In situ X-ray absorption spectroscopy study of lithium insertion into sputtered WO3 thin films

We have performed an in situ X-ray absorption spectroscopy (XAS) study of the effect of Li+ electroinsertion into amorphous sputtered WO3 thin films. Three different potentials have been investigated, which are +0.66, −0.84 and −1.04 V vs SHE. We have estimated by electrochemical and chemical titration that they correspond in LixWO3 to x equal to 0, ca. 0.32 and ca. 0.45, respectively. Shifts of the tungsten LI and LIII-edge positions towards lower energies are observed with lithiation and attributed to the decrease of the W oxidation state. Significant modifications are also observed on the extended X-ray fine structure (EXAFS) spectra. The analysis of first oxygen shells clearly shows an increase of the mean W–O inter-atomic distances upon lithiation which is not due to a crystallization process induced by the cathodic reaction.