Preparation method of high-compacted-density lithium iron phosphate material

Abstract

The application discloses a preparation method of high-compaction-density lithium iron phosphate material, and significantly improves the compaction density and electrochemical performance of the material by grading of large and small lithium iron phosphate particles, optimization of a sintering process, and reasonable selection of a carbon source and a titanium dopant, and specifically as follows: iron phosphate, lithium carbonate, a carbon source and auxiliary materials are mixed, coarse grinding and fine grinding are performed, and then large-particle and small-particle lithium iron phosphate (A material and B material) are respectively prepared by adopting a spray drying and high-temperature calcining process; the A material and the B material are mixed in proportion, auxiliary materials are added and then ground, and finally the end lithium iron phosphate product is obtained by further spray drying, calcining and crushing; the prepared material has a highest compaction density of 2.712 g / cm 3 , a highest 1C discharge specific capacity of 140.5 mAh / g, and a highest 1C 3.2V discharge platform retention rate of 91.4%, and has excellent conductivity, high discharge capacity and good cycle stability, and is suitable for power batteries and energy storage batteries.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a high-pressing-density lithium iron phosphate material and a preparation method thereof. BACKGROUND

[0002] As a cathode material of 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 increasing demand for battery energy density and performance, the traditional lithium iron phosphate material still has deficiencies in pressing density and electrochemical performance. Therefore, improving the pressing density of the material has become one of the key means to improve the volume energy density of lithium batteries.

[0003] At present, the common methods for improving the pressing density of lithium iron phosphate material mainly include the following:

[0004] (1) Particle size distribution optimization: By adjusting the proportion of particles of different sizes in the material, the packing density of the particles is increased, thereby improving the pressing density of the material. However, simply relying on particle size distribution technology cannot maintain high pressing density while considering the electrochemical performance of the material. For example, some existing technologies use a mixture of large and small particles, but due to the limited effect of particle size distribution, the lithium ion diffusion path cannot be effectively shortened, resulting in a decrease in the electrochemical performance of the material.

[0005] (2) Sintering process improvement: By increasing the sintering temperature or prolonging the holding time, the crystal size of the particles is increased to improve the pressing density. However, too high a sintering temperature or too long a sintering time can easily lead to a decrease in the specific surface area of the material and a decrease in the electrical conductivity, thereby affecting the specific capacity and cycle life of the material.

[0006] In summary, the current technical difficulty lies in how to improve the pressing density of lithium iron phosphate material while maintaining its excellent electrochemical performance and cycle stability. Existing process routes often result in a decrease in the specific capacity of the material or an inability to effectively improve the pressing density. Therefore, it is of great research significance and market demand to develop a preparation method for lithium iron phosphate material that can maintain high pressing density while considering high energy density and excellent electrochemical performance. SUMMARY

[0007] The present application provides a preparation method for high-pressing-density lithium iron phosphate material, which combines particle size distribution optimization and sintering process improvement to achieve high pressing density while considering high energy density and excellent electrochemical performance of the material, as follows:

[0008] The method for preparing high-pressing-density lithium iron phosphate material provided by the present application mainly includes the following steps:

[0009] 1. Large particle lithium iron phosphate (A material) preparation

[0010] Iron phosphate, lithium carbonate, carbon source, auxiliary materials and pure water are mixed and treated by high temperature solid phase method. The specific steps include: coarse grinding and fine grinding of the mixed slurry, followed by spray drying and high temperature calcination to obtain large particle lithium iron phosphate sintered material. The material can be further crushed to form A material, and the D50 particle size of the A material is 1-1.4 μm.

[0011] 2. Small particle lithium iron phosphate (B material) preparation

[0012] Iron phosphate, lithium carbonate, carbon source, auxiliary materials and pure water are mixed and treated by high temperature solid phase method. The specific steps include: coarse grinding and fine grinding of the mixed slurry, followed by spray drying and high temperature calcination to obtain small particle lithium iron phosphate sintered material, and further crushing to obtain small particle lithium iron phosphate material, called B material, and the D50 particle size of the B material is 0.5-0.7 μm.

[0013] 3. A material and B material mixing preparation

[0014] A material and B material are mixed in a specific ratio, and auxiliary materials and pure water are added. The mixed material is treated by high temperature solid phase method, and the specific steps include: coarse grinding, fine grinding, spray drying and high temperature calcination of the mixed slurry, and finally high pressure density lithium iron phosphate sintered material is obtained. The material is further crushed to obtain the final high pressure density lithium iron phosphate material product.

