Method for preparing carbon and lithium manganese phosphate double-coated lithium manganate

Abstract

The invention discloses a method for preparing carbon and lithium manganese phosphate double-coated lithium manganate, and relates to the technical field of lithium ion battery positive electrode materials, and the method comprises the following steps: S1, uniformly mixing lithium manganate and lithium phosphate solid phases to obtain a first mixture; s2, phosphoric acid is added into the first mixture, the liquid-phase phosphoric acid and the solid-phase first mixture are in contact and then react and release heat, and a lithium manganate material coated with lithium manganese phosphate is obtained; s3, performing solid-phase mixing on the lithium manganese phosphate coated lithium manganate material and a carbon source to obtain a second mixture; and S4, carrying out solid-phase sintering on the second mixture at 350-500 DEG C. The carbon and lithium manganese phosphate double-coated lithium manganate material obtained by the invention has the characteristics of long cycle life and good rate capability, ingeniously utilizes an exothermic reaction instantaneously initiated by solid-liquid contact, does not need additional heating equipment, and meanwhile, other products generated by the reaction are clean and easy to process.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode materials for lithium-ion batteries, and specifically to a method for preparing lithium manganese oxide double-coated with carbon and lithium manganese phosphate. Background Art

[0002] Since the spinel lithium manganese oxide LiMn2O4 cathode material with three-dimensional lithium-ion channels was first prepared by Hunter in 1981, due to its advantages such as low price, high potential, environmental friendliness, and high safety performance, lithium manganese oxide has been widely used in electric bicycles, 3C digital products and other fields.

[0003] Generally, commercial lithium iron phosphate is coated with carbon materials to improve the conductivity rate performance of the material. At the same time, after coating with carbon materials, the cathode material does not directly contact the electrolyte, thereby reducing side reactions and ultimately improving the cycle performance of the material. However, general commercial lithium manganese oxide materials do not have a carbon coating layer. The main reason is that the manganese in lithium manganese oxide is in the +3.5 valence state. When directly coated with a carbon source, the manganese will be oxidized, and ultimately impure LiMn2O4 will be obtained. The main reasons for the poor cycle performance of lithium manganese oxide materials are manganese dissolution and the Jahn-Teller effect. Therefore, coating the surface of lithium manganese oxide with carbon materials to isolate side reactions with the electrolyte, reduce manganese dissolution, and improve the cycle performance is an important topic. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing lithium manganese oxide double-coated with carbon and lithium manganese phosphate to solve the deficiencies in the above-mentioned prior art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A method for preparing lithium manganese oxide double-coated with carbon and lithium manganese phosphate, comprising the following steps:

[0006] S1: Solid-phase mix lithium manganese oxide and lithium phosphate evenly to obtain a first mixture;

[0007] S2: Add phosphoric acid to the first mixture. After the liquid-phase phosphoric acid contacts the solid-phase first mixture, a reaction will occur and heat will be released. The reaction equation is:

[0008] 12LiMn2O4 + 4Li3PO4 + 20H3PO4 = 24LiMnPO4 + 30H2O + 9O2↑;

[0009] To obtain lithium manganese oxide material coated with lithium manganese phosphate;

[0010] S3: Solid-phase mix the lithium manganese oxide material coated with lithium manganese phosphate and a carbon source to obtain a second mixture;

[0011] S4: Subject the second mixture to solid-phase sintering at 350 - 500 °C to obtain a lithium manganate material double-coated with carbon and lithium manganese phosphate.

[0012] Preferably, the molar ratio of the lithium manganate, lithium phosphate, and phosphoric acid satisfies (3, +∞):1:5.

[0013] Preferably, the carbon source is one or more of sucrose, glucose, fructose, citric acid, phenolic resin, polyvinyl alcohol, polyethylene glycol, starch, carbon black, acetylene black, graphite, graphene, and carbon nanotubes.

[0014] Preferably, if sucrose is selected as the single carbon source, the carbonization reaction of sucrose starts at 350 °C during the solid-phase sintering process.

