Preparation of LiFePO4/C composite powders by ultrasonic spray pyrolysis followed by heat treatment and their electrochemical properties

LiFePO4 powders could be successfully prepared front a precursor solution, which was composed of Li(HCOO)center dot H2O, FeCl2 center dot 4H(2)O and H3PO4 stoichiometrically dissolved in distilled water, by ultrasonic spray pyrolysis at 500 degrees C followed by heat treatment at sintering temperatures ranging from 500 to 800 degrees C in N-2 + 3% H-2 gas atmosphere. Raman spectroscopy revealed that alpha-Fe2O3 thin layers were formed on the surface of as-prepared LiFePO4 powders during spray pyrolysis. and they disappeared after sintering above 600 degrees C. The LiFePO4 powders prepared at 500 degrees C and then sintered at 600 degrees C exhibited a first discharge capacity of 100 mAh g(-1) at a 0.1 C charge-discharge rate. To improve the electrochemical properties of the LiFePO4 powders, LiFePO4/C composite powders with various amounts of citric acid added were prepared by the present method. The LiFePO4/C (1.87 wt.%) composite powders prepared at 500 degrees C and then sintered at 800 degrees C exhibited first-discharge capacities of 140 mAh g(-1) at 0.1 C and 84 mAh g(-1) at 5 C with excellent cycle performance. In this study, the optimum amount of carbon for the LiFePO4/C composite powders was 1.87 wt.%. Front the cyclic voltammetry (CV) and AC impedance spectroscopy measurements, the effects of carbon addition on the electrochemical properties of LiFePO4 powders were also discussed. (c) 2008 Elsevier Ltd. All rights reserved.