A spherical regular and high tap density lithium iron phosphate cathode material, a preparation method and application thereof

Abstract

This application relates to the field of battery technology, and provides a lithium iron phosphate cathode material with regular spherical shape and high tap density, its preparation method, and application. The method involves dissolving an iron source, a phosphorus source, and a lithium source in a solvent at a molar ratio of 1:1:1.02-1.05 to form a solution; then adding a carbon source and a structural reinforcing agent to the solution to form a mixture; the molar ratio of the iron source, carbon source, and structural reinforcing agent is 1:0.1-0.3:0.01-0.02; the obtained mixture is then subjected to coarse and fine grinding, stopping the fine grinding at D50 ≤ 0.3 μm, with a solid content of 35 wt%~45 wt%; the finely ground mixture is then subjected to two-fluid spraying; the liquid pressure is 0.5~0.75 MPa, and the gas source pressure is 0.5~0.8 MPa; the sprayed particles are sintered at 700~750℃, cooled, and sieved to obtain the lithium iron phosphate cathode material; through process innovation, breakthroughs are achieved in low-temperature rate performance and tap density.

Description

Technical Field

[0001] This application belongs to the field of battery technology, and in particular relates to a type of lithium iron phosphate cathode material with regular spherical shape and high tap density, its preparation method and application. Background Technology

[0002] With the development of the new energy industry, lithium iron phosphate (LFP) batteries, leveraging their advantages in safety, cost, and lifespan, coupled with continuous technological innovation, have become a core force driving the global electrification of automobiles and the energy storage revolution. However, due to the low ionic and electronic conductivity of LFP materials, their low-temperature performance and rate performance are poor, limiting the application of LFP batteries in various fields.

[0003] Spherical lithium iron phosphate is not a universal standard; its preparation technology varies from manufacturer to manufacturer. Currently, most existing methods employ co-precipitation, where a precursor is prepared by controlling reaction conditions such as pH, temperature, and stirring speed, followed by high-temperature sintering to obtain spherical lithium iron phosphate. However, the tap density of lithium iron phosphate prepared by this method is still relatively low, and the improvement in low-temperature performance is limited, making it difficult to meet the demands for high-performance lithium battery materials in fields such as start-stop power supplies and cryogenic energy storage. Summary of the Invention

[0004] The purpose of this application is to provide a spherical lithium iron phosphate cathode material with regular shape and high tap density, as well as its preparation method and application, aiming to solve the problem that the spherical lithium iron phosphate prepared by existing methods cannot meet the demand for high-performance lithium battery materials in fields such as start-stop power supplies and low-temperature energy storage.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: This application provides a method for preparing a lithium iron phosphate cathode material with regular spherical shape and high tap density, including the following steps: S1. Dissolve the iron source, phosphorus source, and lithium source in a solvent at a molar ratio of 1:1:1.02-1.05 to form a solution; then add a carbon source and a structural reinforcing agent to the solution to form a mixture; the molar ratio of the iron source, carbon source, and structural reinforcing agent is 1:0.1-0.3:0.01-0.02; S2. The mixture obtained in step S1 is coarsely ground and then finely ground until D50 ≤ 0.3 μm, with a solid content of 35 wt% to 45 wt%. S3. Perform two-fluid spraying on the mixture after fine grinding in step S2; the liquid pressure is 0.5~0.75MPa and the air source pressure is 0.5~0.8MPa.

[0006] S4. The small particles formed by spraying in step S3 are sintered at 700~750℃, cooled and sieved to obtain lithium iron phosphate cathode material.

[0007] As one possible design, the rotation speed of coarse grinding in step S2 is 250~350 rpm / min; the rotation speed of fine grinding is 580~640 rpm / min.

[0008] As one possible design, in step S3, the inlet temperature of the gas source is 200~250℃ and the outlet temperature is 70~90℃.

[0009] As one possible design, the carbon source in step S1 is glucose, sucrose, polyethylene glycol, starch, fructose, maltose, polyacrylic acid, and citric acid monohydrate.

[0010] As one possible design, the structural reinforcing agent is at least one of titanium dioxide, vanadium pentoxide, magnesium oxide, and vanadium trioxide.

