Preparation method of lithium iron phosphate material with high compaction density

Abstract

The invention discloses a preparation method of a high-compaction-density lithium iron phosphate material, through grading of large and small particle lithium iron phosphate, optimization of a sintering process and reasonable selection of a carbon source and a titanium dopant, the compaction density and the electrochemical performance of the material are remarkably improved, and the preparation method specifically comprises the following steps: mixing iron phosphate, lithium carbonate, the carbon source and auxiliary materials; the preparation method comprises the following steps: carrying out coarse grinding and fine grinding, respectively preparing large-particle lithium iron phosphate and small-particle lithium iron phosphate (a material A and a material B) by adopting spray drying and high-temperature calcination processes, mixing the material A and the material B according to a ratio, adding auxiliary materials, grinding, further carrying out spray drying, calcining and crushing to obtain a final lithium iron phosphate product, and the maximum compaction density of the prepared material can reach 2.712 g / cm < 3 >. According to the present invention, the maximum 1C discharge specific capacity can achieve 140.5 mAh / g, the maximum 1C 3.2 V discharge platform retention rate is 91.4%, and the prepared lithium ion battery negative electrode material has characteristics of excellent conductivity, high discharge capacity and good cycle stability, and is suitable for power batteries and energy storage batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for lithium-ion batteries, and particularly relates to a high tap density lithium iron phosphate material and a preparation method thereof. Background Art

[0002] As a cathode material for lithium-ion batteries, lithium iron phosphate is widely used in new energy vehicles and energy storage systems due to its excellent safety, long cycle life, high theoretical capacity, and environmental friendliness. However, with the continuous improvement of market requirements for battery energy density and performance, traditional lithium iron phosphate materials still have deficiencies in tap density and electrochemical performance. Therefore, improving the tap density of materials has become one of the key means to increase the volumetric energy density of lithium batteries.

[0003] Currently, common methods for improving the tap density of lithium iron phosphate materials mainly include the following: (1) Optimization of particle size distribution: By adjusting the proportion of particles with different particle sizes in the material, the packing density of particles is increased, thereby improving the tap density of the material. However, the process relying solely on particle size distribution is difficult to balance the electrochemical performance of the material while maintaining a high tap density. For example, in some existing technologies, a method of mixing large particles and small particles is adopted, but due to the limited grading effect of particles, the lithium ion diffusion path cannot be effectively shortened, resulting in a decline in the electrochemical performance of the material.

[0004] (2) Improvement of sintering process: By increasing the sintering temperature or prolonging the holding time to increase the crystal size of particles, thereby improving the tap density. However, too high a sintering temperature or too long a sintering time is likely to cause a decrease in the specific surface area and conductivity of the material, thereby affecting the specific capacity and cycle life of the material.

[0005] In summary, the current technical difficulty lies in how to maintain excellent electrochemical performance and cycle stability while increasing the tap density of lithium iron phosphate materials. Existing process routes often either lead to a decrease in the specific capacity of the material or cannot effectively increase the tap density. Therefore, developing a preparation method for lithium iron phosphate materials that can balance high tap density, high energy density, and excellent electrochemical performance has important research significance and market demand. Summary of the Invention

[0006] In view of the above technical problems, the present invention provides a preparation method for a high tap density lithium iron phosphate material, which combines the means of optimizing particle size distribution and improving the sintering process, achieving high tap density while taking into account the high energy density and excellent electrochemical performance of the material, specifically as follows: The method for preparing a high tap density lithium iron phosphate material provided by the present invention mainly includes the following steps: 1. Preparation of large particle lithium iron phosphate (Material A) Mix iron phosphate, lithium carbonate, carbon source, auxiliary materials and pure water, and process them by high-temperature solid-phase method. The specific steps include: coarsely grind and finely grind the mixed slurry, then perform spray drying and high-temperature calcination to obtain large-particle lithium iron phosphate sintered material, which can be further pulverized according to requirements to form Material A, and the D50 particle size of the Material A is 1 - 1.4 μm.

[0007] 2. Preparation of small-particle lithium iron phosphate (Material B) Mix iron phosphate, lithium carbonate, carbon source, auxiliary materials and pure water, and process them by high-temperature solid-phase method. The specific steps include: coarsely grind and finely grind the mixed slurry, then perform spray drying and high-temperature calcination to obtain small-particle lithium iron phosphate sintered material, and further pulverize it to obtain small-particle lithium iron phosphate material, called Material B, and the D50 particle size of the Material B is 0.5 - 0.7 μm.

[0008] 3. Preparation by mixing Material A and Material B Mix Material A and Material B in a specific ratio, and add auxiliary materials and pure water. Process the mixture by high-temperature solid-phase method. The specific steps include: coarsely grind, finely grind, spray dry and high-temperature calcine the mixed slurry, and finally obtain high-compactness lithium iron phosphate sintered material. This material is further pulverized to obtain the final high-compactness lithium iron phosphate material product; The mass of the Material B accounts for 5% - 20% of the total mass of Material A and Material B.

