Li ion diffusivity and improved electrochemical performances of the carbon coated LiFePO₄

This study examines the effects of a carbon coating on the electrochemical performances of LiFePO₄. The results show that the capacity of bare LiFePO₄ decreased sharply, whereas the LiFePO₄/C shows a well maintained initial capacity. The Li ion diffusivity of the bare and carbon coated LiFePO₄ is calculated using cyclic voltammetry (CV) to determine the correlation between the electrochemical performance of LiFePO ₄ and Li diffusion. The diffusion constants for LiFePO₄ and LiFePO₄/C measured from CV are 6.56 × 10-16 and 2.48 × 10^-15 cm² s^-1, respectively, indicating considerable increases in diffusivity after modifications. The Li ion diffusivity (DLi) values as a function of the lithium content in the cathode are estimated by electrochemical impedance spectroscopy (EIS). The effects of the carbon coating as well as the mechanisms for the improved electrochemical performances after modification are discussed based on the diffusivity data.