Method for preparing high-compaction lithium iron manganese phosphate by solid phase method

Abstract

The application discloses a method for preparing high-compaction lithium manganese iron phosphate by a solid-phase method, which comprises the following steps: (1) mixing a lithium source, a manganese source, an iron source and a phosphorus source, then adding a carbon source and a ball-milling additive, and grinding again to obtain a mixture A with a particle size D50 of 0.3-0.4 microns; (2) mixing the lithium source, the iron source and the phosphorus source, then adding the ball-milling additive, and grinding again to obtain a mixture B with a particle size D50 of 0.5-0.6 microns; (3) mixing the mixture A and the mixture B, then adding the ball-milling additive and grinding again to obtain a mixture C with a particle size D50 of less than 0.5 microns, and then adding the carbon source and grinding for 1-2 hours; and (4) calcining the mixture C in an inert atmosphere, and crushing to obtain high-compaction lithium manganese iron phosphate. The application effectively solves the problem of uneven distribution of materials in the traditional solid-phase method by using the particle size grading of two kinds of materials, and improves the mixing uniformity of the materials, the compaction density of the materials and the electrochemical performance of the materials.

Description

Technical Field

[0001] This invention relates to the field of lithium manganese iron phosphate preparation technology, and more specifically, to a method for preparing high-pressure lithium manganese iron phosphate by solid-state method. Background Technology

[0002] With the increasing global demand for environmental protection and energy, the development of electric vehicles is receiving more and more attention. As the primary power source for electric vehicles, the performance improvement of lithium-ion batteries is crucial. The market has created a more urgent demand for high-energy-density lithium-ion batteries. With the energy density of lithium iron phosphate nearing its limit, lithium manganese phosphate offers advantages over lithium iron phosphate, including high safety, long cycle life, low cost, and environmental friendliness. Furthermore, it features a dual-voltage platform and can improve energy density by approximately 20% compared to LiFePO4, thus gaining market recognition and favor.

[0003] The preparation methods of lithium manganese iron phosphate can be divided into solid-phase methods and liquid-phase methods. The solid-phase method is a process in which materials of phosphorus source, iron source, manganese source and lithium source are mixed evenly and heat-treated at high temperature to make them interact and form the desired material. It is divided into high temperature solid-phase method and carbothermic reduction method. The liquid-phase method is to prepare a solution of soluble metal salts according to the composition of the material to be prepared, and then select a suitable precipitant or use evaporation, sublimation, hydrolysis or other methods to make the metal ions precipitate or crystallize evenly. Finally, the precipitate or crystallize is dehydrated or heated to decompose to obtain the desired material powder. This includes hydrothermal method, sol-gel method and coprecipitation method.

[0004] High-temperature solid-state reaction is a low-cost method suitable for large-scale production, but it suffers from limited material mixing effects, poor product consistency, and difficulty in controlling particle size distribution and morphology. The particle size distribution and morphology affect the contact effect between particles; poor mixing uniformity, particle size mismatch, and loose particle contact result in low and uneven compaction density. Conversely, good mixing uniformity and uniform particle size lead to more even stress distribution between particles, achieving higher and more uniform compaction density. Compaction density directly impacts the energy density, charge-discharge performance, and other electrochemical properties of the cathode material. Therefore, addressing the poor product consistency issue in high-temperature solid-state reactions is crucial for improving the electrochemical performance of materials.

