Effect of mechanical activation process parameters on the properties of LiFePO4 cathode material

Abstract Pure, nano-sized LiFePO 4 and carbon-coated LiFePO 4 (LiFePO 4 /C) positive electrode (cathode) materials are synthesized by a mechanical activation process that consists of high-energy ball milling and firing steps. The influence of the processing parameters such as firing temperature, firing time and ball-milling time on the structure, particle size, morphology and electrochemical performance of the active material is investigated. An increase in firing temperature causes a pronounced growth in particle size, especially above 600 °C. A firing time longer than 10 h at 600 °C results in particle agglomeration; whereas, a ball milling time longer than 15 h does not further reduce the particle size. The electrochemical properties also vary considerably depending on these parameters and the highest initial discharge capacity is obtained with a LiFePO 4 /C sample prepared by ball milling for 15 h and firing for 10 h at 600 °C. Comparison of the cyclic voltammograms of LiFePO 4 and LiFePO 4 /C shows enhanced reaction kinetics and reversibility for the carbon-coated sample. Good cycle performance is exhibited by LiFePO 4 /C in lithium batteries cycled at room temperature. At the high current density of 2 C , an initial discharge capacity of 125 mAh g −1 (73.5% of theoretical capacity) is obtained with a low capacity fading of 0.18% per cycle over 55 cycles.