A high-density, high-capacity lithium iron phosphate material and its preparation method and application

Abstract

The present invention discloses a high-density, high-capacity lithium iron phosphate material and its preparation method and application, which belongs to the field of electrochemistry; the preparation method of the material includes the following steps: mixing a first titanium-containing iron phosphate, a 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; the precursor material is subjected to a first sintering to obtain a sintered material; the sintered material, a second titanium-containing iron phosphate, a second lithium source, a second carbon source and a second additive are mixed and compacted, and a target product is obtained after a second sintering and crushing. The present invention uses iron phosphates with different titanium contents and regulates the sintering steps to increase the compaction density of the lithium iron phosphate material while maintaining the material with 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. The prepared lithium iron phosphate material has both excellent compaction density and electrochemical capacity.

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 have retreated to the high-end market and their development momentum has slowed down. Lithium iron phosphate batteries are a type of lithium-ion battery that uses lithium iron phosphate as the positive electrode material. Lithium iron phosphate materials have a stable olivine structure and can withstand high temperatures of up to 350-500°C. The risk of thermal runaway is significantly lower than that of ternary lithium batteries. They can remain stable even in extreme conditions such as overcharging, puncture or collision. However, with the increasing requirements for driving range, the demand for lithium iron phosphate with a high compaction density is increasing. In the existing technology, 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] Existing methods for increasing compaction density through sanding and particle size grading have drawbacks. Large particles require higher sintering temperatures or longer sintering times, leading to uncontrolled fusion and growth between smaller particles. This results in a low proportion of small particles, preventing the grading effect and compaction density from being maximized. Existing methods for increasing the compaction density of lithium iron phosphate materials often result in a decrease in material capacity, making it impossible to maintain good electrical performance while increasing 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 its preparation method and application, which can improve the compaction density of the lithium iron phosphate material while maintaining the material with 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:

[0006] A method for preparing a high-density, high-capacity lithium iron phosphate material comprises the following steps:

[0007] A first titanium-containing ferrophosphate, a non-titanium-containing ferrophosphate, a first lithium source, a first carbon source, a first additive and water are mixed to obtain a mixed material. 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 ferrophosphate is 6000-10000 ppm. 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 a magnetic risk will occur, affecting the battery safety. The titanium content of the non-titanium-containing ferrophosphate is controlled to be less than 50 ppm.

[0008] The precursor material is subjected to a first sintering to obtain a sintered material; preferably, the temperature of the first sintering is 600-800°C;

[0009] The sintered material, the second titanium-containing ferric phosphate, the second lithium source, the second carbon source and the second additive are mixed and compacted, and the target product is obtained after a second sintering and crushing; preferably, the ratio of the sintered material and the second titanium-containing ferric phosphate is 7.5: (0.8-1.2); the titanium content of the second titanium-containing ferric phosphate is lower than the titanium content of the first titanium-containing ferric phosphate, the titanium content of the second titanium-containing ferric phosphate is 1000-5000ppm, and the particle size is controlled at 0.8-1.6μm; the compaction pressure is 50-150MPa; the temperature of the second sintering is 700-900℃, and the sintering temperature and time are related. The higher the temperature, the shorter the time required; the lower the temperature, the longer the time required.

[0010] As a preferred technical solution, the mass ratio of the first titanium-containing ferric phosphate to the non-titanium-containing ferric phosphate is 1:(0.6-1.5); the molar ratio of elemental 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. By limiting the usage ratios of the various substances, the materials can be better formed into phases. When the ratios exceed the specified ranges, other substances that affect product performance may be formed.

[0011] As a preferred technical solution, the first and second lithium sources are independently selected from at least one of lithium carbonate, lithium hydroxide, and lithium oxide; the first and second carbon sources are independently selected from at least one of sucrose, glucose, polyethylene glycol, phenolic resin, starch, and citric acid; and the first and second additives are independently selected from one of a titanium-containing compound, a cobalt-containing compound, a vanadium-containing compound, and an aluminum-containing compound. The carbon source increases the conductivity of the material, while the additive further enhances the product's capacity.

