Lithium iron manganese phosphate positive electrode material and preparation method thereof

Abstract

The application relates to a lithium manganese iron phosphate positive electrode material and a preparation method, and belongs to the technical field of battery positive electrode materials. The lithium manganese iron phosphate positive electrode material comprises a lithium manganese iron phosphate material and a carbon-coated material, the lithium manganese iron phosphate material is expressed as LiMn x‑ y Fe 1‑x M y PO4, M is a doping element, the carbon-coated material comprises a carbon source A and a carbon source B, the carbon source A is carborane or a carborane derivative. The doping element can inhibit charge-discharge lattice distortion and strengthen the rigidity of the olivine structure. The carborane or carborane derivative contained in the carbon-coated material has a cage structure, can controllably release B and C active substances in a sintering process, realizes uniform doping and coating, and avoids local agglomeration. After the cage structure is decomposed, a cage-like, hollow fragmented carborane skeleton is left, a loose and elastic composite coating layer is formed, and the cycle stability of the battery is improved.

Description

Technical Field

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

[0002] Lithium manganese iron phosphate (LFP) possesses a high voltage plateau, energy density, and low-temperature performance, making it a promising cathode material for upgrading lithium iron phosphate (LFP). However, LFP currently faces the following challenges: Severe manganese leaching and lattice distortion: During charge and discharge, manganese ions undergo strong Janus-Taylor distortion, causing lattice collapse and continuous leaching of manganese ions, which then react with the electrolyte, leading to high-temperature cycle capacity decay. Conventional single-carbon coating and single-metal doping modifications can only slightly improve conductivity and cannot guarantee lattice stability.

[0003] Common solutions include elemental doping of lithium manganese iron phosphate (LFP) and carbon coating of LFP materials. Elemental doping of LFP can improve crystal structure stability. Conventional carbon coating may result in localized agglomeration, leading to uneven coating and affecting the cycle stability of the battery. Summary of the Invention

[0004] The purpose of this invention is to provide a lithium manganese iron phosphate cathode material to improve battery cycle stability.

[0005] Another object of the present invention is a method for preparing lithium manganese iron phosphate cathode material.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Lithium manganese iron phosphate cathode material, comprising lithium manganese iron phosphate material and carbon coating material, wherein the lithium manganese iron phosphate material is expressed as LiMn x-y Fe 1-x M y PO4, M is a doping element, and the carbon coating material includes carbon source A and carbon source B, where carbon source A is a carborane or a carborane derivative.

[0007] Furthermore, the doping element includes at least one of Zr, Al, Mg, V, or Ti.

[0008] Furthermore, the carbon coating material accounts for 3 to 5% of the mass of the lithium manganese iron phosphate material.

[0009] Furthermore, the mass ratio of carbon source A to carbon source B is 1:3 to 1:5.

[0010] Furthermore, the LiMn x-y Fe 1-x M y In PO4, 0.5≤x<1, 0.1≤y<1, y<x.

[0011] The preparation method of lithium manganese iron phosphate cathode material includes the following steps: S1: Take a compound containing lithium source, manganese source, iron source and doping elements, add water and grind it with a sand mill, then add an ethanol suspension of carborane and continue grinding with a sand mill. After grinding, spray dry to obtain lithium manganese iron phosphate base material. S2: The lithium manganese iron phosphate base material in step S1 is sintered at high temperature in N2 atmosphere at a temperature of 700-730℃. After sintering, it is gradually cooled to room temperature, crushed and ground to obtain lithium manganese iron phosphate powder with a D50 of 50-80μm. S3. The lithium manganese iron phosphate powder and carbon nanotubes from step S2 are immersed in an ethanol suspension of carborane. The mixture is continuously stirred during the immersion process. After immersion, the mixture is spray-dried. The spray-dried product is sintered in an N2 atmosphere at a sintering temperature of 700-730°C. After sintering, the mixture is gradually cooled to room temperature to obtain the lithium manganese iron phosphate cathode material.

[0012] Further, in step S1, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium oxalate, lithium acetate, or lithium nitrate; the manganese source includes one or more of manganese sulfate, manganese acetate, manganese nitrate, or manganese carbonate; the iron source includes one or more of FeSO4·7H2O, ferrous acetate, or ferrous nitrate; and the phosphorus source includes at least one of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, or diammonium hydrogen phosphate.