[0009] Furthermore, in the steps (1), (2) and (3): Use a vertical ball mill for coarse grinding, with the diameter of the zirconium beads used being 5 mm, so that the D90 particle size of the slurry does not exceed 10 μm; use a sand mill for fine grinding, with the diameter of the zirconium beads used being 0.2 - 0.3 mm; use a spray drying tower for granulation; perform high-temperature calcination through a constant-temperature box furnace or a roller hearth kiln; use a mechanical crusher or a jet mill for pulverization to ensure that the particle size and density of the material meet the preparation requirements.

[0010] Furthermore, the batching and process conditions in step (1) are as follows: Iron phosphate and lithium carbonate are batched according to a lithium-iron molar ratio of 1.035 - 1.045, the addition amount of the carbon source is 11% - 12% of the mass of iron phosphate, the solid content of the slurry system is controlled at 40% - 45%; the coarse grinding time is 30 - 60 min, and the D50 particle size of the slurry is controlled at 400 - 450 nm during fine grinding; the inlet air temperature of spray drying is set at 230 °C, and the outlet air temperature is controlled at 110 - 120 °C; the high-temperature sintering temperature is controlled at 770 - 800 °C, and the holding time is 7 - 10 h to ensure the sintering effect and material properties.

[0011] Furthermore, the batching and process conditions in step (2) are: Lithium iron phosphate and lithium carbonate are proportioned according to a lithium-to-iron molar ratio of 1.04 - 1.06. The addition amount of the carbon source is 12 - 13% of the mass of lithium iron phosphate, and the solid content of the slurry system is controlled at 40 - 45%; the rough grinding time is 30 - 60 min, and the fine grinding controls the D50 particle size of the slurry to be 300 - 400 nm; the inlet air temperature of spray drying is set at 230 °C, and the outlet air temperature is controlled at 110 - 120 °C; the high-temperature sintering temperature is controlled at 700 - 740 °C, and the heat preservation time is 7 - 9 h.

[0012] Further, the batching and process conditions in step (3) are as follows: The proportion range of the mass of material B to the sum of the masses of material A and material B is 5 - 20%; the solid content of the slurry system is controlled at 30 - 45%, the rough grinding time is 30 - 60 min, and the fine grinding controls the D50 particle size of the slurry to be 0.6 - 1.5 μm; the inlet air temperature of spray drying is 230 °C, and the outlet air temperature is controlled at 110 - 120 °C; the high-temperature sintering temperature is controlled at 700 - 800 °C, and the heat preservation time is 7 - 10 h.

[0013] Further, the raw materials in step (1) are: The iron-to-phosphorus ratio of lithium iron phosphate is 0.950 - 0.975; the carbon source is one or a combination of glucose, polyethylene glycol, starch, and sucrose; the auxiliary materials are titanium dioxide and 85% phosphoric acid, and the titanium incorporation amount is 2000 - 4000 ppm of the mass of the lithium iron phosphate finished product, and the addition amount of phosphoric acid is 0.4 - 0.8% of the mass of lithium iron phosphate.

[0014] Further, the raw materials in step (2) are: The iron-to-phosphorus ratio of lithium iron phosphate is 0.970 - 0.985; the carbon source is one or a combination of glucose, polyethylene glycol, starch, and sucrose; the auxiliary material is a titanium dopant, and the titanium dopant is one or several of titanium dioxide and titanium coupling agent, and the titanium incorporation amount is 3000 - 5000 ppm of the mass of the lithium iron phosphate finished product.

[0015] Further, the auxiliary materials in step (3) include: Titanium dioxide, titanium citrate, and a dispersant, wherein the addition amount of titanium dioxide is 0.2 - 0.5% of the sum of the masses of material A and material B, the addition amount of titanium citrate is 0.1 - 0.4% of the sum of the masses of material A and material B, and the addition amount of the dispersant is 1 - 4% of the sum of the masses of material A and material B.

[0016] Further, the material A obtained in step (1) can be a sintered material or a crushed material of lithium iron phosphate. The compaction density of the sintered material is 2.33 - 2.50 g / cm 3 and the compaction density of the crushed material is 2.43 - 2.60 g / cm 3, the carbon content of Material A is 1.25 - 1.35% of the mass of lithium iron phosphate.

[0017] Further, the B material prepared in step (2) is a crushed material of lithium iron phosphate, and the tap density is 2.00 - 2.15 g / cm 3 , and the carbon content is 1.30 - 1.50% of the mass of lithium iron phosphate.

[0018] Further, the tap density of the final lithium iron phosphate material product prepared by the above method is greater than 2.55 g / cm 3 . In an embodiment of the present invention, the tap density is greater than 2.70 g / cm 3 .

[0019] The lithium iron phosphate material with high tap density prepared by the present invention belongs to the protection scope of the present invention. By this preparation method, a lithium iron phosphate material with a tap density of 2.572 - 2.712 and excellent electrical properties can be obtained, which also belongs to the protection scope of the present invention. Even if some parameters in the above steps, such as the tap density of Material A or Material B, the titanium doping amount, etc., change, it is still within the protection scope of the present invention.

