UCLA

Finding a promising material and constructing a new method to have both high energy and power are key issues for future energy storage systems. This dissertation addresses three different materials systems to resolve those issues. Pseudocapacitive materials such as RuO2 and MnO2 display high capacitance but Nb2O5, displays a different charge storage mechanism, one highly dependent on its crystal phase rather than its surface area. Various sol-gel techniques were used to synthesize the different phases of Nb2O5 and electrochemical testing was used to study their charge storage with some phases displaying comparable charge storage to MnO2. To overcome the electrical limitations of using an insulating material, the core-shell structure (Nb2O5/C) was also examined and the method could be generalized to improve other pseudocapacitors. Besides electronic conductivity, the diffusion of the electrolyte ions through the shell material is a critical factor for fast charging/discharging in the core-shell structure.

This dissertation also involves another topic, a reconfigurable electrode, that displays both high energy and power density. By constructing a reconfigurable electrode which has different electrical properties (metallic or insulating state) depending on the amount of intercalated `guest' ions into `host' material, it can be used as a battery or electrochemical capacitor material in the insulating or metallic state respectively. Metal oxide bronzes having metal-insulator transition were investigated in this study.