Stable sodium-sulfur electrochemistry enabled by phosphorus-based complexation

Significance Beyond lithium-ion technologies, sodium-sulfur batteries stand out because of their multielectron redox reactions and high theoretical specific energy (1,274 Wh per kg of sulfur). They hold the potential of overcoming the capacity limitation of intercalation-based chemistry (<400 Wh kg−1 ). Major challenges in realizing this potential lie in the formation of undesirable intermediates, irreversible precipitation of solid products, and hence, poor battery cycle life. This work presents a series of sodium phosphorothioate complexes that show superior battery performance at ambient and reduced temperatures. They offer great promise for enabling sodium-based energy storage systems with wide-ranging temperature operability. The coupled experimental characterization and theoretical analysis are valuable for guiding complex synthesis, experimental design, and data interpretation.