Asymmetric supercapacitors based on carbon nanotubes@NiO ultrathin nanosheets core-shell composites and MOF-derived porous carbon polyhedrons with super-long cycle life

Aqueous electrolyte based asymmetric supercapacitors (ASCs) has recently attracted increasing interest by virtue of their operation voltage and high ionic conductivity. Herein, we developed a novel ASC based on carbon nanotubes@nickel oxide nanosheets (CNT@NiO) core–shell composites as positive electrode and porous carbon polyhedrons (PCPs) as negative electrode in aqueous KOH solution as electrolyte. The CNT@NiO core–shell hybrids were prepared through a facile chemical bath deposition method followed by thermal annealing, while PCPs were obtained by direct carbonization of Zn-based metal-organic frameworks (MOFs). Owing to their unique microstructures, outstanding electrochemical properties have been achieved in three-electrode configuration, e.g., 996 F g−1 at 1 A g−1, 500 at 20 A g−1 for the CNT@NiO electrode within 0–0.5 V window, and 245 F g−1 at 1 A g−1 for the PCPs electrode within −1–0 V window. Resulting from these merits, the as-fabricated CNT@NiO//PCPs ASC exhibits maximum energy density of 25.4 Wh kg−1 at a power density of 400 W kg−1 and even remains 9.8 Wh kg−1 at 16,000 W kg−1 (a full charge–discharge within 4.4 s) in the wide voltage region of 0–1.6 V. More importantly, the CNT@NiO//PCPs asymmetric supercapacitor shows ultralong cycling stability, with 93% capacitance retention after 10,000 cycles.