Effect of Oxidation on Charge-Discharge Property of Iron Fluoride for Li-ion Secondary Battery

Anhydrous FeF3 was prepared by drying in vacuum of FeF3•3H2O and surface oxidized FeF3 samples were obtained by the calcination of Anhydrous FeF3 at 473 – 773 K for 10 minutes 3 hours under air. The obtained samples were characterized by use of X-ray diffraction, scanning electron microscopy. FeF3 became stable under atmosphere after oxidation at 673 K for more than 20 minutes. It was found that Fe2O3 was produced by calcination and covered the surface of FeF3 particles. In Charge-discharge measurements, the discharge capacity of these FeF3 samples was 100 225 mAh/g at 0.1 C. The discharge capacity for FeF3 sample calcined at 673 K for 20 min decreased with an increase of the discharge rate and the capacity at a high rate such as 3 C was maintained to be 130 mAh/g which was half value of the theoretical capacity of FeF3 cathode. The surface oxidation could improve the rate capability of FeF3 cathode.