[0015] Preferably, when using a mixed carbon source of glucose and carbon nanotubes, the mass ratio of the two is preferably 3:1.

[0016] Preferably, in step S1, solid-phase mixing is carried out using a high-speed ball mill, the rotation speed of the ball mill is controlled at 300 - 500 r / min, and the mixing time is 2 - 4 hours.

[0017] Preferably, during the addition of phosphoric acid, it is necessary to carry out the process in an inert gas atmosphere, such as an argon environment.

[0018] Preferably, the particle size range of the lithium manganate is 1 - 5 μm.

[0019] Preferably, during the solid-phase sintering process of step S4, the heating rate is controlled at 10 - 20 °C / min.

[0020] Preferably, when mixing the carbon source with the lithium manganate material coated with lithium manganese phosphate in step S3, the environmental humidity needs to be controlled at 20% - 30% RH.

[0021] In the above technical solution, a method for preparing lithium manganate double-coated with carbon and lithium manganese phosphate provided by the present invention:

[0022] Excellent product quality: The generated double-coated product physically isolates the electrolyte, inhibits manganese dissolution, improves thermal stability. The coated carbon layer improves the conductivity rate performance of the lithium manganate itself, and at the same time isolates the direct contact between lithium manganese phosphate and the electrolyte. Finally, the lithium manganate material double-coated with carbon and lithium manganese phosphate has a low manganese dissolution rate, long cycle life, and good rate performance;

[0023] Energy-saving and efficient: By cleverly utilizing the exothermic reaction triggered by the moment of solid-liquid contact, no additional heating equipment is required, greatly reducing energy consumption. At the same time, the reaction is rapid, and the entire coating process takes a short time, significantly improving production efficiency;

[0024] Process Simplification: Compared with the traditional liquid-phase coating process, multiple cumbersome steps are reduced, the process flow is simplified, and the production cost and the difficulty of quality control are lowered.

[0025] Environmentally Friendly: The remaining products generated by the reaction are clean and easy to handle, reducing environmental pollution and conforming to the development concept of green chemistry. Brief Description of the Drawings

[0026] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings.

[0027] Figure 1 XRD pattern of the lithium manganese phosphate-coated lithium manganese oxide material for the method of preparing lithium manganese oxide double-coated with carbon and lithium manganese phosphate according to the present invention;

[0028] Figure 2 Characteristic peaks of LMO and LMP of the lithium manganese oxide double-coated with carbon and lithium manganese phosphate for the method of preparing lithium manganese oxide double-coated with carbon and lithium manganese phosphate according to the present invention. Detailed Embodiments

[0029] To enable those skilled in the art to better understand the technical solutions of the present invention, the following will further introduce the present invention in detail in conjunction with the drawings.

[0030] Please refer to Figure 1-2 , a method for preparing lithium manganese oxide double-coated with carbon and lithium manganese phosphate includes the following steps:

[0031] S1: Solid-phase mix lithium manganese oxide and lithium phosphate evenly to obtain a first mixture;

[0032] S2: Add phosphoric acid to the first mixture. An oxidation-reduction reaction occurs on the surface between the liquid-phase phosphoric acid and the solid-phase first mixture. The reaction equation is:

[0033] 12LiMn2O4 + 4Li3PO4 + 20H3PO4 = 24LiMnPO4 + 30H2O + 9O2↑;

[0034] To obtain the lithium manganese phosphate-coated lithium manganese oxide material;

[0035] S3: Solid-phase mix the lithium manganese phosphate-coated lithium manganese oxide material with a carbon source to obtain a second mixture;

[0036] S4: Solid-phase sinter the second mixture at 350 - 500 °C to obtain the lithium manganese oxide double-coated with carbon and lithium manganese phosphate material.

[0037] The molar ratio of the lithium manganate, lithium phosphate, and phosphoric acid satisfies (3, +∞):1:5.

