Iron(III) fluoride synthesized by a fluorolysis method and its electrochemical properties as a positive electrode material for lithium secondary batteries

Abstract

Abstract Iron(III) fluoride (FeF3) with low crystallinity and high surface area has been synthesized by a fluorolysis method, and applied as a positive electrode material for lithium secondary batteries. The FeF3 prepared with a high molar ratio of hydrogen fluoride exhibits a high surface area and crystallinity. The FeF3 sample treated at 300 °C under a F2/Ar atmosphere exhibits the highest surface area and was selected for further electrochemical test in view of improvement of performance in the potential region of conversion reactions. The initial discharge (lithiation) capacity was 676 mAh g⿿1 that was close to the theoretical capacity of FeF3 (712 mAh g⿿1). Compared to the highly crystalline FeF3 commercially available, the synthesized FeF3 in the present study exhibited a low discharge capacity attributed to the insertion reaction because of the low crystallinity, and showed a low overpotential and larger capacity corresponding to the conversion reaction owing to the higher surface area of the fluorides.