[0005] Existing technologies also employ various methods to address the problems inherent in high-temperature solid-state methods. For instance, Chinese patent CN117996049A discloses a carbon-coated lithium manganese iron phosphate material, its preparation method, and its application. This involves mixing lithium, manganese, iron, and phosphorus sources in a solvent at a molar ratio of (1~1.2):(0.5~0.9):(0.1~0.5):1, followed by centrifugal drying, heat treatment, and calcination to obtain the carbon-coated lithium manganese iron phosphate material. Similarly, Chinese patent CN116216683A discloses a manganese iron phosphate... The method for preparing lithium cathode materials and the prepared cathode materials involve first dispersing lithium, manganese, iron, and phosphorus sources in ultrapure water at a molar ratio of 1:0.5~0.8:0.2~0.5:1, stirring for a period of time, and then adding a carbon source to obtain a mixed slurry. The mixed slurry is then ball-milled for 2~4 hours, sieved, and then sand-milled for 30~50 minutes. After sand milling, it is spray-dried and the powder is collected. Finally, the powder is calcined under an inert atmosphere to obtain lithium manganese iron phosphate. Both of these inventions disperse and mix the raw materials in a solvent. Compared to dry milling, the mixing of each material is more uniform, which can improve the consistency of the product to some extent. However, problems such as precipitation and agglomeration still exist, leading to uneven mixing and limiting the improvement in product consistency.

[0006] Chinese patent CN115676797A also discloses a lithium manganese iron phosphate material, its preparation method, and its application. The method involves first grinding manganese powder and iron powder as raw materials to obtain nano-sized mixed metal powder; then, the nano-sized mixed metal powder, lithium source, and phosphorus source are ball-milled once to obtain primary ball-milled material; the primary ball-milled material is then ball-milled a second time with a flux to obtain secondary ball-milled material; finally, the secondary ball-milled material is sintered under oxidizing and reducing gases to obtain the lithium manganese iron phosphate material. This invention uses manganese powder and iron powder as raw materials, achieving nano-sizing of the mixed metal powder through grinding, resulting in more uniform mixing. The flux further lowers the sintering temperature, and one-step sintering reduces intermediate products and improves production efficiency. Although manganese and iron are nano-mixed, other materials still suffer from uneven mixing. Furthermore, the addition of flux may leave residues, altering the surface properties of the material. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a solid-state method for preparing high-compact lithium manganese iron phosphate. The method employs a stepwise dry grinding process with adjusted distribution of manganese and iron sources to achieve direct sintering after particle size distribution, thereby improving the mixing uniformity of the materials and increasing the compaction density of the materials.

[0008] This invention provides a method for preparing high-pressure lithium manganese iron phosphate using a solid-state method, comprising the following steps:

[0009] (1) Mix lithium source, manganese source, iron source and phosphorus source, then add carbon source and ball milling aid, and then mix and grind until the particle size D50 is 0.3-0.4μm to obtain mixture A;

[0010] (2) Mix lithium source, iron source and phosphorus source, then add ball milling aid, and then mix and grind until the particle size D50 is 0.5-0.6μm to obtain mixture B;

[0011] (3) Mix mixture A and mixture B, then add ball milling aid and grind until the particle size D50≤0.5μm, then add carbon source and grind for 1-2 hours to obtain mixture C;

[0012] (4) The mixture C is calcined in an inert atmosphere and crushed to obtain high-pressure lithium manganese iron phosphate.

[0013] This invention first prepares mixture A and mixture B with different particle sizes, and then mixes and grinds mixture A and mixture B. During the mixing process, particles of different sizes interpenetrate and disperse with each other. Small-sized particles fill the gaps between large-sized particles. Therefore, large-sized particles can act as a supporting framework to prevent small-sized particles from agglomerating together, while small-sized particles can be dispersed around large-sized particles to prevent excessive aggregation of large-sized particles. In this way, the particle size distribution of the material can reduce the local concentration phenomenon that is prone to occur due to a single particle size, making the distribution of the material more uniform at both the macroscopic and microscopic levels, and improving the overall uniformity of the material.