[0015] The mass of the B material accounts for 5%-20% of the total mass of the A material and the B material.

[0016] Further, in the steps (1), (2) and (3):

[0017] A vertical ball mill is used for coarse grinding, and zirconium beads with a diameter of 5 mm are used to make the D90 particle size of the slurry not more than 10 μm; a sand mill is used for fine grinding, and zirconium beads with a diameter of 0.2-0.3 mm are used; a spray drying tower is used for granulation; a constant temperature oven or a roller kiln is used for high temperature calcination; a mechanical crusher or an air flow crusher is used for crushing to ensure that the particle size and density of the material meet the preparation requirements.

[0018] Further, the ingredients and process conditions in step (1) are as follows:

[0019] Iron phosphate and lithium carbonate are dosed according to a lithium-iron molar ratio of 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 controlled at 40-45%; the coarse grinding time is 30-60 min, the fine grinding controls the D50 particle size of the slurry at 400-450 nm; the inlet air temperature of spray drying is set at 230℃, the outlet air temperature is controlled at 110-120℃; the high-temperature sintering temperature is controlled at 770-800℃, and the holding time is 7-10 h to ensure the sintering effect and material properties.

[0020] Further, the dosing and process conditions in step (2) are as follows:

[0021] Iron phosphate and lithium carbonate are dosed according to a lithium-iron molar ratio of 1.04-1.06, the amount of carbon source added is 12-13% 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, the fine grinding controls the D50 particle size of the slurry at 300-400 nm; the inlet air temperature of spray drying is set at 230℃, the outlet air temperature is controlled at 110-120℃; the high-temperature sintering temperature is controlled at 700-740℃, and the holding time is 7-9 h.

[0022] Further, the dosing and process conditions in step (3) are as follows:

[0023] The mass ratio of B material to the sum of A material and B material is in the range of 5-20%; the solid content of the slurry system is controlled at 30-45%, the coarse grinding time is 30-60 min, the fine grinding controls the D50 particle size of the slurry at 0.6-1.5 μm; the inlet air temperature of spray drying is 230℃, the outlet air temperature is controlled at 110-120℃; the high-temperature sintering temperature is controlled at 700-800℃, and the holding time is 7-10 h.

[0024] Further, the raw materials in step (1) are as follows:

[0025] The iron-phosphorus ratio of iron phosphate is 0.950-0.975; the carbon source is one or a combination of several of glucose, polyethylene glycol, starch, and sucrose; the auxiliary material is titanium dioxide and 85% phosphoric acid, the titanium doping amount is 2000-4000 ppm of the mass of lithium iron phosphate product, and the amount of phosphoric acid added is 0.4-0.8% of the mass of iron phosphate.

[0026] Further, the raw materials in step (2) are as follows:

[0027] The iron-phosphorus ratio of iron phosphate is 0.970-0.985; the carbon source is one or a combination of several of glucose, polyethylene glycol, starch, and sucrose; the auxiliary material is a titanium dopant, which is one or several of titanium dioxide and titanium coupling agent, and the titanium doping amount is 3000-5000 ppm of the mass of lithium iron phosphate product.

[0028] Further, the auxiliary materials in step (3) include:

[0029] Titanium white, titanium citrate and dispersant, wherein the addition amount of titanium white is 0.2-0.5% of the mass sum of A material and B material, the addition amount of titanium citrate is 0.1-0.4% of the mass sum of A material and B material, and the addition amount of dispersant is 1-4% of the mass sum of A material and B material.

[0030] Further, the A material prepared in step (1) can be a sintered lithium iron phosphate material or a crushed lithium iron phosphate material, the compaction density of the sintered lithium iron phosphate material is 2.33-2.50 g / cm 3 , the compaction density of the crushed lithium iron phosphate material is 2.43-2.60 g / cm 3 , and the carbon content of the A material is 1.25-1.35% of the mass of lithium iron phosphate.

[0031] Further, the B material prepared in step (2) is a crushed lithium iron phosphate material, the compaction 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.

[0032] Further, the compaction 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 application, the compaction density is greater than 2.70 g / cm 3 .

