Reconfiguring Electrolyte Solvation Chemistry via In Situ Solvent Polymerization for High-Performance Sodium-Ion Batteries.

Ether-based electrolytes exhibit excellent anode compatibility and fast ion kinetics, yet their practical application is hindered by continuous cathode interfacial decomposition due to low oxidation resistance. Traditional solvation-regulation strategies face a trade-off between stabilizing the interface and maintaining bulk ion transport, making synergistic optimization challenging. Herein, we propose an in situ solvent polymerization strategy to develop a liquid polymer electrolyte (NEDL) that concurrently achieves fast ion transport and high interfacial stability. Specifically, trace LiPF6 initiates the partial ring-opening polymerization of 1,3-dioxolane (DOL) in diethylene glycol dimethyl ether (DEGDME), generating PDOL with abundant coordination sites to reconstruct the Na+ solvation structure. This polymer-modulated environment lowers the Na+ desolvation energy barrier, accelerating interfacial kinetics, and drives the formation of an inorganic-enriched, robust interphase that suppresses solvent decomposition. Consequently, under a 16 mg cm-2 mass loading, the Na3Fe2(PO4)P2O7 (NFPP)||Na coin cell delivers 94.76% capacity retention after 500 cycles at 2 C. Moreover, practical NFPP||hard carbon (HC) pouch cells retain 96.59% capacity over 500 cycles at 0.5 C. This work provides fundamental insights into how polymer-chain solvation behavior regulates ion transport kinetics and interfacial properties, offering a viable pathway for designing high-performance sodium-ion battery electrolytes.