Enhanced energy density and wide potential window for K incorporated MnO2@carbon cloth supercapacitor

Based on the redox couple reaction of Mn3+/Mn4+, the theoretical capacitance of manganese dioxide (MnO2) has a very high value of 1370 F/g but the specific capacitance of MnO2 in the reported literature is still under 300 F/g. The potential window of MnO2 in the previously published studies is approximately 1 V which, considering E = 1/2CV2, limits the power and energy densities far below the theoretical value. In this work, we developed an ultra-thin K+ doped δ-MnO2 nanosheets array electrode the potential window of which extended to 0–1.2 V with a highly reversible capacitance of 366 F/g. When the potential window reaches 1.2 V, the fast-redox reaction of MnO2 and the K+ intercalation/deintercalation process restrains water decomposition in kinetics. A high potency aqueous asymmetric supercapacitor (K-MnO2//AC) was drafted with K-MnO2 as a positive electrode which exhibited a stable working potential window of 0–2.2 V in 1 M Na2SO4 aqueous electrolyte. This device has demonstrated an excellent energy density of 56 Wh/kg at a power density of 550 W/kg and an ultralong cycle performance with capacitance retention of 98% over 10,000 cycles at the current density of 10 A/g. This approach leads to new prospects for emerging high workable potential window aqueous energy storage devices.