Reversible Sodium–Sulfur Batteries Enabled by a Synergistic Dual-Additive Design

We demonstrate here that a combination of bismuth triflate and 1,3,2-dioxathiolane 2,2-dioxide additives in a conventional ether-based electrolyte enables Na metal to cycle with a high Coulombic efficiency of above 99% and completely suppresses the dissolution of sodium polysulfides. Bismuth triflate enables a facile dissolution of sodium triflate based on a salt-in mechanism, which increases the sodium salt concentration and effectively prevents the decomposition of the solvent and additive. This process also facilitates the formation of an anion-derived inorganic solid electrolyte interphase. Additionally, the 1,3,2-dioxathiolane 2,2-dioxide additive spontaneously reacts with sodium sulfide to form a thiosulfate-based robust cathode–electrolyte interphase on a sulfurized polyacrylonitrile (SPAN) cathode. The full cell operated under a practical cell configuration attains a capacity retention of 79% for 150 cycles with a capacity of 535 mAh/g of SPAN. This work reveals the synergistic effects of commonly used additives on stabilizing the aggressive sodium–sulfur chemistry and opens great opportunities for practical applications.