Silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material and preparation method thereof

Abstract

A silver particle-modified carbon-coated lithium manganese iron phosphate cathode material and a preparation method thereof relate to the field of material technology. The preparation method comprises the following steps: mixing and dissolving a lithium source, an iron source, a manganese source, and a phosphorus source to obtain a mixed solution; adding a silver ion solution to the mixed solution, performing a first hydrothermal reaction, and obtaining a reaction solution; mixing the reaction solution with a carbon source and a reducing agent, performing a second hydrothermal reaction, separating the solid phase, and obtaining a precursor; and sintering the precursor to obtain the lithium manganese iron phosphate cathode material. During the hydrothermal reaction stage, silver ions can inhibit the rapid growth of high-energy crystal faces, ultimately exposing more high-energy crystal faces. During the sintering stage, the silver ions are reduced to a single substance to modify the carbon layer, forming a "carbon-metal" composite conductive network and improving the conductivity of the carbon layer. The preparation method is simple and convenient to operate, and can quickly and efficiently form a nanoscale lithium manganese iron phosphate cathode material with better electrical properties and a [001] crystal plane orientation, thus having good application prospects.

Description

Technical Field

[0001] The present invention relates to the field of material technology, and in particular to a silver particle-modified carbon-coated lithium manganese iron phosphate positive electrode material and a preparation method thereof. Background Art

[0002] In recent years, with the continued high consumption of traditional energy (such as oil, natural gas, etc.) and the increasingly severe environmental problems it brings, the call for accelerated transformation of energy structure has become stronger. Among the many energy conversion and storage devices, lithium-ion batteries are being widely used in various fields due to their excellent electrochemical performance, high safety, good cost performance and long life, becoming the most promising solution. At the same time, LiMn x Fe 1-x PO4 e - / Li + The poor conductivity of LiMn is one of the reasons that hinder its development. x Fe 1-x Very low Li of PO4 + The ion diffusivity is mainly attributed to its one-dimensional diffusion (along the

[010] direction). Therefore, it is of great significance to design a LMFP material with a short (010) dimension to improve its rate capability and improve its electrical conductivity. Summary of the Invention

[0003] The purpose of the present invention is to provide a silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material and a preparation method thereof, which is simple and convenient to operate, can quickly and efficiently obtain a short (010) size LMFP material, and at the same time improve the conductive properties of its carbon layer, thereby obtaining better battery performance.

[0004] The embodiment of the present invention is achieved as follows:

[0005] A method for preparing a silver particle-modified carbon-coated lithium manganese iron phosphate positive electrode material, comprising:

[0006] Mixing and dissolving a lithium source, an iron source, a manganese source, and a phosphorus source to obtain a mixed solution;

[0007] adding a silver ion solution to the mixed solution to perform a first hydrothermal reaction to obtain a reaction solution;

[0008] The reaction solution is mixed with a carbon source and a reducing agent, subjected to a second hydrothermal reaction, and the solid phase is separated to obtain a precursor;

[0009] The precursor is sintered to obtain the lithium manganese iron phosphate positive electrode material.

[0010] A silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material is prepared by the above-mentioned method for preparing the silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material.

[0011] The beneficial effects of the embodiments of the present invention are:

[0012] The present invention provides a silver particle-modified carbon-coated lithium iron phosphate cathode material and a preparation method thereof. The preparation method comprises: mixing and dissolving a lithium source, an iron source, a manganese source, and a phosphorus source to obtain a mixed solution; adding a silver ion solution to the mixed solution and performing a first hydrothermal reaction to obtain a reaction solution; mixing the reaction solution with a carbon source and a reducing agent, performing a second hydrothermal reaction, separating the solid phase, and obtaining a precursor; and sintering the precursor to obtain the lithium iron phosphate cathode material. During the hydrothermal reaction, the silver ions inhibit the rapid growth of high-energy crystal planes, ultimately exposing more high-energy crystal planes. During the sintering stage, the silver ions are reduced to a single substance and modify the carbon layer, forming a "carbon-metal" composite conductive network and improving the conductivity of the carbon layer. This preparation method is simple and convenient to operate and can quickly and efficiently produce a nanoscale lithium iron phosphate cathode material with excellent electrical properties and a

