Design and fabrication of highly open nickel cobalt sulfide nanosheets on Ni foam for asymmetric supercapacitors with high energy density and long cycle-life

Nickel cobalt sulfides (NiCo-S) are promising electrode materials for high-performance supercapacitors but normally show poor rate capability and unsatisfactory long-term endurance. To overcome these disadvantages, a properly constructed electrode architecture with abundant electron transport channels, excellent electronic conductivity and robust structural stability is required. Herein, considering that in situ transformation can mostly retain the specific structural advantages of the precursors, a two-step strategy is purposefully developed to construct a binder-free electrode composed of interconnected NiCo-S nanosheets on Ni foam (NiCo-S/NF), in which NiCo-S/NF is synthesized via the in situ sulfuration of networked acetate anion-intercalated nickel cobalt layered double hydroxide nanosheets loaded on Ni foam (A-NiCo-LDH/NF). Noticeably, the optimized Ni 1 Co 1 -S/NF exhibits an ultrahigh specific capacitance of 2553.9 F g −1 at 0.5 A g −1 , excellent rate capability (1898.1 F g −1 at 50 A g −1 ) and superior cycling stability (nearly 90% capacitance retention after 10,000 cycles). Furthermore, the assembled asymmetric supercapacitor based on Ni 1 Co 1 -S/NF demonstrates a high energy density of 58.1 Wh kg −1 at a power density of 796 W kg −1 and impressive long-term durability even after a repeated charge/discharge process as long as 70,000 cycles (∼92% capacitance retention). The attractive properties endow the Ni 1 Co 1 -S/NF electrode with significant potential for high-performance energy storage devices.