Insights into the interfacial nanostructuring of NiCoS and their electrochemical activity for ultra-high capacity all-solid-state flexible asymmetric supercapacitors.

Ternary metal sulfide based nanostructured materials are promising for commercialization of the electrochemical energy storage devices. Herein, three different NiCoS nanostructures (nanoflakes, nanosheets, and nanoparticles) were fabricated by electrodeposition. Of these, nanosheets consisting of interconnected nanoparticles formed a highly porous network for supercapacitive energy storage. The electrochemical properties of each electrode were studied in detail and it was observed that the self-supported NiCoS nanosheets possess a highest specific capacity of 590 mA h g (2655 F g) at 0.25 A g current density and cycling stability of 88.7% after 5000 charge-discharge cycles. This excellent behavior is attributed to several factors of the electrode such as high electrochemical active sites and ability of a nanostructure to withstand under high strain and accommodate large number of electrolyte ions during charge-discharge. The electrochemical storage properties of the NiCoS nanosheets were further explored by fabricating battery-like solid-state asymmetric supercapacitor with activated carbon that delivered an ultra-high specific energy and power of 69.7 Wh kg and 8 kW kg, respectively. These outcomes indicate that the novel nanostructured NiCoS network has great potential for the development of energy storage devices.