Synthesis of LiFePO₄ Cathode Active Material for Rechargeable Lithium Batteries by Hydrothermal Reaction

Abstract

Phospho-olivine LiFePO₄ as a cathode material for rechargeable lithium batteries was successfully synthesized by hydrothermal process with an additional heat treatment in order to realize a theoretical electrochemical capacity. Several solutions with various concentrations of Li, Fe, and P were examined, and ascorbic acid was also used as a reducing agent. From an x-ray diffraction measurement, all of the samples synthesized with the molar ratio of Li : Fe : P=2.5 : 1 : 1 were characterized as a phospho-olivine LiFePO₄, independent of the addition of ascorbic acid. In order to improve the discharge and charge capacities, a heat-treatment was carried out. A remarkable increase in the charge and discharge capacities was accomplished for all of samples. The best performance was obtained when LiFePO₄ was prepared under the conditions as follows, the molar composition of Li : Fe : P : Ascorbic acid=2.5 : 1 : 1 : 0.2 in the starting solution, and annealing at 400°C for 1 h under argon atmosphere.