Research Progress on Sodium Chloride Solid Electrolytes

Sodium-ion batteries are widely considered a promising alternative to lithium-ion batteries owing to their low cost and the abundance of sodium resources. Advances in development and application of all-solid-state sodium-ion batteries (ASSBs) critically depend on the availability of solid electrolytes that combine high ionic conductivity with wide electrochemical stability window. Among various solid electrolytes, chloride solid electrolytes have attracted considerable attention in recent years due to their high ionic conductivity, high oxidation potential and favorable deformability. This review provides a comprehensive overview of development of sodium chloride solid electrolytes, emphasizing interplay of chemical composition, crystal structure and ionic conductivity, and further examining how modification approaches, including cation/anion doping, amorphization and heterostructure engineering, govern their ionic transport behavior. In addition, this review also evaluates the electrochemical stability of sodium chloride solid electrolytes, and their chemical and electrochemical compatibility with common cathode materials, which are crucial for enabling practical cell configurations. The interfacial degradation mechanisms that arise at the interface with sodium metal anode are also analyzed, and recent advances in chloride-based ASSBs are concisely reviewed. Finally, key challenges that hinder practical deployment of chloride-based ASSBs are highlighted, and prospective research directions are proposed, which are expected to provide valuable insights to guide future application of chloride solid electrolytes in energy conversion and storage technologies.