Insights into the interfacial nanostructuring of NiCo 2 S 4 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 NiCo ₂ S ₄ 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 NiCo ₂ S ₄ nanosheets possess a highest specific capacity of 590 mA h g ^-1 (2655 F g ^-1 ) at 0.25 A g ^-1 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 NiCo ₂ S ₄ 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 ^-1 and 8 kW kg ^-1 , respectively. These outcomes indicate that the novel nanostructured NiCo ₂ S ₄ network has great potential for the development of energy storage devices.
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