[0033] The high-compaction-density lithium iron phosphate material prepared by the present application falls within the protection scope of the present application, and by the preparation method, a lithium iron phosphate material with a compaction density of 2.572-2.712 and excellent electrical performance can be obtained, which also falls within the protection scope of the present application. Even if some parameters in the above steps, such as the compaction density of A material or B material, the titanium doping amount, etc., are changed, it still falls within the protection scope of the present application.

[0034] The beneficial effects of the present application are as follows:

[0035] 1. Improved compaction density

[0036] By optimizing the particle size distribution, adjusting the sintering process and reasonably selecting the raw material ratio, etc., the present application significantly improves the compaction density of the lithium iron phosphate material, and the prepared material has a compaction density of greater than 2.55 g / cm 3 , preferably 2.712 g / cm 3 , which is much higher than the compaction density obtained by the traditional process, thereby effectively improving the volume energy density of the lithium ion battery and meeting the demand of high-energy-density batteries.

[0037] 2. Improved electrochemical performance

[0038] The present application improves the compaction density, optimizes the conductivity and ion migration channel of the material by adding an appropriate amount of carbon source and titanium dopant, effectively improves the electrochemical performance of the material, and the prepared lithium iron phosphate material has high initial discharge capacity and good cycle stability, the 1C discharge specific capacity can reach 140.5 mAh / g at most, and the 1C 3.2V discharge platform retention rate can reach 91.4% at most, which can meet the requirements of high power and long service life of the battery.

[0039] 3. Improved controllability and production efficiency of preparation process

[0040] The present application adopts a multi-step process of vertical ball milling, sand milling, spray drying and high temperature calcination, realizes accurate control of particle size and particle size distribution, and ensures the uniformity of large and small particle gradation through one-step or multi-step mixing method, the used equipment is simple, the operation is controllable, and the scale production is convenient, which reduces the process complexity and production cost, and improves the production efficiency.

[0041] 4. Wide adaptability

[0042] The present application has good adaptability and process flexibility by properly adjusting the ratio of A material and B material and key process parameters, and the performance of the final material can be customized according to actual needs, so that the lithium iron phosphate material of the present application can be applied to various battery systems, including power batteries, energy storage batteries and the like, further expanding its application scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 SEM image of the lithium iron phosphate material prepared in Example 2 of the present application;

[0044] Figure 2 SEM image of the lithium iron phosphate material prepared in Example 4 of the present application;

[0045] Figure 3 SEM image of the lithium iron phosphate material prepared in Example 5 of the present application;

[0046] Figure 4 SEM image of the lithium iron phosphate material prepared in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0047] The present application will be further described in detail in combination with examples and comparative examples.

[0048] Example 1

[0049] (1) Select a kind of iron phosphorus ratio is 0.965 iron phosphate raw material, according to the lithium iron molar ratio is 1.038 lithium carbonate and iron phosphate is weighed, add 8.6% of the mass of iron phosphate glucose, 2.4% of polyethylene glycol as carbon source, add 0.6% of the mass of iron phosphate titanium dioxide and 0.5% of 85% phosphoric acid; The above ingredients are mixed with pure water, put into a vertical ball mill, and the solid content is adjusted to 40%, and the slurry is coarsely ground for 40 min, so that the D90 particle size of the slurry is not more than 10 μm, the slurry is transferred to a sand mill after passing through a 200 mesh screen, and the grinding time and speed are controlled, so that the D50 particle size of the slurry is about 400 nm; The slurry is adjusted by peristaltic pump, enters the spray drying tower for granulation, the inlet air temperature is set to 230℃, the outlet air temperature is controlled at 110-120℃, and the D50 particle size of the spray material is 25-35 μm; The spray material is sintered in a roller kiln, the sintering temperature is 790℃, and the holding time is 8 h; The sintered material obtained is called A material;

