Achieving Ultrahigh Capacity with Self-Assembled Ni(OH)₂ Nanosheet-Decorated Hierarchical Flower-like MnCo₂O_4.5 Nanoneedles as Advanced Electrodes of Battery–Supercapacitor Hybrid Devices

Abstract

Self-assembled Ni(OH)₂ nanosheet-decorated hierarchical flower-like MnCo₂O_4.5 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 MnCo₂O_4.5@Ni(OH)₂-nanosheet electrode exhibits a high specific capacity of 318 mAh g^-1 at a current density of 3 A g^-1 and still maintains a capacity of 263.5 mAh g^-1 at a higher current density of 20 A g^-1, 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 Fe₂O₃ nanoparticles/reduced graphene oxide as the anode, the BSH device delivers a high energy density of 56.53 Wh kg^-1 when the power density reaches 1.9 kW kg^-1, 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)₂ 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.