Preparation method of lithium iron manganese phosphate positive electrode material by coprecipitation method

Abstract

The invention provides a method for preparing a lithium manganese iron phosphate positive electrode material by a coprecipitation method, which belongs to the technical field of lithium ion batteries and comprises the following steps of: preparing a compact inner core, preparing a shell layer by realizing gradient Ni / Mg concentration by micro-fluidic equipment, treating and calcining by a one-way freezing device, and coating and carbonizing a carbon layer. The inner core (Mn / Ni enrichment) selectively stabilizes Mn < 3 + > / Mn < 4 + > redox pairs through Ni doping, the Jahn-Teller effect is inhibited while the high voltage (4.1 V) is maintained, and fast capacity fading caused by Mn < 3 + > in a traditional LMFP material is avoided; the shell (Fe / Mg enrichment) occupies the Li < + > site through Mg < 2 + > doping to form a pillar effect, and lattice collapse in circulation is inhibited. According to the scheme, voltage-stability-dynamics triple optimization is realized through core-shell component gradual change.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a method for preparing a lithium manganese iron phosphate positive electrode material using a co-precipitation method. Background Art

[0002] Lithium manganese iron phosphate (LMFP) is an upgraded version of lithium iron phosphate. Its creation aimed to further improve energy density while maintaining the safety and recyclability advantages of phosphate. From 2014 to 2016, LFP held a higher market share than ternary materials. While continuously optimizing LFP, researchers also actively developed LMP. However, with the introduction of differentiated subsidies based on energy density in 2017, high-energy-density ternary materials became mainstream, stalling the development of LMP technology.

[0003] Lithium manganese iron phosphate (LMP) is a combination of lithium manganese phosphate (LMP) and lithium iron phosphate (LFP), leveraging the advantages of both. LMP's high voltage platform offers higher energy density, comparable cycling and safety performance to LFP, and superior low-temperature performance. However, its low conductivity, dual voltage platform, and manganese dissolution make industrial production difficult, making it difficult to balance material performance and cost. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing lithium manganese iron phosphate positive electrode material by a co-precipitation method to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for preparing lithium manganese iron phosphate positive electrode material by a co-precipitation method comprises the following steps:

[0007] S1, mixing and dissolving a manganese source, an iron source, and a nickel source, adding a phosphorus source, adjusting the pH, and then adding a lithium source, reacting and aging, washing and drying the precipitate to obtain a LMFP precursor, and calcining to obtain a dense core;

[0008] S2, dissolving a manganese source, an iron source, a nickel source, a magnesium source, and a phosphorus source in deionized water, mixing the solution to prepare a Ni / Mg mixed solution, and achieving a gradual change in Ni / Mg concentration using a microfluidic device;

[0009] S3, dispersing the core prepared in S1 in the gradient solution of S2, adding a lithium source, a pore-forming agent, and a dispersant, adjusting the pH, and performing a secondary reaction to obtain a mixed solution;

[0010] S4, treating the mixed solution obtained in S3 using a one-way freezing device, and calcining the treated solution to obtain a core-porous shell material;

[0011] S5, CNT and Pu prepolymer are mixed, surfactant is added and ultrasonic treatment is performed, and the mixture is coated on the surface of the core-porous shell. After curing, gradient carbonization treatment is performed to form an elastic-conductive interwoven network, and finally hydrogen-containing inert gas is introduced and calcined to obtain the product.

[0012] Preferably, in terms of molar ratio, in step S1, manganese source: iron source: nickel source = (6.5-7.5): (2-3): (0.5-1.5); in step S2, manganese source: iron source: nickel source: magnesium source = 4:5:1:1.

[0013] Preferably, in step S1, the pH is adjusted to 8-9, a lithium source is added, and the mixture is reacted, then stirred and aged for 6 hours, and the precipitate is calcined at 600° C. for 4 hours in an argon atmosphere.

[0014] Preferably, in step S3, the mass ratio of pore-forming agent:LMFP precursor:dispersant is 25:75:(0.1-0.5), the pore-forming agent is ammonium bicarbonate, and the dispersant is polyvinyl pyrrolidone.

[0015] Preferably, in step S3, the pH is adjusted to 7, and a secondary reaction is carried out at 50° C. for 4 hours.