[0038] If sucrose is selected as the single carbon source, during the solid-phase sintering process, sucrose starts to undergo a carbonization reaction at 350°C. The carbon source is one or more of sucrose, glucose, fructose, citric acid, phenolic resin, polyvinyl alcohol, polyethylene glycol, starch, carbon black, acetylene black, graphite, graphene, and carbon nanotubes. If sucrose is selected as the single carbon source, during the solid-phase sintering process, sucrose starts to undergo a carbonization reaction at 350°C, gradually forming a carbon coating layer uniformly distributed on the surface of the material. The thickness of this carbon coating layer is about 5 - 10 nm as detected by high-resolution transmission electron microscopy, which can effectively improve the electronic conductivity of the material.

[0039] When using a mixed carbon source of glucose and carbon nanotubes, the mass ratio of the two is 3:1. When using a mixed carbon source of glucose and carbon nanotubes, a mass ratio of 3:1 is more appropriate. At this time, the prepared double-coated lithium manganate material not only has a good electron transport channel but also has a significantly enhanced structural stability. After being stored at a high temperature (60°C) for 10 days, its capacity attenuation rate is less than 5%.

[0040] In step S1, solid-phase mixing is carried out using a high-speed ball mill. The rotational speed of the ball mill is controlled at 300 - 500 r / min, and the mixing time is 2 - 4 hours. This can enable the lithium manganate and lithium phosphate particles to come into full contact and be mixed evenly. As observed by scanning electron microscopy, the dispersedness of the mixed particles is good, and the agglomeration phenomenon is significantly reduced, laying a foundation for the full progress of the subsequent reaction.

[0041] During the process of adding phosphoric acid, it needs to be carried out in an inert gas atmosphere, such as an argon environment. This can effectively prevent phosphoric acid from being oxidized during the addition process, ensure the stability of the reaction system, and thereby improve the purity and performance of the lithium manganate material coated with lithium manganese phosphate.

[0042] The particle size range of the lithium manganate is 1 - 5 μm. When the particle size of the lithium manganate is within this range, on the one hand, it can ensure its full reaction with lithium phosphate and phosphoric acid. On the other hand, after forming a double-coated structure, the specific surface area of the material is moderate, which is beneficial to improving the electrochemical performance of the material, and its first discharge specific capacity can reach more than 120 mAh / g.

[0043] During the solid-phase sintering process of step S4, the heating rate is controlled at 10–20°C / min. An appropriate heating rate can avoid internal structural defects of the material caused by too rapid temperature changes, ensure the full carbonization of the carbon source and the uniform formation of the lithium manganese phosphate coating layer, and enable the prepared double-coated lithium manganate material to have good consistency and stability.

[0044] When the carbon source is mixed with the lithium manganese oxide material coated with lithium manganese phosphate in step S3, the environmental humidity needs to be controlled at 20%-30% RH. A suitable humidity environment can prevent the carbon source (such as easily hygroscopic carbon sources like sugars) from agglomerating or deteriorating due to moisture absorption, ensuring the uniformity of mixing and the quality of the carbon coating layer formed during the subsequent sintering process. Through infrared spectroscopy analysis, for the products prepared under this humidity condition, the characteristic absorption peaks of the carbon coating layer are sharper and more stable.

[0045] The lithium manganese oxide raw material and lithium phosphate are mixed evenly in the solid phase to obtain a first mixture; phosphoric acid is added to the first mixture to obtain a lithium manganese oxide material LMO@LMP coated with lithium manganese phosphate LiMnPO4;

[0046] Lithium phosphate and phosphoric acid react on the surface of lithium manganese oxide to form lithium manganese phosphate in situ, which completely coats the lithium manganese oxide body. The reaction equation is:

[0047] 12LiMn2O4 + 4Li3PO4 + 20H3PO4 = 24LiMnPO4 + 30H2O + 9O2↑;

[0048] The generated first mixture is mixed with a phosphoric acid solution in a certain proportion. At the moment of solid-liquid contact, due to the special chemical properties of the first mixture and the chemical activity of phosphoric acid, a violent chemical reaction will be immediately triggered. This reaction is an exothermic reaction, and the heat released by the reaction is sufficient to maintain the continuous progress of the reaction without additional heating. During the reaction process, the first mixture reacts chemically with phosphoric acid to generate the required coating product, which uniformly coats the surface of the cathode active material. The entire reaction process is rapid and efficient, and the generated coating product has good consistency and stability. At the same time, in addition to the target coating product, the remaining by-products are H2O and O 2， The product is very clean, environmentally friendly, and easy to handle subsequently;