[0020] The beneficial effects of the present invention are as follows: 1. Improve the tap density By optimizing the particle size distribution, adjusting the sintering process, and reasonably selecting the raw material ratio, etc., the present invention significantly improves the tap density of the lithium iron phosphate material. The tap density of the prepared material is greater than 2.55 g / cm 3 , preferably reaching 2.712 g / cm 3 , which is much higher than the tap density obtained by traditional processes, thereby effectively improving the volume energy density of lithium-ion batteries and meeting the requirements of high-energy-density batteries.

[0021] 2. Improve the electrochemical performance While increasing the tap density, the present invention optimizes the conductivity and ion migration channels of the material by adding an appropriate amount of carbon source and titanium dopant, effectively improving the electrochemical performance of the material. The prepared lithium iron phosphate material has a high initial discharge capacity and good cycle stability. The 1C discharge specific capacity can reach up to 140.5 mAh / g at most, and the retention rate of the 1C 3.2V discharge platform is up to 91.4% at most, which can meet the requirements of high power and long life of the battery.

[0022] 3. Improve the controllability and production efficiency of the preparation process The present invention adopts a multi-step process including vertical ball milling, sand milling, spray drying, and high-temperature calcination, achieving precise control of particle size and particle size distribution. Through a one-step or multi-step mixing method, the uniformity of the large and small particle gradation is ensured. The equipment used is simple, the operation is controllable, facilitating large-scale production. Meanwhile, the process complexity and production cost are reduced, and the production efficiency is improved.

[0023] 4. Wide adaptability By appropriately adjusting the ratio of material A and material B and the key process parameters, the method of the present invention has good adaptability and process flexibility. The performance of the final material can be customized according to actual needs, enabling the lithium iron phosphate material of the present invention to be applicable to a variety of battery systems, including power batteries, energy storage batteries, etc., further expanding its application scenarios. Brief description of the drawings

[0024] Figure 1 SEM image of the lithium iron phosphate material prepared in Example 2 of the present invention; Figure 2 SEM image of the lithium iron phosphate material prepared in Example 4 of the present invention; Figure 3 SEM image of the lithium iron phosphate material prepared in Example 5 of the present invention; Figure 4 SEM image of the lithium iron phosphate material prepared in Comparative Example 2 of the present invention. Detailed description of the specific embodiments

[0025] The following further elaborates on the present application in combination with examples and comparative examples.

[0026] Example 1 (1) Select a ferrophosphate raw material with an iron-phosphorus ratio of 0.965. Weigh lithium carbonate and ferrophosphate according to the requirement of a lithium-iron molar ratio of 1.038. Add 8.6% of glucose and 2.4% of polyethylene glycol based on the mass of ferrophosphate as carbon sources, and add 0.6% of titanium dioxide and 0.5% of 85% phosphoric acid based on the mass of ferrophosphate; mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 40%. Conduct rough grinding for 40 min so that the D90 particle size of the slurry does not exceed 10 μm. After passing the slurry through a 200-mesh sieve, transfer it to a sand mill, control the grinding time and rotation speed so that the D50 particle size of the slurry is about 400 nm; adjust the flow rate of the slurry through a peristaltic pump and enter a spray drying tower for granulation. Set the inlet air temperature to 230 °C and control the outlet air temperature at 110 - 120 °C. The D50 particle size of the spray material is 25 - 35 μm; sinter the spray material in a roller hearth kiln at a sintering temperature of 790 °C for a holding time of 8 h; the obtained sintered material is called material A; (2)Select a ferric phosphate raw material with an iron-to-phosphorus ratio of 0.98. Weigh lithium carbonate and ferric phosphate according to the requirement of a lithium-to-iron molar ratio of 1.05. Add 11% of glucose and 1.5% of polyethylene glycol by the mass of ferric phosphate as carbon sources, and add 0.6% of titanium dioxide and 0.9% of titanium coupling agent by the mass of ferric phosphate as titanium dopants. Mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 40%. Conduct rough grinding for 40 min so that the D90 particle size of the slurry does not exceed 10 μm. After passing the slurry through a 200-mesh sieve, transfer it to a sand mill, control the grinding time and rotation speed so that the D50 particle size of the slurry is about 320 nm. Adjust the flow rate of the slurry through a peristaltic pump and enter a spray drying tower for granulation. Set the inlet air temperature to 230 °C and control the outlet air temperature at 110 - 120 °C. The D50 particle size of the spray material is 25 - 35 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 740 °C for a holding time of 7 h. Conduct air flow pulverization on the sintered material and control the D50 particle size of the pulverized material to be 0.5 - 0.7 μm, which is called Material B. (3)Weigh Material A and Material B in steps (1) and (2) according to a weight ratio of 9:1. The added auxiliary materials include titanium dioxide, titanium citrate, and a dispersant. Among them, the addition amount of titanium dioxide is 0.2% of the sum of the masses of Material A and Material B, the addition amount of titanium citrate is 0.3% of the sum of the masses of Material A and Material B, and the addition amount of the dispersant is 1.3% of the sum of the masses of Material A and Material B. Mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 35%. Conduct rough grinding for 40 min. After passing the slurry through a 200-mesh sieve, transfer it to a sand mill, control the grinding time and rotation speed so that the D50 particle size of the slurry is 0.8 - 1.1 μm. Adjust the flow rate of the slurry through a peristaltic pump and enter a spray drying tower for granulation. Set the inlet air temperature to 230 °C and control the outlet air temperature at 110 - 120 °C. The D50 particle size of the spray material is 15 - 30 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 790 °C for a holding time of 8 h. Conduct mechanical pulverization on the sintered material to obtain the final lithium iron phosphate material product.