[0014] Meanwhile, in particle size distribution, the particle size difference between the materials should not be too large. Otherwise, small-diameter particles will still agglomerate when filling the gaps between large-diameter particles. Due to the large differences in particle motion, small-diameter particles cannot stably and uniformly fill the gaps between large particles, which can easily lead to local agglomeration of small or large particles, resulting in uneven mixing of materials. Furthermore, due to the large particle size difference, there are significant differences in the settling velocity or flow energy of the particles. During subsequent processing, the small particles may separate from the gaps between large particles under the action of external forces, causing the material to stratify or separate, affecting the stability of the mixing effect, thereby affecting the subsequent processing performance, resulting in overall unevenness of the material, affecting the compaction density of the material, and reducing its quality and performance.

[0015] In this invention, the particle sizes D50 of mixture A and mixture B are 0.3-0.4 μm and 0.5-0.6 μm, respectively, with little difference. Mixture B can stably and uniformly fill the gaps in mixture A, avoiding uneven mixing and agglomeration caused by large particle size differences. Furthermore, the small difference in particle motion prevents stratification or separation, resulting in a stable and uniform mixture. This allows for denser packing in subsequent processing, with smaller particles filling the gaps between larger particles and providing a supporting framework, forming a multi-layered, tightly packed structure. This structure effectively reduces porosity between particles, increases packing density, and thus improves the compaction density of the material, further enhancing the energy density of the battery.

[0016] The present invention has a mixture A containing manganese source material with a smaller particle size and a mixture B without manganese source material with a larger particle size. The mixture A containing manganese source material is uniformly filled between the mixture B without manganese source material, which makes the manganese ions more stable during sintering, effectively increases the compaction density of the material, and ensures the electrochemical performance of the material.

[0017] Finally, the two materials are ground to a particle size D50≤0.5μm, which ensures the uniformity of the final material particle size and makes the final coated carbon layer more uniform and dispersed, further improving the material performance. At the same time, adding the carbon source in two steps (1) and (3) can ensure that the carbon coating is more uniform, forming a continuous conductive layer, which makes the material more conductive.

[0018] The molar ratio of mixture A to mixture B is 3.6~4:0.3~0.61.

[0019] The molar ratio of lithium, manganese, iron and phosphorus in mixture A is 1~1.05:0.75~0.85:0.15~0.25:1.

[0020] The molar ratio of lithium, iron, and phosphorus in mixture B is 1~1.05∶1∶1.

[0021] The molar ratio of lithium, manganese, iron, and phosphorus in mixture C is 1~1.05:0.5~0.9:0.1~0.5:1; the molar ratio of the sum of lithium, manganese, and iron to phosphorus is 1~1.05:1:1.

[0022] In this invention, the amounts of mixture A and mixture B are equally important. Mixture A, which contains manganese source particles with small particle sizes, is more abundant than mixture B, which does not contain manganese source particles with large particle sizes. The small-sized particles tightly and uniformly fill the gaps between the large particles, reducing the overall packing porosity and increasing the compaction density of the material. By combining the element ratios of mixture A and mixture B, not only is the particle size distribution fully utilized, but the element ratios of mixture C are also satisfied. The proportions of each substance in mixture C determine the final manganese-iron doping ratio of lithium manganese iron phosphate. The manganese-iron doping ratio affects the performance of the final lithium manganese iron phosphate, and an appropriate manganese-iron doping ratio ensures better electrochemical performance.

[0023] The amount of carbon source added in step (1) is 5 to 10 wt% of the sum of the masses of each material in step (1).

[0024] The manganese source in step (1) is one or more of manganese carbonate, manganese oxalate, manganese tetroxide, and manganese dioxide.

[0025] The lithium source in steps (1) and (2) is at least one of lithium dihydrogen phosphate, lithium carbonate, lithium hydroxide, lithium oxalate or butyllithium.

[0026] The phosphorus source in steps (1) and (2) is at least one of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, and monoammonium phosphate.

[0027] The iron source in steps (1) and (2) is at least one of ferric phosphate, ferric phosphate dihydrate, ferrous oxalate, or ferric citrate.

[0028] The amount of carbon source added in step (3) is 5 to 10 wt% of the sum of the masses of each material in step (3).