[0013] Further, in step S1, the carbon source B includes one or more of carbohydrate carbon sources, nano-carbon materials, or organic polymers.

[0014] Further, in step S1, the amount of carborane added is 0.3 to 0.8% of the mass of the lithium source, manganese source, iron source and the compound of doping elements, and the amount of water added is 1.5 to 2.5 times the mass of the lithium source, manganese source, iron source and the compound of doping elements.

[0015] Furthermore, in step S3, the amount of carborane added is 0.3 to 0.8% of the mass of the lithium source, manganese source, iron source, and dopant element compound.

[0016] The beneficial effects of this invention are: In the lithium manganese iron phosphate cathode material of this invention, doping elements can suppress lattice distortion during charge and discharge, and strengthen the rigidity of the olivine structure. During sintering, the carbon-coated material can controllably release B and C active substances, achieving uniform doping and coating, and avoiding localized agglomeration. B atoms, with an electron-deficient configuration, dope the LMFP lattice, improving Li+ diffusion and electronic conductivity. The carboranes or carborane derivatives contained in the carbon-coated material have a cage-like structure. After the cage-like structure decomposes, it leaves behind a cage-like, hollow, fragmented carbon-boron skeleton, forming a loose, elastic composite coating layer. LMFP batteries experience slight lattice distortion and volume expansion during charge and discharge; the elastic composite boron-carbon layer can buffer stress, suppress particle cracking and pulverization, and improve battery cycle stability. Attached Figure Description

[0017] Figure 1 This is a scanning electron microscope image of the lithium manganese iron phosphate cathode material in Example 1.

[0018] Figure 2 The image shows a scanning electron microscope (SEM) image of the lithium iron phosphate cathode material in Comparative Example 1. Detailed Implementation

[0019] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0020] The preparation method of carborane ethanol suspension in Examples 1-5 includes the following steps: 10g of carborane is added to 500mL of anhydrous ethanol to obtain a carborane ethanol suspension with a mass concentration of 0.02g / mL.

[0021] Example 1 The lithium iron phosphate cathode material of this embodiment includes lithium iron phosphate material and carbon coating material. The formula for lithium iron phosphate material is LiMn. 0.4995 Fe 0.5 Mg 0.0005 PO4. The carbon coating material includes carbon source A and carbon source B, where carbon source A is carborane and carbon source B is carbon nanotubes.

[0022] The preparation method of the lithium iron phosphate cathode material in this embodiment includes the following steps: S1: Weigh out lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and magnesium oxide according to the elemental molar ratio Li / Mn / Fe / P / Mg=1:0.4995:0.5:1:0.0005. Add water twice the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and magnesium oxide. Grind the mixture in a sand mill for 10 minutes. Then add an ethanol suspension of carborane. The amount of carborane added to the ethanol suspension is 0.8% of the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and magnesium oxide. Grind the mixture in a sand mill for 1 hour and then discharge the mixture to obtain a mixed slurry. Spray dry the mixed slurry to obtain lithium manganese iron phosphate base material.

[0023] S2: The lithium manganese iron phosphate base material from step S1 is heated to 350°C in an N2 atmosphere at a heating rate of 5°C / min for 2 hours. Then, it is heated to 710°C at a heating rate of 5°C / min for high-temperature sintering for 10 hours. After sintering, it is gradually cooled to room temperature, crushed, and ground to obtain lithium manganese iron phosphate powder with a D50 of 50μm.

[0024] S3: The lithium manganese iron phosphate powder and carbon nanotubes from step S2 are impregnated in an ethanol suspension of carborane. The amount of carbon nanotubes added is 1.6% of the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and magnesium oxide. The amount of carborane added to the ethanol suspension is 0.8% of the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and magnesium oxide. The impregnation process is continuously stirred for 2 hours. After impregnation, the product is spray-dried. The spray-dried product is sintered in an N2 atmosphere at a temperature of 720℃ for 10 hours. After sintering, the product is gradually cooled to room temperature to obtain the lithium manganese iron phosphate cathode material.

