A reverse gradient co-doping method to form Mn-rich 4+ Lithium iron phosphate cathode material with surface stabilization layer and its preparation method

Abstract

This invention discloses a method for forming Mn-rich mn by reverse gradient co-doping. 4+ This invention relates to a lithium iron phosphate cathode material with a surface-stabilized layer and its preparation method, belonging to the field of lithium-ion battery technology. The preparation method includes gradient co-precipitation, molecular-level mixing and carbon source anchoring, and a three-stage atmosphere calcination step. Through reverse gradient doping of anions and cations, in-situ carbon network construction, and weak surface oxidation reconstruction, a Mn-rich layer is formed on the material surface. 4+ A stabilizing layer is constructed, consisting of a three-level conductive network and a defect dipole structure, to suppress Mn. 3+ The Jahn-Teller effect enhances electron and ion transport efficiency. The material of this invention exhibits high electronic conductivity, structural stability, and few interfacial side reactions. It retains over 94% of its capacity after 2000 cycles at 0.5C, combining high capacity, high rate capability, and ultra-long cycle life. The process is controllable, making it suitable for mass production.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a method for forming Mn-rich cells by reverse gradient co-doping. 4+ Lithium manganese iron phosphate cathode material with surface stabilization layer and its preparation method. Background Technology

[0002] Lithium manganese iron phosphate (LiMn) x Fe 1-x LiFePO4, as an olivine-type phosphate cathode material, combines the excellent structural stability and high safety of lithium iron phosphate (LiFePO4) with the high operating voltage (approximately 4.1V vs Li / Li) of lithium manganese phosphate (LiMnPO4). + Lithium manganese iron phosphate (LFP) boasts advantages such as a 15-25% higher energy density compared to traditional lithium iron phosphate, making it a core candidate material for high-energy-density applications like power lithium-ion batteries and energy storage batteries. However, LFP has low intrinsic electronic conductivity (approximately 10⁻⁶ ppm). -10 -10 -8 S / cm), slow lithium-ion diffusion rate (approximately 10). -14 -10 -12 cm 2 / s), and Mn during charging and discharging 3+ It is prone to Jahn-Teller distortion, which causes lattice expansion and contraction, structural collapse and manganese dissolution, resulting in poor rate performance, rapid high-temperature cycling decay and severe interfacial side reactions, which seriously limit its industrial application.

[0003] To address the aforementioned issues, existing technologies primarily employ modification methods such as elemental doping, carbon coating, nano-sizing, and crystal plane manipulation. Single cation doping (e.g., V, Co, Mg, Zr) can optimize lattice defects and improve ionic conductivity to some extent, but the dopant elements tend to distribute uniformly within the particles, diluting the capacity of the active material and making it difficult to specifically enhance surface and interface stability. Anion doping (e.g., F...) - ,Br - While it can regulate the lattice oxygen environment and suppress manganese dissolution, the lack of synergistic matching between anion and cation doping results in a weak charge compensation effect and limited modification effect. Conventional co-precipitation processes struggle to achieve a gradient distribution of dopants, failing to balance bulk capacity and surface stability. Traditional carbon coatings are mostly physical coatings, resulting in poor carbon layer continuity, weak bonding, and a lack of conductive bridging by highly conductive carbides, thus limiting the improvement of electron transport efficiency.

[0004] In summary, there is an urgent need to develop an integrated preparation technology that enables reverse gradient co-doping of anions and cations and in-situ construction of multi-level conductive networks, in order to overcome the bottleneck of electrochemical performance of lithium manganese iron phosphate. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a method for forming Mn-rich mn by reverse gradient co-doping. 4+ The method for preparing a lithium manganese iron phosphate cathode material with a surface stabilization layer involves gradient co-precipitation, molecular-level mixing and carbon source anchoring, and a three-stage atmosphere calcination process. This is achieved through reverse gradient doping of anions and cations, in-situ carbon network construction, and weak surface oxidation reconstruction, resulting in a Mn-rich layer on the material surface. 4+ A stabilizing layer is constructed, consisting of a three-level conductive network and a defect dipole structure, to suppress Mn. 3+ The Jahn-Teller effect enhances electron and ion transport efficiency; the prepared cathode material has high electronic conductivity, stable structure, and few interfacial side reactions. After 2000 cycles at 0.5C, the capacity retention rate exceeds 94%, combining high capacity, high rate capability, and ultra-long cycle life. The process is controllable and suitable for large-scale production.

