Hierarchical 3D Cobalt-Doped Fe₃ O₄ Nanospheres@NG Hybrid as an Advanced Anode Material for High-Performance Asymmetric Supercapacitors

Hierarchical nanostructure, high electrical conductivity, extraordinary specific surface area, and unique porous architecture are essential properties in energy storage and conversion studies. A new type of hierarchical 3D cobalt encapsulated Fe₃ O₄ nanosphere is successfully developed on N-graphene sheet (Co-Fe₃ O₄ NS@NG) hybrid with unique nanostructure by simple, scalable, and efficient solvothermal technique. When applied as an electrode material for supercapacitors, hierarchical Co-Fe₃ O₄ NS@NG hybrid shows an ultrahigh specific capacitance (775 F g^-1 at a current density of 1 A g^-1 ) with exceptional rate capability (475 F g^-1 at current density of 50 A g^-1 ), and admirable cycling performance (97.1% capacitance retention after 10 000 cycles). Furthermore, the fabricated Co-Fe₃ O₄ NS@NG//CoMnO₃ @NG asymmetric supercapacitor (ASC) device exhibits a high energy density of 89.1 Wh kg^-1 at power density of 0.901 kW kg^-1 , and outstanding cycling performance (89.3% capacitance retention after 10 000 cycles). Such eminent electrochemical properties of the Co-Fe₃ O₄ NS@NG are due to the high electrical conductivity, ultrahigh surface area, and unique porous architecture. This research first proposes hierarchical Co-Fe₃ O₄ NS@NG hybrid as an ultrafast charge-discharge anode material for the ASC device, that holds great potential for the development of high-performance energy storage devices.