[0027] Example 2 (1)Select a ferric phosphate raw material with an iron-to-phosphorus ratio of 0.965. Weigh lithium carbonate and ferric phosphate according to the requirement of a lithium-to-iron molar ratio of 1.038. Add 8.6% of glucose and 2.3% of polyethylene glycol by the mass of ferric phosphate as carbon sources, add 0.6% of titanium dioxide and 0.5% of 85% phosphoric acid by the mass of ferric phosphate; mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 40%. Conduct rough grinding for 40 min so that the D90 particle size of the slurry does not exceed 10 μm. After passing the slurry through a 200-mesh sieve, transfer it to a sand mill, control the grinding time and rotation speed so that the D50 particle size of the slurry is about 400 nm; adjust the flow rate of the slurry through a peristaltic pump, and enter a spray drying tower for granulation. Set the inlet air temperature to 230 °C, control the outlet air temperature at 110 - 120 °C, and the D50 particle size of the spray material is 25 - 35 μm; sinter the spray material in a roller hearth kiln at a sintering temperature of 790 °C for a holding time of 8 h; conduct air flow crushing on the sintered material, control the D50 particle size of the crushed material to be 1 - 1.4 μm, and call it Material A; (2)Select a ferric phosphate raw material with an iron-to-phosphorus ratio of 0.98. Weigh lithium carbonate and ferric phosphate according to the requirement of a lithium-to-iron molar ratio of 1.05. Add 11% of glucose and 1.5% of polyethylene glycol by the mass of ferric phosphate as carbon sources, add 0.6% of titanium dioxide and 0.9% of titanium coupling agent as titanium dopants; mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 40%. Conduct rough grinding for 40 min so that the D90 particle size of the slurry does not exceed 10 μm. After passing the slurry through a 200-mesh sieve, transfer it to a sand mill, control the grinding time and rotation speed so that the D50 particle size of the slurry is about 320 nm; adjust the flow rate of the slurry through a peristaltic pump, and enter a spray drying tower for granulation. Set the inlet air temperature to 230 °C, control the outlet air temperature at 110 - 120 °C, and the D50 particle size of the spray material is 25 - 35 μm; sinter the spray material in a roller hearth kiln at a sintering temperature of 730 °C for a holding time of 8 h; conduct air flow crushing on the sintered material, control the D50 particle size of the crushed material to be about 0.5 - 0.7 μm, and call it Material B; (3)Weigh the material A and material B in step (1) and step (2) according to the weight ratio of 9:1. The auxiliary materials added include titanium dioxide, titanium citrate and dispersant. The addition amount of titanium dioxide is 0.2% of the sum of the masses of material A and material B, the addition amount of titanium citrate is 0.3% of the sum of the masses of material A and material B, and the addition amount of dispersant is 1.4% of the sum of the masses of material A and material B. Mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 40%. Conduct rough grinding for 40 min. The D50 particle size of the slurry is 0.8 - 1.2 μm, and the D100 particle size does not exceed 10 μm. After the slurry passes through a 200-mesh sieve, transfer it to the spray tank. Adjust the flow rate of the slurry through a peristaltic pump and enter the spray drying tower for granulation. Set the inlet air temperature to 230°C, and control the outlet air temperature at 110 - 120°C. The D50 particle size of the spray material is 15 - 30 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 795°C for 8 h. Mechanically crush the sintered material to obtain the final lithium iron phosphate material product.

