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

Carbon-coated LiFePO4/C composite as cathode materials is synthesized by solid-state method using anhydrous FePO4 and hydrous FePO4·2H2O as precursors. The effects of sintering temperature and carbon content on the properties of LiFePO4/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 LiFePO4/C composite. Compared with hydrous FePO4·2H2O, anhydrous FePO4 has good crystallinity, uniform particle morphology and symmetrical size distribution, contributing to LiFePO4/C composite have excellent electrochemical performances. Due to the dehydration of hydrous FePO4·2H2O during synthesis, uneven distribution of carbon content and carbon layer is coated on LiFePO4 surface, deteriorating the electrochemical performance of LiFePO4/C composite. When anhydrous FePO4 was used as the precursor, the LiFePO4/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.