[0006] The technical solution of this invention is as follows: On the one hand, the present invention provides a method for forming Mn-rich mn by reverse gradient co-doping. 4+ The preparation method of lithium manganese iron phosphate cathode material with surface stabilization layer includes the following steps: S1 gradient coprecipitation reaction: manganese source, iron source, vanadium source, and cobalt source are added in stoichiometric ratio (Li(Mn)) / (2-2-2) / ( ... 0.6 Fe 0.4 ) 1x (V a Co b Br y PO4 is dissolved in deionized water to prepare a mixed metal salt solution, where a + b = x, x:y = 1:(1-2), and a:b = 1:(0.5-2). Under an inert atmosphere, the precipitant and bromine source are added to the mixed metal salt solution for co-precipitation. During the reaction, the precipitant addition rate and pH value are controlled in stages to achieve a gradient distribution of dopant elements within the particles. Specifically: First stage: The pH value is controlled at 8-9, and the precipitant addition rate is v1, so that Mn and Fe are optimally distributed. First, precipitation forms a core rich in Mn and Fe. Second, the pH is gradually decreased to 6.5-7.5 while the precipitant addition rate is gradually increased to v2, where v2:v1 = (1.5-3):1, promoting the co-precipitation of V, Co, and Br, forming a shell layer gradually enriched with doped elements. Third, the pH is maintained at 6.5-7.5, and the precipitant addition rate is v2, ensuring uniform coating of the doped elements on the outer layer. After the reaction, the precursor is aged, filtered, and washed to obtain a precursor with a gradient doped structure. S2 Molecular-level mixing and carbon source anchoring: The precursor is mixed uniformly with lithium source, phosphorus source and composite carbon source in solvent. The composite carbon source includes organic carbon source and nitrogen-containing organic compound. A conductive polymer coating layer is formed on the surface of the precursor through in-situ polymerization reaction. After sand milling or ball milling, it is dried to obtain solid powder. S3 Three-Stage Atmosphere Calcination: The solid powder is placed in a protective atmosphere for three-stage calcination. The first stage (pre-carbonization and doping induction): In an inert atmosphere, the temperature is raised to 400-550℃ and held for 2-5 hours. During this stage, the organic carbon source carbonizes to form a preliminary carbon network, and dopant elements begin to enter the crystal lattice. The second stage (crystallization and carbothermic reduction): The atmosphere is switched to a reducing atmosphere, and the temperature is raised to 700-800℃ and held for 8-12 hours. During this stage, a carbothermic reduction reaction occurs, and some V... 5+ and Co 2+ Reduced to a low valence state, it reacts with carbon in situ to generate VC and CoC nanoparticles, which are anchored in the carbon network; the third stage of calcination (surface reconstruction): cooling to 500-600℃, switching to a CO2 or Ar atmosphere, holding for 1-2 hours, and performing a slight oxidation treatment on the material surface to form a surface rich in Mn. 4+ A stable interface layer is formed; the calcined product is subjected to air jet milling and sieved to obtain lithium manganese iron phosphate cathode material.

[0007] Preferably, in step S1, the pH difference between the first stage and the second stage is ≥1.

[0008] Preferably, in step S1, the reaction temperature is 60-70℃.

[0009] Preferably, in step S2, the mass ratio of organic carbon source to nitrogen-containing organic compound in the composite carbon source is (5-20):1, and the amount of organic carbon source added accounts for 3-8% of the total mass of the precursor, lithium source, phosphorus source and composite carbon source.

[0010] Preferably, in step S2, the organic carbon source is glucose, and the nitrogen-containing organic compound is one or more of polyaniline, polypyrrole, and melamine.

[0011] Preferably, in step S3, the inert atmosphere is N2 or Ar.

[0012] Preferably, in step S3, the heating rate is 1-3℃ / min.

[0013] Preferably, in step S3, the reducing atmosphere is a mixture of H2 and Ar, with the volume fraction of H2 being 5-15%.

[0014] On the other hand, the present invention provides a method for forming Mn-rich mn by reverse gradient co-doping. 4+ The surface-stabilized lithium iron phosphate cathode material is formed by reverse gradient co-doping to create a Mn-rich layer. 4+The lithium manganese iron phosphate cathode material with a surface stabilizing layer was prepared by a specific method.

