MnO2 Nanowires@NiCo-LDH Nanosheet Core–Shell Heterostructure: A Slow Irreversible Transition of Hydrotalcite Phase for High-Performance Pseudocapacitance Electrode

A stable MnO2 nanowires@NiCo-layered double hydroxide (LDH) nanosheet core–shell heterostructure is prepared via a simple liquid-phase reaction method, in which the NiCo-LDH nanosheets grow uniformly on the surface of ultralong MnO2 nanowires with a stable tunnel structure. Electrochemical studies indicate that the core–shell heterostructure electrode has high specific capacitances of 708 and 630 C g–1 at 1 A g–1 and 10 A g–1, respectively, and exhibits a capacitance retention of 82.3% after 2000 cycles. According to in situ Raman spectral analysis, the NiCo-LDH material in the core–shell structure electrode reveals a very slow transition from α to β phase in the cycle process compared to the pure NiCo-LDH electrode, which can be attributed to the stable core–shell heterostructure buffering the collapse of the layered NiCo-LDH nanosheets and slowing down the irreversible phase transition during the charging–discharging process by the synergistic effect between one-dimensional nanowires and two-dimensional nanosheets. Moreover, the assembled asymmetric supercapacitor using the core–shell electrode displays a high energy density of 31.9 Wh kg–1 at 1 A g–1, a high power density of 7644.9 W kg–1 at 10 A g–1, and an acceptable capacitance retention of 72.4% after 10 000 cycles, indicating the potential practical application.