Sulfide based solid electrolytes for sodium-ion battery: Synthesis, structure design, stability, and cell performance

As global energy demands soar, all solid-state sodium batteries (ASSNBs) are emerging as promising alternate energy storage solution due to their competitive high energy density vis-a-vis the state-of-the-art lithium-ion batteries (LIBs). Among the essential components, solid-state electrolytes (SSEs) hold a crucial position in improving the electrochemical performance and safety of all-solid-state-batteries (ASSBs). In recent years, there has been a growing interest in exploring sulfide-based inorganic solid state electrolytes (ISSEs) for ASSNBs due to their high room-temperature ionic conductivity. Understanding the crystal structure and stability of these electrolytes is crucial as the parameters directly influence their ionic conductivity and compatibility with other battery components. This review systematically summarizes the development of sulfide-based sodium SSEs for high-performance ASSBs. First the common synthesis techniques for fabricating sulfide based ISSEs are presented, following this the crystal structure and variation of ionic conductivity of the SSEs are explored in detail. Subsequently, their stability encompassing electrochemical, thermal, air and mechanical stability are thoroughly discussed. Furthermore, the overall cell performance of the SSEs is highlighted. Lastly, future perspective of the sulfide based SSEs are emphasized in detail to give readers a broad view of the same.