Nickel sulfide-nickel sulfoselenide nanosheets as a potential electrode material for high performance supercapacitor with extended shelf life

Supercapacitor market is mainly dominated by carbon, oxygen or sulfur based electrode materials. They lack due to the low potential window, low operating current, and low capacitance retention over large charge discharge cycles. Transition metal-based dichalcogenide systems (MX2) are found promising to resolve this research gap. But electrode materials having two different chalcogenide anions (X, X') are to be explored for this purpose. The interfacial interaction between sulfur and selenium in Ni(S,Se)2 is capitalized to yield high-charge storage properties. A facile hydrothermal technique was used to prepare nickel sulfide - nickel sulfoselenide nanosheets as a composite material without the use of any strong reducing agent. The 2D layered structure of the nanosheets contributes to the increased charge storage ability at high current densities. Here, we report a high specific capacitance of 1908 Fg- 1 at a current density of 1 Ag-1 in the fabricated coin cell using PVA/KOH gel electrolyte. While operating at a high current density of 25 Ag-1, the device offers 259 Fg- 1. The symmetric device at high charge densities has also ensured >92 % retention after 28,000 cycles. The shelf life of the same coin cell was tested after 100 days and it exhibited 100 % retention after 3000 cycles at 10 Ag-1. The device with higher mass loading also showed 85 % retention after 60,000 cycles proving the material's stability.