[0025] Figure 1 This is a scanning electron microscope (SEM) image of the lithium manganese iron phosphate cathode material prepared in this embodiment. Figure 1 It can be seen that the lithium manganese iron phosphate cathode material prepared in this embodiment has a small particle size and is relatively uniformly dispersed.

[0026] Example 2 The lithium iron phosphate cathode material of this embodiment includes lithium iron phosphate material and carbon coating material. The formula for lithium iron phosphate material is LiMn. 0.3994 Fe 0.6 Ti 0.0006 PO4. The carbon coating material includes carbon source A and carbon source B, where carbon source A is carborane and carbon source B is carbon nanotubes.

[0027] The preparation method of the lithium manganese iron phosphate cathode material in this embodiment includes the following steps: S1: Weigh out lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and TiO2 according to the elemental molar ratio Li / Mn / Fe / P / Mg=1:0.3994:0.6:1:0.0006. Add water twice the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and TiO2. Grind the mixture in a sand mill for 10 minutes. Then add an ethanol suspension of carborane. The amount of carborane added to the ethanol suspension is 0.5% of the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and TiO2. Grind the mixture in a sand mill for 1 hour and then discharge the mixture to obtain a mixed slurry. Spray dry the mixed slurry to obtain lithium manganese iron phosphate base material.

[0028] S2: The lithium manganese iron phosphate base material from step S1 is heated to 350°C in an N2 atmosphere at a heating rate of 5°C / min for 2 hours. Then, it is heated to 700°C at a heating rate of 5°C / min for high-temperature sintering for 10 hours. After sintering, it is gradually cooled to room temperature, crushed, and ground to obtain lithium manganese iron phosphate powder with a D50 of 80μm.

[0029] S3: The lithium manganese iron phosphate powder and carbon nanotubes from step S2 are impregnated in an ethanol suspension of carborane. The amount of carbon nanotubes added is 4% of the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and TiO2. The amount of carborane added to the ethanol suspension of carborane is 0.5% of the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and TiO2. The impregnation process is continuously stirred for 2 hours. After impregnation, the product is spray-dried. The spray-dried product is sintered in an N2 atmosphere at a sintering temperature of 730℃ for 10 hours. After sintering, the product is gradually cooled to room temperature to obtain the lithium manganese iron phosphate cathode material.

[0030] Example 3 The lithium iron phosphate cathode material of this embodiment includes lithium iron phosphate material and carbon coating material. The formula for lithium iron phosphate material is LiMn. 0.4995 Fe 0.5 Mg 0.0005 PO4. The carbon coating material includes carbon source A and carbon source B, where carbon source A is carborane and carbon source B is carbon nanotubes.

[0031] The preparation method of the lithium manganese iron phosphate cathode material in this embodiment includes the following steps: S1: Weigh out lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium hydrogen phosphate, and magnesium oxide according to the elemental molar ratio Li / Mn / Fe / P / Mg=1:0.4995:0.5:1:0.0005. Add water equal to 1.5 times the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium hydrogen phosphate, and magnesium oxide. Grind the mixture in a sand mill for 10 minutes. Then add a carborane ethanol suspension. The amount of carborane added to the carborane ethanol suspension is 0.3% of the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium hydrogen phosphate, and magnesium oxide. Grind the mixture in a sand mill for 1 hour and then discharge the mixture to obtain a mixed slurry. Spray dry the mixed slurry to obtain lithium manganese iron phosphate base material.

[0032] S2: The lithium manganese iron phosphate base material from step S1 is heated to 350°C in an N2 atmosphere at a heating rate of 5°C / min for 2 hours. Then, it is heated to 730°C at a heating rate of 5°C / min for high-temperature sintering for 10 hours. After sintering, it is gradually cooled to room temperature, crushed, and ground to obtain lithium manganese iron phosphate powder with a D50 of 50μm.

