High-conductivity lithium manganese iron phosphate positive electrode material and preparation method thereof

Abstract

The invention discloses a high-conductivity lithium manganese iron phosphate positive electrode material and a preparation method thereof, and belongs to the technical field of lithium ion battery positive electrode materials. The preparation method of the high-conductivity lithium manganese iron phosphate positive electrode material comprises the following steps: (1) mixing, grinding and drying a solution containing a phosphorus source, a lithium source, an iron source, a manganese source and a carbon source to obtain a first dried material; sintering the first dry material in a nitrogen atmosphere to obtain a first sintered material; (2) adding a solvent, a carbon source, a fluorine source and a nitrogen source into the first sintered material, mixing, grinding and drying to obtain a second dried material; and (3) sequentially sintering and crushing the second dried material to obtain the high-conductivity lithium manganese iron phosphate positive electrode material. Through fluorine-nitrogen synergistic doping, the conductivity of the lithium manganese iron phosphate positive electrode material can be remarkably improved, the material performance is improved, and meanwhile, due to the synergistic effect, the effective conversion rate of a carbon source is increased, so that the use amount of an organic carbon source is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery positive electrode materials, and specifically relates to a lithium manganese iron phosphate positive electrode material that achieves high conductivity by optimizing the carbon layer structure and a preparation method thereof. Background Art

[0002] Lithium iron phosphate (LIFP) is inexpensive, safe, and environmentally friendly, making it suitable for automotive power batteries. However, its low energy density makes it difficult to meet demand. Lithium iron manganese phosphate (LIMnFePO) offers a higher energy density than LFP while also offering the advantages of lower cost and a more stable crystal structure, making it a promising alternative.

[0003] However, the commercial application of lithium manganese iron phosphate materials is limited by the following problems: extremely low conductivity: intrinsic electronic conductivity (10 -9 ~10 -10 S / cm) depends on carbon coating, but the traditional carbon coating process has problems such as low carbon source conversion rate (<80%) and disordered carbon layer (ID / IG>1.0), which leads to insufficient overall conductivity of the material (<5×10 -4 S / cm); low compaction density: excessive carbon residue (>5wt%) hinders the lithium ion transmission path, and the compaction density is generally lower than 2.3g / cm 3 ; Manganese dissolution is serious: Mn 3 + The Jahn-Teller distortion leads to structural collapse and rapid capacity decay (capacity retention rate after 200 cycles is <85%).

[0004] Patent CN119170787A stabilizes the material structure by doping fluorine in the lattice of the lithium manganese iron phosphate positive electrode material, and improves the conductivity by doping and coating the carbon layer with SnO2 / C. Specifically, a microwave-hydrothermal synthesis method is used to prepare a fluorine-doped lithium manganese iron phosphate precursor. The doping of fluorine promotes the diffusion of lithium ions in the positive electrode material, making the structure of the material more stable and improving the conductivity of the positive electrode material. At the same time, SnO2 is doped in chitosan as a carbon source to improve the conductivity of the positive electrode material. At the same time, during the calcination process, part of the tin oxide is reduced to metallic tin due to the carbon thermal reduction reaction, which can further improve the conductivity of the coating layer. The coordination effect between the metal ions (tin ions) in the coating layer and the exposed fluorine atoms in the precursor can enable the chitosan gel to form a uniform and tightly bound carbon coating layer on the surface of the material, so that the positive electrode material obtained by the present invention has excellent cycle performance and rate performance. In this patent, fluorine is doped into the crystal lattice to stabilize the structure, and the carbon layer is doped with metal Sn to improve the conductivity. These effects are additive and do not have a catalytic effect on the carbon layer.

[0005] Another published patent, CN119674008A, provides a method for preparing nitrogen-doped carbon-coated lithium manganese iron phosphate (LMP). This method improves the electronic conductivity of the LMP positive electrode material by forming C-N bonds. Specifically, an organic carbon source containing nitrogen is used to achieve the nitrogen-doped carbon coating effect. Nitrogen atoms create defects and additional electronic states in the carbon lattice through C-N bonds, increasing the carrier concentration and electron mobility of the carbon layer, making electron transport smoother, reducing impedance, and increasing the affinity between the LMP material and the carbon layer, thereby improving electrical performance. In this patent, the carbon layer is doped with nitrogen to increase the material's electronic conductivity, but it also has no catalytic effect on the carbon layer.

