Designing Zwitterionic Gel Polymer Electrolytes with Dual‐Ion Solvation Regulation Enabling Stable Sodium Ion Capacitor

Sodium ion capacitors (SICs) show high energy/power densities owing to the special dual-ion energy storage mechanism with cation intercalation and anion adsorption. However, the strong ion-solvent interactions make it difficult for interfacial ion desolvation, which not only limits the ion transport kinetics, but also results in the solvent co-intercalation into electrode materials. Here, an advanced zwitterionic gel polymer electrolyte (GPE) is developed to weaken the ion-solvent interactions. The 3-(1-vinyl-3-imidazolio) propanesulfonate (VIPS) zwitterions help to lower the desolvation barriers, enabling fast ion transfer kinetics for constructing stable quasi-solid-state SICs. Furthermore, the decomposition of VIPS contributes to the formation of S- and N-based inorganic interphase on the surface of hard carbon anode, which reduces the Na+ ion diffusion barriers and improves electrochemical compatibility. The designed Zwitterionic GPE can stabilize 4.0 V hard carbon//activated carbon SICs with 95.3% capacity retention after 9000 cycles, showing a high energy density of 140.2 Wh kg(-1). This study highlights the regulation of ion-solvent chemistry and provides a guiding principle in electrolyte design for advanced hybrid ion capacitors.