Electrochemical analysis of a-LixWO3 films of 400nm thick prepared by electron beam evaporation over ITO substrates was reported. The chemical potential variation with the fraction of inserted Li, μ(x), was obtained by chronopotentiometry measurements under quasi-equilibrium conditions and the chemical capacitance, Cc, was determined. A power-law dependence, Cc  xa (a ≈ 0.65) was observed for x > 10−3; indicating a wide distribution of site energies. Impedance measurements at different stages of insertion furnished information on the variation of the chemical diffusion coefficient, Dc, with potential (composition). Impedance spectra were analyzed by means of a spatially restricted diffusion model, and Dc was found to vary from 10−10 to 10−12cm2/s; nearly proportional to the reciprocal composition, Dc  1/x. This suggested that the ion transport process was considerably influenced by the extent of intercalation.

Charging and Diffusional Aspects of Li+ Insertion in Electrochromic a-WO3. J.García-Cañadas, F.Fabregat-Santiago, I.Porqueras, C.Person, J.Bisquert, G.Garcia-Belmonte: Solid State Ionics, 2004, 175[1-4], 521-5