[0016] Preferably, in step S4, the one-way freezing device treatment comprises: immersing the bottom copper plate of the one-way freezing device in liquid nitrogen, passing -80°C nitrogen gas through the top, freezing at a rate of 50°C / s, then maintaining at -50°C and 0.05 mbar for 24 hours, and then heating to 25°C at a rate of 1°C / min;

[0017] The calcination includes: calcining at 600° C. for 2 hours in an argon atmosphere to remove polyvinyl pyrrolidone and enhance crystallinity.

[0018] Preferably, in step S5, the mass ratio of PU prepolymer: CNT: surfactant is 95:5:0.5, the surfactant is sodium dodecylbenzenesulfonate, and the coating amount is 8-12% of the total mass of the core-porous shell;

[0019] Preferably, in step S5, the curing is performed at 80°C for 3 hours; the gradient carbonization is performed by adding a catalyst to assist carbonization, and in an Ar gas environment, part of the PU is carbonized at 350°C, 300°C and 350°C in sequence, wherein the catalyst is ferric nitrate and the amount of catalyst added is 1% of the total mass; the calcination is performed by passing argon containing 5% hydrogen and calcining at 50°C for 2 hours.

[0020] Preferably, the manganese source includes one or more of manganous nitrate, manganous sulfate and manganous oxalate;

[0021] The iron source includes one or more of ferrous nitrate, ferrous sulfate, ferrous oxalate and ferrous chloride;

[0022] The nickel source includes one or more of nickel nitrate, nickel sulfate and nickel oxalate;

[0023] The magnesium source includes one or more of magnesium nitrate, magnesium sulfate and magnesium oxalate;

[0024] The lithium source is one or more of lithium carbonate, lithium hydroxide and lithium dihydrogen phosphate;

[0025] The phosphorus source includes one or more of phosphoric acid, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate.

[0026] The invention also discloses a lithium manganese iron phosphate positive electrode material, which is prepared by the above method.

[0027] The beneficial effects of the above technical solution of the present invention are as follows:

[0028] 1. The core of the present invention (Mn / Ni enriched) selectively stabilizes Mn by Ni doping 3+ / Mn 4+ Redox couple, suppressing the Jahn-Teller effect while maintaining a high voltage (4.1 V), avoiding the Mn 3+ The capacity decay is fast; the shell (Fe / Mg enriched) is 2+ Doping occupies Li + The sites form a "pillar effect" that suppresses lattice collapse during cycling. This scheme achieves triple optimization of voltage, stability, and dynamics by gradually varying the core-shell components.

[0029] 2. The present invention uses microfluidic assisted gradient precipitation to achieve a continuous gradient of Ni / Mg concentration in the shell, reducing the core-shell interface stress; through the one-way freezing pore-making technology, liquid nitrogen (-196°C) at the bottom and nitrogen (-80°C) at the top are cooled to form a vertically oriented ice crystal template, and axial through-hole channels are obtained after sublimation, shortening the electrolyte infiltration time to less than 10 seconds; through the gradient distribution of the pore-forming agent, combined with microfluidics, the shell porosity is achieved from dense inside to sparse outside, balancing the Li + Diffusion and mechanical strength.

[0030] 3. The present invention adopts low-temperature gradient carbonization (350℃-300℃-350℃) to form a gradient coating with a dense outer carbon layer and an elastic inner structure, retaining the PU elastic phase and the CNT conductive network, solving the problem of carbon layer fragmentation. By adding ferric nitrate catalyst, the carbonization time is shortened to 40 minutes, and ultrasonic-assisted surfactant dispersion is used to make the CUT evenly distributed in the PU, avoiding CNT breakage caused by traditional ball milling. Through interfacial hydrogen annealing and H2 reduction at 50℃, surface oxygen vacancies are eliminated, the interface bonding strength between the core-shell and coating is enhanced, and the interface impedance is reduced by 50%.