[0012] The present invention also provides a high-density, high-capacity lithium iron phosphate material prepared using the above-described preparation method. The lithium iron phosphate material has a high compaction density and high electrical performance, and has good application prospects in lithium-ion batteries.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The present invention first mixes a first titanium-containing iron phosphate and a non-titanium-containing iron phosphate and other raw materials and then performs a first sintering. Since the titanium element can inhibit particle growth during the sintering process, the titanium-containing iron phosphate grows into small lithium iron phosphate particles, and the non-titanium iron phosphate grows into large lithium iron phosphate particles. After the first sintering, the lithium iron phosphate initially forms a large and small particle gradation. Then, based on the lithium iron phosphate material obtained by the first sintering, a certain amount of the second titanium-containing iron phosphate and other raw materials are added for a 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 based on the particle inhibition effect, different particles grow into medium-sized particles, forming a three-level gradation. Since the material has formed a material with higher gradation and compaction after the first sintering, the second sintering is easier to compact and maintain capacity on the basis of the first sintering, thereby further improving the compaction density of the material, while avoiding the problem in the prior art that increasing the compaction density often leads to a decrease in material capacity. The lithium iron phosphate material prepared using the method of the present invention has both excellent compaction density and electrochemical capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a SEM image of the lithium iron phosphate material prepared in Example 1;

[0016] Figure 2 This is a SEM image of the lithium iron phosphate material prepared in Example 3;

[0017] Figure 3 This is the SEM image of the lithium iron phosphate material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0018] The present invention is further described below with reference to the examples so that those skilled in the art can better understand and implement the present invention, but the examples are not intended to limit the present invention. In addition, unless otherwise specified, the preparation processes in the following examples are conventional means in the prior art and are therefore not described in detail. The raw materials used in the present invention are all commercially available products and can be purchased commercially. Among them, iron phosphates with different titanium contents were purchased from Tongling Nayuan Materials Technology Co., Ltd.

[0019] Example 1

[0020] A method for preparing a high-density, high-capacity lithium iron phosphate material comprises the following steps:

[0021] 1. Weigh 100 g of titanium-containing ferric phosphate (titanium content 8500 ppm), 100 g of non-titanium ferric 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;

[0022] 2. Grind the mixed material and control the particle size to 0.5μm;

[0023] 3. Place the ground material in an oven at 110°C to dry to obtain a precursor material;

[0024] 4. Place the precursor material in a box furnace for the first sintering. The first sintering temperature is set to 750°C, the holding time is set to 7 hours, and the heating rate is set to 1 minute per degree Celsius to obtain a sintered material.

[0025] 5. Weigh 150 g of sintering material, 20 g of titanium-containing iron phosphate (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;

[0026] 6. Compact the mixed materials and set the pressure to 100MPa;

[0027] 7. Place the compacted material in a box furnace for a second sintering. The second sintering temperature is set to 800°C, the holding time is set to 5 hours, and the heating rate is set to one minute per degree Celsius. Finally, use a jet mill to crush the sintered material to obtain lithium iron phosphate material.

[0028] Example 2

[0029] Compared with Example 1, the difference of this embodiment is that: the ratio of titanium-containing iron phosphate to non-titanium iron phosphate in step 1 is changed, and the specific adjustment ratio is 4:6, that is, the amount of titanium-containing iron phosphate is 80g, and the amount of non-titanium iron phosphate is 120g; the other processes are the same as Example 1.

[0030] Example 3

[0031] Compared with Example 1, the difference of this embodiment is that: the ratio of titanium-containing iron phosphate to non-titanium iron phosphate in step 1 is changed, and the specific adjustment ratio is 6:4, that is, the amount of titanium-containing iron phosphate is 120g, and the amount of non-titanium iron phosphate is 80g; the other processes are the same as Example 1.

[0032] Example 4

[0033] Compared with Example 1, the difference of this embodiment is that the titanium content of the titanium-containing ferrophosphate in step 1 is changed to 6000 ppm; the other processes are the same as those of Example 1.

[0034] Example 5

[0035] Compared with Example 1, the difference of this embodiment is that the titanium content of the titanium-containing ferrophosphate in step 1 is changed, specifically adjusted to 10,000 ppm; the other processes are the same as those of Example 1.

