A lithium iron manganese phosphate positive electrode material activated by plasma and assisted by gradient in-situ carbonization and a preparation method thereof

Abstract

The application discloses a plasma-activated auxiliary gradient in-situ carbonized lithium iron manganese phosphate positive electrode material and a preparation method thereof, and belongs to the technical field of lithium batteries. The application first anchors carbon and nitrogen sources on active sites by plasma-activating a precursor, then performs gradient carbonization in sections and performs plasma post-processing in a low-temperature section, and forms a carbon and nitrogen gradient conductive network from inside to outside. The application solves the problems of easy peeling of a carbon layer and poor rate of a traditional process, the 0.2C capacity of the material is more than 157 mAh / g, the rate and cycle stability are significantly improved, and the material is suitable for power batteries and energy storage fields.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material and its preparation method. Background Technology

[0002] With the rapid development of new energy vehicles, large-scale energy storage power stations, and portable energy storage devices, the market has set higher standards for the energy density, rate discharge performance, long-cycle stability, and high-temperature safety of lithium-ion battery cathode materials. Lithium iron phosphate (LFP) has achieved large-scale industrial application due to its stable crystal structure, low risk of thermal runaway, and low raw material cost. However, its energy density improvement is limited by its low operating voltage of around 3.4V, making it difficult to meet the development needs of long-range power batteries and high-energy-density energy storage systems. Lithium iron manganese phosphate (LMFP), as an upgraded system of LFP, partially replaces iron atoms in the crystal lattice with manganese, increasing the main operating voltage to 4.1V. Its theoretical energy density is 15-20% higher than traditional lithium iron phosphate, while retaining the core advantages of phosphate materials such as high safety, low toxicity, and environmental friendliness. It represents a core research direction for next-generation high-performance, cost-effective power battery cathode materials.

[0003] However, native lithium manganese iron phosphate materials have three inherent defects that severely restrict their large-scale application: First, their intrinsic electronic conductivity is extremely low, approaching that of semiconductors or even insulators, resulting in narrow one-dimensional diffusion channels for lithium ions, high charge transport resistance under high current charging and discharging, and significant capacity decay at high rates; Second, manganese ions are prone to Jahn-Teller lattice distortion, leading to increased Mn content during cycling. 2+ Easily oxidized to Mn by electrolyte 3+ Mn 4+ Furthermore, the manganese dissolves out, which on the one hand damages the crystal framework and causes irreversible loss of active materials, and on the other hand, the dissolved manganese migrates to the negative electrode and damages the SEI film, continuously increasing the internal resistance of the battery and significantly shortening the cycle life; thirdly, the precipitation pH range of manganese and iron metal ions in aqueous solution is quite different, and conventional liquid phase mixing is prone to causing elemental segregation, forming local manganese-rich areas, which exacerbates the problems of lattice distortion and manganese dissolution.

[0004] The current mainstream modification methods in the industry are carbon coating, nitrogen doping, and metal ion lattice doping. Among them, carbon-nitrogen co-coating is the optimal route that balances conductivity and interface protection. Numerous patents disclose carbon-nitrogen co-coating modified lithium manganese iron phosphate (LFP) technology. For example, Chinese invention patent CN119181792B discloses a single-doped coated LFP cathode material and its preparation method, and a lithium battery; Chinese invention patent CN118888729A discloses a modified LFP material and its preparation method and application; and Chinese invention patent CN120376588A discloses a carbon-nitrogen co-coated LFP cathode material and its preparation method and application. All of these patents adopt a preparation paradigm of liquid-phase blending, ball milling, and direct one-step high-temperature solid-state sintering. Performance optimization is achieved only by adjusting the types and amounts of carbon and nitrogen sources, resulting in severe homogenization of process paths and numerous technical shortcomings that are difficult to eradicate. (1) Traditional processes rely solely on intermolecular forces to adsorb carbon sources onto the surface of precursor particles without chemical bond anchoring. The carbon coating layer generated by high-temperature carbonization has poor continuity and uneven thickness. During charging and discharging, the material volume repeatedly expands and contracts, and the carbon layer is easily peeled off from the particle surface, exposing the substrate to directly contact the electrolyte, accelerating manganese dissolution and interfacial side reactions, resulting in a cliff-like capacity decay in the later stages of cycling.

