Spectroelectrochemical study of the lithium insertion in vanadium(V) oxide xerogels

Vanadium-oxide gels and xerogels are currently explored as versatile materials in lithium ion batteries. They consist of V2O5 nanoribbons composed by doubly-layered slabs joint by a strongly bond H3O+/H2O intercalated layer. Their thin films exhibit a complex electrochemical behavior encompassing four reduction waves at 0.38, 0.22, −0.42 and −0.81 V vs Ag/AgNO3 (0.503 vs SHE). In order to improve the understanding of such processes, a detailed spectroelectrochemical investigation was carried out based on visible-UV and confocal Raman spectroscopy. Accordingly, the first two waves were ascribed to the partial reduction of non-equivalent, localized VVO centers, keeping most of the representative vanadium-oxide vibrational features. At −0.4 V, a transition to a delocalized mixed-valence configuration became apparent in the optical and Raman spectra, leading to a dramatic current increase coupled with the insertion of lithium ions into the lamellar structure. At −0.8 V a complete conversion into the vanadium (IV) oxide form was observed from the spectroelectrochemical profiles. The nanoribbons doubly-layered structure seems to be preserved, sustaining a reversible and reproducible electrochemical behavior along several repetitive voltammetric cycles.