[0050] (2) Select a kind of iron phosphorus ratio is 0.98 iron phosphate raw material, according to the lithium iron molar ratio is 1.05 lithium carbonate and iron phosphate is weighed, add 11% of the mass of iron phosphate glucose, 1.5% of polyethylene glycol as carbon source, add 0.6% of the mass of iron phosphate titanium dioxide and 0.9% of titanium coupling agent as titanium dopant; The above ingredients are mixed with pure water, put into a vertical ball mill, and the solid content is adjusted to 40%, and the slurry is coarsely ground for 40 min, so that the D90 particle size of the slurry is not more than 10 μm, the slurry is transferred to a sand mill after passing through a 200 mesh screen, and the grinding time and speed are controlled, so that the D50 particle size of the slurry is about 320 nm; The slurry is adjusted by peristaltic pump, enters the spray drying tower for granulation, the inlet air temperature is set to 230℃, the outlet air temperature is controlled at 110-120℃, and the D50 particle size of the spray material is 25-35 μm; The spray material is sintered in a roller kiln, the sintering temperature is 740℃, and the holding time is 7 h; The sintered material is subjected to air jet milling, the D50 particle size of the milled material is controlled to be 0.5-0.7 μm, and is called B material;

[0051] (3) Weigh materials A and B from steps (1) and (2) in a weight ratio of 9:1. The added auxiliary materials include titanium dioxide, titanium citrate, and dispersant. The amount of titanium dioxide added is 0.2% of the total mass of materials A and B, the amount of titanium citrate added is 0.3% of the total mass of materials A and B, and the amount of dispersant added is 1.3% of the total mass of materials A and B. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 35% and coarsely grind for 40 minutes. After the slurry passes through a 200-mesh sieve, transfer it to a sand mill. Control the grinding time and 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 the spray drying tower for granulation. Set the inlet air temperature to 230℃ and the outlet air temperature to 110-120℃. The D50 particle size of the sprayed material is 15-30 μm. μm; the sprayed material is sintered in a roller kiln at a temperature of 790℃ for 8 hours; the sintered material is then mechanically crushed to obtain the final lithium iron phosphate material product.

[0052] Example 2

[0053] (1) Select an iron-to-phosphorus ratio of 0.965 for iron phosphate raw material. Weigh lithium carbonate and iron phosphate according to the requirement of a lithium-to-iron molar ratio of 1.038. Add 8.6% glucose and 2.3% polyethylene glycol by weight of iron phosphate as carbon sources. Add 0.6% titanium dioxide and 0.5% 85% phosphoric acid by weight of iron phosphate. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 40% and perform coarse 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 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℃ and control the outlet air temperature to 110-120℃. The D50 particle size of the sprayed material is 25-35 nm. μm; The sprayed material is sintered in a roller kiln at a temperature of 790℃ and a holding time of 8 h; The sintered material is then subjected to air jet milling to control the D50 particle size of the milled material to be 1-1.4 μm, which is called material A;

[0054] (2) Select an iron-to-phosphorus ratio of 0.98 for the iron-to-phosphorus raw material. Weigh lithium carbonate and iron phosphate according to the requirement of a lithium-to-iron molar ratio of 1.05. Add 11% glucose and 1.5% polyethylene glycol by weight of iron phosphate as carbon sources, and add 0.6% titanium dioxide and 0.9% titanium coupling agent by weight of iron phosphate as titanium dopants. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 40% and perform coarse 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 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 the spray drying tower for granulation. Set the inlet air temperature to 230℃ and the outlet air temperature to 110-120℃. The D50 particle size of the sprayed material is 25-35 nm. μm; The sprayed material is sintered in a roller kiln at a temperature of 730℃ and a holding time of 8 h; The sintered material is then subjected to air jet milling to control the D50 particle size of the milled material to be about 0.5-0.7 μm, which is called B material;

[0055] (3) Weigh materials A and B from steps (1) and (2) in a weight ratio of 9:1. The added auxiliary materials include titanium dioxide, titanium citrate, and dispersant. The amount of titanium dioxide added is 0.2% of the total mass of materials A and B, the amount of titanium citrate added is 0.3% of the total mass of materials A and B, and the amount of dispersant added is 1.4% of the total mass of materials A and B. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 40% and perform coarse grinding for 40 minutes. The D50 particle size of the slurry is 0.8-1.2 μm, and the D100 particle size does not exceed 10 μm. After passing through a 200-mesh sieve, the slurry is transferred to the spray tank. The slurry is fed into the spray drying tower for granulation by adjusting the flow rate through a peristaltic pump. The inlet air temperature is set to 230℃, and the outlet air temperature is controlled at 110-120℃. The D50 particle size of the sprayed material is 15-30 μm. μm; the sprayed material is sintered in a roller kiln at a temperature of 795℃ for 8 hours; the sintered material is then mechanically crushed to obtain the final lithium iron phosphate material product.

