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.