Preparation method of high-compaction-density lithium iron manganese phosphate positive electrode material

Abstract

The application discloses a preparation method of a lithium manganese iron phosphate positive electrode material with high compactness, which comprises the following steps: weighing and premixing a lithium source, a manganese source, an iron source and a phosphorus source according to a molar ratio, adding a carbon source and an additive, and sequentially performing sand milling and spray drying; obtaining a primary sintering material after primary sintering, and dividing the primary sintering material into two parts A and B; taking the primary sintering material A, mixing a carbon source and a phosphorus-containing additive, and premixing and sand milling to a target particle size 1; then adding the primary sintering material B, sand milling to a target particle size 2, discharging, spray drying, sintering and crushing to obtain a finished black material; the application realizes good gradation of large and small particles through gradient control of particle size; the introduction of the phosphoric acid ester phosphorus-containing additive not only adjusts the proportion of P-O bonds in the system, but also significantly improves the sand milling process due to unique lubricity, and improves the sphericity of material particles; the lithium manganese iron phosphate positive electrode material prepared by the method has excellent rate performance and obviously improved compactness.

Description

Technical Field

[0001] This invention relates to the field of lithium iron manganese phosphate cathode material preparation technology, and in particular to a method for preparing and applying a high-density lithium iron manganese phosphate cathode material. Background Technology

[0002] Lithium manganese iron phosphate (LiMn) x Fe 1-x LiFePO4 (LFP) serves as an iterative system for lithium iron phosphate (LiFePO4, LFP), retaining the intrinsic structural stability of the olivine-type polyanionic framework while utilizing Mn... 2+ / Fe 2+ A multi-cation synergistic regulation strategy has achieved a dual breakthrough in energy density and structural stability. In the lithium manganese iron phosphate crystal structure, Li... + Reversible insertion / extraction along the one-dimensional channel (010) crystal plane is achieved. Thanks to the strong covalent bond of PO supporting the transition metal oxygen octahedron (MO6), the lattice structure is stable during charging and discharging, resulting in intrinsic high safety (thermal runaway temperature > 250℃) and good cycle life.

[0003] Although lithium manganese iron phosphate and lithium iron phosphate have similar theoretical specific capacities (~170 mAh g⁻¹) -1 ), but Mn 2+ The introduction of [a specific component] reduces the redox potential of lithium manganese iron phosphate from 3.4 V (vs. Li [another component]). + The energy density of Li is increased to 4.1 V. Based on the energy density formula E=Q×V, its volumetric energy density can reach 650-720 Wh / L. -1 Theoretically, compared to lithium iron phosphate (550-600 Wh / L) -1 This can improve efficiency by 15-25%. Therefore, lithium manganese iron phosphate has become an important technological upgrade route for lithium iron phosphate to overcome its energy density bottleneck.

[0004] However, in practical applications, lithium manganese iron phosphate (LFP) generally suffers from low specific capacity and low compaction density. This limits its full potential for energy density and makes it difficult to meet the growing demand from current power battery manufacturers for improved energy density. Therefore, based on the synergistic optimization requirements of lithium-ion battery energy density and electrode structure stability, constructing a lithium manganese iron phosphate cathode material system that combines high volumetric energy density and excellent electrochemical performance has become a core technological path to overcome the range bottleneck of electric vehicles and achieve improved quality and efficiency in energy storage systems. Summary of the Invention

[0005] In view of the problems existing in the current practical application of lithium manganese iron phosphate, this application provides a method for preparing high-density lithium manganese iron phosphate cathode material. The lithium manganese iron phosphate prepared by this method has a significantly improved compaction density and also has excellent rate performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a high-density lithium manganese iron phosphate cathode material, comprising the following specific steps: Step S1: Weigh the lithium source, manganese source, iron source, phosphorus source and carbon source according to the process requirements, add a certain amount of additives and premix the ingredients, then sand mill, spray dry, sinter and pulverize at a certain temperature to obtain the primary sintered material. The lithium, manganese, iron, and phosphorus sources are added in a molar ratio of Li:Mn:Fe:P = (1.03-1.10):0.6:0.4:(1.00-1.10). The amount of carbon source added is based on a carbon content of 0.01-0.10% in the primary sintering material. The solid content is controlled at 25-40%. The primary grinding particle size is controlled at 0.200-0.400 μm. The sintering temperature is 600-900℃, and the sintering time is 5-15h.