[0011] As one possible design, in step S3, the air source pressure is 0.61 MPa and the liquid pressure is 0.52 MPa.

[0012] As one possible design, the sintering in step S4 is performed in a segmented manner, specifically as follows: Under a nitrogen atmosphere, the temperature is increased to 480-500℃ at a rate of 10-20℃ / h and held for 6-8 hours; then the temperature is increased to 700-750℃ at a rate of 10-20℃ / h and held for 9-10 hours.

[0013] The beneficial effects of this invention are as follows: 1. The carbon source used in this invention is a composite carbon source, that is, two or more carbon sources are used in combination. Carbon sources with small molecules (such as glucose) are easy to decompose at low temperatures to form an initial carbon layer, while carbon sources with large molecules (such as sucrose) have a high carbonization yield and can form a denser carbon layer. The two work together to form a continuous, uniform and highly conductive composite carbon network on the surface and inside of the particles.

[0014] 2. In this invention, a structural stabilizer is introduced and partially doped into the lithium iron phosphate lattice, which can stabilize the crystal structure and broaden the diffusion channels of lithium ions.

[0015] 3. Citric acid monohydrate acts as both a dispersant and a reducing agent. Its decomposition during sintering helps to form a porous structure inside the spheres, alleviates volumetric strain during charging and discharging, and jointly improves the long-cycle stability of the material.

[0016] 4. The lithium iron phosphate prepared by this invention not only inherits the core advantages of high safety, long life and low cost of the lithium iron phosphate system, but also achieves breakthroughs in indicators such as low temperature rate performance and tap density through process innovation. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 Here is an electron microscope image of the lithium iron phosphate cathode material prepared in Example 1; Figure 2 This is an electron microscope image of the lithium iron phosphate cathode material prepared in Comparative Example 1. Detailed Implementation

[0019] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0021] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0022] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0023] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0024] Example 1 This embodiment discloses a method for preparing a lithium iron phosphate cathode material, including the following steps: Step S1: Dissolve 1000 kg of ferric phosphate and 250.5 kg of lithium carbonate in pure water to form an aqueous solution. Add 57 kg of glucose, 50 kg of sucrose and 3.5 kg of titanium dioxide to the aqueous solution and mix them in a self-circulating tank for 30 minutes using a homogenizing pump to obtain a mixture. Step S2: Grind the mixture in a coarse mill for 2 hours at a speed of 300 rpm / min; grind it in a fine mill for 6 hours at a speed of 620 rpm / min, and stop grinding when the fine grinding is controlled to D50≤0.3um; Step S3: The mixture obtained from fine grinding is subjected to two-fluid spraying with a liquid pressure of 0.52 MPa, an air source pressure of 0.61 MPa, a slurry solid content of 40%, an inlet air temperature of 220℃, and an outlet air temperature of 85℃ to obtain a precursor material with D50: 13 μm and D90: 22 μm. Step S4: The precursor material is heated to 480℃ at a rate of 20℃ / h and held for 8 hours under a nitrogen atmosphere to allow glucose to fully decompose and initially carbonize, initiating the initial formation of crystal nuclei. Then, the temperature is increased to 750℃ at a rate of 20℃ / h and held for 9.5 hours to complete the crystal growth of lithium iron phosphate. During this process, a series of chemical reactions occur in the material, gradually forming spherical precursor particles. By precisely controlling the heat treatment temperature and holding time, the particle size and morphology of the precursor particles can be controlled to ensure the acquisition of materials with regular spherical shapes and uniform particle size distribution. Step S5: Cool the sintered material, then sieve it through an ultrasonic vibrating screen with a mesh size of 150, and then remove the magnetic material through an electromagnetizing device to obtain the final lithium iron phosphate cathode material.

[0025] The SEM image of the lithium iron phosphate cathode material prepared by the above-described preparation method in this embodiment is shown below. Figure 1 As shown, by Figure 1 It can be seen that lithium iron phosphate spheres have a rounded shape and are well formed.