[0028] Example 3 (1)Select a ferric phosphate raw material with an iron-phosphorus ratio of 0.965. Weigh lithium carbonate and ferric phosphate according to the requirement of a lithium-iron molar ratio of 1.038. Add 8.6% of glucose and 2.3% of polyethylene glycol based on the mass of ferric phosphate as carbon sources, and add 0.6% of titanium dioxide based on the mass of ferric phosphate. Mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 40%. Conduct rough grinding for 40 min so that the D90 particle size of the slurry does not exceed 10 μm. After the slurry passes through a 200-mesh sieve, transfer it to a sand mill. Control the grinding time and rotation speed so that the D50 particle size of the slurry is about 400 nm. Adjust the flow rate of the slurry through a peristaltic pump and enter the spray drying tower for granulation. Set the inlet air temperature to 230°C, and control the outlet air temperature at 110 - 120°C. The D50 particle size of the spray material is 25 - 35 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 770°C for 8 h. The obtained sintered material is called material A. (2)Select a ferric phosphate raw material with an iron-to-phosphorus ratio of 0.98. Weigh lithium carbonate and ferric phosphate according to the requirement of a lithium-to-iron molar ratio of 1.05. Add 11% of glucose and 1.5% of polyethylene glycol by the mass of ferric phosphate as carbon sources, and add 0.6% of titanium dioxide and 0.9% of titanium coupling agent by the mass of ferric phosphate as titanium dopants. Mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 40%. Conduct rough grinding for 40 min so that the D90 particle size of the slurry does not exceed 10 μm. After passing the slurry through a 200-mesh sieve, transfer it to a sand mill, and control the grinding time and rotation speed so that the D50 particle size of the slurry is about 320 nm. Adjust the flow rate of the slurry through a peristaltic pump and enter a spray drying tower for granulation. Set the inlet air temperature to 230 °C and control the outlet air temperature at 110 - 120 °C. The D50 particle size of the spray material is 25 - 35 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 700 °C and a holding time of 9 h. Conduct air flow pulverization on the sintered material and control the D50 particle size of the pulverized material to be 0.4 - 0.6 μm, which is called Material B. (3)Weigh Material A and Material B in steps (1) and (2) according to a weight ratio of 9:1. The added auxiliary materials include titanium dioxide, titanium citrate, and dispersant. The addition amount of titanium dioxide is 0.2% of the sum of the masses of Material A and Material B, the addition amount of titanium citrate is 0.3% of the sum of the masses of Material A and Material B, and the addition amount of dispersant is 1.7% of the sum of the masses of Material A and Material B. Mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 35%. Conduct rough grinding for 40 min. After passing the slurry through a 200-mesh sieve, transfer it to a sand mill, and control the grinding time and rotation speed so that the D50 particle size of the slurry is 0.8 - 1.1 μm. Adjust the flow rate of the slurry through a peristaltic pump and enter a spray drying tower for granulation. Set the inlet air temperature to 230 °C and control the outlet air temperature at 110 - 120 °C. The D50 particle size of the spray material is 15 - 30 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 795 °C and a holding time of 8 h. Conduct mechanical pulverization on the sintered material to obtain the final lithium iron phosphate material product.

[0029] Example 4 (1)Select a ferric phosphate raw material with an iron-to-phosphorus ratio of 0.965. Weigh lithium carbonate and ferric phosphate according to the requirement of a lithium-to-iron molar ratio of 1.038. Add 8.6% of glucose and 2.3% of polyethylene glycol by mass of ferric phosphate as carbon sources, and add 0.6% of titanium dioxide by mass of ferric phosphate. Mix the above ingredients with pure water, put them into a vertical ball mill, adjust the solid content to 40%, and perform rough grinding for 40 min so that the D90 particle size of the slurry does not exceed 10 μm. After passing the slurry through a 200-mesh sieve, transfer it to a sand mill, control the grinding time and rotation speed so that the D50 particle size of the slurry is about 400 nm. Adjust the flow rate of the slurry through a peristaltic pump and enter a spray drying tower for granulation. Set the inlet air temperature to 230 °C and control the outlet air temperature at 110 - 120 °C. The D50 particle size of the spray material is 25 - 35 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 790 °C for a holding time of 8 h. Perform air jet milling on the sintered material and control the D50 particle size of the milled material to be 1 - 1.4 μm, which is called Material A; (2)Select a ferric phosphate raw material with an iron-to-phosphorus ratio of 0.98. Weigh lithium carbonate and ferric phosphate according to the requirement of a lithium-to-iron molar ratio of 1.05. Add 11% of glucose and 1.5% of polyethylene glycol by mass of ferric phosphate as carbon sources, add 0.6% of titanium dioxide and 0.9% of titanium coupling agent by mass of ferric phosphate as titanium dopants. Mix the above ingredients with pure water, put them into a vertical ball mill, adjust the solid content to 40%, and perform rough grinding for 40 min so that the D90 particle size of the slurry does not exceed 10 μm. After passing the slurry through a 200-mesh sieve, transfer it to a sand mill, control the grinding time and rotation speed so that the D50 particle size of the slurry is about 320 nm. Adjust the flow rate of the slurry through a peristaltic pump and enter a spray drying tower for granulation. Set the inlet air temperature to 230 °C and control the outlet air temperature at 110 - 120 °C. The D50 particle size of the spray material is 25 - 35 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 710 °C for a holding time of 8 h. Perform air jet milling on the sintered material and control the D50 particle size of the milled material to be about 0.5 - 0.7 μm, which is called Material B; (3) Weigh the material A and material B in step (1) and step (2) according to the weight ratio of 9:1. The auxiliary materials added include titanium dioxide, titanium citrate and dispersant. The addition amount of titanium dioxide is 0.4% of the sum of the masses of material A and material B, the addition amount of titanium citrate is 0.3% of the sum of the masses of material A and material B, and the addition amount of dispersant is 2.0% of the sum of the masses of material A and material B. Mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 40%. Conduct rough grinding for 40 min. The D50 particle size of the slurry is 0.8 - 1.2 μm, and the D100 particle size does not exceed 10 μm. After the slurry passes through a 200-mesh sieve, transfer it to the spray tank. Adjust the flow rate of the slurry through a peristaltic pump, and enter the spray drying tower for granulation. Set the inlet air temperature to 230°C, and control the outlet air temperature at 110 - 120°C. The D50 particle size of the spray material is 15 - 30 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 795°C for 8 h. Mechanically crush the sintered material to obtain the final lithium iron phosphate material product.