[0049] The lithium manganese oxide material coated with lithium manganese phosphate is mixed with the carbon source in the solid phase to obtain a second mixture;

[0050] The second mixture is subjected to solid-phase sintering at 350-500 °C to obtain a lithium manganese oxide material LMO@LMP@C coated with both carbon and lithium manganese phosphate. The in-situ coated lithium manganese phosphate on the surface of lithium manganese oxide prevents the direct contact between the electrolyte and lithium manganese oxide, reducing manganese dissolution. In addition, due to the high-voltage characteristics and olivine stable structure of lithium manganese phosphate, the cycle performance of lithium manganese oxide can be further improved. The carbon layer coated on the surface of lithium manganese phosphate improves the conductivity rate performance of the lithium manganese oxide body and isolates the direct contact between lithium manganese phosphate and the electrolyte. Finally, the lithium manganese oxide material coated with both carbon and lithium manganese phosphate has a low manganese dissolution rate, long cycle life, and good rate performance.

[0051] The molar ratio of the lithium manganate, lithium phosphate, and phosphoric acid satisfies (3, +∞):1:5. When the molar ratio of the lithium manganate, lithium phosphate, and phosphoric acid is 3:1:5, theoretically, lithium manganese phosphate with a complete stoichiometric ratio can be completely generated. Therefore, the setting ratio of the lithium manganate exceeds 3 to make the bulk lithium manganate exist.

[0052] Example 1:

[0053] (1) Solid-phase mix lithium manganate LiMn2O4 and lithium phosphate Li3PO4 evenly to obtain a first mixture; the molar ratio of the lithium manganate to the lithium phosphate is 4:1;

[0054] (2) Add phosphoric acid H3PO4 with a concentration of 60% to the first mixture and react at 25 °C. The molar ratio of the lithium phosphate to the phosphoric acid is 1:5. Obtain lithium manganese phosphate LiMnPO4-coated lithium manganate material LMO@LMP; the lithium phosphate and the phosphoric acid react on the surface of the lithium manganate to generate lithium manganese phosphate in situ and completely coat the bulk lithium manganate. The reaction equation is: 12LiMn2O4 + 4Li3PO4 + 20H3PO4 = 24LiMnPO4 + 30H2O + 9O2↑;

[0055] (3) Solid-phase mix the lithium manganese phosphate-coated lithium manganate material with sucrose to obtain a second mixture;

[0056] (4) Solid-phase sinter the second mixture at 350 °C to obtain a carbon and lithium manganese phosphate double-coated lithium manganate material LMO@LMP@C.

[0057] Test the XRD of the LMO@LMP material, and the results are as Figure 1 shown. The existence of the two phases of LMO and LMP can be seen. Test the TEM of the LMO@LMP@C material, and the results are as Figure 2 shown. Three regions of different materials can be seen. Region A is the bulk lithium manganate, region B is the lithium manganese phosphate, and region C is the carbon.

[0058] The prepared lithium manganese oxide double-coated with carbon and lithium manganese phosphate is mixed with a conductive agent and a binder to form a positive electrode paste. In the paste, the proportion of solid substances is as follows: the proportion of the active material is 97.2%, the proportion of the conductive agent (conductive carbon black, conductive graphite, conductive carbon nanotubes, graphene) is 1.7%, and the proportion of the binder (polyvinylidene fluoride) is 1.1%. The content of the solvent N-methylpyrrolidone is adjusted to make the solid content of the paste about 68%. The uniformly stirred paste is respectively coated on the surface of the current collector aluminum foil, dried, rolled and sliced to obtain a positive electrode sheet. A square full cell assembled with the above positive electrode sheet has a nominal capacity of 20 Ah, a thickness of 15 mm, a width of 119 mm, and a height of 208 mm. The battery is tested for the discharge capacity at 1C and 2C rates and the cycle performance of charging at 1C and discharging at 1C, and the ICP content of manganese element on the surface of the negative electrode is tested after the cycle test by disassembling the battery.