[0015] Compared with the prior art, the present invention has the following advantages: 1. This invention is the first to propose a doping structure with reverse gradient distribution of cations and anions. The particle core is rich in Mn and Fe to ensure high capacity, while the surface is enriched with V, Co and Br dopants to enhance interface stability and conductivity. This avoids diluting capacity with dopants and maximizes the surface modification effect, achieving a synergistic improvement in bulk capacity and surface performance.

[0016] 2. In this invention, V 5+ / V 4+ Co 2+ / Co 3+ With Br - Electron buffer pairs are formed, and the electron neutrality of the system is maintained through multivalent charge compensation. 5+ The introduction of the inducing part Co 2+ Oxidized to Co 4+ , while Br - Doping with Mn generates additional electrons, maintaining the system's electroneutrality through charge compensation. This multi-valence coexistence system significantly improves the material's electronic conductivity while suppressing Mn doping. 3+ The Jahn-Teller effect reduces lattice strain and improves the structural stability of the material.

[0017] 3. This invention introduces a reducing atmosphere in the three-stage calcination process, which not only achieves full crystallization of the material, but also generates VC and CoC nano-conductive particles in the carbon network through in-situ carbothermal reduction reaction. These highly conductive carbide nanoparticles act as "conductive bridges" to connect the carbon coating layer and the material bulk, constructing a three-level conductive network of bulk doping-interfacial carbon coating-nano-carbide anchoring, forming a continuous conductive path, and significantly reducing interfacial contact resistance and charge transfer impedance.

[0018] 4. The doping elements of this invention are preferentially enriched on the (010) crystal plane where lithium ions diffuse rapidly, Br - Inducing oxygen vacancies and V / Co lattice distortion to form defect dipoles reduces the activation energy for lithium-ion migration, significantly improving the lithium-ion diffusion rate and high-rate charge / discharge capability.

[0019] 5. The three-stage calcination process of the present invention constructs a Mn-rich layer on the material surface. 4+ A stable interface layer effectively suppresses side reactions between the electrolyte and materials, reduces manganese dissolution and structural degradation, and improves battery cycle life and high-temperature cycle stability.

[0020] 6. This invention integrates gradient co-precipitation, molecular-level mixing, and multi-atmosphere segmented calcination into one process, precisely controlling the doping distribution, conductive network, and surface interface. It solves the bottlenecks of existing technologies such as uneven doping, discontinuous conductive network, and unstable interface. The process is highly controllable and suitable for large-scale production. 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 In this embodiment, reverse gradient co-doping forms a Mn-rich environment. 4+ The preparation method of the lithium manganese iron phosphate cathode material with a surface stabilizing layer includes the following steps: S1 gradient coprecipitation reaction A mixed metal salt solution with a total metal ion concentration of 1.2 mol / L was prepared, wherein the molar ratio of Mn:Fe:V:Co was 0.6:0.4:0.02:0.02. Under nitrogen protection, the above mixed metal salt solution was added to the reactor, and simultaneously 2 mol / L NaOH solution and 0.08 mol / L NH4Br solution were added dropwise to carry out a coprecipitation reaction, with a (V+Co):Br molar ratio of 1:1. During the reaction, the precipitant addition rate and pH value were controlled in stages to achieve a gradient distribution of dopant elements within the particles, specifically: Phase 1 (0-2h): pH controlled at 8.5, NaOH solution drop rate 0.5L / h; Second stage (2-4h): linearly decrease pH to 7, increase the NaOH solution dropping rate to 1.2L / h; Third stage (4-6h): Maintain pH=7, NaOH solution drop rate 1.2L / h.

[0023] The reaction temperature was 60℃, and the stirring rate was 400 rpm. After the reaction was completed, the mixture was aged for 5 h, filtered, washed until neutral, and dried under vacuum at 80℃ for 12 h to obtain a precursor with a gradient doped structure.

[0024] S2 Molecular-Level Mixing and Carbon Source Anchoring Take 100g of the above precursor, add 42.5g of lithium carbonate, 110.2g of ammonium dihydrogen phosphate, and a composite carbon source (8g of glucose + 1.5g of polyaniline), add 300mL of anhydrous ethanol, disperse at high speed for 30min, then transfer to a sand mill and mill until the particle size D50 ≤ 300nm. Dry under vacuum at 80℃ to obtain a solid powder of the precursor complex.