[0056] Example 3

[0057] (1) Select an iron-to-phosphorus ratio of 0.965. Weigh lithium carbonate and iron phosphate according to the requirement of a lithium-to-iron molar ratio of 1.038. Add 8.6% glucose and 2.3% polyethylene glycol by weight of iron phosphate as carbon sources, and add 0.6% titanium dioxide by weight of iron phosphate. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 40% and perform coarse 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 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℃ and the outlet air temperature to 110-120℃. The D50 particle size of the sprayed material is 25-35 nm. μm; The sprayed material is sintered in a roller kiln at a temperature of 770℃ for 8 hours; The resulting sintered material is called material A;

[0058] (2) Select an iron-to-phosphorus ratio of 0.98 for the iron-to-phosphorus raw material. Weigh lithium carbonate and iron phosphate according to the requirement of a lithium-to-iron molar ratio of 1.05. Add 11% glucose and 1.5% polyethylene glycol by weight of iron phosphate as carbon sources, and add 0.6% titanium dioxide and 0.9% titanium coupling agent by weight of iron phosphate as titanium dopants. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 40% and perform coarse 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 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 the spray drying tower for granulation. Set the inlet air temperature to 230℃ and the outlet air temperature to 110-120℃. The D50 particle size of the sprayed material is 25-35 nm. μm; The sprayed material is sintered in a roller kiln at a temperature of 700℃ and a holding time of 9 h; The sintered material is then subjected to air jet milling to control the D50 particle size of the milled material to be 0.4-0.6 μm, which is called B material;

[0059] (3) Weigh materials A and B from steps (1) and (2) in a weight ratio of 9:1. The added auxiliary materials include titanium dioxide, titanium citrate, and dispersant. The amount of titanium dioxide added is 0.2% of the total mass of materials A and B, the amount of titanium citrate added is 0.3% of the total mass of materials A and B, and the amount of dispersant added is 1.7% of the total mass of materials A and B. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 35% and coarsely grind for 40 minutes. After the slurry passes through a 200-mesh sieve, transfer it to a sand mill. Control the grinding time and 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 the spray drying tower for granulation. Set the inlet air temperature to 230℃ and the outlet air temperature to 110-120℃. The D50 particle size of the sprayed material is 15-30 μm. μm; the sprayed material is sintered in a roller kiln at a temperature of 795℃ for 8 hours; the sintered material is then mechanically crushed to obtain the final lithium iron phosphate material product.

[0060] Example 4

[0061] (1) Select an iron-to-phosphorus ratio of 0.965. Weigh lithium carbonate and iron phosphate according to the requirement of a lithium-to-iron molar ratio of 1.038. Add 8.6% glucose and 2.3% polyethylene glycol by weight of iron phosphate as carbon sources, and add 0.6% titanium dioxide by weight of iron phosphate. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 40% and perform coarse 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 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℃ and the outlet air temperature to 110-120℃. The D50 particle size of the sprayed material is 25-35 nm. μm; The sprayed material is sintered in a roller kiln at a temperature of 790℃ and a holding time of 8 h; The sintered material is then subjected to air jet milling to control the D50 particle size of the milled material to be 1-1.4 μm, which is called material A;

[0062] (2) Select an iron-to-phosphorus ratio of 0.98 for the iron-to-phosphorus raw material. Weigh lithium carbonate and iron phosphate according to the requirement of a lithium-to-iron molar ratio of 1.05. Add 11% glucose and 1.5% polyethylene glycol by weight of iron phosphate as carbon sources, and add 0.6% titanium dioxide and 0.9% titanium coupling agent by weight of iron phosphate as titanium dopants. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 40% and perform coarse 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 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 the spray drying tower for granulation. Set the inlet air temperature to 230℃ and the outlet air temperature to 110-120℃. The D50 particle size of the sprayed material is 25-35 nm. μm; The sprayed material is sintered in a roller kiln at a temperature of 710℃ and a holding time of 8 h; The sintered material is then subjected to airflow milling to control the D50 particle size of the milled material to be about 0.5-0.7 μm, which is called B material;

