Mechanism analysis of the capacitance contributions and ultralong cycling-stability of the isomorphous MnO2@MnO2 core/shell nanostructures for supercapacitors

Abstract

A facile method to synthesize isomorphous MnO₂@MnO₂ core/shell nanostructures was developed for the first time by using MnO₂ nanowires as seed crystals. These unique nanoarchitectures consisting of an isomorphous layer of β-MnO₂ nanosheets well grown on the surface of β-MnO₂ nanowires exhibit remarkable electrochemical performance with high capacitance and ultra long cycle life, i.e., nearly 92.2% retention after 20 000 cycles at a current density of 5 A g⁻¹. The enhanced specific capacitance of the MnO₂@MnO₂ electrode is largely contributed by the capacitive processes including double-layer charging and Faradaic pseudocapacity. Particularly, these intriguing behaviors are strongly correlated with the unique isomorphous core/shell hierarchical configuration and high mechanical stability as well as the better interfacial structures between the MnO₂ nanowire core and the ultrathin MnO₂ nanosheet shell. In addition, it is demonstrated that the formation of defective and disordered regions throughout the whole core/shell architecture is the main cause for the unusual increased capacity during the early stages of cyclic charge/discharge.