[0026] Example 2 This embodiment discloses a method for preparing a lithium iron phosphate cathode material, including the following steps: Step S1: Dissolve 1000 kg of ferric phosphate and 250.5 kg of lithium carbonate in pure water to form an aqueous solution. Add a mixture of 57 kg of glucose, 50 kg of sucrose and maltose and a mixture of 3.5 kg of titanium dioxide and magnesium oxide to the aqueous solution. Mix the mixture in a tank by self-circulation using a homogenizing pump for 30 minutes to obtain a mixture. Step S2: Grind the mixture in a coarse mill for 3 hours at a speed of 250 rpm / min; grind it in a fine mill for 4 hours at a speed of 640 rpm / min, and stop grinding after controlling the fine grinding to D50≤0.3um; Step S3: The mixture obtained from fine grinding is subjected to two-fluid spraying with a liquid pressure of 0.64 MPa, an air source pressure of 0.8 MPa, a slurry solid content of 38 wt%, an inlet air temperature of 250℃, and an outlet air temperature of 70℃ to obtain a precursor material with D50: 12 μm and D90: 21 μm. Step S4: The precursor material is heated to 500℃ at a rate of 15℃ / h under a nitrogen atmosphere and held for 6h to allow glucose to fully decompose and initially carbonize, initiating the initial formation of crystal nuclei; then the temperature is increased to 700℃ at a rate of 15℃ / h and held for 10h to complete the crystal growth of lithium iron phosphate. During this process, a series of chemical reactions occur in the material, gradually forming spherical precursor particles. Step S5: Cool the sintered material, then sieve it through an ultrasonic vibrating screen with a mesh size of 150, and then remove the magnetic material through an electromagnetizing device to obtain the final lithium iron phosphate cathode material.

[0027] Example 3 This embodiment discloses a method for preparing a lithium iron phosphate cathode material, including the following steps: Step S1: Dissolve 1000 kg of ferric phosphate and 250.5 kg of lithium carbonate in pure water to form an aqueous solution. Add a mixture of 57 kg of glucose, 50 kg of sucrose and citric acid monohydrate, and a mixture of 3.5 kg of titanium dioxide and vanadium trioxide to the aqueous solution. Mix the mixture in a tank by self-circulation using a homogenizing pump for 30 minutes to obtain a mixture. Step S2: Grind the mixture in a coarse mill for 2.5 hours at a speed of 250 rpm / min; grind it in a fine mill for 6 hours at a speed of 580 rpm / min, and stop grinding when the fine milling is controlled to D50≤0.3um; Step S3: The mixture obtained from fine grinding is subjected to two-fluid spraying with a liquid pressure of 0.75 MPa, an air source pressure of 0.52 MPa, a slurry solid content of 43 wt%, an inlet air temperature of 220°C, and an outlet air temperature of 85°C to obtain a precursor material with D50: 13 μm and D90: 23 μm. Step S4: The precursor material is heated to 490℃ at a rate of 10℃ / h under a nitrogen atmosphere and held for 6h to allow glucose to fully decompose and initially carbonize, initiating the initial formation of crystal nuclei; then the temperature is increased to 730℃ at a rate of 10℃ / h and held for 10h to complete the crystal growth of lithium iron phosphate. During this process, a series of chemical reactions occur in the material, gradually forming spherical precursor particles. Step S5: Cool the sintered material, then sieve it through an ultrasonic vibrating screen with a mesh size of 150, and then remove the magnetic material through an electromagnetizing device to obtain the final lithium iron phosphate cathode material.

[0028] Comparative Example 1 This comparative example discloses a method for preparing lithium iron phosphate materials, including the following steps: Step S1: Dissolve 1000 kg of ferric phosphate and 247.5 kg of lithium carbonate in pure water to form an aqueous solution. Add 88 kg of glucose and 30 kg of polyethylene glycol to the aqueous solution and mix them in a self-circulating tank using a homogenizing pump for 30 minutes to obtain a mixture. Step S2: Grind the mixture in a coarse mill for 2 hours at a speed of 300 rpm / min; grind it in a fine mill for 6 hours at a speed of 620 rpm / min, and stop grinding when the fine grinding is controlled to D50≤0.43um; Step S3: The mixture obtained by fine grinding is centrifuged and sprayed with an atomizer frequency of 50Hz, a slurry solid content of 40wt%, an inlet air temperature of 240℃, and an outlet air temperature of 88℃ to obtain a precursor material with D50: 21um and D90: 45um. Step S4: The precursor material is heated to 800℃ and held at that temperature for 9.5h at a rate of 20℃ / h under a nitrogen atmosphere; Step S5: Cool the sintered material, then sieve it through an ultrasonic vibrating screen with a mesh size of 150, and then remove the magnetic material through an electromagnetizing device to obtain the final lithium iron phosphate material.

