All-solid-state flexible asymmetric supercapacitors with high energy and power densities based on NiCo₂S₄@MnS and active carbon

Electrode material based on a novel core–shell structure consisting of NiCo₂S₄ (NCS) solid fiber core and MnS (MS) sheet shell (NCS@MS) in situ grown on carbon cloth (CC) has been successfully prepared by a simple sulfurization-assisted hydrothermal method for high performance supercapacitor. The synthesized NiCo₂S₄@MnS/CC electrode shows high capacitance of 1908.3 F g⁻¹ at a current density of 0.5 A g⁻¹ which is higher than those of NiCo₂S₄ and MnS at the same current density. A flexible all-solid-state asymmetric supercapacitor (ASC) is constructed by using NiCo₂S₄@MnS/CC as positive electrode, active carbon/CC as negative electrode and KOH/poly (vinyl alcohol) (PVA) as electrolyte. The optimized ASC shows a maximum energy density of 23.3 Wh kg⁻¹ at 1 A g⁻¹, a maximum power density of about 7.5 kw kg⁻¹ at 10 A g⁻¹ and remarkable cycling stability. After 9000 cycles, the ASC still exhibited 67.8% retention rate and largely unchanged charge/discharge curves. The excellent electrochemical properties are resulted from the novel core–shell structure of the NiCo₂S₄@MnS/CC electrode, which possesses both high surface area for Faraday redox reaction and superior kinetics of charge transport. The NiCo₂S₄@MnS/CC electrode shows a promising potential for energy storage applications in the future.