[001] crystal plane orientation, thus having excellent application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0014] Figure 1 This is an SEM image of the silver particle-modified carbon-coated lithium manganese iron phosphate positive electrode material provided in Example 1 of the present invention;

[0015] Figure 2 This is an SEM image of the silver particle-modified carbon-coated lithium manganese iron phosphate positive electrode material provided in Example 2 of the present invention;

[0016] Figure 3 This is an SEM image of the silver particle-modified carbon-coated lithium manganese iron phosphate positive electrode material provided in Example 3 of the present invention;

[0017] Figure 4 SEM spectrum of the silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material provided in Comparative Example 1 of the present invention

[0018] Figure 5 This is a 3C charge-discharge capacity test chart of button batteries prepared from the positive electrode materials of Examples 1 to 4 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0019] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0020] The following specifically describes a silver particle-modified carbon-coated lithium manganese iron phosphate positive electrode material according to an embodiment of the present invention, as well as its preparation method and application.

[0021] The present invention provides a method for preparing a silver particle-modified carbon-coated lithium manganese iron phosphate cathode material, which comprises:

[0022] S1. The lithium source, iron source, manganese source, and phosphorus source are mixed and dissolved to obtain a mixed solution;

[0023] S2. A silver ion solution was added to the mixture to perform a first hydrothermal reaction to obtain a reaction solution;

[0024] S3. The reaction solution is mixed with a carbon source and a reducing agent, subjected to a second hydrothermal reaction, and the solid phase is separated to obtain a precursor;

[0025] S4. Sintering the precursor to obtain a lithium manganese iron phosphate positive electrode material.

[0026] In this preparation method, some silver ions are added before sintering. + The ionic radius (1.15 Å) is similar to that of other metal ions (such as Li + :0.76 Å,Fe 2+ :0.78 Å,Mn 2+ :0.83 Å) is significantly different and it is difficult to directly replace the Li⁺ or transition metal sites in phosphate cathode materials (such as LMFP), but it can act as a surface adsorbed ion and preferentially adsorb on the defects or step sites of a specific crystal plane. At the same time, since the

[010] crystal plane of lithium manganese iron phosphate is a high-energy crystal plane, its surface is rich in uncoordinated atoms and has a high surface charge density, Ag + Adsorption can neutralize local negative charges, reduce surface energy, inhibit the rapid growth of high-energy crystal planes, and ultimately expose more high-energy crystal planes.

[0027] Moreover, in the first hydrothermal reaction, as the lithium manganese iron phosphate crystals grow, the core gradually forms, and Ag + Due to the mismatch of ionic radius, Ag does not participate in crystal formation, resulting in + will always be adsorbed on the surface of the crystal. In the second hydrothermal reaction, due to the addition of the reducing agent, Ag + Reduced to silver particles by reducing agent. + Fe2+ 、Mn 2+ The oxidizing property of Ag is stronger. + It will be reduced first, so there is no need to worry about the Mn in the crystal 2+ 、Fe 2+ During the sintering process, the carbon source undergoes pyrolysis under high temperature and high pressure conditions to generate a carbon coating layer. Silver is evenly dispersed in the carbon layer to form a "carbon-metal" composite conductive network. Since the conductivity of silver is much higher than that of carbon materials (silver conductivity is about 6.3×10 7 S / m, carbon about 10 3 S / m), thus significantly improving the electrical conductivity of the carbon layer.

[0028] Furthermore, the iron source includes at least one of ferrous oxalate, ferrous chloride, and ferrous nitrate; the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, and lithium dihydrogen phosphate; the manganese source includes at least one of manganese oxalate, manganese tetraoxide, manganese sulfate, manganese acetate, and manganese nitrate; and the phosphorus source includes at least one of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, and lithium dihydrogen phosphate. It should be noted that the iron source is preferably a source of divalent iron ions, because trivalent iron ions have a reduction potential comparable to that of silver ions, which consumes the reducing agent and affects the accurate estimation of the reducing agent dosage.

