Five-generation high-compaction lithium iron phosphate material and preparation method thereof

Abstract

The preparation method comprises the following steps: respectively carrying out wet mixing, grinding and spray drying on two parts of iron sources, phosphorus sources, lithium sources, doping agents and carbon sources with different contents to obtain two parts of spray-dried materials, sintering and crushing to obtain lithium iron phosphate semi-finished products A and B; carrying out wet mixing, grinding and spray drying on one part of the lithium iron phosphate semi-finished product B, a carbon source, a lithium source and a doping agent to obtain a spray-dried material, sintering and crushing to obtain a lithium iron phosphate semi-finished product C; and carrying out dry mixing on the residual part of the lithium iron phosphate semi-finished product B, the lithium iron phosphate semi-finished products A and C and a carbon source in proportion, coating the surface with a layer of coating agent, sintering and crushing to obtain the fifth-generation high-compaction lithium iron phosphate material. The lithium iron phosphate semi-finished product is adopted to replace a traditional raw material, the process cost is reduced, and the fifth-generation high-compaction lithium iron phosphate material with excellent electrochemical performance is obtained by combining multiple sintering and special coating modes.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a fifth-generation high-pressure lithium iron phosphate material and its preparation method. Background Technology

[0002] Lithium iron phosphate cathode materials have become the core electrode materials in the fields of new energy power batteries and energy storage due to their high safety, long cycle life and easy availability of raw materials. Its technological development has always focused on improving compaction density in order to break through the industry bottleneck of cell volumetric energy density. It has now completed four generations of technology iterations, and the powder compaction density of the fourth generation products is about 2.60 g / cm³, which is the mainstream application model in the current market.

[0003] With the development of high-end new energy vehicles and large-scale energy storage systems, the industry is placing higher demands on lithium iron phosphate materials. These demands not only require fifth-generation high-compact products with a powder compaction density ≥2.70 g / cm³, but also high fast-charging performance, low impedance, and mass production stability. While existing preparation technologies have gradually improved compaction density through particle size distribution, simple doping, and carbon coating optimization, several shortcomings remain: insufficient control of sintering process parameters easily leads to impurity phases; the carbon coating layer has poor uniformity and weak synergy with doping elements; and the control precision of particle sphericity and particle size distribution is limited, making it difficult to meet the performance requirements of fifth-generation products.

[0004] The development of fifth-generation high-pressure lithium iron phosphate materials has become the focus of industry competition. However, its preparation process has not yet formed a mature large-scale mass production solution. Problems such as high process complexity, high cost, and difficulty in controlling performance consistency need to be solved. Therefore, developing an efficient preparation method suitable for fifth-generation products has become an urgent need to promote the technological upgrading of lithium iron phosphate materials. Summary of the Invention

[0005] The purpose of this invention is to provide a fifth-generation high-pressure compaction lithium iron phosphate material and its preparation method. The method uses lithium iron phosphate semi-finished products to replace traditional raw materials, reducing process costs. Combined with multiple sintering and special coating methods, the resulting fifth-generation high-pressure compaction lithium iron phosphate material has excellent electrochemical performance and stable high powder compaction.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a fifth-generation high-pressure lithium iron phosphate material, comprising the following steps: A first iron source, phosphorus source, lithium source, dopant, and carbon source, and a second iron source, phosphorus source, lithium source, dopant, and carbon source are wet-mixed and ground to achieve a first particle size. Then, they are spray-dried to obtain first and second spray-dried materials. The first spray-dried material is sintered for the first time under an inert gas atmosphere and then pulverized to obtain lithium iron phosphate semi-finished product A. The second spray-dried material is sintered for the second time under an inert gas atmosphere and then pulverized to obtain lithium iron phosphate semi-finished product B. A portion of the lithium iron phosphate semi-finished product B is wet-mixed with a third carbon source, a lithium source, and a dopant, ground, and spray-dried to achieve the second particle size to obtain a third spray-dried material; the third spray-dried material is then sintered for the third time under an inert gas atmosphere and pulverized to obtain lithium iron phosphate semi-finished product C. The remaining portion of the lithium iron phosphate semi-finished product B, lithium iron phosphate semi-finished products A and C, and the fourth carbon source are then dry-mixed in proportion to obtain a mixture. A coating agent is then coated on the surface of the mixture, and a fourth sintering is performed under an inert gas atmosphere. The mixture is then pulverized to obtain the fifth-generation high-pressure lithium iron phosphate material.

[0007] In some possible implementations, the molar ratio of iron to phosphorus (Fe / P) in the lithium iron phosphate semi-finished product A is 0.96-0.99, the molar ratio of lithium to iron (Li / Fe) is 1.02-1.05, the carbon content is 0.3-0.7%, and the molar ratio of the first dopant to iron is 0.001-0.01. In the lithium iron phosphate semi-finished product B, the molar ratio of iron to phosphorus (Fe / P) is 0.96-0.99, the molar ratio of lithium to iron (Li / Fe) is 1.02-1.05, the carbon content is 0.3-0.7%, and the molar ratio of the second dopant to iron is 0.01-0.02. The lithium iron phosphate semi-finished product C has a carbon content of 1.5-2.0%, the content of the third dopant is 0.5-1.5%mol of the content of the portion of lithium iron phosphate semi-finished product B, and the content of the third lithium source is 0.1-2%mol of the content of the portion of lithium iron phosphate semi-finished product B. The wet mixing process specifically includes: using deionized water as a solvent and mixing with a solid content of 30%-40%.

