VO2 Nanoplatelets: A High Energy Electrode Material for Lithium Ion-Hybrid Electrochemical Capacitors

Abstract

Lithium ion hybrid capacitors (LIC) is an energy storage solution that combines the best of both worlds in terms of high power and high energy density. One of the participating electrodes stores charge by a faradaic mechanism (battery) while the other electrode stores charge by the formation of an electrical double layer (supercapacitor). This configuration allows for the exploitation of the niche gap between batteries and supercapacitors, allowing for the development of a possible energy storage solution for Plug in hybrid vehicles with fast charging and long range capabilities. Vanadium dioxide has recently received much attention because of their high capacity when compared to other vanadium analogues. It consists of sheets of VO6 octahedras linked with each other at the corner, the layered structure allows for good lithium kinetics. The high capacity of Vanadium dioxide even at high power loads is postulated to mitigate one of the main issues faced by LIC’s, that the power density of the device is limited by the battery electrode and most battery electrodes tend to fail at high power loads. Vanadium Dioxide nano-platelets were synthesized using a mechanically assisted hydrothermal reaction. The material was characterized using X-ray diffraction to check for phase purity, scanning electron microscopy and high resolution tunneling electron microscopy were used to characterize the effects of agitation on the morphology of the sample. The morphology is then co-related to the electrochemical performance of the material to develop an understanding about the effect of mechanical agitation on cell performance. Comprehensive electrochemical studies were performed on both VO2 and commercial Activated carbon (acts as the supercapacitor electrode) to determine the mass loading in a full cell arrangement. Half cell studies on VO2 were conducted between 2-3 V vs. Li a high capacity of ~250 mAh g-1 was recorded with barely any capacity drop at high current rates. Because of the robustness of VO2 during high current operations it can be applied in applications that require to store a large amount of energy and at the same time be able to undergo fast charge discharge cycles.