Study Of Precursor Preparation And Performance Of LiFePO₄ As Cathode Material For Lithium-ion Battery

Olive-type LiFePO4/C has gained much attention as its high theoretical capacity, flat voltage platform, rich resources, lower price, environmentally friendliness and good safety performance. But its poor rate performance and low tap density restrict its practical application. Homogeneous precipitation method and oxidized precipitate transformation method are adopted to prepare precursor FePO4, and then prepare LiFePO4/C. The relationship between physical performance and electrochemical performance is also investigated.Homogeneous precipitation method is adopted to prepare FePO4 precursor, here the influence of urea amount and surfactant on the structure, morphology as well as electrochemical performance of LiFePO4 is investigated and the results show that at the optimized condition without surfactant, the first discharge capacity is 141.9mAh/g and poor rate performance. The discharge capacity of LiFePO4/C prepared with surfactant PEG reached 151.5mAh/g at 0.1 C rate, and the discharge capacity of 122.5mAh/g is reached at 1C rate, the tap density is 1.17cm3/g.A new method-oxidized precipitate transformation method is put forward to prepare FePO4 precursor. The suspension of Fe3(PO4)2 is prepared at pH=9.5, and then the suspension is oxidized to prepare FePO4 at pH=2. The results show that the particle size of sphere FePO4 is about 100nm. The discharge capacity of LiFePO4/C prepared with FePO4 is 139.8mAh/g at 0.1C rate, and 123.2mAh/g at 2C, showing a well rate performance.The relationship between physical performance and electrochemical performance of LiFePO4/C prepared with FePO4 as raw material is studied, the results show that the tap density and rate performance increase in the range of 6%-11%of carbon content. The rate performance first increases and then decreases as the specific surface area increases.