[0007] The carbon source can be one of sucrose, glucose, citric acid, starch, or polyethylene glycol; the additive can be one or more of titanium dioxide, magnesium oxide, ammonium metavanadate, or niobium pentoxide, with the doping amount controlled between 200 and 5000 ppm.

[0008] Step S2: Divide the primary sintering material obtained in step S1 into two parts, A and B, according to their mass and a certain ratio.

[0009] The mass ratio of the primary sintering material A to the primary sintering material B can be any integer or non-integer ratio between 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, and 1:9, preferably 4:6.

[0010] Step S3: First, take the primary sintering material A, mixed carbon source, and phosphorus-containing additives, weigh and premix them according to the process requirements, and then grind them to the target particle size of 1.

[0011] The amount of mixed carbon source added is based on the carbon content in the finished black material being between 1.2% and 1.6%. The mixed carbon source can be selected from two or more of the following: sucrose, glucose, citric acid, starch, polyethylene glycol, conductive graphite, activated carbon, carbon nanotubes, and graphene.

[0012] The phosphorus source and the amount of primary sintering material added are in a mass ratio of (0.5-5%):1; wherein the phosphorus source can be one or more of phosphoric acid, metaphosphoric acid, pyrophosphoric acid, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium phosphate and phosphate esters, preferably phosphate esters.

[0013] The phosphate esters mentioned include isooctanol polyoxyethylene ether monophosphate or alkylphenol polyoxyethylene ether phosphate.

[0014] The target particle size is controlled between 0.200 and 0.300 μm; the solid content is controlled between 25% and 35%. Step S4: Add the primary sintering material B, grind it to the target particle size of 2, discharge it, spray dry it, sinter it at a certain temperature, and then crush it to obtain the finished black material.

[0015] The target particle size 2 is controlled between 0.400-0.500 μm; the solid content is adjusted to 25-35%. The sintering temperature is 500-750℃, and the sintering time is 5-15h.

[0016] This invention provides a method for preparing high-compact-density lithium manganese iron phosphate (LFP) cathode materials. The process involves two sintering processes: the first sintering aims to obtain pure-phase LFP, while the second sintering performs carbon coating and adjusts particle morphology and size distribution. This method achieves good particle size distribution by controlling the particle size of the milled LFP particles to create different proportions within the system; and by using phosphorus-containing phosphate additives to increase the proportion of PO bonds in the system, whose unique lubricity also improves the grinding effect between particles. This is particularly helpful in improving the sphericity of large particles—because large particles in the system have a larger diameter and require less grinding time to reach this size, they are prone to forming irregular shapes under conventional grinding conditions, which is detrimental to improving compaction density and electrochemical performance. Based on this approach, LFP cathode materials with both excellent rate performance and high compaction density can be obtained.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This method for preparing a high-density lithium manganese iron phosphate cathode material utilizes additional phosphate ester compounds. These compounds adjust the proportion of PO bonds in the system, directionally inducing particle growth during secondary sintering. Their unique lubricity also effectively promotes particle grinding, significantly improving particle sphericity and thus promoting close packing. These effects synergistically enhance the structural stability of the cathode material, effectively suppress manganese dissolution, and significantly improve the material's electrochemical performance.

[0018] 2. The preparation method of the high compaction density lithium manganese iron phosphate cathode material promotes the distribution of large and small particles in the system more directly by artificially controlling the difference in particle size of the output from two sand milling processes, resulting in a better particle gradation effect and a more significant improvement in compaction.

