Reactive Lithium Fluoride Revitalizes Bulk-interface Na-ion Transport in All-solid-state PEO-based Sodium Batteries

Abstract

Poly(ethylene oxide) (PEO)-based electrolytes suffer from low ionic conductivity and interfacial instability, which collectively impede their practical implementation in all-solid-state sodium metal batteries (ASSMBs). Conventional molecular-level strategies aim to enhance Na⁺ conduction by regulating polymer chain organization; however, the strong covalent bonds formed thereby severely restrict the segmental motion critical for ion transport. Herein, we introduce a reactive lithium fluoride to revitalize bulk Na⁺ transport and interfacial stability simultaneously in solid-state PEO-based sodium batteries. The LiF-mediated supramolecular compounds facilitates the formation of intrinsic anion-enriched aggregates and weakens Na⁺-PEO coordination, thereby synergistically enhancing bulk Na⁺ conductivity. Moreover, activated LiF in situ forms a dense, NaF-rich interfacial layer on the sodium anode surface, which homogenizes ion flux and suppresses dendritic growth. Consequently, the resultant electrolyte exhibits synergistic enhancements in ionic conductivity, mechanical robustness, and interfacial compatibility. The ASSMBs paired with a Na₃V₂(PO₄)₃ cathode demonstrate exceptional cycling stability, retaining 82.8% of the initial capacity after 400 cycles at 0.5 C—markedly outperforming state-of-the-art polymer electrolyte-based ASSMBs. This study provides fundamental insights into the supramolecular functionalities of reactive fluorides, thereby offering a viable route to advance high-performance polymer-based ASSMBs.