[0036] Example 6

[0037] Compared with the first embodiment, the present embodiment is different in that the temperature of the first sintering in step 4 is changed to 700° C.; the other processes are the same as those in the first embodiment.

[0038] Example 7

[0039] Compared with the first embodiment, the present embodiment is different in that the temperature of the first sintering in step 4 is changed to 780° C.; the other processes are the same as those in the first embodiment.

[0040] Example 8

[0041] Compared with Example 1, the difference of this embodiment is that the titanium content in the ferric phosphate in step 5 is adjusted to 5000 ppm; the other processes are the same as those in Example 1.

[0042] Embodiment 9

[0043] Compared with Example 1, the difference of this embodiment is that the titanium content in the ferric phosphate in step 5 is adjusted to 1000 ppm; the other processes are the same as those in Example 1.

[0044] Example 10

[0045] A method for preparing a high-density, high-capacity lithium iron phosphate material comprises the following steps:

[0046] 1. Weigh 100 g of titanium-containing ferric phosphate (titanium content 8500 ppm), 100 g of non-titanium ferric 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;

[0047] 2. Grind the mixed material and control the particle size to 0.5μm;

[0048] 3. Place the ground material in an oven at 110°C to dry to obtain a precursor material;

[0049] 4. Place the precursor material in a box furnace for the first sintering. The first sintering temperature is set to 750°C, the holding time is set to 7 hours, and the heating rate is set to 1 minute per degree Celsius to obtain a sintered material.

[0050] 5. Weigh 150 g of sintering 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 them using a ball mill;

[0051] 6. Compact the mixed material and set the pressure to 100MPa;

[0052] 7. Place the compacted material in a box furnace for a second sintering. The second sintering temperature is set to 800°C, the holding time is set to 5 hours, the heating rate is set to one minute per degree Celsius, and the sintered material is crushed using a jet mill to obtain lithium iron phosphate material.

[0053] Example 11

[0054] A method for preparing a high-density, high-capacity lithium iron phosphate material comprises the following steps:

[0055] 1. Weigh 100 g of titanium-containing ferric phosphate (titanium content 8500 ppm), 100 g of non-titanium ferric 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;

[0056] 2. Grind the mixed material and control the particle size to 0.5μm;

[0057] 3. Place the ground material in an oven at 110°C to dry to obtain a precursor material;

[0058] 4. Place the precursor material in a box furnace for the first sintering. The first sintering temperature is set to 750°C, the holding time is set to 7h, and the heating rate is set to 1 minute per degree Celsius;

[0059] 5. Weigh 150 g of sintering 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;

[0060] 6. Compact the mixed material and set the pressure to 100MPa;

[0061] 7. Place the compacted material in a box furnace for a second sintering. The second sintering temperature is set to 800°C, the holding time is set to 5 hours, the heating rate is set to one minute per degree Celsius, and the sintered material is crushed using a jet mill to obtain lithium iron phosphate material.

[0062] Comparative Example 1

[0063] The difference between this comparative example and Example 1 is that the amount of titanium-containing ferric phosphate in step 1 is 200 g, and the amount of non-titanium-containing ferric phosphate is 0 g, and the other processes are consistent with Example 1.

[0064] Comparative Example 2

[0065] The difference between this comparative example and Example 1 is that the amount of titanium-containing ferric phosphate in step 1 is 0 g, and the amount of non-titanium-containing ferric phosphate is 200 g, and the other processes are consistent with Example 1.

[0066] Comparative Example 3

[0067] The difference between this comparative example and Example 1 is that the addition of titanium-containing ferric phosphate in step 5 is abandoned. The specific operation is as follows: the addition amount of titanium-containing ferric phosphate is changed to 0 g, the lithium carbonate is changed to 0 g, and the rest is consistent with Example 1.

[0068] Comparative Example 4

[0069] The difference between this comparative example and Example 1 is that the titanium-containing ferrophosphate in step 5 is replaced by the non-titanium-containing ferrophosphate, and the rest is consistent with Example 1.

