High-Performance Asymmetric Supercapacitor Based on a Bilayer Cu0.7Zn0.3CoNiSyO4−y/Ni3S2 Electrode

Supercapacitors have begun to successfully compete with Li-ion batteries in various portable energy storage applications, owing to their ability to enable fast charging, deliver high power and energy, and offer an exceptionally long cycle life. This paper presents the results of a study on the performance of a positive electrode composed of a CuxZn1−xCoNiSyO4−y whisker layer and an underlying porous Ni3S2 layer, synthesized in a single step via the hydrothermal method. The coating with the nominal composition Cu0.7Zn0.3CoNiS3O/Ni3S2 exhibited a high specific capacitance of 4.10 C cm−2 at a current density of 2 mA cm−2 or 9535 F g−1 at a current density of 1 A g−1, attributed to the synergistic contribution of both layers and the optimized ratio of the four transition metals in the sulfoxide matrix. The assembled asymmetric supercapacitor (ASC), employing the obtained composite as the positive electrode and activated carbon as the negative electrode, exhibited a specific capacitance of 115 F g−1 (200 C g−1). It achieved a high energy density of 48.3 Wh kg−1 at a power density of 870 W kg−1. After 20,000 charge–discharge cycles at a current density of 10 A g−1, the ASC retained 74% of its initial capacitance, highlighting the potential of the CuxZn1−xCoNiSyO4−y electrode for high-performance energy storage applications.