Ultrafast High‐Volumetric Sodium‐Ion Capacitors Based on Compact Nanoarchitectured Carbon Electrodes

Abstract Ultrafast carbon electrodes with high‐volumetric capacities are crucial for the fast‐developing sodium‐ion capacitors (SICs) but have rarely been achieved due to the negative correlation between electrode density and ion transport kinetics. Here, a top‐down strategy to achieve a compact carbon architecture with topological ion transport/diffusion pathways to address this obstacle is reported. The resulting freestanding carbon electrode exhibits a notable volumetric capacity of 242 mAh cm −3 at 0.05 A g −1 and unprecedented high‐rate capability of 107 mAh cm −3 at 50 A g −1 . It achieves an optimal balance between energy density (60.2 Wh L −1 ) and power density (12859 W L −1 ) in a SIC device. The ultrafast and high‐volumetric performance is attributed to the synergistic effect of architecture‐enhanced rapid ion transport/diffusion and carbon nanostructure‐driven fast Na + storage mechanisms involving adsorption/desorption, surface‐redox and solvated Na + co‐intercalation reactions. The nanoarchitectured carbon electrodes show greatly improved Na + diffusion coefficients throughout the potential range, resulting in an extremely short characteristic time (0.013 s) for fast Na + storage.