Zinc-Ion Capacitors with Fast Kinetics at a High Mass Loading

The exploitation of electrode materials with the capability of fast kinetics and high capacity under high mass loading remains a great challenge for zinc-ion capacitors (ZICs). Herein, spherical superstructures of N-doped carbon nanorods (SSNCR-x) are developed to substantially boost the kinetics and Zn2+ storage capability of ZICs. The optimized SSNCR-800 features a gradient carbon nanorods framework with a hierarchical porous structure for facilitating ion diffusion and electron transfer, enabling impressive properties for Zn2+ storage. Consequently, SSNCR-800 displays a highly fascinating property in terms of capacitance and cycle stability as the cathode of ZICs, delivering pronounced energy density (181.2 Wh kg-1) and power density (31.1 kW kg-1), as well as long lifespan with 93.5% capacitance retention after 50,000 cycles. Moreover, the constructed ZICs showcase a high specific capacitance of 215 F g-1 and 91.7% capacitance retention after 10,000 cycles under a mass loading of 50 mg cm-2. Systematic characterization demonstrated that the unique structure peculiarity of SSNCR-800 with high-speed mass transfer channels and abundant accessible electrochemical active sites endows the ZICs with fast kinetics and outstanding capability for Zn2+ storage. This work provides an opportunity to overcome the trade-off between the fast kinetics and high mass loading of ZICs toward practical applications.