Challenges and Advances of Sulfide Solid Electrolytes for High-Energy-Density Sodium Metal Batteries

Abstract

With high ionic conductivity and excellent mechanical properties, sulfide solid electrolytes (SSEs) represent a leading candidate electrolyte system for sodium metal batteries (SMBs), offering enhanced energy density and improved safety. However, their development and practical deployment of SSEs are hindered by intrinsic air instability, poor interfacial compatibility with electrodes, and demanding synthesis conditions. This review provides a comprehensive summary aimed at accelerating the adoption of SSEs in high-energy-density sodium metal batteries. We systematically exam the crystal structures and properties of sulfide sodium-ion conductors, followed by critical challenges related to air stability, electrode–electrolyte interfaces, and synthesis techniques. Subsequently, effective strategies realizing high ionic conductivity, improving chemical/electrochemical stability, and available interfacial compatibility have been thoroughly summarized and discussed. When coupled with different cathodes to assemble SSE-based sodium metal batteries (SSE-SMBs), the interfacial challenges and long-term cycling stability were further discussed. Besides, the advantages and challenges of different cathodes at high energy density are also mentioned. Finally, taking the cathode, SSEs, and anode into account, we identify the challenges of these electrode materials and the areas for improvement to achieve high energy densities.