Preparation method of ultra-high pressure compact density lithium iron manganese phosphate positive electrode material

Abstract

This invention proposes a method for preparing ultra-high compaction density lithium manganese iron phosphate cathode material, including material preparation, dispersion grinding, spray drying, primary sintering, graded crushing, mixing, secondary sintering, and subsequent crushing and packaging. This invention significantly improves compaction density by grading individual materials separately, achieving precise four-level particle size distribution. It is low-cost, uses widely available raw materials, requires no special equipment, and is suitable for large-scale production. Simultaneously, the primary sintering controls the gradation between large and small particles, while the secondary sintering improves the sphericity of the primary particles. Large particles form the framework, enhancing structural stability and cycle life; the high proportion of small particles improves ionic conductivity; and the significantly improved gradation enhances compaction density. This method effectively improves compaction and electrical properties, achieving a balance between processing performance and electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material preparation, specifically relating to a method for preparing an ultra-high pressure real density lithium manganese iron phosphate cathode material. Background Technology

[0002] Lithium manganese iron phosphate (LMFP) is an upgraded olivine-structured cathode material of lithium iron phosphate (LFP). The introduction of manganese ions gives it a higher operating voltage platform, with a theoretical energy density that is about 20% higher than that of LFP. At the same time, LMFP retains the advantages of olivine structure, such as low cost, high safety, and cycle stability, and its low-temperature performance is better than that of LFP, making it a promising candidate for applications in power batteries and energy storage.

[0003] However, the addition of manganese leads to lower intrinsic electronic conductivity and ion mobility in LMFPs. The industry typically uses methods such as nano-sizing and carbon coating to improve conductivity, but these methods significantly reduce compaction density, increase specific surface area, and deteriorate electrode processing performance.

[0004] Currently, the mainstream approach in the industry for low-voltage lithium manganese iron phosphate (LMFP) production is particle size distribution. This involves adjusting the primary and secondary particles of LMFP through various methods, using sufficiently fine particles to fill the gaps between larger particles, thereby increasing the compaction density of LMFP. Simultaneously, high-valence ions such as vanadium and titanium are added for doping to ensure excellent electrical performance. Existing methods include: ① controlling the particle size of LMFP through grinding, achieving particle size distribution in the slurry stage, mixing slurries of different particle sizes, spray drying, and sintering to form an effective particle size distribution in situ; ② controlling the formation of fine and large particles through segmented sintering to improve compaction. However, both of these methods have limitations. The growth of ground particles during sintering is uncontrollable, and segmented sintering significantly increases energy loss, leading to resource waste. The above methods have significant drawbacks: uncontrollable particle growth during sintering; and high energy consumption, high cost, and difficulty in stable mass production during segmented sintering.

[0005] Therefore, developing a simple, controllable gradation, low energy consumption, and high compaction density LMFP preparation method is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the aforementioned issues, this invention proposes a method for preparing ultra-high compaction density lithium manganese iron phosphate cathode material. This method achieves precise particle size distribution through crushing and grading, and enhances sphericity and conductivity through secondary sintering. It improves compaction density while ensuring electrochemical performance, and the process is stable and easy to mass-produce.

[0007] This invention is achieved through the following technical solution: This invention proposes a method for preparing ultra-high pressure real density lithium manganese iron phosphate cathode material, comprising the following steps: S1: Material preparation: Prepare lithium source, iron source, manganese source, sucrose, PEG and additives, wherein the manganese / iron molar ratio is 8:2 to 5:5, the (manganese + iron) / phosphorus molar ratio is 0.96 to 0.98, the lithium / (manganese + iron) molar ratio is 1.02 to 1.05, and the sucrose to PEG mass ratio is 2:8 to 5:5; and prepare deionized water as a solvent. S2: Dispersion and Grinding: Weigh out 50% solids content deionized water and add it to the stirring and dispersing device and turn on the stirring. Add lithium source, iron source and manganese source, carbon source and additive in sequence, and disperse completely before adding the next one. After all materials have been added, continue stirring for a certain period of time to ensure that they are fully dispersed. After being evenly dispersed, transfer the mixture to the grinding equipment for grinding until the slurry particle size D50 is 0.25~0.4μm. S3. Spray drying: The slurry with qualified particle size from S2 grinding is transferred to the spray drying equipment for spray drying to obtain spray-dried material. During spray drying, the inlet air temperature is 190-220℃ and the outlet air temperature is 80-100℃, so that the moisture content of the spray-dried material is 1.0%-1.5%. S4. First sintering: The spray-dried material after S3 spray drying is transferred to the kiln for sintering. Nitrogen gas is introduced throughout the sintering process, and the oxygen content is controlled between 1 and 3 ppm. The sintering heating rate is 1.5℃ / min. After heating to 750-820℃, it is held for about 10 hours, and then cooled down according to the normal kiln temperature to produce semi-finished material. S5. Grading and Grinding: The semi-finished material sintered in S4 is transferred to the grinding equipment for grinding; by adjusting the parameters of the grading wheel, the grinding D50 is controlled, and LMFP pulverized materials with different D50s are obtained through multiple grindings; the pulverized materials from the cyclone collector in the grading equipment with different grading parameters are collected separately, and the pulverized materials in the cloth bag are also collected; the pulverized materials collected in the cloth bag are screened through a 200-mesh sieve to remove foreign matter, and light fine powder is obtained; S6. Mixing: Add the crushed materials of different particle sizes collected in S5 to the mixer in proportion, and add titanium dioxide and carbon source to mix and obtain a mixture. S7. Secondary sintering: The mixture obtained in S6 is transferred into a kiln for secondary sintering. The sintering temperature is between 650 and 750°C and the holding time is between 2 and 4 hours to obtain the secondary sintered material. S8. Crushing and Packaging: The material after secondary sintering is crushed to the target particle size and then vacuum-packed.

