Atomic-level structure engineering of Ni-substituted NixCo3-xS4 for enhancing performance of supercapacitors

Supercapacitor combining advantages of conventional capacitor and battery is an outstanding energy storage device with high energy density and power density. Co3S4 is an attractive material for supercapacitors due to its high theoretical capacitance. However, its low experimental capacitance limits its practical application due to sluggish ion transport kinetics and pronounced volumetric expansion during energy storage process. This study designs and configurates double-shelled hollow NixCo3-xS4 spheres via atom-level structure engineering, where Ni atoms replace Co atoms and regulate the valences of Co. Among these sulfides with different amount of Ni substitution, Ni1.5Co1.5S4 shows the highest specific capacitance 2210 Fg(-1) at 0.5 A g(-1), even maintains 1154 F g(-1) at a high current density of 20 A g(-1) and good cycle stability (87.0% retention after 3000 cycles). The excellent electrochemical properties of Ni1.5Co1.5S4 can be attributed to the optimized amount of Ni substitution, accordingly improved conductivity and fast transportation of OH-. What's more, Ni1.5Co1.5S4//activated carbon (AC) asymmetric device also delivers excellent energy density (36.94 Wh kg(-1) at 0.15 kW kg(-1)). (C) 2019 Elsevier B.V. All rights reserved.