Coral-like structured nickel sulfide-cobalt sulfide binder-free electrode for supercapattery

High-efficiency and lightweight electrodes are advantageous for acquiring high-energy density and flexible supercapattery. Herein, binder-free electrodes were fabricated by growing directly nickel sulfide (NiS) nanoflakes and coral-like nickel sulfide-copper sulfide (NiCuS) on nickel foam using hydrothermal method. Structural studies show that both electrodes are composed of multiphases crystalline structure. Morphological studies reveal that the incorporation of Cu ion has greatly influenced the morphology of NiS, i.e., from nanoflake arrays to coral-like structure (built by interconnected nanotubular). The electrochemical studies demonstrate that the presence of Cu in NiCuS significantly improved the specific capacity of NiS from 382 to 688 C/g at 10 A/g. Moreover, the rate capability of NiS is enhanced from 69 to 78% capacity retention. The origin of the enhancement in performance shown by NiCuS as compared with NiS is due to the enhancement in electroactive sites and reduced internal resistance contributed from the presence of different valence states. In order to access the real-time performance of NiCuS electrode, supercapattery was assembled. The device exhibits the energy density of 23 Wh/kg at 388 W/kg and degraded only 16% of its initial capacity after 5000 cycles.