[0008] Preferably, the lithium source in steps S1 and S2 is lithium carbonate and lithium dihydrogen phosphate, the iron source is spherical iron phosphate, the manganese source is manganese oxide, the carbon source is sucrose, the PEG is a dispersant and auxiliary carbon source, and the additives are magnesium oxide, titanium dioxide and vanadium pentoxide.

[0009] Preferably, in step S2, after lithium carbonate, lithium dihydrogen phosphate, manganese oxide and iron phosphate are added slowly in sequence, they are dispersed for 10-30 minutes each. After adding sucrose, PEG and additives, they are dispersed for 30-50 minutes.

[0010] Preferably, the slurry obtained in step S2 has a solid content of 25% to 37% by weight.

[0011] Preferably, the multi-stage pulverized material obtained in step S5 includes: Powdered material ①: D50 is 2-3 μm; Powdered material ②: D50 is 0.8~1.3μm; Powdered material ③: D50 is 0.3~0.6μm; Crushed material ④: Light fine powder collected in a cloth bag and passed through a 200-mesh sieve.

[0012] Preferably, in step S6, the mass ratio of pulverized material ①, pulverized material ②, and pulverized material ③ is 3:1:1, and the amount of pulverized material ④ added is 5-20% of the total mass of the three.

[0013] Preferably, the sintering heating rate in step S4 is 1.5℃ / min.

[0014] The preparation method of ultra-high pressure real density lithium manganese iron phosphate cathode material proposed in this invention can bring the following beneficial effects: 1. This invention significantly improves compaction density by classifying individual materials into four precise particle sizes. This method only requires controlling particle size through crushing and grading; it is simple to operate and easy to mass-produce. 2. This invention has low cost, uses widely available raw materials, requires no special equipment, and is suitable for large-scale production; 3. The product of this invention controls the gradation between large and small particles through a first firing, and then improves the sphericity of the primary particles through a second firing. Large particles form the skeleton to improve structural stability and cycle life; the high proportion of small particles improves ionic conductivity; and the gradation significantly improves compaction density. This method can effectively improve compaction and electrical properties, achieving a balance between processing performance and electrochemical performance. Attached Figure Description

[0015] Figure 1 SEM image of lithium manganese iron phosphate prepared in Example 3, magnified 20,000 times. Detailed Implementation

[0016] To more clearly explain the overall concept of this invention, the following description is provided in conjunction with the appendix to the specification. Figure 1 Detailed explanations will be provided using examples. Example

[0017] A method for preparing an ultra-high pressure real density lithium manganese iron phosphate cathode material includes the following steps: S1: Preparation: Prepare 2 kg of spherical iron phosphate, 1.84 kg of manganese oxide, 2.114 kg of lithium dihydrogen phosphate, 0.504 kg of lithium carbonate, 0.0134 kg of magnesium oxide, 0.0067 kg of titanium dioxide, 0.001 kg of vanadium pentoxide, 0.2944 kg of PEG, 0.3456 kg of sucrose, and 18.6 kg of deionized water; S2: Dispersion and Grinding: First, weigh a portion of deionized water and add it to the grinder, then turn on the stirrer. Add the lithium, manganese and iron sources, sucrose, PEG and additives in the following order: lithium carbonate, manganese source, iron source, sucrose, PEG and additives. First, add lithium carbonate and stir to disperse for 10-30 minutes. Then add lithium dihydrogen phosphate (dissolve lithium dihydrogen phosphate in water first, then add it slowly) and stir to disperse for 10-30 minutes. Next, add manganese oxide and spherical iron phosphate and stir to disperse for 10-30 minutes. Finally, add magnesium oxide, sucrose, PEG and other additives and stir to disperse for 30-50 minutes to ensure complete dispersion. After thorough dispersion, put the mixture into the grinding equipment for grinding. Grind the slurry to a particle size of D50 of 0.25-0.4μm.

