furthermore, compared to spray coating, carbon layers coated by vapor deposition are more stable and have certain advantages in terms of conductivity and specific capacity. During the vapor deposition process, the deposition time is particularly important. If the deposition time is too long and the carbon coating layer is too thick, the conductivity will be enhanced but the specific capacity will be reduced.

[0128] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a manganese iron phosphate-coated ternary cathode material, characterized in that, The method comprises the following steps: Pre-coating, coating the carbon conductive network and the phosphorus source containing phosphate on the ternary positive electrode material to obtain a pre-coated ternary positive electrode material; Synthesis of manganese iron phosphate coating layer, dispersing the pre-coated ternary positive electrode material in a solution containing divalent manganese ions and iron ions to react, and using the phosphate in the phosphorus source of the pre-coated ternary positive electrode material as a reaction site to synthesize manganese iron phosphate, thereby obtaining a manganese iron phosphate coated ternary positive electrode material; The pre-coating includes phosphorus source coating and carbon conductive network coating; the carbon conductive network coating is performed by vacuum vapor deposition coating on the surface of the phosphorus source. Alternatively, the pre-coating is performed by using a mixture of the phosphorus source and the carbon source to coat the ternary positive electrode material.

2. The method of claim 1, wherein the manganese iron phosphate-coated ternary cathode material is prepared by the steps of: The gas used in the vapor deposition is methane and acetylene. ​ 3. The method for preparing the ternary cathode material coated with manganese iron phosphate according to claim 2, characterized in that, The molar ratio of methane to acetylene is 1:1 to 5:

1.

4. The method for preparing the ternary cathode material coated with manganese iron phosphate according to claim 1, characterized in that, The temperature of the carbon conductive network coating step is 300-500℃, the time is 2-10h, and the pressure is 18-22kpa.

5. The method for preparing the ternary cathode material coated with manganese iron phosphate according to claim 1, characterized in that, The phosphorus source coating is performed by mixing the ternary positive electrode material, the phosphorus source, and a dispersant, and then performing ball milling.

6. The method of claim 5, wherein the manganese iron phosphate-coated ternary cathode material is prepared by the steps of: The mass ratio of the ternary positive electrode material, the phosphorus source, and the dispersant is (5-15):1:(6-20). ​ 7. The method of claim 5, wherein the manganese iron phosphate-coated ternary cathode material is prepared by the steps of: The phosphorus source is at least one of ammonium polyphosphate, ammonium orthophosphate, diammonium hydrogen phosphate, or ammonium dihydrogen phosphate. ​ 8. The method for preparing the ternary cathode material coated with manganese iron phosphate according to claim 5, characterized in that, The dispersant is one or both of ethanol and water.

9. The method for preparing the ternary cathode material coated with manganese iron phosphate according to claim 5, characterized in that, In the ball milling step, the ball milling speed is 200-500 r / min, the ball-to-material ratio is (10-50):1, and the ball milling time is 3-10 h.

10. The method for preparing the ternary cathode material coated with manganese iron phosphate according to claim 9, characterized in that, The ball milling is performed in a planetary ball mill.

11. The method for preparing the ternary cathode material coated with manganese iron phosphate according to claim 9, characterized in that, After the ball milling step, drying is performed at 60-100℃ for 0.5-3 h.

12. The method of claim 1, wherein the manganese iron phosphate-coated ternary cathode material is prepared by the steps of: The ternary positive electrode material is coated by using a mixture of the phosphorus source and the carbon source, the ternary positive electrode material is placed in a spray coating device, spray coating is performed, and then sintering is performed. ​ 13. The method of claim 12, wherein the manganese iron phosphate-coated ternary cathode material is prepared by the steps of: In the spray coating step, the coating solution used is a mixed solution of an organic matter and phosphoric acid and / or a phosphate. ​ 14. The method of claim 13, wherein the manganese iron phosphate-coated ternary cathode material is prepared by the steps of: The mass ratio of the organic matter to phosphoric acid and / or the phosphate is 1:1 to 3. ​ 15. The method of claim 13, wherein the manganese iron phosphate-coated ternary cathode material is prepared by the steps of: The mixed solution accounts for 1% to 15% of the mass of the ternary positive electrode material. ​ 16. The method of claim 13, wherein the manganese iron phosphate-coated ternary cathode material is prepared by the steps of: The phosphate is at least one of ammonium dihydrogen phosphate, ammonium phosphate, and diammonium hydrogen phosphate. ​ 17. The method of claim 13, wherein the manganese iron phosphate-coated ternary cathode material is prepared by the steps of: The organic matter is at least one of sucrose, glucose, and starch. ​ 18. The method of claim 12, wherein the manganese iron phosphate-coated ternary cathode material is prepared by the steps of: The spray coating time is 0.5-3 h. ​ 19. The method of claim 12, wherein the manganese iron phosphate-coated ternary cathode material is prepared by the steps of: The sintering is performed at 300-600℃ in an air atmosphere for 2-10 h. ​ 20. The method of claim 1, wherein the preparation of the iron-manganese phosphate-coated ternary cathode material is characterized by, In the solution containing divalent manganese ions and iron ions, the concentration of manganese ions is 0.1-1 mol / L, and the concentration of iron ions is 0.1-1 mol / L.

21. The method of claim 1, wherein the preparation of the iron-manganese phosphate-coated ternary cathode material is characterized by, The reaction time is 0.5-3 h.

22. The method of claim 1, wherein the manganese iron phosphate-coated ternary cathode material is prepared by the steps of: The ternary positive electrode material is lithium nickel cobalt manganese oxide. ​ 23. A manganese iron phosphate-coated ternary cathode material, characterized in that, Obtained according to the method of any one of claims 1-22.

24. A method for preparing a lithium iron manganese phosphate-coated ternary cathode material, characterized in that, The manganese iron phosphate coated ternary positive electrode material of any one of claims 1-22 is mixed with a lithium source and a dispersant, ground, dried, and sintered to obtain a manganese iron lithium phosphate coated ternary positive electrode material.

25. The method of claim 24, wherein the lithium iron manganese phosphate-coated ternary cathode material is prepared by the steps of: The drying is spray drying, the inlet air temperature of the spray drying is 200-250℃, and the outlet air temperature is 100-120℃. ​ 26. The method of claim 24, wherein the lithium iron manganese phosphate-coated ternary cathode material is prepared by the steps of: The lithium source is one or more of lithium carbonate, lithium hydroxide, lithium oxalate, and lithium acetate. ​ 27. The method of claim 24, wherein the lithium iron manganese phosphate-coated ternary cathode material is prepared by the steps of: The mixing and grinding time is 1-5 h. ​ 28. The method of claim 24, wherein the lithium iron manganese phosphate-coated ternary cathode material is prepared by the steps of: The sintering is performed in a protective atmosphere at 300-800℃ for 2-10 h. ​ 29. The method of claim 28, wherein the lithium iron manganese phosphate-coated ternary cathode material is prepared by a process comprising: mixing a lithium source, a manganese source, a transition metal source, and a phosphate source to form a mixture; and heating the mixture to form the lithium iron manganese phosphate-coated ternary cathode material. The protective atmosphere is a reducing atmosphere or argon.

30. Use of the manganese iron phosphate-coated ternary cathode material of claim 23 in a battery cathode material.

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