Rational design of nickel cobalt sulfide/oxide core-shell nanocolumn arrays for high-performance flexible all-solid-state asymmetric supercapacitors

The development of wearable electronics has created a surge of interest in designing flexible energy storage device with high energy density and long lifespan. In this work, we have successfully fabricated a flexible asymmetric supercapacitor (ASC) based on the NiCo2S4@NiCo2O4 nanocolumn arrays (NCAs). The nickel cobalt sulfide/oxide core-shell nanostructures were rationally synthesized through a facile stepwise approach. The NiCo2S4@NiCo2O4 NCAs based electrode delivered a high specific capacitance of 2258.9 F g−1 at a current density of 0.5 A g−1. The as-assembled flexible ASC device exhibited a high energy density of 44.06 Wh kg−1, a high power density of 6.4 kW kg−1, and excellent cycling stability by retaining 92.5% after 6000 cycles. Excitingly, the electrochemical property of the ASC device could be maintained under severe bending, indicating superior flexibility and mechanical stability. The NiCo2S4@NiCo2O4 core-shell NCAs possess enormous potential for future wearable electronic applications.