Synthesis of FePO4 cathode material for lithium ion batteries by a sonochemical method

Hydrated amorphous FePO₄ was synthesized by a sonochemical reaction method, in which a solution of (NH₄)₂HPO₄ and FeSO₄·7H₂O was irradiated by an ultrasonic wave. From this material, two kinds of cathode materials were easily prepared: (1) an amorphous sample prepared by heating at 350 °C and (2) a crystalline sample prepared by heating at 700 °C. Both samples consisted of homogeneous sub-micron particles. The amorphous sample of FePO₄ exhibited high discharge capacities with more than 100 mAh g⁻¹ in the range of 3.9-2.0 V versus Li/Li⁺ at a current rate of 0.2 C. The sonochemical synthesis proposed herein has the following advantages: no use of oxidation agents for production of trivalent iron ions, reduction in reaction time, control of particle size, and enlargement in surface area for the preparation of the cathode material.