Analysis of the chemical diffusion coefficient of lithium ions in Li3V2(PO4)3 cathode material

The chemical diffusion coefficients of lithium ions (DLi+) in Li3V2(PO4)3 between 3.0 and 4.8 V are systematically determined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). The DLi+ values are found to be dependent on the voltage state of charge and discharge. Based on the results from all the three techniques, the true diffusion coefficients (DLi+true) measured in single-phase region are in the range of 10−9 to 10−10 cm2 s−1. Its apparent diffusion coefficients (DLi+app) measured in two-phase regions by CV and GITT range from 10−10 to 10−11 cm2 s−1 and 10−8 to 10−13 cm2 s−1, respectively, depending on the potentials. By the GITT, the DLi+ varies non-linearly in a “W” shape with the charge–discharge voltage, which is ascribed to the strong interactions of Li+ with surrounding ions. Finally, the chemical diffusion coefficients of lithium ions measured by CV, EIS and GITT are compared to each other.