[0029] Optionally, the molar ratio of Li:P:(Fe+Mn) provided by the lithium, iron, manganese, and phosphorus sources is 0.99-1.05:0.98-1.01:0.98-1.01. The molar ratio of Mn:Fe provided by the manganese and iron sources is (5:5)-(8:2). Within this ratio range, the overall performance of lithium manganese iron phosphate is better.

[0030] The mass of silver in the silver ion solution is 0.05% to 0.5% of the combined mass of the lithium, iron, manganese, and phosphorus sources. The silver ion content should not be too high, as it can cause silver ions to enter the core crystals, forming elemental doping and affecting the crystal structure of the lithium manganese iron phosphate. Within this range, the silver ion content is sufficient to induce crystallization and improve the conductivity of the carbon layer.

[0031] Furthermore, the temperature of the first hydrothermal reaction is 150~250℃ and the duration is 4~16h. Under the above reaction conditions, the crystallization process is more gentle and controllable, making Ag + It can better migrate to the crystal surface and continuously induce crystal face growth in a directional manner.

[0032] Optionally, the carbon source includes at least one of glucose, sucrose, polyvinyl pyrrolidone, or polyethylene glycol; and the total carbon content of the silver particle-modified carbon-coated lithium manganese iron phosphate cathode material is 1 wt% to 3 wt%. This ratio is conducive to forming a uniform carbon coating layer.

[0033] The reducing agent includes at least one of ascorbic acid, citric acid, oxalic acid and formic acid. The use of the reducing agent is mainly used to reduce silver ions to silver elemental particles. According to the reaction formula of the reducing agent and silver ions, the amount of the reducing agent is 1.01 to 1.05 times its theoretical amount. For example, taking ascorbic acid as an example, according to the redox reaction formula of silver ions and ascorbic acid, 0.5 mol of ascorbic acid is required to reduce 1 mole of silver ions. Then the theoretical amount of ascorbic acid is 0.5 mol, and the actual amount needs to be in excess of 1% to 5%. The actual amount of ascorbic acid is 0.505 to 0.525 mol. By selecting a mild reducing agent and controlling the amount of the reducing agent, Fe 2+ 、Mn 2+ The second hydrothermal reaction temperature is 150-250°C and the duration is 4-16 hours. Under these conditions, the reduction process is more gentle and controllable.

[0034] Furthermore, the precursor is sintered at a temperature of 400-800°C for 2-10 hours. Under these conditions, the carbon source can be better pyrolyzed to form a uniform carbon coating layer.

[0035] An embodiment of the present invention further provides a silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material, which is prepared by the above-mentioned method for preparing the silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material.

[0036] Furthermore, the lithium iron manganese phosphate cathode material is a

[001] -oriented nanomaterial with a rod-like structure. The rod-shaped lithium iron manganese phosphate crystal core grows in the

[001] direction and is coated with a silver-modified carbon coating. Compared to traditional materials, this lithium iron manganese phosphate cathode material has better rate performance and conductivity.

[0037] The features and performance of the present invention are further described in detail below with reference to the embodiments. Example 1

[0038] This embodiment provides a silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material, the preparation method of which is as follows:

[0039] S1. Mix and dissolve manganese sulfate, ferrous sulfate, phosphoric acid, and lithium hydroxide to obtain a mixed solution, wherein the ratio of manganese to iron is 6:4.

[0040] S2. Pour the mixed solution into an autoclave and add silver nitrate solution (the mass of silver should be 0.1% of the total mass of the lithium source, iron source, manganese source, and phosphorus source) to the mixed solution. Perform the first hydrothermal reaction at 160°C for 6 hours to obtain a reaction solution.

[0041] S3. The reaction solution was mixed with polyvinylpyrrolidone and ascorbic acid (the amount of ascorbic acid was 0.52 times the molar amount of silver ions) and subjected to a second hydrothermal reaction at 180°C for 12 hours. After completion of the reaction, the mixture was cooled to room temperature and centrifuged to obtain a precursor.