[0019] 3. The method of the present invention has a simple process flow and low equipment requirements, which can effectively improve production efficiency and thus is suitable for application in large-scale industrial production. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of the lithium iron manganese phosphate cathode material of Example 1 of the present invention. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0022] To better understand the present invention, the following description, in conjunction with embodiments and related drawings, further illustrates the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0023] Example 1 This embodiment provides a method for preparing a high-density lithium manganese iron phosphate cathode material, including the following steps: Step S1: Lithium carbonate, manganese tetroxide, iron phosphate, and phosphoric acid are weighed according to a molar ratio of Li:Mn:Fe:P = 1.05:0.6:0.4:1.07. Glucose is added as a carbon source to ensure the carbon content of the primary sintering material is 500 ppm, along with titanium dioxide and magnesium oxide at doping levels of 3000 ppm and 3500 ppm respectively, to form a mixed slurry. The solid content of the slurry is adjusted to 35%, and the particle size of the primary milling output is controlled between 0.360 ± 0.010 μm. The spray drying outlet temperature is 85℃; the sintering temperature is 650℃, and the sintering time is 10 h. After air jet milling, the primary sintering material is obtained.

[0024] Step S2: Divide the obtained primary sintering material into two parts according to the mass ratio of primary sintering material A: primary sintering material B = 4:6.

[0025] Step S3: First, take the primary sintering material A, add a carbon source mixture consisting of sucrose and polyethylene glycol to make the carbon content of the finished black material 1.55±0.10%, and 0.5% of phosphate ester (isooctyl alcohol polyoxyethylene ether monophosphate) of the primary sintering material. After premixing, grind the slurry to a particle size of 0.300±0.010 μm. Step S4: At this point, add the primary sintering material B, and add an appropriate amount of pure water according to the slurry state to adjust the solid content to 35-40%. Control the particle size of the secondary sand mill output to 0.450±0.010 μm; the spray drying outlet temperature is 85℃; the sintering temperature is 650℃, and the sintering time is 5h. After air jet milling, lithium manganese iron phosphate cathode material with both high compaction density and excellent rate performance can be obtained.

[0026] SEM images of the lithium iron phosphate cathode material prepared according to Example 1 are shown below. Figure 1 As shown.

[0027] Example 2 This embodiment provides a method for preparing a high-density lithium manganese iron phosphate cathode material, including the following steps: Step S1: Lithium carbonate, manganese tetroxide, iron phosphate, and phosphoric acid are weighed according to a molar ratio of Li:Mn:Fe:P = 1.05:0.6:0.4:1.07. Glucose is added as a carbon source to ensure the carbon content of the primary sintering material is 500 ppm, along with titanium dioxide and magnesium oxide at doping levels of 3000 ppm and 3500 ppm respectively, to form a mixed slurry. The solid content of the slurry is adjusted to 35%, and the particle size of the primary milling output is controlled between 0.360 ± 0.010 μm. The spray drying outlet temperature is 85℃; the sintering temperature is 650℃, and the sintering time is 10 h. After air jet milling, the primary sintering material is obtained.

[0028] Step S2: Divide the primary sintering material obtained above into two parts according to the mass ratio of primary sintering material A: primary sintering material B = 5:5.

[0029] Step S3: First, take the primary sintering material A, add a carbon source mixture consisting of sucrose and polyethylene glycol to make the carbon content of the finished black material 1.55±0.10%, and 0.5% of phosphate ester (alkylphenol polyoxyethylene ether phosphate ester) by mass of the primary sintering material. After premixing, grind the slurry to a particle size of 0.300±0.010 μm. Step S4: At this point, add the primary sintering material B, and add an appropriate amount of pure water according to the slurry state to adjust the solid content to 35-40%. Control the particle size of the secondary sand mill output to 0.450±0.010 μm; the spray drying outlet temperature is 85℃; the sintering temperature is 650℃, and the sintering time is 5h. After air jet milling, lithium manganese iron phosphate cathode material with both high compaction density and excellent rate performance can be obtained.

[0030] Example 3 This embodiment provides a method for preparing a high-density lithium manganese iron phosphate cathode material, including the following steps: Step S1: Lithium carbonate, manganese tetroxide, iron phosphate, and phosphoric acid are weighed according to a molar ratio of Li:Mn:Fe:P = 1.05:0.6:0.4:1.07. Glucose is added as a carbon source to ensure the carbon content of the primary sintering material is 500 ppm, along with titanium dioxide and magnesium oxide at doping levels of 3000 ppm and 3500 ppm respectively, to form a mixed slurry. The solid content of the slurry is adjusted to 35%, and the particle size of the primary milling output is controlled between 0.360 ± 0.010 μm. The spray drying outlet temperature is 85℃; the sintering temperature is 650℃, and the sintering time is 10 h. After air jet milling, the primary sintering material is obtained.