[0008] In some possible implementations, the grinding is carried out by one or more of a high-efficiency ball mill or a sand mill in series; the first particle size specifically includes a particle size D50 of 0.25-0.45 μm; the second particle size specifically includes a particle size D50 of 0.2-0.3 μm.

[0009] In some possible implementations, the spray drying specifically includes setting the inlet air temperature to 220-280°C and the outlet air temperature to 90-110°C.

[0010] In some possible implementations, the first sintering and pulverization specifically includes: sintering through a roller furnace or box furnace to obtain a first sintered product, setting the first sintering temperature to 750-850℃, the first sintering time to 6-8h, and the sintering furnace pressure to 50-200Pa, and then subjecting the first sintered product to airflow pulverization to obtain the lithium iron phosphate semi-finished product A, with a particle size D50 of 1.8-2.2um and D99 ≤ 20um; The second sintering and pulverization specifically includes: sintering through a roller furnace or box furnace to obtain a second sintering product, setting the second sintering temperature to 650-750℃, the second sintering time to 6-8h, and the sintering furnace pressure to 50-200Pa; the second sintering product is then subjected to airflow pulverization to obtain the lithium iron phosphate semi-finished product B, with a particle size D50 of 0.8-1.2um and D99 ≤ 20um; The third sintering and pulverization specifically includes: sintering through a roller furnace or box furnace to obtain the third sintering product, setting the third sintering temperature to 650-750℃, the third sintering time to 6-8h, and the sintering furnace pressure to 50-200Pa, and then subjecting the third sintering product to airflow pulverization to obtain the lithium iron phosphate semi-finished product C, with a particle size of D10≥0.25um, D50:0.5-0.7um, and D99≤10um; The fourth sintering and pulverization specifically includes: sintering through a roller furnace or box furnace to obtain the fourth sintering product, setting the fourth sintering temperature to 700-800℃, the fourth sintering time to 4-6h, and the sintering furnace pressure to 50-200Pa, and then subjecting the fourth sintering product to airflow pulverization to obtain the fifth-generation high-pressure lithium iron phosphate material with particle sizes D10≥0.35um, D50:1-1.5um, and D99≤10um.

[0011] In some possible embodiments, the coating agent is 0.1-0.5% of the mixture by weight, and the coating is performed by a coating machine or a honeycomb mill; the preparation method of the coating agent includes: a metal oxide, such as nano-alumina, zirconium oxide, niobium oxide, and lithium phosphate or lithium dihydrogen phosphate are mixed in a 1:1 mass ratio with a volatile liquid as the medium and a solid content of 50-60%, and then wet-mixed to 50-100 nm. The resulting suspension is the coating agent.

[0012] In some possible implementations, the first and second iron sources include one or more of iron phosphate, iron oxide, ferrous phosphate, and hydroxyferric phosphate; the first and second phosphorus sources include one or more of iron phosphate, ferrous phosphate, hydroxyferric phosphate, ammonium dihydrogen phosphate, phosphoric acid, and lithium phosphate; the first, second, and third lithium sources include one or more of lithium carbonate, lithium hydroxide, and lithium phosphate; the first, second, third, and fourth carbon sources are organic carbon sources, specifically including one or more of glucose, sucrose, polyethylene glycol, and polyvinyl alcohol; and the first, second, and third dopants include one or more of titanium dioxide, ammonium metavanadate, niobium pentoxide, and manganese carbonate.

[0013] In some possible implementations, during the proportional dry mixing, the remaining portion of lithium iron phosphate semi-finished product A, lithium iron phosphate semi-finished product B, and lithium iron phosphate semi-finished product C are mixed in a ratio of 7:1:2 to 2:3:5; the remaining portion of lithium iron phosphate semi-finished product B accounts for 20-60% of lithium iron phosphate semi-finished product B; and the fourth carbon source accounts for 1.2-1.5% of the content of the high-pressure compacted lithium iron phosphate material.

[0014] In some possible implementations, the dry mixing is carried out by one or more of a VC mixer and a high-speed mixer, with the mixing speed set to 800-1200 r / min and the mixing time to 30-90 min.

[0015] In a second aspect, the present invention provides a fifth-generation high-pressure lithium iron phosphate material, characterized in that it is prepared based on the preparation method described in any one of the first aspects.

[0016] The present invention provides a fifth-generation high-pressure lithium iron phosphate material and its preparation method, which has the following advantages compared with the prior art: 1. This invention has no special requirements for initial raw materials, allowing for a wide range of choices. It uses lower-cost raw materials, has no specific crystal form or morphology requirements, and can also have higher impurity content, reducing costs by about 10%. Furthermore, it achieves a higher conversion rate from raw materials to finished products. The conventional conversion rate from iron phosphate + lithium carbonate + carbon source to lithium iron phosphate is about 75%, while this invention, using hydroxy iron phosphate or ferrous phosphate + lithium phosphate + carbon source to lithium iron phosphate, can achieve a conversion rate of about 90%, reducing costs by about 3%. Overall, the cost can be reduced by 10-15%.