[0005] (2) One-step high-temperature sintering simultaneously completes crystallization and carbonization. In the low-temperature stage, the carbon source decomposes too quickly, which can easily cause carbon agglomeration. In the high-temperature stage, the grains grow too much and block the lithium-ion diffusion channels. At the same time, a single temperature range cannot take into account the carbon skeleton formation, graphitization and complete crystal growth, making it difficult to balance rate performance and cycle stability.

[0006] In summary, existing carbon-nitrogen co-coated lithium manganese iron phosphate (LFP) technologies are limited to the traditional process framework of "liquid-phase mixing + single high-temperature sintering." Performance improvements are only achieved through optimization of carbon and nitrogen raw material formulations, resulting in low technological barriers and limited modification effects. This makes it difficult to simultaneously meet the industrialization demands for high specific capacity, excellent rate performance, and ultra-long cycle life. Therefore, there is an urgent need to develop a completely new process route that breaks through the traditional sintering modification paradigm and addresses core pain points such as cycle degradation of LFP at the microstructural level. Summary of the Invention

[0007] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a plasma-activated gradient in-situ carbonization lithium manganese iron phosphate cathode material and its preparation method. This solves the problems of easy carbon layer detachment and poor rate capability in traditional processes. The material has a 0.2C capacity of over 157mAh / g, and the rate capability and cycle stability are significantly improved, making it suitable for power batteries and energy storage fields.

[0008] The technical solution of this invention is as follows: In a first aspect, the present invention provides a method for preparing a lithium manganese iron phosphate cathode material by plasma-activated assisted gradient in-situ carbonization, comprising the following steps: Preparation of S1 precursor solution: According to the stoichiometric ratio Li:Mn:Fe:Mg:P=(1-1.1):x:y:(1-xy):1, where 0.4≤x≤0.7, 0.3≤y≤0.6, dissolve the lithium source, manganese source, iron source, magnesium source and phosphorus source in deionized water, add complexing agent and stir thoroughly to prepare the precursor solution; S2 Spray drying: The precursor solution obtained in step S1 is spray dried with an inlet air temperature of 180-250℃ and an outlet air temperature of 80-120℃ to obtain LMFP precursor powder. S3 Plasma activation pretreatment: The LMFP precursor powder obtained in step S2 is subjected to plasma activation treatment in a nitrogen-containing atmosphere. The treatment power is 50-300W and the treatment time is 5-30min, so that controllable lattice defects and active sites are generated on the surface and near-surface layer of the precursor particles, and an initial nitrogen-containing active layer is formed on the surface. S4 Carbon source solution wetting and defect site anchoring: The LMFP precursor powder treated in step S3 is immersed in a carbon source solution with nitrogen-doped carbon precursor added to it. The mixture is stirred and adsorbed at 20-60℃ for 1-6 hours. The surface active sites introduced by plasma activation are used to achieve preferential adsorption and anchoring of carbon source molecules. After solid-liquid separation and drying, carbon source pre-anchored precursor powder is obtained. S5 Gradient In-situ Carbonization Sintering: The precursor powder with carbon source pre-anchored in step S4 is placed in a protective atmosphere for gradient in-situ carbonization sintering, including: (1) Plasma post-treatment / first stage heating: heat to 300-450℃, and apply plasma treatment in this temperature range with an additional power of 50-100W and a time of 5-15min to promote local carbonization of carbon source at the binding site with active sites on the surface of precursor particles, forming a thin-layer internal carbon network framework. (2) Second stage of heating: heat to 550-650℃ and keep warm for 2-4 hours to further graphitize the first carbonized layer and initially induce the decomposition of the carbon source of the outer carbon layer; (3) Third stage of heating: raise to 680-750℃ and keep warm for 4-8 hours to completely carbonize the remaining carbon source to form a dense outer carbon layer, while LMFP completes crystallization; (4) Cooling: Cool naturally to room temperature to obtain the target product.

