Ex situ reflection mode EXAFS at the Ti K-edge of lithium intercalated TiO2 rutile

The near surface structure of Li-intercalated rutile TiO2-electrodes was investigated with grazing incidence reflection mode XAFS (EXAFS and 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 which enables the electrochemical processing of samples which are sensitive towards 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 thickness of which is increasing with decreasing intercalation potential. A detailed XANES and EXAFS data analysis gives strong evidence that the structure of this layer is identical compared to that of polycrystalline Li-titanate Li0.6TiO2 (anatase type space group imma).