Versatile Synthesis of Carbon-Rich LiFePO[sub 4] Enhancing Its Electrochemical Properties

Abstract

LiFePO4/C composites were prepared by using organo-phosphonates as a source of iron, phosphorus and carbon. Fe[RPO3]·H2O (R = methyl or phenyl group) were decomposed in presence of Li2CO3 at high temperature and under nitrogen flux. During the high temperature synthesis the phosphonate is oxidized and reacting with lithium forms the electro-active material. The organic constituent of the precursor is oxidized to form carbon that interacting with the LiFePO4 surface, decrease the charge transfer resistance. The materials were characterized by chemical analysis, TG, DTA, X-ray powder diffraction and SEM. The LiFePO4/C composites were used to prepare electrodes for the electrochemical characterization. The material prepared starting from the phenyl-phosphonate showed impressive specific energy, specific power and capacity retention upon cycling The specific energy evaluated at C/10 rate was about 550 Wh kg-1. The specific power calculated at 30C rate was in excess at 14000 W kg-1 while the specific energy was about 28 % of the energy delivered at C/10. No capacity fading was observed upon cycling. The performance of LiFePO4 prepared with methyl-phosphonate as precursor was found to be slightly lower, probably due to the lower carbon content.