In situ electrochemical lithium intercalation into amorphous oxide thin films

Abstract

Abstract Lithium intercalation and de‐intercalation in amorphous MoO 3 electrodes were investigated using electrochemical techniques and in situ grazing incidence reflection mode X‐ray absorption spectroscopy. A new electrochemical cell suited for in situ investigations with X‐rays under grazing incidence in a protective He atmosphere was built. A Kapton sealed electrolyte compartment, the bottom of which was the amorphous MoO 3 working electrode, was placed in this steel container so that a well‐defined electrochemistry analysis was possible in parallel to the X‐ray investigations. We present the results of potentiodynamic polarization experiments, as well as potentiostatic current transients, in close connection to surface‐sensitive in situ X‐ray absorption spectra. The results show that the Mo 6+ ions of the amorphous oxide electrode are reduced by electrochemical lithiation, leading to a formal Mo 5+ oxidation state. Angle‐dependent experiments reveal that the intercalation is not complete for the applied conditions, i.e. the Li ions are not homogeneously distributed in the entire volume of the amorphous working electrode. In addition, a certain amount of Li remains in the Mo oxide electrode after a complete intercalation/de‐intercalation cycle. The results suggest that Li ions are accumulated at the electrode/electrolyte interface during both intercalation and de‐intercalation. Copyright © 2006 John Wiley & Sons, Ltd.