[0031] Step S2: Divide the obtained primary sintering material into two parts according to the mass ratio of primary sintering material A: primary sintering material B = 6:4.

[0032] Step S3: First, take the primary sintering material A, add a carbon source mixture consisting of sucrose and polyethylene glycol to make the carbon content of the finished black material 1.55±0.10%, and 0.5% of phosphate ester (isooctyl alcohol polyoxyethylene ether monophosphate) of the primary sintering material. After premixing, grind the slurry to a particle size of 0.300±0.010 μm. Step S4: At this point, add the primary sintering material B, and add an appropriate amount of pure water according to the slurry state to adjust the solid content to 35-40%. Control the particle size of the secondary sand mill output to 0.450±0.010 μm; the spray drying outlet temperature is 85℃; the sintering temperature is 650℃, and the sintering time is 5h. After air jet milling, lithium manganese iron phosphate cathode material with both high compaction density and excellent rate performance can be obtained.

[0033] Example 4 This embodiment provides a method for preparing a high-density lithium manganese iron phosphate cathode material, including the following steps: Step S1: Lithium carbonate, manganese tetroxide, iron phosphate, and phosphoric acid are weighed according to a molar ratio of Li:Mn:Fe:P = 1.05:0.6:0.4:1.07. Glucose is added as a carbon source to ensure the carbon content of the primary sintering material is 500 ppm, along with titanium dioxide and magnesium oxide at doping levels of 3000 ppm and 3500 ppm respectively, to form a mixed slurry. The solid content of the slurry is adjusted to 35%, and the particle size of the primary milling output is controlled between 0.360 ± 0.010 μm. The spray drying outlet temperature is 85℃; the sintering temperature is 650℃, and the sintering time is 10 h. After air jet milling, the primary sintering material is obtained.

[0034] Step S2: Divide the primary sintering material obtained above into two parts according to the mass ratio of primary sintering material A: primary sintering material B = 3:7.

[0035] Step S3: First, take the primary sintering material A, add a carbon source mixture consisting of sucrose and polyethylene glycol to make the carbon content of the finished black material 1.55±0.10%, and 0.5% phosphoric acid by mass of the primary sintering material. After premixing, grind the slurry to a particle size of 0.300±0.010 μm. Step S4: At this point, add the primary sintering material B, and add an appropriate amount of pure water according to the slurry state to adjust the solid content to 35-40%. Control the particle size of the secondary sand mill output to 0.450±0.010 μm; the spray drying outlet temperature is 85℃; the sintering temperature is 650℃, and the sintering time is 5h. After air jet milling, lithium manganese iron phosphate cathode material with both high compaction density and excellent rate performance can be obtained.

[0036] Comparative Example 1 This embodiment provides a method for preparing lithium manganese iron phosphate cathode material, including the following steps: Step S1: Lithium carbonate, manganese tetroxide, iron phosphate, and phosphoric acid are weighed according to a molar ratio of Li:Mn:Fe:P = 1.05:0.6:0.4:1.07. Glucose is added as a carbon source to ensure the carbon content of the primary sintering material is 500 ppm, along with titanium dioxide and magnesium oxide at doping levels of 3000 ppm and 3500 ppm respectively, to form a mixed slurry. The solid content of the slurry is adjusted to 35%, and the particle size of the primary milling output is controlled between 0.360 ± 0.010 μm. The spray drying outlet temperature is 85℃; the sintering temperature is 650℃, and the sintering time is 10 h. After air jet milling, the primary sintering material is obtained.

[0037] Step S2: Take the primary sintering material and add a carbon source mixture consisting of sucrose and polyethylene glycol to make the carbon content of the finished black material 1.55±0.10%, and 0.5% of phosphate ester (isooctanol polyoxyethylene ether monophosphate) of the primary sintering material by mass fraction for premixing. Control the particle size of the secondary sand mill output to 0.300±0.010 μm; the spray drying outlet temperature is 85℃; the sintering temperature is 650℃, the sintering time is 5h, and the lithium manganese iron phosphate cathode material can be obtained after air jet pulverization.