[0031] 4. The present invention optimizes the preparation process and reduces the calcination and carbonization temperatures. The shell calcination only requires 600°C and the PU carbonization only requires 350°C. By replacing supercritical drying with freeze drying, the directional freezing rate is combined with low-pressure sublimation, avoiding the need for high-cost equipment and reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the accompanying drawings, several embodiments of the present invention are shown in an illustrative and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:

[0033] Figure 1 1 is a comparison chart of rate performance between Example 1 of the present invention and Conventional Example 1;

[0034] Figure 2 SEM of Example 1 of the present invention Figure 1 ;

[0035] Figure 3 SEM of Example 1 of the present invention Figure 2 . DETAILED DESCRIPTION

[0036] A method for preparing lithium manganese iron phosphate positive electrode material by a co-precipitation method comprises the following steps:

[0037] S1, manganese source, iron source and nickel source are mixed and dissolved in deionized water in a molar ratio of (6.5-7.5): (2-3): (0.5-1.5), and the total metal concentration is controlled to be 0.5-1M. Then, a phosphorus source of the same concentration is added and the pH is adjusted to 8-9. Finally, the stoichiometric ratio of Li:Mn is used. (1-x-y) Fe x Ni y PO4=1:1.1~1.2, the balance is added with lithium source, stirred and aged at 60℃ for 6 hours to promote grain growth, centrifuged, the precipitate is washed and dried to obtain LMFP precursor, and the LMFP precursor is calcined at 600℃ in argon atmosphere for 4 hours to obtain a dense core;

[0038] S2, dissolving the manganese source: iron source: nickel source: magnesium source in deionized water at a molar ratio of 4:5:1:1, controlling the total metal concentration to be the same as the total metal concentration in step S1, and then adding the phosphorus source solution of the same concentration, mixing, preparing a Ni / Mg mixed solution, and realizing a gradual change of the Ni / Mg concentration through a microfluidic device.

[0039] S3, disperse the core prepared in S1 in the gradient solution of S2, and add the core in the stoichiometric ratio (Li:Mn (1-x-y) Fe x Ni y PO4 / Mn(1-x-y) Fe x Mg y A lithium source was added (PO4=1:1.1~1.2, remainder), and a pore-forming agent (NH4HCO3) and polyvinylpyrrolidone (PVP) were added in a mass ratio of NH4HCO3:LMFP precursor:PVP=25:75:(0.1~0.5), the pH was adjusted to 7, and a secondary reaction was carried out at 50°C for 4h to obtain a mixed solution.

[0040] In step S3, the pH is adjusted to 7 to induce Li + Co-precipitation with transition metal phosphates relies on precise fluid control of microfluidic devices, which allows the Ni / Mg concentration in the solution to change gradually. The Ni concentration decreases linearly until it reaches 0%, and the Mg concentration is initially 0% and increases linearly, forming a uniform transition concentration gradient. During the co-precipitation process, the Ni / Mg ratio gradually changes with the thickness of the coating layer, forming a shell with a gradient composition.

[0041] S4, treating the mixed solution obtained in S3 using a one-way freezing device, and calcining it at 600° C. for 2 hours in an argon atmosphere to remove PVP and enhance crystallinity, thereby obtaining a core-porous shell material;

[0042] Among them, the one-way freezing device treatment includes: immersing the bottom copper plate of the one-way freezing device in liquid nitrogen, passing -80℃ nitrogen gas from the top, freezing at a rate of 50℃ / s, then maintaining at -50℃ and 0.05mbar for 24 hours, and then heating to 25℃ at a rate of 1℃ / min.

[0043] Here, a large temperature gradient is created between liquid nitrogen (approximately -196°C) at the bottom and nitrogen at -80°C at the top. Combined with a high unidirectional freezing rate, this allows ice crystals to grow rapidly from the bottom upward, forming a vertically arranged pore structure. The material is then maintained at -50°C and 0.05mbar for 24 hours before being heated to 25°C at a rate of 1°C / min. This is known as low-pressure freeze drying, which removes ice and / or other solvents by sublimation, preventing the presence of liquids that could cause structural collapse while preserving the material's porous structure. The temperature is then raised slowly to avoid structural damage caused by excessive heating, ensuring thorough drying.

