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 4.8V 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 (D-Li+(true)) measured in single-phase region are in the range of 10(-9) to 10(-10) cm(2) s(-1). Its apparent diffusion coefficients (D-Li+(app)) measured in two-phase regions by CV and GITT range from 10(-10) to 10(-11) cm(2) s(-1) and 10(-8) to 10(-13) cm(2) 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. (C) 2009 Elsevier Ltd. All rights reserved.