The Structural Evolution of V₂O₅ Nanocrystals during Electrochemical Cycling Studied Using In operando Synchrotron Techniques

The structural evolution of vanadium oxide (V₂O₅) nanocrystals was studied during Li⁺ ion intercalation and deintercalation (i.e. electrochemical discharge/charge) processes using in operando high-energy x-ray diffraction (HEXRD) and in operando x-ray adsorption near edge spectroscopy (XANES). The HEXRD results clearly show that V₂O₅ undergoes phase transformations during the first Li⁺ ion intercalation (i.e. discharge) process. The analysis of the XANES data suggests that the average oxidation state of vanadium in fully charged V₂O₅ nanocrystals decreases to less than +5 after the first four cycles. The combined results of the unchanged crystal structure (HEXRD) and the decreased oxidation state (XANES) lead to the conclusion that some of the Li⁺ ions are trapped within the V₂O ₅ framework and the V₂O₅ exists as Li_0.18V₂O₅ instead of pure V₂O ₅ after the first four cycles, while the trapped Li⁺ ion may increase the stability of V₂O₅ framework.