[0029] The SEM image of the lithium iron phosphate material prepared in this comparative example is shown below. Figure 2 As shown.

[0030] The physical and chemical properties of the lithium iron phosphate materials prepared in Example 1 and Comparative Example 1 were tested, and the results are shown in Table 1.

[0031] Table 1. Physical and electrochemical properties of the powders from Example 1 and the comparative example.

[0032] As shown in Table 1, the spherical lithium iron phosphate material synthesized in Example 1 has significantly improved and made breakthroughs in tap density and electrical performance compared with the lithium iron phosphate material synthesized in Comparative Example 1, thus meeting the demand for high-performance lithium battery materials in fields such as start-stop power supplies and cryogenic energy storage.

[0033] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a lithium iron phosphate cathode material with regular spherical shape and high tap density, characterized in that, The preparation method includes the following steps: S1. Dissolve the iron source, phosphorus source, and lithium source in a solvent at a molar ratio of 1:1:1.02-1.05 to form a solution; then add a carbon source and a structural reinforcing agent to the solution to form a mixture; the molar ratio of the iron source, carbon source, and structural reinforcing agent is 1:0.1-0.3:0.01-0.02; S2. The mixture obtained in step S1 is coarsely ground and then finely ground until D50 ≤ 0.3 μm, with a solid content of 35 wt% to 45 wt%. S3. The mixture after fine grinding in step S2 is subjected to two-fluid spraying; the liquid pressure is 0.5~0.75MPa, and the air source pressure is 0.5~0.8MPa; S4. The small particles formed by spraying in step S3 are sintered at 700~750℃, cooled and sieved to obtain lithium iron phosphate cathode material.

2. According to the preparation method of lithium iron phosphate cathode material with regular spherical shape and high tap density as described in claim 1, the rotation speed of coarse grinding in step S2 is 250~350 rpm / min; the rotation speed of fine grinding is 580~640 rpm / min.

3. According to the preparation method of lithium iron phosphate cathode material with spherical regularity and high tap density as described in claim 1, the inlet temperature of the gas source in step S3 is 200~250℃ and the outlet temperature is 70~90℃.

4. According to the preparation method of lithium iron phosphate cathode material with regular spherical shape and high tap density as described in claim 1, the carbon source in step S1 is at least two of glucose, sucrose, polyethylene glycol, starch, fructose, maltose, polyacrylic acid and citric acid monohydrate.

5. The method for preparing lithium iron phosphate cathode material with regular spherical shape and high tap density according to claim 1, wherein the structural reinforcing agent is at least one of titanium dioxide, vanadium pentoxide, magnesium oxide, and vanadium trioxide.

6. According to the preparation method of lithium iron phosphate cathode material with regular spherical shape and high tap density as described in claim 1, the gas source pressure in step S3 is 0.61 MPa and the liquid pressure is 0.52 MPa.

7. According to the preparation method of lithium iron phosphate cathode material with spherical regularity and high tap density as described in claim 1, the sintering in step S4 is carried out in a segmented manner, specifically as follows: Under a nitrogen atmosphere, the temperature is increased to 480-500℃ at a rate of 10-20℃ / h and held for 6-8 hours; then the temperature is increased to 700-750℃ at a rate of 10-20℃ / h and held for 9-10 hours.

8. A lithium iron phosphate cathode material prepared by the preparation method according to any one of claims 1-7, characterized in that, The lithium iron phosphate cathode material has a 0.1C charge strength > 158 mAh / g and a compaction density > 2.10 g / cm³. 3 .

9. A lithium battery, characterized in that, The positive electrode of the lithium battery is mainly made of the lithium iron phosphate positive electrode material as described in claim 8.

10. A battery with a charging rate of 5C / 10C, ​​characterized in that, The positive electrode of the battery is mainly made of the lithium iron phosphate positive electrode material as described in claim 8.

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