[0029] The carbon source in steps (1) and (3) is one or more of starch, sucrose, glucose, polyethylene glycol and citric acid.

[0030] The ball milling aid in steps (1) to (3) is one or more of titanium dioxide, aluminum oxide or magnesium oxide, and its addition amount is 0.01 to 2 wt% of the sum of the mass of each material in each step.

[0031] The inert protective atmosphere in step (4) is one or more of nitrogen, helium, neon, argon, krypton, xenon, and radon.

[0032] The calcination in step (4) is a segmented calcination. The first segment is held at 300~450℃ for 2~5h, and the second segment is held at 650~850℃ for 8~12h. The heating rate is 1~5℃ / min.

[0033] The slow, segmented heating process prevents uneven carbonization of organic matter, which could affect the quality of subsequent carbon coating. Pre-carbonization at low temperatures forms a uniform carbon layer framework, while further graphitization at high temperatures improves electronic conductivity. Simultaneously, Mn... 3+ It is easy to induce Jahn-Teller distortion. Segmented calcination and slow heating can suppress Mn / Fe segregation and maintain the stability of the olivine structure.

[0034] The compacted density of the high-pressure compacted lithium manganese iron phosphate obtained after crushing in step (4) is greater than 2.45 g / cm³. 3 .

[0035] In summary, this invention prepares a mixture A containing manganese and a mixture B without manganese by using phosphorus, iron, manganese, and lithium sources in different raw materials and proportions. Mixtures A and B have specific different particle sizes. During the mixing and grinding process of mixtures A and B, the particle size distribution of the two materials effectively solves the problem of uneven material distribution in traditional solid-state methods, improving the mixing uniformity. Simultaneously, mixture A, containing manganese, has more small-sized particles than mixture B, which contains larger-sized particles. These smaller particles densely and uniformly fill the gaps between larger particles, reducing the overall packing porosity, ensuring manganese stability, and increasing the compaction density of the material, resulting in high-compacted lithium manganese iron phosphate, thereby improving the energy density of batteries prepared using this material. Furthermore, the elemental proportions of mixtures A, B, and C meet the manganese-iron doping ratio requirements for lithium manganese iron phosphate, ensuring the electrochemical performance of the material. In addition, the method of this invention only involves dry grinding and calcination processes, simplifying the production process and improving production efficiency. Attached Figure Description

[0036] Figure 1 This is the XRD pattern of the high-pressure lithium manganese iron phosphate prepared in Example 1.

[0037] Figure 2 The image shows a SEM image of the high-pressure lithium manganese iron phosphate prepared in Example 1. Detailed Implementation

[0038] The embodiments of this application will now be described in more detail. This application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to provide a more thorough and complete understanding of the application. It should be understood that the embodiments of this application are for illustrative purposes only and are not intended to limit the scope of protection of this application.

[0039] Example 1:

[0040] High-pressure lithium manganese iron phosphate was prepared according to the following steps:

[0041] (1) After uniformly mixing 310.32g lithium carbonate, 689.70g manganese carbonate, 301.64g iron phosphate and 690.17g ammonium dihydrogen phosphate, 159.35g glucose and 19.92g titanium dioxide ball milling aid were added, and the mixture was dry-milled in a high-energy ball mill until the particle size D50 was 0.35μm to obtain mixture A;

[0042] (2) Mix 77.58g of lithium carbonate and 301.64g of iron phosphate, add 3.78g of ball milling aid titanium dioxide, and dry mill using a high-energy ball mill until the particle size D50 is 0.50μm to obtain mixture B;

[0043] (3) Mix mixture A and mixture B, then add 11.95g of ball milling aid titanium dioxide and grind with a high-energy ball mill until the particle size D50 is 0.40μm, then add 143.45g of glucose and grind for 1h to obtain mixture C; wherein the molar ratio of lithium, manganese, iron and phosphorus in mixture C is 1.05∶0.6∶0.4∶1;

[0044] (4) The mixture C was calcined in a nitrogen atmosphere. The calcination was carried out in stages. The first stage was held at 400℃ for 4 hours and the second stage was held at 750℃ for 12 hours. The heating rate was 3℃ / min. After crushing, high-pressure lithium manganese iron phosphate with a D50 of 1.50μm was obtained.

