Kinetics of electrochemical insertion of lithium into WO

Abstract A kinetic study of the electrochemical insertion of lithium into the original form of WO 3 , formed by the heat-treatment of H 2 WO 4 at 448 K, were carried out using an ac impedance method. The chemical diffusion coefficients, D , of lithium in the oxide were measured as functions of the lithium composition and temperature by using several kinds of electrolytes. The obtained values of D , based on a geometric surface area, depended strongly on the lithium composition and the kind of electrolytes. The D values, obtained using 1M LiClO 4 and 1M LiAsF 6 solutions of propylene carbonate, were of the order of 10 −11 cm/s at 298 K for 0.2 x x WO 3 , corresponding to a lithium self-diffusion coefficient of the order of 10 −12 cm 2 /s, while using the 1M LiBF 4 and 1 M LiPF 6 solutions considerably lower values of D , 10 −13 −10 −12 cm 2 /s, were obtained for 0.2 x 3 obtained using the former electrolyte (20–40 kJ/mol) is typical of diffusion in intercalation materials, whereas that obtained using 1M LiBF 4 solution (∼60 kJ/mol) corresponds to the kinetics controlled by the surface layer.