Spectroscopic investigation of lithium intercalation in thin films of anatase titanium dioxide

Thin films of anatase TiO2 have been deposited on tin-doped indium oxide OTO) and Sb-doped tin oxide using electron beam evaporation. Subsequently these samples have been mounted into an electrochemical cell. Assuming a composition of LixTiO2 with x being 0.5 or 1, voltammetric measurements show that all lithium is present within the first 15 or '7.5 nm of the TiO2 film, respectively. Stepped potential experiments in combination with optical transmission measurements show that de-intercalation is much faster than intercalation. Differential absorption spectra as a function of intercalation potential suggest that the observed dark coloring of intercalated anatase can be attributed to electron traps at Li+ sites. This contradicts assumptions made in literature that the coloring mechanism of anatase is based on intervalence charge transfer from Ti4+ to Ti3+.