Kinetic behavior of LiFePO4/C cathode material for lithium-ion batteries

The composite cathode materials of LiFePO₄/C were synthesized by spray-drying and post-annealing method. The crystalline structure and morphology of products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The charge-discharge kinetics of LiFePO₄/C electrode was investigated using electrochemical impedance spectroscopy (EIS). The results show that the increment of the resistance has a close relation to the appearance of the FePO₄ phase during charge-discharge course, and that the ohmic resistance, charge transfer resistance and lithium-ion diffusion coefficients of the LiFePO₄/C electrode do not change much by extended cycling tests, implying a relatively superior cyclability of the battery. The effect of cell temperature on the electrochemical reaction behaviors of LiFePO₄/C electrode was also investigated using the EIS. It is confirmed that the effect of the cell temperature on the impedance results mainly from the enhancement of the lithium-ion diffusion at elevated temperatures.