[0009] Preferably, in step S1, the complexing agent is citric acid and ethylenediaminetetraacetic acid.

[0010] Preferably, in step S3, the discharge method used for plasma activation pretreatment is dielectric barrier discharge, radio frequency discharge, or microwave discharge.

[0011] Preferably, in step S3, the nitrogen-containing atmosphere is nitrogen, ammonia, or a mixture of the two, and the gas flow rate is 20-100 sccm.

[0012] Preferably, in step S4, the carbon source in the carbon source solution is one or more of glucose, sucrose, polyethylene glycol, polyvinyl alcohol, and citric acid, and the concentration of the carbon source solution is 5-20 wt.%.

[0013] Preferably, in step S4, the nitrogen-doped carbon precursor is one or more of melamine, urea, dicyandiamide and polydopamine, and its mass ratio with the carbon source is (0-1):1.

[0014] Preferably, in step (1), the heating rate is 2-5℃ / min.

[0015] Preferably, in step (2), the heating rate is 1-3℃ / min.

[0016] Preferably, in step (3), the heating rate is 0.5-2℃ / min.

[0017] On the other hand, the present invention provides a plasma-activated assisted gradient in-situ carbonized lithium manganese iron phosphate cathode material, which is prepared by the above-mentioned preparation method of plasma-activated assisted gradient in-situ carbonized lithium manganese iron phosphate cathode material.

[0018] Compared with the prior art, the present invention has the following advantages: 1. This invention breaks through the existing technical paradigm of carbon and nitrogen coating, constructing a high-barrier process innovation path. It uniquely employs a three-stage combined process of "plasma activation pretreatment → defect site anchoring → gradient in-situ carbonization sintering," opening up a completely new technical path beyond the selection of carbon and nitrogen source formulations. This process route does not rely on specific carbon or nitrogen source formulations, significantly increasing the technical barrier and making it more difficult to circumvent infringement.

[0019] 2. This invention introduces controllable lattice defects and active sites on the surface and near-surface of precursor particles through plasma activation. These active sites are used to preferentially adsorb and anchor carbon source molecules. Combined with a three-stage gradient heating carbonization process, a three-dimensional conductive network with both carbon and nitrogen doping concentrations increasing gradient from the interior of the LMFP core layer to the outer surface is successfully constructed. Compared with traditional carbon coatings that only act on the particle surface in existing technologies, the gradient carbon layer of this invention extends the conductive network from the surface to the interior of the particles and grain boundaries, significantly improving the overall performance of the material.

[0020] 3. Because this invention significantly improves the actual specific capacity (>157mAh / g at 0.2C) and the stability of the working voltage platform of lithium manganese iron phosphate while maintaining the advantages of high safety and low cost, the energy density of the cathode material is improved compared with traditional lithium iron phosphate cathode materials, which can meet the comprehensive requirements of new generation power batteries and energy storage systems for high energy density, long cycle life and excellent rate performance. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 The method for preparing the plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material in this embodiment includes the following steps: Preparation of S1 precursor solution Lithium carbonate, manganese chloride tetrahydrate, ferrous oxalate, magnesium nitrate, and ammonium dihydrogen phosphate were weighed and dissolved in deionized water according to the molar ratio of Li:Mn:Fe:Mg:P = 1.05:0.6:0.35:0.05:1. Citric acid and ethylenediaminetetraacetic acid (molar ratio 1:1, total molar amount is twice the molar amount of metal ions) were added, and the mixture was stirred at 50°C for 2 hours until completely dissolved to prepare a precursor solution.

[0023] S2 spray drying The above precursor solution was spray-dried at an inlet air temperature of 220°C and an outlet air temperature of 105°C to obtain LMFP precursor powder.

[0024] S3 plasma activation pretreatment The precursor powder obtained by spray drying was placed in a dielectric barrier discharge plasma reactor and subjected to plasma activation pretreatment in a nitrogen:ammonia = 4:1 mixed atmosphere. The treatment power was 150W, the treatment time was 15min, and the gas flow rate was 50sccm, so that controllable lattice defects and active sites were generated on the surface and near-surface of the precursor particles.

