Electrochemical intercalation of lithium into vanadium pentaoxide: an in situ X-ray absorption study

Abstract

An X-ray absorption study at the vanadium K edge has been performed on the Li_xV₂O₅(x= 0–0.78) system. For this, an electrochemical cell has been designed in order to allow in situ measurements. The spectra were recorded every 0.03 Li (mol V₂O₅)^–1 using the same sample left in the X-ray beam. The study of the XANES spectra shows that the vanadium environment becomes more symmetrical as the intercalation progresses. Furthermore, the Natoli rule applied to these spectra reveals a mean lengthening of the vanadium–oxygen bond of 0.05 Å. This result is confirmed by the EXAFS study. This EXAFS study also reveals a shortening of the vanadium–vanadium bond of 0.08 Å. The results are interpreted as being due to the partial reduction of vanadium(V) to vanadium(IV), and its move from its initial position in a square pyramid towards the basal oxygen plane of the pyramid.