[0030] Example 5 The difference from Example 4 is that the addition amount of titanium dioxide in step (3) is 0.3% of the sum of the masses of material A and material B, and the sintering temperature of the spray material in the roller hearth kiln is 798°C.

[0031] Comparative Example 1 In this comparative example, the traditional one-step method is used to prepare the lithium iron phosphate material, which is as follows: Select a ferric phosphate raw material with an iron-to-phosphorus ratio of 0.965. Weigh lithium carbonate and ferric phosphate according to the requirement of a lithium-to-iron molar ratio of 1.038. Add 8.6% of glucose and 2.3% of polyethylene glycol based on the mass of ferric phosphate as carbon sources. Add 0.6% of titanium dioxide and 0.5% of 85% phosphoric acid based on the mass of ferric phosphate. Mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 40%. Conduct rough grinding for 40 min so that the D90 particle size of the slurry does not exceed 10 μm. After the slurry passes through a 200-mesh sieve, transfer it to a sand mill, and control the grinding time and rotation speed so that the D50 particle size of the slurry is about 400 nm. Adjust the flow rate of the slurry through a peristaltic pump, and enter the spray drying tower for granulation. Set the inlet air temperature to 230°C, and control the outlet air temperature at 110 - 120°C. The D50 particle size of the spray material is 25 - 35 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 795°C for 8 h. Mechanically crush the sintered material to obtain the final lithium iron phosphate material product.

[0032] Comparative Example 2 In this comparative example, material B is not used for grading in the two-stage grinding, which is as follows: (1) Select a ferric phosphate raw material with an iron-to-phosphorus ratio of 0.965. Weigh lithium carbonate and ferric phosphate according to the requirement of a lithium-to-iron molar ratio of 1.038. Add 8.6% of glucose and 2.3% of polyethylene glycol by the mass of ferric phosphate as carbon sources. Add 0.6% of titanium dioxide and 0.5% of 85% phosphoric acid by the mass of ferric phosphate. Mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 40%. Conduct rough grinding for 40 min so that the D90 particle size of the slurry does not exceed 10 μm. After passing the slurry through a 200-mesh sieve, transfer it to a sand mill, and control the grinding time and rotation speed so that the D50 particle size of the slurry is about 400 nm. Adjust the flow rate of the slurry through a peristaltic pump and enter a spray drying tower for granulation. Set the inlet air temperature to 230°C and control the outlet air temperature at 110 - 120°C. The D50 particle size of the spray material is 25 - 35 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 790°C for a holding time of 8 h. The obtained sintered material is called Material A. (2) Weigh Material A in step (1). The added auxiliary materials include titanium dioxide and a dispersant. The addition amount of titanium dioxide is 0.25% of the mass of Material A, and the addition amount of the dispersant is 0.5% of the mass of Material A. Mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 40%. Conduct rough grinding for 40 min. After passing the slurry through a 200-mesh sieve, transfer it to a sand mill, and control the grinding time and rotation speed so that the D50 particle size of the slurry is 0.8 - 1.1 μm. Adjust the flow rate of the slurry through a peristaltic pump and enter a spray drying tower for granulation. Set the inlet air temperature to 230°C and control the outlet air temperature at 110 - 120°C. The D50 particle size of the spray material is 15 - 30 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 795°C for a holding time of 8 h. Mechanically crush the sintered material to obtain the final lithium iron phosphate material product.

[0033] Comparative Example 3 In this comparative example, B material was not used for grading in the secondary grinding, specifically as follows: (1)Select a ferric phosphate raw material with an iron-to-phosphorus ratio of 0.965. Weigh lithium carbonate and ferric phosphate according to the requirement of a lithium-to-iron molar ratio of 1.038. Add 8.6% of glucose and 2.3% of polyethylene glycol by mass of ferric phosphate as carbon sources, and add 0.6% of titanium dioxide by mass of ferric phosphate. Mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 40%. Conduct rough grinding for 40 min so that the D90 particle size of the slurry does not exceed 10 μm. After passing the slurry through a 200-mesh sieve, transfer it to a sand mill, control the grinding time and rotation speed so that the D50 particle size of the slurry is about 400 nm. Adjust the flow rate of the slurry through a peristaltic pump and enter a spray drying tower for granulation. Set the inlet air temperature to 230°C and control the outlet air temperature at 110 - 120°C. The D50 particle size of the spray material is 25 - 35 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 790°C for 8 h. Conduct air flow pulverization on the sintered material and control the D50 particle size of the pulverized material to be 1 - 1.4 μm, which is called Material A. (2)Weigh Material A in step (1). The added auxiliary materials include titanium dioxide, titanium citrate, and a dispersant. The addition amount of titanium dioxide is 0.3% by mass of Material A, the addition amount of titanium citrate is 0.3% by mass of Material A, and the addition amount of the dispersant is 2% by mass of Material A. Mix the above ingredients with pure water, put them into a vertical ball mill, and adjust the solid content to 40%. Conduct rough grinding for 40 min. After passing the slurry through a 200-mesh sieve, transfer it to a sand mill, control the grinding time and rotation speed so that the D50 particle size of the slurry is 0.8 - 1.1 μm. Adjust the flow rate of the slurry through a peristaltic pump and enter a spray drying tower for granulation. Set the inlet air temperature to 230°C and control the outlet air temperature at 110 - 120°C. The D50 particle size of the spray material is 15 - 30 μm. Sinter the spray material in a roller hearth kiln at a sintering temperature of 795°C for 8 h. Conduct mechanical pulverization on the sintered material to obtain the final lithium iron phosphate material product.