[0038] Comparative Example 2 This embodiment provides a method for preparing lithium manganese iron phosphate cathode material, including the following steps: Step S1: Lithium carbonate, manganese tetroxide, iron phosphate, and phosphoric acid are weighed according to a molar ratio of Li:Mn:Fe:P = 1.05:0.6:0.4:1.07. Glucose is added as a carbon source to ensure the carbon content of the primary sintering material is 500 ppm, along with titanium dioxide and magnesium oxide at doping levels of 3000 ppm and 3500 ppm respectively, to form a mixed slurry. The solid content of the slurry is adjusted to 35%, and the particle size of the primary milling output is controlled between 0.360 ± 0.010 μm. The spray drying outlet temperature is 85℃; the sintering temperature is 650℃, and the sintering time is 10 h. After air jet milling, the primary sintering material is obtained.

[0039] Step S2: Take the primary sintering material and add a carbon source mixture consisting of sucrose and polyethylene glycol to make the carbon content of the finished black material 1.55±0.10%, and 0.5% of phosphate ester (alkylphenol polyoxyethylene ether phosphate ester) of the primary sintering material by mass fraction for premixing. Control the particle size of the secondary sand mill output to 0.450±0.010 μm; spray drying outlet air temperature is 85℃; sintering temperature is 650℃, sintering time is 5h, and lithium manganese iron phosphate cathode material can be obtained after air jet pulverization.

[0040] Comparative Example 3 This embodiment provides a method for preparing lithium manganese iron phosphate cathode material, including the following steps: Step S1: Lithium carbonate, manganese tetroxide, iron phosphate, and phosphoric acid are weighed according to a molar ratio of Li:Mn:Fe:P = 1.05:0.6:0.4:1.07. Glucose is added as a carbon source to ensure the carbon content of the primary sintering material is 500 ppm, along with titanium dioxide and magnesium oxide at doping levels of 3000 ppm and 3500 ppm respectively, to form a mixed slurry. The solid content of the slurry is adjusted to 35%, and the particle size of the primary milling output is controlled between 0.360 ± 0.010 μm. The spray drying outlet temperature is 85℃; the sintering temperature is 650℃, and the sintering time is 10 h. After air jet milling, the primary sintering material is obtained.

[0041] Step S2: Divide the primary sintering material obtained above into two parts according to the mass ratio of primary sintering material A: primary sintering material B = 4:6.

[0042] Step S3: First, take the primary sintering material A and add a carbon source mixture consisting of sucrose and polyethylene glycol to make the carbon content of the finished black material 1.55±0.10%. After premixing, grind the slurry to a particle size of 0.300±0.010 μm. Step S4: At this point, add the primary sintering material B, and add an appropriate amount of pure water according to the slurry state to adjust the solid content to 35-40%. Control the particle size of the secondary sand mill output to 0.450±0.010 μm; the spray drying outlet temperature is 85℃; the sintering temperature is 650℃, and the sintering time is 5h. After air jet milling, lithium manganese iron phosphate cathode material with both high compaction density and excellent rate performance can be obtained.

[0043] Comparative Example 4 This embodiment provides a method for preparing lithium manganese iron phosphate cathode material, including the following steps: Step S1: Lithium carbonate, manganese tetroxide, iron phosphate, and phosphoric acid are weighed according to a molar ratio of Li:Mn:Fe:P = 1.05:0.6:0.4:1.07. Glucose is added as a carbon source to ensure the carbon content of the primary sintering material is 500 ppm, along with titanium dioxide and magnesium oxide at doping levels of 3000 ppm and 3500 ppm respectively, to form a mixed slurry. The solid content of the slurry is adjusted to 35%, and the particle size of the primary milling output is controlled between 0.360 ± 0.010 μm. The spray drying outlet temperature is 85℃; the sintering temperature is 650℃, and the sintering time is 10 h. After air jet milling, the primary sintering material is obtained.

[0044] Step S2: Take the primary sintering material and add a carbon source mixture consisting of sucrose and polyethylene glycol to premix it so that the carbon content of the finished black material is 1.55±0.10%. Control the particle size of the secondary sand mill output to be 0.300±0.010 μm. The spray drying outlet temperature is 85℃. The sintering temperature is 650℃ and the sintering time is 5h. After air jet pulverization, lithium manganese iron phosphate cathode material can be obtained.

