Comparison of the effects of FePO4 and FePO4·2H2O as precursors on the electrochemical performances of LiFePO4/C

Abstract Carbon-coated LiFePO 4 /C composite as cathode materials is synthesized by solid-state method using anhydrous FePO 4 and hydrous FePO 4 ·2H 2 O as precursors. The effects of sintering temperature and carbon content on the properties of LiFePO 4 /C composite are compared by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and charging–discharging test. The crystallinity, morphology, and particle size distribution of these two precursors are compared to investigate their effect on the electrochemical performances of LiFePO 4 /C composite. Compared with hydrous FePO 4 ·2H 2 O, anhydrous FePO 4 has good crystallinity, uniform particle morphology and symmetrical size distribution, contributing to LiFePO 4 /C composite have excellent electrochemical performances. Due to the dehydration of hydrous FePO 4 ·2H 2 O during synthesis, uneven distribution of carbon content and carbon layer is coated on LiFePO 4 surface, deteriorating the electrochemical performance of LiFePO 4 /C composite. When anhydrous FePO 4 was used as the precursor, the LiFePO 4 /C composite sintered at 700 °C with carbon content of 0.4 by molar ratio show high discharge capacity and stable cycling performance, with discharge capacity of 106.3 mA h g −1 at 10 C, and a capacity retention rate of 99.2% after 200 cycles at 1 C.