Rational design of asymmetric aqueous supercapacitor based on the composites of reduced graphene oxide with manganese-doped nickel sulfide-tin sulfide as positive electrode and manganese sulfide negative electrode

Development of asymmetric supercapacitor device leads to the enhancement of energy density by coupling a battery type positive electrode and an electrochemical double layer capacitance (EDLC) type negative electrode material. The potential window of each electrode collectively contributes in widening the overall potential window. The low capacitance values of the EDLC type materials hinder it from practical applications. Therefore, this study focuces on the improvement in energy density of the device by tailoring the capacitance of positive and negative electrode materials. Herein, manganese doped Ni sulfide-Sn sulfide/reduced graphene oxide (rGO) composite and manganese sulfide/rGO composite are used as positive and negative electrode materials, respectively. Manganese is used as dopant in Ni–Sn sulfide/rGO composite to enhance the electrochemical activity by producing more active sites owing to its multiple oxidation states and lower electronegativity of manganese. The specific capacitance values of ∼810 and 390 F g−1 at 2 A g−1 current density are recorded for positive and negative electrode materials, respectively. The device exhibits high energy density of ∼50.37 W h kg−1 at a power density of 1086 W kg−1. The retention in original specific capacitance is ∼85% after 10,000 galvanostatic charge-discharge cycles.