Construction of Cation-Conducting and Anion-Capture Solid Electrolyte Interphase for Highly Stable Sodium Metal Batteries

Sodium metal batteries are promising for grid-scale storage but suffer from dendrite growth due to anion-induced cation mobility limitations. To address this, we designed an artificial solid-electrolyte interphase (SEI) by grafting a fast Na+ ion conductor, Na5GdSi4O12, with oxygen vacancies (NGSO-Vo), onto a glass fiber (GF) separator. This unique structure combines fast Na+ conduction (8.55 mS cm-1) with anion immobilization, achieving a high Na+ transference number (0.9) in a conventional NaClO4/PC electrolyte. The NGSO-Vo-modified GF exhibits exceptional mechanical stability, effectively suppressing dendrite growth. As a result, Na||Na symmetric cells achieve an ultrahigh current density (30 mA cm-2) and long-term cycling (1500 h at 20 mA cm-2). Moreover, Na3V2(PO4)2F3||Na pouch cells with high mass loading (24 mg cm-2) demonstrate a record stability (4000 h). This work presents a simple yet universal strategy to enhance Na-metal battery durability, paving the way for practical energy storage applications.