[0034] Experimental Section

[0035] Experiment 1 Take the lithium iron phosphate material products prepared in Examples 1 - 5 and Comparative Example 1 for powder property testing, and the results are shown in Table 1.

[0036] Table 1 Performance Test Results

[0037] As can be seen from Table 1, the powder compaction of the lithium iron phosphate material product prepared in Example 1 is 2.572 g / cm 3, the D50 particle size is 1.29 μm, the 1C discharge specific capacity is 138.2 mAh / g, and the 1C 3.2V discharge platform retention rate is 91.4%; the powder compaction of the lithium iron phosphate material product prepared in Example 2 is 2.613 g / cm 3 , the D50 is 1.39 μm, the 1C discharge specific capacity is 139.1 mAh / g, and the 1C 3.2V discharge platform retention rate is 91.0%; the powder compaction of the lithium iron phosphate material product prepared in Example 3 is 2.617 g / cm 3 , the D50 is 1.20 μm, the 1C discharge specific capacity is 139.9 mAh / g, and the 1C 3.2V discharge platform retention rate is 88.5%; the powder compaction of the lithium iron phosphate material product prepared in Example 4 is 2.643 g / cm 3 , the D50 is 1.22 μm, the 1C discharge specific capacity is 140.5 mAh / g, and the 1C 3.2V discharge platform retention rate is 91.2%; the powder compaction of the lithium iron phosphate material product prepared in Example 5 is 2.712 g / cm 3 , the D50 is 1.37 μm, the 1C discharge specific capacity is 135.4 mAh / g, and the 1C 3.2V discharge platform retention rate is 90.4%; the powder compaction of the lithium iron phosphate material product prepared in Comparative Example 1 is 2.519 g / cm 3 , the D50 is 1.09 μm, the 1C discharge specific capacity is 135.5 mAh / g, and the 1C 3.2V discharge platform retention rate is 88.6%; the powder compaction of the lithium iron phosphate material product prepared in Comparative Example 2 is 2.664 g / cm 3 , the D50 is 1.63 μm, the 1C discharge specific capacity is 129.3 mAh / g, and the 1C 3.2V discharge platform retention rate is 83.0%; the powder compaction of the lithium iron phosphate material product prepared in Comparative Example 3 is 2.638 g / cm 3 , the D50 is 0.934 μm, the 1C discharge specific capacity is 135.3 mAh / g, and the 1C 3.2V discharge platform retention rate is 89.2%; It can be seen from the above results that the lithium iron phosphate material prepared by the present invention has a high compaction density, and both the 1C discharge specific capacity and the 1C 3.2V discharge platform retention rate are greater than those of the comparative examples.

[0038] Experiment 2 The lithium iron phosphate materials prepared in Example 2, Example 4, Example 5 and Comparative Example 2 were subjected to electron microscope scanning, and the results are as Figures 1-4As shown, it can be seen from the figure that the materials of Examples 2 and 4 have no oversized particles, and the small particles are perfectly filled in the gaps between the large particles, thus preparing materials with high compaction density; some large particles appear in the material of Example 5, further improving the compaction density of the material; however, oversized particles appear in the material of Comparative Example 2, and the proportion of small particles decreases, resulting in the deterioration of the electrical properties of the material.

Claims

1. A method for preparing a high compaction density lithium iron phosphate material, characterized in that: The following steps are involved: (1) mixing iron phosphate, lithium carbonate, a carbon source, auxiliary materials and pure water, and treating the mixture by a high temperature solid phase method to generate lithium iron phosphate crystals, and sequentially subjecting the lithium iron phosphate crystals to coarse grinding, fine grinding, spray drying, high temperature calcination or high temperature calcination and crushing to obtain a large-particle lithium iron phosphate material, referred to as material A, wherein the D50 particle size of the material A is 1-1.4 μm; (2) mixing iron phosphate, lithium carbonate, carbon source, auxiliary materials and pure water, and treating them by high temperature solid phase method to generate lithium iron phosphate crystal II, and sequentially coarse grinding, fine grinding, spray drying and high temperature calcining the lithium iron phosphate crystal II to obtain small-particle lithium iron phosphate sintered material, and further crushing to obtain material B, wherein the D50 particle size of the material B is 0.5-0.7 μm; (3) Mixing material A and material B, adding auxiliary materials and pure water, and subjecting to high-temperature solid phase treatment to generate lithium iron phosphate crystals III, and sequentially subjecting the lithium iron phosphate crystals III to coarse grinding, fine grinding, spray drying, high-temperature calcination and pulverization to obtain a high compaction density lithium iron phosphate material; the mass of the material B accounts for 5%-20% of the total mass of the materials A and B.

