Quasi-in-situ reflection mode XANES at the TiK-edge of lithium intercalated TiO2 rutile and anatase

The near surface structure of Li-intercalated rutile and anatase TiO2 electrodes was investigated with grazing incidence reflection mode XANES spectroscopy. Though real in situ experiments are not feasible due to the extremely strong parasitic absorption of the electrolyte, a new cell was constructed. It enables the electrochemical processing of samples which are sensitive to oxidation as well as it permits reflection mode X-ray experiments after the controlled emersion of the electrodes from the electrolyte. Our results show that even Li containing electrolytes and Li intercalated electrodes can be processed inside the cell. During the electrochemical Li intercalation in rutile, only a thin surface layer of some few nm thickness was changed by the lithiation. The structure of this layer seems to have a similar structure compared to the Li titanate Li0.6TiO2 (space group imma). The anatase layer could be fully intercalated showing the characteristic Li-titanate structure. In the surface region the Li intercalation results in an edge shift that corresponds to Ti3+ states in contrast to the Ti3.4+ states in the bulk. (C) 2003 Elsevier Science B.V. All rights reserved.