A sintering method for mass production of high-compacted-density lithium iron phosphate

Abstract

The application belongs to the technical field of lithium battery positive electrode materials, and particularly relates to a sintering method for mass production of high-pressing-density lithium iron phosphate, which comprises the following specific steps: pure water, anhydrous iron phosphate, a lithium source, a carbon source and an additive are mixed, and are subjected to dispersion and grinding to obtain slurry A; spray drying is performed to obtain lithium iron phosphate precursor powder B; a ball loading machine is used for loading, and the program of the ball loading machine is adjusted as follows: the ball loading is performed according to the specifications of 7-9 kg and 3-5 kg; the sagger is sent into a roller furnace filled with a nitrogen atmosphere for sintering to obtain lithium iron phosphate semi-product C; and after airflow crushing, lithium iron phosphate product D is obtained. The sintering process of lithium iron phosphate is simply improved, the mixing of large and small particles of lithium iron phosphate is realized, the pressing density of lithium iron phosphate is improved, and the specific capacity of lithium iron phosphate is also considered; the method has little change to the original production line, can fully utilize the original production line for production, and has low cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery positive electrode materials, and particularly relates to a sintering method for mass production of high-pressing-density lithium iron phosphate. BACKGROUND

[0002] Lithium iron phosphate is a mainstream lithium ion battery positive electrode material, and has the advantages of high specific capacity, low price and environmental friendliness. However, the low pressing density limits the energy density of the lithium ion battery. At present, the main industrial production method is the carbon thermal reduction method, and the product index is relatively stable.

[0003] With the rapid development of the new energy automobile market, mainstream power battery manufacturers in the market have put forward higher requirements for lithium iron phosphate materials, including high energy density, low cost, fast charging and discharging and the like. In order to improve the energy density of the lithium iron phosphate battery, it is necessary to improve the capacity, voltage platform or pressing density of the lithium iron phosphate material. However, the capacity and voltage of the lithium iron phosphate on the market are close to the theoretical value, and the space for improvement is small. Therefore, it is necessary to improve the pressing density of the lithium iron phosphate to improve the energy density thereof. However, the conventional method for improving the pressing density of the lithium iron phosphate will cause the reduction of the specific capacity of the lithium iron phosphate.

[0004] Patent CN108011104A discloses a high-pressing-density lithium iron phosphate positive electrode material and a preparation method thereof. In the scheme, two kinds of particle slurries with different sizes are selected, the large-particle slurry and the small-particle slurry are mixed in a certain ratio in the grinding stage, and then the high-pressing-density lithium iron phosphate is prepared through drying treatment and heat treatment respectively. The prepared lithium iron phosphate has high density. Although the large and small particles are mixed uniformly in the slurry stage, the large and small particles are often layered in the drying and granulation process, and the gaps between the large particles are difficult to be effectively filled by the small particles. Meanwhile, two or more kinds of slurry grinding particle sizes are needed, and the control process is complex in industrial production, which brings instability.

[0005] Patent CN107256968A discloses a high-pressing-density lithium iron phosphate and a preparation method thereof. In the method, the large-particle and small-particle mixed iron phosphate raw materials are mixed with a lithium source, and then a lithium iron phosphate precursor with an iron phosphate skeleton is obtained through one-step grinding, and the high-pressing-density lithium iron phosphate is obtained through calcination. However, the particle size of the mixed large and small particle iron phosphate raw materials has a relatively strict requirement (the particle size of the small particle iron phosphate is 0.05-0.3 microns), which increases the difficulty of raw material supply (the particle size of the commercially available iron phosphate is generally 2.0-10.0 microns). How to control the mass ratio of the large and small particles also puts forward higher requirements for the modification of the original production line, and the raw material batching bin needs to be increased, which directly leads to the complication of the control process in industrial production.

[0006] Therefore, it is of great research significance and economic value to develop a preparation method for improving the compaction density of lithium iron phosphate material through a simple and industrialized process. SUMMARY

[0007] The purpose of the present application is to provide a sintering method for mass production of high compaction density lithium iron phosphate, which improves the compaction density of lithium iron phosphate by mixing large and small particles of lithium iron phosphate through simple improvement of the lithium iron phosphate sintering process, and takes into account the specific capacity of lithium iron phosphate; the method has little change to the original production line and can fully utilize the original production line for production, thus being low in cost.

