Influence of carbon sources on LiFePO4/C composites synthesized by the high-temperature high-energy ball milling method

Carbon-coated LiFePO₄ composites were synthesized by a new method of high-temperature high-energy ball milling (HTHEBM). Fe₂O₃ and LiH₂PO₄ were used as raw materials. Glucose, sucrose, citric acid and active carbon were used as reducing agents and carbon sources, respectively. In this method, high-energy ball milling and carbon coating worked together and, therefore, fine and homogeneous LiFePO₄/C particles with excellent properties were obtained in a relatively short synthesis time of 9 h. Moreover, the synthesis process could be completely finished at a relatively lower temperature of 600 °C for high-energy ball milling transforming mechanical energy into thermal energy. The results of X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical performance tests indicated that carbon source had an important influence on the properties of LiFePO₄/C composites synthesized by the HTHEBM method. It was proved that the LiFePO₄ composites coated with glucose had the best properties with 1 μm geometric mean diameter and 150.3 mA h g⁻¹ initial discharge capacity at a current rate of 0.1 C. After the 20th cycle test, the reversible capacity was 148 mA h g⁻¹ at 0.1 C, showing a retention ratio to the initial capacity of 98.5%.