[0042] S4. The precursor was dried at 60°C for 6 h and then sintered at 650°C for 6 h to obtain a lithium manganese iron phosphate cathode material.

[0043] The SEM spectrum of the silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material prepared in this example is as follows: Figure 1 As shown, the overall structure is a rod-shaped structure, the growth direction of the rod-shaped lithium manganese iron phosphate crystal core is the

[001] direction, and the outside is coated with a silver-modified carbon coating layer, which has a better compaction density. Example 2

[0044] This embodiment provides a silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material, the preparation method of which is as follows:

[0045] S1. Mix and dissolve manganese oxalate, ferrous chloride, ammonium phosphate, and lithium nitrate to obtain a mixed solution, wherein the ratio of manganese to iron is 5:5.

[0046] S2. Pour the mixed solution into a high-pressure reactor and add silver nitrate solution (the mass of silver should be 0.05% of the total mass of the lithium source, iron source, manganese source, and phosphorus source) to the mixed solution. Perform the first hydrothermal reaction at 250°C for 4 hours to obtain a reaction solution.

[0047] S3. The reaction solution was mixed with glucose and ascorbic acid (the amount of ascorbic acid was 0.505 times the molar mass of silver ions) for a second hydrothermal reaction at 250°C for 4 h. After the reaction was complete, the mixture was cooled to room temperature and centrifuged to obtain a precursor.

[0048] S4. The precursor was dried at 60°C for 6 h and then sintered at 800°C for 2 h to obtain a lithium manganese iron phosphate cathode material.

[0049] The SEM spectrum of the silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material prepared in this example is as follows: Figure 2 As shown, the overall structure is a rod-shaped structure, the growth direction of the rod-shaped lithium manganese iron phosphate crystal core is the

[001] direction, and the outside is coated with a silver-modified carbon coating layer, which has a better compaction density. Example 3

[0050] This embodiment provides a silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material, the preparation method of which is as follows:

[0051] S1. Mix and dissolve manganese nitrate, ferrous nitrate, phosphoric acid, and lithium carbonate to obtain a mixed solution, wherein the ratio of manganese to iron is 7:3.

[0052] S2. The mixed solution was added to a high-pressure reactor. Silver nitrate solution (the mass of silver should be 0.5% of the total mass of the lithium source, iron source, manganese source, and phosphorus source) was added to the mixed solution. A first hydrothermal reaction was carried out at 150°C for 16 hours to obtain a reaction solution.

[0053] S3. The reaction solution was mixed with polyethylene glycol and ascorbic acid (the amount of ascorbic acid was 0.51 times the molar mass of the silver ion) and subjected to a second hydrothermal reaction at 150°C for 16 hours. After completion of the reaction, the mixture was cooled to room temperature and centrifuged to obtain a precursor.

[0054] S4. The precursor was dried at 60°C for 6 h and then sintered at 400°C for 10 h to obtain a lithium manganese iron phosphate cathode material.

[0055] The SEM spectrum of the silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material prepared in this example is as follows: Figure 3 As shown, the overall structure is a rod-shaped structure, the growth direction of the rod-shaped lithium manganese iron phosphate crystal core is the

[001] direction, and the outside is coated with a silver-modified carbon coating layer, which has a better compaction density. Example 4

[0056] This embodiment provides a silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material, the preparation method of which is as follows:

[0057] S1. Mix and dissolve manganese sulfate, ferrous sulfate, phosphoric acid, and lithium hydroxide to obtain a mixed solution, wherein the ratio of manganese to iron is 6:4.

[0058] S2. Pour the mixed solution into an autoclave and add silver nitrate solution (the mass of silver should be 0.1% of the total mass of the lithium source, iron source, manganese source, and phosphorus source) to the mixed solution. Perform the first hydrothermal reaction at 160°C for 6 hours to obtain a reaction solution.

