Electrolyte Engineering for Room-Temperature Sodium-Sulfur Batteries: Challenges, Strategies, and Future Perspectives

The urgent need for sustainable and high-performance energy storage beyond lithium-ion batteries has propelled the development of room-temperature sodium-sulfur batteries (RT-NSBs), which leverage earth-abundant elements to offer a high theoretical energy density. However, the practical realization of RT-NSBs is severely constrained by formidable challenges originating at the electrolyte, primarily the detrimental polysulfide shuttle effect, the uncontrolled growth of sodium dendrites, and sluggish reaction kinetics. Addressing these intertwined issues through rational electrolyte design is paramount for unlocking the potential of this technology. This review offers a comprehensive comparison of liquid, gel polymer, and solid-state electrolytes for RT-NSBs, establishing a mechanistic framework that connects solvation chemistry, interfacial reactions, and electrochemical behavior to actionable electrolyte design principles. The fundamental operating principles and key challenges are first outlined. Subsequently, a systematic overview of state-of-the-art strategies across different electrolyte platforms is presented, emphasizing the underlying mechanisms and notable achievements. Furthermore, the pivotal role of advanced characterization techniques in elucidating complex solvation structures, electrode-electrolyte interphases, and sulfur redox pathways is discussed to accelerate the rational design of electrolytes. Finally, this review points out the remaining challenges and potential directions to accelerate the transition of RT-NSBs into practical, next-generation energy storage solutions.