Lithium iron phosphate and preparation method thereof

Abstract

The invention discloses lithium iron phosphate and a preparation method thereof, the lithium iron phosphate comprises a lithium iron phosphate positive electrode material composed of nanoscale lithium iron phosphate particles and a composite coating coated on the surfaces of the nanoscale lithium iron phosphate particles, the particle size of the nanoscale lithium iron phosphate particles is 50-200nm, the composite coating comprises a carbon layer and a metal oxide layer, the thickness of the carbon layer is 5-20nm, and the thickness of the metal oxide layer is 5-20nm. The thickness of the metal oxide layer is 3-10nm, and the metal oxide is one or a mixture of two of aluminum oxide and titanium oxide. According to the high-capacity lithium iron phosphate / graphite battery prepared from the lithium iron phosphate positive electrode material, the capacity retention ratio is improved by 5-13% or above compared with that of an unimproved battery after 1500 times of circulation at the high temperature of 45 DEG C, and the service life of the battery in a high-temperature environment is effectively prolonged.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a lithium iron phosphate and its preparation method. Background Technology

[0002] In practical applications of lithium iron phosphate / graphite batteries, high temperatures severely impact battery performance and lifespan. Extensive research data shows that when the ambient temperature rises to 45°C, the battery capacity degradation pattern undergoes a significant shift, evolving from a gradual linear degradation at room temperature to a dramatic logarithmic degradation. Related experimental data shows that at 45°C, after 1000-1500 cycles, the remaining battery capacity may only be around 70%-80%, while at room temperature, the remaining capacity typically remains above 85% after the same number of cycles—a clear difference. Furthermore, high-temperature conditions drastically reduce the number of battery cycles, significantly shortening battery lifespan. A deeper examination of the underlying reasons reveals several key aspects. From the perspective of the cathode material, LiFePO4 particles fracture at high temperatures, releasing Fe elements which then deposit on the anode surface. This process intensifies the growth of the SEI film, thereby blocking the graphite structure and interfering with the normal insertion and extraction of lithium ions. Meanwhile, the SEI film on the anode thickens excessively at high temperatures, causing a sharp decrease in porosity and severely hindering the transport channels for lithium ions, resulting in poor high-temperature cycle life for lithium iron phosphate batteries. Existing lithium iron phosphate cathode materials are inadequate for handling high-temperature challenges, failing to meet the stringent requirements of long lifespan and high stability in high-temperature environments. Therefore, developing a lithium iron phosphate cathode material that can effectively suppress high-temperature degradation is urgently needed. This is not only crucial for improving battery performance but also has immeasurable practical significance for promoting the application and development of new energy vehicles, energy storage, and other industries in high-temperature regions. Summary of the Invention

[0003] Based on the technical problems existing in the background technology, this invention proposes a lithium iron phosphate battery and its preparation method to solve the problem of rapid performance degradation of existing lithium iron phosphate / graphite batteries under high temperature environment.

[0004] The present invention proposes a lithium iron phosphate cathode material comprising nano-sized lithium iron phosphate particles and a composite coating covering their surface. The nano-sized lithium iron phosphate particles have a particle size between 50-200 nm. The composite coating comprises a carbon layer and a metal oxide layer. The carbon layer has a thickness of 5-20 nm, and the metal oxide layer has a thickness of 3-10 nm. The metal oxide is one or a mixture of two of aluminum oxide and titanium oxide.

[0005] This invention also proposes a method for preparing lithium iron phosphate, comprising the following steps: S1: Preparation of nano-lithium iron phosphate particles: Iron source (such as ferrous sulfate), lithium source (such as lithium carbonate), and phosphorus source (such as ammonium dihydrogen phosphate) are mixed in stoichiometric ratio, and appropriate amounts of dispersant and solvent are added. After ball milling, a precursor slurry is obtained. The precursor slurry is spray-dried to obtain precursor powder. The precursor powder is heated to 300-400℃ at a heating rate of 3-5℃ / min under an inert atmosphere and held for 1-2 hours. Then, it is heated to 700-800℃ at a heating rate of 5-8℃ / min and held for 3-5 hours. After cooling, nano-lithium iron phosphate particles are obtained. S2: Carbon coating: Disperse the nano-lithium iron phosphate particles in a solution containing a carbon source (such as glucose or sucrose), sonicate for 30-60 min to make the carbon source uniformly adsorbed on the particle surface, and then dry at 100-120℃ to obtain lithium iron phosphate particles with carbon source adsorbed on the surface. Then, heat them to 600-700℃ at a heating rate of 5-10℃ / min under an inert atmosphere and keep them at that temperature for 2-3 h to make the carbon source pyrolyze and form a carbon layer coating the surface of the lithium iron phosphate particles. S3: Coated Metal Oxide Layer: Lithium iron phosphate particles with a carbon layer on their surface are dispersed in a solution containing metal salts (such as aluminum nitrate or tetrabutyl titanate). A metal oxide sol is formed on the particle surface using the sol-gel method. The sol is dried at 80-100℃ and then calcined at 400-500℃ for 1-2 hours to transform the metal oxide sol into a metal oxide layer, thus obtaining the final lithium iron phosphate cathode material.

