nHighly N/O co-doped carbon nanospheres for symmetric supercapacitors application with high specific energy

Carbon nanospheres (CSs) with high synthetic yield, large specific surface area (SBET), high heteroatom dopant and hierarchical porosity exhibits unique advantages in supercapacitor applications, yet integrating all these merits into one material is still challengeable. Herein, we developed a template-free CuCl2-activation strategy to high-yield preparation of highly N/O co-doped porous CSs derived from a quinone-amine polymer precursor. It is found that the mild activating effect of CuCl2 not only can retain the initial nanosphere structure of the precursor, but also can enable the target CSs to achieve high-level N/O dopants (14.9/10.6 at.%), large SBET (2957.8 m2 g−1), and ultrahigh carbon yield (~60%). Benefiting from these merits, the optimal CS-CuCl2-800 sample exhibits a delightful capacitance of 273.9 F g–1 at 0.5 A g–1, excellent cyclic performance (capacitance retention, ~96.5%) during 10,000 charging/discharging cycles at 2 A g–1, and a moderate energy output of 8.0 Wh kg–1 in 6 M KOH electrolyte. When used ion-liquid electrolyte, the energy density of the device is further boosted to 80.3 Wh kg–1, and the corresponding solid-state supercapacitors based on the ionic liquid gel electrolyte still maintain an high energy output of 71.3 Wh kg–1, which is superior to many reported solid-state supercapacitors. Therefore, the facile activation strategy together with tunable properties, high carbon yield, and excellent electrochemical performance indicate promising application prospects in the large-scale fabrication of commercial porous carbons.