Mechanism and kinetic studies on the synthesis of LiFePO4via solid-state reactions

Abstract

Three classical iron sources including FePO₄·2H₂O, FeC₂O₄·2H₂O and Fe₂O₃ are explored to study the mechanism and kinetics of LiFePO₄ synthesis via solid-state reactions. During the initial formation of LiFePO₄, the reactivity of FePO₄ appears to be higher than that of FeC₂O₄ because the latter involves two stages including the decomposition of FeC₂O₄ and then the formation of LiFePO₄. Fe₂O₃ shows the lowest reactivity among the solid-state reactions. Meanwhile, the optimal sintering temperature for FePO₄ to form LiFePO₄ is lower than those for FeC₂O₄·2H₂O and Fe₂O₃. A larger primary particle size should be responsible for the lower specific capacity of LiFePO₄ synthesized with micro-Fe₂O₃. The kinetic mechanism for obtaining single-phase LiFePO₄ corresponds to the diffusion model, calculated by using Coats–Redfern and Doyle equations in which FeC₂O₄·2H₂O and FePO₄·2H₂O obey 3-dimensional diffusion (cylinder, GB equation) and Fe₂O₃ obeys 1-dimensional diffusion.