Carbon-Coated, Bismuth-Substituted, Lithium Iron Phosphate as Cathode Material for Lithium Secondary Batteries

Abstract

Carbon-coated, bismuth-doped, lithium iron phosphates, LiFe 1x Bi x PO 4 (0x0.05), have been synthesized by a solid-state reaction method. From the optimization, the carbon-coated LiFe 0.95 Bi 0.05 PO 4 phase showed superior performances in terms of phase purity and high discharge capacity. The structural, morphological, and electrochemical properties were studied and compared to carbon-coated, LiFePO 4 . The Li/LiFe 0.95 Bi 0.05 PO 4 with carbon coating cell delivered an initial discharge capacity of 145 mAh/g and was 30 mAh/g higher than the Li/LiFePO 4 with carbon coating cell. Cyclic voltammetry revealed excellent reversibility of the LiFe 0.95 Bi 0.05 PO 4 with carbon coating material. High rate capability studies were also performed and showed a capacity retention over 93% during the cycling. It was concluded that substituted Bi ion play an important role in enhancing battery performance of the LiFePO 4 material through improving the kinetics of the lithium insertion/extraction reaction on the electrode.