High-Performance Asymmetric Supercapacitor Based on Hierarchical NiMn₂O₄@CoS Core–Shell Microspheres and Stereotaxically Constricted Graphene

Three-dimensional self-assembled hierarchical NiMn 2 O 4 @CoS core–shell microspheres were synthesized via facile hydrothermal and post-electrodeposition methods on a Ni substrate. The microspheres were irregularly composed of many nanoflakes, whose diameter was approximately 1.8 μm. The NiMn 2 O 4 @CoS composites were used as electrode materials exhibiting a ultrahigh specific capacitance and excellent cycle performance for pseudocapacitors. The specific capacitance of the composite electrode reached 1751 F/g at a current density of 1 A/g and 1270 F/g at a higher current density of 30 A/g. Most importantly, the specific capacitance still maintained 95% of the original value after 5000 cycles at 10 A/g. A NiMn 2 O 4 @CoS//stereotaxically constricted graphene (SCG) asymmetric supercapacitor device also showed a high energy density of 44.56 W h kg –1 at a power density of 700.51 W/kg and an enormous power density of 20.99 kW/kg at 29.1 W h kg –1 . Moreover, the capacitance still maintained 94% of the original value even after 5000 cycles at 10 A/g. This outstanding electrochemical performance possibly makes NiMn 2 O 4 @CoS the next candidate electrode material for supercapacitor applications.