3D hierarchical CoO@MnO₂ core-shell nanohybrid for high-energy solid state asymmetric supercapacitors

A unique morphology, high specific surface area, extraordinary porosity, and excellent conductive networks are typical favorable properties of pseudocapacitors; however, fully comprehending and interpreting this substantive topic still remains a great challenge. Herein, we present a new strategy for the direct growth of a cobalt monoxide@manganese oxide core-shell nanostructure on 3D Ni foam (CoO@MnO₂/Ni foam). This is accomplished by simple, scalable, in situ fabrication methods to produce a material that can be employed as an advanced electrode material for high-energy solid state asymmetric supercapacitors (ASCs). The cost-effective, binder-free 3D CoO@MnO₂ core-shell nanostructure delivers excellent electrochemical properties with an ultra-high specific capacitance (1835 F g^-1 at a current density of 1 A g^-1), tremendous rate capabilities with an extraordinary capacitance of 1198 F g^-1 at a current density of 20 A g^-1, and outstanding stability (97.7% capacitance retention after 10 000 cycles). ASCs with a maximum potential window of 1.8 V are fabricated by using a 3D CoO@MnO₂ core-shell nanohybrid as the positive electrode and N-doped graphene (NG) as the negative electrode in order to validate the outstanding performance for practical energy storage devices. Impressively, the ASCs delivered a high specific capacitance (191 F g^-1 at 1 A g^-1), excellent energy density (∼85.9 W h kg^-1), an ultra-high power density (∼16 769 W kg^-1 at 51.7 W h kg^-1), and remarkable cycle stability (86.8% capacitance retention after 10 000 cycles). These findings provide a new method to design 3D CoO@MnO₂ core-shell nanostructures that are cost-effective and binder-free electrode materials for the development of high-performance energy storage devices.