Preparation of multi-shelled ZnMn2O4 hollow spheres@Ni(OH)2 nanosheets for high-performance hybrid supercapacitors

Abstract

Herein, multi-shelled ZnMn₂O₄ hollow nanospheres were synthesized via a mixed solvothermal method using colloidal carbon spheres as templates. Subsequently, a layer of Ni(OH)₂ nanoflakes was densely grown on the surface of the ZnMn₂O₄ nanospheres through a secondary hydrothermal process, yielding a heterostructure nanoflower-like ZnMn₂O₄@Ni(OH)₂ electrode material. ZnMn₂O₄@Ni(OH)₂ shows high specific capacitance through the synergistic mechanism that the multi-shelled ZnMn₂O₄ nanospheres act as “charge storage” and the Ni(OH)₂ nanosheets act as “charge transducers” to quickly introduce charges into the ZnMn₂O₄ nanospheres. The resulting ZnMn₂O₄@Ni(OH)₂ electrode material exhibits a specific capacitance of 816.36 F g⁻¹ at a current density of 1 A g⁻¹, which is higher than that of individual ZnMn₂O₄ hollow nanospheres and Ni(OH)₂ nanoflakes. An asymmetric supercapacitor device was fabricated by integrating the ZnMn₂O₄@Ni(OH)₂ nanoflowers with activated carbon. The device demonstrated a high energy density of 74.8 Wh·kg⁻¹ at a power density of 3240 W·kg⁻¹ and a long cycle life of 75 % capacitance retention after 5000 cycles. The simple synthesis route and excellent performance of the ZnMn₂O₄@Ni(OH)₂ electrode material show strong potential for future energy storage applications. The results provide the future energy-storage devices with excellent electrochemical properties by the hetero-growth of transitional metal oxides/hydroxides.