Recent advances in electrolytes for room-temperature sodium-sulfur batteries: A review

Room temperature sodium-sulfur (RT Na–S) battery is an emerging energy storage system due to its possible application in grid energy storage and electric vehicles. In this review article, recent advances in various electrolyte compositions for RT Na–S batteries have been highlighted along with discussion on important aspects of using carbonate and glyme based liquid electrolytes. The role of using ionic liquids and other materials as additives to improve the electrochemical performance of RT Na–S cells are critically explained. Recent development and progress on solid electrolytes along with their inherent drawbacks such as poor interfacial contact and low ionic conductivity are covered in detail. The specific advantages of gel polymer electrolytes in comparison with solid and liquid electrolytes have also been discussed. Experimental results especially the electrochemical properties such as discharge capacity, OCV and recyclability have been critically discussed with reference to the type of electrolyte used for assembling Na–S cell. The review focuses on recent advances in liquid, solid and gel polymer electrolytes with their major benefits and challenges for RT Na–S cells. The perspectives on further development of these solid/liquid/gel electrolytes have also been explained.