[0044] S5, in terms of mass ratio, PU prepolymer: CNT (carbon nanotube): sodium dodecylbenzenesulfonate = 95:5:0.5 are mixed, ultrasonically treated, and coated on the surface of the core-porous shell. The coating amount is 8-12% of the total weight of the core-porous shell material. Curing is carried out at 80°C for 3 hours, and then 1% of the total weight of the coating amount of iron nitrate is added as a catalyst. In an argon atmosphere, carbonization is carried out at 350°C for 10-15 minutes, 300°C for 15-20 minutes, and 350°C for 8-12 minutes in sequence to partially carbonize the PU to form an elastic-conductive interwoven network. Finally, calcination is carried out at 50°C for 2 hours in an argon atmosphere containing 5% hydrogen gas volume fraction.

[0045] When PU is heated in an inert atmosphere, the urethane bonds in the main chain gradually break at temperatures between 250 and 400°C, forming a carbon residue (amorphous carbon or graphite crystals). This solution uses a gradient carbonization process to selectively decompose some of the chain segments in PU, preserving some of the cross-linked structure to maintain elasticity. Thermogravimetric analysis shows that under these conditions, the target carbon residue rate is 20% to 40%, and nanoindentation testing shows that its elastic modulus remains between 0.4 and 1 GPa.

[0046] In the above steps, the manganese source includes one or more of manganous nitrate, manganous sulfate and manganous oxalate; the iron source includes one or more of ferrous nitrate, ferrous sulfate, ferrous oxalate and ferrous chloride; the nickel source includes one or more of nickel nitrate, nickel sulfate and nickel oxalate; the magnesium source includes one or more of magnesium nitrate, magnesium sulfate and magnesium oxalate; the lithium source is one or more of lithium carbonate, lithium hydroxide and lithium dihydrogen phosphate; and the phosphorus source includes one or more of phosphoric acid, diammonium hydrogen phosphate and ammonium dihydrogen phosphate.

[0047] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0048] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0049] Example 1

[0050] A method for preparing lithium manganese iron phosphate positive electrode material by a co-precipitation method comprises the following steps:

[0051] S1, 7.5 mol Mn(NO3)2, 2 mol Fe(NO3)2 and 0.5 mol Ni(NO3)2 were mixed and dissolved in 10 L deionized water, 10 L 1 M NH4H2PO4 was added, and then the pH was slowly adjusted to 8.5. Then 11 mol Li2CO3 was added, and the mixture was stirred and aged at 60 ° C for 6 hours. The precipitate was washed and dried to obtain LMFP precursor. The LMFP precursor was calcined at 600 ° C in an argon atmosphere for 4 hours to obtain a dense core.

[0052] S2, 4 mol Mn(NO3)2, 5 mol Fe(NO3)2, 1 mol Ni(NO3)2 and 1 mol Mg(NO3)2 were mixed and dissolved in 10 L of deionized water, and 10 mol NH4H2PO4 was added at the same time. The flow rate was controlled by a microfluidic device to achieve a gradual change in Ni / Mg concentration.

[0053] S3, disperse the core prepared in S1 in the Ni / Mg gradient solution obtained in S2, add Li2CO3, NH4HCO3 and PVP, then adjust the pH to 7, and react at 50°C for 4h to obtain a mixed solution, wherein the amount of Li2CO3 added is 12 mol, and the mass ratio is NH4HCO3:LMFP precursor:PVP=25:75:0.3.

[0054] S4, treating the mixed solution obtained in S3 using a one-way freezing device, and after the treatment, calcining the mixed solution at 600° C. for 2 hours in an argon atmosphere to obtain a core-porous shell material.

[0055] S5, PU prepolymer, CNT and sodium dodecylbenzene sulfonate are ultrasonically mixed in a mass ratio of 95:5:0.5, and coated on the surface of the core-porous shell. The coating amount is 10% of the total weight of the core-porous shell material. It is cured at 80°C for 3 hours, and then ferric nitrate is added. In an argon atmosphere, the PU is partially carbonized at 350°C for 15 minutes, 300°C for 15 minutes, and 350°C for 10 minutes to form an elastic-conductive interwoven network. Finally, it is calcined at 50°C for 2 hours in an argon atmosphere containing 5% hydrogen gas volume fraction.