[0017] 2. This invention uses lithium iron phosphate semi-finished products to replace the iron / phosphorus / lithium sources in traditional processes. After pre-sintering, this material is basically crystallized and complete. Combined with secondary and tertiary sintering, the chemical composition of the material is more complete, the crystallinity is better, and the surface carbon coating is also better, so the discharge capacity and rate performance are better. Moreover, the lattice defects of the material after the first / secondary sintering treatment are repaired by appropriate additives and the third sintering treatment, which further improves the doping effect. The particle size can still be controlled within a small range, with no abnormally large particles, thus improving the electrochemical performance.

[0018] 3. This invention employs a special coating method, in which a nano-sized wet coating agent can uniformly form an adsorption layer on the surface of lithium iron phosphate semi-finished product. After sintering and tempering treatment, a uniform coating effect is obtained, which can effectively improve electrochemical performance. The surface coating layer can also improve the dispersion effect between particles and further enhance the compaction of powder.

[0019] 4. The material used in the secondary sintering process consists of lithium iron phosphate semi-finished products A, B, and C. Due to differences in material composition (doping amount and carbon content of the three), and the difference in particle size between semi-finished product C and semi-finished products A and B after secondary grinding and sintering, a gradation with different particle sizes can be formed. Semi-finished products A and B are not subjected to secondary wet grinding, so the surface morphology of the particles is not damaged. After a third sintering, tempering, and coating treatment, the proportion of particles of different sizes remains basically unchanged, the roundness of the particle surface is further optimized, the dispersion effect between particles is improved, and the coordination effect between particles is significantly improved. Finally, a stable fifth-generation high-pressure solid density of ≥2.70 g / cm³ and extremely low powder resistivity are obtained.

[0020] 5. The variety of semi-finished products has been improved, and the particle size distribution of the finished products has been improved, such as from grade 5-6 to grade 7-8, which is more conducive to improving compaction density while ensuring electrochemical performance. Attached Figure Description

[0021] Figure 1 Here is a SEM image of the finished product from Example 1; Figure 2 SEM image of the finished product of Comparative Example 1; Figure 3 This is a SEM image of the finished product in Comparative Example 2. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. At the same time, in the description of the embodiments of this application, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0023] The particle size D50 of Examples 1-5 and Comparative Examples 1-3 was measured by wet laser particle size distribution method.

[0024] Example 1 This embodiment provides a fifth-generation high-pressure lithium iron phosphate material, the preparation method of which includes the following steps: Based on the following information regarding the lithium iron phosphate semi-finished product A: the molar ratio of iron to phosphorus (Fe / P) is 0.97, the molar ratio of lithium to iron (Li / Fe) is 1.05, the carbon content is 0.5%, and the molar ratio of the first dopant content to the iron content is 0.006, 2000g of iron phosphate, 504.8g of lithium carbonate, 100g of glucose, 60g of polyethylene glycol, and 6.9g of titanium dioxide were weighed and wet-mixed with deionized water as the solvent, achieving a solid content of 40%. The mixture was then ground to achieve the first particle size and subsequently spray-dried, with the first inlet air temperature set at 280℃. The outlet air temperature is 100℃, and the first spray-dried material is obtained. The first sintering is carried out in a nitrogen atmosphere through a box furnace. Nitrogen gas is passed through for more than 2 hours before heating. The temperature is increased to the first sintering temperature at 2.5℃ / min. The first sintering temperature is set to 820℃, the first sintering time is 8h, and the sintering furnace pressure is 100Pa. After sintering, the material is cooled to below 80℃ in the furnace and then removed from the furnace to obtain the first sintered product. The first sintered product is subjected to air jet milling to obtain lithium iron phosphate semi-finished product A, with a particle size D50 of 2.0um and D99≤20um. Based on the following parameters: the molar ratio of iron to phosphorus (Fe / P) is 0.97, the molar ratio of lithium to iron (Li / Fe) is 1.05, the carbon content of lithium iron phosphate semi-finished product B is 0.5%, and the molar ratio of the second dopant content to the iron content is 0.015, 2000g of iron phosphate, 504.8g of lithium carbonate, 100g of glucose, 60g of polyethylene glycol, and 17.3g of titanium dioxide are weighed out. Using deionized water as a solvent, a solid content of 40% is used for wet mixing and grinding to achieve the first particle size. Then, spray drying is performed, with the first inlet air temperature set at 280°C. The second spray-dried material was obtained at ℃ and the outlet air temperature was 100℃. It was then sintered for the second time in a nitrogen atmosphere using a box furnace. Nitrogen gas was passed through the furnace for more than 2 hours before heating. The temperature was increased to the second sintering temperature at 2.5℃ / min. The second sintering temperature was set at 730℃ and the second sintering time was 8 hours. The furnace pressure was 100Pa. After sintering, the material was cooled to below 80℃ and removed from the furnace to obtain the second sintered product. The second sintered product was then subjected to air jet milling to obtain lithium iron phosphate semi-finished product B, with a particle size D50 of 1.0 μm and D99 ≤ 20 μm.

