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

Pure, nano-sized LiFePO4 and carbon-coated LiFePO4 (LiFePO4/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 degrees C. A firing time longer than 10 h at 600 degrees 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 LiFePO4/C sample prepared by ball milling for 15h and firing for 10h at 600 degrees C. Comparison of the cyclic voltammograms of LiFePO4 and LiFePO4/C shows enhanced reaction kinetics and reversibility for the carbon-coated sample. Good cycle performance is exhibited by LiFePO4/C in lithium batteries cycled at room temperature. At the high current density of 2C, 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. (c) 2007 Elsevier B.V. All rights reserved.