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

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 beta-MnO2 nanosheets well grown on the surface of beta-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.