Improving Supercapacitor Performance with Ni(2-x)CoS4/Ni2CoS4/Ni In-situ Gradient Electrode

Transition metal sulfides are considered potential electrode materials for supercapacitors because of their low electronegativity, high electrochemical activity, and rich oxidation–reduction properties , but they also have the disadvantages of poor cycle stability and low magnification performance. In-situ growth sulfides on the current collector can strengthen the structural stability of the electrode to a certain extent, but this method only obtains a weak binding of the sulfide and current collector. With the progress of cycling, repeated structural evolution will inevitably lead to metal dissolution and sulfide shedding. In this study, nickel-poor reactants were cleverly adopted to synthesize one in-situ sulfide on nickel foam (NF) by activating the nickel element in NF to participate in the formation of sulfide, so as to obtain the in-situ electrode material with flower shape and gradient Ni content, named as Ni (2-x) CoS 4 /Ni 2 CoS 4 /Ni electrode. By further compounding polyaniline (PANI) on the surface of Ni (2-x) CoS 4 /Ni 2 CoS 4 /Ni electrode, the in-situ gradient Ni (2-x) CoS 4 /Ni 2 CoS 4 /Ni-PANI composite electrode (ISG-NCS-PANI) was obtained. This in-situ bimetallic sulfide has not only high stability, but also high reactivity. The flower shape with a large specific surface area is also beneficial to enhance the rate performance. As a result, the specific capacitance of the composite electrode is up to 2909.4 F g −1 at 1 A g −1 . After 5000 cycles, the capacity remains 83.8 %. The asymmetric supercapacitor (ASC) composed of activated carbon (AC) negative electrode has a specific capacitance of 211.11 F g −1 at 1 A g −1 . The power density of 749.99 W kg −1 shows the maximum energy density of 65.97 Wh kg −1 . The above results prove that ISG-NCS-PANI electrode holds significant potential for application prospect in the domain of energy storage and conversion.