[0025] S4 carbon source solution wetting and defect site anchoring The precursor powder, which was pretreated by plasma activation, was immersed in a carbon source solution. The carbon source was glucose, and the concentration of the carbon source solution was 10 wt.%. Polydopamine of 40% of the glucose mass was added, and the mixture was stirred and adsorbed at 40 °C for 2 h. The surface active sites introduced by plasma activation were used to achieve preferential adsorption and anchoring of carbon source molecules. After solid-liquid separation and drying, carbon source pre-anchored precursor powder was obtained.

[0026] S5 gradient in-situ carbonization sintering The precursor powder pre-anchored with carbon source was placed in a tube furnace and subjected to gradient in-situ carbonization sintering in an argon atmosphere (flow rate 100 mL / min): the temperature was increased to 400℃ at a rate of 3℃ / min, and plasma treatment was applied at this temperature with a power of 80W for 10 min; then the temperature was increased to 620℃ at a rate of 2℃ / min and held for 3 h; then the temperature was increased to 700℃ at a rate of 1℃ / min and held for 6 h; the temperature was naturally cooled to room temperature and ground through a 200-mesh sieve to obtain the target product.

[0027] Example 2 The method for preparing the plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material in this embodiment includes the following steps: Preparation of S1 precursor solution Lithium carbonate, manganese chloride tetrahydrate, ferrous oxalate, magnesium nitrate, and ammonium dihydrogen phosphate were weighed and dissolved in deionized water according to the molar ratio of Li:Mn:Fe:Mg:P = 1.05:0.6:0.35:0.05:1. Citric acid and ethylenediaminetetraacetic acid (molar ratio 1:1, total molar amount is twice the molar amount of metal ions) were added, and the mixture was stirred at 50°C for 2 hours until completely dissolved to prepare a precursor solution.

[0028] S2 spray drying The above precursor solution was spray-dried at an inlet air temperature of 220°C and an outlet air temperature of 105°C to obtain LMFP precursor powder.

[0029] S3 plasma activation pretreatment The precursor powder obtained by spray drying was placed in a radio frequency discharge plasma reactor and subjected to plasma activation pretreatment under a pure nitrogen atmosphere. The treatment power was 200W, the treatment time was 10min, and the gas flow rate was 50sccm, so that controllable lattice defects and active sites were generated on the surface and near-surface of the precursor particles.

[0030] S4 carbon source solution wetting and defect site anchoring The precursor powder, which was pretreated by plasma activation, was immersed in a carbon source solution. The carbon source was glucose and the concentration of the carbon source solution was 10 wt.%. The mixture was stirred and adsorbed at 40 °C for 2 h. The surface active sites introduced by plasma activation were used to achieve preferential adsorption and anchoring of carbon source molecules. After solid-liquid separation and drying, carbon source pre-anchored precursor powder was obtained.

[0031] S5 gradient in-situ carbonization sintering The precursor powder pre-anchored with carbon source was placed in a tube furnace and subjected to gradient in-situ carbonization sintering in an argon atmosphere (flow rate 100 mL / min): the temperature was increased to 400℃ at a rate of 3℃ / min, and plasma treatment was applied at this temperature with a power of 80W for 10 min; then the temperature was increased to 620℃ at a rate of 2℃ / min and held for 3 h; then the temperature was increased to 700℃ at a rate of 1℃ / min and held for 6 h; the temperature was naturally cooled to room temperature and ground through a 200-mesh sieve to obtain the target product.

[0032] Example 3 The method for preparing the plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material in this embodiment includes the following steps: Preparation of S1 precursor solution Lithium carbonate, manganese chloride tetrahydrate, ferrous oxalate, magnesium nitrate, and ammonium dihydrogen phosphate were weighed and dissolved in deionized water according to the molar ratio of Li:Mn:Fe:Mg:P = 1.05:0.55:0.4:0.05:1. Citric acid and ethylenediaminetetraacetic acid (molar ratio 1:1, total molar amount is twice the molar amount of metal ions) were added, and the mixture was stirred at 50°C for 2 hours until completely dissolved to prepare a precursor solution.