[0006] Neither of the two patent solutions mentions the catalytic mechanism for the graphitization conversion of the carbon layer, nor does it mention improving the effective conversion rate of the carbon source and reducing the amount of carbon source used. Summary of the Invention

[0007] Based on the problems existing in the background technology, the present invention provides a highly conductive lithium iron manganese phosphate positive electrode material and a preparation method thereof, which improves the conductivity and electrochemical properties of the lithium iron manganese phosphate positive electrode material. The present invention is mainly used in the preparation process of the lithium iron manganese phosphate positive electrode material, especially in the carbon thermal reaction process, and can play a catalytic effect.

[0008] The present invention is implemented through the following technical solutions:

[0009] The present invention discloses a method for preparing a highly conductive lithium manganese iron phosphate cathode material, comprising the following steps:

[0010] (1) mixing, grinding, and drying a solution containing a phosphorus source, a lithium source, an iron source, a manganese source, and a carbon source to obtain a first dried material; sintering the first dried material under a nitrogen atmosphere to obtain a first sintered material;

[0011] (2) adding a solvent, a carbon source, a fluorine source, and a nitrogen source to the first sintered material, mixing, grinding, and drying to obtain a second dried material;

[0012] (3) Sintering and crushing the second dried material in sequence to obtain a highly conductive lithium manganese iron phosphate positive electrode material.

[0013] Furthermore, based on the molar ratio of phosphorus, lithium, iron and manganese, the molar ratio of the phosphorus source, lithium source, iron source and manganese source is x:y:z:(1-z), wherein 1≤x≤1.05, 1≤y≤1.1, and 0.1≤z≤0.9.

[0014] Furthermore, in step (1), the lithium source is selected from at least one of lithium carbonate, lithium acetate, lithium nitrate, lithium hydroxide, lithium chloride, lithium dihydrogen phosphate, and lithium citrate;

[0015] The iron source is selected from at least one of ferrous sulfate, ferrous oxalate, ferrous acetate, ferric citrate, ferric nitrate, ferric chloride, ferric phosphate, iron powder, and ferric oxide;

[0016] The manganese source is selected from at least one of manganese sulfate, manganese oxalate, manganese acetate, manganese nitrate, manganese chloride, manganese carbonate, manganese tetraoxide, manganese dioxide, and manganese phosphate;

[0017] The phosphorus source is selected from at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, lithium dihydrogen phosphate, dilithium hydrogen phosphate, iron phosphate, and manganese phosphate.

[0018] Furthermore, in step (1), the amount of carbon source added is 2-8% of the mass of the theoretically generated lithium manganese iron phosphate.

[0019] Furthermore, in step (1) and step (2), the carbon source is selected from at least one of glucose, sucrose, starch, polyethylene glycol, oxalic acid, polyacrylamide, cellulose, citric acid, levulinic acid, polyvinyl pyrrolidone, graphite, carbon nanotubes, and graphene.

[0020] Furthermore, in step (2), the mass ratio of the carbon source, the fluorine source, the nitrogen source and the first sintering material is (5-12): (0.5-3): (0.5-3): 100.

[0021] Furthermore, in step (2), the fluorine source is at least one of magnesium fluoride, lithium fluoride, aluminum fluoride, manganese fluoride, ammonium fluoride, and hydrofluoric acid;

[0022] The nitrogen source is at least one of polyvinyl pyrrolidone, melamine, urea, biuret, ammonium fluoride, and ammonia water;

[0023] The solvent is selected from at least one of water, ethanol, isopropanol and acetone.

[0024] Furthermore, in step (1), the sintering temperature is 600-800°C and the holding time is 4-12 hours;

[0025] In step (3), the sintering temperature is 650-850° C., and the holding time is 4-12 hours.

[0026] The second aspect of the present invention discloses a highly conductive lithium manganese iron phosphate positive electrode material prepared by the above method.