[0008] The present application provides a sintering method for mass production of high compaction density lithium iron phosphate, comprising the following specific steps:

[0009] S1. Mixing, dispensing and grinding pure water, anhydrous iron phosphate, a lithium source, a carbon source and an additive to obtain slurry A;

[0010] S2. Spraying and drying the slurry A obtained in S1 to obtain lithium iron phosphate precursor powder B;

[0011] S3. Loading the lithium iron phosphate precursor B obtained in S2 into a pot through an automatic pot loading machine, and adjusting the program of the automatic pot loading machine to load the pot according to the loading amount of 7-9 kg and 3-5 kg specifications;

[0012] S4. After loading, the lithium iron phosphate precursor B is sent into a roller hearth furnace filled with a nitrogen atmosphere for sintering to obtain lithium iron phosphate semi-product C;

[0013] S5. After airflow crushing of the lithium iron phosphate semi-product C obtained by heat treatment in S4, lithium iron phosphate product D is obtained.

[0014] The sintering sagger is made of graphite, a good conductor of heat with a fast heat transfer rate and excellent thermal conductivity. However, the lithium iron phosphate precursor powder contains more gaps and air, resulting in significantly lower thermal conductivity compared to the sagger. The lithium iron phosphate precursor near the surface layer of the sagger and on the inner wall of the sagger reaches a sintering temperature closer to the actual temperature of the kiln cavity. However, the lithium iron phosphate precursor in the center of the inner layer of the sagger experiences a temperature gradient due to the heat transfer from the furnace cavity to the center, resulting in a sintering temperature lower than the actual temperature of the kiln cavity. Therefore, there are differences in the sintering temperature of the material in different locations within the same sagger. Therefore, this invention utilizes the temperature differences at different locations within the sagger. By controlling the amount of material packed in the sagger, a smaller amount results in a larger proportion of precursors in the surface layer or near the inner wall of the sagger, leading to a higher overall sintering temperature and a majority of large particles. Conversely, a larger amount results in a smaller proportion of precursors in the surface layer or near the inner wall of the sagger, leading to a lower overall sintering temperature and a majority of small particles. This achieves a wider range of particle size distribution, thereby improving the compaction of lithium iron phosphate while maintaining its specific capacity.

[0015] Preferably, in the above technical solution S1, the mass ratio of pure water, anhydrous iron phosphate, lithium source, carbon source and additive is 2200:1000:220-260:100-140:1-10.

[0016] Preferably, in the above technical solution S1, the particle size of the slurry A is ≤0.45μm.

[0017] Preferably, in the above technical solution S2, the spray drying conditions are: inlet air temperature of 240-280℃ and outlet temperature of 80-100℃. This technical solution uses spray drying, resulting in uniform particle size.

[0018] Preferably, in the above technical solution S3, the ratio of the number of 7-9kg and 3-5kg saggers is 1:9-9:1. In this technical solution, the automatic sagger filling machine is programmed to handle varying quantities of material, including some saggers with larger quantities and others with smaller quantities, and the ratio of the larger to smaller quantities is controlled. This achieves a wide range of particle size distribution, eliminating the need to pre-process the ferric phosphate raw material into different sized particles. The process is simple, energy-saving, and significantly reduces costs.

[0019] Preferably, in the above technical solution S4, the sintering conditions are: sintering temperature 700-780℃, and constant temperature time 8-12h.

[0020] Preferably, in the above technical solution, the sagger is made of graphite.

[0021] Preferably, in the above technical solution, the particle size of the lithium iron phosphate product D is 0.8-1.5μm.

[0022] Preferably, in the above technical solution, the lithium source is one or more of lithium carbonate, lithium acetate, lithium hydroxide, and lithium nitrate.

[0023] Preferably, in the above technical solution, the carbon source is one or more of polyethylene glycol, sucrose, glucose, and starch; and the additive is titanium dioxide.

[0024] Advantages compared to existing technologies:

[0025] 1. This invention achieves the mixing of lithium iron phosphate particles of different sizes by simply optimizing the sintering process. This eliminates the need to select different raw materials or to complicate the grinding process to achieve the mixing of lithium iron phosphate particles of different sizes. The process is simple and the cost is low.

[0026] 2. This invention controls the amount of material packed in the sagger. In the same sagger, a smaller amount of material results in a larger proportion of precursor material in the surface layer or near the inner wall of the sagger, leading to a higher overall sintering temperature and a majority of large particles. Conversely, a larger amount of material results in a smaller proportion of precursor material in the surface layer or near the inner wall of the sagger, leading to a lower overall sintering temperature and a majority of small particles. This achieves a wider range of particle size distribution, thereby improving the compaction of lithium iron phosphate while maintaining its specific capacity.

