Enhanced rate performance of nano–micro structured LiFePO 4/C by improved process for high-power Li-ion batteries

Abstract

A spherical carbon-coated nano–micro structured LiFePO 4 composite is synthesized for use as a cathode material in high-power lithium-ion batteries. The composites are synthesized through carbothermal reduction with two sessions of ball milling (before and after pre-sintering of precursor) followed by spray-drying with the dispersant of polyethylene glycol added. The structure, particle size, and surface morphology of the cathode active material and the properties of the coated carbon are investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. Results indicate that the LiFePO 4/C composite has a spherical micro-porous morphology composed of a large number of carbon-coated nano-spheres linked together with an ordered olivine structure. The carbon on the surface of LiFePO 4 effectively reduces inter-particle agglomeration of the LiFePO 4 particles. A galvanostatic charge–discharge test indicates that the LiFePO 4/C composites exhibit initial discharge capacities of 155 mAh g −1 and 88 mAh g −1 at 0.2 C and 20 C rates with the end of discharge voltage of 2.5 V, respectively. This behavior is ascribed to the unique spherical structure, which shortens lithium ions diffusion length and improves the electric contact between LiFePO 4 particles.