[0006] The beneficial effects of the present invention are: 1. Reduce particle breakage: Compared with large-sized particles, nano-sized lithium iron phosphate particles experience less stress due to volume changes during high-temperature cycling, which can effectively reduce particle breakage and lower the risk of Fe leaching.

[0007] 2. Suppressing Fe leaching: The carbon layer and metal oxide layer in the composite coating effectively block the leaching of Fe, and the carbon layer improves the conductivity of the material, further reducing battery polarization caused by increased resistance. The metal oxide layer also enhances the chemical stability of the material and suppresses side reactions at high temperatures.

[0008] 3. Improved battery performance: The high-capacity lithium iron phosphate / graphite battery prepared using the lithium iron phosphate cathode material of this invention has a capacity retention rate that is 5-13% higher than that of the unimproved battery after 1500 cycles at 45°C, effectively extending the battery's service life in high-temperature environments. Detailed Implementation

[0009] The present invention will be further explained below with reference to specific embodiments. Example

[0010] This embodiment proposes a lithium iron phosphate cathode material comprising nano-sized lithium iron phosphate particles and a composite coating covering their surface. The nano-sized lithium iron phosphate particles have a particle size between 50-200 nm. The composite coating comprises a carbon layer and a metal oxide layer. The carbon layer has a thickness of 5-20 nm, and the metal oxide layer has a thickness of 3-10 nm. The metal oxide is one or a mixture of two of aluminum oxide and titanium oxide.

[0011] This invention also proposes a method for preparing lithium iron phosphate, comprising the following steps: S1: Preparation of nano-lithium iron phosphate particles: Iron source (such as ferrous sulfate), lithium source (such as lithium carbonate), and phosphorus source (such as ammonium dihydrogen phosphate) are mixed in stoichiometric ratio, and appropriate amounts of dispersant and solvent are added. After ball milling, a precursor slurry is obtained. The precursor slurry is spray-dried to obtain precursor powder. The precursor powder is heated to 300-400℃ at a heating rate of 3-5℃ / min under an inert atmosphere and held for 1-2 hours. Then, it is heated to 700-800℃ at a heating rate of 5-8℃ / min and held for 3-5 hours. After cooling, nano-lithium iron phosphate particles are obtained. S2: Carbon coating: Disperse the nano-lithium iron phosphate particles in a solution containing a carbon source (such as glucose or sucrose), sonicate for 30-60 min to make the carbon source uniformly adsorbed on the particle surface, and then dry at 100-120℃ to obtain lithium iron phosphate particles with carbon source adsorbed on the surface. Then, heat them to 600-700℃ at a heating rate of 5-10℃ / min under an inert atmosphere and keep them at that temperature for 2-3 h to make the carbon source pyrolyze and form a carbon layer coating the surface of the lithium iron phosphate particles. S3: Coated Metal Oxide Layer: Lithium iron phosphate particles with a carbon layer on their surface are dispersed in a solution containing metal salts (such as aluminum nitrate or tetrabutyl titanate). A metal oxide sol is formed on the particle surface using the sol-gel method. The sol is dried at 80-100℃ and then calcined at 400-500℃ for 1-2 hours to transform the metal oxide sol into a metal oxide layer, thus obtaining the final lithium iron phosphate cathode material. Example 1

[0012] A method for preparing lithium iron phosphate includes the following steps: S1: Preparation of nano-lithium iron phosphate particles: 1 mol ferrous sulfate, 1 mol lithium carbonate, and 1 mol ammonium dihydrogen phosphate were added to 500 mL of deionized water containing 5 g polyvinylpyrrolidone dispersant, and ball-milled for 8 h to obtain a precursor slurry. The precursor slurry was spray-dried to obtain a precursor powder. The precursor powder was heated to 300 °C at a heating rate of 3 °C / min under an argon atmosphere, held for 1 h, then heated to 700 °C at a heating rate of 5 °C / min, held for 3 h, and cooled to obtain nano-lithium iron phosphate particles; S2: Carbon coating: The above-mentioned nano-lithium iron phosphate particles were dispersed in 200 mL of ethanol solution containing 5 g of glucose and ultrasonically treated for 30 min. After drying at 100 °C, the temperature was increased to 600 °C at a heating rate of 5 °C / min under an argon atmosphere and held for 2 h to form a carbon coating. S3: Coated metal oxide layer: Lithium iron phosphate particles with a carbon layer on the surface are dispersed in 200 mL of isopropanol solution containing 5 g of aluminum nitrate, dried at 80 °C using the sol-gel method, and then calcined at 400 °C for 1 h to form an aluminum oxide coating, thus obtaining the final lithium iron phosphate cathode material. Example 2

