Optimized synthesis of LiFePO4 cathode material and its reaction mechanism during solvothermal

Abstract LiFePO4 has been widely considered as a promising cathode material for lithium ion batteries because of its nontoxicity, high specific capacity, good safety characteristics and low cost. However, the actual fabrication of LiFePO4 typically uses LiH2PO4, NH4H2PO4 or H3PO4 as phosphorus sources, possibly leading to the corrosion of the experimental facilities and release of toxic gas during the synthesis process. Hence, we use phytic acid (PhyA) as a new eco-friendly and sustainable phosphorus source to synthesize LiFePO4. Results show that the reaction time and temperature have significant effects on the morphology. LiFePO4 prepared at 180 °C for 4 h (LFP-4) shows unique hierarchical structure and exhibits best electrochemical performance over a wide test temperature (25–55 °C). Through time-dependent experiments to explore the reaction mechanism of LiFePO4, it is found that an intermediate Fe3(PO4)2 is produced that acts as the substrate for the subsequent preparation of LiFePO4. After carbon coating, LFP/C-4 (after carbon coating, LFP-4 labeled as LFP/C-4) shows an outstanding initial discharge capacity (156.9 mAh g−1, 1C at 25 °C) and high temperature behavior (147.1 and 126.8 mAh g−1 at 1C and 2C under 55 °C). This result is highly important for the controllable synthesis and improvement of electrochemical characteristics of LiFePO4 cathode material.