Engineering the Interface between Sodium Metal and Inorganic Solid Electrolytes in Solid-State Batteries: From Interfacial Challenges to Functionalization Strategies

Abstract

Solid-state sodium batteries (Na-SSBs) have emerged as promising candidates for next-generation energy storage systems owing to the natural abundance and low cost of sodium, as well as the potential to utilize high-capacity sodium metal anodes. However, the practical implementation of Na metal in combination with inorganic solid electrolytes remains limited by severe interfacial challenges, including chemical and electrochemical instability, as well as poor interfacial contact resulting in void evolution and dendrite growth during cycling. These phenomena lead to increased interfacial resistance, non-uniform sodium deposition, and rapid performance degradation. In this review, we discuss the fundamental interfacial processes occurring between sodium metal and the major classes of inorganic solid electrolytes, including β-alumina solid electrolytes (BASE), NASICON-type oxides, sulfides, complex hydrides, and halide-based electrolytes. Particular emphasis is placed on the origins of interfacial instability, including thermodynamic incompatibility, mixed conducting interphase formation, chemo-mechanical degradation, and wetting limitations. Furthermore, recent interface engineering and surface functionalization strategies are summarized, including metallic and ceramic coatings, artificial interphases, alloy interlayers, carbon-based modifications, polymeric interlayers, and composite sodium anodes. By correlating electrolyte chemistry, interfacial phenomena, and surface engineering strategies, this review provides perspectives for the rational design of stable sodium metal interfaces toward powerful Na-SSBs.