[0045] Example 2:

[0046] High-pressure lithium manganese iron phosphate was prepared according to the following steps:

[0047] (1) After uniformly mixing 329.70g lithium carbonate, 804.65g manganese carbonate, 226.23g iron phosphate and 805.18g ammonium dihydrogen phosphate, 173.26g glucose and 21.66g titanium dioxide ball milling aid were added, and the mixture was dry-milled in a high-energy ball mill until the particle size D50 was 0.35μm to obtain mixture A;

[0048] (2) Mix 58.16g of lithium carbonate and 226.23g of iron phosphate, add 2.84g of ball milling aid titanium dioxide, and dry mill using a high-energy ball mill until the particle size D50 is 0.50μm to obtain mixture B;

[0049] (3) Mix mixture A and mixture B, then add 12.25g of ball milling aid titanium dioxide and grind with a high-energy ball mill until the particle size D50 is 0.40μm, then add 146.96g of glucose and grind for 2h to obtain mixture C; wherein the molar ratio of lithium, manganese, iron and phosphorus in mixture C is 1.05∶0.7∶0.3∶1;

[0050] (4) The mixture C was calcined in a nitrogen atmosphere. The calcination was carried out in stages. The first stage was held at 400℃ for 4 hours and the second stage was held at 750℃ for 12 hours. The heating rate was 3℃ / min. After crushing, high-pressure lithium manganese iron phosphate with a D50 of 1.50μm was obtained.

[0051] Example 3:

[0052] High-pressure lithium manganese iron phosphate was prepared according to the following steps:

[0053] (1) After uniformly mixing 329.70g lithium carbonate, 804.65g manganese carbonate, 226.23g iron phosphate and 805.18g ammonium dihydrogen phosphate, 187.17g glucose and 23.40g titanium dioxide ball milling aid were added, and the mixture was dry-milled in a high-energy ball mill until the particle size D50 was 0.35μm to obtain mixture A;

[0054] (2) Mix 38.79g of lithium carbonate and 150.82g of iron phosphate, add 1.90g of ball milling aid titanium dioxide, and dry mill using a high-energy ball mill until the particle size D50 is 0.50μm to obtain mixture B;

[0055] (3) Mix mixture A and mixture B, then add 12.64g of ball milling aid titanium dioxide and grind with a high-energy ball mill until the particle size D50 is 0.40μm, then add 151.76g of glucose and grind for 1.5h to obtain mixture C; wherein the molar ratio of lithium, manganese, iron and phosphorus in mixture C is 1.05∶0.8∶0.2∶1;

[0056] (4) The mixture C was calcined in a nitrogen atmosphere. The calcination was carried out in stages. The first stage was held at 400℃ for 4 hours and the second stage was held at 750℃ for 12 hours. The heating rate was 3℃ / min. After crushing, high-pressure lithium manganese iron phosphate with a D50 of 1.50μm was obtained.