[0013] A method for preparing lithium iron phosphate includes the following steps: S1: Preparation of nano-lithium iron phosphate particles: 1 mol ferrous sulfate, 1 mol lithium carbonate, and 1 mol ammonium dihydrogen phosphate were added to 600 mL of deionized water containing 8 g sodium polyacrylate dispersant, and ball-milled for 10 h to obtain a precursor slurry. The precursor slurry was spray-dried to obtain a precursor powder. The precursor powder was heated to 350 °C at a heating rate of 4 °C / min under a nitrogen atmosphere, held at that temperature for 1.5 h, and then heated to 750 °C at a heating rate of 6 °C / min, held at that temperature for 4 h, and cooled to obtain nano-lithium iron phosphate particles; S2: Carbon coating: The above-mentioned nano-lithium iron phosphate particles were dispersed in 300 mL of ethanol solution containing 8 g of sucrose and ultrasonically treated for 45 min. After drying at 110 °C, the temperature was increased to 650 °C at a heating rate of 7 °C / min under a nitrogen atmosphere and held for 2.5 h to form a carbon coating. S3: Coated metal oxide layer: Lithium iron phosphate particles with a carbon layer on the surface are dispersed in 300 mL of anhydrous ethanol solution containing 8 g of tetrabutyl titanate, dried at 90 °C using the sol-gel method, and then calcined at 450 °C for 1.5 h to form a titanium oxide coating, thus obtaining the final lithium iron phosphate cathode material.

[0014] Comparative example: Using conventional commercial lithium iron phosphate cathode material that has not undergone nano-sizing and composite coating.

[0015] Performance testing: The positive electrode materials prepared in Examples 1 and 2, as well as the positive electrode materials of the comparative example, were assembled with graphite negative electrodes to form commercial lithium iron phosphate / graphite batteries with a capacity of 26650-4Ah. After 1500 cycles of 1C charge-discharge at 45℃, the capacity retention rate of the comparative battery was 78.3%. The capacity retention rate of the battery in Example 1 was 85.2%; The capacity retention rate of the battery in Example 2 was 90.1%.

[0016] The results show that the lithium iron phosphate cathode material prepared by this invention can significantly improve the cycle performance of the battery under high temperature conditions.

[0017] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A lithium iron phosphate cathode material comprising nano-sized lithium iron phosphate particles and a composite coating covering their surface, characterized in that, The nano-sized lithium iron phosphate particles have a particle size between 50-200 nm. The composite coating includes a carbon layer and a metal oxide layer. The carbon layer has a thickness of 5-20 nm, and the metal oxide layer has a thickness of 3-10 nm. The metal oxide is one or a mixture of aluminum oxide and titanium oxide.

2. A method for preparing lithium iron phosphate, characterized in that, Includes the following steps: S1: Preparation of nano-lithium iron phosphate particles: Iron source, lithium source and phosphorus source are mixed in stoichiometric ratio, and appropriate amounts of dispersant and solvent are added. After ball milling, a precursor slurry is obtained. The precursor slurry is spray-dried to obtain precursor powder. The precursor powder is heated to 300-400℃ at a heating rate of 3-5℃ / min under an inert atmosphere and held for 1-2 hours. Then, it is heated to 700-800℃ at a heating rate of 5-8℃ / min and held for 3-5 hours. After cooling, nano-lithium iron phosphate particles are obtained. S2: Carbon coating: Disperse the nano-lithium iron phosphate particles in a solution containing a carbon source, sonicate for 30-60 min to make the carbon source uniformly adsorbed on the particle surface, and then dry at 100-120℃ to obtain lithium iron phosphate particles with carbon source adsorbed on the surface. Then, heat them to 600-700℃ at a heating rate of 5-10℃ / min under an inert atmosphere and keep them at that temperature for 2-3 h to make the carbon source pyrolyze and form a carbon layer coating the surface of the lithium iron phosphate particles. S3: Coated metal oxide layer: Lithium iron phosphate particles with a carbon layer on the surface are dispersed in a solution containing metal salt. The sol-gel method is used to form a metal oxide sol on the particle surface. The sol is dried at 80-100℃ and then calcined at 400-500℃ for 1-2 hours to transform the metal oxide sol into a metal oxide layer, thereby obtaining the final lithium iron phosphate cathode material.