[0063] (3) Weigh materials A and B from steps (1) and (2) in a weight ratio of 9:1. The added auxiliary materials include titanium dioxide, titanium citrate, and dispersant. The amount of titanium dioxide added is 0.4% of the total mass of materials A and B, the amount of titanium citrate added is 0.3% of the total mass of materials A and B, and the amount of dispersant added is 2.0% of the total mass of materials A and B. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 40% and coarsely grind for 40 minutes. The D50 particle size of the slurry is 0.8-1.2 μm, and the D100 particle size does not exceed 10 μm. After passing through a 200-mesh sieve, the slurry is transferred to the spray tank. The slurry is fed into the spray drying tower for granulation by adjusting the flow rate through a peristaltic pump. The inlet air temperature is set to 230℃, and the outlet air temperature is controlled at 110-120℃. The D50 particle size of the sprayed material is 15-30 μm. μm; the sprayed material is sintered in a roller kiln at a temperature of 795℃ for 8 hours; the sintered material is then mechanically crushed to obtain the final lithium iron phosphate material product.

[0064] Example 5

[0065] The difference from Example 4 is that the amount of titanium dioxide added in step (3) is 0.3% of the total mass of material A and material B, and the temperature of the sprayed material being sintered in the roller kiln is 798°C.

[0066] Comparative Example 1

[0067] This comparative example uses a traditional one-step method to prepare lithium iron phosphate materials, as detailed below:

[0068] Select an iron-to-phosphorus ratio of 0.965 for the iron-to-phosphorus raw material. Weigh lithium carbonate and iron phosphate according to the requirement of a lithium-to-iron molar ratio of 1.038. Add 8.6% glucose and 2.3% polyethylene glycol (based on the weight of iron phosphate) as carbon sources, and add 0.6% titanium dioxide and 0.5% 85% phosphoric acid (based on the weight of iron phosphate). Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 40% and coarsely grind for 40 minutes to ensure 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 speed to ensure that the D50 particle size of the slurry is about 400 nm. The slurry is then fed into a spray drying tower for granulation by adjusting the flow rate with a peristaltic pump. The inlet air temperature is set to 230℃, and the outlet air temperature is controlled at 110-120℃. The D50 particle size of the sprayed material is 25-35 nm. μm; the sprayed material is sintered in a roller kiln at a temperature of 795℃ for 8 hours; the sintered material is then mechanically crushed to obtain the final lithium iron phosphate material product.

[0069] Comparative Example 2

[0070] In this comparative example, material B was not used for gradation in the two-stage grinding process, as detailed below:

[0071] (1) Select an iron-to-phosphorus ratio of 0.965 for iron phosphate raw material. Weigh lithium carbonate and iron phosphate according to the requirement of a lithium-to-iron molar ratio of 1.038. Add 8.6% glucose and 2.3% polyethylene glycol by weight of iron phosphate as carbon sources. Add 0.6% titanium dioxide and 0.5% 85% phosphoric acid by weight of iron phosphate. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 40% and perform coarse 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 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℃ and control the outlet air temperature to 110-120℃. The D50 particle size of the sprayed material is 25-35 nm. μm; The sprayed material is sintered in a roller kiln at a temperature of 790℃ for 8 hours; The resulting sintered material is called material A;

[0072] (2) Weigh material A in step (1). The added auxiliary materials include titanium dioxide and dispersant. The amount of titanium dioxide added is 0.25% of the mass of material A, and the amount of dispersant added is 0.5% of the mass of material A. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 40% and coarsely grind for 40 min. After the slurry passes through a 200-mesh sieve, transfer it to a sand mill. Control the grinding time and 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 the spray drying tower for granulation. Set the inlet air temperature to 230℃ and control the outlet air temperature at 110-120℃. The D50 particle size of the spray material is 15-30 μm. Sinter the spray material in a roller kiln at a sintering temperature of 795℃ and a holding time of 8 h. Mechanically crush the sintered material to obtain the final lithium iron phosphate material product.

