Ultrafast Chemical Pre‐Sodiation of Pseudocapacitive CaV ₈ O ₂₀ Anodes for High‐Performance Sodium‐Ion Capacitors

ABSTRACT The practical implementation of sodium‐ion capacitors (SICs) is impeded by structural degradation of anode materials and irreversible depletion of active sodium during initial solid‐electrolyte interphase formation. Herein, we propose a synergistic design paradigm that combines a structurally robust calcium vanadate (CaV 8 O 20 ) anode with a gas‐free, scalable chemical pre‐sodiation approach. Driven by the “spectator effect” of Ca 2+ pillars, the pseudocapacitive CaV 8 O 20 framework enables highly reversible, quasi‐zero‐strain Na + transport, ensuring 90% capacity retention after 600 cycles in half‐cells. To overcome the initial active sodium losses, a rapid roll‐to‐roll chemical pre‐sodiation utilizing a highly reducing Na‐benzophenone solution is employed, yielding nearly 100% coulombic efficiency within just 2 min. Consequently, the pre‐sodiated full‐cell SIC delivers an exceptional specific energy of 176 Wh kg −1 and specific power of 380 W kg −1 , alongside an outstanding lifespan of 10,000 cycles (87% retention). Coupled with stepwise operando electrochemical impedance spectroscopy to elucidate diffusion kinetics, this work establishes a scalable pathway to ultrastable, high‐performance SICs.