[0027] Beneficial effects of the present invention:

[0028] 1. Fluorine (usually in the form of gas or fluorine-containing precursors) has strong oxidizing properties at high temperatures and can selectively etch amorphous regions or defect structures in carbon materials, leaving more ordered sp 2Hybridized carbon skeleton. This "selective removal" promotes the densification of carbon structure and the growth of graphite crystals. The high electronegativity of fluorine can polarize the electron cloud in the carbon skeleton, enhance the stability of CC bonds, and promote sp 2 The formation of hybrid structures reduces the energy barrier required for graphitization. After nitrogen atoms are incorporated into the carbon lattice, pyridine-type, pyrrole-type or graphite-type nitrogen is formed. These doping sites can provide additional electronic active centers, promote the migration and rearrangement of carbon atoms, and accelerate the graphitization process. At the same time, nitrogen doping can weaken the van der Waals force between carbon layers, promote the sliding and rearrangement of carbon layers, and provide nucleation sites for the directional growth of graphite crystals by forming local defects (such as five-membered rings or seven-membered rings). The present invention uses a synergistic etching-doping mechanism of fluorine and nitrogen: the etching effect of fluorine preferentially removes disordered carbon, and nitrogen doping stabilizes the ordered graphite region. The two work together to form a "dynamic balance", which significantly increases the proportion of graphitized carbon.

[0029] 2. The mechanism of action of the present invention is mainly the following three points: (1) fluorine element selectively removes disordered carbon and optimizes the carbon skeleton; (2) nitrogen element doping stabilizes the ordered structure and provides catalytic active sites; (3) the synergistic effect significantly reduces the graphitization energy barrier and improves the conversion efficiency. The presence of fluorine and nitrogen can change the reaction path of the pyrolysis of organic carbon sources such as glucose. Fluorine accelerates dehydration and decarboxylation reactions, reducing the formation of tar-like byproducts. At the same time, the strong oxidizing property of fluorine can inhibit the adsorption of oxygen on the surface of the carbon material (such as CO or CO2 generation), thereby reducing the effect of disordered carbon; while nitrogen doping enhances the stability of the carbon skeleton and reduces carbon loss at high temperatures, because nitrogen can promote the condensation of aromatic rings to form more stable polycyclic aromatic hydrocarbon intermediates, which are ultimately converted into graphitized carbon. Combined with the above synergistic effects, not only can the conductivity of lithium manganese iron phosphate positive electrode materials be significantly improved and the material performance be improved, but also the effective conversion rate of the carbon source is increased due to the synergistic effect, thereby reducing the amount of organic carbon source used. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are used to further explain the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0031] Figure 1 This is a SEM image of the lithium manganese iron phosphate positive electrode material prepared in Example 1 of the present invention;

[0032] Figure 2 This is an SEM image of the lithium manganese iron phosphate positive electrode material prepared in Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described in detail below with reference to specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0034] Example 1

[0035] A method for preparing a highly conductive lithium manganese iron phosphate positive electrode material comprises the following steps:

[0036] (1) Lithium carbonate, ferrous sulfate, manganese sulfate, and phosphoric acid were weighed according to the molar ratio of Li:Fe:Mn:P=1:0.7:0.3:1, added to deionized water, and stirred and dissolved at 70°C for 2 hours; glucose was added (the amount added was 6% of the mass of the theoretically generated lithium manganese iron phosphate), and stirring was continued for 1 hour, and then ball milled in a planetary ball mill at 300 rpm for 6 hours; the ball-milled mixed solution was dried at 90°C for 10 hours to obtain a first dry material; the first dry material was placed in a tubular furnace, heated to 700°C at 3°C / min under a nitrogen atmosphere (flow rate 50 mL / min), kept warm for 8 hours, and naturally cooled to room temperature to obtain a first sintered material.

[0037] (2) The first sintered material, glucose, magnesium fluoride, and melamine were added to deionized water in a mass ratio of 100:10:2:2, and ball-milled in a planetary ball mill at 300 rpm for 4 hours; the ball-milled mixture was dried at 90°C for 10 hours to obtain a second dried material; the second dried material was placed in a tubular furnace, heated to 750°C at 3°C / min under a nitrogen atmosphere (flow rate 50 mL / min), kept warm for 8 hours, and naturally cooled to room temperature.

[0038] (3) The sintered product was crushed in a planetary ball mill at 400 rpm for 1.5 hours and sieved to obtain a highly conductive lithium manganese iron phosphate positive electrode material.

