Self-supported hierarchical core–shell Co9S8@NiCo2O4 hollow nanoneedle arrays for asymmetric supercapacitors

Abstract

Self-supported core–shell Co₉S₈@NiCo₂O₄ hollow nanoneedle arrays are prepared on carbon fibers (CFs) through a facile two-step hydrothermal and electrodeposition method for high performance supercapacitors. Within the hybrid nanostructures, the high conductivity Co₉S₈ hollow nanoneedles can act as backbones for anchoring the NiCo₂O₄ nanosheets with high capacity. As a result, the hierarchical hybrid structure exhibits a high specific capacitance of 1022.5 F g⁻¹ at a current density of 1 A g⁻¹. Moreover, an asymmetric supercapacitor (ASC) is successfully assembled by using the core–shell Co₉S₈@NiCo₂O₄ nanoneedle arrays on carbon fibers as the positive electrode and activated carbon (AC) as the negative electrode, exhibiting a high energy density of 24.85 W h kg⁻¹ at a power density of 222 W kg⁻¹ as well as a long-term cycling performance with 88.9% initial capacitance retention. Two ASC devices in series can power three red or white parallel LEDs. Therefore, these results suggest that this core–shell hybrid nanostructure has great potential for energy storage systems.