[0027] 3. This invention requires almost no modification to the existing production line, allowing production to be carried out using the existing line, greatly saving on modification costs and increasing output. Detailed Implementation

[0028] The above-described technical features of the present invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. However, the present invention is not limited to these embodiments, nor are these embodiments limited in any way.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the formulations involved in the following examples are all commercially available products that can be purchased from the market.

[0030] The present invention will be further described in detail below with reference to embodiments:

[0031] Example 1

[0032] A sintering method for mass production of high-density lithium iron phosphate includes the following specific steps:

[0033] S1. Pure water, anhydrous iron phosphate, lithium source, carbon source and additives are mixed and prepared, dispersed and ground to obtain slurry A, the particle size of slurry A is ≤0.45μm; wherein, the mass ratio of pure water, anhydrous iron phosphate, lithium source, carbon source and additives is 2200:1000:240:100:3; the lithium source is lithium carbonate; the carbon source is glucose and polyethylene glycol; the additive is titanium dioxide;

[0034] S2. Spray dry the slurry A obtained in S1 to obtain lithium iron phosphate precursor powder B; wherein the inlet air temperature of the spray dryer is 260℃ and the outlet temperature is 90℃.

[0035] S3. The lithium iron phosphate precursor B obtained in S2 is packed into saggers using an automatic sagger packing machine. The program of the automatic sagger packing machine is adjusted to pack saggers in 7-9kg and 3-5kg sizes. The ratio of the number of saggers in 7-9kg and 3-5kg sizes is 1:1.

[0036] S4. After loading into the crucible, the crucible of lithium iron phosphate precursor B is sent into a roller furnace filled with nitrogen atmosphere for sintering at a temperature of 760℃ and a holding time of 12h to obtain lithium iron phosphate semi-finished product C.

[0037] S5. The lithium iron phosphate semi-finished product C obtained from the heat treatment in S4 is subjected to air jet milling to obtain the lithium iron phosphate finished product D.

[0038] Example 2

[0039] A sintering method for mass production of high-density lithium iron phosphate includes the following specific steps:

[0040] S1. Pure water, anhydrous iron phosphate, lithium source, carbon source and additives are mixed and prepared, and then dispersed and ground to obtain slurry A, the particle size of slurry A being ≤0.45μm; wherein, the mass ratio of pure water, anhydrous iron phosphate, lithium source, carbon source and additives is 2200:1000:240:120:5; the lithium source is lithium carbonate; the carbon source is sucrose or glucose; the additive is titanium dioxide;

[0041] S2. Spray dry the slurry A obtained in S1 to obtain lithium iron phosphate precursor powder B; wherein the inlet air temperature of the spray dryer is 240℃ and the outlet temperature is 95℃.

[0042] S3. The lithium iron phosphate precursor B obtained in S2 is packed into saggers using an automatic sagger packing machine. The program of the automatic sagger packing machine is adjusted to pack saggers in 7-9kg and 3-5kg sizes. The ratio of the number of saggers in 7-9kg and 3-5kg sizes is 3:7.

[0043] S4. After loading into the crucible, the crucible of lithium iron phosphate precursor B is sent into a roller furnace filled with nitrogen atmosphere for sintering at a temperature of 750℃ for 10 hours to obtain lithium iron phosphate semi-finished product C.

[0044] S5. The lithium iron phosphate semi-finished product C obtained from the heat treatment in S4 is subjected to air jet milling to obtain the lithium iron phosphate finished product D.

[0045] Example 3

[0046] A sintering method for mass production of high-density lithium iron phosphate includes the following specific steps:

[0047] S1. Pure water, anhydrous iron phosphate, lithium source, carbon source and additives are mixed and prepared, and then dispersed and ground to obtain slurry A, the particle size of slurry A being ≤0.45μm; wherein, the mass ratio of pure water, anhydrous iron phosphate, lithium source, carbon source and additives is 2200:1000:260:140:10; the lithium source is lithium carbonate; the carbon source is starch; the additive is titanium dioxide;

[0048] S2. Spray dry the slurry A obtained in S1 to obtain lithium iron phosphate precursor powder B; wherein the inlet air temperature of the spray dryer is 280℃ and the outlet temperature is 80℃.

[0049] S3. The lithium iron phosphate precursor B obtained in S2 is packed into saggers using an automatic sagger packing machine. The program of the automatic sagger packing machine is adjusted to pack saggers in 7-9kg and 3-5kg sizes. The ratio of the number of saggers in 7-9kg and 3-5kg sizes is 7:3.

[0050] S4. After loading into the crucible, the crucible of lithium iron phosphate precursor B is sent into a roller furnace filled with nitrogen atmosphere for sintering at a temperature of 780℃ and a holding time of 12h to obtain lithium iron phosphate semi-finished product C.