[0056] Example 2

[0057] The preparation method of lithium manganese iron phosphate positive electrode material by the coprecipitation method in the above embodiment 1 is adopted, wherein:

[0058] In S1, the molar ratio of manganous nitrate, ferrous nitrate, and nickel nitrate is 6.5:2.5:1;

[0059] In S3, the mass ratio of NH4HCO3, LMFP precursor and PVP is 25:75:0.1;

[0060] In S5, the coating amount of the PU prepolymer, CNT and sodium dodecylbenzene sulfonate mixture is 8% of the total weight of the core-porous shell material; in an argon atmosphere, the PU is partially carbonized by carbonization at 350°C for 10 minutes, 300°C for 20 minutes, and 350°C for 10 minutes.

[0061] Example 3

[0062] The preparation method of lithium manganese iron phosphate positive electrode material by the coprecipitation method in the above embodiment 1 is adopted, wherein:

[0063] In S1, the molar ratio of manganous nitrate, ferrous nitrate, and nickel nitrate is 6.5:2:1.5;

[0064] In S3, the mass ratio of NH4HCO3, LMFP precursor and PVP is 25:75:0.5;

[0065] In S5, the coating amount of the PU prepolymer, CNT and sodium dodecylbenzene sulfonate mixture is 12% of the total weight of the core-porous shell material. In an argon atmosphere, carbonization is carried out at 350°C for 13 minutes, 300°C for 18 minutes, and 350°C for 9 minutes.

[0066] Comparative Example 1

[0067] The difference from Example 1 is that in step S4, the mixed solution obtained in S3 is not treated using a one-way freezing device, but is directly centrifuged, and the precipitate is washed, dried, and calcined at 600° C. for 2 hours.

[0068] Comparative Example 2

[0069] The difference from Example 1 is that in step S5, no catalyst is added, and carbonization is carried out at a constant temperature of 350° C. for 90 minutes.

[0070] Traditional Example 1

[0071] Step 1, press LiMn x Fe (1-x) Ferrous sulfate and manganous sulfate were weighed in a stoichiometric ratio and dissolved in deionized water to control the total metal concentration to 0.5-1 M. 0.1-0.5 wt% ascorbic acid was added to prevent Fe 2+ oxidation.

[0072] Step 2: Dilute H3PO4 to the same concentration as the metal salt, mix the metal salt solution and the phosphorus source solution in a molar ratio of Fe:Mn:P=(1-x):x:1, slowly add ammonia water or sodium hydroxide under the protection of inert gas to adjust the pH to 8-9, stir and react at 60-80℃ for 2-4 hours to generate a light green precipitate, namely Mn x Fe(1-x) PO4·nH2O precursor.

[0073] Step 3: Take the precipitate from step 2 and wash it with deionized water and ethanol alternately for 3 to 5 times to remove the residual SO4 2- and NH4 + , and vacuum dried to obtain precursor powder.

[0074] Step 4: According to the stoichiometric ratio (Li: Mn x Fe (1-x) PO4=1:1) The precursor powder is mixed with lithium carbonate and / or lithium hydroxide, 5-10 wt% glucose or sucrose is added as a carbon source, carbon-coated, and then calcined at 600-800°C in an inert gas for 6-12 hours to obtain lithium manganese iron phosphate material.

[0075] The results of the tests on Examples 1 to 3, Comparative Examples 1 to 2 and Conventional Example 1 are shown in Table 1 and Figures 1 to 3 As shown:

[0076] Table 1 Comparison of performance data between traditional example and embodiment

[0077]

[0078] Through the above table and Figure 1 By comparison, it can be seen that the performance parameters of Examples 1 to 3 of the present invention are significantly better than those of Comparative Examples 1 to 2 and Traditional Example 1. Among them, the amount of Mn dissolution is relatively greatly reduced, the maximum temperature of the process of the present invention is much lower than that of the traditional example, and the carbonization time of the present invention is shortened to 40 minutes compared with the carbonization time of 90 minutes in Comparative Example 2, the cost is reduced, and the product meets market application needs.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not limiting. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing lithium manganese iron phosphate positive electrode material by co-precipitation method, characterized in that: The following steps are involved: S1, mixing and dissolving a manganese source, an iron source, and a nickel source, adding a phosphorus source, adjusting the pH, and then adding a lithium source, reacting and aging, washing and drying the precipitate to obtain a LMFP precursor, and calcining to obtain a dense core; S2, dissolving a manganese source, an iron source, a nickel source, a magnesium source, and a phosphorus source in deionized water, mixing the solution to prepare a Ni / Mg mixed solution, and achieving a gradual change in Ni / Mg concentration using a microfluidic device; S3, dispersing the core prepared in S1 in the gradient solution of S2, adding a lithium source, a pore-forming agent, and a dispersant, adjusting the pH, and performing a secondary reaction to obtain a mixed solution; S4, treating the mixed solution obtained in S3 using a one-way freezing device, and calcining the treated solution to obtain a core-porous shell material; S5, CNT and Pu prepolymer are mixed, surfactant is added and ultrasonic treatment is performed, and the mixture is coated on the surface of the core-porous shell. After curing, gradient carbonization treatment is performed to form an elastic-conductive interwoven network, and finally hydrogen-containing inert gas is introduced and calcined to obtain the product.