[0057] Example 4:

[0058] High-pressure lithium manganese iron phosphate was prepared according to the following steps:

[0059] (1) After uniformly mixing 310.32g lithium carbonate, 689.70g manganese carbonate, 301.64g iron phosphate and 690.17g ammonium dihydrogen phosphate, 159.35g glucose and 19.92g titanium dioxide ball milling aid were added, and the mixture was dry-milled in a high-energy ball mill until the particle size D50 was 0.30μm to obtain mixture A;

[0060] (2) Mix 77.58g of lithium carbonate and 301.64g of iron phosphate, add 3.78g of ball milling aid titanium dioxide, and dry mill using a high-energy ball mill until the particle size D50 is 0.60μm to obtain mixture B;

[0061] (3) Mix mixture A and mixture B, then add 11.95g of ball milling aid titanium dioxide and grind with a high-energy ball mill until the particle size D50 is 0.40μm, then add 143.45g of glucose and grind for 1.5h to obtain mixture C; wherein the molar ratio of lithium, manganese, iron and phosphorus in mixture C is 1.05∶0.6∶0.4∶1;

[0062] (4) The mixture C was calcined in a nitrogen atmosphere. The calcination was carried out in stages. The first stage was held at 400℃ for 4 hours and the second stage was held at 750℃ for 12 hours. The heating rate was 3℃ / min. After crushing, high-pressure lithium manganese iron phosphate with a D50 of 1.50μm was obtained.

[0063] Example 5:

[0064] High-pressure lithium manganese iron phosphate was prepared according to the following steps:

[0065] (1) After uniformly mixing 329.70g lithium carbonate, 804.65g manganese carbonate, 226.23g iron phosphate and 805.18g ammonium dihydrogen phosphate, 173.26g glucose and 21.66g titanium dioxide ball milling aid were added, and the mixture was dry-milled in a high-energy ball mill until the particle size D50 was 0.30μm to obtain mixture A;

[0066] (2) Mix 58.16g of lithium carbonate and 226.23g of iron phosphate, add 2.84g of ball milling aid titanium dioxide, and dry mill using a high-energy ball mill until the particle size D50 is 0.60μm to obtain mixture B;

[0067] (3) Mix mixture A and mixture B, then add 12.25g of ball milling aid titanium dioxide and grind with a high-energy ball mill until the particle size D50 is 0.40μm, then add 146.96g of glucose and grind for 1h to obtain mixture C; wherein the molar ratio of lithium, manganese, iron and phosphorus in mixture C is 1.05∶0.7∶0.3∶1;

[0068] (4) The mixture C was calcined in a nitrogen atmosphere. The calcination was carried out in stages. The first stage was held at 400℃ for 4 hours and the second stage was held at 750℃ for 12 hours. The heating rate was 3℃ / min. After crushing, high-pressure lithium manganese iron phosphate with a D50 of 1.50μm was obtained.

[0069] Example 6:

[0070] High-pressure lithium manganese iron phosphate was prepared according to the following steps:

[0071] (1) After uniformly mixing 329.70g lithium carbonate, 804.65g manganese carbonate, 226.23g iron phosphate and 805.18g ammonium dihydrogen phosphate, 187.17g glucose and 23.40g titanium dioxide ball milling aid were added, and the mixture was dry-milled in a high-energy ball mill until the particle size D50 was 0.30μm to obtain mixture A;

[0072] (2) Mix 38.79g of lithium carbonate and 150.82g of iron phosphate, add 1.90g of ball milling aid titanium dioxide, and dry mill using a high-energy ball mill until the particle size D50 is 0.60μm to obtain mixture B;

[0073] (3) Mix mixture A and mixture B, then add 12.64g of ball milling aid titanium dioxide and grind with a high-energy ball mill until the particle size D50 is 0.40μm, then add 151.76g of glucose and grind for 1h to obtain mixture C; wherein the molar ratio of lithium, manganese, iron and phosphorus in mixture C is 1.05∶0.8∶0.2∶1;

[0074] (4) The mixture C was calcined in a nitrogen atmosphere. The calcination was carried out in stages. The first stage was held at 400℃ for 4 hours and the second stage was held at 750℃ for 12 hours. The heating rate was 3℃ / min. After crushing, high-pressure lithium manganese iron phosphate with a D50 of 1.50μm was obtained.