[0051] S5. The lithium iron phosphate semi-finished product C obtained from the heat treatment in S4 is subjected to air jet milling to obtain the lithium iron phosphate finished product D.

[0052] Comparative Example 1

[0053] A sintering method for lithium iron phosphate differs from Example 1 in that the saggers are all of the 7-9 kg specification, while the rest is the same as in Example 1.

[0054] Comparative Example 2

[0055] A sintering method for lithium iron phosphate differs from Example 1 in that the saggers are all of the 3-5 kg ​​specification, while the rest is the same as Example 1.

[0056] The products obtained in Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests using conventional production testing methods, and the results are shown in Table 1. Specifically, particle size was measured using a Malvern laser particle size analyzer, compaction density was measured using a powder compactor, resistivity was measured using a four-probe resistivity meter, specific surface area was measured using a liquid nitrogen adsorption specific surface area analyzer, and capacity was measured using coin cells.

[0057] Table 1

[0058]

[0059] As can be seen from the data in Table 1, the technical solution of the present invention can take into account both the advantages of high compaction density and high discharge capacity. As can be seen from the data of Example 1, Comparative Example 1 and Comparative Example 2, the compaction density and discharge capacity can be adjusted by controlling the number of saggers with different filling amounts.

[0060] In summary, this invention controls the amount of material packed in the sagger. With a smaller amount packed in the same sagger, the proportion of precursor material in the surface layer or near the inner wall of the sagger is larger, resulting in a higher overall sintering temperature and a majority of large particles. Conversely, with a larger amount packed in the sagger, the proportion of precursor material in the surface layer or near the inner wall is smaller, resulting in a lower overall sintering temperature and a majority of small particles. This achieves a wider range of particle size distribution, thereby improving the compaction of lithium iron phosphate while maintaining its specific capacity. This sintering method eliminates the need for different raw material selection or complex grinding processes to mix lithium iron phosphate particles of different sizes. The process is simple, can be used on existing production lines, significantly reducing modification costs and achieving high output.

[0061] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sintering method for mass production of high compact density lithium iron phosphate, characterized by, The method comprises the following specific steps: S1. Mixing, dispensing and grinding pure water, anhydrous iron phosphate, a lithium source, a carbon source and an additive to obtain slurry A; S2. Spray drying the slurry A obtained in S1 to obtain lithium iron phosphate precursor powder B; S3. Loading the lithium iron phosphate precursor B obtained in S2 into a hopper through an automatic hopper loader, adjusting the program of the automatic hopper loader as follows: loading according to the loading amount of 7-9 kg and 3-5 kg specifications; the number ratio of the hopper for the loading amount of 7-9 kg and 3-5 kg specifications is 1:9-9:1; the hopper is made of graphite; S4. After loading, the hopper of the lithium iron phosphate precursor B is sent into a roller hearth furnace filled with a nitrogen atmosphere for sintering to obtain lithium iron phosphate semi-product C; S5. After airflow crushing of the lithium iron phosphate semi-product C obtained by heat treatment in S4, lithium iron phosphate product D is obtained.

2. The sintering method of mass production of high-density lithium iron phosphate according to claim 1, characterized in that, In S1, the mass ratio of the pure water, the anhydrous iron phosphate, the lithium source, the carbon source and the additive is 2200:1000:220-260:100-140:1-10.

3. The sintering method of mass production of high-density lithium iron phosphate according to claim 1, characterized in that, In S1, the particle size of the slurry A is ≤0.45 μm.

4. The sintering method of mass production of high-density lithium iron phosphate according to claim 1, characterized in that, In S2, the spray drying conditions are as follows: the inlet air temperature is 240-280 ℃, and the outlet temperature is 80-100 ℃.

5. The sintering method of mass production of high-density lithium iron phosphate according to claim 1, characterized in that, In S4, the sintering conditions are as follows: the sintering temperature is 700-780 ℃, and the constant temperature time is 8-12 h.

6. The sintering method of mass production of high-density lithium iron phosphate according to claim 1, characterized in that, The particle size of the lithium iron phosphate product D is 0.8-1.5 μm.

7. The sintering method of mass production of high-density lithium iron phosphate according to claim 1, characterized in that, The lithium source is one or more of lithium carbonate, lithium acetate, lithium hydroxide and lithium nitrate.

8. The sintering method of mass production of high-density lithium iron phosphate according to claim 1, characterized in that, The carbon source is one or more of polyethylene glycol, sucrose, glucose and starch; and the additive is titanium dioxide.

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