The electrochemistry of stable sulfur isotopes versus lithium.

Sulfur in nature consists of two abundant stable isotopes, with two more neutrons in the heavy one (34 S) than in the light one (32 S). The two isotopes show similar physicochemical properties and are usually considered an integral system for chemical research in various fields. In this work, a model study based on a Li-S battery was performed to reveal the variation between the electrochemical properties of the two S isotopes. Provided with the same octatomic ring structure, the cyclo -34 S8 molecules form stronger S-S bonds than cyclo -32 S8 and are more prone to react with Li. The soluble Li polysulfides generated by the Li-34 S conversion reaction show a stronger cation-solvent interaction yet a weaker cation-anion interaction than the 32 S-based counterparts, which facilitates quick solvation of polysulfides yet hinders their migration from the cathode to the anode. Consequently, the Li-34 S cell shows improved cathode reaction kinetics at the solid-liquid interface and inhibited shuttle of polysulfides through the electrolyte so that it demonstrates better cycling performance than the Li-32 S cell. Based on the varied shuttle kinetics of the isotopic-S-based polysulfides, an electrochemical separation method for 34 S/32 S isotope is proposed, which enables a notably higher separation factor than the conventional separation methods via chemical exchange or distillation and brings opportunities to low-cost manufacture, utilization, and research of heavy chalcogen isotopes.