Sulfide electrolytes for all-solid-state sodium batteries: fundamentals and modification strategies

Sulfide solid-state electrolytes (SSSEs) have garnered overwhelming attention as promising candidates for high-energy-density all-solid-state sodium batteries (ASSSBs) due to their high room-temperature ionic conductivity and excellent mechanical properties. However, the poor chemical/electrochemical stability, narrow electrochemical windows, and limited adaptability to cathodes/anodes of SSSEs hinder the performance and application of SSSEs in ASSSBs. Consequently, a comprehensive understanding of the preparation methods, fundamental properties, modification techniques, and compatibility strategies between SSSEs and electrodes is crucial for the advancement of SSSE-based ASSSBs. This review summarizes the SSSEs based on their compositional makeup and crystal structure, aiming to elucidate the Na⁺ conduction mechanisms. It also provides an overview of modification strategies designed to enhance ionic conductivity, chemical/electrochemical stability, and interfacial compatibility with electrodes. Furthermore, we outline the challenges and strategies related to the interfaces of SSSEs with cathodes/anodes. Finally, we discuss the existing challenges facing SSSEs and propose the future research directions for SSSE-based ASSSBs.