[0039] Figure 1 This is the SEM image of the lithium manganese iron phosphate positive electrode material prepared in this embodiment. It can be seen from the figure that fluorine and nitrogen synergistically doped, there is less free carbon between the particles, the doped fluorine element selectively removes disordered carbon, optimizes the carbon skeleton, and the electrical conductivity and electrical properties are better. The doping of nitrogen elements can also enhance and stabilize the carbon skeleton.

[0040] Example 2

[0041] A method for preparing a highly conductive lithium manganese iron phosphate positive electrode material comprises the following steps:

[0042] (1) Lithium acetate, ferrous oxalate, manganese oxalate, and ammonium dihydrogen phosphate were weighed according to the molar ratio of Li:Fe:Mn:P=1:0.6:0.4:1, added to a mixed solvent of deionized water and ethanol, and stirred and dissolved at 70°C for 3 hours; 4 g of sucrose (the amount added was 6% of the theoretical mass of lithium manganese iron phosphate) was added, and stirring was continued for 1 hour, and then ball milled in a planetary ball mill at 350 rpm for 8 hours; the ball-milled mixed solution was dried at 85°C for 12 hours to obtain a first dry material; the first dry material was placed in a tubular furnace, heated to 680°C at 4°C / min under a nitrogen atmosphere (flow rate 60 mL / min), kept warm for 7 hours, and naturally cooled to room temperature to obtain a first sintered material.

[0043] (2) The first sintered material, sucrose, ammonium fluoride, and urea were added to a mixed solvent of deionized water and ethanol in a mass ratio of 100:10:2:2, and ball-milled at 350 rpm in a planetary ball mill for 5 hours; the ball-milled mixture was dried at 85°C for 12 hours to obtain a second dried material; the second dried material was placed in a tubular furnace, heated to 780°C at 4°C / min under a nitrogen atmosphere (flow rate 60 mL / min), kept warm for 8 hours, and naturally cooled to room temperature.

[0044] (3) The sintered product was crushed in a planetary ball mill at 450 rpm for 1.5 hours and sieved to obtain a highly conductive lithium manganese iron phosphate positive electrode material.

[0045] Example 3

[0046] A method for preparing a highly conductive lithium manganese iron phosphate positive electrode material comprises the following steps:

[0047] (1) Lithium hydroxide, ferric citrate, manganese citrate, and disodium hydrogen phosphate were weighed according to the molar ratio of Li:Fe:Mn:P=1:0.8:0.2:1, added to deionized water, and stirred and dissolved at 75°C for 2.5 hours; citric acid was added (the amount added was 6% of the mass of the theoretically generated lithium manganese iron phosphate), and stirring was continued for 1 hour, and then ball milled in a planetary ball mill at 320 rpm for 7 hours; the ball-milled mixed solution was dried at 95°C for 11 hours to obtain a first dry material; the first dry material was placed in a tubular furnace, heated to 720°C at 2.5°C / min under a nitrogen atmosphere (flow rate 45 mL / min), kept warm for 9 hours, and naturally cooled to room temperature to obtain a first sintered material.

[0048] (2) The first sintered material, citric acid, lithium fluoride, and polyvinyl pyrrolidone were added to deionized water in a mass ratio of 100:8:2:2, and ball-milled in a planetary ball mill at 320 rpm for 5 hours; the ball-milled mixture was dried at 95°C for 11 hours to obtain a second dried material; the second dried material was placed in a tubular furnace, heated to 800°C at 2.5°C / min under a nitrogen atmosphere (flow rate 45 mL / min), kept warm for 9 hours, and naturally cooled to room temperature.

[0049] (3) The sintered product was crushed in a planetary ball mill at 420 rpm for 1.5 hours and sieved to obtain a highly conductive lithium manganese iron phosphate positive electrode material.

[0050] Comparative Example 1

[0051] The difference between this comparative example and Example 1 is that the positive electrode material is not doped with fluorine element, that is, magnesium fluoride is not included in step (2), the first sintered material, glucose, and melamine are added to deionized water in a mass ratio of 100:10:2, and ball milled in a planetary ball mill at 300 rpm for 4 hours; the remaining steps are the same as in Example 1.

