Nickel sulfide/activated carbon nanotubes nanocomposites as advanced electrode of high-performance aqueous asymmetric supercapacitors

Highlights: • Activated carbon nanotubes (ACNTs) possess plentiful active sites. • ACNTs as conductive support to deposit NiS and alleviate particles agglomeration. • The nanostructured NiS/ACNTs composite possesses outstanding performances. • The effects of electrolyte concentration on the NiS/ACNTs electrode are studied. • The NiS/ACNTs//AC ASCs delivers high energy density and power density. -- Abstract: Hexagonal nickel sulfide is extensively studied and used for supercapacitors due to its high theoretical specific capacitance (1060 F g⁻¹), simple synthesis craft and low cost. However, the poor electrical conductivity and easy agglomeration severely restrict its practical application. Herein, we design the composite materials of the nickel sulfide nanoparticles and activated carbon nanotubes (NiS/ACNTs) with plentiful active group by hydrothermal method and subsequent annealing treatment, thus effectively inhibiting the agglomeration of NiS nanoparticles and producing good supercapacitor behaviors. Benefiting from the superiority of composite structure, the NiS/ACNTs hybrid electrode delivers a high specific capacitance of 1266 F g⁻¹ at a current density of 1.0 A g⁻¹ and sustains a capacitance value of 1028 F g⁻¹ at 10 A g⁻¹ (81% of initial specific capacitance). Moreover, the asymmetric supercapacitors (ASCs) with NiS/ACNTs cathode and activated carbon (AC) anode exhibit a high energy density of 36.0 Wh kg⁻¹ at a power density of 806 W kg⁻¹ and a good capacitance retention of 83% after 2000 cycles at 2.0 A g⁻¹. Therefore, the combination of the battery-type materials and carbon materials will a significant exploration to solve particle agglomeration and develop the high electrochemical performance ASCs.