High-compaction and high-capacity lithium iron phosphate material as well as preparation method and application thereof

Abstract

The invention discloses a high-compaction and high-capacity lithium iron phosphate material as well as a preparation method and application thereof, and belongs to the field of electrochemistry. The preparation method of the material comprises the following steps: mixing first titanium-containing iron phosphate, titanium-free iron phosphate, a first lithium source, a first carbon source, a first additive and water, grinding and drying to obtain a precursor material; sintering the precursor material for the first time to obtain a sintered material; and mixing the sintered material, second titanium-containing iron phosphate, a second lithium source, a second carbon source and a second additive, compacting, sintering for the second time, and crushing to obtain a target product. Through cooperative use of iron phosphate with different titanium contents and regulation and control of the sintering step, the compaction density of the lithium iron phosphate material is improved, the material has high capacity, the technical problem that the compaction density and the capacity of the lithium iron phosphate cannot be considered at the same time in the prior art is solved, and the preparation method is suitable for industrial production. The prepared lithium iron phosphate material has excellent compaction density and electrochemical capacity at the same time.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemistry, and in particular relates to a high-density, high-capacity lithium iron phosphate material and a preparation method and application thereof. Background Art

[0002] At present, new energy batteries are mainly composed of lithium iron phosphate batteries, ternary batteries and high nickel batteries. Among them, lithium iron phosphate batteries are rapidly seizing the market with their cost advantages and technological breakthroughs, while ternary batteries are retreating to the high-end market and their development momentum is slowing down. Lithium iron phosphate battery is a lithium-ion battery that uses lithium iron phosphate as the positive electrode material. The lithium iron phosphate material has a stable olivine structure and a high temperature tolerance of up to 350-500°C. The risk of thermal runaway is significantly lower than that of ternary lithium batteries. It can remain stable even in extreme conditions such as overcharging, puncture or collision. However, with the increasing requirements for cruising range, there is an increasing demand for lithium iron phosphate with high compaction density. In the prior art, the compaction density of lithium iron phosphate positive electrode materials is generally low, far lower than its theoretical density, which limits its application in the field of power batteries.

[0003] The existing technology of using sand grinding particle size grading to improve compaction density has defects. Large particle raw materials need to increase the sintering temperature or extend the sintering time, which leads to uncontrollable fusion and growth between small particles, making the proportion of small particle size particles too low, and the grading effect and compaction density cannot be maximized. The existing method of improving the compaction density of lithium iron phosphate materials often leads to a decrease in material capacity, and it is impossible to maintain good electrical properties while increasing the compaction density. Summary of the invention

[0004] The purpose of the present invention is to provide a high-density, high-capacity lithium iron phosphate material and a preparation method and application thereof, which can improve the compaction density of the lithium iron phosphate material while maintaining the material having a high capacity, thereby overcoming the technical problem in the prior art that the compaction density and capacity of lithium iron phosphate cannot be taken into account at the same time.

[0005] To achieve the above object, the technical solution adopted by the present invention is: A method for preparing a high-density, high-capacity lithium iron phosphate material comprises the following steps: A first titanium-containing iron phosphate, a non-titanium-containing iron phosphate, a first lithium source, a first carbon source, a first additive and water are mixed to obtain a mixed material, and the mixed material is ground to a particle size requirement of less than 0.5 μm, and then dried to obtain a precursor material; preferably, the titanium content of the first titanium-containing iron phosphate is 6000-10000 ppm, and when the titanium content is lower than 6000 ppm, the material capacity will decrease; when it is higher than 10000 ppm, the material compaction decreases and magnetic risks will occur, affecting the safety of the battery; the titanium content of the non-titanium iron phosphate is controlled to be less than 50 ppm; The precursor material is sintered for the first time to obtain a sintered material; preferably, the temperature of the first sintering is 600-800 °C; The sintered material, the second iron titanium phosphate, the second lithium source, the second carbon source, and the second additive are mixed and then compacted, and the target product is obtained after the second sintering and pulverization; preferably, the ratio of the sintered material to the second iron titanium phosphate is 7.5: (0.8-1.2); the titanium content of the second iron titanium phosphate is lower than that of the first iron titanium phosphate, the titanium content of the second iron titanium phosphate is 1000-5000 ppm, and the particle size is controlled at 0.8-1.6 μm; the pressure of the compaction is 50-150 MPa; the temperature of the second sintering is 700-900 °C, and the temperature and time of sintering are related. The higher the temperature, the shorter the required time; the lower the temperature, the longer the required time.

[0006] As a preferred technical solution, the mass ratio of the first iron titanium phosphate to the iron phosphate without titanium is 1: (0.6-1.5); the molar ratio of elemental iron to phosphorus in the precursor material is (0.95-1.05): 1; the molar ratio of lithium to iron is (1.01-1.06): 1. By limiting the dosage ratio between various substances, the material can form a better phase. When the ratio exceeds the range defined in the present invention, other substances that affect the product performance will be formed.

