Amorphous Vanadium Oxides with Metallic Character for Asymmetric Supercapacitors

Abstract Exploiting high-capacitance and broad-potential anode materials is of critical for boosting the energy density of aqueous asymmetric supercapacitors. Herein, we have reported the synthesis of the amorphous vanadium oxide nanosheet arrays with metallicity by defect engineering, which enables the oxygen vacancy content as high as 28.5%. The DOS calculations and the XPS analysis further disclose the disappearance of band gap. The oxygen vacancy can also accelerate the ions migration on their (sub-) surface with lower energy barrier. Consequently, the as-obtained anode delivers an ultrahigh specific capacitance of 554 mF·cm-2 (346 F·g-1) at 1 mA·cm-2 (0.625 A·g-1) with a capacitance retention of 66% even at 32 mA·cm-2. After assembling into a flexible quasi-solid-state asymmetric supercapacitor, the energy density can reach as high as 161.8 μWh·cm-2 at 0.5 mW·cm-2. This finding has extended the defect engineering strategy to regulate the crystal structure and electrical conductivity for high-performance electrochemical devices.