Controlled synthesis of NiCo2S4@NiCo2O4 Core@Shell nanostructured arrays decorated over the rGO sheets for high-performance asymmetric supercapacitor

Abstract The electrode materials which show high stability and energy density are essential to design efficient and stable energy storage devices. Herein, we use a novel and binder free method to synthesize NiCo2S4@NiCo2O4 core@shell nanoneedle like structures over the graphene sheet (rG/NCS/NCO). The core@shell nanostructured arrays provide high active surface area, which facilitates to electrolyte diffusion and provides enough space for sulfur integration during charge-discharge reaction. As a result, the rG/NCS/NCO electrode shows specific capacitance (SC) of 1590 F/g at a current density of 5 A/g and high stability (2000 charge-discharge cycle) with impressive rate capability. Further, an asymmetric supercapacitor (ASC) device is fabricated with rG/NCS/NCO as a positive electrode and reduced graphene oxide (rGO) synthesized using lemon juice as a negative electrode. The as-fabricated rG/NCS/NCO//rGO ASC device delivers SC of 104 F/g at current density 3 A/g with energy density 32 Wh/kg and power density 375 W/kg with long durability for 1000 charge-discharge cycles. This study signifies a giant step towards the fabrication of high-performance commercial supercapacitors.