[0007] As a preferred technical solution, the first lithium source and the second lithium source are each independently selected from at least one of lithium carbonate, lithium hydroxide, and lithium oxide; the first carbon source and the second carbon source are each independently selected from at least one of sucrose, glucose, polyethylene glycol, phenolic resin, starch, and citric acid; the first additive and the second additive are each independently selected from one of a titanium-containing compound, a cobalt-containing compound, a vanadium-containing compound, and an aluminum-containing compound. The role of the carbon source is to increase the conductivity of the material, and the role of the additive is to further improve the capacity of the product.

[0008] The present invention also provides a high-compaction and high-capacity lithium iron phosphate material, which is prepared by the preparation method as described above. This lithium iron phosphate material has a high tap density and good electrical properties, and has good application prospects in lithium-ion batteries.

[0009] Compared with the prior art, the present invention has the following beneficial effects: The present invention first mixes raw materials such as the first titanium-containing iron phosphate and titanium-free iron phosphate and then performs the first sintering. Since titanium elements can inhibit particle growth during the sintering process, the titanium-containing iron phosphate grows into small lithium iron phosphate particles, and the titanium-free iron phosphate grows into large lithium iron phosphate particles. After the first sintering, the lithium iron phosphate initially forms a particle size grading of large and small particles. Then, based on the lithium iron phosphate material obtained from the first sintering, raw materials such as a certain amount of the second titanium-containing iron phosphate are added for the second sintering, and the titanium content of the second titanium-containing iron phosphate is controlled to be lower than that of the first titanium-containing iron phosphate, so that particles of medium size grow based on different particle inhibition effects, forming a three-level grading. Since the material with a relatively high grading compaction has been formed after the first sintering, the second sintering is more likely to be compacted and maintain the capacity on the basis of the first sintering, thereby further improving the compaction density of the material, and at the same time avoiding the problem that increasing the compaction density often leads to a decrease in the material capacity in the prior art; the lithium iron phosphate material prepared by the method in the present invention has excellent compaction density and electrochemical capacity at the same time. Description of the Drawings

[0010] Figure 1 SEM image of the lithium iron phosphate material prepared in Example 1; Figure 2 SEM image of the lithium iron phosphate material prepared in Example 3; Figure 3 SEM image of the lithium iron phosphate material prepared in Comparative Example 1. Detailed Description of the Invention

[0011] The following further illustrates the present invention in conjunction with embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited do not limit the present invention. In addition, in the preparation processes of the following embodiments, if there is no special description, they are all conventional means in the prior art, so they will not be described in detail; the raw materials used in the present invention are all commercially available products and can be purchased in the market; among them, iron phosphates with different titanium contents are all purchased from Tongling Nayuan Material Technology Co., Ltd.

[0012] Example 1 A preparation method of a high-compaction and high-capacity lithium iron phosphate material includes the following steps: 1. Weigh 100 g of titanium-containing iron phosphate (titanium content 8500 ppm), 100 g of titanium-free iron phosphate, 18 g of glucose, 49 g of lithium carbonate, and 0.5 g of titanium dioxide, add water and mix and stir for 2 h to obtain a mixed material; 2. Grind the mixed material and control the particle size to 0.5 μm; 3. Place the ground material in an oven at 110 °C for drying to obtain a precursor material; 4. Place the precursor material in a box furnace for the first sintering. The first sintering temperature is set at 750 °C, the heat preservation time is set at 7 h, and the heating rate is set at 1 °C per minute to obtain a sintered material. 5. Weigh 150 g of the sintered material, 20 g of iron phosphate with titanium (titanium content 3000 ppm), 9.8 g of lithium carbonate, 0.5 g of ammonium metavanadate, 10 g of starch, and 5 g of polyethylene glycol, and mix them using a ball mill. 6. Compact the uniformly mixed material, and set the pressure at 100 MPa. 7. Place the compacted material in a box furnace for the second sintering. The second sintering temperature is set at 800 °C, the heat preservation time is set at 5 h, and the heating rate is set at 1 °C per minute. Finally, use a jet mill to crush the sintered material to obtain the lithium iron phosphate material.

[0013] Example 2 Compared with Example 1, the difference in this example is: change the ratio of iron phosphate with titanium to iron phosphate without titanium in step 1, and the specific adjusted ratio is 4:6, that is, the amount of iron phosphate with titanium used is 80 g, and the amount of iron phosphate without titanium used is 120 g; other processes are the same as those in Example 1.