[0070] SEM test analysis:

[0071] Figure 1 These are SEM images of the material prepared in Example 1 at different sizes, wherein Figure a is a SEM image with a scale length of 15 μm; Figure b is a SEM image with a scale length of 8 μm;

[0072] Figure 2 These are SEM images of the material prepared in Example 3 at different sizes, wherein Figure a is a SEM image with a scale length of 15 μm; Figure b is a SEM image with a scale length of 8 μm;

[0073] Figure 3 These are SEM images of the material prepared in Comparative Example 1 at different sizes, wherein Figure a is a SEM image with a scale length of 15 μm; Figure b is a SEM image with a scale length of 8 μm;

[0074] From the above SEM images, it can be seen that the size of the particles of the materials prepared in Example 1 and Example 3 is significantly different, and gradation can be formed; in Comparative Example 1, the size difference of the particles is small and the gradation effect is not obvious.

[0075] Battery assembly test

[0076] Button cells were assembled using the lithium iron phosphate materials prepared in the above embodiments and comparative examples as the positive electrode active material. The method is as follows: the battery model is CR2025, and the battery composition includes a positive electrode (lithium iron phosphate, PVDF, NMP in a ratio of 8:1:1), an electrolyte (Sinovin lithium hexafluorophosphate electrolyte), a separator, a negative electrode (lithium sheet) and a button cell casing; charging 50uA - voltage ≥3.8V, discharging 50uA - voltage ≤2.5V.

[0077] Compaction density test

[0078] The lithium iron phosphate materials prepared in the above embodiments and comparative examples were subjected to a powder compaction density test; the test method was as follows, the test machine was Yuanneng PCD2000, the test pressure was 4 tons, and the pressure was 295.3 MPa.

[0079] The test results are shown in Table 1 below:

[0080] Table 1

[0081]

[0082] Table 1 shows that the materials prepared in each embodiment of the present invention and the batteries assembled from the materials can simultaneously achieve high compaction density and electrical performance. The batteries in Comparative Examples 1 and 3 have good electrical performance but low compaction density. Comparative Example 2 has a high compaction density but poor electrical performance. In Comparative Example 4, due to the lack of further addition of titanium-containing ferric phosphate in Step 5, the particle grading effect is poor, resulting in poor compaction density and electrical performance of the resulting material.

[0083] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

Claims

1. A method for preparing a high-density, high-capacity lithium iron phosphate material, characterized by: The following steps are involved: A first titanium-containing ferric phosphate, a non-titanium-containing ferric phosphate, a first lithium source, a first carbon source, a first additive, and water are mixed, and the mixture is ground and dried to obtain a precursor material; the titanium content of the first titanium-containing ferric phosphate is 6000-10000 ppm; and the mass ratio of the first titanium-containing ferric phosphate to the non-titanium-containing ferric phosphate is 1:(0.6-1.5); The precursor material is sintered for the first time to obtain a sintered material; The sintered material, the second titanium-containing ferric phosphate, the second lithium source, the second carbon source, and the second additive are mixed and compacted, and the target product is obtained after a second sintering and crushing; the titanium content of the second titanium-containing ferric phosphate is 1000-5000ppm; the ratio of the sintered material to the second titanium-containing ferric phosphate is 7.5: (0.8-1.2).

2. The preparation method according to claim 1, wherein: The molar ratio of elemental 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.

3. The preparation method according to claim 1, wherein: The first lithium source and the second lithium source are independently selected from at least one of lithium carbonate, lithium hydroxide, and lithium oxide.

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

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

6. The preparation method according to claim 1, wherein: The temperature of the first sintering is 600-800° C.; the compacting pressure is 50-150 MPa.

7. The preparation method according to claim 1, wherein: The temperature of the second sintering is 700-900°C.

8. A high-density, high-capacity lithium iron phosphate material, characterized by: The invention relates to a novel crystalline silicon nitrate-containing slurry prepared by the preparation method according to any one of claims 1 to 7.

9. A lithium-ion battery, characterized in that: The lithium-ion battery contains the high-density, high-capacity lithium iron phosphate material as claimed in claim 8.

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