[0045] To verify the quality of the high-pressure lithium manganese iron phosphate cathode material prepared by the method provided in this invention, physical property characterization and electrochemical performance testing were performed. The electrochemical performance testing voltage range was 2.5-4.5 V, and the test results are shown in Table 1.

[0046] Table 1. Test items and test results for Examples 1, 2, 3, and 4 and Comparative Examples 1, 2, 3, and 4.

[0047] Comparative analysis of the test results of Examples 1-4 and Comparative Examples 1-4 shows that particle size distribution can be effectively achieved by artificially controlling the particle size gradient in this system. This process has a significant effect on improving the compaction density of the finished lithium manganese iron phosphate product. Experimental data show that different primary / secondary feeding ratios have significant differences in their effects on the compaction density and specific surface area of ​​the material, with the improvement effect being significantly better than that of a single feeding method. In addition, experiments introducing additional phosphorus-containing additives in the secondary sintering stage confirm that this method can effectively adjust the proportion distribution of PO bonds in the material. Compared with phosphoric acid, the introduction of phosphate esters effectively improves the roundness of large particles, which not only effectively improves the compaction density but also improves the electrochemical performance of the material.

[0048] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations; therefore, any obvious variations or modifications derived therefrom remain within the scope of protection of this invention.

Claims

1. A method for preparing a high-density lithium manganese iron phosphate cathode material, characterized in that, The method includes: Step S1: Weigh the lithium source, manganese source, iron source, phosphorus source and carbon source according to the process requirements, add a certain amount of additives and premix the ingredients, then sand mill, spray dry, sinter and pulverize at a certain temperature to obtain the primary sintered material. Step S2: Divide the primary sintering material obtained in step S1 into two parts, A and B, according to their mass and a certain ratio; Step S3: First, take the primary sintering material A, mixed carbon source, and phosphorus-containing additives, weigh and premix them according to the process requirements, and grind them to the target particle size 1. The phosphorus-containing additives are selected from isooctanol polyoxyethylene ether monophosphate or alkylphenol polyoxyethylene ether phosphate. The target particle size 1 is controlled between 0.200-0.300 μm. Step S4: Add primary sintering material B to particle size 1, grind to target particle size 2 and discharge, spray dry, sinter at a certain temperature, and pulverize to obtain finished black material; target particle size 2 is controlled between 0.400-0.500 μm.

2. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S1, the amounts of lithium source, manganese source, iron source and phosphorus source added are in the molar ratio of Li:Mn:Fe:P = (1.03-1.10):0.6:0.4:(1.00-1.10); the amount of carbon source added is based on the carbon content in the primary sintering material being between 0.01-0.10%.

3. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S1, the solid content is controlled at 25-40%; the particle size of the first grinding is controlled between 0.200-0.400 μm; the sintering temperature is 600-900℃ and the sintering time is 5-15h.

4. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S1, the carbon source is selected from sucrose, glucose, citric acid, starch, and polyethylene glycol; the additive is selected from one or more of titanium dioxide, magnesium oxide, ammonium metavanadate, and niobium pentoxide, and the doping amount is controlled between 200-5000 ppm.

5. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S2, the mass ratio of the primary sintering material A to the primary sintering material B is 9:1 to 1:

9.

6. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 5, characterized in that, In step S2, the mass ratio of the primary sintering material A to the primary sintering material B is any one of 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, and 1:

9.

7. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S3, the solid content is controlled between 25% and 35%.

8. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S3, the amount of mixed carbon source added is based on the carbon content in the finished black material being between 1.2% and 1.6%; the mixed carbon source is selected from one or more of sucrose, glucose, citric acid, starch, polyethylene glycol, conductive graphite, activated carbon, carbon nanotubes, and graphene.

9. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S2, the amount of phosphorus-containing additive added is the sum of the masses of primary sintering material A and primary sintering material B, in a total mass ratio of (0.5%-2%):

1.

10. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The phosphorus source is selected from one or more of phosphoric acid, metaphosphoric acid, pyrophosphoric acid, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium phosphate, and phosphate esters.

11. The method for preparing a high-density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S4, the solid content is controlled at 35-40%; the sintering temperature is 600-750℃; and the sintering time is 5-15h.

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