[0059] The capacity of the battery at 1C is 20.9 Ah, the capacity at 2C rate is 20.6 Ah, and the 2C / 1C rate retention is 98.6%. The retention rate after 1000 cycles of charging at 1C and discharging at 1C at room temperature is 80%, and the manganese element content on the surface of the negative electrode after the cycle is 800 ppm.

[0060] Example 2:

[0061] (1) Lithium manganese oxide LiMn2O4 and lithium phosphate Li3PO4 are mixed uniformly in solid phase to obtain a first mixture; the molar ratio of lithium manganese oxide to lithium phosphate is 5:1;

[0062] (2) Phosphoric acid H3PO4 with a concentration of 70% is added to the first mixture and reacted at 25 °C. The molar ratio of lithium phosphate to phosphoric acid is 1:5. Lithium manganese phosphate LiMnPO4-coated lithium manganese oxide material LMO@LMP is obtained; lithium phosphate and phosphoric acid react on the surface of lithium manganese oxide to form lithium manganese phosphate in situ and completely coat the lithium manganese oxide body. The reaction equation is: 12LiMn2O4 + 4Li3PO4 + 20H3PO4 = 24LiMnPO4 + 30H2O + 9O2↑;

[0063] (3) The lithium manganese phosphate-coated lithium manganese oxide material is mixed with sucrose in solid phase to obtain a second mixture;

[0064] (4) The second mixture is sintered in solid phase at 500 °C to obtain a lithium manganese oxide material LMO@LMP@C double-coated with carbon and lithium manganese phosphate.

[0065] The prepared lithium manganese oxide double-coated with carbon and lithium manganese phosphate is mixed with a conductive agent and a binder to form a positive electrode paste. In the paste, the proportion of solid substances is as follows: the proportion of the active material is 97.2%, the proportion of the conductive agent (conductive carbon black, conductive graphite, conductive carbon nanotubes, graphene) is 1.7%, and the proportion of the binder (polyvinylidene fluoride) is 1.1%. The content of the solvent N-methylpyrrolidone is adjusted to make the solid content of the paste about 68%. The uniformly stirred paste is respectively coated on the surface of the current collector aluminum foil, and after drying, it is roll-pressed and sliced to obtain a positive electrode sheet. A square full cell assembled with the above positive electrode sheet has a nominal capacity of 20 Ah, a thickness of 15 mm, a width of 119 mm, and a height of 208 mm. The battery is tested for the discharge capacity at 1C and 2C rates and the charge-discharge cycle performance at 1C charge and 1C discharge, and the ICP content of manganese elements on the negative electrode surface is tested after the cycle test.

[0066] The capacity of the battery at 1C is 20.8 Ah, the capacity at 2C rate is 20.5 Ah, and the 2C / 1C rate retention rate is 98.6%. The retention rate after 1000 cycles of charge-discharge at 1C at room temperature is 79%, and the content of manganese elements on the negative electrode surface after the cycle is 900 ppm.

[0067] Comparative Example 1:

[0068] Since directly coating the carbon material on lithium manganese oxide and sintering will oxidize manganese elements, it is impossible to obtain lithium manganese oxide material coated with carbon material.

[0069] The difference between Comparative Example 1 and Example 1 is that no coating layer is provided.

[0070] Experimental method: The uncoated lithium manganese oxide raw material is mixed with a conductive agent and a binder to form a positive electrode paste. In the paste, the proportion of solid substances is as follows: the proportion of the active material is 97.2%, the proportion of the conductive agent (conductive carbon black, conductive graphite, conductive carbon nanotubes, graphene) is 1.7%, and the proportion of the binder (polyvinylidene fluoride) is 1.1%. The content of the solvent N-methylpyrrolidone is adjusted to make the solid content of the paste about 68%. The uniformly stirred paste is respectively coated on the surface of the current collector aluminum foil, and after drying, it is roll-pressed and sliced to obtain a positive electrode sheet. A square full cell assembled with the above positive electrode sheet has a nominal capacity of 20 Ah, a thickness of 15 mm, a width of 119 mm, and a height of 208 mm. The battery is tested for the discharge capacity at 1C and 2C rates and the charge-discharge cycle performance at 1C charge and 1C discharge, and the ICP content of manganese elements on the negative electrode surface is tested after the cycle test.

