Nanostructural modifications of V2O5 thin films during Li intercalation studied in situ by AFM

EC-AFM was used to study in situ the surface nanostructure of V2O5 thin films grown on vanadium metal and its changes during lithium electrochemical intercalation corresponding to the reversible α-to-δ phase transition. The results evidence the lateral extension and contraction of the oxide nanograins and the flattening of the oxide film surface. The increase and decrease of the lateral dimensions of the grains show that the surface reflects the volume expansion and contraction resulting from the dimensional changes of the oxide structure when lithium is inserted and de-inserted. An increase of ∼10% and ∼15% with respect to pristine oxide film was observed after the formation of the ε and δ phases, respectively. The lateral extension of the grains (∼7%) and surface flattening subsist after de-intercalation showing the non-fully reversible change of the oxide nanostructure at the interface with the electrolyte. Repeated cycling causes aging characterized by the amplification of the lateral extension of the grains (∼17%) and flattening of the oxide surface with respect to the pristine oxide film. It also modifies the surface of the oxide grains by creating new planes indicative of surface reconstruction and/or the emergence of slip planes.