Reflection mode XAFS at the Ti K-edge of lithium intercalated TiO₂ electrodes

Lithium intercalation and deintercalation in crystalline TiO₂-electrodes (rutile and anatase modifications) was investigated ex situ using grazing incidence reflection mode x-ray absorption spectroscopy in a specialized cell which permits the removal of the electrolyte and the subsequent measurement of grazing incidence x-ray absorption spectra under a protecting noble gas atmosphere. Small changes observed in near edge x-ray absorption spectra indicated that the Ti⁴⁺ ions are reduced by the electrochemical lithiation, depending on the TiO₂ modification, Ti^3.5+ states as well as Ti³⁺ states are observed for rutile and anatase, respectively. Angle dependent experiments reveal that the intercalation is not complete for rutile, while anatase seems to be fully intercalated. In addition, a certain amount of Li remains in the anatase electrode after a complete intercalation – deintercalation cycle. The results suggest that Li-ions are generally accumulated at the electrode/electrolyte interface during both intercalation and deintercalation.