Determination of sodium ion diffusion coefficients in sodium vanadium phosphate

Carbon-coated Na3V2(PO4)(3) (NVP) was prepared by a standard sol-gel procedure. The apparent diffusion coefficients of sodium ions in the rhombohedral NVP have been determined by different techniques such as galvanostatic intermittent titration technique (GITT) and cyclic voltammetry (CV). It was found that the apparent diffusion coefficients range from 6 x 10(-13) cm(2) s(-1) to 2 x 10(-15) cm(2) s(-1). These sodium ion apparent diffusion coefficients follow a similar trend as observed for lithium ions in the closely related monoclinic modification of Li3V2(PO4)(3), demonstrating a minimum at the potential where the ion extraction/insertion occurs.