2. The method for preparing a high compaction density lithium iron phosphate material according to claim 1, characterized in that: In the step (1), the molar ratio of iron phosphate to lithium carbonate is 1.035-1.045; the amount of carbon source added is 11-12% of the mass of iron phosphate, the solid content of the slurry system is 40-45%, the coarse grinding time is 30-60 min, the D50 particle size of the slurry after fine grinding is 400-450 nm, the spray drying inlet temperature is 230°C, the outlet temperature is controlled at 110-120°C, the high temperature calcination temperature is 770-800°C, and the insulation time is 7-10 h.

3. The method for preparing a high compaction density lithium iron phosphate material according to claim 2, characterized in that: In the step (1), the iron-phosphorus ratio of the iron phosphate is 0.950-0.975; the carbon source is one or more combinations of glucose, polyethylene glycol, starch, and sucrose; the auxiliary materials are a titanium dopant and 85% phosphoric acid, and the titanium dopant is titanium dioxide; the addition of the titanium dopant makes the titanium element 2000-4000 ppm of the mass of the lithium iron phosphate finished product.

4. The method for preparing a high compaction density lithium iron phosphate material according to claim 3, characterized in that: The material A obtained in step (1) is a lithium iron phosphate sintered material or a crushed material, and the compacted density of the sintered material is 2.33-2.50 g / cm 3 The compacted density of the crushed material is 2.43-2.60 g / cm 3 The carbon content of material A is 1.25-1.35% of the mass of lithium iron phosphate.

5. The method for preparing a high compaction density lithium iron phosphate material according to claim 1, characterized in that: In the step (2), the molar ratio of iron phosphate to lithium carbonate is 1.04-1.05; the amount of carbon source added is 12-13% of the mass of iron phosphate, the solid content of the slurry system is 40-45%, the coarse grinding time is 30-60 min, the D50 particle size of the slurry after fine grinding is 300-400 nm, the spray drying inlet temperature is 230°C, the outlet temperature is controlled at 110-120°C, the high temperature calcination temperature is 700-740°C, and the insulation time is 7-9 h.

6. The method for preparing a high compaction density lithium iron phosphate material according to claim 5, characterized in that: In the step (2), the iron-phosphorus ratio of the iron phosphate is 0.970-0.985; the carbon source is one or more of glucose, polyethylene glycol, starch, and sucrose; the auxiliary material is a titanium dopant, and the titanium dopant is one or more of titanium dioxide and a titanium coupling agent. The addition of the titanium dopant makes the titanium element 3000-5000 ppm of the mass of the lithium iron phosphate finished product.

7. The method for preparing a high compaction density lithium iron phosphate material according to claim 6, characterized in that: The material B obtained in step (2) is a lithium iron phosphate crushed material with a compaction density of 2.00-2.15 g / cm 3 The carbon content is 1.30-1.50% of the mass of lithium iron phosphate.

8. The method for preparing a high compaction density lithium iron phosphate material according to claim 1, characterized in that: In the step (3), the solid content of the slurry system is 30-45%, the coarse grinding time is 30-60 min, so that the D90 particle size of the slurry does not exceed 10 μm, the fine grinding makes the D50 particle size of the slurry 0.6-1.5 μm, the spray drying inlet temperature is 230°C, the outlet temperature is controlled at 110-120°C, the high temperature calcination temperature is 700-800°C, and the insulation time is 7-10 h.

9. The method for preparing a high compaction density lithium iron phosphate material according to claim 8, characterized in that: In the step (3), the auxiliary materials include titanium dioxide, titanium citrate and a dispersant. The amount of titanium dioxide added is 0.2-0.5% of the total mass of material A and material B, the amount of titanium citrate added is 0.1-0.4% of the total mass of material A and material B, and the amount of dispersant added is 1-4% of the total mass of material A and material B.

10. The method for preparing a high compaction density lithium iron phosphate material according to claim 1, characterized in that: In the steps (1), (2) and (3), a vertical ball mill is used for coarse grinding, and the diameter of the zirconium beads in the vertical ball mill is 5 mm; a sand mill is used for fine grinding, and the diameter of the zirconium beads in the sand mill is 0.2-0.3 mm; a spray drying tower is used for spray drying, and calcination is carried out in a constant temperature box furnace or a roller kiln; and a mechanical pulverizer or a jet mill is used for pulverization; In the steps (1) and (2), the D50 particle size of the spray material is 25-35 μm, and in the step (3), the D50 particle size of the spray material is 15-30 μm.

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