[0025] Based on the following: The carbon content of lithium iron phosphate semi-finished product C is 2.0%, the content of the third dopant is 1%mol of the total content of lithium iron phosphate semi-finished product B, and the content of the third lithium source is 1%mol of the total content of lithium iron phosphate semi-finished product B. 1000g of lithium iron phosphate semi-finished product B, 2.4g of lithium carbonate, 5.7g of titanium dioxide, 60g of glucose, and 50g of polyethylene glycol were weighed and wet-mixed with deionized water as solvent, with a solid content of 40%. The mixture was then ground to achieve the second particle size, followed by spray drying. The second inlet air temperature was set to 240℃, and the outlet air temperature to 100℃. The third spray-dried material is sintered for the third time in a nitrogen atmosphere using a box furnace. Nitrogen gas is passed through the furnace for more than 2 hours before heating. The temperature is increased to the third sintering temperature at a rate of 2.5℃ / min. The third sintering temperature is set at 700℃, the sintering time is 8 hours, and the furnace pressure is 100Pa. After sintering, the material is cooled to below 80℃ in the furnace before being removed from the furnace, yielding the third sintered product. The third sintered product is then subjected to air jet milling to obtain lithium iron phosphate semi-finished product C, with particle sizes D10≥0.25um, D50:0.55um, and D99≤10um.

[0026] In this embodiment, the first particle size is D50: 0.35um, and the second particle size is D50: 0.25um.

[0027] The remaining portions of lithium iron phosphate semi-finished products A, B, and C are mixed in a ratio of 4:2:4. A fourth carbon source increases the carbon content of the mixture by 0.3%. 400g of lithium iron phosphate semi-finished product A, 200g of lithium iron phosphate semi-finished product B, and C are weighed out. 400g of glucose, 10g of polyethylene glycol, and 10g of other compounds were dry-mixed using a high-speed mixer at a speed of 1000 rpm for 60 minutes to obtain a mixture. A coating agent, weighing 0.3% of the mixture, was applied to the surface of the mixture using a coating machine. The mixture underwent a fourth sintering process in a nitrogen atmosphere using a box furnace. Nitrogen gas was purged for at least 2 hours before heating. The temperature was increased to the fourth sintering temperature of 750℃ at a rate of 2.5℃ / min, and the sintering time was 6 hours. The furnace pressure was 100Pa. After sintering, the mixture was cooled to below 80℃ before being removed from the furnace, yielding the fourth sintered product. This product was then subjected to airflow pulverization to obtain a fifth-generation high-pressure lithium iron phosphate material with particle sizes D10 ≥ 0.35 μm, D50 ≥ 1.25 μm, and D99 ≤ 10 μm.

[0028] In this embodiment, the grinding process involves stirring and dispersing the material in a high-efficiency ball mill for 30 minutes, followed by grinding in a sand mill.

[0029] In this embodiment, the coating agent is prepared as follows: Niobium oxide and lithium phosphate were weighed in a 1:1 mass ratio of 300g each. They were wet-mixed using alcohol as a medium and the solid content was 50%. The mixture was then ground until the particle size D50 was about 0.15um. The resulting suspension was the coating agent.

[0030] In other embodiments, the inlet air temperature can be set to 220°C, and the outlet air temperature can be set to 90 or 100°C; the first sintering temperature can be set to 750 or 850°C, the first sintering time to 6 or 7 hours, the sintering furnace pressure to 50 or 200 Pa, the second sintering temperature to 650°C, the second sintering time to 6 or 7 hours, the third sintering temperature to 650 or 750°C, the third sintering time to 6 or 7 hours, and the fourth sintering temperature to 700°C, the fourth sintering time to 4 or 5 hours.

[0031] In other embodiments, the solid content of the wet mixture can be 30 or 35%.

[0032] In other embodiments, the first and second iron sources may further include iron oxide and ferrous phosphate; the first and second phosphorus sources may further include phosphoric acid and ferrous phosphate; the first, second, and third lithium sources may further include one or more of lithium hydroxide and lithium phosphate; the first, second, third, and fourth carbon sources are organic carbon sources and may further include sucrose; the first, second, and third dopants may include one or more of ammonium metavanadate, niobium pentoxide, and manganese carbonate.

[0033] Example 2 The only difference between this embodiment and Embodiment 1 is that: The composition of lithium iron phosphate semi-finished product B is adjusted as follows: the molar ratio of iron to phosphorus (Fe / P) is 0.97, the molar ratio of lithium to iron (Li / Fe) is 1.05, the carbon content is 0.5%, and the molar ratio of the second dopant content to the iron content is 0.01. Weigh out 2000g of iron phosphate, 504.8g of lithium carbonate, 100g of glucose, 60g of polyethylene glycol, and 11.5g of titanium dioxide. The particle size D50 of lithium iron phosphate semi-finished product B is 0.8um. The composition of lithium iron phosphate semi-finished product C is adjusted as follows: the content of the third lithium source is 1.5%mol of the total content of lithium iron phosphate semi-finished product B, and 8.5g of titanium dioxide is weighed out. The particle size D50 of lithium iron phosphate semi-finished product A is 2.2um; the first particle size is 0.25um and the second particle size is 0.2um; the particle size D50 of lithium iron phosphate semi-finished product C is 0.7um. The remaining portion of lithium iron phosphate semi-finished product A, lithium iron phosphate semi-finished product B, and lithium iron phosphate semi-finished product C are mixed in a ratio of 3:3:4. 300g of lithium iron phosphate semi-finished product A, 300g of lithium iron phosphate semi-finished product B, and 400g of lithium iron phosphate semi-finished product C are weighed out. The particle size D50 of the resulting fifth-generation high-pressure compaction lithium iron phosphate material is 1µm.