[0075] Comparative Example 1:

[0076] 387.90g of lithium carbonate, 689.70g of manganese carbonate, 603.28g of iron phosphate, and 805.15g of ammonium dihydrogen phosphate were weighed and mixed. Then, 320.22g of glucose and 36.75g of titanium dioxide were added and dry-milled using a high-energy ball mill until the particle size D50 was 0.40μm. The mixture was then placed in a nitrogen atmosphere and calcined at 400℃ for 4h in the first stage and 750℃ for 12h in the second stage, with a heating rate of 3℃ / min. After sintering, the mixture was crushed to a D50 of 1.50μm to obtain lithium manganese iron phosphate.

[0077] Comparative Example 2:

[0078] 387.90g of lithium carbonate, 689.70g of manganese carbonate, 603.28g of iron phosphate, and 805.15g of ammonium dihydrogen phosphate were weighed and mixed. Then, 320.22g of glucose and 36.75g of titanium dioxide were added, and 5280ml of pure water was added and stirred evenly. The mixture was wet-milled using a sand mill until the slurry D50 was 0.40μm. After spray drying, a yellow powder was obtained. The mixture was placed in a nitrogen atmosphere and calcined at 400℃ for 4h in the first stage and 750℃ for 12h in the second stage, with a heating rate of 3℃ / min. After sintering, the powder was crushed to a D50 of 1.50μm to obtain lithium manganese iron phosphate.

[0079] The high-compact lithium manganese iron phosphate prepared in the above embodiments and the lithium manganese iron phosphate prepared in the comparative example were used to form coin cells, and their compaction density and charge-discharge performance were tested.

[0080] Appendix Figure 1 The XRD pattern of the high-pressure lithium manganese iron phosphate prepared in Example 1 shows that its diffraction peaks correspond well with the standard card of lithium manganese iron phosphate, indicating that the prepared material is indeed lithium manganese iron phosphate and has excellent crystallinity; (See attached image) Figure 2 The image shows the SEM image of the high-pressure lithium manganese iron phosphate prepared in Example 1. It can be seen that the sample has achieved particle size distribution and is relatively uniform.

[0081] Comparative Example 1 was prepared by grinding lithium manganese iron phosphate according to the proportions of Example 1 and using the same equipment until the final particle size was uniform; Comparative Example 2 was prepared by following the steps and conditions of Comparative Example 1, but by taking a wet grinding step and adding a spray drying process.

[0082] Table 1 shows the test results of lithium manganese iron phosphate obtained in each example and comparative example. The results show that the compaction density and electrochemical performance of lithium manganese iron phosphate obtained in Examples 1-6 are significantly improved compared with those of the comparative examples, proving that the method of the present invention can not only improve the compaction density of lithium manganese iron phosphate, but also improve its electrochemical performance at the same time. Among them, comparative example 1 did not have stepwise grinding and particle size distribution, resulting in low compaction density and relatively poor electrochemical performance. The lithium manganese iron phosphate prepared by wet grinding and spray drying in comparative example 2 has a significantly lower compaction density, but its electrochemical performance is improved. Compaction density and electrochemical performance cannot be improved at the same time, indicating that the method of the present invention can significantly improve the compaction density of lithium manganese iron phosphate and ensure good electrochemical performance. In addition, it can be seen from the examples that the material with a manganese-iron ratio of 6:4 has better electrochemical performance. Comparing examples 1-3 with examples 4-6, when the particle size difference between mixture A and mixture B is large, the particle size distribution effect is better, and the compaction density of the obtained lithium manganese iron phosphate is higher, proving that a suitable particle size distribution and a suitable ratio of each element can effectively improve compaction density and electrochemical performance.

[0083]

[0084] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection of the claims.

