Hollow Spherical NiCo2S4@N-CNT Composites with High Energy Density for All-Solid-State Supercapacitors

NiCo2S4@N-CNT composites with multidimensional hierarchical structures are rationally designed and synthesized by a simple two-step hydrothermal strategy, aiming to achieve excellent electrochemical performances for supercapacitor applications. The hollow spherical NiCo2S4 nanoparticles with both zero- and two-dimensional architecture are interconnected by the conductive bridges of nitrogen-doped carbon nanotubes (N-CNTs, 1D). This unique structure can provide a much rougher surface, rich two-phase interface, and porous channels exposed to electrolytes with fast ion diffusions and electron transmissions, as well as effectively relieve the expansion/contractions during charging and discharging. As such, the asymmetric all-solid-state supercapacitor device assembled by NiCo2S4@N-CNTs and activated carbons can provide an energy density high up to 59.37 W h kg–1 at the power density (750 W kg–1). Even if the power density is increased up to 1.5 kW kg–1, it still can achieve the energy density superior to 45.6 W h kg–1. These results can provide the open interesting perspective to design the favorable structure of bimetallic sulfides for supercapacitor applications.