Microwave-assisted hydrothermal synthesis of vanadium oxides for Li-ion supercapacitors: The influences of Li-ion doping and crystallinity on the capacitive performances

摘要

Vanadium oxides (VO_x·nH_2O) with long cycle-life for Li-ion supercapacitors have been successfully synthesized by means of the microwave-assisted hydrothermal synthesis (MAHS) method, a faster and more energy-saving method than the conventional hydrothermal synthesis. Such oxides show capacitor-like, lithium-ion intercalation/de-intercalation responses in aqueous media. Although electrochemical activation is required to reveal the capacitor-like behavior of VO_x·nH_2O, doping Li ions by adding LiCl into the precursor solution not only effectively shortens the activation time but also enhances the specific capacitance of VO_x·nH_2O. This kind of materials shows the promising application potential in the aqueous-based Li-ion supercapacitors. X-ray diffraction (XRD), Raman spectroscopic, and X-ray photo-electron spectroscopic (XPS) analyses are employed to identify the fine tune-up in microstructures of various VO_x·nH_2O.