[0034] Example 3 The only difference between this embodiment and Embodiment 1 is that: The composition of lithium iron phosphate semi-finished product A is adjusted as follows: the molar ratio of iron to phosphorus (Fe / P) is 0.97, the molar ratio of lithium to iron (Li / Fe) is 1.05, the carbon content is 0.5%, and the molar ratio of the first dopant content to the iron content is 0.008. 1700g of hydroxyferric phosphate, 502.6g of lithium carbonate, 23g of ammonium dihydrogen phosphate, 100g of glucose, 60g of polyethylene glycol, and 9.2g of titanium dioxide are weighed out. The particle size D50 of lithium iron phosphate semi-finished product A is 1.8um. The first particle size is D50: 0.45um, the second particle size is D50: 0.3um; the particle size D50 of lithium iron phosphate semi-finished product B is 1.2um; the particle size D50 of lithium iron phosphate semi-finished product C is 0.5um. The remaining portions of lithium iron phosphate semi-finished product A, lithium iron phosphate semi-finished product B, and lithium iron phosphate semi-finished product C are mixed in a ratio of 4.5:1.5:4. 450g of lithium iron phosphate semi-finished product A, 150g of lithium iron phosphate semi-finished product B, and 400g of lithium iron phosphate semi-finished product C are weighed. The particle size D50 of the resulting fifth-generation high-pressure compaction lithium iron phosphate material is 1.5um.

[0035] Example 4 The only difference between this embodiment and Embodiment 1 is that: The composition of lithium iron phosphate semi-finished product A is adjusted as follows: the molar ratio of iron to phosphorus (Fe / P) is 0.97, the molar ratio of lithium to iron (Li / Fe) is 1.05, the carbon content is 0.5%, and the molar ratio of the first dopant content to the iron content is 0.006. Weigh out 1700g of hydroxyferric phosphate, 502.6g of lithium carbonate, 23g of ammonium dihydrogen phosphate, 100g of glucose, 60g of polyethylene glycol, and 6.9g of titanium dioxide. The composition of lithium iron phosphate semi-finished product B is adjusted as follows: the molar ratio of iron to phosphorus (Fe / P) is 0.97, the molar ratio of lithium to iron (Li / Fe) is 1.05, the carbon content is 0.5%, and the molar ratio of the second dopant content to the iron content is 0.02. Weigh out 1700g of hydroxyferric phosphate, 502.6g of lithium carbonate, 23g of ammonium dihydrogen phosphate, 100g of glucose, 60g of polyethylene glycol, and 23.0g of titanium dioxide. The second sintering temperature is set at 750℃.

[0036] Example 5 The only difference between this embodiment and Embodiment 1 is that the weight of the coating agent is set to 0.5% of the mixture, and the fourth sintering temperature is set to 800°C.

[0037] Comparative Example 1 The preparation method of this comparative example is different from that of Example 1, but the elemental doping amount of the fifth-generation high-pressure lithium iron phosphate material is the same.

[0038] The preparation method includes the following steps: According to the following conditions: Fe / P molar ratio of 0.97, Li / Fe molar ratio of 1.05, carbon content of 0.2%, and dopant content to Fe molar ratio of 0.006, 2000g of iron phosphate, 504.8g of lithium carbonate, 80g of glucose, 30g of polyethylene glycol, and 6.9g of titanium dioxide were weighed out and wet-mixed with deionized water as solvent, with a solid content of 40%. After grinding, the particle size D50 was 0.35um, and then spray-dried, with the inlet air temperature controlled at 280℃ and the outlet air temperature at 100℃, to obtain the first spray-dried material.

[0039] The first spray-dried material was sintered for the first time in a nitrogen atmosphere using a box furnace. Nitrogen gas was passed through the furnace for more than 2 hours before heating. The temperature was increased to 800℃ at 2.5℃ / min and sintered for 8 hours. The furnace pressure was 100Pa. After sintering, the material was cooled to below 80℃ and removed from the furnace to obtain the first sintered product. The first sintered product was then subjected to air jet milling to obtain lithium iron phosphate semi-finished product A, with a particle size D50 of 5µm and D99 ≤ 50µm.

[0040] According to the following conditions: Fe / P molar ratio of 0.97, Li / Fe molar ratio of 1.05, carbon content of 0.2%, and dopant content to Fe molar ratio of 0.02, 2000g of iron phosphate, 504.8g of lithium carbonate, 80g of glucose, 30g of polyethylene glycol, and 23g of titanium dioxide were weighed out. Using deionized water as solvent, the mixture was wet-mixed with a solid content of 40%, ground, and spray-dried to achieve a particle size D50 of 0.35um. The inlet air temperature was controlled at 280℃ and the outlet air temperature at 100℃ to obtain the second spray-dried material.

