2D Nickel Sulfide Electrodes with Superior Electrochemical Thermal Stability along with Long Cyclic Stability for Supercapatteries

Supercapatteries are contemporary electrochemical energy‐storage devices that bridge the gap between the conventional supercapacitors and rechargeable batteries. Supercapatteries utilize battery‐type electrode‐active materials for their charge storage. Among the various futuristic materials, transition‐metal dichalcogenides receive prominent attention due to their excellent charge‐storage capabilities. Herein, the microwave‐assisted hydrothermal synthesis of layered two‐dimensional (2D) nickel sulfide nanosheets (NSN) and their application as electrode‐active materials in high‐performance asymmetric supercapatteries are reported. The layered 2D architecture is preferred for the electrode‐active materials as the layered electrode nanostructure provides a hindrance‐free movement to the electrolyte ions through it during the charge‐storage process that include intercalation/deintercalation mechanisms. The electrochemical thermal stability of the 2D NSN electrode reveals that its stability in KOH (aqueous) electrolyte is better than that in LiOH (aqueous) and NaOH (aqueous) electrolytes. The supercapattery electrode synthesized using 2D NSN exhibits excellent electrochemical charge‐storage performances bearing a maximum specific capacity of 594.77 C g −1 (an equivalent mass‐specific capacitance of 991.29 F g −1 ) in 2 M KOH (aqueous) electrolyte. The electrochemical cycling performance of the 2D NSN electrode shows a stability over 40 000 cycles without any significant capacity loss. An asymmetric supercapattery device fabricated with 2D NSN electrode as positrode and activated carbon as negatrode exhibits a maximum mass‐specific capacity of 143.58 C g −1 with a corresponding energy density of 29.91 Wh kg −1 in 2 M KOH (aqueous) electrolyte.