[0071] The capacity of the battery at 1C is 20.7 Ah, the capacity at 2C rate is 20.2 Ah, and the 2C / 1C rate retention rate is 97.6%. The retention rate after 1000 cycles of charge-discharge at 1C at room temperature is 70%, and the content of manganese elements on the negative electrode surface after the cycle is 2100 ppm.

[0072] Comparative Example 2:

[0073] The difference between Comparative Example 2 and Example 2 is that: no carbon coating layer is provided, and the experimental method is as follows:

[0074] (1) Solid-phase mix lithium manganate LiMn2O4 and lithium phosphate Li3PO4 evenly to obtain a first mixture; the molar ratio of lithium manganate to lithium phosphate is 5:1;

[0075] (2) Add phosphoric acid H3PO4 to the first mixture, and the molar ratio of lithium phosphate to phosphoric acid is 1:5. Obtain lithium manganate phosphate LiMnPO4-coated lithium manganate material LMO@LMP; lithium phosphate and phosphoric acid react on the surface of lithium manganate to generate lithium manganate phosphate to be in-situ completely coated on the lithium manganate body, and the reaction equation is: 12LiMn2O4 + 4Li3PO4 + 20H3PO4 = 24LiMnPO4 + 30H2O + 9O2↑.

[0076] Mix the prepared lithium manganate phosphate-coated lithium manganate with a conductive agent and a binder to make a positive electrode paste. In the paste, the proportion of solid substances, the proportion of the active material is 97.2%, the proportion of the conductive agent (conductive carbon black, conductive graphite, conductive carbon nanotubes, graphene) is 1.7%, and the proportion of the binder (polyvinylidene fluoride) is 1.1%. Adjust the content of the solvent N-methylpyrrolidone to make the solid content of the paste about 68%. Coat the evenly stirred paste on the surface of the current collector aluminum foil respectively, and after drying, roll and slice to obtain a positive electrode sheet. Assemble a square full cell using the above positive electrode sheet. The nominal capacity of the square cell is 20 Ah, the thickness is 15 mm, the width is 119 mm, and the height is 208 mm. Conduct 1C and 2C rate discharge capacity tests and 1C charge and 1C discharge cycle performance tests on the battery, and disassemble the battery after the cycle test to test the ICP content of manganese elements on the negative electrode surface.

[0077] The capacity of the battery at 1C is 20.6 Ah, the capacity at 2C rate is 20.1 Ah, and the 2C / 1C rate retention rate is 97.6%. The retention rate after 1000 cycles of 1C charge and 1C discharge at room temperature is 75%, and the manganese element content on the negative electrode surface after the cycle is 1500 ppm.

[0078] Comparison table of Example 1, Example 2, Comparative Example 1 and Comparative Example 2:

[0079]

[0080]

[0081] From the perspective of combining Examples 1 and 2 with Comparative Examples 1 and 2, coating lithium manganese phosphate on the surface of lithium manganate cannot improve the rate performance of the battery, but can improve the cycling ability and reduce the manganese content deposited on the negative electrode surface after 1000 cycles, breaking through the technical bottleneck of manganese oxidation caused by direct carbon coating of lithium manganate. By using the LMP layer as a "buffer layer" to avoid direct contact between carbon and LMO and ensure the stable manganese valence state (+3.5), after further coating carbon materials on the surface of lithium manganese phosphate, the rate performance of the battery can be improved, while further enhancing the cycling performance of the battery and reducing the manganese content deposited on the negative electrode surface after 1000 cycles.