[0018] S3. Spray Drying: After the slurry reaches the required particle size, it enters the spray drying step to obtain spray-dried material. During the spray drying process, the inlet and outlet air temperatures are strictly controlled. The inlet air temperature is 190-220℃, and the outlet air temperature is 80-100℃, ensuring that the moisture content of the spray-dried material is 1.0%-1.5%. S4. First sintering: The spray-dried material is transferred to the sintering equipment for sintering. The oxygen content is controlled between 1-3 ppm throughout the sintering process. The sintering heating rate is 1.5℃ / min, the temperature is raised to 750-820℃, and the temperature is held for about 10 hours. S5. Grading and Crushing: The sintered semi-finished material is transferred to the crushing equipment for particle crushing. Crushing is performed using different grading parameters. The crushed material from the cyclone collector and the crushed material from the filter bag are collected separately, and the fine powder on the filter bag is sieved separately to remove foreign matter and retain the light fine powder. The particle size requirements for the pulverized material collected in the cyclone collector are as follows: Pulverized material ① 3um ≥ D50 ≥ 2um, Pulverized material ② 0.80um ≤ D50 ≤ 1.3um, Pulverized material ③ 0.30um ≤ D50 ≤ 0.6um. The frequency of the classifying wheel should be adjusted according to these requirements to achieve the desired particle size. The crushed material collected in the cloth bag is sieved through a 200-mesh sieve. The light fine powder remaining after sieving is named crushed material ④. S6. Mixing: Mix the crushed material ①, crushed material ②, and crushed material ③ in a ratio of 3:1:1, and add crushed material ④ at 5% of the weight of the mixture. At the same time, add carbon source (sucrose) and titanium source (titanium dioxide) and mix for 30 minutes. S7. Secondary sintering: The resulting mixture is sintered at a temperature of 650-750℃ for 2-4 hours. This yields the secondary sintered material. S8. Crushing and Packaging: The obtained secondary calcined material is crushed to the required particle size and then vacuum-sealed and packaged. Example

[0019] Difference from Example 1: The amount of pulverized material ④ added is 10%.

[0020] The remaining steps are the same as in Example 1. Example

[0021] Difference from Example 1: The amount of pulverized material ④ added is 15% (optimal). The remaining steps are the same as in Implementation 1. Example

[0022] Difference from Example 1: The amount of pulverized material ④ added is 20%.

[0023] The remaining steps are the same as in Implementation 1.

[0024] Comparative Example The raw materials and steps 1-4 are the same as in Example 1. The sintered material obtained in step S4 is not graded or graded. Carbon source and titanium source are directly added for particle crushing treatment, and then sintered and crushed again to obtain the control sample.

[0025] The compaction density and electrochemical performance of the finished products obtained in Examples 1-4 and the comparative examples were tested, and the compaction density and electrochemical performance of the finished products are shown in Table 1.

[0026] Table 1. Comparison of compaction density and electrochemical performance of Examples 1-4 and comparative examples. sample Powder compaction density (g / cm3) 0.1C discharge capacity mAh / g First-time efficiency % 1C discharge capacity mAh / g Example 1 2.41 155.2 95.8 145.5 Example 2 2.45 156.8 96.2 146.9 Example 3 2.50 156.2 96.5 146.3 Example 4 2.43 156.0 96.3 146.1 Comparative Example 2.30 153.5 95.0 141.8 From Table 1 and Figure 1 It can be seen that the optimal compaction density is achieved when the amount of pulverized material ④ added is 15%. In the comparative example, without grading, mixing, or adding fine powder ④, conventional pulverization followed by direct secondary sintering results in low compaction density due to the uniform particle size, poor gradation, and large gaps between particles, preventing dense packing. In contrast, in Example 4, the amount of pulverized material ④ added is 20%, resulting in excessive fine powder, agglomeration, a slight increase in porosity, and a slight decrease in compaction density.

