Ultralong lifespan and high energy density soft-pack asymmetric supercapacitors based on electrochemically activated porous nickel oxide nanosheet array

Nickel oxide (NiO) with high theoretical capacity is considered a promising energy storage material, however, its actual capacitance and stability are unsatisfactory. In this work, a facile electrochemical activation is proposed to significantly improve the electrochemical performance of porous NiO nanosheet arrays on carbon cloth (CC) in-situ prepared by facile hydrothermal method and subsequent high-temperature calcination. Experimental characterization and density functional theory calculations have shown that this electrochemical activation process can introduce more oxygen vacancies and defects, reduce the crystallinity and nickel valence state of NiO, increase the structural looseness of the nanosheet array and electrical conductivity as well as adsorption energy for hydroxide. By utilizing these structural regulations, the specific capacitance of electrochemically activated NiO/CC is significantly enhanced from 308 to 914 F g−1. The soft-pack asymmetric supercapacitor offers a high energy density of 38.5 Wh kg−1 and exhibit an ultralong lifespan of up to 20,000 cycles with 96.2% capacitance retention. Such a soft-pack asymmetric supercapacitor illuminates different electronic devices, demonstrating enormous potential in practical applications.