[0041] Half of the second spray-dried material was sintered for the second time in a nitrogen atmosphere using a box furnace. Nitrogen gas was passed through the furnace for more than 2 hours before heating. The temperature was increased to 700℃ at 2.5℃ / min and sintered for 8 hours. The furnace pressure was 100Pa. After sintering, the material was cooled to below 80℃ and removed from the furnace to obtain the first sintered product. The first sintered product was then subjected to air jet milling to obtain lithium iron phosphate semi-finished product B, with a particle size D50 of 2µm and D99 ≤ 20µm.

[0042] The other half of the second spray-dried material is sintered for the third time in a nitrogen atmosphere. The sintering is carried out in a box furnace. Nitrogen gas is passed through for more than 2 hours before heating. The temperature is increased to 600℃ at 2.5℃ / min and sintered for 8 hours. The pressure of the sintering furnace is 100Pa. After sintering, the material is cooled to below 80℃ in the furnace and then removed from the furnace to obtain the first sintered product. The first sintered product is then subjected to air jet milling to obtain lithium iron phosphate semi-finished product C, with a particle size D50 of 2μm and D99≤20μm.

[0043] Weigh 2.4g of lithium carbonate, 40g of glucose, 30g of polyethylene glycol, and 1000g of lithium iron phosphate semi-finished product A. Use deionized water as a solvent and wet mix with a solid content of 40%. Grind the mixture to achieve a particle size D50 of 1.60um to obtain lithium iron phosphate slurry D, which has a carbon content of 1.4% and a lithium content that is 0.1%mol higher than that of lithium iron phosphate semi-finished product A.

[0044] Weigh out 2.4g of lithium carbonate, 40g of glucose, 30g of polyethylene glycol, and 1000g of lithium iron phosphate semi-finished product B. Use deionized water as solvent and wet mix with a solid content of 40%. Grind the mixture to achieve a particle size D50 of 0.80um to obtain lithium iron phosphate slurry E, which has a carbon content of 1.4% and a lithium content that is 0.1%mol higher than that of lithium iron phosphate semi-finished product B.

[0045] Weigh out 2.4g of lithium carbonate, 40g of glucose, 30g of polyethylene glycol, and 1000g of lithium iron phosphate semi-finished product C. Use deionized water as a solvent and wet mix with a solid content of 40%. Grind the mixture to achieve a particle size D50 of 0.25um to obtain lithium iron phosphate slurry F, which has a carbon content of 1.4% and a lithium content that is 0.1%mol higher than that of lithium iron phosphate semi-finished product C.

[0046] Lithium iron phosphate slurry D, E, and F were mixed in a ratio of 4:2:4 and then spray-dried. The inlet air temperature was controlled at 240℃ and the outlet air temperature at 100℃ to obtain the third spray-dried material.

[0047] The third spray-dried material is sintered for the third time in a nitrogen atmosphere using a box furnace. Nitrogen gas is passed through the furnace for more than 2 hours before heating. The temperature is increased to 780℃ at 2.5℃ / min and sintered for 8 hours. The furnace pressure is 100Pa. After sintering, the material is cooled to below 80℃ and removed from the furnace to obtain the fourth sintered product. The fourth sintered product is then subjected to air jet milling to obtain the fifth-generation high-pressure lithium iron phosphate material with particle sizes D10≥0.35um, D50:1.25um, and D99≤10um.

[0048] Comparative Example 2 The preparation method of this comparative example is different from that of Example 1, but the elemental doping amount of the fifth-generation high-pressure lithium iron phosphate material is the same.

[0049] The preparation method includes the following steps: According to the lithium iron phosphate semi-finished product A, the Fe / P molar ratio is 0.97, the Li / Fe molar ratio is 1.05, the carbon content is 1.40%, and the dopant content to Fe molar ratio is 0.015. Weigh out 2000g of iron phosphate, 504.8g of lithium carbonate, 160g of glucose, 80g of polyethylene glycol, and 17.1g of titanium dioxide. Use deionized water as solvent and wet mix with a solid content of 40%. Grind the mixture until the particle size D50 is 0.35um, and then spray dry it to obtain the spray-dried material.

[0050] The spray-dried material was sintered for the first time in a nitrogen atmosphere using a box furnace. Nitrogen gas was passed through the furnace for more than 2 hours before heating. The temperature was increased to 830℃ at 2.5℃ / min and sintered for 8 hours. The furnace pressure was 100Pa. After sintering, the material was cooled to below 80℃ and removed from the furnace to obtain the first sintered product. The first sintered product was then subjected to air jet milling to obtain lithium iron phosphate semi-finished product A, with a particle size D50 of 2µm and D99 ≤ 20µm.

[0051] The lithium iron phosphate semi-finished product A is sintered a second time in a nitrogen atmosphere using a box furnace. Nitrogen gas is passed through the furnace for more than 2 hours before heating. The temperature is increased to 750℃ at 2.5℃ / min and sintered for 6 hours. The furnace pressure is 100Pa. After sintering, the product is cooled to below 80℃ and removed from the furnace to obtain the second sintered product. The second sintered product is then subjected to air jet milling to obtain the fifth-generation high-pressure compact lithium iron phosphate material with particle sizes D10≥0.35um, D50:1.25um, and D99≤10um.

[0052] Comparative Example 3 The only difference between this comparative example and Example 1 is that the mixture was directly sintered for the fourth time in a nitrogen atmosphere without being coated with a coating agent.

