Core–shell ultramicroporous@microporous carbon nanospheres as advanced supercapacitor electrodes
In this paper, we report a novel design and synthesis of core–shell ultramicroporous@microporous carbon nanospheres (UMCNs) for advanced supercapacitor electrodes. Polymer colloids (10–14 nm) are obtained by time-controlled polymerization of phloroglucinol and terephthalaldehyde (P/T). UMCNs with ultramicropores in the inner core and abundant micropores in the outer shell are fabricated by the copolymerization of resorcinol and formaldehyde (R/F) on the surfaces of P/T colloids with the presence of ammonia, followed by carbonization and further KOH activation. The as-prepared UMCNs have an adjustable diameter (52–74 nm) and a high specific surface area (up to 2156 m2 g−1). Inter-particle mesoporosity among UMCNs creates ion buffer reservoirs and reduces the ion diffusion distance, while micropores offer highly efficient ion channels and also show high capability for charge accumulation. Moreover, regular ultramicropores benefit the fast transportation and diffusion of electrolyte ions. Consequently, UMCNs with a unique 3D core–shell nanostructure exhibit superb electrochemical performance such as very high specific capacitance (411 F g−1 at 1 A g−1), ultra-high rate capability (charge–discharge operation under an extremely high current density of 100 A g−1), excellent long-term cycle stability (10 000 cycles) and reasonable energy density at high power density (5.94 W h kg−1 at 50 kW kg−1) in a 6 M KOH electrolyte. This finding opens up a new window for well-developed carbon nanoarchitectures to support advanced supercapacitor devices for high rate electrochemical energy storage.