Study of Antisite Defects in Hydrothermally Prepared LiFePO4 by in Situ X-ray Diffraction

Hydrothermal synthesis has proven to be a cost-effective, energy-efficient approach for the manufacture of lithium iron phosphate (LiFePO4) and its related materials. However, hydrothermally prepared LiFePO4 typically suffers from antisite defects, where some of the iron resides on lithium sites and restricts lithium-ion mobility. A post-heat-treatment temperature of around 700 °C is generally used to eliminate cation disorder, but little is known about these antisite defects or their concentration as a function of the post-heat-treatment temperature. In this study, time-resolved, synchrotron X-ray diffraction reveals that antisite defects are completely eliminated above 500 °C, suggesting that the electrochemical performance may be significantly enhanced by a milder postsynthesis heat treatment. The preliminary electrochemical results show a significant enhancement in the electrochemical capacity with the defect-free material, with the specific capacity increasing by approximately 60% at a C/20 rate.