[0052] Comparative Example 2

[0053] The difference between this comparative example and Example 1 is that the positive electrode material is not doped with nitrogen, that is, melamine is not included in step (2), the first sintered material, glucose, and magnesium fluoride are added to deionized water in a mass ratio of 100:10:2, and ball milled in a planetary ball mill at 300 rpm for 4 hours; the remaining steps are the same as in Example 1.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 1 is that the positive electrode material is not doped with fluorine and nitrogen, that is, magnesium fluoride and melamine are not included in step (2). The first sintered material and glucose are added to deionized water in a mass ratio of 100:10 and ball-milled in a planetary ball mill at 300 rpm for 4 hours; the remaining steps are the same as in Example 1.

[0056] Comparative Example 4

[0057] The difference between this comparative example and Example 1 is that the positive electrode material is not doped with fluorine and nitrogen, and the amount of glucose added in step (1) is 15% of the theoretical mass of the generated lithium manganese iron phosphate, specifically:

[0058] (1) Lithium carbonate, ferrous sulfate, manganese sulfate, and phosphoric acid were weighed according to the molar ratio of Li:Fe:Mn:P=1:0.7:0.3:1, added to deionized water, and stirred and dissolved at 70°C for 2 hours; glucose was added (the amount added was 15% of the mass of the theoretically generated lithium manganese iron phosphate), and stirring was continued for 1 hour, and then ball milled in a planetary ball mill at 300 rpm for 6 hours; the ball-milled mixed solution was dried at 90°C for 10 hours to obtain a first dry material; the first dry material was placed in a tubular furnace, heated to 700°C at 3°C / min under a nitrogen atmosphere (flow rate 50 mL / min), kept warm for 8 hours, and naturally cooled to room temperature to obtain a first sintered material.

[0059] (2) The first sintered material and glucose were added to deionized water in a mass ratio of 100:10, and ball-milled in a planetary ball mill at 300 rpm for 4 hours; the ball-milled mixture was dried at 90°C for 10 hours to obtain a second dried material; the second dried material was placed in a tubular furnace, heated to 750°C at 3°C / min under a nitrogen atmosphere (flow rate 50 mL / min), kept warm for 8 hours, and naturally cooled to room temperature.

[0060] (3) The sintered product was crushed in a planetary ball mill at 400 rpm for 1.5 hours and sieved to obtain a highly conductive lithium manganese iron phosphate positive electrode material.

[0061] Figure 2 This is the SEM image of the lithium manganese iron phosphate positive electrode material prepared in this comparative example. It can be seen from the figure that when the fluorine source and nitrogen elements are not doped, the conductivity and electrical properties of the final sample are relatively low, the degree of graphitization of the carbon layer is low, the conductivity is poor, and there is obviously more free carbon between the particles, and the specific surface area is also relatively high.

[0062] Test example

[0063] The lithium iron manganese phosphate cathode materials prepared in the Examples and Comparative Examples were tested for conductivity, BET, and carbon content using a powder conductivity tester, a specific surface area analyzer, and a carbon-sulfur analyzer. Furthermore, the lithium iron manganese phosphate cathode materials were assembled into button-type half-cells and charged using constant current and constant voltage. The physical, chemical, and electrochemical properties are shown in Table 1.

[0064] Table 1 Test results of lithium manganese iron phosphate positive electrode materials prepared in Examples and Comparative Examples

[0065]

[0066] From the results in Table 1, it can be seen that compared with the lithium manganese iron phosphate doped with fluorine or nitrogen in Comparative Examples 1-2 or the lithium manganese iron phosphate not doped with fluorine and nitrogen in Comparative Examples 3-4, the lithium manganese iron phosphate with fluorine and nitrogen prepared in Examples 1-3 of the present invention has significantly improved conductivity and discharge capacity after being assembled into button batteries. The amount of carbon source used in Examples 1-3 is significantly lower than that in Comparative Example 4 of the traditional high-carbon formula, but the performance of the positive electrode material finally obtained is better than that in Comparative Example 4, indicating that fluorine-nitrogen synergistic doping can improve the utilization efficiency of the carbon layer at a lower carbon dosage, so that more carbon is converted into a conductive carbon layer. In Comparative Examples 1 and 2 with single element doping, the utilization efficiency of the carbon source is relatively low due to the lack of synergistic effect, and part of the carbon is lost in the form of CO or CO2.

