Rational design of activated graphitic carbon spheres with optimized ion and electron transfer channels for zinc-ion hybrid capacitors.

Herein, three-dimensional activated graphitic carbon spheres (AGCS) were constructed by simultaneous activation-graphitization of Fe-tannic acid coordination spheres with the assistance of KOH. Nanosheets-assembled AGCS with complex intersecting channel system can expose more active sites for charge storage. Simultaneous activation-graphitization can relieve trade-off relationship between porosity and conductivity of carbon materials. Benefiting from multiple synergistic effects of large specific surface area (2069 m g), abundant ion-accessible micropores (>0.78 nm), good electronic conductivity (I/I = 1.11), and moderate amount of oxygen doping, the optimized AGCS-2 has favored ion and electron transfer channels. AGCS-2 based zinc-ion hybrid capacitor (ZIHC) displays a high specific capacity of 148.6 mA h g (334 F g) at 0.5 A g, a remarkable energy density of 119.0 W h kg at 1440 W kg, and superior cycling life with 96% capacity retention after 10,000 cycles. This simultaneous activation-graphitization strategy may open up a new avenue to design novel carbon spheres linking optimal pores and graphitic carbon structure for ZIHC application.