High-Performance Asymmetric Supercapacitors Based on the Ni1.5Co1.5S4@CNTs Nanocomposites

In this paper, the Ni1.5Co1.5S4@CNTs nanocomposites containing different carbon nanotubes (CNT) content were prepared by a one-step hydrothermal method. More hydroxyl and carboxyl groups were introduced on the surface of CNTs by acidizing treatment to increase the dispersion of CNTs. The acid-treated CNTs can more fully compound with Ni1.5Co1.5S4 nanoparticles to form heterostructure. When the CNTs content is 10wt.%, the Ni1.5Co1.5S4@CNTs-10 nanocomposite exhibits the highest specific capacity of 210mAhg(-1) in KOH aqueous electrolytes at current density of 1Ag(-1). The superior performances of the Ni1.5Co1.5S4@CNTs-10 nanocomposite are attributed to the effective synergic effects of the high specific capacity of Ni1.5Co1.5S4 and the excellent conductivity of CNTs. An asymmetric supercapacitor (ASC) was assembled based on Ni1.5Co1.5S4@CNTs-10 positive electrode and activated carbon (AC) negative electrode, which delivers a high energy density of 61.2Whkg(-1) at a power density of 800Wkg(-1), and maintains 34.8Whkg(-1) at a power density of 16079Wkg(-1). Also, the ASC device shows an excellent cycling stability with 91.49% capacity retention and above 94% Columbic efficiency after 10 000 cycles at 10Ag(-1). This aqueous asymmetric Ni1.5Co1.5S4@CNTs//AC supercapacitor is promising for practical applications due to its advantages such as high energy density, power delivery and cycling stability.