[0073] Comparative Example 3

[0074] In this comparative example, material B was not used for gradation in the two-stage grinding process, as detailed below:

[0075] (1) Select an iron-to-phosphorus ratio of 0.965. Weigh lithium carbonate and iron phosphate according to the requirement of a lithium-to-iron molar ratio of 1.038. Add 8.6% glucose and 2.3% polyethylene glycol by weight of iron phosphate as carbon sources, and add 0.6% titanium dioxide by weight of iron phosphate. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 40% and perform coarse 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 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℃ and the outlet air temperature to 110-120℃. The D50 particle size of the sprayed material is 25-35 nm. μm; The sprayed material is sintered in a roller kiln at a temperature of 790℃ and a holding time of 8 h; The sintered material is then subjected to air jet milling to control the D50 particle size of the milled material to be 1-1.4 μm, which is called material A;

[0076] (2) Weigh material A in step (1). The added auxiliary materials include titanium dioxide, titanium citrate and dispersant. The amount of titanium dioxide added is 0.3% of the mass of material A, the amount of titanium citrate added is 0.3% of the mass of material A, and the amount of dispersant added is 2% of the mass of material A. Mix the above ingredients with pure water and put them into a vertical ball mill. Adjust the solid content to 40% and coarsely grind for 40 minutes. After the slurry passes through a 200-mesh sieve, transfer it to a sand mill. Control the grinding time and 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 the spray drying tower for granulation. Set the inlet air temperature to 230℃ and control the outlet air temperature to 110-120℃. The D50 particle size of the sprayed material is 15-30 μm. Sinter the sprayed material in a roller kiln. The sintering temperature is 795℃ and the holding time is 8 minutes. h; The sintered material is mechanically crushed to obtain the final lithium iron phosphate material product.

[0077] Experimental Section

[0078] Experiment 1

[0079] The lithium iron phosphate materials prepared in Examples 1-5 and Comparative Example 1 were subjected to powder performance testing, and the results are shown in Table 1.

[0080] Table 1 Performance Test Results

[0081]

[0082] As shown in Table 1, the compacted powder of the lithium iron phosphate material product prepared in Example 1 is 2.572 g / cm³. 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 plateau retention rate is 91.4%; the lithium iron phosphate material product prepared in Example 2 has a powder compaction of 2.613 g / cm³. 3 The D50 is 1.39 μm, the 1C discharge specific capacity is 139.1 mAh / g, and the 1C 3.2V discharge plateau retention rate is 91.0%. The lithium iron phosphate material product prepared in Example 3 has a powder compaction of 2.617 g / cm³. 3 The D50 is 1.20 μm, the 1C discharge specific capacity is 139.9 mAh / g, and the 1C 3.2V discharge plateau retention rate is 88.5%. The powder compaction of the lithium iron phosphate material product prepared in Example 4 is 2.643 g / cm³. 3 The D50 is 1.22 μm, the 1C discharge specific capacity is 140.5 mAh / g, and the 1C 3.2V discharge plateau retention rate is 91.2%. The powder compaction of the lithium iron phosphate material product prepared in Example 5 is 2.712 g / cm³. 3The D50 is 1.37 μm, the 1C discharge specific capacity is 135.4 mAh / g, and the 1C 3.2V discharge plateau retention rate is 90.4%.

[0083] The lithium iron phosphate material product prepared in Comparative Example 1 had a powder compaction of 2.519 g / cm³. 3 The D50 is 1.09 μm, the 1C discharge specific capacity is 135.5 mAh / g, and the 1C 3.2V discharge plateau retention rate is 88.6%; the lithium iron phosphate material product prepared in Comparative Example 2 has a powder compaction of 2.664 g / cm³. 3 The D50 is 1.63 μm, the 1C discharge specific capacity is 129.3 mAh / g, and the 1C 3.2V discharge plateau retention rate is 83.0%; the lithium iron phosphate material product prepared in Comparative Example 3 has a powder compaction of 2.638 g / cm³. 3 The D50 is 0.934 μm, the 1C discharge specific capacity is 135.3 mAh / g, and the 1C 3.2V discharge plateau retention rate is 89.2%. The results show that the lithium iron phosphate material prepared by the present invention has high compaction density, and the 1C discharge specific capacity and 1C 3.2V discharge plateau retention rate are both greater than those of the comparative example.

[0084] Experiment 2

[0085] The lithium iron phosphate materials prepared in Examples 2, 4, 5 and Comparative Example 2 were subjected to electron microscopy scanning, and the results are as follows: Figures 1-4 As shown in the figure, it can be seen that the materials of Examples 2 and 4 have no ultra-large particles, and the small particles fill the gaps between the large particles quite perfectly, thus preparing a high compaction density material; the material of Example 5 has some large particles, which further improves the compaction density of the material; however, the material of Comparative Example 2 has ultra-large particles, and the proportion of small particles is reduced, resulting in the deterioration of the electrical properties of the material.