[0033] S2 spray drying The above precursor solution was spray-dried at an inlet air temperature of 220°C and an outlet air temperature of 105°C to obtain LMFP precursor powder.

[0034] S3 plasma activation pretreatment The precursor powder obtained by spray drying was placed in a dielectric barrier discharge plasma reactor and subjected to plasma activation pretreatment in a nitrogen:ammonia = 4:1 mixed atmosphere. The treatment power was 150W, the treatment time was 15min, and the gas flow rate was 50sccm, so that controllable lattice defects and active sites were generated on the surface and near-surface of the precursor particles.

[0035] S4 carbon source solution wetting and defect site anchoring The precursor powder, which was pretreated by plasma activation, was immersed in a carbon source solution. The carbon source was sucrose, and the concentration of the carbon source solution was 15 wt.%. Melamine with a mass of 50% of sucrose was added, and the mixture was stirred and adsorbed at 40 °C for 4 h. The surface active sites introduced by plasma activation were used to achieve preferential adsorption and anchoring of carbon source molecules. After solid-liquid separation and drying, carbon source pre-anchored precursor powder was obtained.

[0036] S5 gradient in-situ carbonization sintering The precursor powder pre-anchored with carbon source was placed in a tube furnace and subjected to gradient in-situ carbonization sintering in an argon atmosphere (flow rate 100 mL / min): the temperature was increased to 380℃ at a rate of 3℃ / min, and plasma treatment was applied at this temperature with a power of 50W for 15 min; then the temperature was increased to 600℃ at a rate of 2℃ / min and held for 4 h; then the temperature was increased to 720℃ at a rate of 1℃ / min and held for 5 h; the temperature was naturally cooled to room temperature and ground through a 200-mesh sieve to obtain the target product.

[0037] Comparative Example 1 The difference from Example 1 is that step S3 is omitted. Instead, the LMFP precursor powder is directly mixed with glucose (10% of the theoretical LMFP mass) and polydopamine (40% of the glucose mass) and ball-milled. The mixture is then calcined at 700°C for 10 hours under an argon atmosphere at a rate of 5°C / min to obtain carbon-coated LMFP material.

[0038] Comparative Example 2 The difference from Example 1 is that the precursor powder after plasma activation pretreatment in step S3 is mixed with glucose (10% of the theoretical LMFP mass) and polydopamine (40% of the glucose mass) and ball-milled, and then calcined at 700°C for 10 hours under an argon atmosphere at a rate of 5°C / min to obtain the cathode material.

[0039] Comparative Example 3 Commercially available conventional carbon-coated lithium manganese iron phosphate cathode material was selected (with similar chemical composition and Mg doping).

[0040] Comparative Example 4 The difference from Example 1 is that no plasma treatment is applied in step S5.

[0041] The cathode materials prepared in Examples 1-3 and Comparative Examples 1-4 were assembled into CR2032 coin cells. The test conditions were: voltage range of 2-4.3 V and test temperature of 25℃. The test results are summarized in Table 1.

[0042] Table 1 Performance test results of the assembled batteries in Examples 1-3 and Comparative Examples 1-4 Example 1 achieved an initial discharge specific capacity of 160.1 mAh / g at 0.2C, with an initial coulombic efficiency of 99.1%, significantly better than Comparative Example 1 (155.1 mAh / g, 97.8%) and Comparative Example 3 (150.8 mAh / g, 96.8%). Example 1 also achieved a discharge specific capacity of 132.5 mAh / g at a high rate of 5C, which is 13.8% higher than Comparative Example 1 (116.4 mAh / g) and 32.2% higher than Comparative Example 3 (100.2 mAh / g), fully demonstrating the advantages of the gradient conductive network constructed in this invention under high-rate charge and discharge conditions.

