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.