[0053] According to the national standard GB / T 30835-2014 "Carbon Composite Lithium Iron Phosphate Cathode Material for Lithium-ion Batteries", relevant physicochemical and electrochemical properties of Examples 1-5 and Comparative Examples 1-3 were tested. In the fabrication of the coin cell, the mass ratio of active material, conductive agent and binder was 90:5:5, and the charge / discharge voltage range was 2.0-3.8V.

[0054] The results are shown in Table 1: Table 1 Basic properties of lithium iron phosphate materials Example 1, SEM images of Comparative Examples 1-2 are shown below. Figure 1-3 As shown.

[0055] Comparing the basic performance data of Examples 1-5 and Comparative Example 1, the lithium iron phosphate material powder compaction of Examples 1-5 was significantly improved, with an average increase of approximately 0.10. Figure 1-3 It can be seen that the particle surface of Example 1 is smooth, especially the large particles, and there is basically no agglomeration between particles. The small particles still maintain their size and proportion, and the coordination effect is better. The powder resistivity of Examples 1-5 is significantly lower than that of Comparative Example 1. At the same time, the 1C discharge specific capacity and the proportion of 1C 3.2V discharge capacity of Examples 1-5 are both improved compared with Comparative Example 1, which proves that Examples 1-5 have significant improvements in particle surface morphology optimization and coating effect compared with Comparative Example 1.

[0056] Comparing the basic performance data of Examples 1-5 and Comparative Example 2, the compaction of lithium iron phosphate material powder in Examples 1-5 was also significantly improved, with an average increase of approximately 0.12. Figure 1 , 3 It can be seen that the particles in Example 1 are smaller and more numerous, with a more reasonable gradation; at the same time, there are no abnormally large particles, and the proportion of large particles is relatively small, which is more conducive to electrochemical performance under compaction conditions; the specific surface area and powder resistivity of Examples 1-5 are significantly lower than those of Comparative Example 2, which is more friendly to the battery cell usage stage; at the same time, the 0.1C discharge capacity and 1C discharge capacity of Examples 1-5 are increased by about 5mAh / g and 10mAh / g respectively compared with Comparative Example 2, and the 1C 3.2V discharge capacity of Examples 1-5 reaches more than 92%, with higher energy efficiency, which fully demonstrates the significant improvement of Examples 1-5 in primary particle size control, gradation effect and coating effect compared with Comparative Example 2.

[0057] Comparing the basic performance data of Examples 1-5 and Comparative Example 3, the compaction of lithium iron phosphate material powder in Examples 1-5 also showed a significant improvement, with an average increase of approximately 0.06. Figure 1-3 It can be seen that the particle surface of Example 1 is more rounded than that of Comparative Examples 1-2, and the dispersion and coordination effects between particles are better. The powder resistivity of Examples 1-5 is lower than that of Comparative Example 3. At the same time, the 0.1C discharge capacity and 1C discharge capacity of the material are increased by about 3 mAh / g and 6 mAh / g, respectively, compared with Comparative Example 3. This proves that the coating method and coating agent pretreatment method used in Examples 1-5 have a significant effect on improving compaction density and electrochemical performance compared with Comparative Example 3.

[0058] In summary, compared with existing technologies, this invention significantly improves upon existing technologies in terms of primary particle size control, particle morphology optimization, doping effect, and coating effect. It also demonstrates significant advantages over existing technologies in terms of compaction, rate capability, and low-temperature performance. The fifth-generation high-compact lithium iron phosphate material prepared by this invention achieves a powder compaction density of 2.75 g / cm³. 3 Under the condition of around 100%, it also has the advantage of high-rate low-temperature performance.

[0059] Obviously, those skilled in the art can make various modifications and variations to the embodiments of the present invention without departing from the spirit and scope of the invention. Therefore, if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A method for preparing a fifth-generation high-pressure lithium iron phosphate material, characterized in that, Includes the following steps: A first iron source, phosphorus source, lithium source, dopant, and carbon source, and a second iron source, phosphorus source, lithium source, dopant, and carbon source are wet-mixed and ground to achieve a first particle size. Then, they are spray-dried to obtain first and second spray-dried materials. The first spray-dried material is sintered for the first time under an inert gas atmosphere and then pulverized to obtain lithium iron phosphate semi-finished product A. The second spray-dried material is sintered for the second time under an inert gas atmosphere and then pulverized to obtain lithium iron phosphate semi-finished product B. A portion of the lithium iron phosphate semi-finished product B is wet-mixed with a third carbon source, a lithium source, and a dopant, ground, and spray-dried to achieve the second particle size to obtain a third spray-dried material; the third spray-dried material is then sintered for the third time under an inert gas atmosphere and pulverized to obtain lithium iron phosphate semi-finished product C. The remaining portion of the lithium iron phosphate semi-finished product B, lithium iron phosphate semi-finished products A and C, and the fourth carbon source are then dry-mixed in proportion to obtain a mixture. A coating agent is then coated on the surface of the mixture, and a fourth sintering is performed under an inert gas atmosphere. The mixture is then pulverized to obtain the fifth-generation high-pressure lithium iron phosphate material.