[0033] S3: The lithium manganese iron phosphate powder and carbon nanotubes from step S2 are impregnated in an ethanol suspension of carborane. The amount of carbon nanotubes added is 3% of the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium hydrogen phosphate, and magnesium oxide. The amount of carborane added to the ethanol suspension is 0.3% of the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium hydrogen phosphate, and magnesium oxide. The impregnation process is continuously stirred for 2 hours. After impregnation, the product is spray-dried. The spray-dried product is sintered in an N2 atmosphere at a temperature of 700℃ for 10 hours. After sintering, the product is gradually cooled to room temperature to obtain the lithium manganese iron phosphate cathode material.

[0034] Example 4 The lithium iron phosphate cathode material of this embodiment includes lithium iron phosphate material and carbon coating material. The formula for lithium iron phosphate material is LiMn. 0.4995 Fe 0.5 V 0.0005 PO4. The carbon coating material includes carbon source A and carbon source B, where carbon source A is carborane and carbon source B is glucose.

[0035] The preparation method of the lithium iron phosphate cathode material in this embodiment includes the following steps: S1: According to the elemental molar ratio Li / Mn / Fe / P / V=1:0.4995:0.5:1:0.0005, weigh out lithium carbonate, manganese sulfate, FeSO4·7H2O, ammonium dihydrogen phosphate, and vanadium pentoxide. Add water twice the total mass of lithium carbonate, manganese sulfate, FeSO4·7H2O, ammonium dihydrogen phosphate, and vanadium pentoxide. Grind the mixture in a sand mill for 10 minutes. Then add a carborane ethanol suspension. The amount of carborane added to the carborane ethanol suspension is 0.8% of the total mass of lithium carbonate, manganese sulfate, FeSO4·7H2O, ammonium dihydrogen phosphate, and vanadium pentoxide. Grind the mixture in a sand mill for 1 hour and then discharge the mixture to obtain a mixed slurry. Spray dry the mixed slurry to obtain lithium manganese iron phosphate base material.

[0036] S2: The lithium manganese iron phosphate base material from step S1 is heated to 350°C in an N2 atmosphere at a heating rate of 5°C / min for 2 hours. Then, it is heated to 710°C at a heating rate of 5°C / min for high-temperature sintering for 10 hours. After sintering, it is gradually cooled to room temperature, crushed, and ground to obtain lithium manganese iron phosphate powder with a D50 of 50μm.

[0037] S3: The lithium manganese iron phosphate powder and carbon nanotubes from step S2 are impregnated in an ethanol suspension of carborane. The amount of carbon nanotubes added is 2% of the total mass of lithium carbonate, manganese sulfate, FeSO4·7H2O, ammonium dihydrogen phosphate, and vanadium pentoxide. The amount of carborane added to the ethanol suspension is 0.8% of the total mass of lithium carbonate, manganese sulfate, FeSO4·7H2O, ammonium dihydrogen phosphate, and vanadium pentoxide. The impregnation process is continuously stirred for 2 hours. After impregnation, the product is spray-dried. The spray-dried product is sintered in an N2 atmosphere at a sintering temperature of 720℃ for 10 hours. After sintering, the product is gradually cooled to room temperature to obtain the lithium manganese iron phosphate cathode material.

[0038] Example 5 The lithium iron phosphate cathode material of this embodiment includes lithium iron phosphate material and carbon coating material. The formula for lithium iron phosphate material is LiMn. 0.4995 Fe 0.5 V 0.0005 PO4. The carbon coating material includes carbon source A and carbon source B, where carbon source A is carborane and carbon source B is graphene.

[0039] The preparation method of the lithium iron phosphate cathode material in this embodiment includes the following steps: S1: Weigh out lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and vanadium pentoxide according to the elemental molar ratio Li / Mn / Fe / P / V = 1:0.4995:0.5:1:0.0005. Add water twice the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and vanadium pentoxide. Grind the mixture in a sand mill for 10 minutes. Then add a carborane ethanol suspension. The amount of carborane added to the carborane ethanol suspension is 0.5% of the total mass of lithium carbonate, manganese nitrate, FeSO4·7H2O, ammonium dihydrogen phosphate, and vanadium pentoxide. Grind the mixture in a sand mill for 1 hour and then discharge the mixture to obtain a mixed slurry. Spray dry the mixed slurry to obtain lithium manganese iron phosphate base material.

