Freestanding core-shell Ni(OH)2@MnO2 structure with enhanced energy density and cyclic performance for asymmetric supercapacitors

Abstract Core-shell structural Ni(OH) 2 @MnO 2 electrodes with widened potential window and great stability are prepared through a two-step strategy, in which freestanding Ni(OH) 2 discs grow on nickel-foam as core and wrinkled MnO 2 coatings are electrodeposited as shell. The MnO 2 shell successfully inhibits the O 2 evolution process at the high oxidation potential so that the potential window of Ni(OH) 2 @MnO 2 electrode is up to 1 V. Besides, the Ni(OH) 2 @MnO 2 electrode presents a high specific capacity of 642.3 C g −1  at 1 mV s −1 and a long cyclic life without capacity fading, which is a breakthrough against the poor stability of reported Ni(OH) 2 /MnO 2 electrodes Remarkably, an asymmetric supercapacitor (ASC) constructed by Ni(OH) 2 @MnO 2 electrode and activated carbon electrode delivers a high energy density of 66.7 Wh kg −1 at a power density of 485.7 W kg −1 under potential window of 1.7 V. Furthermore, the ASC exhibits an energy density of 17.8 Wh kg −1 at a high power density of 14571.4 W kg −1 and a capacitance retention of 101.4% after 15,000 cycles, showing great rate capability and stable cyclic performance.