[0025] S3 Three-Stage Atmosphere Roasting The above-mentioned composite solid powder was placed in a tube furnace for three-stage calcination: First stage of roasting: N2 atmosphere, temperature increased to 500℃ at 2℃ / min, and held for 4 hours; Second stage of roasting: switch to H2 / N2 mixed gas (H2 volume fraction 8%), heat up to 780℃ at 3℃ / min, and hold for 10h; Third stage of roasting: Cool down to 550℃, switch to CO2 atmosphere, and keep warm for 1.5 hours; The product was allowed to cool naturally to room temperature. The calcined product was then subjected to air jet milling and passed through a 300-mesh sieve to obtain the finished lithium manganese iron phosphate cathode material.

[0026] Example 2 In this embodiment, reverse gradient co-doping forms a Mn-rich environment. 4+ The preparation method of the lithium manganese iron phosphate cathode material with a surface stabilizing layer includes the following steps: S1 gradient coprecipitation reaction A mixed metal salt solution with a total metal ion concentration of 1.2 mol / L was prepared, wherein the molar ratio of Mn:Fe:V:Co was 0.6:0.4:0.02:0.02. Under nitrogen protection, the above mixed metal salt solution was added to the reaction vessel, and simultaneously 2 mol / L NaOH solution and 0.08 mol / L NH4Br solution were added dropwise to carry out a coprecipitation reaction, with a (V+Co):Br molar ratio of 1:2. During the reaction, the precipitant addition rate and pH value were controlled in stages to achieve a gradient distribution of dopant elements within the particles, specifically: Phase 1 (0-2h): pH=8, NaOH solution dropping rate 0.5L / h; Second stage (2-4h): linearly decrease pH to 6.5, increase NaOH solution dropping rate to 0.75L / h; Third stage (4-6h): Maintain pH=6.5, NaOH solution drop rate 0.75L / h.

[0027] The reaction temperature was 65℃, and the stirring rate was 400 rpm. After the reaction was completed, the mixture was aged for 5 h, filtered, washed until neutral, and dried under vacuum at 80℃ for 12 h to obtain a precursor with a gradient doped structure.

[0028] S2 Molecular-Level Mixing and Carbon Source Anchoring Take 100g of the above precursor, add 42.5g of lithium carbonate, 110.2g of ammonium dihydrogen phosphate, and a composite carbon source (10g of glucose + 1g of polypyrrole), add 300mL of anhydrous ethanol, disperse at high speed for 30min, then transfer to a sand mill and mill until the particle size D50 ≤ 300nm. Dry under vacuum at 80℃ to obtain a solid powder of the precursor complex.

[0029] S3 Three-Stage Atmosphere Roasting The above-mentioned composite solid powder was placed in a tube furnace for three-stage calcination: First stage of roasting: Ar atmosphere, temperature increased to 400℃ at 1℃ / min, and held for 5h; Second stage of roasting: switch to H2 / N2 mixed gas (H2 volume fraction 5%), heat up to 700℃ at 3℃ / min, and hold for 12h; Third stage of roasting: Cool down to 500℃, switch to Ar atmosphere, and keep warm for 2 hours; The product was allowed to cool naturally to room temperature. The calcined product was then subjected to air jet milling and passed through a 300-mesh sieve to obtain the finished lithium manganese iron phosphate cathode material.

[0030] Example 3 In this embodiment, reverse gradient co-doping forms a Mn-rich environment. 4+ The preparation method of the lithium manganese iron phosphate cathode material with a surface stabilizing layer includes the following steps: S1 gradient coprecipitation reaction A mixed metal salt solution with a total metal ion concentration of 1.2 mol / L was prepared, wherein the molar ratio of Mn:Fe:V:Co was 0.6:0.4:0.02:0.02. Under nitrogen protection, the above mixed metal salt solution was added to the reactor, and simultaneously 2 mol / L NaOH solution and 0.08 mol / L NH4Br solution were added dropwise to carry out a coprecipitation reaction, with a (V+Co):Br molar ratio of 1:1. During the reaction, the precipitant addition rate and pH value were controlled in stages to achieve a gradient distribution of dopant elements within the particles, specifically: Phase 1 (0-2h): pH=9, NaOH solution dropping rate 0.5L / h; Second stage (2-4h): linearly reduce pH to 7.5, increase the NaOH solution dropping rate to 1.5L / h; Third stage (4-6h): Maintain pH=7.5, NaOH solution drop rate 1.5L / h.

[0031] The reaction temperature was 70℃, and the stirring rate was 400 rpm. After the reaction was completed, the mixture was aged for 5 h, filtered, washed until neutral, and dried under vacuum at 80℃ for 12 h to obtain a precursor with a gradient doped structure.