[0027] Meanwhile, in Examples 1-4, the high proportion of small particles and ultrafine powder shortens the ion migration path, significantly improving conductivity. This optimized gradation allows for more complete material activation and smoother lithium-ion insertion / extraction, resulting in a substantial increase in discharge capacity. Simultaneously, large particles provide a structural framework, secondary sintering enhances sphericity and structural strength, and multi-level particles construct rapid ion transport channels, resulting in rate performance significantly superior to conventional processes. This invention, by adding two steps after primary sintering—graded pulverization and precise four-level particle gradation—results in lithium manganese iron phosphate cathode materials with significantly improved compaction density, higher conductivity, larger specific capacity, more stable cycling, and superior rate performance.

[0028] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for preparing an ultra-high pressure real density lithium manganese iron phosphate cathode material, characterized in that, Includes the following steps: S1: Material preparation: Prepare lithium source, iron source, manganese source, sucrose, PEG and additives, wherein the manganese / iron molar ratio is 8:2 to 5:5, the (manganese + iron) / phosphorus molar ratio is 0.96 to 0.98, the lithium / (manganese + iron) molar ratio is 1.02 to 1.05, and the sucrose to PEG mass ratio is 2:8 to 5:5; and prepare deionized water as a solvent. S2: Dispersion and Grinding: Weigh out 50% solids content deionized water and add it to the stirring and dispersing device and turn on the stirring. Add lithium source, iron source and manganese source, carbon source and additive in sequence, and disperse completely before adding the next one. After all materials have been added, continue stirring for a certain period of time to ensure that they are fully dispersed. After being evenly dispersed, transfer the mixture to the grinding equipment for grinding until the slurry particle size D50 is 0.25~0.4μm. S3. Spray drying: The slurry with qualified particle size from S2 grinding is transferred to the spray drying equipment for spray drying to obtain spray-dried material. During spray drying, the inlet air temperature is 190-220℃ and the outlet air temperature is 80-100℃, so that the moisture content of the spray-dried material is 1.0%-1.5%. S4, First sintering: The spray-dried material after S3 spray drying is transferred into the kiln for sintering. Nitrogen gas is introduced throughout the sintering process, and the oxygen content is controlled between 1 and 3 ppm. The sintering heating rate is 1.5℃ / min. After heating to 750~820℃, the temperature is held for about 10 hours, and then the kiln is cooled down normally to produce semi-finished material. S5. Grading and crushing: The semi-finished material sintered in S4 is transferred to the crushing equipment for crushing; by adjusting the parameters of the grading wheel, the crushing D50 is controlled, and LMFP crushed materials with different D50s are obtained through multiple crushing processes. The pulverized material from the cyclone collector in the grading equipment with different grading parameters is collected separately, and the pulverized material in the cloth bag is also collected; the pulverized material collected in the cloth bag is sieved through a 200-mesh sieve to remove foreign matter, and light fine powder is obtained; S6. Mixing: Add the crushed materials of different particle sizes collected in S5 to the mixer in proportion, and add titanium dioxide and carbon source to mix and obtain a mixture. S7. Secondary sintering: The mixture obtained in S6 is transferred into a kiln for secondary sintering. The sintering temperature is between 650 and 750°C and the holding time is between 2 and 4 hours to obtain the secondary sintered material. S8. Crushing and Packaging: The material after secondary sintering is crushed to the target particle size and then vacuum-packed.

2. The method for preparing an ultra-high pressure real density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The lithium source mentioned in steps S1 and S2 is lithium carbonate and lithium dihydrogen phosphate, the iron source is spherical iron phosphate, the manganese source is manganese oxide, the carbon source is sucrose, the PEG is a dispersant and auxiliary carbon source, and the additives are magnesium oxide, titanium dioxide and vanadium pentoxide.

3. The method for preparing an ultra-high pressure real density lithium manganese iron phosphate cathode material according to claim 2, characterized in that, In step S2, after slowly adding lithium carbonate, lithium dihydrogen phosphate, manganese oxide and iron phosphate in sequence, each needs to be dispersed for 10-30 minutes. After adding sucrose, PEG and additives, disperse for 30-50 minutes.

4. The method for preparing an ultra-high pressure real density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The slurry obtained in step S2 has a solid content of 25% to 37% by weight.

5. The method for preparing an ultra-high pressure real density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The multi-stage pulverized material obtained in step S5 includes: Powdered material ①: D50 is 2-3 μm; Powdered material ②: D50 is 0.8~1.3μm; Powdered material ③: D50 is 0.3~0.6μm; Crushed material ④: Light fine powder collected in a cloth bag and passed through a 200-mesh sieve.

6. The method for preparing an ultra-high pressure real density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S6, the mass ratio of pulverized material ①, pulverized material ②, and pulverized material ③ is 3:1:1, and the amount of pulverized material ④ added is 5-20% of the total mass of the three.

7. The method for preparing an ultra-high pressure real density lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S4, the heating rate for each sintering step is 1.5℃ / min.

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