Electrolytes/Interphases: Enabling Distinguishable Sulfur Redox Processes in Room-Temperature Sodium-Sulfur Batteries

Sodium and sulfur offer a promising application in rechargeable batteries due to their low cost, abundant resources and high energy density. Room-temperature (RT) Na–S batteries have been proposed by paring S cathodes with Na anodes in non-aqueous liquid electrolytes. Over decades, researchers have mainly focussed on the development of superior electrodes by nano-engineering efficient S cathodes and stable Na anodes. These studies have effectively improved the electrochemical performance of RT Na–S batteries, validating their bright prospects as stationary energy storage devices for the modern renewable energy trajectory. In comparison, the research on electrolytes receives much less attention, and there is a lack of understanding regarding the impacts of different electrolytes on electrode interfaces and overall battery mechanisms. In this review, multiple-kinds of electrolytes and the interfaces between electrolytes and electrodes in RT Na–S batteries are comprehensively discussed. Challenges and recent progress are presented in terms of the sulfur electrochemical mechanisms: The solid-solid and solid-liquid conversions. With the presentation of the S redox mechanism, future prospects of electrolyte optimizations, cathode, and anode as well as interfacial improvement are systematically discussed.