[0014] Example 3 Compared with Example 1, the difference in this example is: change the ratio of iron phosphate with titanium to iron phosphate without titanium in step 1, and the specific adjusted ratio is 6:4, that is, the amount of iron phosphate with titanium used is 120 g, and the amount of iron phosphate without titanium used is 80 g; other processes are the same as those in Example 1.

[0015] Example 4 Compared with Example 1, the difference in this example is: change the titanium content of the iron phosphate with titanium in step 1, and specifically adjust it to 6000 ppm; other processes are the same as those in Example 1.

[0016] Example 5 Compared with Example 1, the difference in this example is: change the titanium content of the iron phosphate with titanium in step 1, and specifically adjust it to 10000 ppm; other processes are the same as those in Example 1.

[0017] Example 6 Compared with Example 1, the difference in this example is: change the temperature of the first sintering in step 4, and set the first sintering temperature at 700 °C; other processes are the same as those in Example 1.

[0018] Example 7 Compared with Example 1, the difference in this example is: change the temperature of the first sintering in step 4, and set the first sintering temperature at 780 °C; other processes are the same as those in Example 1.

[0019] Example VIII Compared with Example I, the difference in this example lies in that: the titanium content in iron phosphate in Step 5 is adjusted to 5000 ppm; other processes are the same as those in Example I.

[0020] Example IX Compared with Example I, the difference in this example lies in that: the titanium content in iron phosphate in Step 5 is adjusted to 1000 ppm; other processes are the same as those in Example I.

[0021] Example X A preparation method of high tap density and high capacity lithium iron phosphate material, comprising the following steps: 1. Weigh 100 g of titanium-containing iron phosphate (titanium content 8500 ppm), 100 g of titanium-free iron phosphate, 18 g of glucose, 49 g of lithium carbonate and 0.5 g of titanium dioxide, add water and mix and stir for 2 h to obtain a mixed material; 2. Grind the mixed material and control the particle size to 0.5 μm; 3. Place the ground material in an oven at 110 °C for drying to obtain a precursor material; 4. Place the precursor material in a box furnace for the first sintering, set the first sintering temperature to 750 °C, the holding time to 7 h, and the heating rate to 1 °C per minute to obtain a sintered material; 5. Weigh 150 g of the sintered material, 30 g of iron phosphate (titanium content 3000 ppm), 14.7 g of lithium carbonate, 0.5 g of ammonium metavanadate, 15.3 g of starch and 7.7 g of polyethylene glycol, and mix using a ball mill; 6. Compact the uniformly mixed material, and set the pressure to 100 MPa; 7. Place the compacted material in a box furnace for the second sintering, set the second sintering temperature to 800 °C, the holding time to 5 h, and the heating rate to 1 °C per minute, and crush the sintered material using a jet mill to obtain a lithium iron phosphate material.

[0022] Example XI A preparation method of high tap density and high capacity lithium iron phosphate material, comprising the following steps: 1. Weigh 100 g of titanium-containing iron phosphate (titanium content 8500 ppm), 100 g of titanium-free iron phosphate, 18 g of glucose, 49 g of lithium carbonate and 0.5 g of titanium dioxide, add water and mix and stir for 2 h to obtain a mixed material; 2. Grind the mixed material and control the particle size to 0.5 μm; 3. Place the ground material in an oven at 110 °C for drying to obtain a precursor material; 4. Place the precursor material in a box furnace for the first sintering. The first sintering temperature is set at 750 °C, the heat preservation time is set at 7 h, and the heating rate is set at 1 °C per minute. 5. Weigh 150 g of the sintered material, 40 g of iron phosphate (titanium content 3000 ppm), 19.6 g of lithium carbonate, 0.5 g of ammonium metavanadate, 21.34 g of starch, and 10.66 g of polyethylene glycol, and mix them using a ball mill. 6. Compact the uniformly mixed material, and set the pressure at 100 MPa. 7. Place the compacted material in a box furnace for the second sintering. The second sintering temperature is set at 800 °C, the heat preservation time is set at 5 h, and the heating rate is set at 1 °C per minute. Use a jet mill to crush the sintered material to obtain the lithium iron phosphate material.

[0023] Comparative Example 1 The difference between this comparative example and Example 1 is that: the amount of titanium-containing iron phosphate in Step 1 is 200 g, and the amount of titanium-free iron phosphate is 0 g, and other processes are the same as those in Example 1.

[0024] Comparative Example 2 The difference between this comparative example and Example 1 is that: the amount of titanium-containing iron phosphate in Step 1 is 0 g, and the amount of titanium-free iron phosphate is 200 g, and other processes are the same as those in Example 1.

[0025] Comparative Example 3 The difference between this comparative example and Example 1 is that: the addition of titanium-containing iron phosphate in Step 5 is abandoned. The specific operation is as follows: the addition amount of titanium-containing iron phosphate is changed to 0 g, and lithium carbonate is changed to 0 g, and other aspects are the same as those in Example 1.

