Defect-domains enabling VO2 nanosheet arrays with fast charge transfer for 3.0 V aqueous supercapacitors

Abstract

Defective metal oxides are of great significance to promote reaction activity for high energy and power densities supercapacitors in aqueous electrolytes. Herein, we demonstrate a monoclinic VO2 nanosheet arrays electrode with tailorable defect-domains by a simple thermal-induced strategy. It is found that the defect-domains stemmed from the residual trivalent vanadium of V2O3 precursor directly influence the intrinsic conductivity of VO2. The relationships between defect-domains and electrochemical performance are built and the defect-optimized VO2 can greatly accelerate the electrochemical reaction kinetics with decreased polarization effect. It exhibits a high specific capacitance of 180.3 F g-1 at 0.5 A g-1 and 78.8 F g-1 even at 10 A g-1 within a large potential window of -1.5 ~ 0.15 V with superior cycle stability in “water in salt” electrolyte. A 3.0 V aqueous asymmetric supercapacitor device is assembled with MnO2 nanosheet arrays as cathode, which delivers a very high energy density of 120.3 Wh kg-1 at 1.5 kW kg-1, almost as good as sodium/potassium ion batteries.