Optimization of carbon coatings on LiFePO4: Carbonization temperature and carbon content

LiFePO4/C composite cathode materials were synthesized by carbothermal reduction route using inexpensive FePO4 as raw material and glucose as reductive agent and carbon source. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infrared (FTIR), laser Raman spectroscopy and constant-current charge/discharge test. The results indicate that the structure of conductive carbon, depending on the carbonization (synthesis) temperature, is closely related to the electrochemical performance of LiFePO4/C composites. The quality of carbon coating on the LiFePO4 particle surface is determined by the carbon content, and only a proper carbon content (about 3%) can lead to a more uniform carbon distribution. Electrochemical results show that the optimal sample synthesized at 700 °C and with a carbon content of 3.1%, delivers a high discharge capacity of 116.0 mAh g−1 at 5C rate, and the discharge capacity shows little degradation after 100 cycles at 2C rate. The excellent high-rate dischargeability and cycling performance of the optimal sample can be attributed to its high carbonization degree and uniform carbon coating.