2. The preparation method according to claim 1, characterized in that, In the lithium iron phosphate semi-finished product A, the ratio of iron to phosphorus (Fe / P) is 0.96-0.99, the ratio of lithium to iron (Li / Fe) is 1.02-1.05, the carbon content is 0.3-0.7%, and the molar ratio of the first dopant to iron is 0.001-0.

01. In the lithium iron phosphate semi-finished product B, the molar ratio of iron to phosphorus (Fe / P) is 0.96-0.99, the molar ratio of lithium to iron (Li / Fe) is 1.02-1.05, the carbon content is 0.3-0.7%, and the molar ratio of the second dopant to iron is 0.01-0.

02. The lithium iron phosphate semi-finished product C has a carbon content of 1.5-2.0%, the content of the third dopant is 0.5-1.5%mol of the content of the portion of lithium iron phosphate semi-finished product B, and the content of the third lithium source is 0.1-2%mol of the content of the portion of lithium iron phosphate semi-finished product B. The wet mixing process specifically includes: using deionized water as a solvent and mixing with a solid content of 30%-40%.

3. The preparation method according to claim 1, characterized in that, The grinding is carried out by one or more of a high-efficiency ball mill and a sand mill in series; the first particle size specifically includes a particle size D50 of 0.25-0.45um; the second particle size specifically includes a particle size D50 of 0.2-0.3um.

4. The preparation method according to claim 1, characterized in that, The spray drying specifically includes setting the inlet air temperature to 220-280℃ and the outlet air temperature to 90-110℃.

5. The preparation method according to claim 1, characterized in that, The first sintering and pulverization specifically includes: sintering through a roller furnace or box furnace to obtain the first sintered product, setting the first sintering temperature to 750-850℃, the first sintering time to 6-8h, and the sintering furnace pressure to 50-200Pa; the first sintered product is then subjected to airflow pulverization to obtain the lithium iron phosphate semi-finished product A, with a particle size D50 of 1.8-2.2um and D99≤20um; The second sintering and pulverization specifically includes: sintering through a roller furnace or box furnace to obtain a second sintering product, setting the second sintering temperature to 650-750℃, the second sintering time to 6-8h, and the sintering furnace pressure to 50-200Pa; the second sintering product is then subjected to airflow pulverization to obtain the lithium iron phosphate semi-finished product B, with a particle size D50 of 0.8-1.2um and D99 ≤ 20um; The third sintering and pulverization specifically includes: sintering through a roller furnace or box furnace to obtain the third sintering product, setting the third sintering temperature to 650-750℃, the third sintering time to 6-8h, and the sintering furnace pressure to 50-200Pa, and then subjecting the third sintering product to airflow pulverization to obtain the lithium iron phosphate semi-finished product C, with a particle size of D10≥0.25um, D50:0.5-0.7um, and D99≤10um; The fourth sintering and pulverization specifically includes: sintering through a roller furnace or box furnace to obtain the fourth sintering product, setting the fourth sintering temperature to 700-800℃, the fourth sintering time to 4-6h, and the sintering furnace pressure to 50-200Pa, and then subjecting the fourth sintering product to airflow pulverization to obtain the fifth-generation high-pressure lithium iron phosphate material with particle sizes D10≥0.35um, D50:1-1.5um, and D99≤10um.

6. The preparation method according to claim 1, characterized in that, The coating agent is 0.1-0.5% of the mixture by weight, and is applied by a coating machine or a honeycomb mill. The preparation method of the coating agent includes: a metal oxide, such as nano-alumina, zirconium oxide, niobium oxide, and lithium phosphate or lithium dihydrogen phosphate are mixed in a 1:1 mass ratio with a volatile liquid as the medium and a solid content of 50-60%, and then wet-mixed to 50-100 nm. The resulting suspension is the coating agent.

7. The preparation method according to claim 1, characterized in that, The first and second iron sources include one or more of iron phosphate, iron oxide, ferrous phosphate, and hydroxyferric phosphate; the first and second phosphorus sources include one or more of iron phosphate, ferrous phosphate, hydroxyferric phosphate, ammonium dihydrogen phosphate, phosphoric acid, and lithium phosphate; the first, second, and third lithium sources include one or more of lithium carbonate, lithium hydroxide, and lithium phosphate; the first, second, third, and fourth carbon sources are organic carbon sources, specifically including one or more of glucose, sucrose, polyethylene glycol, and polyvinyl alcohol; the first, second, and third dopants include one or more of titanium dioxide, ammonium metavanadate, niobium pentoxide, and manganese carbonate.

8. The preparation method according to claim 1, characterized in that, In the dry mixing process, the remaining portion of lithium iron phosphate semi-finished product A, lithium iron phosphate semi-finished product B, and lithium iron phosphate semi-finished product C are mixed in a ratio of 7:1:2-2:3:5; the remaining portion of lithium iron phosphate semi-finished product B accounts for 20-60% of lithium iron phosphate semi-finished product B; the carbon content of the high-pressure compacted lithium iron phosphate material is 1.2-1.5%.

9. The preparation method according to claim 1, characterized in that, The dry mixing is carried out by one or more of a VC mixer and a high-speed mixer, with the mixing speed set to 800-1200 r / min and the mixing time to 30-90 min.

10. A fifth-generation high-pressure lithium iron phosphate material, characterized in that, Prepared according to the preparation method according to any one of claims 1-9.

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