Achieving Ultrahigh Capacity with Self-Assembled Ni(OH) Nanosheet-Decorated Hierarchical Flower-like MnCoO Nanoneedles as Advanced Electrodes of Battery-Supercapacitor Hybrid Devices.

Self-assembled Ni(OH) nanosheet-decorated hierarchical flower-like MnCoO nanoneedles were synthesized via a cost-effective and facile hydrothermal strategy, aiming to realize a high-capacity advanced electrode of a battery-supercapacitor hybrid (BSH) device. It is demonstrated that the as-synthesized hierarchical flower-like MnCoO@Ni(OH)-nanosheet electrode exhibits a high specific capacity of 318 mAh g at a current density of 3 A g and still maintains a capacity of 263.5 mAh g at a higher current density of 20 A g, with an extremely long cycle lifespan of 87.7% capacity retention after 5000 cycles. Moreover, using the unique core-shell structure as the cathode and hollow FeO nanoparticles/reduced graphene oxide as the anode, the BSH device delivers a high energy density of 56.53 Wh kg when the power density reaches 1.9 kW kg, and there is an extraordinarily good cycling stability with the capacity retention rate of 90.4% after 3000 cycles. It is believed that the superior properties originate from desirable core-shell structures alleviating the impact of volume changes as well as the existence of two-dimensional Ni(OH) nanosheets with more active sites, thereby improving the cycle stability and achieving ultrahigh capacity. These results will provide more access to the rational material design of diverse nanostructures toward high-performance energy storage devices.