[0059] S3. The reaction solution was mixed with polyvinylpyrrolidone and ascorbic acid (the amount of ascorbic acid was 0.52 times the molar mass of the silver ion) and subjected to a second hydrothermal reaction at 180°C for 12 hours. After completion of the reaction, the mixture was cooled to room temperature and centrifuged to obtain a precursor.

[0060] S4. The precursor was dried at 60°C for 6 hours, then sintered at 450°C for 2 hours, and then heated to 750°C and sintered for another 6 hours to obtain a lithium manganese iron phosphate cathode material.

[0061] Comparative Example 1

[0062] This comparative example provides a carbon-coated lithium manganese iron phosphate positive electrode material, and its preparation method is as follows:

[0063] S1. Mix and dissolve manganese sulfate, ferrous sulfate, phosphoric acid, and lithium hydroxide to obtain a mixed solution, wherein the ratio of manganese to iron is 6:4.

[0064] S2. The mixed solution was added to a high-pressure reactor and polyvinyl pyrrolidone was added for a hydrothermal reaction at 180°C for 12 h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged to obtain a precursor.

[0065] S4. The precursor was dried at 60°C for 6 hours and then sintered at 650°C for 6 hours to obtain lithium manganese iron phosphate cathode material. Figure 4 Without the participation of silver ions, lithium manganese iron phosphate has no ability to grow in a directional manner during the crystallization process, and the obtained positive electrode material is spherical as a whole and has uneven size, which is significantly different from the lithium manganese iron phosphate positive electrode material of the embodiment of the present invention.

[0066] Comparative Example 2

[0067] This comparative example provides a carbon-coated lithium manganese iron phosphate positive electrode material, and its preparation method is basically the same as that of Example 1, except that in step S2, the amount of silver is increased to 2%.

[0068] Comparative Example 3

[0069] This comparative example provides a carbon-coated lithium manganese iron phosphate positive electrode material, and its preparation method is basically the same as that of Example 1, except that in step S2, the temperature of the first hydrothermal reaction is increased to 350°C.

[0070] Comparative Example 4

[0071] This comparative example provides a carbon-coated lithium manganese iron phosphate positive electrode material, and its preparation method is basically the same as that of Example 1, except that in step S3, the amount of ascorbic acid is increased to 0.65 times the molar mass of silver ions.

[0072] Test Example 1

[0073] The lithium manganese iron phosphate positive electrode materials provided in Examples 1 to 4 and Comparative Examples 1 to 4 were used as battery positive electrode materials to assemble and test the compaction density, powder resistivity, and the rate of 0.1C, 1C and 3C (refer to Figure 5 The gram capacity under the conditions shown in Table 1 is tested.

[0074] Table 1. Test results of lithium manganese iron phosphate cathode materials

[0075] Compacted density (g / cc) Powder resistivity (Ω·cm) 0.1C discharge specific capacity (mAh / g) 1C discharge specific capacity (mAh / g) 3C discharge specific capacity (mAh / g) Example 1 2.273 24.166 152.045 148.808 146.627 Example 2 2.251 22.690 153.632 147.069 145.745 Example 3 2.204 23.896 148.378 146.393 144.527 Example 4 2.238 22.965 149.462 141.321 143.276 Comparative Example 1 2.221 35.432 149.828 138.299 132.464 Comparative Example 2 2.241 12.954 148.234 144.574 140.975 Comparative Example 3 2.214 24.451 148.724 140.540 137.538 Comparative Example 4 2.235 23.14 143.715 132.832 125.745

[0076] As can be seen from Table 1, the silver particle-modified carbon-coated lithium manganese iron phosphate positive electrode materials provided in Examples 1 to 4 of the present invention have a compacted density of 2.204 to 2.273 g / cm³ and a powder resistivity of 11.690 to 12.965 Ω·cm, significantly improving their electrical conductivity compared to the material not modified with silver ions (Comparative Example 1). Furthermore, compared to Comparative Example 1, their discharge specific capacity at a 0.1C rate is essentially the same, but their discharge specific capacity at high rates is significantly improved, and the difference becomes increasingly significant as the rate increases.