[0082] Comparison table of traditional process and the process of the present invention:

[0083] Defects of traditional process Innovative solution of this scheme Degree of performance improvement Direct carbon coating leads to manganese oxidation LMP layer isolates carbon from LMO Manganese dissolution ↓62%-67% High energy consumption in liquid-phase coating (requires heating) Driven by self-exothermic reaction Energy consumption ↓40% Serious by-product pollution Zero-pollution by-products Wastewater ↓80%

[0084] The generated H2O and O2 can be directly discharged without generating waste liquid containing phosphorus and manganese. Compared with the traditional coating process (requiring pickling and water washing), the wastewater discharge is reduced by 80%. The exothermic reaction triggered by the instantaneous contact of solid and liquid without external heating is used for in-situ reaction, and no additional heating equipment is required to maintain the spontaneous progress of the reaction, with energy saving of more than 40%. Through structural innovation, process optimization and material coordination, the industry problem of being difficult to balance high cycling stability and high rate performance of lithium manganate is broken through, providing a new path for the practical application of manganese-based cathode materials.

[0085] Only some exemplary embodiments of the present invention have been described by way of illustration. Undoubtedly, for those of ordinary skill in the art, the described embodiments can be modified in various different ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the protection scope of the claims of the present invention.

Claims

1. A method for preparing lithium manganate double-coated with carbon and lithium manganese phosphate, characterized by comprising the following steps: S1: Solid-phase mix lithium manganate and lithium phosphate evenly to obtain a first mixture; S2: Add phosphoric acid to the first mixture, and a redox reaction occurs on the surface between the liquid-phase phosphoric acid and the solid-phase first mixture to obtain a lithium manganate material coated with lithium manganese phosphate; S3: Solid-phase mix the lithium manganate material coated with lithium manganese phosphate and a carbon source to obtain a second mixture; S4: Solid-phase sinter the second mixture at 350-500 °C to obtain a lithium manganate material double-coated with carbon and lithium manganese phosphate.

2. The method for preparing lithium manganate double-coated with carbon and lithium manganese phosphate according to claim 1, characterized in that, In step S2, the concentration of phosphoric acid ≥ 60%, and the temperature ≥ 25 °C.

3. A method for preparing lithium manganese oxide double-coated with carbon and lithium manganese phosphate according to claim 1, characterized in that, The molar ratio of the lithium manganate, lithium phosphate, and phosphoric acid satisfies (3, +∞):1:

5.

4. A method for preparing lithium manganese oxide double-coated with carbon and lithium manganese phosphate according to claim 1, characterized in that, The carbon source is one or more of sucrose, glucose, fructose, citric acid, phenolic resin, polyvinyl alcohol, polyethylene glycol, starch, carbon black, acetylene black, graphite, graphene, and carbon nanotubes.

5. A method for preparing lithium manganese oxide double-coated with carbon and lithium manganese phosphate according to claim 4, characterized in that, If sucrose is selected as the single carbon source, during the solid-phase sintering process, sucrose undergoes a carbonization reaction at 350 °C.

6. A method for preparing lithium manganese oxide double-coated with carbon and lithium manganese phosphate according to claim 4, characterized in that, When using a mixed carbon source of glucose and carbon nanotubes, the mass ratio of the two is 3:

1.

7. A method for preparing lithium manganese oxide double-coated with carbon and lithium manganese phosphate according to claim 1, characterized in that, In step S1, the solid-phase mixing is carried out using a high-speed ball mill, the rotational speed of the ball mill is controlled at 300-500 r / min, and the mixing time is 2-4 hours.

8. A method for preparing lithium manganese oxide double-coated with carbon and lithium manganese phosphate according to claim 1, characterized in that, During the addition of phosphoric acid, it needs to be carried out in an inert gas atmosphere, such as an argon environment.

9. A method for preparing lithium manganate double-coated with carbon and lithium manganese phosphate according to claim 1, characterized in that, The particle size range of the lithium manganate is 1-5 μm.

10. A method for preparing lithium manganate double-coated with carbon and lithium manganese phosphate according to claim 1, characterized in that, When the carbon source is mixed with the lithium manganate material coated with lithium manganese phosphate in step S3, the environmental humidity needs to be controlled at 20%-30% RH.

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