Hierarchical core-shell nickel hydroxide@nitrogen-doped hollow carbon spheres composite for high-performance hybrid supercapacitor

Designing electrode materials with high performance and maximum utilization is of great desire for supercapacitors, which highly depend on the intrinsic electrochemical properties and the optimal frameworks of the electrode materials. The hierarchical core-shell structure with various types of pores can make the most of the electrode material due to the easy access of electrolyte into the interior electrode and large exposure of electrode into the electrolyte. In this work, nickel hydroxide@nitrogen-doped hollow carbon spheres (Ni(OH)2@NHCSs) electrode material with a hierarchical core-shell structure was obtained using a hard template and the following chemical-precipitation method. Ni(OH)2@NHCSs electrode displays an excellent specific capacity of 214.8 mA h g-1 (that is 1546.6 F g-1), higher than the Ni(OH)2 counterpart (108.9 mA h g-1, that is 784.1 F g-1) at 1 A g-1 in 2 M KOH electrolyte. The assembled Ni(OH)2@NHCSs||NHCSs hybrid supercapacitor (HSC) delivers an energy density of 37.5 W h kg-1 at 800.0 W kg-1 and an outstanding stability with 79.2% of retention rate for 10,000 cycles at a current density of 8 A g-1. The Ni(OH)2@NHCSs electrode exhibits excellent electrochemical performance primarily contributed by its unique hierarchical core-shell structure, high specific surface area and enhanced electrical conductivity.