Na+ pre-intercalated Na0.11MnO2 on three-dimensional graphene as cathode for aqueous zinc ion hybrid supercapacitor with high energy density

It is a critical challenge to build electrochemical energy storage devices with both high energy density and remarkable power density. Although zinc ion hybrid supercapacitors (Zn-ion HSCs) with battery-type cathode and capacitor-type anode have attracted widespread attention, cathode materials possessing high stability and good electrical conductivity are still worth pursuing. Herein, Na+ pre-intercalated δ-MnO2 nanoflakes (Na0.11MnO2) were grown on three-dimensional graphene (3DG) by a facile electrodeposition method. Benefiting from the in situ growth of MnO2 on high-crystallinity graphene and Na+ pre-intercalation in layered δ-MnO2, the Na0.11MnO2/3DG electrode shows a superior specific capacitance of 1240 F g−1 at the current density of 0.2 A g−1 and excellent cycling stability with 90% capacitance retention after 9000 cycles in 2 M ZnSO4/0.2 M MnSO4 aqueous electrolyte. Moreover, the assembled Na0.11MnO2/3DG//AC Zn-ion HSCs device delivers superb energy density of 74.3 Wh kg−1 and high power density of 9.6 kW kg−1, as well as satisfactory cycling lifespan with 83% capacitance retention after 5000 cycles. This work may pave a way for rational design of layer-structured MnO2 cathode in aqueous energy storage devices with both high energy and power densities.