[0077] In contrast, in Comparative Example 2, we increased the amount of silver. It can be seen that although the powder resistivity is further reduced, the discharge capacity is reduced because part of the silver is doped in the lithium manganese iron phosphate.

[0078] In Comparative Example 3, the temperature of the first hydrothermal reaction was increased, and the crystals grew too fast, which also resulted in the effect of directional crystal growth being inferior to that of the embodiment. In addition, there was a certain degree of silver ion doping, which also led to a decrease in the discharge specific capacity.

[0079] In Comparative Example 4, more reducing agent was used, and some manganese and iron ions were reduced, resulting in a decrease in discharge capacity. The magnitude of the decrease was even greater than that in Comparative Example 1. Therefore, controlling the amount of reducing agent used in the present invention is very critical.

[0080] In summary, embodiments of the present invention provide a silver particle-modified carbon-coated lithium iron manganese phosphate cathode material and a preparation method thereof. The preparation method comprises: mixing and dissolving a lithium source, an iron source, a manganese source, and a phosphorus source to obtain a mixed solution; adding a silver ion solution to the mixed solution and performing a first hydrothermal reaction to obtain a reaction solution; mixing the reaction solution with a carbon source and a reducing agent, performing a second hydrothermal reaction, separating the solid phase, and obtaining a precursor; and sintering the precursor to obtain the lithium iron manganese phosphate cathode material. During the hydrothermal reaction stage, the silver ions can inhibit the rapid growth of high-energy crystal planes, ultimately exposing more high-energy crystal planes. During the sintering stage, the silver ions are reduced to a single substance and modify the carbon layer, forming a "carbon-metal" composite conductive network and improving the conductivity of the carbon layer. This preparation method is simple and convenient to operate and can quickly and efficiently form a nanoscale lithium iron manganese phosphate cathode material with excellent electrical properties and a

[001] crystal plane orientation, thus having excellent application prospects.

[0081] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material, characterized in that: include: Mixing and dissolving a lithium source, an iron source, a manganese source, and a phosphorus source to obtain a mixed solution; adding a silver ion solution to the mixed solution to perform a first hydrothermal reaction to obtain a reaction solution; The reaction solution is mixed with a carbon source and a reducing agent, subjected to a second hydrothermal reaction, and the solid phase is separated to obtain a precursor; Sintering the precursor to obtain the lithium manganese iron phosphate positive electrode material; The mass of silver in the silver ion solution is 0.05% to 0.5% of the total mass of the lithium source, the iron source, the manganese source, and the phosphorus source; The temperature of the first hydrothermal reaction is 150-250°C and the duration is 4-16 hours; According to the reaction formula of the reducing agent and silver ions, the amount of the reducing agent is 1.01 to 1.05 times its theoretical amount.

2. The preparation method according to claim 1, characterized in that The iron source includes at least one of ferrous oxalate, ferrous chloride and ferrous nitrate; the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate and lithium dihydrogen phosphate; the manganese source includes at least one of manganese oxalate, manganese tetraoxide, manganese sulfate, manganese acetate and manganese nitrate; and the phosphorus source includes at least one of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate and lithium dihydrogen phosphate.

3. The preparation method according to claim 1, characterized in that The molar ratio of Mn:Fe provided by the manganese source and the iron source is (5:5) to (8:2).

4. The preparation method according to claim 1, wherein The carbon source includes at least one of glucose, sucrose, polyvinyl pyrrolidone or polyethylene glycol; the total carbon content of the silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material is 1wt% to 3wt%.

5. The preparation method according to claim 1, characterized in that The reducing agent includes at least one of ascorbic acid, citric acid, oxalic acid and formic acid.

6. The preparation method according to claim 1, characterized in that The temperature of the second hydrothermal reaction is 150-250° C., and the duration is 4-16 hours.

7. The preparation method according to claim 1, wherein The precursor is sintered at a temperature of 400-800° C. for 2-10 h.

8. A silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material, characterized in that: The lithium manganese iron phosphate positive electrode material is prepared by the preparation method of the silver particle modified carbon-coated lithium manganese iron phosphate positive electrode material according to any one of claims 1 to 7.

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