[0040] S2: The lithium manganese iron phosphate base material from step S1 is heated to 350°C in an N2 atmosphere at a heating rate of 5°C / min for 2.5 hours. Then, it is heated to 700°C at a heating rate of 5°C / min for high-temperature sintering for 10 hours. After sintering, it is gradually cooled to room temperature, crushed, and ground to obtain lithium manganese iron phosphate powder with a D50 of 80μm.

[0041] S3: The lithium manganese iron phosphate powder and carbon nanotubes from step S2 are impregnated in an ethanol suspension of carborane. The amount of carbon nanotubes added is 3% of the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and vanadium pentoxide. The amount of carborane added to the ethanol suspension is 0.5% of the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate, and vanadium pentoxide. The impregnation process is continuously stirred for 2 hours. After impregnation, the product is spray-dried. The spray-dried product is sintered in an N2 atmosphere at a sintering temperature of 720℃ for 10 hours. After sintering, the product is gradually cooled to room temperature to obtain the lithium manganese iron phosphate cathode material.

[0042] Comparative Example 1 The lithium manganese iron phosphate cathode material in this comparative example is roughly the same as the lithium manganese iron phosphate cathode material in Example 1, except that no carborane was added, and carbon source B was used to make up the amount of carborane.

[0043] The preparation method of the lithium manganese iron phosphate cathode material in this comparative example is roughly the same as that in the example, except that no carborane ethanol suspension is added in steps S1 and S3.

[0044] Figure 2 Here is a scanning electron microscope (SEM) image of the lithium iron phosphate cathode material in this comparative example. Figure 2 It can be seen that the lithium iron phosphate cathode material in this comparative example has relatively large particles and severe particle agglomeration.

[0045] Comparative Example 2 The preparation method of the lithium manganese iron phosphate cathode material in this comparative example is roughly the same as that in the example. The difference is that in step S1, no carborane ethanol suspension is added, and in step S3, the amount of carborane added to the carborane ethanol suspension is 1.6% of the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate and magnesium oxide.

[0046] The lithium manganese iron phosphate cathode material of this comparative example was prepared by the same method used for preparing lithium manganese iron phosphate cathode materials of this comparative example.

[0047] Comparative Example 3 The preparation method of the lithium manganese iron phosphate cathode material in this comparative example is roughly the same as that in the example, except that the amount of carborane added to the ethanol suspension of carborane in step S1 is 1.6% of the total mass of lithium carbonate, manganese carbonate, FeSO4·7H2O, ammonium dihydrogen phosphate and magnesium oxide, and no carborane ethanol suspension is added in step S3.

[0048] The lithium manganese iron phosphate cathode material of this comparative example was prepared by the same method used for preparing lithium manganese iron phosphate cathode materials of this comparative example.

[0049] Comparative Example 4 The preparation method of the lithium manganese iron phosphate cathode material in this comparative example is roughly the same as that in the example, except that magnesium oxide is not added in step S1, and the amount of magnesium oxide is made up by manganese carbonate.

[0050] The lithium manganese iron phosphate cathode material of this comparative example was prepared by the same method used for preparing lithium manganese iron phosphate cathode materials of this comparative example.

[0051] Experimental Example 1 The positive electrode materials of Examples 1 and Comparative Examples 1-4 were dissolved in NMP with carbon black and PVDF respectively in a mass ratio of 8:1:1 to prepare positive electrode slurries. These slurries were then coated onto the surface of carbon-coated aluminum foil to prepare positive electrode sheets. The prepared positive electrode sheets were assembled with graphite negative electrodes to obtain lithium-ion batteries (CR2032 button half-cells). The separator was a polypropylene microporous membrane, Celgard 2400. The electrolyte was 1 mol / L LiPF6 dissolved in a 1:1 volume ratio of ethylene carbonate solution and methyl ethyl carbonate mixture.

[0052] The assembled CR2032 button cell was subjected to charge-discharge cycle testing. The test voltage range was 2.0V to 4.5V.

[0053] During the rate test, the device is first activated at 0.1C for 5 cycles, and then charge and discharge tests are performed at current densities of 0.1C, 1C, and 5C.

[0054] During the cyclic test, the device is first activated at 0.1C for 5 cycles, and then charged and discharged at 1C.

