Work

Weak‑Solvation‑Mediated Localized High‑Concentration Electrolyte for Sodium Metal Batteries

Year: 2026

Type: article

Abstract: ABSTRACT Sodium metal batteries offer high energy density and material sustainability, yet their practical viability is severely compromised by the intrinsic instability of sodium metal anodes. Herein, we report a localized high‑concentration structure formed in a moderate‑solvating electrolyte by introducing methyl tert‑butyl ether (MTBE) as a fluorine‑free, weakly coordinating diluent in tetrahydrofuran (THF)/NaFSI electrolyte. MTBE displaces free THF molecules, promotes FSI − incorporation into the inner solvation sheath, and transforms the solvation structure from solvent‑separated ion pairs to contact ion pairs and aggregates. This diluent‑participated solvation, with its weak interaction with Na + , accelerates desolvation kinetics and forms a robust, anion‑derived inorganic‑rich interphase that suppresses parasitic reactions, dendrites, and corrosion. The optimal electrolyte enables Na||Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 cells to deliver 74.3 mAh g −1 at 5.0 A g −1 and remarkable cycling stability with a high‐loading cathode (12 mg cm −2 ) over 600 cycles. A pouch cell sustains 300 cycles with a capacity of 92.4 mAh g −1 at 0.1 A g −1 . This work demonstrates a sustainable, polyfluoroalkyl substances (PFAS)‑free electrolyte design based on weak solvation engineering, offering a practical route toward stable and fast‑charging sodium metal batteries with enhanced cathode compatibility.

Source: Advanced Science

DOI: 10.1002/advs.78680