[0043] Example 1 showed a capacity retention of up to 94.5% after 500 cycles at 1C rate, which was far superior to Comparative Example 1 (88.7%) and Comparative Example 3 (81.5%). This indicates that the active sites introduced by plasma activation and the seamless conductive network formed by gradient carbonization effectively suppressed manganese dissolution and structural degradation during the charge and discharge process.

[0044] Comparative Example 2, which only underwent plasma activation but used conventional one-step sintering, showed significantly worse performance than Example 1. This demonstrates that the three-stage combined process of "plasma activation pretreatment + defect site anchoring + gradient in-situ carbonization sintering" of the present invention has a synergistic effect, rather than being a simple superposition of single steps. Meanwhile, Comparative Example 4, which did not undergo plasma post-treatment, also showed lower performance than Example 1, indicating that the auxiliary application of low-power plasma treatment during the first stage of heating plays an important role in the formation of the internal carbon network framework.

Claims

1. A method for preparing a plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material, characterized in that, Includes the following steps: Preparation of S1 precursor solution: According to the stoichiometric ratio Li:Mn:Fe:Mg:P=(1-1.1):x:y:(1-xy):1, where 0.4≤x≤0.7, 0.3≤y≤0.6, dissolve the lithium source, manganese source, iron source, magnesium source and phosphorus source in deionized water, add complexing agent and stir thoroughly to prepare the precursor solution; S2 Spray drying: The precursor solution obtained in step S1 is spray dried with an inlet air temperature of 180-250℃ and an outlet air temperature of 80-120℃ to obtain LMFP precursor powder. S3 Plasma activation pretreatment: The LMFP precursor powder obtained in step S2 is subjected to plasma activation treatment in a nitrogen-containing atmosphere. The treatment power is 50-300W and the treatment time is 5-30min. S4 Carbon source solution wetting and defect site anchoring: The LMFP precursor powder treated in step S3 is immersed in a carbon source solution with nitrogen-doped carbon precursor added to it. The mixture is stirred and adsorbed at 20-60℃ for 1-6 hours. After solid-liquid separation and drying, carbon source pre-anchored precursor powder is obtained. S5 Gradient In-situ Carbonization Sintering: The precursor powder with carbon source pre-anchored in step S4 is placed in a protective atmosphere for gradient in-situ carbonization sintering, including: (1) Plasma post-treatment / first stage heating: heat to 300-450℃, and apply plasma treatment in this temperature range with an additional power of 50-100W for 5-15min; (2) Second stage of heating: raise the temperature to 550-650℃ and keep it warm for 2-4 hours; (3) Third stage of heating: raise the temperature to 680-750℃ and keep it warm for 4-8 hours; (4) Cooling: Cool naturally to room temperature to obtain the target product.

2. The method for preparing the plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, In step S1, the complexing agents are citric acid and ethylenediaminetetraacetic acid.

3. The method for preparing the plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, In step S3, the discharge method used for plasma activation pretreatment is dielectric barrier discharge, radio frequency discharge, or microwave discharge.

4. The method for preparing the plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, In step S3, the nitrogen-containing atmosphere is nitrogen, ammonia, or a mixture of the two, and the gas flow rate is 20-100 sccm.

5. The method for preparing the plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, In step S4, the carbon source in the carbon source solution is one or more of glucose, sucrose, polyethylene glycol, polyvinyl alcohol, and citric acid, and the concentration of the carbon source solution is 5-20 wt.%.

6. The method for preparing the plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, In step S4, the nitrogen-doped carbon precursor is one or more of melamine, urea, dicyandiamide and polydopamine, and its mass ratio with the carbon source is (0-1):

1.

7. The method for preparing the plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, In step (1), the heating rate is 2-5℃ / min.

8. The method for preparing the plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, In step (2), the heating rate is 1-3℃ / min.

9. The method for preparing the plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, In step (3), the heating rate is 0.5-2℃ / min.

10. A plasma-activated assisted gradient in-situ carbonization lithium manganese iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode material was prepared by the plasma-activated assisted gradient in-situ carbonization method as described in any one of claims 1-9.

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