Ultrafast Chemical Pre-Sodiation of Pseudocapacitive CaV8O20 Anodes for High-Performance Sodium-Ion Capacitors.

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 (CaV8O20) anode with a gas-free, scalable chemical pre-sodiation approach. Driven by the "spectator effect" of Ca2+ pillars, the pseudocapacitive CaV8O20 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.