Claims

1. A method for preparing high-pressure lithium manganese iron phosphate via solid-state process, characterized in that, Includes the following steps: (1) Mix lithium source, manganese source, iron source and phosphorus source, then add carbon source and ball milling aid, and then mix and grind until the particle size D50 is 0.3-0.4μm to obtain mixture A; (2) Mix lithium source, iron source and phosphorus source, then add ball milling aid, and then mix and grind until the particle size D50 is 0.5-0.6μm to obtain mixture B; (3) Mix mixture A and mixture B in a molar ratio of 3.6~4:0.3~0.61, then add ball milling aid and grind until the particle size D50≤0.5μm, then add carbon source and grind for 1~2h to obtain mixture C; (4) The mixture C is calcined in an inert atmosphere and crushed to obtain high-pressure lithium manganese iron phosphate.

2. The method for preparing high-pressure lithium manganese iron phosphate by solid-state method according to claim 1, characterized in that, The molar ratio of lithium, manganese, iron and phosphorus in mixture A is 1~1.05:0.75~0.85:0.15~0.25:

1.

3. The method for preparing high-pressure lithium manganese iron phosphate by solid-state method according to claim 1, characterized in that, The molar ratio of lithium, iron, and phosphorus in mixture B is 1~1.05∶1∶1.

4. The method for preparing high-pressure lithium manganese iron phosphate by solid-state method according to claim 1, characterized in that, The molar ratio of lithium, manganese, iron, and phosphorus in mixture C is 1~1.05∶0.5~0.9∶0.1~0.5∶1; The molar ratio of lithium, manganese, iron, and phosphorus is 1~1.05∶1∶1.

5. The method for preparing high-pressure lithium manganese iron phosphate by solid-state method according to claim 1, characterized in that, The amount of carbon source added in step (1) is 5 to 10 wt% of the sum of the masses of each material in step (1).

6. The method for preparing high-pressure lithium manganese iron phosphate by solid-state method according to claim 1, characterized in that, The manganese source in step (1) is one or more of manganese carbonate, manganese oxalate, manganese tetroxide, and manganese dioxide.

7. The method for preparing high-pressure lithium manganese iron phosphate by solid-state method according to claim 1, characterized in that, The lithium source in steps (1) and (2) is at least one of lithium dihydrogen phosphate, lithium carbonate, lithium hydroxide, lithium oxalate or butyllithium.

8. The method for preparing high-pressure lithium manganese iron phosphate by solid-state method according to claim 1, characterized in that, The phosphorus source in steps (1) and (2) is at least one of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, and monoammonium phosphate.

9. The method for preparing high-pressure lithium manganese iron phosphate by solid-state method according to claim 1, characterized in that, The iron source in steps (1) and (2) is at least one of ferric phosphate, ferric phosphate dihydrate, ferrous oxalate or ferric citrate.

10. A method for preparing high-pressure lithium manganese iron phosphate by solid-state method according to claim 1, characterized in that, The amount of carbon source added in step (3) is 5 to 10 wt% of the sum of the masses of each material in step (3).

11. A method for preparing high-pressure lithium manganese iron phosphate by solid-state method according to claim 1, characterized in that, The carbon source in steps (1) and (3) is one or more of starch, sucrose, glucose, polyethylene glycol and citric acid.

12. The method for preparing high-pressure lithium manganese iron phosphate by solid-state method according to claim 1, characterized in that, The ball milling aid in steps (1) to (3) is one or more of titanium dioxide, aluminum oxide or magnesium oxide, and its addition amount is 0.01 to 2 wt% of the sum of the mass of each material in each step.

13. The method for preparing high-pressure lithium manganese iron phosphate by solid-state method according to claim 1, characterized in that, The calcination in step (4) is a segmented calcination. The first segment is held at 300~450℃ for 2~5h, and the second segment is held at 650~850℃ for 8~12h. The heating rate is 1~5℃ / min.

14. The method for preparing high-pressure lithium manganese iron phosphate by solid-state method according to claim 1, characterized in that, The compacted density of the high-pressure compacted lithium manganese iron phosphate obtained after crushing in step (4) is greater than 2.45 g / cm³. 3 .

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