Kinetic-matching between electrodes and electrolyte enabling solid-state sodium-ion capacitors with improved voltage output and ultra-long cyclability

Abstract

Broader context: A kinetic-matched bilayer ionogel electrolyte and an ultra-high kinetic anode were proposed to overcome the kinetic imbalance in solid-state sodium-ion capacitors. The COMSOL Multiphysics simulation proved that as-formed asymmetrical ionogel electrolyte could efficiently weaken the concentration gradient up to 0.3 M at 5 A g −1 and relieve polarization. A sodium-ion capacitor exhibited high energy density of 94.8 Wh kg −1 at 1925.0 W kg -1 and ultra-long-term ability of 10,000 cycles within 4.0 V owing to the double kinetic-matchings design. • A new kinetic-matched design was proposed for solid-state sodium-ion capacitors. • An ultra-high kinetic anode was fabricated via a “Phase Engineering” route. • A COMSOL simulation verified the function of the asymmetric ionogel electrolyte. • The kinetic-balanced sodium-ion capacitor exhibited high stability of 10,000 cycles. Sodium-ion capacitors (SICs) are attracting extensive attentions owing to their high energy density and the availability of abundant sodium element. However, kinetic imbalance between cathodes and anodes or between electrodes and electrolytes at interfaces originating from different ions storage mechanisms need to be well minimized. Thus, it is significant to design specific ion-matching enabled electrodes and electrolytes. Here, an ultra-high kinetic TiO 2 (A)/TiO 2 (B)@C/CNT nanohybrid electrode with rich textured interfaces and a capacity of 251 mAh g −1 was fabricated via a “Phase Engineering” route. In particular, the effects induced by cubic and monoclinic phases were distinguished by an In-situ XRD technique. Moreover, a bi-layered ternary ionogel electrolyte was constructed to achieve optimal kinetic balance and ion matching. Impressively, the optimized bilayer solid electrolyte exhibited an ionic conductivity of 5.22 × 10 -3 S cm −1 and a high Na + transference number of ~ 0.611, resulting to a weakened concentration gradient of 0.3 M at 5 A g −1 and enhanced intercalation/deintercalation of Na + at the anode/electrolyte interface. The enhanced kinetic matching was verified by a COMSOL Multiphysics simulation. Significantly, the double-kinetic-matching design on both electrodes and electrolyte rendered a sodium-ion capacitor (SIC) with an energy density of 94.8 Wh kg −1 at 1925.0 W kg −1 and an ultra-long cyclability of 10,000 cycles at an effective operating potential of 4.0 V. This work demonstrates an effective strategy to high performance solid-state sodium-ion capacitors via the synergistic optimization of electrodes and electrolyte and highlights the importance of understanding the kinetic matching.