A novel vanadium oxide deposit for the cathode of asymmetric lithium-ion supercapacitors

Hydrous vanadium oxide (denoted as VO_x·yH₂O) deposited at 0.4 V shows promising capacitive behavior in aqueous media containing concentrated Li ions. VO_x·yH₂O annealed in air at 300 °C for 1 h shows highly reversible Li-ion intercalation/de-intercalation behavior with specific capacitance reaching ca. 737 and 606 F g^? 1 at 25 and 500 mV s^? 1 in 12 M LiCl between ?0.2 and 0.8 V. In 14 M LiCl, retention of specific capacitance is about 95% when the scan rate is increased from 25 to 500 mV s^? 1. This work is the first report showing the ultrahigh rate of Li-ion intercalation/de-intercalation in VO_x·yH₂O. A so-called Li-ion supercapacitor of the asymmetric type consisting of a VO_x^.yH₂O cathode and a WO₃^.zH₂O anode is proposed here.