Hierarchically porous carbon with heteroatom doping for the application of Zn-ion capacitors

Zinc-ion capacitors (ZICs) are newly emerged hybrid devices consisting of battery-type anodes and capacitive-type cathodes, which are expected to meet high energy-power demands. The performance of ZICs is usually limited by the poor performance of porous carbon cathodes. In this work, heteroatom doped, hierarchically porous carbons were developed using a straightforward and scalable one-step method. The specific surface areas and pore size distributions could be tailored by adjusting the precursor ratio and their effects on the electrochemical performance were investigated. The fabricated ZICs showed the highest capacity of 168.4 mAh g−1 with an energy density of 131.9 Wh kg−1 at 0.5 A g−1. The highest power density of 30.8 kW kg−1 could be achieved at 40 A g−1, allowing a fast complete discharging of a ZIC device in 6.6 s. Furthermore, the cycling stability of the device was investigated, registering nearly 100% capacity retention and almost 100% Coulombic efficiency after 12,000 cycles at 10 A g−1. The morphology and impedance tests measured at different charge and discharge conditions shed some light on the mechanism of the hybrid capacitive behavior. The proposed carbon cathodes offer great potential for ZICs in energy storage applications.