Claims

1. A method for preparing a high-density lithium iron phosphate material, characterized in that, Includes the following steps: (1) Iron phosphate, lithium carbonate, carbon source, auxiliary materials and pure water are mixed and processed by high temperature solid phase method to generate large particle lithium iron phosphate material. The specific method is as follows: Iron phosphate, lithium carbonate, carbon source, auxiliary materials and pure water are mixed and then subjected to coarse grinding, fine grinding, spray drying, high temperature calcination or high temperature calcination and pulverization in sequence to obtain large particle lithium iron phosphate material, which is called material A. The D50 particle size of material A is 1-1.4 μm. (2) Iron phosphate, lithium carbonate, carbon source, auxiliary materials and pure water are mixed and processed by high temperature solid phase method to generate small particle lithium iron phosphate pulverized material. The specific method is as follows: After mixing iron phosphate, lithium carbonate, carbon source, auxiliary materials and pure water, coarse grinding, fine grinding, spray drying and high temperature calcination are carried out in sequence to obtain small particle lithium iron phosphate sintered material. Further pulverization is carried out to obtain small particle lithium iron phosphate pulverized material, which is called B material. The D50 particle size of the B material is 0.5-0.7 μm. (3) Mix material A and material B, add auxiliary materials and pure water, and perform high-temperature solid-state treatment to generate high-pressure dense lithium iron phosphate material. The specific method is as follows: Mix material A and material B, add auxiliary materials and pure water, and then perform coarse grinding, fine grinding, spray drying, high-temperature calcination and pulverization in sequence to obtain high-pressure dense lithium iron phosphate material; the mass of material B accounts for 5%-20% of the total mass of material A and material B; In step (3), the auxiliary materials include titanium dioxide, titanium citrate and dispersant. The amount of titanium dioxide added is 0.2-0.5% of the total mass of materials A and B, the amount of titanium citrate added is 0.1-0.4% of the total mass of materials A and B, and the amount of dispersant added is 1-4% of the total mass of materials A and B.

2. The method for preparing a high-density lithium iron phosphate material according to claim 1, characterized in that, In step (1), iron phosphate and lithium carbonate are mixed in a molar ratio of 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 inlet air temperature of spray drying is 230℃; the outlet air temperature is controlled at 110-120℃; the high-temperature calcination temperature is 770-800℃; and the heat preservation time is 7-10 h.

3. The method for preparing a high-density lithium iron phosphate material according to claim 2, characterized in that, In step (1), the iron-to-phosphorus ratio of iron phosphate is 0.950-0.975; the carbon source is one or more combinations of glucose, polyethylene glycol, starch, and sucrose; the excipients are 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 finished lithium iron phosphate product.

4. The method for preparing a high-density lithium iron phosphate material according to claim 3, characterized in that, The material A obtained in step (1) is lithium iron phosphate sintered material or pulverized material, and the compacted density of the sintered material is 2.33-2.50 g / cm³. 3 The compacted density of the crushed material is 2.43-2.60 g / cm³. 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-density lithium iron phosphate material according to claim 1, characterized in that, In step (2), iron phosphate and lithium carbonate are mixed in a molar ratio of 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 inlet air temperature of spray drying is 230℃; the outlet air temperature is controlled at 110-120℃; the high-temperature calcination temperature is 700-740℃; and the heat preservation time is 7-9 h.

6. The method for preparing a high-density lithium iron phosphate material according to claim 5, characterized in that, In step (2), the iron-to-phosphorus ratio of 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, which is one or more of titanium dioxide and titanium coupling agent, and the addition of the titanium dopant makes the titanium element 3000-5000 ppm of the finished lithium iron phosphate product.

7. The method for preparing a high-density lithium iron phosphate material according to claim 6, characterized in that, The compacted density of material B obtained in step (2) is 2.00-2.15 g / cm³. 3 The carbon content is 1.30-1.50% of the mass of lithium iron phosphate.

8. The method for preparing a high-density lithium iron phosphate material according to claim 1, characterized in that, In 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 air temperature is 230℃, the outlet air temperature is controlled at 110-120℃, the high temperature calcination temperature is 700-800℃, and the heat preservation time is 7-10 h.

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

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