Amorphous MoOx (a-MoOx, 2 < x < 3) thin films were deposited by a reactive magnetron sputtering method. As the Li-ion storage electrodes, the a-MoOx thin films exhibit a high capacity of 338 mu Ah.cm(-2) (about 845 mAh.g(-1)) at a current density of 90 mu A cm(-2) even after 100 electrochemical cycles, and have a rate capacity of 158 mu Ah cm(-2) at a high current density of 2000 mu A cm(-2). The phase analysis revealed that all the a-MoOx thin films maintained an amorphous characteristic after having been charged-discharged at various stages. In-situ electron-beam irradiation (EBI) induced crystallization of the a-MoOx thin films was performed by using a transmission electron microscopy. By analyzing the EBI induced crystalline phases of the a-MoOx thin films, the possible electrochemical reactions during the charge-discharge processes were discussed. According to the developed investigation method, the possible electrochemical mechanism in the a-MoOx thin films were proposed to undergo a conversion reaction such as MoOx + 2xLi(+) + 2xe(-) <-> Mo + xLi(2)O during the electrochemical processes. (C) 2014 Elsevier Ltd. All rights reserved.