Hierarchical Nanosheets/Walls Structured Carbon-Coated Porous Vanadium Nitride Anodes Enable Wide-Voltage-Window Aqueous Asymmetric Supercapacitors with High Energy Density.

The energy density of aqueous asymmetric supercapacitors (ASCs) is usually limited by low potential windows and capacitances of both anode and cathode. Herein, a facile strategy to fabricate hierarchical carbon-coated porous vanadium nitride nanosheet arrays on vertically aligned carbon walls (CC/CW/p-VN@C) as anode for aqueous ASCs is reported. The potential window of CC/CW/p-VN@C electrode can be stably extended to -1.3 to 0 V (vs Ag/AgCl) with greatly improved specific capacitance (604.8 F g at 1 A g), excellent rate capability (368 F g at 60 A g), and remarkable electrochemical stability. To construct ASCs, a Birnessite NaMnO nanosheet arrays (CC/CW/NaMnO) cathode is similarly built. Benefiting from the matchable potential windows and high specific capacitances of the rationally designed anode and cathode, aqueous CC/CW/p-VN@C||CC/CW/NaMnO ASCs with a wide voltage window of 2.6 V are fabricated. Moreover, the ASCs showcase an ultrahigh energy density up to 96.7 W h kg at a high power density of 1294 W kg, and excellent cycling stability (92.5% retention after 10 000 cycles), outperforming most of previously reported ASCs and even comparable to that of organic electrolyte supercapacitors (SCs). This efficient strategy for fabricating 2.6 V aqueous ASCs suggests a promising research system for high energy density SCs.