Pan Hongge

Synergetic effect of the crystallinity, particle size of LiFePO 4 and the in-situ introduced Fe 2 P on its high-rate capability

LiFePO 4 /C composite with high crystallinity, sub-micron particle size and suitable content of in-situ introduced Fe 2 P was synthesized by a sol-gel method, in which LiOH, Fe 2 C 2 O 4 and NH 4 H 2 PO 4 were used as starting materials, and ethylene glycol was used as complexing agent and carbon source. The precursor of LiFePO 4 was calcined at a comparatively low temperature for relatively long time combined a following calcination at a comparatively high temperature for relatively short time. The composite shows high-rate capability as cathode material for lithium-ion batteries. The structure and the electrochemical properties of the LiFePO 4 /C composites synthesized by different calcination parameters were analyzed by X-ray diffraction, scanning electron microscopy, element analysis and electrochemical testing of galvanostatic charge-discharge, etc. The results show that the step-wise calcination at different temperatures for different times is an effective approach to obtain suitable amount of in-situ Fe 2 P, control the particle size and enhance the crystallinity of LiFePO 4 , which results in a significant improvement in the high-rate capability of LiFePO 4 . The LiFePO 4 /C composite synthesized at a calination temperature of 600℃ for 20 h followed by a further calcination at 700℃ for 4 h has 4wt% Fe 2 P and 3wt% C. The composite possesses discharge capacities of 140, 110 and 100 mAh/g at discharge rates of 1, 10 and 20 C, respectively.