[0067] The specific surface area in Examples 1-3 is significantly higher than that of all comparative examples. The higher specific surface area is conducive to electrolyte infiltration and lithium ion transport at the electrode / electrolyte interface, which is one of the reasons why the examples perform well in high-rate performance. Fluorine-nitrogen co-doping may form more micropores and mesoporous structures through selective etching and structural reorganization, while maintaining the conductive connectivity of the carbon layer. It can be seen from the capacity retention results of 500 cycles at 1C that the button-type half-cells prepared from the positive electrode materials of Examples 1-3 have excellent cycle stability, indicating that the fluorine-nitrogen co-doped carbon layer not only has good conductivity, but also has good structural stability, and can maintain the integrity of the electrode and the conductive network during long-term cycling.

[0068] Finally, it should be noted that the above-described embodiments merely represent several implementation methods of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made by a person skilled in the art without departing from the spirit of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention should be based on the appended claims.

Claims

1. A method for preparing a highly conductive lithium manganese iron phosphate positive electrode material, characterized in that: The following steps are involved: (1) mixing, grinding, and drying a solution containing a phosphorus source, a lithium source, an iron source, a manganese source, and a carbon source to obtain a first dried material; sintering the first dried material under a nitrogen atmosphere to obtain a first sintered material; (2) adding a solvent, a carbon source, a fluorine source, and a nitrogen source to the first sintered material, mixing, grinding, and drying to obtain a second dried material; (3) Sintering and crushing the second dried material in sequence to obtain a highly conductive lithium manganese iron phosphate positive electrode material.

2. The preparation method according to claim 1, characterized in that In step (1), the molar ratio of the phosphorus source, lithium source, iron source and manganese source is x:y:z:(1-z), calculated based on the molar ratio of phosphorus, lithium, iron and manganese, wherein 1≤x≤1.05, 1≤y≤1.1, and 0.1≤z≤0.

9.

3. The preparation method according to claim 1, characterized in that In step (1), the lithium source is selected from at least one of lithium carbonate, lithium acetate, lithium nitrate, lithium hydroxide, lithium chloride, lithium dihydrogen phosphate, and lithium citrate; The iron source is selected from at least one of ferrous sulfate, ferrous oxalate, ferrous acetate, ferric citrate, ferric nitrate, ferric chloride, ferric phosphate, iron powder, and ferric oxide; The manganese source is selected from at least one of manganese sulfate, manganese oxalate, manganese acetate, manganese nitrate, manganese chloride, manganese carbonate, manganese tetraoxide, manganese dioxide, and manganese phosphate; The phosphorus source is selected from at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, lithium dihydrogen phosphate, dilithium hydrogen phosphate, iron phosphate, and manganese phosphate.

4. The preparation method according to claim 1, characterized in that In step (1), the amount of carbon source added is 2-8% of the mass of the theoretically generated lithium manganese iron phosphate.

5. The preparation method according to claim 1, characterized in that In step (1) and step (2), the carbon source is selected from at least one of glucose, sucrose, starch, polyethylene glycol, oxalic acid, polyacrylamide, cellulose, citric acid, levulinic acid, polyvinyl pyrrolidone, graphite, carbon nanotubes, and graphene.

6. The preparation method according to claim 1, characterized in that In step (2), the mass ratio of the carbon source, the fluorine source, the nitrogen source and the first sintering material is (5-12): (0.5-3): (0.5-3):

100.

7. The preparation method according to claim 1, characterized in that In step (2), the fluorine source is at least one of magnesium fluoride, lithium fluoride, aluminum fluoride, manganese fluoride, ammonium fluoride, and hydrofluoric acid; The nitrogen source is at least one of polyvinyl pyrrolidone, melamine, urea, biuret, ammonium fluoride, and ammonia water; The solvent is selected from at least one of water, ethanol, isopropanol and acetone.

8. The preparation method according to claim 1, characterized in that In step (1), the sintering temperature is 600-800° C. and the holding time is 4-12 hours; In step (3), the sintering temperature is 650-850° C., and the holding time is 4-12 hours.

9. A highly conductive lithium manganese iron phosphate positive electrode material, characterized in that: Prepared by the method according to any one of claims 1 to 8.

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