Hydrothermal‐Pyrolysis Vulcanization Microporous Anode Unleashing Low‐Potential Capacity to Remedy Voltage Window Loss in Sodium‐Ion Capacitors

Sodium‐ion capacitors (SICs) are a novel hybrid energy storage device that synergistically combines the high‐energy attributes of batteries with the high‐power characteristics of supercapacitors. Differences in the kinetics of the anode and cathode at different potential windows are the main reason for the poor overall electrochemical performance of SICs. However, singularly optimizing the anode kinetics without considering the potential window constraints is insufficient to achieve optimal device performance. This paper focuses on the kinetic and capacity performance of the anode in a low potential window. To this end, the designed microporous S‐doped carbon spheres (HPDCS─S‐700) anode delivers exceptional low‐potential sodiation performance (0–1 V capacity contribution: 246.2 mAh g −1 ) while maintaining ultrafast ionic kinetics. The effect of different cathode and anode potential window matches on system performance is decoupled in real time by a three‐electrode system. The optimized anode exhibits perfect voltage window compatibility with activated carbon cathodes, enabling an energy density of 120.64 Wh kg −1 coupled with an extraordinary power density of 13.7 kW kg −1 . Also, the device demonstrates excellent cycling stability, retaining performance over 45 000 cycles at 5 A g −1 . These findings establish a universal framework for high‐performance energy storage devices with harmonized energy‐power cyclability metrics.