Water-based asymmetric supercapacitors with 2.5 V wide potential and high energy density based on Na0.6CoO2 nanoarray formed via electrochemical oxidation

The voltage limit of water-based asymmetric supercapacitors is usually 2 V, which prevents further improvement of energy density. Na0.6CoO2 nanoarrays with high Na content are formed on carbon cloth (CC) by cyclic electrochemical oxidation (EO) and can work stably in 0–1.2 V wide potential, and the specific capacitance is up to 575.98C g−1 at 1 A g−1. Using carbon coated Fe2O3 nanoarrays on CC as the negative electrode and Na0.6CoO2/CC as the positive electrode, a water-based asymmetric supercapacitor (ASC) which can operate stably in 0–2.5 V wide voltage window is assembled. The Na0.6CoO2/CC//Fe2O3@C/CC ASC exhibits an energy density of 133.92 Wh kg−1 at a power density of 1250 W kg−1, which is better than previously reported Co-based supercapacitors. This study provides a scheme for the working voltage of water-based ASCs to be further expanded to more than 2 V. Utilizing cationic pre-inserted Co3O4 nanoarray to construct high operating voltage composite electrode should have broad application prospect.