[0055] The test results are shown in Table 1.

[0056] Table 1. Performance test results of CR2032 button half-cells in Example 1 and Comparative Examples 1-4

[0057] As shown in Table 1, in Comparative Examples 1 and 2, no carborane was added during the preparation stage of the lithium manganese iron phosphate base material, resulting in poor cycle stability of the CR2032 button cell. This indicates that adding a small amount of carborane can improve the cycle stability of the CR2032 button cell. In Comparative Example 3, carborane was added during the preparation stage of the lithium manganese iron phosphate base material, but the amount added was relatively large, and no carborane was added during the carbon coating stage. The cycle stability of the CR2032 button cell was worse than that of Example 1, indicating that the amount of carborane added and the stage of addition have a certain impact on the cycle stability of the CR2032 button cell. In Comparative Example 4, no doping elements were added, and the cycle stability of the CR2032 button cell was also poor.

Claims

1. A lithium iron phosphate cathode material, characterized in that, This includes lithium manganese iron phosphate materials and carbon-coated materials, wherein the lithium manganese iron phosphate material is expressed as LiMn. x-y Fe 1-x M y PO4, M is a doping element, and the carbon coating material includes carbon source A and carbon source B, where carbon source A is a carborane or a carborane derivative.

2. The lithium iron phosphate cathode material according to claim 1, characterized in that, The doping element includes at least one of Zr, Al, Mg, V or Ti.

3. The lithium iron phosphate cathode material according to claim 1, characterized in that, The carbon coating material accounts for 3 to 5% of the mass of the lithium manganese iron phosphate material.

4. The lithium iron phosphate cathode material according to claim 1, characterized in that, The mass ratio of carbon source A to carbon source B is 1:3 to 1:

5.

5. The lithium iron phosphate cathode material according to claim 1, characterized in that, The LiMn x-y Fe 1-x M y In PO4, 0.5≤x<1, 0.1≤y<1, y<x.

6. The method for preparing the lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, Includes the following steps: S1: Take a compound containing lithium source, manganese source, iron source and doping elements, add water and grind it with a sand mill, then add an ethanol suspension of carborane and continue grinding with a sand mill. After grinding, spray dry to obtain lithium manganese iron phosphate base material. S2: The lithium manganese iron phosphate base material in step S1 is sintered at high temperature in N2 atmosphere at a temperature of 700-730℃. After sintering, it is gradually cooled to room temperature, crushed and ground to obtain lithium manganese iron phosphate powder with a D50 of 50-80μm. S3. The lithium manganese iron phosphate powder and carbon source B from step S2 are impregnated in an ethanol suspension of carborane. The impregnation process is continuously stirred. After impregnation, the product is spray-dried. The spray-dried product is sintered in an N2 atmosphere at a sintering temperature of 700-730°C. After sintering, the product is gradually cooled to room temperature to obtain the lithium manganese iron phosphate cathode material.

7. The method for preparing lithium manganese iron phosphate cathode material according to claim 6, characterized in that, In step S1, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium oxalate, lithium acetate, or lithium nitrate; the manganese source includes one or more of manganese sulfate, manganese acetate, manganese nitrate, or manganese carbonate; the iron source includes one or more of FeSO4·7H2O, ferrous acetate, or ferrous nitrate; and the phosphorus source includes at least one of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, or diammonium hydrogen phosphate.

8. The method for preparing lithium manganese iron phosphate cathode material according to claim 6, characterized in that, In step S1, the carbon source B includes one or more of carbohydrate carbon sources, nano-carbon materials, or organic polymers.

9. The method for preparing lithium manganese iron phosphate cathode material according to claim 6, characterized in that, In step S1, the amount of carborane added is 0.3 to 0.8% of the mass of the lithium source, manganese source, iron source and the compound of doping elements, and the amount of water added is 1.5 to 2.5 times the mass of the lithium source, manganese source, iron source and the compound of doping elements.

10. The method for preparing lithium manganese iron phosphate cathode material according to claim 6, characterized in that, In step S3, the amount of carborane added is 0.3 to 0.8% of the mass of the lithium source, manganese source, iron source and the compound of the doping element.

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