All-solid-state asymmetric supercapacitors based on Fe-doped mesoporous CoO and three-dimensional reduced graphene oxide electrodes with high energy and power densities.

An asymmetric supercapacitor offers opportunities to effectively utilize the full potential of the different potential windows of the two electrodes for a higher operating voltage, resulting in an enhanced specific capacitance and significantly improved energy without sacrificing the power delivery and cycle life. To achieve high energy and power densities, we have synthesized an all-solid-state asymmetric supercapacitor with a wider voltage range using Fe-doped CoO and three-dimensional reduced graphene oxide (3DrGO) as the positive and negative electrodes, respectively. In contrast to undoped CoO, the increased density of states and modified charge spatial separation endow the Fe-doped CoO electrode with greatly improved electrochemical capacitive performance, including high specific capacitance (1997 F g and 1757 F g at current densities of 1 and 20 A g, respectively), excellent rate capability, and superior cycling stability. Remarkably, the optimized all-solid-state asymmetric supercapacitor can be cycled reversibly in a wide range of 0-1.8 V, thus delivering a high energy density (270.3 W h kg), high power density (9.0 kW kg at 224.2 W h kg), and excellent cycling stability (91.8% capacitance retention after 10 000 charge-discharge cycles at a constant current density of 10 A g). The superior capacitive performance suggests that such an all-solid-state asymmetric supercapacitor shows great potential for developing energy storage systems with high levels of energy and power delivery.