2. The method for preparing lithium manganese iron phosphate positive electrode material by coprecipitation method according to claim 1, characterized in that: In terms of molar ratio, in step S1, manganese source: iron source: nickel source = (6.5-7.5): (2-3): (0.5-1.5); in step S2, manganese source: iron source: nickel source: magnesium source = 4:5:1:

1.

3. The method for preparing lithium manganese iron phosphate positive electrode material by coprecipitation method according to claim 1, characterized in that: In step S1, the pH is adjusted to 8-9, a lithium source is added, and the mixture is reacted, and then stirred and aged for 6 hours. The precipitate is calcined at 600° C. for 4 hours in an argon atmosphere.

4. The method for preparing lithium manganese iron phosphate positive electrode material by coprecipitation method according to claim 1, characterized in that: In step S3, the mass ratio of pore-forming agent:LMFP precursor:dispersant is 25:75:(0.1-0.5), the pore-forming agent is ammonium bicarbonate, and the dispersant is polyvinyl pyrrolidone.

5. The method for preparing lithium manganese iron phosphate positive electrode material by coprecipitation method according to claim 1, characterized in that: In step S3, the pH is adjusted to 7, and a secondary reaction is carried out at 50° C. for 4 h.

6. The method for preparing lithium manganese iron phosphate positive electrode material by coprecipitation method according to claim 1, characterized in that: In step S4, the one-way freezing device treatment includes: immersing the bottom copper plate of the one-way freezing device in liquid nitrogen, passing -80°C nitrogen gas through the top, freezing at a rate of 50°C / s, then maintaining at -50°C and 0.05 mbar for 24 hours, and then heating to 25°C at a rate of 1°C / min; The calcination includes: calcining at 600° C. for 2 hours in an argon atmosphere to remove polyvinyl pyrrolidone and enhance crystallinity.

7. The method for preparing lithium manganese iron phosphate positive electrode material by coprecipitation method according to claim 1, characterized in that: In step S5, the mass ratio of PU prepolymer:CNT:surfactant is 95:5:0.5, the surfactant is sodium dodecylbenzenesulfonate, and the coating amount is 8-12% of the total mass of the core-porous shell.

8. The method for preparing lithium manganese iron phosphate positive electrode material by coprecipitation method according to claim 1, characterized in that: In step S5, the curing is performed at 80°C for 3 hours; the gradient carbonization is performed by adding a catalyst to assist carbonization, and in an Ar gas environment, part of the PU is carbonized at 350°C, 300°C and 350°C in sequence, wherein the catalyst is ferric nitrate; the calcination is performed by passing argon containing 5% hydrogen and calcining at 50°C for 2 hours.

9. The method for preparing lithium manganese iron phosphate positive electrode material by coprecipitation method according to claim 1, characterized in that: The manganese source includes one or more of manganous nitrate, manganous sulfate and manganous oxalate; The iron source includes one or more of ferrous nitrate, ferrous sulfate, ferrous oxalate and ferrous chloride; The nickel source includes one or more of nickel nitrate, nickel sulfate and nickel oxalate; The magnesium source includes one or more of magnesium nitrate, magnesium sulfate and magnesium oxalate; The lithium source is one or more of lithium carbonate, lithium hydroxide and lithium dihydrogen phosphate; The phosphorus source includes one or more of phosphoric acid, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate.

10. A lithium iron manganese phosphate positive electrode material, prepared by the method for preparing a lithium iron manganese phosphate positive electrode material by the coprecipitation method according to any one of claims 1 to 9.

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