[0032] S2 Molecular-Level Mixing and Carbon Source Anchoring Take 100g of the above precursor, add 42.5g of lithium carbonate, 110.2g of ammonium dihydrogen phosphate, and a composite carbon source (20g of glucose + 1g of melamine), add 300mL of anhydrous ethanol, disperse at high speed for 30min, then transfer to a sand mill and mill until the particle size D50 ≤ 300nm. Dry under vacuum at 80℃ to obtain a solid powder of the precursor complex.

[0033] S3 Three-Stage Atmosphere Roasting The above-mentioned composite solid powder was placed in a tube furnace for three-stage calcination: First stage of roasting: N2 atmosphere, temperature increased to 550℃ at 3℃ / min, and held for 2 hours; Second stage of roasting: switch to H2 / N2 mixed gas (H2 volume fraction 15%), heat up to 800℃ at 3℃ / min, and hold for 8h; Third stage of roasting: Cool down to 600℃, switch to CO2 atmosphere, and keep warm for 1 hour; The product was allowed to cool naturally to room temperature. The calcined product was then subjected to air jet milling and passed through a 300-mesh sieve to obtain the finished lithium manganese iron phosphate cathode material.

[0034] Comparative Example 1 The difference from Example 1 is that in step S1, a conventional co-precipitation process is used, the pH is kept constant at 7 throughout the reaction, and the precipitant addition rate is kept constant at 0.5 L / h.

[0035] Comparative Example 2 The difference from Example 1 is that in step S3, a N2 atmosphere is used during the second stage of roasting.

[0036] Comparative Example 3 The difference from Example 1 is that in step S3, the third stage of roasting is not performed.

[0037] The positive electrode materials of Examples 1-3 and Comparative Examples 1-3 were uniformly mixed with conductive agent and binder at a mass ratio of 8:1:1. Solvent was added to prepare a positive electrode slurry, which was then uniformly coated onto an aluminum foil current collector. After drying, rolling, and slicing, a positive electrode sheet was formed. Using a lithium metal sheet as the negative electrode and a polypropylene porous membrane as the separator, lithium-ion battery electrolyte was injected. CR2032 coin cells were assembled in an inert atmosphere glove box and subjected to electrochemical performance testing after standing.

[0038] The performance of the batteries assembled in Examples 1-3 and Comparative Examples 1-3 was tested, and the test results are shown in Table 1: Table 1 Performance test results of the assembled batteries in Examples 1-3 and Comparative Examples 1-3 As shown in Table 1, the performance of Comparative Example 1 is inferior to that of Example 1. This is because the uniform doping in Comparative Example 1 results in no gradient distribution of V, Co, and Br within the particles. The doped elements dilute the capacity of the bulk active material and fail to preferentially accumulate on the surface, thus failing to effectively enhance surface stability and conductivity. Mn and Fe still account for a relatively high proportion on the surface, and surface Mn... 3+ Jahn-Teller distortion is prone to occur, which leads to increased manganese dissolution during high-temperature and long-term cycling, severe interfacial side reactions, and a significant increase in impedance.

[0039] In Comparative Example 2, the second-stage calcination did not use a reducing atmosphere, preventing the in-situ generation of highly conductive VC and CoC nanoparticles through carbothermal reduction. Without these "conductive bridges," the electron transport efficiency between the carbon coating and the bulk material decreased, and the interfacial contact resistance increased, leading to a decline in rate performance and cycle stability. Simultaneously, the lack of nanocarbide anchoring resulted in a discontinuous conductive network and increased charge transfer impedance.

[0040] Comparative Example 3 lacked a third stage of calcination, thus failing to form Mn-rich formations on the material surface. 4+ A stable interface layer. Surface Mn remains Mn 2+ / Mn 3+ The manganese is the primary component, and it is easily corroded and dissolved by the electrolyte, leading to increased interfacial side reactions and elevated interfacial impedance. Manganese dissolution is more severe under high-temperature cycling, accelerating capacity decay; therefore, the decrease in cycle retention at 55℃ is particularly noticeable.

[0041] In summary, gradient doping, in-situ generation of conductive carbides, and surface Mn enrichment are key factors. 4+ The synergistic effect of the three components in the stabilizing layer is a key technical feature of this invention for achieving high-performance lithium manganese iron phosphate cathode materials. The absence of any one of these components will significantly affect rate performance, high-temperature cycling stability, or interfacial impedance.