[0026] Comparative Example 4 The difference between this comparative example and Example 1 is that: the titanium-containing iron phosphate in Step 5 is replaced with titanium-free iron phosphate, and other aspects are the same as those in Example 1.

[0027] SEM Test Analysis: Figure 1 SEM images of the material prepared in Example 1 at different sizes. Among them, Figure a is the SEM image with a scale bar length of 15 μm; Figure b is the SEM image with a scale bar length of 8 μm. Figure 2 SEM images of the material prepared in Example 3 at different sizes. Among them, Figure a is the SEM image with a scale bar length of 15 μm; Figure b is the SEM image with a scale bar length of 8 μm. Figure 3 SEM images of the material prepared in Comparative Example 1 at different sizes. Among them, Figure a is the SEM image with a scale bar length of 15 μm; Figure b is the SEM image with a scale bar length of 8 μm. It can be seen from the above SEM images that there are obvious differences in the sizes of the particles prepared in Example 1 and Example 3, and a grading can be formed; in Comparative Example 1, the difference in particle sizes is small and the grading effect is not obvious.

[0028] Battery assembly test Using the lithium iron phosphate materials prepared in the above-mentioned examples and comparative examples as the positive electrode active materials respectively, button cells were assembled as follows: the battery model is CR2025, and the battery composition includes a positive electrode (the ratio of lithium iron phosphate, PVDF, and NMP is 8:1:1), an electrolyte (Saiwei lithium hexafluorophosphate electrolyte), a separator, a negative electrode (lithium sheet), and a button cell housing, etc.; charging at 50 μA - voltage ≥ 3.8 V, discharging at 50 μA - voltage ≤ 2.5 V.

[0029] Apparent density test The lithium iron phosphate materials prepared in the above-mentioned examples and comparative examples were subjected to powder apparent density tests; the test method is as follows. The test machine is Yuaneng PCD2000, the test pressure is 4 tons, and the pressure is 295.3 MPa.

[0030] The test results are shown in Table 1 below: Table 1

[0031] It can be seen from Table 1 that the materials prepared in the embodiments of the present invention and the batteries assembled from these materials can simultaneously have high apparent density and electrical performance; although the batteries in Comparative Example 1 and Comparative Example 3 have good electrical performance, their apparent density is low; although the apparent density in Comparative Example 2 is relatively high, its electrical performance is poor. In Comparative Example 4, due to the lack of further addition of titanium-containing lithium iron phosphate in step 5, the particle grading effect is not good, and the apparent density and electrical performance of the obtained materials are both poor.

[0032] Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A preparation method of a high-compaction and high-capacity lithium iron phosphate material, characterized in that: It includes the following steps: Mix the first titanium-containing iron phosphate, titanium-free iron phosphate, the first lithium source, the first carbon source, the first additive and water, and obtain a precursor material through grinding and drying; the titanium content of the first titanium-containing iron phosphate is 6000-10000 ppm; The precursor material is sintered for the first time to obtain a sintered material; Mix the sintered material, the second titanium-containing iron phosphate, the second lithium source, the second carbon source, and the second additive and then compact them, and obtain the target product through the second sintering and pulverization; the titanium content of the second titanium-containing iron phosphate is 1000-5000 ppm.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the first titanium-containing iron phosphate to the titanium-free iron phosphate is 1:(0.6-1.5).

3. The preparation method according to claim 1, wherein: The molar ratio of element iron to phosphorus in the precursor material is (0.95-1.05):1, and the molar ratio of lithium to iron is (1.01-1.06):

1.

4. The preparation method according to claim 1, characterized in that: The first lithium source and the second lithium source are each independently selected from at least one of lithium carbonate, lithium hydroxide, and lithium oxide.

5. The preparation method according to claim 1, characterized in that: The first carbon source and the second carbon source are each independently selected from at least one of sucrose, glucose, polyethylene glycol, phenolic resin, starch, and citric acid.

6. The preparation method according to claim 1, wherein: The first additive and the second additive are each independently selected from one of a titanium-containing compound, a cobalt-containing compound, a vanadium-containing compound, and an aluminum-containing compound.

7. The preparation method according to claim 1, characterized in that: The temperature of the first sintering is 600-800 °C; the pressure of the compaction is 50-150 MPa.

8. The preparation method according to claim 1, characterized in that: The temperature of the second sintering is 700-900 °C.

9. A high-compaction and high-capacity lithium iron phosphate material, characterized in that: It is prepared by using the preparation method described in any one of claims 1 to 8.

10. A lithium-ion battery, characterized in that: The lithium ion battery contains the high-compaction and high-capacity lithium iron phosphate material described in claim 9.

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