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.