Claims

1. A method for forming Mn-rich mn through reverse gradient co-doping 4+ The method for preparing lithium manganese iron phosphate cathode material with surface stabilization layer is characterized by, Includes the following steps: S1 gradient coprecipitation reaction: manganese source, iron source, vanadium source, and cobalt source are added in stoichiometric ratio (Li(Mn)) / (2-2-2) / ( ... 0.6 Fe 0.4 ) 1x (V a Co b Br y PO4 was dissolved in deionized water to prepare a mixed metal salt solution, where a + b = x, x:y = 1:(1-2), and a:b = 1:(0.5-2). Under an inert atmosphere, the precipitant and bromine source were added to the mixed metal salt solution for co-precipitation. During the reaction, the precipitant addition rate and pH value were controlled in stages: First stage: pH value was controlled at 8-9, and the precipitant addition rate was v1; Second stage: pH value was gradually decreased to 6.5-7.5, while the precipitant addition rate was gradually increased to v2, v2:v1 = (1.5-3):1; Third stage: pH value was maintained at 6.5-7.5, and the precipitant addition rate was v2; After the reaction was completed, the precursor with a gradient doped structure was obtained after aging, filtration, and washing. S2 Molecular-level mixing and carbon source anchoring: The precursor is mixed uniformly with lithium source, phosphorus source and composite carbon source in solvent. The composite carbon source includes organic carbon source and nitrogen-containing organic compound. A conductive polymer coating layer is formed on the surface of the precursor through in-situ polymerization reaction. After sand milling or ball milling, it is dried to obtain solid powder. S3 Three-Stage Atmosphere Calcination: The solid powder is placed in a protective atmosphere for three-stage calcination. The first stage of calcination: in an inert atmosphere, the temperature is raised to 400-550℃ and held for 2-5 hours. The second stage of calcination: the temperature is switched to a reducing atmosphere and the temperature is raised to 700-800℃ and held for 8-12 hours. The third stage of calcination: the temperature is lowered to 500-600℃ and the temperature is switched to a CO2 or Ar atmosphere and held for 1-2 hours. The calcined product is then subjected to air jet milling and sieved to obtain lithium manganese iron phosphate cathode material.

2. The reverse gradient co-doping method for forming Mn-rich mn as described in claim 1 4+ The method for preparing lithium manganese iron phosphate cathode material with surface stabilization layer is characterized by, In step S1, the pH difference between the first stage and the second stage is ≥1.

3. The reverse gradient co-doping method for forming Mn-rich mn as described in claim 1 4+ The method for preparing lithium manganese iron phosphate cathode material with surface stabilization layer is characterized by, In step S1, the reaction temperature is 60-70℃.

4. The reverse gradient co-doping method for forming Mn-rich samples as described in claim 1 4+ The method for preparing lithium manganese iron phosphate cathode material with surface stabilization layer is characterized by, In step S2, the mass ratio of organic carbon source to nitrogen-containing organic compound in the composite carbon source is (5-20):1, and the amount of organic carbon source added accounts for 3-8% of the total mass of precursor, lithium source, phosphorus source and composite carbon source.

5. The reverse gradient co-doping method for forming Mn-rich mn as described in claim 1 4+ The method for preparing lithium manganese iron phosphate cathode material with surface stabilization layer is characterized by, In step S2, the organic carbon source is glucose, and the nitrogen-containing organic compound is one or more of polyaniline, polypyrrole, and melamine.

6. The reverse gradient co-doping method for forming Mn-rich mn as described in claim 1 4+ The method for preparing lithium manganese iron phosphate cathode material with surface stabilization layer is characterized by, In step S3, the inert atmosphere is either N2 or Ar.

7. The reverse gradient co-doping method for forming Mn-rich mn as described in claim 1 4+ The method for preparing lithium manganese iron phosphate cathode material with surface stabilization layer is characterized by, In step S3, the heating rate is 1-3℃ / min.

8. The reverse gradient co-doping method for forming Mn-rich samples as described in claim 1 4+ The method for preparing lithium manganese iron phosphate cathode material with surface stabilization layer is characterized by, In step S3, the reducing atmosphere is a mixture of H2 and Ar, with an H2 volume fraction of 5-15%.

9. A method for forming Mn-rich mn through reverse gradient co-doping 4+ The lithium iron phosphate cathode material with a surface stabilizing layer is characterized in that... Mn-rich formation is achieved by reverse gradient co-doping as described in any one of claims 1-8. 4+ The lithium manganese iron phosphate cathode material with a surface stabilizing layer was prepared by a specific method.

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