Graphene-Karst Cave Flower-like Ni–Mn Layered Double Oxides Nanoarrays with Energy Storage Electrode

A hierarchically flower-like structure with nanoarrays coupled with 3D macroporous sponge graphene combines the preponderances of the hierarchical nanoarchitecture and composition to enhance electrochemical performance. A graphene-karst cave flower-like Ni-Mn layered double oxides (GL) electrode material was prepared through a mild hydrothermal-carbonization process. As an electrode material, the resulting GL composite exhibited excellent performance with high specific capacitance (1,648 and 1,252 F g−1 at 0.5 and 10 A g−1, respectively) and good cycling stability (almost 96% retention after 6,000 charge-discharge cycles) for energy storage electrode. The GL composite material acting as a positive electrode for the asymmetric supercapacitor also exhibited high specific capacitance of 116.56 F g−1 at 0.5 A g−1 and excellent cycling stability with 86.7% capacitance retention after 6,000 cycles at a current density of 5 A g−1. This outstanding electrochemical performance may be attributed to the synergistic effect of the layered double oxides and 3D macroporous graphene oxide sponge.