The structural evolution of vanadium oxide (V2O5) nanocrystals was studied during Le 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 Le ions are trapped within the V2O5 framework and the V2O5 exists as Li0.18V2O5 instead of pure V2O5 after the first four cycles, while the trapped Li (+) ion may increase the stability of V2O5 framework. (C) 2014 Elsevier Ltd. All rights reserved.