Advances in Room-Temperature Solid-State Sodium-Sulfur and Potassium-Sulfur Batteries: Materials, Challenges, and Prospects

Sodium-sulfur (Na-S) and potassium-sulfur (K-S) batteries exhibit significant potential due to their high theoretical capacity, low cost, and abundance of raw materials; however, their commercialization is hindered by challenges such as interfacial instability, dendrite growth, and polysulfide shuttling. Solid-state electrolytes (SSEs) present a promising solution to these issues, offering superior safety, higher energy density, and extended cycle life. This review highlights recent advancements in SSEs for Na-S and K-S systems, beginning with a comparative analysis of lithium-ion batteries (LIBs) to underscore the advantages of Na-S and K-S chemistries, including cost efficiency, material sustainability, and rapid ion transport in solid-state configurations. Key obstacles, such as sulfur's insulating nature, severe polysulfide shuttle effects, and uncontrolled dendrite formation, are critically examined. Progress in inorganic, polymer, and composite SSEs is comprehensively evaluated, emphasizing innovations in ionic conductivity and interfacial engineering. Finally, strategies for optimizing SSE designs are proposed, aiming to accommodate the intrinsic ion transport mechanisms of Na-S and K-S battery chemistries while addressing key challenges.